Polycrystalline diamond support block for bearing grinding

In the inner diameter grinding and groove grinding of precision bearings, the bearing surface in contact with the surface of the support block is the reference for machining and positioning. The selection of the support block, especially the end material, will directly affect the roundness groove of the bearing ring. The difference in size, appearance and processing efficiency also affect the service life of the bearing support, which requires the bearing support material to have good wear resistance, low friction coefficient, good heat dissipation performance, good surface roughness and good material stability.

Performance comparison of several supports

There are roughly three kinds of bearing support materials currently used internationally, namely cemented carbide, polycrystalline diamond (PCD) and polycrystalline pure diamond (CVD) materials. Most domestic bearing companies use cemented carbide materials.

1.1 Cemented carbide

Traditional bearing support materials mostly use cemented carbide, which has good wear resistance, but for large-scale bearing production, its service life is not satisfactory. The auxiliary time spent on frequent replacement of the support and due to the support end The incidence of poor ferrule processing caused by wear is considerable; and the cemented carbide contains metal additives (such as cobalt), and its friction coefficient is higher (greater than 0.15), which increases the friction resistance of the support to the ferrule during processing, which is easy to cause the bearing The appearance of damage affects the machining accuracy of the bearing.

1.2 Polycrystalline diamond

As a substitute for cemented carbide, polycrystalline diamond (PCD) material is applied to the bearing industry, which greatly promotes the precision of precision bearing processing and makes the service life of the bearing support longer than that of the original cemented carbide material. Ten hours suddenly extended to more than 2 years, almost becoming semi-permanent. However, the polycrystalline diamond material is made of small diamond single crystals plus metal additives such as cobalt and nickel, and is sintered under high temperature and high pressure. It has particle characteristics, which makes it difficult to improve the surface roughness. In addition, because polycrystalline diamond contains cobalt, nickel, etc. Metal additives make its chemical stability worse, and shadows easily appear on the bearing surface. In order to remove it, it is necessary to increase the outer diameter super-precision after the groove is super-finished, which affects the processing accuracy of the bearing and increases the processing cost.

1.3 Polycrystalline diamond CVD

Diamond material is grown in a low-pressure closed system using Chemical Vapor Deposition (CVD) technology-direct current plasma-hot wire method. This technology is an ideal technology for tool and heat sink applications. Because it is pure diamond without any additives, it has higher wear resistance and better chemical stability than polycrystalline diamond (PCD), its life is longer, and its roughness is better; CVD diamond material and steel The friction coefficient of the material is very low (<0.1), which greatly reduces the frictional resistance of the bearing support to the bearing during processing.

2 Use of CVD

We apply the domestic CVD diamond material to the radial bearing of the bearing to replace the radial bearing of the foreign PCD diamond material. After a year of use, domestic CVD diamond is used as a radial support for various performance indicators, such as the relationship curve between the shape and size of the processed ferrule and n. And at low speed, with the increase of speed, the carrying capacity shows a rapid decline trend.

3 Design of EC type cylindrical roller bearing

As a cylindrical roller bearing used to withstand large axial loads, the traditional design obviously cannot meet the requirements. How to improve the axial load carrying capacity of cylindrical roller bearings, many countries have carried out a lot of research work in this area. The main improvement is to improve the lubrication condition of the rib contact area, so that it is conducive to the formation of elastohydrodynamic lubrication. The bench test of SKF of Sweden shows that the axial load carrying capacity of the bearing after the improvement is 2.5 times that before the improvement.

The specific method is to make the original straight ribs of the ferrule into oblique ribs, and to make the roller end in contact with it into a spherical surface.

In the EC-type design, the key issue is to determine the flange inclination angle a and the spherical radius R. Recently, the value of angle a varies greatly from country to country, ranging from 7 to 130. Most values are between 10'~ 30'. Luoyang Bearing Research Institute and Tsinghua University jointly conducted research and analysis on the lubrication state of cylindrical roller bearing roller end faces and ring ribs, and came to the following conclusions:

(1) An oil film lubrication condition can be formed at the roller end surface and ribs, especially at high speeds, a better elasto-fluid lubricating oil film can be formed.

(2) The load distribution along the axial and radial directions of the rollers are similar.

(3) The inclination angle of the rib has a great influence on the axial load carrying capacity. Generally speaking, there is a better value. As the speed decreases, the better value increases accordingly; as the load increases, the better value also increases. But in the case of high speed and light load, its influence is not very prominent.

The above analysis shows that in the EC type design of general cylindrical roller bearings, the rib inclination a can be selected between 12' and 20 according to different situations. The position of the contact point is set at 1/2 of the rib height, as shown in Figure 3.

The spherical radius R of the roller end surface can be calculated by the formula