JPH02283783A - Fine, sintered alumina abrasive made by using fine high-purity alpha-alumina powder prepared from aluminum ammonium carbonate, and manufacture of the same abrasive - Google Patents

Abstract

PURPOSE:To obtain the title abrasive which has high hardness, high purity, and high density and can be suitably utilized for precision polishing, by thermally decomposing aluminum ammonium carbonate to give a fine alpha-alumina powder, molding this powder, and baking it at a specified temperature. CONSTITUTION:Aluminum ammonium carbonate is thermally decomposed to give a fine alpha-alumina powder (A) which contains at least 80% (on the number basis) primary particles having a diameter of 0.2mum or less, has a mean secondary particle diameter of 0.25mum or less, contains at least 40wt.% particles having a diameter of 0.2mum or less, and gives a dense sinter having a density of at least 98% of a theoretical density when sintered at 1350 deg.C or lower under normal or reduced pressure. Component A, water (B) and a dispersant (C) are mixed for at least 10hr. The mixture is formed preferably into strings or narrow strips of 0.2-0.3mm in diameter or width, dried at 50-150 deg.C, pre-baked at 600-800 deg.C for 20-30min, and crushed to give a powder having a diameter of 300-350mum. This powder is sifted, baked at 1200-1400 deg.C in an oxidizing atmosphere, and then sifted to regulate the particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alumina abrasive material, particularly abrasive grains, used as a grindstone, coated abrasive paper, etc., and a method for producing the same.

[Prior Art and Problems] Conventionally, alumina abrasives have been produced using a method of melting alumina raw materials 11 to 11 in an air furnace (melting method), or a method of sintering at a temperature sufficiently lower than the melting point of the raw materials (sintering method). was manufactured by. In these cases, the sintering method is preferred from the viewpoint of energy saving. A typical example of the sintering method is to use bauxite powder as a raw material, and after injection molding,
There is a method of producing abrasive grains by firing at 0-1600'c, but this abrasive grain is not used for heavy grinding such as slab grinding in boat fishing. Therefore, although abrasive grains produced by the fusion method have drawbacks from the viewpoint of energy saving, they are often used in general precision grinding because they yield abrasive grains with relatively excellent grinding performance.

In recent years, two types of research and proposals have been made to obtain alumina abrasives sintered at lower temperatures. For example, JP-A-58-32369 discloses that a raw material (alumina hydrate) is first gelled and then fired. However, the abrasive grains obtained by this method are effective as a coated abrasive paper.

It is not suitable for use as a grinding wheel.

The present invention provides high hardness that can be preferably used for precision grinding by means completely different from the above-mentioned conventional technology.

The aim is to develop high-purity, high-density alumina abrasives.

[Means for solving the problem] The present inventor has developed a high-purity, easy-to-sinter product made from aluminum ammonium carbonate, which is a completely different raw material from alumina hydrate (boehmite type), which is a common raw material for conventional sintering methods. Abrasive grains with dense and submicron crystal grains can be produced by molding and sintering the crystallized α-alumina fine powder or by pressure sintering (hot press method or HIP method). Furthermore, it has been discovered that the grinding wheels and abrasive paper produced using the abrasive grains have excellent grinding performance. That is, the present invention has solved the above-mentioned problems by the following means.

(1) A method for producing an alumina sintered abrasive material, which uses fine α-alumina powder obtained by thermally decomposing aluminum ammonium carbonate as a raw material, and sintering it at a temperature of 1400'C or less.

(2) A method for producing an alumina-based sintered abrasive material, which uses fine α-alumina powder obtained by thermally decomposing aluminum ammonium carbonate as a raw material and sinters it under pressure at a temperature of 1400'C or less. In particular, when performing pressure sintering,
A manufacturing method in which hexagonal boron nitride (HBN) grains are mixed as a squeezing medium.

(3) By the above manufacturing method, the purity is 99.8% or more, and the average crystal grain size is 0.1-1. OJZm (preferably Ha0.2~1
．． On).

