Porous abrasive articles with agglomerated abrasives and method for making the agglomerated abrasives

WITH POROUS ABRASIVE ARTICLES AND OF BONDED ABRASIVES

METHOD FOR PRODUCING ABRASIVES BONDED

The invention relates to bonded abrasive articles or grinding tools made porous by the use of certain agglomerated abrasive grains and agglomerates of abrasive grain manufacturing processes.

The grinding tools are manufactured in a variety of grades or structures determined by the relative percentage by volume of abrasive grains, a binder and a porosity within a composite abrasive grain matrix. In many grinding operations, the porosity of the grinding tool, particularly the nature of permeable or interconnected porosity enhances the efficiency of the grinding operation and quality of the workpiece is corrected. Pore ​​inducers, such as ventilated alumina and naphthalene, may be added to abrasive composite mixtures to permit pressure rectification and handling an abrasive porous untreated article and to produce an adequate volume percent porosity in the ultimate tool.

Natural porosity arising from packing of the abrasive grains and binder particles during pressure molding is insufficient to achieve a porosity character that is desirable for some grinding operations. Pore ​​inducers have been added to achieve high percentages of porosity, however, open channels or interconnected porosity can not be achieved with the pore inducers known in the art (e.g., hollow ceramic spheres or glass). Some pore inducers must be removed by calcining the abrasive material (e.g., walnut shells and naphthalene), giving rise to various manufacturing difficulties. In addition, the densities of pore inducers, binding materials and abrasive grains vary significantly, often causing stratification of the abrasive mix during handling and molding, and, in turn, loss of homogeneity in the structure Three dimensions of the finished abrasive article.

The volume percent of interconnected porosity, or fluid permeability, has been found to be a more significant determinant of grinding performance of abrasive articles than just the porosity in volume percent. US Patent No. A-5 738 696 issued to Wu discloses a bonded abrasive manufacturing process utilizing elongated abrasive grain having an aspect ratio of at least 5: 1. Agglomerated abrasive wheels have a permeable container structure 55 to 80%, by volume, interconnected porosity. The interconnected porosity allows removal rate of material from the grinding debris (swarf) and passage of cooling fluid within the wheel during grinding. The existence of interconnected porosity was confirmed by measuring the permeability of the wheel to the flow of air under controlled conditions. The filamentary abrasive grains are not agglomerated or otherwise coated with the binder prior to assembling the wheel. US Patent No. 5 738 697 A issued to Wu mentioned high permeability grinding wheels having a significant amount of interconnected porosity (40 to 80% by volume). These wheels are made from a matrix of fibrous particles having an aspect ratio of at least 5: 1. The fibrous particles may be abrasive grains of alumina sintered sol gel abrasive grain or ordinary, non-fibrous mixed with various materials, fibrous filler such as ceramic fiber, polyester fiber, glass fiber and mats and agglomerates constructed with the fiber particles. The filamentary abrasive grains are not agglomerated or are differently coated with binder prior to assembling the wheel.

The abrasive grain has been agglomerated for various purposes, primarily among them to allow use of a smaller particle (grit) to achieve the same grinding efficiency as a larger abrasive grit size. In many instances abrasive grain has been agglomerated with binder materials to achieve a less porous structure and a denser grinding tool, and having abrasive grains more strongly agglomerated.

It has been reported that the agglomerated abrasive grains improve the efficiency of rectification through mechanisms entirely unrelated to the amount or character of the porosity of the abrasive article.

U.S. Patent No.-A-2 194 472 issued to Jackson mentions coated abrasive tools made with agglomerates of a plurality of relatively fine abrasive grain and any of the binders normally used in coated or bonded abrasive tools. Organic binders are used to adhere the agglomerates to the backing of the coated abrasives. The agglomerates lend an open face coating to coated abrasives made with relatively fine grain. The coated abrasives made with the agglomerates in place of individual abrasive grains are characterized as being relatively fast cutting, long-lived and suitable for preparing a fine surface finish quality in the work piece.

US Patent No.-A-2,216,728 issued to Benner mentions abrasive grains / agglomerates aggregates made from any type of binder. The purpose of the aggregates is to achieve very dense wheel structures for retaining diamond or CBN grain during grinding operations. If the aggregates are made with a porous structure, then this is the purpose of allowing inter-aggregate binder materials to flow into the pores of the aggregates and make fully dense structure during calcination. The aggregates allow the use of abrasive grains expenses otherwise lost in production.

US Patent No. A-3 046 482 mentions issued to Hurst abrasive microsegments cut agglomerated abrasive grains and organic binder materials in the form of pyramids or other tapered shapes. Mitered abrasive micro-segments adhere to a fibrous substrate and used to make coated abrasives and to line the surface of thin grinding wheels. The invention is characterized as producing a longer cutting life, controlled flexibility of the tool, high strength and speed safety, resilient action and highly efficient cutting action relative to tools made without micro- bonded abrasive grain segments.

Patent No.-A-3 982 359 issued to Elbel teaches the formation of resin binder and abrasive grain aggregates having a hardness greater than that of the resin binder used to agglomerate the aggregates within an abrasive tool . Larger grinding speeds and longer lifespan are obtained in the agglomerated rubber wheels containing the aggregates.

US Patent No.-A-4,355,489 issued to Heyer says an abrasive article (wheel, disc, belt, sheet, block and the like) made from an agglomerated matrix wavy filaments together on manual touch points and abrasive agglomerates, having a void volume of about 70 to 97%. The agglomerates can be made from resin or vitrified bonds and any abrasive grain.

U.S. Patent No.-A-4 364 746 issued to Bitzer mentioned abrasive tools comprising different abrasive agglomerates having different strengths. The agglomerates are made from abrasive grain and resin binders, and may contain other materials, such as fiber piece, to add strength or hardness.

U.S. Patent No.-A-4 393 021 issued to Eisenberg, et al., Discloses a process of making abrasive agglomerates from abrasive grain and a resin binder utilizing a sieve web and rolling of a paste of grain and binder through the web to make extrusions as worm. Extrusions are hardened by heating and then crushed to form agglomerates.

U.S. Patent No.-A4 799 939 issued to Bloecher teaches abrasive grain agglomerates may be eroded, hollow bodies and organic binder and the use of these agglomerates in coated abrasives and bonded abrasives. The greater material removal, extended life and utility in the rectification conditions in the wet state are claimed for abrasive articles comprising the agglomerates. The agglomerates are preferably from 150 to 3000 microns in their largest dimension. To make the agglomerates, the hollow bodies, grain, binder and water are mixed as a slurry, the slurry is solidified by heat or radiation to remove the water, and the solid mixture is crushed in a jaw crusher or roller and screened.

U.S. Patent No.-A-5 129 189 issued to Wetscher mentioned abrasive tools having a resin binder matrix containing conglomerates of abrasive grain and resin and filler material, such as cryolite.

US Patent No.-A-5,651,729 issued to Benguerel teaches a grinding wheel having a core and an abrasive rim made from a binder resin and crushed agglomerates of diamond or CBN abrasive grain with a metal or ceramic binder . The benefits of the wheels made reported with the agglomerates include high chip two dead spaces, high wear resistance, characteristics of autoaiguisage, high mechanical resistance of the wheel and the ability to directly bond the abrasive rim to the soul of the wheel. In one embodiment, the edges of correction used diamond or CBN agglomerates are crushed to a size of 0.2 to 3 mm to form the agglomerates.

US Patent No. 4, AA-311 489 issued to Kressner mentioned agglomerates of fine abrasive grain (<200 microns) and cryolite, optionally with a silicate binder, and their use in the manufacture of coated abrasive tools.

US Patent No.-A-4,541,842 issued to Rostoker mentions coated abrasives and abrasive wheels made with aggregates of abrasive grain and a foam made from a mixture of vitrified binder materials with other raw materials such as carbon black or carbonates, suitable for foaming during firing of the aggregates. The "pellet" aggregates contain a greater percentage of binder than grain on a volume percentage basis. Pellets used to make abrasive wheels are sintered at 900 ° C (to a density of 70 lbs / square foot; 1.134 g / cm3) and the vitrified bond used to make the wheel is fired at 880 ° C. The wheels made with 16 volume% pellets were performing the correction with an efficiency similar to that of comparative wheels made with 46 volume% abrasive grain. The pellets contain open cells within the vitrified bond matrix, with the relative smaller abrasive grains clustered around the perimeter of the open cells. A rotary kiln is mentioned for pre-calcining aggregates raw chipboard later or in subsequent foam and sinter to make the pellets.

US Patent No. 5 975 988, issued to Christianson mentioned coated abrasive articles include a backing and an organic agglomerated abrasive layer where the abrasive is present in the form of truncated four-sided pyramids or cubes. The agglomerates are made from superabrasive grains bonded in an inorganic binder having a coefficient of thermal expansion which is the same or which is substantially the same as a coefficient of thermal expansion of the abrasive grain.

WO 00/51788 issued to Stoetzel, et al., Refers to abrasive articles having a backing, an organic binder containing hard inorganic particles dispersed within it, and abrasive particle agglomerates bonded to the support. The abrasive particles in the agglomerates and the hard inorganic particles in the organic binder are substantially the same size. Agglomerates may be randomly or trimmed accurately and are made with an organic binder. The hard inorganic particles may be any of a number of abrasive grain particles.

US-6 086 467 issued to Imai, et al., Mention that the grinding wheels contain abrasive grain and grain patterns filler grain having a smaller size than the abrasive grain. The vitrified bond may be used and the filler grain may be chromium oxide. The size of the grain patterns is 1/3 or larger than the size of the abrasive grain. The benefits include a controlled erosion of the binder and the abrasive grain retention in low force grinding applications utilizing superabrasive grain in which the superabrasive grain can be diluted to minimize grinding forces. Load grain patterns can be formed with wax. No sintering reasons are mentioned.

WO 01/04227 A2 patent issued to Adefris, et al., Refers to an abrasive article comprising a rigid backing and ceramic abrasive composites made of abrasive particles in a porous ceramic matrix. The composites are held to the backing with a metal coating, such an electroplated metal.

None of these prior art developments suggest the manufacture of abrasive articles using abrasive grain agglomerated, porous, and binder particles to control the percentage and character of porosity and to maintain porosity in the form of a porosity permeable, interconnected in bonded abrasive products. No suggestion is made concerning the use of a method by rotating cooker to make a variety of abrasive grain agglomerates for use in the abrasive articles. The methods and tools of the invention provide new structures from agglomerated mixtures of existing abrasive grain and binder combinations, and they are sophisticated in that they allow the controlled design and manufacture of broad ranges of structures abrasive articles having porosity characteristics beneficial, bi-modal, interconnected. Such bimodal porosity, interconnected enhances the performance of the abrasive tool, particularly in areas of high contact, precision grinding operations such as surface grinding single deep passes, inner diameter grinding and grinding processes tooling.

The invention is a bonded-abrasive tool, having a structure permeable to fluid flow, the tool comprising: a) about 5 to 75 volume% sintered agglomerates, comprising a plurality of abrasive grains held with a bonding material, the bonding material being characterized by a melting temperature between 500 and 1400 ° C and the sintered agglomerates having a three-dimensional shape and an initial size distribution prior to manufacture of the tool b) a binder ; and c) about 35-80 volume% total porosity, including at least 30% by volume of connected porosity; wherein at least 50% by weight, of the sintered agglomerates within the bonded abrasive tool retain a plurality of abrasive grains held in a three-dimensional shape after manufacture of the tool.

In another embodiment, the invention includes a bonded abrasive tool, vitrified, a) about 5 to 75 volume% sintered agglomerates of a plurality of abrasive grains with a binder material, the binder material being characterized by a A viscosity at the melting temperature of the bonding material; b) a vitrified bond characterized by a viscosity B at the melting temperature of the bonding material, the viscosity B being at least 33% lower than viscosity A; and c) a porosity of about 35 to 80% by volume, including at least 30 volume% interconnected porosity.

The invention further includes a bonded-abrasive tool, vitrified, having a structure permeable to fluid flow, the tool comprising: a) about 5 to 60 volume% sintered agglomerates of a plurality of abrasive grains with a bonding material, the bonding material being characterized by a melting temperature A; b) a vitrified bond characterized by a melting temperature B, melting temperature B being at least 150 ° C lower than the melting temperature A; and c) a porosity of about 35 to 80% by volume, including at least 30 volume% interconnected porosity.

In yet another aspect of the invention, the tool is a bonded-abrasive tool, having a structure permeable to fluid flow, the tool comprising: a) about 34 to 56 volume% abrasive grain; b) about 3 to 25% by volume of binder; and c) about 35-80 volume% total porosity, including at least 30 volume% interconnected porosity; wherein the interconnected porosity has been created without the addition of pore inducing media and without the addition of elongated shaped materials having a ratio of length to form transverse width of at least 5: 1.

