Glossary of rubberterms

Abrasion: Surface wear caused by relative motion between contacting objects
Abrasion Resistance: The ability of a rubber compound to resist surface wearing by mechanical action
ABS: Acrylonitrile-butadiene-styrene
Accelerator: A chemical compound that speeds up the vulcanization of natural or synthetic rubbers
Adhering Flash: Extremely thin flash (usually less than .002' thick) that adheres to the finished part during molding or deflashing processes
Age Protection - Active: the use of a chemical additive in a rubber compound which is preferentially attached by oxygen or ozone thereby sacrificially protecting the rubber
Age Protection - Passive: The use of a chemical additive in a rubber that will migrate to the surface of a rubber part to form a protective physical barrier
Aging: The change in physical and chemical characteristics of an elastomer that has been exposed to a particular environment over time
Alloy: A composite material produced by blending polymers or copolymers with other polymers under selected conditions to achieve greater physical properties
Ambient Temperature: The temperature of the environment surrounding a particular object
Aniline Point: The lowest temperature at which equal parts of aniline and a test liquid (such as oil) will uniformly mix or blend. The aniline point of oil is a measure of aromaticity (the amount of unsaturated hydrocarbons present). The lower the aniline point, the more unsaturants are present and the higher the potential for swelling certain rubber compounds
Annealing: A process of holding a material at a temperature near, but below, its melting point, to permit stress relaxation without distortion of shape. Often used on molded article to relieve stresses set up by flow into the mold
Antioxidant: Any organic compound that slows the process of oxidation
Antiozonant: Any substance that slows the severe oxidizing effect of ozone on elastomers. Exposure to ozone typically causes surface cracking in many rubbers
AQL: Accepted quality level
Aromatic: A major group of unsaturated cyclic hydrocarbons containing one or more rings. A typical aromatic compound is benzene, which has a six carbon ring, containing three double bonds
ASA: Acrylic-styrene-acrylonitrile
ASTM: American Society for Testing Materials
ASTM: American Society for Testing and Materials, An organization for issuing standard specifications on materials, including metals and alloys
Axial: The change in physical and chemical characteristics of a rubber compound that has been exposed to a particular environment over time
Axial Seal: Squeezed, like a gasket, on both the top and bottom surfaces of the seal's cross section. A face seal
Backup ring: A washer-like device of a relatively hard, tough material installed in the gland on the downstream side of the seal to prevent seal extrusion into the diametrical gap while under pressure
Backup washer: A washer made from certain material that will add strength or support when installed next to the seal. This prevents the seal from being pinched and evenly distributes the load
Base Line: The mark from which all features are dimensioned
Batch Control: A process of keeping separate a batch of a rubber compound from the time it is molded through the entire production process up to and including the Shipping Department
Batch Number: The assigned number that identifies a batch or rubber
Bloom: A milky surface discoloration caused by the migration of certain compound components (such as antiozonants) to the rubber's surface after molding or storage. The waxy film serves as a protective coating shielding the part from oxidation. This discoloration DOES NOT adversely affect material performance
Bond: The mechanical or chemical force that holds an elastomer to some other object. Mechanical bonding includes component interference and no molecular cross-bridging between the elastomer and substrate, whereas chemical bonding involves contact adhesives with heat and pressure to adhere an elastomer to a primed surface
Bonding: The method of securing molded rubber directly to an insert. There are two types; A. Mechanical, where the insert is designed with ribs, grooves or holes which enable the adhesive action with rubber when molded around the insert. B. Chemical, where the insert is treated with a point that has an adhesive action with rubber when molded around the insert
Bore: A hole machined in a component which permits the passage of a shaft
Brittleness: Tendency to crack upon physical deformation
Carbon Black: A black material used as a filler in rubber. It gives the rubber its black color and the hardness characteristics
Cavity: The features of a mold which are directly responsible for forming the final shape of a molded part
Charge: The measurement or weight of material used to load a mold at one time or during one cycle
Chemical bonding: A method for bonding rubber to secondary parts by applying special adhesives to the part prior to molding
Circularity: the form tolerance of the surface of a molded or ground ball in reference to a perfect sphere. Also referred to as "roundness"
Clamping Pressure: The pressure applied to the mold to keep it closed during a cycle
