Most plastic caps and many other plastic closure types are created using large industrial injection molded plastic machines. Injection molded plastic injects a small amount of plastic into a cap-shaped mold. The plastic is then dried and released from the machine in one smooth motion. Watching a plastic cap machine in first-person action is an interesting process. It is amazing to see how humans have been able to transform basic parts into fully-functional parts that can create other useful tools and pieces for everyday life. Many plastic cap machines can create hundreds or even thousands of plastic caps within just a minute or two.
A plastic closure machine works something like this:
The plastic pellets are added to a large hopper in the machine. The hopper melts the plastic and carries it to the part of the machine that will inject the hot plastic into the mold.
32 or more rotating piston molds rotate around a central motor. The plastic is injected into the molds in one smooth motion by the pistons as they travel around in a circle. The pressure from the two sides of the piston give the plastic caps the desired shape and quickly dry the plastic until it is hard enough to release from the mold.
In one smooth motion, the pistons release the cap at just the right moment and it releases into a metal passageway that directs the cap into a storage bag or another conveyor belt. The process is so fast, that there are always at least 4 or 5 plastic caps inside the chute at any one time. Most machines can create thousands of plastic caps in just a few minutes.
Depending on the machine, it is possible to program the machine to create caps of varying sizes and specifications. Some machines can create threaded caps, while others create pop-off caps or plugs only.