JPH06184526A - High-strength superabrasive grain and its production - Google Patents

Abstract

PURPOSE:To obtain high-strength abrasive grains having strength adjusted by using specific diamond grains. CONSTITUTION:The high-strength superabrasive grains comprise diamond grain having a static crushing strength of 15kg/mm<2> or higher. pref. 20kg/mm<2> or higher. The abrasive grains having strength thus adjusted are obtd. by mixing raw superhard material grains (diamond grains) with an impact buffer (e.g. common salt), subjecting the mixture to impact due to moving hard balls (e.g. steel balls) in order to crush relatively weak superhard grains while avoiding impact exceeding a certain level, separating and recovering crushed superhard material from the buffer, and removing superhard material fragments having too small grain sizes. The figure shows the distribution of strength of diamond powder of the invention.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to high strength superabrasive grains, and in particular to superabrasive grains such as diamond or cubic boron nitride having improved individual grain strength, and methods of making the same.

[0002]

2. Description of the Related Art Ultra-hard materials such as diamond and cubic boron nitride are fixed as abrasive grains to a tool base material by a metallic or ceramic binder and used for high-load grinding and cutting work. There is. When used in such a tool, it is desirable that all the abrasive grains have uniform physical properties, particularly uniform strength above a certain level. When the strength values have large variations, the weak abrasive grains are crushed by the impact generated between the workpiece and the workpiece during grinding / cutting and easily broken off from the bonding material, so that they do not contribute to the processing. That is, the number of processing points decreases. On the other hand, high-strength abrasive grains are subjected to excessive load, which promotes wear and detachment, resulting in
This means that the tool as a whole will not be able to demonstrate the desired machining capacity. Therefore, from the viewpoint of improving the efficiency of grinding / cutting and ensuring the tool life, it is desired that the entire abrasive grains maintain a certain level of strength or more.

As a method for evaluating the strength of superabrasive grains, there are a method by impact crushing, a method by striking, and a method by a crushing test under static load (for example, “Diamond Tool”, pp. 213 to 239, Nikkei Tech. Books, 198
7), there is no common evaluation method that has been approved by the Japanese industry, and each manufacturing company has decided to use its own method.

For the strength of superabrasive grains as an aggregate, for example, an evaluation method using an impact load called a pot mill method is known. This is qualitatively put the sample diamond powder and steel balls in a steel capsule, shake for a certain time,
The weight of the particles that have been crushed and passed through a sieve one step below the original particle size is weighed, and evaluated as the weight% of the passed sieve with respect to the total amount of the recovered sample.

By the way, looking at, for example, diamond abrasive grains, it is difficult to obtain an abrasive grain product having the same physical properties, especially strength, even if it is of the same grade, as a result of variations in forming conditions within and between lots. is there. This is mainly due to the difference in crystal growth rate depending on the P-T condition in synthetic products and the difference in ambient conditions during crystal formation. This also applies to boron nitride abrasives. On the other hand, it is considered that the natural diamond abrasive grains are caused by the difference in the degree of cracking due to the difference in the impact condition when the abrasive grains are produced by crushing, as well as the conditions for producing the rough stone.

[0006] Further, commercially available diamond abrasive grains, even in high-grade high-grade products, are found to have crystals with imperfect shapes and crystals containing a large amount of inclusions under observation under a microscope. It also shows a low strength value in the crush test. For example, as shown in FIG. 1, which shows the distribution of the crushing strength performed on 100 commercially available 40/50 mesh diamond abrasive grains, even if the abrasive particles are currently called the highest grade, the crushing strength is 30 kg. / mm ² or less of particles of 30% or more, 20 kg / mm ² or less, even about 20%
The intensity distribution width extends downward, and so on.

In the production of superabrasive grains, for the purpose of adjusting the shape of the abrasive grains and preparing smaller size abrasive grains,
The crushing process is widely used. This process is generally performed by a ball mill, in order to increase the throughput per unit time.
It is carried out by an impact crushing method such as a vibration mill or a jet mill. However, in these impact crushing methods, it is unavoidable that the abrasive grains are indiscriminately crushed mainly by cleavage cleavage, and at the same time, many cracks are generated inside the particles. Therefore, in the conventional process using impact crushing, the limit of the strength of the obtained abrasive grains is relatively low, and it is impossible to cope with the further improvement of the strength.