Clearance (in a sealing system): The space between components in a mechanical system which is present to allow for manufacturing, thermal, and dynamic variations in the size and position of the components. As measured, it is equal to the distance between the sealing surface and the entrance to the seal groove. In a radial sealing system, this will be the space between the O.D. of the shaft or piston and the I.D. of the bore. As the clearance in a system increases, the tendency of the seal to dislodge from the grove and enter into the clearance space also increase, especially in applications where pressure is present. Care should be taken in radial applications to note whether clearances are being stated as radial clearances or as diametral clearances
Coating: A uniform layer of chemical primers or adhesives applied to a surface 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 desired properties
Coefficient of Thermal Expansion: Value used to determine the amount of linear dimensional change for a particular elastomer, which is temperature dependent
Cold Flexibility: Flexibility following elastomer exposure to a specified low temperature for a specified period of time
Cold Flow: A term describing the tendency of certain materials to continue to deform or "creep" under constant sealing pressure (compressive load)
Compound: A mixture of a polymer and associated chemical ingredients necessary to produce a finished rubber material. The term is commonly used when referring to a specific rubber formulation
Compression Molding: A molding process in which the uncured rubber compound is placed directly into the mold cavity, and compressed to its final shape by the closure of the mold
Compression Set: the permanent deformation experienced by a rubber material when compressed for a period of time. The term is commonly used in reference to a test conducted under specific conditions wherein the permanent deformation, expressed as a percentage, is measured after a prescribed period of time. A low compression set is desirable in molded rubber parts such as seals and gaskets, which must retain their dimensions to maintain an effective seal.
Compressive Strength: The maximum compressive stress carried by a test specimen during a compression test
Concentricity: A condition in which two or more features (cylinder, cones, spheres, hexagons, etc..) in any combination, have a common axis
Conversion Fahrenheit to Celsius: F=(Â° C x 9/5) +32 C=(Â° F - 32) x 5/9
Conversion Celsius to Fahrenheit: C = (Â° F - 32) x 5.9 F = (Â° C x 9.5) + 32
Conversion Kilograms to Pounds: kg = lbs x 0.454 lbs = kg x 2.205
Conversion Millimeters to Inches: mm = in x 25.4 in = mm x 0.03937
Conversion Pounds to Kilograms: lbs = kg x 2.205 kg = lbs x 0.454
Cooling Channels: Channels located within the body of a mold through which a cooling medium is circulated to control the mold surface temperature
Copolymer: An elastomer (polymer) resulting from the chemical combination of two dissimilar monomers. For example, Buna N from Butadiene and Acrylonitrile
CPK: Describes how capable the stable process is of meeting design specifications. The CPK measures the distance from the process average (xbar) to the nearest specification and compares it to the natural variation in the process
Cracking: Sharp breaks or fissures in rubber surfaces resulting from excessive strain or exposure to adverse environmental factors
Crazing: Fine cracks which may extend in a network on or under the surface or through a layer of plastic material
Creep: The progressive relaxation of an elastomeric material under constant sealing pressure (compressive load). Also known as cold flow. also called shrink
Cross-linking Agents: A chemical or chemicals that bond the polymer chains of a rubber together during the molding process
Cross-Section (of a seal): the axial thickness or radial width of an O-Ring or Quad-RingÂ® seal. For an O-Ring, this will be the circular diameter of its cross-section. For a Quad-Ring,Â°Â® this will be the length of a side of a square circumscribed about the cross-section
Cross-Sectional Reduction (of a seal): The reduction in thickness of a seal's cross-sectional a result of material displacement caused by an applied stretch to the seal See also Necking
Cross Section-Axial: When the part is flat (relative), the cross section that is at 90 to the linear plane
Cross Section-Radial: When the part is flat (relative), the cross section in the linear plane
Cure: A. One complete cycle. B. The thermo process that causes a chemical change in the raw stock, turning it into the finished rubber part
Cure Time: The preset time needed to complete the curing process
Cure Weight: The prescribed weight of stock needed to make one cure of parts, usually stated on the load card (7-card) in ounces or grams
Curing: An informal (slang) term for the vulcanizing process that cross-links a rubber to form its characteristic elastic properties See also Vulcanization
Curing temperature: The temperature of vulcanization
Cylinder: Chamber in which a piston is driven
Cross-Sectional Compression: The deformation placed on a rubber part to affect a seal. It is expressed as a percentage of the seal's original (undeformed) cross-section. See also Squeeze
Damping: The ability of an elastomer to absorb forced vibrational energy
Daylight Opening: The clearance between two platens of a clamping press in the open position
Deflashing: Any of various processes used to remove extraneous rubber from a molded rubber part
