JPS623111B2 - - Google Patents

Description

[Detailed Description of the Invention] Diamond sintered bodies produced by sintering diamond powder have recently begun to be increasingly used in applications such as wire drawing dies, and are solidifying their foundation as important industrial materials.

Diamond sintered bodies currently on the market are diamond powder bound with a catalytic metal, actually a cobalt alloy, which converts graphite into diamond.

The existing diamond tool market can be broadly divided into wire drawing dies, cutting tools, dressers, mining civil engineering tools, and others, but the diamond sintered bodies currently on the market have become widespread only in the former two types. However, it has not spread to other markets. The inventors first investigated the cause of this problem in various ways regarding the dresser market. The inventors discovered that the diamond particle size in the sintered body has a large effect on the dresser use, leading to the present invention. The diamond grain size in diamond sintered bodies currently on the market is 50 microns or less even for wire drawing dies, and several microns for cutting tools. It is not clear why only particles of this size are commercially available. However, it is clear from the example of cemented carbide B that a material that is too rough is not suitable for cutting tools.

Grain growth of diamond crystals during sintering is not observed very much, so the size of diamond crystals in the sintered body is mostly controlled by the particle size of the raw diamond powder, especially in the case of coarse crystals of 50 microns or more. . Therefore, in order to obtain a sintered body with a particle size of 50 microns or more, it is necessary to use raw material powder with a particle size of 50 microns or more. However, this is very difficult in terms of sintered body production technology. This is because such coarse powder cannot be pressed and molded, and it is also difficult to wrap it in metal foil and give it a certain shape. However, the present inventors proposed an extremely successful method (Japanese Unexamined Patent Publication No. 52-96909).
A coarse-grained sintered body was made using In other words, all you need to do is fill the powder into a thick-walled metal can.
There is no problem even when coarse powder of about mm size is used as the raw material.
The present inventors created diamond sintered bodies of various grain sizes using such technology that they possessed, and
We conducted performance tests for dresser applications, which have not yet been fully successful. As a result, raw material powder with a diameter of 0.25 mm or more was used.

That is, it has been discovered that a sintered body in which most of the diamond crystals in the sintered body have a size of 0.25 mm or more exhibits excellent performance as shown in FIG.

As shown in the figure, if a coarser raw material of 30/40 mesh or more is used, it is expected that the performance will further improve, but since the maximum particle size of currently commercially available artificial diamond powder is this, it was not possible to test it.

There are commercially available natural products, but they are expensive and not practical.

The reason why the coarser the grains, the higher the performance, is thought to be as follows.

The grain size of the dresser and the abrasive grain of the grinding wheel have various size relationships. If the grain size of the grinding wheel is larger than that of the dresser,
This is a mutual comparison of the wear resistance of the diamond sintered body during dressing, including the binder phase. In the opposite case, it would be the same as dressing with single crystal diamond.

The grain size of dressed grindstones is usually less than 100 mesh (149 microns, American standard sieve standard; all mesh sizes hereinafter are based on the same standard).
Therefore, in the case of diamond grain size of 60 meshes (250 microns) or more, it can be regarded as the same as in the case of single crystal diamond. This is considered to be one major reason why coarse grains are preferable.

Further, in a diamond sintered body containing a catalyst metal, a diamond-diamond bond sufficiently grows and develops during sintering to form a so-called diamond skeleton. This is also favorable in terms of the performance of the dresser. In order to obtain such a sintered body in which diamond crystal grains are firmly bonded to each other, diamond is sintered under high temperature and high pressure conditions where diamond is stable, with catalytic metals used for diamond synthesis such as ferrous metals coexisting with diamond. obtained by In this case, the raw diamond particles are dissolved into the catalyst metal from their surface portions and re-precipitated to form a skeleton between the diamond particles.

