Static pressure NTN bearings have high rotation precision, good rigidity, high bearing capacity, no wear and high durability. The following are some of the experiences of static pressure NTN bearings in the process of repair and try to obtain, for your reference only.
1. Small hole throttle:
(1). Change the internal throttling to external throttling, and add a pressure gauge to instantly display the upper and lower chamber pressure. 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 1.25 is preferred based on years of experience. 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 4 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 NTN bearing stiffness is very large, but the machine tool often appears in the operation of the tiling, 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).
3. Improvement of the oil supply system:
In the static pressure NTN bearing oil supply system, except for the coarse filter and the fine filter, the other components have a protective effect on the static pressure NTN bearing. The oil supply system is improved on the basis of 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 pressure and pressure of the chamber. When the pressure difference is greater than a certain value, in order to stop immediately, so as to avoid the axle lock. Such as: pressure 2MPa, oral pressure 1.2 ~ 1.6MPa, less than 1.2MPa will stop.
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