Rubber friction properties

Miyata and Yamaoka [152] used scanning probe microscopy to determine the microscale friction force of silicone-treated polymer film surfaces. Polyurethane acrylates cured by an electron beam were used as polymer films. The microscale friction obtained by scanning probe microscopy was compared with macroscale data, such as surface free energy as determined by the Owens-Wendt method and the macroscale friction coefficient determined by the ASTM method. These comparisons showed a good linear relationship between the surface free energy and friction force, which was insensitive to the nature of polymer specimens or to silicone treatment methods. Good linearity was also observed between the macroscale and microscale friction force. It was concluded that scanning probe microscopy could be a powerful tool in this field of polymer science. Evrard et al. [153] reported coefficient of friction measurements for nitrile rubber. Frictional properties of polyacetals, polyesters, polyacrylics [63], reinforced and unreinforced polyamides, and polyethylene terephthalate [52] have also been studied. 

It has been shown that, with the help of irradiation, the incompatible PTFE surface can be functionalized to enhance its compatibility with rubber matrixes. A loading of 30 phr PTFE has been found sufficient to improve the mechanical and friction properties. Furthermore, the influence of radiation-induced free radicals and structural alterations on the properties of rubber compounds has been investigated. The radicals generated during irradiation are available for chemical coupling... 

An ISO standard for the frictional properties of rubber was published in 199937 and is probably one of the most comprehensive of friction standards. It is based on plane on plane geometry on the basis that rubber samples are most readily available in sheet form and for many applications measurement between two planar surfaces most nearly approaches service behaviour. 

Next 129Xe experiments on an EPDM terpolymer, which is present as the elastomer component in a composite material with carbon black will be discussed. The question investigated for these materials is whether the existence of any polymer-filler interaction can be detected by 129Xe NMR. This interaction influences the mobility of the elastomer chains in a relatively large shell around the filler particles. This fraction is called the bound rubber fraction. It is generally believed that the bound rubber fraction influences the mechanical and frictional properties of the filled elastomer [17, 18]. 

M.-R. Pourhossaini, M. Razzaghi-Kashani, Effect of silica particle size on chain dynamics and frictional properties of styrene butadiene rubber nano and micro composites. Polymer, ISSN 0032-3861 55 (9) (April 25, 2014) 2279-2284. http //dx.doi.0rg/lO.lOl6/j. polymer.2014.03.026. 

A large volume usage of S-B-S-based compounds is in footwear. Canvas footwear, such as sneakers and unit soles, can be made by injection molding. Frictional properties resemble those of conventionally vulcanized rubbers and are superior to those of the flexible thermoplastics, such as plasticized poly(vinyl chloride). The products remain flexible under cold conditions because of the good low temperature properties of the polybutadiene segment. 

These theories of rubber friction have at least two major defects in common. First they ignore the nature of the counterface the friction is apparently determined solely by the properties of the rubber. But is the friction of rubber on glass the same as rubber on P.T.F.E. Secondly they do not consider whether sliding takes place truly at the interface or within the rubber itself. 

Walters reached a similar conclusion from his experimental results. He obtained the friction-temperature relations at constant sliding speed. The temperature of maximum friction at a constant speed, increases linearly with the glass transition temperature. It appeared however, that in a graphical plot of the linear relation the point corresponding to the results obtained with butyl rubber falls distinctly outside the line. In our work with butyl rubber such an anomalous behaviour has been confirmed. Instead of relating the speed of maximum friction to Tg, Grosch related it to the frequency at which the loss modulus is a maximum. That correlation has been found to be valid to several rubbers includ ing butyl rubber. On the other hand, it is not surprising to expect that besides Tg, there are other parameters which have an important influence upon friction properties. 

In the forthcoming part, a quantitative theory will be given, which is perforce approximate on account of the reasons mentioned above. It still offers a clear picture of the process moreover it has been found to be useful in the prediction of frictional properties during the development of rubber compounds for specific... 

This paper describes the effect of velocity and temperature on the friction coefficient of both filled and unfilled rubber vulcanizates sliding on smooth ice. It has been shown that the mechanism of the friction of rubber on ice is the same as that on other smooth surfaces under similar low sliding speed conditions and that the maximum friction coefficients are similar. The Williams Landel and Ferry equation is used to superpose curves of the velocity dependence of the friction coefficient at different temperatures to produce a master curve and therefore to demonstrate the viscoelastic nature of the frictional mechanism. The frictional behaviour depends on the condition of the ice track and a tentative explanation for this observation is suggested. The frictional properties of vulcanizates containing various amounts of a reinforcing carbon black filler have been studied. 

Several ASTM standards give methods of pavement testing and methods of result calculation. A British pendulum tester is used to measure surface frictional properties. The pendulum slider is positioned in contact with the tested surface which was previously thoroughly cleaned and wetted. A rubber slider gliding on the surface causes a swing of the drag point, which increases with surface fiic-... 

Variable slip technique is used to measure the friction coefficient between tire and pavement. The test equipment consists of an automotive vehicle. Each test wheel contains a variable brake system. The resulting resistive force caused by friction between the tire and the pavement surface is sampled and recalculated to slip friction numbers. Frictional properties of pavement surface as a function of speed are measured by a d5mamic friction tester. A disk spins with its plane parallel to the test surface. The rubber sliders come into contact with the pavement, and torque is monitored when rotational velocity reduces, due to friction. A graph of friction vs. speed is plotted. 

Coefficients of friction of light conveyor belts are determined according to European standards. Metallic test panel under load, which generates together with panel normal force of 50 N, is pulled on the surface of test piece. Forces required to initiate movement and maintaining it are recorded and results used for calculation of static and d5mamic coefficients of friction. ISO, and identical British standard, " contain method of determination of frictional properties of rubber. 

BSISO 15113 1999,BS903-A61 2000 Rubber. Detemiination of frictional properties. 

In the absence of skidding, the coefficient of static friction applies at each instant, the portion of the tire that is in contact with the pavement has zero velocity. Rolling tire friction is more of the type discussed in Section XII-2E. If, however, skidding occurs, then since rubber is the softer material, the coefficient of friction as given by Eq. XII-5 is determined mainly by the properties of the rubber used and will be nearly the same for various types of pavement. Actual values of p, turn out to be about unity. 

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