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.
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.
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 recycled plastic pallets, she suggests you check out her friends www.ptm.com/global.
