The SKF traffic light concept
Most grease suppliers indicate the specific values for the low and high temperature limits in their product information. The SKF traffic light concept is distinctly different from that. SKF recognizes that the really important temperatures for reliable operation lie within a smaller range. This range depends largely on the type of base oil and thickener used as well as the additives. The relevant temperatures are given by the SKF traffic light concept. They are schematically illustrated in diagram 1 and diagram 2 in the form of a double traffic light.
It is evident that grease in the red zones should not be applied at all, as damage may occur. Within the green zone the grease functions reliably, and the grease life can be determined accurately.
At temperatures in the amber zone above the high temperature performance limit (HTPL), grease ages and oxidize with increasing rapidity and the by-products of the oxidation have a detrimental effect on lubrication. An amber zone also exists for low temperatures. Short periods in this zone, e.g. during a cold start, are not harmful since the heat caused by friction brings the bearing temperature into the green zone.