How is a plastic chair made?

Plastics play a very important part in our daily lives, found in everything from cars, soft drinks bottles to refrigerators. Plastic chairs are useful due to their light weight, durability and versatility and are made in three main ways, which all involve metal molds that have been carved into the desired shape. The combination of plastics used will have an impact upon the resulting strength of the chair.

Creating the plastic

Plastics are created from a variety of raw materials and monomers. The hydrocarbon raw materials are obtained from the “cracking process” used in refining oil and natural gas. Once obtained, they are chemically processed to make hydrocarbon monomers and other carbon monomers via polymerisation reactions in large polymerisation plants. The reactions produce polymer resins pellets or beads, which are then processed into final plastic products. Generally they are heated, molded and allowed to cool.

Rotational molding

This is the most popular form of furniture molding, wherein a large metal mold is injected with plastic resin pellets before being heated to melting point. The mold is turned mechanically rotated in three dimensions to evenly distribute the plastic along the walls of the mold, making large, hollow items like hollow chairs. After several minutes of spinning, the mold is then allowed to cool before the hollow chair is removed.

Injection molding

Injection molding is another method of making plastic furniture. The resin pellets are heated and mechanically mixed in a chamber, before being forced under high pressure into a cooled mold. The mold does not spin, and manufactures must use a high level of precision as the plastic is injected to ensure a uniform end result. The end result is a solid plastic chair.

Gas assisted injection molding

Injection molding can also be performed using gas. Otherwise known as blow molding, the resin pellets are heated and compressed into a liquid tube. The resin goes into the chilled mold, and compressed air gets blown into the resin tube in various parts of the mold. The air expands the toothpaste-like resin against the walls of the mold, making a hollow plastic chair with some solid parts.

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About the Author

Sarah Knight has been writing articles on travel and the environment for more than five years. She has previously worked in marketing and publicity, publishing website content and press releases for an environmental conservation charity. Her work has been published in "The Guardian," "The Telegraph" and "Evergreen" magazine. She has a BSc in geography and an MSc in environmental management.