Plastic & Silicone Glossary

  • A
    • 2-Component Molding

      A means of producing a part with two or more materials, 1st part is generally thermoplastic injection molded part or a plastic or metal part inserted into the mold. Liquid silicone rubber or plastic is then injected onto to the part, attaching by means of mechanical or chemical bond

    • Abrasion

      Surface wear caused by relative motion between two or more contacting objects

    • Abrasion Resistance

      The ability of a rubber compound to resist surface wearing by mechanical action

    • ABS


    • Absorption

      The physical mechanism by which one substance takes up another substance into its interior

    • Accelerated Life Test

      Any set of test conditions designed to reproduce, in a short time, the deteriorating effect obtained under normal service conditions

    • Accelerator

      A substance that speeds up curing or vulcanization of natural/synthetic rubbers

    • Acid Resistance

      Withstands the action of acid

    • Acrylic

      A polymer for which resistance to air and hot oil at temperatures above 30 degrees Fahrenheit is required

    • Adhere

      To cling or stick together

    • Adhesion

      Tendency of rubber to bond or cling to a contact surface

    • After Cure

      Continuation of curing after heat source removed ie injection mold or compression mold.

    • Aging

      The change in physical and chemical properties of an elastomer that has been exposed to a particular environment over time

    • Aging, Accelerated

      Tests run on destructive influence of light, oxygen, heat and ozone in as short a period as possible

    • Air Trap

      Surface markings or depressions due to air caught between the material being cured and the mold surface

    • Ambient Temperature

      The temperature of the environment surrounding a particular object

    • Aniline Point

      The lowest temperature at which equal volume of pure, fresh aniline and oil will completely dissolve in one another is the aniline point of the oil.

    • Annealing

      A process of holding a material at a temperature near, but below, its melting point, to permit stress relaxation without distortion of shape.

    • 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

    • ASA


    • ASTM

      American Society for Testing and Materials, An organization for issuing standard specifications on materials

    • Axial Seal

      A face seal squeezed on both the top and bottom surfaces of the seal’s cross section

  • B
    • 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

    • Bake Out

      A process whereby a vacuum system is heated for a given time at some predetermined temperature to de-gas all the components, such as gauges, fittings, valves, seals

    • Base Line

      The mark from which all features are dimensioned or measured from

    • Batch

      The product of one mixing operation or shipment of Liquid Silicone Rubber

    • Batch Number

      The assigned number that identifies a batch of Silicone Rubber

    • Blemish

      A mark, deformity or injury which impairs appearance

    • 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 (i.e. antiozonants) to the rubber’s surface after molding or storage. The milky film serves as a protective coating shielding the part from oxidation

    • Bond

      The term commonly used to denote the attachment of a given elastomer to some other member, classified as follows:
       1) Mechanical: purely physical attachment accomplished by through holes, interlocking fingers, envelope design in silicone rubber
       2) Cold: adhesion of previously vulcanized elastomer to another member through use of suitable bonding agent
       3) Chemical: adhesion of an elastomer to a previously primed or glass particle surface using heat and pressure, thus curing the silicone rubber

    • 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 OD of a silicone rubber seal ring and the ID of a bore

    • Boss

      Protuberance on a plastic part designed to add strength, facilitate alignment, provide fastenings, etc

    • Brittleness

      Tendency to crack upon physical deformation

  • C
    • 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

    • Chemical bonding

      A method for bonding rubber to secondary parts by applying special adhesives or having a glass element on part prior to liquid silicone molding

    • 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 of an silicone injection molding machine

    • Clearance

      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.

    • Coating

      A uniform layer of chemical primers or adhesives applied to a surface to produce a chemical bond between the liquid silicone rubber and substrate. May also refer to 2-component silicone molding or special surface treatments that can be applied to silicone rubber to achieve desired properties

    • Coefficient of Thermal Expansion

      Average expansion per degree over a stated temperature range, expressed as a fraction of initial dimension, linear or volumetric

    • Cold Flexibility

      Flexibility following silicone rubber 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

    • Cold Runner

      Runner less liquid silicone injection molding system of delivering liquid silicone to heated cavity

    • Cold Slug

      The first bit of material to enter a silicone injection mold; so called because in passing through a sprue orifice it is cured

    • Color Jet Printing

      This system involves two main components, the core and the binder. It begins with a layer of the core laid out on the building platform, and then the binder is ejected from inkjet printer heads. This effectively bonds and sets the material, while adding the color.

