GB604591A - Improvements in, and in methods of making, wire drawing dies - Google Patents

Abstract

604,591. Powder metallurgy; making drawing-dies. CALLITE TUNGSTEN CORPORATION. March 6, 1945, No. 5606. Convention date, Jan. 13, 1944. [Classes 83 (ii) and 83 (iv)] [Also in Group II] A method of making a wire-drawing die comprises grinding a nib to provide parallel sides, placing the nib on a central support in a mould, pouring metal powder into the mould over and around the nib, compacting the powder, removing the compact and nib from the mould and sintering to form a dense metallic mount for the nib and then drilling a die opening through both the mount and the nib. A diamond 1 which is to form the nib of the die is ground with upper and lower faces 3, 4, and window faces 5 and 6 and is formed with a conical recess 2 in its lower face. It is then placed in a mould where it rests on a support 7 and is positioned by a needle 17 entering the recess 2. Rods 14 and 15 are inserted between the window faces 5 and 6 and the sides of the mould and a quantity of metal powder 20 is poured in and compressed by a plunger 21 at a pressure of from five to twenty tons per square inch. A conical nipple at the bottom of the plunger forms a recess 23 in the top face of the compact which is removed from the mould and heated in a dry hydrogen atmosphere for half-an-hour at a temperature of from 300-400‹C. This step is followed by the final sintering for half-an-hour also in a dry hydrogen atmosphere. The rods 14, 15 may be of a plastic, which will vaporise under the heat treatment or may be of graphite within a nickel sleeve, the graphite being subsequently drilled out or burned out. Lateral openings are thus left through the die to enable the drilling of the nib to be observed. Starting from the recess 23, the upper part of the mould is drilled and finally the diamond is drilled. The metal powder may be a bronze, comprising 80 per cent copper and 20 per cent tin or brass comprising 60 per cent copper and 40 per cent zinc, in which case the final sintering temperature would be just below the melting-point of the alloy. Preferably, a heat and alkali resistant alloy is used, comprising nickel 64.8 per cent; copper 24.3 per cent; chromium 0.9 per cent and silver 10.0 per cent. To prepare this alloy, 90 per cent nickel powder and 10 per cent chromium powder of 200 mesh or finer are mixed and sintered and then crushed and ground to a fine powder. A mixture of 70 per cent nickel and 30 per cent copper is similarly treated and the two alloy powders thus produced are mixed in the proportions 1 per cent to 20 per cent of the first and 99 per cent to 80 per cent of the second. 90 per cent of this mixture is mixed with 10 per cent silver to form the alloy powder which is poured into the mould. The chromium may be replaced by zirconium, beryllium or aluminium. The final sintering temperature is from 800‹ C.-900‹C. In a modified form, the diamond may be replaced by a nib of tungsten carbide, in which case the rods 14, 15 are omitted from the mould assembly.