Elastomers, Thermoforming and Line Bending

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Elastomers These plastics have long chain molecules which distort when compressed, but return to their original shape, giving them elastic properties.

Thermoplastic Elastomers

can be processed using conventional processes e.g. injection and blow moulding

all waste and scrap can be recycled

speeds up processing as there is no need to wait for molecular cross links to form

Applications

electrical components such as insulating coatings for wires and cables

overmoulding of grips and power tool bodies, pens, toothbrushes etc

seals and hoses in automotive and industrial applications

Liquid Silicon Rubber (LSR)

Made up of two components which have to be mixed together very well and then 'moulded' for the cross links to form. LSR is popular because of its ability to retain insulating properties and elastic behaviour from -50˚c to 250˚c.

Uses include electrical connectors, products for infants such as bottle teats, baking trays, spatulas and medical equipment.

Thermoforming A process similar to vacuum forming, this processes uses heat to make plastic pliable enough to mould

Process

1. plastic heated to just above its softening point

2. the mould halves close and a vacuum is applied through the lower half - the upper half ensures the level of detail

3. plastic is cooled, removed from the mould and trimmed

Advantages

low cost

good for smooth shapes with additional detail e.g. letters, symbols

Disadvantages

deep mould result in a thinner wall when the plastic has been stretched

limited to simple designs

trimming is usually needed

Line bending This process is used to form straight, small curved bends in a sheet thermoplastic.

Process

1. Material is softened using a strip heater, so that that part of plastic becomes pliable

2. Once plastic is pliable, it is removed from the heater and placed on a bending jig. The plastic is held down whilst it cools into the required shape.

It is limited to producing only simple shapes.