Calcium grease: oils thickened with calcium soap.
Calcium sulfonate grease: a calcium neutralized grease thickened with sulfonic
acid and fatty acids. Sulfonate greases have inherent rust inhibition (see complex
Capillary action: the tendency of a liquid in contact with a small bore (capillary)
tube to rise above the level of the surrounding liquid.
Carbon residue: the residue remaining after the evaporation and pyrolysis of a
sample of oil under specified conditions. Tests that determine carbon residue are
the Ramsbottom and Conradson methods, ASTM D-524 and D-189, respectively.
Case hardening: the process of hardening steel surfaces by changing the
structure of a thin layer on its surface. Methods include carburizing, cyaniding,
nitriding and induction or flame hardening.
Catalyst: a material or agent that promotes or produces a chemical action but
does not itself participates in the chemical action.
Cavitation (hydraulics): when the absolute pressure in a pump intake line is
reduced below the vapor pressure of the liquid, the fluid may vaporize, or “boil”,
or the dissolved air in the fluid may separate. In either case, as the bubbles go
through the pump, they collapse or implode and damage the metal of the pump.
Centerline (gears): line that intersects the geometrical centers of the pinion and
Centerline average – average height of peaks and valleys (asperities) on a
Centipoise: a unit of absolute viscosity; one centipoise equals 0.01 poise. At the
same temperature, centipoises equals centistokes multiplied by specific gravity
(cp = cSt x sp. grav.).
Centistoke: a unit of kinematic viscosity, abbreviated as cSt: one centistoke
equals 0.01 stoke. At the same temperature, centistokes equals centipoises
divided by specific gravity (cSt = cp/sp.grav.).
Centralized lubrication: a system of non-recirculating lubrication that supplies
a metered amount of lubricant from a central location to individual lubrication
Centrifuge: an instrument that employs centrifugal or rotating force to separate
substances of different densities, useful for precipitating solids from a liquid or
separating liquids of different densities.
Centrifugal pump: a pump with a rotating element, shaft and impeller and a
stationary casing. In this pump, fluid is propelled at high velocity as centrifugal
force at the periphery of the impeller blades discharges pressurized fluid into the
Cetane number: a number that expresses the ignition quality of a diesel fuel,
equal to the percent by volume of cetane (C16H34) blended with methyl
naphthalene that has the same ignition performance as the test fuel. A CFR test
engine is used to determine this number.
Cetane index: the theoretical cetane number calculated according to ASTM D976,
using API gravity and mid-boiling point.
CFR engine: an ASTM test engine developed by the Cooperative Fuel Research
Committee to measure the cetane numbers of diesel fuels and octane numbers of
Chain lubrication: a dip or splash system that uses a chain to distribute
lubricant to bearings, similar, in a way, to an oil ring; or any system designed to
lubricate a conveyor chain.
Channeling (grease): a term describing the usually desirable tendency of grease
to form a channel by working down in a bearing, leaving shoulders of unworked
grease that serve as both reservoirs and seals.
Channeling (liquids): the undesired formation of troughs or channels in flow-
type lubricants due to thickening during cold weather. Since such behavior
occurs near the pour point of the lubricant, lubrication may be marginal until the
lubricant warms up from being worked (see channeling point).
Channeling point (gears): a federal test that measures the tendency of lubricants
at low temperatures to form plastic structures of sufficient strength to resist flow
under gravitational forces only. This test is specified and required for MIL 2105type
Check valve (hydraulics): in hydraulic and lubrication systems, a valve
permitting flow in only one direction.
Chelation: the reaction of a metal with another substance called a “chelator” to
form a very stable, soluble metal complex that may resist subsequent waste
treatment processes designed to remove the metal ion from the solution.
Chelators in cleaner formulations prevent soap scum formation by combining
with hard-water metals like calcium and magnesium.
Chlorinated paraffin: an additive used for severe or difficult metal cutting or
metal working operations.