An alumina abrasive material having a relative density of 95% or more relative to theory (equivalent to a density of 3.80 g/cJ or more) and a hardness of 210 Pa or more can be obtained, and a grinding wheel or coated abrasive paper made using this as abrasive grains can be obtained. It has extremely excellent grinding performance.

[Preferred Embodiments and Effects] A-1. Manufacturing method of abrasive material (means 1) In the manufacturing method of means 1 of the present invention, pressure molding or injection molding may be used, but if manufactured by the following casting molding method,
Since the process is simple and low cost, it is preferable from the viewpoint of industrial mass production, and therefore, a method for producing an abrasive by the casting method will be described below.

In particular, this manufacturing method is preferably carried out according to the procedure shown in FIG. However, as long as the gist of the present invention is not changed, it goes without saying that other embodiments may be included. For example, the steps indicated by brackets [ ] in the figure may be omitted.

(1) Preparation of raw materials The main raw material is fine α-alumina powder obtained by thermally decomposing aluminum ammonium carbonate (for example,
9447). In particular, the easily sinterable alumina powder disclosed in JP-A-81-201 [i19te], namely (a) 1350
When sintered at a temperature below ℃ under normal pressure or reduced pressure, it should give a dense sintered body with a theoretical density of 98% or more, (b) primary particles with a diameter of 0.2- or less % or more (based on quantity).

(C) The average secondary particle size is 0.25 μl or less, and the content of particles with a secondary particle size of 0.2 μm or less is 40% by weight or more; (d) The alumina is substantially α-alumina. , is preferable.

(2) Mixing The above (1) fine α-alumina powder is mixed with water and a dispersant to form a slurry. A dispersant is added to stabilize the slurry. As the dispersant, a known organic type can be used as appropriate, and an anionic type is preferable. A binder may be added in a small amount as appropriate.

In order to obtain a high-density abrasive, it is preferable not to add any additives. or,
A sintering aid such as MgO may be added as appropriate in an amount of 1vt% or less. A ball mill or the like is used as a mixing means, and α-A
i! 203a! Use your body. The particle size of the medium is 5-25 a
It is preferable to select one within the range of m. The mixing time varies depending on the particle size of the medium, etc., but is preferably 10 hours or more.

(3) Molding As a molding method, conventionally for boat fishing, injection or pressure molding is used, thereby forming a block.

It was formed into a plate shape. According to the present invention, although these methods may be used, it has been found that cast molding is particularly preferably applicable to the raw material. Compared to injection molding or pressure molding, this casting molding can easily obtain thin sheet-like products, and since it is difficult for impurities to enter, it is suitable for obtaining high-purity and fine α-A and ezOa abrasives. suitable.

Moreover, it is simple in terms of process, and particles having a particle size other than the desired size after sieving in a later step can be recovered and reused, so it can be manufactured at low cost and is preferable from the standpoint of industrial mass production. This casting process is carried out by pouring the slurry onto a polyethylene sheet, for example.
Form into 3 strings or thin strips.

(4) Drying Drying is carried out to facilitate the next step of crushing. The temperature is preferably set at 50-15.0°C.

(5) Preliminary firing is carried out as appropriate to increase the strength of the pre-fired product and to make it easier to crush. It is sufficient to conduct the reaction for 20 to 30 minutes at a temperature of 600 to 800°C.

(8) Crushing This crushing is performed by compressing the material without crushing it by impact.
This refers to the case where it can be powdered to a particle size of 0 μm or less. For example, ceramic rollers are used to prevent contamination of impurities.
It is preferable to obtain a powder with a diameter of about 300 to 350 μm.

(7) For the sieving, a regular vibrating sieve can be used. It is preferable to set the opening to be somewhat larger than the particle size of the abrasive as a product. This is because firing shrinkage should be taken into account. For example, in the case of a No. 60 abrasive, the number is set to No. 45 to No. 55. Particles outside the desired particle size range are collected and reused.

(8) Firing at 1200-1400°C, preferably 1250-1350°C
The sintering process is carried out at a low temperature in order to appropriately control the grain size and prevent abnormal grain growth. Therefore, it is suitable from the viewpoint of energy saving, and an oxidizing atmosphere may be used.

