Abrasion: The wearing away of a surface by
mechanical action, such as rubbing, scraping or erosion.
Abrasion Resistance: The ability of a rubber compound to resist
Absorption: The physical mechanism by which one
substance takes up another substance (liquid, gas or vapor) into its
Accelerated Life Test: Any set of test conditions
designed to reproduce, in a short time, the deteriorating effect obtained
under normal service conditions.
Accelerated Service Test: A service or bench test
in which some service condition, such as speed, temperature or continuity of
operation, is exaggerated in order to obtain a result in shorter time.
Accelerator: A substance which hastens the
vulcanization of an Elastomer, causing it to take place in a shorter time or
at a lower temperature.
Acid Resistance: With stands the action of acids.
Acrylic: A polymer for which resistance to air
and hot oil at temperatures above 30 degrees Fahrenheit are required.
Adhere: To cling or stick together.
Adhesion: Tendency of rubber to bond or cling to
a contact surface.
After Cure: Continuation of vulcanization after
the desired cure is effected and the heat source removed (Also Referred to
Aging: To undergo changes in physical properties
with age or lapse of time.
Aging, Accelerated: Tests run on various rubbers
to find out, in as short a period as possible, the destructive influence of
light, oxygen, heat and ozone.
Aging, Oxygen Bomb: A means of accelerating the
change in the physical properties of rubber compounds by exposing them to
action of oxygen at an elevated temperature and pressure.
Air Bomb: Similar to an oxygen bomb, but used
Air Checks: Surface markings or depressions due
to trapping air between the material being cured and the mold surface.
Air Curing: Vulcanization of a rubber product in
air, as distinguished from in a press or steam vulcanizer.
Alpha Particles: Positively charged particles
composed of two protons and neutrons (often referred to simply as helium
atom molecule); characterized by limited penetration.
Ambient Temperature: The surrounding temperature
relative to the given point of application.
Aniline Point: The lowest temperature at which
equal volume of pure, fresh aniline and oil will completely dissolve in one
another is the aniline point of the oil.
Antidioxidant: An organic substance which
inhibits or retards oxidation.
Antiozonant: A substance that retards or prevents
the appearance of cracks from action of ozone when the Elastomer is exposed
under tension, either statically or dynamically, to air containing ozone.
Antirad: A material which inhibits radiation
Atmospheric Aging Resistance: Loss of physical
properties due to the normal action of its surroundings (weather).
Atmospheric Cracking: Cracks produced in the
surface of rubber articles by exposure to atmospheric conditions.
Backrinding: Distortion at the parting line,
usually in the form of a ragged indentation.
Back-Up-Ring: (Anti extrusion device) A ring of
relatively hard and tough material, placed in the gland between the O-Ring
and groove side walls, to prevent extrusion of the O-Ring.
Bake Out: A process whereby a vacuum system is
heated for a given time at some predetermined temperature to degas all the
components,i.e. gauges, fittings, valves, seals.
Banbury (TM) Mixer: A specific type of internal
mixer used to blend fillers and other ingredients with an Elastomer.
Batch: The product of one mixing operation.
Bench Test: A modified service test in which the
service conditions are approximated, but the equipment is conventional
laboratory equipment and not necessarily identical with that in which the
product will be employed.
Beta Particles: Negatively charged particles or
electrons, characterized by limited penetration.
Bleeding: Migration to the surface of
plasticizers, waxes or similar materials, to form a film or bead.
Blemish: A mark, deformity or injury which
Blister: A raised spot in the surface, or a
separation between layers, usually forming void or air-filled space in the
Bloom: A dusty or milky looking deposit that
sometimes appears on the surface of an molded product after molding and
storage, caused by migration of a liquid or solid to the surface. Not to be
confused with dust from external sources.
