Patent GB-1381781-A (GB)
Title: Manufacture of articles of flowable hardenable material
IPC: B28B13/06
Filed: 1972-02-01
Abstract: 1381781 Rotational casting of sheets W C BARRATT 31 Jan 1973 [1 Feb 1972] 4712/72 Heading B5A Sheets (e.g. wall panels, roof sections, decorative tiles) are made by distributing a cement mixture from a charging head 23, Fig. 1, around the interior of a cylindrical mould 10 rotating about a horizontal axis and having a removable end plate 22; forming the mixture into a cylinder 70 by rotation of the mould; removing the end plate 22; inserting a mandrel 40, Fig. 7, into the mould to engage the cement cylinder 70; removing the cement cylinder on the mandrel; dividing the cement cylinder 70 longitudinally either by casting it with a discontinuity or slitting it after moulding; and rotating the mandrel to lay out the cylinder as a sheet on to a surface to harden. The cement mixture may contain asbestos fibres which become preferentially orientated circumferentially. In Figs. 1, 2 and 7, the mould 10 comprises a metal cylinder 12 perforated to allow dewatering of the cement mixture and having reinforcing rings 15 resting on driven rollers 16. An annular plate 21 is bolted to one end of the cylinder 12 and at the other end a removable plate 22 is mounted on stub shaft 26 to rotate with the mould. The charging head 23 is moved into the mould by carriage 24 and carries a pin 35 which engages a locating ring 33 on plate 22. Cement mix containing only 70% water is fed through pipe 36 and pipes 36a directly on to the mould surface with shutter 38 open as shown. A trough formed by closing shutter 38 may be filled with material, e.g. aggregate or glass, metal or plastics particles with a binding agent, which is distributed over the mould before the cement mix to form a laminated sheet The cement layer is compacted by lowering a spreader 86 carrying a vibrator 92. Excess water collecting inside the cement layer is pumped off through a discharge pipe 90 by lowering a skimmer 88. The end plate 22 is withdrawn by cylinder 31 operating lever 28 for inserting the mandrel 40, Fig. 7. The mandrel has axles at each end for lifting and allowing at least 360 degrees rotation, axle 42 being longer than the mould. The mandrel face is perforated with lines of holes connected to longitudinal chambers 44 selectively connectible by valves 55 to headers 48 and 49 supplying vacuum and pressurized air respectively for holding the cement sheet on the mandrel and then releasing the sheet during unrolling on to a surface 72 (Fig. 8, not shown). The sheet is slit by lowering the mandrel on to a blade (73) at one end of the surface (72). The sheet may be pressed between platens in a press and may be rolled out and pressed by the mandrel on to a platen which is curved or carries a design. The sheet may be sprinkled with aggregate or be rolled out on to a layer of aggregate or a previously formed sheet, the layers being bonded by pressing. A wire mesh liner may be placed in the mould initially and become bonded into the cement or removed for re-use. In Fig. 16-18 the charging arrangement is similar but the mandrel and mould are not perforated. The mould has a displaceable end ring 121 and a removable rubber liner 170 having a thickened portion adjacent the ring 121. A cement cylinder 149 is cast on to the liner with the ring 121 in its innermost position, and an expandable mandrel 140 rotatably mounted in carriage 144 is inserted until the ring 121 is displaced outwardly by spring loaded pin 166. At the same time a lever 163a on the mandrel is engaged by an arm 164 on the rotating mould causing rotation of the mandrel and opening a valve 163 to release pressurized air stored in hollow axle 144 into cylinder 161, Fig. 16, which expands the mandrel by operation of linkages 155, 158. Thus the mandrel engages the cement cylinder and a flange 142 on the end of the cylinder enters the space left by the ring 121 to engage the cement cylinder and the liner and facilitate their removal from the mould. The mould 141 and the liner 170 have longitudinal slits, Fig. 18b. Metal edge pieces 171 on the liner are held together by clips 175 (Fig. 14, not shown) which are removed after moulding, one of the edge pieces being engaged under a pallet edge 186 and the other held by clips 194 to the mandrel while the cement cylinder is slit by a wire band saw. Successive sheets are rolled out to form a stack, Fig. 18a, by raising walls 189 which act as guides for grooves in mandrel axles 145. A cover is fitted over the side walls 189 to form a steam curing chamber. In Fig. 20 and 22 a removable metal liner 240 has inwardly turned flanges 242 engaging a sealing strip 244. The flanges have two rows of holes, a first row 246b engaged by lines of hooks 247 mounted on the mould and operated by levers 248a, and a second row 246a similarly engaged by hooks in a recess in a mandrel 250a. Thus a liner 240 initially attached to the mould is released and attached to the mandrel after moulding. The liner is then attached to one end of a pallet by hooks engaging the holes 246b. No slitting is necessary because the flanges 246 form a longitudinal discontinuity in the cylinder. To form sheets with designs a metal liner having an embossed silicone rubber layer is used.  In Fig. 28, a mandrel with vacuum ports 270 for holding the cement cylinder has a recessed hook arrangement 256 for holding a member 275 which forms a longitudinal discontinuity in the cement cylinder. The skimmer may be omitted and the water inside the cylinder allowed to flow away through holes in an end plate which are opened by relative rotation of another plate having complementary holes.