Proceedings of SerbiaTrib '13

esistance was found for composite containing 18vol. % of carbon and 7 vol. % of graphite (Figure1). The coefficient of friction values were from 0.11to 0.16 (Figure 2). This behaviour can be attributedto the presence of hard carbon particles, which areembedded within the matrix and impart additionalstrength to the composite. Wear testing and SEManalysis showed that three-body abrasion wasprobably the dominant mode of failure for PTFE +18 vol. % carbon + 7 vol. % graphite composite.Table 2. Composition (vol. %) of materialsDesignationSpecific wear rate, mm 3 /Nm × 10 –4AB109876543210MaterialPure PTFE75 % PTFE + 18 %amorphous carbon + 7 %hexagonal graphiteCharacteristic offiller material99 % pure PTFEpowderCarbon particles(diameter: 10 – 25μm); graphite flakes(size: 25 – 50 μm)C 85 % PTFE + 15 % E-glass E-glass fibres(diameter: 10 μm;D 75 % PTFE + 25 % E-glass length: 50 – 75 μm)5 N; 0.1 m/ssA B C DMaterialFigure 1. Average specific wear rate of PTFE and PTFEcomposites (adopted from [7])Coefficient of friction0.300.250.200.150.100.050.00ACBD0 200 400 600 800 1000Sliding distance, mFigure 2. Frictional behaviour of PTFE and PTFEcomposites (adopted from [7])Unal et al. [8] studied PTFE composites filledwith glass fibres (17 %), bronze (25 %) or carbon(35 %). Experiments were performed under loadrange from 5 to 30 N (0.18 – 1.06 MPa) and speedrange from 0.32 to 1.28 m/s. The results showedthat, for pure PTFE and its composites, thecoefficient of friction decrease with the increase inload. For the ranges of load and speed used in thisinvestigation, the coefficient of friction showedvery little sensitivity to the sliding speed and largesensitivity to the applied load, particularly at highload values. Figure 3 shows that sensitivity for thepure PTFE, but it is quiet similar for composites, aswell. Adding glass fibres, bronze and carbon fillersto PTFE were found effective in reducing the wearrate. The maximum reductions in wear rate andcoefficient of friction were obtained by PTFEreinforced with 17 % of glass fibres. The specificwear rate for PTFE + 17 % glass fibres was almosttwo orders of magnitude lower than for pure PTFE.By means of microscopy, it is noticed that thePTFE with glass fibre filler form a good thin anduniform transfer film which have positive influenceto the wear rate.Coefficient of friction0.300.250.200.150.100.050.000.32 m/s0.64 m/s0.96 m/s1.28 m/sPTFECoefficient of friction0.800.700.600.500.400.300.200.100.00PTFE5 N10 N20 N30 NFigure 3. Sensitivity of PTFE coefficient of friction tothe sliding speed (for 20 N load) and applied load (for0.32 m/s speed) (adapted from [8])A single influence of glass particles (25 vol. %;40 μm) and bronze particles (40 vol. %; 48 μm) onwear behaviour of PTFE based composites wasstudied by Mudasar Pasha et al. [9]. The tests weredone on a pin-on-disc tribometer with differentnormal loads (20 – 100 N, i.e. 0.2 – 1 MPa), slidingspeeds (1.5 – 5.5 m/s) and distances (500 – 2500m). The experimental results indicate that theweight loss increases with increasing load andsliding speed (Figure 4). The PTFE + 40 % bronzecomposite exhibits better wear resistance compareto the others (Figure 5). The transfer film formedon the counterpart surface, sliding against PTFE +40 % bronze, is smooth, thin and uniform, which13 th International Conference on Tribology – Serbiatrib’13 137