Method of making abrasive shards, shaped abrasive particles with an opening, or dish-shaped abrasive particles

European).

EP 2 373 458

METHOD OF MANUFACTURE OF ABRASIVE SHELVES, SHAPED ABRASIVE PARTICLES OR BUTTON

ABRASIVE PARTICLES

State of the art

Abrasive particles and abrasive products made of abrasive particles are useful in abrasive, finishing or grinding various materials and surfaces during the production of goods. Therefore, there is still a need to improve the cost, performance or life of abrasive particles and / or abrasive products.

Triangular shaped abrasive particles and abrasive products using triangular shaped abrasive particles are disclosed in US Patent 5,201,916 to Berg, 5,366,523 to Rowenhorst;

and 5,984,988 to Berg. In one embodiment, the shape of the abrasive particles included an equilateral triangle. Abrasive particles are useful in the production of abrasive products with increased cutting speeds.

WO 2009/085841 A2 (& EP-2 242 618 A2, prior art according to Article 54 (3) EPC) relates to a method comprising: providing a multi-cavity mold;

filling multiple cavities with an abrasive dispersion, the abrasive dispersion includes particles in a liquid that can be transformed into alpha corundum, a liquid comprising a volatile component; removing at least a portion of the volatile component from the abrasive dispersion over time, the abrasive dispersion resides in a plurality of cavities thus forming a plurality of precursor abrasive particles of a predetermined size and breaking at least most of the many abrasive precursor particles into at least two parts when multiple precursor abrasive particles reside in many seats, creating a broken amount of precursor abrasive particles.

Summary of the Invention

Shaped abrasive particles can generally have a higher yield than randomly crushed abrasive particles. By controlling the shape of the abrasive particle, it is possible to control the resulting efficiency of the abrasive particle. Different abrasive applications may require different types of shaped abrasive particles. Therefore, having a process that you can produce

Many different types of shaped abrasive particles on the same production line are highly desirable.

The inventors have determined that by controlling process parameters and using a polymer production tool having multiple mold cavities, different types of shaped abrasive particles can be produced from the same mold. In particular, the inventors defined the split of shaped abrasive particles while they are still in mold to produce abrasive shards instead of solid, intact shaped abrasive particles. The inventors have also defined a method of forming shaped abrasive particles while they are still in the mold to form an opening through the shaped abrasive particle. Finally, the inventors also defined a method of controlling the formation of shaped abrasive particles that are still in mold to form a concave surface on the shaped abrasive particle to produce a cup-shaped abrasive particle. Thus, depending on the process parameters, using the same production tool having multiple mold cavities, you can produce full, intact abrasive particles, abrasive fragments, shaped hole abrasive particles or cup-shaped abrasive particles.

Accordingly, in one embodiment, the invention relates to a method comprising: providing a mold having a plurality of seats, the plurality of seats includes polymer surfaces; filling many sol-gel cavities, where the sol-gel contains particles that can be converted into alpha corundum in a liquid, the liquid contains a volatile component; removing at least a portion of the volatile component from the sol-gel when the sol-gel is in multiple nests and controlling the sol-gel rheology in the mold based on sol-gel plasticity, the presence or absence of a release agent from the mold, and drying rate thereby forming a precursor shaped abrasive particles of a type selected from the group consisting of abrasive debris, shaped abrasive particles with a hole, and shaped cup abrasive particles.

Brief description of the drawings

One skilled in the art should note that this discussion is only a description of some embodiments and is not intended to be

EP 2 373 458 to limit the broader aspects of the present disclosure, which broader aspects are incorporated into the exemplary structure.

FIG. 1 is a photograph of a top view of a mold having a plurality of seats containing precursor abrasive particles.

FIG. 2 is a photograph of cup-shaped abrasive particles formed on the left side of the mold shown in FIG. 1.

FIG. 3 is a photo of broken pieces of abrasive particles formed on the right side of the mold shown in FIG. 1.

FIG. 4 is a cross-sectional view of one embodiment of 10 precursor shaped abrasive particles in a mold cavity.

FIG. 5 is a micrograph of a scanning electron microscope of a representative abrasive fragment similar to the abrasive particles shown in FIG. 3.

FIG. 6A-6C show shaped abrasive particles with a hole. 15 FIG. 7 is a photograph of cup-shaped abrasive particles compared to shaped abrasive particles having an opening.

FIG. 8 is a top view of a mold having a plurality of seats containing precursor shaped abrasive particles with an opening.

FIG. 9 is a perspective view of cup-shaped abrasive particles.

FIG. 10 is a side view of the cup-shaped abrasive particles shown in FIG. 9.

FIG. 11 is a photo showing a concave or cup-shaped surface of a cup-shaped abrasive particle.

The repeated use of reference designations in the description and drawings is intended to show the same or analogous features or elements of the disclosure.

definitions

The expressions "contain", "have" and "include" used herein are legally equivalent and not limiting. Therefore, in addition to the listed elements, functions, steps and restrictions, there may be non-listed elements, functions, steps or additional restrictions.

EP 2 373 458

The term "abrasive dispersion" as used herein means an alpha alumina precursor introduced into the mold cavity that can be converted to alpha alumina. The composition refers to an abrasive dispersion until the appropriate volatiles are removed to solidify the abrasive dispersion.

As used herein, the term "shaped parent abrasive particle" means a non-sintered abrasive particle created by removing a sufficient amount of volatile component from an abrasive dispersion disposed in a mold cavity to form a solid solid that can be removed from the mold cavity and can generally retain its formed shape in subsequent processing operations.

The term "precisely formed surface" as used herein means a surface which is formed by at least partially drying, dehydrating or curing the abrasive dispersion present in the mold cavities.

The term "abrasive debris" as used herein means a sintered alpha corundum abrasive particle produced by the process of the invention.

The term "shaped abrasive particle" as used herein means a ceramic abrasive particle with at least a portion of the abrasive particle of a predetermined shape that is transmitted by the mold cavity used to form the shaped parent abrasive particle.

Except in the case of abrasive shards (e.g. as described in US 2009/0169816 A1), the shaped abrasive particle will generally have a predetermined geometric shape that substantially reflects the mold cavity used to form the shaped abrasive particle. The shaped abrasive particle used herein does not include abrasive particles obtained by a mechanical crushing operation.

Detailed description of the invention

Before proceeding with the description of the process used to produce various types of shaped abrasive particles, various types will be described in detail.

Abrasive shards

Referring to FIG. 3 and 5, abrasive particles 20 are shown. Abrasive particles 20 include broken alpha corundum abrasive particles

EP 2 373 458 formed into the form of many 21 corundum alpha abrasive debris. Referring to FIG. 4, a precursor shaped abrasive particle 23 is shown in mold 34. Each of the alpha corundum abrasive particles 21 comprises at least a first accurately formed surface 22, a second accurately formed surface 24 intersecting with the first accurately formed surface at a specified angle, and a third surface 26 opposite the first precisely formed surface 22 and the broken surface 28. The first precisely formed surface 22 may be formed by contact with the bottom surface 30 of seat 32 in mold 34. In FIG. 4 only a portion of the cavity 32 in the mold 34 is shown in cross section. Typically, the mold 34 has a plurality of seats to economically produce abrasive alpha 21 corundum debris. The first precisely formed surface 22 substantially reproduces the surface finish and shape of the bottom surface 30 of the seat 32.

