Accu-Shape Gasket Cutting

At Accu-Shape Die Cutting, gaskets embody a host of different technologies. There are myriad natural and synthetic materials they can be made out of, many cutting and finishing processes that can be used to tailor them to specific applications and conditions, and many measurements and tests used to evaluate them. The following Gasket Glossary features a long list of words and terms – from abrasion to zinc oxide – used in aspects of gasket design, manufacturing, and application to help you understand gaskets and grasp our manufacturing diversity.


Abrasion: The wearing away of a material surface by friction. Particles become detached by a combined cutting, shearing, and tearing action. Furnace carbon blacks are the best ingredients found for increasing the resistance of rubber compounds to abrasion.

Abrasion Resistance: The resistance of a material to loss of surface particles due to friction.

Accelerated Aging: These are procedures for subjecting pressure-sensitive label stock (and other materials) to special environmental conditions to predict the course of natural aging.

Acetate: A plastic synthesized from cellulose dissolved in acetic acid which exhibits rigidity, dimension stability, and ink receptivity.

Acid Resistant: Withstands the action of acids.

Acrylic Adhesive: Adhesive made from acrylic monomers that have been polymerized. They have good resistance to UV radiation, plasticizers, and extreme temperatures.

Adapters: A V-shaped ring, either male or female, to fit together with V-shaped rings to form a set of adjustable hydraulic packing.

Adhesion (a): The state in which two surfaces are held together by interfacial forces which may consist of molecular forces or interlocking action, or both.

Adhesion (b): The clinging or sticking of two material surfaces to one another. In rubber parlance, the strength of bond or union between two rubber surfaces cured or uncured. It also describes bonds between cured rubber surfaces and non-rubber surfaces such as those of glass, metal, wood, or fabric.

Adhesion Failure: The separation of two materials at the surface interface rather than within one of the materials itself.

Aging (a): (1) The irreversible change of material properties after environmental exposure for an interval of time; (2) Exposing materials to an environment for an interval of time.

Aging (b): Changes in physical and mechanical properties that occur when low carbon steel is stored for some time. Aging is also accelerated by exposure of steel to elevated temperatures.

Aging (c): A progressive change in the chemical and physical properties or rubber, especially vulcanized rubber, usually marked by deterioration. Aging may be retarded by the use of antioxidants.

Artificial Aging: Speeding up the natural aging cycle by heating the metal for a short time.

Air Curing: Vulcanizing a rubber product in air, as distinguished from vulcanizing in a press or steam vulcanizer.

Aluminum: A pliable, lightweight metal that has good electrical and thermal conductivity, high reflectivity, and resistance to oxidation.

Aluminum Seal Rings: Sealing rings for pistons made from high-grade aluminum alloy.

AMS: American Military Standards.

Annealing: A process involving high-temperature heating and cooling of the as-rolled cold rolled steel substrate to make it softer and more formable.

Anodize: The controlled oxidation of aluminum using an electro-chemical process to create a porous surface that is receptive to color dying.

Anti-Extrusion Rings: Also called back-up rings or anti-extrusion rings, used to fit behind rubber O-ring seals to prevent extrusion into the gap between the metal pieces.

Antioxidant: Usually organic and nitrogenous. A substance which inhibits or retards oxidation and other types of aging. Some antioxidants cause staining or discoloration of rubber compounds on exposure to light and are used only in black or dark-colored goods. Others (phenolic), described as non-staining, are used in white or light-colored goods.

Anti-Stick Coatings: Surface treatments that prevent gasket materials from adhering to flanges.

Anti-Vibration Mounts: Rubber molded pieces used as padding between a motor and the frame to prevent vibration transfer to the machine to which it is mounted.

Apportionment: Referred to here as a part of Reliability Engineering. Synonymous with the term Reliability Apportionment, which is the assignment of reliability goals from system to subsystem in such a way that the whole system will have the required reliability.

Assortment Kits: A convenient package containing several sizes of the same seal, O-ring, or retainer ring.

ASTM: American Society for Testing and Materials.

Automatic U-joints: Also called u-cups, these shaped sealing rings are made from a strong pliable plastic or rubber.


Backer Coat: Usually refers to the coating on the reverse side of a prepainted sheet. The backer coating is generally not as narrowly specified with reference to its color, thickness, and composition, as is the topcoat.

Backrinding: Defect in which the rubber adjacent to the mold parting line shrinks below the level of the molded product, often leaving the parting line ragged and torn.

Backringing: Distortion at the mold parting line, usually in the form of wrinkles, folds, tears, or indentions. In severe cases may cause overall dimensional changes.

Baffle Rings: A ring used to slow the flow of fluids along a shaft.

Ball Valve Seats: A PTFE ring shaped to fit against the ball in a flow control valve.

Batch: The product of the one mixing operation in an intermittent process.

Bearings: A machined or molded plastic ring used as a guide ring or wear ring in a hydraulic cylinder.

Beater Additives: A water-based process used to make gasket material where the elastomer is chemically deposited onto the fibers and fillers.

Bearing Seals: A seal ring made to snap-fit into a ball, roller, or spherical bearing to exclude dust, dirt, or trash.

Bellows: A corrugated rubber or plastic piece which can stretch with a shaft to keep the shaft clean.

Belts: A v-belt, flat belt, or drive belt made from plastic or rubber.

Bezel: A grooved rim, which holds another covering or item. Similar to a frame.

Bias Angle: (1) Acute angle between the direction of the cut and the diameter of the wrap in the production of wrapping for hose; (2) Acute angle between the direction of the cut and the direction of the cords in the production of fabric plies.

Bill of Material: Total list of all components/materials required to manufacture the product.

Binder: The elastomer (or rubber) used in gasket material.

Bloom: An efflorescent coating creating a discoloration or visual change on the surface of a material. Sometimes caused by the migration of a substance to the surface of product, it can also be normal in some organic materials (sulfur or wax bloom).

Blister: A cavity or sac that deforms the surface of a material.

Blowing Agent: Chemicals mixed with a compounded into many formulations that form gases to create cellular structures, such as sponge rubber.

Bond: The union of materials by use of adhesives.

Bonded Seals: A seal created by a flat steel washer with a rubber sealing ring molded into the center that fits over a bolt.

Bonding Agents: Substances or mixtures of substances used for attaching rubber to metal, fabrics, or other substrates. Generally, the rubber compound is vulcanized by heat in the process. Cyclized rubber or rubber isomers, halogenated rubber, rubber hydrochloride, reaction product of natural rubber and acrylonitrile, and polymers containing diisocyanates are all used.

Brittleness: Tendency to crack when subjected to deformation.

Bumpers: A rubber or plastic part used to prevent metal-to-metal contact.

Buna N: A general term for the copolymers of butadiene and acrylonitrile. Typical commercial polymers are Hycar and Paracril.

Buna S: A general term for the copolymers of butadiene and styrene.

Bushing: A rubber or plastic spacer to provide a wear surface around a shaft.

Butadiene: CH2 = CH – CH = CH2. A gaseous hydrocarbon of the diolefin series that boils at 5°C. Also known as erythrene, divinyl, pyrollylene, polymerizable, and polybutadiene. Butadiene is the chief raw material for making the synthetic rubbers today. Co-polymerized with styrene it yields SBR or GR-S; with acrylonitrile the various Buna N or nitrile synthetic rubbers are obtained.

Butyl: Isobutylene isoprene (IIR). Produced by copolymerizing isobutylene with isoprene. These rubbers exhibit excellent impermeability to gases, excellent dielectric properties, good tear-resistance, good aging at elevated temperatures, and good chemical stability.

Butt Joint: Joining two ends of material whereby the junction is perpendicular to the ID of an O-ring.

Butyl: A synthetic rubber of the polybutene type exhibiting very low permeability to gases.

