Patent GB-385629-A (GB)
Title: Improvements in and relating to methods of and apparatus for producing hard metal compositions
IPC: B22F3/14
Filed: 1931-06-19
Abstract: 385,629. Inertia switches and switches, partly magnetic. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Taylor, G. F.; 115, Balltown Road, Niskayuna, New York, U.S.A.) June 19, 1931, No. 17815. Convention date, June 19, 1930. [Class 38 (v).] In a process of making hard metal compositions of the character described in Specifications 231,524 and 251,929, [both in Class 82 (i), Metals, Extracting &c.], by simultaneously pressing powdered materials and heating them by electricity to sintering temperature, a substantially cold mould of electrically insulating material is used in a closed chamber in which is maintained a vacuum or an attenuated atmosphere of an inert gas such as hydrogen. The powdered material 33, for example tungsten carbide and cobalt, is placed between steel or molybdenum plungers 23, 24, in a mould 22 made of glass, porcelain, magnesia, thoria, &c. and held inside a glass cylinder 2. After flushing out with hydrogen from a pipe 21, the cylinder is evacuated through a pipe 20. An electric current passing through conductors 27, 28, and through the powder, heats it almost instantly to its sintering temperature, and simultaneously atmospheric pressure alone or supplemented by a load on a lever 30 bearing on a bellows 10, causes a member 11 to move downwards to compress the powder. At the end of the movement the current may be cut off manually, or automatically by means of a mechanical device, such as clock-mechanism, an inertia switch, or an electrical control system set into operation by the movement. To initiate a flow of current through the material 1, a condenser 37 may be discharged through it by closing a switch 40 to reduce its resistance. On closing a switch 41 a current may then pass through the material from a transformer 56. If an electrical control system is employed an inertia switch 43 is mounted on the end of the lever 30. On closing a pushbutton switch 57 a coil 58 is energized from a main 59, and closes through contactors 62, 63, the primary circuit of the transformer 56, a maintaining circuit for the coil 58 being at the same time completed through contactors 65, 66, and a switch 60, from a main 61. A condenser 53<1> and the grid 54 of an arc discharge device 55 are negatively charged from a battery 53. When on sintering the material, the lever 30 drops, the armature 45 of the inertia switch 43 passes from a magnet 46 to a magnet 47, disengages contacts 49, 50, and engages contacts 51, 52, to join the positive side of the battery 53 to the condenser 53<1> and the grid 54. The discharge device 55 is made conducting when the negative charge on the grid 54 is reduced to a certain value, or when a desired positive charge is built up on the grid, a coil 68 then becoming energized and opening the maintaining circuit for the coil 58 at the contactor 56. When the maintaining circuit for the coil 58 is opened, the circuit for the primary winding of the transformer 56 is interrupted at the contactors 62, 63, and current ceases to flow through the pressed material. The time of flow of the current through the material after the member 11 reaches the end of its travel is determined by adjustment of a resistor 67, the capacity of the condenser 53<1>, and the characteristics of the discharge device 55. Specifications 113,835, 288,521, and 289,477, [all in Class 82 (i), Metals, Extracting &c.], also are referred to.