The second precisely formed surface 24 of the abrasive shrapnel 21 can be formed by contact with the side wall 36 of the seat 32 in the mold 34. The side wall 36 is designed to cut the bottom surface 30 at a certain angle a. The second precisely formed surface 24 substantially reproduces the surface finish and the wall shape side 36 of seat 32. A second precision-molded surface 24 is formed by contact with side wall 36 of seat 32. In this form, at least two surfaces (22, 24) of the resulting abrasive shrapnel are precisely formed, and the intersection angle between the two surfaces is predetermined based on the selected mold geometry.

The third surface 26 of the abrasive debris 21 opposite the first precisely formed surface 22 may be randomly wavy or corrugated because it comes in contact with air after filling the cavity 32 with the abrasive dispersion. The third surface 26 has not been accurately formed because it is not formed in contact with the seat 32. Often, the third surface 26 is formed by scratching or cleaning the upper surface 38 of the mold 34 to remove excess abrasive dispersion from the mold. The cleansing or scratching step may result in a delicate wavy or irregular third surface 26, which becomes enlarged. In this form, the third surface 26 is similar to an extruded surface that is also not precisely formed. In progress

In extrusion, the sol-gel is forced out of the matrix. Thus, the sol-gel surface has scratches, gouges and / or score lines obtained as a result of the extrusion process. These traces were formed by the relative movement between the matrix and the gel. In addition, the extruded surfaces of the matrix may have a substantially smooth plane. In contrast, precisely formed surfaces can reproduce a sinusoidal surface or other more complex geometric surfaces having significant differences in height over the length of the surface.

The broken surface 28 of the abrasive debris 21 extends substantially between the first precisely formed surface 22 and the opposing third surface 26 and between the opposing side walls of the seat 32 when the depth of the seat is relatively small compared to the surface of the bottom surface 30. The broken surface 28 is characterized by sharp, jagged typical points for the fragile breakthrough. A fractured surface 28 may be formed by a drying process that causes at least two precursor shaped abrasive particles to break or break into at least two parts, remain in the cavity 32. This results in abrasive debris 21 having a smaller size than the mold cavity 32 in which they were created. Abrasive shards, after being formed, may resemble pieces of a puzzle from which the original shape of the mold cavity in which they were made can be formed. Cracking or breaking of the precursor shaped abrasive particles occurs when it is ensured that the surface tension of the abrasive dispersion relative to the walls of the cavity 32 will be greater than the internal attraction forces of the abrasive dispersion when the abrasive dispersion dries in the cavity.

Referring to FIG. 5, with respect to the abrasive fragment 21 shown, the broken surface 28 is present along the right side of the abrasive fragment. A second precisely formed surface 24 is present along the left, inclined surface of the abrasive debris 21. The third surface 26 faces forward and has some unevenness and undulation due to the scratching operation. The first precisely formed surface 22 is hidden from view and facing backwards. The abrasive shard in FIG. 5 was produced in a triangular mold socket. One of the vertices of the triangle is in the lower left part of the abrasive fragment.

EP 2 373 458

Referring to FIG. 1, the breaking process generates a discontinuous amount of broken, precursor, shaped abrasive particles in each mold cavity. Generally, about 2 to 4 broken, precursor, shaped abrasive particles are produced in each nest 32. In this form, the inventive process results in several very small particles (particles), which translates into less waste compared to a situation where a crushing operation would be used to reduce the intact triangular particle, as shown in FIG. 2. Due to the breaking process, each of the abrasive shards retains part of its original molded shape as opposed to the crushing process, which results in abrasive particles can be obtained without any precisely formed surfaces. In this form, the grain size of broken, precursor shaped abrasive particles is relatively small and more uniform than that of crushed particles. The final number of broken, precursor, shaped abrasive particles produced in each nest may vary depending on the size and shape of the nest, drying speed and temperature used to break the precursor, shaped abrasive particles within the mold. In various embodiments of the invention, about 10, 9, 8, 7, 6 are produced less or equally in each mold cavity,

5, 4, 3, 2 broken, precursor, shaped abrasive particles.

Because the precursor shaped abrasive particles are processed in such a way as to deliberately break them, at least most (more than 50 percent) of the precursor shaped abrasive particles are broken into at least two parts in the mold cavity 32, when the precursor shaped abrasive particles become dried. In various embodiments, about 75 percent to about 100 percent, or about 90 percent to 100 percent, or about 98 to 100 percent of the precursor shaped abrasive particles are broken into at least two parts while in the mold cavity.

Because the precursor shaped abrasive particles are deliberately broken in the mold, they retain at least part of the original molded shape of the side wall and bottom. This feature allows you to provide abrasive debris that is sharper than crushed particles that can have a lot more rounded or block shapes. Broken, precursor, shaped

The abrasive particles can have a large aspect ratio and very sharp edges at the point where the broken surface 28 meets the precisely formed surfaces. In this form, the alpha corundum abrasive shards have excellent performance when used as an abrasive product.

Broken, precursor shaped abrasive particles are calcined and sintered to form abrasive alpha corundum debris. Alpha corundum abrasive shards can be produced in a wide range of particle sizes, depending on the size of the cavity being formed and the number of broken elements formed at the stage of breaking the process. Typically, abrasive alpha corundum debris are in the size range from 0.1 to 5000 microns, 1 to 2000 microns, 5 to 1500 microns, or in some embodiments from 50 to 1000 or even from 100 to 1000 microns.

According to the detailed description of US 2009/0169816 Al, abrasive alpha corundum shards have excellent grinding performance compared to conventional crushed alpha corundum grains having the same rated degree of abrasion.

Shaped abrasive particles

In FIG. 6A, 6B and 6C, an exemplary shaped abrasive particle 120 with an opening 122 is shown. The material from which the shaped abrasive particle 120 with an opening 122 is made includes alpha corundum. In general, shaped abrasive particles 120 with an opening 122 include thin bodies having a first surface 124 and a second surface 126 separated by a side wall 128 with a thickness t. In some embodiments, sidewall 128 can be minimized for particles where the surfaces converge to a thin edge or a point where they meet inside the thicker wall 128. In one embodiment, the first surface 124 is substantially flat, the second surface 126 is substantially flat or both surfaces are substantially flat. In one embodiment, the first surface 124 and the second surface 126 are substantially parallel to each other. In other embodiments, the first surface 124 and the second surface 126 may not be parallel in such a way that one surface is sloped relative to the surface of the other, and the imaginary tangent lines to each surface intersect at a point.

EP 2 373 458

The sidewall 128 of the shaped abrasive particle 120 with the opening 122 may be different and forms a perimeter 129 of the first surface 124 and the second surface 126. In one embodiment, the perimeter 129 of the first surface 124 and the second surface 126 is selected to be a geometric shape, and the first surface 124 and the second surface 126 are selected to have the same geometric shape, but still differ in size, with one surface larger than the other surface. In one embodiment, the perimeter 129 of the first surface 124 and the perimeter 129 of the second surface 126 was illustrated with a triangular shape.

The opening 122 in one embodiment extends completely through the first surface 124 and the second surface 126, as best seen in FIG. 6B, 6C and 7. In other embodiments, the aperture 122 includes a blind hole that may not completely pass through both surfaces. In one embodiment, the size of the opening 122 is quite large relative to the surface of the first surface 124 or the second surface 126. As shown in FIG. 6A, in one embodiment, the orifice 122 has a rectangular shape resembling the shape of the perimeter 129 of the shaped abrasive particle 120. In this embodiment, the shaped abrasive particle 120 with the opening 122 forms an integrated connection of a plurality of sides 130 joined by their respective ends to form a closed polygon. In other examples, the aperture 122 may be round, oval, or other geometric shape.