The invention further includes methods for making the agglomerates and the tools of the invention.

The invention includes a method of agglomerating abrasive grain, comprising the steps: a) feeding the grain and a bonding material selected from the group consisting essentially of vitrified binder materials, vitrified materials, ceramic materials , inorganic binders, organic binders, water, solvent and combinations thereof, within a rotary calcination kiln at a controlled feed rate; b) rotating the kiln at a controlled speed; c) heating the mixture at a heating rate determined by the feed rate and the speed of the kiln to temperatures of about 145 to 1 300 ° C, d) rotating the grain and the bond material in the oven until the bonding material adheres to the grain and a plurality of grains adhere together to create a plurality of sintered agglomerates; and e) recovering the sintered agglomerates from the kiln.

The invention also includes sintered agglomerates of abrasive grain, made by means of a process comprising the steps: a) feeding abrasive grain with a binder material into a rotary calcination kiln at a controlled feed rate; b) rotating the kiln at a controlled speed; c) heating the mixture at a heating rate determined by the feed rate and the speed of the kiln to temperatures from about 145 to 1 300 ° C, d) rotating the grain and the bond material in the oven until that the bonding material adheres to the grain and a plurality of grains adhere together to create a plurality of sintered agglomerates; and e) recovering the sintered agglomerates from the kiln, whereby the sintered agglomerates have an initial three-dimensional shape, a loose packing density of <1.6 g / cm3 and comprise a multitude of abrasive grains.

Using this process, an abrasive tool, comprising 5 to 75 volume% abrasive grain agglomerates, is made via a process comprising the steps: a) feeding abrasive grain and a material binder selected from the group consisting essentially of vitrified binder materials, vitrified materials, ceramic materials, inorganic binders, organic binders and combinations thereof, within a rotary kiln calcination at a controlled feed rate; b) rotating the kiln at a controlled speed; c) heating the mixture at a heating rate determined by the feed rate and the speed of the kiln to temperatures from about 145 to 1300 ° C; d) rotating the mixture in the kiln until the binder material adheres to the grain and a plurality of grains adhere together to create a plurality of sintered agglomerates; e) recovering the sintered agglomerates from the kiln, the sintered agglomerates consisting of a plurality of bonded abrasive grains by bonding material having an initial three-dimensional shape and a loose packing density of <1.6 g / cm3; f) molding the sintered agglomerates into a composite shaped body; and g) heat-treating the composite molded article to provide the abrasive tool.

The correction methods using the abrasive tools of the invention, in particular, the surface-grinding processes, are also mentioned.

Figure 1 is a schematic drawing of a rotary kiln for carrying out the method of manufacturing the abrasive grain agglomerates of the invention.

Figure 2 is a photomicrograph of a cross section of an abrasive wheel of the invention made with agglomerated grain (lighter areas of photos), and having intra-agglomerate porosity (smaller darker areas of photo) and inter-agglomerate, the interconnected porosity (darker areas of the picture).

Figure 3 is a photomicrograph of a cross section of a comparative abrasive wheel of the prior art, showing the absence of agglomerated grain and the absence of large interconnected porosity in the structure of the grinding wheel.

The agglomerates of abrasive grains of the invention are structures or granules in three dimensions including sintered porous composites of abrasive grain and bond material. The agglomerates have a loose packing density (LPD) <1.6 g / cm3, an average size of about 2 to 20 times the average abrasive grain size, and a porosity of about 30 to 88% by volume. The abrasive grain agglomerates preferably have a minimum crush strength of 0.2 MPa.

The abrasive grain may include one or more grain (s) abrasive (s) known (s) for use in abrasive tools, such as the alumina grains, including fused alumina, sintered alumina and sintered sol gel, sintered bauxite, and the like, silicon carbide, alumina-zirconia, aluminoxynitrure, ceria, boron suboxide, garnet, flint, diamond, including natural diamond and synthetic, cubic boron nitride (CBN), and combinations thereof. Any shape or grit sizes may be used. For example, the grain may include sintered alumina grains ground frost, elongated with a high aspect ratio of the type mentioned in US Patent No. 5,129,919.

Suitable particle sizes for use in the present invention range from regular abrasive grits (e.g., greater than 60 to 7000 microns) to microabrasifs grains (for example, 0.5 to 60 microns), and mixtures of these sizes. For a given abrasive grinding operation, it may be desirable to agglomerate an abrasive grain with a grain size smaller than a grain size of grain (non-agglomerated) abrasive normally selected for this abrasive grinding operation. For example, the abrasive grain size of 80 to agglomerate may be substituted by the abrasive grain 54, grain 100 agglomerated by the abrasive grain 60 and the agglomerate grain 120 by the abrasive grain 80.

The preferred sintered agglomerate size for typical abrasive grains to the range from about 200 to 3000, more preferably 350 to 2000, preferably from 425 to 1000 microns in average diameter. For microabrasive grain, preferred sintered agglomerate sizes range from 5 to 180, more preferably from 20 to 150, preferably from 70 to 120 microns in average diameter.

The abrasive grain is present at about 10 to 65% by volume, more preferably 35 to 55% by volume, and preferably 48 to 52 volume% of the agglomerate.

Useful agglomerating materials in the manufacture of the agglomerates preferably include ceramic and vitrified materials the, preferably of the type of those used as binder systems to bonded abrasive tools, vitrified. These agglomerated materials, vitrified can be a precalcined glass ground into a powder (a frit), or a material of various raw materials such as clay, feldspar, lime, borax, and sodium carbonate, or a combination of sintered materials and raw materials. Such materials fuse and form a liquid glass phase at temperatures ranging to about 500 to 1 400 ° C and wet the surface of the abrasive grain to create binding rods upon cooling, thus holding the abrasive grain in the within a composite structure. Examples of suitable agglomerating materials for use in the agglomerates are given in Table 2 below. Preferred agglomerating materials are characterized by a viscosity of about 345 to 55,330 poise at 1180 ° C, and a melting temperature of about 800 to 1300 ° C.

In the preferred embodiment, the binder material is a binder composition comprising a vitreous composition of calcined oxides 71% by weight of B2O3 and S1O2, 14% by weight of AfeOa, less than 0.5% by weight alkaline earth oxides and 13 wt% alkali oxides.

The binder can also be a ceramic material including, but not limited to, silica, alkali, alkaline-earth, mixed alkali silicates and alkaline earth, aluminum silicates, silicates of zirconium, hydrated silicates, aluminates, oxides, nitrides, oxynitrides, carbides, oxycarbides and combinations and derivatives thereof. In general, ceramic materials differ from glassy or vitrified materials in that the ceramic materials comprise crystalline structures. Some glassy phases may be present in combination with crystalline structures, particularly in ceramic materials in an unrefined state. Ceramic materials in a raw state, such as clays, cements and minerals, may be used in the present invention. Specific examples of suitable ceramic materials for use herein include, but are not limited to silica, the sodium silicates, mullite and the other aluminosilicates, for zirconia-mullite, the aluminate magnesium, magnesium silicate, zirconium silicates to, feldspar and other alkali-alumino-silicates, the spinels, the calcium aluminate, the magnesium aluminate and other alkali aluminates, the oxide zirconium to zirconium oxide stabilized with diyttrium trioxide, the magnesium oxide, the calcium oxide, the cerium oxide to the titanium oxide or other rare earth additives , the talc, the iron oxide to aluminum oxide in the boehmite, the boron oxide, the cerium oxide, the aluminum oxide-oxynitride, nitride of boron, silicon nitride, graphite and combinations ceramic materials.

The bonding material is used in the form of powders and can be added to a liquid vehicle to insure a uniform, homogeneous mixture of binder material with abrasive grain during manufacture of the agglomerates.

A dispersion of organic binders is preferably added to the components of caking material in powder form such as molding or processing aids. These binders may include dextrins, starch, animal glue protein, and other types of glues; a liquid component, such as water, solvent, viscosity or pH modifiers; and mixing aids. Use of organic binders improves agglomerate uniformity especially the uniformity of the dispersion of the binder material on the grain, and the structural quality of the pre-calcined or gross agglomerates and the calcined abrasive tool containing the agglomerates. Because the binders are eliminated by combustion during firing of the agglomerates, they do not become an integral part of the finished agglomerate nor of the finished abrasive tool.

An inorganic adhesion promoter may be added to the mixture to improve adhesion of the abrasive grains caking materials as needed to improve the mix quality. The inorganic adhesion promoter may be used with or without an organic binder in preparing the agglomerates.

Although caking materials melting at high temperatures are preferred in the agglomerates of the invention, the bond material may also comprise other inorganic binders, organic binders, organic binders materials, metal binder materials and combinations thereof. Caking materials used in the abrasive tool industry to serve as binders for organic bonded abrasives, coated abrasives, metal bonded abrasives and the like are preferred.

The binder material is present in about 0.5 to 15% by volume, more preferably 1 to 10% by volume and preferably 2 to 8% by volume of the agglomerate.

The preferred percentage by volume of porosity within the agglomerate is as high as technically possible within the mechanical strength limitations needed to manufacture agglomerates with an abrasive tool and rectification therewith. Porosity may range from 30 to 88% by volume, preferably 40 to 80% by volume and preferably from 50 to 75% by volume. A part (e.g., up to about 75% by volume) of the porosity within the agglomerates is preferably present as interconnected porosity, or porosity permeable to the flow of fluids, including liquids (e.g., fluid cooling of correction and chips) and air.

The density of the agglomerates may be expressed in many ways. The bulk density of the agglomerates may be expressed as the LPD. The relative density in the relative density of the agglomerates may be expressed as a percentage of initial relative density, or as a ratio of the relative density of the agglomerates based on the components used to make the agglomerates, taking into account the porosity volume interconnected in the agglomerates.

The initial average density, expressed as a percentage, may be calculated by dividing the LPD (p) by a theoretical density of the agglomerates (po), assuming a zero porosity. The theoretical density may be calculated according to the volumetric rule of mixing methods from the weight percentage and density of the bonding material and the abrasive grain contained in the agglomerates. For the sintered agglomerates of the invention, a percentage of maximum density is 50 volume%, with a maximum percentage of 30% density by volume being more preferred.

The density can be measured by a volumetric fluid displacement technique to include interconnected porosity and exclude closed cell porosity. Density is the ratio of the volume of the sintered agglomerate measured by fluid displacement to the volume of the materials used to make the sintered agglomerates. The volume of the materials used to make the agglomerate is a measure of the apparent volume based on the quantities and packing densities of the abrasive grain and binder material used to make the agglomerates. For the sintered agglomerates of the invention, a maximum density of the sintered agglomerates preferably is 0.7, with a maximum density of 0.5 being more preferred.

The agglomerates may be formed by a variety of techniques in many forms and sizes. These techniques may be conducted before, during or after cooking the mixture of the initial stage ("vintage") of grain and bond material. The step of heating the mixture to melt and to flow the bonding material, thereby adhering the binder material to the grain and fixing the grain in an agglomerated form is referred to as firing, calcining or sintering. All methods known in the art for agglomerating mixtures of particles may be used to prepare the abrasive agglomerates.

In a first embodiment of the process used in this document to make the agglomerates, the initial mixture of grain and caking material is agglomerated before firing the mixture so as to create a relatively weak mechanical structure referred to as "raw agglomerate" or " agglomerate precooked. "

To drive the first embodiment, the abrasive grain and the caking materials may be agglomerated in the green state by many different techniques, for example, in a plate granulator, and then fed into a rotary calcination apparatus for sintering . Raw agglomerates may be placed onto a tray or rack and baked, without rotating, in a continuous or batch process.

The abrasive grain may be conveyed into a fluidized bed, then wetted with a liquid containing the bonding material to bond the bonding material to the grain, sorted for agglomerate size, and then cured in an oven or in a calciner.

The tray granulation can be carried out by adding grain to a mixer bowl, and measuring a liquid component containing the binder material (e.g., water, or organic binder and water) onto the grain, with mixing, to agglomerate them together. A liquid dispersion of binder material, optionally with an organic binder, may be sprayed onto the grain, and then the coated grain may be mixed to form agglomerates.

A low-pressure extrusion apparatus may be used to extrude a paste of grain and bond material into sizes and shapes which are dried to form agglomerates. A paste may be made from the agglomerating materials and grain with an organic binder solution and extruded into elongated particles with the apparatus and methods mentioned in the patent US-A-4 393 021.

