Causes of grease discoloration due to bearing clearance
After disassembling a motor with large vibration, the grease in the bearing became silvery gray (originally milky white), what is the problem? Is it normal for the bearing grease to become discolored, and what color is normal for the grease to become? What is the normal color of grease? Some bearing grease also change color, from milky white to brown, and the discolored part is around the rolling body, what is the reason? If it becomes silver gray is due to the tight fit, small clearance, friction caused by large, but the same bearing has the phenomenon of outer ring running. What is the reason for this? Grease discoloration in the bearing is the case, even if not put in the bearing, but also will change color. This is because. First, there is an oxidation problem with the grease. When grease is placed (or run) for a period of time, there will be a lot of contact with oxygen, and at the same time, the metal (the bearing itself) acts as a catalyst in this oxidation reaction. So, when calculating the grease replenishment interval in bearings, oxidation should also be considered. Nowadays, there are many greases with antioxidant additives. This does not mean that it will not oxidize. Second, the bearing operation itself, the temperature (the bearing itself, or the environment) will change, which leads to the base oil in the grease constantly in and out of the thickener, while each time the base oil goes back, not necessarily completely back. After a long time in this way, the performance of the grease will change and will not meet the lubrication, so the lubrication should be reapplied. The color of grease with insufficient base oil is likely to change. Also, if the temperature is abnormal, the performance of the grease changes a lot, so that, there will be discoloration. If the temperature is very high, it will carbonize. The color will become darker. Thirdly, during the operation of the bearing, impurities are mixed inside the grease. This impurity may be the bearing itself flaking off, or it may be the outside world entering. May be solid, may be liquid, these will affect the nature of grease. In addition, you said that the fit is tight and the clearance is small, resulting in grease discoloration. This reasoning should be like this: tight fit, small working (remaining) clearance, bearing load area increases, heat, resulting in grease denaturation, resulting in grease color change. And you say running circle, the first possibility that you have a problem with the fit of the bearing chamber, the second, the internal clearance is too small, the friction is large, resulting in running circle. The latter is a possibility that cannot be achieved by tightening the fit. The more tuning the worse. Also, you are talking about judging whether the situation is normal based on the color of the grease. This is very difficult to judge, different grease internal additives are different, different operating conditions, different temperature range, it is impossible to have a uniform standard. Even if it is the same grease, it may have a slightly different formulation due to different batches from the factory. Please do not use this color change as a basis, it is not reliable.
We have rich experience on precision bearing manufacturing and are ranked NO.1 in China and NO.3 all over the world.
We can tailor the overall solution for the use of precision bearings.
HONB– Accountability & Innovation
- YRT rotary table bearing
- YRTS rotary table bearing (high speed series)
- YRTM with integral angular measuring system series
- ZKLDF axial angular contact ball bearing series
- RA series crossed roller bearing
- SX series crossed roller bearing
- CRBH series crossed roller bearing
- RE series crossed roller bearing
- RU series crossed roller bearing
- RB series crossed roller bearing
- XR/JXR series crossed taper roller bearing
- Crossed roller bearing
- Harmonic reducer bearing
- Harmonic reducer bearing-SHG(SHF)
- RV series robot special bearing
- HYR flexible bearing
- Address:Chuangye Road, Konggang Industrial cluster district, Luoyang city, Henan province, China