POROUS CLAY COOKWARE WITH IMPROVED THERMAL SHOCK ABSORPTION AND COMPOSITION FOR MAKING THE SAME

摘要

An improved preparation for making clay baking stones and other porous clay cookware for use in a closed barbecue or in a conventional oven, and a recommended method of manufacture are disclosed. Cookware produced using this preparation will be capable of absorbing thermal shock well in excess of requirements established for ovenware: "Must withstand quenchin g from 150 degrees C into cold water."(1). The disclosed preparation will withstand repeated quenching from 300 degrees C into cold water and returning to the hot cooking appliance. This preparation is adequately fused to prevent disintegration in the case o f a throughly wetted product being subjected to freeze thaw cycles and retain its thermal shock absorption capacity. Also, thoroughly wetted product is not prone to damage caused by steam formation when heated in a household cooking appliance. The preparation can be applied to any reasonably plastic pottery clay known to be food safe when fired to between 4% and 14% absorption. This plastic clay is blended wi th 15% to 50% coarse grog or pitchers. The grog or pitchers must provide a minimum of 5% material retained at 20 mesh, plus 5% material retained at 30 mesh to the blend. The blended clay-grog/ pitchers are fired to the same temperature required to achieve 4%- 14% absorption for the plastic clay alone. Absorption of the blended material will be higher than for the plastic clay alone. From 8% to 20% absorption for the fired blend of clay grog are appropriate. A higher absorption rate would indicate a product with undesirably low conductivity for cooking purposes and/or a soft product pron e to breakage. Lower absorption indicates a compromised thermal shock absorption capacity. Hydraulic pressing in plaster dies using an air release system is the recommended forming method. Manoeuvring product can be facilitated by the use of a vacuum hand. Edges of pressed product can be finished by compressing with a roller tool while still plastic. Further testing is required in order to define the minimum and maximum wall thicknesses, and maximum product diameter. Also testing will be done to determine thermal expansion rates for ceramic materials prepared in this manner. as well as thermal conductivity rates and hardness ratings.