GB577714A - Improvements in or relating to thermostatic metals - Google Patents

Abstract

577,714. Thermostats. MALLORY METALLURGICAL PRODUCTS, Ltd. April 6, 1944, No. 6428. Convention date, April 10, 1943. [Class 64 (ii)] [Also in Groups II, XXII and XXXVII] A bimetallic element for thermostats con. sists of a strip of low expansion metal, e.g., that known under the registered Trade Mark " Invar," and a strip of high expansion silver alloy containing, e.g., 0.1- 10 per cent. of nickel. 2-35 per cent. of copper ; and the balance of silver. The low-expansion metal may be a 42 per cent. nickel steel; or an alloy of, e.g., 28 per cent nickel, 18 per cent. cobalt and 54 per cent. iron ; 31 per cent. nickel, 5 per cent. cobalt and 64 per cent. iron ; or 8 per cent. chromium, 30 per cent. nickel, 25 per cent. cobalt and 37 per cent. iron. The high expansion alloy may consist of 2 per cent. nickel, 21 per cent. copper, and 77 per cent. silver. A small percentage of zinc, tin, beryllium, antimony, aluminium, cadmium, magnesium, indium, manganese, silicon or iron may be added in place of a corresponding percentage of silver. The percentage of zinc or tin may be from 3 to 5, and of indium, manganese, silicon or iron from 0.05- 5. Beryllium is stated to be most beneficial from 0.25-1.5 per cent. where the copper content is from 20- 30 per cent., and aluminium from 1.5- 5 per cent. where the copper content is from 2- 5 per cent. The bimetallic element may be made by passing the low expansion strip through a furnace together with the silver alloy strip. The latter strip is fused and passes with the other strip into a cooling zone where the silver alloy solidifies and the compound strip may then be cold rolled. In a modification, the silver alloy strip may be formed on the low-expansion strip by electron depositions. The strips may be made from metallic powders. Thus, the high expansion strip may be made by mixing silver, copper and nickel powders and pressing, sintering and working them, the strip being bonded to the low expansion strip and the two rolled together to the required dimensions. The silver alloy strip 21, Fig. 3, and the strip 23 of low-expansion alloy may be passed through furnaces 22, 24 respectively and bonded together by a strip 27 of, e.g., silver solder, the bond being, effected by rollers 25, 26. In another arrangement, the strips are preheated in a reducing atmosphere, preferably in independe it furnaces, so that they can be heated to different temperatures, and bonded together by passing between pressure rollers. A ternary element may be formed by interposing a strip of brass, cadmium, copper, phosphor bronze, silicon bronze or a copper alloy, such as copper or silver brazing material, between the high and the low expansion strips. A thermal switch may comprise a low expansion strip 10, Fig. 1, bonded to a high expansion silver alloy strip 11, the compound strip being secured to a metal bar 12 carrying an electric contact 15.