Delamination: The surface of the finished part separates or appears to be composed of layers of solidified resins. Strata or fish scale-type appearance where the layers may be separated
Density: Weight per unit volume of a substance expressed in grams per cubic centimeter
Diametrical Clearance: The gap between the two mating metal surfaces forming a gland's internal cavity. Through slight oversizing and accompanying "squeeze" the O-Ring seals this gap to prevent system leakage
Diaphragm Gate: Used in symmetrical cavity filling to reduce weld-line formation and improve filling rates
Die Cut: The process of stamping out the I.D. or O.D. parting line flash or feed from a part. The part is placed on a mechanical fixture to perform this function
Dispersion: Finely divided particles of a material in suspension in another substance
Double Injection: A molding defect that is 100% avoidable by following proper molding procedure. It is identified by a flat raised injection that peals away by using your thumb nail. It is caused by not completely unloading a mold of its parts and another cure is run on top of the parts that were left in the mold from the previous cure
Draft: The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold
Durometer: Standard rubber industry test instrument which uses an indenter to measure the hardness of molded rubber. While other scales are available, the hardness of rubber is most commonly reported by a durometer using the Shore A scale
Dwell: A pause in the application of pressure to a mold, made just before the mold is completely closed, allowing any gases formed or present to escape from the molding material
Dynamic Seal: A seal used in an environment that subjects it or a mating surface to movement
Elastic Limit: Maximum stress that a material will stand before permanent deformation occurs
Elasticity: A rubber's ability to return to its original size and shape after removal of the stress causing deformation such as stretching, compression, or torsion. It is the opposite of plasticity. The term elasticity is often loosely employed to signify the "stretchiness" of rubber
Elastomer: Any of various polymers having the elastic properties of rubber
Elongation: Generally referred to in terms of tensile (pull apart) testing, elongation is the increase in length of a test specimen, expressed as a percentage of its original (unstretched) length... relative to a given load at the breakpoint
EMI: Electromagnetic interference
Encapsulating: Enclosing an article (usually an electronic component) in a closed envelope of plastic, by immersing the object in a casting resin to polymerize or, if hot, to cool
Extending Flash: Flash that is formed at the parting line of a mold
Extrusion: When part or all of a component is forced from its groove by high continuous or pulsating pressure
Face Seal: A sealing system in which the sealing occurs in the axial direction of the seal. If the seal ring were to be placed flat upon a desktop, the seal compression would occur between the top and bottom of the seal
Family Mold: A multi-cavity mold where each of the cavities forms one of the component parts of the assembled finished part
FDA: Food & Drug administration
Feed: The area or orifice where rubber is injected or transferred into a mold cavity
Filler: A finely divided material used to reinforce or modify elastomer physical properties, impart certain processing properties, or reduce cost. Typical examples are carbon black, clays, calcium carbonates and silicas
Flash: Extraneous material protruding from the surface of a molded part. Flash is generally found on a molded part at the parting line locations
Flexural strength: The ability of a material to flex without permanent distortion or breaking
Flow: The ability of heated plastic or uncured rubber to travel in the mold and runner systems during the molding process
Flow Line: A disturbance in the homogeneous structure of a molded part generally caused when material knitted or blended with itself during the molding operation
Flow Marks: Wavy surface appearance of an object molded caused by improper flow of the plastic into the mold. A mark made by the freezing-in of a visible flow pattern
Friction (Break-out): Friction developed in dynamic seal situations during machine start-up. When machine operation is irregular, O-rings tend to conform (adhere) to the microfine grooves of surrounding glandular surfaces, requiring extra initial force to break them out of these microfine grooves
FRP: Fiber reinforced plastics
Cooling: Block of metal or wood used to maintain the proper shape or dimensional accuracy of a part after it is removed from the mold until it is cool enough to retain its shape without further appreciable distortion. Also known as "shrink fixture"
Gasket: A static (stationary) sealing device used to retain fluids under pressure or to seal out foreign matter
Gate: In injection and transfer molding, the orifice through which the melt enters the cavity. Sometimes the gate has the same cross-section as the runner leading to it; often, it is severely restricted
Geometric Dimensioning & Tolerancing: A means of specifying engineering design and drawing requirements with respect to actual function and relationship of part features. Furthermore, it is a technique which properly applied ensures the most economical and effective production of these features
