Development of an Accelerated Testing Methodology of Rotary Oil Seals for Off-Highway Vehicles

This paper will describe the development of an accelerated testing methodology for an off-highway vehicle rotary oil seal system. There are two typical field failure mechanisms associated with off-highway input pinion shaft oil seals: 1) excessive abrasive wear of soft seal lip and hard shaft surface due to abrasive environment; 2) excessive heat and degradation of the seal lip due to lack of lubricity and wear of the shaft surface run against this seal. The accelerated testing of the rotary oil seal consisted of a combination of the following factors; shaft run-out, eccentricity, testing temperature, rotation and reciprocal motion of the seal lip relative to the shaft surface. The combination of these factors especially reciprocal motion reproduces the same failure mechanism, i.e. shaft wear grooves and oil seal lip wear observed on the field usage samples with 6,300 hours service in only 350 hours of accelerated testing.

The methodology consists of evaluating the following parameters; the number of test cycles before a leak occurs, oil seal lip wear and depth of the wear groove on the shaft surface in contact with the seal oil lip. An important part of this methodology is a detailed metallurgical and metrological examination/comparison of the field and lab tested samples. This examination includes Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analysis of the oil seal lips and 2D and 3D analysis of the shaft surface. The test matrix consisted of two seal materials and three different seal designs (double, triple and quad lips) tested in conjunction with two different shaft surface machining techniques (grinding and burnishing) and associated surface roughness characteristics, and their influence on seal lip wear will be presented.