Some Exploration and Testing of Hydrostatic Bearings in Grinding Machine Repairs

Source: China Bearing Network | Time: 2014-04-06

Hydrostatic bearings are widely used in various grinding machines, such as M210, M131W, 3160A, as well as in diamond boring heads like 2A710 and FYT10. These bearings offer high precision, excellent rigidity, strong load capacity, and long service life with no wear. With the development of CNC technology, hydrostatic bearings have also become a key component in the spindles of CNC machine tools. Many static pressure grinders and diamond boring heads are in use within the company, and during their repair, several tests and explorations were conducted, leading to valuable experiences. 1. **Hole Saver** - **External Saver Modification**: Instead of internal savers, external ones were installed with pressure gauges that display the pressure in the upper and lower oil chambers in real-time. This makes maintenance easier and allows for regular cleaning, which is not possible with internal savers. - **Savings Ratio (Î²)**: The theoretical savings ratio Î² should be between 1.2 and 1.5, with 1.25 being ideal based on experience. During repairs, the spindle, front and rear bearing pads must be precisely machined, with strict control over concentricity, roundness, and taper to ensure an optimal Î² value. The e value (the misalignment between the main shaft and the bearing bush) can be determined based on the machine's load, allowing for the best Î² performance. - **Oil Chamber Adjustment**: If the main shaft is not installed, the oil columns from each oil outlet must be common (observed visually). If not, the aperture of the saver should be adjusted to modify the flow rate. For example, in a four-chamber system, the oil column height for the lower, left, and right chambers usually ranges from 20 to 25 mm, with small holes ranging from 0.25 to 0.4 mm in diameter. 2. **Film Reaction Issues** Hydrostatic bearings have high stiffness, but during operation, some machine tools may exhibit issues like tilting, pulling, or sudden pressure drops. The main cause is the film reaction. In practice, the bearing becomes locked and wrinkled due to: - Plastic deformation of the film under load. - Slow response when the external load changes suddenly, causing the axis and tile to collide. - Fatigue deformation after prolonged use, altering the reaction parameters. To address this, increasing the film thickness and using fatigue-resistant materials can significantly improve performance. Typically, a rigid film of 4mm thickness is used, along with a 0.05mm thick tin foil paper on the cavity pad. The spindle is adjusted to be 0.05mm higher than the reference position, forcing the spindle (grinding wheel assembly, cutting force) to return to the center. 3. **Improvement of Oil Supply System** Enhancing the oil supply system of the hydrostatic bearing goes beyond basic filtration. Other components also play a crucial role in ensuring the stability of the hydrostatic bearing. - **Pressure Monitoring**: A pressure relay and gauge are added after the saver plate, allowing operators to monitor chamber and inlet pressures. If the pressure difference exceeds a set threshold, the system stops immediately to prevent the spindle from locking. For instance, if the inlet pressure is 2 MPa, the outlet should be between 1.2 and 1.6 MPa; below 1.2 MPa, the system should shut down. - **Digital Measurement Device**: A gap of 0.04â€“0.05 mm exists between the main shaft and the bearing bush, with oil providing resistance. By measuring the resistance change, the gap size can be determined. One pole is the main shaft, the other is the bearing bush, and the resistance signal is sent to a photoelectric alarm and control amplifier, enabling the spindle motor to start/stop automatically and avoid tile conflicts.
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