    • Compound

      A mixture of a polymer and associated chemical ingredients necessary to produce a finished high consistency rubber material. The term is commonly used when referring to a specific rubber not liquid silicone rubber which is delivered in closed system

    • Compression Molding

      A traditional molding process in which the uncured high consistency rubber compound is placed directly into the mold cavity, and compressed to its final shape by the closure of the mold. Considered unacceptable for many applications because parts must be deflash causing debris.

    • Compression Set

      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 is expressed as a percentage and measured after a prescribed period of time. 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

    • Conductive Silicone Rubber

      A silicone rubber capable of conducting electricity. Most generally applied to silicone rubber products used to conduct static electricity or as an RF shield

    • Conversion Fahrenheit to Celsius

      F = (° C x 9/5) +32 or C = (° F – 32) x 5/9

    • Cooling Channels

      Channels located within the body of a plastic injection mold through which a cooling fluid is circulated to control the mold surface temperature

    • Core

      The mail portion of a liquid silicone rubber injection or plastic mold.

    • Core & Cavity Set

      A sub set of a liquid silicone rubber injection or plastic mold that fits within a mold base. This technique generally lowers silicone or plastic tooling investment

    • Core Bar

      A steel bar used to hold machined core in place in the liquid silicone injection mold

    • CPE

      Chlorinated Polyethylene

    • CPVC

      Chlorinated Polyvinyl Chloride

    • Cracking

      Sharp breaks or fissures in silicone rubber surfaces resulting from excessive strain or exposure to adverse environmental factors

    • Creep

      The progressive relaxation of an elastomeric material under constant sealing pressure (compressive load)

    • 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

    • Cross-linking Agents

      A chemical or chemicals that bond the silicone rubber polymer chains of a silicone rubber together during the liquid silicone molding process

    • Cross-Sectional Compression

      The deformation placed on a silicone rubber part to affect a seal. It is expressed as a percentage of the seal’s original cross-section

    • Cure

      The heat induced process that causes a chemical change in the liquid silicone rubber material, turning it into the finished silicone rubber part

    • Cure Time

      The preset time needed to complete the liquid silicone rubber curing process

    • Curing temperature

      The temperature of liquid silicone rubber thermoset vulcanization

  • D
    • Damping

      The ability of a silicone elastomer to absorb forced vibrational energy

    • Daylight Opening

      The clearance between two platens of a silicone injection molding machine 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 silicone rubber from a silicone injection molded rubber part. Generally the sign of poor mold design or maintenance.

    • 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 compression of 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 ID or OD by placing the part 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

    • 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 liquid silicone rubber from a nozzle or nozzle sprue bushing area while or prior to shooting

    • Durometer

      Standard rubber industry hardness test for liquid silicone rubber molded or extruded parts. The hardness scale most commonly used for silicone rubber durometer is 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

  • E
    • EC

      Ethyl cellulose

    • Edge Gate

      A method of injecting liquid silicone rubber into the mold cavity

    • Ejector Housing

      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

      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

      The property of an article, generally liquid silicone rubber, which tends to return to its original shape after deformation

    • Elastomer

      Any natural or synthetic material with resilience or memory sufficient to return to its original shape after major or minor distortion, i.e. liquid silicone rubber

    • EMI

      Electromagnetic interference

    • Encapsulating

      Enclosing an article in a closed envelope of liquid silicone rubber or plastic, by immersing or over molding the object in a silicone rubber or plastic

    • EP

      Ethylene propylene

    • EPDM

      Ethylene propylene diene monomer rubber

    • ESCR

      Environmental stress crack resistance

    • ETFE


    • EVA

      Ethylene-vinyl acetate

    • Extending Flash

      Flash that is formed at the parting line of a liquid silicone mold, can be minimized by good silicone mold practices

    • Extrusion

      When part or all of a component is forced from its groove by high continuous or pulsating pressure

  • F
    • 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. Frequently used in large silicone rubber parts

    • FDA

      Food & Drug administration

    • Feather Edge

      The sharp, thin edge on parts such as wiper seals. Also called a knife edge

    • 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 to perform secondary operation.

    • Flame Resistance

      The resistance to burning of material that will not withstand combustion under ordinary conditions

    • Flash

      Excess rubber left around a liquid silicone rubber part after molding, due to space between mating mold surfaces; removed by trimming. Sign of poor silicone rubber mold maintenance or design.

