SE464872B - PROCEDURES FOR THE MANUFACTURING OF GRINDING MATERIALS, ACCORDING TO THE PROCEDURE OF MANUFACTURED GRINDING MATERIALS AND USE OF THE SAME - Google Patents

Description

464 872 10 15 20 25 30 35 2 rapid cooling, however, increases grinding grains of zircon corundum to five to six times relatively normal melting corundum.

The performance addition with zircon corundum abrasives compared to normal corundum decreases when grinding metallic materials, eg steel, with decreasing grain size very steep and is roughly equalized at grain size P 80, a phenomenon that can similarly be observed with other high power abrasives.

It is further known to manufacture corundum abrasive materials with superior performance properties on the basis of sintered alumina (DE-OS 32 19 607). For the production of high-quality sintered corundum abrasive material, very fine crystalline alumina monohydrate in nitric acid water dispersion is mixed with other dissolved metal-containing sintering aids and transferred to a gel, which after careful drying is decomposed to abrasive grain size. During the subsequent calcination between 250 and 800 ° C, the chemically bound water and the oxygen residue are - - primarily extremely toxic and environmentally hazardous nitrogen oxides. During the rest of the process, the grains are heated to sintering temperatures up to 160 ° C, until a density of at least 85% of the theoretical density is reached.

Similar processes for the production of sintered corundum abrasive materials are described in EP-OS 0 024 099 and US-PS 4,518,397, with the restriction that the very finely dispersed alumina monohydrate used as raw material may only be contaminated to a total content of not more than .05% by weight with alkali or alkaline earth metal ions. In EP-OS 0 152 768 it is proposed to grind the sol and the gel in addition in a swing mill, whereby a sintering pro-; product with increased density and without areas with uniformly oriented α-alumina crystallites. Common to all four of the above processes is that they can be carried out only via a sol-gel process with extremely finely divided alumina monohydrate of the boehmite type. The relatively expensive raw materials, which can only be extracted via hydrolysis of organoaluminum compounds and the costly, complicated process technology, also increase the costs of sol-gel abrasives to many times the costs of normal molten corundum. Cost-friendly sinter corundum materials, such as tabular clay soil, show a significantly poorer grinding capacity compared with molten corundum and are thus completely unsuitable for general use in grinding tools.

The object of the invention is to provide a method for cost-friendly manufacture of an abrasive material, which is clearly superior to normal melting rounds with respect to the abrasive effect.

This object is solved in a process according to the preamble of the main claim by grinding the dispersion consisting of clay-containing raw materials, silicic oxygen-containing compounds and the additives to less than 1 μm particle size into a sinter lick that can be sintered.

Conveniently, the dried mill slicer is compacted in a press.

According to a very expedient embodiment of the method according to the invention, in which the heat treatment takes place in three steps, the dried mill slicer is preheated in the first step to 250 - 600 ° C, kept in the second step for a time of 10 - 30 minutes at 1100 - 1400 ° C and is subsequently heated in the third step to 1400 - 1700 ° C and sintered to a density of more than 85% of the theoretical density of the corundum in such a way that in addition to α-alumina a silicate phase also arises and the diameter of the corundum crystals amounts to less than 5 um.

Advantageously, the diameter of the corundum crystals is less than 1 μm.

However, when practicing the method of the invention, it is also possible to preheat the dried grinder in two steps in the first step to approximately 250-600 ° C and in the second step to heat it to approximately 1400 °. - 1700 ° C.

Further features of the process according to the invention or the sintered abrasive material thus produced appear from the subclaims.

The essence of the invention is primarily to be seen in the fact that of affordable raw materials, which are subjected to a defined ceramic work-up, while maintaining a defined firing curve, a very fine crystalline sintered corundum is produced with at least 85% of the theoretical density of the corundum. Abrasive materials according to the invention contain as main component α-alumina and as side components a silicate phase and at least one crystalline compound of divalent, trivalent or tetravalent metals or a combination thereof. Side components mean that their sum does not exceed 45% by weight. The crystalline compounds can be simple or compound oxides, eg spinels. They can either as separate phases be distributed in the matrix, eg zirconia, or instead be completely or partially dissolved in the corundum lattice, eg chromium oxide. The silicate phase may be present in whole or in part as glass.

