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Dictionary of Lubricant Terms


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SAE (SOCIETY OF AUTOMOTIVE ENGINEERS) - organization responsible for the establishment of many U.S. automotive and aviation standards, including the viscosity classifications of engine oils and gear oils.

SATURATED HYDROCARBON - hydrocarbon with the basic formula CnH2n+2; it is saturated with respect to hydrogen and cannot combine with the atoms of other elements without giving up hydrogen. Saturates are more chemically stable than unsaturated hydrocarbons.

SAYBOLT FUROL VISCOSITY - the efflux time in seconds required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Furol viscometer, under carefully controlled temperature, as prescribed by test method ASTM D 88. The method differs from Saybolt Universal viscosity only in that the viscometer has a larger orifice to facilitate testing of very viscous oils, such as fuel oil (the word “Furol” is a contraction of “fuel and road oils.”) The Saybolt Furol method has largely been supplanted by the kinematic viscosity method. See viscosity.

SAYBOLT UNIVERSAL VISCOSITY - the efflux time in seconds required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer, under carefully controlled temperature, as prescribed by test method ASTM D 88. This method has largely been supplanted by the kinematic viscosity method. See Saybolt Furol viscosity.

SCALING - the deposition and growth of insolubles and oxides on cooling system walls.

SCAVENGER - a component of lead anti-knock compounds that reacts with the lead radical to form volatile lead compounds that can be easily scavenged from the engine through the exhaust system. Also, an individual who collects used lubricating oils for some secondary use.

SCORING - mechanical disturbance of a rubbing surface with definite surface roughness in line with motion, and characterized by the transfer of metal by dragging which results in progressive deterioration.

SCRATCHING - mechanical disturbance of a rubbing surface with definite surface roughness in line with motion, but no progressive surface deteriorization due to debris.

SCUFFING - mechanical disturbance of a rubbing surface with no appreciable surface roughness to feel.

SEAL SWELL (RUBBER SWELL) - swelling of rubber (or other elastomer) gaskets, or seals, when exposed to petroleum, synthetic lubricants, or hydraulic fluids. Seal materials vary widely in their resistance to the effect of such fluids. Some seals are designed so that a moderate amount of swelling improves sealing action.

SEIZING - sticking together of two surfaces characterized by the presence of small particles of material which have become welded to the surface.

SERIES 3 - obsolete specification for heavy-duty engine oils used in Caterpillar Tractor Company diesel engines. Caterpillar now specifies that the oil for its engines comply with Military Specification MIL-L-2104C or API Engine Service Category CD.

SHEAR RATE - rate at which adjacent layers of fluid move with respect to each other, usually expressed as reciprocal seconds (also see shear stress.) When the fluid is placed between two parallel surfaces moving relative to each other:

SHEAR INDEX (SI) - the measure of an oil’s percentage viscosity loss.

SHEAR STABILITY INDEX (SSI) - the measure of the VI improver’s contribution to an oil’s percentage kinematic viscosity loss.

SHEAR STRESS - frictional force overcome in sliding one “layer” of fluid along another, as in any fluid flow. The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity). The ratio between shear stress and shear rate is constant; this ratio is termed viscosity. The higher the viscosity of a Newtonian fluid, the greater the shear stress as a function of rate of shear. In a non-Newtonian fluid--such as a grease or a polymer-containing oil (e.g. multi-grade oil)--shear stress is not proportional to the rate of shear. A non-Newtonian fluid may be said to have an apparent viscosity, a viscosity that holds only for the shear rate (and temperature) at which the viscosity is determined. See Brookfield viscosity.

SI (SYSTEME INTERNATIONAL, INTERNATIONAL SYSTEM OF UNITS) - metric-based system of weights and measures adopted in 1960 by the 11th General Conference on Weights and Measures, in which 36 countries, including the U.S., participated. SI consists of seven base units: meter (m) = length, kilogram (kg) = mass, second (s) = time, ampere (A) = electric current, Kelvin (K) = thermodynamic temperature, mole (mol) = amount of substance, candela (cd) = luminous intensity. There are two supplemental units: radian (rad) = plane angle, and steradian (sr) = solid angle.

SINGLE-GRADE OIL - engine oil that meets the requirements of a single SAE viscosity grade classification.

SLUDGE - a deposit, principally composed of engine oil and fuel debris, which does not drain from engine parts but can be removed by wiping with a soft cloth.

SOLUBLE OILS - oils which, following the addition of emulsifiers and stabilizers, are readily capable of mixing with water. They are used as drilling, cutting and cooling oils in metalworking.

SOLVENT - compound with a strong capability to dissolve a given substance. The most common petroleum solvents are mineral spirits, xylene, toluene, hexane, heptane, and naphthas. Aromatic-type solvents have the highest solvency for organic chemical materials, followed by naphthenes and paraffins. In most applications the solvent disappears, usually by evaporation, after it has served its purpose. The evaporation rate of a solvent is very important in manufacture: rubber cements often require a fast-drying solvent, whereas rubber goods that must remain tacky during processing require a slower-drying solvent. Solvents have a wide variety of industrial applications, including the manufacture of paints, inks, cleaning products, adhesives, and petrochemicals. Other types of solvents have important applications in refining. See solvent extraction.