Bond: The term commonly used to denote the
attachment of a given Elastomer to some other member. Bonds may be
classified by types, as follows: (a) Mechanical - purely physical attachment
accomplished by such means as "through" holes, interlocking fingers,
envelope design, riveting, etc.; (b) Cold - adhesion of previously
vulcanized Elastomer to another member through use of suitable contact
cements; (c)Vulcanized - adhesion of an Elastomer to a previously primed
surface using heat and pressure, thus vulcanizing the Elastomer at the same
Break: A separation or discontinuity in any part
of an article.
Break-Out: Force to inaugurate sliding. Expressed
in same terms as friction. An excessive break-out value is taken as an
indication of the development of adhesion.
Brittleness: Tendency to crack when deformed.
Buna-N: See Nitrile.
Buna-S: A general term for the copolymers of
butadiene and styrene. Also known as SBR and GRS.
Butaprene: See Nitrile.
Butt Joint: Joining two ends of a seal whereby
the junction is perpendicular to the mold parting line.
Butyl: A copolymer of iso-butylene and isoprene.
Calender: A machine used to form a sheet of
rubber between steel rollers.
Cell: A single small cavity surrounded partially
or completely by walls.
Chemical Bonding: A method of bonding rubber to
inserts by applying special adhesives to the insert prior to molding.
Chemigum: (TM, R.T. Vanderbilt Co.) See Nitrile.
Closure Dimension: Dimensions of a molded rubber
product that are affected by flash thickness (mold closure) variation.
Coating: A uniform layer of chemical primers or
adhesives to produce a chemical bond between the rubber and substrate. May
also refer to special surface treatments that can be applied to rubber to
achieve special properties.
Coefficient of Thermal Expansion: Average
expansion per degree over a stated temperature range, expressed as a
fraction of initial dimension. May be linear or volumetric.
Cold Flexibility: Flexibility following exposure
to a predetermined low temperature for a predetermined time.
Cold Flow: Continued deformation under stress.
Cold Resistance: Able to withstand the effects of
cold or low temperatures without loss of serviceability.
Commercially Smooth: Degree of smoothness of a
surface of an article which is acceptable for use.
Compound: A term applied to a mixture of polymers
and other ingredients to produce a usable rubber material.
Compression Molding: Molding process in which a
preload of rubber compound is normally placed directly in the mold cavity,
and compressed to shape by closure of the mold.
Compression Modulus: The ratio of the compression
stress to the resulting compression strain (the latter expressed in the
direction of force). Compression Modulus may be either static or dynamic.
Compression Set: The amount by which a rubber
specimen fails to return to its original shape after release of compressive
Conductive Rubber: A rubber capable of
conducting electricity. Most generally applied to rubber products used to
conduct static electricity.
Copolymer: A polymer consisting of two different
monomers chemically combined.
Corona Resistance: The ability of a rubber acting
as insulator to withstand the effects of high voltage discharge. Indications
of failure appear as surface cracks.
Corrosion (Packing): Corrosion of rigid member
(usually metal) where it contacts packing. The actual corroding agent is
fluid medium trapped in the interface.
Corrosive (Packing): A property of packing
whereby it is assumed (often incorrectly) to promote corrosion of a rigid
member of a trapped fluid.
Cracking: The sharp break or fissure in the
surface. Generally due to excessive strain.
Creep: The progressive relaxation of a given
rubber material while it is under stress. This relaxation eventually results
in permanent deformation, or "set".
Cross-Linking Agents: A chemical, or chemicals,
that bonds the polymer chains together to form a thermoset rubber product.
Cross-Section: A seal as viewed if cut at right
angles to the molding line, showing internal structure.
Cure: See Vulcanization.
Cure Date: Date when an O-Ring was molded, i.e.
"4 Q 96" means "Fourth Quarter, 1996".
Curing Temperature: The temperature at which the
rubber product is vulcanized.
Cylinder: Chamber in which piston, plunger, ram,
rod or shaft is driven by, or against, the system fluid.
Damping:The quality of an Elastomer to absorb
forced vibrational energy.
Deflashing: Any of various processes used to
remove the waste edge from a molded rubber part.