Gland: The space in a mechanical system into which a seal is installed. the gland consists of the seal groove and any additional space required to achieve the proper compression of the seal. Care should be taken to distinguish between the terms gland and groove, which are separate but related concepts
Groove: The machined glandular recess into which the seal is fitted
Groove Depth: The measured depth of a feature, frequently a slot, machined or otherwise created in a mechanical system to physically locate and constrain a seal. Care should be taken to distinguish between the terms Gland Depth and Groove Depth, which are separate but related concepts
Hardness: A measurement of the resistance to penetration of a rubber sample by an indenter. High values indicate harder materials while low values indicate softer materials. See also Durometer, IRHD, and Shore A
HDT: Heat-deflection test
Heat deflection temperature: The temperature at which a standard plastic test bar deflects 0.010 in. (.254mm) under a stated load of either 66 or 264 psi (4.55 or 18.2 Bar)
Heat Sealing: A method of joining plastic parts or films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied by conduction or dielectrically
Hermetic Seal: An airtight seal
HM: High-modulus
HMC: High-strength molding compound
HMW: High molecular weight
Honing: A machining process that sharpens, enlarges, and smooths material through the use of a fine-grit stone
Impact Resistance: Relative susceptibility of plastics to fracture by shock as indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow
Injection: The cone shaped holes that taper down to the cavity area normally in the top plate of a transfer type mold. The stock is forced through these holes when the mold is under pressure. The rubber then fills the cavity area and forms a rubber part
Injection Molding: A molding method in which a rubber or plastic material is heated and forced under pressure into the mold cavity
Injection Pressure: The pressure on the face of the injecting ram when injecting material into the mold
Injection Ram: The ram or screw that applies pressure to the molten plastic material to force it into the mold cavities
Insert: A term referring to a metal or plastic component, placed ("inserted") into a mold cavity prior to the start of the molding cycle, to which rubber or plastic is chemically and/or physically bonded during the molding process
Internally Lubricated Rubber: A rubber formulation containing lubricating materials. An internally lubricated rubber is designed to reduce the materials coefficient of friction
IRHD (International Rubber hardness Degrees): A system of characterizing an elastomer by its resistance to penetration of a known geometry indenter by a known force. the microtechnique is reproducible on irregular as well as flat surfaces and on cross sections as small as 1mm in thickness (.04"). Measurements taken using the IRHD scale are similar, but not identical, to those obtained using the Shore A scale
I.D. (Inner Diameter): The innermost (smallest diameter) surface of a circular object, such as a bore or a round seal. the term I.D. is frequently used to indicate both the circumferential surface itself as well as the measured diameter of that surface
Jig: A tool for holding parts of an assembly during the manufacturing process
Laminar Flow: The flow of a resin in a mold is accompanied by solidification of the layer in contact with the mold surface that acts as an insulator through which material flows to fill the remainder of the cavity
LCP: Liquid crystal polymer
LIM: "Liquid injection molding" is a closed manufacturing process using LSR in an injection molding machine
Low temperature Flexibility: The ability of an elastomeric product to be flexed or bent at low temperatures without cracking
LSR: "Liquid silicone rubber" is composed of a two-component, low viscosity, heat-curable rubber system
L/D Ratio: The term used to define an extrusion screw. This is the screw length to screw diameter ratio
Mechanical bond: A method of creating a molded part where the rubber is mechanically attached to an overmolded insert through the use of holes, depressions or projections on the insert
Melt Index: A measure in grams of plastic material that can be forced through an orifice of 0.0825 inches when subjected to a force of 2160 grams in 10 minutes at 190Â°C
Memory: Ability of an elastomeric material to return to its original size and shape after deformation
Metric Units: Milli Centi Deci Meters Liters kilo Deka Grams Hecto
Microhardness: A measurement of rubber hardness for specimen's below .25 inches (6.35mm) in thickness. Microhardness, like Shore A durometer, is also a measurement of indentation
Mismatch: Unequal O-ring cross-sectional radii caused by dimensional differences in the mold cavity
Modulus: A measure of resistance of a material to deformation. It is measured by the force required to reach a predetermined compression or extension
Modulus of Elasticity (tension): Force which would be required to stretch a substance to double its normal length, on the assumption that it would remain perfectly elastic, i.e., obey Hooke's Law throughout the test. The ratio of stress to strain within the perfectly elastic range
