Artists create objects of astonishing beauty by carefully blowing air into a mass of melted glass to form various shapes. Glass blowing originated hundreds of years ago, but the basic principles of this art are used today in plastics manufacturing to create containers, toys, medical devices, and many other items. This transition was made possible through 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 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.
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.
Individual serving containers and other small items can also be manufactured using injection stretch molding. A nozzle injects melted plastic, it is allowed to cool, and then is reheated and extended. Metal exterior molds are used, and high-pressure air helps complete the process. All of these methods work well using base plastics that can be reused, often more than once.
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 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 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.
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.
Individual serving containers and other small items can also be manufactured using injection stretch molding. A nozzle injects melted plastic, it is allowed to cool, and then is reheated and extended. Metal exterior molds are used, and high-pressure air helps complete the process. All of these methods work well using base plastics that can be reused, often more than once.
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 recycle plastic pallets, she suggests you check out her friends www.ptm.com/global.
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