In various embodiments, the ratio of the aperture surface 122 divided by the face of the larger of the first surface 124 or the second surface 126 may be between about

0.05 to about 0.95 or about 0.1 to about 0.9 or about 0.1 to about 0.7 or about 0.1 to about 0.5. For the purpose of this calculation, the end face results from a peripheral enclosed surface 129 without subtracting any surface of the hole 122. As described below, shaped abrasive particles having a larger hole 122 relative to the surface size have better abrasive performance.

In various embodiments, the surface or size of the first surface 124 and the surface or size of the second surface 126 are substantially equal. In other embodiments, the first surface 124 or the second surface 126 may be smaller than the others

EP 2 373 458 surface. Referring to FIG. 6B and 6C, to change the relative dimensions of each surface, the tilt angle a can be changed between the second surface 126 and the side wall 128 of the shaped abrasive particle 120. In one embodiment of the invention, the tilt angle a can be about 90 degrees such that the area of ​​both surfaces will be substantially equal. In another embodiment of the invention, the tilt angle α may be greater than 90 in such a way that the area of ​​the first surface 124 will be greater than the area of ​​the second surface 126. In another embodiment of the invention, the tilt angle α may be less than 90 such that the area of ​​the first surface 124 will be smaller than the area of ​​the second surface 126. In other embodiments, the tilt angle α may be between about 95 and 130 degrees, between about 95 degrees and about 125 degrees, or between about 95 degrees and about 115 degrees. Without being limited to theory, an angle of inclination other than 90 degrees leads to the fact that shaped abrasive particles 120 tilt instead of providing a 90 degree angle relative to the back of the coated abrasive particle, because the base of the shaped abrasive particle 120 in the coated abrasive (side wall 128) is inclined due to the angle of inclination. Because the shaped abrasive particles 120 are mostly inclined or inclined to one side due to the inclined base on which they rest, they can have an angle of less than 90 degrees to the ground, thereby improving the quality of the cut.

Shaped abrasive particles 120 with an aperture 122 may have many unexpected advantages over solid, intact shaped abrasive particles without an aperture. First, the shaped abrasive particle 120 with the hole 122 has better cutting performance compared to solid shaped abrasive particles. Without wishing to be bound by theory, it is believed that better cutting parameters result from limiting the size of the wear plane on which abrasive particles are located. As the shaped abrasive particles wear out, a larger and larger surface will appear worn on the working surface of the shaped abrasive particle, blunting the shaped abrasive particle. In contrast, as the shaped abrasive particles 120 with the hole 122 wear, the size of the worn plane may initially increase until the shaped abrasive particle is worn into the hole 122. At this point, the presence of

The opening 122 effectively limits the overall size of the wear plane, creating two smaller wear planes instead of the one large wear plane present in the previous embodiment. The newly formed smaller wear planes again sharpen the shaped abrasive particle 120 improving its performance relative to full, shaped abrasive particles.

Secondly, it is believed that the aperture 122 in the shaped abrasive particle 120, in some embodiments, can act as a reservoir holding more grinding compounds A1d or oversized than full shaped abrasive particles without the aperture 122. In addition, because the A1d grinding is present on the surface and in the center of the shaped abrasive particle 120 with the hole 122, the A1d grinding is present both during the initial use of the abrasive particle and in the later phase, as the shaped abrasive particle 120 with the hole 122 is consumed to the A1d grinding tank in the hole 122, thereby improving the cutting parameters.

Finally, in some embodiments, it is believed that the aperture 122 in the shaped abrasive particles 120 can act as an anchor point to secure the shaped abrasive particles 120 to the substrate even more securely using a primer or flooding layer, thereby limiting the "flaking" of the shaped abrasive particle 120 while working. When shaped abrasive particles 120 with an aperture 122 are used to form a coated abrasive product, the cured primer or primer can penetrate completely through the shaped abrasive particle 120. In this form, the shaped abrasive particles 120 with the aperture 122 are attached more securely to the coating in the compared to solid, shaped solid particles, which are attached only by the force of adhesion to the sides of the particles. In general, shaped abrasive particles 120 with orifice 122 are "bonded" to the backing or filler layer because the coating can penetrate through orifice 122 thereby firmly attaching the particle as opposed to full, shaped abrasive particles bonded only with their sides.

In various embodiments of the invention, in a coated abrasive product, the aperture 122 in shaped abrasive particles 120 with aperture 122 may include a primer layer, a potting layer, an oversize layer, an A1d cut, a hollow space, or any combination thereof.

EP 2 373 458

FIG. 7 is a photograph comparing shaped abrasive particles 120 each with orifice 122 with swordlike abrasive particles 220. FIG. 8 shows a photograph of a production tool having multiple cavities. Precursor shaped abrasive particles are processed in a mold to induce the formation of a hole 122 in each precursor shaped abrasive particle as it dries.

Cup-shaped abrasive particles

Referring to FIG. 9, 10 and 11, exemplary cup-shaped abrasive particles 220 are shown. The material of which cup-shaped abrasive particles 220, abrasive fragments or shaped abrasive particles with a hole are made includes alpha corundum. Alpha corundum particles can be made from an alumina monohydrate dispersion that is gelatinized, shaped, dried to maintain shape, calcined, and then sintered as described later. The shape of the shaped abrasive particle is maintained without the need for a binder to form an agglomerate comprising the abrasive particles in the binder from which the shaped structure is then formed.

Essentially, cup-shaped abrasive particles 220 include thin bodies having a first surface 224 and a second surface 226 separated by a sidewall 228 having a variable thickness T. Basically, the sidewall thickness is greater at the corners of the cup-shaped abrasive particles and thinner at midpoints along each edge. In such form, Tm is less than Tc. In some embodiments, the sidewall 228 is an inclined sidewall having an angle of inclination a greater than 90 degrees, as described later. There may be more than one inclined sidewall, and the slope or angle of each inclined sidewall may be the same as shown in FIG. 9 and 10.

The side wall 228 of the cup-shaped abrasive particle 220 may have a different shape and forms a perimeter 229 of the first surface 224 and the second surface

226. In one embodiment, the perimeter 229 of the first surface 224 and the second surface 226 is selected to be a geometric shape, and the first surface 224 and the second surface 226 are selected to have the same geometric shape, but still differ in size, with one surface larger than the other surface. In one embodiment

Perimeter 229 of first surface 224 and perimeter 229 of second surface 226 was illustrated with a triangular shape. In some embodiments, an equilateral triangle shape is used, and in other embodiments, an isosceles triangle shape.

In some embodiments, the first surface 224 is recessed and the second surface 226 is substantially flat. Recessed means that the inside thickness of the first surface 224, Ti, is less than the thickness of the shaped abrasive particle along the perimeter. In one embodiment, the recessed surface has a substantially flat center portion and upwardly facing corners as shown. In other embodiments, the recessed surface is substantially convex. According to the detailed description, it is believed that the recessed surface is formed by a sol-gel in a mold 34 forming a meniscus causing the first surface to remain recessed, as best seen from the left side of FIG. 7.

