Bearing lubrication is essential for ensuring proper bearing operation, preventing direct contact between the raceway and rolling element surfaces, reducing internal friction and wear, extending bearing life, enhancing bearing performance, and preventing rust and corrosion caused by foreign matter intrusion. This article introduces 11 commonly used bearing lubrication methods, hoping to be helpful in your work and studies.
1. Manual Lubrication
This is the most basic method: using an oiler to supply oil when the bearing's lubricating oil is insufficient. However, this method is difficult to maintain a constant oil level, and there is a significant risk of forgetting to add oil. It is usually only used in light-load, low-speed, or intermittent operation situations. For best operation, a dust cover or ball valve should be installed on the oil filling hole, and a filter device such as felt, cotton, or wool should be used.
II. Drop Lubrication
It is typically used for light and medium load bearings with a circumferential speed of less than 4 to 5 m/s. A roughly fixed amount of lubricating oil is supplied from the container through holes, needles, valves, etc. The most classic type is the oil drip cup. The amount of oil dripped varies significantly depending on the viscosity of the lubricating oil, the bearing clearance, and the position of the oil supply hole.
III. Oil Ring Lubrication
A rotating ring attached to the shaft carries the lubricating oil from the oil sump to the bearing (this lubrication method is only applicable to horizontal shafts). It is suitable for medium-speed and high-speed bearings with a shaft diameter greater than 50mm. The oil ring should ideally be seamless. If the bearing width-to-diameter ratio is less than 2, only one oil ring is needed; otherwise, two oil rings are required.
IV. Oil Rope Lubrication
The oil rope draws lubricating oil from the oil cup into the bearing through capillary action and siphon effect. It is mainly used for light and medium load bearings with circumferential speeds of less than 4 to 5 m/s. In addition, the oil rope can also act as a filter throughout the process.
V. Oil Pad Lubrication
Using the capillary action of an oil pad, lubricating oil from the oil sump is applied to the shaft diameter surface. This method keeps the friction surfaces clean, but dust can clog the capillaries, causing insufficient oil supply. The oil supply of oil pad lubrication is typically only 1/20th that of oil lubrication.
VI. Oil bath lubrication
This lubrication method involves immersing a portion of the bearing in lubricating oil. It is commonly used for thrust bearings on vertical shafts but not suitable for radial bearings on horizontal shafts.
VII. Splash Lubrication
The lubricating oil is supplied to the bearing by splashing up the rotating parts in the oil tank, which is suitable for bearings with higher speeds.
8. Spray Lubrication
The lubrication method of spraying atomized lubricating oil onto friction surfaces is suitable for high-speed bearings.
9. Pressure-fed oil lubrication
The lubrication method relies on the pressure of a lubrication pump to supply oil to the bearing and recovers the lubricating oil flowing out of the bearing to the oil sump for recycling. It is the lubrication method with the largest and most stable oil supply and is suitable for high-speed, heavy-load, and important sliding bearings.
10. Circulating oil lubrication
The filtered oil is pumped to the bearing components, and the lubricating oil after passing through the bearing is filtered and cooled before use. Since the circulating oil can carry away some heat, thus cooling the bearing, this method is suitable for bearing components with high rotational speeds.
XI. Jet Lubrication
High-pressure oil is injected into the bearing through a nozzle using an oil pump. The oil injected into the bearing then flows into the oil sump at the other end of the bearing. When the bearing rotates at high speed, the rolling elements and cage also rotate at a relatively high speed, causing the surrounding air to form an airflow. It is difficult to deliver lubricating oil to the bearing using ordinary lubrication methods. In this case, high-pressure injection must be used to spray lubricating oil into the bearing. The nozzle should be positioned between the center of the inner ring and the center of the cage.
Bearing lubrication is an ongoing process, and the oil replacement cycle varies depending on the bearing's operating conditions and the amount of oil. Generally, when used in a clean environment with an operating temperature below 50°C and minimal dust, the oil should be replaced once a year. When the oil temperature reaches 100°C, it should be replaced every 3 months or less.
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