High temperature may cause irreversible damage to bearings

All lubricant products are designed with the operating temperature range in mind. If the temperature is too high, the lubricant will soften and become thinner, losing its consistency and/or undergoing severe oxidation; If the temperature is too low, it will result in very high starting torque of the bearing and/or low grease separation.

Low temperature limit (LTL) is the lowest temperature at which lubricating grease can easily start a bearing; The high temperature limit (HTL) is determined by the thickening agent of the grease, and for soap based grease, it is determined by the drip point of the grease. The drop point temperature indicates that the loss of viscosity of the lubricating grease is irreversible when the temperature is higher than the drop point, and the lubricating grease will become liquid. It is not recommended to use lubricating grease beyond the low and high temperature limits.

Within the temperature range between the low temperature performance limit (LTPL) and the high temperature performance limit (HTPL), lubricating grease can reliably exhibit its performance characteristics, mainly reflected in its oil film formation ability, oil separation performance, oxidation rate, and rheological properties. The viscosity of base oil, apparent viscosity of lubricating grease, oxidation, and other lubricating grease properties exhibit "Arhenius" behavior, that is, the performance of lubricating grease is more or less exponentially related to temperature. Therefore, in the green temperature range, the grease life also exhibits "Arhenius" behavior, so the grease life can be reasonably predicted in the green temperature range. Operating within the yellow temperature range between High Temperature Performance Limit (HTPL) and High Temperature Limit (HTL), the lifespan of the lubricating grease will be very short. There are also yellow temperature zones in low-temperature areas.

The determination of the ultimate critical temperature is determined through testing of lubricating grease. The high temperature limit is determined by the drip point of the lubricating grease, while the low temperature limit is determined by the low temperature torque and oil separation performance of the lubricating grease. The green area can be determined through grease life testing, and the boundary temperatures (LTPL and HTPL) are determined by the critical point at which significant Arhenius behavior changes occur. McCusker suggests that the criterion for selecting the highest operating temperature should not exceed 55 ℃ below the drip point.

However, it is strongly recommended to follow the specific technical specifications and usage instructions of the lubricant product. Most bearing manufacturers have specified the temperature range for specific bearing lubricants in their product catalogs.

Obviously, other methods can also be used to determine the usage temperature of lubricating grease, such as oil separation, rheological properties, and antioxidant capacity measurement results.