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 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 can be shaped in several ways. Extrusion methods employ a screw-shaped device that evenly forces the soft mass into a mold. Inside that space, pressurized air fills the cavity from the center of the plastic outward, forming the soft material into an exact duplication of the interior walls, and exactly reproducing the originally engineered shape.
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.
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.
There is no escaping the fact that plastics come from hydrocarbons. Even though the material accounts for less than five percent of all petroleum production, the numbers are significant. Today, improved methods of recycling and re-use greatly are reducing the chances of this material ending up in a land fill or floating for years at sea.
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 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 can be shaped in several ways. Extrusion methods employ a screw-shaped device that evenly forces the soft mass into a mold. Inside that space, pressurized air fills the cavity from the center of the plastic outward, forming the soft material into an exact duplication of the interior walls, and exactly reproducing the originally engineered shape.
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.
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.
There is no escaping the fact that plastics come from hydrocarbons. Even though the material accounts for less than five percent of all petroleum production, the numbers are significant. Today, improved methods of recycling and re-use greatly are reducing the chances of this material ending up in a land fill or floating for years at sea.
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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