What Should You Do When the Bearing Temperature of a CNC Lathe Is Too High?

The temperature of the CNC lathe guide bearing is too high, which causes the bearing to burn out. This is a common fault problem. Next, let's talk about how to deal with the problem of high temperature of the CNC lathe bearing.

1. The function of the guide bearing

The purpose of setting the guide bearing of the CNC lathe is to limit the generator main shaft to run only within the specified clearance range of the guide bearing and bear the radial load on the generator main shaft.

2. The working principle of the guide bearing

The working principle of the thin oil lubricated block bearing is mainly to use the high-speed rotation of the unit, the lubricating oil enters the joint surface of the bearing and the journal to lubricate the bearing. The hot oil after lubrication is cooled by the oil cooler and enters the joint surface of the bearing and the journal again. As the unit runs, the lubricating oil is automatically reciprocated and cooled. When the main shaft rotates, a stable oil wedge is formed between the journal and the journal surface, thereby bearing the radial load and transmitting it to the guide bearing seat, and then to the frame.

3. Composition of guide bearings

The guide bearings of CNC lathes are thin oil lubricated block bearings, which are mainly composed of bearing caps, lubricating oil tanks, coolers, return oil pipes, bearing shells, bearing seats, weight screws and thermometers. The guide bearing shells of the two units at Station B are divided into eight shells, which are evenly distributed on the guide shaft necks of the generator main shaft according to the circumference.

4. Analysis of the causes of increased bearing temperature and increased unit vibration

Based on the observation of operation and analysis of maintenance conditions, we believe that there are two main reasons for the increase in bearing temperature and increased unit vibration:

① The bearing clearance increases, which is much larger than the design clearance, causing the lubricating oil to enter the water guide bearing surface. It is not easy to form an oil wedge, resulting in poor lubrication and thus leading to increased guide bearing temperature and increased unit vibration;

② There are too few contact points on the bearing surface, and the contact surface is insufficient, which does not meet the equipment specification requirements.

5. Solution to the increase in guide bearing temperature

According to the manufacturer's design requirements, when the cooling water temperature of the CNC lathe unit does not exceed 25°C under continuous operation, the temperature of the shell and the oil temperature should not exceed 65°C. The temperature of the bearing and the oil are not only related to the temperature of the cooling water, but also to the circulation of the lubricating oil and the clearance between the bearing and the spindle journal.

The allowable clearance of the guide bearing of the CNC lathe is 0.2~0.3mm (double-sided clearance). The lower part of the bearing is immersed in the lubricating oil. When the spindle rotates clockwise, the lubricating oil can easily enter the guide bearing bearing surface and produce an oil wedge to lubricate the bearing surface. Even when the spindle swings, although the clearance between the fits is very small, due to the short distance, good lubrication condition, less heat generated by friction, and good cooling effect, it generally does not cause the bearing temperature to rise, let alone the burning of the bearing.