Moisture Marks or Welds: Marks on the finished part that are caused from moisture in the resin and look like weld lines except they may be in the wrong areas for weld lines
Mold: Typically made from steel. Product is formed within machined cavity
Mold Base: Refer to mold frame
Mold Cavity: Hollow space of the mold within which the uncured rubber compound is shaped and cured to the desired finished product form
Mold Finish: The surface finish of the mold which imparts the desired surface quality to the finished molded product
Mold Shrinkage: The difference in dimension, expressed in inches per inch, between a part and the cavity in which it was molded, when both are measured while at room temperature
MSDS: Material safety data sheet
Mold: A mold which is open when the material is introduced and shapes the material by heat and by the pressure of closing
Nominal Dimension: The mean dimension of a molded article, from which small dimensional (plus and minus) deviations are allowed as manufacturing tolerances
Non-fill: An unintentional void or absence of material in the rubber structure of a part
Nozzle: The hollow cored metal nose screwed into the extrusion end of the heating cylinder of an injection machine or a transfer chamber where there is a separate structure. A nozzle is designed to form a seal under pressure between the heating cylinder or the transfer chamber and the mold. The front end of nozzle may be either flat or spherical in shape
O-Ring: A doughnut-shaped object, or torus, that functions as a seal, blocking the passage of liquids or gases, by being compressed between the two mating surfaces comprising the walls of the cavity (gland) into which the ring is installed
Oil Resistant: Ability of vulcanized rubber to resist swelling and other detrimental effects of exposure to various oils
Orange Peel: A surface finish on a molded part that is rough and splotchy. Usually caused by moisture in the mold cavity
Oscillating Seal: Most commonly used in faucet valves, in this application the inner or outer member of the gland moves in an arc around the axis of a shaft. Movement is limited to a few turns in one direction and a few turns in the return direction (i.e. faucet on, faucet off)
Outgassing: Primarily occurring in vacuum situations, the volatile (evaporative) components of some rubber compounds may become vaporized in the vacuum and released (outgassed) by the compound into the surrounding environment
Overflow: A designed escape reservoir for rubber compound used to insure mold cavity fill and also allowance for excess compound
Overflow Groove: A groove around the periphery of a mold cavity used to accept any excess material from the cavity during molding. Additional material beyond that which is required to fill the cavity is usually introduced into the cavity to ensure that the part is completely formed and to minimize the presence of entrapped air and voids
Oxidation: The reaction of oxygen with a rubber compound, typically resulting in surface cracking of the rubber material. As oxidation involves the transfer of electrons, reduction in the physical strength of elastomers may also occur from exposure to the oxidizing agent
O.D. (Outer Diameter): The outermost (largest diameter) surface of a circular object, such as a shaft or a round seal. the term O.D. is frequently used to indicate both the circumferential surface itself as well as the measured diameter of that surface
Packing: The filling of the mold cavity or cavities as full as possible without causing undue stress on the molds or causing flash to appear on the finished parts
Parting line: The witness line on the surface of a molded part corresponding to the location where the mold plates were in contact
Permanent Set: The deformation remaining in a rubber specimen following both stress and relaxation over a period of time
Permeation: The diffusion of a medium (generally a gas) through a rubber or plastic material
Pinch Off: A raised edge around the mold cavity that seals off the part and separates excess material as the mold closes around the parison in the flow-molding operation
Piston Seal: A bore seal in which the seal is mounted in a groove machined into a piston. The term piston seal usually implies an application involving linear reciprocating motion
Plasticize: to soften a material and make it plastic or moldable, either by means of a plasticizer or the application of heat
Plasticizer: A chemical agent added to the rubber compound batch mix to soften the elastomer for processing, as well as to improve physical properties of the compound product (i.e., increase elongation, reduce harness, improve tack)
Polymer: A long molecular chain material formed by the chemical combination of many similarly structured, small molecular units
Post-curing: The process of baking or autoclaving parts after molding. This process is used to improve the heat and compression set resistance of specific elastomers (e.g. silicones and fluorocarbons)
Pot: The chamber in a transfer or injection mold where raw material is placed before it is transferred into the cavity
Preload: The term used for the weighed up stock that is placed in the mold for making a cure
Pressure Injection: The pressure on the face of the injection ram at which molding material is injected into a mold. It is usually expressed as P.S.I.
