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.
The process begins with a heated raw plastic tube called a parison, a word that originally referred to a mass of unformed, melted glass. Once the parison is sealed carefully inside a mold, air is forced through under pressures that range from 25 to 150 psi, evenly forcing the material onto the inner shape. The plastic is spread throughout the mold at a precise thickness, and cools quickly.
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.
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.
The process begins with a heated raw plastic tube called a parison, a word that originally referred to a mass of unformed, melted glass. Once the parison is sealed carefully inside a mold, air is forced through under pressures that range from 25 to 150 psi, evenly forcing the material onto the inner shape. The plastic is spread throughout the mold at a precise thickness, and cools quickly.
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.
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 reusable plastic pallets, she suggests you check out her friends www.ptm.com/global.