Technical Committee Lubricants
Investigation of the pit load capacity of case-hardened gear pairs when lubricated with gear greases
In this research project the influence of flow greases NLGI 00 on the pitting load-carrying capacity of
case carburized gears is systematically investigated.
In the range of limited life and infinite life the pitting life time and the pitting load-carrying capacity of gear greases in NLGI 00 on the basis of a base oil of ISO VG 680 is lower than that of the respective base oil in the test method C-PT/8.3/90. This is caused by the unfavourable heat dissipation and the higher bulk temperature of the test gears with grease lubrication. In the test method C-PT/5.5/90 with reduced circumferential speed gear grease in NLGI 00 and its base oil ISO VG 680 show comparable bulk temperatures and pitting life times.
In the range of limited life the pitting life time of gear greases in NLGI 00 correlates with the kinematic viscosity of the base oil. But in the range of infinite life the base oil viscosity of gear greases in NLGI 00 influences the pitting load-carrying capacity only slightly.
For gear greases in NLGI 00 a good comparability can be stated for the experimental and the calculated pitting load-carrying capacity with the calculation according to Knauer if appropriate friction coefficients, e.g. measured values are used.
In the range of boundary friction and high lubricant temperatures the thickener of gear greases in NLGI 00 decreases the friction in comparison to the base oil.
The research project (15240 N) of the research association DGMK was financed by the Federal Ministry of Economics and Technology via the AiF in the programme for the promotion of "Industrielle Gemeinschaftsforschung (IGF)".