Effects of Dispersant and ZDDP Additives on Fretting Wear
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ORIGINAL PAPER
Effects of Dispersant and ZDDP Additives on Fretting Wear A. Kontou1 · R. I. Taylor2 · H. A. Spikes1 Received: 14 June 2020 / Accepted: 10 November 2020 © The Author(s) 2020
Abstract This paper examines the effect of dispersant and anti-wear additives on fretting wear in lubricated bearing steel contacts. Reciprocating sliding ball-on-flat fretting tests with a stroke length of 50 μm have been carried out on steel-to-steel contacts in both dry and lubricated conditions. Wear and friction coefficient have been measured, and surface characterisation has been carried out using optical techniques to investigate fretting wear. The presence of base oil reduces fretting wear markedly compared to dry conditions, but fretting damage is still observed at low reciprocation frequencies. As frequency is increased, there is a transition from oxidative to adhesive/scuffing damage. The anti-wear additive ZDDP is effective in forming a tribofilm on the surfaces and reducing visible oxidation and wear. A succinimide dispersant also reduces the accumulation of solid debris but does not alleviate wear damage. The combination of both ZDDP anti-wear additive and dispersant in base oil appears to provide significant protection against fretting wear. Keywords Fretting wear · Fretting · Wear · ZDDP · Boundary lubrication · Dispersant · Lubrication
1 Introduction When surfaces rub together in very low-amplitude oscillation, they may experience fretting damage. This can be a problem with many engineering components that experience vibration or repeated flexure, including couplings, bearing/ housing interfaces, piston rings and wire ropes. Fretting wear can occur in the rolling bearings of machines transported by sea, where it is often termed “false brinelling”, while frequent start–stop to improve fuel consumption can enhance fretting wear in combustion engine components. In electric vehicles, the absence of a combustion engine can lead to different vibration patterns from those in which an engine is present, and lead to unexpected fretting damage.
* H. A. Spikes [email protected] A. Kontou [email protected] R. I. Taylor [email protected] 1
Tribology Group, Department of Mechanical Engineering, Imperial College London, London, UK
Shell Global Solutions Ltd, Shell Centre, York Road, London SE1 7NA, UK
2
There is some confusion in the literature regarding the definition of fretting and the different types of damage it produces. According to Waterhouse, “fretting is the relative oscillatory tangential movement of small amplitude which may occur between contacting surfaces subjected to vibration” [1]. The terms fretting damage and fretting wear describe the harmful results of this fretting motion. The former refers to any form of material damage accumulation, while the latter is used when the damaging effect is assessed according to the amount of material removed from the surface. Fretting fatigue is the formation of fatigue cracks due to the cyclic stresses resulting from fretting [1] and fret
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