| |
Blow Molding: The Engineering of Plastic Parts
Ever wonder how those bottles your Coca Cola comes in are made? Many types of plastic bottles, automotive parts, and other plastic products are created through a process called Blow Molding. The process itself is not as complicated as it sounds, but the products produced through the Blow Molding process are staples in our everyday lives.
There are two main types of blow molding: Extrusion and Injection Molding. Extrusion Blow Molding is a basic process that incorporates the use of molten plastic, a parison, and a divided mold. This process is quite similar to that used in glass blowing. First the parison, a hot hollow tube of molten plastic, is released from an extruder into the blow molding machinery. At this time one end of the parison is sealed shut while the other end remains open. Compressed air is then injected through the opening, forcing the molten plastic to expand. Eventually the plastic will expand to the point where it reaches the walls of the mold and takes its shape. The newly molded plastic remains in the mold until cooled. This method is commonly used for producing automotive fuel tanks or water tanks as this process is not very effective for precision molding.
Injection Blow Molding is basically the same process, only a bit more precise than Extrusion Blow Molding. In this process, a device called the blow stem is placed in an injection mold. Melted thermoplastic material is then injected into the mold to create the preform around the blow stem. Both the preform and the blow stem are then placed into a two piece molding chamber and compressed air is injected through the blow stem into the preform. The process is basically the same as Extrusion Blow Molding from here. The preform expands to fit the mold and is left to cool. Once the part is cooled the two parts of the mold release the finished product. So there you have it. A very simple process called Blow Molding is the process by which the bottles are made that contain your favorite soda. Without this process we’d still be getting our soda and milk out of glass bottles like grandma and grandpa used to. Imagine having to revert back to that system!
|
|
