Selection of plain bearing lubricants

1. Selection of sliding bearing lubricant
Plain bearings generally use ordinary mineral oils and greases as lubricants. china ptfe powder for greases as lubricants. In special cases (such as high temperature systems), synthetic oils, water and other liquids can be used.

2, the main factors that should be considered when choosing lubricating oil for sliding bearings
(1) Load
As a general rule, oil with higher viscosity should be used for heavy loads, and oil with lower viscosity should be used for light loads. In order to accurately measure the size of the sliding bearing load, the load level is generally defined by the size of the load per unit area of ​​the bearing. Table 3 lists 3 classes that differentiate bearing load sizes.

(2) Speed
The speed of the main shaft is an important factor in selecting the viscosity of the lubricating oil. According to the theory of oil wedge formation, at high speed, the lubrication between the main shaft and the bearing is in the range of liquid lubrication. In order to reduce internal friction, low-viscosity oil must be used; at low speed, in the range of boundary lubrication, high-viscosity oil must be used. .

(3) Clearance
The clearance between the spindle and the bearing depends on the operating temperature, load, minimum oil film thickness, friction loss, as well as the eccentricity of the shaft and the bearing, the surface roughness of the shaft and the bearing, and the surface roughness of the workpiece. Bearings with small clearances require low-viscosity oil, and those with large clearances use high-viscosity oil.

(4) Bearing temperature
For ordinary plain bearings, the most important property of a lubricant is its viscosity. If the viscosity is too low, the bearing capacity will be insufficient; if the viscosity is too high, the power loss and operating temperature will be too high. The viscosity of mineral oil decreases with increasing temperature. The viscosity-temperature curve of typical mineral oil can be found in the relevant information. The performance of a grease is largely determined by the viscosity of the base oil and the type of thickener used in its formulation.

To reduce the bearing temperature, the supply of lubricant must be controlled so that the temperature rise of the lubricant flowing through the bearing is limited to below 20°C. The average temperature of the bearing can be estimated as follows:

θb=θs+20℃

where θb——the average temperature of the bearing (℃);

θs——lubricant outlet temperature (℃).

(5) Bearing structure
Load, speed, clearance, temperature, bearing structure, etc. are all factors that act together. When choosing lubricating oil for sliding bearings, the influence of these factors should be comprehensively considered.