Glossary



SAE: Society of Automotive Engineers

SAE numbers/SAE oil viscosity classification: number assigned by the SAE to crankcase, transmission and rear axle lubricants to indicate their viscosity ranges; may be converted to ISO and/or ASTM/STLE classifications.

Salt spray test: (ASTM B-117) determines the effectiveness of a slushing oil in preventing rust and corrosion.

Saponification (grease): process in which a fat or some other compound of an acid and an alcohol reacts with an alkali to form a soap and glycerin or other alcohol.

Saponification (analysis): the process used to measure the ester content of a material (see saponification number).

Saponification number: (ASTM D-94) the number of milligrams of potassium hydroxide required to saponify the fats and/or esters in a one-g sample of a given material.

Saturates: synonym for alkane hydrocarbons, or saturated hydrocarbons.

Saybolt SUS/SFS: (ASTM D-88) the number of seconds required for 60 ml of a fluid to flow through the orifice of the standard Saybolt Universal viscometer (SUS) or a Saybolt Furol viscometer (SFS) at a given temperature under specified conditions. Since the orifice of a Saybolt Furol viscometer is larger than that of a Universal viscometer, it is used for more viscous fluids.

Seal swell: an increase in elastomer volume or linear dimension of a specimen immersed in liquid or exposed to a vapor; harness and durability of the elastomer may also be affected. Swell characteristics vary with the elastomer, but high aniline point oils cause less swell than low aniline point oils.

Secondary divider valve (lube systems): divider valve that receives flow from the master divider valve.

Seed oils: see vegetable oils

Self-aligning bearing: bearing held by four points or in some other arrangement that permits an automatic change in the position of the bearing to conform to an out-of-line shaft or journal.

Self-lubricated bearing: bearing supplied with lubrication in the bearing material, i.e., graphite in a powdered metal bearing or oil in a wood or microporous bearing; not generally suited for heavy loads or high operating temperatures.

SEM (scanning electron microscope): tool used to examine failed bearings, wear particles and debris.

Semisynthetic (metalworking): a metalworking lubricant containing water.

Semisynthetic: a lubricant formulated with 20% or more of polymeric fluid as a base stock component.

Sequence valve (hydraulics): device assuring that actuators move in a certain sequence in a hydraulic system.

Sequestering agent: a compound that reacts with metallic (positively charged) ions in a solution to keep them in solution, thereby preventing the metallic ions from forming a sludge or depositing on the workpiece.

Series-progressive (lube systems): positive, single-line lubrication system utilizing piston divider valves for metering and distribution; each divider valve must cycle completely in sequence before downstream valves and pistons are activated.

Servo valve: a high-performance directional and flow control valve usually operated by a torque motor; similar to a proportional valve but superior in terms of frequency response and hysteresis.

Shear stability/mechanical shear stability: measure of the change in consistency of a grease after it has been subjected to prolonged shearing by means of a mechanical device like a grease worker (10,000 strokes) or a roll test; the percentage change in penetration values is an indicator of shear stability.

Silicones: generic term for a class of synthetic lubricants that replace carbon atoms with a chain of alternating oxygen and silicon; also known as siloxanes. These fluids are water-resistant polymers with very high viscosity indexes, excellent fluidity at low temperatures and good oxidation and thermal stability at higher temperatures. They do not have high load-carrying capacity.

Sintered metal: a bronze or iron bearing material frequently used where self- lubrication, low coefficient of friction, accurate dimensions and simplicity of installation without machining are desirable.

Sleeve bearing: a 360° cylindrical plain bearing, sometimes called a bushing, that supports a journal or roll neck, aptly called a sleeve.

Sliding velocity (gears): computed differential sliding speed in either the arc of approach or arc of recess.

Slinger (seals): prevents oil leakage from high-speed journal bearings; uses centrifugal force to throw oil that leaks through the bearing into a groove that returns the oil to the reservoir.

Slumpability: characterizes the capacity of a grease to flow towards a suction inlet without a follower plate.

Slushing oil: oil or grease-like material applied to metal as a temporary protective coating against rust, corrosion, etc.

Soap: a compound formed by the reaction of a fatty acid with an alkali; soaps used as grease thickeners are most stearates.

Soda/sodium base grease: grease prepared from lube oil and a sodium soap.

Soil load (cleansers): the percentage of soil contained by a cleaning solution, usually expressed in volume/volume units. Soil load content in an alkaline cleaner bath is ordinarily determined by an acid split procedure.

Solenoid: a coil, that when energized, attracts a sliding iron core; used to control position of a spool in a valve body.

Solid bonded lubricants: powdered lubricants like graphite, molybdenum disulfide, etc., are adhesively bound to clean, solid surfaces through proprietary processes to form thin tightly-bonded films; used for lightly loaded bearings in specialty applications.

Soluble cutting oil/soluble oil: oil with an emulsifier that forms an emulsion, used as a metalworking fluid or hydraulic fluid.

Solvent: a compound capable of dissolving a given substance to form a solution. Water is a polar solvent, hydrocarbons are non-polar.

Solvent extraction: a refinery process that utilizes oil and a polar solvent like phenol, N-methyl pyrolidone, furfural, etc., to selectively separate unsaturates from lubricant distillates, in order to improve properties such as oxidation stability, viscosity index and additive response.