Butyl Rubber: A copolymer of isobutylene and isoprene, polymerized almost instantaneously in methyl chloride with aluminum chloride at about ≤140°F. Butyl is resistant to ozone and the action of many other corrosive chemicals. Butyl rubber is resistant to permeation by gases.


Caliper: The thickness of a sheet material. The thickness is usually expressed in one thousands of an inch and in millimeters (e.g., 0.050 is expressed as 50 mils).

Camber: The deviation of a side edge from a straight line, the measurement being taken on the concave side with a straight edge.

Carbon black (a): Elemental carbon in finely divided form used to reinforce elastomeric compounds.

Carbon Black (b): Finely divided carbon formed by the incomplete combustion of natural gas or petroleum in large, closed furnaces.

Carbon Steel: Steel which owes its properties chiefly to carbon without substantial amounts of other alloying elements; also known as straight carbon steel or plain carbon steel.

Catalyst: A chemical in small quantities which accelerates a chemical reaction without itself necessarily becoming part of the final product.

Cavity: The area on a die where blades are formed to cut. A die with one or more cutouts that are the same size for each label cut.

Cellular Rubber: Rubber products which contain cells or small hollow receptacles. The cells may either be open or interconnecting or closed and not interconnecting.

Characteristics Matrix: An analytical technique for displaying the relationship between process parameters and manufacturing stations.

Checking: Short, shallow cracks on the surface of a rubber product that are created by damage from environmental conditions.

Checking Sunlight: The development of minute surface fissures as a result of exposing rubber articles to sunlight, generally accelerated by bending or stretching.

Chemical Resistance: The resistance offered by elastomer products to physical or chemical reactions as a result of contact with or immersion in various solvents, acids, alkalis, salts, etc.

Chemical Treatment: An aqueous solution of corrosion-inhibiting chemicals, typically chromates or chromate/phosphate.

Chevron Packings: Also called v-packing, vee packing, Chevron packing, parachute packing, or v-set packing. A complete vee packing set contains multiple v-shaped sealing rings stacked and nested together with a male adapter on one end and a female adapter on the other end.

Chloroprene: 2-Chloro-l, 3-butadiene, a volatile, colorless liquid which boils at 59°C, synthesized from acetylene. It is used in the manufacture of neoprene, which is obtained by polymerizing chloroprene under suitable conditions.

Chevrons: See Chevron Packing above.

C.I.: The abbreviation for cloth-inserted, indicating a sheet of rubber containing one or more plies of fabric covered with rubber.

Closed Cell: A cell totally enclosed by its walls and hence not interconnecting with other cells.

Coil Breaks: Creases or ridges in sheet that appear as parallel lines across the direction of rolling, and that generally extend the full width of the sheet or strip.

Cold Flow: Continued deformation under stress.

Cold Rolled Products: Flat rolled products for which the required final thickness has been obtained by rolling at room temperature.

Cold Working: Applying a mechanical force (such as deep drawing) to metal at room temperature at such a rate that strain-hardening occurs.

Color Standard: A painted sheet panel with a prescribed color of paint representing the precise color it is intended to produce in the pre-painted sheet. The color standard will preferably also be expressed in terms of physical attributes of hue, lightness, and saturation called tristimulus values or derivatives of these values. A complete color standard definition will usually include painted panels representative of the limits of acceptable deviation from the precise standard color, as well.

Coefficient of Expansion: The coefficient of linear expansion is the ratio of the change in length per degree to the length at 0°C. The coefficient of surface expansion is two times the linear coefficient. The coefficient of volume expansion (for solids) is three times the linear coefficient. The coefficient of volume expansion for liquids is the ratio of the change in volume per degree to the volume at 0°C.

Commercial Steel (CS): Sheet of this quality is for simple bending or moderate forming. Commercial Steel sheet can be bent flat upon itself in any direction at room temperature.

Compact Seals: Multi-piece seal sets which are generally used as piston seals in a hydraulic cylinder. Made to fit in a limit space, compact piston seals contain a primary sealing component, guide rings, and back-up rings in one convenient set.

Compound (a): A term applied to either vulcanized or unvulcanized mixtures of elastomers and other ingredients necessary to make a useful rubber-like material.

Compound (b): In chemistry, it is the material resulting from the chemical union of two or more elements in definite proportions and in which the properties of the individual elements have disappeared. In rubber manufacture, it is the composition or formula of stock, the ingredients of which, however, may not all be chemically combined and is therefore more of a physical mixture.

Compression Deflection Characteristics: The tests for compression-deflection characteristics constitute methods of compression stiffness measurement. One compression test involves the determination of a load required to case a specified deflection, and another is a compression test in which a specified weight or compressive force is placed on the specimen, and the resulting deflection is measured and recorded.

Compression Set (a): The residual decrease in thickness of a test specimen measured 30 minutes after removal from a suitable loading device in which the specimen has been subjected for a definite time to compressive deformation under specified conditions of load application and temperature. Method a measures compression set of vulcanized rubber under constant load. Method B employs constant deflection.

Compression set (b): The residual deformation of a material after removal of the compressive stress.

Compressibility: The percent of loss of thickness when subjected to a given load applied by a disc of a given diameter for a specified short time and at a specified temperature. Defined by ASTM F-36 test procedures.

Conductivity: To conduct or transmit heat or electricity.

Conductive Adhesive: An adhesive that incorporates conductive fibers. These fibers have the ability to conduct electricity through the thickness of the adhesive and/or in the plane of the adhesive. Ideal for EMI/RFI shielding and EMI/RFI gasket attachments.

Conformability: The ability of an adhesive tape to mold itself to the shape of an object without wrinkling or creasing.

Converting: The process of taking a material or adhesive and altering it from one form to another.

Contact Stain: Discoloration of a product by another material or by a rubber article in the area directly touching it.

Copolymer (a): A polymer consisting of two different monomers chemically combined.

Copolymer (b): A copolymer is a polymer consisting of molecules containing large numbers of units of two or more chemically different types in irregular sequence. Butadiene and styrene form a copolymer known as GR-S.

Copper Seal Rings: Rings made from thin copper formed over fibrous filler to seal in high temperature.

Corrosion: Gradual chemical or electrochemical attack on a metal by atmospheric moisture or other agents.

Crazing: A surface effect on rubber parts characterized by many small cracks.

Creep: The deformation, in either cured or uncured rubber under stress, which occurs with lapse of time after the immediate deformation.

Creep Relaxation: In a flange gasket, loss of stress accompanied by constantly decreasing compressed thickness. This type of relaxation is encountered in bolted flange joints.

Cross Linked: The establishment of a chemical bond between the molecular chains of a given polymer, thereby enhancing physical properties.

Critical Surface: Intended for material applied to critical exposed/painted applications where cosmetic surface imperfections are objectionable. The prime side surface will be free of repetitive type imperfections, gouges, scratches, scale, and slivers. This surface can only be furnished as a pickled product.

Cross Section: An O-ring as viewed if cut at right angles to the axis showing internal structure.

Crush Washers: A washer made to be crushed to form a seal.

Crown: A contour on a sheet where the thickness increases from some edge measurement to the center.

Cup Packing: Sealing devices made in the shape of a cup with outer lips curved upward usually made from rubber, fabric reinforced rubber or polyurethane.

Cure: The act of vulcanization. See Vulcanization.

Cushioning Seals: Sealing rings mounted into a cylinder to cushion the stroke or prevent metal-to-metal contact.

Custom Molded Products: Special shaped parts molded from rubber or plastic made to fit the machine or device it is used in.

Cut: The distance between cuts or parallel faces of articles produced by repetitive slicing or cutting of long pre-shaped rods or tubes such as lathe cut washers.

Cut Edge: Removal of the as-rolled hot mill edge. Coil ends are cropped back to gauge when cut edge is ordered.

Cut Outs: The spaces or holes designated in the label. This material is punched and removed during the manufacturing process.

