In the plastics industry products are produced in a number of different fashions which include injection molding, vacuum molding and blow molding. Blow molding is used when the end result is a strong, hollow, custom molded plastics container. There are many such containers formed in this fashion, some examples are plastic drums, beverage bottles, brine tanks and fuel tanks. The process is actually quite simple, it involves melting plastic into a tube, the tube, called a parison is placed batten two hales of a mold and air under pressure is pumped into the parison until the molten plastic fills the mold halves. Once the mold halves are opened, the finished blow molded part id ejected.
Plastic is an extremely strong material. A very thin soft drink bottle can withstand the pressure of carbonated liquid because the polymer chains in the bottle form in two directions, the plastic is stretched without giving up strength, the blow molding process takes advantage of these properties to allow the manufacture of thin, strong custom molded plastics.
The blow molding process explained:
To blow mold a container of any given size requires a piece of plastic which has been preformed, usually in a plastic injection molding machine. To keep this piece of plastic warm, the injection molding machine is in close proximity to the blow molding machine. This piece of plastic is called a “parison” and looks very much like a test tube only upside down; it has a collar and threads. This parison is mechanically loaded into the blow molding machine and the two piece mold comes together around it. The mold is in the shape of the bottle or flask which is being manufactured at the time.
At this stage of the process a hollow tube called a “ramrod” is pushed into the center of the parison, stretching the warm plastic as it pushes forward. Air under pressure is then fed into the hollow ramrod, this in turn forces the warm plastic to enter the mold and conform to the shape. Because the air is fed into the parison under strict controls thee stretching is even and the plastic remains strong and uniform in thickness.
It’s easy to think of plastic injection molding as if a latex balloon was being inflated. As long as the pressure is controlled the material expands in a uniform fashion, it will eventually fill the cavity of the mold.
Custom molded plastics produced by blow molding are a process undertaken by Clack Corporation. Clack can produce blow molded products from two ounces to five gallons in capacity.
