Oil lubrication technology
The motor will malfunction during use, especially the bearing part. Most bearing malfunctions are caused by insufficient lubrication.
Angular contact ball bearings require some form of lubrication to function properly. The function of lubrication is to provide a microscopic film between the rolling elements to prevent wear and slippage. In addition, the lubricant protects the surface from corrosion and the area from particulate contamination.
The most common type of lubricant is grease. Grease provides the simplest method of lubrication. However, grease lubrication does have limitations. For continuous operation, grease-filled spindles generally do not exceed 850,000. As speeds increase, operating temperatures rise, and grease begins to break down. Most greases are rated for temperatures below 300 degrees Fahrenheit. Types of grease that can withstand high speeds are usually ester oil based and barium complex thickeners. An example is the Kluber Isoflex NBU-15. Regarding the amount of grease, more is not better. Excessive amounts of grease can lead to agitation and heating, which can lead to the deterioration of the grease. Between races, about 20 to 30% of the open area should be filled. After the grease has been filled, a careful break-in period is required to distribute the grease adequately in the bearing.
In general, greased high-speed shafts should not be allowed to change grease between bearing changes. When replacing bearings, the bearings are carefully filled with clean grease. Positive air overpressure is often used to prevent contamination from entering the bearing, which can lead to rapid bearing failure.
In many cases, especially when high speeds are required, grease bearings are not sufficiently lubricated. The oil is then used as a lubricant and transported in various ways. As mentioned earlier, grease can support bearing speeds up to 850,000. Oil lubrication can support speeds up to 1,500,000 dN.
A common method of oil lubrication is oil mist. An oil reservoir is used, and compressed air is mixed with the oil. This produces oil droplets that are carried by the air stream to the bearing area. The main advantages of oil mist are a good supply of lubricant, simplicity, and the fact that, in addition to lubricating the bearings, the oil mist also cleans and cools the bearings. The system is best suited to spindles with high speeds and relatively light loads. Oil mist is somewhat difficult to measure and control, so if the amount of oil delivered to the bearing must be fairly accurate, then oil mist may not be the best system to use.
Another common method of oil lubrication is oil injection. An oil jet uses a high pressure pump to deliver oil directly to the bearing rings. This system is suitable for spinners that must withstand high loads, high speeds, and high temperatures. Care must be taken to ensure that the oil passes quickly through the bearing, otherwise, the oil will spin. The system requires a complex pump, tank, and temperature control system, however, it is sometimes necessary to support very high performance spindles. Another system, pulse oil-air, injects a small amount of compressed air into the bearing cavity. The frequency of injection may be related to the operation of the spindle or simply timed.
Conclusion
Bearing lubrication is a critical component of the overall high-speed spindle system. Depending on the size, type, and speed of the bearings, the bearing lubrication may be a permanent grease package or some type of oil system. Maintenance of the lubrication system is critical and must be closely monitored to ensure proper bearing conditions are maintained. Oil mist, oil jet, and pulsed oil-air systems require the provision of clean, dry, and continuous air. In addition, using the correct type, quantity and cleanliness of lubricant is essential.
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