Lubrication modes boundary

From an engineering standpoint, SF can be regarded as an aqueous electrolyte solution containing proteins, lipids and hyalnronic acid [12]. SF is also important for implants since a few weeks into the healing process, it surrounds the artificial joint. The predominant lubrication mode is in the mixed and boundary regimes [13]. In this study, we focus on the role of the most abundant protein in SF—human serum albumin (HSA). A screening study involving proteins and lipids was used... 

In examining the action of boundary lubricant compounds in reducing fi iction or wear or both between solids in sliding contact, it maybe helpful to consider at least the following five modes of fihn formation on or protection of surfaces (1) physisorption, (2) chemisorption, (3) chemical reactions with the sohd surface, (4) chemical reactions on the solid surface, and (5) mere interposition of a solid or other material. These modes of surface protection are discussed in more detail in Reference 2. 

Provided that a cutting fluid acts as a lubricant at the chip-tool interface, the problem is the mode of its access to this boundary. In all cases, the fluid must penetrate down the interface in a directirMi opposed to the motion of the chip flow. There had been argument about the approach of the fluids through the chip-tool, and hence, the access from the sides of the tool or from the flank face was thought to be important. 

The action of lubricant additives has been analysed under boundary lubrication on metal couples of Cr-bearing steel plates and cast iron pins in reciprocating mode using model oil systems. Tribological parameters have been measured in addition to analyses of the wear films lubricated with different oils base oil, oil+ZDDP (Zinc Dialkyldithiophosphate), oil+ZDDP plus addition of Ca-sulphonate detergent and oil+MoDTP (Molybdenum Dithiophosphate). 

The modes of lubrication in metal-on-metal hip implants range frtnn boundary, mixed to fluid-film... 

For UHMWPE-on-metal/ceramic hip implants, the mode of lubrication is predominantly boundary. 

Much has been done [3,4,5,6] to reveal the mode of lubrication in such Joints through the measurement of friction in Joint simulators of increasing sophistication. Each simulator was capable of measuring the friction to high accuracy. The recorded values of friction were generally similar to those associated with mixed or boundary lubrication. When plotted in the form of a Stribeck curve, the friction factors revealed variations consistent with the expected characteristics for mixed lubrication, with suggestions of either boundary or fluid-film lubrication when relatively low or high viscosity lubricants were used respectively. 

It has been demonstrated elsewhere [10,13] that the mode of lubrication (boundary mixed fluid-film) plays a major role in determining the steady-state wear rate in metal-on-metal total replacement hip joints. 

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