The corundum crystals which make up the abrasive material according to the invention should have diameters below 5 μm, preferably less than 2 μm and preferably less than 1 μm, and they are randomly distributed relative to each other with respect to their crystallographic axes.

In the case of a sintered sol-gel abrasive material, for example according to DE-OS 32 19 607, the crystallites are uniformly oriented over ranges of 0.5 - 20 μm. This restriction is eliminated, since the abrasive material according to the invention does not have to be manufactured via a sol and subsequent yellowing and the raw materials used do not have to be suitable for this either.

From other sintered aluminas, the abrasive material according to the invention differs by its uniform, very fine crystalline structure and the special, multiphase composition, which gives the abrasive material its increased toughness and outstanding wear properties and thereby makes it a high-power abrasive material. with superior grinding properties. For the manufacture of the abrasive, simple and cost-effective raw materials can be used, for example aluminum hydroxide or calcined clay soil (alumina) extracted therefrom, either individually or in a mixture of both. There is no restriction with regard to purity as required in EP-OS 0 024 099 or with regard to fineness or specific surface area according to the said patent applications, but also DE-OS 32 19 607. The calcined clay soil may contain 0 - 98% α-alumina.

The alumina-containing raw materials are subjected together with 0.3 - 8, preferably 1 - 2% by weight of SiO2, and 0.2 - 12, preferably 1 - 6% by weight of a spinel-forming, divalent metal oxide or other compound of the corresponding metal and in where applicable, additional additives for wet grinding. The above information refers to weight% calculated on the mentioned oxides and is related to the amount of finished abrasive material.

Grinding can take place in aqueous suspension or suspensions of organic liquids and is continued until the raw materials used have a particle size of substantially less than 1 μm, but preferably less than 0.1 μm.

In essence, this means more than 95%, calculated on volume shares of solid material. Any grinding procedure can be applied which gives the required fineness.

The dried or freed of organic solvents can then be added to the actual sintering process either directly or after further mixing and compaction steps, preferably compaction by dry pressing and here preferably if the pressing is isostatic. The drying can take place at temperatures between 50 and 600 ° C, preferably between 100 and 160 ° C. The decomposition of the shaped or unshaped material into abrasive grain size can take place both before and after the sintering moment.

The ceramic firing of the goods into pieces or broken, shaped or unformed into sintered abrasive material according to the invention takes place in several steps: in the first heating section the material is gently heated to a temperature between 250 and 600 ° C and kept at this temperature for a few minutes. This step is intended for the evaporation of chemically bound water or the burning off of any organic constituents. Thereafter, the goods are rapidly transferred to a temperature between 1100 and 1400 ° C and kept for a further 10 - 30 minutes at this temperature value, after which it is rapidly heated to a temperature between 1400 and l700 ° C, preferably 1450 - l550 ° C and sintered to a density of more than 85% of the theoretical density. If there is no aluminum hydroxide (Al (OH) 3) in the starting materials, the second stage can also be skipped and the goods heated directly from the first calcination stage to the final sintering temperature. Higher firing temperatures than proposed according to the invention, long sintering times and long heating ratios reduce the grinding effect of the finished material. The superiority of sintered abrasive materials according to the invention compared to conventional melting corundums is to be illustrated in the examples below, but without these covering the whole scope of the invention.

Example 1 From 2000 g of calcined clay soil (alumina), 1000 g of aluminum hydroxide, 42 g of quartz flour, 130 g of magnesium oxide, 5 l of water and 250 ml of 60% acetic acid are made by intensive grinding in a ball mill a slick with a particle size as to the majority is below 0.1 [mu] m and is carefully dried in an electrically heated dryer. The slurry thus dewatered is pulverized and calcined for 45 minutes at 500 ° C. Thereafter, molded bodies are manufactured from this powder by means of an isostatic press at a pressure of 2 kbar and the shaped bodies are heated in an electrically heated laboratory oven. The oven is heated within about 60 minutes from ambient temperature to 600 ° C, then heated rapidly within about 10 minutes to 1300 ° C and kept at this temperature for 20 minutes. Thereafter, the temperature is further raised in less than 5 minutes to 1500 ° C and the shaped body is fired for a further 30 minutes.

After cooling, the density was determined to be 93% of the theoretical and the shaped bodies were decomposed in a jaw crusher.