Cystalinity: Stretched natural rubber forms a highly oriented state and shows X-ray diffraction patterns and other properties common to truly crystalline materials. The amorphous and crystalline regions are not mechanically separable phases, but the same molecule may at the same time have part of its length in a crystalline, and the remainder in an amorphous region.


Damper: The use of a variety of materials to deaden or damp a vibration.

Deep Drawing: The process of working metal blanks in dies on a press into shapes which are usually more or less cup-like in character.

Deep Drawing Steel (DDS): Sheets of this designation should be used when drawn steel will not provide enough ductility for fabricating parts to stringent drawing requirements, or applications that require the sheet be free from aging. DDS is made by special steelmaking and finishing practices.

Density: The weight per unit volume of a material: usually expressed in PCF (pounds per cubic foot).

Design Failure Mode and Effects Analysis (DFMEA): An analytical technique used by a design responsible engineer/team as a means to assure, to the extent possible, that potential failure modes and their associated causes/mechanisms have been considered and addressed.

Design for Manufacturability and Assembly: A simultaneous engineering process designed to optimize the relationship between design function, manufacturability, and ease of assembly.

Design Information Checklist: A mistake proofing checklist designed to assure that all important items are considered in establishing design requirements.

Design Reviews: A proactive process to prevent problems and misunderstandings.

Design Validation: Testing to ensure that product conforms to defined user needs and/or requirements. Design validation follows successful design verification and is normally performed on the final product under defined operating conditions. Multiple validations may be performed if there are different intended uses.

Design Verification: Testing to ensure that all design outputs meet design input requirements. Design verification may include activities such as:

Dielectric Strength: The measure of a product’s ability to resist passage of a disruptive discharge produced by an electric stress; the voltage that an insulating material can withstand before breakdown occurs.

Die Cutting: When parts are cut into individual pieces using a steel rule die. A sharp steel rule die is formed to the desired shape in a wooden carrier for cutting labels. A die may be one or more up (one cavity or more).

Die Guide: A guide around a label that assists with positioning of die and/or keeping art to edge tolerances.

Die Impression: A piece of material that has been cut with a die, but not cut all the way through.

Discs: Flat, round, saucer-shaped pieces made from rubber or plastic.

Disperse: To cause particles or molecules of matter to separate and become uniformly scattered throughout a medium. In a rubber compound, the particles of compounding ingredients are dispersed in the rubber. In latex, rubber globules are dispersed in an aqueous medium.

Distributor Seals: Sealing rings used to seal in oil and seal out dust, dirt, or trash on an automobile engine electric spark distributor.

Double Acting Seals: Seal rings which seal in two directions, on the push and the pull stroke of a hydraulic or pneumatic cylinder.

Double-Coated: Tape with adhesive on both sides.

Drawing Steel (DS): Sheets of this quality have more ductility and is more consistent in performance than commercial steel due to higher standards in production, selection, and melting of the steel.

Duck: A firm, compact, heavy, plain weave fabric made from cotton, synthetic fibers, or a combination of both. Duck is also known as canvas, army duck, belt duck, harvester duck, hose duck, and shoe duck.

Ductility: The ability to permit change of shape without fracture. In flat rolled steel, ductility is usually measured by hardness or mechanical properties in a tensile test.

Dumb-Bell (Test-Piece): In the physical testing of rubber, a test-piece is used that is shaped like a dumb-bell, i.e., constricted in the middle and flaring out at the ends, as distinguished from circular or ring test-piece. The dumb-bell is the most commonly used form or test-piece. Dimensions are set by ASTM standards.

Duocone Seals: A special cone-shaped sealing ring.

Durability: The probability that an item will continue to function at customer expectation levels at the useful life without requiring overhaul or rebuild due to wearing out.

Durometer: The most common Durometer, Type A or A-2, is an instrument for determining the hardness or rubber by measuring its resistance to the penetration (without puncturing) of a blunt indentor point impressed on the rubber surface against the action of a spring; a hand and special scale indicate the resistance to penetration. The scale reads from zero to 100, zero (0) being very soft and 100 being very hard. The Type D durometer has a sharp indentor point and is used to measure varying degrees of hard rubber up to ebonite.

Dust Seals: Seals used to keep dust out of machines or devices.


Elasticity: The property of a part or material which tends to return to its original shape after deformation.

Elastic Modulus: The value of the load (in pounds per square inch of original cross-section) required to give an intermediate elongation. It is also called the modulus at that elongation. Tensile-stress observations of this sort are useful in characterizing compounds by referring to the position and shape of its stress-curve.

Elastomer: A macromolecular material which in the vulcanized state at room temperature can be stretched repeatedly to at least twice its original length and which, upon release of the stress, immediately returns to approximately its original length.

Elongation: In the physical testing of rubber, the increase in length of a test-piece when stretched, usually expressed as a percentage of the original length; for example, a 1-in. piece stretched to 6 in. has an elongation of 500%. Elongation at break, the elongation of a test-piece at the moment of rupture, is usually expressed as percentage of the original length.

Emboss: A process of forming a portion of the substrate that rises above the normal level of the substrate.

Embossed sheet: An embossed sheet is one with a prominent, impressed texture or pattern on its surface(s). If the defined texture is applied only to the surface, it is most properly termed a coined surface. If the texture or pattern carries through the entire body of the sheet and appears on both surfaces, it is a true embossed surface.

Embrittlement: The process in which a rubber compound becomes brittle during low or high temperature exposure or in the process of aging.

Encapsulated O-rings: A rubber O-ring with a thin jacket of PTFE or PTFE surrounding the softer core material, which lets it be used in chemical applications.

EPDM: Ethylene Propylene Dienemethylene Terpolymer: A polymer created in a sulfur cure system. Known for resisting weathering and high temperatures, EPDM rubbers are used extensively in outdoor applications. They withstand exposure to all types of weather, including sunlight, ozone, and oxidants. Excellent resistance to animal and vegetable oils, water, steam, and oxygenated solvents.

Etching: To produce a pattern or design on a hard material by eating into the material’s surface.

Excluders: Also called wipers or scrapers, these devices are used in hydraulic and pneumatic cylinders to scrape the rod clean and keep debris out of the cylinder.

Expanded Rubber: Cellular rubber with closed cells made from a solid rubber compound.

Extra Deep Drawing Steel: Sheet of this designation has superior formability and excellent uniformity. It is produced from steel having a very low carbon content with stabilizing elements added to make it interstitial-free. It is a non-aging steel sheet with high resistance to thinning during drawing, and is suitable for critical forming applications.

Extra Smooth Galvanized: This extra-smooth finish is imparted to hot-dip metallic-coated steel sheet by temper rolling after coating to decrease the surface relief that occurs when the molten coating solidifies. The spangle pattern (grain pattern) is made distinctly less visible by the matte finish imparted by the rolling operation. Most extra-smooth sheet is intended for either pre-painted or post-painting applications.

Extrusion: (1) Distortion, under pressure, of portion of seal into clearance between mating metal parts. (2) Material, under pressure, which is forced through the opening of a die in order to obtain a desired cross-sectional shape.


Face Seals: Rubber rings used like a gasket between two flat pieces of metal.

Failure Modes Analysis (FMA): A formal, structured procedure used to analyze failure mode data from both current and prior processes to prevent similar failure modes in the future.

Fastener Seals: See Bonded Seals.

Feasibility: A determination that a process, design, procedure, or plan can be successfully accomplished in the required timeframe.

Fiber Seal Rings: A gasket or other die cut, waterjet cut, or formed ring used to seal between two surfaces.

Filler: Any compounding material, usually in powder form, added to rubber in a substantial volume to improve quality or lower cost. The most important reinforcing filler is carbon black. The most important inert filler, diluent, or extender is whiting.

Finish, Mold: The quality or appearance of the machined surface of a mold.

Finish, Product: The quality or appearance of the surface of a rubber product.

