High temperature may cause irreversible damage to the bearing

All grease products are designed with the operating temperature range taken into account. If the temperature is too high, the grease will soften and become thin and lose consistency and / or severe oxidation will occur; if the temperature is too low, the starting torque of the bearing will be very high and / or the grease separation will be very low.

The low temperature limit (LTL) is the lowest temperature when the grease can make the bearing start without difficulty; the high temperature limit (HTL) is determined by the grease thickener, and for soap based grease, it is determined by the drop point of the grease. The drop point temperature shows that the loss of consistency of grease is irreversible when the temperature is higher than the dropping point, and the grease will become liquid. Grease is not recommended to work outside the low and high temperature limits.

In the temperature range between the low temperature performance limit (ltpl) and the high temperature performance limit (htpl), grease can give full play to its performance characteristics, which are mainly reflected in the oil film forming ability, oil separation performance, oxygenation rate and rheological property. The viscosity of base oil, apparent viscosity of grease, oxidation and other properties of grease show "Arrhenius" behavior, that is, the performance of grease is more or less exponentially related to temperature. Therefore, in the green temperature region, the grease life also shows "Arrhenius" behavior, so the grease life can be reasonably predicted in the green temperature region. Operating in the Yellow temperature region between the high temperature performance limit temperature (htpl) and the high temperature limit (HTL), the grease life is very short. There are also yellow temperature regions in the low temperature region.

The limit critical temperature is determined by grease test. The high temperature limit is determined by the drop point of the grease, and the low temperature limit is determined by the low temperature torque and oil separation performance of the grease. The green zone can be determined by the grease life test, and the boundary temperatures (ltpl and htpl) are determined by the critical point where the arhenius behavior changes significantly. McCusker suggested that the maximum operating temperature should not be higher than 55 ℃ below the drop point.

However, in any case, it is strongly recommended to follow the specific technical specifications and instructions for the grease product. Most bearing manufacturers specify temperature ranges for specific bearing greases in their product catalogues.

Obviously, other methods can also be used to determine the service temperature of grease, such as the measurement results of oil separation, rheology and oxidation resistance.