Repair Methods for Static Pressure Import Bearings in Grinding Machines

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Static pressure import bearings are known for their high precision, excellent rigidity, high load capacity, and long service life. Here are some practical experiences gathered during the repair and testing of such bearings. These insights may help you better understand the process. 1. **Hole Saver** - **External vs. Internal Savings**: Replacing internal savings with external ones allows for real-time monitoring of upper and lower chamber pressures via added pressure gauges. This makes maintenance easier, especially when clearing blockages, which is not possible with internal savers. - **Savings Ratio (β)**: The theoretical value of β ranges between 1.2 and 1.5. Based on years of experience, a ratio of 1.25 is often ideal. During repairs, the spindle's precision and the alignment of front and rear bearing pads must be strictly controlled to ensure proper β values. The e-value (misalignment between the main shaft and bearing bush) can be determined based on the machine tool’s load, ensuring optimal performance. - **Oil Chamber Adjustment**: If the oil column isn’t evenly distributed across all outlets, adjust the saver’s aperture to balance the flow. For example, in a four-chamber system, the oil column in the left and right chambers should typically be between 20–25 mm, with small holes ranging from 0.25 to 0.4 mm in diameter. 2. **Thin Film Reaction Saver** - Thin film reaction bearings have high stiffness, but they can sometimes cause issues like tiling, pulling, or sudden pressure drops during operation. The key factor is the thin film itself. Common causes of bearing lock-up or pulling include: - Plastic deformation of the film under heavy loads, - Slow reaction time when the load changes suddenly, causing conflict between the shaft and the bearing, - Fatigue from prolonged use, leading to deformation and altered reaction parameters. - To improve this, increasing the film thickness and using more fatigue-resistant materials can yield great results. Typically, a rigid film of 4mm thickness is used instead of 1.4mm, along with a 0.05mm thick tin foil paper in the cavity pad. The spindle is adjusted to be 0.05mm higher than the reference point, forcing the grinding wheel component to return to its central position under load. 3. **Improvement of the Oil Supply System** - In addition to coarse and fine filtration, the oil supply system plays a crucial role in protecting hydrostatic bearings. Improving the original system can enhance performance. - **Pressure Monitoring**: After the saving plate, connect the oil outlet to a pressure relay and gauge (previously placed before the accumulator). This allows operators to monitor both chamber and inlet pressures. If the pressure difference exceeds a certain threshold, it can prevent the axis from locking. For instance, if the inlet pressure is 2 MPa, the outlet should stay between 1.2–1.6 MPa; below 1.2 MPa would trigger an alarm. - **Digital Detection Device**: A gap of 0.04–0.05mm exists between the main shaft and the bearing bush. The oil resistance changes as the gap varies. By measuring the resistance between the bearing and the shaft, we can detect the gap size. This signal can then be sent to a photoelectric alarm and control system, allowing the spindle motor to start or stop automatically, preventing any potential damage caused by misalignment.

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