As described, the first surface 224 is recessed in such a way that the thickness, Tc, at the vertices or corners 230 will be greater than the thickness, Ti, inside the first surface 224. In this form, when the cup-shaped abrasive particle 220 is deposited in the position shown in FIG. 10, the tops or corners 230 are relatively higher than the inside of the first surface 224. Without wishing to be bound by theory, it is believed that the recessed first surface 224 increases the amount of material removed by the cup-shaped abrasive particle 220. In particular, the ice cream scoop or spoon has a concave shape that effectively allows insertion into the material and removes a significant amount of material. The measuring cup is much more effective than a knife or flat thin body when inserting and removing large amounts of material. Similarly, a hollow chisel having a concave surface provides a sharper edge. In a similar manner, it is believed that placing the recessed surface in the cup-shaped abrasive particle 220 provides better abrasive performance of the cup-shaped abrasive particle relative to similarly shaped abrasive particles having a flat first surface 224 and a flat second surface 226.

In addition, it is believed that providing a thinner inner portion of the shaped abrasive particle can improve the grinding performance of the cup-shaped abrasive particle when a sharp upward tip or corner is worn. When the inner part is thinner, they are used

EP 2 373 458 two factors that improve grinding performance. The first, corresponding worn plane generated during use of the cup-shaped abrasive particle will have a smaller surface area compared to the shaped abrasive particle having a thicker central portion. If one particle has a thickness corresponding to half the next particle, the resulting wear plane will be half the size due to the change in thickness. The second, thinner inner part can translate into a greater breakthrough of cup-shaped abrasive particles during use, thereby improving the ability of the particle to re-sharpen itself thanks to breakthrough mechanics. Thicker particles are less likely to break than thinner particles.

In various embodiments, the thickness ratio Tc / Ti is between 1.25 to 5.00 or from 1.30 to 4.00 or from 1.30 to 3.00. To calculate the thickness ratio, fifteen randomly selected cup particles were inspected. The height of each corner of each particle was measured, and then all heights were averaged to determine the average Tc. For example, in the case of a triangle, three Tc measurements will be made per shaped abrasive particle and 45 measurements for the whole to determine the average Tc. If the shaped abrasive particle is round, oval or otherwise has no corners or tops, then three points equidistant from each other on the perimeter should be measured for each shaped abrasive particle. Then, the smallest thickness, Ti, is measured for the interior of the first surface 224 of each molecule. Often, the translucency of the shaped solid particle can be used to determine the minimum internal thickness, and then the results are averaged to determine the average Ti. The thickness ratio is determined by dividing the average Tc by the average Ti. A light microscope equipped with an XY stage and a vertical measuring stage can be used to measure the thickness of various portions of cup-shaped abrasive particles. Triangular cup-shaped abrasive particles made according to the invention have been measured and have a thickness ratio of 1.55 to 2.32 in some embodiments. Triangular shaped abrasive particles produced according to the current state of the art in accordance with US Patent No. 5,366,523 entitled Abrasive Article Containing Shaped Abrasive Particles to Rowenhorst et al. Were measured and showed

EP 2 373 458 a thickness ratio of 0.94 to 1.15, which means that they are substantially flat and have the same probability of having a slightly smaller thickness in the middle and a slightly larger thickness in the middle. Cup-shaped abrasive particles having a thickness ratio over 1.20 are statistically different from Rowenhorst particles, with a 95% confidence interval.

Referring to FIG. 9, to change the relative dimensions of each surface, the angle of inclination may be changed and between the second surface 226 and the side wall 228 of the cup-shaped abrasive particle 220. Without being limited to theory, an angle of inclination other than 90 degrees leads to the cup-shaped abrasive particles 220 tilting instead of providing a 90 degree angle to the back of the coated abrasive particle because the base of the cup-shaped abrasive particle 220 in coated abrasive (sidewall 228) is inclined due to the angle of inclination. Because the cup-shaped abrasive particles 220 are mostly inclined or inclined to one side due to the inclined base on which they rest, they can have an angle of attack less than 90 degrees relative to the workpiece, thereby improving the quality of the cut.

In various embodiments, the tilt angle α may range from about 95 degrees to about 130 degrees or from about 95 degrees to about 125 degrees or from about 95 degrees to about 120 degrees or from about 95 degrees to about 115 degrees or from about 95 degrees to about 110 degrees or from about 95 degrees to about 105 degrees or from about 95 degrees to about 100 degrees.

The first surface 224, which is recessed, provides an acute angle λ between sidewall 228 and first surface 224. This provides the cup-like abrasive particle 247 of the saw tooth that enters and removes material; in particular, when the tilt angle α is greater than 90 degrees in such a way that the abrasive particles are sharpened or tilt after being formed into a coated abrasive product.

To further optimize tilt orientation, cup-shaped abrasive particles are applied to the ground in the form of an open embankment. Closed embankment is defined as the maximum mass of abrasive particles or a mixture of abrasive particles that can be applied to the backing layer of an abrasive product in a single pass by the manufacturer. An open embankment is the amount of abrasive particles or a mixture of abrasive particles that weigh less than the maximum usable mass that can be applied to the grams

EP 2 373 458 backing layer of an abrasive article. With an open coating of abrasive particles, less than 100% of the undercoat will be covered, leaving open areas and visible resin layers between the particles. In various embodiments, the open area in the abrasive layer may occupy a percentage of from about 10% to about 90% or from about 30% to about 80%.

It is believed that if too many cup-shaped abrasive particles with an inclined side wall are placed on the substrate, there will be insufficient spacing between the particles to allow them to lean before the curing of the primer and flooding layer. In various embodiments, above 50.60, 70, 80; or 90 percent of cup-shaped abrasive particles with an β orientation angle of less than 90 degrees.

In another embodiment of the cup-shaped abrasive particles, the first surface 224 may be convex and the second surface 226 may be concave. These cup-shaped abrasive particles have a substantially constant thickness and resemble a triangle segment taken from a spherical coating. Referring to FIG. 11, a photograph is provided of a cup-shaped abrasive particle 220 having a concave second surface 226 and a convex first surface 224. The sides of each triangle are approximately 1.2 mm in circumference of the first surface

224. The particles had a thickness of about 0.35 mm.

A method for producing various types of shaped abrasive particles

A method for producing various types of shaped abrasive particles is defined in claims 1 to 16.

This method includes providing a sol-gel comprising molecules that can be converted to alpha corundum in a liquid, a liquid including a volatile component. The first step of the method is to provide an nucleated or non-nucleated abrasive dispersion that can be converted to alpha corundum. The alpha alumina precursor composition often includes a liquid that is a volatile component. In one embodiment, the volatile component is water. The abrasive dispersion should contain an amount of liquid that is sufficient to provide the abrasive dispersion with a low enough viscosity to allow the mold cavities to be filled and the mold surface to be restored, but not too high, as this can make the subsequent removal of liquid from the mold cavity too expensive. In one embodiment, the abrasive dispersion comprises from 2% to 90% by weight of the particles,

EP 2 373 458 which can be converted into alpha corundum, such as alpha alumina (boehmite) monohydrate molecules, and at least 10% by weight or from 50% to 70% or from 50% to 60% by weight of a volatile component such as water. Conversely, the abrasive dispersion in some embodiments contains from 30% to 50% or from 40% to 50% by weight solids.

Alumina hydroxides other than boehmit can also be used.

Boehmit can be prepared using known techniques or obtained commercially. Examples of commercially available boehmite include products under the trade names "DISPERAL" and "DISPAL", which Sasol North America, Inc. offers or "HiQ10 40" available from BASF Corporation. These alumina monohydrates are relatively pure, i.e. they contain less (if any) hydride phases than other monohydrates and have a large surface area. The physical properties of the resulting shaped abrasive particles and the resulting particle size will generally depend on the type of material used in the abrasive dispersion.

