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Dictionary of Lubricant Terms


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FATTY ACID - any monobasic (one displaceable hydrogen atom per molecule) organic acid having the general formula CnH2n+1 COOH. Fatty acids derived from natural fats and oils are used to make soaps used in the manufacture of greases and other lubricants. See grease.

FDA (FOOD AND DRUG ADMINISTRATION) - agency administered under the U.S. Department of Health and Human Services (formerly Health, Education and Welfare) “to enforce the Federal Food, Drug, and Cosmetic Act and thereby carry out the purpose of Congress to ensure that foods are safe, pure, and wholesome, and made under sanitary conditions; drugs and therapeutic devices are safe and effective for their intended uses; cosmetics are safe and prepared from appropriate ingredients; and that all of these products are honestly and informatively labeled and packaged.”

FILM STRENGTH - See lubricity.

FIRE POINT - temperature at which the vapor concentration of combustible liquid is sufficient to sustain combustion, as determined by test method ASTM D 92, Cleveland Open Cup. See slush point.

FIRE-RESISTANT FLUID - lubrication used especially in high temperature or hazardous hydraulic applications. Three common types of fire-resistant fluids are: (1) water-petroleum oil emulsions, in which the water prevents burning of the petroleum constituent; (2) water-glycol fluids; and (3) non-aqueous fluids of low volatility, such as phosphate esters, silicones, and halogenated hydrocarbon type fluids. See synthetic lubricant.

FLASH POINT - the temperature at which a product’s vapor can be ignited momentarily by a flame, using ASTM D 92 Cleveland Open Cup method (preferred for engine oils), D 56 Tag Closed Tester, D 93 Pensky-Martens Closed Tester or D 1310 Tag Open Cup methods.

FLOC POINT - temperature at which waxy materials in a lubricating oil separate from a mixture of oil and Freon (Registered trademark of E.I. Dupont de Nemours, Inc.) R-12 refrigerant, giving a cloudy appearance to the mixture; also called Freon floc point. Generally used to evaluate the tendency of refrigeration oils to plug expansion valves or capillaries in refrigerant systems. Not to be confused with cloud point, the temperature at which wax precipitates from an undiluted oil.

FLUID FRICTION - See friction.

FOAMING - occurrence of frothy mixture of air and petroleum product (e.g. lubricant, fuel oil) that can reduce the effectiveness of the product, and cause sluggish hydraulic operation, air binding of oil pumps, and overflow of tanks or sumps. Foaming can result from excessive agitation, improper fluid levels, air leaks, cavitation, or contamination with water or other foreign materials. Foaming can be inhibited with an anti-foam agent. The foaming characteristics of a lubricating oil can be determined by blowing air through a sample at a specified temperature and measuring the volume of foam, as described in test method ASTM D 892.

FRETTING (CORROSION) - wear occurring on mating surfaces due to slight relative motion resulting from dynamic stresses.

FRICTION - resistance to the motion of one surface over another. The amount of friction is dependent on the smoothness of the contacting surfaces, as well as the force with which they are pressed together. Friction between unlubricated solid bodies is independent of speed and area. The coefficient of friction is obtained by dividing the force required to move one body over a horizontal surface at constant speed by weight of the body. Coefficients of rolling friction (e.g., the motion of a tire or ball bearing) are much less than the coefficient of sliding friction (back and forth motion over two flat surfaces). Sliding friction is thus more wasteful of energy and can cause more wear. Fluid friction occurs between the molecules of a gas or liquid in motion, and is expressed as shear stress. Unlike solid friction, fluid friction varies with speed and area. In general, lubrication is the substitution of low fluid friction in place of high solid-to-solid friction. See tribology.

FUEL ECONOMY OIL - engine oil specially formulated to increase fuel efficiency. A fuel-economy of oil works by reducing the friction between moving engine parts that wastefully consumes fuel energy. There are two known means of accomplishing this goal: (1) by reducing the viscosity of the oil to decrease fluid friction and (2) by using friction-reducing additives in the oil to prevent metal-to-metal contact, or rubbing friction, between surface.

FUEL INJECTION - method of introducing fuel under pressure through a small nozzle into the intake system of cylinders of an engine. Fuel injection is essential to the diesel cycle, and an alternative to conventional carburetion in the gasoline engine. In some designs, each cylinder has a cam-operated injector, which is a plunger pump that delivers precisely metered quantities of fuel at precise intervals. The fuel is injected in a minutely divided spray at high discharge. The amount of the charge is controlled by the throttle pedal. A combination of fuel injection and carburetion is used in advanced emission-control systems, involving fuel injection into the throttle body of the carburetor. Fuel injection offers certain advantages over carburetion, including: more balanced fuel distribution in the cylinders for improved combustion, more positive delivery of fuel to the cylinder (hence, easier starting and faster acceleration), and higher power output because of improved volumetric efficiency. See carburetor.

FULL-FLUID-FILM LUBRICATION - presence of a continuous lubricating film sufficient to completely separate two surfaces, as distinct from boundary lubrication. Full-fluid-film lubrication is normally hydrodynamic lubrication, whereby the oil adheres to the moving part and is drawn into the area between the sliding surfaces, where it forms a pressure, or hydrodynamic, wedge. See ZN/P curve. A less common form of full-fluid-lubrication is hydrostatic lubrication, wherein the oil is supplied to the bearing area under sufficient external pressure to separate the sliding surfaces.

FZG FOUR-SQUARE GEAR OIL TEST - test used in developing industrial gear lubricants to meet equipment manufacturers’ specifications. The FZG test equipment consists of two gear sets, arranged in a four-square configuration, driven by an electric motor. The test gear set is run in the lubricant at gradually increased load stages until failure, which is the point at which a 10 milligram weight loss by the gear set is recorded. Also called Niemann four-square gear oil test.

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