Plastics

Thanks to Mr. Joe Neary of Summerhill College for this presentation

Types of Plastics

Thermosetting plastic Thermoplastic

Thermosetting plastic

Is plastic which has been heated to form into a shape

When the plastic cools and sets, it cannot be reheated to take another shape as the chemical process which takes place when it is heated cannot be replaced

These plastics therefore can withstand high temperature

Polyurethane and polyester are thermosetting plastics

Thermoplastics

Thermoplastics can be softened and reshaped by reheating again and again

Different thermoplastics soften at varying temperatures

Examples: AcrylicPolyvinyl Chloride (PVA)

Polythene

Working with Plastic

Plastics can be:Cut with sawsFiled with planesDrilled Edges can be sanded to produce a

smooth finish

Cutting Plastic

Can be cut by hand or on a band saw Hand saw should be held at a low angle to reduce

tear out Polystyrene (foam) can be cut with a heated wire

Filing Plastic

Edge of plastic after it is cut must be planed to finish Work should be held low in a vice to secure the piece

and to support it File can be used to bring a piece down to a line

Step 1: Piece is cross filed down to the line Step 2: Piece is draw filed to remove any file marks Step 3: Edge is sanded to produce a smooth finish

Instead of files a block plane can be used to finish the edge

Draw Filing Cross Filing

Drilling Plastic

Can use a wood or metal twist drill bit Speed of drill should be fast to prevent

chipping however the piece should be drilled slowly

Waste piece of timber should be placed under the plastic to support the piece, prevent break out and to protect the bench or drill press

Drilling Plastic

Bending Plastic

Popular with thermoplastics because process can be reshaped with no ill effect

Important to complete all shaping and drilling of piece before bending it

Method: Strip heating ( localised along bend line) Oven heating (heats the whole piece-curving)

Important not to overheat plastic as it will bubble and melt and to allow for the bend in the length of the piece by adding the thickness of the sheet to the length

Bending Plastic

Bending plastic