In a dry granulation process, a sheet or a fabricated block (e) from abrasive grain imbedded in dispersion or paste of the bonding material may be dried (e) and then a roll compactor may be used to crush the composite of grain and bond material.

In another method of manufacture of raw or precursor agglomerates, the mixture of the bonding material and the grain may be added to a molding device and the mixture molded in shapes and precise sizes, for example, as mentioned in the US Patent n0o6 217 413 B1.

In a second embodiment of the process useful herein for making agglomerates, a simple mixture of grain and bond material (optionally with an organic binder) is fed into a rotating device calcination of the type shown in Figure 1. The mixture was rotated at an rpm / min predetermined, also with a predetermined inclination with application of heat. Agglomerates are formed as the mixture of binder material is heated, melts, flows and adheres to the grain. The steps of baking and sintering are carried out simultaneously at speeds and feed volumes and controlled application of heat. The feed rate generally is set to yield a flow occupying roughly 8 to 12%, by volume, of the tube (that is to say, the portion of the furnace) of the rotary calcination apparatus. The maximum temperature exposure within the apparatus is selected to keep the viscosity of agglomerating material in a liquid state at a viscosity of at least about 1000 poise. This avoids excessive flow of the bonding material on the surface of the tube and loss of binder material from the surface of the abrasive grain.

A rotary calcination apparatus of the type illustrated in Figure 1 may be used to drive the agglomeration process for agglomerating and cook the agglomerates in a single process step. As shown in Figure 1, a feed hopper (10) containing the mixture of feed (11) of the agglomerating materials and abrasive grain is fed into a means (12) for measuring the mixture in a hollow heating tube (13). The tube (13) is positioned under an angle of inclination (14) of approximately 0.5 to 5.0 degrees such that the feedstock (11) can be gravity fed to the interior of the hollow tube (13). Simultaneously, the hollow tube (13) is rotated in the direction of arrow (a) at a level of speed controlled to rotate the feed (11) and the heated mix (18) as and as it passes along the length of hollow tube.

A portion of the hollow tube (13) is heated. In one embodiment, the heating portion may comprise three heating zones (15, 16, 17) having a length dimension (d1) of 60 inches (152 mm) in the length (d2) of 120 inches (305 mm) of hollow tube (13). The heating zones permit the operator to control the processing temperature and to vary it as needed to sinter the agglomerates. In other camera models, the hollow tube may only comprise one or two heating zones (s), or it may comprise more than three heating zones. Although not illustrated in Figure 1, the apparatus is equipped with a heating device and mechanical control, electronic and temperature and detection of functional devices for driving the thermal process. As can be observed in the cross section of the hollow tube (13), the feedstock (11) is converted to a heated mixture (18) within the tube and it exits the tube and is collected in the form granules agglomerate (19). The wall of the hollow tube has an inner diameter dimension (d3) which may range from 5.5 to 30 inches (14 to 76 mm) and a diameter (d4) which may range from 6 to 36 inches (15 91 mm), depending on the model and the type of material used to construct the hollow tube (eg, refractory metal alloy, refractory brick, silicon carbide, mullite).

The inclination angle of the tube may range from 0.5 to 5.0 degrees and the rotation of the tube may operate at 0.5 to 10tr / min. The feed rate of a rotary calciner at a small scale may extend from about 5 to 10 kg / hour, and an industrial production scale feed rate may range from about 227 to 910 kg / hour. The rotary calciner may be heated to a sintering temperature of 800 to 1 400 ° C, and the feed material may be heated at up to 200 ° C / minute and progressively as the load supply enters the heated zone. Cooling occurs in the last portion of the tube as the feedstock moves from a heated zone to an unheated area. The product is cooled, for example, with a water cooling system, to room temperature and collected.

Rotary calcination Appropriate machinery can be obtained from Harper International, Buffalo, New York, or Alstom Power, Inc., Applied Test Systems, Inc. and other equipment manufacturers. The apparatus may optionally be equipped with electronic devices, and control of in-process detection of a cooling system of various models supply apparatus and other optional devices.

During the agglomeration of abrasive grain caking material with temperatures below treatment (for example, from about 145 to about 500 ° C), an alternative embodiment of this rotary kiln apparatus may be used. The alternative embodiment, a rotary dryer, is equipped to supply heated air to the discharge end of the tube to heat the abrasive grain mixture, cure the bonding material, bonding it to the grain, and agglomerate there the abrasive grain as it is collected from the apparatus. As used herein, the term "rotary kiln calcination" includes such rotary dryer devices.

In a third embodiment of the process useful herein for making agglomerates, a mixture of abrasive grain, agglomerating materials and an organic binder system is fed into an oven, without pre-agglomeration and heated. The mixture is heated to a sufficiently high temperature to cause melting, the flow and adhesion of the bonding material to the grain, then cooled to make a composite. The composite is crushed and sorted to make the sintered agglomerates.

In the fourth embodiment, the agglomerates are not sintered before making the abrasive tool, rather the "raw" agglomerates are molded with the binder material to form a tool body and the body is fired to form the tool abrasive. In a preferred embodiment of this method, a bonding material, high viscosity vitrified (forming a fluid when melted) is used to agglomerate grain in the green state. The raw grains are oven-dried and mixed with a second binder composition, vitreous, preferably lower viscosity, and they are molded in the form of a green abrasive tool. This tool is believed cooked to a temperature effective to melt, but to avoid the flow of bonding material, vitrified high viscosity. The firing temperature is chosen to be sufficiently high to melt the composition of a glass bonding material; caking away the grain, and by flowing the binder composition, the binder agglomerates and forming tool. It is not essential to select different viscosity materials and materials with different melting temperatures for conducting this method. Other combinations of materials caking and binding materials known in the art may be used in this technique for making abrasive tools from green state agglomerates.

The bonded abrasive tools of the invention include abrasive grinding wheels, segmented wheels, discs, hones, stones and other abrasive composites hewn monolithic, or segmented. The abrasive tools of the invention comprise about 5 to 75% by volume, preferably 10 to 60% by volume, preferably 20 to 52 volume% abrasive grain agglomerates.

In a preferred embodiment, the abrasive tools, chipboard, vitrified comprise about 3 to 25% by volume, more preferably 4 to 20% by volume, and preferably 5 to 19% by volume of binder. Together with agglomerates of abrasive grain and binder, these tools comprise about 35 to 80 volume% porosity, this porosity including at least 30% porosity volume interconnected, preferably 55 to 80 volume% porosity, this porosity including at least 50 volume% interconnected porosity. The abrasive tools, bonded, vitrified may include from 35 to 52 volume% sintered agglomerates, 3-13% by volume of vitrified and 35-70% porosity volume.

The amount of interconnected porosity is determined by measuring the permeability of the tool according to the fluid process of US Patent No. -A-5 738 696. As used herein, Q / P = the fluid permeability of an abrasive tool, where Q means flow rate expressed as cm3 of air flow, and P means differential pressure. The term Q / P represents the pressure differential measured between the abrasive tool structure and the atmosphere at a given flow rate of a fluid (e.g., air). This permeability Q / P is proportional to the product on the pore volume and the square of the pore size. The sizes of pores larger are preferred. The pore geometry and abrasive grain size are other factors affecting Q / P, with larger grit size producing the highest relative permeability.

The abrasive tools of the invention are characterized by higher fluid permeability values ​​than those of comparable prior art tools. As used herein, the "comparable prior art tools" are those tools made with the same abrasive grain and binding materials at the same porosity and the same volume percentages of binder as those of the invention. In general, abrasive tools of the invention have fluid-permeability values ​​of about 30 to 100% higher than the comparable values ​​abrasive tools of the prior art. The abrasive tools preferably are characterized by fluid permeability values ​​to at least 10% higher, more preferably at least 30% better than those of comparable prior art tools.

Exact relative fluid permeability parameters for particular shapes and sizes of agglomerates, types of binder and porosity levels may be determined by the practitioner by applying the law of D'Arey to empirical data for a given type abrasive tool.

The porosity inside the wheel from the open spacing provided by the natural packing density of the tool components, particularly the abrasive agglomerates, and, optionally, by adding conventional pore induction media . Suitable pore inducing media include, but are not limited to, hollow glass spheres, to the crushed walnut shells, the hollow spheres or beads of plastic material or organic compounds, foamed glass particles to, the mullite ventilated and vented alumina, and combinations thereof. The tools may be manufactured with open-cell pore inducers, such as beads of naphthalene, or other organic granules that burn during firing of the tool to leave void spaces within the matrix of the tool, or they may be manufactured with hollow pore inducing media, with closed cells (for example, hollow glass spheres). Preferred abrasive tools of the invention either do not contain pore inducing media, or contain a minor amount of induction media effective pore added to produce an abrasive tool with a porosity level including at least 30% by volume is interconnected porosity.

Bonded abrasive tools of the invention have a porous structure. In this structure, the average diameter of the sintered agglomerates is less than or equal to the average dimension of the interconnected porosity when the interconnected porosity is measured at a maximum opening point.

The finished tools optionally contain added secondary abrasive grains, fillers, grinding aids and pore inducing media, and combinations of these materials. The total volume percentage of abrasive grain in the tools (agglomerated and non-agglomerated grain) may range from about 34 to about 56% by volume, more preferably from about 36 to about 54 volume%, and most preferably from about 36 to about 46 volume% of the tool. The bonded abrasive tools preferably have a density of at least 2.2 g / cm3.

When an abrasive grain is used in combination with the abrasive agglomerates, the agglomerates preferably provide from about 5 to about 100 volume% of the total abrasive grain of the tool and more preferably from about 30 to about 70% by volume of the total abrasive in the tool. When such secondary abrasive grains are used, these abrasive grains preferably provide from about 0.1 to about 95% by volume of the total abrasive grain of the tool, and more preferably from about 30 to about 70% by volume . Suitable secondary abrasive grains include, but are not limited to, various aluminum oxides, sol gel alumina with, in the sintered bauxite, silicon carbide, alumina-zirconia, in aluminoxynitrure in ceria, boron suboxide, cubic boron nitride, diamond, garnet and the grain of flint, and combinations thereof.

The abrasive tools of the present invention preferably are bonded with a vitreous bond. All the various binding agents known in the art of making abrasive tools may be selected for use in the present invention. Examples of suitable binders can be found in U.S. Patent Nos 4 543 107; 4,898,597; 5,203,886; 5,401,284; 5,536,283; 5,095,665; 5,863,308; and 5,094,672, which are hereby incorporated by reference.

After firing, these vitreous binder compositions preferably include, but are not limited to a combination of the following oxides: S1O2, Al2O3, Na20, L12O and B2O3. Other oxides such as K2O, ZnO, ZrC> 2 and alkaline earth oxides, such as CaO, MgO and BaO, may be present. Cobalt oxide (CoO) and other coloring sources may be included where desired a binder color. Other oxides, such as Fe203, Ti02 and P2O5, and other compounds existing as an impurity in the raw materials may be included in the binder. Frits may be used in addition to raw materials (or unfired) binding, or instead of binding materials. The raw materials for the binder may include clay, kaolin, alumina, lithium carbonate, borax pentahydrate or boric acid, commercial sodium carbonate, flint and wollastonite, and such other materials binders such as known in the art. The vitrified bond may be a glassy material or a ceramic material, with or without amorphous regions.

Organic binders are preferably added to powdered binder components, fritted or raw, as molding aids or processing. These binders may include dextrins, starch, animal protein glue and other types of glue, a liquid component such as water, viscosity or pH modifiers and auxiliaries mixed. Use of binders improves the grinding wheel uniformity and the structural quality of the grinding wheel pressed raw or pre-cooked and cooked wheel. Because the binders are burned during firing, they do not become part of the binder or of the finished abrasive tool.

An inorganic adhesion promoter may be added to the mixture to improve adhesion of the vitreous binders for abrasive grain agglomerates as needed during mixing and molding processes. The inorganic adhesion promoter may be used with or without an organic binder in preparing the agglomerates.

For some of the agglomerates, the abrasive tool can be manufactured without added binder material, provided sufficient binder material is present in the tool to yield appropriate mechanical strength properties in the abrasive tool during manufacturing of the tool and the use of the tool in grinding operations. For example, an abrasive tool may be constructed from at least 70 volume% agglomerates, having a binding material content of at least 5% by volume of the agglomerate.

The density and hardness of the abrasive tools are determined by the choice of the agglomerates, type of binder and other components of the tool, the level of porosity, together with the size and type of mold and release process chosen .