The abrasive dispersion is in a sol-gel state. The term "gel" as used herein corresponds to the three-dimensional network of solid particles dispersed in a liquid. The abrasive dispersion may contain a modifying additive or a modifying additive precursor. The modifying additive may have the task of improving some desired property of the abrasive particles or increasing the efficiency of the next sintering step. Modifying additives or precursors of modifying additives may be in the form of soluble salts, usually water-soluble salts. They consist mainly of a metal-containing compound and can be a precursor of magnesium oxide, zinc, iron, silicon, cobalt, nickel, zirconium, hafnium, chromium, yttrium, praseodymium, samarium, ytterbium, neodymium, lanthanum, gadolinium, cerium, dysprosium, erbium , titanium and mixtures thereof. The specific concentrations of said additives that may be present in the abrasive dispersion may be different, based on the skill in the art. The introduction of a modifying additive or modifier precursor will usually result in the transformation of the abrasive dispersion into a gel. The abrasive dispersion can be turned into a gel by applying heat for a certain period of time.

To enhance the conversion of hydrated or calcined alumina to alpha alumina, the abrasive dispersion may also contain a nucleating agent. Nucleating agents suitable for the present disclosure include alpha alumina particles, alpha iron oxide or precursor thereof, titanium oxides and titanates, oxides

EP 2 373 458 chromium or any other materials that will nucleate the transformation. The amount of nucleating agent, if used, should be adequate to affect alpha corundum transformation. The nucleation of such abrasive suspensions has been disclosed in US Patent No. 4,744.802 to Schwabel.

To produce a more stable hydrosol or colloidal abrasive dispersion, a peptizing agent may be added to the abrasive dispersion. Suitable peptizing agents are monobasic acids or acidic compounds such as acetic acid, hydrochloric acid, formic acid or nitric acid. Polybasic acids can also be used, but they can quickly gel the abrasive dispersion, making it difficult to perform operations on it, or to add additional ingredients to it. Some commercial sources of boehmite contain titers of acid (such as absorbed formic or nitric acid) that will assist in the formation of a stable abrasive dispersion.

The abrasive dispersion can be formed by any suitable methods such as simply mixing the alumina monohydrate with water containing the peptizing agent or by forming an alumina monohydrate suspension to which the peptizing agent is added. To reduce the tendency to form bubbles or air bubbles while mixing, anti-foaming agents or other suitable chemicals may be added. Additional chemicals such as wetting agents, alcohols or coupling agents can be added as needed. As disclosed in US Patent No. 5,645,619 of July 8, 1997 to Erickson et al., Abrasive alpha alumina grain may contain silicon or iron oxide. As disclosed in US Patent No. 5,551,963 of September 3, 1996 to Larma, abrasive alpha-alumina grain may contain zirconium. Alternatively, as disclosed in US Patent No. 6,277,161 of August 21, 2001 to Castro, abrasive alpha corundum grain may have a microstructure or additives.

The second process step involves providing a mold 34 having a plurality of seats 32. Many seats include polymer surfaces. Referring to FIG. 1

4 and 8, mold 34 has a substantially flat bottom surface 30 and a plurality of seats 32. A plurality of seats can be formed in the production tool. The production tool can be a tape, sheet, continuous web, coating roller such as a rotogravure roller, sleeve mounted on a coating roller, or die. The production tool includes polymer material. Examples of suitable materials

Polymeric ones include thermoplastics such as polyesters, polycarbonates, poly (ether sulfone), poly (methyl methacrylate), polyurethanes, polyvinyl chloride, polyolefins, polystyrene, polypropylene, polyethylene or combinations thereof, as well as thermosetting materials. In one embodiment, the entire tool is made of a polymer or thermoplastic material. In another embodiment, the surfaces of the production tools that come into contact with the sol-gel during drying, for example, the surfaces of multiple seats, include polymeric or thermoplastic materials, and other parts of the production tools can be made of other materials. A suitable polymer coating can, for example, be applied to a metal tool to change the surface tension properties.

The polymer tool can be recreated based on a metal reference tool. the reference tool will be the reverse of the one desired for the production tool. The reference tool can be created in the same way as the production tool. In one embodiment, the reference tool is made of metal, e.g., nickel, by diamond cutting. The polymer material in the form of a sheet can be heated together with the master tool so that after compression of these two elements, the master tool pattern is embossed in the polymer material. The polymer or thermoplastic material can also be squeezed or poured onto a master tool and only then pressed. The thermoplastic material is cooled to solidify and produce a production tool. If a thermoplastic production tool is used, care must be taken not to generate too much heat that could distort the thermoplastic production tool, reducing its service life. More information on the construction and manufacture of a production tool or reference tool can be found in US Patent Nos. 5,152,917 (Pieper et al.); 5,435,816 (Spurgeon et al.); 5,672,097 (Hoopman et al.); 5,946,991 (Hoopman et al.); 5,975,987 (Hoopman et al.); and 6,129,540 (Hoopman et al.).

Access to the seats 32 may be provided from the opening in the upper surface 38 or from the opening (not shown) in the lower surface 30. In some cases, the seating 32 may extend through the entire thickness of the mold 34. Alternatively, the seating 32 may extend only through part mold thickness 34. In one embodiment, the top surface 38 is substantially

EP 2 373 458 parallel to the bottom surface 30 of the mold 34, whose seats have a substantially constant depth. At least one side of the mold 34, i.e. the side where the seat is formed, may remain open to the atmosphere at the stage where the volatile component is removed.

The seat 32 has a certain three-dimensional shape. In one embodiment, the shape of the socket may be described as being a triangle, viewed from above, having an inclined side wall 36 such that the lower mold surface 30 is slightly smaller than the opening in the upper surface 38. The inclined side wall is believed to facilitate particle removal abrasive stem from the mold. In various embodiments of the disclosure, the specific angle? May be in the range of about 95 to about 130 degrees, or from about 95 degrees to about 120 degrees, for example 98 degrees. In another embodiment, the mold 34 contained a plurality of triangular seats. Each of these many triangular nests includes an equilateral triangle.

Alternatively, other socket shapes such as circles, rectangles, squares, hexagons, stars, or combinations thereof may all be used, all of which have a substantially constant depth dimension. The depth dimension is equal to the perpendicular distance from the top surface 38 to the lowest point of the bottom surface 30. In addition, the socket may have the inverse of other geometrical shapes, for example, pyramidal, pyramidal with a bevelled top, spherical bevelled, spheroidal bevelled, conical or beveled beveled. The depth of a given nest may be constant or may vary in length and / or width. The sockets of a given mold can have the same shape or have different shapes.

The third step of the method is to fill the sockets in the form with an abrasive dispersion using any traditional technique. In one embodiment, the upper surface 38 of the mold 34 is covered with the abrasive dispersion. The abrasive dispersion can be pumped onto the upper surface 38. Then, to push the abrasive dispersion completely into the seats 32 of the mold 34, you can use a scraper or leveling bar. The remaining part of the abrasive dispersion that is not in the nest 32 can be removed from the upper surface 38 of the mold 34 and recycled. In some embodiments, a knife roller coater or a slotted vacuum coater may be used. In some embodiments, remain on the upper surface

EP 2 373 458 may have a small part of the abrasive dispersion, and in other embodiments, there is essentially no dispersion on the upper surface 38. The pressure exerted by the scraper or leveling bar is usually less than 100 psi or less than 50 psi or less than 10 psi. In some embodiments, to provide a constant thickness of the resulting shaped abrasive particles, substantially no exposed abrasive dispersion surface extends beyond the upper surface 38.

