18 polymers were characterized with respect to their friction and wear behaviour in contact with steel in environments of air and water. These were six unfilled materials, i.e. polyamide 66 (PA 66), polyoxymethyfene (POM), polyethyleneterephthalate (PETP), polyetheretherketone (PEEK), polyphenylenesuiphide (PPS) and polyethe~mide; also, the same base materials filled with poIytetrafluoroethylene (PTFE) or PTFE pIus glass fibre were used. Two types of experiments were performed, i.e. measurement of the coefficient of friction f as a function of the contact temperature T, ('f-Tc diagrams"), and measurements of friction and wear in 20 h tests. The f-Z'= diagrams were obtained in air; the 20 h tests were performed in air and in water at a temperature of 20 "C. In air the polymers ran against rings of ball-bearing steel (AISI 52100); in water the rings were made of stainless steeI (AISI 316). It turned out that in air addition of PTFE was generally beneficial; PA 66, POM, PETP and PEEK, all filled with PTFE, performed exceptionally well (specific wear rates k appreciably lower than 1 X lo-" m3 N-r m-'). In water, however, PTFE did not function at all. Now PA (with or without PTFE), unfilled POM and PETP filled with PTFE and glass fibre met the k < 1 x lO_" m3 N-r m-l criterion. With a few exceptions, addition of glass fibre produced unfavourable effects, in air as well as in water. The observed phenomena are explained tentativefy in terms of pofymer structures and transfer and wear mechanisms, whereby special attention is paid to the ratio of friction over strength.
SUMMARYThe friction properties and the well reproducible endurance limits of MoSr-lubricant films, prepared from the dry powder, were studied on rigs. Special consideration was given to : (i) automation of the rubbing-in process, (ii) the control of temperature and atmosphere, (iii) photographic recording of the friction surface.The influence of Physical factors was found to be similar to that known already for resin coated MO'& films. Life expectancy is dramatically shortened by certain chemical factors: (a) instantaneously scoring pairs of metals as substrates, and (b) mechano-chemical reaction with water vapour and with oxygen. In a neutral atmosphere the life of the lubricant film becomes very long.In a film of metallic lustre and under conditions of dynamic loading, blisters, ultimately of microscopic dimensions, are rapidly formed. Blistering can be enhanced by physical means, e.g. addition of amorphous carbon, or by oxidation. Prolonged oxidation leads to embrittlement and finally descaling of the MO& film from the substrate.
Friction experiments on lubricated concentrated contracts were performed to study; (a) the transitions between the different lubrication modes when operating in the lubricants liquid-state regime and (b) the frictional behavior of these contacts, under conditions of full-film lubrication, taking into account the lubricants liquid-state and solid-state behavior. On the basis of these results a flow diagram is presented for lubricated concentrated contacts, from which the lubrication mode as well as the frictional behavior can be obtained as a function of the operational conditions, under which these contacts are functioning.
The relationship between a Lubrication Mode Diagram (LMD) for concentrated contacts (LCC's) both decreasing with time. In references 1 , 2 , 3 and 6 , the influence of a great number of parameters (radius of curvature, viscosity, additives, roughness, etc.) on the transitions is described
The lubrication mechanism of fully submerged sliding point contacts of AISI 52100 steel has been studied as a function of surface roughness and oxygen content of the lubricant. Strong indications are found that, at relatively low values of normal load and sliding speed, a partial elastohydrodynamic lubricant film (incompletely) separates the surfaces. This film survives asperity contacts because newly formed contacts oxidize rapidly. Collapse of the lubricant film occurs if oxidation can no longer keep ahead of the formation of new asperity contacts. Increasing surface roughness and decreasing oxygen content of the lubricant both cause a reduction in load carrying capacity. Depending upon the value of the speed of sliding, collapse of the EHD film either leads to “incipient scuffing” or to severe wear (scoring). This effect is probably associated with a metallurgical transformation in the steel at a particular value of the conjunction temperature.
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