Bearing lubrication has several purposes, including ensuring normal operation of the bearing, preventing direct contact between the raceway and the rolling element, reducing friction and wear inside the bearing, prolonging its service life and improving its performance.
Additionally, it helps prevent rust and corrosion caused by foreign objects entering the bearing.
In this article, we will introduce 11 commonly used lubrication methods for bearings. We hope this information is helpful in your design process.
1. Manual lubrication
The lubrication method is the most basic approach to bearing lubrication. When there is insufficient lubricant in the bearing, a lubricator can be used to supply oil. However, this method can be challenging to maintain a consistent oil level, and the risk of neglecting topping up is greater. This method is typically used in light load, low speed or intermittent operations.
To optimize operation, it is best to install a dust cap or ball valve on the lubrication hole and use a filtering device such as felt, cotton or wool.
2. Drip point lubrication
The drip method is typically used for light to medium load bearings with a peripheral speed of less than 4 to 5 meters per second. An approximately constant amount of lubricating oil is supplied from a container through holes, needles, valves, etc.
The most classic example is the dripping oil cup. The amount of oil dripping can vary greatly depending on the viscosity of the lubricant, bearing clearance and the position of the oil supply hole.
3. Oil ring lubrication
The oil ring method involves a ring that hangs on the shaft and rotates, bringing oil from a pool of oil into the bearing. This method is only suitable for lubricating horizontal shafts.
It is suitable for medium to high speed bearings with shaft diameters greater than 50 mm and works best with a seamless oil ring. When the bearing aspect ratio is less than 2, only one oil ring is required, otherwise two oil rings are required.
4. Lubrication of the cable with oil
The oil cable method relies on the capillary and siphon action of the oil cable to introduce lubricating oil from the oil cup into the bearing. This method is mainly used for light to medium load bearings with a peripheral speed of less than 4 to 5 meters per second. The oil cable also plays a filtering function throughout the process.
5. Oil pad lubrication
The oil pad method uses the capillary action of the oil pad to distribute the lubricating oil from the oil pool to the surface of the shaft diameter. This method can keep the friction surface clean, but dust can also clog the pores, resulting in insufficient oil supply. The amount of oil supplied by the oil lubrication method is normally only 1/20 of the amount supplied by oil lubrication.
6. Oil bath lubrication
The immersion method involves submerging a part of the bearing in lubricating oil. This method is often used for vertical shaft thrust bearings, but is not suitable for horizontal shaft radial bearings.
7. Splash lubrication
The splash lubrication method involves supplying lubricating oil to the bearing through the movement of rotating parts in the oil tank. This method is suitable for high-speed bearings.
8. Spray lubrication
The atomization method involves spraying the lubricant in a fine mist onto the friction surface. This method is suitable for high-speed bearings.
9. Oil lubrication under pressure
The pressure lubrication method involves supplying oil to the bearing through pressure from a lubrication pump. The lubricating oil flowing from the bearing is then collected and returned to the oil reservoir for recycling. This method is the most stable and efficient oil supply method and is suitable for critical, high-speed and heavy-load sliding bearings.
10. Lubrication with circulating oil
The circulation lubrication method involves supplying filtered oil to bearing parts via an oil pump. The lubricating oil after passing through the bearing is filtered and cooled before being reused. Because circulating oil can remove some of the heat and cool the bearing, this method is suitable for high-speed bearing components.
11. Jet lubrication
The high pressure injection method involves using an oil pump to inject high pressure oil into the bearing through a nozzle. The oil then flows into the oil groove through the other end of the bearing. This method is necessary when the bearing rotates at high speed and the surrounding air forms an airflow, making it difficult for general lubrication methods to reach the bearing.
The lubricant must be sprayed onto the bearing using high pressure. The nozzle must be positioned between the inner ring and the center of the cage.
Lubrication method selection principles
After evaluating the advantages and disadvantages of various lubrication methods, the appropriate method can be selected based on actual operating conditions. The main selection principles can be summarized as follows:
- If the bearing operating speed and temperature rise rate are reasonable, grease lubrication should be considered first.
- Of all lubricating oil methods, drip lubrication has the highest comprehensive index in terms of technology and economy, so careful consideration should be given to the selection process. Automated systems can be applied to control oil drip lubrication, making them a good choice for the future.
- For heavy bearings with low speeds or hollow bearings with high speeds, pressure cycle lubrication may be the best option.
- High-speed light load bearings can be lubricated with dispersed drops or oil mist, while high-speed heavy loads must be spray lubricated.
- Splash lubrication and oil bath lubrication have comprehensive technical and economic indicators and should be avoided if possible.
- When selecting the lubrication method for a bearing in a complete set of equipment, it is important to consider the lubrication methods and characteristics of other components. Using the same model or type of lubricant as much as possible can reduce operating costs.
Final Words
Bearing lubrication is a continuous process and the lubricant replacement cycle depends on the conditions of use and the amount of oil. When used in a clean environment with an operating temperature below 50°C and minimal dust, the lubricant should generally be replaced once a year. If the oil temperature reaches 100°C, it must be replaced every three months or sooner.