In one embodiment, the interior surfaces of the socket including side wall 36 and bottom surface 30 are free of mold release aids. Typical release agents include, for example, oils such as peanut oil or mineral oil, silicones, polytetrafluoroethylene, zinc stearate and graphite. The absence of a mold release aid helps ensure that the precursor shaped abrasive particles adhere to the cavity walls as the abrasive dispersion dries, causing at least most of the precursor shaped abrasive particles to crack in the mold. In other embodiments, the mold release means serves to form intact shaped abrasive particles. It is preferred that the release agent is applied to the surfaces of the production tool in contact with the sol-gel in an amount of about

0.1% to about 5% by weight of a release agent, such as peanut oil, in a liquid such as water or alcohol, such that from about 0.2 g / m2 per unit surface area of ​​the mold² up to about 4.7 g / m2² (from about 0.1 mg / in2 to about 3.0 mg / in2) or from about 0.2 g / m2² up to about 7.3 g / m2² (from about 0.1 mg / in 2 to about 5.0 mg / in 2) release agent.

The fourth stage of the process involves controlling the rheology of the sol-gel in the mold to prepare different types of shaped abrasive particles. In particular, the inventors have determined that the sol-gel viscosity, the presence or absence of a mold release aid and the drying rate cooperate to clearly shape the final abrasive particle using a thermoplastic or polymeric mold. By controlling these variables, the kinetics and thermodynamics of the system are balanced, thus affecting the type of shaped abrasive particle produced. Thus, the same mold cavity produces abrasive debris, shaped abrasive particles

EP 2 373 458 having an opening, cup-shaped abrasive particles or shaped abrasive particles having two parallel surfaces.

In general, by eliminating the mold release agent and using a polymer or thermoplastic mold, it can enable the formation of abrasive debris because the sol-gel adheres to the mold and breaks.

Essentially, by using a release agent and a sol-gel with greater plasticity, which dries faster, it allows you to obtain a meniscus in the form of a sol-gel forming cup-shaped abrasive particles. Basically, by increasing the drying rate and applying a mold release agent on the surface of the polymer mold, it will increase the size of the meniscus in contact with air in the cup-shaped abrasive particle. The formation of an even larger meniscus results in a hole in the shaped abrasive particle. The plasticity of sol-gel plasticity (maximum viscosity as a function of shear rate) can be measured with a rheometer in such

Bohlin Gemini 200 available from Malvem Instruments Ltd with headquarters, Worcestershire, United Kingdom.

Table 1 below shows some process parameters that have been seen to produce different types of shaped abrasive particles. However, since the resulting type of shaped abrasive particle depends on the complex rheology of the sol-gel in the mold during drying, process conditions overlap and variables may need to be tuned, depending on the particular sol-gel and the surface tension properties of the mold.

Table 1: Typical process parameters controlling the type of abrasive particle

<td>Variable</td><td>cupped molecule abrasive</td><td>abrasive chippings</td><td>shaped particles abrasive with a hole</td><td>Shaped abrasive particle with parallel surfaces</td>

<td>Center releasing form</td><td>None to 7.8 g / m2²(5.0 mg / in²) e.g. 1.5 g / m2²(1.0 mg / in²)</td><td>None to &lt; 0.08 g / m2²(0.05 mg / in²) e.g. 0.39 g / m2²(0.25 mg / in²)</td><td>0.78 g / m2² up to 7.8 g / m2²(0.5 mg / in² up to 5.0 mg / in²) e.g. 0.39 g / m2²(0.25 mg / in²)</td><td>0 g / sq m² down 7.8 g / m2²(0 mg / in² down 5.0 mg / in²) e.g. 0.78 g / m2²(0.5 mg / in²)</td>

EP 2 373 458

<td>Plasticity sol-gel</td><td>η&gt; 6000 for example. &gt; 12,000 Pa p</td><td>η&gt; 1000 Pa s e.g. &gt; 6000 Pa p</td><td>η&gt; 4000 Pa s e.g.&gt; 8000 Pa s</td><td>η&gt; 4000 Pa s e.g. η&gt; 8000 Pa s</td>

<td>Drying time needed to allow demoulding</td><td>2 to 7.5 minutes Typically, slower drying in lower ones temperatures e.g. 2.5 minutes</td><td>1.5 to 7.5 minutes e.g. 2.0 minutes</td><td>1.5 to 7.5 minutes Typically, faster drying in the higher temperatures e.g. 2.0 minutes</td><td>10 minutes to 24 hours e.g. 1 hour</td>

Abrasive shards

To produce abrasive debris, the sol-gel is broken during in-mold drying.

Preferably, the sol-gel volatile component is quickly removed by evaporation. A sufficient amount of the volatile component must be quickly removed from the abrasive dispersion to ensure its rapid solidification, thereby forming many precursor shaped abrasive particles that are broken into at least two parts. Broken, precursor, shaped abrasive particles have approximately the same shape as the shape of the mold cavity, but are broken every two or more parts. Typically, up to 40 percent of the liquid is removed from the abrasive dispersion at this stage.

In some embodiments, removal of the volatile component by evaporation occurs at temperatures above the boiling point of the volatile component. The upper limit of drying temperature often depends on the material from which the mold is made. For polypropylene tools, the tool temperature should be less than the melting point of the plastic. The drying temperature to break at least most of the precursor shaped abrasive particles into at least two or more parts also depends on the solids content of the abrasive dispersion and the volatile component in the dispersion.

In one embodiment, with an aqueous dispersion containing from about 40 to 50 percent solids and a polypropylene mold, drying temperatures can be from about 90 degrees Celsius to about 165 degrees Celsius or from about 105 degrees Celsius to about 150 degrees Celsius or from about 105 degrees Celsius to about 120 degrees Celsius. Higher temperatures can faster

EP 2 373 458 breaks precursor shaped solid particles, but can also lead to degradation of the polypropylene tool, limiting its usefulness as a mold.

Alternatively, or in combination with rapid evaporation, a mechanical apparatus can be used to break the percaster shaped abrasive particles into at least two parts, while still in the mold cavity. For example, a pair of pressure rollers can be used to apply normal force to the mold, to deflect and crack precursor shaped solid particles. The pressure rollers may include a knurled or spline roller that is pressed against the upper surface 38 and an elastomer roller that is pressed against the lower surface of the mold as the mold passes the pressure. It is also possible to bend or sharp bend the mold to break the precursor shaped abrasive particles in the mold.

Referring to FIG. 1, a multi-nest form is depicted

32. The mold cavities contain a lot of precursor shaped solid particles 23. The mold is made of polypropylene material. Each of the seats includes an equilateral triangle whose side is approximately 2.8 mm (0.110 inch) long (measured at the upper surface 38 (FIG. 4)). Each seat 32 is designed in such a way that the side wall 36 intersects the bottom surface 30 at a predetermined angle of about 98 degrees. Each seat 32 has a depth of about 7.1 mm (0.28 inches), measured perpendicularly from the bottom surface 30 to the top surface 38.

