For the sealing expert, the world of sealing terminology comes naturally.
But for those who don't live and breathe seals every day, the list of terms can quickly become quite daunting.
Thanks to our partners at Minnesota Rubber, this blog post will examine Part 1 of Sealing Terminology - the terms you may come across when looking for fluid sealing products.
Abrasion – Surface wear caused by relative motion between contacting objects
Abrasion Resistance – The ability of a rubber compound to resist surface wearing by mechanical action
ABS – Acrylonitrile-butadiene-styrene
Accelerator – A chemical compound that speeds up the vulcanization of natural or synthetic rubbers
Adhering Flash – Extremely thin flash (usually less than 0.002′ thick) that adheres to the finished part during molding or deflashing processes
Age Protection – Active – the use of a chemical additive in a rubber compound which is preferentially attached by oxygen or ozone thereby sacrificially protecting the rubber
Age Protection – Passive – The use of a chemical additive in a rubber that will migrate to the surface of a rubber part to form a protective physical barrier
Aging – The change in physical and chemical characteristics of an elastomer that has been exposed to a particular environment over time
Alloy – A composite material produced by blending polymers or copolymers with other polymers under selected conditions to achieve greater physical properties
Ambient Temperature – The temperature of the environment surrounding a particular object
Aniline Point – The lowest temperature at which equal parts of aniline and a test liquid (such as oil) will uniformly mix or blend. The aniline point of oil is a measure of aromaticity (the amount of unsaturated hydrocarbons present). The lower the aniline point, the more unsaturants are present and the higher the potential for swelling certain rubber compounds
Annealing – A process of holding a material at a temperature near, but below, its melting point, to permit stress relaxation without distortion of shape. Often used on molded article to relieve stresses set up by flow into the mold
Antioxidant – Any organic compound that slows the process of oxidation
Antiozonant – Any substance that slows the severe oxidizing effect of ozone on elastomers. Exposure to ozone typically causes surface cracking in many rubbers
AQL – Accepted quality level
Aromatic – A major group of unsaturated cyclic hydrocarbons containing one or more rings. A typical aromatic compound is benzene, which has a six carbon ring, containing three double bonds
ASA – Acrylic-styrene-acrylonitrile
ASTM – American Society for Testing and Materials, An organization for issuing standard specifications on materials, including metals and alloys
Axial – The change in physical and chemical characteristics of a rubber compound that has been exposed to a particular environment over time
Axial Seal – Squeezed, like a gasket, on both the top and bottom surfaces of the seal’s cross section. A face seal
Back Rind – Distortion of the mold parting line, usually in the form of a ragged or torn indentation
Backup ring – A washer-like device of a relatively hard, tough material installed in the gland on the downstream side of the seal to prevent seal extrusion into the diametrical gap while under pressure
Backup washer – A washer made from certain material that will add strength or support when installed next to the seal. This prevents the seal from being pinched and evenly distributes the load
Base Line – The mark from which all features are dimensioned
Batch Control – A process of keeping separate a batch of a rubber compound from the time it is molded through the entire production process up to and including the Shipping Department
Batch Number – The assigned number that identifies a batch or rubber
Billet – A term used (primarily in the Rubber Mold Industry) to describe mold cavity or core inserts which can easily be replaced in production molds
Blisters – A raised spot on the seal’s surface created by an internal void, or air-filled pocket
Bloom – A milky surface discoloration caused by the migration of certain compound components (such as antiozonants) to the rubber’s surface after molding or storage. The waxy film serves as a protective coating shielding the part from oxidation. This discoloration DOES NOT adversely affect material performance
Bond – The mechanical or chemical force that holds an elastomer to some other object. Mechanical bonding includes component interference and no molecular cross-bridging between the elastomer and substrate, whereas chemical bonding involves contact adhesives with heat and pressure to adhere an elastomer to a primed surface
