If the lubricating film provided by the trace grease separates the bearing contact surface, the bearing can continue to operate with stable low friction torque and low friction heat over its entire operating speed range, since it does not cause liquid due to agitation of excess lubricant. Friction heating, or causing thermal expansion of the bearing components to generate additional stress, so proper disposal, trace grease lubrication can be used for lubrication of high speed or even ultra high speed bearings.
In addition, the micro-fat lubrication does not require metering and monitoring devices or precision oil supply pipes and other accessories, and does not produce oil mist, which makes it superior to oil mist lubrication and fuel injection lubrication, which is inexpensive and easy to maintain, especially it The lubrication system has almost no space and weight, which is undoubtedly very attractive to aviation machinery.
Compared with trace oil lubrication, trace grease lubrication has low evaporation speed, less leakage, higher load carrying capacity, better damping effect, low and stable working temperature, stable friction torque, and can seal and prevent liquid. And solid dirt enters the bearing and there are fewer failures, so the machine tool spindle, which is lubricated with a small amount of grease, can operate for more than five years without maintenance, even for up to ten years. Moreover, since the amount of heat generation is small, it is easy to maintain the accuracy of the spindle system.
A soap-based grease with a low-viscosity oil as a base oil, which is commonly used for the implementation of a small amount of grease lubrication. The grease has a network structure formed by interweaving fine fibers, and functions as an oil storage tank. The sintered metal bearing is very similar. The lubricating oil is supplied to the bearing by capillary action. After the thickness of the formed lubricating film reaches a stable value, it no longer increases with the increase of the rotational speed, so the friction torque is stable.
In order to ensure the successful implementation of trace grease lubrication under high speed conditions, it is necessary to control the three steps of cleaning, filling grease and running.
Before applying lubrication, the working surfaces of the components of the bearing must be cleaned and completely dried. Any remaining original lubricating oil, grease or rust inhibitor must be completely removed with volatile solvents.
The filling amount of grease is determined according to the bearing structure, working speed, oil storage space and the effect of sealing and dustproof. It is necessary to ensure that the contact surface has sufficient oil film thickness to prevent direct contact between metal and metal and provide sufficient Liquid lubrication. The grease itself must also be extremely pure.
Running-in is the most important part of the three links. It must start from the low-speed running. When the temperature reaches a steady state, the speed will be gradually increased, and the running will stop when the temperature rises rapidly.
After the system is cooled to room temperature, the running is resumed at the running speed before stopping, so that the running is repeated until the spindle reaches the heat balance temperature of 35 to 40 °C under the condition of operating at the working speed.
If the temperature monitor is not available, the running speed should be controlled below the maximum working speed. The speed increment is 10r/min for each running. Each speed is continuously running for 15min, then it is cooled to room temperature, and so on.
If the bearing speed cannot be changed, the spindle can be operated at the working speed for 15 minutes, then stopped to cool to room temperature, and then run repeatedly until the above heat balance temperature is reached.
After the running is successful, the temperature rise of the bearing system will be lower than 10 °C under the condition of the maximum working speed of the spindle. In order to control the temperature rise in such a small range, it is necessary to use a retaining ring for self-regulating bearing clearance, or to appropriately select the shape and size of the rolling element so that it does not have additional stress in contact with the raceway after being thermally expanded.
During the running-in period, excess grease is forcibly discharged into the cavity of the bearing housing. Only a small amount of grease required for minor lubrication is left in the contact area of the bearing. Other contact surfaces, such as ribs, pockets, etc. The lubricating oil film has also been appropriately adjusted by running.