Hydrostatic bearings are widely used in M210, M131W, 3160A grinders and 2A710, FYT10 diamond boring heads for their high turning accuracy, good rigidity, high bearing capacity, no wear, and high durability. With the development of numerical control technology, hydrostatic bearings are also widely used in machining centers and other CNC machine tool spindles. One of the first engine plants of the Tosoh Corporation had a number of static pressure grinders and static pressure diamond boring heads. Some explorations and trials were carried out during maintenance and some experience was gained.
1. The orifice restrictor (1) changes the internal throttling to external throttling, and a pressure gauge is added to instantly show the pressure in the upper and lower chambers. To facilitate maintenance, in particular, it can be easily cleaned on a regular basis, which is unmatched by internal throttles. (2) Throttling ratio. The theoretical value of the throttling ratio β is between 1.2 and 1.5, and 1.25 is preferred based on years of experience. In this way, it is necessary to strictly control the geometric accuracy of the spindle, the geometric accuracy of the front and rear axles, the coaxiality, the roundness and the taper in order to ensure the β value. Determine the value of e (the amount of eccentricity between the spindle and the geometric center of the bearing shell) based on the load capacity of the machine tool to optimize the beta value. (3) When the oil chamber is not equipped with a main shaft, the oil column of each oil outlet must be the same (observation method). If not, change the orifice of the restrictor and change the flow rate. Taking 4 chambers as an example, generally, the oil column of the lower, left, and right chambers is between 20-25 mm, and the diameter of the small holes is 0.25-0.4 mm.
2. The film feedback throttle device diaphragm feedback throttling bearing stiffness is very large, but the machine often appears in the operation of holding tile, pulling hair, pressure drop and so on. The film feedback is the most critical film. In practice, it is believed that the main reasons for the locking and pulling of the bearing are: 1) plastic deformation of the film; 2) slow feedback. When the load changes abruptly, the shaft and the tile have already rubbed when the film has not reacted; 3 the film fatigues. The thin film used for a long time, fatigue deformation, equivalent to changing the feedback parameters. Increasing the thickness of the film and using some materials that are resistant to fatigue can achieve good results. Generally, rigid membranes, preloads, and gaps are used. The specific method is: change the 1.4mm thick film to a 4mm thick rigid film, and padded 0.05mm thick tin foil in the lower chamber to adjust the spindle to a position 0.05mm higher than the ideal position. The purpose is to return exactly to the ideal center when the spindle is stressed (grinding wheel weight, cutting force).
3. Improvement of the oil supply system In the hydrostatic bearing oil supply system, except for coarse filtration and fine filtration, the remaining components have a protective effect on hydrostatic bearings. The oil supply system was improved on the basis of the original system. (1) Connect the pressure relay and pressure gauge (originally in front of the accumulator) to the outlet port behind the throttle plate so that the operator can see the cavity pressure and inlet pressure. When the pressure difference is greater than a certain value, in order to immediately stop, so as not to lock the shaft. Such as: import pressure 2MPa, out of the mouth pressure 1.2 ~ 1.6MPa, less than 1.2MPa shutdown. (2) Increase the gap between the spindle of the hydrostatic bearing and the bearing shell of the digital detection device. There is a certain resistance value in the oil between them. The change of the resistance value can be detected and the gap can be known. . Take the spindle as a pole and the bearing pad as the other pole, measure the resistance change. This signal is processed and sent to the photoelectric alarm and control system amplifier to control the start and stop of the spindle motor, so as to avoid the friction between the shaft and the tile.
1. The orifice restrictor (1) changes the internal throttling to external throttling, and a pressure gauge is added to instantly show the pressure in the upper and lower chambers. To facilitate maintenance, in particular, it can be easily cleaned on a regular basis, which is unmatched by internal throttles. (2) Throttling ratio. The theoretical value of the throttling ratio β is between 1.2 and 1.5, and 1.25 is preferred based on years of experience. In this way, it is necessary to strictly control the geometric accuracy of the spindle, the geometric accuracy of the front and rear axles, the coaxiality, the roundness and the taper in order to ensure the β value. Determine the value of e (the amount of eccentricity between the spindle and the geometric center of the bearing shell) based on the load capacity of the machine tool to optimize the beta value. (3) When the oil chamber is not equipped with a main shaft, the oil column of each oil outlet must be the same (observation method). If not, change the orifice of the restrictor and change the flow rate. Taking 4 chambers as an example, generally, the oil column of the lower, left, and right chambers is between 20-25 mm, and the diameter of the small holes is 0.25-0.4 mm.
2. The film feedback throttle device diaphragm feedback throttling bearing stiffness is very large, but the machine often appears in the operation of holding tile, pulling hair, pressure drop and so on. The film feedback is the most critical film. In practice, it is believed that the main reasons for the locking and pulling of the bearing are: 1) plastic deformation of the film; 2) slow feedback. When the load changes abruptly, the shaft and the tile have already rubbed when the film has not reacted; 3 the film fatigues. The thin film used for a long time, fatigue deformation, equivalent to changing the feedback parameters. Increasing the thickness of the film and using some materials that are resistant to fatigue can achieve good results. Generally, rigid membranes, preloads, and gaps are used. The specific method is: change the 1.4mm thick film to a 4mm thick rigid film, and padded 0.05mm thick tin foil in the lower chamber to adjust the spindle to a position 0.05mm higher than the ideal position. The purpose is to return exactly to the ideal center when the spindle is stressed (grinding wheel weight, cutting force).
3. Improvement of the oil supply system In the hydrostatic bearing oil supply system, except for coarse filtration and fine filtration, the remaining components have a protective effect on hydrostatic bearings. The oil supply system was improved on the basis of the original system. (1) Connect the pressure relay and pressure gauge (originally in front of the accumulator) to the outlet port behind the throttle plate so that the operator can see the cavity pressure and inlet pressure. When the pressure difference is greater than a certain value, in order to immediately stop, so as not to lock the shaft. Such as: import pressure 2MPa, out of the mouth pressure 1.2 ~ 1.6MPa, less than 1.2MPa shutdown. (2) Increase the gap between the spindle of the hydrostatic bearing and the bearing shell of the digital detection device. There is a certain resistance value in the oil between them. The change of the resistance value can be detected and the gap can be known. . Take the spindle as a pole and the bearing pad as the other pole, measure the resistance change. This signal is processed and sent to the photoelectric alarm and control system amplifier to control the start and stop of the spindle motor, so as to avoid the friction between the shaft and the tile.
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