Thermosets 261

abrasion

The physical wearing away of a material due to friction. Abrasion resistance in polyurethane is higher than in many other thermosets.

additives

A substance added to a plastic during manufacturing in order to improve or alter its properties. Additives can help add strength to a plastic.

advanced composites

A high-performance material consisting of long reinforcement fibers and thermoset resins with superior mechanical properties. Advanced composites can be used as a coating on concrete to prevent damage during earthquakes.

aluminum

A lightweight, inexpensive metal with high thermal and electrical conductivity. Aluminum molds can be used in reaction injection molding due to the lower processing temperatures involved.

atoms

The smallest particle of a substance. Atoms combine to form molecules, creating the backbone of a polymer molecule chain.

BMC

Bulk molding compound. A composite formed into a block of sticky material with the consistency of dough. BMC is created by combining unsaturated polyester resin with an initiator, a filler, and reinforcement fibers.

brittleness

A property that makes a material difficult to bend, stretch, or form without breaking. Brittle materials tend to fracture easily when bent or stretched unless they have been treated with additives or modifiers.

bulk molding compound

BMC. A composite formed into a block of sticky material with the consistency of dough. Bulk molding compound is created by combining unsaturated polyester resin with an initiator, a filler, and reinforcement fibers.

butyl rubber

A synthetic elastomer produced from the combination of the organic compounds isobutylene and isoprene. Butyl rubber can resist damage from ultraviolet radiation.

carbon

A nonmetallic chemical element. Carbon is used as reinforcement material in many composites.

casting

A plastic shaping process that involves pouring heated liquid resin into a mold until the material hardens into a solid. Casting does not involve significant pressure.

ceramics

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics include traditional materials such as brick and clay, as well as advanced ceramics used in abrasives and cutting tools.

chemical bonds

A strong attraction holding atoms together in a molecule. Chemical bonds include primary bonds and secondary bonds.

chloroprene

A synthetic elastomer derived from an organic compound. Chloroprene was one of the first successful synthetic rubbers.

closed mold

A two-part mold that uses pressure to shape resin. Closed molds are used in compression molding and other thermoset shaping processes that require pressure.

composite

A material made by combining a binding resin with small particles of solid reinforcements. Composites often include a thermoset plastic resin as the binding ingredient.

composites

A material made by combining a binding resin with small particles of solid material. Composites often use a thermoset as the binding resin.

compounding

The process of mixing additives and resin together. Compounding prepares elastomers for manufacturing.

compression molding

A thermoset molding process that forces resin into a heated closed mold using high amounts of pressure. Compression molding holds thermoset resin between the mold halves until it cures into its final shape.

corrugated panels

A thick, molded sheet that has alternating parallel ridges to provide strength. Corrugated panels can be made using fiberglass-reinforced plastic and other composites.

covalent bonds

A chemical bond formed between atoms by the sharing of electron pairs. Covalent bonds are a strong type of primary bond that forms in a thermoset during cross-linking.

creep resistance

A material's ability to resist distortion caused by a load over an extended period of time. Creep resistance is a property often found in thermoset elastomers.

cross-linking

The formation of covalent bonds between polymer molecule chains. Cross-linking is a chemical reaction that occurs before a thermoset is manufactured.

curing

The process of using a combination of heat, ultraviolet radiation, and/or pressure to harden a thermoset. Curing creates a chemical reaction that permanently cross-links molecules.

curing agents

A chemical or group of chemicals added to a thermoset that controls or accelerates curing. Curing agents provide engineers a measure of control during the cross-linking process.

cycle time

The amount of time required to complete one manufacturing process. Cycle time changes according to the type of plastic and the shaping operation.

damping

The ability of a material to absorb vibration. Damping properties in plastics are higher than damping properties in metals.

deformation

The change in an object&;#39;s size or shape as a result of stress. Deformation of an object can be permanent or temporary.

dip-casting

A thermoset casting process that creates a solid plastic coating on a part by dipping a solid object in liquid resin. Dip-casting does not use a mold.

