A brief description of common maintenance precautions for grinding machine static pressure bearings
Grinder static pressure bearings are widely used on grinders due to their high slewing accuracy, good rigidity, high bearing capacity, no wear, and high durability. At the same time, with the rapid development of numerical control technology, static pressure bearings are also widely used on the spindles of CNC machine tools such as machining centers. The common maintenance precautions for the hydrostatic bearing of the grinder are as follows:
I. Improvement of fuel supply system
In the grinder static pressure bearing oil supply system, in addition to the coarse filter and fine filter, the other components have a protective effect on the grinder static pressure bearing. Improve the oil supply system based on the original system.
1. Connect the pressure relay and pressure gauge (originally in front of the accumulator) at the oil outlet behind the throttle plate, so that the operator can see the size of the cavity pressure and the inlet pressure. When the pressure difference is greater than a certain value, it is necessary to stop immediately to prevent the bearing pads from locking up. For example: the inlet pressure is 2MPa, the outlet pressure is 1.2 ～ 1.6MPa, and it will stop when the pressure is lower than 1.2MPa.
2.Add digital detection device
There is a gap of 0.04 ～ 0.05mm between the main shaft of the hydrostatic bearing of the grinding machine and the bearing pad. The oil in the gap has a certain resistance value. After detecting the change of this resistance value, we can know the size of the gap. With the main axis as one pole and the bearing pad as the other pole, measure the change in resistance. After processing this signal, it is sent to the photoelectric alarm and control system amplifier to control the start and stop of the spindle motor to avoid friction between the shaft and the tile.
Second, the small hole throttle
1. Change the internal throttling to external throttling, and install a pressure gauge to display the pressure in the upper and lower chambers in real time. Make maintenance convenient, especially it can be easily 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 according to many years of experience, 1.25 is preferred. In this way, in the maintenance, the geometric accuracy of the main shaft, the geometric accuracy of the front and rear bearing pads, coaxiality, roundness and taper need to be strictly controlled in order to ensure the β value. Determine the e value (the eccentricity between the spindle and the geometric center of the bearing pad) 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 columns of the oil outlets must be consistent (observation method). If they are not consistent, the method of changing the orifice diameter of the throttle should be adopted to change its flow rate. Take 4 cavities as an example. Generally, the oil column in the lower, left and right cavities is between 20-25mm, and the diameter of the small holes is 0.25-0.4mm.
Third, the film feedback throttle
The rigidity of the hydrostatic bearing of the grinder using the thin film feedback restrictor is very large, but the machine also often encounters the phenomenon of embracing, pulling, and pressure drop during operation. The most critical thing for film feedback is the film. In practice, the main reasons for the grinding and pilling of the hydrostatic bearing bushes are:
1) Caused by plastic deformation of the film;
2) Feedback is slow. When the external load is abrupt, when the film has not responded, the shaft and the pad have been rubbed;
3) Film fatigue. The film has a long service life and fatigue deformation, which is equivalent to changing the feedback parameters;
Increasing the thickness of the film and switching to some fatigue-resistant materials can achieve good results. Generally, a rigid film, pre-loading, and gap clearance are used. The specific method is: change the 1.4mm thick film to 4mm thick rigid film, and place 0.05mm thick tin foil in the lower cavity, and adjust the main shaft to a position 0.05mm higher than the ideal position. The purpose is to return to the ideal center when the spindle is stressed (grinding wheel weight, cutting force).