Degassing: The intentional, but controlled,
outgassing of a rubber substance or other material.
Dielectric Properties: The ability of a material
to resist puncture due to electric stress. The property is expressed in
terms of "volts per MIL thickness".
Diffusion: The mixing of two or more substances
(solids, liquids, gasses, or combinations thereof) due to the intermingling
motion of their individual molecules. Gasses diffuse more readily than
Durometer: (A) An instrument for measuring the
hardness of a rubber; measures the resistance to the penetration of an
indenter point into the surface of the rubber; (B) Numerical scale of rubber
Dynamic: An application in which the seal is
subject to movement, or moving parts contact the seal.
Dynamic Packing: A package employed in a joint
whose members are in relative motion.
Dynamic Seal: A seal required to prevent leakage
past parts which are in relative motion.
Elasticity: The property of an article which
tends to return to its original shape after deformation.
Elastomer: Any natural or synthetic material with
resilience or memory sufficient to return to its original shape after major
or minor distortion.
Electron Volt: Unit of energy in atom
calculations equal to 1.602 X 1012 ergs.
Elongation: Generally means "ultimate
elongation", or percent increase in original length of a specimen when it
EPDM (EPT, Nordel [TM, DuPont Co.]): Terpolymer
of Ethylene-Propylene-Diene (noted for excellent ozone resistance).
Erg: Unit of energy (C.G.S.) equal to one dyne
centimeter, or approximately equal to the work done by force of One (1)
milligram, causing a movement of one (1) centimeter.
Evaporation: The direct conversion from liquid to
vapor state of a given fluid.
Extrusion: Distortion or flow, under pressure, of
a portion of a seal into clearance between mating parts.
Feather Edge: The sharp, thin edge on parts, such
as wiper seals and cups. (Also called "Knife Edge").
Fixed Dimension: Dimensions on a rubber product
that are not affected by flash thickness or mold closure variation.
Flame Resistance: The resistance to burning of
material that will not withstand combustion under ordinary conditions.
Flash: Excess rubber left around a rubber part
after molding, due to space between mating mold surfaces; removed by
Flex Cracking: A surface cracking induced by
repeated bending or flexing.
Flex Resistance: The relative ability of a rubber
article to withstand dynamic bending stress.
Flexural Strength: The ability of a material to
flex without permanent distortion or breaking.
Flock: Fibrous filler sometimes used in rubber
Flow: Ability of heated plastic, or uncured
rubber, to travel in the mold and runner system during the molding process.
Flow Cracks: Surface imperfections due to
improper flow and failure of stock to knit or blend with itself during the
Fluid: A liquid or a gas.
Fluorocarbon: (Viton) [Viton is a Registered
trademark of DuPont Dow Elastomers], Fluorel [TM, 3M Co.]) A polymer
designed to meet the most rigid requirements in oils, solvents, synthetic
lubricants and corrosive chemicals, at elevated temperatures.
Friction: Resistance to motion due to contact of
Friction (Break Out): Friction developed during
initial or starting motion.
Friction (Running): Constant friction developed
during operation of a dynamic O-Ring.
Fuel (Aromatic): Fuel which contains benzene or
aromatic hydrocarbons; causes little swell of rubber.
Fuel (Non-Aromatic): Fuel which is composed of
straight chain hydrocarbons; causes little swell of rubber.
Gama Radiation: Electromagnetic disturbance
(photons) emanating from an atomic nucleus. This type of radiation travels
in wave form, much like X-Rays or light, but has a shorter wave length
(approx. 1 Ado or 107 mm). It is very penetrating.
Gasket: A device used to retain fluids under
pressure, or seal out foreign matter. Normally refers to static seal.
Gas Permeability: The degree to which a substance
resists permeation of gas under pressure.
Gates: The openings in an injection or transfer
mold that ensure the even flow of material into the cavity.
