Friction, wear and abrasion

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. 

Wear factor is a proportionality parameter related to the wear of a non-lubricating surface against a mating surface below the PV limit of the material. Equation (3.2) shows the calculation of wear rate of a material. 

Abrasion resistance is usually measured by the Taber Test procedure described by ASTM D1044. Abrasion resistance of unfilled semicrystalline polymers is linked to the degree of crystallinity that is itself related to the molecular stmcture and weight of the resin and its processing. Table 3.54 includes the results of testing two types of perfluoroalkoxy polymers, PFA and MFA, and ECTFE. Notice the large difference between wear index (weight loss by abrasion in 1000 cycles) of ECTFE which is a partially 

Velocity, ft/min Wear Factor, [(cm -min)/(N m min)] x 10 Dynamic Coefficient of Friction Duration, hr 

Mating Surface (Finish of 406 nonometers) Pressure, MPa Velocity, cm/sec Wear Factor, 10 in min/ftlb.hr  

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