JPH09169971A - Cubic boron nitride abrasive grain and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject abrasive grain useful as a grinding abrasive grain, a whetstone, coated abrasive, etc., having a specific relatively low bulk specific gravity prescribed as a particle size distribution and a prescribed relatively high toughness value, continuing excellent cutting quality. SOLUTION: This abrasive grain has a particle size distribution based on a regulation of JIS-B4130, belonging to #325/400 to #60/80 and satisfies relative equations, equation 1 (a1 =2.581!×10<-9> χ<3> -2.894×10-<7> χ2-9.491×10<-4> χ+1.892; a2 =4.316×10<-9> χ<3> -1.662×10<-6> χ<2> -5.992×10<-4> χ+1.714) and equation II (3.245×10<-6> χ<3> -2.566×10<-3> χ<2> +7.125×10<-1> χ+9. 264; b2 =3.245×10<-6> χ<3> -2.556×10<-3> χ<2> +7.125×10<-1> χ-6.736) when the maximum particle size (the minimum value) of each fraction of particle size is χ. A raw material mixture obtained by mixing hexagonal boron nitride with a catalyst for synthesizing cubic boron nitride is further blended with 5-50vol.% of a component inert to a cubic boron nitride synthesis and retained at a high temperature under pressure to give the objective abrasive grain.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cubic boron nitride abrasive grain having a low bulk specific gravity and a high toughness value, a method for producing the same, a grinding wheel made of such an abrasive grain, and such an abrasive grain. The present invention relates to an abrasive cloth paper that is included as an abrasive.

[0002]

2. Description of the Related Art Cubic boron nitride (hereinafter abbreviated as cBN) is hexagonal boron nitride (hereinafter abbreviated as hBN).
Is produced at a high temperature and high pressure which is a thermodynamic stable condition of cBN. Since cBN particles have hardness second only to diamond and are superior in chemical stability, especially stability to iron-based work materials, to diamond, they are used as grinding grains for grinding stones, polishing cloth paper, etc. There is.

A method for producing cBN particles is described in JP-A-59 / 59.
-57905, JP-A-59-73410, JP-A-5
Many proposals have been made, including 9-73411,
The cBN particles obtained by these general production methods have excellent hardness and chemical stability as described above. However, although these cBN particles are not problematic for use in ordinary electrodeposition grindstones or metal bond grindstones, they cannot be said to be suitable for use as grinding abrasives that require sharpness. The cBN particles used for grinding abrasives that require sharpness have a low bulk specific gravity, that is, a sharp shape, and
It is desired that the meat quality of cBN be precise.

As a result of repeated studies for the purpose of providing cBN particles having a sharp shape and relatively dense meat quality, the present applicant has found that hBN contains C source, Si source, alkali hydride and alkali hydride. A process for treating a reaction system containing an earth or other cBN synthesis catalyst at high temperature and high pressure was found, and a patent application was previously filed (Japanese Patent Laid-Open No. 2-3593).
1). The cBN particles produced by the method described in JP-A-2-35931 have high bulk specific gravity and high toughness, and the outer surface of the particles is based on (111), and is dense and transparent. Has sharp edges,
It was found that when it was used for a grinding wheel, it showed good sharpness, but as the grinding continued, the edges became round and the sharpness became dull.

Further, as another method for obtaining cBN particles having a sharp shape, JP-A-51-37897 discloses that a powder compact or a pre-sintered body is prepared without mixing powder of hBN and a catalyst for cBN synthesis. Sludges are treated with each other under the conditions of temperature and pressure suitable for the synthesis of cBN.
A method of making BN particles is described. According to this method, when the hBN sleeve and the catalyst core are arranged and the hBN sleeve is cracked when pressure is applied and the catalyst is melted by heating, the dissolved catalyst enters the cracked part, resulting in the elongated cBN. It is estimated that particles are obtained. However, even if a crack is generated in the hBN sleeve at the time of pressurization, if a pressure of 5 GPa, which is usually required when synthesizing cBN particles, is applied, the generated crack is compressed in the same manner as the part where the crack is not generated, It is considered difficult for the molten catalyst to enter preferentially. Further, in this method, since the hBN part and the catalyst part are separately arranged, the conversion amount is small and it is industrially disadvantageous.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to improve the problems of the prior art as described above, the meat quality is dense and transparent, the shape is sharp, that is, the bulk specific gravity is low, and Good sharpness when used as a grinding grain, and when the grinding load is small and the cutting edge decreases and the resistance increases, a self-generated blade appears, a new cutting edge appears, and if good sharpness continues Has the characteristics to say,
The object is to provide cBN abrasive grains useful as grinding grains.