Chromatography: a powerful method for analyzing fluids and determining their
components by selective adsorption or size exclusion, using liquid or gas as the
eluent. In the adsorptive procedure, the substance flows slowly through a
column of adsorbent; as different substances pass at different speeds, they
separate from each other and can sometimes be isolated and identified. In other
cases, the chromatogram (a trace of the signal from the detector) is utilized to
fingerprint a lubricant. Liquid chromatography is used for lubricants because of
their low volatility. Paper chromatography, an adsorptive method, is often used
to examine or establish the sludge or dispersive characteristics of a lubricant. Gel
permeation chromatography, a size exclusion method, separates polymeric
(oxidized oil/sludge) material from a lubricant base stock by molecular weight.
Circular pitch (gears): distance measured on the pitch circle between a point on
the face of one tooth and the same point on the adjacent tooth; equal to pi
divided by the diametral pitch.
Circulating oil system: a lubrication system in which the fluid that has passed
through a bearing or a group of bearings is recirculated by a pump. System
components may include settling tanks, filters, pumps, heat exchangers, etc.
Pressure is usually controlled by a pressure control valve.
Clarifier: an apparatus or device that eliminates color or cloudiness from a fluid,
mechanically or chemically separating out foreign material by gravity separation,
centrifugal action, filtration, simple heating or chemical treatment.
Clay treatment: a process in which used oil, from which all water has been
removed is brought into contact with activated clay at elevated temperatures
ranging from 180-210°F; acidic by-products in the used oil are adsorbed on the
surface of the clay. The batch process mixes the clay with the oil, the continuous
process passes the oil through a bed of clay; in either case, and the oil is filtered
Clay thickener: inorganic, non-melting grease thickener, commonly activated
Cleanliness rating: a rating based on the number of particles of specified sizes in
a measure of fluid. The ISO standard specifies particle counts at five microns
and 15 microns.
Cleveland open cup: see flash point, fire point.
Closure plug (lube systems): removable plug on the end of a bore.
Cloud Point – the temperature at which a cloud or haze of wax crystals appears
at the bottom of a sample of lubricating oil in a test jar, when cooled under
Coalescing separator: a device that combines or unites separate particles of a
substance through chemical affinity, physical trapping, etc. Coalescing filters
often trap and remove water from lubricants. Coalescence involves merging
particles of a dispersed phase.
Coastal pale oil: naphthenic petroleum oil refined from crude traditionally
obtained from the Gulf or the Pacific coast.
Coefficient of friction: the number obtained by dividing the force that resists
motion between two bodies by the normal force that brings the bodies together
(see static friction, dynamic friction, stick-slip ratio).
Coefficient of friction – the force required to move one body over a horizontal
surface at constant speed divided by the weight of the body. For example, if a
force of 4kg is required to move a body weighing 10 kilograms, the coefficient of
friction is 0.4.
Coefficient of friction of solids is independent of load. Coefficient of friction of
liquids is a function of the viscosity of the fluid, speed and pressure of the
Cohesion: the property of a substance that causes it to resist being pulled apart
by mechanical means.
Coking: undesired build-up of hard carbon deposits on equipment associated
with high heat.
Cold test: test that determines the pour point of oil.
Collar thrust bearing: the simplest form of thrust bearing; a thrust collar in roll
neck bearing service bears against the roll body at the fillet between the journal
and roll body.
Colloid: a suspension of extremely small particles (5-5000 angstroms) in a liquid;
the particles do not settle and are not easily separated by filtration. Colloids are
considered ionized particulates immune to agglomeration. Greases are colloidal
systems with thickeners dispersed in lubricating oil.
Colloidal lubricating solids: lubricating solids (especially graphite and
molybdenum disulfide) that are pulverized to colloidal size and mechanically
dispersed in a fluid.
Color standards: among the many different color tests, the most popular for
steel mill lubricants are ASTM D-1500 color (for standard fluids) and visual color
(for dyed fluids or greases). ASTM D-1500 utilizes an optical instrument to
determine the darkness of oils by comparison with standard colored discs.
Complex soap (grease): a thickener in which the soap crystals or fibers are
formed by the co-crystallization of two or more compounds, a selected soap and
a completing agent such as a salt or an additive. The resulting complex soap
usually increases the dropping point of the grease. Aluminum, calcium and
lithium are common complex soaps.
