Chapter 12: Glossary

A

Amorphous:

Usually refers to plastic materials that are not crystalline. The long molecular chains have no defined structure, but are arranged at random.

Abrasive wear:

Wear caused by contact with hard particles.

Additive:

Anything compounded into or blended with a polymer to modify its characteristics, such as flame retardants, pigments, and so on.

Adhesive wear:

Wear resulting from metal-to-metal contact, such as between screw flights and the inside of a barrel.

B

Ball check:

A specific design type of non-return valve used in injection blow moulding. It is placed at the end of the screw, to prevent plastic from flowing backward during injection. It works by using a ball that allows the material to flow in one direction, but restricts the flow in the other.

Barrel:

The thick-walled steel cylinder in an extruder or moulding machine. It contains the screw and is normally fitted with heater bands and cooling devices. Most barrels are made with a hard, wear-resistant liner.

Barrier screw:

A screw in a plastics processing machine that has two sets of flights, one having a slightly smaller diameter than the other. It improves melting by separating solid from melted polymer.

Blister:

An imperfection on the surface of a part. It resembles a blister on human skin and can have several causes.

Blow needles:

Small-diameter hollow steel tubes that are used to inject blowing air into a part. They are smaller in diameter than blow pins...