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 production method begins with a tube of raw plastic material called a parison, a word taken from artisans describing a mass of melted glass. The parison is carefully sealed between the sections of a mold, and pressurized air is forced in at 25 to 150 psi. This makes the soft plastic assume the inner shape. It coats the interior with a uniform thickness of material, and rapidly cools.
The materials used to create a parison consist mainly of polypropylene, polyethylene, or polyvinyl chloride pellets. All are considered thermoplastics, which become malleable at high temperatures, but do not turn to liquid like other varieties. The tubes are made to fit a particular order, and different sizes can be added to the production line for rapid turnover.
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.
This process can be continuous or intermittent, based on design requirements and quantities. Larger containers for juice or milk are often made using variants of the extrusion method, but other items are best produced through injection molding. Using this method, soft polymers are forced into a type of central pin, which is then inflated, cooled, and ejected.
Injection stretch molding is a similar method used mainly to create small items or individual serving bottles. Preforms are created through injection, cooled, and then reheated and stretched using the core rod. High pressure air is blown in to help form the shape within a metal mold. All three processes can be completed using plastics that can be recycled.
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 production method begins with a tube of raw plastic material called a parison, a word taken from artisans describing a mass of melted glass. The parison is carefully sealed between the sections of a mold, and pressurized air is forced in at 25 to 150 psi. This makes the soft plastic assume the inner shape. It coats the interior with a uniform thickness of material, and rapidly cools.
The materials used to create a parison consist mainly of polypropylene, polyethylene, or polyvinyl chloride pellets. All are considered thermoplastics, which become malleable at high temperatures, but do not turn to liquid like other varieties. The tubes are made to fit a particular order, and different sizes can be added to the production line for rapid turnover.
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.
This process can be continuous or intermittent, based on design requirements and quantities. Larger containers for juice or milk are often made using variants of the extrusion method, but other items are best produced through injection molding. Using this method, soft polymers are forced into a type of central pin, which is then inflated, cooled, and ejected.
Injection stretch molding is a similar method used mainly to create small items or individual serving bottles. Preforms are created through injection, cooled, and then reheated and stretched using the core rod. High pressure air is blown in to help form the shape within a metal mold. All three processes can be completed using plastics that can be recycled.
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 eco plastic solutions then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.
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