Patent GB-892691-A (GB)
Title: Method of and apparatus for corrugating sheets of fibrous cement
IPC: B28B1/52
Filed: 1960-06-10
Abstract: 892,691. Moulding corrugated fibrous cement sheets. EURASBEST A.G. June 10, 1960 [June 10, 1959; Nov. 16, 1959], No. 20482/60. Class 87(2). Prefabricated fresh sheets of fibrous cement are corrugated, as shown in Fig. 2, by placing a flexible layer 10 of fabric or the like penetrable by air over the corrugated cover 2 provided with suction holes 3 of a rigid suction box 1, tensioning transversely to the corrugations the flexible layer 10 on which is placed a fibrous cement sheet 6, and exposing the sheet 6 together with the layer 10 to the action of a vacuum at first in one longitudinal zone of the sheet and subsequently in other longitudinal zones so as to draw the sheet 6 towards the cover 2 and form corrugations in it. The suction box 1 is divided into chambers 5 by partitions 4, each chamber being connected through a valve, manual or automatic, to a suction pipe leading to a vacuum generator. To prevent any structural change of the critical vertex regions of the crests of the corrugated sheets due to their being acted upon by the vacuum, the zones of the cover 2 extending along the vertex lines are free from holes 3. In another embodiment, Fig. 3, the corrugation vertices are provided by rolls 16, the cover being completed by cover strips 2<SP>1</SP> bent into U-shape and provided with suction holes 3 with narrow slots 17 being left between the strips 2<SP>1</SP> and the rolls 16. The rolls 16 may be rotatably supported on the walls 1<SP>1</SP> of the suction box 1 and, if necessary, driven synchronously. The partitions 4 terminate a short distance below the rolls 16 against which they are sealed by rubber strips 18. A modification comprises the provision of a channel 20 below each trough of the cover 2. As soon as each corrugation is effected by the action of a 30% vacuum in the chambers 5, the channel 20 is connected to a strong vacuum of about 80% which helps to condense the fibrous cement material of the corrugation trough. Preferably, the corrugation in the centre of the sheet is first formed and then successively two further corrugations at a time are formed on either side of the centre. The flexible layer 10 may be tensioned by means of metal bars inserted into hollow seams at its longitudinal edges, the weight of the bars being sufficient for the layer when stretched to support the plane sheet of fibrous cement placed on it. A mechanically or electrically operated looking device holds the metal bars in their raised position after corrugation while the corrugated sheet is removed. Alternatively, as shown in Fig. 4, the flexible layer 10 may be secured to tensioning rolls 22, 22<SP>1</SP> rotatably supported on the walls 1<SP>1</SP> of the suction box 1 and be attached by piston rods 36, 36<SP>1</SP> to loading weights 33, 33<SP>1</SP> movable in cylinders 34, 34<SP>1</SP>. The torque of an electric motor 30 is transmitted to sprocket wheels 24, 24<SP>1</SP> and thence to rolls 22, 22<SP>1</SP> through the driving pinion 29, endless chain 28, sprocket wheel 27, and chain strands 32, 32<SP>1</SP>. The raising and lowering speeds of the weights 33, 33<SP>1</SP> can be regulated by adjusting air inlet and outlet valves 38, 38<SP>1</SP> on the cylinders 34, 34<SP>1</SP>. In this embodiment, the crest of the centre corrugation is formed, not by a roller 16, but by a cover strip 2a provided with suction holes.