Proceedings of SerbiaTrib '13

dispersion of the micro glass beads. The blackcarbon was added for both technological andtribological reasons.Table 1. The tested materialsConcentration [%, wt]Material symbol Micro glassBlackPBTPAbeadscarbonPBT 100 - - -GB10 88 10 1.5 0.5GB20 77.5 20 2 0.5The tests were done using a block-on-ringtribotester, functioning on a CETR tribometerUMT-2 Multi-Specimen Test System.The ring was the external ring of the taperedrolling bearing KBS 30202 (DIN ISO 355/720),having the dimensions of Ø35 mm × 10 mm andwas made of steel grade DIN 100Cr6, having 60-62HRC and Ra = 0.8 μm on the exterior surface.The block was manufactured by cutting partsfrom the bone samples, having the dimensions of16.5 mm × 10 mm × 4 mm.The tests were run in dry condition, forcombination (F, v), F being the normally appliedload (F = 1.0 N, F = 2.5 N and F = 5.0 N) and vbeing the sliding speed (v = 0.25 m/s, v = 0.50 m/sand v = 0.75 m/s). The sliding distance was thesame for all tests, L = 7500 m.For evaluating the mass loss of the blocks, ananalytical balance METTLER TOLEDO was used,having the measuring accuracy of 0.1 mg.The SEM images were done with the help of thescanning electron microscope Quanta 200 3D,having a resolution of 4 nm, a magnification×1.000.000.3. EXPERIMENTAL RESULTS3.1 Friction coefficientIn order to compare the three tested materials, theextreme values and the average value of the frictioncoefficient were graphically presented in Figure 1 asa function of the sliding speed and the normal load.These values (the lowest value, the highest value andthe average one) were calculated based on therecorded values during each test (sampling rate being10 values per second). Thus, it could be appreciatedthe stability of the friction coefficient by the size ofthe scattering interval and an average energyconsumption by the average value of the frictioncoefficient.For actual applications working under similarconditions of speed and load, the author wouldrecommend the materials with a smaller scatteringinterval and lower values of the average frictioncoefficient.The low loads and speeds produce a largerscattering interval for the friction coefficient, but theload and speed increase makes the frictioncoefficient diminish the average value and to narrowthe scattering interval. A research report from NASA[12] had evidenced high average values of thefriction coefficient of over 0.6, for three polymerssliding against steel (the tribotester: polymeric ballon steel disk).From these research reports and theexperimentally obtained data during this study, theauthors point out the importance of the laboratorytests for evaluating the friction coefficient and othertribological characteristics.0.80.6µ 0.40.200.80.6µ 0.40.200.80.6µ 0.40.20TBP10BG20BGF = 1 NTBP10BG20BGTBP10BGv = 0.25 m/s v = 0.50 m/s v = 0.75 m/sMaterialTBP01BG02BGF = 2.5 NTBP01BG02BGTBP01BGv = 0.25 m/s v = 0.50 m/s v = 0.75 m/sMaterialTBP10BG20BGF = 5 NTBP10BG20BGTBP10BGv = 0.25 m/s v = 0.50 m/s v = 0.75 m/sMaterialFigure 1. Variation of friction coefficient of PBT andcomposites with different micro glass beads content, forthe sliding distance L = 7500 m20BG02BG20BG114 13 th International Conference on Tribology – Serbiatrib’13