Friction & Wear Properties Of CaCO₃ Whisker-filled POM Composites

Polyoxymethylene(POM) is one of the five major engineering plastics. Because of highlighted creep resistance,self-lubricating,wear-resistance and excellent mechanical properties,POM is widely used in machinery,automotive, instrumentation,electronics and other fields as anti-friction and wear-resistant components.However,under dry friction pure POM has higher friction coefficient which can bring serious abrasive wear,so it can not be applied to high-speed and high-load harsh working conditions.At present,No paper is available on the friction and wear behaviors of CaCO₃ whisker(W-CaCO₃) and polytetrafluoroethylene (PTFE) ultra-fine powders filled POM composites under different loads and different lubrication conditions.This paper researched on the friction and wear behaviors of W-CaCO₃ and PTFE filled POM composites prepared by injection molding.The tribological behaviors of filled POM composites were evaluated on MM200 block-on-ring apparatus.The friction and wear behaviors under dry friction and water lubrication influence of different contents of CaCO₃ whisker and different loads to the composites were researched.By measuring limiting PV value,the carrying capacity of the composites on special loads were researched.The morphologies of the wear traces were observed by scanning electron microscopy(SEM).It was found that CaCO₃ whisker can be significantly improved friction and wear properties.Under dry friction condition,along with content of CaCO₃ whisker increased,the friction coefficient of the composites is continuously decreased,and the wear rate increased after the first lower;under water lubrication,the friction coefficient reduced,and the wear rate increased compared to dry friction.With the load increased,under dry friction and water lubrication conditions,the friction coefficient and the wear rate showed slow upward trend,and were lower than pure POM.CaCO₃ whisker can improve limiting PV values,and 12%W-CaCO₃/POM composites have the best value and carrying capacity.At the same time,the crystallization of W-CaCO₃/POM composites were investigated by polarizing microscopy and DSC,and the effects of crystallization on mechanical properties,tribological properties were researched.It found that,CaCO₃ whisker can make crystallization temperature,crystallization rate decreased,and crystallinity increased,but high content of CaCO₃ whisker have little effect on POM nucleation or obstruct the nucleation.With crystallinity increased,the mechanical properties,friction coefficient significantly decreased,but the wear rate increased in the high crystallinity.The paper also studied on the tribological behaviors of PTFE/W-CaCO₃/POM composites and showed that PTFE can further reduce the friction coefficient and wear rate of the composites,under dry friction and water lubrication conditions, with the content of PTFE increased and the particle size decreased,the friction coefficient and wear rate decreased in varying degrees,and the tribological behaviors transformed abrasive wear into micro-cutting and micro-furrows.