TRANSFER LAYER DYNAMICITY IN ROLL-SLIP OF POLYMER METAL PAIRS

Abstract

Polymer-metal pairs are found in many engineering applications, especially in rolling/sliding conditions. Transfer layer formation is imperative in friction and wear investigations on using these tribo-pairs. In the existing literature quantitative description was given for the formation of protective layer from the post mortem analysis (preferentially for sliding configurations). Since there is a dynamicity involved in the transfer layer the straight forward answer from the quantitative postmortem responses is rather uncertain. In the current research, rolling/sliding tests were performed for polymer and it’s composite against metal to explore the underlying mechanisms using both qualitative and quantitative approaches. The tests were performed with intermediate pauses to observe the surface changes where characterization based on surface morphology and roughness (Ra) are used. The results show that the transfer layer deposition occurs in four stages which are explained from the view point of change in Surface roughness Ra in correspondence to its micrographs of the surface topography. The four stages can be categorized as 1. Scouring 2. Running-in 3. Transition and 4. Steady stage. Results show that in polymers the Ra increases during the scouring stage subsequently it decreases on reaching the steady stage. In steel counter parts the Ra does not change significantly during the scouring period. However, the Ra increases in the running-in period followed by a transition region leading to a steady state. Among the polymer and its composites the pure polymer shows significant change in roughness due to the difference in strength. The change in Ra for steel in the steady region also depends upon the contact materials, the mechanical and tribological properties of the polymer. Thus the stages can be used to study the transfer layer behaviour and understand the underlying mechanism in segregating the wear mechanisms both quantitatively and qualitatively.