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Glossary

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S

SAE EP Lubricant Tester

A machine designed to test the extreme-pressure properties of a lubricant under a combined rolling and sliding action. The revolving members are two bearing cups which rotate at different speeds. This tester is described in Federal Test Method Standard 791, Method 6501.1. Also called a McKee machine.

SAE Viscosity Number

System for classifying crankcase, transmission, and differential lubricants, according to their viscosities, established by the Society of Automotive Engineers. SAE numbers are used in connection with recommendations for crankcase oils to meet various design, service, and temperature requirements affecting viscosity only; they do not denote quality.

Sample preparation

Fluid factors that can enhance the accuracy of the particulate analysis. Such factors include particle dispersion, particle settling, and sample dilution.

Saturation level

The amount of water that can dissolve in a fluid.

Saybolt Color

A color standard for petroleum products. The procedure for determining Saybolt color and description of the Saybolt chronometer are given in ASTM Method D 156.

Saybolt Furol Viscosity

The time, in seconds, for 60 ml of fluid to flow through a capillary tube in a Saybolt Furol viscometer at specified temperatures between 70°F and 210°F. This Method is appropriate for high-viscosity oils such as transmission, gear, and heavy fuel oils. ASTM Method D 88 describes the equipment and procedure.

Saybolt Universal Viscosity (SUV) or Saybolt Universal Seconds, (SUS)

The time in seconds required for 60 cubic centimeters of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions. (ASTM Designation D 88.)

Scaling

The deposition and growth of insolubles and oxides on cooling system walls.

Scoring

Damage of a rubbing surface that is characterized by a definite surface roughness in line with motion. It is created by the transfer of metal by dragging, which results in progressive deterioration.

Scratching

Damage of a rubbing surface that is characterized by a definite surface roughness in line with motion. The damage, however, is not created by progressive surface deteriorization due to debris.

Scuffing

Abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives.

Scuffing particles

Large twisted and discolored metallic particles resulting from adhesive wear due to complete lubricant film breakdown.

Seizing

Sticking together of two surfaces characterized by the presence of small particles of material which have become welded to one or both of the surfaces.

Semisolid

Any substance having the attributes of both a solid and a liquid. Similar to semiliquid but being more closely related to a solid than a liquid. More generally, any substance in which the force required to produce a deformation depends both on the magnitude and on the rate of the deformation.

Separate Test

A test to determine the tendency of oil to separate from a lubricating grease under conditions prescribed in ASTM Method D 1742. Service SJ, SH, SG, SF, SE, SD, SC, SB, SA, CH-4, CG-4, CF, CF-4, CF-2, CE, CD, CD-II, CC, CB, CA.

Shear index

The measure of an oil's percentage viscosity loss.

Shear rate

Rate at which adjacent layers of fluid move with respect to each other, usually expressed as reciprocal seconds.

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 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.

Silt

Contaminant particles 5 µm and less in size.

Silting

A failure generally associated with a valve which movements are restricted due to small particles that have wedged in between critical clearances (e.g., the spool and bore.)

Single-grade oil

An engine oil that meets the requirements of a single SAE viscosity grade classification.

Single-pass test

Filter performance tests in which contaminant which passes through a test filter is not allowed to recirculate back to the test filter.

Sintered medium

A metallic or nonmetallic filter medium processed to cause diffusion bonds at all contacting points.

Sleeve bearing

A journal bearing, usually a full journal bearing.

Sludge

Coagulated insoluble material formed as a result either of deterioration reactions in an oil or of contamination of an oil, or both.

Soap

General term denoting the salt of a fatty acid. The ordinary soaps are those of sodium and potassium. The soaps of lithium, calcium, sodium, and aluminum are the principal thickeners used in grease making.

Solid

Any substance having a definite shape which it does not readily relinquish. More generally, any substance in which the force required to produce a deformation depends upon the magnitude of the deformation rather than upon the rate of deformation.

Soluble oils

Oils that have the ability to mix with water after emulsifiers and stabilizers have been added. They are used as drilling, cutting and cooling oils in metalworking.

Solvency

Ability of a fluid to dissolve inorganic materials and polymers, which is a function of aromaticity.

Solvent

A compound that has the ability to dissolve a given substance.

Solvent extraction

Refining process used to separate reactive components from lube distillates in order to improve the oil's oxidation stability, viscosity index, and response to additives.

Sour crude

Crude oil containing appreciable quantities of hydrogen sulfide or other sulfur compounds.

Spalling

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

Specific gravity (liquid)

The ratio of the weight of a given volume of liquid to the weight of an equal volume of water.

Specific gravity

The ratio of the weight of a given volume of material to the weight of an equal volume of water.

Spectrographic analysis

Determines the concentration of elements represented in the entrained fluid contaminant.

Spectrographic Oil Analysis Program (SOAP)

Procedures for extracting fluid samples from operating systems and analyzing them spectro-graphically for the presence of key elements.

Spin-on filter

A throw-away type bowl and element assembly that mates with a permanently installed head.

Spindle oil

A low viscosity oil used principally for lubricating textile spindles and for light, high-speed machinery.

Splash lubrication

A system of lubrication in which parts of a mechanism dip into and splash the lubricant onto themselves and/or other parts of the mechanism.

Starting Fluid (diesel)

A fluid, such as diethyl ether, which has a wide flammability range; used to start diesel engines at extremely low temperatures.

Static friction

The force just sufficient to initiate relative motion between two bodies under load. The value of the static friction at the instant relative motion begins is termed break-away friction.

Stoke (St)

Kinematic measurement of a fluid's resistance to flow defined by the ratio of the fluid's dynamic viscosity to its density.

Strainer

A coarse filter element (pore size over approximately 40 µm)

Suction filter

A pump intake-line filter in which the fluid is below atmospheric pressure.

Sulfated ash

The ash content of fresh, compounded lubricating oil as determined by ASTM Method D 874. Indicates level of metallic particles in the oil.

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.

Sulfurized oil

Oil to which sulfur or sulfur compounds have been added. The compounds react with a rubbing surface at an elevated temperature to form a protective film.

Superclean

10 particles > 10 micron per milliliter

Supercharger

A device that pumps intake air into 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. 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.

Surface fatigue wear

The formation of surface or subsurface cracks and fatigue crack propagation. It results from cyclic loading of a surface.

Surface filtration

Filtration which primarily retains contaminant on the influent surface.

Surface tension

The contractile surface force of a liquid by which it tends to assume a spherical form and to present the least possible surface. It is expressed in dynes/cm or ergs/cm2.

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.

Surge

A momentary rise of pressure in a circuit.

SUS (SSU)

Saybolt Universal Seconds. A measure of lubricating oil viscosity used in the oil industry.

Swarf

The cuttings, and grinding fines that result from metal working operations.

Switch, pressure

An electric switch operated by fluid pressure.

Synergism

A situation where a mixture of two or more separate additive materials results in a total effect greater than that of the sum of them.

Synthetic hydrocarbon

Oil molecule with superior oxidation quality tailored primarily out of paraffinic materials.

Synthetic lubricant

A lubricant produced by chemical synthesis rather than by extraction or refinement of petroleum to produce a compound with planned and predictable properties.

Synthetic Oils

Oil produced by synthesis rather than by extraction or refinement.