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gas blanket - atmosphere of inert gas (usually nitrogen) lying above a lubricant in a tank and preventing contact with air. In the absence of such a covering , the lubricant would be subject to oxidation. Gas blankets are commonly used with heat transfer fluids and electrical insulating oil s.
Gas Bubble Separation Time of Petroleum Oils - the number of minutes needed for gas entrained in a steam turbine oil to reduce in volume to 0.2%, under the conditions of ASTM D 3427-75. Compressed gas is blown through the test oil , which has bee n heated to a temperature of 25, 50, or 75°C; measurement begins after the gas flow is stopped . See air entrainment.
gas chromatography - see chromatography.
gas engine - internal combustion engine, either two or four-stroke cycle, powered by natural gas or LPG. Comm only used to drive compressors on gas pipelines, utilizing as fuel a portion of the gas being compressed. Gas engine combustion chamber temperatures are typically hotter than in gasoline or diesel engines and thus have a greater tendency toward nitration (formation of nitrogen oxides, which can degrade the crankcase oil) and piston deposits (which can impair engine performance and damage engine parts.) Gas engine oils are specially formulated to control these tendencies. See engine deposits.
gasohol - blend of 10 volume percent anhydrous ethanol (ethyl alcohol) and 90 volume percent unleaded gasoline.
gas oil - liquid petroleum distillate, higher boiling than naphtha; initial boiling point may be as lo w as 204°C (400°F). Gas oil is called light or heavy, depend in g on its final boiling point. It is used in blending fuel oil and as refinery feedstock in cracking operations. See distillation.
gasoline (automotive) - blend of light hydrocarbon fractions of relatively high anti-knock value . Automotive , or motor , gasoline may consist of the following components: straight-run naphthas, obtained by the primary distillation of crude oil; natural gasoline, which is "stripped", or condensed, out of natural gas; cracked naphthas; reformed naphthas; and alkylate. (See alkylation , catalytic cracking, reforming). A high-quality gasoline has the following properties : (1) proper volatility to ensure easy starting and rapid warm-up; (2) clean-burning characteristics to minimize harmful combustion chamber deposits; (3) additives to prevent rust, oxidation, and deposits in carburetors, intake valves and fuel injectors;(4) sufficiently high octane number to prevent engine knock. See aviation gasoline.
gassing tendency - measure of an electrical insulating oil's ability to absorb hydrogen under electrical stress, as determined by ASTM D 2300B. An oil that evolves hydrogen has a positive gassing tendency, which is undesirable, since hydrogen can be hazardous under certain conditions.
gas turbine - see internal combustion engine, turbine.
gauge pressure - see pressure.
G.C. - gas chromatography.
gear - machine part which transmits motion and force from one rotary shaft to another by means of successively engaging project ions, called teeth. The smaller gear of a pair is called the pinion; the larger, the gear. When the pinion is on the driving shaft, the gear set acts as a speed reducer; when the gear drives, the set acts as a speed multiplier. The basic gear type is the spur gear, or straight-tooth gear, with teeth cut parallel to the gear axis. Spur gears transmit power in applications utilizing parallel shafts. In this type of gear, the teeth mesh along their full length, creating a sudden shift in load from one tooth to the next, with consequent noise and vibration . This problem is overcome by the helical gear, which has teeth cut at an angle to the center of rotation, so that the load is transferred progressively along the length of the tooth from one edge of the gear to the other. When the shafts are not parallel, the most common gear type used is the bevel gear, with teeth cut on a sloping gear face, rather than parallel to the shaft. The spiral bevel gear has teeth cut at an angle to the plan e of rotation, which, like the helical gear, reduces vibration and noise. A hypoid gear resemble s a spiral bevel gear, except that the pinion is offset so that its axis does not intersect the gear axis; it is widely use d in automobiles between the engine drives haft and the rear axle. Offset of the axes of hypoid gears introduces additional sliding bet ween the teeth, which, when combined with high loads, requires a high quality EP oil. A worm gear consists of a spirally grooved screw moving against a toothed wheel; in this type of gear, where the load is transmitted across slid- ing, rather than rolling, surfaces, compounded oils or EP oils are usually necessary to maintain effective lubrication.
gear box housing - casing for gear sets that transmit power from one rotating shaft to another. A gear box has a number of functions: it is precisely bored to control gear and shaft alignment, it contains the gear oil, and it protects the gears and lubricant from water, dust, and other environmental contaminants. Gear boxes are used in a wide range of industrial , automotive , and home machinery, e.g., paper mills, automotive transmissions, electric mixers. Not all gears are enclosed in gear boxes; so me are open to the environment and are commonly lubricated by highly adhesive greases. See open gear.
