Mechanical degradation of lubricating grease in an EHL line contact

Abstract

Mechanical degradation of grease in an EHL line contact between two steel rollers is studied. Three successive lubricating phases involving “fully grease covered rollers,” “slippage and grease separation,” and “formation of liquid lubricant reservoirs” are observed and characterized. Traction results are presented for a grease undergoing long-term mechanical degradation process. To gain further insight, a prediction model for assessment of reduction of grease consistency is applied. It is shown that both high shear rate and shear stress cause significant and rapid mechanical degradation within the EHL contact. However, grease tends to accumulate on either side of the contact and forms two “side walls” that tends to block the lubricant from leakage, akin to a soft seal. The edges of the side walls are subjected to much slower degradation rate and are capable of providing lubrication to the contact over a relatively long time.