1/17/2018
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`Types of Molding Processes | Sciencing
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`Types of Molding Processes
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`By Philippa Jones; Updated April 24, 2017
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`Molding is primarily used during the manufacturing process of plastic. Plastic is a
`synthetic materials, and to form it into the desired shape different molding processes
`are used. Each process requires the manipulation of molten plastic, and then leaving it
`to set. Thermoplastics can then be melted down and reformed if necessary, however
`thermoset plastics cannot be reheated.
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`Casting
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`Casting is a basic molding process as it requires the least amount of complex
`technology. Plastic is simply heated so it turns into a (cid:216)uid, and then transferred into a
`mold. It is left to cool and the mold is removed. This process can be used for intricate
`shapes and performed under a low pressure. However, it is a common process used for
`making plastic sheeting, starting from 0.5 inches thick and greater.
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`Injection Molding
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`Injection molding is used for creating high-quality three-dimensional objects, that can be commercially reproduced. The molding process begins by
`melting plastic in a hopper. Then the plastic is injected into a tightly closed, chilled mold. The plastic quickly takes the shape of the surrounding mold.
`Once it has completely set, the mold is opened and the plastic object is released. Yogurt pots, butter tubs, toys and bottle caps are made using this
`process.
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`Blow Molding
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`Blow molding is a process used for making piping and milk bottles. Plastic is heated until molten. Then it is injected into a cold mold. The mold has a
`tube set within it, which has a particular shape when in(cid:216)ated. So, while the plastic is molten, air is blown into the tube and the plastic is formed around
`the tubing. It is then left to cool and removed from the mold.
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`Compression Molding
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`The most labor-intensive type of molding process is compression molding. Therefore, it is only used for large-scale production purposes, and not for
`mass production. For example, boat hulls and car tires are made using this method. Molten plastic is poured into a mold. Then a second mold is pressed
`into it. This squeezes the plastic into the desired shape before being left to cool and removed from the mold.
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`Rotational Molding
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`Toys, shipping drums, storage tanks and items of consumer furniture are made using rotational molding. Each object is made by coating a mold from
`the inside. A mold is held in place between two mechanical arms. Then, the arms rotate the mold constantly at the same level, while molten plastic is
`placed inside. As it turns, the plastic coats the inside of the mold to create a new hollow, plastic object.
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`References
`American Chemistry Council: How is Plastic Made?
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`About the Author
`
`Based in Bristol, Philippa Jones has been a music journalist and script writer since 2007, working across a range of radio
`programs in the U.K. and Australia. Her articles have appeared in "Impact Magazine," "The Mic" and in local newspapers. She
`holds a Bachelor of Arts in politics from the University of Nottingham.
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