Still another object of the present invention is to provide an industrially advantageous method for producing such abrasive grains, a grinding wheel made of such abrasive grains, and an abrasive cloth paper having such abrasive grains as an abrasive. To provide.

[0008]

According to the present invention, a cubic boron nitride abrasive grain having a low bulk specific gravity and a high toughness value, the grain size distribution based on JIS-B4130 is # 325 / When the maximum grain size (minimum numerical value) of each category of grain size that belongs to the range of 400 to # 60/80 and is based on the same rule is χ, bulk specific gravity and toughness are represented by the following formulas (1) and (2): a ₂ ≤ bulk specific gravity ≤ a ₁ (1) b ₂ ≤ toughness ≤ b ₁ (2) (however, a ₁ = 2.581 × 10 ^-9 χ ³ -2.894 × 1
0 ⁻⁷ χ ² −9.491 × 10 ⁻⁴ χ + 1.892 a ₂ = 4.316 × 10 ⁻⁹ χ ³ −1.662 × 10 ⁻⁶ χ ²
−5.992 × 10 ⁻⁴ χ + 1.714 b ₁ = 3.245 × 10 ⁻⁶ χ ³ −2.566 × 10 ⁻³ χ ²
+ 7.125 × 10 ⁻¹ χ + 9.264 b ₂ = 3.245 × 10 ⁻⁶ χ ³ −2.566 × 10 ⁻³ χ ²
A cubic boron nitride abrasive grain is provided which is characterized by satisfying + 7.125 × 10 ⁻¹ χ−6.736).

Further, according to the present invention, a method of synthesizing cubic boron nitride abrasive grains by holding a raw material mixture containing hexagonal boron nitride and a catalyst for synthesizing cubic boron nitride at high temperature and high pressure. In the method for producing the cubic boron nitride abrasive grains, the raw material mixture further comprises 5 to 50% by volume of a raw material mixture containing an ingredient inert to the synthesis of cubic boron nitride. Provided.

Further, according to the present invention, the above-mentioned c
A grinding grain consisting of BN grain is provided. Further, according to the present invention, there is provided an abrasive cloth paper containing the above cBN abrasive grains as an abrasive.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The cBN abrasive grains of the present invention are characterized by having a relatively low specific bulk specific gravity and a relatively high specific toughness value, which are defined as a function of their particle size distribution. That is, the cBN abrasive grains of the present invention are JIS-B
The particle size distribution based on the regulations of 4130 is # 325/400.
When the maximum grain size (minimum numerical value) of each category of grain size belonging to the range of # 60/80 and based on the same rule is defined as χ, the bulk specific gravity and the toughness are defined by the above (1) and (2), respectively. It is characterized by entering the range.

According to JIS-B4130, the classification of the particle size of the cBN particles and the particle size distribution characteristics of the particles belonging to each particle size classification (determined by the particle size test using a specific electroform sieve) are specified as shown in Table 1 below. (However, regarding the classification of particle size, only the range of particle size classification # 325/400 to # 60/80 relevant to the present invention is listed in Table 1.)

[0013]

[Table 1] Let χ be the maximum grain size (minimum value) of each of the above grain sizes.
For example, in the grain size classification of # 60/80, χ = 60, # 14
In the particle size classification of 0/170, χ = 140, # 325/40
In the particle size classification of 0, χ = 325.

The cBN abrasive grains of the present invention have bulk specific gravity and toughness satisfying the following formulas (1) and (2), respectively, corresponding to the grain size χ of each grain size category. a ₂ ≤ bulk specific gravity ≤ a ₁ (1) b ₂ ≤ toughness ≤ b ₁ (2) For example, the particle size distribution of a cBN abrasive grain sample is particle size classification # 14.
When it is in the range of 0/170 to # 100/120, the particles belonging to each of all the particle size categories (three particle size categories in total) within this range satisfy the above formulas (1) and (2). ing.

The bulk specific gravity of the cBN abrasive grains of the present invention is lower than that of commonly used cBN abrasive grains, and the toughness thereof is also generally lower than that of commonly used cBN abrasive grains. The cBN of the present invention defined by the above formulas (1) and (2)
Table 2 below shows the permissible ranges of the bulk specific gravity and toughness of abrasive grains as numerical values together with the bulk specific gravity and toughness of commonly used cBN abrasive grains.

