Most of the plastic products purchased at the local departmental store are made from plastic injection moulding. Some well-known plastic products such as chairs, toys, and electronics are all manufactured through the process of plastic injection moulding.
Injection moulding was a response to billiard manufacturing in the 19th century which used ivory from African elephants. There were so many billiard balls being made at the time that it was endangering the African elephant population.
The injection moulding process is relatively simple in principle. It involves an injection of melted plastic into a mould to create a product. However, the injection moulding machine is much more complex then people know. There are three main parts which are the injection unit, mould, and the clamp. Plastic pellets in the hopper are fed into the barrel of the injection unit.
A screw pushes the pellets forward inside the barrel and heated bands wrapped around the barrel warm up the plastic. The pellets are moved forward by the screw and eventually melt. The mixture is extremely hot when it reaches the front of the barrel. Molten plastic in front of the screw then moves forward. The screw injects the hot plastic into the mould. The plastic becomes harder usually within a minute and the mould opens with the plastic product. The mould closes back again and the manufacturing process continues.
One of the most important parts of the machine is the reciprocating screw. It has flights which are wrapped around the shaft. The screw rotates and transports the plastic through the barrel. It mixes the plastic within the flights. The action of the screw agitates the pellets within the flights to make a consistent mixture. The screw’s movement also heats the plastic because of the clever design which presses the plastic next to the wall for consistent heating.
The design was truly revolutionary at its time and only a few important heating modifications have been made since its early creation. It is an invention that has stood the test of time.