Influence of Re-adhesion on the Wear and Friction of Glass Fibre-Reinforced Polyester Composites

Based on the well-known pin-on-disc test rig, a new test setup for online measuring of wear and friction behaviour of polymer matrix composites has been developed. In contrast to a traditional friction-and-wear test rig, a steel pin and composite disc are used for studying the influence of wear debris and fibre orientation. During sliding, a thin adhesive film is possibly formed on the wear track of a composite disc, consisting of wear debris that is squeezed under the steel pin and that finally smoothens onto the composite surface. By optical microscopy, it was observed that most of the debris particles originate from the edges of the wear track. The thin film deforms continuously, with large and dark wear particles observed at the edge of the wear track. A lower coefficient of friction is achieved when the particles are re-adhered to the mating surface. The film formation mechanism depends on the normal force, sliding velocity, and bulk composite structure: because pultruded composite profiles are presently used with a layered structure, a change in film properties is observed depending on the wear depth.     

Influence of Re-adhesion on the Wear and Friction of Glass Fibre–Reinforced Polyester Composites

Based on the well-known pin-on-disc test rig, a new test setup for online measuring of wear and friction behaviour of polymer matrix composites has been developed. In contrast to a traditional friction-and-wear test rig, a steel pin and composite disc are used for studying the influence of wear debris and fibre orientation. During sliding, a thin adhesive film is possibly formed on the wear track of a composite disc, consisting of wear debris that is squeezed under the steel pin and that finally smoothens onto the composite surface. By optical microscopy, it was observed that most of the debris particles originate from the edges of the wear track. The thin film deforms continuously, with large and dark wear particles observed at the edge of the wear track. A lower coefficient of friction is achieved when the particles are re-adhered to the mating surface. The film formation mechanism depends on the normal force, sliding velocity, and bulk composite structure: because pultruded composite profiles are presently used with a layered structure, a change in film properties is observed depending on the wear depth.     

Thermal and spectroscopic analysis of worn polyoxymethylene surfaces and wear debris explaining degradation and polymerisation mechanisms

Degradation and polymerization of polyoxymethylene homopolymer (POM-H) surfaces after sliding at 8 to 150 MPa and 0.005 m/s over a total sliding distance of 3000 m is investigated by using thermal analysis (DSC, TGA, DTA) and Raman spectroscopy of worn surfaces or wear debris. There is mainly mechanical interaction and slight softening at 8 MPa (relatively high friction, low wear), softening at 16 to 55 MPa (decreasing friction and high wear) and finally melting at 150 MPa (very low friction, overload wear). At low contact pressures, wear debris remains amorphous and degradation of noncrystallised material during sliding manifests in broadening of the melting peak below the melting temperature. Degradation of C–O–C due to chain scission and radical reactions into CH₃ end groups are illustrated by Raman spectra. It is confirmed that the debris has long resident times and the maximum polymer surface temperature (T* = 93°C) is below the crystallisation temperature. At intermediate contact pressures, crystallisation results in a polymer fraction with higher thermal resistance. From the calculated temperatures T* = 120 to 150°C, crystallisation is beneficial for coherent transfer with larger particle sizes. At high contact pressures, the wear debris is immediately removed from the contact interface due to melting (T* = 200°C) and has thermal properties similar to the bulk material. There is no reaction between the debris in the interface, resulting in a thick polymer transfer film.     

On the efficiency of internal lubricants for polymers under different sliding conditions

When polymers are used as bearing materials or are processed over tooling under dry sliding conditions, the formation of a transfer layer at the interface controls friction and wear properties. The film formation may be enhanced by the addition of internal lubricants. This article reviews some effects of internal lubricants, such as graphite, polytetrafluoroethylene, and internal silicone oil, on the friction and wear of bulk polymers such as polyimide, polyester, and polyamide. Known lubricating mechanisms are complemented by an interpretation of tribophysical reactions in the sliding interface. Test results are obtained during small and large‐scale laboratory testing under high‐load and high‐temperature conditions and are further related to the effect of contact conditions. The study reveals that some lubricants are not effective under the entire range of sliding temperatures and/or normal loads. For internally lubricated polymers, the efficiency of internal lubricants strongly depends on the contact geometry. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers     