[0016]

[Table 2]

Here, "bulk specific gravity" means JIS-R61.
26 of “Bulk specific gravity test method for artificial abrasives”, sampling amount is 20.0 ± 0.1g, cylinder volume is 8.0 ±
It is determined by a measuring method with 0.10 ml and a dropping distance of 95.0 ± 1.0 mm. In addition, "toughness" means that a fixed amount of a test sample sieved with a sieve screen specified by the particle size and one steel ball are placed in a capsule with a volume of 2 ml for a certain period of time (3
(0.0 ± 0.3 seconds) After crushing, the material is sieved with a designated sieve screen and expressed as a percentage by weight of the sample remaining on the screen.

When the bulk specific gravity of the cBN abrasive grains exceeds the above allowable range, that is, when the particle shape becomes blocky, the sharpness of the abrasive grains deteriorates. The lower limit of the permissible bulk specific gravity is a grinding performance, especially a requirement for maintaining a high grinding ratio.If the bulk specific gravity is lower than the permissible limit, the proportion of irregularly shaped grains such as flat or needle-like particles is large. As a result, the grinding performance, especially the grinding ratio, decreases.

Although the toughness often depends on the shape of the abrasive grain, the upper limit of the toughness at each grain size is the strength required to cause spontaneous cutting of the abrasive grain cutting edge to maintain sharpness, If the toughness exceeds the permissible limit, the self-developing blade action becomes difficult to occur, and the sharpness decreases. On the other hand, the lower limit of toughness in each grain size classification is the minimum strength required to maintain the self-developing blade appropriately, and if it is lower than the tolerable lower limit, the damage of the abrasive grains becomes faster and the grinding performance, especially the grinding The ratio decreases.

The sharpened and long-life abrasive grain intended in the present invention has a grain size distribution within the above-mentioned predetermined range, and the bulk specific gravity and toughness of each grain in each grain size category are expressed by the above formula ( It is obtained only when 1) and (2) are satisfied.

The cBN abrasive grain of the present invention is prepared according to a conventional method.
In a method of subjecting hBN to high temperature and high pressure conditions, in a starting mixture of hBN and a catalyst for cBN synthesis,
It can be obtained by adding a component inert to the cBN synthesis, such as alumina. That is, cB
When a component such as alumina, which is inactive for cBN synthesis, is added to the sample space for N synthesis in addition to the catalysts for hBN and cBN synthesis, the cBN particles produced under high temperature and high pressure grow in the process. When C. comes in contact with an inert component, it does not grow further in that direction, and as a result, the shape of cB is sharp.
N particles are obtained.

As hBN, commercially available hBN having a purity of 98% or more can be used. The catalyst for cBN synthesis includes (1) alkali metals such as Li, nitrides thereof (such as Li ₃ N), double nitrides (such as Li ₃ BN ₂ ) (2) alkaline earths such as Ca, Sr, Mg and Ba. Metals, their nitrides (Ca ₃ N ₂ , Sr ₃ N ₂ , Mg
₃ N ₂ , Ba ₃ N _2, etc.), multiple nitrides (Ca ₃ B ₂ N ₄ , Sr _{3
B 2 N 4, Mg 3 B} 2 N 4, Ba 3 B , such as ₂ N ₄₎ (3) alkali and alkaline earth composite nitride of a metal (LiCaBN _2,
LiBaBN ₂ etc.) can be used. Among these catalysts for cBN synthesis, the stability of the catalyst is good,
Further, (3) a composite nitride of alkali and alkaline earth metal is preferable in that a dense and transparent growth layer can be easily obtained.

The amount of the cBN synthesis catalyst used is hBN100.
5 to 50 parts by weight is preferable with respect to parts by weight. As the inactive component for cBN synthesis, a substance that does not undergo phase transition or decomposition under high temperature and high pressure in the cBN synthesis region and does not react with the catalyst for cBN synthesis is used, and specific examples thereof include aluminum oxide and oxidation. Examples thereof include zirconium, mullite, silicon carbide and the like. Aluminum oxide is preferable in consideration of price and availability. The form of the inactive component is not particularly limited, but a granular material is basically used, and the allowable particle size range is generally about 5 to 5,000 μm.

The amount of the component inert to cBN synthesis is 5 to 50% by volume of the sample space. If the amount used is less than 5% by volume, the effect of sharpening the shape is small. Further, if it exceeds 50% by volume, the conversion amount of cBN decreases, which is industrially disadvantageous. The conditions for high-temperature and high-pressure treatment of the raw material mixture in which the catalyst for cBN synthesis and the above-mentioned inactive components are mixed with hBN may be the same as the conventional one, and generally, the pressure is 4 to 6 GPa and the temperature is 1.
An appropriate amount is selected within the range of 400 to 1,600 ° C. and the time of 5 minutes to 10 hours. The most preferable conditions are a pressure of about 5 GPa, a temperature of about 1,450 ° C., and a time of about 15 minutes.

