WEAR RESISTANCE | MODIFICATION
these lubricants combine. “Internal lubricants must have a synergistic effect with the transferred layer,” he said. Equilibria can be affected by external lubrication, which may dissolve the transfer layer and/or replace it with a less effective lubricant layer. This can actually increase the CoF and accelerate wear, according to Espejo Conesa, who also discussed self-healing in polymer systems through phenomena such as viscoelastic recovery, migration of fillers, other particles in a matrix, and even induced polymerisation. Omya OML is a new coated mineral processing
aid from Omya International that is claimed to combine the value of a functional additive and mineral carrier. Franck Baradel, Market Manager Technical Polymer Applications describes it as a synergist for new technical compounds that can improve heat dissipation and flame retardancy as well as tribological properties. “Omya OML may partially substitute expensive lubricants in wear and abrasion resistant compounds (PTFE micropowder, MoS2
, silicone) while eliminating the break-in
period, optimising processing (compounding, converting, demoulding) and limiting the fluoro- polymer content in the recipe,” he says.
Tackling noise Witcom, a supplier of high-performance engineer- ing plastics compounds, has developed a range of internally lubricated thermoplastics that are particularly effective at keeping noise levels low. “Noise is caused by high frequency vibrations which in turn are the result of high speed fluctua- tion of the coefficient of friction over time. Our new compound formulations ensure that friction
Figure 4: Graph showing the effect of multiwall carbon nanotubes (MWNT) and graphene oxide (GO) on wear and friction in ultra-high molecular weight polyethylene. The results show a simultaneous reduction of friction and wear with a direct correlation between the two. Measurements from pin-on-disc tests. Source: Dr A Golchin at Luleå University of Technology
Cracks caused by wear can be “healed” by induced polymerisation, one of a number of self-healing micro-encapsulant mechanisms under investigation at the University of Leeds Source: University of Leeds
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