Bonding – The method of securing molded rubber directly to an insert. There are two types; A. Mechanical, where the insert is designed with ribs, grooves or holes which enable the adhesive action with rubber when molded around the insert. B. Chemical, where the insert is treated with a point that has an adhesive action with rubber when molded around the insert
Bore – A hole machined in a component which permits the passage of a shaft
Bore Seal – A sealing system, usually in a radial orientation, in which the primary sealing surface is between the O.D. of a seal ring and the I.D. of a bore
Boss – Protuberance on a plastic part designed to add strength, facilitate alignment, provide fastenings, etc
Break-out – The force required to overcome initial seal to gland surface adhesion, when part movement is intermittent. A common term used to describe one form of friction
Bridge Tooling – Using the SLA mold as the master for short-run injection molding using spec material
Brittleness – Tendency to crack upon physical deformation
Buff – A physical or mechanical means of removing parting line flash
CA – Cellulose acetate
CAB – Cellulose acetate-butyrate
CAP – Cellulose acetate-propionate
Carbon Black – A black material used as a filler in rubber. It gives the rubber its black color and the hardness characteristics
Cavity – The features of a mold which are directly responsible for forming the final shape of a molded part
Charge – The measurement or weight of material used to load a mold at one time or during one cycle
Chemical bonding – A method for bonding rubber to secondary parts by applying special adhesives to the part prior to molding
Chipping – A defect normally created in the after molding flash removal process where fragile part surfaces and edges are chipped
Circularity – the form tolerance of the surface of a molded or ground ball in reference to a perfect sphere. Also referred to as “roundness”
Clamping Plate – A plate fitted to a mold and used to fasten the mold to a plate
Clamping Pressure – The pressure applied to the mold to keep it closed during a cycle
Clearance (in a sealing system) – The space between components in a mechanical system which is present to allow for manufacturing, thermal, and dynamic variations in the size and position of the components. As measured, it is equal to the distance between the sealing surface and the entrance to the seal groove. In a radial sealing system, this will be the space between the O.D. of the shaft or piston and the I.D. of the bore. As the clearance in a system increases, the tendency of the seal to dislodge from the grove and enter into the clearance space also increase, especially in applications where pressure is present. Care should be taken in radial applications to note whether clearances are being stated as radial clearances or as diametral clearances
Coating – A uniform layer of chemical primers or adhesives applied to a surface to produce a chemical bond between the rubber and substrate. May also refer to special surface treatments that can be applied to rubber to achieve desired properties
Coefficient of Thermal Expansion – Value used to determine the amount of linear dimensional change for a particular elastomer, which is temperature dependent
Cold Flexibility – Flexibility following elastomer exposure to a specified low temperature for a specified period of time
Cold Flow – A term describing the tendency of certain materials to continue to deform or “creep” under constant sealing pressure (compressive load)
Cold Slug – the first material to enter an injection mold; so called because in passing through a sprue orifice it is cooled below the effective molding temperature
Compound – A mixture of a polymer and associated chemical ingredients necessary to produce a finished rubber material. The term is commonly used when referring to a specific rubber formulation
Compression Molding – A molding process in which the uncured rubber compound is placed directly into the mold cavity, and compressed to its final shape by the closure of the mold
Compression Set – the permanent deformation experienced by a rubber material when compressed for a period of time. The term is commonly used in reference to a test conducted under specific conditions wherein the permanent deformation, expressed as a percentage, is measured after a prescribed period of time. A low compression set is desirable in molded rubber parts such as seals and gaskets, which must retain their dimensions to maintain an effective seal.