The cBN abrasive grain of the present invention is useful as a grinding abrasive grain as described above. More specifically, examples thereof include a grindstone (vitrified, electrodeposition and metal bond) and abrasive cloth paper. Also, nickel is mainly formed on the surface of the cBN particles,
It can also be used as a resinoid grindstone by coating a metal such as cobalt.

[0026]

【Example】

Hereinafter, the present invention will be described more specifically with reference to Examples. Example 1 (Preparation of Abrasive Grains) hBN (UHP-1, Showa Denko KK, average particle size 8 to 1)
0 μm, purity 98%) 100 parts by weight of LiCaBN ₂ as a cBN synthesis catalyst and 10 parts by weight of aluminum oxide (WA # 180 manufactured by Showa Denko KK) were added so as to be 20% by volume of the sample space to form a sample. . Sample to 5GP
a, yellow and transparent cBN particles could be obtained by high-pressure and high-temperature treatment at 1500 ° C. The obtained cBN particles were processed and the particle size was adjusted to JIS-B4130 particle size classification 80/100 and 230/270. The bulk specific gravity and toughness of the particles in each particle size category are as follows. Grain size classification Bulk specific gravity toughness 80/100 1.74 42 230/270 1.62 73

Comparative Example 1 (Preparation of Abrasive Grains) cBN particles were obtained in the same manner as in Example 1 except that aluminum oxide was not added. The particle size classification of the obtained cBN particles and the bulk specific gravity and toughness of the particles in each particle size classification were as follows. Grain size classification Bulk specific gravity toughness 80/100 1.88 45 230/270 1.78 78

Comparative Example 2 (Preparation of Abrasive Grains) cBN particles were obtained in the same manner as in Comparative Example 1 except that high pressure and high temperature treatment was performed at a pressure of 6.5 GPa and a temperature of 1650 ° C. The particle size classification of the obtained cBN particles and the bulk specific gravity and toughness of the particles in each particle size classification were as follows. Grain size classification Bulk specific gravity toughness 80/100 1.90 34 230/270 1.72 60

Comparative Example 3 (Preparation of Abrasive Grains) The cBN particles obtained in Example 1 were put on a shape separator,
Particles having a sharper shape were collected intensively. The particle size classification of the obtained cBN particles and the bulk specific gravity and toughness of the particles in each particle size classification were as follows. Grain size classification Bulk specific gravity toughness 80/100 1.63 31 230/270 1.51 58

Example 2 ( Preparation of Grinding Wheel Segment) Using the cBN abrasive grains (particle size 80/100, bulk specific gravity 1.74, toughness 42) obtained in Example 1, a mixture was prepared according to the following formulation, and 150 95 after pressure molding at ℃
Main-baking was performed at 0 ° C to prepare a grindstone segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Example 3 ( Preparation of grindstone segment) The cBN abrasive grains (grain size 230/270, obtained in Example 1)
A bulk specific gravity of 1.62 and toughness 73) was used to prepare a mixture according to the following formulation, and after pressure molding at 150 ° C., 9
Main-baking was performed at 50 ° C. to prepare a grindstone segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 4 ( Preparation of Grinding Wheel Segment) Using the cBN abrasive grains (particle size 80/100, bulk specific gravity 1.88, toughness 45) obtained in Comparative Example 1, a mixture was prepared according to the following formulation, and 150 95 after pressure molding at ℃
Main-baking was performed at 0 ° C to prepare a grindstone segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 5 ( Preparation of grindstone segment) Grain size 80/100 obtained in Comparative Example 2 and bulk specific gravity of 1.9
Using cBN abrasive grains having 0 and toughness 34, a mixture was prepared according to the following formulation, pressure-molded at 150 ° C, and then main-baked at 950 ° C to prepare a grinding wheel segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 6 ( Preparation of grindstone segment) Grain size 80/100 obtained in Comparative Example 3 and bulk specific gravity of 1.6
A mixture was prepared by using cBN abrasive grains having 3 and toughness 31 according to the following formulation, pressure-molded at 150 ° C., and then main-baked at 950 ° C. to prepare a grinding wheel segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 7 ( Preparation of Grinding Wheel Segment) The cBN abrasive grains (grain size 230/270, obtained in Comparative Example 1)
Using a bulk specific gravity of 1.78 and a toughness of 78), a mixture was prepared according to the following formulation, and after pressure molding at 150 ° C.,
A main grinding was performed at 50 ° C to prepare a grinding wheel segment. The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 8 ( Preparation of grindstone segment) Grain size 230/270 obtained in Comparative Example 2, bulk specific gravity of 1.
A mixture was prepared according to the following formulation using cBN abrasive grains having a hardness of 72 and a toughness of 60, and was pressure-molded at 150 ° C., followed by main firing at 950 ° C. to prepare a grindstone segment.
The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Comparative Example 9 ( Preparation of grindstone segment) Grain size 230/270 obtained in Comparative Example 3 and bulk specific gravity of 1.
A mixture was prepared by using cBN abrasive grains having a hardness of 51 and a toughness of 58 according to the following formulation, pressure-molded at 150 ° C, and then main-baked at 950 ° C to prepare a grindstone segment.
The porosity of the grindstone segment after firing was 30% by volume. cBN particles 50% by volume Borosilicate-based vitrified bond 20% by volume Phenolic resin 10% by volume

