Calendering

Calendering  is a process where a large amount of molten plastic is placed between rollers and rolled to turn it into sheets.  The rollers are hot and  keep the plastic in its semi - molten state allowing it to be rolled thinner and thinner as it passes through rollers which are closer and closer together. When it is at the required thickness it is rolled through cold rollers to enable it to go hard and is then wound into rolls. Examples of this final product might be cling film, a plastic bed sheet for a baby or damp proof sheeting which is placed under house foundations.
If during the rolling process sheets of fabric are pressed into the plastic the result is the kind of material that plastic seat covers are made from or fabric bags which students use for school (these are often plastic coated inside). Vinyl wallpaper can be made if paper is introduced during the rolling process to give vinyl plastic a paper backing. If the rollers have a pattern on them this will be pressed into the plastic during the final rolling stage.

You can recycle most of it you know.

Blow Moulding
This process is very similar to glass blowing. Plastic bottles are made using this process.

A plastic tube of thermoplastic is placed inside a split mould which is then clamped together sealing one end of the tube. Air is blown into the semi - molten tube and it blows up like a balloon to cover the sides of the mould (which could be shaped like a bottle or the wheel of a child's toy for example) and as it touches the sides of the mould it cools and stays the shape of the mould. When the mould is split apart the waste bits are cut off and reused.

Plastic Extrusion

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