(9) Sieving is carried out as appropriate in order to size the product. For example 5
The grains are sized to numbers 0 to 60 (300 to 250 μ-).

A-2. Manufacturing method of abrasive (means 2) The manufacturing method (pressure sintering) of means 2 of the present invention may be carried out in substantially the same manner as the procedure of means 1 described above.

However, since pressure sintering is used, it goes without saying that a separate molding process is not required.

In this pressure sintering, it is preferable to use α-alumina, which is an alumina raw material, with a powder particle size of 0.05 to 0.5 μm, preferably 0.05 to 0.1 μm.

In addition, hexagonal boron nitride (H
It is preferable to mix particles such as BN) and graphite (C). For example, in the case of HBN, one particle size of 2 to 5 μ■ is
It is preferable to blend it at 100% (weight ratio to α-alumina). For pressure sintering, various methods such as ordinary hot press, hydrostatic press (HIP), vacuum HP (VUP), powder vehicle method, etc. can be employed as appropriate depending on the use and purpose.

Regarding temperature conditions etc. in pressure sintering, see 3. For example, in the case of (normal) hot press, temperature: 1100-1300℃ Pressure: 200-400kg f/cd atmosphere: Ar
(Argon) or N2 (Nitrogen) Also, in the case of HIP, temperature: 1000-1300℃ Pressure: 200-1500kg f/cd atmosphere
It is preferable to set it to Ar, N2 or 0□.

In addition, we have also improved the purity of α-M203 powder as a raw material (99
, 99% or more) makes it possible to sinter alumina at a lower temperature (approximately 1200°C) compared to conventional low-purity cases.

B. Abrasive material The abrasive material of the present invention thus obtained has high purity and has a fine and uniform structure of corundum (α-alumina) throughout. That is.

Purity 99.89fi, more than 99.9%, average grain size 0.1 to 1.0 μm (submicron order), even 0.2 to 0.4 μm, relative density to theory 95% or more, and 98% or more, hardness 21GPa, even 23GPa
It can be obtained as the above abrasive material. Moreover, each crystal has a uniform grain size, especially 8 of all crystals.
0% or more is included in the range of upper and lower limits of width 0.2 μm (for example, if the average crystal grain size is 0.5 μm, 0.3~
0.7 μm) can be easily obtained. This abrasive material is white, translucent, and has a glossy appearance.2 It is also particularly suitable for high-performance precision grinding.

C1 Grindstone Using the above abrasive material, a grindstone having excellent grinding performance can be obtained, for example, in the following manner. As a binder,
A vitrified binder may be used. Vitrified bonding agent has vitreous properties.

Includes crystalline substances. In particular, it is preferable to use a material that can be fired at a temperature of 1200°C or lower, preferably 1100°C or lower. Examples of compositions of vitrifluid binders include:

Examples include borosilicate glass and lead-borosilicate glass. Alternatively, crystallized glass may be used. It is preferable to add an organic adhesive such as dextrin as a binder for the grindstone. These blending ratios are appropriately selected depending on the application and the like.

Next, after mixing these compounds, they are subjected to molding. The molding is preferably carried out at a density of about 2 to 3 g/ctR. When forming a thin film on the surface of the holder, casting may be used. Next, it is fired at a low temperature of 1200°C or less, preferably 1100'C or less. Perform in an oxidizing atmosphere.

The grinding wheel thus obtained can have a wide range of abrasive grain ratios of 20 to 50% and porosity of 40 to 80%.

The grinding wheel of the present invention can be suitably used for precision grinding of tools, dies, heat-resistant alloys, and the like. In addition, it is also useful as other abrasive materials such as abrasive cloth paper.

[Example] The present invention will be explained below based on two examples.