Gate Mark: A raised spot or small depression on
the surface of an injection or transfer molded part, where the gates
interface the cavity. (Also called "Sprue Mark")
Gland: The cavity into which an O-Ring is
installed. Includes the groove and mating surface of the second part, which
together confine the O-Ring.
GRS: See SBR.
Hardness: Resistance to a disturbing force.
Measured by the relative resistance of a material to an intender point of
any one of a number of standard hardness testing instruments. (See Durometer).
Hardness, Shore (TM, Wilson-Shore Instruments) A:
the rubber Durometer hardness as measured on a Shore (TM, Wilson-Shore
Instruments) "A" Gauge. Higher numbers indicate harder materials; lower
numbers, softer materials.
Heat Aging: A test for degradation of physical
properties as a result of exposure to high temperature conditions.
Heat Deflection Temperature: The temperature at
which a standard plastic test bar deflects 0.010 in. under a stated load of
either 66 PSI or 264 PSI.
Hermetic Seal: An airtight seal having no
evidence of detectable leakage.
Homogeneous: (A) General - a material of uniform
composition throughout; (B) In seals, a rubber seal without fabric or metal
Hydrocarbon Solvents - Aromatic: Solvents having
basic benzene structure, usually coat tar types such as benzene, toluene
Hypalon: DuPont trade name for chlorosulphonated
polyethylene; an Elastomer.
Identification: Colored dots or stripes on seals
for identification purposes; seldom used.
Immediate Set: The deformation found by
measurement immediately after removal of the load causing the deformation.
Immersion: Placing an article into fluid,
generally so it is completely covered.
Impact: The single, instantaneous stroke or
contact of a moving body with another, either moving or at rest, such as a
large lump of material dropping on a conveyor belt.
IRHD (International Rubber Hardness Degrees): A
method to characterize an Elastomer by its resistance to penetration of a
known geometry indenter by a known force. The micro technique is reproduced
on irregular, as well as flat, surfaces, and on cross sections as small as
1mm in thickness (.4"). The readings are similar, but not identical, to
Shore (TM, Wilson-Shore Instruments) A. (See Durometer)
Injection Molding: Molding in which the rubber or
plastic stock is heated and, while in the flowable state, is forced or
injected into the mold cavity.
Insert: Typically, a metal or plastic component
to which rubber or plastic is chemically and/or physically bonded during the
Isoprene-acrylonitrite Rubber: A low-plasticity
copolymer with around 34 per cent ACN.
Knit Mark: A witness mark on a molded part,
usually occurring at the midpoint between two transfer or injection sprue
locations. Caused by the incomplete joining of the uncured rubber or plastic
from each sprue during molding.
Leakage Rate: The rate at which a fluid (either
gas or liquid) passes a barrier. Total Leakage Rate includes the amounts
that diffuse or permeate the material of the barrier as well as the amount
that escapes around it.
Life Test: A laboratory procedure used to
determine the amount and duration of resistance of an article to specific
sets of destructive forces or conditions.
Linear Expansion: Expansion in any one linear
dimension, or the average of all linear dimensions.
Logy: Sluggish, low snap or recovery of a
Low Temperature Flexibility: The ability of a
rubber product to be flexed, bent or bowed at low temperature without
MM Hg: Millimeters of Mercury: In vacuum work, a
measure of absolute pressure, being the height of a column of Mercury that
the air or other gas will support. Standard atmospheric pressure will
support a Mercury column 760 millimeters high. Any value less than that
represents some degree of vacuum.
Mechanical Bond: A method of physically bonding
rubber to inserts through the use of holes, depressions or projections in
Memory: The tendency of a material to return to
original shape after deformation.
Microhardness: An electronic measurement of
rubber hardness for specimens below .25 inch in thickness. Micro hardness,
like Shore (TM, Wilson-Shore Instruments) A Durometer, is also a measure of
Mirror Finish: A bright, polished surface.
Mismatch: Unsymmetrical seal caused by dissimilar
cavities in mating mold sections.
Modulus: Tensile stress at specific elongation.
(Usually 100% elongation for Elastomers.)
