Search Results

Tribological properties of three different ceramic materials i.e., reacted silicon nitride, pressureless sintered silicon nitride and alumina-titanium carbide composites were investigated as cam roller followers using a motorized valve train apparatus. One pair of each ceramic rollers and one pair of 52100 steel rollers were tested against a nodular cast iron camshaft. The contact areas were lubricated by a jet of mineral oil at 88°C. The tests were conducted at camshaft speeds of 250 and 3000 r.p.m which approximate idling and rated operating speeds of an engine. The experiments were conducted for a period of 900 hours. At the end of each 100 hours of testing, the wear on the cam lobes and the ceramic rollers were measured. Also replicas were taken from the worn surfaces of ceramic rollers, steel rollers and cam lobes and examined under scanning electron microscope to record the progression of surface damage and the wear mechanisms were identified.

Experimental and analytical research were performed on the contact fatigue wear of cam roller follower (needle roller bearing). A new fatigue test machine with a special two-bar loading system was designed to increase the efficiency and the reliability of the tests. The performance test indicated that the end clearance between the roller and rocker had a significant influence on friction and heat generation in the roller follower. The nondestructive testing procedure showed that there were possibly three wear mechanisms in the wear process, but the dominant one was subsurface crack initiation and propagation. Based on the observed wear mechanism two crack initiation dominate contact fatigue models were used to predict the wear life. The life prediction parameters were determined from statistic analysis of the experiment data. The Lundberg-Palmgren model [1] predicts shorter lives and dose not fit with the experiment data.

Research leading to analytical modelling of surface pitting failure in contacts similar to those in spur and helical gears is reported. Development of this model is based on observations of surface pitting morphology, analysis of crack initiation and propagation for a single or a set of distributed cracks. The morphological experiments on a geared roller fatigue tester revealed slow growing surface cracks followed by a rapid growth of a single crack leading to a pit. Near surface inclusion is found to be the cause of this rapid growth. Models for determining the life for developing a single surface crack and for propagating this crack to form a single deep pit are also described.