GB495832A - Improvements in or relating to the manufacture of electric fuzeheads such as are used, for example, in blasting detonators - Google Patents

Abstract

495,832. Electric fuzeheads; compound sheet materials. TAYLOR, W., HALL, C. R. L., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. May 18, 1937, No. 13904. [Class 9 (i)] [Also in Group VIII] A process for the manufacture of metalfoil-coated sheets or boards of insulating- material, suitable for use in the manufacture of low-tension electric fuzeheads for blasting- detonators, comprises preparing one face of a sheet of brass foil by an etching treatment and thereafter attaching the foil by its prepared surface to a sheet or board of insulating-material by means of a thermoplastic cement. The etching treatment consists in treating the foil with ammonia, preferably in aqueous solution, under oxidizing conditions until a black coating forms, treating the superficially-oxidized foil with an aqueous solution of ammonium chloride or like acidic salt, or with a concentrated aqueous solution of a caustic alkali preferably at raised temperature, until the superficial coating is completely converted into a loosely adherent deposit and thereafter removing the deposit by washing, with or without abrasion, and drying the etched foil. In carrying out this treatment, two strips of brass foil may be placed in contact and rolled up in a spiral with a reticulated spacer adapted to maintain the sheets of foil in contact on the inner surfaces and thus substantially to prevent the access of liquid to the juxtaposed surfaces while permitting the access of the liquids to the exposed surfaces. If desired, the treatment with the discharging salt solution may be carried out in two stages with an intermediate washing. The thermoplastic cement may be applied to the etched surfaces by means of a volatile solvent and the cemented faces of the foil are then brought into contact with the pressboard sheet and caused to adhere thereto by the application of pressure at a raised temperature. If it is desired to coil up and store the coated foil, a thermoplastic cement of such a nature that the coating is not tacky at room temperature is employed, e.g. a solution of polyvinyl acetate in a volatile organic solvent such as a mixture of benzene and alcohol. The cement may, however, be applied to the presssboard instead of to the etched metal surfaces. In the manufacture of low tension electric fuzeheads, combs are stamped out from the composite sheet and the metal coating on one side at the tips of the combs and the insulating layer immediately underneath may be milled away as described in Specification 495,833 so as to provide steps for the bridge wire of each tooth.