Primary Sealing Surface: The primary location in a sealing system where a seal and a mating surface come in contact with the intention of forming a barrier to prevent the passage of some type of medium, such as a fluid or a gas. The Primary Sealing Surface is usually distinguished from other sealing surfaces by the presence of relative motion in the case of a dynamic seal, or by the interface of assembled components in the case of a static seal. this term is often used interchangeably with the more generic term Sealing Surface
Purging: Cleaning one color or type of material from the cylinder of an injection molding machine by forcing it out with the new color of material to be used in subsequent production. Purging materials are also available
Plate: A retainer plate with a depressed area for cavity blocks used in injection molding
Pressure: In injection molding and in transfer molding, the pressure which is applied to the mold to keep it closed, in opposition to the fluid pressure of the compressed molding material
Pressure Clamping: In injection molding and in transfer molding, the pressure which is applied to the mold to keep it closed, in opposition to the fluid pressure of the compressed molding material
QS 9000: Quality System model, used in conjunction with the ISO 9000 standard, for the automotive industry
Radial Seal: Compression is applied perpendicular to the seal center-line
Rapid Prototyping: Fabrication of a physical, three-dimensional part of arbitrary shape directly from a numerical description (typically a CAD model) by a quick, highly automated and totally flexible process.
Reciprocating Seal: Seals used in moving piston and rod situations
Reinforcing Agent: Fillers, such as Carbon Black, added to the elastomeric batch mix to improve such physical properties as tensile strength
Resilience: The capability of returning to original size and shape after deformation
RF: Radio-Frequency
RH: Rockwell hardness
RIM: Reaction injection molding
Rockwell Hardness: A standard method for measuring the hardness of metals. The hardness is expressed as a number related to the depth of residual penetration of a steel ball or diamond cone ("brale") after a minor load of 10 kilograms has been applied to hold the penetrator in position. This residual penetration is automatically registered on a dial when the major load s removed from the penetrator. Various dial readings combined with different major loads, give "scales" designated by letters varying from "A" to "H" the "B" and "C" scales are most commonly in use.
Rotary Seal: Seals for rotating shafts, with the turning shaft protruding through the I.D. (hole) of the O-ring
RP: Reinforced plastics
RTV Molding: A procedure where a part is molded in a silicone surrounding to reproduce up to twenty urethane parts
Rubber: A common name for both naturally occurring and synthetically made elastomers
Natural Rubber: A natural product of the juices of certain tropical plants (latex), improved through heat treating with sulfur (vulcanization)
Rubber: Man-made elastomers such as Nitrile, Fluorocarbon, Silicone, etc.
Synthetic Rubber: Man-made elastomers such as Nitrile, Fluorocarbon, Silicone, etc.
Scorching: Premature curing of compounded rubber stock during processing or storage, with the potential for adversely affecting material flow and plasticity during subsequent shaping and curing processes
Seal-Off: A feature on an insert which is used to control which surfaces of the part will be covered by rubber during the molding process. A seal-off usually takes the form of a flat surface which seats against a corresponding mold surface to restrict the flow of rubber
Seal: Any device used to prevent the passage of a fluid (gas or liquid) or fine particles
Sealing System: The components and attributes which compose the sealing environment, including the seal, the components being sealed, the medium or media being sealed, and the environmental conditions such as temperature, pressure, and motion
Shaft: A load-bearing and/or power-transmitting member o fa mechanical system which is generally cylindrical in shape and frequently rotates or reciprocates
Shore A: A hardness scale used to measure the hardness of molded rubber. The Shore A scale is most effectively used to measure rubber with a hardness from 10 to 95 Shore A. For materials harder than 90 to 95 Shore A, the Shore D scale is recommended (see also durometer)
Shrinkage: The linear contraction upon cooling of a molded rubber or thermoplastic part
Single Cavity Mold: A mold having only one cavity and producing only one finished part per cycle
SPC: (statistical Process Control) Methods of controlling our processes to prevent defects from being made
SPE: Society of Plastics Engineers
Specific Gravity: The ratio of the mass o f a unit volume of a material to that of the same volume of water at a specified temperature
Specific Gravity: Society of Plastics Engineers
Spiral Failure: Generally found on long stroke, hydraulic piston seals, spiral failure results when certain segments of the O-ring slide, while other segments simultaneously roll. At a single point on its periphery, the O-ring gets caught on an eccentric component, or against the cylinder wall, causing twisting and development of 45 degree angle, surface cuts
Spiral Twist: A type of seal failure resulting from a twisting action that strains or ruptures the rubber
