| 摘要 |
1,067,528. Asbestos-cement boards. JOHNSMANVILLE CORPORATION. March 1, 1965 [April 16, 1964], No. 8572/65. Headings D2A and D2B. [Also in Division F2] In a method of forming a fibrous sheet by deposition of a slurry on a conveyor the variation of thickness of the sheet across the width thereof is controlled by adding a flocculating agent at spaced locations to the slurry. The slurry contains asbestos fibres, cement, and silica. with the flocculating agent being as described in Specification No. 887,997, to form an asbestos-cement pipe by winding the sheet on a rotating mandrel 94, Fig. 10 (not shown), which has two rolls 106, 108 hydraulically pressed thereon, the rolls being permitted to rise as the pipe thickness increases. Alternatively an asbestos-cement sheet or board may be formed. As shown slurry flows over a weir 8 from a trough 2 containing a gate valve into a flow pan 20 having baffles 28 therein. The flocculating agent is supplied through piping 60 which has swivel joints so that nozzles 64, 65 may be positioned at the desired points. The slurry flows into vats containing two cylinder moulds which form a two-ply sheet on the conveyor. The flocculating agent may be added so that a sheet of uniform thickness is obtained-i.e. by counteracting any tendency for the apparatus to form a non- uniform sheet-, or so that a sheet having a greater thickness at the centre is obtained. |