Modulus of Elasticity: One of several
measurements of stiffness or resistance to deformation, but often
incorrectly used to indicate specifically static tension modulus.
Mold Cavity: Hollow space, or cavity, in the
mold, which is used to impart the desired form to the product being molded.
Mold Finish: The uninterrupted surface produced
by intimate contact of rubber with mold surface at vulcanization.
Mold Lubricant: A material usually sprayed onto
the mold cavity surface prior to the introduction of the uncured rubber, to
facilitate the easy removal of the molded part.
Mold Marks: Indentations or ridges embossed into
the skin of the molded product by irregularities in the mold cavity.
Mold Register: Accuracy of alignment/fit of mold
Molding Solutions: In the field of custom molded
rubber or plastic, the solution to your problems.
Mooney Scorch: The measurement of the rate at
which a rubber compound will cure or set up by means of the Mooney
Viscometer test instrument.
Mooney Viscosity: Measurement of the plasticity
or viscosity of an uncompounded, or compounded vulcanized, Elastomer seal
material by means of the Mooney Shearing Disk Viscometer.
Neoprene: (TM, DuPont) (GR-M) A polymer of
chloroprene which is prepared from coal, salt and limestone.
Nitrile: (see also Buna-N) The most commonly used
Elastomer for O-Rings because of its resistance to petroleum fluids, its
good physical properties, and its useful temperature range.
Nominal Dimension: Nearest fractional equivalent
to actual decimal dimension.
Non-aromatic: Straight chain organic structures,
such as petroleum type solvents.
Non-blooming: The absence of "bloom".
Occlusion: (A) The mechanical process by which
vapors, gases, liquids or solids are entrapped within folds of a given
substance during working or solidification; (B) the materials so trapped.
Off-register: Misalignment of mold halves causing
out-of-round O-Ring cross section.
Oil Resistant: Ability to vulcanize rubber to
resist the swelling and deteriorating effects of various types of oils.
Oil Swell: The change in volume of a rubber
article due to absorption of oil or other fluid.
O-Ring: A torus; a circle of material with round
cross section which effects a seal through squeeze or pressure.
O-Ring Seal: The combination of a gland and
O-Ring providing a fluid tight closure. (Some designs permit minimum
O-Ring Seal / Moving (Dynamic): O-Ring seal in
which there is relative motion between some gland parts and the O-Ring;
oscillating, reciprocating or rotary motion.
O-Ring Seal / Non-moving (Static): O-Ring seal in
which there is no relative motion between any part of the gland and the
O-Ring. (Distortion from fluid pressure or swell from fluid immersion is
Optimum Cure: State of vulcanization at which the
most desirable combination of properties is attained.
Outgassing: A vacuum phenomenon wherein a
substance spontaneously releases volatile constituents in the form of vapors
or gases. In rubber compounds, these constituents may include water vapor,
plasticizers, air, inhibitors, etc.
Over-Cure: A degree of cure greater than the
optimum, causing some desirable properties to be degraded.
Overflow Groove: A groove around the mold cavity
used to accept excess material from the cavity and to create a better "pack"
for the part.
Oxidation: The reaction of oxygen on a compound,
usually detected by a change in the appearance or feel of the surface, or by
a change in the physical properties, or both.
Oxygen Bomb: A chamber capable of holding oxygen
at an elevated pressure which can be heated to an elevated temperature. Used
for an accelerated aging test.
Ozone Resistance: Ability to withstand the
deteriorating effect of ozone (which generally causes cracking.)
Packing: A flexible device used to retain fluid
under pressure, or seal out foreign matter. Normally refers to a dynamic
Parting Line: The line on the surface of a molded
part where the mold plates meet.
Permanent Set: The deformation remaining after a
specimen has been stressed in tension for a definite period, and released
for a definite period.
Permeability: The rate at which liquid or gas,
under pressure, passes through a solid material by diffusion and solution.
