Pressure Velocity Values Research Articles

The effects of crystallinity on the mechanical properties and the limiting PV (pressure×velocity) value of PTFE

In this work, the effects of crystallinity on the LPV (short for the limiting PV) value and tribological behaviors were investigated under different surface roughness and velocities. The experiment results revealed that the one which had a higher degree of crystallinity exhibited higher mechanical and thermal properties, lower friction coefficient and higher LPV value. The wear resistance was enhanced with the increase of crystallinity in rubbery state, since larger energy was needed to break the links between crystallites. In the present study, LPV value of PTFE reached to 2.5Mpam/s under 2m/s. Surface roughness of 0.5µm was the very profile in this work, which exhibited the best performance with the lowest friction coefficient and highest LPV value under 1m/s.

Tribological properties of pitch-based 2-D carbon–carbon composites

The present study reports the tribological properties of various two dimensional carbon–carbon (C–C) composites composed of pitch coke reinforced with graphitized chopped PAN fiber and 8 H/S carbon yarn fabric. An experimental investigation was made of the effects of carbon fiber type, densification process parameters, kinetic energy loading, and friction surface morphology on the tribological properties of C–C composites. Experimental results indicate that heat treatment temperature of chopped carbon fiber, applied pressure during carbonization cycle, carbon fabric exposure on the friction surface, and kinetic energy loading strongly affect both the friction coefficient and the wear rate. The exposure of fabric filler at the friction surface was found to have a dominant effect on the increase of friction coefficient and wear rate. It was also found that the friction coefficient decreases but wear rate increases with increasing kinetic energy loading. Furthermore, the wear rate and friction coefficients are strongly dependent not only on the PV (pressure×velocity) value but also on the kinetic energy loading.

An experimental determination of kinetic friction for hardened dry steel pairs

The effect of pressure-velocity and time on the friction of selected metal combinations at sliding speeds of 22.3 and 54.4 ft min −1 was studied. A pin-disc friction machine was used and friction tests were conducted in which the pin traced a wear path (track) on the outside circumferential edge of the disc. The pressure-velocity value was varied by changing both the force on the pin and the angular velocity of the disc and was based on the Hertz contact pressure and area. The pressure-velocity values were 1.05 × 10 6 and 3.23 × 10 6 Ibf in −2 ft min −1. The specimen material combinations studied were Stellite and boronized and carburized steel pins in dry sliding contact with carburized steel discs. With increased sliding time, surface films were worn away, the real area of contact increased and the friction coefficient increased. The friction values indicated an approach to a steady state value, especially for the low pV tests. The friction coefficients for both pV values were significantly different for the three material combinations tested. The Stellite pin sliding on the carburized disc had the lowest kinetic friction coefficient and the carburized pin sliding on the carburized disc had the highest friction coefficient. The boronized pin sliding on the carburized disc exhibited an initial coefficient comparable with that in the carburized-on-carburized test. Steady state values from the boronized-on-carburized test were, however, significantly lower.