Compounding: see blending.
Compound: in chemistry, a distinct substance formed by the combination of two
or more elements in definite proportions by weight and possessing physical and
chemical properties different from those of the constituent elements. In
petroleum processing, generally connotes fatty oils and similar materials foreign
to petroleum, added to lubricants to impart special properties; such lubricants
are known as ‘compounded oils”.
Compressibility: the change in volume of a unit of fluid when subjected to a
unit change of pressure. Typical hydraulic fluids exhibit compressibility at very
high pressures, and compressibility may strongly affect frequency response in
Compression set (elastomer): the deformation that remains in an elastomer after
it has been subjected to and released from a compressive stress for a period of
time. Compression set measurements are used to evaluate the creep and stress
relaxation properties of rubber.
Concentricity (bearings): the uniformity of journal (or bearing) thickness
measured in a plane normal to the axis of the journal; also used to describe the
inside diameter axial exactness of a bore or the hole of the hose.
Condition monitoring: the use of specialized techniques that monitor the
condition of equipment and detect the onset of failure in sufficient time to plan a
maintenance intervention that prevents failure; these techniques include
lubricant analysis, vibration analysis, thermography, motor current signature
analysis, NDT surface inspections, ultrasonics, acoustic emission and process
Conjugate action (gears): transmission of uniform rotary motion from one shaft
to another by gear teeth, where the normals (perpendiculars) to the tooth profiles
at all possible points of contact pass through a fixed point, known as the pitch
point, in the common centerline between the two shafts.
Consistency (grease): describes the hardness of a grease (its resistance to
deformation), indicating relative softness or hardness with the application of
force. Test method ASTM D-217 measures the extent of penetration of a cone
under a fixed load and for a specific interval: the greater the penetration, the
softer the grease. Using this method, NLGI grades the softest grease (deepest
penetration) as 000, the hardest as 6.
Contact ratio (gears): measure of the extent to which more than one tooth carries
the load; for spur gears, this should be no less than 1:2-1:4, i.e., 20-40% of the
Controlled volume pump/constant volume pump: see positive displacement
Copper strip test (ASTM D-130 and D-4048): for specific periods of time at
certain temperatures, exposes copper strips to petroleum products to measure
the amounts of copper-corrosive substances they contain; the darkness of the
polished copper strip determines the extent of corrosion.
Counterbalance valve: a hydraulic device for restraining a load that might
otherwise fall faster than desired because of gravity.
Coupling: a frequently-used alternative term for “fitting”: a straight connector
for fluid lines; or a large-diameter device that connects the ends of two shafts,
between a motor shaft and a gear drive unit, for example (these may be either
solid or flexible, to allow for misalignment).
Cracking (oil): the application of heat and pressure that breaks down large
molecules to form smaller molecules.
Crambe oil: a vegetable oil pressed from the seed of Crambe abyssinica, related
to rape and mustard.
Cross porting (lube systems): a means of discharging lubricant from several
injectors through a common outlet.
Crown gear (gears): a bevel gear with a plane pitch surface. Among bevel gears,
the crown gear corresponds to the rack in spur gears.
Cup grease: see calcium grease.
Cutback solvent: see diluent.
Cutting fluid/oil: petroleum or chemical based products (or a combination of
the two) that cools and lubricates tools when cutting metals; used in such
processes as drilling, reaming, broaching, threading, milling, turning, shaving
Cycle indicator pin (lube systems): a pin attached to the piston of a divider
valve section; as the piston cycles, the pin extends from and retracts into the end
of the section. Used to monitor divider valve action and control lube cycle.
Cylinder: a device that converts fluid power into linear force and motion.
Cylinder oil (steam cylinder oils): a medium to high viscosity oil used for once-
through lubrication of cylinders in air compressors and steam engines, and for
valves and other elements in the cylinder area. High viscosities compensate for
the thinning effects of the high temperatures involved. Steam cylinder oils are
compounded with fatty oils to function where conditions are wet or saturated, or
where low-pressure steam is present.
Cylinder stock: a heavy lubricating oil stock made from distillation residue of
paraffin base crude; used primarily for blending.