Granulated powder for continuous casting of metals and his manufacturing method

The present invention relates to insulating granulates which when insulation and / or suitable release agent for high temperature applications, as well as their preparation.

In the current applications of high-temperature-resistant fillers, For example, in the iron, foundry and construction industries, come Sande and ash or mixtures thereof are used, which by itself temperature stability and reaction passivity distinguished. These additives are partly in its dust form accumulating form, added partly in the form of granules. The powdered substances are occurring because of the dust effect as harmful and should therefore successively comparable to granules Functionality to be replaced.

The granules are to be used in different particle sizes and be by spray or Pelletiertellergranulierung with partly considerable produced technical effort. For applications in the iron and steel processing industry is in addition to the temperature and transport stability called low carbon content because the carbon content in the additive Property of iron and steel changed in an undesirable kind. In addition to the properties mentioned in the foundry industry, a constant volume the aggregate over the entire temperature range desirable since Volume change of the filling and release agents used in unwanted Changing the mold geometry results. In the construction sector, however, are in addition to thermal stability, the sound insulating properties of outstanding Importance.

From DE 197 28 368 it is known that finely powdered acidic or basic insulating are combined in a matrix of gelling materials into granules can suitable as an insulating cover means in the steel foundry. The Granulates have against the powdery insulation means a reduced bulk density on. As gelling materials are guar gum and hydroxyethyl cellulose called. A disadvantage of these granules is that of the gelling material Thus, considerable amounts of carbon may be present, leading to a may cause contamination of the steel.

There is therefore a need for further separation and insulating means on the basis of granulated Pellets with defined chemical and physical properties in procedurally controllable, reproducible particle sizes, which by itself high temperature and material stability and are distinguished therefore for applications are in different industries, in which powdery Substances or mixtures thereof, or granules with insulating, volume-constant come filling or release agents / additives for use and associated manufacturing process.

Surprisingly, it has now been found that amorphous silica the addition of water can be processed into granules, which desired the have properties.

The object of the invention is therefore achieved by insulating Granules consisting of an amorphous silica powder by pelleting the addition of water in a ratio of solid: water from 1: 0.25 to 1: 1.5 are available.

The granules of the invention have the advantage of good environmental at manufacturing point controllable particle size and bulk density. In addition to a conventional material dosing by hand is an automated task possible. In experiments it has been found that a temperature stability up to 1600 ° C is guaranteed. At the same time the granules behave reaction engineering inert and thus offer the certainty that they employed as a filler not having the substances to be processed react.

As SiO₂-Lieferant Come all silicon powder in question, the high proportions amophes SiO₂ or silicic acid. Particularly suitable are silica fume, Siliziumdioxidfilterstaub and mixtures of micro silica or Siliziumdioxidfilterstaub and rice husk ash in different proportions by weight. The addition other additives for defined Schüttdichten- or particle size control is possible. The composition of the starting materials and the mixing ratio of the components involved allows control of the grain size. At the same time, these parameters also affect the for the iron and Foundry industry important carbon.

When silicon dioxide is preferred Siliziumdioxidfilterstaub, the carbon-free in the obtained silicon or silicon manufacturing industry and a consistently high SiO₂Content of at least 90% comprising, are used. particular preference a dust filter is used, selected from the flue gas scrubbing residue incineration is obtained in the silicone manufacturing. It is immaterial whether the silicon powder is present in already dry state or in a wet chunk form as a filter cake. The silica may without further drying in the form the resulting filter cake are used. The existing humidity this is often sufficient to cause by stirring a direct granulation. It is appropriate, a flocculated filter cake by Breaking up, for example, by crushing / grinding / Seven, in particular by pressing the brockigen SiO₂ through perforations to pretreat so an important granulating porous structure is obtained.

It has also shown that from the dewatering with a chamber filter press incurred filter cake having a moisture content of 60% directly without further addition of water can be granulated after being digested previously and has been in a loosened, open-pored (potting soil-like) Consistency is present.

In Filterschlämmen with low humidity shares must the dried and optionally ground filter cake by defined addition of water initially in the Granulierungsbereich be accommodated, wherein a crushing or grinding to Reach the open-pore structure similarly as described is preferred.

In any case, the granulation of a defined moisture content has been take place, depending on the SiO used₂ at a water content of up to may be 150% based on the total mass. Useful amounts of water are 25 to 150%; typically suitable proportions of 30 to 80%, in particular 30 to 70% particularly well. This easy to empirically determining moisture content must be adhered to very precisely for a particular initial mixture, because too little water will not create granules are formed only local clumps in the powder. Further addition of water can germinate the granules and increasingly grow its size. This happens to be wet in a Granulierungsgleichgewicht the platoon level water to erdartigaufgeschlossenen Mass combined with the germs. By further addition of water is the Granulierungsgleichgewicht again in an unfavorable area shifted: the granules lose their structure and there is a function the amount of water a viscous liquid to slightly pasty slurry which only renewed solid addition be moved back into the Granulierungsbereich can.

