JPS6345118A - Production of sintered abrasive alumina grain - Google Patents

Abstract

PURPOSE:To produce the titled abrasive grain having high sintered density and excellent abrasive performance, by adding an acid to a specific alumina hydrate, subjecting to hydrothermal treatment and drying and calcining the treated product. CONSTITUTION:An Al salt (e.g. AlCl3.6H2O) is added with 2-4mol% metallic aluminum and 1-8wt% (in terms of oxide) modifying component of sintered alumina (e.g. MgCl2.6H2O) and optionally a silica source (e.g. colloidal silica) and the components are made to react with each other at 80-100 deg.C. The obtained aqueous solution of basic aluminum salt is added with an alkaline neutralizing agent [e.g. (NH4)2CO3] to obtain a hydrated alumina containing a reforming component and optionally a silica source. The hydrated product is optionally added with a silica source and subjected to hydrothermal treatment at 120-300 deg.C for >=1hr in the presence of 0.02-0.20ml of an acid (e.g. nitric acid) per 1g of solid component. The obtained treatment product is dried at <=150 deg.C without agitation, crushed, preliminarily calcined at 600-800 deg.C, calcined at 1,100-1,500 deg.C and quenched to obtain the objective grain.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides high grinding performance, especially polishing belts, polishing disks,
This invention relates to alumina sintered abrasive grains suitable for offset grindstones, flexible grindstones, etc.

(Prior technology) Conventionally, sintered abrasive grains that have been used in large quantities include those made by adding a binder to Bayer alumina powder or bauxite powder, molding it, and then sintering it at a high temperature of 1,600°C or higher, but it has poor performance. The range of applications for which it is used is limited. Thereafter, a new type of method for producing sintered abrasive grains was disclosed, in which sintering was performed at a low temperature of 1500° C. or lower using a sol-gel method. The grinding performance of the abrasive grains produced by this method is said to be far superior to commercially available fused alumina abrasive grains, and to be comparable or superior to commercially available fused alumina-zirconia abrasive grains.

All of the methods disclosed in the following patents are products of alumina hydrate (denoted as A1203-820, but the actual product corresponding to this is 1.5-1.7 hydrate). Name r DISPERAL ■” or r CATA
The raw material is a colloidal dispersion (so-called alumina sol) of PAL@J.

Published Patent Publication No. 58-32369 discloses a method in which a modifying component, such as magnesia or zirconia, is mixed with the colloidal dispersion and then gelled, and then slowly sintered at a temperature of 1250° C. or higher for several hours. In this case, calcium and alkali metals must not be substantially contained (containing less than about O, OS weight %).

Published Patent Publication No. 57-207672 is a similar method, but in this case calcium is contained in 0-1.8% by weight and sodium is contained in O-0.4% by weight, which is 120% by weight.
It is said that it is acceptable if the material is rapidly heated to a temperature higher than 0° C. for a period of less than 10 minutes and sintered.

Published Patent Publications 1987-742H and 1982-807
No. 85 both relate to electrophoresis, in which a colloidal dispersion containing the above-mentioned modifying component is prepared, and after drying what has adhered to the cathode and/or crotch due to electrophoresis, 12
This method involves rapidly heating the material to 00°C or higher and sintering it.

Published Patent Publication No. 59-83932 describes a method for producing undoped, high-purity alumina particles with closed pores, in which gels or deposits obtained by a sol-gel method or an electrophoresis method are dried and then This method involves rapidly heating the material to 1200°C or higher and sintering it.

(Problems to be Solved by the Invention) However, these disclosed methods have the following problems. That is, first, in order for alumina monohydrate used as a raw material to be dispersed in a colloidal form, the -order particle size must be 0.11L11.
It must be an ultrafine powder, usually r D l5P
Like ERAL@J, it is expensive because it is obtained by high-temperature hydrolysis of aluminum compounds such as alkyl aluminum and aluminum alkoxide.
This makes the abrasive grains very expensive.

