Clay bodies of china and ball clays containing heat treated clay

Details Clay bodies of china and ball clays containing heat treated clay Clay bodies of china and ball clays containing heat treated clay

1990-05-04

1992-09-01

Dixon, Jr., William R.

Compositions: ceramic

Ceramic compositions

Clay containing

106416, 106486, 501144, C04B 3304, C04B 3324

Patent

active

051438712

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to materials for use in the manufacture of ceramic articles. In particular, the invention provides a composition that is suitable for use in the manufacture of china articles, for example vitreous china ware such as sanitary ware, and a method of making a china article in which the said composition is used.
In one known method of making china articles (the slip-casting method) an aqueous slip is introduced into a plaster mould. De-watering of the slip occurs through the plaster mould. After de-watering sufficient to form a cast article of the desired thickness has occurred, excess slip is drained from the mould, the article is allowed to harden and, after removal from the mould, is trimmed, dried, glazed and fired. In this method the de-watering step may take from 1 to 11/2 hours and, typically, a further period of 11/2 hours is required for hardening before the cast article can be removed from the mould.
In another known method (the pressurised casting method) an aqueous slip is placed in a mould and the mould is pressurised to accelerate de-watering of the slip. The mould may be of, for example, porous plastics material, mineral fibres, or sand/resin blocks. In one version of the pressurised casting method the mould is of porous plastics material and, at a pressure of 300 in.sup.-2 (2.1.times.10.sup.6 Nm.sup.-2), adequate de-watering may be accomplished within a period of from 8 to 10 minutes. In this version of the pressurised casting method, the following steps are generally carried out: the mould is filled with the slip, the mould is pressurised for a period of from 8 to 10 minutes, excess slip is drained from the mould, the article is consolidated by applying air pressure such that further de-watering of the material occurs through the mould, and the resulting cast article is then released and removed from the opened mould. The total time required for completion of these steps will normally be of the order of 12 to 15 minutes.
In the known methods discussed above an aqueous slip comprising china clay, ball clay, a flux and a filler is generally used. A typical aqueous slip might consist, for example, of 25% by weight china clay, 25% by weight ball clay, 20% by weight flux, 30% by weight filler and water in an amount which is sufficient to give a liquid slip of relatively low viscosity. Other ingredients, for example, a deflocculating agent, may be included. The flux may be, for example, a feldspar-containing flux, for example nepheline syenite, or any other suitable material which melts at the temperature to be used for the firing step to fuse the other ingredients together. The filler is normally a silica filler and may be for example sand, quartz or flint. Flint which has been fired at a temperature of the order of 1000.degree. C. and crushed may be used as the filler. The slip may comprise, in replacement of a part of the china clay and/or a part of the ball clay, from 5 to 15% grog (that is, ground faulty china ware). The grog is thus material which has already been subjected to conditions suitable for firing china, for example firing at a temperature of 1200.degree. C. The thickness of the cast articles is normally in the region of from 8 to 10 mm.
The present invention provides a composition comprising
a treated clay product which has been prepared by heating clay, the heating conditions being such that kaolinite in the clay is converted to metakaolin, while substantially avoiding the formation of mullite; and
raw ball clay and/or raw china clay.
The term "raw" is used herein in relation to clay to mean a clay which has not been subjected, subsequent to its extraction from the ground, to conditions which would be likely to effect a crystalline transformation of any of the ingredients of the clay.
Preferably, the treated clay product has been prepared by heating ball clay. Advantageously, the composition comprises the treated ball clay and raw ball clay in a ratio of from 1:2 to 4:1 by weight. Instead of, or in addition to, the raw ball clay, the composition may com

REFERENCES:
patent: Re20555 (1937-11-01), Sproal
patent: 1830934 (1931-11-01), Curtis
patent: 3309214 (1967-03-01), Podschus et al.
patent: 3941872 (1976-03-01), Pusrar
patent: 4017324 (1977-04-01), Eggers
patent: 5011534 (1991-04-01), Berube et al.
"Introduction to the Principles of Ceramic Processing" James S. Reed, 1988 pp. 463, 464 and 380-386.

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