In addition, Example 1 is an example in which a vitrified grindstone was manufactured using an abrasive material manufactured by the casting method of the present invention, and its grinding performance was compared with that of a conventional melt-type abrasive material. Example 2 is an example in which a coated abrasive paper was manufactured using an abrasive material produced by press-molding raw materials and firing at a firing temperature of 1400° C. or lower, and the grinding performance was compared with that of a similar melt-type abrasive material. Example 3 is an example of pressure sintering.

Example 1 α was placed in a plastic polymer container with an internal volume of 500 ml.
- Alumina fine powder (manufactured by Daiki Kagaku Kogyo ■; Taimicron TM)
-DR) 100 g, 35.1 mj of pure water, 0.9 g of polycarboxylic acid type ammonium salt (manufactured by Toagosei ■; Aron A-6114) as a dispersant, and 200 g of alumina balls as a medium were mixed for about 18 hours. An alumina slurry was prepared.

After separating this slurry from the medium, the slurry was transferred into a vacuum container and vacuum defoamed for about 20 minutes to obtain a test slurry. The slurry was spread on a polyethylene sheet to a thickness of about 0.3 mm and immediately dried in a dryer (about 100'C). This dried product was placed in an electric furnace, heated to 700'C at a temperature increase rate of about 20C/m1n, and pre-baked at the same temperature for 30 minutes. This pre-fired product was crushed with a roller and sieved to the desired particle size, then put into the electric furnace again, heated at a temperature increase rate of about 17°C/win to 1350'C, and baked at the same temperature for about 60 minutes. . This fired product has an average crystal grain size of 0.2 to 0.5 μm.
It had a microcrystalline structure of α-alumina, a hardness (Vickers value) of 22 GPa, and a density of 3.94.

No. 60 abrasive grains were sieved from this composition, and a vitrified whetstone was manufactured using the abrasive grains in the following manner.

89.9 parts by weight of abrasive grains, 100 parts by weight of vitrified binder
1 part by weight, dextrin (existing binder) 3. lffl
After adding and mixing ffi part, pressurize to mold density 2.20f
/cIII. Next, this green grindstone was placed in an electric furnace and heated to 100°C at a temperature increase rate of 50°C/Ilr.

It was baked at the same temperature for 6 hours. Thereafter, heating was stopped, and the mixture was left to cool in a sealed furnace. The vitrified binder used consisted of feldspar, clay and frit glass (borosilicate glass). The obtained grinding wheel had abrasive grains 4B and 9% by volume.
, binder 8.1% by volume, remainder pores, specific gravity 2.0
It is 6. In addition, the dimensions of the grinding wheel (grinding wheel) are outer diameter 20h.
m x thickness 19 mm x inner diameter 78 mm, 2 ff 1 m.

Next, a grinding test was conducted on this grinding wheel. still,
For comparison, the same abrasive grains as the whetstone used in the example.

The same shape consists of fused alumina type single crystal abrasive grains (132A manufactured by Pacific Random) with binder content (46.9%, 8.1%) and therefore the same specific gravity <2.08).

Grinding wheels of the same size were used.

The test conditions are as follows: Machine: Okamoto Heiken CF G-52A N Grinding wheel peripheral speed:
2000m/1n, 1fi00m/1n
Cutting mini Δ” 20gm/pass, ΔR10μ
m/pass dry plunge Down Cut Work material: 5KD-1 (HRc80) Dimensions: Length 100 x Height 50 x Width 10 (ffim) Cutting width: 10m+.

Doshi Suni single stone diamond dresser The results are shown in Table 1.

Table 1 As is clear from Table 1, the grinding wheel of this example was single crystal 32
Compared to the comparative grinding wheel made of fused alumina, the grinding ratio is 3.6 to 4.0 times higher, the roughness on two surfaces is the same, the power consumption and noise are lower, and there is less grinding burn. It showed excellent grinding performance.

