Engineering Chemistry S Datta

SILICATE TECHNOLOGY 429
Process: It consists of the following steps:
1. Slurry preparation: The mixture of weighed ingredients is taken in a blunger and
stirred well with water to form a creamy liquid known as clay slip.
2. Ageing: The slip is filter-pressed. The residual cake contains 10-30% water. The cakes
are dumped for some days. This improves the plasticity of the clay mixture because
of uniform hydration and gelation.
3. Deairing: The aged cakes are deaired in a pug mill by slicing with knives and putting
under vacuum.
4. Shaping.
5. Trimming and drying: The shaped articles after airdrying are trimmed and then
dried in hot air.
6. Glazing: The dried articles known as blanks are glazed. In few cases glaze is put on
the blanks before firing. But in most cases, blanks are fired to produce biscuits. The
firing is done in a tunnel furnace. Usual maximum temperature is 1400°C.
Storage
Clay
Water
Screen
Cutter
Vac
Crusher
Brick
(a)
Vac
Screen
Clay flint water
Feldspar
Jigger
Extruder
Mag.
separator
Slurry
Cutter
Agitation
Blunger
Slurry
Dinner
plate
Drager
Press
(b)
Filter press
Fig. 19.7 Flow diagram: (a) Brick manufacture (b) Dinner plate manufacture.