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Purposes and methods of lubricationLubrication has important effects on the function of the bearing. Whether the lubricant and the method are suitable or not shall influence the bearing life.The advantages of lubrication:
1)Reducing the friction and wear by lubricating every part of the bearing.
2) Taking away the heat generated inside the bearing caused by friction or other reasons.
3) Forming an oil film in the rolling contact surface in order to elongate the bearing life.
4) Preventing the bearing from rusting and dust contamination.
The lubricating methods include oil lubrication and grease lubrication. The comparisons of these two methods are given in Table1.
Talbe1 Comparisons between oil lubrication and grease lubrication | Item | Grease | Oil | | Sealing device | Simple | More complicate, requiring maintenance | | Lubricating function | Good | Very good | | Rotational speed | Low speed to medium speed | Applicable to high speed | | Change of lubricant | Troublesome | Simple | | Life of lubricant | Very short | Long | | Cooling effects | Without | Possible(using forced oil circulation) | | Elimination of inclusion | Impossible | Easy |
Grease lubrication
Grease put inside the bearing can last a comparatively long time without replenishment, and the sealing device is very simple. Therefore it is extensively applied.
There are two methods for grease lubrication: one is to put the grease inside the sealed bearings in advance, the other is to fill the grease of certain amount inside the housing and refill it or change the grease inside at intervals.
Moreover, for machine with several bearings requiring lubrication, the method of centralized greasing through pipes connecting the places to be lubricated is adopted.
1) Amount of lubricating grease
The amount of lubricating grease to be filled in the housing depends on the structure and volume of the housing. Normally it is preferred to fill the volume by 1/3 to 1/2.
If too much grease is filled, the grease may turn bad, age or soften due to the heat caused by rotation.
But for bearings with low rotation speed, sometimes 2/3 to the whole volume shall be filled with grease in order to avoid the intrusion of foreign matters.
2)The replenishment and change of grease
The replenishment and change of grease is closely related to the lubricating method. No matter which method id applied, the grease must be clean and care be taken to avoid intrusion of dirt.
The grease to be replenished with should be of the same brand.
Try to ensure that the replenished grease has entered into the inside space of the bearing.
Oil lubricationOil lubrication is applied to high-speed and heat-resistant bearings and ineffective for reducing vibration and lowering noise. Mostly it is used in cases where the grease lubrication is not suitable.Oil lubrication has the following methods:
(1) Oil bath lubrication (2) Oil drip lubrication (3) Splash lubrication
(4) Oil circulating lubrication (5) Oil jet lubrication (6) Oil mist lubrication
(7) Oil air lubrication
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