GB1279980A - Method for the manufacture of building units of fired, bloated clay - Google Patents

Abstract

1279980 Moulding expanded clay INCENTIVE AB 12 June 1969 29924/69 Heading B5A [Also in Divisions C1 and E1] Building units of fired expanded clay, e.g. bricks, blocks, planks, boards, wall elements, are produced from expandable clay pieces -heated, on a moulding surface and between side surfaces determining the width of the expanded clay, for a period not exceeding 6 hours, and preferably not exceeding 4 hours, to 1000- 1200‹ C., and preferably 1050‹ to 1150‹ C., at which temperature it is maintained for 10 to 60 minutes so that the clay melts and expands to form a substantially closed cell product from which, after cooling, the uneven upper surface is trimmed, e.g. by sawing, milling or grinding. The units are preferably fired in a tunnel furnace providing infra-red heat from the roof thereof. The clay is preferably in pieces which may be spherical, or cylindrical, or thin strands. As mould release agents there may be employed thin layers of chamotte, or sand which is sprayed on to the mould walls in a binder, which adhere to the fired product, or mineral fibre, e.g. rockwool, which do not adhere to the fired product, applied to the mould as mats or sprayed on in a binder. The products may be provided with one or opposed moulded facings of unexpanded clay, disposed on the base or at the sides of the moulding surface and simultaneously fired therewith. The unexpanded facing layer may be prefired at a temperature below 1000‹ C., e.g. 900‹ C., whereby it is not expanded by gases evolved therefrom, whereafter the temperature is raised fora short time, e.g. 0À5 to 1 hour, to a value, e.g., 1025-1050‹ C., below that, e.g., 1125-1150‹ C., at which the expanding clay is added for a final firing and simultaneously fusing therewith. Alternatively, the unexpanded facing layer and the expanded clay may simultaneously be fired by selecting for the unexpanded layer a material having the higher melting point and firing the two materials at an intermediate temperature, the higher melting point material being of different composition or preferably comprising the same material as the expanded clay which has been raised in melting- point by the addition thereto of sand, chamotte, or crushed brick. Details are given of suitable compositions (see Division C1) and of the thermal and strength properties of the units (see Division E1). A plurality of the units may be assembled to form a pre-fabricated panel having binder, e.g. mortar, filled joints. In the Fig. 3 embodiment, the mould comprises an endless belt 2, passing through a tunnel furnace 1 wherein the heating and cooling cycle is conducted, which carries mould side walls 3 which are automatically raised and lowered at the entry and exit of the tunnel 1, the clay pieces being deposited from a hopper 5. The mould may mould a continuous length, which may be subjected to additional rolling or extruding within the furnace 1 immediately after the clay expansion zone thereof, and which length is cut transversely at the tunnel exit. Alternatively, the building units may each be defined between transverse mould members 4, carried by an endless chain, which may automatically be inserted and withdrawn from between the side walls 3 respectively at the tunnel entry and exit. In the Fig. 8 embodiment, the units are moulded with facing layers of unexpanded clay, two whereof, 10 and 11, are extruded on to either side of a conveyer belt and are cut into lengths 15 by a device 12 at the entry to a tunnel furnace 13. The lengths 15 may be prefired, as described above, prior to deposition on the belt therebetween of clay pieces 16, from a hopper 17 located prior to the final firing zone wherein the expanding clay and facing lengths 15 are fused together, and wherein the lengths 15 may be supported by stationary or moving backing walls 19, or by rollers. The upper surfaces of the moulded length is trimmed by a hand saw or cutter 20, whereafter it is cut transversely between the lengths 15 by a flying saw 20 and then cut longitudinally by a saw 22 to produce units faced on one side with unexpanded clay.