Pour point grease

One hquid in this class intended for aircraft engine use is described in military specification MIL-L-87100 for operation from +15 to 300°C. Limitations of this class of synthetics are pour points of +5°C and higher, relatively poor lubricity, and high cost of 265/L ( 1000 + /gal) (44). Polyphenyl ether greases are available with good radiation resistance for appHcations in the temperature range of +5 to 288°C. 

Branched-chain acids have a wide variety of industrial uses as paint driers (7), vinyl stabilizers (8), and cosmetic products (9). Cobalt and manganese salts of 2-ethyIhexanoic acid and neodecanoic acid are used as driers for paint, varnishes, and enamels litbium, magnesium, calcium, and aluminum salts of 2-ethyIhexanoic acid are used in the formation of greases and lubricants (see Driers and metallic soaps). Derivatives of isostearic acid have been used as pour point depressants in two-cycle engine oils, as textile lubricants, and in cosmetic formulations. Further industrial appHcations can be found (10). 

More recent developments in this country have included synthesis of relatively stable oils of low volatility, low pour point, and high viscosity index by esterification of octyl alcohols, such as 2-ethylhexanol, with dibasic acids such as adipic acid and sebacic acid (3). Octyl alcohols may be synthesized from petroleum hydrocarbons via the oxo process. Although of relatively high cost, these synthetic oils find general application in making greases for lubrication of antifriction bearings and instruments in aircraft. 

The standard tests used to determine the properties of petroleum and petroleum products are commonly applied to grease. Among these are aniline point (ASTM D-611), carbon residue (ASTM D-189,ASTM D-524, ASTM D-4530, IP 13, IP 14, IP 398), fire point (ASTM D-92), flash point (ASTM D-92), pour point (ASTM D-97), and viscosity (ASTM D-445). However, because of the complexity of grease formulations and the variety of uses, many other tests are also deemed necessary to estimate performance in service. Other tests not included in this chapter may be found elsewhere under the test methods for lubricating oil (Chapter 12). Some modification of the test method may be necessary because of the different character of grease vis-a-vis lubricating oU. 

The lower cost dialkyl benzenes are used in a wide variety of industrial and metalworking products. In particular, their sulphur-free chemistry has led to extensive use as rolling and drawing oils for copper. The synthesised alkyl benzenes, even when their chemistry is optimised, generally exhibit poorer properties than PAOs. However, their excellent solvency and low pour point make them suitable for lubricants designed for extremely low-temperature operations in arctic greases, gear oils, hydraulic and power transmission fluids. 

At low temperatures, grease hardens, leading to poor pumpability and rheological properties. Typically the pour point of base oil is considered the low-temperature limit of grease. Below this temperature, the base oil will not flow properly and therefore will not provide sufficient lubrication. 

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