    • 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 liquid silicone molded part generally caused when material knitted or blended with itself during the silicone molding operation

    • Flow Marks

      Wavy surface appearance of an object silicone molded caused by improper flow of the liquid silicone rubber or plastic into the mold. A mark made by the freezing-in of a visible flow pattern

    • Fluid

      A liquid or gas

    • Fluorocarbon

      Viton [® DuPont Dow Elastomers], Fluorel [TM, 3M Co.] Polymer designed to meet the most rigid requirements in oils, solvents, synthetic lubricants and corrosive chemicals, at elevated temperatures

    • Friction

      Resistance to motion due to contact of surfaces.

    • Friction, Break Out

      Friction developed during initial or starting motion.

    • 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 fixture-less base

  • G
    • Gamma Radiation

      Electromagnetic disturbance (photons) emanating from an atomic nucleus. This type of radiation travels in wave form, similar to X-Rays or light, but has a shorter wave length (approx. 1 Ado or 107 mm)

    • Gasket

      A static (stationary) sealing device used to retain fluids under pressure or to seal out foreign matter

    • Gate

      A silicone injection molding or plastic orifice through which the silicone rubber or plastic enters the cavity

    • Gate Edge

      A gate that is cut along one edge of the silicone rubber or plastic mold cavity

    • Gate Fan

      Large cross sectional area for feeding plastic into the silicone rubber or plastic cavity. Flow channel tapered from the silicone rubber or plastic runner to the gate

    • Gate Flash

      A gate that encompasses entire periphery of the silicone rubber or plastic part. Usually of low sectional thickness in relation to silicone rubber or plastic part

    • Gate Mark

      A raised spot or small depression on the surface of a silicone rubber or plastic injection molded part where the gates interface the cavity

    • Gate Sprue

      The type of gate in which the liquid silicone rubber or plastic is injected directly from the molding press into the cavity

    • 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, 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

  • H
    • Hardness

      A measurement of the resistance to penetration of a silicone rubber sample by an indenter on a Durometer tester. High values indicate harder materials while low values indicate softer materials.

    • HDPE

      High-density polyethylene

    • HDT

      Heat-deflection test

    • Heat deflection temperature

      The temperature at which a standard plastic test bar deflects 0.010 in. under a load of either 66 or 264 psi

    • Heat Sealing

      A method of joining plastic parts or films by simultaneous application of heat and pressure to areas in contact.

    • Hermetic Seal

      An airtight seal

    • HIP

      High-impact polystyrene

    • HME

      High-vinyl modified epoxy

    • HMW

      High molecular weight

    • Hob

      A master model in hardened steel. Also the wearing in of an A&B plate of a silicone injection mold

    • Honing

      A machining process that sharpens, enlarges, and smooths material through the use of a fine-grit stone

    • Hot Runner Manifold

      Runner less plastic injection molding of a thermoplastic, the melt stays molten until is reaches gate at cavity.

    • Hot Stamping

      Engraving operation for marking plastics in which roll leaf is stamped with heated metal dies onto the face of an article by means of felt rolls, ink is applied to type or by means of heat and pressure, type is impressed into the material, leaving the marking compound in the indentation

  • I
    • ID (Inner Diameter)

      The innermost (smallest diameter) surface of a circular object, such as a bore or a round seal

    • Impact Resistance

      Relative susceptibility of plastics or silicone rubber to fracture by shock as indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow

    • Injection Molding

      A molding method in which a liquid silicone rubber or plastic material is heated and forced under pressure into the mold cavity

    • Injection Pressure

      The pressure on the face of the silicone injecting ram when injecting material into the mold

    • Injection Tearout

      A molding defect identified by a hole in the silicone liquid rubber part at varying widths and depths located at the point where the silicone rubber is injected into the cavity area

    • Insert

      A term referring to a metal or plastic component, placed (“inserted”) into a mold cavity prior to the start of the molding cycle, to which rubber or plastic is chemically and/or physically bonded during the molding process

    • Insert Molding

      A means of producing a part with two or more materials, the metal, plastic or liquid silicone rubber part is inserted into the mold and plastic or silicone rubber is injected onto to the part attaching by means of mechanical or chemical bond

    • Internally Lubricated Rubber

      A silicone rubber formulation containing lubricating materials incompatible with the silicone rubber structure causing it to leach out as a lubricant

    • Isoprene-acrylonitrite Rubber

      A low-plasticity copolymer with around 34 per cent ACN.