Finite Element Analysis: A technique for modeling a complex structure. When the mathematical model is subjected to known loads, the displacement of the structure may be determined.

Flange Packing: A pipe flange gasket.

Flange Seals: A seal used on the bolt-up flange on a hydraulic system, usually on the hose fitting or pipe flanges.

Flash: Excess rubber on a molded product caused by cavity overflow at the parting lines where the mold sections are separated.

Flatness: Flatness is a measure of a cut length sheet’s ability to conform to a flat horizontal surface. Maximum deviation from that surface is the degree to which the sheet is out of flat. Flatness is often expressed quantitatively in either Steepness or I-Units.

Flex Cracking: Cracking of the surface of rubber articles such as tires and footwear resulting from constantly repeated bending or flexing in service.

Flow Marks: Surface imperfections due to improper flow and failure of stock to knit or blend with itself during the molding operation.

Foil: Another name for thin-gauge aluminum.

Friction: Resistance to motion due to the contact of surfaces.


Gap Seals: A seal ring used to seal between the gaps of metal or plastic.

Gasket: A flat, non-moving, compressible rubber-like device squeezed between two flat surfaces forming a static seal. Gaskets can be made from homogeneous rubber, fabric reinforced rubber, fibrous materials with rubber binders, flexible graphite, PTFE, and many other materials. Some gaskets are made from a combination of metal and fibrous materials and some are all metal. An O-ring, while not flat, is also referred to as a gasket at times.

Gasket (Mechanical): Usually a deformable material clamped between stationary faces to effectively seal the coupling. Gaskets are used to guard against the passage of liquids, gases, etc.

Gate: (rubber injection or transfer mold): The orifice used to control the flow of rubber, and through which a shaped cavity in a mold is filled with rubber.

Gland Bearing Rings: Also called guide rings or wear rings. Used as a bearing surface for the rod of a hydraulic ram or cylinder.

Gland Seals: Seals or packings used as the main sealing device in a ram or cylinder.

Glass Temperature (Tg): The temperature at which a rubber becomes glass-like. A more recent name for the Second Order Transition point.

Glass Transition Point: Temperature at which a material loses its glass-like properties and becomes a semi-liquid.

Globe Valve Discs: PTFE rings used to seal in a globe valve.

Gloss: The property of a surface related to its ability to reflect light. The most common type of gloss in term of appearance is specular gloss. The parameters which must be specified for determining this property are the angles of incidence of the light source, the angle of viewing of the gloss, and the angular dispersions of the measuring beams.

Glyd Ring: Also known as wear rings or guide rings. Made from plastic, PTFE, or soft metal to act as a bearing surface for a cylinder rod.

Grain: The unidirectional orientation of rubber or filler particles occurring during processing (extrusion, milling, calendering), resulting in anisotropy of a rubber vulcanizate.

Grain Direction: The arrangement of a pattern on the material.

Grease Seals: Also called oil seals, rotary seals, or shaft seals. They are made of rubber to seal grease in housings with rotating shafts.

Green Strength: (1) An uncured rubber’s resistance to deformation, (2) Uncured adhesion between plied or spliced surfaces.

Grommets: A rubber ring used to fit into a hole in sheet metal. They let wires, shafts and rods through a housing without touching the metal.

Guiding Elements: Wear rings, guide rings, and bearing rings for hydraulic cylinder rods.

Gauge: The thickness of a material.

Guide Rings: See also wear rings, guide rings, or bearing rings. They are usually made from a form of PTFE.


H-Ring: Also called H-Wiper. An H shaped rod wiper ring made from NBR or polyurethane for a hydraulic or pneumatic cylinder.

Hand: The subjective or relative “feel” of a material, indicating pliability, texture, and even desirability of a material for tactile contact.

Hardness (a): The relative resistance of rubber to the penetration (without puncturing) of a blunt point impressed on its surface.

Hardness (b): Resistance of metal to penetration of the surface.

Hat Packings: Usually made from leather, it is used as a rod seal or ram seal in a hydraulic cylinder.

Heat History: The accumulated amount of heat a rubber stock has been subjected to during processing operations, usually after incorporation of the vulcanizing agents. Incipient cure or scorch can take place if heat history has been excessive.

Heavy Gauge Foil: Aluminum foil greater than 0.008 thick (8 mils).

High Pressure Seals: Seals to be used in high pressure hydraulic applications made from PTFE, urethane, or fabric reinforced material.

Hot Rolled Sheet: Steel sheet that is processed to its final thickness by rolling at high temperatures on a specially designed hot-rolling facility. Also commonly known as hot rolled unprocessed.

Hot Rolled Sheet Non-Temper Rolled: A U.S. Steel definition for product supplied as a coil directly off the hot strip mill with no additional processing.

Hot Rolled Sheet Pickled: A U.S. Steel definition for a mill edge coil that is pickled, oiled, and temper rolled with coil ends cropped back to meet gauge tolerances.

Hot Rolled Sheet Pickled Non-Temper Rolled: A U.S. Steel definition for a mill edge coil that is pickled and oiled with coil ends cropped back to meet gauge tolerances.

Hydraulic Cylinder Kits: A selection of seals used to completely repair a cylinder or ram.

Hydraulic Packings: Packing rings used in a hydraulic ram or cylinder.

Hydrolysis: Chemical decomposition of a substance involving the addition of water.

Hysteresis (a): The heat generated by rapidly deforming a vulcanized rubber part. It is the difference between the energy of the deforming stress and the energy of the recovery cycle.

Hysteresis (b): Hysteresis or energy loss is the difference between the work input and the work output as measured under the curves or extension and retraction (stress and elongation curves). The difference becomes heat build-up.


Inclusions: Particles of foreign material (such as oxides, sulfides, or silicates) in steel as cast.

Impact Test: A test which is intended to evaluate the brittleness, toughness, adhesion, and hardness of paint films applied to metals by subjecting them to an indent impact force.

Injection Molding: A method of forming articles (such as plastic) by heating the molding material until it can flow and injecting it into a mold.

Insert: A part, usually metal, placed in a mold that appears as an integral part of the molded product.

Internal Mixer: An enclosed mixing machine for rubber or other suitable material, inside or which two heavy mixing rotors revolve in opposite directions with a small clearance between themselves. The mixing chamber is jacketed or otherwise arranged for water-cooling, and is provided with a feeding hopper which can be closed by a pneumatically operated, vertical ram. Leading examples are the Banbury, Boiling, and Shaw mixers.

IRHD (International Rubber Hardness): For complete definition, see ASTM D 1415-68 Standard Method of Test for International Hardness of Vulcanized Natural and Synthetic Rubbers.

Isolators: A term used to describe a bearing seal, which replaces an oil seal and provides more reliable sealing.


Kantseal: A brand name of a special seal.

Kiss-Cut: Die-cutting material so that it remains attached in sheet or roll-form. The finished pieces are easily peeled from the release liner. It is often used on release liners to accommodate their use.

Knit mark: Visible mark where raw stock did not unite into a homogeneous mass during the vulcanization. This is also called poor knitting. See Flow marks.

K-Type Fluid Seals: A K shaped sealing ring used in hydraulic or pneumatic cylinders.


Labyrinth Seals: A non-contacting, rotary seal with a series of internal grooves to divert the flow and lubricating fluids in the direct of its source used on a shaft.

Laminate: Product made by bonding together two or more layers of like or unlike materials.

Lantern Rings: A spacer ring with grooves and port holes used in the stuffing box of a pump or other rotating equipment utilizing braided packings, allowing an outside source of lubrication.

Lathe Cut Seals: A seal or gasket ring cut square on a lathe.

Liner Side: The adhesive side covered by the release liner.

Lip Packing and Rings: Could be the description of a U-cup or of an oil seals. A seal with a lip design to provide sealing.