By the stirring period, the granules can be further increased, if necessary, the. after conversion into the granulating reach their final spherical shape. Is the Quality of the granules formed in the stirrer already sufficient, on a Pelleting be dispensed in dish.

Used as SiO₂-Lieferant Also used rice husk ash, is to consider that the ash does not contain any lumps or husks, since these undesirable in pellet production to uncontrolled Brocken education leads. With the addition of rice hull ash is a special low carbon ash with about 5% carbon content are preferred. The part of Rice hull ash is for cost reasons preferably up to 30%. This results in a total carbon content of less than 2%, preferably below 1%, in the finished granules. Such granules are particularly suitable for Application as an aggregate or insulation in the iron and foundry industry.

When granule formation, the components used are in a controlled manner cake by pasting with water to form granules. The silicon dioxide and optional additives have expediently a grain size on which the desired granule size is below, preferably well below. For a granule size of 0.5 mm for example is a particle size of the starting materials well suited by a maximum of 0.1 mm. A higher technical Effort driven finer grinding remains in this granule size without appreciable effect.

In one embodiment, substances are used as additives in the Food Chemistry suitable as thickeners are used. to Application they are first prepared in a low percent solution, by having to already successful Anteigung the Right Components Water and an incipient formation of granules the size of the granules to influence. By being the addition of dilute thickener solution the granules can be increased as needed, so that depending on the application specifically granules are produced up to several centimeters in diameter can. By agglomerating property of the additive is also a determine increase in the bulk density, which in turn depends on employed and percentage composition of SiO₂Component (n). It should be noted that this addition is not necessary for the formation of granules is.

Refractory oxides or carbonates of the alkali and alkaline earth metals, such as For example, MgO, CaO, CaCO₃, Fe₂O₃, Can also be used as additives be used. In this case, changed by the basic or acidic Properties of the components in aqueous solution, the pH of the produced Granules and by the formation of eutectics is the melting point of the Mixtures compared to pure SiO₂ lowered. To control the pH may also, unless this is to be achieved by addition of additives, the from the filter dust to be used in finishing through silica aqueous solutions of acidic or basic precipitation additions are affected, so that the granules production already by a dust filter with a defined pH takes place. The impact of under the filter dust precipitation for use coming precipitant which lead to accelerated formation of solids, have to be considered here.

The granules of the invention are preferably made of silica prepared in an agitator with addition of water and optionally additives. Insofar as a possible uniform for optimal flow behavior Spherical shape is desired, a further processing closes in a pelletizing plate at.

It is also possible for the granules by agglomeration or other granulation make as pelleting in a stirrer. should preferably no or only very small compressive forces are applied in the granulation. Good example screen granulators or Vertical granulators and are Fluidized bed granulation. The well known compacting methods are only suitable when a slightly higher bulk density is acceptable.

In producing the granules is first a SiO₂, For example, a submitted silica filter sludge. This can immediately while stirring with Water are made into a paste; alternatively, the filter sludge before the Adding water rice hull ash can be added in varying proportions, which is then added in the next step as a homogenous mixture with water.

Upon stirring the mixture into a paste form after a short time germs that already the structure of to forming granules contain. with growing Stirring time increases the diameter of the nuclei, to a granulate in the desired size is formed. If the amount of water added is too large, lose the granules again its consistency and it forms a paste-like slurry, only by adding more Festsoff (filter dust or rice hull ash) again in the necessary for granulation SiO₂brought -water ratio can be.

To further control the granule size, the already formed Granules are treated with the described additives; by a Adding rice hull ash is granule enlargement possible. Since the already formed granules during agitation, is a subsequent treatment However, the same in the granulating disc is not strictly necessary, leading to a regular spherical shape that is desired for certain applications.

Regardless of the action taken, by the increase in size Abpulvern with rice hull ash or filter dust are stopped in which showed that the rice hull ash for this process particularly well suitable is. A rice hull ash addition of about 0.5% based on the Total mixture is sufficient. It formed matt black granules with a Size of 0.5 - 5 mm, depending on the stirring time and rice husk ash addition.

A sprinkling of granules formed with weakly concentrated liquid thickener as an additive allows the size to increase, so that the granules can be built up to balls with several centimeters in diameter. This results in contrast to the thickener Outdoors granules shiny black Granules powdered again by filler or rice hull ash can be.

The process of enlargement of the resulting granules in the same manner feasible in the granulating disc; the granules differ only in the more rounded shape. An alternative in the granulating is a final Spraying of the granular material with water, which softens the surface of the granules and passes through the rotary plate in a perfect spherical shape.

It is advantageous to filter dust from the outset in a predetermined ratio to mix with rice hull ash, in this way the pellet size is better controllable. Here, the rice hull ash in any as needed Weight ratios are added; in practice shares have up to 30% Ash led to a good result. At the same time allows the addition of but rice hull ash, the bulk density increase.