Next, even if we try to make nearly 100% pure alumina sintered abrasive grains from only a colloidal dispersion of alumina l hydrate,
It has been confirmed that the performance as an abrasive grain is significantly inferior.
For this purpose, magnesia (in the form of magnesium salt as a precursor) is used to suppress abnormal grain growth and to make the structure finer and denser, and zirconia (in the form of zirconium salt) is used to increase toughness. Addition of modifying components such as However, since these salts have the effect of promoting gelation, when added to a colloidal dispersion, gelation immediately begins and a significant increase in viscosity occurs, making it difficult to homogeneously mix the modifying components. It is difficult and requires a great deal of ingenuity in equipment and operation, and sometimes even fine tissues cannot be uniformly dispersed, resulting in non-uniform areas and deterioration of performance.

In addition, this increase in viscosity tends to increase as the concentration of alumina monohydrate increases, so there is an upper limit to the concentration of alumina monohydrate for homogeneous mixing of the modifying components, and rDIS
For 1.5-1.7 hydrates such as PERAL@J, usually 2
It is 5% by weight or less, preferably around 20%. This solid content concentration is related to productivity and gel density, and although a higher concentration is economically and emotionally desirable, it is subject to limitations for the reasons mentioned above.

An object of the present invention is to obtain a highly concentrated alumina solution using an inexpensive raw material as a starting material, and to economically produce highly harmful and high performance alumina sintered abrasive grains from the solution.

(Means for Solving the Problems) The present inventor has proposed that a method using a basic aluminum salt containing a modifying component as a starting material is effective as a method for improving the drawbacks of the above-mentioned conventional sol-gel method, etc. He discovered this and applied for a patent. As a result of further research, it was discovered that by adding silica to this, the sintered density of the abrasive grains increased, the grinding performance was further improved, and the sintering temperature could be lowered.

That is, the present invention adds a neutralizing agent to an IIX-based aluminum salt containing a magnesia source, a zirconia source, etc., which is a modifying component of an alumina sintered body, or a modifying component and a silica source, and produces an alumina hydrate containing the above components. If this hydrate does not contain a silica source, add a silica source, then add an acid to the hydrate containing the modifying component and silica source, and perform hydrothermal treatment to obtain the hydrate. This is a method for producing alumina sintered abrasive grains, which comprises drying and then firing a treated product.

In the conventional sol-gel method described above, no silica is found in general alumina sintered abrasive grains, such as bauxite sintered abrasive grains, which contain a large amount of silica, and Bayer alumina contains silica. There are also alumina sintered abrasive grains that contain a small amount of abrasive grains, but those produced by the dry method and those produced by the wet method as in the present invention are different in wood quality, and the properties of the abrasive grains are significantly different. is as described above.

The method of the present invention provides higher density alumina sintered abrasive grains than the sol-gel method disclosed above, which are far superior to commercially available fused alumina abrasive grains and fused alumina-zirconia abrasive grains. It was found that it has good grinding performance.

Next, the present invention will be explained in detail in the order of steps.

a, 11! Synthesis of Basic Aluminum I42 There are various methods for producing basic aluminum m, but a preferred method for obtaining a highly concentrated aqueous solution is the method of adding metallic aluminum to various types of aluminum jl. The aluminum salts used are usually aluminum chloride (AlCl2-8820) and nitrate Wafuluminum (A
I(No3)3・9H20), but aluminum acetate (At2(CH3COO)4・4H20), aluminum sulfate + AI, , (S04), 3-18)120)
It is also possible to use Although there are no particular limitations on the starting concentration, 2 to 4 mol% is used in order to provide an appropriate reaction rate.

Modifying component 1j to be added, water-soluble magnesium compound, zirconium compound, zinc compound, nickel compound,
Commonly known modifying ingredients for alumina sintered bodies, such as chromium compounds and cobalt compounds, can be used to suppress abnormal grain growth in alumina and increase toughness.
In terms of performance and cost, magnesium compounds are preferred. Various magnesium salts are used as magnesium compounds, but magnesium chloride (MgCI2-6)1.
．． 0) and magnesium nitrate ()Ig(NO3)2 Φ6
8201 is preferred. The amount added (content relative to the total amount) is 1 to 8% by weight in terms of oxide after firing in view of the performance of the abrasive grains, and preferably 4 to 6% by weight. Since there may be losses in the process, it is possible to adjust by adding more than the theoretical value in advance, or by adding the insufficient amount during the hydrothermal treatment described below.

