Ball
Clay
The wide use of ball clay is mainly due to its contribution of
workability, plasticity and strength to the bodies in drying.
BALL
CLAY is a variety of Kaolinite, like china-clay. It differs from
china-clay in having high plasticity and less refractoriness. In
chemical composition, ball and china clays do not differ greatly
except that the former contains a larger proportion of silica. It has
derived its name from the practice of removing it in the form of
ball-like lumps from the clay pits in the UK. The main utility of ball
clay is its plasticity and it is mixed with non-plastic or less
plastic clays to make them ecquire the requisite plasticity. The high
plasticity of ball clay is attributed to the fact that it is
fine-grained and contains a small amount of montmorillonite. Over 85%
of the particle sizes present in ball clay are of one micron or less
in diameter. It is light to white in colour and on firing may range
from white buff. Pyrometric cone equivalent to ball clay hardly ever
exceeds 33.
Usually the following proportions (weight percent) of ball clay are
commonly used invarious types of ceramics composition:
- Vitreous
sanitary-ware 10 to 40
- Hotel
china-ware 6 to 15
- Floor
and wall tiles 12 to 35
- Spark
plug porcelain 10 to 35
- Semi-vitreous
white ware 20 to 45
- Saggar
bodies 10 to 25
- Glass
melting-pot bodies 15 to 20
The
wide use of ball clay is mainly due to its contribution of
workability, plasticity and strength to the bodies in drying. Ball
clay, on the other hand, also imparts high-drying shrinkage which is
accompanied by a tendency towards warping, cracking and sometimes even
dunting. This undesirable property is balanced by the addition of
grog.
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