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.
The process begins with a heated raw plastic tube called a parison, a word that originally referred to a mass of unformed, melted glass. Once the parison is sealed carefully inside a mold, air is forced through under pressures that range from 25 to 150 psi, evenly forcing the material onto the inner shape. The plastic is spread throughout the mold at a precise thickness, and cools quickly.
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.
A parison can be shaped in a variety of ways. Screw-like machinery forces these masses into their molds during a process called extrusion. Almost immediately, pressurized air is sent through a tube into the center of the material and expands outward, creating precise shapes and surface details that can be rapidly and accurately reproduced.
Depending on what is being made, extrusion is continuous or intermittent. Variations are commonly used to make large bottles for milk or juice, but some containers are more efficiently produced using an injection process. The plastic is injected into a core pin, air is forced in, cooled, and the entire item ejected in one continuous operation.
Individual serving containers and other small items can also be manufactured using injection stretch molding. A nozzle injects melted plastic, it is allowed to cool, and then is reheated and extended. Metal exterior molds are used, and high-pressure air helps complete the process. All of these methods work well using base plastics that can be reused, often more than once.
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.
The process begins with a heated raw plastic tube called a parison, a word that originally referred to a mass of unformed, melted glass. Once the parison is sealed carefully inside a mold, air is forced through under pressures that range from 25 to 150 psi, evenly forcing the material onto the inner shape. The plastic is spread throughout the mold at a precise thickness, and cools quickly.
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.
A parison can be shaped in a variety of ways. Screw-like machinery forces these masses into their molds during a process called extrusion. Almost immediately, pressurized air is sent through a tube into the center of the material and expands outward, creating precise shapes and surface details that can be rapidly and accurately reproduced.
Depending on what is being made, extrusion is continuous or intermittent. Variations are commonly used to make large bottles for milk or juice, but some containers are more efficiently produced using an injection process. The plastic is injected into a core pin, air is forced in, cooled, and the entire item ejected in one continuous operation.
Individual serving containers and other small items can also be manufactured using injection stretch molding. A nozzle injects melted plastic, it is allowed to cool, and then is reheated and extended. Metal exterior molds are used, and high-pressure air helps complete the process. All of these methods work well using base plastics that can be reused, often more than once.
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 over 20 years of professional sales experience, 10 of them directly in the plastic pallets and materials handling industry. On her spare time she works on applied-sustainability projects. If you are interested in recycle plastic pallets, she suggests you check out her friends www.ptm.com/global.
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