Lubricants continued

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

AMo MCTKFG UposaibS lubricant, container coatings McroKlear 418 Surfynol SM-740 Surfynol SM-745 lubricant, continuous Hm Rapeseed (Brasska canktesttis) oil lubricant, CR Nqpcowax 22-DS lubricant, dry film coalings DuPont Diy Film DuPont Diy Hhi 250/IRA DuPont Diy Fikn/IPA DuPont Diy FIm/W lubricant, dry film connectors MAC-480... 

Film stability is a primary concern for applications. LB films of photopoly-merizable polymeric amphiphiles can be made to crosslink under UV radiation to greatly enhance their thermal stability while retaining the ordered layered structure [178]. Low-molecular-weight perfluoropolyethers are important industrial lubricants for computer disk heads. These small polymers attached to a polar head form continuous films of uniform thickness on LB deposi-... 

The mercury-sealed stirrer may be replaced by a Kyrides stirrer (Fig. II, 7, 12) formed from a P.V.C. gland and lubricated with a mixture of vaseline and light paraffin. The continuous passage of nitrogen may be dispensed with if a fairly wide tube dipping into a little mercury is connected to the top of the condenser the latter serves to retain the nitrogen atmosphere. 

Smoke, Flash, and Fire Points. These thermal properties may be determined under standard test conditions (57). The smoke poiat is defined as the temperature at which smoke begias to evolve continuously from the sample. Flash poiat is the temperature at which a flash is observed whea a test flame is appHed. The fire poiat is defiaed as the temperature at which the fire coatiaues to bum. These values are profouadly affected by minor coastitueats ia the oil, such as fatty acids, moao- and diglycerides, and residual solvents. These factors are of commercial importance where fats or oils are used at high temperatures such as ia lubricants or edible frying fats. 

Fig. 2. Comparative temperature limits of mineral od and synthetic lubricant, where D represents continuous service U service dependent on starting...

Rust inhibitors usually are corrosion inhibitors that have a high polar attraction toward metal surfaces and that form a tenacious, continuous film which prevents water from reaching the metal surface. Typical mst inhibitors are amine succinates and alkaline-earth sulfonates. Rust inhibitors can be used in most types of lubricating oils, but factors of selection include possible corrosion of nonferrous metals or formation of emulsions with water. Because mst inhibitors are adsorbed on metal surfaces, an oil can be depleted of its mst inhibitor. In certain cases, it is possible to correct the depletion by adding more inhibitor. 

Except for fire-resistant fluids, synthetic lubricants have not captured a significant portion of the general lubricant or hydrauhc markets, primarily because the cost is two to four times that of other premium lubricants. However, development of satisfactorily formulated products continues. 

Phosphate ester fluids are the most fire resistant of moderately priced lubricants, are generally excellent lubricants, and are thermally and oxidatively stable up to 135°C (38). Fire-resistant iadustrial hydrauHc fluids represent the largest volume commercial use. AppHcations are made ia air compressors and continue to grow for aircraft use (tributyl and/or an alkyl diaryl ester) and ia hydrauHc control of steam turbiaes ia power generation (ISO 46 esters). 

The wide range of soHd lubricants can generally be classified as either inorganic compounds or organic polymers, both commonly used in a bonded coating on a matching substrate, plus chemical conversion coatings and metal films. Since solid-film lubricants often suffer from poor wear resistance and inabihty to self-heal any breaks in the film, search continues for improved compositions. 

Lubricating oil used in intermittent service must show the least possible variation in viscosity with respect to temperature and must be changed at frequent intervals to remove the foreign matter collected during service. The stabiUty of such oil is therefore of less importance than the stabiUty of oil used in continuous service for prolonged periods without renewal. Lubricating oil for continuous service must be extremely stable because the engines in which it is used operate at fairly constant temperature without frequent shutdown. 

Joints are stmcturaHy unique. They permit bodily movement and are bound together by fibrous tissues known as ligaments. Most larger joints are encapsulated in a bursa sac and surrounded by synovial fluid which lubricates the joint continuously to reduce friction. The skeleton is constmcted of various types of moveable joints. Some joints allow for no movement, such as those connecting the bones of the skull. Other joints permit only limited movement. For example, the joints of the spine allow limited movement in several directions. Most joints have a greater range of motion than the joints of the skull and spine. 

Sedimentation equipment can be divided into batch-operated settling tanks and continuously operated thickeners or clarifiers. The operation of the former is simple. Whereas use has diminished, these are employed when small quantities of Hquids are to be treated, for example in the cleaning and reclamation of lubricating oil (see Recycling, oil). Most sedimentation processes are operated in continuous units. 

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