dip-coating

A casting process that involves dipping a solid mold into a liquid elastomer resin and then separating the mold from the resin. Dip-coating processes are used to make surgical gloves and other latex products.

elasticity

A material's ability to revert to its original shape after being stretched or compressed. Elastomers have high elasticity.

elastomers

A group of plastics that can stretch and then return to their original shape without permanent deformation. Elastomers are usually thermosets but they can also be thermoplastics.

electrical insulators

A material with low electrical conductivity used to house a conductor. Electrical insulators can be made using fiberglass-reinforced plastic or other polymers.

engineering composites

A material consisting of shorter reinforcement fibers and thermoset resins with lower mechanical properties. Engineering composites can provide more strength than conventional plastic, but they are not as strong as advanced composites.

epoxies

A thermoset formed from an oxygen atom attached to two adjacent carbon atoms of a hydrocarbon. Epoxies generally have high heat and solvent resistance.

fatigue resistance

Opposition to failing or breaking down from use. The fatigue resistance level of natural rubber is significantly improved after vulcanization.

fiberglass

A lightweight and strong material composed of fine glass fibers. Fiberglass particles are used as reinforcement material in many composites.

fiberglass-reinforced plastic

FRP. A composite made from a thermoset resin, typically polyester, combined with chopped glass fibers. Fiberglass-reinforced plastic's strength depends on the reinforcing fibers.

fiberglass-reinforced plastic

FRP. A composite made from a thermoset resin, typically polyester, combined with long, thin glass reinforcing fibers. Fiberglass-reinforced plastic's strength depends on the reinforcing fibers.

filler

A plastic resin particle added to a material to take up space and reduce material shrinkage. Fillers can also be used to lower the cost of a material.

foam

A plastic with tiny bubbles created within the resin that are retained when the part cools. Foamed polyurethane can be used in protective packaging and in cushioning applications.

foaming agent

A material that generates gases to produce foam. Foaming agents add stability to foamed plastic parts.

FRP

Fiberglass-reinforced plastic. A composite made from a thermoset resin, typically polyester, combined with chopped glass fibers. FRP's strength depends on the reinforcing fibers.

grinding wheels

A tool consisting of abrasives and bond material. Grinding wheels can include phenolics as bond material because of their high hardness properties.

hard

Able to resist penetration, indentation, or scratching. Hard plastics, such as many thermosets, tend to be wear resistant.

hardener

A curing agent that starts and controls the cross-linking process. Hardeners are mixed with epoxies to create a thermoset with maximum properties.

inhibitor

A substance that controls the reaction rate in a chemical reaction, such as curing. Inhibitors added to polyester resins extend their storage life by slowing the cross-linking process.

initiator

A chemical that begins a cross-linking reaction. Initiators are commonly a peroxide.

injection molding

A molding process in which resin is heated in a barrel and then injected into a mold by a reciprocating screw. Injection molding can produce large items such as car dashboards and smaller items such as packing peanuts.

latex

A milky resin produced in plants that is the main source of natural rubber. Latex rubber is treated with heat and chemicals in order to be used commercially.

loads

A force or pressure placed on an object. A load-bearing composite can withstand sudden force or pressure.

macromolecules

A large molecule that consists of repeating molecular units. Macromolecules link together to form polymer chains.

matrix

The plastic resin that binds together the solid reinforcing fibers of a composite. The matrix allows a composite to be shaped.

mechanical properties

The collection of properties that describe a material's ability to compress, stretch, bend, scratch, dent, or break. Mechanical properties of a plastic are determined by its molecular structure.

metals

A naturally occurring material with high electrical and thermal conductivity. Metals include copper, iron, nickel, and lead.

mixhead

A device that combines two or more liquid reactants at a high velocity. The mixhead on a reaction injection molding machine releases the mixed resin and injects it into a mold.

mold casting

A plastic shaping process in which molten resin is poured into an open mold where it cures and hardens. Mold casting does not require significant amounts of pressure.

molding

A plastic shaping process in which heated liquid resin is forced into a mold and then released once it cools and solidifies. Molding involves high pressure.

