JPH042296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing cubic boron nitride grinding grains.

(Prior technology) CBN (referring to cubic boron nitride. The same applies hereinafter)
stands for HBN (hexagonal boron nitride. The same applies hereinafter)
It is produced by processing CBN at high temperature and pressure, which are the thermodynamically stable conditions for CBN.

CBN has a hardness that is second only to diamond, and its chemical stability, especially with respect to ferrous work materials, is superior to that of diamond, so its use as a grinding abrasive is increasing.

There are various proposals regarding methods for producing CBN particles, such as in JP-A-59-57905, JP-A-59-73410, and JP-A-59-73411. CBN particles obtained by such a general manufacturing method have no problems when used in ordinary electrodeposited grinding wheels or metal bonded grinding wheels, but
Not suitable for applications where sharpness is particularly required.

CBN particles used in grinding abrasive grains that require such sharpness are desired to be dense, transparent, have sharp cutting edges, and have high crushing strength.

In Japanese Patent Application Laid-Open No. 61-31306, the applicant
We proposed a method using LiMBN ₂ (where M is an alkali metal) and Ca ₅ Si ₂ N ₆ as catalysts.
According to this method, a small amount of Si is incorporated into CBN from the catalyst and appears on a specific plane, so the (111) plane of the crystal develops and the corners of CBN particles become sharp, making them excellent as grinding abrasive grains. CBN particles can now be obtained. Similarly, the present applicant's JP-A-61-
No. 17405 also uses LiMBN ₂ as a catalyst (however,
M is alkali metal) and Si using L ₈ SiN ₄
We proposed a method to obtain CBN particles with sharp corners by incorporating them into CBN particles.

(Problems to be Solved by the Invention) The present inventors investigated the external configuration of the CBN particles produced in the above-mentioned Japanese Patent Application Laid-Open Nos. 61-31306 and 1982-17405, and found the following. I gained knowledge.
In other words, the outer shape constituent planes are basically eight {111} planes, but in most of the CBN particle constituent planes, the {111} planes do not directly intersect with each other, and the {100} plane and the {111} plane
The faces intersect, resulting in the absence of the sharp edges of the {111} polyhedron.

In order to solve the above problems of the prior art, an object of the present invention is to provide a method for providing CBN particles that have sharper corners than conventional CBN particles and have even better performance as abrasive grains.

(Means for Solving the Problems) As a result of intensive research into the external configuration of conventional Si-containing CBN particles, the present inventors found that the object of the present invention can be achieved by the following method.

That is, the first method is characterized by subjecting a reaction system that combines HBN, a C source, a Si source, and an alkali hydride, alkaline earth hydride, or other CBN synthesis catalyst to high temperature and high pressure treatment. This is a method for producing CBN abrasive grains, and the second method involves subjecting a reaction system that combines HBN, an alkali hydride or alkaline earth hydride, a Si source, and a CBN synthesis catalyst to high-temperature, high-pressure treatment. This is a manufacturing method of CBN grinding abrasive grains.

According to these methods, having a sharp cutting edge
It was found that CBN abrasive grains can be obtained. On the other hand, in the conventional method proposed by the present applicant, in which Si is taken in from the catalyst by using a Si-containing catalyst, the effect of increasing the number of {111} planes by Si is insufficient, and one patch CBN obtained in
In the powder, there are quite a few particles that do not have sharp edges or corners, which are formed by the direct intersection of {111} planes.

Note that a separate patent application filed by the present applicant includes a method of subjecting a reaction system that combines HBN, a C source, an alkali hydride and an alkaline earth hydride, a Si source, and a CBN synthesis catalyst to high-temperature, high-pressure treatment. Compared to this method, the CBN abrasive grains obtained by the present invention C contain some particles whose {111} planes do not directly intersect, but they are more effective as CBN abrasive grains than those obtained by the conventional method. Excellent performance.

C source, Si source, alkali hydride or alkaline earth hydride mixed with HBN, and
The CBN synthesis catalyst preferentially causes the growth of {111} planes, making it possible to produce CBN abrasive grains with the desired sharp cutting edge. The effects of the substances used are as follows.

