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Gasket Glossary, Vol. 4 (R through Z)

Questions about a term that has something to do with gaskets? Get a concise definition here.

Gaskets embody a host of different technologies. There are the myriad natural and synthetic materials they can be made out of, the cutting and finishing processes used to tailor them to specific applications and conditions, and the measurements and test engineers rely on to evaluate them. Here’s a long list of words and terms used in one these aspects of gasket design, manufacturing, and application, from abrasion to zinc oxide.

Go to a specific letter: R S T U V W Y Z


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.

TAGS: Fasteners
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