Compressive Strength – The maximum compressive stress carried by a test specimen during a compression test
Concentricity – A condition in which two or more features (cylinder, cones, spheres, hexagons, etc..) in any combination, have a common axis
Conversion Fahrenheit to Celsius – F=(° C x 9/5) +32 C=(° F – 32) x 5/9
Conversion Celsius to Fahrenheit – C = (° F – 32) x 5.9 F = (° C x 9.5) + 32
Conversion Factors – From To Multiply by ___________________________________ lbs/ft2 kg/m2 4.88241 lbs/in2 (psi) kg/cm2 0.070307 gallons (gal) liters (l) 3.78533 gal/min 1/sec 0.063088 miles km 1.609
Conversion Grams to Ounces – gm = oz x 28.349527 oz = gm x 0.0352739
Conversion Inches to Millimeters – in = mm x 0.03937 mm = x 25.4
Conversion Kilograms to Pounds – kg = lbs x 0.454 lbs = kg x 2.205
Conversion Millimeters to Inches – mm = in x 25.4 in = mm x 0.03937
Conversion Ounces to Grams – oz = gm x 0.0352739 gm = ox x 28.349527
Conversion Pounds to Kilograms – lbs = kg x 2.205 kg = lbs x 0.454
Cooling Channels – Channels located within the body of a mold through which a cooling medium is circulated to control the mold surface temperature
Copolymer – An elastomer (polymer) resulting from the chemical combination of two dissimilar monomers. For example, Buna N from Butadiene and Acrylonitrile
Core Bar – A commonly used term to describe a male portion (usually opposite of cavity) of a mold detail which usually produces a hole or recess in a molded part
Core Bar – A steel bar used to hold machined core pins in place in the mold
Core Pins – Steel pins in a cavity that forms a hole or opening in a part
CPE – Chlorinated polyethylene
CPK – Describes how capable the stable process is of meeting design specifications. The CPK measures the distance from the process average (xbar) to the nearest specification and compares it to the natural variation in the process
CPVC – Chlorinated polyvinyl chloride
Cracking – Sharp breaks or fissures in rubber surfaces resulting from excessive strain or exposure to adverse environmental factors
Crazing – Fine cracks which may extend in a network on or under the surface or through a layer of plastic material
Creep – The progressive relaxation of an elastomeric material under constant sealing pressure (compressive load). Also known as cold flow. also called shrink
Cross-linking Agents – A chemical or chemicals that bond the polymer chains of a rubber together during the molding process
Cross-Section (of a seal) – the axial thickness or radial width of an O-Ring or Quad-Ring® seal. For an O-Ring, this will be the circular diameter of its cross-section. For a Quad-Ring®, this will be the length of a side of a square circumscribed about the cross-section
Cross-Sectional Compression, Percent (of a seal) – The deformation placed on a rubber part to affect a seal. It is expressed as a percentage of the seal’s original (undeformed) cross-section. See also Squeeze
Cross-Sectional Reduction (of a seal) – The reduction in thickness of a seal’s cross-sectional a result of material displacement caused by an applied stretch to the seal. See also Necking
Cross Section-Axial – When the part is flat (relative), the cross section that is at 90 to the linear plane
Cross Section-Radial – When the part is flat (relative), the cross section in the linear plane
Cure – A. One complete cycle. B. The thermo process that causes a chemical change in the raw stock, turning it into the finished rubber part
Cure Time – The preset time needed to complete the curing process
Cure Weight – The prescribed weight of stock needed to make one cure of parts, usually stated on the load card (7-card) in ounces or grams
Curing – An informal (slang) term for the vulcanizing process that cross-links a rubber to form its characteristic elastic properties. See also Vulcanization
Curing temperature – The temperature of vulcanization
Cylinder – Chamber in which a piston is driven
Damping – The ability of an elastomer to absorb forced vibrational energy
Daylight Opening – The clearance between two platens of a clamping press in the open position
Deburr – Removal of material from a drilled or punched hole, waste from saw cuts of material or sharp or rough edges
Deep Injection – A common molding defect identified by the deep depression in the rubber part at the point of injection
Deflashing – Any of various processes used to remove extraneous rubber from a molded rubber part
Delamination – The surface of the finished part separates or appears to be composed of layers of solidified resins. Strata or fish scale-type appearance where the layers may be separated
Density – Weight per unit volume of a substance expressed in grams per cubic centimeter
Diametrical Clearance – The gap between the two mating metal surfaces forming a gland’s internal cavity. Through slight oversizing and accompanying “squeeze” the O-Ring seals this gap to prevent system leakage
Diaphragm Gate – Used in symmetrical cavity filling to reduce weld-line formation and improve filling rates
Die Cut – The process of stamping out the I.D. or O.D. parting line flash or feed from a part. The part is placed on a mechanical fixture to perform this function
Direct Gate – The sprue feeds directly into the mold cavity
