Page 28 - Curriculum Visions Dynamic Book

Stages in industrial brickmaking
1. Winning. The clay has first to be excavated from the ground. This process is called “winning.”
2. Preparation. The clay is crushed to break up stones. If the source of clay is shale rock, grinding wheels are used.
3. Forming. Water is added to the clay and mixed using rotating blades. This is called “pugging.” It makes the clay plastic.
4a. Stiff-mud process. Clay is mixed with just enough water to make a mouldable material. The clay is then pushed through a die, and rollers add a surface texture. The long rod of textured clay is then cut up using a blade (guillotine). The stiff-mud process produces the strongest bricks.
4b.Soft-mud process. Sticky clays, which have a higher water content, are made in batches in moulds.
4c. Dry-press process. Clays with a water content of less than 10% are used. The clay is pressed into steel moulds by a hydraulic ram.
Winning Crushing and storage
5. Drying. When wet clay comes from moulding or cutting machines, it must be dried before it can be fired. This happens in ovens whose temperatures are set between 38°C and 204°C. Drying takes between one and two days. The heat for these ovens is waste heat coming from the firing kilns.
6. Firing and cooling. Firing takes between two days and a week. Both batch kilns and tunnel kilns take about the same firing time. In the first stage the free water is first evaporated at a temperature of about 204°C. Next, water is taken from the clay water molecules at temperatures
of 150°C to 500°C. As
the temperature rises to 500–980°C, the clay
begins to oxidize,
and at 900–1,300°C
it vitrifies. Once it
has vitrified enough,
the bricks are slowly
cooled.
Pulverizing
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Screening