molding compounds

A type of composite in which the matrix and reinforcement have already been combined before they are sent to the manufacturer. Molding compound is available in bulk form and sheet form.

molecules

Two or more atoms joined together by chemical bonds. Large polymer molecules bond together to form long polymer chains.

monomers

A small molecule that chemically bonds with thousands of similar molecules to form a long polymer chain. Monomers can bond to atoms along a polymer chain or to atoms branching off from a chain.

natural rubber

An elastomer extracted as a sap from tropical trees. Natural rubber must be vulcanized for commercial use.

open mold

An open cavity that has no rigid second piece to enclose the resin and apply pressure. Open molds are used in casting processes and some low-pressure molding processes.

permeability

A measure of a material's ability to either resist or absorb liquid or gas. Low permeability levels in butyl rubber result in an airtight material.

phenolics

A thermoset resin made from the reaction between an organic compound and molecules of phenol, a compound derived from petroleum. Phenolics are a chemically stable family of thermosets that include many different variations.

plastics

A lightweight polymer material that has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Plastic is composed of large polymer molecules.

plunger

A pump that pushes resin through machine components into a mold. A plunger is used in reaction injection molding and transfer molding to force liquid resin into a closed mold.

plywood

A thin, strong wooden board consisting of two or more layers glued and pressed together. Plywood often contains thermoset resins as an adhesive.

polyester

A synthetic polymer that contains ester, a basic organic chemical compound, in its main molecule chain. Polyester can be manufactured as a thermoplastic or thermoset depending on its chemical structure.

polyethylene

A common plastic that can be either a thermoplastic or a thermoset. Polyethylene is used to make sheet molding compound.

polymer

A material made of very large molecules. Polymers are either natural or synthetic.

polyurethane

A chemically complex thermoset that is composed of organic units joined by urethane links. Polyurethane can be rigid or pliable.

polyurethanes

A chemically complex thermoset that is composed of organic units joined by urethane links. Polyurethane can be rigid or pliable.

preinitiated resin

A thermoset resin that has been mixed with an initiator. Preinitiated resin allows for an even distribution of the initiator throughout the resin.

primary bonds

A strong chemical bond between tightly clustered atoms. Primary bonds allow cross-links to form between molecule chains in a thermoset.

primary shaping processes

A process that manufactures a product directly in its usable form without any secondary machining. Primary shaping processes are used for thermosets.

prototypes

A preliminary model of a product used to evaluate the performance of a design. Prototypes are often made of plastic.

reaction injection molding

RIM. A thermoset molding process that involves forcing liquid resin into a heated, horizontal closed mold and curing it in the mold. Reaction injection molding uses a two-part resin.

reactive sites

A specific portion of a polymer monomer chain that engineers create to allow for a chemical reaction between two or more substances. Reactive sites are necessary for cross-linking to occur in a thermoset.

reciprocating screw

A component of an injection molding machine that melts the resin and builds up pressure. Reciprocating screws inject melted resin into a mold cavity.

reinforcement

A material added to a plastic or composite that provides strength and stiffness. Reinforcements are typically fiberglass or carbon fibers.

reinforcements

A material added to a plastic or composite that provides strength and stiffness. Reinforcements are typically fiberglass or carbon fibers.

resin

A raw polymer, usually in the form of beads or pellets, that is not yet molded into its final shape. Resin is melted to form plastic parts.

resin charge

A block of solid resin used to fill a mold during one molding cycle. Resin charges are often preheated before molding.

rigidity

A material property that makes a material unable to bend or resistant to bending. Rigid thermosets can resist damage from vibration.

