GB932941A - Improvements in and relating to the manufacture of bricks - Google Patents

Abstract

In the manufacture of bricks small pieces of clay are lightly calcinated in air, in order to oxidise and remove carbonaceous matter, to oxidise iron compounds and to dehydrate the material without destroying the alkaline earth carbonates, allowed to cool, ground and mixed with 10 to 30% by weight of calcium hydroxide before being made plastic by the addition of water and poured into moulds where the bricks are allowed to harden. The clay or brick earth used as raw material may be of the kind normally used for making red bricks and the calcining process may be performed in a kiln or furnace, e.g. a rotary kiln, at 550 to 700 DEG C. Before the addition of water the clay and Ca(ON)2 may be mulled such that 50% of the mixture passes a 200 B.S. sieve. The hardening may be natural although it is preferable to expedite the process by steam treatment, e.g. in an autoclave. In the example Lancashire Boulder Clay is heated in a kiln in air at 650 DEG C. for 3 hours, cooled, ground and added to Ca(ON)2 before remilling, adding water and allowing the moulded brick to harden under a load of 1/2 ton. After two days the bricks are placed in an autoclave and subjected to steam at 100 lbs./in2 for six hours.