  • J
    • Jetting

      A turbulent flow of plastic or silicone rubber accelerating the speed of the melt can be caused by undersized gate or bad mold design

    • Jig

      A tool for holding parts of an assembly during the manufacturing process

  • K
    • Knit Line

      Place or line where two or more flow fronts come together after going around a flow restriction or post

    • Knock Out (Ejector) Pins

      Normally pins or blades that, when activated internally to the plastic or liquid injection mold, eject the part from the mold

    • Knock Out (Ejector) Plate

      A plate in a plastic or liquid silicone rubber injection mold connects and drives the ejector pins in the plastic or silicone mold

  • L
    • L/D Ratio

      The length over diameter ratio defining a silicone rubber injection or plastic screw

    • Laminar Flow

      The flow of a resin in a plastic or liquid silicone rubber mold is accompanied by solidification of the layer in contact with the mold surface that acts as an insulator through which material flows to fill the remainder of the cavity

    • Land

      A shut off surface of a cavity on a plastic or liquid silicone rubber mold by which excess air escapes

    • LCP

      Liquid crystal polymer

    • LDPE

      Low-density polyethylene

    • LIM

      Liquid injection molding is injection molding silicone rubber, Casco Bay Molding’s specialty

    • LLDPE

      Linear low-density polyethylene

    • LMW

      Low molecular weight

    • LSR

      Liquid silicone rubber is generally a platinum cured, two-component, low viscosity, heat-curable silicone rubber system delivered in a closed drums or buckets. Casco Bay Molding’s specialty

  • M
    • Machine Shot Capacity

      This is the maximum weight of PS (not silicone rubber) which can be displaced or injected by a single stroke

    • MBS


    • MDPE

      Medium-density polyethylene

    • Mechanical Bond

      A method of physically bonding liquid silicone rubber to inserts through the use of holes, depressions or projections in the insert

    • Melt Index

      A measure in grams of plastic material that can be forced through an orifice of 0.0825 inches when subjected to a force of 2160 grams in 10 minutes at 190°C

    • Memory

      Ability of a silicone rubber or elastomeric material to return to its original size and shape after deformation

    • Menstrual Cup

      A Menstrual Cup is a safe, healthy, and affordable alternative to pads and tampons for menstruating women. Instead of absorbing menstrual blood, menstrual cups are inserted to “collect” it. This allows the menstrual cup to be worn for up to 10-12 hours in-between emptying.  They are typically made from USP Healthcare-Grade Class VI Silicone, but there are a few “offenders” produced overseas from inferior materials.

      Casco Bay Molding produces the Casco Cup & Case, an all-in-one solution to the problem of messy cloth baggies that typically accompany other menstrual cup brands.

    • Mismatch

      Unequal cross-sectional match between the two mold halves, seen in silicone injection molded parts.

    • MMA

      Methyl methacrylate monomer

    • Modulus

      Tensile stress at specific elongation, normally 100% elongation for silicone elastomers

    • Modulus of Elasticity

      One of several measurements of stiffness or resistance to deformation, but often incorrectly used to indicate specifically static tension modulus

    • Moisture Marks or Welds

      Marks on the finished part that are caused from moisture in the resin and look like weld lines except they may be in the wrong areas for weld lines

    • Mold

      Typically made from steel for liquid silicone tooling, article is produced by injecting silicone into machined cavity

    • Mold Base

      Mold frame that holds mold cavities

    • Mold Cavity

      Hollow space of the mold within which the liquid silicone rubber is injected and cured to the desired finished product form

    • Mold Finish

      The surface finish of the silicone injection mold which imparts the desired surface quality to the finished molded silicone product

    • Mold Marks

      Slight irregularities in the surface of molded articles caused by mold machining marks, or damage to the mold itself

    • Mold Shrinkage

       The difference in dimension, expressed in inches per inch, between a silicone part and the steel cavity in which it was injection silicone molded, when both are measured while at room temperature

    • Mold Three Plate

      Integral moving plates in a conventional silicone injection mold, containing the cavities and allowing the injection point or gate to feed directly into the part

    • MOQ

      Minimum Order Quantity

    • MSDS

      Material safety data sheet

    • MUD Set

      MUD stands for Master Unit Die. A MUD set is a purchased universal injection mold base which reduces injection mold fabrication cost. Great for short runs, quick overturn and repair.

