Manufacture of Refractories

Manufacture of a refractory consists of the following steps:

1. Crushing: The raw materials in the form of big lumps are crushed to about 25mm size.
2. Grinding: The crushed materials are ground down into 200 mesh size by using crushers, pulverizers, hammer mills, ball mills and screens.
3. Screening: It involves the purification of the refractory raw materials. It is essential to remove the unwanted materials from the raw materials for producing better refractories.
4. Storage: After screening and mineral dressing, the pure materials are stored in storage bins with bucket elevators.
5. Mixing: It is done for the proper distribution of the plastic materials throughout the mass. This makes moulding easier.
6. Moulding: Moulding can be done mechanically or by hand. Mechanical moulding produces refractories having more density and strength than that produced by hand-moulding.
7. Drying: Slow drying is employed to remove the moisture from the refractories which helps to avoid voids and high shrinkage.
8. Firing: The refractories are fired in kiln at the temperature as higher than their use temperature so as to stabilise and strengthen their structure. Depending upon the nature of the bricks the firing temperature will be different.

Firing helps:
(a) to remove water of hydration and
(b) to impart high crushing strength.