Dispersion – Finely divided particles of a material in suspension in another substance
Distorted – A molded rubber part that is not in proper shape. It is usually a defect and caused by a part being partially dislodged from a cavity. The part then takes a set
Double Injection – A molding defect that is 100% avoidable by following proper molding procedure. It is identified by a flat raised injection that peals away by using your thumb nail. It is caused by not completely unloading a mold of its parts and another cure is run on top of the parts that were left in the mold from the previous cure
Draft – The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold
Drooling – The extrusion or leakage of molten resin from a nozzle or nozzle sprue bushing area while filling or shooting
Durometer – Standard rubber industry test instrument which uses an indenter to measure the hardness of molded rubber. While other scales are available, the hardness of rubber is most commonly reported by a durometer using the Shore A scale
Dwell – A pause in the application of pressure to a mold, made just before the mold is completely closed, allowing any gases formed or present to escape from the molding material
Dynamic Seal – A seal used in an environment that subjects it or a mating surface to movement
EC – Ethyl cellulose
Edge Feed – A method of feeding rubber into the mold cavity. In this case, the point of injection is at the edge of the part
Ejector Housing – A “U” shaped frame which is an integral part of the tool containing the ejector retainer plate and ejector plate
Ejector Pin – (knockout Pin) A pin or plate that is driven into a mold cavity from the rear as the mold opens to force out the finished part
Ejector Plate – The part of the mold which backs up the retainer plate and keeps the knockout pins from falling out
Ejector Retainer Plate – The part of the mold which locates and retains the knockout pins
Ejector Rod – A bar that actuates the ejector assembly when the mold opens
Elastic Limit – Maximum stress that a material will stand before permanent deformation occurs
Elasticity – A rubber’s ability to return to its original size and shape after removal of the stress causing deformation such as stretching, compression, or torsion. It is the opposite of plasticity. The term elasticity is often loosely employed to signify the “stretchiness” of rubber
Elastomer – Any of various polymers having the elastic properties of rubber
Elongation – Generally referred to in terms of tensile (pull apart) testing, elongation is the increase in length of a test specimen, expressed as a percentage of its original (unstretched) length… relative to a given load at the breakpoint
EMA – Ethylene-methyl acrylate
EMI – Electromagnetic interference
Encapsulating – Enclosing an article (usually an electronic component) in a closed envelope of plastic, by immersing the object in a casting resin to polymerize or, if hot, to cool
EP – Ethylene propylene
EPDM – Ethylene propylene diene monomer rubber
ESCR – Environmental stress crack resistance
ETFE – Ethylene-tetrafluoroethylene
EVA – Ethylene-vinyl acetate
Extending Flash – Flash that is formed at the parting line of a mold
Extrusion – When part or all of a component is forced from its groove by high continuous or pulsating pressure
Face Seal – A sealing system in which the sealing occurs in the axial direction of the seal. If the seal ring were to be placed flat upon a desktop, the seal compression would occur between the top and bottom of the seal
Family Mold – A multi-cavity mold where each of the cavities forms one of the component parts of the assembled finished part
Fan Gate – This gate is used to help reduce stress concentrations in the gate area by spreading the opening over a wider area. Less warpage of parts can usually be expected by the use of this gate type
FDA – Food & Drug administration
Feather Edge – The sharp, thin edge on parts such as wiper seals. Also called a “knife edge”
Feed – The area or orifice where rubber is injected or transferred into a mold cavity
File Transfer Protocol (FTP) – A safe and secure way to send a file from one data port to another. By using this method of data transferring, it allows both the sender and the receiver to acknowledge the transfer. It is like a cyberspace handshake
Filler – A finely divided material used to reinforce or modify elastomer physical properties, impart certain processing properties, or reduce cost. Typical examples are carbon black, clays, calcium carbonates and silicas
Fillet – A rounded filling of the internal angle between two surfaces of a part
Fin – The web of material remaining in holes or openings in a molded part which must be removed for final assembly
Fixture – Block of metal or wood used to maintain the proper shape or dimensional accuracy of a part after it is removed from the mold until it is cool enough to retain its shape without further appreciable distortion. Also known as shrink fixture
Flash – Extraneous material protruding from the surface of a molded part. Flash is generally found on a molded part at the parting line locations
Flexural strength – The ability of a material to flex without permanent distortion or breaking