    • MW

      Molecular weight

  • N
    • Neoprene (GR-M)

      A DuPont Dow Elastomers polymer of chloroprene which is prepared from coal, salt and limestone, not injection molded

    • Nitrile

      Or Buna-N, The most commonly used elastomer for O-Rings because of its resistance to petroleum fluids, its good physical properties, and its useful temperature range

    • Nominal Dimension

      The mean dimension of a liquid silicone injection molded article, from which small dimensional (plus and minus) deviations are allowed as manufacturing tolerances

    • Non-fill

      An unintentional void or absence of material in the liquid silicone rubber part

    • Nozzle

      The hollow cored metal nose of a liquid silicone injection screw and barrel that seats off against an LSR mold

  • O
    • O-Ring

      A doughnut-shaped object that functions as a seal, blocking the passage of liquids or gases, by being compressed between the two mating surfaces comprising the walls of the cavity into which the ring is installed

    • OD, Outer Diameter

      The outermost, largest, surface of a circular object, such as a shaft or a round seal. the term OD is frequently used to indicate both the circumferential surface itself as well as the measured diameter of that surface

    • OEM

      Meaning Original Equipment Manufacturer, is a company that makes a component part that is used in another company’s end product.

    • Off-register

      Misalignment of mold halves causing out-of-round O-Ring or part cross section

    • Oil Resistant

      Ability of liquid silicone or natural rubber to resist swelling and other detrimental effects of exposure to various oils

    • Orange Peel

      A surface finish on a liquid silicone molded part that is rough and splotchy

    • Original Equipment Manufacturer (OEM)

      A company who makes components that are used in other products

    • Oscillating Seal

      Most commonly used in faucet valves, in this application the inner or outer member of the gland moves in an arc around the axis of a shaft. Movement is limited to a few turns in one direction and a few turns in the return direction (i.e. faucet on, faucet off)

    • Outgassing

      A phenomenon wherein a substance (i.e. silicone or natural rubber) spontaneously releases volatile constituents in the form of vapors or gases normally during curing process with liquid silicone rubber.

    • Overflow

      A designed escape reservoir for liquid silicone rubber, used to insure mold cavity fill and also allowance for excess compound, generally frowned upon because part requires post molding trimming

    • Ozone Resistance

      Ability to withstand the deteriorating effect of ozone, which generally causes cracking

  • P
    • PA

      Polyamide (nylon)

    • Pack Out

      The filling of the liquid silicone mold cavity or cavities as full as possible without causing undue stress on the silicone mold or causing flash to appear on the finished parts

    • PAI


    • PAN


    • Parting line

      The witness line on the surface of a silicone molded part corresponding to the location where the LSR mold plates were in contact

    • PB


    • PBT

      Polybutylene terephthalate

    • PBTP

      Polybutylene terephthalate

    • PC


    • PCTFE


    • PE


    • PEC

      Polyphenylene ether copolymer

    • PEEK

      Polyetherether ketone

    • PEH

      Polyphenylene ether homopolymer

    • PEI


    • PEO

      Polyethylene oxide

    • Permanent Set

      The deformation remaining in a liquid silicone rubber specimen following both stress and relaxation over a period of time

    • Permeability

      The rate at which liquid or gas, under pressure, passes through a solid material by diffusion and solution. In silicone rubber terminology: the rate of gas flow, expressed in atmospheric cubic centimeters per second, through an elastomeric material, one centimeter square and one centimeter thick

    • PES


    • PET

      Polyethylene terephthalate

    • PETG

      Glycol-modified PET

    • PETP

      Polyethylene terephthalate

    • PETP

      Polyethylene terephthalate

    • PF


    • PFA

      Perfluoroalkoxy (resin)

    • PH

      Determines the concentration of either an acid or a base

    • PI


    • PIB


    • Plastic Jet Printing

      This process involves melting a solid plastic and extruding it layer by layer until the 3D -model is formed. In more complicated shapes, sometimes a soluble plastic is also extruded as a support piece, these can either be defined by the designer, or automatically rendered in the 3D modeling program.

