PLASTIC ARTICLES

A plastic material is one which can be moulded into the shape we want. The first plastic materials were ones that are to be found in nature, such as wax, resin and clay. We know that clay can be fashioned into cups and saucers.

Today are chemists have found out to make new materials which can be pressed into whatever shapes are wanted and then made hard so that they can be used by us.

There are several kinds of stuffs, but they all fall into one or other of two groups. Those in one group are put while cold into a metal mould of the right shape. They are pressed into shape and then made hard by heat. Once they harden they keep their shape. The other group is made soft by heat. Then it is squirted as a thick liquid into a metal mould of the right shape. The plastic become firm in their new shape as they cool.

Let us take a simple article as a plastic tumbler, which is shaped like a glass. For this they use the method known as compression mould. A metal mould of the shape of the outside of the tumbler is made and into this some plastic material is put. It is in the form of a powder. Then another metal mould, having the shape of the inside of the tumbler, comes down and pressed into this powder. The powder spreads out and fills the space between the inner and outer mould. The mould get very hot and the powder joins together to form a firm tumbler.

When the top mould is lifted up, the tumbler can be taken out. It will always keeps the same shape.

Another method, called injection moulding is used to make plastic toys. A metal mould has in it a hollow space in the shape of a toy. The plastic material is heated and it turns to a thick liquid. This liquid is squirted into the hollow space shaped like a toy. It fills up this space, and when the liquid cools and becomes hard it is now in the form of a toy.