Abrasive wheels may be molded and pressed through any means known in the art, including hot pressing techniques, hot and cold. Care must be taken in selecting the molding pressure to form the raw grinding wheels to avoid crushing an excessive amount of abrasive grain agglomerates (e.g., more than 50% by weight, of the agglomerates) and to preserve the three-dimensional structure of the agglomerates. The maximum applied pressure, suitable for the manufacture of wheels of the invention depends on the shape, size, thickness and the binder component of the abrasive wheel, and the molding temperature. In current manufacturing processes, the maximum pressure may extend from about 3 100 to 20 000 bps / square inch (218 to 1406 kg / cm2). Molding and pressing are preferably conducted at about 775 to 1550 kg / cm2, more preferably 465 to 1085 kg / cm2. The agglomerates of the invention have sufficient mechanical strength to withstand the molding and pressing steps carried out in typical commercial manufacturing processes for making abrasive tools.

The abrasive wheels may be fired by methods known to those skilled in the art. Baking conditions are primarily determined by the actual binder and abrasives used, and by the type of binder material contained in the abrasive grain agglomerate. Depending on the chemical composition of the binder selected, a vitrified bond may be fired at 600 to 1250 ° C, preferably 850 to 1200 ° C, to provide the mechanical properties necessary for grinding metals, ceramics or other materials. The vitrified agglomerate body may also be impregnated after firing in a conventional manner with a grinding aid, such as sulfur, or with a vehicle, such as epoxy resin, to carry a grinding aid within pores of the wheel.

The choice of suitable vitrified bond will depend upon the agglomeration process is used and that a melting temperature or a melting point or viscosity differential must be maintained between the binder material and the binder of the agglomerate.

In the manufacture of an agglomerated vitrified grinding wheel or other abrasive tool from the abrasive agglomerates, one technique several general techniques may be selected. In the first, a vitrified bond material, relatively higher firing temperature (e.g., that melts at above about 1000 ° C), is applied to agglomerate the grain. Then a second binder composition vitrified, lower firing temperature (e.g., melting at about 650 to 975 ° C) powder is mixed with the grain agglomerates and molded into the form of an abrasive tool. The tool to flood stage is fired at the lower firing temperature of the second binder material to create a finished abrasive tool. In a preferred embodiment, the vitrified bond has a curing temperature of the binder of at least 150 ° C lower than the melting temperature or melting of the bond tool.

In the second technique, viscosity differentials between the melted glasses in their liquid state are exploited to use the same firing temperature for making the agglomerate and firing the abrasive wheel. A high viscosity vitrified bond material is used to agglomerate grain in a first firing step. Then cooked agglomerates are mixed with a second binder composition of lower viscosity vitrified, and molded in the form of a green abrasive tool. The molded tool may be fired at about the same temperature as the temperature of the first firing step used to make the agglomerates, because when it is in a hot liquid state, the bonding material will not be lightened and not let the grain escape. The original three-dimensional configuration of the agglomerate thus can be maintained.

In a preferred embodiment of this technique, the viscosity of the vitrified bond to the melting temperature of the binder material is at least 33% lower than the viscosity of the bonding material at its melting temperature. Thus, when the viscosity of the bond material is about 345 to 55,300 poise at 1180 ° C, the preferred vitrified bond material is characterized by a viscosity of about 30 to 37,000 poise at 1180 ° C.

In the third technique, a binder material of intermediate firing temperature (e.g. about 850-975 ° C) is used to agglomerate grain, but agglomeration is done at a temperature above the melting temperature or melting the bonding material (for example, 1000 to 1200 ° C). the agglomerates are mixed with the same binder material as that used as vitrified binder composition and the mixture is molded in the form of a green abrasive tool. The raw tool is fired at a lower temperature (e.g., about 850 to 975 ° C) than the temperature used to melt the bond material to agglomerate the grain. The lower temperature is effective to bond the agglomerates together. This process maintains the three-dimensional structure of the agglomerates because the first layer of binder material does not flow at the firing temperature of the abrasive tool.

In a fourth technique, the same composition is used to serve as a bonding material and a binder for the wheel and the agglomeration is carried out and the baking at the same temperature. In theory it is considered that the fact that the bond material was melted to form a glass adhered to the abrasive grain during agglomeration, the properties of the materials were modified binders. Thus, the molten bonding material within the sintered agglomerates flows at a higher temperature than the unfused binder material, and the agglomerates retain their shape when the wheel is being cooked. In a preferred embodiment the composition used for the bonding material and the binder contains some raw materials and do not consist of a fritted glass composition.

In a fifth technique for making vitrified abrasive tools, the tool is made without added binder material. The agglomerates are packed inside of a mold for tools, pressed and fired at a temperature in the range of about 500 to 1400 ° C to form the tool. Caking materials used to make the agglomerates comprise a vitrified binder composition and the binder material is present in sufficient amount in the agglomerate (e.g., about 5 to 15% by volume of the agglomerate) to bond the agglomerates together in the 'finished vitrified abrasive tool.

The agglomerates can be bonded with any known type of binders, such as organic binder or resin and metal bonds, known in the art of manufacturing bonded abrasive tools. The percentage by volume range for agglomerates suitable for use in vitrified abrasive tools is also satisfactory for metal and organic bonded tools. The organic and metal bonded tools usually comprise higher volume percentages of binder and volume percentages of porosity lower than vitrified bonded tools, and the abrasive grain content may be higher. The organic and metal bonded tools may be mixed, molded and processed or sintered according to various processing methods, and with various proportions of abrasive grain or agglomerate, binders and porosity components as are known in the art. The agglomerates of the invention can be used in metal bonded single layer tools, as well as monolithic tools, three-dimensional structures, multilayer and segmented matrix abrasive tools as are known in the trade.

The abrasive tools of the invention include grinding wheels, discs, hones and stones and sticks and they are particularly effective in grinding applications having large surface area contact between the abrasive tool and the workpiece . Such applications or grinding operations include, but are not limited to corrections single deep pass and other corrections precision surfaces, porous tooling grinding operations, the grinding operations of internal diameter and fine grinding surface ceramics and other brittle workpieces.

Fine grinding operations or polishing using an abrasive grain size of micron or sub-micron benefit from use of tools made with the agglomerates of the invention. Compared with conventional tools and systems superfinishing or polishing tools of the invention made with such abrasive agglomerates will erode at grained grinding forces with little or no lower surface of the workpiece to be machined during a damage precision finishing operations (e.g., to produce finished mirror on glass and ceramic components). The life remains satisfactory due to the agglomerated structures, particularly in single layer tools, but also the tools to slurry and three-dimensional matrix.

'In grinding and precision grinding, the friability of the agglomerates contributes to fewer surfacing cycles. Due to the interconnected porosity of the tools, coolant supply and debris removal are enhanced resulting in cooler grinding operations, less thermal damage of the workpieces and less wear of the machines rectification. Due to the smaller grain size abrasive grains in agglomerated form give the grinding efficiency of a larger grit size grain, but leave a smoother surface finish, the basic quality of the workpiece to machine often improves significantly.

The following examples are offered for purposes of illustration of the invention and not for purposes of limitation.

Example 1

Was prepared a series of samples of agglomerated abrasive grains in a rotary calcination apparatus (model # HOU electric cooking-5D34-RT-28, maximum temperature of 1 200 ° C, 30 KW input, equipped with a metal tube refractory inner diameter of 5.5 "(14 cm), 72" (183 cm) long, manufactured by Harper International, Buffalo, New York). Was replaced refractory metal tube by a tube of the same dimensions silicon carbide, and the apparatus was modified so that it operates at a maximum temperature of 1 550 ° C. The process of agglomeration was carried under atmospheric conditions, a setting value of temperature control of the hot zone of 1180 ° C with a rotation speed of the camera tube 9 rev / min, an inclination angle of 2.5 to 3 degrees tube, and a material feed rate of 6 to 10 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1. The yield of usable free-flowing granules (defined as -12mesh on plate) was 60 to 90% of the total weight of the feedstock prior calcination.

Samples were manufactured agglomerates from a simple mixture of abrasive grain, bond material and water mixtures described in Table 1-1. The compositions of caking vitrified materials used to prepare the samples are listed in Table 2. Samples were prepared from three types of abrasive grain: fused alumina 38A, 32A fused alumina Norton SG grain and alpha alumina sintered sol gel, obtained from Saint-Gobain Ceramics & Plastics, Inc., Worcester, MA, USA, in the grit sizes listed in Table 1.

After agglomeration in the rotary calcination apparatus, the agglomerated abrasive grain samples were screened and tested for their loose packing density (LPD), size distribution and their resistance agglomerates. These results are shown in Table 1.

Table 1-1 Characteristics of agglomerated granules

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j (&lt;&lt;r α The percentage by volume of bonding material is a percentage of solids within the granule (i.e., the bond material and grain) after firing, and does not include the percentage by volume porosity.

The percentage was calculated by volume bond material agglomerates cooked using the LOI (loss of ignition - ignition loss) average in the raw materials bond material.

Was calibrated sintered agglomerates with test sieves of the EU standards mounted on a vibrating screening apparatus (Ro-Tap; Model RX-29; WS Tyler Inc. Mentor, OH). The sieve mesh sizes ranged from 18 to 140, as appropriate for different samples. Was measured bulk packing density of the sintered agglomerates (LPD) through the American National Standard procedure for Bulk Density of Abrasive Grains.

The initial average relative density, expressed as a percentage, was calculated by dividing the LPD (p) by a theoretical density of the agglomerates (po), assuming a zero porosity. The theoretical density was calculated according to the volumetric rule of mixing methods from the weight percentage and density of the bonding material and the abrasive grain contained in the agglomerates.

The resistance of the agglomerates was measured by means of a compaction test. Compaction tests were performed using a lubricated die steel of one inch (2.54 cm) diameter on an Instron® universal testing machine (model MTS 1125, 20,000 lbs (9072 Kg)) with a sample 5 grams of agglomerate. The sample was poured agglomerate in the die and slightly leveled by tapping the outside of the die. A punch is inserted from the top and a crosshead lowered until a force ("initial position") was observed on the recording apparatus. The pressure at the constant rate of increase (2 mm / min) was applied to the sample up to a maximum of 180 MPa of pressure. The volume of the agglomerate sample (the compacted LPD of the sample), observed as a displacement of the crosspiece (stress) was recorded as the relative density as a function of the logarithm of the applied pressure. Then riddled the residual material to determine the percentage crushed fraction. Different pressures were measured to establish a graph of the relationship between the log of the applied pressure and the crushed fraction in percentage. The results are reported in Table 1 as the log of the pressure at the point where the milled fraction equates to 50 weight percent of the agglomerate sample. The crushed fraction is the ratio of the weight of crushed particles passing through the smaller screen based on the weight of the initial sample weight.

These agglomerates had LPD, a particle size distribution, and molding strength and retention characteristics of the granule size suitable for use in the commercial manufacture of abrasive grinding wheels. The finished agglomerates sintered had three-dimensional shapes varying among triangular shapes, spherical, cubic, rectangular and other geometric shapes. Agglomerates consisted of a plurality of individual abrasive grits (e.g., 2 to 20 grains) bonded together by vitreous bonding material at the contact points grain to grain.

The size of the agglomerates of granules increased with an increase in amount of agglomerating material in the agglomerate granule over the of range of 3 to 20% by weight of the binder material.

Was observed adequate compaction resistance for all samples 1-9, indicating that the vitreous bond material had evolved and flowed to create an effective binder among the abrasive grains within the agglomerate. Agglomerates made with 10 weight% of agglomerating material had significantly higher compaction resistance compared to those made with 2 or 6 weight% of agglomerating material.

Lower LPD values ​​were an indicator of a higher degree of agglomeration. The LPD of the agglomerates decreased with increase of the weight percent of the bonding material and with decreasing abrasive grit size. Relatively large differences between 2 and 6% by weight of binder material, compared with relatively small differences between 6 and 10% by weight of binder material indicate a weight percentage of binder material below 2% by weight may be inadequate for the formation of agglomerates. The higher weight percentages, located at above about 6% by weight, the addition of more agglomerating materials may not be beneficial to provide significantly greater or stronger agglomerates.

As suggested by the results for granule size, agglomerate samples agglomerating material C having the lowest molten glass viscosity at the agglomerating temperature, had the lowest LPD of the three among caking materials. The abrasive type did not have significant effect on the HPA.

Table 2 binder material used in the agglomerates

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d. The variation of bond material A-1 exposed in parentheses was used for the samples of Example 2.

b. Impurities (e.g., Ti02 and Fe203) are present in about 0.1 to 2%. Example 2

Were manufactured further samples of agglomerates using other embodiments of processing and various feedstock materials.

