PROCESSING OF CERAMICS, PLASTICS AND RUBBER

 

Pottery

The art of using clay to make various objects is called pottery.

Clay must be prepared before use in pottery. Any trace of sand is

removed. The clay is mixed with water and pounded as in to

remove air bubbles and also to make the clay more plastic so that

becomes easier to mould and shape. If sand and air bubbles are

not removed, any article made from such clay may explode or

crack during the period of heating the freshly moulded article.

 

There are different ways in which the prepared clay can be used

to mould different articles. The simplest way to make a pot is by

the pinch pot method’

 

A hollow is first formed with the thumb in a small ball of clay.

By carefully pressing between the fingers, the wall is gradually

made thinner as the form develops. The final form, containing

some cracks, is then smoothed by using fingers and a small

quantity of water.

 

The Potter’s Wheel

The pinch pot method does no involve any apparatus. Most

pottery articles are made by using what is called the ‘potter’s

wheel’. A potter’s wheel is a device with a rotating horizontal disc

upon which clay is moulded by a potter

 

The K­iln

Any article just moulded from clay is soft. To harden the moulded

article, it is baked in a fire. One simple way of baking is by using firewood.

A more sophisticated way of heating is by using what is

called a kiln. A kiln is an oven or furnace for baking finished

articles. Different kilns use different fuels to produce fire fo

baking. Such fuels include wood, coal, oil and gas. An example of

a kiln using gas is shown in Fig. 6.14. The hot air transfers heat to

the finished pieces as it travels through the chamber

 

 

Mud

In order to make mud, we dig pure earth which docs not contain

Sand. It is moistened with water, and made plastic by pounding

with feet. The soft mud is then pressed by hand into a wooden

mould. The soft bricks are dried initially by exposing them to the

Sun: They ale made stronger by baking them later on using

firewood.

 

Concrete

Concrete blocks arc made by mixing cement, aggregate and sand

with water. The mixture is turned into a uniform paste by using a Shovel or a concrete mixer. The paste is then shoveled into aa

moulding machine. The moulded blocks are removed and placed

on level ground to dry. The blocks are ready for use after drying

for some days.

 

Plastics

 

There are many ways of making plastics from the molten måterial.

The choice of method depends upon the plastic product to be made

and its use. The typical methods of processing plastics are

Compression moulding, Injection mouldin, Vacuum forming,

Extrusion, Calendering. These methods arc described below.

 

 

Compression moulding

Compression moulding is the forcing of a material into a mould

with pressure and heat This is one of the methods of

processing thermoset materials. The moulding material or resin is

first heated in an oven. It is then poured into the open cavity in the

lower part of the mould. This lower part is called the female

section of the mould. The plunger, or male section of the mould,

moves down to close the mould. The pre-heating of the material in

the oven is not sufficient to mould the plastic. So the material is

subjected to further heating by either electricity or steam. The

material is pressed by forcing the male section down into al

cavities or the mould.

 

During the process, the material hardens into a permanent

 

shape. The mould is then opened and the finished product is taken

Out.

 

Injection moulding

This method or moulding is generally used for thermoplas.

materials. In injection moulding, the mould is not heated as in

compression moulding. The kind or thermoplastic, in terms or colour and quality, is

selected and red into the reed hopper in powder form. The plastic

material is heated in the heating chamber between the hopper and

the mould. The right amount or heated material is then forted by

the plunger into the mould. The plastic is formed as it is forced

into the mould. The article stays in the mould until it is completely

cool. Then it is removed. Plastic products such as valves and the

air-intake grill or an air conditioner and nylon hair comb are made

by the injection moulding method.

 

 

 

 

Updated: January 22, 2020 — 5:37 am

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