Machinery's Handbook, 31st Edition
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Oil Additives Table 6. Properties of Common Lubricant Solids Additives
Average Particle Size
Moisture Sensitivity
Solid Additive Molybdenum Disulphide
Color Load Capability Thermal Stability
Gray- Black > 100,000 (psi) < 750 ° F < 1–6 micron Detrimental Gray- Black < 50,000 (psi) < 1200 ° F 2–10 micron Necessary
Graphite
Polytetrafluoroethylene PTFE
White < 6,000 (psi)
No Effect
< 500 ° F < 1 micron
1 micron = 0.00003937 inch; 1 psi = 6.8947 kPa; Temp. in ° C = ( ° F – 32)/1.8 Solids additives shown in Table 6, can be added to both mineral and synthetic base oil stocks. In certain high temperature and high-pressure conditions, solids can be mixed with a mineral spirits carrier and applied directly to the bearing surfaces as a dry solid lubricant. The volatile carrier flashes off with the heat and leaves a dry solid film on the bearing surface. Synthetic-Based Oils.— Originally developed to cope with extreme high temperature sit uations encountered in early jet engines, synthetic based oil differs from mineral based oil in that its base stock is man-made. Using a polymerization similar to that used in plastics manufacturing, synthetic based oils are scientifically designed with identifiable molecu - lar structures, resulting in fluids with highly predictable properties. Synthetic lubricants deliver many advantages; their stability under severe high and low temperature operating conditions enables equipment to operate in extreme conditions with a high degree of reliability. Although there are many different synthetic base stocks, industry is primarily served by the following five common synthetic lubricant types. Poly-Alph-Olefins (PAOs): PAOs, Table 7, are often described as man-made mineral oils (synthesized hydrocarbons) and were amongst the first developed synthetic lubricants for popular use in automotive crankcase oils. They are formulated in a similar molecular structure to that of pure paraffin through the synthesis of ethylene gas molecules into a polymerized uniform structure. They have a wide range of uses that include crankcase oil, gear oil, compressor oil, and turbine oils. Table 7. Poly-Alph-Olefins (PAOs) Positive Features Negative Features Low pour point (down to –90 ° F or –68 ° C) Cost (4–8 × mineral oil cost)
High viscosity index, VI > 140 High viscosity range Good mineral oil compatibility Good seal compatibility Excellent corrosion stability
Poor additive solubility Poor biodegradability
Poly-alkylene Glycols (PAGs): PAGs, Table 8, are also known as organic chemical Ucon fluids that possess excellent lubricity and a unique property that causes decomposed or oxidized products to volatilize (clean burn) or become soluble, resulting in no sludge, varnish, or damaging particles to be formed at high temperatures. PAG’s are polymers of alkylene oxides and are used for compressor oils, hydraulic oils (water glygols), and severe duty gear oils.
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