    • Plasticize

      To soften a silicone rubber by making it plastic, less viscous or moldable, either by means of a plasticizer or the application of heat

    • Plasticizer

      A chemical agent added to the rubber compound batch mix to soften the elastomer for processing, as well as to improve physical properties of the compound product (i.e., increase elongation, reduce harness, improve tack)

    • Plate Retainer

      The plate on which demountable pieces, such as mold cavities, ejector pins, guide pins, and bushings are mounted during molding

    • Plate Stripper

      A plate that strips a liquid silicone molded piece from core pins or force plugs. The stripper-plate is set into operation by the opening of the mold

    • Platen Movable

      The large back platen of an silicone injection molding machine to which the back half of the mold is secured during operation. The platen is moved horizontally or vertically by either a hydraulic ram or a toggle mechanism

    • Platen Stationary

      The large front plate of an silicone injection molding machine to which the front plate of the mold is secured during operation

    • Platens

      The mounting plates of a press to which the entire mold assembly is bolted

    • PMMA

       Polymethyl methacrylate

    • PMS


    • PMT


    • Polymer

      A material formed by joining together many (poly) individual units (mer) of one or more monomers; synonymous with elastomer

    • Post Cure

      The process of baking or autoclaving silicone parts after molding. This process is used to improve the heat and compression set resistance of specific elastomers- like silicone and fluorocarbons.

    • PP


    • PPAP

      (Part Production Approval Process) Our ability, as product supplier, to meet requirements determined by our customers through continued process documentation and analysis. See PPAP link for more information.

    • PPO

      Polyphenylene oxide

    • PPS

      Polyphenylene sulfide

    • Pressure Injection

      The pressure on the face of the injection ram at which molding silicone rubber is injected into a mold, liquid silicone rubber generally uses much lower injection pressures when compared with plastic injection

    • PS


    • PTFE


    • PU


    • Purging

      Cleaning one color or type of liquid silicone rubber from the cylinder of an injection molding machine by forcing it out with the new color of LSR

    • PVC

      Polyvinyl chloride

    • PVDF

      Polyvinylidene Fluoride

    • PVF

      Polyvinyl Fluorid

  • Q
    • QS 9000

      Quality System model, used in conjunction with the ISO 9000 standard, for the automotive industry

    • Quench Bath

      The cooling medium used to quench molten thermoplastic materials to the solid state

    • Quick Cast

      An SLA build style that produces a thin shell with a honeycombed interior. This method is used mostly for investment castings when the SLA model will be used as a sacrificial mold

  • R
    • Radial Seal

      Compression is applied perpendicular to the seal center-line

    • Rapid Prototyping

      Fabrication of a physical, three-dimensional part of arbitrary shape directly from a numerical description, typically a CAD model, by a quick, highly automated and totally flexible process.

    • Reciprocating Seal

      Seals used in moving piston and rod situations

    • Regrind

      A process that finely grinds plastic part runners and rejected parts

    • Relative Humidity

      The ratio of the quantity of water vapor actually present in the atmosphere, to the greatest amount possible at a given temperature

    • Resilience

      The capability of returning to original size and shape after deformation

    • RF


    • Rockwell Hardness

      A standard method for measuring the hardness of metals. The hardness is expressed as a number related to the depth of residual penetration of a steel ball or diamond cone after a minor load of 10 kilograms has been applied to hold the penetrate in position, designated by letters varying from “A” to “H” the “B” and “C” scales are most commonly in use.

    • Rotary Seal

      Seals for rotating shafts, with the turning shaft protruding through the I.D. (hole) of the O-ring

    • RTV Molding

      A procedure where a part is molded in a silicone mold to reproduce up to twenty urethane parts

    • Rubber

      A common name for both naturally occurring and synthetically made elastomers like liquid silicone rubber

    • Rubber Synthetic

      Man-made elastomers such as Nitrile, Fluorocarbon, Silicone and liquid Silicone rubber

    • Rubber-Natural

      A natural product of the juices of certain tropical plants (latex), improved through heat treating with sulfur (vulcanization)

    • Runnerm

      The channel that connects the sprue with the gate for transferring the molten liquid silicone rubber to the cavities

  • S
    • SAN


    • SBR

      Styrene-butadiene (rubber)

    • Seal

      Any device used to prevent the passage of a fluid, liquid or fine particles

    • Seal Off

      A feature on two liquid silicone mold halves or cavity inserts seal off the cavity with the exception of the silicone injection gate and air venting ports

    • Selective Laser Sintering (SLS)

      This method of rapid prototyping utilizes a laser to soften a powdered material, (typically metal),  and binding it together into a form pre-defined by a 3D-model.

