JPH03287687A - Sintered silicon nitride abrasive and its manufacture - Google Patents

Abstract

PURPOSE:To easily obtain the title abrasive which is dense and has fine crystals with high hardness by mixing a specified Si3N4 powder and a specified sintering aid powder, subjecting the mixture to a specified processing, and baking it. CONSTITUTION:An Si3N4 powder having a mean crystalline particle diameter of 1mu or smaller is mixed with 3-20wt.% (based on Si3N4) sintering aid powder selected from alumina and rare earth element oxides (including yttria) (e.g. Al2O3 and Y2O3), having a mean crystalline particle diameter of 1mu or smaller. This mixture is cold molded, crushed, mixed with hexagonal boron nitride serving as solid hydraulic medium, and then baked at 1,700 deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a silicon nitride abrasive material used as a grinding wheel, coated abrasive paper, etc., and a method for producing the same.

[Prior Art and Problems] Conventionally, a general abrasive material made of alumina or silicon carbide has been used as abrasive particles, which are abrasive particles constituting an abrasive material, particularly a grinding wheel. However, in recent years, diamond, cubic boron nitride (
The importance of superhard abrasives made of CBN is gradually shifting.

However, such super hard abrasives are 10% harder than general abrasives.
Since it is 0 to 200 times more expensive, it is not practical as an abrasive that is consumed in large quantities. Therefore, we have developed general abrasive materials that can be used for precision grinding.
Various improvements have been attempted to improve performance.

For example, regarding alumina abrasives, sintered abrasives made using the so-called sol-gel method have been proposed (Japanese Patent Laid-Open Nos. 56-32389 and 80-231462). but,
The sol-gel method has a complicated process, many unstable factors, and is generally unsuitable for mass production. or.

Sufficient improvement cannot be obtained in wet grinding, which accounts for more than 90% of precision grinding.

Therefore, the present invention is useful for high-performance precision grinding,
It is an object of the present invention to provide a method for easily obtaining a new abrasive material that is particularly low-cost, highly practical, and suitable for wet grinding, which accounts for the majority of precision grinding.

[Means for Solving the Problems and Effects] As a result of intensive studies in order to solve the problems, the inventors of the present invention have found that silicon nitride is the main component, a predetermined sintering aid is added thereto, and these We have discovered that an abrasive obtained by molding, crushing, and sintering 2 as an ultrafine powder can achieve extremely excellent precision grinding when used in grinding wheels, etc. This led to the completion of the invention.

That is, the present invention is a method for producing a silicon nitride sintered abrasive, in which alumina, rare earth oxide (yttria), and alumina and rare earth oxides (ittria) having an average crystal grain size of 1 m or less are added to silicon nitride powder having an average crystal grain size of 1 m or less. 3 to 20% by weight (based on silicon nitride) of sintering aid powder selected from (including) was mixed, this was cold-formed and crushed, and hexagonal boron nitride was mixed as a solid pressure medium to form a 1700 It is characterized by being fired at a temperature below ℃. In this case, the firing is particularly characterized in that it is performed by pressure sintering.

The silicon nitride sintered abrasive thus obtained is made of alumina,
It has a grain boundary phase composed of rare earth oxides (including ittria), has a silicon nitride content of 80% by weight or more, and has an average grain size of 0.2 to 1. It is characterized by being a sintered grain having characteristics of On, relative density (actual density/theoretical density) of 90% or more, and hardness of 21 GPa or more. A grinding wheel or coated abrasive paper made using this abrasive material has extremely excellent grinding performance, and has an extremely high grinding ratio that cannot be achieved with conventional general abrasive grains in precision grinding, particularly wet grinding.

Conventionally, general abrasives include alumina abrasives, such as brown alumina abrasives (represented by the symbol rAJ), as described above.

(same hereinafter), white alumina abrasive (MA), or silicon carbide abrasive such as black silicon carbide abrasive (C), green silicon carbide abrasive (GC); There are no known seed materials that have been put to practical use (see JIS R8111 "Artificial abrasives").

Silicon nitride has the highest strength and toughness among current ceramic materials, and has excellent thermal shock resistance, making it promising as an abrasive material. Despite this, silicon nitride has not yet been put into practical use as an abrasive material because silicon nitride is extremely difficult to sinter.