Splits: A common molding defect. It is found when the rubber part is stretched and the part will tear normally at the knit point. Excessive lube or sometimes too hot a cure temperature is the cause
Squeeze: An informal (slang) term for the deformation placed on a rubber part to affect a seal. Although it is usually expressed as a percentage of a seal's original (undeformed) cross-section, it is also occasionally expressed as an absolute value of the deformation. See also Cross-sectional Compression, Percent
Stack Up Tolerance: The summation of sealing system tolerance's
Static Seal: A seal that, except for pulsations caused by cycle pressure, does not move in its environment
Statistical Process Control (SPC): the use of statistical techniques on processes and their output to establish process stability and increase capabilities
Strain: the deformation caused by an applied stress
Stress: Force per original cross section that is applied to a specimen
Stress Relaxation: Decreasing stress with constant strain over a given time interval (viscoelastic response)
Surface Finish: A term usually used in reference to the roughness parameter of a surface's texture, general expressed in units of microinches (Âµin) or micrometers (Âµm)
Surface Grinder: A commonly used machine tool which is used to grind mold plates and components to a specified dimension and to provide a high accuracy and smooth surface finish
Swell: The linear or volumetric change of a material resulting from immersion in a particular liquid for a specified period of time. Swell is a general indicator of the compatibility of a material for use in a particular environment
Tack: The degree of adhesion of materials of identical nature to each other
Tear Resistance: Resistance to the growth of a cut in the seal when tension is applied
Tear Strength: The force required to rupture a sample of stated geometry
Temperature Range: The working range marked by the limits of minimum and maximum operating temperatures for effective seal performance
Tensile Strength: the extension force per cross-sectional area required to fracture a material specimen
Terpolymer: A polymer resulting from the chemical combination of three monomers
Thermal Expansion: Linear or volumetric expansion caused by temperature increases
Thermoplastic: A material which when thermally processes undergoes a reversible phase change to become plastic and capable of being molded to a desired shape. Upon cooling, the material reverts to its original properties
Thermoplastic Elastomer (TPE): A material which combines the processing characteristics of a plastic but displays rubber-like properties upon completion of processing
Thermoset: A material, either an elastomer or plastic, which when thermally processed undergoes an irreversible chemical reaction to achieve its final material state
TIR: A measurement of roundness with relationship to a center-line and expressed in total diametric deviation
Torque: A turning or twisting force, generally associated with the rotation of a shaft
Total Indicator Reading (TIR): A term used to indicate how the measurement of the roundness of a part, as rotated about its center-line, should be interpreted
Toughness: Property of resisting fracture or distortion. Usually measured by impact test, high impact values indicating high toughness
TPE: "Thermoplastic Elastomer" combines the rubber-like performance of elastomers with the processing advantages of plastic. Scrap material can be recycled without significant loss in physical properties, unlike thermoset materials
TPE: Thermoplastic elastomers
TPR: Thermoplastic rubber
TPU: Thermoplastic polyurethane
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 sprues into the mold cavity
Trim: Removal of excess material (flash) from a molded rubber article
UHM: Ultra-high-modulus
UHMW: Ultra-high molecular weight
UL: Underwriters' Laboratories
Ultimate Elongation: The % of specimen stretching at the point of breaking. Generally referred to in tensile testing
Ultimate Elongation: Expressed as a percentage of its original length, a measure of how far a material will stretch before breaking
Undercut: A feature on a part which has a corresponding feature in the part's mold which is perpendicular to the direction of mold movement. An undercut complicates the manufacture of a molded part by making it difficult to remove the finished part from the mold
Viscosity: The measurement of the resistance of a material to flow under stress
Volume Change: The measure of the swell or shrinkage of a material resulting from immersion in a particular media for a specified period of time at a specified temperature
Volume Swell: A term generally used to describe the increase in physical size of a specimen immersed in a particular chemical agent
Vulcanization: The thermally initiated, irreversible process whereby polymer chains are cross-linked to form the final physical and chemical state of a rubber
Weathering: The detrimental effect upon an elastomer or plastic after outdoor exposure
Weld Lines: (knit lines) The marks visible on a finished part made by the meeting of two flow fonts during molding
Width: The cross-sectional diameter of an O-ring. one half the distance between the I.D. and O. D. of the ring

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