Is it normal for the bearing grease to turn silver grey?
March 25, 2022
Causes of discoloration of grease caused by bearing clearance After the motor with large vibration is disassembled, the grease in the bearing turns silver-gray (originally milky white), what is the problem? Is it normal for the bearing grease to change color, and what color is the grease turning into? To what extent is it normal? normal. Some bearing grease also changes color, from milky white to brown, and the discolored part is around the rolling element. 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 of running in the outer circle, why is this?
There are cases where the grease is discolored in the bearing, even if it is not placed in the bearing, it will discolor. This is because: First, grease has oxidation problems. Grease sits (or runs) for a period of time and 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 are now available with 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 leave the thickener, and each time the base oil goes back, it may not go back completely. After a long time, the performance of the grease will change, and the lubrication will not be satisfied, so re-lubrication should be applied. For greases with insufficient base oil, the color may change. Also, if the temperature is abnormal, the properties of the grease also change greatly, so there will be discoloration. If the temperature is high, it will carbonize. The color will darken. Third, during the operation of the spherical roller bearing, impurities are mixed into the grease. This impurity may be peeled off by the bearing itself, or it may be entered by the outside world. It may be solid, it may be liquid, and these will affect the properties of the grease. Never let the bearing work under long-term load Many people don't understand why the bearing can't work under load for a long time? This is because if the bearing is working under load for a long time, it may cause the bearing to strike in advance at any time, and there will be some damage that cannot be estimated, so Never allow the bearing to work under long-term load. The importance of bearing installation Correct installation of bearings is the guarantee of their extended service life. Many people do not have the professional knowledge in this area, and they are not particularly in place during installation, which may easily lead to improper bearing installation and mechanical operation accidents. As a professional mechanical maintenance engineer, it must be Be aware of bearing installation. Bearing long-term load work should pay attention to observe the track of the raceway surface. When the bearing rotates, the raceway surfaces of the inner ring and the outer ring of the bearing are in rolling contact with the rolling elements, so the running track is a dark surface, and the running track attached to the raceway surface is not abnormal, so the load can be known. Therefore, when disassembling the bearing, please pay close attention to and observe the running track of the raceway surface. If you carefully observe the running trajectory, you will know whether the radial load and axial load of the bearing have extreme rigidity unevenness on the bearing housing. It can be checked whether an unexpected load is added to the spherical roller bearing and whether the installation error is too large, etc., and become a clue to investigate the cause of bearing damage.
