When the speed or operating temperature of the bearing is too high to be suitable for grease; when excessive heat needs to be removed from the bearing; when the connecting parts (such as gears) are oil lubricated, lubricating oil can be used to lubricate the bearing. Common lubrication methods are as follows.

1. Oil bath lubrication. The simplest oil lubrication method is oil bath lubrication. As shown in Figure 1. The rotating parts in the bearing carry the oil to other parts of the bearing, and then flow back to the oil pool of the bearing seat. When the bearing is stationary, the oil level should be slightly lower than the center of the lowest rolling element of the bearing. In order to effectively control the correct oil level, it is recommended to use an oil level keeper or similar device.

2. Oil slinger. In bearing applications where the speed and operating temperature require reliable oil supply, it is recommended to use an oil slinger lubrication method. As shown in Figure 2. The oil slinger is suspended on the sleeve on one side of the bearing and immersed in the oil pool at the bottom of the bearing seat. As the shaft rotates, the oil slinger will send oil from the oil pool to an oil sump. The oil will flow through the bearing and return to the oil pool. The bearing seat is designed according to the lubrication method of the oil slinger.

3. Circulating oil lubrication. High speed operation will cause the temperature of the bearing to rise and accelerate the aging of the lubricant. In order to avoid frequent replacement of lubricants and reach overflow lubrication conditions, circulating oil lubrication can be used. As shown in Figure 3. The circulation of oil is usually controlled by a pump. After the lubricant passes through the bearing, it is generally returned to the oil tank and filtered, or if necessary, cooled before flowing back to the bearing. Effective filtration reduces the degree of contamination and extends the service life of the bearing. Cooling the lubricant can keep the operating temperature of the bearing at a low level.

4. Oil spray lubrication. In applications with very high speeds, the bearing must have enough but not excessive lubricant to ensure that the bearing can be fully lubricated without causing excessive operating temperatures. In this case, using oil spray lubrication is a particularly effective method. As shown in Figure 4. The lubricant is sprayed into the bearing from one side at high pressure. The oil spray must have a fairly high speed (≥15m/s) to pass through the turbulence caused around the bearing under high-speed rotation.

5. Oil-air lubrication. Also known as oil spot lubrication, it uses compressed air to spray a very small amount of precisely metered lubricant directly onto each bearing. This method lubricates the bearings with the least amount of oil, achieving higher speeds and lower operating temperatures than any other lubrication method. Compressed air is used to cool the bearings and to create additional pressure in the bearing seat to prevent contaminants from entering. See Figure 5.

To extend the service life of the bearing, no matter which oil lubrication method is used, the cleanliness of the lubricant must be ensured. When using circulating oil lubrication and oil-air lubrication, there must be an oil supply pipe of appropriate size so that the lubricant after passing through the bearing can flow out of the bearing configuration.