Sour crude/sweet crude: sour crudes contain appreciable quantities of hydrogen sulfide, disulfides or other sulfur compounds; sweet crudes do not.

Specific gravity: the ratio of the density of a substance to the density of water, often at a specified temperature.

Spherical roller bearings: rolling bearings designed with barrel-shaped rollers, suitable for most heavy-duty service (see rolling element bearings).

Spider (gears): a design consisting of a ring or solid center with projections, used to space and align gears, e.g., the part that controls the sun gears in automotive differential gears.

Spindle oil: light-bodied, high-quality R&O oils fortified with anti-wear agents, used principally for lubricating high-speed metalworking machine spindles like grinders. (NOTE: these machinery spindles are not to be confused with the mill spindles that couple mill pinions to mill rolls; that application requires completely different kinds of lubricants for the spindle carriers and the coupling ends).

Spiral bevel gear (gears): quieter and stronger than the spur gear; assumes some of the sliding action of a worm gear, but more than one tooth carries the load.

Splash lubrication: system in which parts of a mechanism dip into a lubricant sump and splash the lubricant onto themselves and/or other parts of the machine by mechanical or other means.

Split bearings: bearings divided into two parts that completely encircle the journal when fitted together, often with shims on each side for adjustment or fitting; can be adjusted to compensate for wear to the bearing or the journal, or both, by removing shims or by filing to fit the two parts together to any desired clearance.

Spun bearing: bearing of which the bearing material is centrifugally spun instead of poured; this method of applying the material yields a finer grain and better bonding of the bearing material to the shell or back.

Spun gear (gears): gear with a straight tooth parallel to the shaft axis, also known as an involute gear.

Squeeze film: phenomenon occurring when two surfaces suddenly come together, trapping the lubricant momentarily, as with gear teeth or rolling element bearings; high fluid pressure develops in the film, raising its viscosity and helping to keep the moving surfaces apart. This phenomenon also occurs during elastrohydrodynamic lubrication.

SRV: a reciprocating test device for evaluating friction and wear.

Static friction: force just sufficient to initiate relative motion between two bodies under load.

Static grounding: use of a grounded conductive material to prevent the accumulation of static electric charges.

Static electricity: accumulated stationary electrical charges generated by friction.

Static transmitted load (gears): tangential pitch line force transmitted from one gear to another without regard to dynamic efforts.

Stator: may refer to the stationary member in a steam turbine, a hydraulic torque converter or the framework surrounding the armature of a direct current motor or generator.

Steam refined: term applied to unfiltered residual cylinder oils from which lighter fractions have been distilled by the direct application of steam.

Step bearing: plane-surface bearing that supports the lower end of a vertical shaft.

Stick-slip (slip-stick): a condition occurring in slow moving or oscillating sliding bearings under near boundary conditions, where there are fluctuations of velocity and friction coefficients, including periods of static friction. It is a critical factor in precision machine tool operations, where such conditions can result in erratic motion and improper machining of parts.

STLE: Society of Tribologists and Lubrication Engineers (formerly, the American Society of Lubrication Engineers, or ASLE).

Stoke: the standard unit of kinematic viscosity in the cgs system, expressed in cm2/s.

Strainer filter: see oil strainer.

Stray mist suppressant: (ASTM D-3705) a polymer added to mist oils to reduce the stray mist.

Strong acid/strong base numbers: (ASTM D-974) the quantity of acid or base, expressed in equivalent numbers of milligrams of KOH, required to neutralize strong acid (pH 4/g) or base (pH 11/g) constituents.

Stress concentration factor (gears): factor affecting beam strength, related to the radius of the fillet at the tooth base; the larger the radius, the lower the stress concentration.

Stub teeth (gears): gear teeth in which the working depth is less than 2.0 divided by normal diametral pitch.

Stuffing box: see packing box.

Subplate sections (lube systems): baseplates that support the working valve sections of stackable subplate divider valves, containing internal porting, outlet ports and tie bolt holes.

Sun gear: the center gear that remains in mesh with the planet gears (see planetary transmission).

Surface finish: the surface roughness of a component as measured by a surface profilometer.

Surface tension: the attractive force exerted by molecules below the surface upon molecules at the surface/air interface. The strength of the surface tension varies with the polarity of the liquid; high-polar substances like water have higher surface tension than low-polar substances like organic solvents and oils.

Surfactant: any surface modifying material that imparts anti-wear, extreme pressure or rust inhibition properties, spreadability, etc.

Surfactant (cleansers): a compound that reduces surface tension when dissolved in water or aqueous solution, or that reduces interfacial tension between two liquids or a liquid and a solid. The three types of surfactants are wetting agents, detergents and emulsifiers.

Synthetic lubricants/fluids: man-made products created by chemically combining specific compounds, producing substances with specialized lubricating qualities to meet specific objectives. This group includes the following subgroups: synthesized hydrocarbons, principally polyalphaolefin; organic esters, e.g., the diesters and polyol esters; polyglycols, some of which are used in water-glycol FR fluids; phosphate esters, FR fluids with good lubricating characteristics; and others, e.g., silicones, silicate esters, polyphenyl esters and fluorocarbons.