INA bearing surface grinding causes defects

During the grinding process, the INA bearing is ground by a high-speed rotating grinding wheel. Therefore, if the machine is not operated and adjusted according to the operation instructions during grinding, various defects will occur on the working surface of the INA bearing. As a result, the overall quality of the INA bearing is affected. In the precision grinding of INA bearings, due to the high roughness requirements, the grinding marks on the working surface can be observed by the naked eye.

Performance showing cross spiral traces

The reason for this kind of trace is mainly due to the poor straightness of the busbar of the grinding wheel and the unevenness. When grinding, the grinding wheel and the workpiece are only partially in contact. When the workpiece or the grinding wheel reciprocates several times, the performance of the workpiece will reappear. The spiral is visible to the naked eye. The pitch of these spirals is related to the workpiece table speed and the workpiece rotation speed, and is also related to the grinding wheel axis and the table rail.

(1) The main reason for the formation of spirals

1. The grinding wheel is poorly trimmed, the corners are not chamfered, and the coolant is not used for trimming;

2. The guide rail guides too much lubricating oil, causing the workbench to float;

3. The machine tool accuracy is not good;

4. Grinding pressure is too large.

(2) The cause of the formation of the spiral

1. The V-shaped guide rail is not rigid, and the grinding wheel is offset when grinding, but the edge of the grinding wheel is in contact with the working surface;

2. When the quarrel is repaired, the commutation speed of the worktable is unstable, and the precision is not high, so that the edge of the grinding wheel is slightly trimmed;

3. The workpiece itself is poorly rigid;

4. There are crushed and spalled sand on the grinding wheel and iron scraps from the workpiece grinding on the surface of the grinding wheel. For this purpose, the finished grinding wheel should be rinsed or brushed with cooling water;

5. The grinding wheel is not well trimmed, and there are partial bulges.

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Some experience in grinding hydrostatic KOYO bearing repair

Static pressure KOYO bearings are widely used in M210, M131W, 3160A grinding machines and 2A710, FYT10 diamond boring heads due to their high rotation accuracy, good rigidity, high bearing capacity, no wear and high durability. With the development of numerical control technology, static pressure KOYO bearings are also widely used in the spindles of CNC machines such as machining centers. The first engine plant of Yituo Co., Ltd. has many static pressure grinders and static pressure diamond hoes. Some explorations and attempts have been made in the maintenance and some experience has been gained.

Small orifice restrictor

(1) Change the internal throttling to external throttling, and add a pressure gauge to instantly display the upper and lower chamber pressures. It is easy to maintain, especially it can be cleaned regularly, which is unmatched by the internal throttle.

(2) Throttling ratio. The theoretical value of the throttle ratio β is between 1.2 and 1.5, and based on years of experience, 1.25 is preferred. In this way, the geometric accuracy of the main shaft, the geometrical accuracy of the front and rear bearing pads, the concentricity, the roundness and the taper need to be strictly controlled in order to ensure the β value. The e value (the eccentricity of the main axis and the geometric center of the bearing bush) is determined according to the load carrying capacity of the machine tool to optimize the β value.

(3) When the oil chamber is not equipped with the main shaft, the oil column of each oil outlet must be consistent (observation method). If it is inconsistent, the flow rate should be changed by changing the orifice diameter of the throttle. Taking the four chambers as an example, the oil column of the lower, left and right chambers is generally between 20 and 25 mm, and the diameter of the small holes is 0.25 to 0.4 mm.

2. Thin film feedback throttle

The film feedback throttle KOYO bearing stiffness is very large, but the machine tool often appears in the operation of holding the tile, pulling, falling pressure and so on. The most critical of the film feedback is the film. In practice, the main reasons for the bearing lock and pulling are: 1 plastic deformation of the film; 2 slow feedback. When the external load is abrupt, the shaft and the tile have already rubbed when the film has not reacted; 3 the film is fatigued. The film is used for a long time and fatigue deformation, which is equivalent to changing the feedback parameters.

Increased film thickness and the use of some fatigue-resistant materials can achieve good results. Generally, a rigid film, a preload, and a gap are reserved. The specific method is: change the 1.4mm thick film to a 4mm thick rigid film, and place a 0.05mm thick tin foil in the lower cavity to adjust the spindle to a position 0.05mm higher than the ideal position. The purpose is to return to the ideal center just after the spindle is stressed (grinding weight, cutting force).

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