Effects of impregnating PTFE filled with added graphite on wear behavior of sintered bronze plain bearings

Abstract

In this study, self-lubricating porous bronze plain bearing samples were manufactured differently from conventional plain bearings and the wear behaviours were investigated. Plain bearing samples were manufactured by sintering of pre-alloyed spherical CuSn11 bronze powders with grain size of 100– 200 μm. Then, special polymeric composite mixtures were prepared as PTFE (polytetrafluoroethylene) and graphite (GR) additive PTFE mixtures. The GR additive PTFE mixtures were prepared by addition of the GR powder with an average particle size of 200 μm at ratios of 10 wt.% and 20 wt.% into the PTFE solution. Next, the polymeric composite mixtures were impregnated into the porous structure of samples by the spray pulverization coating method. The purpose of the impregnation process was to minimise wear at a longer sliding distance by the gain of self-lubricating property to the samples. The plain bearing samples were produced as three different types (PTFE, PTFE + 10% GR and PTFE + 20% GR). Wear tests were carried out using a plain bearing test rig at different sliding speeds (0.5, 1.0 and 1.5 m s–1) and under applied loads (30, 50 and 70 N). Wear values were determined as weight loss of the samples. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used for the wear analysis of the samples. The results show that the mixtures of PTFE with GR significantly reduced the wear loses of plain bearing surfaces under dry sliding conditions. The PTFE + 10% GR sample had the lowest wear loss under 0.5 m s–1 sliding speed and 30 N applied load conditions after 2.5 hour in comparison with other samples. In other words, the PTFE + 10% GR sample showed lower wear than (31.25%) PTFE sample (without GR additive) and (2.65%) PTFE + 20% GR sample. Also, the wear loss of the PTFE + 20% GR sample (3.67 mg) was slightly increased (difference 1.27 mg/53%) compared to the PTFE + 10% GR sample (2.40 mg) under average load and sliding speed conditions.

Augmented multi-scale instrumented indentation test characterization of complex multi-layered coatings for tribological application

“…However, despite the wide application of this class of coatings, a thorough characterization of the mechanical behaviour of PTFE-based metal-polymer composite coatings with reinforcing low-friction metal structures is still missing. Some research papers have been published on this topic, but only application-oriented tribological results were presented [3,4].…”

“…Dynamic indentation allows evaluating viscoelastic properties of the material in terms of the loss modulus E '' and the storage modulus E ' , whose evaluation is essential to provide a thorough evaluation of polymeric materials also apt for damping [16,17]. Instrumented indentation test will be performed with an Anton Paar STeP6 platform equipped with the measuring heads NHT 3 and MCT 3 hosted in the metrological room at the MInd4Lab laboratory of the Politecnico di Torino.…”

“…PTFE+Pb characterization. The layer of PTFE+Pb was mechanically characterized by Anton Paar NHT 3 . Quasistatic indentation cycles (loading and unloading of 30 s, holding of 10 s) at 10 mN mapped an equally spaced grid of 7×7 indentions with a step of 90 µm.…”

“…In fact, the PTFE+Pb has a resistivity greater than the sintered bronze layer. A set of 36 CMC indentations were performed with Anton Paar MCT 3 , each featuring 15 cycles with a quadratic increase of the maximum load from 0.5 N to 30 N and with the loading, holding and unloading each lasting 30 s. A further set of 18 CMC indentations ranging from 0.01 N to 0.5 N (other parameters were left the same) was performed to get data at shallow depths. ECR was set up in controlled current at 10 mA with a maximum voltage of 6 V to avoid sparks.…”