Each seat 32 on the left side of the mold was coated with a thin layer of 0.1 peanut oil in methyl alcohol, which acts as a mold release agent. Each nest on the right side of the mold was uncovered and free of mold release agent. The polypropylene production tool coated with 0.1% peanut oil in methyl alcohol had a surface energy of 35 dynes / cm, which translated into some degree of breakage of the precursor shaped abrasive particles. The uncoated tool without the use of any mold release agent had a surface tension of about 32 dynes / cm, which resulted in the breakage of virtually all precursor shaped abrasive particles. Preferably, the surface tension of the contacting surface of the tool

The production rate is less than about 33 dyne / cm. Surface tension can be measured using surface tension measurements available from Enercon Industries Corporation. Test solutions are applied with a cotton swab to spread the solution on the production tool in accordance with ASTI D2578-04a "Standard Test Method for Wetting Tension of Polyethylene and Polypropylene Films".

After filling each nest with an abrasive dispersion, the mold was put into the oven and heated at a temperature of about 110 degrees C for 45 minutes. Approximately 99.7% by weight of precursor shaped abrasive particles on the right side of the mold in FIG. 1 has been broken into about 2 or 4 parts, thus producing many broken, precursor-shaped abrasive particles in each nest. Broken, precursor, formed abrasive particles in the mold were subjected to sonotrode in order to remove them from the mold. The resulting abrasive debris after firing was sieved into the -35 + 40 fraction and then photographed as shown in FIG. 3. In contrast, the left side of the mold in FIG. 1, on which a form release agent containing peanut oil was applied and after drying under identical conditions, resulted in about 18% by weight of broken abrasive particles.

Shaped abrasive particles

In order to produce the orifice 122 in the particles, when they are in the mold, the volatile component is removed at a high evaporation rate. Sufficient volatile component must be quickly removed from the abrasive dispersion to ensure rapid solidification, thereby forming a large meniscus that leads to the formation of hole 122.

In some embodiments, removal of the volatile component by evaporation occurs at temperatures above the boiling point of the volatile component. The upper limit of drying temperature often depends on the material from which the mold is made. For polypropylene tools, the temperature should be less than the melting point of the plastic.

In one embodiment, with an aqueous dispersion containing from about 40 to 50 percent solids and a polypropylene mold, drying temperatures can be from about 90 degrees Celsius to about 165 degrees Celsius or from about 105 degrees Celsius to about 150 degrees Celsius or from about 105

EP 2 373 458 degrees Celsius to about 120 degrees Celsius. Higher temperatures resulted in the creation of larger holes, but also the degradation of the polypropylene tool, limiting its usefulness as a mold.

In one embodiment, the sol has been prepared by combining 600 parts deionized water, 24 parts nitric acid 400, 400 parts boehmite alumina (DISPERAL, Sasol North America Inc., Houston TX), 45.6 parts silica sol (Nycol 215 from Eka Nobel, Inc. of Augusta, GA) and 76.2 parts of a 9% solution of iron oxide (as Fe2O3) in water, followed by mixing in a high speed mixer for two minutes.

The mixture was allowed to stand for one hour to form a soluble gel.

The sol-gel was applied to a polymer tool with holes in the shape of equilateral triangles about 2.286 mm (90 mils) on each side and at a thickness of 0.762 mm (30 mils), pressing the sol-gel into the holes with a spatula. The coated tool was attached to a stretching frame and placed in an oven (LABDRYER LTE, Warner Mathis USA, Inc., Concord, North Carolina) set at 145 degrees Celsius; the fan was set at 2000 rpm, blowing air over the coating surface until the coating temperature reached 21 degrees Celsius. The resulting shaped, dried particles uniformly had central holes 122, as shown in FIG. 8. The abrasive precursor particles can be burned to produce shaped abrasive particles 120 with orifices 122.

Cup-shaped abrasive particles

In one embodiment, a sample of boehmit zolużel was prepared based on the following recipe: alumina monohydrate powder (4824 parts) with the trade name "DISPERAL" was dispersed by a 13 minutes high shear mixing solution containing water (7087 parts) and 70% aqueous acid nitrogen gas (212 parts).

The resulting sol-gel was aged before coating for at least 1 hour. The sol-gel was pushed into the production tool with triangular shaped mold cavities 0.71mm (28 miles) deep and 2.8mm (110 miles) long sides. The angle of inclination α between the side wall and the bottom of the mold was 98 degrees. The sol-gel was pressed into the nests by means of a vacuum spreader

EP 2 373 458 slotted so as to completely fill the holes of the production tool. As a release agent, 2% peanut oil in water was applied to the production tool in an amount of about 1 g / m2² (1 mg / in²). The sol-gel coated production tool was passed through a length convection oven

8.2 m (27 feet) at 0.05 meters per second (10 feet per minute) set at 135 degrees Celsius at 60% air speed in section 1 of zone 4.11 m (13.5 feet) and at 121 degrees Celsius at 40% air speed in section 2 of the 4.11 m (13.5 ft) zone. The cup-like, precursor abrasive particles were removed from the production tool by passing it over the sonotrode. Cup-like precursor abrasive particles were calcined at about 650 ° C and then saturated with mixed nitrate solution of the following concentration (given for oxides): 1.8% each with MgO, Y2O3, Nd2O3 and La2O3. Excess nitrate solution was removed and the saturated cup-like precursor abrasive particles were allowed to dry, after which the particles were again calcined at 650 degrees Celsius and sintered at about 1400 degrees Celsius, thereby completing the formation of cup-shaped abrasive particles. Both calcining and sintering were carried out using rotary kilns.

Optionally, the fifth step of the process involves removing multiple precursor shaped abrasive particles from the mold cavities. Many precursor shaped ceramic abrasive particles can be removed from the mold cavities using the following methods, alone or in combination: by gravity, by vibration, by ultrasonic vibration, by vacuum or by compressed air to remove particles from the mold. During the production of broken, precursor shaped abrasive particles, when the particles are removed from the nests, they can be reassembled, like puzzles, to the shape of the mold nests in which they were formed.

Precursor shaped abrasive particles can be dried further out of the mold. If the abrasive dispersion is dried to the desired level in the mold, this additional drying step is not necessary. However, in some cases, it may be economical to use this additional drying step to minimize the time the abrasive dispersion remains in the mold. Shaped abrasive particles

The mother liquors will be dried usually from 10 to 480 minutes or from 120 to 400 minutes at a temperature from 50 ° C to 160 ° C or from 120 ° C to 150 ° C.

Optionally, the sixth process step involves calcining many precursor shaped abrasive particles. During calcining, essentially all volatile material is removed and the various components present in the abrasive dispersion are converted to metal oxides. The shaped parent abrasive particles are generally heated to a temperature of 400 ° C to 800 ° C and kept within this temperature range until free water is removed or over 90 weight percent of any bound volatile material. In an optional step, it may be desirable to introduce a modifying additive through the impregnation process. By impregnation into the pores of the calcined shaped parent abrasive particles, water-soluble salt may be introduced. Then many of the precursor shaped abrasive particles are fired again. This option is described further in European Patent Application No. 293.163.

Optionally, the seventh step of the process includes sintering calcined many precursor shaped abrasive particles to form shaped abrasive particles, e.g., abrasive debris 21, shaped abrasive particles 120 with orifice 122 or cup-shaped abrasive particles 220.