Example 2 α-Alumina powder (manufactured by Daimei Chemical ■; Taimicron TM-
DS) into a mold, press molding pressure 1 ton/cj, molding density 2.24 g/c+8. It was molded to have an outer diameter of 50-1 x a thickness of 1 am. This molded body was placed in an electric furnace, heated to 400°C at a temperature increase rate of 3°C/m1n, degreased at the same temperature for 2 hours, and then heated to approximately 700°C at a temperature increase rate of 20°C/m1n.
and pre-baked at the same temperature for 30 minutes. This pre-fired product was crushed with a roll crusher and sieved to a desired particle size, then put into the electric furnace again, heated to 1350°C at a temperature increase rate of 20°C/mln, and fired at the same temperature for 60 minutes. Furthermore, under the same conditions, at 1250°C.

It was fired at a temperature of 1300°C. Table 2 shows the characteristics of the fired product thus obtained.

Table 2 Next, after sieving No. 60 abrasive grains from the 1350° C. fired product, the abrasive grains were used to manufacture a fiber disk with an outer diameter of 180 mm and dry grinding was performed. still.

As a comparative example, a fiber disk of the same shape and size made of fused alumina type abrasive grains (manufactured by Showa Denko ■; A) was used as in the previous example.

The test conditions in this case are as follows.

Machine: Sander Hitachi P HD-180c Grinding time = 1 minute XIO times Work material: SPC Dimensions: Length lo x height 25OX width 10 (mm) load
Heavy: 3LBS The grinding rate (Kawaaki, after 9 to 10 minutes) and total grinding layer were investigated. The results are shown in Table 3.

Table 3 As is clear from Table 3, the whetstone of this example was.

It exhibited 3.45 times the amount of total grinding power compared to the comparative example grindstone.

Example 3 α-Alumina fine powder (manufactured by Omachi Chemical Industry Co., Ltd.; Taimicron TM-D) was placed in a plastic polymer container with an internal volume of 1.
A R) 273 parts, 100 parts of pure water, 2 parts of polycarboxylic acid type ammonium salt (manufactured by Toagosei ■; Aron A-8114) as a dispersant, and 546 parts of alumina balls as a medium were added and subjected to fractional rational treatment for about 20 hours. An alumina slurry was prepared.

Thereafter, after separating this slurry from the medium, the slurry was transferred into a vacuum container and vacuum defoamed for about 20 minutes to obtain a slurry for testing. The slurry was spread on a polyethylene sheet to a thickness of about 0.3 mm and immediately dried in a dryer (about 100° C.). This dried product is pressed with a roller to obtain the desired particle size (300 to 500 μm).
After that, the sieve was heated to 700°C at a heating rate of about 20°C/win in an electric furnace and degreased at the same temperature for about 20 minutes. 350 g of this degreased product and hexagonal boron nitride HBN powder with an average particle size of 2 to 5 as a pressing medium (Ube Chemical Co., Ltd.;
UBN) 200g was placed in a plastic bag and mixed by shaking well by hand. This mixture is made into a tube with a diameter of 250 mm and an inner diameter of 80I.
Place it in a cylindrical mold for high-temperature hot pressing of IIm, set it in a high-temperature pressure firing furnace made by Fuji Denpa Kogyo ■, and heat it at 20℃/w.
Heated to 1200℃ at a heating rate of
A pressure of 0 kgf/C- was applied and firing was performed for 60 minutes. After firing, the fired product was separated from the IBN powder (the pressing medium) through a sieve, ultrasonically cleaned with water, and dried to obtain a product. In addition, samples 2 to 4 were produced in the same manner as shown in Table 4 under different high-temperature hot press conditions. Table 4 shows the characteristics of the fired product thus obtained.

Table 4 As mentioned above, all fired products with Nα1-4 are 0.1-0.8μ
It has a microcrystalline structure of α-alumina, has an altitude of 22 GPa or more, a density of 3.97 or more, and the color tone of the abrasive material.

It was white and translucent. From these fired products, a No. 80 sieve was used to produce a vitrifluid grindstone as follows. 89.7 parts by weight of abrasive, 10.3 parts by weight of vitrified binder, and 3.151 parts of dextrin (organic binder) were added, mixed and then pressurized to form a molding density of 2.2゜r/cJ into 2 total 4 pieces. Manufactured. Next, these green grindstones were placed in an electric furnace, heated to 1100°C at a temperature increase rate of 50°C/llr, and fired at the same temperature for 6 hours. Thereafter, heating was stopped and the mixture was left to cool in a sealed furnace. Vitrified binders include feldspar,
A glass made of viscosity and frit glass (borosilicate glass) was used.