The type of diamond raw material powder used to manufacture the diamond sintered body for dressers of the present invention is, for example, currently used for metal bond diamond cutting blades made by infiltration or low-pressure hot pressing for cutting stones, etc. Saw grade diamonds are the most suitable.

Synthetic diamond abrasive grains currently on the market can be roughly divided into those for resin bonded whetstones and those for metal bonded whetstones, but abrasive grains for cutting blades have the highest abrasive grain strength and are crystalline. It has few defects inside. Such high-quality abrasive grains are synthesized by strictly controlling manufacturing conditions. In the sintered body for a dresser of the present invention,
When sintering is performed using coarse particles of 0.25 mm or more, or when pressurized under high pressure, some of the particles are crushed and fill the gaps between particles, and the fine particles are dissolved in the catalyst and recycled. Depart. However, most of the grains have high strength as crystal grains themselves, so they maintain their shape even when pressed under ultra-high pressure of, say, 55Kb, and even when sintered, the strength of the abrasive grains is lost. Never.

Furthermore, when coarse diamond particles of 0.25 mm or more are sintered under ultra-high pressure as in the present invention, the individual diamond particles undergo slight plastic deformation under high pressure and high temperature, which causes a work hardening phenomenon. As a result, the hardness of the diamond crystal of the sintered body becomes higher than that of the raw diamond crystal, and the wear resistance improves. In particular, when coarse-grained diamond crystals are used as in the present invention, the amount of deformation required to fill the gaps between particles under high pressure and high temperature is greater than when fine-grained diamond powder is used. A hardening phenomenon occurs.

In the present invention, it is preferable that 60% by volume or more of the diamond crystals in the diamond sintered body be diamond crystals of 250 microns or more, and it has been confirmed that if the content is less than 60% by volume, the wear resistance is significantly reduced.

Catalytic metals used in the production of the sintered body of the present invention include metals such as Fe, Ni, Co, Cr, Mn, Ta, etc., or in the case of alloys thereof, these metals and other metals, such as Cu, Ti, etc. Alloys may be used.

Examples will be described below.

Example 1 Diamond powder for Saw Grade 30/40, 40/5
After filling powders in the particle size range of 0 and 50/60 mesh into separate mild steel containers, cover the container with an iron powder-embossed lid, place a small piece of copper on top, and keep the entire container at 10 ^-4 mmHg. It was heated in a vacuum furnace to 1150°C while maintaining the degree of vacuum at . When removed from the furnace, the copper was completely melted and infiltrated into the iron powder stamping, and the lid was firmly attached to the mild steel container. The entire container was then hot-pressed to 55 kb at 1400°C using an ultra-high pressure and high temperature device used for diamond synthesis.
The molten metal consisting of a copper-iron phase penetrated between the filled diamond powder, yielding a strong sintered body with a strong skeleton structure of diamond.

The dimensions of the obtained sintered body were 5 x 5 x 0.5 mm. When this was brazed to the tip of a W rod and tested as a dresser, it showed excellent performance as shown in FIG. The test was performed using a 120/140 mesh Alundum grinding wheel.

Furthermore, when the surfaces of these sintered bodies were polished with diamond paste and observed using an interference microscope, slip lines due to plastic deformation were observed in most of the crystal grains in all of the sintered bodies.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the influence of the diamond raw material particle size on the dresser characteristics in Example 1. The vertical axis shows the wear amount ratio for a constant dresser wear, and the horizontal axis shows the raw material particle size (mesh range).
0/60 mesh corresponds to 297 micron/250 micron.

Claims (1)

[Claims] 1. In a diamond sintered body made of diamond and a metal that can serve as a catalyst for converting graphite to diamond, the diamond crystals in the diamond sintered body are mainly diamond crystals of 250 microns or more, and the diamond A sintered diamond body for dressing, characterized by crystals having a skeleton structure. 2. Diamond crystals in the diamond sintered body
Claim 1 characterized in that 60% or more by volume is diamond crystals of 250 microns or more
A diamond sintered body for dressing as described in .