There are impurities such as WBN, HBN, pyrophyllite, graphite, magnesium, and iron in CBN micro powder. In addition, it and the binder powder contain adsorption oxygen, water vapor, etc., which is not good for sintering. Therefore, the purification of raw materials is one of the important steps to ensure the polycrystalline properties. During the development, we used the following methods to purify CBN powder and binder materials: first, CBN badge powder was treated with NaOH at about 300 C to remove pyrophyllite and HBN. Then perchloric acid was boiled to remove the graphite. Finally, remove the metal by boiling it on the hot plate with HCl and washing it with distilled water until neutral.Co, Ni, Al, etc. of the binder were treated by hydrogen reduction. Then mix CBN and binder in a certain ratio evenly into the graphite mold, into a vacuum furnace with pressure less than 1E2, heat 800~1000°C for 1h, remove the dirt on its surface, adsorption of oxygen and water vapor, so as to make the CBN grain surface very clean.
In terms of the selection of binder materials and the amount of binder added, the total amount of binder added should be sufficient but not too much. The experimental results show that the wear resistance and bending strength of polycrystalline are closely related to the average free path (bond layer thickness). When the average free path is 0.8-1.2m3, the wear ratio of polycrystalline is the highest, and the incorporation of the binder is 10%-15% (mass ratio).
In addition to the choice of binding agent, the determination of CBN particle size and particle size ratio is also crucial, the root of the machining precision and surface quality requirements, the manufacture of cutting tools used CBN particle size is roughly divided into coarse particle size 20~30 m. Medium size 3~10 microns. Fine 2 microns. It is difficult to make the tool with high precision with the coarse-grained polycrystalline, but it has high wear resistance and impact resistance.