Lip Seals: Seal rings having lips to provide a flexible, dynamic sealing against a shaft.

Loaded Lip Seals: A hydraulic U-cup which has an O-ring or quad ring fitted into the U-shaped groove to assure good low pressure sealing on a reciprocating shaft.

Loaded U-Cups: Same as loaded lip seals.

Low Film: A thin film of oil on the shaft of a hydraulic cylinder.

Low Temperature Flexibility: The ability of a rubber product to be flexed, bent, or bowed at specified low temperature without loss of serviceability.


Magnesia: (a) Heavy calcined: Magnesium oxide by calcination of magnetite (natural magnesium carbonate), and then ground for use as a compounding ingredient for molded goods and hard rubber. (b) Light calcined: Magnesium oxide by calcinations of purified magnesium carbonate and/or magnesium hydroxide. It has a fine particle size and a bulk factor of 10 to 30 pds. per cubic ft. Used chiefly in neoprene stocks. (c) Extra light calcined: Prepared similarly by calcinations of magnesium carbonate, but with a bulk factor of 4 to 6 pds. per cubic ft. Used chiefly in neoprene stocks.

Maintainability: The probability that a failed system can be made operable in a specified interval or downtime.

Mandrel: A bar, serving as a core, around which rubber is extruded, forming a center hole.

Masterbatch: A preliminary mixture of rubber and one or more compound ingredients for such purposes as more thorough dispersion or better processing, and which will later become part of the final compound in a subsequent mixing operation.

Masticate: To work rubber on a mixing mill or in an internal mixer till it becomes soft and plastic.

Masticator: A machine for plasticizing rubber by mechanical work.

Matte: A satin or flat finish on the surface of a label.

Matte Finish: A more uniform surface finish imparted to the sheet surface by temper rolling with shot-blasted rolls.

Mechanical Properties: The properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications.

MerKamm: This is a basic Camprofile with no outer ring. It is used in confined spaces or recessed flanges such as tongue-and-groove or male/female flanges.

MerKamm IG Gasket: This is designed with an integral outer guide ring for aligning accuracy. This is primarily used in standard ANSI B 16.5 flanges, raised face or flat face flanges.

MerKamm LG Gasket: This is designed with a loose-fitting outer guide ring. It is used for flanges where thermal expansion may be encountered.

Metal O-rings: An O-ring with a small vent hole usually made from hollow stainless steel tubing.

Micrometer: A caliper for making precise measurements that has a spindle moved by a finely threaded screw.

Mill: A machine consisting of two adjacent, heavy, chilled iron rolls set horizontally which revolve in opposite directions used for mechanically working of rubber. For masticating and mixing compounds, the rolls are smooth and revolve at different speeds. For creeping and washing rubber, mills have scored or fluted rolls and differential speeds and may be equipped to spray the rubber with water. Mills with even-speed rolls are occasionally used for different purposes. Mills can be hollow and equipped for internal heating with steam or cooling with water.

Mils: Thousandths of an inch.

Mixing: The process of adding ingredients or a rubber compound into rubber, usually done on a mixing mill or in an internal mixer. The mixing process consists of (1) breaking down the rubber, (2) gradual incorporation or compounding ingredients, (3) final working of the rubber after all ingredients are in, and (4) removing the mixed compound from the mill in sheets.

Modulus: The ratio of stress to strain. In the physical testing of rubber, the load necessary to produce stated percentage of elongation, compression, or shear.

Modulus: In the physical testing of rubber, the ratio of stress to strain—i.e., the load in pounds per square inch or kilos. Per square cm. of initial cross-sectional area necessary to produce a stated percentage-elongation. It is a measure of toughness. It is influenced by pigmentation, state of cure, quality or rubber and other factors.

Mold Register: Method used to align the parts of a mold.

Monomer: A simple chemical compound that enters into the production of a polymer.

Mooney Scorch: A measure of the incipient curing characteristics of a rubber compound using the Mooney viscometer.

Mooney Viscometer: A laboratory testing machine for measuring the plasticity of raw rubber or unvulcanized rubber compounds. A knurled steel rotor disc winch is centrally embedded in a heated rubber specimen firmly held in a cavity under pressure. The specimen is rotated at a low speed (2 rpm). The resistance offered by the plastic rubber mass to the rotation of the rotor disc is the measure of the rubber’s plasticity. The machine is also used to determine the scorch characteristics of rubber mixes.

Mooney Viscositr: A measure of the viscosity of a rubber or rubber compound determined in a Mooney shearing disc viscometer.

Mounts: A rubber molded part used as a motor mount or to mount device against a frame without allowing vibration to pass through the mounting.

Mylar: A non-metallic material derived from polyester.


Natural Rubber: Natural Polyisoprene-NR. Excellent properties, outstanding performance in many mechanical applications. High resilience, high tensile and tear properties, and excellent resistance to cold flow. When exposed to petroleum derivatives, ozone, sunlight, and oxygen, natural rubber and its heat-aging properties are inferior to many synthetics.

Nebar: A special type of gasket material used in electrical transformers.

Neoprene: Synthetic rubber made by polymerizing 2-chlor-1, 3-butadiene. Neoprene compounds are rioted for their resistance to oil, sunlight, and ozone. There are various types, most of which are vulcanizable without the use or sulfur.

Nerve: The elastic resistance of unvulcanized rubber or rubber compounds to permanent deformation during processing.

Nilos Rings: A special seal ring.

Nitrile Rubber: A generic term comprising the various copolymers of butadiene and acrylonitrile. The copolymers vary essentially in their butadiene-to-acrylonitrile ratios, Mooney values, and staining properties. They are resistant to solvents, oils, and greases, as well as bending and abrasion. Some trade names are Chemigum, Krynac, Nipol, Hycar, and Paracril. German engineers first produced nitrile rubbers, naming them Buna N and Perbunan.

Non-Blooming: The absence of a bloom.

Non-Metallic: Any material that lacks the characteristics of a metal.

Novathan: A name for a type of polyurethane sealing material.


O.D.: Outside diameter measured at tangency between bottom radius and side.

Oil Resistance (a): Ability to withstand swelling by a specified oily liquid for specified time and temperature, expressed as percentage swelling or volume increase of specimen.

Oil Resistance (b): Ability of vulcanized elastomer compositions to resistance to change in size and shape, and to losing physical (mechanical) properties due to contacts with or immersion in an oil.

Oil Resistant: The ability of a vulcanized rubber to resist the swelling and deteriorating effects of various types of oils.

Oil Seals: Also called grease seals, rotary seals, or shaft seals. They are made of rubber and seal grease in housing with a rotating shaft.

Open Cells: A porous material with cells or cavities not totally enclosed by walls, and hence interconnecting with other cells.

Open Steam Cure: A vulcanization process that takes place under direct steam pressure in an autoclave. It is used where direct pressure molding is not possible. In the case of vulcanization of sheeting or coated fabrics, rolls of product are wound onto steel drums (with suitable a interleaf) and placed in the autoclave for cure. Some tubing and shaped products can be placed on pans for extra curing.

Optimum Cure (a): State of vulcanization at which maximum desired property is attained.

Optimum Cure (b): The physical properties of a rubber compound vulcanized at a given temperature for increasing periods of time undergo continuous change. For example, tensile strength may rise to a maximum, continue on a plateau, and then decline, whereas breaking elongation may continuously decrease. Therefore it is impossible to choose any one time of cure at which every property will be at its optimum. Hence, optimum cure is a compromise and may be considered as that time required to obtain the combination of properties most desirable for the article under consideration.

Opti-Seal: A special seal ring to provide optimum sealing.

