Plastic Extrusion Overview 230

acrylonitrile-butadiene-styrene

ABS. A thermoplastic material with good heat, chemical, and impact resistance. Acrylonitrile-butadiene-styrene is used to manufacture medical equipment housing.

additive manufacturing

AM. Also known as 3D printing, the process of joining or solidifying materials to make an object based on a three-dimensional (3D) computer model. Additive manufacturing methods typically build up layers of material to create an object.

additives

Any substance that is added to a material during manufacturing in order to improve or change the material's properties. Additives used in plastic include colorants and thermal stabilizers.

blown film extrusion

A plastic manufacturing method in which air is forced through the center of a tube of hot plastic, causing it to stretch and become a thin balloon. Blown film extrusion is used to make plastic bags and wrapping.

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.

chemical resistance

The ability of a material to resist chemical changes. Chemical resistance prevents gradual degradation caused by the atmosphere, moisture, or other substances.

co-extrusion

The process of extruding two or more types of plastic through a die, creating a layered plastic sheet. Co-extrusion creates sheets of plastic with the properties of each type of plastic.

cooling rollers

Metal, cylindrical devices on which plastic sheets are wound to cool them. Cooling rollers transfer heat from the plastic so that it retains its shape.

cooling tanks

An enclosed cooling trough. Cooling tanks can contain water in which plastic is submerged, or they can contain misters to cool the plastic.

cooling troughs

A part of an extruder that contains water to cool plastic after it is forced through a die. Cooling troughs often use rollers to hold the plastic under the water.

corrode

To deteriorate the useful properties in a material due to exposure to elements. Corrosion in plastics can be caused by ultraviolet light or by certain chemicals.

corrosion-resistant

The ability of a material to resist destruction or deterioration due to chemical or environmental exposure. Corrosion resistance varies across different plastics.

creep resistance

The tendency of a material to withstand a constant force over an extended period of time. Creep resistance is a property found in polyvinyl chloride (PVC).

elastomers

A type of plastic that can be repeatedly stretched without losing its initial shape. Elastomers include different varieties of rubber.

extruder

A machine used in plastics extrusion. An extruder uses a screw to push melted plastic through a shaping die.

extrusion

A molding process that forces raw material through a die opening. Extrusion is a continuous process that can create parts with a uniform cross-section.

fatigue

Progressive structural damage to an object due to repeated or excessive bending and flexing. Fatigue leads to failure.

feed barrel

The holding chamber of an extrusion molding machine in which material is melted, compressed, and mixed. The feed barrel is typically heated and contains a screw to move material through the barrel.

Feed throat

The component on the extruder machine where resin granules enter the feed barrel. The feed throat connects the hopper and the feed barrel. Generally, the throat will be cooled in some way to prevent premature melting of the resin in the hopper.

film extrusion

A plastic manufacturing process in which plastic is shaped into a thin sheet or film with a die and rollers. Film extrusion, also called sheet extrusion, creates thin plastic that is often used as material in later manufacturing processes.

high-density polyethylene

HDPE. A common thermoplastic known for its high strength-to-density ratio. High-density polyethylene is often used to make corrosion-resistant pipes, as well as bleach and detergent containers.

hopper

A large, funnel-shaped device located on top of the feed barrel on extrusion and injection molding machines. The hopper serves as the entryway for resin into the feed barrel.

hydrogen chloride

A chemical that can cause damage to the skin, eyes, throat, and larynx. Hydrogen chloride is produced when polyvinyl chloride breaks down.

impact-resistant

Designed to resist impact. Impact-resistant plastics generally do not break when dropped or struck.

inner ring

A part of a round extrusion die that attaches to the center of the spokes of a spider. An inner ring shapes the inside diameter of plastic tubing in blown film and tubing extrusion.

low-density polyethylene

LDPE. A flexible and translucent polyethylene. Low-density polyethylene is often used to make transparent plastic wrap used in food manufacturing.

melt

Liquified plastic material. Melt is produced when an extruder heats resin granules and pushes the material down the barrel.

metals

A hard, strong material that conducts electricity and heat. Metals include steel, aluminum, iron, and bronze.

natural rubber

An important commercial elastomer that is harvested from the sap of tropical trees. Natural rubber is used to create products like tires.

