WHAT IS BALL CLAY?
BALL CLAY/PLASTIC CLAY
Ball clays or plastic clays are fine grained, highly plastic sedimentary clays, which fire to a light or near white colour. They are used mainly in the manufacture of ceramic whiteware and are valued for their key properties of plasticity, unfired strength and their light fired colour.
Ball clays exhibit highly variable compositions and consist of a mixture, primarily of kaolinite, mica and quartz, with each contributing different properties to the clay. The crystallinity of the key component, kaolinite, has a marked influence on ceramic performance.
Ball clay acts as a binding agent and contributes to plasticity, workability and strength in a pre-fired ceramic body. Some are highly valued for their fluid and casting properties, particularly in the manufacture of sanitaryware.
Ball clays are relatively scarce, globally because of the unusual combination of geological factors required for their formation and subsequent preservation. Production of ball clay in the UK dates back to the early 17th century and became important in the late 17th and early 18th century when the Staffordshire potters recognised its attributes.
The UK is a leading world producer and exporter of high quality ball clays. Production peaked at over a million tonnes in 2000.
Ball clay production is confined to the South West of England in the Bovey and Petrockstowe basins in Devon and the Wareham basin in Dorset. The Bovey basin is the most important source, both in terms of total sales (72%) and the diversity of the clays produced. The UK is a leading exporter of ball clay with some 83% of total sales being exported in 2002. Over 50% of the world’s production of vitreous china sanitaryware contains a proportion of UK ball Clay as an essential ingredient. Imports of ball clay are negligible and ball clay makes a small, but important, positive contribution to the balance of payments.
Ball clay are almost entirely used as ceramic raw materials for sanitaryware, wall and floor tiles and tableware. These sectors account for over 80% of total sales. It is combined with other ingredients such as kaolin, silica sand and flux and is a vital part of the mix even in small quantities.
BALL CLAY PRODUCTION
Ball clay is extracted from the ground by surface working (open pit method), underground mining having ceased in 1999. Extraction involves excavators and dump trucks to selectively remove individual grades of clay to storage and blending facilities. The ratio of waste to clay is variable, but overall is in the order of 1 to 1.5.
Ball clay undergoes limited processing. Most is size reduced and some 70% is sold in this form. This allows the clays to be more easily handled and blended. The blending being essential to optimise clay use and to consistently meet customer specifications. Some are also dried and milled and are dispatched in bulk or bags. For the sanitaryware market some products are refined to remove impurities and these are sold in both slurried and dried forms.
Waste is not a significant problem and by-products of sand are sold as aggregates into the construction market.
For further information please visit the websites at:
www.sibelco.com and www.imerys.com