Flow – The ability of heated plastic or uncured rubber to travel in the mold and runner systems during the molding process
Flow Line – A disturbance in the homogeneous structure of a molded part generally caused when material knitted or blended with itself during the molding operation
Flow Marks – Wavy surface appearance of an object molded caused by improper flow of the plastic into the mold. A mark made by the freezing-in of a visible flow pattern
Fluid – A liquid or gas
Fr – Fiber reinforced
Friction (Break-out) – Friction developed in dynamic seal situations during machine start-up. When machine operation is irregular, O-rings tend to conform (adhere) to the microfine grooves of surrounding glandular surfaces, requiring extra initial force to break them out of these microfine grooves
FRP – Fiber=reinforced plastics
Fused Disposition Modeling Process (FDM) – Thermoplastic modeling material is fed into the temperature-controlled FDM extrusion head and heated to a liquid state. The head extrudes and deposits the material in ultra-thin layers onto a fixtureless base
Gasket – A static (stationary) sealing device used to retain fluids under pressure or to seal out foreign matter
Gate – In injection and transfer molding, the orifice through which the melt enters the cavity. Sometimes the gate has the same cross-section as the runner leading to it; often, it is severely restricted
Gate Edge – A gate that is cut along one edge of the mold cavity
Gate Fan – Large cross sectional area for feeding plastic into the cavity. Flow channel tapered from the runner to the gate
Gate Flash – A gate that encompasses entire periphery of part. Usually of low sectional thickness in relation to part
Gate Mark – A raised spot or small depression on the surface of an injection or transfer molded part where the gates interface the cavity. See also Sprue Mark
Gate Pin-Point – A restricted orifice, usually used in a three plate-type mold, through which molten resin flows into a mold cavity
Gate Ring – The clearance between the force plug and the vertical wall of the cavity in a positive or semi-positive mold; also the ring of excess material which escapes from the cavity into this clearance space
Gate Sprue – The type of gate in which the plastic is injected directly from the molding press into the cavity
Gate Straight-in – the rectangular area between the runner and the part. This area is tapered on three sides so the smallest area is at the point of contact with the part
Gate Underside – The orifice found between the “A” and “B” plate which carries the resin into the cavity in an overlap of the part in such a manner so as to obtain a clean break on the part. Usually found in thermoset molding
Gates – the openings in an injection or transfer mold whereby material enters the mold cavity
Geometric Dimensioning & Tolerancing – A means of specifying engineering design and drawing requirements with respect to actual function and relationship of part features. Furthermore, it is a technique which properly applied ensures the most economical and effective production of these features
Gland – The space in a mechanical system into which a seal is installed. the gland consists of the seal groove and any additional space required to achieve the proper compression of the seal. Care should be taken to distinguish between the terms gland and groove, which are separate but related concepts
Gland Depth – The gland depth (pictorially depicted and described as Dimension “C” throughout this book) is the distance from the sealing surface to the seal groove surface. The gland depth-determines how much the seal is compressed and therefore how much cross-sectional compression (squeeze) is applied to the seal. In a radial sealing application, the gland depth is used to calculate the seal groove diameter by either adding or subtracting (depending on the type of seal) twice its value from the diameter of the sealing surface. In an axial (face) sealing application, the gland depth equals the groove depth when it is a zero clearance application (two directly contacting surfaces, such as a cover) or, when clearance is present, it is the distance from the sealing surface to the seal groove surface (such as in a rotary face seal application). It should be noted that the Gland depth and Clearance is separate sealing system parameters and a change in one of these parameters does not result in a change to the other. Of example, if the clearance in a system needed to be increased, the required gland depth to achieve the desired seal compression would remain the same, but the seal groove diameter would need to be adjusted to achieve the desired gland depth. Care should also be taken to distinguish between the terms gland depth and groove depth, which are separate but related concepts. See the Application section of this publication for more information on calculations involving Gland Depth
GP – General Polymers
Groove – The machined glandular recess into which the seal is fitted
Groove Depth – The measured depth of a feature, frequently a slot, machined or otherwise created in a mechanical system to physically locate and constrain a seal. Care should be taken to distinguish between the terms Gland Depth and Groove Depth, which are separate but related concepts