In rubber terminology: the rate of gas flow, expressed in atmospheric cubic
centimeters per second, through an elastomeric material, one centimeter
square and one centimeter thick.
Permeation: The diffusion of a media (generally a
gas) through a rubber or plastic component.
PH: Determines the concentration of either an
acid or a base.
Pit (or Pock) Mark: A circular depression,
Plasticity: When subject to sufficient shearing
stress, any given body will be deformed. After stress is removed, if there
is no recovery, the body is completely plastic. If recovery is complete and
instantaneous, the body is completely elastic. A balance between the two is
Plasticizer: A substance, usually a heavy liquid,
added to an Elastomer to decrease stiffness, improve low temperature
properties, and improve processing.
Plastometer: An instrument for measuring the
plasticity of a raw or unvulcanized compounded rubber.
Polymer: A material formed by joining together
many (poly) individual units (mer) of one or more monomers; synonymous with
Polymerization: Chemical reaction whereby simple
materials, either one or more, are converted to complex material which
possesses properties entirely different from the original materials used to
start the reaction.
Polyurethane: An organic material noted for its
high abrasion, ozone, corona and radiation characteristics.
Porosity: Quality or state of being porous.
Post Cure: The second step in the vulcanization
process for some specialized Elastomers. Provides stabilization of parts and
drives off decomposition products resulting from the vulcanization process.
Pot: The chamber, in the transfer or injection
mold, where raw material is placed before it is transferred into the cavity.
Pure Gum State: A non pigmented, translucent
Radiation: An emission, of varying content, from
a disturbed atom undergoing internal change. There are two broad
classifications: (A) Corpuscular, comprising streams of particles, either
neutral or charged, e.g. protons, neutrons, electrons; and (B)
Electromagnetic, comprising wave-like emissions as gamma, ultraviolet, etc.
Radiation Damage: A measure of the loss in
certain physical properties of organic substance, such as Elastomers, due
principally to ionization of the long chain of molecules; believed to result
in redundant cross-linking and possible scission of the molecules. The
effect is cumulative.
Radiation Dosage: The total amount of radiation
energy absorbed by a substance. This value is usually expressed in "ergs per
gram", and is denoted by the following units: (A) Roentgen - a quantity of
gamma or X-Ray radiation equal to approximately 83 ergs of absorbed energy
per gram of air; (B) REP (Roentgen Equivalent - Physical) - a quantity of
ionization that causes an energy absorption of approximately 83 to 93 ergs
per gram of tissue; (C) REM (Roentgen Equivalent - Man) - similar to REP,
except used to denote biological effects; and; (D) RAD - the unit of dosage
related to Elastomers, independent of type of radiation specimen, and
denoting energy absorption level of 100 ergs per gram of Elastomer:
approximately equal to 1.2 Roentgens.
Rebound: A measure of the resilience, usually as
a percentage of vertical return of a body which has fallen and bounced.
Reciprocating Seal: Seal used in linear motion
Register: The accurate matching of the plates in
Reinforcement Agent: Material dispersed in an
Elastomer to improve compression, shear or other stress properties.
Relative Humidity: The ratio of the quantity of
water vapor actually present in the atmosphere, to the greatest amount
possible at a given temperature.
Resilience: Ability of an Elastomer to return to
original size and shape after deforming forces are removed; generally
expressed in per cent of the ratio of energy removed, to the energy used in
compressing. (Resilient: having that capability.)
Rotary Seal: A seal, such as an O-Ring or a
Quad-Ring seal, exposed on either the ID or OD sealing surface to a rotating
component,e.g. shaft seals.
Rough Trim: Removal of superfluous material by
pulling or picking; usually the removal of a small portion of the flash or
sprue which remains attached to the product.
Rubber: See Elastomer.
Rubber Natural: Raw or crude rubber obtained from
Rubber, Synthetic: Manufactured or man-made
Runner: The system for leading rubber and plastic
materials into the gate of an injection mold.
Runout (Shaft): Expressed in inches and/or TIR
(Total Indicator Reading); refers to twice the radial distance between shaft
axis and axis of rotation.
