Many beautiful objects have been created by breathing air into a mass of colored, melted glass to form a hollow shape. The process dates back centuries, and in modern times has been transformed into an industrial application for producing plastic products, including containers, toys, medical devices and auto parts. That transition was made possible by the emergence of blow molding.
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 raw tubes of plastic are made primarily from pellets of polyethylene, polypropylene, or polyvinyl chloride. These are thermoplastics, which melt at a rate and consistency making them ideal for mass production. The tubes can be made to order in virtually any size and quantity needed for a particular job, and are inserted into the molds in rapid assembly-line fashion.
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.
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 raw tubes of plastic are made primarily from pellets of polyethylene, polypropylene, or polyvinyl chloride. These are thermoplastics, which melt at a rate and consistency making them ideal for mass production. The tubes can be made to order in virtually any size and quantity needed for a particular job, and are inserted into the molds in rapid assembly-line fashion.
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.
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 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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