Abrasive grains with a grain size of P36 according to the FEPA standard are disposed of from the decomposed goods and processed in a conventional manner into an abrasive on a substrate. For this method, a commercial grade volcanic fiber substrate is provided with a layer of 0.84 mm adhesive. The binder consists to about 50% of a liquid phenolic resole with a molar ratio of phenol: formaldehyde of about 1: 1.5 and a proportion of solids amounting to about 80% and about 50% ground chalk with an average particle size of about 20 μm. By means of a squeegee coating, a quantity of approx. 230 g / m2 is applied and then, according to a procedure customary for the production of abrasives on a substrate, the abrasive material P36 is applied electrostatically to the resin-coated volcanic fiber, more specifically in a quantity of approx. 900 g / m2. The substrate thus coated is dried and then cured by means of a standard temperature program. Then a second bonding layer of about 490 g / m2 is applied by means of rollers.

For the second coating, the same binder system was used as for the base coating, however, about 50% by weight of the chalk is replaced with synthetic cryolite. The volcanic fiber thus coated is then heated for 30 minutes to 90 ° C, 60 minutes to 100 ° C, and each 30 minutes to 110 and 120 ° C, respectively, and finally heated for 60 minutes to 130 ° C and the binder system is finally cured. After drying, the abrasive material is uniformly flexible on the volcanic fiber substrate and punched into boards with a diameter of 125 mm, which are reclimatized in a conventional manner to a moisture content below 8%.

The volcanic fiber grinding wheels thus obtained are tested in 464 872 10 15 20 25 30 35 8 a conventional high frequency disc grinder against cold rolled fine sheets of CK45-03 (DIN 17200) with the dimensions 500 x 100 x 2 mm. For this purpose, the grinding wheel is moved at an angle of 10 degrees at a speed of 6500 revolutions per minute per cycle five times during each 9.5 seconds of time over the long edge of the steel plate, after which the amount of sample material chip is determined by Weighing. The compressive force at the beginning of the experiment amounts to 40 N and is increased for each new cycle by 5 N to a constant load of 60 N. The experiment continues until less than 10 g of chip is formed within a cycle. The entire material felling then constitutes the grinding effect of the test disc in grams. For comparison purposes, a volcanic fiber grinding wheel is otherwise manufactured in the same way, however, with a normal melting corundum of grain size P36 and tested under the same conditions. The grinding effect for this disc is set as 100% for the relative comparison.

The board made with sintered abrasive material according to the invention provides an abrasive effect of 350% of the abrasive effect of a normal comparative disc with normal melting corundum.

Example 2 2500 g of calcined alumina, 50 g of quartz flour, 150 g of magnesium oxide, 6 l of water and 240 ml of 90% acetic acid are prepared according to the procedure of Ex. 1 a sintered abrasive material with a density of 94% of the theoretical density and processed in the same way into volcanic fiber boards and tested. The grinding effect obtained amounts to 374% of the grinding effect for the comparative plate coated with normal corundum.

Example 3 The procedure of ex. 1 and 2 are repeated (substantially) in; however, with a mixture of 2500 g of calcined alumina, 35 g of quartz flour, 75 g of zirconium silicate, 150 g of magnesium oxide, 5 l of water and 240 ml of 90% acetic acid. The isostatically compacted moldings are slowly heated to 600 ° C and then rapidly to 220 ° C and maintained at this temperature for 25 minutes. In connection with this, the temperature is rapidly increased to 144 ° C, and the shaped bodies are sintered for 30 minutes to a density of 93% of theory. The grinding test is performed in the manner already described and gives a grinding effect of 384% of the grinding effect of the normal corundum-coated volcanic fiber grinding wheel.

Example 4 In accordance with the procedure of Example 1, 2500 g of calcined alumina, 40 g of quartz flour, 125 g of magnesium oxide, 225 g of citric acid and 4 l of water are made into a grinder with particle sizes predominantly less than 0.1 μm and dried gently. for 24 hours.

During this time, the suspension shrinks into an admittedly soft but still brittle solid. The individual pieces are broken up in a jaw crusher and the fraction between 0.5 and 1 μm is separated from the grinding material. The intended goods are filled into an alumina crucible and heated in an electrically heated oven slowly from ambient temperature to 500 ° C and kept at this temperature for 100 minutes. Thereafter, the temperature is rapidly raised within 15 minutes to 1500 ° C and kept constant for 45 minutes.