SBR: Copolymer of Butadiene and Styrene; an all
purpose type synthetic, similar to natural rubber. (Butadiene is a gaseous
material of petroleum; Styrene, a reaction product of ethylene and benzene.)
Scorching: Premature curing or setting up of a
raw compound during processing.
Seal: Any device used to prevent the passage of a
fluid, gas or liquid.
Seal-Off: A minimum .032 inch (.813 mm) step on
an insert that minimizes flash on the OD, and prevents flash from forming
across the insert.
Service: Operating conditions to be met.
Shaft: Reciprocating or rotating member, usually
within a cylinder; not in contact with the walls.
Shelf Aging: The change in a material's
properties which occur in storage with time.
Shore (TM, Wilson-Shore Instruments) A: See
Shore (TM, Wilson-Shore Instruments) M: A
Durometer hardness instrument, using a micro-indenter designed for the
purpose of measuring O-Ring hardness.
Shrinkage: 1) The ratio between a mold cavity
size and the size of a product molded in that cavity, 2) Decreased volume of
a seal, usually caused by extraction of soluble constituents by fluids
followed by air drying.
Silicone Rubber: Elastomer that retains good
properties through extra wide temperature ranges.
Size, Actual: Actual dimension of the product,
including tolerance units.
Size, Number: Number assigned to indicate inside
and cross section diameters of an O-Ring; established in the SAE standard AS
568, adopted by the military and industry.
Sliding Core: A pin on a mold that automatically
retracts when the mold opens.
Sorption: A term used to denote the combination
of adsorption and absorption processes in the same substance.
Specific Gravity: Ratio of the weight of a given
substance, to the weight of an equal volume of water, at any specific
temperature. Sphericity: The measure of a tolerance of a molded ball, or
ground ball, in reference to a perfect sphere; also described as
Spiral Twist: A type of seal failure in
reciprocating application that results from the twisting action that strains
or ruptures the rubber.
Sprue: The primary feed channel that runs from
the outer face of an injection or transfer mold, to the mold gate in a
single cavity mold, or to the runners in a multiple cavity mold.
Sprue Marks: Marks left on the surface of a
rubber part, generally elevated, after removal of the sprue or cured
compound in the gate, through which the compound is injected or transfer
Squeeze: Cross section diametrical compression of
O-Ring between surface of the groove bottom and surface of the other mating
metal part in the gland assembly.
Static Seal: Part designed to seal between parts
having relative motion. (See Gasket)
Statistical Process Control (SPC): The use of
statistical techniques on processes and their output, to establish process
stability and increase capabilities.
Strain: Deflection due to force.
Stress: Force per unit of original cross section
Stress Relaxation: Decreasing stress with
constant strain over a given time interval. (Viscoelastic response.)
Sublimation: The direct conversion of a substance
from solid state to vapor state, passing through a transitory liquid state.
The vapor, upon recondensing, reforms into the solid state with no
intervening liquid phase.
Surface Finish: A numerically averaged value of
surface roughness, generally in units of microinches or micrometers.
Sun Checking: Surface cracks, checks or grazing
caused by exposure to direct or indirect sunlight.
Swell: Increased volume of a specimen, caused by
immersion in a fluid (usually liquid).
Tack: The degree of adhesion of materials of
identical nature to each other.
Tear Strength: The force required to rupture a
sample of stated geometry.
Tear Resistance: Resistance to growth of a cut or
nick when tension is applied to the cut specimen. Commonly expressed as
pounds per square inch thickness.
Temperature Range: Maximum and minimum
temperature limits in which a seal compound will function in a given
Tensile Strength: Force, in pounds per square
inch, required to cause the rupture of a specimen of rubber material.
Tension Modulus: Resistance to being stressed;
defined as the force, in pounds, necessary to stretch a piece of rubber, one
square inch in cross section, a specified amount. Normally expressed as a
percentage of original length, and the stress as pounds per square inch at
the fixed elongation.