O-rings: O-ring seals are circular rings of various cross-sectional configurations installed in a gland to close off a passageway and prevent escape or loss of a fluid or gas. An O-ring is specified by three of its features: its dimensions, material, and hardness. Material and hardness specify the elastomeric compound and Shore A (durometer) hardness of the compound used to manufacture the O-ring. An O-ring’s dimensions are described by stating its inside diameter (I.D.) and its cross-section. Designing for O-rings depends on three major and interrelated variables: the operating conditions and the environment the seal will experience, and the gland geometry into which the seal will be installed. The three variables account for the fact that there are so many different types of seals and applications.

Overcure: A state of excessive vulcanization resulting from overstepping the optimum cure—e.g.., vulcanizing longer than necessary to attain full development of physical strength. It is manifested by softness or brittleness, as well as an impaired ability to resist age resisting.

Oxidation: Active oxygen degrading organic materials. Rate of degradation increases with rising temperatures.

Ozone: An allotropic from oxygen (03) produced by electrical discharges in air. It is a gas with a characteristic odor and is a powerful oxidizing agent. Rubber compounds in a stretched condition are susceptible to the deteriorating action of ozone in the atmosphere, which results in a surface cracking.

Ozone cracking: The surface cracks, checks, or crazing caused by exposure to an atmosphere containing ozone.


Packaging: A unit that provides protection and containment of items plus ease of handling by manual or mechanical means.

Packing: An adjustable sealing device on a ram, valve stem, or pump shaft. If packing leaks, it is simply tightened slightly to “control” the leakage. For pumps and valves, packings can be rope-like, braided into continuous lengths, and then cut to size to fit a shaft. For hydraulic applications, V-shaped fabric reinforced rubber rings are used. Early hydraulic packings were made from leather.

Pads: A rubber part used as an anti-vibration device.

Parachute Packings: Also called V-Packing, Vee packing, Chevron Packing, or V-set packing. A complete vee packing set contains multiple V-shaped sealing rings stacked and nested together with a male adapter on one end and a female adapter on the other end.

Parbacks: A back-up ring with a concave shape on one side, used as an anti-extrusion ring for an O-ring.

Pattern Coating: Adhesive applied in alternating bands of adhesive and non-adhesive.

Perforated: To make a line of holes for purposes of easing the separating of two or more items.

Permanent Set: The amount by which an elastic material fails to return to its original form after deformation. In the case of elongation, the difference between the length after retraction and the original length, expressed as a percentage of the original length. Permanent set depends on quality and type of rubber, degree and type of filler loading, state of vulcanization, and amount of deformation.

Permeability: To permit gas to pass through the molecular structure of a given material.

Pickling: Removing surface oxides from metals by a chemical reaction.

Piston Bearing Rings: Also called guide rings, wear rings, piston guide rings. Rings usually made from nylon or POM and are used on the piston of a hydraulic or pneumatic cylinder.

Piston Seals and Packings: Any seal or packing ring used on the piston of a hydraulic or pneumatic cylinder.

Piston T-Seals: A T-shaped rubber seal, with back-up rings of a harder material on each side, used as a piston seal.

Plasticity: A measure of the resistance to shear of an unvulcanized elastomer, or the tendency of a material to remain deformed after reducing the deforming stress to or below its yield stress.

Plasticizer: A substance that softens or plasticizes another substance through its solvent action.

Plunger Pump Seals: Packing seal rings used to seal the plunger of a reciprocating pump.

Plunger Seals: Sealing rings used on a plunger.

Plug: A cone-shaped rubber part used to be forced into a tube end or hole to make a complete seal.

Pneumatic Seals: Any seal or packing ring, usually flexible rubber, used to seal against compressed air instead of hydraulic fluid or other liquid.

Pock marks: Uneven blister-like elevations, depressions, or pimpled appearance.

Points of Tangency: The points at which the straight portions of the shell walls intersect the beginning of the radius corners.

Poisson’s Ratio: The ratio of lateral concentration per unit of diameter to longitudinal extension per unit of length in a bar of material longitudinally stressed. For a body which does not change its volume on deformation, it is 0.5. For metals, the ratio is usually considerably less than 0.5. In the case of vulcanized rubber or pure gum, which have practically no volume change on extension, it shows a ratio of approximately 0.5 for small deformations; compounded rubber may increase in volume on extension, consequently the ratio drops below 0.5. For rubber the ratio is constant only for small extensions.

Polyester: A durable substrate that is resilient to moisture, solvents, oils, and chemicals. It is available as clear or white material and with a moralized finish.

Polymer: A material formed by the joining together of many individual units or monomers. A polymer is a long chain of monomer units prepared by means of an addition and/or a condensation polymerization. The units may be the same or different. There are copolymers, dipolymers, tri- or terpolymers, quadripolymers, and high polymers.

Porosity: The presence of numerous small holes or voids.

Post cure: Heat or radiation treatment, or both, for a cured or partially cured thermosetting plastic or rubber composition that improves one or more properties.

Preliminary Bill of Material: An initial bill of material completed prior to design and print release.

Preliminary Process Flow Chart: An early depiction of the anticipated manufacturing process for a product.

Press-in Wipers: A wiper or scraper ring for a hydraulic cylinder which has a metal outside diameter so it can be press-fitted into a housing.

Pressure Sensitive: Describes an adhesive that can be applied to a substrate by using light pressures.

Pressure Vessel Steel (PVS): Steel intended for pressure vessels and similar end use applications.

Process Failure Mode and Effects Analysis (PFMEA): An analytical technique used by manufacturing engineers to ensure potential failure modes and their associated causes/mechanisms have been considered and addressed.

Processing Aids: Materials including waxes, low-molecular-weight polyethylene, metal soaps, and petroleum oils, which dissolve or lubricate rubbers, softening them and act as processing aids.

Product Assurance Plan: A part of the Product Quality Plan. It is a prevention-oriented management tool that addresses product design, process design, and, when applicable, software design.

Production Trial Run: Product made using all production tools, processes, equipment, environments, facilities, and cycle times.

Protectors: A rubber or plastic cap or cup-shaped ring used to protect threads or fragile items during shipping or assembly.

Prototypes: A finished product made during the design process to determine the feasibility or suitability of a project.

Pusher Rings: A ring that fits against another sealing device to push it and activate or energize it in the absence of pressure or in low-pressure applications.


Radial Shaft Seals: Also called grease seals, rotary seals or shaft seals. Made of rubber to seal grease in housings with a rotating shaft.

Radius Corners: Rounded corners. Measured from the center of a diameter to its circumference.

Rebound: Rebound is a measure of the resilience, usually as the percentage of vertical return of a body which has fallen and bounced.

Rebound Test: Method of determining the resilient properties of vulcanized rubber by measuring rebound of a steel ball or pendulum falling from a defined height onto a rubber sample.

Register: The accurate matching of the plates of a mold.

Reinforcing Agent: In rubber compounding, a finely-divided substance or filler which, when properly dispersed in rubber, improves physical properties in the vulcanized product—e.g., greater energy of resilience, greater resistance to abrasion, or higher modules of elasticity and tensile strength. Certain grades of furnace blacks are the most important reinforcing agents for black stocks. For light-colored stocks, calcium silicate, precipitated calcium carbonates, silica, and clay are the most commonly used.

Release Liner: Coated paper applied to the adhesive to protect it until ready for use.

Reliability: The probability that an item will continue to function at customer expectation levels at a measurement point, under specified environmental and duty cycle conditions.

Removable Adhesive: An adhesive that can be removed from a surface without leaving a residue.

Reproducibility: The variation in the average of measurements made by different operators using the same gage when measuring identical characteristics of the same parts.

Removable Adhesive: Residue-free adhesive, easily removed from a surface.

Resilience (a): The property of a material that lets it return to its original size and shape after removing the stress which caused the deformation.

Resilience (b): The energy returned by vulcanized rubber when it is suddenly released from a state of strain or deformation. The returned energy, expressed as a percentage of the original potential energy, is a measure of the resilience. Various rebound testers are used to measure rebound.