[0008]

An object of the present invention is to create a condition close to a crushing test by adjusting the impact applied to the abrasive grains in the crushing process of the abrasive grains. , Is to improve the strength of the abrasive grains as a whole by selectively crushing and removing essentially low-strength particles such as particles containing a large amount of impurities or having cracks, agglomerated particles, etc. .

[0009]

Means for Solving the Problems The gist of the present invention is to polish a raw material ultra-hard material particle by a motion of a hard ball to crush and remove a relatively weak ultra-hard material particle, thereby adjusting the strength. When preparing the particles, by subjecting the ultra-hard material particles to the impact of a hard ball in a mixed state with an impact cushioning material, the impact exceeding a certain level on the raw ultra-hard material particles is suppressed, and further, the crushed ultra-hard material A method for producing high-strength superabrasive particles, characterized in that the material is separated and recovered from the buffer material, and the ultrahard material fragments having an excessively small grain size are removed.

Such a cushioning material has a function of alleviating the impact of a steel ball used as an impact medium, and after the crushing step, physical means such as magnetic properties and specific gravity difference, or waste liquid treatment. Any material can be used as long as it can be easily separated and removed from the abrasive grains by an easy chemical means. Graphite, calcium carbonate,
It is a non-metal powder such as salt, silica sand, alumina, polyethylene, or polystyrene, or a single substance or a combination of iron and other various metal powders.

As an abrasive grain crushing device using balls,
Various horizontal and vertical crushers such as ball mills, vibration mills, tower mills and attritors can be used. In the crushing by the roll mill, it is preferable that the opposing rolls are made of cemented carbide, and the pressing pressure between the rolls is controlled within a predetermined range by the strength of the adjusting spring or the hydraulic pressure. When superabrasives such as diamond and cubic boron nitride are treated with these buffers in these crushers, the impact of the balls on the abrasives is mitigated and the parameters are optimized for compression crushing. Close conditions are created.

On the other hand, the ball itself may be lined with rubber or plastic, or a relatively soft material such as copper or copper alloy may be used as the ball. This structure can be used as an alternative to or in combination with the cushioning material.

Subsequent to the crushing step, the crushed particles are separated by sieving to obtain abrasive grains consisting of high-strength particles that have not been crushed. In order to improve the physical properties of the abrasive grains, it is more effective to use other separation methods, for example, shape selection using the difference in outer shape, magnetic force selection using the difference in the amount of intervening metal in the particles, and electrostatic separation method. is there.

[0014]

[Operation] In the conventional crushing process, it is unavoidable that diamond particles are damaged by the edges of other diamond particles and the resulting minute cracks reduce the strength of the abrasive grains. In the invention, such drawbacks are effectively prevented.

As a tester for measuring the crush strength under static load, for example, the one shown in FIG. 1 can be used. A sample diamond particle 1 is placed between two diamond sintered body plates 2 and 3 arranged in parallel. At this time, the particle size of the particle 1 is obtained from the output of the differential transformer 6 supplied to the instruction / recording device 5 via the amplifier 4. Next, iron particles 9 are poured into the container 8 at the end of the load arm 7 and the push rod 1
With 0, a load is gradually applied to the diamond particle 1.
Then, when the load value at the time when the sample particles are destroyed is read as the output of the load cell 11 on the pointing / recording device 5 via the amplifier 12, the tensile strength σ _t is obtained from the following equation. σ _t = P _max /0.32A where P _max is the load applied when the diamond particles are crushed, and A is the projected area of the diamond particles.