Terpolymer: A polymer consisting of three
different monomers, chemically combined.
Thermal Expansion: Expansion caused by increase
in temperature; may be linear or volumetric.
Thermoplastic: A plastic capable of being
repeatedly softened by increase of temperature, and hardened by decrease of
Thermoplastic Rubber: Rubber that does not
require chemical vulcanization and will repeatedly soften when heated and
stiffen when cooled; and which will exhibit only slight loss of original
Thermoset: An Elastomer or plastic cured under
application of heat or chemical means, to make a product substantially
infusible or insoluble.
Thiokol: An organic polysufide.
Threshold: The maximum tolerance of an Elastomer
to radiation dosage, expressed as a total number of ergs per gram (or rads)
beyond which physical properties are significantly degraded. This is
generally an arbitrary value, depending on function and environment.
Torque: The turning force of a shaft.
Torr: The unit of pressure used in vacuum
measurement; equal to 1/760 of a standard atmosphere, and for practical
purposes, is equivalent to one millimeter of Mercury (mmHg).
Torsion Strength: Ability of rubber to withstand
Total Indication Reading (TIR): System that
measures the roundness of a part in relationship to a center line.
Transfer Molding: A method of molding in which
material is placed in a pot, located between the top plate and plunger, and
squeezed from the pot through gates (or sprues) into the mold cavity.
Trapped Air: Air which is trapped in a product or
a mold during cure. Usually causing a loose ply or cover, or a surface mark,
depression or void.
Trim: The process involving removal of mold
Trim Out: Damage to mold skin or finish by close
Under Cure: Degree of cure less the optimum; may
be evidenced by tackiness, loginess or inferior physical properties.
Ultimate Elongation: A measure of how far a
material will stretch before breaking; expressed as a percentage of its
Undercut: A groove on either the outside or the
inside of a molded part.
Vacuum: The term denoting a given space that is
occupied by a gas at less then atmospheric pressure. For degrees of vacuum,
see Vacuum Level.
Vacuum Level: The term used to denote the degree
of vacuum evidenced by its pressure in torr (or mmHg):(a) Rough vacuum = 760
torr to 1 torr, (b) Medium vacuum = 1 torr to 10-3 torr, (c) High vacuum =
10-3 torr to 10-6 torr, (d) Very High vacuum = 10-6 torr to 10-9 torr, (e)
Ultra High vacuum = below 10-9 torr.
Vapor: The gaseous state of a fluid that normally
exists as a liquid under atmospheric conditions, i.e. a gas whose
temperature is below its critical temperature.
Vapor Pressure: The maximum pressure exerted by a
liquid or a solid, heated to a given temperature in a closed container.
Vibration Dampening: The ability of an Elastomer
to absorb vibrational or shock energy.
Viscosity: The property of fluids and plastic
solids by which they resist an instantaneous change of shape, i.e.
resistance to flow.
Void: The absence of material, or an area devoid
of materials where not intended.
Volatilization: The transition of either a liquid
or a solid directly into vapor state. In the case of a liquid, this
transition is called evaporation, whereas in the case of a solid, it is
Volume Change: A change in the volume of a seal
as result of immersion in a fluid; expressed as a percentage of the original
Volume Swell: An increase in the physical size
caused by the swelling action of a liquid.
Vulcanization: A thermosetting reaction involving
the use of heat and pressure, resulting in greatly increased strength and
elasticity of rubber-like materials.
Vulcanizing Agent: A material which produces
vulcanization of an Elastomer.
Weather Resistance: The ability to withstand
weathering factors, such as: oxygen, ozone, atmospheric pollutants, erosion,
temperature cycling and ultraviolet radiation.
Weathering: The detrimental effect upon an
Elastomer or plastic after outdoor exposure.
Width: Seal cross-section or thickness.
Wiper Ring: A ring employed to remove excess
fluid, mud, etc., from a reciprocating member before it reaches the packings.