THE EFFECT OF OPERATING-CONDITIONS ON HEAVY-DUTY ENGINE VALVE SEAT WEAR

Engine valve seat wear affects engine performance. To improve valve qu ality and life is a common goal for both valve and engine manufacturer s. By performing tests on a valve seat wear simulator, the effect of c ycles, load and temperature on heavy duty intake valve/insert seat wea r was investigated. The test temperatures ranged from 180 to 650 degre es C, the number of cycles was varied from 150 000 to 3 420 000, and t he test loads were applied from 6615 to 24 255 N. The relationship of valve and insert seat wear as a function of cycles, load and temperatu re was experimentally established. A load dependent wear transition wa s found to exist and suggests different wear mechanisms operating in t hese different regions. Higher temperatures produced lower seat wear, which was attributed to parting agents or oxide films and valve head d eformation. The intake valve/insert (Silcrome 1/Silcrome XB) seat wear mechanisms were found to be a complex combination of adhesion, shear strain and abrasion. Shear strain or radial flow was found to be an im portant valve seat wear mechanism from the microstructure analysis of cross-sectioned valve seats, and two-dimensional and three-dimensional worn seat profiles. The oxide films which formed during testing were found to play a significant role. They can prevent the direct metal to metal contact and reduce the coefficient of friction on the seat surf ace, thus reducing adhesive wear and deformation controlled wear.