gear oil (automotive) - long- life oil of relatively high viscosity for the lubrication of rear axles and some manual transmissions. Most final drives and many accessories in agricultural and construction equipment also require gear oils. Straight (non-additive) mineral gear oils are suitable for most hypoid rear axles (see gear) and for some manual transmissions. Use of such oils is declining, however, in favor of EP (extreme -pressure) gear oils (see EP oil) suitable both for hypoid gears (see gear) and for all straight mineral oil applications. An EP gear oil is also appropriate for off highway and other automotive applications for which the lubricant must meet the requirements of Military Specification MIL-L-2105D.
gear oil (industrial) - high quality with good oxidation stability, rust protection, and resistance to foaming, for service in gear housings and enclosed chain drives. A turbine oil or R&O oil is the usual gear oil recommendation for non shock loaded reducers. Specially formulated industrial EP gear oils (see EP oil) are used where highly loaded gear sets or excessive sliding action (as in worm gears) is encountered. See gear, gear box.
gear shield - highly adhesive lubricant of heavy consistency, formulated with asphaltic compounds or polymers for protect ion of exposed gears and wire rope in circumstances where the lubricant cannot readily be replenished. Many gear shield lubricants must be softened with heat or cut back with solvents before they can be applied. See open gear, solvent cutback.
gear-type coupling - see.flexible coupling.
general purpose oils - see once-through lubrication.
Generation 5 lubricant - an LMOA-approved locomotive crankcase oil that meets critical OEM oxidation corrosion, and .friction tests and that has been successfully field tested in accordance with LMOA procedures, including I 00,000 mile s of operation and 1 8 0-day minimum drain intervals.
gilsonite - a naturally occurring asphalt min ed from rock fissures. It is hard and brittle, and has a high melting point. It is used in the manufacture of rust preventives, paints, sealants, and lacquers.
gloss - property of wax determinable by measuring light reflected from a wax-treated paper surface. Gloss stab ili ty is evaluated after a sample of treated paper has been held at an elevated temperature for a specified period.
gram calorie - see calorie.
graphite - a soft form of elemental carbon, gray to black, in color. It occurs naturally or is synthesized from coal or other carbon sources. It is used in the manufacture of paints , lead pencils, crucibles , and electrodes, and is also widely used asa lubricant, either alone or added to conventional lubricants.
gravure - see printing processes.
grease - mixture of a fluid lubricant (usually a petroleum oil ) and a thickener (usually a soap) dispersed in the oil. Because greases do not flow readily, they are used where extended lubrication is required and where oil would not be retained. The thickener may play as important a role as the oil in lubrication. Soap thickeners are formed by reacting (saponifying) a metallic hydroxide, or alkali, with a fat, fatty acid, or ester. The type of soap used depends on the grease properties desired. Calcium (lime) soap greases are highly resistant to water, but unstable at high temperatures. Sodium soap greases are stable at high temperature s, but wash out in moist conditions. Lithium soap greases resist both heat and moisture. A mixed-base soap is a combination of soaps, offering some of the advantages of each type. A complex soap is formed by the reaction of an alkali with a high-molecular-weight fat or fatty acid to form a soap, and the simultaneous reaction of the alkali with a short-chain organic or inorganic acid to form a metallic salt (the complexing agent). Complexing agents usually in crease the dropping point of grease. Lithium , calcium, and aluminum greases are common alkalis in complex-soap greases. Non soap thickeners, such as clays, silica gels, carbon black, and various synth e tic organic materials are also used in grease manufacture. A multi-purpose grease is designed to provide resistance to heat, as well as water, and may contain additives to increase load-carrying ability and inhibit rust. See block grease, bulk appearance, colloid, consistency (grease), fire-resistant grease, penetration (grease).
grease cup - grease applicator screwed into a tapped hole in a bearing; grease is fed from the c up to the bearin g either mechanically by means of a screw-down cap or plunger, or automatically by means of a spring loaded plunger. See grease gun.
grease gun - device for injecting pressurized grease into a bearing; the bearing receives the grease through a spring-loaded ball-check valve that lets the grease in , but prevents it from running back out. A grease gun contains a reservoir for grease, a nozzle that fits tight against the fitting or clamps on to it, and a means for applying pressure to the grease. A grease gun has advantages over a grease cup: it can handle a harder grease, and the pressure ca n drive the fresh charge of grease into very tight clearances and flush out old grease that may have become contaminated with foreign matter. See high-pressure-injection injury.
grease gun injury - see high pressure injection injury.
grid-type coupling - see flexible coupling.
gum in gasoline - oily, viscous contaminant that may form, due to oxidation during storage. Gum formation in gasoline can cause serious fuel system problems, such as carburetor malfunctioning and in take valve sticking. The amount of gum in motor gasoline, aviation gasoline, and aircraft turbine fuel can be determined by evaporating a measured sample by means of air or steam flow at controlled temperature, and weighing the residue, as described in test method ASTM D 381.