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.
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.
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.
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 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.
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.
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.
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 taught plastics molding techniques for over 15 years. He specializes in injection molding and thermoforming. If you are interested in learning more about recycle plastic pallets then he recommends you visit his friends at PTM: Custom Plastics Injection Molding Company.
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