A series of agglomerates were formed (samples nos10 13) at different sintering temperatures, ranging from 1 100 to 1 250 ° C, using a rotary calcination apparatus (model # HOU-6D60-RTA-28, equipped a tube mullite of 120 inches (305 cm) long, 5.75 inches (15.6 cm) inner diameter, 3/8 inch (0.95 cm) thick, having a heated length of 60 inches (152 cm) with three zones of temperature control. The apparatus was manufactured by Harper International, Buffalo, New York). Used was a Brabender feeder unit with volume regulation feed rate to measure the abrasive grain and the bond material mixture into the heating tube of the rotary calcination apparatus. The process of agglomeration was carried under atmospheric conditions, with a rotational speed of the unit tube 4 rev / min and an inclination angle of 2.5 degrees tube, and a feed rate of 8 Kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1. The choice of temperature and other variables used to make these agglomerates are set forth in Table 2-1.

All samples contained a mixture, on a weight percentage basis, of 89.86% of abrasive grain (grit 38A alumina grain 60 obtained from Saint-Gobain Ceramics &amp; Plastics, Inc.) to 140.16 ^ binder mixture (6.3% by weight of binder based on AR30 liquid protein, 1.0% Carbowax 3350 PEG and 2.86% of agglomerating material A). This mixture was producing 4.77 vol% bond material and 95.23 volume% grain in the sintered agglomerate granules. The calculated theoretical density of the agglomerate granules (assuming a zero porosity) was 3.852 g / cm3.

Before placing the mixture into the supply unit, the green state agglomerates I were trained by simulated extrusion. To prepare extruded agglomerates was heated liquid protein binder to dissolve the Carbowax 3350 PEG. Is then slowly added the binder material while stirring the mixture. Was added abrasive grains in a high shear mixer (44 inch (112 cm) diameter) and the prepared mixture of agglomerating binder material was slowly added to the grain in the mixer. The combination was mixed for 3 minutes. Is riddled the combination mixed in the wet state through a sieve of 12 mesh-shaped box (screen size of the EU standards) onto trays in a layer of a maximum depth of one inch (2.5 cm ) to form wet agglomerates, raw (uncooked) extrudates. Were dried in the oven at 90 ° C for 24 hours the layer of extruded agglomerates. After drying, passed again screened agglomerates using a box-shaped sieve 12 to 16 mesh (sieve size of the EU standards).

It was observed during rotary calcination that the agglomerates made in the green state appeared to be breaking when they were heated, and then, re-formed as they exited the loose end of the heated portion of the rotary tube calcination. The larger agglomerated granules made in the green state, relative to those of agglomerated granules after firing easily appeared on samples of visual inspection.

After curing, it was observed that the sizes of the agglomerated particles were sufficiently uniform to be used for commercial purposes, with a particle size distribution situated above a range of about 500 to 1200 microns. Particle size distribution of the measurements are set forth in Table 2-2 below. Yield, size, crush strength and LPD were acceptable for commercial use in making grinding wheels.

Table 2-1

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°) setting value of temperature control of the rotary calcination apparatus (for all 3 zones).

b) "n / a" indicates that no measurement was made.

Table 2-2 particle size distribution for cooked agglomerates

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Example 3

Agglomerates were prepared (Samples Nos 14 to 23) as described in Example 2, except that the constant temperature maintained at 1000 ° C, we used a rotary calcination apparatus model #KOU -8D48-RTA-20, equipped with a fused silica tube 108 inches (274 cm) long, 8 inches (20 cm) internal diameter, with a heated length of 48 inches (122 cm) with three zones the temperature control. The apparatus was manufactured by Harper International, Buffalo, New York. We examined various methods for the preparation of pre-cooked mixture of grain and bond material. We drove the agglomeration process under atmospheric conditions, with a rotational speed of the camera tube to 4tr 3 / min, an angle of inclination of 2.5 degrees tube, and a feed rate of 8 to 10 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

All samples contained 30 lbs (13.6 Kg) abrasive grain (the same grain used in Example 2, except that sample 16 contained 25 lbs (11.3 kg) of alumina grains ground Norton gel SG® grain 70 obtained from Saint-Gobain Ceramics and Plastics, Inc.) and 0.9 pounds (0.41 kg) of agglomerating material A (yielding 4.89 volume% bond material in the sintered agglomerates. It dispersing the binder material in different binder systems prior to addition of the grain. The binder system of Example 2 ("binder 2") was used for some samples and other samples were made using AR30 liquid protein binder ( "binder 3") in the weight percentages listed below in Table 3. Sample 20 was used to prepare agglomerates in the green state, uncooked by the simulated extrusion method of Example 2 .

The variables tested and the test test results are summarized below in Table 3.

Table 3 Treatments binders in the raw state

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These results confirm that the agglomeration in the raw state is not necessary to form a quality and acceptable yields of agglomerated sintered pellets (compare samples 18 and 20). Insofar as the percentage by weight of the binder 3 used in the initial mix increased from 1 to 8%, the LPD showed a trend towards a moderate decrease, indicating that the use of a binder has a beneficial, but not essential on the agglomeration process. Thus, rather unexpectedly, it did not appear necessary to pre-form a desired shape or a size of granule agglomerates before the sintering in a rotary calcination apparatus. Was reached the same LPD merely by feeding a wet mixture of the agglomerate components into the rotary calcination apparatus and by rotating the mixture as it passes through the heated portion of the apparatus.

Example 4

Agglomerates were prepared (samples our 24 to 29) as described in Example 2 except that the temperature was maintained constant at 1200 C and is examined various methods for the preparation of precooked mixture of grain and binder material. All samples (except samples 28-29) contained a mixture of 300 pounds (136, 4 kg) abrasive grain (same grain as Example 2: A 38 alumina 60 grit) and 9.0 pounds (4, 1 kg) of agglomerating material A (yielding 4.89 volume% bond material in the sintered agglomerate).

Sample 28 (same composition as Example 2) contained 44.9 lbs (20.4 Kg) of grain and 1.43 pounds (0.6 kg) of bonding material A. On the bonding material associated to the mixture of liquid binder (37.8 wt% (3.1 lbs) of AR30 binder in water) and added to the grain 4.98 pounds of this combination. The viscosity of the liquid combination was 784 CP at 22 ° C (Brookfield viscometer LVF of).

Sample 29 (same composition as Example 2) contained 28.6 lbs (13 Kg) of grain and 0.92 pound (0.4 kg) of agglomerating material A (yielding 4.89 volume% bond material in the sintered agglomerate). Was associated the bonding material to the liquid binder mixture (54.7 wt% (0.48 pound) of Duramax® resin B1052 and 30.1 wt% (1.456 lbs) Duramax resin B1051 resin of in water) and this combination was added to the abrasive grain. The Duramax resins were obtained from Rohm and Haas, Philadelphia, PA.

We drove the agglomeration process under atmospheric conditions at a speed of rotation of the tube of the apparatus of 4 rev / min and an inclination angle of 2.5 degrees tube, and a feed rate of 8 to 12 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

Was pre-agglomerated sample 28, before calcination, in a device manufactured by Niro fluidized bed, Inc., Columbia, Maryland (model MP-2/3 ™ Multi-Processor equipped with a cone size of MP- 1 (3 feet (0.9 meter) in diameter at its widest width) were selected following process variables for conducting the sample from the fluid bed process. inlet air temperature 64 at 70 ° C air flow at the inlet 100 300 cubic meters / hour flow rate of the granulating liquid 440 g / min bed depth (initial charge 3 to 4 kg) about 10 cm air pressure 1 external mixing nozzle bar two fluids 800 microns opening

Was charged with the abrasive grain in the bottom of the apparatus and directed air through the diffuser plate of the fluidized bed upwardly and within the grain. At the same time, the liquid was pumped mixture of binder material and a binder to the external mix nozzle and then sprayed from the nozzles through the plate diffuser and into the grain, then the coating of individual abrasive grains. Agglomerates raw stage were formed during the drying of the bonding material and binder mixture.

Pre-agglomerate the sample was 29, before calcination, in a low pressure extrusion process using a Benchtop Granulator ™ manufactured by LCI Corporation, Charlotte, North Carolina (equipped with a perforated basket having holes of 0, 5 mm in diameter). Is manually loaded grain mixing, agglomerating and binder material in the perforated basket (the extruder screen), were forced through the screen by rotating blades and collected in a stacker. Were dried in the oven pre-agglomerates extruded at 90 ° C for 24 hours and they were used as feedstocks for the rotary calcination process.

The variables tested and the test results are summarized below and in Tables 4-1 and 4-2. These tests confirm the results set forth in example I 3 are also observed at a higher firing temperature (1200 versus 1000 ° C). These tests also illustrate that low-pressure extrusion and the pre-agglomeration in a fluidized bed can be used to make agglomerated granules, but an agglomeration step before rotary calcination the is no need to manufacture the agglomerates of the invention.

Table 4-1 Characteristics of agglomerates

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Table 4-2 Particle size distribution of the particles in the agglomerates

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Example 5

Was prepared additional agglomerates (sample numbers 30 to 37) as described in Example 3, except that the sintering was performed at 1180 ° C, different types of abrasive grains were tested, and. we mixed 30 pounds (13.6 kg) of abrasive grains with 1.91 pounds (0.9 kg) of agglomerating material A (to yield 8.94 volume% of agglomerating material in the sintered agglomerate granules ). Binder 3 of Example 3 was compared to water as a binder for the agglomeration raw stage. Samples 30-34 were using 0.9 pound (0.4 kg) of water as a binder. Samples 35-37 used 0.72 pound (0; 3 kg) of binder 3. The variables tested are summarized below in Table 5.

The process of agglomeration was carried under atmospheric conditions, with a rotational speed of the camera tube of 8.5 to 9.5 rev / min and an inclination angle of 2.5 degrees tube, and a feed rate of 5 to 8 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

After agglomeration, were screened samples of agglomerated abrasive grains and tested for their loose packing density (LPD), size distribution and their resistance agglomerates. These results are shown in Table 5.

Table 5

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These results again demonstrate the utility of water as a temporary binder for the agglomerates in the rotary calcination process. In addition, mixtures of grain types, grain sizes, or both, may be agglomerated by the method of the invention and these agglomerates can be coated at a temperature of 1180 ° C in the rotary calciner . A significant increase in crush strength was observed when abrasive grain elongated high aspect ratio (that is to say,&gt; 4: 1) was used in the agglomerates (sample 33). Example 6

Another series of agglomerates was prepared (sample numbers 38 to 45) as described in Example 3, except that used different sintering temperatures, and which have been tested various types of mixtures size grain abrasive grains, different caking materials. In some of the feedstock mixtures are used nutshells to serve as pore induction organic filler material (walnut shell was obtained from Composition Materials Co., Inc., Fairfield, Connecticut, in a US sieve size 40/60). The variables tested are summarized below in Table 6. All samples contained a mixture of 30 pounds (13.6 kg) of abrasive grains and 2.5 wt% of binder 3, on a weight basis of grain with varying amounts of agglomerating materials as shown in Table 6.

The process of agglomeration was carried under atmospheric conditions, with a rotational speed of the camera tube of 8.5 to 9.5 rev / min and an inclination angle of 2.5 degrees tube, and a feed rate of 5 to 8 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

After agglomeration, were screened samples of agglomerated abrasive grains and tested them for their loose packing density (LPD), average size and resistance to crushing agglomerates (see Table 6). The properties of all agglomerates were acceptable for use in manufacturing abrasive grinding wheels. It appears that these data indicate that the use of organic pore inducers, that is to say, nut shells, showed no significant impact on the characteristics of the agglomerates.

Table 6

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to. The% is based on total solids (grain, bond material and pore inducer) and does not include the porosity of the agglomerate.

Example 7

Agglomerate samples were used 10 to 13 and 24 to 27 prepared according to Examples 2 and 4, respectively, to produce grinding wheels (finished size: 20 x 1 x 8 inch) 50.8 x 2.54 x 20 3 cm). These wheels were tested in a grinding operation to single deep pass over comparative wheels made without agglomerates, but containing pore inducer filler material.

To produce the grinding wheels, the agglomerates were added to a mixer along with a liquid binder and a binder composition Vitreous corresponding powder clumping material Table 1-2. Then molded, dried, cooked the wheels at a maximum temperature of 900 ° C, the calibrait, finished, balanced out and inspected according to commercial grinding wheel manufacturing techniques known in the art.

The composition of the wheels (including volume percent abrasive, the binder and porosity in the fired wheels), density, and modulus properties of the wheels are described in Table 7-1. We made ​​the wheels to a modulus of elasticity corresponding to a standard hardness quality grinding wheels between the D and E grades on the hardness scale quality of the Norton Company. Preliminary tests have shown that the wheels formulated from agglomerated grain with a volume% structure (that is to say, volume% grain, binder and pores, to a total of 100% ) identical to that of a comparative wheel made ​​without agglomerated grain were in fact considerably lower density, had a lower elastic modulus, and were softer than the comparative wheel. Thus, density and elastic modulus higher than the calculated volume% structure, were selected as indicators of the critical wheel hardness for wheels made ​​with agglomerated grain and tested in these grinding studies.