The reason why the CBN abrasive grains obtained by the conventional method lose their sharp edges is that oxide foreign substances such as B ₂ O ₃ are present in the synthesis system, which interferes with the crystal growth process and causes the {111} plane to become horizontal. This is thought to be due to the fact that growth in the {111} vertical direction (especially the {100} direction) is relatively promoted while growth in the {111} direction is relatively inhibited. Therefore, in order to synthesize CBN abrasive grains with sharp cutting edges, it is necessary to make the entire synthesis system during CBN growth especially dull to oxides. Therefore,
In the first method of the present application, a C source is added to the raw material. The C source is produced under high temperature and high pressure conditions during CBN synthesis.
It is presumed that purification is achieved by reducing and decomposing oxidized foreign substances such as B ₂ O ₃ and neutralizing their effect on growth.

In addition, in the second method of the present application, by using alkali hydrides (earth), hydrogen can be used to neutralize impurities that inhibit {111} growth in the synthetic system, and to produce a transparent material with few internal defects. We discovered that it is possible to synthesize beautiful crystals. Alkali hydrides (earth) also act as catalysts for CBN synthesis, but in the case of the present invention, CBN
The aim is to obtain high-strength crystals with fewer internal defects by increasing the purity of the crystals. By using a Si source in addition to the C source in the first method or the alkali hydride or alkaline earth hydride in the second method, the effect of Si can be further improved.

Hereinafter, preferred embodiments of the present invention will be described in more detail.

When HBN with a purity of 95% or more is used, CBN having a desired tip can be stably produced.

As C sources, fatty acids such as stearic acid and palmitic acid, hydrocarbons such as docosane (CH ₃ (CH) ₂₀ CH ₃ ) and terphenyls, carbon alone or as an inorganic compound, carbon black, B ₄ C, etc. are used. be able to. Among these carbon sources, CBN is more stable than crystallized carbon sources such as graphite, and as mentioned above, it is a component of the compound when added, but it is in an active state that decomposes from the compound during CBN growth. This is desirable.

The amount of carbon source to be used is preferably determined to be 0.1 to 100 moles of C per 1 mole of B ₂ O ₃ accompanying as a foreign substance in HBN. Normal purity HBN
The amount of C source used is 0.01~ for all raw materials.
It is 15%.

As the Si source, compounds such as Si powder, B ₄ Si, and Si ₃ N ₄ can be used. The Si source may be mixed into the raw material mixture, but in order to increase the Si content in CBN, it is preferable to include it in the CBN synthesis catalyst in advance. As a method for this inclusion, a method is adopted in which the Si source and the CBN synthesis catalyst are heated and melted. The amount of Si source used is Si per 1 mol of HBN.
is preferably 10 ⁻⁵ to 10 ⁻² mol. If this usage is less than 10 ^-5 , the CBN of Si
On the other hand, if the amount exceeds 10 ^-2 mol, Si will have macroscopic defects in CBN.
The amount of the source used is preferably within the above range.

As the alkali hydride and alkaline earth hydride, LiH, NaH, CaH ₂ , SrH ₂ and the like can be used. The amount of these hydrogen sources used is preferably 0.1 to 10% based on the total raw materials.

Alkali hydride or alkaline earth hydride
5-50% when used as a CBN synthesis catalyst
It is preferable that

CBN synthesis catalysts include (a) alkalis such as Li, Na, and K, nitrides of these (Li ₃ N, Na ₃ N, etc., double nitrides (Li ₃ BN _2, etc.)), (b) Ca, Sr, Alkaline earth elements such as Mg and Ba, and their nitrides (Ca ₃ N ₂ , Sr ₃ N ₂ ,
Mg ₃ N ₂ , Ba ₃ N _2, etc.), double nitrides (Ca ₃ BN ₂ , etc.)
and (c) composite nitrides of alkali and alkaline earth (LiCaBN ₂ , LiBaBN _2, etc.) can be used. Among these CBN synthesis catalysts, (c) is preferred from the viewpoint of stably producing CBN abrasive grains having desired sharp edges. The amount of CBN synthesis catalyst used is preferably 5 to 50 parts by weight per 100 parts by weight of HBN.

When the amount of C source added increases due to the large amount of B ₂ O ₃ in the HBN powder, boron is produced according to the following reaction formula.