As the silica source to be added, it is important that both silica and alumina are mixed homogeneously down to the fine structure, and for this purpose colloidal silica and ethyl silicate, which have fine particles and good dispersibility, are preferred.

The amount added (weight % of the total amount of the modifying component and silica source calculated as oxides) is from 1% by weight to 8% by weight, preferably from 3 to 6% by weight. If it is 1% by weight, it has almost no effect, and if it exceeds 8% by weight, the mullite structure becomes too large, resulting in a decrease in grain strength and, therefore, a decrease in grinding performance, which is not preferable.

The reaction between aluminum salt and metallic aluminum is carried out by adding granular, flaky, etc. aluminum to an aqueous solution of aluminum salt, and
This is done by heating to about 0 to 100°C.

The modifying component and the silica source may be added to the raw materials before the reaction, or to the basic aluminum aqueous solution after the reaction.Furthermore, the silica source, unlike the modifying component, is an alumina hydrate. Since it has no gelling effect, it can also be added to the slurry of alumina hydrate described below. The resulting reaction product, apart from the modifying component, has the following general formula AI (OH)nX (wherein, X is C1,
No3 Natono2 6-n is a basic aluminum salt represented by the anion (O<n<8). When the ratio of AI to X is 2 or more, a gray carmela-like solid may be formed, but it can be used without problems by adding water to a predetermined concentration. In addition, basic aluminum salts can be prepared by adding, for example, an aqueous solution of HCI, H)103, etc. to an aqueous solution of Al(OH)3 under predetermined conditions and reacting. Addition of modifying components can also be carried out in the same manner as described above.

b. Neutralized basic aluminum salt aqueous solution (normal concentration is A)
(15 to 25% by weight (calculated as 12O3)) is neutralized by adding an alkali to obtain an alumina hydrate containing a modifying component or a modifying component and a silica source. Depending on the type of modifying component, the decomposition rate may be slow and the content may not reach the predetermined level. In that case, the content may be adjusted by adding it to the slurry in the subsequent process. As the alkali, pore salts such as ammonium carbonate and sodium carbonate, heavy acid salts such as ammonium bicarbonate and sodium bicarbonate, and hydroxides such as aqueous ammonia and sodium hydroxide are used, but in order to avoid the inclusion of metal impurities. Ammonium salts are preferred.

There are no particular restrictions on the neutralization temperature as long as it is below the boiling point, but
In order to suppress crystallization of the product and reduce the hydrothermal treatment temperature and time, a low temperature of 50° C. or lower is preferable.

Alumina hydrate containing the obtained modifying component or modifying component and silica source (the form of the hydrate is, on average, AlO.4H2
O): If necessary, repeat the aging @filtration and washing to remove by-products. Centrifugal dehydration method, filter press method, etc. are used for filtration.

After sufficient washing, in order to increase the solid content concentration in the slurry, it is preferable to dry it at a temperature of 150°C or less and grind it into a dry powder.The particle size of the dry powder is determined in order to shorten the hydrothermal treatment time. The finer it is, the better, but 170 meshes or less is sufficient. If a drying process using organic matter is used during drying, pulverization becomes unnecessary. Drying temperature is 150
Characteristics above ℃.

This is not desirable as it causes deterioration.

C0 wood heat treatment Water is added to the resulting dry powder to a predetermined concentration, stirred to form a slurry, and then acid and, if necessary, a modifying component is added to adjust the concentration, followed by hydrothermal treatment. If this slurry does not contain a silica source, a predetermined amount thereof is added.

The solid content concentration is preferably as high as possible in order to reduce the energy required for drying and solidification in the next step, but if it exceeds 40% by weight in terms of alumina l hydrate, peptization will be insufficient and this is not desirable in terms of abrasive grain performance. is 15 in terms of alumina hydrate
~40% by weight is used, most preferably 25-35% by weight.

The acids used are inorganic acids such as nitric acid and hydrochloric acid, and organic acids such as acetic acid and formic acid, preferably monovalent acids. Polyvalent acids such as sulfuric acid and phosphoric acid have a peptizing effect on alumina. Inferior.

The amount of acid added is preferably such that the pH of the solution after hydrothermal treatment is 1 to 3 in order to achieve complete peptization, and usually an amount of 0.02 to 0.20 m is used per 1 gm of solid content.