RIM

Reaction injection molding. A thermoset molding process that involves forcing liquid resin into a heated, horizontal closed mold and curing it in the mold. RIM uses a two-part resin.

safety shoes

Footwear that protects the feet and ankles from impact and heat. Safety shoe materials can include chloroprene because of its flame resistance.

scrap

Any material not used to create the final part. Scrap from thermoset processes is not recyclable.

sealants

An adhesive substance applied to a joint that dries and hardens to provide a seal. Sealants such as silicone can provide an airtight and waterproof seal.

secondary shaping process

A manufacturing process carried out on a material that has already undergone a primary shaping process. Secondary shaping processes can be used with thermoplastics.

shaping

The process of forming plastic resin. Shaping processes for thermosets include compression molding and transfer molding.

sheet molding compound

SMC. A composite formed into a sheet. Sheet molding compound is created by applying a preinitiated paste of resin and filler to a moving sheet of polyethylene, followed by strands of fiberglass.

sheet molding compound

SMC. A composite formed into a sheet. Sheet molding compound is created by applying a premixed, preinitiated paste of resin and filler to a moving sheet of polyethylene, followed by strands of fiberglass.

shrinkage

The reduction in size of a part as it contracts while cooling within a mold. Shrinkage of a plastic can be offset by using additives.

silicone

A thermoset composed of inert synthetic compounds with alternating silicon atoms and oxygen atoms. Silicone can be used as a liquid, solid resin, or rubbery material.

SMC

Sheet molding compound. A composite formed into a sheet. SMC is created by applying a preinitiated paste of resin and filler to a moving sheet of polyethylene, followed by strands of fiberglass.

solvents

A chemical substance that attempts to dissolve another substance, causing material degradation. Common solvents include alcohol, gasoline, and chlorine.

synthetic

An artificial or human-made material that does not occur in nature. Synthetic plastics include nylon and polyester.

tensile strength

A material's ability to resist forces that attempt to pull it apart or stretch it. The tensile strength of natural rubber is significantly improved after vulcanization.

thermoplastic elastomers

TPE. An elastomeric material that is manufactured to behave like a thermoplastic. Thermoplastic elastomers are easier to mold and shape than thermoset elastomers but do not have thermal resistance or high elasticity.

thermoplastics

A group of plastics that can be repeatedly heated, shaped, and cooled. Thermoplastics do not have cross-linked molecule chains.

thermoset polyester

A lightweight and strong thermoset that is commonly used in composites. Thermoset polyester, also known as unsaturated polyester, is a low-cost material.

thermosets

A group of plastics that are permanently hardened by heating. Thermosets, also known as thermosetting plastics, have covalent bonds and cross-linked molecule chains.

thermosetting plastics

A group of plastics that are permanently hardened by heating. Thermosetting plastics, also known as thermosets, have covalent bonds and cross-linked molecule chains.

three-dimensional

Having or appearing to have length, depth, and width. A three-dimensional structure is created when thermoset molecule chains form cross-links.

tool steel

A very strong and durable carbon alloy steel. Tool steel is used to make high-cost molds used in many plastic-shaping operations.

toxic

Poisonous or harmful. Toxic substances can cause injury or death.

transfer molding

A thermoset molding process that involves forcing a preheated resin charge into a heated, vertical closed mold and allowing it to cure. Transfer molding combines elements of reaction injection molding and compression molding.

transfer pot

A chamber in a transfer molding machine that preheats thermoset resin until it liquefies. After the resin is heated in the transfer pot, a plunger forces it into a closed mold where it cures.

ultraviolet radiation

UV radiation. Energy transmitted as invisible wavelengths. Ultraviolet radiation is used in the curing process for some thermosets.

unsaturated polyester

A lightweight and strong thermoset that is commonly used in composites. Unsaturated polyester, also known as thermoset polyester, is a low-cost material.

UV radiation

Ultraviolet radiation. Energy transmitted as invisible wavelengths. UV radiation is used in the curing process for some thermosets.

vibration damping pads

Machine components that can absorb potentially harmful vibrations. Vibration damping pads are often made from butyl rubber.

viscoelastic

Having both elasticity and viscosity. The viscoelastic properties of some plastics, such as polyurethane, can result in a wear-resistant product.

viscosity

A measure of a material's resistance to flow. Viscosity decreases as temperatures increase.

viscous

Having the ability to resist flow. Viscous resins tend to be sticky.

vulcanization

A manufacturing process that uses additives, chemicals, heat, and pressure to increase the number of cross-linked bonds in an elastomer. Vulcanization is similar to curing and adds strength and toughness to an elastomer.