[0016]

Example 1 As a material to be treated, a crushing strength of 20 kg /
Approximately 4 kg of salt of 200 g of 40/50 mesh diamond containing about 20% of the part of mm ² or less, and 10 k
g of a steel ball was placed in an iron barrel having an inner diameter of 25 cm, and this was placed at 40 r. p. m. It was rotated at the speed of. The mixture of salt diamonds was taken out after 3 hours, and salt was removed using water to recover the diamond. The minimum crushing strength of this lot was 18 kg / mm ² , and the strength distribution was as shown in FIG.

[0017]

Example 2 The operation of Example 1 was repeated using iron powder as a buffer material instead of salt. Crush strength is 15kg
200 g of 40/50 mesh diamond containing about 15% of less than 1 / mm ² of iron powder (100 mesh) of about 15 kg and a steel ball of 10 kg are put in the above barrel and operated under the same conditions as above. It was After 5 hours, the mixture was taken out of the barrel, iron powder was removed by magnetic separation, and diamond was recovered. The minimum strength of this lot is 2
At 2 kg / mm ² , the crush strength distribution was as shown in FIG.

For comparison, FIG. 4 shows the crush strength distribution of the conventional product measured by the same method.

[0019]

EFFECTS OF THE INVENTION In the present invention, particles that are brittle and have low strength are selectively crushed and removed by sieving. Therefore, 15 or 20 kg / m 2 is used in the above evaluation method.
Particles with a crush strength of less than m ² were essentially removed,
It is possible to obtain abrasive grains having a relatively narrow strength range.

Since the obtained abrasive grains do not include low-strength abrasive grains that are crushed and lost during grinding / cutting, substantially all the grains contribute to the machining, Improved machining efficiency and tool life can be obtained.

In the crushing treatment of the present invention, since the abrasive grains are subjected to the grinding action simultaneously with the compression crushing, particles having a biaxial ratio close to 1 can be obtained. This shape is particularly advantageous when used for long-life metal bonds and for vitrified use, and when the abrasive grains are fine particles, the influence of buoyancy is exerted during classification using gravity in the subsequent process. The difference is small, so the separation effect is large.

[Brief description of drawings]

FIG. 1 is a static load crush strength tester that can be used in the present invention.

[Explanation of symbols]

As a testing machine to measure the crushing strength under static load,
For example, the one shown in FIG. 1 can be used. Sample 1 Diamond particle 2 Diamond sintered body plate 3 Diamond sintered body plate 4 Amplifier 5 Indication / recording device 6 Differential transformer 7 Arm 8 Container 9 Iron grain 10 Push rod 11 Load cell 12 Amplifier

FIG. 2 is a strength distribution of diamond powder produced by the method of the present invention and measured by the testing machine of FIG.

FIG. 3 is a strength distribution of another diamond powder produced by the method of the present invention and measured by the testing machine of FIG.

FIG. 4 is a strength distribution of two conventional diamond powder products.

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[Procedure amendment]

[Submission date] December 17, 1992

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Claims (7)

[Claims] 1. A static load crush strength of 15 kg / mm
High-strength abrasive grains composed of ^two or more diamond particles. 2. The high-strength abrasive grain according to claim 1, which has a static load crush strength of 20 kg / mm ² or more. 3. Ultra-hard material particles are prepared in the case of preparing abrasive grains whose strength is adjusted by impacting the raw ultra-hard material particles by the movement of hard balls to crush and remove the relatively weak ultra-hard material particles. By subjecting the hard ball to a shock in a mixed state with a shock absorbing material, the shock exceeding a certain level with respect to the raw material super hard material particles is suppressed, and further, the crushed super hard material is separated and recovered from the shock absorbing material, and A method for producing high-strength superabrasive grains, which is characterized by removing fragments of superhard material having an undersized grain. 4. The method for producing high-strength superabrasive particles according to claim 1, wherein the buffer material is at least one selected essentially from graphite, calcium carbonate, salt, silica sand, alumina, polyethylene and polystyrene. 5. The buffer material is essentially a metal powder,
The method for producing a high-strength superabrasive grain according to claim 1. 6. The method for producing high-strength superabrasive grains according to claim 1, wherein the superhard material is diamond. 7. The superhard material is cubic boron nitride,
The method for producing a high-strength superabrasive grain according to claim 1.