GB411331A - Improvements in and relating to acoustic diaphragms and to the manufacture thereof - Google Patents

Abstract

411,331. Diaphragms. McKAY, R. F., Fort Dunlop, Birmingham.-(International Latex Processes, Ltd. ; 10, Lefebvre Street, St. Peter's Port, Guernsey, Channel Islands.) Aug. 31, 1933, No. 24139. [Class 40 (iv).] Acoustic and like diaphragms, preferably of conical form, are manufactured from a mixture of cotton fibre or wood pulp, together with a binder of a natural rubber dispersion produced from natural latex. Trinidad asphalt and resins may be added as fillers. The cotton fibre or wood pulp is beaten up with water in a paper-maker's beating-machine, after which a small amount of alkali may be added, followed by the latex. A dilute solution of an acid or acid salt is then added after thorough mixing, in order to form a binding coating of the latex all over the fibre or the pulp. The liquid thus formed is circulated through a vat 1 and maintained at constant level therein. A reversible frame, carrying oppositely-disposed rows of moulds 12 connected through pipes 9 to suction apparatus 42, is raised out of and lowered into the tank on guides 3 by fluidpressure piston-apparatus 18, 19 controlled by valves 22-25 operated by a cam-actuated lever 26. When the lever 26 is raised to open the valves 22, 23, fluid pressure is admitted to the pistons to raise the moulds, while when the lever is lowered, the exhaust valves 24, 25 are opened to allow the moulds to descend by gravity. By reversing the mould-carrying frame one set of moulds can be removed or the articles stripped therefrom while the other set is being dipped. The rate of withdrawal of the moulds can be varied at different points to vary the thickness of the deposit at different points of the diaphragm. The moulds preferably are removed and passed through a hot-air drying-apparatus while the diaphragms are still on them. Finally the dried diaphragm is pressed in heated finishing dies which may also impress a pattern or design upon parts of it. The periphery of the diaphragm may be corrugated and the rim and apex may be dipped into latex before being pressed in the dies. Specification 359,950, [Group V], is referred to.