Electrostatic monitoring of boundary and mixed lubrication

Abstract

Previous work has shown that electrostatic charge signals can be used to detect the onset of wear in lubricated tribocontacts. Preliminary investigations have shown the viability of this system when tested on a laboratory-based pin-on-disc rig, a reciprocating laboratory wear rig and in an FZG gear scuffing rig. These preliminary experiments have indicated several charging mechanisms could be involved, namely tribocharging, surface charge variations, debris generation and exo-emissions. This paper details further studies looking at the levels of charge generated under boundary and mixed lubrication for base oils and formulated lubricants using a pin-on-disc facility. Results will be presented that show major differences in charge levels between base oil and formulated oil and the dynamic nature of charge within the wear track. The onset of scuffing will be related to surface contact potential differences and phase transformations. Precursor charge events prior to catastrophic metal/metal interaction within the contact are identified and their use for early detection of wear and boundary film failure discussed. Charge sign inversion is discussed in relation to space charge caused by additive adsorption.