The lubrication difficulty of high-precision fag bearing is that the lubricant is easy to fly away and is not easy to adhere to the rolling surface, or cannot enter the fag bearing because it is blocked by the high-speed air flow around the fag bearing.
However, the lubricant entering the fag bearing is too fast, which High Precision sometimes causes damage to the fag bearing, such as pitting and scaling of the cage, which aggravates friction and wear.
The working temperature of high-speed fag bearings is mostly about 200 ℃ and often higher. Without High Precision strong cooling, the temperature will continue to rise, which is very unfavorable to the strength and hardness of fag bearings.
Once fag bearings lose the ability to maintain accurate shape, it will High Precision aggravate high-speed friction and make the temperature rise rapidly, It further leads to the reduction of material strength and hardness and makes fag bearing fail soon.
As the high-speed fag bearing is very sensitive to wear and easy to produce wear debris, if it is not removed from the fag bearing in time, it will also High Precision cause a vicious circle and make the fag bearing fail quickly.
Therefore, the task of high-speed fag bearing lubrication must effectively deliver the lubricant to the moving surface in fag bearing, remove the High Precision heat from fag bearing, and remove the wear debris or dirt in fag bearing.
The lubrication methods commonly used in high-speed fag bearings and High Precision effective lubricants are introduced as follows:
1. Jet lubrication method
Spray lubrication method is to spray lubricating oil into fag bearing at the High Precision speed of 10-20m / s from the nozzle hole close to fag bearing, usually into the gap formed between cage and inner ring or outer ring to lubricate and cool fag bearing.
For small ball fag bearings with an High Precision inner diameter of 30-35mm, the DMN limit of jet lubrication is 3 million, and for larger fag bearings, it is 2.5 million.
Double hole or multi hole nozzle can not only increase the oil supply, but also improve the use efficiency of lubricating oil. Multiple nozzles or nozzles on both end faces can High Precision improve the effect of lubrication and cooling.
However, when the DMN value is close to 2 million, due to the influence of centrifugal inertia and wind resistance, the oil sent to fag bearing is only 70% or less of the nozzle flow.
2. Under ring lubrication method
The under ring lubrication method uses centrifugal inertia to spray oil directly to the raceway surface through many radial holes on the inner ring, and part of the oil flows axially below the inner ring to cool the inner ring.
The oil entering the raceway is divided into left and right channels to flow out, and the wear debris falling from parts such as cage is washed away.
The oil consumption of this lubrication method is much less than that of oil injection lubrication, the power loss caused by the dynamic mixing of oil is also less, the heating condition of fag bearing has been greatly improved, and even the temperature of inner ring may be lower than that of outer ring, thus reducing the failure rate of fag bearing.
This lubrication method can also be used to cool the outer ring. When the inner and outer rings are lubricated in this way, the allowable DMN value of fag bearing can be further improved.
The achievable large DMN value is 3 million for large ball fag bearings with an inner diameter of 120 ~ 200mm; For tapered roller fag bearing with inner diameter of 120mm, it is 2.4 million, while for short cylindrical roller fag bearing with combined inner ring, it is 3 million
3. Double lubrication method
In essence, this method is to form a hydrostatic oil film sliding fag bearing with the inner ring hole and Journal of the rolling fag bearing, so as to greatly reduce the speed of the rolling fag bearing, so as to achieve the purpose of reducing the effect of centrifugal force.
Such a double lubricated fag bearing can significantly reduce the speed of the inner ring of the rolling fag bearing, thus allowing the main shaft to have a higher speed, The DMN value equivalent to fag bearing can be further improved.
4. Oil air lubrication method
The great advantage of oil-gas lubrication method is that under the condition of not changing the structure of fag bearing, only by reducing the friction of fag bearing, it is possible to achieve a high speed with DMN value of 800000 ~ 1.5 million. For fag bearing with more internal sliding, the advantage of this method is more significant.
5. Lubricant for high speed fag bearing
The lubricant of high-speed fag bearing should be considered as the lubricant of high-temperature fag bearing, that is, synthetic oil with good performance at high temperature or grease based on this synthetic oil. Recently, diester oil mil-l-7808 and mil-l-23699 are widely used in fag bearings of jet engines.