The sintered grains are hard and tough and have a density of 95% of the theoretical density of corundum.

With the abrasive material P36 obtained according to FEPA, volcanic fiber grinding wheels are manufactured according to example 1. The grinding test gives 381% of the grinding effect of the comparative plate coated with normal corundum.

Example 5 From 2500 g of calcined alumina, 45 g of quartz flour, 125 g of magnesium oxide, 225 g of citric acid and 4 l of water are made in accordance with the procedure of Example 4 abrasive material, however, the sintering temperature only amounts to 1450 ° C. The grinding test gives an effect of 414 % relative to the grinding board coated with normal corundum and 135% of the grinding effect of a zircon corundum coated volcanic fiber board. 464 10 15 872 10 Example 6 The procedure of Example 5 is repeated, but with 50 instead of 45 g of quartz flour. The ground mill is slowly heated within 8 hours from ambient temperature to 1500 ° C and sintered at this temperature for 12 hours. The finished abrasive material exhibits 97% of the theoretical density for corundum and crystallite diameters of more than 1 μm. The abrasion test gives an abrasive effect of 289% of the abrasive effect of the normal corundum coated volcanic fiber board and still 95% of the abrasive effect of a zircon corundum coated abrasive disk.

It is of course within the scope of the invention to apply the method also for the manufacture of ceramic molded parts on the basis of sintered alumina. In this particular case, the disintegration of the shaped body into abrasive grain size is thus eliminated. 'l få'

Claims (10)

10 15 20 25 30 464 872 ll PATENT REQUIREMENTS Process for the production of abrasive grain material on the basis of sintered alumina and metal-containing additives of a dispersion, which is dewatered, the residue is dried, decomposed to abrasive grain size and in several steps subjected to a heat and sintering treatment, characterized in that it of alumina-containing raw materials, silicic acid-containing compounds and the additives consisting of the dispersion are ground down to a particle size of less than 1 μm to a slick. 2. A method according to claim 1, characterized in that the dispersion is ground down to a sinterable slick with particle sizes below 0.1 μm. 3. A method according to claims 1 and 2, characterized in that the dried slicer is compacted in a press. Process according to Claims 1 to 3, characterized in that calcined clay or aluminum hydroxides or mixtures thereof are used as alumina-containing raw materials and further compounds of the metals silicon, zirconium, titanium, chromium, iron, magnesium, zinc, cobalt and nickel separately or in combination. 5. A method according to claims 1-4, characterized in that the dried slicer in a first step is preheated to 250 - 600 ° C for evaporation of chemically bound water or burning off of any organic constituents in a second step during 10 - 30 minutes is maintained at a temperature of 1100 - 140 ° C and then in a third step until heated to 1400 - 1700 ° C and sintered until a density of more than 85% of the theoretical density of corundum is reached and that in addition to u alumina also formed a silicate phase and the corundum crystals diameter is less than 5 μm. 464 10 15 20 25 30 872 12 6. A method according to claim 5, characterized in that heating and sintering take place until the diameter of the corundum crystals amounts to less than 1 μm. A method according to claims 1-4, wherein the heat treatment takes place in two steps, * 1 characterized in that the dried slicer in the first step is preheated to 250 - 600 ° C and in the second step as long as heated to 1400 - 1700 ° C and sintered until a density of more than 85% of the theoretical density of corundum is reached and that in addition to α-alumina a silicate phase is also formed and the diameter of the corundum crystals is less than 5 μm. Sintered abrasive grain material, prepared according to one or more of Claims 1 to 7, based on sintered alumina with metal-containing additives of a dispersion, which is dewatered, the residue is dried, decomposed to abrasive grain size and subjected in several steps to a heat and sintering treatment. characterized in that the abrasive grain material in addition to α-alumina and a silicate phase also contains further dissolved or dispersed, simple or complex metal oxides dissolved in the corundum matrix and that the corundum crystals of the abrasive grain material have a diameter below 5 μm. Abrasive grain material according to claim 8, characterized in that the proportion of metal oxides in addition to alumina and silica amounts to 0.2 - 45% by weight. Use of abrasive grain material according to claims 8 and 9 produced according to one or more of the methods 1 to 7 in strip, blade or disc-shaped abrasive tools.