Life lubricants

Einally, at the end of their useful life, lubricants will be regarded as a valuable resource and re-refined/recycled into new lubricant products and fuels. Acceptance of recycled base stocks into new lubricant formulations will take time and require rigorous quality testing but will, and must, inevitably happen. 

Lubricants are included in PVC compounds—especially rigids— to control fusion and metal release. There are two extremes of lubrication internal and external. External lubrication mainly facilitates metal release. Internal lubrication aids fusion and also has similar effect on polymer chains as plasticization however, much less internal lubricant is added than plasticizer. Real-life lubricants have a spectrum of properties between these two poles. 

Because EP additives ate effective only by chemical action, their general use should be avoided to minimize possible corrosion difficulties and shortened lubricant life in any appHcation where they ate not necessary. For long-time operation of machines, conversion from boundary to hill-film operation is desirable through changes such as higher oil viscosity, lowered loading, or improved surface finish. 

Oils in Greases. Essentially the same type of oil is used in compounding a grease as would normally be selected for oil lubrication. Petroleum oils are used in about 99% of the grease produced and commonly are in the SAE 20—30 viscosity range with about 100 130 mm /s viscosity at 40°C. Such oils provide low volatiHty for long life at elevated temperatures (50) together with low torque down to subzero temperatures. 

Bonded Solid-Film Lubricants. Although a thin film of soHd lubricant that is burnished onto a wearing surface often is useful for break-in operations, over 95% are resin bonded for improved life and performance (62). Use of adhesive binders permits apphcations of coatings 5—20 p.m thick by spraying, dipping, or bmshing as dispersions in a volatile solvent. Some commonly used bonded lubricant films are Hsted in Table 12 (62) with a more extensive listing in Reference 61. 

Substrate Properties. It is clear from equation 5 that higher hardness of the substrate lowers friction. Wear rate of the film also is generally lower. Phosphate undercoats on steel considerably improve wear life of bonded coatings by providing a porous surface which holds reserve lubricant. The same is tme for surfaces that are vapor- or sandblasted prior to appHcation of the soHd-film lubricant. A number of typical surface pretreatments are given in Table 13 to prepare a surface for solid-film bonding (61). 

Under severe conditions and at high temperatures, noble metal films may fail by oxidation of the substrate base metal through pores in the film. Improved life may be achieved by first imposing a harder noble metal film, eg, rhodium or platinum—iridium, on the substrate metal. For maximum adhesion, the metal of the intermediate film should ahoy both with the substrate metal and the soft noble-metal lubricating film. This sometimes requires more than one intermediate layer. For example, silver does not ahoy to steel and tends to lack adhesion. A flash of hard nickel bonds weh to the steel but the nickel tends to oxidize and should be coated with rhodium before applying shver of 1—5 p.m thickness. This triplex film then provides better adhesion and gready increased corrosion protection. 

To overcome these difficulties, drilling fluids are treated with a variety of mud lubricants available from various suppHers. They are mostly general-purpose, low toxicity, nonfluorescent types that are blends of several anionic or nonionic surfactants and products such as glycols and glycerols, fatty acid esters, synthetic hydrocarbons, and vegetable oil derivatives. Extreme pressure lubricants containing sulfurized or sulfonated derivatives of natural fatty acid products or petroleum-base hydrocarbons can be quite toxic to marine life and are rarely used for environmental reasons. Diesel and mineral oils were once used as lubricants at levels of 3 to 10 vol % but this practice has been curtailed significantly for environmental reasons. 

Oxirane is used as a fumigant for grain and a sterilant e.g. for space vehicles bound for putative abodes of life), but mainly for the manufacture of 1,2-ethanediol ( ethylene glycol ), emulsifiers, plastics and resins (below), plasticizers, synthetic rubber and synthetic fibers. Methyloxirane is used mainly to make detergents, hydraulic fiuids and lubricants. 

So the support system serves to lubricate and cool the faces of the secondary seal while the first is performing its functions. The pressure applied to the support system governs the optimum life of the dual arrangement, and it also governs what happens when one of the two seals fails. 

Figure 13-9a shows the relative separation of the full-film, mixed-film, and boundary. If a full-film exists, the bearing life is almost infinite. The limitation in the case of full-film is due to lubricant breakdown, shock load, bearing surface erosion, and fretting of bearing components. Figures 13-9b and 13-9c are cross sections showing the various contamination types. Oil additives are contaminants that form beneficial surface films. 

As a part of the lubrication program, oil should be periodically tested. The testing requires drawing oil from the system for a laboratory analysis. The usual tests conducted to determine the condition of oils include viscosity, pH and neutralization number, precipitation, color and odor, and a check for foreign particles in the oil. The results should be reviewed and compared with new oil characteristics to determine the life characteristics of the oil. 

Some of the problems can be solved with specially selected oil grades. Another solution is synthetic oils, but cost is a problem particularly with silicone oils. Alternatives must be reviewed to match service life of the lubricant with lubrication requirements in the compressor. 

For chemical service, some lubrication qualities may be sacrificed in order to obtain a fluid compatible with the process gas. In these applications, alternate bearing materials such as graphite or silver have been required. While the requirements may make the operation somewhat special and require considerable care, the life of the compressor and service can be greatly improved. 

Several steps can be taken to maximize the run time for the reciprocating compressor. Since wear is a function of rubbing speed, the piston speed can be kept to a minimum. Chapter 3 made recommendations for piston speed. Reliability problems due to valves are reputed to account tor 40% of the maintenance cost of the compressor. Valves are the single largest cause for unplanned shutdowns. Basically, valve life can he increased by keeping the speed of the compressor as low as practical. At 360 rpm, the valves are operated six times a second. At 1,200 rpm, ihc valves operate 20 times a second or 1,728,000 times in a day. It is not difficult to understand why the valves are considered critical. To keep the reliability in mind, valve type, material selection and application considerations such as volume ratio, gas corrosiveness, and gas cleanliness need attention by the experts. One final note is that while lubrication is an asset to the rubbing parts, it is not necessarily good for valve reliability. 

Dispersion polymer, which leads to products with improved tensile strength and flex life, is not easily fabricated by the above techniques. It has, however, been found possible to produce preforms by mixing with 15-25% of a lubricant, extruding and then removing the lubricant and sintering. Because of the need to remove the lubricant it is possible to produce only thin-section extrudates by this method. 

There is persisting interest in nylon-RIM materials as alternatives to polyurethane-RIM. Advantages of the nylon materials are the better shelf life and lower viscosity of the reaction components, ability to mould thick-walled articles, absence of a need for mould lubrication and the ability to avoid using isocyanates with their associated hazards. The main disadvantages of nylon-RIM are the need to have heated storage tanks and elevated temperature reactions, difficulties in catalyst handling and the high water absorption of the product. Possible markets include exterior car body components and appliance and business machine components. 

Detector tubes should be refrigerated when not in use to prolong shelf life. They should not be used when cold. They should be kept at room temperature or in a shirt pocket for one hour prior to use. Lubrication of the piston pump may be required if volume error is greater than 5 %. 

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