It is said that this is because the addition of a sintering aid (MgO) is essential, and the presence of this aid reduces strength and hardness at high temperatures, as well as low oxidation resistance (Japanese Patent Publication No. 59-177).
51>. Incidentally, as far as the applicant is aware, this Patent Publication No. 59-17751 is the only patented invention regarding silicon nitride abrasives. A precipitated layer of silicon nitride is formed on the surface, and this is crushed to produce a pure silicon nitride abrasive (containing no auxiliaries), which provides excellent high-temperature mechanical properties. However, such a method requires complicated equipment, and since it is a CVD method, it is not suitable for mass production, and therefore has not been put into practical use.

The present invention uses silicon nitride as the main ingredient, which has not yet been put to practical use as an abrasive.

A predetermined amount of a sintering aid selected from alumina and rare earth oxides is blended into this, and these are used as ultrafine powder of 1 or less (usually submicron), and after molding, they are once crushed and fired. , precision grinding, especially in wet grinding.

The present invention has succeeded in providing a silicon nitride abrasive material that can be put to practical use as a substitute for the conventionally widely used alumina abrasive materials and silicon carbide abrasive materials.

[Preferred Means and Effects] In obtaining the novel silicon nitride abrasive of the present invention, three or more components selected from rare earth oxides including alumina (AjzOs) and ittria are used as sintering aids.
Add at least % by weight (hereinafter referred to as "%"). On the other hand, even with the addition of this auxiliary agent, it is necessary that the abrasive material has high strength and hardness at high temperatures sufficient for use as an abrasive material for precision grinding.

Therefore, the total amount of auxiliary agents should be 20% or less. In particular, it is preferable to add 3 to 10% alumina and 3 to 10% itria, and it is optimal to add about 5% alumina and 5% itria.

The average crystal grain size of this raw material powder is silicon nitride, which is the main component, and alumina, which is a subcomponent (auxiliary component).

The number of rare earth oxides is 14 or less. The resulting silicon nitride sintered grains have a fine crystal structure of 1/a or less, which contributes to achieving a high grinding ratio when used as an abrasive. Preferably, the average particle size of the raw material powder is 0.2 to 0.4-.

The molding can be performed using various known methods such as pressure molding.

Slip casting can be selected and used depending on the purpose. Since the cold-formed product is crushed afterwards and before firing, the shape of the molded product is also lumpy.

It does not particularly matter whether it is in the form of a sheet or even a string.

By crushing, the particles are ground to a particle size that approximately corresponds to a particle size suitable for use as an abrasive. For precision grinding of steel, for example 250-~
It is preferable to set it to about 350p (#80 to #8o).

When firing this pulverized silicon nitride material.

A solid pressure medium is mixed in order to apply uniform pressure to each powder and obtain sintered grains of the desired particle size as an abrasive material, especially abrasive grains. As this solid pressure medium, hexagonal boron nitride (HBN), which has low hardness and is inexpensive, is preferable, and its average particle size is 1.
~2-2 The mixed amount is 80~ for the crushed silicon nitride
It is best to set it to about 120%. Other pressure media such as graphite (C)
may form silicon carbide. The firing method may be either normal pressure sintering or pressure sintering, but pressure sintering, or hot press (HP ) sintering, hydrostatic hot press (HIP) sintering, or atmospheric pressure sintering performed at a predetermined nitrogen partial pressure (for example, 9 kg/c- or more). The firing temperature is preferably 1700° C. or lower from the viewpoint of preventing decomposition of silicon nitride.

The silicon nitride sintered particles thus obtained are 1g11 or less,
In particular, it is a polycrystalline body of silicon nitride having an extremely fine average grain size of about 0.2 to 0.5, and a grain boundary phase whose main constituent is an auxiliary agent is present by liquid phase sintering. This grain boundary phase is, for example, Si3N4- n Y2O3-mAR20,
A crystalline phase consisting of a compound represented by

It exists as a glass phase such as nitride glass. In this regard, silicon nitride abrasive abrasive grains made by crushing fine-grain crystalline or blended crystalline silicon nitride as a precipitated layer obtained on a substrate by the CVD method of Japanese Patent Publication No. 59-17751 contain an auxiliary agent. It is completely different from being basically a single crystal or an aggregate thereof with no high purity.

