Why is lubricating oil commonly used for pumps while grease is commonly used for motors?
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I would like to ask everyone: all the pumps and compressors I’ve seen use lubricating oil for lubrication, while smaller motors commonly use grease for lubrication; larger motors, on the other hand, rely on circulating lubricating oil. Why isn’t the pump lubricated with grease, like motors are?
The structure is too complex; there’s no need to incur additional costs for operation when grease can meet the requirements.
Aren’t the bearings of a motor rolling bearings?
If a lubricant is used in small motors, how does the rotor function? Adding isolation devices as well as a lubrication system not only increases costs but also complicates the operation of the equipment. Lubricant is a liquid lubricant used in various types of machinery to reduce friction and protect the machinery as well as the components being processed. Its main functions include lubrication, cooling, rust prevention, cleaning, sealing, and cushioning. The use of lubricating oil or grease depends on the equipment design, cost-effectiveness, etc. What is said may not be correct; it is for reference only.
Since the motor does not experience axial forces, there are no thrust bearings, the radial load is low, and no lubricating oil is required. Large motor bearings experience high radial loads; generally, sliding bearings are used, which require lubricating oil for lubrication. There are also types that do not use bearing bushes, mainly for motors below 1120 KW, but the bearings are prone to failure.
I was wrong, sorry; it’s a sliding bearing
The choice between lubricating oil and grease depends mainly on the magnitude of the load on the bearings. A higher load generates more heat, resulting in higher bearing temperatures. Lubricating oil has a better heat-disipation capacity than grease, and it also makes it easier to implement forced lubrication; therefore, lubricating oil is generally chosen in design. However, in the case of centrifugal pump bearing housings with low loads and lower temperatures, grease can be used for lubrication just like in small and medium-sized motors. The downside is that routine maintenance becomes much more complicated, the effort required to change the oil is equivalent to that of performing a full maintenance task, and the service life of the bearings will definitely be reduced.
I have seen small centrifugal pumps abroad that are lubricated with grease.