Insight into water lubrication performance of polyetheretherketone

Polyetheretherketone (PEEK) is a kind of polymer with excellent mechanical properties combined with good wear resistance and has been widely used in the engineering field. In order to explore the possibility for PEEK using as a water-lubricated bearing material, an in-depth study on the water lubrication performance of PEEK was conducted by using a series of experiments. The water lubrication performances combined with the lubricating mechanism were evaluated both by the friction coefficient and by the wear behavior of PEEK. The results indicated that PEEK was suitable for water-lubricated bearing productions. The water film could form effectively between the friction pairs under high sliding velocity, while the transfer film could form under low sliding velocity. Both the water film and the transfer film could improve the water lubrication performance for the friction pairs. Moreover, sliding velocities and contact pressures highly influence the water lubrication performance of PEEK. The increase in contact pressure or the decrease in sliding velocity would exacerbate the wear of material. The stick–slip phenomena also occurred on the specimens under low sliding velocity. The main purpose of this study is to provide an experimental basis for PEEK using as a water-lubricated bearing material.     

Tribological behavior of Kevlar fabric composites filled with nanoparticles

The friction and wear characteristics of ZnO‐ or montmorillonite‐nanoparticle‐filled Kevlar fabric composites with different filler proportions when sliding against stainless steel pins under dry friction conditions were studied, with unfilled Kevlar fabric composites used as references. The worn surface and transfer film of Kevlar fabric composites were then examined with a scanning electron microscope. It was found that ZnO and montmorillonite as fillers could improve the tribological behavior of the Kevlar fabric composites with various applied loads, and the best antiwear property was obtained with the composites containing 5 wt % ZnO or montmorillonite. This indicated that these nanoparticles could prevent the destruction of Kevlar fabric composites during the friction process. The transfer film established by these nanoparticles during the sliding wear of the composites against their metallic counterpart made contributions to reducing the friction coefficient and wear rate of the Kevlar fabric composites measured in the test. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microstructure,thermal, physico–mechanical and tribological characteristics of molybdenum disulphide‐filled polyamide 66/carbon black composites

With an objective to investigate the influence of molybdenum disulphide (MoS₂) on physico–mechanical and tribological properties of polyamide 66 (PA 66), was compounded with MoS₂ in the presence of carbon black (CB). The compounded material was injection molded to make test specimens to evaluate physico–mechanical, thermal, and tribological (wear, friction, and laser etching) characteristics. It was found that tensile strength, percentage elongation at break, and tensile modulus of PA 66/CB/MoS₂ composite increased linearly with increase in MoS₂ content. The impact strength of the PA 66 matrix increased from 37.2 to 43.2 J/m with an increase in MoS₂ content. The wear behavior of PA 66/CB/MoS₂ composites have been investigated under dry sliding conditions at different normal loads, sliding distances, and sliding velocities at room temperature. It was found that the introduction of MoS₂ in the presence of CB has certainly reduced the friction, wear behavior of PA 66 with improvement in laser etching resistance. MoS₂ could increase the adhesion between the transfer film and the counterface surface. The ability of the synergistic fillers in helping the formation of thin, uniform, and continuous transfer film would contribute to enhance the wear resistance of PA 66 composites. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Tribological properties of PTFE‐filled thermoplastic polyimide at high load,velocity, and temperature

The effect of 20 wt% polytetrafluoroethylene (PTFE) fillers on the friction and wear properties of thermoplastic polyimides (TP) are investigated, under dry sliding in line contact against steel under 50 to 200 N, 0.3 to 1.2 m/s, and 60 to 260°C. Besides the lubricating mechanisms of PTFE based on mechanical shear, the thermal and tribophysical interactions in the sliding interface are considered in this research by using thermoanalytical measurements, Raman spectroscopy, and calculating the maximum polymer sliding temperature T*. The effect of hydrolysis of the TP bulk material, causing high friction at 100 to 140°C, is covered by PTFE. A transition at pv‐values 2.2 MPa m/s (T* = 120°C) is due to thermally controlled sliding of PTFE, while a transition at pv‐values 3.2 MPa m/s (T* = 180°C) remains controlled by degradation of the TP bulk material into monomer fractions. The reduced coefficient of friction in the presence of PTFE leads to smaller degradation and orientation of the molecular back‐bone and side‐chains within the TP structure. The formation of a homogeneously mixed transfer film is only observed at 180 to 260°C. The PTFE forms a fibrillar structure during wear at high sliding velocities, while they wear as separate particles at high normal loads. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Friction and wear properties of polyimide matrix composites reinforced with short basalt fibers