Another important for some areas of use aspect, the pH of neutrality Granules, which are at pH eighth An additive pH-neutral should behave as changes in pH negative impact on the to processed material and the forms in which processed the material and is transported, can lead to.

In contrast to the process known from DE 197 28 368 is the present Manufacturing process without combining the powders used to Matrix of the assistance of a gelling material. The use of the amorphous SiO₂ enables a direct granulation.

By varying the starting materials, Anteigung by defined addition of water and controlling the reaction conditions by residence time and Tilt / rotation speed of the pelletizing disk, a granule in a defined Grain size from 0.5 to 5 mm in size are produced, this by itself thermal and mechanical stability is characterized by in the high temperature range.

The granule size can also go through the residence time in the stirrer or later Pelletizing plate be affected. In both cases, an extension leads to a zoom in of the granules, at which the evaporation of the water the granule surface this increasingly dries and granulation to Stopped coming. An enlargement of the granules is only possible as long as the Outside of the granules having a residual moisture content, the paste by their Surface allows depositing additional material. The same applies to the Stirring or granulating: Increasing speed leads to a Enlargement of the granules, in particular during stirring exceeding a defined number of revolutions of the stirrer depending on container size can have destructive effects on the granules. By changing the Inclination of the granulating disc is given another opportunity, growth the granules to control. A larger angle of inclination can be determined by the steepness the granules by the greater gravity while reducing friction with increased speed to the lower edge of the container falls, the Zusammenbackungsprozeß is enhanced. This also leads to a Enlargement of the granule diameter. A subsequent screening , the particle size range according to the respective customer requirements further be limited.

This is in the industry füllstoffverarbeitenden important because depending on the application a certain reproducible particle size is required, the present invention is achieved by varying the production parameters. The grain size is combined with the bulk density of crucial since during the application or introduction of the granules into or onto the forms of a independent bleeding for the dosage is necessary.

The date next to the application powdery materials have here the Disadvantage of a lack of flow properties, and are therefore less favorable in handling and dosage. Especially the production of pellets with a defined Particle size leads to a possibility of customer and application specific Adjustment for the respective field of application.

The granules of the invention have a bulk density of 0.2 to 0.7 kg / l, for example from 0.5 kg / l and thus meet the requirement for a lightweight granules with a low bulk density.

The finished product can according to the customer in sacks or big bags of different Size, transported and placed in the container or silo.

The following examples are intended to illustrate the invention without, however, on to restrict the specific embodiments described. All information are, unless indicated otherwise, on wt .-%.

example 1

60 g Microsilica (Elcem, Norway) with the following composition: SiO₂: 91.1%, Fe₂O₃: 2.5%, Al₂O₃: 0.9%, MgO: 1.1%, K₂O: 1.7%, Na₂O: 0.4%, SO₃: 0.4% residual moisture 0.5% and total carbon content. 1.65% were mixed with 30 g of water. The mass was intense in the stirrer mixed, were formed granulate germs at prolonged stirring time Size increased. In order to achieve a smooth surface, the granules were dusted with 5 g rice hull ash. The granules had a particle size of 0.5 to 3 mm and a bulk density of 0.6 kg / l.

Example 2:

48 g of silicon dioxide powder from Example 1 were mixed with 12 g rice hull ash with the following composition SiO₂: 87%, CaO: 1%, Al₂O₃: 0.2%, Na₂O: 0.2%, K₂O: 2%, Fe₂O₃: 0.15%, C_ges: 6.2% residual moisture 1.1% and 25 g of water. The mass was stirred in the stirrer, being formed open-cell pellets after a short time, the rotating at slow Stirrer grow. Continue stirring leads to about 3 mm large lumps which representing the formation of the granules. Further treatment in pelletizing disc recirculation to smooth pellets, which continue to grow. Powdering with SiO₂ stops the enlargement and leads to more uniform surface and round structure. The granules had a grain size 2-5 mm and a bulk density of 0.62 kg / l.

Example 3:

160 kg of silica powder having the composition SiO₂: 96.7%, CaO: 1%, Al₂O₃: 0.2%, Na₂O: 0.03%, K₂O: 0.01%, Fe₂O₃: 0.2%, C_ges: 0.75%, residual moisture 1% were with 40 kg of rice husk ash with the following composition: SiO₂: 87%, CaO: 1%, Al₂O₃: 0.2%, Na₂O: 0.2%, K₂O: 2%, Fe₂O₃: 0.15%, C_ges: 6.2% residual moisture 1.1% and 138 kg of water are mixed in an Eirich mixer. About a doser and an auger is the conglomerate supplied to a granulator and in a belt dryer dried. By powdering with SiO₂ or spraying with Water the pellets can be influenced in the plate in size. A Screening tumble lead dust particles and large chunks in the Eirich mixer back. The pellets had a bulk density 0.5 kg / l and a Erweichungstemepratur of 1,600 ° C.