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

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.

Simultaneous friction and wear reduction of Ni-P/PTFE composites under dry sliding condition

Purpose The purpose of this paper is to elucidate the tribology behavior of polytetrafluoroethylene (PTFE) incorporated with three types of nickel–phosphorus (Ni-P) particles (i.e. low phosphorus [LP], medium phosphorus [MP] and high phosphorus [HP]) under dry sliding condition. Design/methodology/approach Ni-HP, Ni-MP and Ni-LP particles fabricated via an electroless plating process were incorporated into PTFE matrix with different additions to prepare Ni-P/PTFE composites (Ni-LP/PTFE, Ni-MP/PTFE and Ni-HP/PTFE). The tribology tests for these samples were carried out on a reciprocating ball-on-disc tribometer. The thermal stabilities, mechanical and tribological properties, morphologies and components of aforesaid Ni-P/PTFE composites were analyzed. Findings The marvelous effect of Ni-P incorporation on the simultaneous reduction in friction and wear of PTFE was corroborated. Originality/value Compared with that of pristine PTFE sample, the reduction on friction with a value of 27% and the reduction in wear about 94% for Ni-HP/PTFE composite is validated, which is probably related to the increased crystallinity and hardness due to the presence of Ni-P particles.

Investigation of Snow Milling Mechanics to Optimize Winter Tire Traction

ABSTRACT A detailed understanding of effects occurring in the contact patch between tire tread and snow surface is needed to maximize tire grip in winter conditions. The main focus of this study is quantifying the snow milling effects of individual tire tread block elements during sliding. Tests are carried out using the high-speed linear friction tester (HiLiTe), located at the Institute of Dynamics and Vibration Research at Leibniz University of Hannover, Germany. Test tracks are prepared using artificially produced snow. To solely investigate snow milling effects and exclude material properties of rubber, in a first instance the tread block samples are made of polytetrafluoroethylene (PTFE). Because PTFE is at the same time rigid and hydrophobic, known friction mechanisms such as adhesion and hysteresis can be neglected, leaving only the tread pattern milling mechanics to transmit frictional forces to the snow track. The PTFE samples are shaped in such a way that they mimic the geometry of different siped rubber tread blocks under load, varying the sipes' number, shape, and tilt angle. Results show the benefit of multiple sipes and give information on the evolution of transmittable forces with respect to sliding distance. It is found that the block element shape and tilt angle are directly linked to the frictional force, showing a distinct optimum for specific angle and shape combinations. In addition, forces are not depending on sliding speed, but on sliding distance. The snow milling results of PTFE block elements are then compared to siped rubber block samples. Corresponding high-speed videos show that PTFE sample snow milling mechanics can be directly applied to rubber samples.

Effect of Material Thickness on Attenuation (dB) of PTFE Using Finite Element Method at X-Band Frequency

PTFE samples were prepared with different thicknesses. Their electric field intensity and distribution of the PTFE samples placed inside a rectangular waveguide were simulated using finite element method. The calculation of transmission/reflection coefficients for all samples thickness was achieved via FEM. Amongst other observable features, result from calculation using FEM showed that the attenuation for the 15 mm PTFE sample is −3.32 dB; the 30 mm thick PTFE sample has an attenuation of 0.64 dB, while the 50 mm thick PTFE sample has an attenuation of 1.97 dB. It then suffices to say that, as the thickness of the PTFE sample increases, the attenuation of the samples at the corresponding thicknesses increases.

Dynamics of Crystalline and Amorphous Polytetrafluoroethylene Studied by Multiple Quantum NMR

ABSTRACTWe report a new technique for probing polymer dynamics through the refocussing of multiple quantum (MQ) nuclear magnetic resonance (NMR) coherences. The MQ-NMR experiment follows the correlated behavior of multiple spin-1/2 nuclei interacting through dipolar couplings. Motion which modulates the dipolar coupling strengths on the same time scale as the experiment (∼1 to 20 kHz) alters the intensity of the observed coherences. Temperature dependent 19F data are presented on polytetrafluoroethylene samples of varying crystallinity. For the as-polymerized 98% crystalline PTFE sample, a sharp increase in MQ coherence refocussing occurs, centered at -298 K. The 64% crystalline melt-quenched sample shows a increase at the same temperature but which has a lower intensity. Thus, the ∼298 K peak is most associated with motion in the crystalline phase. This temperature is intermediate between the two first order transition at 293 and 303 K. Oscillations in the refocussed fractions are observed from 208 to 230 K for the 98% crystalline sample, while this ratio is constant over the same temperature range for the 64% crystalline sample. These oscillations may be associated with paracrystalline defects found only in the first sample. Thus, the MQ refocussing experiment is able to clearly differentiate between polymer samples which have different thermal histories. The sharpness of the MQ refocussing features and their variations in magnitude, shape, and sign with temperature are signatures of the molecular level details of the underlying dynamics which produce them.

Probing the Chemistry and Spectroscopy of Radiation-Sensitive Polymers by Parallel-Detection EELS

Investigation of neat polymers by TEM is often thwarted by their sensitivity to the incident electron beam, which also limits the usefulness of chemical and spectroscopic information available by electron energy loss spectroscopy (EELS) for these materials. However, parallel-detection EELS systems allow reduced radiation damage, due to their far greater efficiency, thereby promoting their use to obtain this information for polymers. This is evident in qualitative identification of beam sensitive components in polymer blends and detailed investigations of near-edge features of homopolymers.Spectra were obtained for a poly(bisphenol-A carbonate) (BPAC) blend containing poly(tetrafluoroethylene) (PTFE) using a parallel-EELS and a serial-EELS (Gatan 666, 607) for comparison. A series of homopolymers was also examined using parallel-EELS on a JEOL 2000FX TEM employing a LaB6 filament at 100 kV. Pure homopolymers were obtained from Scientific Polymer Products. The PTFE sample was commercial grade. Polymers were microtomed on a Reichert-Jung Ultracut E and placed on holey carbon grids.