Short basalt fiber (BF) reinforced polyimide (PI) composites were fabricated by means of compression‐molding technique. The friction and wear properties of the resulting composites sliding against GCr15 steel were investigated on a model ring‐on‐block test rig under dry sliding conditions. The morphologies of the worn surfaces and the transfer films that formed on the counterpart steel rings were analyzed by means of scanning electron microscopy. The influence of the short BF content, load, and sliding speed on the tribological behavior of the PI composites was examined. Experimental results revealed that the low incorporation of BFs could improve the tribological behavior of the PI composites remarkably. The friction coefficient and wear rate decreased with increases in the sliding speed and load, respectively. The transfer film that formed on the counterpart surface during the friction process made contributions to reducing the friction coefficient and wear rate of the BF‐reinforced PI composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

不同条件下环氧树脂的摩擦磨损性能研究

通过测试环氧树脂(EP)在干摩擦及水、300#液体石蜡润滑下的摩擦性能,考察了环氧树脂的磨损率与载荷和滑动速度之间的关系,并采用扫描电子显微镜对材料磨损表面进行了观察,对磨损机理进行了分析。结果表明,在不同条件下,环氧树脂磨损率有较大变化,石蜡润滑下的磨损率比干摩擦磨损率小2个数量级。干摩擦下EP的破坏是脆性断裂和剥落,水润滑下EP破坏是疲劳磨损,石蜡润滑下EP的破坏是塑性变形和剥层磨损。     

Tribological Behaviour of Electroless Ni-P Deposits Under Elevated Temperature

Electroless Ni-P (EN) coatings have already proven their aptness for improving the tribological performance of the base material. This is possible due to their high hardness, good wear resistivity and corrosion resistance. However, the performance evaluation of the EN coatings under high temperature or the assessment of their thermal stability is yet to be conducted. The present work deals with the study of tribological characteristics viz. friction and wear of EN coatings at elevated temperatures (100 °C, 300 °C and 500 °C) by varying the tribological testing parameters viz. applied load and sliding velocity. A detailed study of the tribological behaviour of the coating is undertaken individually for the as-deposited and heat treated samples. The results obtained are compared among each other and also with that of the room temperature (RT) tests of the coating. It is found that the friction coefficient (COF) and wear rate of EN coatings mostly increases with increase in load for all the test temperatures. However, for variation in sliding velocity, both COF and wear rate show a reverse trend. The as-deposited samples show lesser wear rate particularly at high temperature, which may be because of the in situ heat treatment received during the test. The asdeposited coatings yield better results especially when the test temperature is kept above or near the phase transformation temperature of the coating. The surface morphology, composition of coatings and crystalline structure are studied with the help of scanning electron microscopy, energy dispersed X-ray analysis and X-ray diffraction analysis respectively. The coating displays a nodular morphology and is amorphous in the as-deposited phase.With heat treatment, the coating turns crystalline. A mixed adhesive and abrasive wear mechanism is observed for the EN coatings tested at elevated temperature. Adhesive wear is accompanied by micro-cracks. Tribo-oxidation is confirmed from energy dispersive X-ray spectrometry.     

The effect of steel fiber orientation on frictional properties of asbestos-free friction materials

The frictional properties of the composites reinforced with continuous steel fibers have been evaluated in LNBR modified phenolic resin based friction materials. The fiber orientations are introduced regarding the sliding direction, i.e. parallel (P) along the fiber direction, normal (N) and antiparallel (AP). The specific wear rates are increased if the sliding path is shifted from the P to the AP and N direction. The coefficient of friction is also dependent on the fiber alignment directions. The coefficients of these materials fall in the range of 0.49 to 0.54. The initial sliding interaction is plowing action if the turnplate temperature is below 250°C. Meanwhile, with the increase of the temperature, as ironed transfer film developed on the specimen, the interaction became adhesive and steady-state friction is established. The wear resistance of the composite is found to relate to the stability of the film.     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effects of lubricating‐oil additives on the friction and wear properties of polymers and their composites sliding against steel under oil‐lubricated conditions

