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Improving methods in the maintenance of hydrostatic imported bearings

by:JNSN     2021-10-23

The imported hydrostatic bearing has high rotation accuracy, good rigidity, high bearing capacity, no wear and high durability. The following are some experiences gained from exploring and trying the static pressure imported bearings in the repair process, for your reference only.

1. Orifice restrictor:

(1). Change the internal throttling to the external throttling, and install a pressure gauge to display the pressure of the upper and lower chambers immediately . Makes maintenance convenient, especially it can be easily cleaned regularly, which is unmatched by the internal throttle.

(2). Throttle ratio. The theoretical value of the throttling ratio β is between 1.2 and 1.5, and 1.25 is better based on years of experience. In this way, in maintenance, it is necessary to strictly control the geometric accuracy of the spindle, the geometric accuracy of the front and rear bearings, the coaxiality, the roundness and the taper in order to ensure the β value. Determine the e value (the amount of eccentricity between the spindle and the geometric center of the bearing bush) according to the load-bearing capacity of the machine tool to make the β value the best.

(3). When each oil cavity is not equipped with a spindle, the oil column of each oil outlet must be the same (observation method), if not, the method of changing the aperture of the throttle should be adopted to change the 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 hole is 0.25-0.4mm.

2. Membrane feedback throttle:

The stiffness of the membrane feedback throttling bearing is very large, but the machine tool often has phenomena such as shingling, fraying, and pressure drop during operation. . The most critical part of the film feedback is the film. In practice, it is believed that the main reasons for the blocking and roughening of the bearing bush are: ① caused by the plastic deformation of the film; ② slow feedback. When the external load changes suddenly and the film has not reacted, the shaft and the bush have rubbed; ③The film is fatigued. The film has a long use time 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-preserving method are used. The specific method is: change the 1.4mm thick film to a 4mm thick rigid film, and pad 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 exactly when the spindle is stressed (grinding wheel weight, cutting force).

3. Improvement of the oil supply system:

In the hydrostatic imported bearing oil supply system, in addition to coarse filtration and fine filtration, the remaining components have a protective effect on the hydrostatic bearing. Improve the oil supply system on the basis of the original system.

(1). Connect a pressure relay and a 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, stop the machine immediately to prevent the bearing from locking up. For example, the inlet pressure is 2mpa, and the outlet pressure is 1.2~1.6mpa. If it is lower than 1.2mpa, it will stop.

(2). Add a digital detection device: there is a 0.04-0.05mm gap between the main shaft and the bearing bush of the wear-resistant electrode static pressure imported bearing, and the oil in between has a certain resistance value. The change in resistance value can tell the size of the gap. Take the main shaft as one pole and the bearing bush as the other pole, and measure the resistance change. This signal is processed and sent to the photoelectric alarm and the control system amplifier to control the start and stop of the spindle motor to avoid friction between the shaft and the bush.

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