    • Shore A

      A hardness scale used to measure the hardness of molded silicone rubber. The Shore A scale is most effectively used to measure liquid silicone rubber with a hardness from 10 to 95 Shore A

    • Short shot

      A condition where there is insufficient liquid silicone rubber is introduced into a LSR mold cavity to completely fill the cavity, resulting in a partially formed part

    • Shot

      The complete amount of silicone rubber required to fill all silicone mold cavities completely

    • Shot Capacity

      The maximum weight of liquid silicone rubber which an injection machine can inject with one forward motion of the screw

    • Shrinkage

      The ratio between a mold cavity size and the size of a product molded in that cavity

    • Single Cavity Mold

      A silicone injection mold having only one cavity and producing only one finished part per cycle

    • Sink Marks

      A shallow depression or dimple on the surface of a finished plastic part due to shrinkage or low fill of the cavity, much less prevalent in liquid silicone rubber parts

    • Sliding Core

      A pin on a mold that automatically retracts when the mold opens

    • SMA

      Styrene maleic anhydride

    • SPC

      (Statistical Process Control) Methods of controlling our processes to prevent defects from being made

    • 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

    • Spiral Twist

      A type of seal failure resulting from a twisting action that strains or ruptures the rubber

    • Splay Marks

      Marks or droplet-type imperfections found on the surface of the finished parts that may be caused by the spraying of the melt through the gates and into the cool cavity

    • Sprue

      The primary feed channel that runs from the outer face of a silicone injection mold to the mold runner and gates

    • Sprue Bushing

      A hardened steel insert in the silicone injection mold that accepts the silicone molding machine nozzle and provides an opening for transferring the silicone or molten plastic

    • SPS

      Syndiotactic Polystyrene :High heat resistant thermoplastic material with crystalline structure. Generally glass filled. Used in under hood-automotive or other high heat applications i.e. sterilization cassettes and electrical connectors. Casco Bay Molding has extensive experience injection molding and ultrasonically welding SPS.

    • Static Mixer

      A helix like device that mixes two liquids by redirecting the flow path into each other repeatedly, common with RTV Silicone and some liquid silicone rubber applications

    • Static Seal

      A seal that, except for pulsations caused by cycle pressure, does not move in its environment

    • Statistical Process Control (SPC)

      The use of statistical techniques on processes and their output to establish process stability and increase capabilities

    • Steel Safe

      Steel Safe Rule:   Add Plastic = Removing Steel, Removing Plastic = Adding Steel (welding or inserting). When it comes to mold-making, you can always cut more metal away – making your plastic part larger, walls thicknesses wider, etc. – but adding metal back to the mold – removing walls, thinning features, etc.-  can be extremely costly, and often times not possible.

    • Stereolithography (SLA)

      This form of 3D-printing utilizes a UV laser to cure photo-reactive liquid resin layer by layer into a solid form pre-defined by a 3D modeling file.

    • Strain

      the deformation caused by an applied stress

    • Stress

      Force per original cross section that is applied to a specimen

    • Stress Relaxation

      Decreasing stress with constant strain over a given time interval or viscoelastic response

    • Stripper Plate

      A plate that strips a molded plastic or liquid silicone rubber part from core pins

    • Sublimation

       The direct conversion of a substance from solid state to vapor or gas state

    • Submarine Gate

      Tunnel gate, a type of edge gate where the opening from the runner into the mold is located below the mold parting line

    • Suck Back

      A method of decompressing a molds runner system by retracting the screw on a plastic or silicone injection molding machine

  • T
  • U
    • USP Medical Grade Class VI

      For a material to be considered USP Class VI, it must pass a series of tests performed by the material supplier to determine the amount of irritation the material causes. These tests are:

      Acute System Toxicity Test: Oral, dermal, and inhalation.

      Intracutaneous Test: Exposed tissues are subject to contact with the material in question.

      Implantation Test: Samples of the material are implanted into a living animal for 5 days.

      Based on the result of these tests, the material is assigned a class between I and VI, (VI being the strictest & least irritating).

      More detailed information can be found here.

  • V
  • W
  • X
  • Y
  • Z