The effects of lubricating‐oil additive zinc dialkyldithiophosphate (ZDDP) on the friction and wear properties of polymers and their composites sliding against GCr15 bearing steel were studied by using an MHK‐500 ring‐on‐block wear tester (Timken wear tester). Then the frictional surfaces of the friction pairs were examined by using electron probe microanalysis (EPMA). Experimental results show that the ZDDP contained in liquid paraffin has little effect on the friction coefficients of the polyimide (PI) or polyamide 66 (PA66) against GCr15 bearing steel friction pairs compared with that under the lubrication of liquid paraffin, but it slightly reduces the friction coefficients of polytetrafluoroethylene (PTFE) or its composites against GCr15 bearing steel friction pairs. Under lubrication of liquid paraffin containing 2 wt % ZDDP, the ZDDP film absorbed on the frictional surfaces of the PTFE composites–GCr15 bearing steel friction pairs exhibits obvious antiwear properties; it greatly reduces the wear of pure PTFE and the PTFE composites filled with Pb, PbO, and MoS₂; and the wear of the PTFE composites can be reduced by one order of magnitude compared with that under lubrication of pure liquid paraffin. Meanwhile, the inorganic fillers Pb, PbO, and MoS₂ contained in PTFE have little effect on the absorption of ZDDP to the frictional surfaces, so they have little effect on the friction coefficients of the PTFE composites–GCr15 bearing steel friction pairs under the lubrication of liquid paraffin containing 2 wt % ZDDP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1240–1247, 2000     

Study on the tribological properties of porous sweating PEEK composites under ionic liquid lubricated condition

The tribological behaviors of novel porous Polyetheretherketone (PEEK) composites under 1‐hexyl‐3‐methylimidazolium tetrafluoroborate ionic liquid lubricated condition were investigated. The effect of sliding velocity and applied load on the sweating tribological properties and the stability of lubricating oil film was also studied. Results indicated that when the sliding velocity was 0.69 m/s and the applied load was 250 N, the friction coefficient and wear rate of the ionic liquid lubricated porous sweating activated carbon fiber/polytetrafluoroethene/PEEK composites showed the minimum values, were 0.0197 and 4.145 × 10^?15 m³/Nm, respectively. The friction coefficients fluctuated in a narrow range of 0.0162–0.0215. It was found that the porous sweating PEEK composites under ionic liquid lubricated condition showed good low‐friction and antiwear performance, especially under the condition of high sliding velocity and applied load. The formed transfer film due to the tribo‐chemical reaction as well as boundary lubricating film is effective in improving the carrying capacity and antiwear properties of the porous sweating PEEK composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40989.     

采油螺杆泵衬套橡胶摩擦磨损性能分析

对MPX-2000型磨损试验机进行改造并设计了专用夹具,利用金属圆环与衬套橡胶盘状试样在油水介质和油水砂介质中进行螺杆-衬套副的磨损模拟试验,测定衬套橡胶在不同法向载荷和滑动速度条件下的摩擦因数和磨损量。结果表明,衬套橡胶试样在油水和油水砂介质中的摩擦因数随法向载荷的增大而减小,随滑动速度的提高先增大后有所减小,而磨损量随法向载荷的增大而增加,随滑动速度的提高而减小。衬套橡胶试样在油水介质中的磨损主要表现为摩擦机理,而在油水砂介质中则主要表现为摩擦机理和湿磨粒磨损机理。     

Effect of nanometer SiC filler on the tribological behavior of PEEK under distilled water lubrication

The composites of polyetheretherketone (PEEK) filled with nanometer SiC of different proportions were prepared by compression molding. The tribological behaviors of the composites under lubrication of distilled water were investigated and compared with that under dry sliding, on an M‐200 friction and wear test rig, by running a plain carbon steel (AISI 1045 steel) ring against the composite block. The worn surfaces of nanometer SiC filled‐PEEK and the transfer film were observed by means of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). As the results, nanometer SiC as the filler greatly improves the wear resistance of PEEK under dry sliding and distilled water lubrication, though the composites show different dependence of wear resistance on the filler content. Nanometer SiC‐filled PEEK showed signs of slight scuffing under distilled water lubrication, while a thin, uniform, and tenacious transfer film was formed on the surface of the counterpart steel ring. On the contrary, unfilled PEEK under lubrication of water showed signs of severe plowing and erosion, while the worn surface of the counterpart ring was very rough, and a discontinuous PEEK transfer film was formed. Thus, the different friction and wear behaviors of unfilled PEEK and nanometer SiC‐filled PEEK can be attributed to the different characteristics of the corresponding transfer films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 609–614, 2000     

