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