The obtained grinding wheel had an abrasive grain ratio of 46.9% by volume and a binder of 8%.
．． 1% by volume, the remainder being pores, and the specific gravity is 2.07.

In addition, the dimensions of the grinding wheel (grinding wheel) are 1 outer diameter 2ooIII
I x thickness 19mm II x inner diameter 76.2mm.

Next, a grinding test was conducted on this grinding wheel. For comparison, the same abrasive grains as the whetstone used in the example were used.

Fused alumina single crystal abrasive grains with binder content (46.9%, 8.1%) (manufactured by Pacific Random ■; 32A)
Grinding wheels of the same shape and size were used.

The test conditions are as follows: Machine: Okamoto Heiken CF G-52A N Grinding wheel peripheral speed:
2000m/sin Depth of cut: ΔR20μs/pass Dry plunge Down Cut Work material: 5KD-1 (HRc80) Dimensions: Length 100X Height 50X Width 10 (IIIm) Limb cutting width: 1Om+s Doss: Single stone dresser Results are shown in Table 5.

Table 5 As is clear from Table 5, the grindstones of the two examples were single crystal 32
Compared to the comparative example grindstone made of A-fused alumina, the grinding ratio is 2.2 to 3.4 times higher, the surface roughness and power consumption are the same, the noise is lower, and there is less grinding burn. It showed excellent grinding performance.

[Effects of the Invention] As described above, according to the present invention, a highly pure, fine, dense, and highly hard (translucent) abrasive material can be easily obtained. Furthermore, a grinding wheel made of such an abrasive material can be suitably used for precision grinding of tools, dies, heat-resistant alloys, etc., and has much better grinding performance than commercially available grinding wheels made of fused alumina abrasive grains. Therefore, it is extremely promising as an abrasive material for precision grinding that can replace very expensive superabrasive grains.

Further, if the cast molding method of the present invention is used, it is preferable from the viewpoint of mass production, and since the firing temperature is low at 1400° C. or less, it is also preferable from the viewpoint of energy saving, and therefore has high industrial value.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an example of the manufacturing method according to Means 1 of the present invention, and FIG. 2 is a flowchart showing an example of the manufacturing method according to Means 2. Applicant Noritake Co., Ltd. Agent Patent Attorney Asahi Kato Michidai 1 See Figure α-A! 203 fine powder (thermal decomposition product of aluminum ammonium carbonate) Figure 2 α-Ai'20sll powder (thermal decomposition product of aluminum ammonium carbonate) Abrasive

Claims (7)

[Claims] (1) Use fine α-alumina powder obtained by thermally decomposing aluminum ammonium carbonate as a raw material, mold it,
A method for producing an alumina sintered abrasive, characterized by firing at a temperature of 400°C or less. (2) A method for producing an alumina-based sintered abrasive, which uses fine α-alumina powder obtained by thermally decomposing aluminum ammonium carbonate as a raw material and sinters it under pressure at a temperature of 1400° C. or lower. (3) The manufacturing method according to claim 2, wherein hexagonal boron nitride (HBN) grains are mixed as a compression medium when pressurizing and sintering the α-alumina powder. (4) Purity obtained by the manufacturing method according to claim 1: 99.
8% or more, an average grain size of 0.2 to 1.0 μm, a relative theoretical density of 95% or more, and a hardness of 21 GPa or more. (5) Purity obtained by the manufacturing method according to claim 2: 99.
8% or more, an average grain size of 0.1 to 1.0 μm, a relative theoretical density of 95% or more, and a hardness of 21 GPa or more. (6) A grinding wheel characterized by using the abrasive material according to claim 4 or 5 as abrasive grains. (7) A coated abrasive paper characterized in that the abrasive material according to claim 4 or 5 is used as abrasive grains.