All grease products are designed with the operating temperature range in mind. If the temperature is too high, the grease will soften and thin, lose consistency and/or undergo violent oxidation; if the temperature is too low, the starting torque of the bearing will occur. Very high and/or the grease has a very low oil content.
The low temperature limit (LTL) is the lowest temperature at which the grease can enable the bearing to start without difficulty; the high temperature limit (HTL) is determined by the grease thickener. For soap-based grease Said to be determined by the dropping point of the grease. The dropping point temperature indicates that at temperatures above the dropping point, the loss of consistency of the grease is irreversible and the grease will become a liquid. Greases are not recommended for operation 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), the grease can reliably exert its performance characteristics, which are mainly reflected in the oil film formation ability, oil separation performance, Oxidation rate and rheology, etc. Base oil viscosity, apparent grease viscosity, oxidation, and other grease properties exhibit "Arhenius" behavior, i.e., the properties of the grease are more or less exponential with temperature. Therefore, in the green temperature area, the grease life also shows "Arhenius" behavior, so the grease life can be reasonably predicted in the green temperature area. Grease life will be very short when operating in the yellow temperature zone between the High Temperature Performance Limit (HTPL) and the High Temperature Limit (HTL). There are also yellow temperature areas in low temperature areas.
The ultimate critical temperature is determined by testing the grease. The high temperature limit is determined by the dropping 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 grease life testing and the boundary temperatures (LTPL and HTPL) are determined by the critical point at which a noticeable change in Arhenius behavior occurs. McCusker recommends that the guideline for selecting the maximum operating temperature is no higher than 55°C below the dropping point.
In any case, it is strongly recommended to follow the grease product's specific technical specifications and instructions for use. Most bearing manufacturers specify temperature ranges for specific bearing greases in their catalogs.
Obviously, other methods can also be used to determine the service temperature of grease, such as oil separation, rheology and antioxidant capacity measurements. .
