After a motor with a large vibration was disassembled, the grease in the bearing turned silver-gray (it was milky white in the first place). What caused the problem? Is it normal for the bearing grease to change color? What color does the grease change to? What? The degree is normal. Some bearing grease also changes color, from milky white to brown, and the discolored part is around the rolling elements. What is the reason? If it turns silver gray, it is caused by tight fit, small clearance and large friction , but the same bearing has the phenomenon that the outer ring runs around. Why is this? There are cases where the grease changes color in the bearing, even if it is not placed in the bearing, it will change color. This is because: First, there is an oxidation problem with grease. When the grease is left (or run) for a period of time, it will have a lot of contact with oxygen, and at the same time, the metal (the bearing itself) acts as a catalyst in this oxidation reaction. Therefore, when calculating the replenishment interval of grease in the bearing, the problem of oxidation should also be considered. Many greases now have antioxidant additives. This does not mean that it will not oxidize. Second, the temperature of the bearing itself (the bearing itself, or the environment) will change, which causes the base oil in the grease to continuously enter and exit the thickener, and at the same time, every time the base oil returns, it does not necessarily go back completely. After a long time like this, the performance of the grease will change, and the lubrication will not be satisfied, so the lubrication must be reapplied. Greases with insufficient base oil may change in color. Also, if the temperature is abnormal, the performance of the grease will change greatly, so there will be discoloration. If the temperature is high, it will carbonize. Color will darken. Third, during the operation of the bearing, impurities are mixed inside the grease. This kind of impurity may be peeled off by the bearing itself, or it may be entered by the outside world. May be solid, may be liquid, these will affect the grease properties. In addition, you said that the fit is tight and the clearance is small, which will cause the grease to change color. The reasoning should be something like this: tight fit, small working (residual) clearance, increased bearing load zone, heat generation, causing grease denaturation, causing grease color change. As for the running circle you mentioned, firstly, there may be a problem with the cooperation of your bearing chamber, and secondly, the internal clearance is too small and the friction force is large, resulting in running circles. The latter possibility cannot be realized by adjusting the tight fit. The more tuned the worse. Also, what you’re talking about is judging by the color of the grease to see if the situation is normal. It is very difficult to judge this point. Different greases have different internal additives, different operating conditions, and different temperature ranges. It is impossible to have a unified standard. Even if it is the same grease, the formula may be slightly different 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