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Degating - separate parts from runners Delamination - the surface peels off in layers Dowels/Guidepins - used to mate mold cavities Distortion - a warped molding

Dwell - a delay time after filling the mold

Ejector Pins - push the part out of the mold as it is opened

Feed - the volume of plastic injected into the mold as it is advanced Flash - a thin flat section that has “squirted” out of the mold Gassing - trapped gas marks and burns the mold

Gates - the entry port between the runners and the parts Granules - the pellet form that raw plastic is delivered in. Granulation/Grinder - will reduce parts to granules for reuse

Inserts - parts placed in the mold before closure and injection. These become an embedded part of the final product

Nozzle - the plastic is ejected through the nozzle to the mold. Polymers - The chemical category of plastics

Powder - a finely ground material

Preheating - plastic may be heated before use to remove moisture contaminants Purging - a few purging shots are made when changing the material

Ram - opens and closes the platens Regrind - reclaimed plastic granules

Release Agent/Spray - A spray, such as silicone, can be sprayed into tight molds to ease part removal.

Runners - connect the gate to the sprue

Safety gate - the gate must close and shut the operator out for the press to close. Shot - one injection of plastic

Short shot - insufficient plastic is injected Shrinkage - reduction in size as mold cools Sinking - Surface deformation on parts.

Sprue - excess plastic between the injector nozzle and the mold

Vent - A small gap that allows air to escape as it is displaced by molten plastic Warped - Cooling stresses cause a part to twist, or warp, to a new shape.

46.3 EXTRUSION

•The basic process - plastic is melted and pushed through an extrusion die with a desired cross section. The plastic leaves the die in roughly the right shape. It is then passed through a sizing and cooling apparatus. Finally, for wound product, it passes through pullers, and onto a spool.

•Basically a screw, like that described in injection molding is used to melt the plastic and generate pressures.

•Some additive for plastics are,

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-white chalk, used as a filler

-plasticizers, improve flexibility

-stabilizers, improve light and heat resistance

-pigments

-lubricants minimize sticking and improve flow

•Typical extrusion conditions are, [Source, unknown]

•The typical extruder barrel is between 20:1 and 28:1 for length to dia., and typical pressures are 10 to 20 ksi.

•Typical motor characteristics are,

-5 to 10 lbs of material per hour for each horsepower

-the motor is geared down to drive the screw (often variable)

•Breaker plate,

-at end of screw, and before extrusion die,

-it increases back pressure for the screw

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-converts rotational to parallel flow

-it stops unmelted plastic and debris

•Special heads can be used to coats wires, etc.

Die Body

Die Retaining Ring

Wire

Core Tube

Die

Guider Tip

46.4 PRACTICE PROBLEMS

1.TRUE / FALSE - Plastic is melted in the hopper before it is extruded.

2.TRUE / FALSE - A reciprocating injection moulding process has a screw that moves.

3.TRUE / FALSE - Steam is the most common method used to weld plastics.

4.The key tag shown below has a flat profile. There is a hole on the right hand side for the keyring, and a large hole in the main body of the ring.