Table 7-1 Characteristics of abrasive wheels

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a) 37.50% by volume of abrasive grain, the comparative wheels contained a greater volume percentage of abrasive grain (that is to say, 1 to 3 volume% more) than the experimental wheels made with 37.50% by volume of agglomerated grain, bond material and intra-agglomerate porosity.

b) fluid permeability was measured (air) by the test methods mentioned in U.S. Patent Nos 5 738 696 and 5 738 697, assigned to Norton Company. The permeability to air of relative values ​​are expressed in cm 3 / second / inch of water units.

c) Comparative wheel samples were commercial products obtained from Saint-Gobain Abrasives, Inc., Worcester, MA, and marked with the names of the wheels shown for each sample in Table 7-1.

d) Values ​​for volume% of binder in the experimental wheels do not include the volume% vitreous bond material used on the grains to make the agglomerates. The volume% binder represents only the added materials to make the wheels.

The grinding wheels were tested in a grinding operation to single deep pass over comparative commercial wheels recommended for use in grinding operations single deep pass (the comparative wheels are described in Tables 7-1 and 7- 2). The comparative wheels had the same shape dimensions, comparable to the qualities of hardness and were otherwise suitable comparative wheels compared to the experimental wheels in a rectification study single deep pass, but they were made without agglomerates.

Terms correction:

Machine: Hauni-Blohm Profimat410

Mode: rectification single deep pass single strand

Cutting Depth: 0.125 inches (0.318 cm)

Grinding wheel speed: speed of 5500 surface feet per minute (28 m / sec) Table speed: varying increments of 2.5 in / min (6.4 cm / min) from 5 to 17.5 inches / minute (12.7 to 44.4 cm / minute) or until failure is observed (workpiece burn or machine to failure of the grinding wheel or machine) Coolant: Master Chemical Trim E210 200, at a 10% concentration with deionized well water, 95 gal / min (360 L / min)

Material of the workpiece: AISI 4340 steel hardness 48-50 Rc surfacing mode: rotary diamond, non-continuous surfacing compensation: 40 micro-inches / rev (1 micrometer / rev) Total Compensation of radial surfacing: 0.02 inches / rev (0.5 mm / rev)

Gear ratio: 0.8

In these grinding passages were increased table speed until the failure is observed. Failure was indicated by burning of the workpiece or by excessive wheel wear as indicated by power data, the measuring wheel wear (WWR) measurements and surface finish visual inspection of the ground surface. The material removal rate (MRR maximum) to which the failure occurred was noted.

As set forth in Table 7-2, below, these grinding tests demonstrated that the experimental wheels containing the agglomerates were able to consistently achieve maximum rates of material removal, higher than those of comparative wheels . Experimental wheels were also evidence of acceptable values ​​for other less critical parameters, correction observed in the single pass grinding operations (that is to say, WWR, power and surface finish at the maximum MRR).

Table 7-2 Results of the grinding test

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a) 37.50% vol. abrasive grain, the

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comparative wheels contained a vol%. Higher abrasive grain (that is to say, 1 to 3 vol.% or more) than the experimental wheels made with 37.50 vol.% agglomerate grain, consolidated material, bonding material and intra-agglomerate porosity.

Example 8

A sample of agglomerate abrasive grain was prepared (60) in the rotary calcination apparatus, with a silicon carbide tube, described in Example 1 and illustrated in Figure 1. The process of agglomeration was carried under atmospheric conditions, at 1 350 ° C with a rotation speed of the camera tube 9 rev / min, an angle of inclination of 3 degrees of the tube, and a feed rate of 6 to 10 kg / hour .

Were manufactured sample of agglomerate from a mixture of alumina abrasive grains 38A, 60 grit size (same grain as used in Examples 1 and 6), 5.0% by weight bonding material F (based on weight of abrasive grain) and 2.5 wt% of binder 3 in water (50/50 mixture by weight based on the weight of abrasive grain).

After agglomeration in the rotary calcination apparatus, the sorted agglomerated abrasive grain and tested for the loose packing density (LPD) and other attributes by the methods described above. The yield of usable free-flowing agglomerates (defined as -12mesh on board) was 72.6% of the feedstock before sintering. The LPD of the agglomerate was 1.11 g / cm3 and the relative density was 28.9%. We used these sintered agglomerates to produce grinding wheels with a finished size of 16.25 X 0.75 X 5.00 inches (41.3 x 2.4 x 12.8 cm).

To produce the grinding wheels, the agglomerates were added to a mixer together with a vitreous binder composition powder (corresponding to the agglomerating material C of Table 1-2) and liquid binder 3 to make a mixture. The wheels were then molded from this mixture, dried, fired at a maximum temperature of 900 ° C, graded, finished, balanced and inspected according to commercial grinding wheel manufacturing techniques known in the art. We manufactured the wheels to match in terms of elastic modulus value to comparative wheels having a standard wheel hardness grade in the range of quality E on the scale of quality hardness of the Norton Company.

The characteristics of the fired wheels and a comparative commercial wheel, obtained from Saint-Gobain Abrasives, Inc., Worcester, MA, are described in Table 8-1 below.

Table 8-1 Grinding wheels

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u) A ^ 3, 50% by vol. abrasive grain component, the comparative sample wheels contained in a percentage of abrasive grain larger volume (e.g., about 1 to 3% by volume. more) than the experimental wheels of the invention containing a mixture of 37.50% vol. agglomerate grain, bond material and intra-agglomerate porosity.

b) was measured permeability to fluids (air) by the test methods mentioned in Patent US 5 738 696 and 5 738 697, assigned to Norton Company. The air permeability relative values ​​are expressed in cm 3 / second / inch of water units.

c) Values ​​for the% by vol. binder excluding vol%. of bonding material used on the grains to make the agglomerates. The vol%. binder represents only the added materials to make the wheels.

The grinding wheels were tested as described in Table 8-1 in a grinding test single deep pass. We set the parameters of the grinding test single deep pass to produce the following conditions rectification.

Terms correction:

Machine: Hauni-Blohm Profimat410

Mode: rectification single deep pass single strand

Cutting Depth: 0.125 inches (0.318 cm)

Grinding wheel speed: 5500 feet per minute (28 m / sec)

Table speed: varying increments of 2.5 in / min (6.4 cm / min) from 5 to 15 inches / minute (12.7 to 38.1 cm / minute) or until that a failure is observed (workpiece burn or machine to failure of the grinding wheel or machine) Coolant: Master Chemical Trim E210 200, at a 10% concentration with deionized well water, 95 gal / min (360 L / min)

Material of the workpiece: AISI 4340 steel hardness 48-50 Rc

Fashion surfacing: rotary diamond, non-continuous

Compensation surfacing: 40 micro-inches / rev (1 micrometer / rev)

Total compensation of the radial surfacing: 0.02 inches

Gear ratio: 0.8

In these grinding passages were increased table speed until the failure is observed. Failure was indicated by burning of the workpiece or by excessive wheel wear as indicated by power data, wheel wear measurements (WWR), measurements of surface finish and visual inspection of the ground surface. The material removal rate (MRR) (that is to say, maximum MRR before failure) which the failure occurred was noted. It has also made measurements of surface finish.

As outlined in Table 3-2 below, these grinding tests demonstrated that the experimental wheels containing the agglomerates were able to achieve consistently maximum rates of removal of material before burning the workpiece. The maximum MRR for the comparative wheel appeared at a table speed of only 12.5 inch / minute (5.29 mm / sec), while the maximum MRR for the experimental wheel appeared at a table speed of 15 inches / minute (6.35 mm / sec).

Experimental wheels were also show values ​​comparable, and commercially acceptable for the other grinding parameters observed at the highest MRR achieved by the comparative wheels in this single deep pass operation (that is to say, power and finished surface to the table speed of 5.29 mm / sec).

Table 8-2 Results of the grinding tests

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Example 9

Grinding wheels were tested with the sample made of agglomerate 35 of Example 5 in a transverse advance grinding process to dry surface, typical methods used in the workshop of grinding operations tooling. Were compared to a comparative commercial wheel wheels of the invention in this test.

The wheels containing agglomerates were made by the method of Example 8 and baked them at a maximum temperature of 900 ° C, however, the size of the wheels was 7 x 0.5 x 1.25 inch (17 , 8 x 1.3 x 3.2 cm). The fired wheels contained 40% agglomerates, 11 to 12.1% vitrified bond and 47.9 to 49% porosity, on a percentage volume basis. Baking conditions for the wheels of the invention and the properties of the fired wheels and the comparative wheels are in Table 9-1.

Table 9-1 Grinding wheels

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a) 40.0% vol. abrasive grain component, the wheels of the comparative sample contained a percentage of abrasive grain larger volume (see Table 9-2 below) that the experimental wheels of the invention containing 40.0% vol. agglomerated grain (including bond material and intra-agglomerate porosity).

b) was measured air permeability by the test methods mentioned in U.S. Patent Nos 5 738 696 and 5 738 697, assigned to Norton Company.

c) Values ​​for the% by vol. binder excluding vol%. of bonding material used on the grains to make the agglomerates. The vol%. binder represents only the added materials to make the wheels.

The volume percentage of abrasive grain and vitreous bond material of the agglomerates used in the experimental wheels is set forth in Table 9-2, below.

Table 9-2 Composition of the adjusted wheel for the components of the agglomerates

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a) 40.0% vol. abrasive grain, are comparative wheels contained a vol%. larger abrasive grain (that is to say, 1 to 3 vol.% more) than the experimental wheels made with 40.0 vol.% agglomerate grain, bond material and intra-agglomerate porosity. Terms correction:

Machine: Brown and Sharpe surface rectifier

Mode: dry surface grinding

Cross feed: 0.508mm

Grinding wheel speed: 3500 r / min; 6500 SFPM

Table speeds: 50 SFPM (15,240 mm / min)

Coolant: none

Material of the workpiece: D3 steel hardness 60 Rc 203.2 mm long x 47.8 mm wide surfacing mode: single point diamond Compensation surfacing: 0,025 Fixed surfacing: 254 mm / min

In these grinding passages were increased distribution from the top until the failure is observed. In surface grinding operations of the tooling, as in grinding operations single deep pass, the most significant performance parameter is the relative capacity at maximum material removal rate (MRR) of the wheel. Thus, a maximum MRR at which grinding failure occurred was noted for each grinding wheel, and failure was indicated by visual burn observations of the workpiece, excessive power, or an excessive rate of wear of the grinding wheel ( WWR). It has also made measurements of surface finish.

As set forth in Tables 9-3 and 9-4, below, this grinding test demonstrated that the experimental wheels containing the agglomerates consistently reached higher maximum material removal rates before the degradation of the grinding wheel by wear. In addition, higher MRR were achieved with lower power while maintaining comparable surface roughness values.

Table 9-3 Results of the grinding tests

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Table 9-4 Measurement Results-grinding tests wear meules3

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a) was measured wheel wear by variation of the process ("angles holding test") described in US Patent No. 5 401 284, assigned to Norton Company. For the data in this table were measured values ​​A and D at the perimeter of the grinding wheel along the grinding face of the grinding wheel, and measured the B and C values ​​at equidistant points near the center the grinding face of the wheel. As to the grinding progresses, the relative stability of values ​​A and D, compared to values ​​B

and C is an indicator of the resistance of the grinding wheel wear. The "surface" is the amount of material removed from the wheel. The% wear of the face of the wheel reflects the width of the wear of the grinding wheel in the center of the grinding face of the grinding wheel, near the points where the values ​​B and C are measured.

Example 10

Were tested wheels made with abrasive grain agglomerates in an inner diameter grinding test (Di).

Agglomerates was prepared (Sample 61) as described in Example 2 except that the temperature was maintained constant at 1170 ° C (sample 61). Additionally, it has been used a rotary calcination apparatus model # KOU-8D48-RTA-20, equipped with a silicon carbide tube of 108 inches (274 cm) long, 8 inches (20 cm) diameter inside, with a heated length of 48 inches (122 cm) with three temperature control zones. This apparatus was manufactured by Harper International, Buffalo, New York. The process of agglomeration was carried under atmospheric conditions, with a rotational speed of the camera tube 6 rev / min, an angle of inclination of from 2.5 to 3.0 degrees tube, and a speed power of 8 to 10kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

Agglomerate the sample 61 was manufactured with 30 pounds (13.63 kg) of abrasive grain (32A alumina grain 120 grain, obtained from Saint-Gobain Ceramics and Plastics, Inc.) and 1.91 pounds ( 0.87 kg) of agglomerating material A (yielding 6.36 wt% of binder material in the sintered agglomerate). The binder material was dispersed in water (0.9 pound; 0.41 kg) prior to the addition of grain. The agglomerates had an average size of 260 microns and a loose packing density (LPD) of 1.13 g / cm3.