The hydrothermal treatment is performed at 120 to 300°C for 1 hour or more, and depending on the energy of the equipment, is preferably used at 150 to 180°C for 2 to 8 hours.

Hydrothermal treatment is important in the present invention, and even if the alumina hydrate slurry obtained in the previous step is dried as it is without hydrothermal treatment, it will not become a glassy solid mass but will be powdered.
By hydrothermal treatment, amorphous alumina hydrate becomes pseudo-boehmite and hardens into a glass-like form when dried. It is necessary to sinter this.

d. Drying, Grinding, and Classification The hydrothermally treated liquid is dried to form a glassy solid mass, which is then ground and classified to a predetermined particle size.

For drying, spread the treatment solution on a vat to a thickness of several cps, and leave to dry at 150°C or less. It is preferable to move the bat slowly within the soaking zone for better drying efficiency.
In addition, there is no need for uneven drying.The lower the drying temperature, the higher the density of the abrasive grains, which is preferable in terms of performance, but it should be selected appropriately in consideration of productivity. A temperature of 150° C. or higher is not preferable because unnecessary particle sizes cannot be redispersed in water and regenerated.

crusher, roll crusher, hammer crusher,
Ball mills, rod mills, etc. are used, but since acicular grains are likely to occur, it is better to regrind the solidified material before firing. This is because it is difficult to collect and reuse. It is also desirable to grind before firing in order to create sharp edges on the abrasive grains.

For classification, a vibrating sieve or a regular steel sieve is used, but the yield during firing is 'E? The opening of the sieve should be determined taking into account the rk.

e. Firing The grains adjusted to a predetermined grain size are fired and sintered. Prior to firing, it is convenient to perform preliminary firing at 600 to 800°C to remove bound water and residual acid, but direct firing may be used if there is no problem with the equipment.

Firing is done in electric furnaces such as Matsufuru furnaces, bogie furnaces, tunnel kilns, rotary kilns, etc. If the firing furnace is full, sintering will be insufficient and the abrasive grain strength will be weak, and if the temperature exceeds 1500°C, sintering will progress too much and the abrasive grains will deteriorate. The self-sharpening effect of the cutting edge is poor. Although there are no particular restrictions on the rate of temperature rise and fall and the holding time, rapid heating and cooling are preferred from the viewpoint of abrasive grain performance.

(Function) According to the present invention, by adding a relatively large amount of silica, the sintered density becomes higher than when no additive is added even under the same sintering conditions. Furthermore, since sinterability is improved by adding silica, the sintering temperature can also be lowered.

These reasons are thought to be due to the formation of a mullite phase due to the reaction between alumina and silica, but the details are currently unknown.

FIG. 1 shows the relationship between the amount of silica added and the density in the alumina sintered abrasive grains according to the present invention, and shows the increase in density due to the addition of silica.

Figure 2 similarly shows the relationship between sintering temperature and density, and shows that when comparing the same density, the sintering temperature is considerably lower in the case of silica addition than in the case of no silica addition. .

In either case, 4.8% by weight of l'1gO was contained as a modifying component.

(Example) Next, the present invention will be explained in more detail by way of examples.

Example l 800 ml water 7-luminium chloride (AlCl
2-6820) 200g, magnesium nitrate (xg (No3), ・8) 120) Bog as a modifying component was dissolved, heated to 80 to 100°C while cooling under reflux, and then preliminarily treated with 10% hydrochloric acid. 90 g of lathe-cut pieces of metal aluminum whose surface had been activated by washing and drying were added and reacted. After the reaction was completed, the reaction solution was filtered and basic aluminum chloride with a concentration of 40.3% by weight was prepared as a furnace solution. An aqueous solution was obtained. As a result of solute analysis, A12(OH)2.2CI
, 8, and the magnesia content was 4.8% by weight in terms of oxide (magnesia in the alumina and magnesia contents).

Next, 150 g of this aqueous solution was diluted by adding 600 g of water, and while stirring at room temperature, 130 ml of a 15% by weight ammonium carbonate aqueous solution was added dropwise at 10 mn/1 n to neutralize the alumina hydrate. was generated. During the process, the viscosity increased as the amount of alumina hydrate increased, so water was added successively to make the final liquid volume 2000S. After aging for 1 hour, filtration and water washing were repeated. Finally, it was washed with A7T and dried at 100°C to obtain 35 g of alumina hydrate, which was crushed in a ball mill to form a 170 mesh under.

