High coefficient of friction

Friction Materials. PhenoHc friction materials are made from mol ding compounds developed to meet the extraordinary demands required by friction elements in the transportation industries. Friction materials are used for brake linings, clutch facings, and transmission bands. A moderately high coefficient of friction, which is temperature-independent, is needed. In addition, the material must be high in strength, low in wear and abrasion, and resistant to moisture and hydrauHc fluids. 

SUicone elastomers have a relatively high coefficient of friction and the resulting lack of lubricity can cause pain and tissue damage on device insertion and removal. Therefore, the tissue side of the prosthesis must be smoothed, polished, and even also lubricated to eliminate friction. 

PPEs are handicapped by an inherent sensitivity to fire and to common chemicals, such as hydrocarbons, chlorinated solvents and concentrated mineral acids. They have rather high coefficients of friction and are slightly attacked by UV and weathering, requiring UV protection. The number of producers is limited. 

PPE has a high coefficient of friction and is generally not suitable for self-lubricating parts. 

Neat and glass fibre reinforced grades can be used for tribological applications with rather high coefficients of friction in a range from 0.3 up to 0.5. 

General-purpose grades have a high coefficient of friction, 0.35-0.45 for example, but special grades are marketed for tribological applications with coefficients of friction ranging from 0.15 up to 0.2. 

Moderate coefficient of friction and low wear rate. Medium performance bearing material. Wear accelerated by water. Relatively low temperature limit Performance similar to nylon. Durable in rolling contacts High operating temperature limit. Resistant to most chemical reagents. Suitable for high contact stress. High coefficient of friction in pure form... 

It is deduced that competitive adsorption between ZDDP and MoDTC onto the surface occurred during the run, because Mo concentration on the surface with ZDDP + MoDTC oil was lower than that obtained with the oil containing MoDTC alone. The adsorption of the additive on a surface results in formation of a film composed of the decomposition compounds or reaction compounds of the additives with the metal surface. The decline in the Zn/Mo atomic concentration ratio in the film composition with test time indicates that the decomposition products of ZDDP, which had a high coefficient of friction, were preferentially formed and subsequently, Mo compounds were formed. Similarly, an increase in the concentration of MoS2 with time was also observed. A necessary condition for the production of an effective surface film for reducing friction is the previous formation of the compounds derived from ZDDP. 

Friction Between Two Surfaces Answer the following questions or discuss statements (a) Two clean, highly polished steel surfaces when brought into contact appear to stick as if having very high coefficient of friction, (b) Would the dynamic coefficient of friction between steel and a polymer increase or decrease with increasing surface... 

Thick Aims, however, are associated with relatively high coefficients of friction. Those additives which are effective at reducing friction are ... 

Polymers with bulky side chains in their structure show relatively high coefficients of friction against glass and the transferred material consists of macroscopic fragments intermingled with thin-film regions. 

Titanium may appear to be the ideal metal, as its stiffness is the closest to bone (Table 1). It has the lowest density (nearly half that of the other two metals), and it has the highest resistance to corrosion due to the formation of a nonreactive layer of titanium oxide on the surface of the metal. However, its shear strength is low, making it unsuitable for use in screws and bone plates. It also has a high coefficient of friction when in contact with itself or another metal, making it unsuitable as a load-bearing surface. 

FIGURE 12.36 Effect of the coefficient of friction between bolted metal plates. (Above) High coefficient of friction the force is transmitted between the two surfaces in contact. (Below) Low coefficient of friction the force on the plates is transmitted as shear stress on the bolt. 

Consideration of properties discussed helps define areas of application. These areas are those which require elastomeric materials anchor high coefficient of friction which will not be subjected to excessively high temperatures. Uses for radial teleblock polymers generally fall into three categories ... 

This is an assessment of the coefficient of friction of material in terms of dynamic (sliding) friction against steel. It should be remembered that friction is influenced by temperature, surface contamination and most importantly by the two material surfaces. An excellent rating indicates a low coefficient of friction (see Table 5.1). A very poor rating indicates a high coefficient of friction. 

Dahlquist and Fregert (1979) Neonates Face, knees, dorsal toes 418 Babies nursed prone on sheets with high coefficient of friction. Change to textile with lowest coefficient of friction decreased symptoms to 30% (dermatitis partly due to alkaline remnants of detergents in the sheets)... 

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