How to choose the right lubricating oils or greases for bearings?
Lubricating oils and greases are the most common lubricants in the use of bearings. When we maintain bearings, lubrication is of great help to the operation of bearings, such as reducing the coefficient of friction.
So what do we need to know when choosing bearing lubricants and greases for lubrication? First of all, we need to know what the bearing lubricants are. Second, we need to understand the performance selection of lubricants. Then we need to understand the principles of bearing lubricants. Finally, we choose the lubricants. In this way, the most reasonable lubrication effect can be ensured when the bearing is lubricated.
Common lubricants for bearings:
Lubricating oil-liquid, the most widely used;
Grease-semi-solid, generally used at low and medium speeds;
Solid lubricants are mainly used as additives for oils and fats, but can also be used alone.
Lubricant performance selection:
Viscosity-characterizes the amount of internal frictional resistance in a flowing liquid. It is the most important performance index and the main basis for selecting lubricants.
Oily-also known as lubricity, characterizes the adsorption of polar molecules in oil to metal surfaces. If the oiliness is good, the friction coefficient is small.
Freezing point-reflects the low temperature performance of lubricating oil.
Flash point-reflects the high temperature performance of lubricating oil.
Selection principle of lubricating oil:
1. High pressure or work under impact and variable load conditions, oil with high viscosity should be selected;
2. When the speed is high, oil with low viscosity should be selected to reduce friction loss;
3. When the working temperature is high, the oil with high viscosity should be selected, because the viscosity will decrease as the temperature increases.
Performance selection of grease:
Penetration-characterizes the thin consistency of grease, similar to the viscosity of oil;
Dropping point-characterizes the high temperature resistance of grease.
Selection principles of grease:
1. There is water vapor in the working environment, choose calcium-based grease;
2. High working temperature, choose sodium base grease;
3. If there is water vapor and the working temperature is high, lithium-based grease should be selected.
Solid lubricant: powder or film solid used on the surface to prevent and protect the friction surface from damage and reduce friction and wear during relative movement is called solid lubricant. Solid lubricants have a wide operating temperature range, strong bearing capacity, good anti-slip properties, high vacuum resistance, radiation resistance, wide conductivity range, corrosion protection, and dust prevention, so they are a special class of lubricants. The disadvantage is that the friction coefficient is generally greater than lubricating grease, and the energy loss is large; it can not play a cooling role; the film making process is complicated, etc.