| The vitrification characteristics of fireclays enable their use in the manufacture of bricks to meet specifications for water absorption and frost resistance.The proportion of fireclay used in the body varies from 50 to 100 per cent, depending on the properties of the fireclays and other clays included in the blend, and the technical and aesthetic properties required in the final product. Fired colour, determined by iron content, and carbon and sulphur content are the main criteria on which the suitability of a fireclay for facing brick manufacture is judged. Pale and buff coloured bricks made using alternative materials have inferior qualities in terms of durability, crushing strength and water absorption which may not satisfy required performance standards.
Fireclays are mixed in roughly equal proportions with clays and shales for the manufacture of clay pipes.The fireclay adds plasticity, an important property governing the ease with which the material can be shaped. It also widens the temperature range within which vitrification takes place, thus making firing more manageable.This blending of materials found in association with coal not only provides the required properties for the manufacturing process, but also enables deposits which would otherwise be discarded to be utilised.
The relatively high alumina and low alkalis content of some fireclays also make them suitable for use in the manufacture of certain refractory products.
The fired aesthetic qualities of fireclay are also essential for the manufacture of some stoneware pottery. |
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