In this test, compared to the comparative commercial grinding wheels of the invention. The comparative wheel had the same shape and dimensions was made with the same abrasive grain, but without agglomerates. The comparative wheel-32A120 LVFL the model was obtained from Saint-Gobain Abrasives, Inc., Worcester, MA.

To make the experimental wheel, the agglomerates were added to a mixer at the same time a powdered vitrified binder composition and the liquid binder 3 to make a mixture. The wheels were then molded from this mixture, dried, fired at a maximum temperature of 900 ° C, graded, finished, balanced and inspected according to commercial grinding wheel manufacturing techniques known in the art.

The wheels were 1A type wheels, with a finished size of 1.8 X 1.0 X 0.63 inches (4.57 x 2.54 x 1.60 cm). The composition and characteristics of the experimental and comparative wheels are listed below in Table 10-1 lê.

Table 10-1 Meules

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a) A 52% vol. of abrasive grain component, the comparative sample wheels of the contained a larger volume percentage grain than the wheels of the invention containing 48% by vol. a grain mixture agglomerated with binder material. After deducting the percent of binder material, the experimental wheels contain only 43.4% by vol. grain, 8.6% in flight. grain in less than the standard comparative wheel of the same quality.

b) The grain of abrasive grain size of 120 corresponds to 142 microns.

c) Values ​​for the% by vol. binder excluding vol%. of bonding material used on the grains to make the agglomerates. The vol%. binder represents only the added materials to make the wheels.

Were tested for abrasive wheels described in Table 10-1 in an inner diameter grinding test (Di). Di were fixed the grinding test parameters to produce the following conditions rectification. Terms of corrections:

Machine: rectifier Okuma ID

Mode: Di wet, grinding by swallowing, diving Grinding wheel speed: 18,000 rev / min Working speed: 600 r / min

Coolant: Master Chemical Trim E210, 5% in deionized well water

Material of the workpiece: 52 100 Steel hardness Rc 60

Rings: 2.225 x 0.50 inches (5.65 x 1.28 cm)

Fashion surfacing: rotary diamond single tip surfacing Ratio: 0,650 Fixed surfacing: 0.364 mm / rev

In these tests was conducted three sets of rectification to input constant speeds and was conducted five corrections for each set. The input speed sets a nominal material removal rate for each test. In Di of grinding operations, the most significant performance parameters are the G ratio (MRR / rate of wheel wear (WWR)), the specific energy required to grind at a set input speed and resulting finished surface. The data in the table below are given for each set of input gears; the surface finish data represents the value after the fifth correction of each set.

As set forth in Table 10-2, below, these grinding tests demonstrated that the performance of the experimental wheel containing the agglomerates was comparable to, or better than, that of the comparative wheel in terms of G ratio (MRR / wear rate of the grinding wheel (WWR)), specific energy correction and surface finish. These results are surprising in view of the significantly lower volume percentage of abrasive grain in the experimental wheel. With normal wheel structures, the vol%. abrasive grain is the most significant variable in determining the G report In the absence of other variables, a higher content of grain results in a proportionately higher G ratio. A reduction in the volume percentage of grain needed to achieve the same or better ratio G represents a significant technical improvement in the abrasive tool.

Table 10-2 Grinding Test Results

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to. The report gave G (for the experimental wheel) is an adjusted value for the lower volume percentage of abrasive grain in the experimental wheel. In other words, the volume percentage of grain in the experimental wheels is only 83.46% of the volume percentage of grain in the comparative wheels. Thus, the G ratio values ​​of the experimental wheels in the parentheses have been normalized to% by vol. Grain comparative wheels to obtain a performance measure based on the total use of abrasive grain.

Example 11

The agglomerated abrasive grain was used to make the invention of large wheels in order to confirm the feasibility of manufacturing such wheels without the use of added pore inducers and using such wheels in the single deep pass rectification.

The agglomerated abrasive grain was prepared (sample 62) in the rotary calcination apparatus, with a silicon carbide tube, described in Example 1 and illustrated in Figure 1 was conducted in the agglomeration process conditions air, at 1350 ° C with a rotation speed of the camera tube 9 rev / min at an angle of inclination of 3 degrees of the tube, and a feed rate of 6 to 10 kg / hour .

Was manufactured the agglomerate grain sample 62 from a 50/50 mixture of alumina abrasive grain 32A and 38A, both 60 grit size (same grain as used in Examples 1 and 6) , 5.0 wt% of agglomerating material E (based on weight of abrasive grain) and 2.5% by wt binder 3 (50/50 weight mixture in water based on the weight of abrasive grain).

After agglomeration in the rotary calcination apparatus, the sorted agglomerated abrasive grain samples and tested for the loose packing density (LPD) and other attributes by the methods described above. The production of granules usable free-flowing (defined as -12 mesh to pan) was 74.1% of the total weight of the feedstock prior calcination. The LPD of the agglomerate was 1.14 g / cm3 and the density was 30.0%.

We used these sintered agglomerates to produce grinding wheels single deep pass relatively large (e.g., 20 inches (50.8 cm) diameter). Comparative wheels of this size normally are made with ventilated alumina or other solid pore inducers or closed cells as auxiliary to stiffen the structure and prevent distortion of the shape of the grinding wheel from sagging during the cooking gradually as the vitrified bond melts and flows. The ventilated alumina is particularly effective to prevent sagging but is not desirable in terms of grinding performance as it creates closed cell porosity.

To make the experimental abrasive wheels, the agglomerates were added to a mixer at the same time a binder composition vitrified powder (corresponding to the binder material C of Table 2) and a liquid binder 3 to make a mixture. The wheels were then molded from this mixture, dried, cooked to a temperature a maximum temperature of 900 ° C, graded, finished, balanced and inspected according to commercial grinding wheel manufacturing techniques known in the art. The fired wheels were then finished to a size of 20 x 1 x 8 inch (50.8 x 2.5 x 20.3 cm). A moderate degree of sagging, but commercially acceptable experimental wheels were observed during cooking millstones.

The wheels were designed to correspond in volume percentage composition and density to comparative commercial wheels having a standard wheel hardness grade between the C and D quality on the hardness scale quality of the Norton Company.

The characteristics of experimental and comparative are finished abrasive wheels described in Table 11-1 below. Although the percentages of composition and density of the grinding wheel would have predicted that the wheels having equivalent wheel hardness values, in fact, the modulus of elasticity confirmed the experimental wheels were of a softer quality than Comparative wheels. The air permeability values ​​show the porosity of the experimental wheel, in contrast to those of the comparative wheel, is a porosity having an open permeability, permitting free flow of coolant in the wheel and elimination Easy grinding debris from the grinding face of the wheel.

Table 11-1 Grinding wheels

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a) 36.0% vol. abrasive grain component, the comparative sample wheels of the contained a larger volume percentage grain (that is to say, about 1 to 2 vol.% or more) than the wheels of the invention containing a mixture of 36.0 vol.% a combination of agglomerated grain and bond material.

b) was measured permeability to fluids (air) by the test methods described in U.S. Patent Nos 5 738 696 and 5 738 697, assigned to Norton Company. Of air permeability relative values ​​are expressed in cm 3 / second / inch of water units.

The grinding wheels were tested in the single deep pass grinding operation described in Example 7 along with the comparative wheel single deep pass rectification described in Table 11-2. The comparative wheel was a standard commercial product available from Saint-Gobain Abrasives, Inc., Worcester, MA. She had the same shape and dimensions was also comparable to the experimental wheels, but it was made with a ventilated alumina filler and no agglomerate abrasive grain.

Table 11-2 Grinding Test Results

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These results demonstrate the feasibility of manufacturing and using a grinding wheel single deep pass dimensions tested without the use of a porosity filler material such as closed ventilated alumina.

Example 12

The particle size distribution of the agglomerates was compared before and after molding abrasive grinding wheels of the invention to examine the integrity and strength of the agglomerates in the abrasive wheels manufacturing processes. The particle size distribution of the agglomerates was then compared with the abrasive grain size distribution of the grain used to make the agglomerates to confirm that the agglomerates still comprised a plurality of abrasive grains after molding grinding wheels.

Agglomerates were prepared (samples our 63, 64, 65) as described in Example 2 except that the temperature was kept constant at 1200 ° C (for samples 63 and 64) or at 1300 ° C ( Sample 65). Additionally, we used a rotary calcination apparatus (Bartlett-Snow Model TM), manufactured by Alstom Power, Naperville, IL, equipped with a patented metal alloy tube high temperature of 120 inches (305 cm) long 6.5 inches (16.5 cm) internal diameter having a heated length of 72 inches (183 cm) with four temperature control zones. Was carried out the agglomeration process under atmospheric conditions at a speed of rotation of the camera tube 9 rev / min, an angle of inclination of 2.5 degrees tube, and a feed rate of 10 to 14 kg / hour. The apparatus used was substantially identical to the apparatus illustrated in Figure 1.

Were manufactured samples of agglomerates 63, 64 and 65 with abrasive grains obtained from Saint-Gobain Ceramics and Plasitics, Inc. and different caking materials as described in Table 12-1 below.

Table 12-1: agglomerates compositions

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Were mixed and molded to the size and shape described in Example 10 for experimental wheels using a powdered vitrified binder composition and the liquid binder 3. The binder composition used for wheels containing agglomerates 63 and 64 corresponded to the material agglomerating C, and for wheels containing agglomerate 65 corresponded to the agglomerating material E, described in Table 2. The percentages by volume of the agglomerates, the binder and porosity are described in Table 12-2 below.

After molding the wheels under pressure to obtain a grinding wheel "flood" and before firing these molded wheels were removed by washing the binder materials of the structure of grinding wheels flood under running water and the agglomerates were recovered and the abrasive grains. The size of the agglomerates and the recovered grains was determined by screening them through a series of US sieve of mesh size screens and measuring the weight fraction for each screen. The results are shown in Table 12-2, below, for wheels made to three groups of different specifications.

Table 12-2: size distribution of the agglomerates after molding grinding wheels

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The data of Table 12-2 demonstrate that from the average dimensions of the sintered agglomerates (before and after processing) a plurality of abrasive grains has been retained in the sintered agglomerates after they have been molded to form a grinding wheel. While the initial size of the agglomerates has been reduced by a minor percentage (e.g., a drop of 998 to 824 pm, or a 17% reduction, for sample 12-1), the majority of the agglomerates have retained their size initial.

The distribution of weight fractions after screening each sample is given in Table 12-2A, 12-2b and 12-2c, below for samples 12-1,12-2 and 12-3, respectively.

Table 12-2A: particle size distributions of particles in the sample 12-1

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The data in Table 12-2A shows that the largest single grains in the size distribution of the initial sample of the grains are of 425 pm size. Data on the initial particle size distribution of the agglomerates showed that all agglomerates exceed 425% m. After molding and washing, the retained pressed agglomerates are all above 300 m%, and 91.4% by weight of the agglomerates are larger than the largest single grain (425 pm), confirming the retention of a multitude of grains after molding a grinding wheel comprising the sintered agglomerates.

Table 12-2b: particle size distributions for the sample 12-2

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The data in Table 12-2b shows that the largest single grains in the size distribution of the initial sample grains are of 425 pm size. Data on the initial particle size distribution of the agglomerates showed that 99.8% by weight of the agglomerates exceeding 425 pm. After molding and washing, the retained pressed agglomerates are larger than 300 microns, and 91.4% of the agglomerates are larger than the largest single grain (425 pm), confirming the retention of a multitude of grains after molding.

Table 12-2c: Particle size distributions of particles in the sample 12-3

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The data in Table 12-2c shows that the largest single grains in the size distribution of the initial grit sample are 425 microns in size. Data on the initial particle size distribution of the agglomerates showed that 97.5% by weight of the agglomerates exceeding 425 pm. After molding and washing, selected aggregates, pressed are larger than 300 microns, and 89.99% by weight of the agglomerates are larger than the largest single grain (425 pm) confirming the retention of a multitude of grains after molding.

These results demonstrate that the agglomerates produced according to the invention have sufficient strength to withstand the molding and handling of commercial abrasive wheel. The abrasive grains present in the molded wheel retain the structural characteristics of three-dimensional agglomerates of the initial abrasive grain. A major percentage (that is to say, at least 85% by weight) of the agglomerates provides a multitude of abrasive gains held in a three-dimensional shape of approximately the same size as the initial size of the sintered agglomerates after handling and molding.