In addition, in the present invention, the silicon nitride molded product is crushed in advance before sintering and sintered in the presence of an HBN solid pressure medium, so the fired product itself has a particle size of, for example, about 200 to 300 mm. It can be obtained as extremely dense silicon nitride sintered grains. Therefore, high breaking energy is required.

There is no need to separately crush the sintered body.

Using such a silicon nitride sintered abrasive material, a grinding wheel and coated abrasive paper are manufactured according to a conventional method. When manufacturing a general vitrified grindstone as a grinding wheel for precision grinding, which is the object of the present invention, it is preferable to use a vitreous bonding agent with a firing temperature of about 1000°C. The grinding wheel obtained in this way has a grinding performance equal to or better than that of a grinding wheel made using conventional general abrasive materials (alumina, silicon carbide), and its characteristics are particularly good in wet precision grinding. It is demonstrated in It can be applied to metals in general as work materials, and is particularly effective for heat-resistant alloys and super tool steels. In this case, it goes without saying that welding is difficult.

[Example] Silicon nitride powder with an average particle size of 0.3 and an average particle size of 0.51
AezOs 5% and average particle size 1. ogl's Y2o25
5 of Ube Industries' commercial product prepared by mixing and adding %
Cold isostatic pressing of N-C-OA powder (C, 1, P,)
Approximately 100 to 200 g was packed into a plastic bag, degassed, and vacuum packed. And 2 bags of vacuum bag
A pressure of ton/c- was applied to C,1,Pl. C,
1.P.

Thereafter, the C, 1, P product, which was somewhat hard and made of silicon nitride, was taken out of the plastic bag, crushed in a mortar, etc., and sieved to a desired particle size. This silicon nitride molded powder sieved to a desired particle size and hexagonal boron nitride ()I as a pressure medium
BN) powder and 300 g of each were taken and mixed gently in a plastic bag. This mixed powder was filled into a graphite mold with an inner diameter of 80 mm, which was set in a hot press firing furnace (manufactured by Fuji Denpa Kogyo ■) and heated to 1600°C at a temperature increase rate of 20°C/sin.
After firing, the silicon nitride sintered grains were sieved from the IBN powder as a pressure medium, and then completely cleaned using an ultrasonic cleaner. The washed silicon nitride sintered grains were dried in a drier to completely remove moisture.The sintered grains were made of silicon nitride grains with an average grain size of 0.2 to 0.5. It has an elementary microcrystalline structure and has a Vickers hardness of 22 GPa.
(2,24X 10akg/j), Density 3J teat=. The #BO abrasive grains are screened again from the sintered abrasive grains, and the abrasive grains are used to create a vitrified grinding wheel, and a conventionally known fused alumina type single crystal abrasive material (32
Grinding performance was compared with A).

The grinding wheel was made by mixing 88.1 parts by weight of abrasive grains, 11.9 parts by weight of a ceramic binder component, and 3.1 parts by weight of dextrin, and then pressurizing the mixture to give a molding density of 1.88 g/c1i. Next, this raw grindstone before firing is placed in an electric furnace for 55 minutes.
It was heated to 1000°C at 0°C/Hr. The ceramic binder used was made of feldspar, clay, and fritted glass.

The grinding wheel after firing contained 4B abrasive material (abrasive grains), 9% by volume, and 8.1% by volume of binder. Table 1 shows the properties of the grindstone for grinding tests. The dimensions of the grindstone were 200 m in outer diameter x 19 m in thickness x 76.2 m in inner diameter.

Table 1 Properties of grinding wheels for grinding tests Dressing: Heavy stone dressing The results are shown in Table 2. The high power values m and i are values per 10 degrees of the grinding wheel width, and the maximum noise is within the range of 27 to 130 dB, so it is an A characteristic value (Month S). (The same applies hereinafter) Table 2 Next, a grinding test was conducted on the grinding wheels shown in Table 1. For comparison, a grinding wheel of the same shape and size and made of fused alumina single crystal abrasive grains (manufactured by Pacific Random ■; 32A) having the same abrasive grains and binder content as the grinding wheel of the example was used for comparison.