nylon

A semicrystalline thermoplastic that gains strength when the fibers are stretched. Nylon is a commonly used term for polyamides (PA).

overcoating

A plastic extrusion process in which a sheet of hot extruded plastic is pressed onto a part or product. Overcoating is used to coat paper products such as milk cartons.

overjacketing

A plastic extrusion process in which a tube of hot extruded plastic is pressed onto wires. Overjacketing provides the insulation on many electric wires and cables.

personal protective equipment

PPE. An article of clothing or a device worn to minimize exposure to hazards and prevent injury. Personal protective equipment may include safety glasses, safety gloves, ear plugs, respirators, or steel-toed boots.

plastics

A lightweight polymer material that has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Most plastics are easily shaped and formed.

polyamide

PA. A semicrystalline thermoplastic that gains strength when the fibers are stretched. Polyamides are commonly referred to as nylon.

polycarbonate

PC. A type of thermoplastic with high heat and impact resistance. Polycarbonate is used in hard hats and eyeglass lenses.

polyethylene

PET. A common thermoplastic that is highly resistant to electricity and heat. Polyethylene is used in many products, including durable plastic bags and water bottles.

polypropylene

PP. A thermoplastic that is resistant to fatigue. Polypropylene is used in a wide range of products, from laboratory equipment to microwavable soup cans.

polystyrene

PS. An amorphous thermoplastic that can be molded or foamed. Polystyrene is often used in insulation.

polyvinyl chloride

PVC. A thermoplastic that can be manufactured to produce both rigid and flexible materials. Polyvinyl chloride is used to manufacture many common products, such as corrosion-resistant pipes.

properties

A measurable quality or attribute of a specific material. Properties include aspects such as hardness, toughness, and ductility.

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.

round die

A component of an extruder with a circular opening used to shape plastic that is forced through or against it. Round dies are used in tubing and blown film extrusion.

screw

A component of the extruder that melts and compresses the resin. Screws push melted resin down the barrel and through a shaping die.

self-extinguishing

Unable to fuel a flame. One self-extinguishing plastic is polyvinyl chloride (PVC).

shaping die

A component of an extruder that shapes material. A shaping die is used in extrusion while a mold cavity is used in injection molding.

sheet extrusion

A plastic manufacturing process in which plastic is shaped into a thin sheet or film with a die and rollers. Sheet extrusion, also called film extrusion, creates thin plastic that is often used as material in later manufacturing processes.

slot die

A component with a long, narrow opening used to shape plastic that is forced through or against it. Slot dies are used in sheet and film extrusion.

solvents

A chemical used to dissolve another material. Solvents are often used to dissolve surface contaminants such as grease or oil.

spider

A part of a round extrusion die featuring spokes that meet around the center on which an inner ring is attached. A spider allows melt to flow over it and around the inner ring, creating a tube.

spool

A cylindrical device on which plastic film or tubing is wound for later use. Spools are found at the end of sheet and film, tubing, and blown film extrusion lines.

synthetic

A material produced through deliberate processes rather than natural origins. Synthetic materials are artificial or human-made.

thermoforming

A secondary plastic shaping process that forces heated plastic sheets around a mold. Thermoforming processes use mechanical, air, or vacuum pressure.

thermoplastics

A grouping of plastics that can be repeatedly reheated and re-shaped. Thermoplastics are the most commonly used plastics.

thermosets

A grouping of plastics that, once cooled, can never be reheated and reshaped. Thermosets will char or burn if reheated, so they are not generally suitable for extrusion.

tubing extrusion

A plastic manufacturing method in which melt is forced through a round die with an inner ring, forming a long, hollow tube. Tubing extrusion makes tubes and pipes, and is also the basis of blown film extrusion.

twin screw extruders

A plastic extruder that contains two side-by-side screws. Twin screw extruders use pressure to melt plastics that are sensitive to heat.

ultraviolet degradation

UV degradation. The deterioration of a material due to overexposure to the ultraviolet radiation in sunlight. Ultraviolet degradation in plastic can be reduced by using additives or adding capping to show surfaces during the manufacturing process.

viscosity

The resistance to flow of a fluid or semifluid substance. Viscosity describes how easily a substance flows.