SOLVENT EXTRACTION - refining process used to separate reactive components (unsaturated hydrocarbons) from lube distillates in order to improve the oil’s oxidation stability, viscosity index (VI), and response to additives. Commonly used extraction media (solvents) are: phenol, N-methylpyrrolidone (NMP), furfural, liquid sulfur dioxide, and nitrobenzene. The oil and solvent are mixed in an extraction tower, resulting in the formation of two liquid phases: a heavy phase consisting of the undesirable unsaturates dissolved in the solvent, and a light phase consisting of high quality oil with some solvent dissolved in it. The phases are separated and the solvent recovered from each by distillation. The unsaturates portion, or extract, while undesirable in lubricating oils, is useful in other applications, such as rubber extender oils.

SOLVENT NEUTRAL - high-quality paraffin-base oil refined by solvent extraction.

SOUR CRUDE - crude oil containing appreciable quantities of hydrogen sulfide or other sulfur compounds, as contrasted to sweet crude.

SPALLING - surface disintegration associated with loss of particles from the surface and associated with adhesion.

SPARK-IGNITION ENGINE - see internal combustion engine.

SPECIFIC GRAVITY - for petroleum products, the ratio of the mass of a given volume of product and the mass of an equal volume of water, at the same temperature. The standard reference temperature is 15.6°C (60°F). Specific gravity is determined by test method ASTM D 1298: the higher the specific gravity, the heavier the product. Specific gravity of a liquid can be determined by means of a hydrometer, a graduated float weighted at one end, which provides a direct reading to which it sinks in the liquid. A related measurement is density, an absolute unit defined as mass per unit volume - usually expressed as kilograms per cubic meter (kg/m3). Petroleum products may also be defined in terms of API gravity (also determinable by ASTM D 1298), in accordance with the formula:

Hence, the higher the API gravity value, the lighter the material, or the lower its specific gravity.

STICK-SLIP MOTION - erratic, noisy motion characteristic of some machine ways, due to the starting friction encountered by a machine part at each end of its back-and-forth (reciprocating) movement. This undesirable effect can be overcome with a way lubricant, which reduces starting friction.

STOICHIOMETRIC - the exact proportion of two or more substances that will permit a chemical reaction with none of the individual reactants left over. See combustion.

STRAIGHT MINERAL OIL - petroleum oil containing no additives. Straight mineral oils include such diverse products as low-cost once-through lubricants and thoroughly refined white oils. Most high-quality lubricants, however, do contain additives. See mineral oil.

STYRENE - colorless liquid (C8H8) used as the monomer (see polymer) for polystyrene and styrene-butadiene rubber.

STYRENE-BUTADIENE RUBBER (SBR) - general-purpose synthetic rubber with good abrasion resistance and tensile properties. SBR can be greatly extended with oil without degrading quality. Applications include automobile tires and wire insulation.

SULFATED ASH - using ASTM D 874, the ash that remains after the sample has been carbonized and the residue subsequently treated with sulfuric acid and heated to constant weight. See ash.

SULFONATE - hydrocarbon in which a hydrogen atom has been replaced with the highly polar (SO2OX) group, where X is a metallic ion or alkyl radical. Petroleum sulfonates are refinery by-products of the sulfuric acid treatment of white oils. Sulfonates have important applications as emulsifiers and chemical intermediates in petrochemical manufacture. Synthetic sulfonates can be manufactured from special feedstocks rather than from white oil base stocks. See polar compound.

SUPERCHARGER - device utilizing a blower or pump to provide intake air to the carburetor of an internal combustion engine at pressures above atmospheric. Supercharging provides a greater air charge to the cylinders at high crankshaft speeds and at high altitudes, thereby boosting engine power without increasing engine size. Because supercharging maintains maximum intake charge, it offers particular advantages at high altitudes, where the atmosphere contains less oxygen. Some supercharger systems utilize after-cooling to further increase the density of the charge. The blower may be geared to the crankshaft or, in the case of the turbocharger, it may consist of a turbine driven by the exhaust gases to operate the centrifugal blower.

SURFACTANT - surface-active agent that reduces interfacial tension of a liquid. A surfactant used in a petroleum oil may increase the oil’s affinity for metals and other materials.

SWEEP (OF A PISTON) - internal cylinder surface area over which a piston of a reciprocating compressor moves during its stroke. Total piston sweep is a consideration in the determination of oil-feed rates for some reciprocating compressor cylinders, and may be determined as: length of stroke x cylinder circumference diameter x 2 x no. of cylinders x rpm x minutes of operation

SWEET CRUDE - crude oil containing little or no sulfur. See sour crude.

SYNTHETIC LUBRICANT - lubricating fluid made by chemically reacting materials of a specific chemical composition to produce a compound with planned and predictable properties; the resulting base stock may be supplemented with additives to improve specific properties. Man synthetic lubricants - also called synlubes - are derived wholly or primarily from petrochemicals; other synlube raw materials are derived from coal and oil shale, or are lipochemicals (from animal and vegetable oils). Synthetic lubricants may be superior to petroleum oils in specific performance areas. Many exhibit higher viscosity index (VI), better thermal stability and oxidation stability, and low volatility (which reduces oil consumption). Individual synthetic lubricants offer specific outstanding properties: phosphate esters, for example, are fire resistant, diesters have good oxidation stability and lubricity, and silicones offer exceptionally high VI. Most synthetic lubricants can be converted to grease by adding thickeners. Because synthetic lubricants are higher in cost than petroleum oils, they are used selectively where performance or safety requirements may exceed the capabilities of a conventional oil. The following is a list of the principal classes of synthetic lubricants: alkylated aromatics(organic hydrocarbon), olefin oligomers(organic hydrocarbon), dibasic acid esters (organic ester), polyol esters (organic ester), polyglycols, phosphate esters, silicones, silicate esters, halogenated hydrocarbons.

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