Sliding load velocity, wear rate

Coefficient of friction is inversely proportional to pressure and proportional to velocity. Wear rate of fluoropolymers is proportional to load (/ ) and velocity (V). Combinations of pressure and velocity are defined where the material can be used, thus a FV limit is defined. Above this PV limit, the wear increases exponentially because of the heat that is generated as a result of motion. Generally, a polymer or its compounds can be characterized by PV limit, deformation under load, and wear factor. Wear factor or specific wear rate is defined as the volume of material worn away per unit of sliding distance and per unit of load. 

The search for complete understanding of friction properties led to the methods (17), (18) accounting for the combined effects of the main factors. Prom Ref. (l ) relations are found for the friction coefficient, temperature, wear rate versus sliding velocities and loads. Then by the data obtained, a set of curves is drawn in P — V coordinates, having the same values of the friction coefficient, temperature, and wear rate. It is clear that great difficulties arise in obtaining and using this volume of information. Crease (j ) finds only... 

Similar tests are conducted for all the rest ranges of sliding velocities. The test results are presented as curves from which a complex of loads and velocities is selected that corresponds to wear rate of 25 after 100 h opera-... 

Figure 3. Wear rate dependence on load and sliding velocity.

The friction joint has been tested using a shaft on a bush friction machine with 2cm friction area, 0.35 MPa load and 2.4 m/s sliding velocity. A 40-mm-diameter shaft has been made of a carbon steel of 40-45 HRC hardness and 0.8-1.0 xm surface roughness. The outer bush material was aluminum, the inner was copper, the polymer layer was 200-p.m-thick PVB. A 0.1 N solution of NaCl was fed into the friction zone, the wear rate was determined by weighing. The test results are presented in Table 4.7. 

Wear tests were carried out at room temperature imder dry condition. Normal load values of 0.98, 1.96, 2.94, 3.92, and 4.9 N were used. Sliding velocity was fixed at 0.02 m/s, and the sliding distance was 120 mm. Wear of the pin was measured by a gravimetric method using an electronic balance at a 0.0001 g precision. Each worn surface was measured with a profilometer after the wear test to obtain profiles normal to the direction of friction. The profiles were used to calculate the wear rate. The wear rate, w, is defined as w = V/L, where V is the wear volume and L is the sliding distance. Each point of the diagrams from the experimental results is an average of five tests and measiu-ements. 

Figure 6. Specific wear rate (Ws) of T-BFRP composite vs. sliding distance at different applied loads and 2.8 m/s sliding velocity under dry/wet contact conditions.

Figures 20.8 and 20.9 show the fiiction coefficient and specific wear rate variation of pure PTFE and PTFE/nanoserpentine composites as a function of shding velocity under a normal load of 2.85 MPa for 60 min. Despite the reversed U shape of the friction coefficient variation for pure PTFE, it is evident that the change of sliding velocity has no significant effect on the friction coefficient of both materials, especially for the PTFE/nanoserpentine composites. In aU wear tests, the friction coefficient of materials varies from 0.090 to 0.114. As for the wear resistance of...

A pin on flat apparatus (Fig. 2) was used to measure wear rate under concentrated contact and reciprocating motion. The square plate is made of alumina, zirconia or alumina/zirconia nanocomposite ceramics. The pin of medical grade alumina had an end face with 10 mm spherical radius. The lower plate oscillates while the vertical load is applied to the pin by dead weights. Friction force is measured with strain gauges attached to the double leaf springs. Applied load is 30 N, oscillation frequency is 2 c/s, stroke is 10 mm and mean sliding velocity is hence 40 mm/s. Wear test was performed in 30 vol.% bovine serum solution kept at 37 °C. Wear volume of the pin was calculated from the area of the wear surface while the wear volume of the disc was calculated by the weight loss. 

Reply bv the Authors At high humidity conditions the wear rates decreased. The decrease in wear rates started at higher relative humidity levels as the load and sliding velocity increased. The Fig. 6 in the paper summarized the effect of humidity on the wear rates of the coating for different loading conditions. 

Fig. 12. Transfer film formed on abraded steel (AISI 02 tool steel) surface (i a = 0.11 fim) as a result of dry sliding (a) unfilled and (b) filled PEEK after 70,000 cycles of sliding. The filled specimen had 25 vol% of CuS + 10 vol% of PTFE. The unfilled PEEK specimen does not show uniform film formation and, in contrast, the filled specimen forms uniformly covered film on the steel counterface. The tests were conducted on a pin-on-disk apparatus with 63 mm track diameter, sliding velocity 1 m/s and a normal load of 19.6 N (pressure 0.654 MPa). There was about 90% reduction in the wear rate as a result of transfer film formation, while the coefficient of friction for the composite was higher ( 0.43) in comparison to that for the virgin PEEK ( 0.4) (75). It was concluded in this work that first Cu atoms are formed as a result of reduction of CuS during the sliding interaction. Then fluorine atoms in the PTFE molecules react with Fe atoms of the counterface in the presence of Cu and thus forming FeF2. This chemical reaction helped in the formation of strong transfer layer on the counterface which was not possible for the case of PEEK with CuS (40 vol%) alone without the presence of PTFE molecules. Reprinted from Ref. 75, copyright 1995, with kind permission om Elsevier Science.

All friction and wear testing was performed using a pin-on-dlsk machine ( ). A 3.175 mm diameter AISI 52100 steel ball was loaded, using a pneumatic device, against the polylmide film which was rotated at a rate to give a sliding velocity of 0.628 m/s. The ball was commercially lapped to a surface roughness of... 

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