B ₂ O ₃ +3C→B+3CO Since this B is not desirable for the synthesis of BCN grinding abrasive grains having the desired tip, an N source is added to add B.
It is preferable to fix it as BN and make it harmless. Melamine, urea, etc. can be used as this N source. Although the amount used depends on the amount of B generated, it is usually preferably 10 ^-4 to 10 ^-1 mol per 1 mol of HBN.The present invention will be explained in more detail below with reference to Examples.

(Example) Example 1 HBN (Showa Denko UHP-1; average particle size 6
~8μ, purity 98%, _{B2O3 0.5} %) 100 parts (parts by weight,
melamine (C ₃ H ₆ H ₆ ) as a C source
2.65 parts, containing 1% silicon as 3CBN synthesis catalyst
Add 15 parts of LiCaBN ₂ and mix the formed sample with 40
By processing under the conditions of ~60 kbar and 1,400 to 1,600°C, it was possible to obtain CBN particles that were transparent and yellow in color and had sharp edges. This CBN
The average particle size of the particles was approximately 130μ, and the purity was 99.8%.

Example 2 A treatment was carried out under the same conditions as in Example 1 except that 3 parts of LiH was used as the alkali hydride instead of melamine. As a result, CBN particles with strong transparency and sharp edges similar to those of Example 1 could be obtained. The CBN particles had an average particle size of about 130μ and a purity of 99.8%.

Example 3 The melamine of Example 1 was converted into stearic acid-CH ₃
When the treatment was carried out under the same conditions except that 1 part of (CH ₂ ) ₁₆ COOH was used, it was possible to obtain CBN particles having a slightly dark brown color and similarly sharp edges.

Example 4 The CBN particles obtained in Example 1 and Example 2 were sized to #120/140 and then electrodeposited to an outer diameter of 150.
mm, thickness 10mm grinding wheel. Specifications such as the amount of abrasive grains used are similar to the conventional {111} planes that do not intersect directly.
This is the applicant's product using CBN, and is the same as the SBN-T used for comparison. These grindstones were subjected to a grinding test under the following conditions.

Grinding wheel peripheral speed - 2000m/min Table speed - 15m/min Depth of cut - 40μm Workpiece - SKH51 60cm ³ When grinding the workpiece, the power required for grinding with the conventional product was 3030W, whereas with the grinding wheel of the present invention it was 2788W. (Example 1), 2848W (Example 2)
, 8% and 6% less power, respectively.

Example 5 100 parts of CBN, 1 part of stearic acid as a C source, and 1 part of N
A mixture of 0.5 parts of urea as a source and 10 parts of LiBN ₂ containing 1% silicon as a CBN synthesis catalyst was used and treated at high temperature and high pressure in the same manner as in the example, resulting in CBN particles with sharp edges without blackness. I was able to get it.

Example 6 100 parts of HBN, 1 part of docosane as a C source, 0.3 parts of B ₄ Si as a silicon source, and as a CBN synthesis catalyst,
When 10 parts of LiSrBN ₂ was added and mixed and treated at high temperature and high pressure in the same manner as in Example 1, it was possible to obtain CBN particles with slightly blackish sharp edges.

(Effect of the invention) Since the present invention is configured as explained above,
The CBN grinding abrasive grains of the present invention have sharper edges than conventional products, and have extremely excellent performance for use in grindstones that require sharpness.

Further, according to the method of the present invention, CBN particles having sharper edges than conventional products can be stably produced.

Claims (1)

[Claims] 1. A method for synthesizing cubic boron nitride from hexagonal boron nitride at high temperature and pressure, in which, together with HBN, a C source, a Si source, and an alkali hydride, alkaline earth hydride, or other cubic A method for producing cubic boron nitride grinding grains, characterized by subjecting a reaction system in combination with a crystalline boron nitride synthesis catalyst to high temperature and high pressure treatment. 2. In a method for synthesizing cubic boron nitride from hexagonal boron nitride at high temperature and pressure, a reaction combining hexagonal boron nitride, an alkali hydride or alkaline earth hydride, a Si source, and a CBN synthesis catalyst A method for producing cubic boron nitride grinding abrasive grains, characterized by subjecting the system to high temperature and high pressure treatment. 3. The method for producing cubic boron nitride grinding grains according to claim 1 or 2, characterized in that the combined reaction system is further combined with an N source. 4. The method for producing cubic boron nitride grinding grains according to any one of claims 1 to 3, wherein the cubic boron nitride synthesis catalyst also serves as a Si source.