Lubricants action

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

To facilitate and accelerate folding and crystallization of polymer chains, internal plasticizers are often added to PET to serve as crystallation promoters. Such additives are usually based on poly(ether ester)s. These plasticizers are liquids that are typically added at levels of 2-4 wt%. They reduce cycle time in injection moulding operations by increasing the rate of crystalline formation. They also plasticize the resin and act as processing aids by virtue of their lubricating action in the melt. On a molecular level, these plasticizers reduce the intermolecular... 

The problem- points in high-pressure machines are certainly the dynamic shaft- and piston-or plunger seals. Seals create special problems when they slide rapidly under high-pressure and if the fluid being sealed has no lubricating actions. Cyclic stress creates additionally fatigue problems in the seal. 

Evidently, fretting is worse in air than in an inert atmosphere.25 There is less damage in a humid atmosphere than in dry air since humidity can have a lubricant action, and the hydrated oxides are less hard than the dry oxides.25,90,93 Surfaces subjected to fretting wear have a characteristic appearance with red-brown patches on ferrous metals and adjacent areas that are highly polished because of the lapping quality of the hard iron oxide debris. 

It was suggested that "as in the case of M0S2" the oil-soluble compounds react chemically with the metal surface, giving a system including molybdenum, iron, suiphur and oxygen. As has been shown earlier, this comment is inaccurate. The oxidised condition in molybdenum disulphide lubrication represents the end of its useful life, so that this mechanism provides no explanation for the lubricating action of the oil-soiuble molybdenum compounds. 

While molybdenum disulphide lubrication is adversely affected by liquids, liquid lubrication can be improved by molybdenum disulphide. There is in fact a considerable industry based on the use of molybdenum disulphide in liquids, in dispersions, lubricating oils, greases, anti-seizes and pastes. There is an important contradiction in the fact that in many situations the lubricating action of molybdenum disulphide is either partly or completed destroyed by the presence of liquids, whereas in other situations it can provide useful lubrication benefits in a liquid medium. A great deal of effort has been applied in attempts to establish the mechanism and the conditions by which lubrication by molybdenum disulphide can occur in the presence of a liquid. 

Groszek, A.J. and Witheridge, R.E., Surface Properties and Lubricating Action of Graphite and M0S2, ASLE Trans., 14, 254, (1971). 

Tkachenko, Yu. G., Koval chenko, M.S., Yulyugin, V.K., Bovkin, G.A. and Yurchenko, D.Z., Lubricating Action of MoSj on Rubbing Sintered Materials, Soviet Powder Metallurgy and Metal Ceramics, 17, 552, (1978). 

The conservation of generated heat. ( ) The intensifying of the friction ajnd the reduction of the lubricating action. (5) The lowering of the ignition temperature. The condition (l) is concerned mainly with the method and (2),(3)i( ) and (5) with the device. 

To act as an effective lubricant in a tablet, the lubricant must be dispersed over the surface of the powder particles or granules. The more complete this layer, the more effective the lubricant action will be. However, this has two deleterious consequences. The first is that each powder particle presents a hydrophobic and hence water repellent exterior. It is well known that the presence of a lubricant based on fatty acids slows disintegration and dissolution, and has been shown to cause bioavailability problems. 

Lubricants based on fatty acids, because of their low water solubility, are unsuitable for tablets which must be dissolved in water before use. Polyethylene glycol 6000 (macrogol 6000) is soluble in water, but its lubricant activity is limited. Magnesium lauryl sulfate has been suggested as a water-soluble substitute for magnesium stearate. In addition to its lubricant action, this substance, like sodium lauryl sulfate, is an effective wetting agent. ... 

ZoandaAy lubAd.catd.on is a familiar term in the vocabulary of the tribologist. In the general concept of the boundary lubricated condition, the lubricant film between the two surfaces is no longer a liquid layer instead the surfaces are separated by films of only molecular dimensions. Friction is influenced by the nature of the underlying surface and by the chemical constitution of the lubricant films. This view of lubricating action at the solid surface was introduced by Sir W. B. Hardy [1] as an extension of Osborne Reynolds concept that hydrodynamic action within the liquid film is a process treated by continuum methods which are not applicable at the discontinuity or "boundary" between liquid and solid. 

TABLE 10-15. ENHANCEMENT OF LUBRICATING ACTION OF PARAFFIN OIL BY A PREDEPOSITED SULFIDE FILM ON STEEL... 

The basic mechanism of the critical temperature concept is simple. Lubrication failure is envisioned as occurring at the conjunction of the rubbing surfaces, and it is the critical temperature at this conjunction that controls the lubricating action. This temperature, T, is made up... 

Of the lamellar solids which do show lubricating action, the two most familiar to the lubrication engineer are molybdenum disulfide (M0S2) and graphite. The lubricant-grade M0S2 of commerce is made by processing... 

Figure 19-5. Effect of load and sliding speed on the lubricating action of molybdenum disulfide. From data by Haltner and Oliver [36].

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