This alumina hydrate had an Al2O3 content of 80% by weight, and the magnesia content was 1.8i% by weight in terms of oxide. 30g of this alumina hydrate powder was dispersed in 55g of water, and a solid concentration 35% by weight (21% in terms of Al2O3 concentration)
．． 2% by weight) to form a slurry. To this slurry, 3.3 g of colloidal silica with a silica concentration of 20% by weight, 4.2 g of magnesium nitrate to adjust the magnesia concentration, and 2.01 g of nitric acid were added, and after thoroughly mixing to make it homogeneous, the mixture was poured into a glass pressure-resistant container. Te inside.

Hydrothermal treatment was performed at ℃ for 3 hours.

The high viscosity liquid obtained by such method and conditions is 100,
It was prepared in units, transferred to a enamel vat to a thickness of 2 to 3 cm, and dried in a hot air drying bag at 80° C. for 24 hours to form a glassy solid mass. This solid mass was crushed with a roll crusher and sieved to a size of 500 to 1000 ml.

The sieved grains were placed in an aluminum crucible, pre-calcined in a Matsufuru furnace at 600°C for 5 hours to remove crystal water and acid radicals, and then heated to 1350°C at a heating rate of 5°C/win. It was held for 5 hours. After cooling to room temperature, it was taken out and sieved into a particle size atmosphere for polishing cloth (36).

Analysis of this sample revealed that it contained approximately 4% by weight of silica and approximately 5% by weight of magnesia.

5
After being held for a minute, the mixture was immediately taken out to room temperature, cooled, and then sieved to a particle size of 136 for thick cloth.

The silica content was about 4% by weight as in Example 1.

Comparative Example l Same method as Example 1 except for adding silica,
Under these conditions, sintered abrasive grains with a grain size of 36 for rubbing cloth were obtained.

Comparative Example 2 Same method as Example 2 except for adding silica,
Under these conditions, sintered abrasive grains having a particle size of R3B for thick cloth were obtained.

Comparative Example 3 Sintered abrasive grains having a particle size of 13B for thick cloth were obtained by rapidly heating at 1400° C. in the same manner as in Example 2 except for adding silica.

Using the grains obtained in the grinding test examples and comparative examples, the outer diameter was 178φll1
1. Using a pulcanized fiber board with a hole diameter of 23φ and a thickness of 0.85 m5 as a base material, an abrasive disk was manufactured by a conventional method.

Next, this was installed on the Hitachi PDH-180B electric type Sangoo, and the work material was a 545C flat plate (38W x 500mm x
10t+ss) was ground for 20 minutes with a load of 8kg.

The cumulative amount of grinding is shown in Table 1.

The abrasive disks of Examples 1 and 2 exhibited grinding performance 1.2 to 1.3 times that of Comparative Examples 1 and 2 without silica added,
The sintering temperature was equivalent to that of Comparative Example 3, which was 50°C higher.

(Leaving space below) Table 1 (Effects of the invention) According to the present invention, high-density alumina sintered abrasive grains can be obtained economically from inexpensive raw materials, and if the sintered density is the same as before, sintered Another great advantage is that the freezing temperature can be lowered.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of silica added and density, and FIG. 2 is a graph showing the relationship between sintering temperature and density.

Claims (4)

[Claims] (1) A neutralizing agent is added to a basic aluminum salt containing a modifying component of an alumina sintered body or a modifying component and a silica source to produce an alumina hydrate containing the modifying component or modifying component and a silica source. If the hydrate does not contain a silica source, add a silica source, then add an acid to the hydrate containing the modifying component and the silica source, and perform hydrothermal treatment to obtain a treated product. A method for producing alumina sintered abrasive grains, which comprises drying and then firing. (2) The method for producing alumina sintered abrasive grains according to claim 1, wherein the modifying components are MgO and ZrO_2. (3) The method for producing alumina sintered abrasive grains according to claim 1 or 2, wherein the silica content is 1 to 8% by weight. (4) The method for producing alumina sintered abrasive grains according to claim 1, 2, or 3, wherein the firing is performed at 1,100 to 1,500°C.