Preparation of Grinding Wheel and Grinding Test The grindstone segments prepared in Examples 2 and 3 and Comparative Examples 4 to 9 were adhered to an aluminum base metal according to a conventional method to be grinded, and then ground under the following conditions. The test was conducted. Grinding wheel: 14A1 type, 150 ^D × 125 ^J × 15 ^T × 5 ^U × 3 ^X × 76.2 ^H Grinder: Horizontal axis surface grinder (grinding wheel motor 3.7 KW) Work material: SKII-51, (HRC 62 to 64), surface to be ground 200 mm long × 100 mm width Grinding method: Wet surface traverse grinding method Grinding conditions: Grinding wheel peripheral speed 1800 m / min, table speed 15 m / min Cross feed 2 mm / pass, depth of cut 20 and 30 μm Grinding fluid: JIS Table 3 to Table 6 show W2 type cBN exclusive liquid, 50 times liquid, 9 l / min grinding results.

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

[Table 5]

[0043]

[Table 6]

[0044]

EFFECTS OF THE INVENTION The cBN abrasive grain of the present invention has a dense and transparent meat quality and a sharp shape, that is, a low bulk specific gravity,
Therefore, the sharpness when used as a grinding abrasive grain is good, and moreover, when the grinding load is small and the cutting edge is reduced and the resistance is increased, the self-generated blade is caused, a new cutting edge appears, and a good sharpness is obtained. It has the characteristic of being persistent. Therefore, the cBN abrasive grains are suitable for grinding grains and are useful as a grindstone, a polishing cloth, and the like.

Front page continued (72) Inventor Masakazu Maki 1 Shiga, Shiojiri City, Nagano Prefecture Shigaji Plant, Showa Denko KK

Claims (4)

[Claims] 1. A cubic boron nitride abrasive grain having a low bulk specific gravity and a high toughness value, wherein the grain size distribution based on JIS-B4130 is # 325/400 to # 60/8.
When the maximum grain size (minimum value) of each category of grain size that belongs to the range of 0 and is based on the same rule is χ, bulk specific gravity and toughness are represented by the following formulas (1) and (2): a ₂ ≤ bulk specific gravity ≤ a ₁ (1) b ₂ ≤ toughness ≤ b ₁ (2) (where a ₁ = 2.581 × 10 ^-9 χ ³ -2.894 × 1
0 ⁻⁷ χ ² −9.491 × 10 ⁻⁴ χ + 1.892 a ₂ = 4.316 × 10 ⁻⁹ χ ³ −1.662 × 10 ⁻⁶ χ ²
−5.992 × 10 ⁻⁴ χ + 1.714 b ₁ = 3.245 × 10 ⁻⁶ χ ³ −2.566 × 10 ⁻³ χ ²
+ 7.125 × 10 ⁻¹ χ + 9.264 b ₂ = 3.245 × 10 ⁻⁶ χ ³ −2.566 × 10 ⁻³ χ ²
+ 7.125 × 10 ⁻¹ χ−6.736), which is a cubic boron nitride abrasive grain. 2. A method for synthesizing cubic boron nitride abrasive grains by holding a raw material mixture, which comprises hexagonal boron nitride and a catalyst for synthesizing cubic boron nitride, under high temperature and high pressure, in the raw material mixture. The method for producing cubic boron nitride abrasive grains according to claim 1, characterized in that a raw material mixture further containing 5 to 50% by volume of an ingredient inert to the synthesis of cubic boron nitride is used. 3. A grinding wheel made of the cubic boron nitride abrasive grains according to claim 1. 4. An abrasive cloth paper comprising the cubic boron nitride abrasive grains according to claim 1 as an abrasive material.