Retarder: Any substance whose presence in relatively small proportions retards a chemical reaction. Specifically, a substance which, when added in small proportion to a rubber compound, retards the rate of vulcanization. An anti-scorching agent such as phthalic anhydride or salicylic acid. Extreme reversion can cause tackiness.

Reversion (a): A deterioration of physical properties such as a decrease in hardness and tensile strength, or an increase in elongation that may occur after excessive vulcanization of some elastomers. Or a similar change in properties after air aging at elevated temperatures. Natural rubber, butyl, polysulfide, and epichlorobydrin polymers exhibit this effect. Most other polymers will harden and suffer loss of elongation on hot air aging.

Reversion (b): The softening of some vulcanized rubbers when they are heated too long. Usually accompanied by an increase in extensibility, a decrease in tensile strength, and a lowering of the stress required to produce a given elongation. Extreme reversion may result in tackiness; the rubbers revert to an unvulcanized, then to a non-polymeric condition.

Rheology: The science of deformation and flow of matter. Deals with the laws of plasticity, elasticity and viscosity and their connections with paints, plastics, rubber, oils, glass, cement, etc.

Rheometer: An oscillating disk cure meter used for determining vulcanization characteristics of a rubber compound.

Rim Seal: A sealing device used on the rim of round plate or rim of a wheel.

Rings: Round sealing devices.

RMS: Root Mean Square: The measure of surface roughness, obtained as the square root of the sum of the squares of micro-inch deviation from true flat.

Rod Seals: Any seal used on the rod of a hydraulic or pneumatic cylinder made from rubber or plastic.

Rollers: A round, flat ring used as a wheel or guide.

Rotary Seals: Seals used on rotating shafts. See Lips Seals, Grease Seals, Oil Seals.

Roto Glyd: A flat plastic, PTFE or PTFE, ring used on a rotating shaft.

Rubber: A material that is capable of recovering from large deformations quickly and forcibly. it can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in boiling solvent, such as benzene, methyl ethyl ketone, and ethanol-toluene azeotrope. A rubber in its modified state, free of diluents, retracts within 1 minute to less than 1.5 times its original length after being stretched at room temperature (18 to 29°C) twice its length and held for 1 minute before release.

Rubber-Based Adhesive: Made from natural and synthetic rubber compounds. They have excellent initial tack but low temperature and aging resistance.

Rubber Lates: Colloidal aqueous emulsion of an elastomer.


SBR (Rubber): Styrene Butadiene, Buna S, GRS. A synthetic copolymer composed of styrene and butadiene. Used more often than any other synthetics produced. SBR has similar resistance to solvents and chemicals as natural rubber. It can be bonded to a wide range of materials.

Scorch: Premature vulcanization of a rubber compound, generally due to excessive heat history. Also see Mooney Scorch.

Scorching: A term frequently used to denote premature vulcanization of a rubber compound occurring on a mill or calendar or in an extruder. Same as burning or setting up.

Scoring: Marking the substrate with lines, grooves, or notches for bending or contouring purposes.

Scraper Rings: A ring which rides tight against a rod, with a sharp lip to scrape or wipe off excess oil, dirt, or dust in a hydraulic or pneumatic cylinder.

Scrapers: Also called wiper rings. They ride tight against a rod, with a sharp lip to scrape or wipe off excess oil, dirt, or dust in hydraulic or pneumatic cylinders.

Seal: An elastomeric ring-shaped component used in a constantly moving, dynamic application with a reciprocating or rotating shaft. It provides a near positive no leak mode in hydraulic cylinders, rams, mixers and gear boxes. (Note: no sealing device is absolutely 100% positive). Seal rings can be U-shaped, V-shaped, O-shaped, metal-inserted, radial-lipped, multiple-lipped, or a simple flat ring.

Seal Cages: A special device used to assist a seal ring.

Seal Kits: Any group of seals, O-rings, wiper rings, or back-up rings used to repair a specific hydraulic cylinder.

Seam: A line, groove, or ridge formed by the joining of edges. A seam can be a weak or vulnerable area, especially for EMI considerations.

Seat: A stationary ring which is pressed into housing and acts as the matching face of a mechanical seal.

Seamless Construction: An exceptional attribute of deep drawn shells. Deep drawn shells have no seam.

Shaft Repair Kits: A package of seals which includes all seals needed to repair the rod end of a hydraulic or pneumatic cylinder.

Shaft Seal and Packings: Any seal ring used on the rod of a hydraulic ram.

Sheet Materials: Rubber or fibrous material used to make gaskets.

Shelf Life: The length of time a product can be stored, under specific conditions, before the product expires. Each product varies depending on the material, adhesive, and printing process.

Shims: Flat, thin, metal gasket-like parts used as spacers to position machinery or align equipment.

Shore A Hardness: An indentation method of rating the hardness of rubber using a Shore Durometer with the A scale from 0 to 100.

Shrinkage: Contraction of molded rubber upon cooling.

Skin: A relatively dense layer at the surface of a cellular material.

Silicone: Offers a wide range of operating temperatures from -80°F to +400°F. Excellent dry heat resistance. Silicone compounds are inert and comply with ASTM, military, and FDA specifications. They are widely used by food, medical, electrical, and filter manufacturers. They should not be used in dynamic seals because of poor tensile, tear, and abrasion resistance

Silicone Adhesive: Adhesives made from silicone polymers. They have excellent high temperature resistance.

Simulation: The practice of mimicking some or all of the behavior of one system with a different, dissimilar system.

Single Acting Seals: Rings which are designed to seal only in one axial direction.

Slip O-Rings: A type of ring which fits over an O-ring to relieve friction.

Smoke Sheets: Natural rubber sheets that passing through a mill that puts a conventional ribbing design on them. They are then washed and hung on racks in a smoke house where they undergo a combined smoking and drying process.

Snap-in Wipers: A rod wiper made from one homogeneous material, either rubber or polyurethane, which is designed to snap-fit into a matching machined groove.

Spacers: A ring with flat sides that provide specific dimensional spacing between two components.

Special Characteristics: Product and process characteristics designated by the customer including governmental regulatory and safety.

Specific Gravity: The ratio of the mass of a unit volume of a material to that of the same volume of water at a specified temperature.

Specifications (Specs): The details of a part: dimensions, material call outs, type style, size information, etc.

Speedy Sleeves: The name of a thin, round tube which slips over a rotating shaft to provide a new, clean sealing surface for rubber lip oil or grease seal.

Sponge Rubber: Cellular structure produced by adding a gasifying substance to a rubber compound, then expanding and curing it in a heated mold. Cells may be open (interconnecting) or closed.

Splice: A joint or junction made by lapping or butting edges, straight or on a bias, and held together through vulcanization or mechanical means.

Spring Energized Seals: Any sealing ring that uses a metal garter spring or finger spring to assist in energizing the seal when there is enough pressure. Also called spring-loaded seals.

Sprue: (1) The primary feed channel that runs from the outer face of an injection or transfer mold to the mold gates in a single cavity mold or to runners in a multiple cavity mold; (2) The piece of material formed or partially cured in the primary feed channel.

Sprue Mark: A mark, usually elevated, left on the surface of an injection or transfer molded part after removal of the sprue.

Squeeze: Cross section diametrical compression of O-ring between bottom surface of the groove and the surface of the other mating metal part in the gland assembly.

State of Cure: The cure condition of vulcanization relative to that which yields properties.

Stem Packing: A type of homogeneous or multi-braided packing used on the stem of a valve to stop leakage.

Step Seal: A seal ring with a step cut groove to match up against a housing machine to fit.

Strain Hardening: Tempering through strain. Same as work hardening.

Strength-to-Weight Ratio: The ratio of a material’s tensile strength to its weight.

Stress: Force per unit of original cross sectional area required to stretch a specimen to a defined elongation.

Stress relaxation: The decrease in stress after a given time of constant strain.