Before sintering, the calcined shaped parent abrasive particles are not completely compacted and thus do not have the desired hardness for use as abrasive particles. Sintering is carried out by heating calcined shaped parent abrasive particles to a temperature of 1000 ° C to 1650 ° C and keeping them in this temperature range until essentially all of the alpha alumina monohydrate (or equivalent) is converted to alpha alumina and the porosity drops less than 15% by volume. The time for which calcined shaped parent abrasive particles must be subjected to the sintering temperature to achieve this level of conversion depends on various factors, but is usually from five seconds to 48 hours. In another embodiment, the duration of the sintering step is from one minute to 90 minutes. After sintering, the abrasive particles may have a hardness of 10 GPa, 16 GPa, 18 GPa, 20 GPa or more on the Vickers scale.

To modify the described method, other steps such as rapid heating of the material from the calcining temperature may be used

EP 2 373 458 to sintering temperature, centrifugation of the abrasive dispersion to remove deposits, waste, etc. In addition, if desired, the method can be modified by combining two or more method steps. Conventional method steps that can be used to modify the method of the present disclosure are described in more detail in US Patent No. 4,314,827 to Leitheiser. In addition, any shaped abrasive particles may have grooves on one of the surfaces.

The grooves are formed by a plurality of edges in the bottom surface of the mold cavity, which has been seen to facilitate the removal of precursor shaped abrasive particles from the mold.

Pryzkłady

The objects and advantages of the present disclosure are further illustrated by the following non-limiting examples. You should not interpret certain materials and the quantities they declare in these examples, as well as other conditions and particulars, as excessively limiting this disclosure. Unless otherwise specified, all parts, percentages, ratios, etc. in the examples and the rest of the specification are given by weight.

Example 1 Preparation of abrasive shards

A boehmit gel composition was prepared based on the following recipe: alumina monohydrate powder (1 235 parts) with the trade name "DISPERAL" was dispersed by continuous mixing of a solution containing water (3 026 parts) and 70% aqueous nitric acid (71 parts). The resulting sol was then heated to a temperature of about 125 ° C in a continuous drier to produce a 44% solids dispersion. The sol-gel was pressed into a production tool with triangular shaped mold cavities 0.71 mm (28 miles) deep and 2.8 mm (110 miles) long sides. The angle of inclination α between the side wall and the bottom of the mold was

98 degrees. During the construction of the production tool, 50% of the mold cavities were manufactured to have 8 parallel edges emerging from the surface of the lower cavities, which intersect with one side of the triangle at an angle of 90 degrees. The parallel protrusions were spaced every 0.277 mm, and the cross-sectional protuberances were triangular in shape

EP 2 373 458

0.0127 mm and an angle of 45 between the sides of each convexity at the apex, as described in Patent Application No. 64792US002 cited above. The sol-gel was pressed into the sockets with a spatula so that all holes in the tool were completely filled. No mold release agent was used on the production tool, and the sol-gel coated production tool was placed in a convection oven at 110 degrees Celsius and dried for 40 minutes to break the precursor shaped abrasive particles when they were in the production tool cavities . Broken, precursor, shaped abrasive particles were removed from the production tool by passing it over the sonotrode. Broken, precursor shaped abrasive particles were calcined at about 650 ° C and then saturated with mixed nitrate solution of the following concentration (given for oxides): 1.8% each of MgO, Y2O3, Nd2O3 and La2O3. Excess nitrate solution was removed and saturated, broken, precursor shaped abrasive particles were allowed to dry, after which the particles were again calcined at 650 ° C and sintered at about 1400 ° C. Both calcining and sintering were carried out using rotary kilns. Typical abrasive alpha corundum shards produced by the above method are shown in FIG. 3.

Samples of cup-shaped triangular particles of alpha corundum were prepared in a similar manner to that described above, except before filling, a mold releasing agent containing 0.1% peanut oil in methyl alcohol was applied to the production tool. Typical abrasive alpha corundum triangles produced by the above method are shown in FIG. 2. Looking more closely, you can see the result of the sol-gel meniscus (areas where a bright reflex line appears along the edges) in such a way that the circumference of the cup-shaped abrasive particles is thicker than the recessed center portion of the first surface.

As more fully described in Provisional Patent Application No. US 2009/0169816 A1, abrasive debris resulted in randomly crushed alpha-corundum abrasive grains and prior art abrasive triangles produced according to the method disclosed in US Patent No. 5,366,523 to Rowenhorst.

EP 2 373 458

Example 2 Preparation of cup-shaped abrasive particles with REO admixture

A boehmite sol-gel sample was prepared based on the following recipe: alumina monohydrate powder (4824 parts) with the trade name "DISPERAL" was dispersed by high shear mixing of a solution containing water (7087 parts) and 70% aqueous nitric acid (212 parts) by 13 minutes. The resulting sol-gel was aged before coating for at least 1 hour. The sol-gel was pushed into the production tool with triangular shaped mold cavities 0.71 mm (28 miles) deep and 2.8 mm (110 miles) long sides. The angle of inclination α between the side wall and the bottom of the mold was 98 degrees. When constructing the production tool, 25, 50% of the mold cavities were manufactured to have 8 parallel edges emerging from the surface of the lower cavities, which intersect with one side of the triangle at an angle of 90 degrees. The parallel protuberances were spaced every 0.277 mm, and the transverse cross-sectional shape was triangular 0.0127 mm high and 45 degrees between the sides of each protuberance at the apex.

The sol-gel was pressed into the sockets on the vacuum gap coater in such a way that all holes in the production tool were completely filled. As a release agent, 2% peanut oil in water was applied to the production tool in an amount of about 1 g / m2² (1 mg / in²) peanut oil. The gel-coated production tool was passed through a 8.2 m (27 ft) convection oven at a speed of 10 feet per minute set at 135 degrees Celsius at 60% air speed in section 1 of the 4.11 m (13.5 ft) zone and at 121 degrees Celsius at 40% air speed in section 2 of the 4.11 m (13.5 ft) zone. The shaped parent abrasive particles were removed from the production tool by passing it over the sonotrode. The shaped mother abrasive particles were calcined at a temperature of about 650 degrees Celsius, and then saturated with a mixed nitrate solution with the following concentration (given for oxides): 1.8% each of MgO, Y2O3, Nd2O3 and La2O3. Excess nitrate solution was removed and saturated shaped mother abrasive particles were allowed to dry, after which the particles were

EP 2 373 458 again calcined at 650 ° C and sintered at a temperature of about 1400 degrees Celsius. Both calcining and sintering were carried out using rotary kilns.

Example 3 Preparation of shaped abrasive particles with REO-admixture holes

The above procedure was used for the cup-shaped solid particles, with the difference that the production tool was not coated with a form release agent containing peanut oil during the second use.

It is believed that limiting the amount of peanut oil in the mold cavities is a condition for forming the hole 122 in each individual triangular molecule. Each resulting triangular abrasive particle had a hole 122 near the center. FIG. 7 shows shaped abrasive particles from two preparation procedures. Cup-shaped abrasive particles tend to be thicker at the tops and along the periphery and to have a recessed central portion. In addition, not all cup-like particles of FIG. 7 were shown in a way that visibly depressed the surface. One of the cup-shaped particles in the upper left corner is shown with a flat second surface 226 shown.

Within the scope of this disclosure, those skilled in the art may use in practice other modifications and variations of this disclosure, as set forth in detail in the appended claims. It should be noted that aspects of the various embodiments may be replaced in whole or in part, or combined with other aspects of the various embodiments.

The above description, which was given to enable those skilled in the art to put the claimed disclosure into practice, should not be construed as limiting the scope of the disclosure that is defined by the claims.

EP 2 373 458