聚四氟乙烯磨损机理的探讨

Study on the Wear Mechanism of Polytetrafluoroethylene

作者用MPX-200型栓-盘摩擦磨损试验机测试了模压聚四氟乙烯的磨损性能,考察了滑动速度、负菏、温度及偶件表面粗糙度对磨损的影响。磨屑分子量的测试结果表明,其大小与聚四氟乙烯磨损的严重程度成正比;磨屑的分子量比聚四氟乙烯本体的小,在本试验条件下磨屑分子量的降低为2—3个数量级;当超过极限PV值时,磨屑分子量的下降幅度急剧变小。作者指出,聚四氟乙烯之磨损随温度的变化与其所处的力学状态有关。通过电子显微镜和电子探针对试样、偶件和磨屑的表面观察,作者提出了聚四氟乙烯薄带状磨屑的形成机理,认为它是由聚四氟乙烯分子链受剪拉伸成束及较弱的束断裂的形式所产生。

The wear characteristics of polytetrafluoroethylene (PTFE) were tested on the model MPX-200 pin-on-disk tester in this paper. The effects of sliding speed, load, temperature and surface roughness of counterparts on wear were determined. The results shown that the wear of PTFE severely increases along with the increasing of sliding speed, load and surface roughness of counterparts.The relationship between wear and temperature is complex, but when the temperature is higher than 125℃ the wear also severely increases along with the rising of temperature. It is suggested that the changes of wear of PTFE along with the temperature is related to its mechanics state, i. e. under the higher temperature the PTFE material has higher deformability and forms longer fibers, the thin film-like debris in which the fibers are cross connected can be generated under the action of load;under the lower temperature the material is of lower deformability and the flake debris which are formed with shorter fibers can be produced. During the wear process of PTFE, both the orientation of molecular chains in the amorphous area and the rearrangement of molecular chains in the crystal area has taken part in the film-forming process. On the basis of surface observations of the samples,counter-couples and debris using SEM and EPMA. The forming mechanism, of thin band-like debris is suggested.That this kind of debris is formed after stretching or breaking molecular chain of PTFE.The results of DSC determination shown that the molecular weight of debris of PTFE is less than that of bulk PTFE.In the given conditions the molecular weight of debris decreases 2-3 orders of magnitude, above the PV value limit the decreasing amplitude of molecular weight of debris is getting small rapidly.