Polymer Pin Research Articles

Contact Configuration Effects on the Dry and Lubricated Wear of Polymers

An investigation into the wear of polymers in tribologicql contact with steel is reported. Five polymers, polypropylene, poly(etrajiuoroethylene, high density polyethylene (HDPE), Nylon 6:6, and polyetheretherketone (PEEK), were tested in polymer pin on metal plate and metal pin on polymer plate configurations, with and without lubrication. The metal pin on polymer plate configuration gave significantly lower wear rates for all the polymers tested, suggesting that contact conditions are less severe than for the reverse configuration. Lubrication reduced the wear rate under both configurations, although with PEEK, which wears mainly by an abrasive mechanism, this reduction was negligible. Lubrication was also ineffective with HDPE in the metal pin on polymer plate configuration, film lubrication conditions not being attained. The results are discussed in terms of proposed friction and lubrication mechanisms.

Solid lubricant additives for bismaleimide resin

AbstractBismaleimides are the addition type of polyimide resin. They are synthesized by reaction of diamino compounds with maleic anhydride. By varying the structure of the diamino compound it is possible to make various bismaleimides. This paper discusses improvement of the friction and wear properties of bismaleimide resin, by the addition of solid lubricant additives such as MoS2, graphite and PTFE.The bismaleimide tested has the following structure: magnified image On heating, bismaleimide cross links through its unsaturated bonds, thus producing a highly cross linked polyimide. The friction and wear measurements were done on a Plint friction and wear machine (pin on disc type), wherein polymer pins slid against a steel disc at different loads and speeds.The polymer itself had a high coefficient of friction, ranging from 0.3 to 0.6 and a higher wear rate. Solid lubricant additives helped in improving its friction and wear characteristics. The addition of graphite brought the coefficient of friction to 0.3 but wear remained high at high loads. Best results were obtained with additions to the resin of MoS2‐Sb2O3 and PTFE. Composites with MoS2‐Sb203 and PTFE had low coefficient of friction and low rate of wear, at low as well as at high loads. It appears that these solid lubricant additives transfer to the counterface, thereby reducing effective counterface roughness, hence reducing both friction and wear.

Investigation of the wear mechanism of carbon-fiberreinforced acetal

The friction and wear characteristics of acetal reinforced with 25 wt.% of randomly dispersed carbon fibers were investigated and compared with those of the base resin. The addition of carbon fibers to the polymer decreased the coefficient of friction and wear rate for the composite material sliding against a hardened and ground steel disk for extended periods of time. A number of surface topography parameters pertinent to the wear process, i.e. arithmetic average roughness, autocorrelation function, asperity density, tip radius of curvature, distribution of the radii of curvature and heights of asperity peaks, and ordinale heights, were calculated and evaluated for the sliding surface of the disk. The worn surfaces of filled and unfilled polymer pins were examined by scanning electron microscopy to investigate the probable wear mechanism for these materials. It was found that the wear of reinforced polymers proceeds by the pulling-out of the broken and worn fibers.

Friction and Wear of Semicrystalline Polymers Sliding Against Steel Under Water Lubrication

Two types of experiments were carried out in this work. In one experiment, the smooth steel sphere was slid on polymer plates at a very low speed. Water reduced to some extent or very much the friction of polymers. In another experiment, the polymer pins were rubbed against the stainless steel disk at various speeds. In the sliding of polymers on the disk without the transferred polymer, a slight reduction of friction generally occurred under boundary lubrication; however, it occurred clearly in some cases on the disk with the transferred polymer. In these experiments, surface roughness plays an important role in boundary lubrication with water. The wear of polymers increases generally under lubrication. The amount of polymer transferred under lubrication is similar to that transferred in the dry condition. However, the features of worn surfaces of polymers under lubrication are different from those in a dry condition. The mechanism of polymer wear under lubrication is discussed on the basis of these findings.

Estimation of wear particle thickness in polymermetal sliding

Sliding experiments between polymer pins and a steel disc were performed to study the size distributions of polymer wear particles with varying loads and also to estimate the thickness of these particles. Optical microscope examination of the loose wear particles revealed that they resembled a flattened ellipsoid in shape and their size was not strongly dependent on load. The thickness of the wear particles was estimated from an analysis based on a model in which the effect of both the normal and shear stresses on the junction as well as the surface energy of the particle material was considered. It was found that the thickness lies in a range the lower and higher values of which depend upon whether the particle escapes from the interface as soon as it is formed or is trapped between the sliding surfaces before it escapes from the interface.

Combined rotating and linear motion effects on the wear of polymers

The unusually low friction of polytetrafluoroethylene, PFTE, is utilised in many commercial applications1. Unfortunately this low friction is often accompanied by rather high wear, and it is generally necessary to modify the polymer, usually by the incorporation of solid inorganic filler particles, to reduce the wear to acceptable levels1,2. Although several attempts have been made to establish the mechanism of this improved wear behaviour, the optimisation of filler type, size and concentration remains an empirical exercise, and several relatively simple wear testing machines have been developed to assess prospective materials3,4. These tests attempt to reproduce the sliding conditions encountered in practice. A widely used test is the pin-on-disk configuration where a fixed pin of polymer is loaded against a rotating disk. The load and relative velocity are fixed and the pin describes a circular path over the disk surface for a pre-determined period, after which the wear is measured, generally by weighing the polymer pin. Important additional variables are the environment, the surface topography of the disk, the temperature and the geometry of the pin5. In the process of conducting such a series of measurements we have identified and report here an additional variable which may be of general importance: the radius, R, of the path described by the pin on the disk.