Artisans create beautiful objects by manually forcing air into melted glass while it is still hot, forming hollow shapes. That process has existed for centuries, and has been adapted to the industrial production of many commercial plastic items. These include containers of all sizes for liquids, automobile parts, toys, and many other applications. The development of blow molding made this transition possible.
This industrial process starts with a basic, raw plastic form called a parison, a name taken from artisans for an unformed glob of melted, malleable glass. The parison is placed inside a mold via machinery and air is pumped in at pressures ranging from 25 to 150 psi, creating an even coating over the interior. That layer has a uniform thickness, and cools down rapidly.
The raw tubes of plastic are made primarily from pellets of polyethylene, polypropylene, or polyvinyl chloride. These are thermoplastics, which melt at a rate and consistency making them ideal for mass production. The tubes can be made to order in virtually any size and quantity needed for a particular job, and are inserted into the molds in rapid assembly-line fashion.
Once inside, the parison of molten material is formed using several basic processes. Extrusion utilizes a screw-like device to force the unformed mass into a mold in carefully controlled quantities. Once inside, pressurized air instantly fills the mold from the center outward, forcing the plastic into the precisely detailed shape of the mold interior.
Extrusion can be intermittent or continuous, depending on the style and quantity of the product. Large milk or juice containers are commonly made using variations of this method, but others are produced most effectively using injection molding. Injection forces the polymer into a core pin, which is inflated with air, allowed to cool, and then ejected.
Stretch injection is a similar process that is used mainly to make individual serving containers and other small objects. Injectors create a preform, which is cooled, reheated and extended using a core rod. During this process, air under high pressure is carefully blown in to extend the shape within a mold made of metal. All of these processes can use recyclable plastics.
Although it is derived primarily from hydrocarbons, less than five percent of oil production becomes plastic. While that is a large number, recycling and other green practices can help prevent containers from becoming landfill or ocean debris. The inherent advantages of using these methods to make reusable containers helps balance environmental concerns.
This industrial process starts with a basic, raw plastic form called a parison, a name taken from artisans for an unformed glob of melted, malleable glass. The parison is placed inside a mold via machinery and air is pumped in at pressures ranging from 25 to 150 psi, creating an even coating over the interior. That layer has a uniform thickness, and cools down rapidly.
The raw tubes of plastic are made primarily from pellets of polyethylene, polypropylene, or polyvinyl chloride. These are thermoplastics, which melt at a rate and consistency making them ideal for mass production. The tubes can be made to order in virtually any size and quantity needed for a particular job, and are inserted into the molds in rapid assembly-line fashion.
Once inside, the parison of molten material is formed using several basic processes. Extrusion utilizes a screw-like device to force the unformed mass into a mold in carefully controlled quantities. Once inside, pressurized air instantly fills the mold from the center outward, forcing the plastic into the precisely detailed shape of the mold interior.
Extrusion can be intermittent or continuous, depending on the style and quantity of the product. Large milk or juice containers are commonly made using variations of this method, but others are produced most effectively using injection molding. Injection forces the polymer into a core pin, which is inflated with air, allowed to cool, and then ejected.
Stretch injection is a similar process that is used mainly to make individual serving containers and other small objects. Injectors create a preform, which is cooled, reheated and extended using a core rod. During this process, air under high pressure is carefully blown in to extend the shape within a mold made of metal. All of these processes can use recyclable plastics.
Although it is derived primarily from hydrocarbons, less than five percent of oil production becomes plastic. While that is a large number, recycling and other green practices can help prevent containers from becoming landfill or ocean debris. The inherent advantages of using these methods to make reusable containers helps balance environmental concerns.
About the Author:
Genevive B. Mata has taught plastics molding techniques for over 15 years. He specializes in injection molding and thermoforming. If you are interested in learning more about plastic injection molding services then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.
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