There are many kinds of plain bearings, and the service conditions and importance often vary greatly. Therefore, the requirements for lubricants vary. Select the Lubricating Materials corresponding lubricating materials according to different sliding bearings.
If a lubricating film can be formed on the surface of the sliding bearing Lubricating Materials to separate the moving pair, the friction of the sliding shaft can be greatly reduced.
Since the surface of the moving pair is not in direct contact, wear is also Lubricating Materials avoided. Sliding bearing has large bearing capacity, high rotation accuracy and anti impact effect of lubricating film. Therefore, lubricating film is widely used in engineering.
The formation of lubrication film is the basic condition for the normal operation of sliding bearing. The factors affecting the formation of lubrication film are lubrication mode; Relative motion speed of motion pair; The physical properties of the lubricant and the surface roughness of the moving pair.
The main purpose of lubrication is to reduce the loss of friction power and reduce or prevent wear. At the same time, it also plays a role in cooling. Now it is lubricated with lubricating oil. The lubricating grease has high viscosity, is not easy to leak from the bearing, and its bearing capacity is large.
1. General principles for selecting lubricating oil
Lubricating oil is widely used in sliding bearings. Hydrodynamic bearings Lubricating Materials usually use lubricating oil as lubricant. In principle, when the rotating speed is high and the pressure is small, the lubricating oil with low viscosity shall be selected.
On the contrary, when the speed is low and the pressure is high, the lubricating oil with high viscosity should be selected. The viscosity of lubricating oil decreases with the increase of temperature. Therefore, the viscosity of lubricating oil for bearings working at high temperature should be higher.
1.1. Under the working conditions of low speed, heavy load, impact and variable load, high viscosity Lubricating Materials lubricating oil shall be applied to form oil film. Low viscosity lubricating oil is selected for high-speed and light load to reduce friction loss.
1.2. High viscosity lubricating oil shall be selected for high working temperature. If the temperature is too high, the lubricating oil with low carbon content and high flash point shall be selected. If the temperature is too low, the lubricating oil with low freezing point shall be selected.
1.3. High viscosity lubricating oil shall be selected for machining rough or Lubricating Materials worn surfaces.
1.4. Low viscosity lubricating oil shall be selected for ring lubrication: high quality lubricating oil shall be selected for splash lubrication to prevent Lubricating Materials oxidation or stirring emulsification.
The use of grease can also form a film that completely separates the sliding surface. Because the grease is a semi-solid lubricant, its fluidity is very poor. Therefore, there is no cooling effect. It is often used in bearings with low requirements, difficult to often supply oil, or low speed, heavy load and swing movement.
2.1. When the pressure is high and the sliding speed is low, select the variety with smaller penetration. On the Lubricating Materials contrary, select varieties with greater penetration.
2.2. The dropping point of the lubricating grease used shall generally be about 20 to 30 degrees higher than the working temperature of the bearing, so as to avoid excessive loss of lubricating grease during operation.
2.3. In the wet or humid environment with water, calcium base or aluminum base grease with strong water resistance should be selected. Sodium base or compound calcium base grease should be selected in high temperature environment.
2. Lubrication mode of sliding bearing
2.1. Manual lubrication
When it is found that the lubricating oil of the bearing is insufficient, oil shall be supplied with an oiler in time, which is the original method. This method is difficult to maintain a certain amount of oil, and there is a great risk of forgetting to refuel due to negligence.
It is usually only used for light load, low-speed or intermittent movement. Dust cover or ball valve shall be set on the oil filling hole, and felt, cotton, wool, etc. shall be used as the filtering device.
2.2. Drip lubrication
Roughly quantitative lubricating oil is supplied from the container through holes, needles, valves, etc. the classic is the drip cup. The amount of oil dripping varies significantly with the viscosity of lubricating oil, bearing clearance and the position of oil supply hole. It is used for light load and medium load bearings with circumferential speed less than 4 ~ 5m / s.
2.3. Oil ring lubrication
It can only be used for the lubrication method of horizontal shaft. The lubricating oil from the oil pool is brought into the bearing by a ring that is hung on the shaft and can rotate.
Suitable for medium and high speed bearings with shaft diameter greater than 50mm. The oil ring is seamless. When the width diameter ratio of the bearing is less than 2, only one oil ring can be used, otherwise two oil rings are required.
2.4. Oil rope lubrication
The lubricating oil in the oil cup is led into the bearing by the capillary action and siphon action of the oil rope, which is used for light load and medium load bearings with circumferential speed less than 4 ~ 5m / s. The oil rope can also filter.
2.5. Oil pad lubrication
Use the capillary action of the oil pad to apply the lubricating oil in the oil pool to the surface of the shaft diameter. This method can keep the friction surface clean, but the dust will also block the pores and cause insufficient oil supply. The oil supply of oil pad lubrication is usually only 1 / 20 of that of oil lubrication.
2.6. Oil bath lubrication
The lubrication method of immersing a part of the bearing in lubricating oil. This method is often used in the thrust bearing of vertical shaft, but not in the radial bearing of horizontal shaft.
2.7. Splash lubrication
The bearing is supplied with lubricating oil splashed by the slap of rotating parts in the oil tank, which is suitable for bearings with higher speed.
2.8. Spray lubrication
The lubrication method of atomizing and spraying lubricating oil on the friction surface is suitable for high-speed bearings.
2.9. Pressure supply lubrication
Supplying oil to the bearing by the pressure of the lubrication pump and recovering the lubricating oil from the bearing to the oil pool for recycling is a large and stable lubrication method, which is suitable for high-speed, heavy-duty and important sliding bearings.