The grinding test conditions are as follows.

Machine: Okamoto Heiken CPG-52AN Grinding wheel peripheral speed:
2[100rn/aIn cutting depth: 68201m
/pass dry plunge down cut workpiece material: 5KD-1 (hc60) (dimensions): length 100 x height 50 x width 10 (fin)
(Working width) = lO As is clear from Table 2, the grinding wheel of this example is single crystal 3
The grinding ratio is 5 compared to the comparative example grinding wheel made of 2A abrasive grains.
, 3 times as much, the surface roughness and power consumption were the same, the noise was low, and the grinding performance was extremely excellent, with less grinding burn.

In addition, a wet grinding test using a water-soluble grinding oil was conducted using the grindstone shown in Table 1. For comparison, 82A abrasive grains in Table 1 (Comparative Example 1) and commercially available alumina ceramic abrasive grains (Comparative Example 2) were used.
) (SG grindstone manufactured by Two-Tone Company) was used.

These grinding wheels have a grinding specific gravity of 2.02, an abrasive volume (%) of 48.9%, and a binder volume (%) of the grinding wheels.
8.1%, and the whetstone had the same structure as the whetstone shown in Table 1.

The grinding test conditions are as follows.

Machine: Okamoto Heiken CFG-52AN Grinding wheel speed:
2000m/sin depth of cut: ΔR20taA/
pass wet plunge down cut 5KD-1 (HRo 60) Length 100 x Height 50 x Width 10 (fin) 10 fin weight dresser Water-soluble Simperial HD90 10x solution The results are shown in Table 3.

Workpiece material: (Dimensions) = (Workpiece width) Grinding oil: (The following is a margin) Table 3 As is clear from Table 3, the grinding wheel using the silicon nitride sintered abrasive material of this example was In a wet grinding test using water-soluble grinding oil, the grinding ratio was 6 times higher than that of the 32A grinding wheel, and it showed excellent grinding performance with comparable surface roughness, power consumption, and noise. At the same time, when compared with commercially available alumina ceramic abrasive grain grinding wheels, the grinding ratio was 4.3 times higher, and the maximum power consumption and noise were at the same level. Therefore, it showed much better performance than conventional grinding wheels made using general abrasives.

[Effects of the Invention] As described above, according to the present invention, a dense silicon nitride abrasive having high hardness and fine crystals can be easily obtained. In addition, grinding wheels made of such abrasives can be suitably used for precision grinding of tools, dies, etc. made of heat-resistant alloys, etc., and have extremely superior performance compared to commercially available grinding wheels made of fused alumina abrasive grains. shows. Also, in wet grinding using water-soluble grinding oil, it shows significantly superior performance compared to commercially available fused alumina abrasive grains and sintered alumina ceramic abrasive grains. Therefore, it is extremely useful as an abrasive material that can be put to practical use even in precision grinding where very expensive ultra-hard abrasive materials are used.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a manufacturing method according to an embodiment of the present invention. Silicon nitride fine powder silicon nitride mixed fine powder diagram

Claims (6)

[Claims] (1) 3 to 20% of sintering aid powder selected from alumina and rare earth oxides (including yttria) having an average crystal grain size of 1 μm or less is added to silicon nitride powder having an average crystal grain size of 1 μm or less. Silicon nitride sintered material is produced by mixing % by weight (based on silicon nitride), crushing the mixture after cold forming, mixing hexagonal boron nitride as a solid pressure medium, and sintering it at a temperature of 1700°C or less. Method for manufacturing abrasive material. (2) The manufacturing method according to claim 1, wherein the firing is performed by pressure sintering. (3) Has a grain boundary phase consisting of alumina and rare earth oxides (including yttria), and has a silicon nitride content of 8
1. A silicon nitride abrasive material characterized by being sintered grains having the following properties: 0% by weight or more, an average grain size of 0.2 to 1.0 μm, a relative density of 90% or more, and a hardness of 21 GPa or more. (4) A grinding wheel characterized by using the silicon nitride abrasive material according to claim 3. (5) The grinding wheel according to claim 4, which is used for wet precision grinding. (6) A coated abrasive paper characterized by using the silicon nitride abrasive material according to claim 3.