Lubrication dynamic

The lubricant dynamics can alter the nanoscale aerodynamics of the slider. Conversely, the lubricant morphology and dynamics may be altered because of the presence of the slider. For these types of applications, a molecule-level understanding of the lubricant interaction with nanoscale airbearing and solid surfaces is critical. The HDD industry must cope with problems of lubricant film uniformity, roughness [5], durability [6], and stability [7] in order to achieve its goal of increasing areal density. 

Here, we adopted a spin analogy/lattice gas model, or SRS model, as shown in Fig. 1.28(a), which represents an oversimplified molecular structure yet still captures the essence of the molecule-surface interactions for describing SME profiles. Similar techniques using the Ising model to study other physical systems have been investigated [148,149,160] however, none of the literature deals with the simulation of PFPE lubricant dynamics described here. 

Figure 5 Plot of collapse velocity against lubricant dynamic viscosity for a film-thickness of 250 lx (tests 4, 5, 6).

III) For conditions when the lubricant dynamic viscosity was reduced by heating the supply oil, the collapse velocity was shown to Increase substantially. This Is consistent with the Influence of viscous forces expressed through the grouping (nU) and order-of-magnltude analysis has demonstrated that the other Important Influential film force at the Interface would be that due to surface tension. 

Figure 7.38 Lubricated friction test dynamic coefficient of friction versus ZN/P by thrust bearing test against steel with Sunvis 31 oil lubricant of DuPont Engineering Polymers Vespel SP-21—15% graphite-filled PI [9], ZN/P is the nondimensional parameter controlling lubricant film thickness. Z, lubricant dynamic viscosity N, revolutions P, contact surface pressure.

However, as with any lubricated, dynamically loaded, tribological components, the lubrication mechanism might well change throughout each cycle of operation and the search for a single mode of operation might be finitless or even misleading. 

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

Using friction attaclnnents (see section (bl.20.2.4)). many remarkable discoveries related to tiiin-film and boundary lubrication have been made with the SEA. The dynamic aspect of confined molecules at a sliding interface has been extensively investigated and the SFA had laid the foundation for molecular tribology long before the AFM teclnhque was available. 

The often-cited Amontons law [101. 102] describes friction in tenns of a friction coefiBcient, which is, a priori, a material constant, independent of contact area or dynamic parameters, such as sliding velocity, temperature or load. We know today that all of these parameters can have a significant influence on the magnitude of the measured friction force, especially in thin-film and boundary-lubricated systems. 

Dry Lubricant. The static and dynamic coefficients of friction for the parylenes are low and virtually the same. This feature is an advantage in the use of a parylene coating as a dry lubricant on the bearing surfaces of miniature stepping motors. Coating a threaded ferrite core significantly reduces the abrasion to coil forms (82). 

Unfilled Teflon PFA has been tested in mechanical appHcations using Teflon FEP-100 as a control (24). Tests were mn on molded thmst bearings at 689.5 kPa (100 psi) against AISI 1080, Rc 20,16AA steel, and at ambient conditions in air without lubrication. A limiting PV value of 5000 was found. Wear factors and dynamic coefficients of friction are shown in Table 4. 

Much confusion exists as to the best choice of lubricant additives for a given situation. Evaluation both in the laboratory and in the field is difficult because of the dynamic nature of the drilling fluid and the wide range of factors that influence drill string torque and drag. Liquid lubricants are used at concentrations of 0.25—4 vol %, soHd materials at ca 6—29 kg/m (2—10 Ib/bbl). 

Lubricity. In any mechanical seal design, there is rubbing motion between the dynamic seal faces. This rubbing motion is often lubricated by the fluid being pumped. Most seal mauufac turers hmit the speed of their seals to 90 ft/sec (30 m/sec). This is primarily due to centrifugal forces acting on the seal, which tends to restrict the seal s axial flexibihty. 

An important characteristic of biomolecular motion is that the different types of motion are interdependent and coupled to one another. For example, a large-scale dynamic transition cannot occur without involving several medium-scale motions, such as helix rearrangements. Medium-scale motions cannot occur without involving small-scale motions, such as side-chain movement. Finally, even side-chain motions cannot occur without the presence of the very fast atomic fluctuations, which can be viewed as the lubricant that enables the whole molecular construction to move. From the point of view of dynamic... 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

The hrst apparatus for nanotribology research is the Surface Force Apparatus (SFA) invented by Tabor and Win-terton [1] in 1969, which is used to study the static and dynamic performance of lubricant him between two molecule-smooth interactions. 

Lubricating Films Using Wedged Spacer Layer Optical Interferometry, Proceedings, 14th Leeds-Lyon Symposium on Tribology, Interface Dynamics, Leeds, 1988, pp. 275-279. 

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