Up Time Magazine - February/March 2009 - (Page 31) often occur simultaneously, resulting in film collapse, machine component interaction and greatly increased frictional resistance. Surface Protecting Lubricant Additives – OEM’s and machine owners collectively recognize that conditions will cause the oil films to degrade and fail. Even though the oil film collapses, the machines will continue to run causing degradation of the machine surfaces. In order to protect the contact area of the lubricated surfaces, lubricant suppliers employ the use of a wide variety of chemicals intended to chemically bond to metal surfaces to create an organo-metallic boundary layer. Although these tarnish-like films are very thin they do offer protection from excessive wear, and prolong machine component lifecycles. The use of insoluble (solid film) lubricant additives provides another avenue for reducing frictional resistance from surface contact. Boric acid esters, Teflon, Molybdenum Disulfide and Graphic all have a well established track record for surface friction reduction. Energy conservation claims have been made by several high performance lubricant manufacturers, including Lubrication Engineers, Engineered Lubricant, Whitmore’s Lubricants, Royal Purple, Castrol Performance Lubricants, and several others. These companies create specialized additives that accomplish a variety of end results, including friction reduction from surface improvement. Most of these companies consider their additive technologies to be central to their survival and are tight-lipped about product composition, but there is no debating that there are additive agents that improve lubricity (the ‘slipperiness’ property) of the lubricant that then helps reduce energy consumption. Energy Consumption Influence of Base Oil Type and Weight – In markets that have federally mandated energy efficiency requirements, such as automotive engines and refrigeration systems, base oil and additive choices are heavily influenced by the material’s energy efficiency impact. It is widely known that oil viscosity directly influences energy consumption. As viscosity increases the amount of energy used to overcome viscous drag also increases. It is less well known that the type of base oil (molecular composition) influences energy consumption in a couple of ways. Some polar stocks, specifically esters and polyglycols, Figure 2 - All machine surfaces have a significant amount of roughness, and potential for frictional energy losses a few things to consider. The Nature of Machine Surfaces – Machine surfaces are rough. Figure 2 illustrates typical surface profiles for all machined surfaces. Even finely prepared bearing element and race surfaces exhibit undulations. As shown in Figure 3, machined surfaces have a wavelike profile. The average of the height of the ridges, value ‘r’, differs based on the OEM’s finish technique. Element bearing finishes will have maximum surface heights in the 0.2 micron range, and average heights in the 0.4 micron range (RMS). Ground gear finishes will have surface heights approaching three microns, and averages heights approaching 0.6 microns (RMS). Separating Machine Surfaces – The dynamic oil film thickness must always be greater than the heights of the combined surfaces in order to avoid frictional energy losses. The ideal condition would be an oil film that is three to five times thicker than the height of the combined surfaces. Component suppliers provide formulas and standardized tools that are useful in establishing minimum viscosity operating requirements. Reputable suppliers provide engineering support to their customers to help refine lubricant selections, and for most applications, the first run selections are not difficult. Inadequate film conditions occur as a consequence of changes in load, changes in machine operating temperatures, changes in lubricant condition (particularly contamination with gases or fluids), and accidents in lubricant handling and application, which lead to viscosity errors. These condition changes Figure 3 - Oil films must be greater than the combined maximum asperity heights to avoid contact and parasitic energy losses. www.uptimemagazine.com 31 http://www.uptimemagazine.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.