Substrate: A material upon the surface of which an adhesive promoter is applied for any purpose, such as bonding or coating.

Subsystem: A major part of a system which has the characteristics of a system, usually consisting of several components.

Swelling (1): The increase in volume or linear dimensions of a specimen immersed in a liquid or exposed to a vapor.

Swelling (2): The property of raw or unvulcanized rubber absorbing organic liquids such as benzene, gasoline, etc., arid swelling too many times its original volume. In a general sense, it may be any increase in volume of a solid substance caused by the absorption of a liquid.

Switch Seals: Seals used in electrical switching devices to keep moisture out.

System: A combination of several components or pieces of equipment integrated to perform a specific function.


Tack: The ability to self-adhere; a sticky or adhesive quality.

Team Feasibility Commitment: A commitment by the Product Quality Planning Team that the design can be manufactured, assembled, tested, packaged, and shipped in sufficient quantity at an acceptable cost, and on schedule.

Tear Resistance: Resistance to tearing, measured as the force required to tear completely across a specially-designed nicked rubber test piece or right-angled test piece by elongating it at a specified rate. Express in lb. per inch of thickness of specimen.

Tear Strength: The maximum load required to tear apart a specified specimen, the load acting substantially parallel to the major axis of the test specimen.

Telescopic Packing: Packing sets used on telescopic cylinders, each stage having a different diameter.

Temperature Range: Lowest temperature at which rubber remains flexible and highest temperature at which it will function.

Tensile Strength: The capacity of a materiel to resist a force tending to stretch it. Ordinarily the term is used to denote the force required to stretch a material to rupture, and is known as breaking load, breaking stress ultimate tensile strength. lit rubber testing, it is the load in lb. per square inch or kilos per square centimeter of original cross-sectional area, supported at the moment of rupture by a piece of rubber being elongated at a constant rate.

Tensile Stress: The applied force per unit of original cross sectional area of a specimen.

Tensile Stress at Given Elongation: The tensile stress required to stretch a uniform section of a specimen to a given elongation.

Tension Set: The extension remaining after a specimen has been stretched and allowed to retract.

Texture: A screen-printing process that applies a coating to the surface of the substrate. The coatings are available in fine or coarse finishes. This process allows for protection from chemical attack. It can also improve the light distribution of a LED or protect the surface of an overlay from scratches.

Thermoplastic Rubber: Rubber that does not require chemical vulcanization and will repeatedly soften when heated and stiffen when cooled. It will exhibit only slight loss of its original characteristics.

Thermosetting Rubber: Chemically vulcanized rubber that cannot be remelted or remolded without destroying its original characteristics.

Timing Plan: A plan that lists tasks, assignments, events, and timing required to provide a product that meets customer needs and expectations.

Tips: A rubber cup-shaped part used on the end of a rod or shaft to provide shock resistance or cushioning.

Tolerance: The specification of allowable deviation from exact original (measurable) specifications.

Transfer Tape: An unsupported adhesive on a liner.

Trim: The process Involving removal of mold flash.

T-Seals: A T-shaped rubber sealing ring with harder back-up rings on each side for rod or piston sealing.

Tube Springs: A rubber or plastic cushioning device used to assist spring or cover the outer portion of a coil spring.


U-Cup: a type of seal used in a hydraulic or pneumatic cylinder. Its cross section is U-shaped to allow oil to energize the seal body to properly block oils and seal correctly.

Undercure: Degree of cure less than optimum. May be evidenced by tackiness, loginess (lack of snap or resilience), or inferior physical properties.

UL94: Underwriters Laboratory’s rating for flame spread.

Ultimate Elongation: The maximum elongation prior to rupture.

Undercure: State of vulcanization less than optimum. It may be evidenced by tackiness or inferior physical properties.

U-Packing: A U shape cup sealing ring designed to seal in one direction along a shaft or rod in a hydraulic or pneumatic cylinder.


V-Packing: Also known as Vee Packing, Vee Sets, Chevron Packing, and Parachute Packing. A multiple ring set of packings whose center rings or sealing rings are V-shaped to form sealing lips. The V-rings stack on top of each other and have a male and female adaptor on each end to make the set flat. This packing type is adjustable.

Valve Discs: A PTFE or PTFE disc used on a valve as a seat to provide positive sealing when shut off.

Value Engineering (Value Analysis): A planned, clean-sheet approach to problem solving, focusing on specific product design and process characteristics. Where value analysis is employed to improve value after production has begun, value engineering is employed to maximize value prior to expenditures of facilities and tooling money.

Valve Packing: Braided packing used in the stuffing box of a valve stem to make a positive seal.

Valve Seats: A PTFE or PTFE disc or ring used on a valve as a seat to provide positive sealing when shut off.

Valve Stem Packing: Braided packing used in the stuffing box of a valve stem to make a positive seal.

Vee Packing: Also called V-packing, chevron packing, parachute packing, or v-set packing. A complete vee packing set contains multiple V-shaped sealing rings stacked. It is nested together with a male adapter on one end and a female adapter on the other end.

Vibration Mounts: A rubber piece used to eliminate vibration between two components.

Vinyl: Vinyl is a cost-effective and highly versatile material. It is strong, durable, abrasion- and moisture-resistant, withstands rust and corrosion, is electrically non-conductive, and has excellent fire performance properties. Vinyl can be produced in almost any color, with products ranging from opaque to crystal-clear.

Viscosity: The resistance of a material to flow under stress.

Voice of the Customer: Customer feedback, both positive and negative, including likes, dislikes, problems, and suggestions.

Voice of the Process: Statistical data that is fed back to people in the process-making decisions about the process stability and/or capability as a tool for continual improvement.

Voids: The absence of material or an area devoid of materials where not intended.

Vulcanizate: Rubber in its cured or vulcanized state.

Vulcanizating Agent: Any material which vulcanizes rubber such as sulfur, polysulfides, organic polynitro derivatives, ro peroxides.

Vulcanization: An irreversible process during which a rubber compound changed its chemical structure (for example, by cross-linking) to become less plastic and more resistant to swelling by organic liquids. Elastic properties are also brought out, improved, or extended over a greater range of temperatures.


Washers: Round, flat rings used as spacers, gaskets, or slip devices under the head of a bolt.

Water Absorption: A material’s weight and volume increase after immersion in water.

Water Resistance: The ability to withstand swelling by water for a specified time and temperature.

Wear Rings: Wear rings, guide rings, guiding rings, or bearing rings for hydraulic cylinder rods.

Wear Sleeves: Wear rings, guide rings, guiding rings, or bearing rings for hydraulic cylinder rods.

Wear Strips: Strips of abrasion-resistant plastic, PTFE, or PTFE material used as wear rings, guide rings, guiding rings, or bearing rings for hydraulic cylinder rods.

Wetting: Completeness of contact between particles dispersed in a medium, such as carbon black rubber.

Wiper Ring: A ring which rides tight against a rod, with a sharp lip to scrape or wipe off excess oil, dirt, or dust in a hydraulic or pneumatic cylinder.


Yield Point: The load or stress which causes a marked increase in the deformation of a sheet without increasing the applied load. Yield point is one of the characteristics of low-carbon steels after they have been annealed. The yield point is usually calculated using a tensile-test specimen, and it is the load commensurate with the point beyond the elastic limit at which the specimen lengthens considerably without an additional increase in load.

Yield Strength: The stress at which a material exhibits a specified deviation from a linear proportionality between load and elongation. In the tension test, the load associated with an offset of 0.2% from linearity is used for many metals to calculate the yield strength.

Young’s Modulus: The ratio of normal stress to corresponding stress or compressive stresses below the proportional limit of the material.


Zinc Oxide: Accelerators of vulcanization do not always exert their full influence unless the rubber mixture contains substances known as activators. Zinc oxide is an activator and gives its best activity in the presence of an organic acid like stearic acid, with which it forms a rubber-soluble soap.

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