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 tubes of unformed plastic consist mainly of polypropylene, polyvinyl chloride, and various forms of polyethylene. These materials are thermoplastics, meaning that they melt at a rate and consistency ideal for industrial production, unlike those which become liquid when heated. They can be custom made, and are designed to be inserted mechanically.
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.
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.
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 tubes of unformed plastic consist mainly of polypropylene, polyvinyl chloride, and various forms of polyethylene. These materials are thermoplastics, meaning that they melt at a rate and consistency ideal for industrial production, unlike those which become liquid when heated. They can be custom made, and are designed to be inserted mechanically.
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.
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.
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 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 reusable plastic pallets, she suggests you check out her friends www.ptm.com/global.
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