Example 13

Were compared with structures of abrasive grinding wheels made with the agglomerates of the invention under a scanning electron microscope to comparative wheels structures. The comparative wheels were made without the agglomerates, but included the same abrasive grain and binder materials in the same volume percentages of grain, binder and porosity as the grinding wheels of the invention.

The agglomerates were prepared (Sample No. 66) as described in Example 10 except that the temperature was kept constant at 1150 ^ 0.

Was produced agglomerate the sample 66 with 150 pounds (68.04 kg) of abrasive grain (grit 32A alumina grain 80, obtained from Saint-Gobain Ceramics and Plastics, Inc.) and 10.23 pounds ( 4.64 Kg) of agglomerating material (yielding 6.82 wt% of binder material in the sintered agglomerate). The binder material was dispersed in the binder 3 (3.75 pounds; 1.701 Kg) prior to addition to the grain.

Was manufactured experimental wheels as described in Example 10 from the agglomerate sample 66. The comparative commercial wheels of 32A80L8VFL model, obtained from Saint-Gobain Abrasives, Inc., were chosen for comparison.

We took a photograph of a cross section of each wheel at a magnification of 40X. These photographs are shown in Figures 2 (experimental cheeses with clusters) and 3 (comparative wheels without agglomerates). It can be seen that the agglomerates and the pores are irregularly and randomly shaped and sized. The comparative wheel has a more ordered structure and regular. It is possible to observe two types of pores in the wheels made with the agglomerates: intra-agglomerate pores and larger inter-agglomerate pores appearing as distinct channels between agglomerates. TO

From permeability testing of the experimental wheels it has been established that the intra-agglomerate pores are interconnected and they render the entire wheel permeable to fluids. Thus, the abrasive wheels of the invention exhibit a porosity that includes a major amount of interconnected porosity (that is to say, at least 30% by volume interconnected porosity) and, preferably, a distribution bimodal porosity. The abrasive wheels of the invention are characterized by a composite structure much more open than conventional wheels.

As can be observed in Figures 2 and 3, the maximum dimension of the intra-agglomerate pores is about 2-20 times greater than the maximum dimension of the intra-agglomerate pores. The exact ratio of pore size depends upon the composition of the wheels. The ratio of 2 to 20 applies to these wheels made with a range of about 8 to 10% by volume of binder, and an average abrasive grain size of about 260 microns. In general, for the abrasive wheels of the invention, as the percentage by volume of binder increases from this range, the intra-agglomerate pores become smaller, but the inter-agglomerate pores retain a maximum dimension roughly equivalent to the size Maximum abrasive grain used in the agglomerates. As the volume percent of binder decreases from this range, the intra-agglomerate pores become relatively larger, but the inter-agglomerate pores retain a maximum dimension roughly equal to the maximum dimension of the abrasive grain used in the agglomerates.

In further microscopic examinations of the wheels made with agglomerates, particularly with agglomerates containing at least 6% by weight of agglomerating material, it has been observed that increasing the weight percentage of added binder material results in a wheel structure having intra-agglomerate pores much smaller. For example, with a higher weight percentage of binder material and a higher percentage by volume of binder, the ratio of sizes can be about 20 to 200 times larger than the inter-agglomerate pores than for the intra-agglomerate pores. It is considered that the binder material added to the agglomerates is drawn into the zone interconnected agglomerates during mixing, molding and thermal processing of the wheels, making it closer or away a closing part of the intra-agglomerate porosity and end causing loss of bimodal pore distribution.

Example 14

Agglomerates were prepared by a method the sintered batch furnace from the materials described in Table 14-1. The abrasive grain was grit 38A alumina grain size 100 (0.173 mm) obtained from Saint-Gobain Ceramics and Plastics, Inc., Worcester, MA.

Table 14-1: composition of sintered agglomerates

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In the first step of forming the agglomerate particles were mixed particles of abrasive grain and walnut shell in a Hobart® mixer (laboratory Model N-50). It has the following wet the mixture with an effective amount of organic liquid binder (a mixture of 40 wt% liquid animal glue, 30 wt% powdered maleic acid and 3% by weight of water ) for the adhesion of the bonding material powder to the grain. After wetting of these particles, binder was added and a mixed powder material mixture containing the components (a composition vitrified binder having the fired composition shown above as the "bonding material A"). The binder material adhered to the wetted particles and this mixture were then dispersed so loose on a thin slab of ceramic firing.

The mixture was fired at 1230 ° C for four hours in an electric furnace. After firing, there was obtained the sintered agglomerates from the mixture cooked by grinding the mixture in a mortar with a pestle. The sintered agglomerates were sized in three sizes with US standard testing sieves. mounted on a vibrating screening apparatus (Ro-Tap; Model RX-29; WS Tyler Inc. Mentor, OH). The bulk packing density of the sintered agglomerates (LPD) was measured by the procedure of the American National Standard for Bulk Density of Abrasive Grains.

After the sizing process, the sintered agglomerates had three-dimensional shapes (varying among triangular, cubic, rectangular and various other geometric shapes) and were of size and LPD shown in Table 14-2.

Table 14-2: sintered agglomerates sized

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Was manufactured additional agglomerates by slight variations of this process. The variations included the following. Is riddled wet mixture prepared through sieves in the form of boxes (8 to 12 mesh) onto trays. The screened material was then air-dried or oven. We loaded the material in thin ceramic slabs. Was baked thin ceramic tiles containing the material in kilns or tunnel under firing conditions ranging from 1225 to 1280 ° C for periods ranging from 30 to 360 minutes. We eliminated the fired material of thin ceramic plates and is transformed through a roll crusher to break the material agglomerates.

The crushed material was calibrated to the desired range using a Ro-Tap unit.

Grinding wheels

The finished wheels were 3.0 x 0.525 x 1.25 inches (7.6 X 1.34 X 3.2 cm) in size. The composition of the wheels (volume percent of fired wheels), density, air permeability, the quality and the grinding module properties are described in Table 14-3.

Table 14-3: Grinding wheels

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to. Agglomerates contained 97 wt% of alumina 100 grit 38A grain and 3% by weight of binder material A and screened them to a particle size of -40 / + 60 mesh (250 to 425 pm).

b. Was measured permeability to fluids (air) according to the test methods mentioned in U.S. Patent Nos 5 738 696 and 5 738 697, assigned to Norton Company. The air permeability relative values ​​are expressed in cm 3 / second / inch of water units. (Was used on the device nozzle size 2.2).

c. A 36 volume% abrasive grain, the comparative wheels contained a higher percentage of abrasive grain volume (that is to say 1 to 3 volume% more) than the experimental wheels made with 36 to 40% by volume agglomerate grain, bond material and intra-agglomerate porosity.

The binder used for the grinding of samples 1, 2 and 3 of the invention was a vitrified bond material having the fired molar composition of the bonding material B of Table 2, above. The binder used in the comparative wheel sample had the fired molar composition of the binder material A of Table 2.

The sintered agglomerates and the mixture binder of Samples 1, 2 and 3 of the invention were dry blended in a Hobart mixer, placed into molds, cold pressed and fired at a maximum temperature of 735 ° C for 4 hours to form a grinder.

Comparative wheel sample was made by mixing vitrified binder components with the abrasive grain in a Hobart mixer. The abrasive grain used in the comparative sample was a 38A alumina grain, grain size 100 (125 pm), obtained from Saint-Gobain Ceramics &amp; Plastics, Inc., Worcester, MA. After the mixture was molded, pressed and fired the mixture at 1230 ° C for 4 hours to form the grinding wheel.

Grinding Test 14-A

The wheels of the invention were tested and the comparative wheels in a grinding test single deep pass, internal diameter using the following conditions.

Terms correction:

Machine: Heald CF stripper OD / ID

Mode: single deep pass grinding internal diameter (ID)

Grinding wheel speed: 6319 r / min; foot surface 4968 per minute (25m / sec)

Working speed: 20 r / min

Fashion correction: DI tilt swallowing

Input speed: 0.025 inch (0.64 mm) / 0.050 inch (1.27 mm) on diameter

Coolant: Trim E210 ratio of 5% with deionized well water, 9 gal / min (34 L / min)

Material of workpiece: 52100 Steel 4 inch DI

(10.2 cm) x 0.250 inch (1 cm), 62.0-Rc hardness

Rotary Surfacing: AX1440, comp. 0.0005 inch, 0.005 inch Correction, 2600 rev / min.

In these grinding passages, the maximum material removal rate of the material (MRR) at the initial burning of the workpiece (or initial wheel failure) were measured and the results observed. Results of these grinding tests are shown in Table 14-4.

Table 14-4: rectification test results

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The results show that the wheels made according to the invention were superior in MRR to the closest comparative grinding wheels, and the superior performance did not cause excessive current absorption (specific energy Ws / mm 3) or a damage to the surface of the workpiece. The experimental wheels also exhibited improvements in the ratio G and the index of grindability. In addition, the grain size of the grain used in the sintered agglomerates of the wheels of the invention was less than the grain size of the grain used in the comparative wheel. All other variables being equal, the lower grain sizes G produced reports and an index of fitness to lower rectification. Thus, the superior performance of the inventive wheels was significant and unexpected. Grinding Test 14-B

Was conducted a second set of corrections passages with the same group of wheel samples under the following conditions of surface grinding using 4340 steel as the workpiece.

Terms correction:

Machine: Brown &amp; Sharp Micr-a-size Grinder

Mode: single deep pass Surface Grinding

Grinding wheel speed: 6000 r / min

Table speeds: 0

Power down: 1,270 mm

Input advance: 1,270 mm

Coolant: Trim VHPE 210, 1: 20 with deionized water wells, 9 gal / min (34 L / min)

Material of workpiece: 4340 Steel; hardness 51 Rc; length 95.4 mm; width of 203.2mm

Surfacing: single point diamond tool, comp. 0.025 mm, speed 254 mm / min

Table 14-5: Results of the grinding tests (average of multiple passes)

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The G Report and grindability could not be measured for this passage.

The results show that the wheels made according to the invention were superior in terms of G Report and proficiency index correction to the closest comparative grinding wheels, and superior performance did not cause excessive current absorption or damage to the surface of the workpiece.

Example 15

Were manufactured Additional abrasive wheels from sintered agglomerates prepared according to the method of Example 14, except different types of abrasive grains and agglomerating materials were used in the sintered agglomerate samples. The compositions of the agglomerates and abrasive grinding wheels are described in Table 15-1. In the wheels of the invention, the vitrified binder materials were selected to have a melting temperature of at least 150 ° C higher than the melting temperature of the conglomerate materials in the agglomerates used to make the grinding wheels.

All sintered agglomerates contained 3 wt% of binder material and 97 wt% grain and were screened to a particle size of -20 / + 45 mesh (sieve size of the standards, Inc) (355 to 850 pm).

The finished wheels were 7.0 x 0.50 x 1.25 inches (17.8 X 1.27 X 3.2 cm) in size. The composition of the wheels (volume percent of fired wheels), density, and modulus properties of the wheels are described in Table 15-1.

The binder for the experimental wheels had the molar composition of the agglomerating material B of Table 2 and the wheels made with this binder were baked at 735 ° C for 4 hours. Was manufactured comparative grinding wheels with a vitrified bond having the molar composition of the agglomerating material C of Table 2 and these wheels were fired at 900 ° C for 8 hours. Comparative wheels made without sintered agglomerates contained 40% by volume of abrasive grain and either 10.26 vol% (H grade hardness) or 6.41 vol% (F grade hardness) vitrified bond.

Table 15-1: agglomerates and abrasive wheels

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has 40 volume% abrasive grain, the comparative wheels contained a greater volume percentage of abrasive grain (that is to say, about 2 to 8 volume% more) than the experimental wheels made with 40% by volume agglomerated grain, bond material and intra-agglomerate porosity.

b was measured permeability to fluids (air) according to the test methods mentioned in U.S. Patent Nos 5 738 696 and 5 738 697, assigned to Norton Company. The air relative permeability values ​​are expressed in cm 3 / second / inch of water units. (We used a nozzle size of 2.2).

The properties of these wheels, especially the permeability values ​​in the air within a single wheel grade, demonstrate a higher degree of interconnected porosity in the structures of the experimental wheels made from agglomerated abrasive grain as compared to comparative wheels made to the same volume percent porosity and the same quality with the same grain and binder materials. This structural difference has been observed in different wheel hardness qualities, with different types of grain and binder and for different volume percentages of abrasive wheel components.