Friction and wear behaviors of several polymers under oil-lubricated conditions

The friction and wear properties of polytetrafluoroethylene (PTFE), polyimide (PI), and polyamide 66 (PA66) sliding against GCr15 bearing steel under both dry and oil-lubricated conditions were studied by using an MHK-500 ring-block wear tester (Timken wear tester), and then Stribeck's curves of PTFE, PI, and PA66 under lubrication of the oil were given out. The worn surfaces of these polymers and the transfer films formed on the counterfaces were examined by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that the friction and wear-reducing properties of PTFE, PI, and PA66 can be greatly improved by lubrication with liquid paraffin, and the friction coefficients can be decreased by 1 order of magnitude compared to those in dry friction condition. Under lubrication of liquid paraffin, the friction coefficients of PTFE, PI, and PA66 decrease with the increase of load, but the wear increases with the increase of load. The variations of friction coefficients with load for PTFE, PI, and PA66 under lubrication of liquid paraffin can be described properly by the Stribeck's curves, as given out in this article. Under higher loads and sliding speeds in liquid paraffin lubrication, the friction and wear reducing properties of PA66 are the best, and those of PTFE are the worst; therefore, PA66 is also very suitable for applications in oil-lubricated conditions. Meanwhile, SEM and optical microscope investigations show that the wear and transfer of PTFE, PI, and PA66 can be greatly reduced by lubrication of liquid paraffin, but they still take place. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2175–2182, 1998     

Friction and wear mechanisms of PA66/PPS blend reinforced with carbon fiber

The mechanical and tribological properties of carbon fiber (CF) reinforced polyamide 66 (PA66)/polyphenylene sulfide (PPS) blend composite were studied in this article. It was found that CF reinforcement greatly increases the mechanical properties of PA66/PPS blend. The friction coefficient of the sample decreases with the increase of CF content. When CF content is lower (below 30%), the wear resistance is deteriorated by the addition of CF. However, the loading of higher than 30% CF significantly improves the tribological properties of the blend. The lowest friction coefficient (0.31) and the wear volume (1.05 mm³) were obtained with the PA66/PPS blend containing 30% CF. The transfer film and the worn surface formed by sample during sliding were examined by scanning electron microscopy. The observations revealed that the friction coefficient of PA66/PPS/CF composite depends on the formation and development of a transfer film on the counterface. The abrasive wear caused by ruptured CFs (for lower CF content) and the load bearing ability of CFs (for higher CF content) are the major factors affecting the wear volume. In addition, the improvements of mechanical properties, thermal conductivity, and self‐lubrication of bulk CFs are also contributed to the wear behavior of PA66/PPS/CF composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Friction coefficient and wear resistance of a modified polypropylene impregnated with different oils

The aim of the study was to determine the changes in the sliding friction coefficient and wear mechanism of PP impregnated by oils with respect to the unmodified PP under dry sliding conditions. The study showed that the impregnation of the PP clearly influenced the wear rate of PP and its friction coefficient. During the test, the wear behavior of the unmodified and impregnated polypropylenes was investigated using ASTM G77-98 standard wear test equipment in which the specimens were worn by counter sample made by steel 100Cr6. The recording program of the test system enabled the visualization and registration of the following parameters: specimen rotation and load value, linear wear of specimen, friction coefficient, and temperature of specimen and environment. The wear of the specimens was evaluated by weight loss and their wear mechanisms were investigated using scanning electron microscopy. The predominant wear mechanism between a polymer and steel was adhesion. However, at the high sliding velocity, when a higher temperature was generated, the predominant mechanism of wear was thermal wear. Impregnation of PPs moved the thermal wear into the higher sliding velocity values and caused better resistance of the PPs to melting and plastic flow. The most important finding of this investigation was that impregnation of PPs improved their tribological properties at a low value of load represented by the sliding velocity.