Patent GB-301431-A (GB)
IPC: C21D9/00
Filed: 1928-11-29
Abstract: 301,431. British Thomson-Houston Co., Ltd., (Assignees of Ipsen, C. L., and McFarland, J. L.). Nov. 29, 1927, [Convention date]. Resistance furnaces.-In a tunnel furnace, particularly for brazing and annealing in an inert atmosphere in which the goods' 27 are carried through a heating chamber 13 and a cooling zone by trays 28 supported on idle rollers 25, 26, charging and discharging openings 18, 19, are arranged in the bottom of the furnace at the ends there of, and roller track 52 is provided for the passage of the trays of finished goods to a loading and unloading station below the entrance end of the furnace. The heating chamber 13 is lined with refractory bricks 12 separated from an outer shell 10 by a layer 14 of diatomaceous earth, the bricks 12 supporting electric heating-elements 15 and being arranged to provide restricted passages 13<a>, 13<b>, leading to and from 'the actual heating chamber 13. The cooling zone of the furnace is surrounded by a water-circulating jacket having supply and discharge pipes 23, 24. In connection with the openings 18, 19, are provided elevators 35, 36, fitted with rollers 46 which form continuations of the furnace rollers 25, 26 and are inclined downwardly towards the end of the furnace so that a tray 28 may be securely held by contact with a retaining-stop 46<a>. The elevators are formed with sand troughs 50 into which extend, when the elevators are raised, sealing flanges 49; the latter carry hinged doors 50<a> which are opened by a yoke 51 on the upward movement of the elevator and close by gravity when the latter descends. The elevators are supported by chains 37, 38 carrying counterweights and passing over pulleys 39, 40 mounted on shafts 41, the latter also carrying pulleys 42 on which are wound cables 43 secured at one end to the pulleys and at the other to pistons moving in compressed-air cylinders 44, 45. An hydraulic cylinder 47 is provided at the charging end of the furnace to operate a. ram 48 for pushing the train of trays 28 along the rollers 25, 26. The supply of fluid to the cylinders 44, 45, 47 is controlled by reversing-valves operated by handles 56, 57, 55 respectively. Locking-devices 62, 63, 61 are provided for the handles 56, 57, 55 and are interconnected and automatically operated so that the elevators 35, 36 and pusher 48 can only be actuated in the proper sequence. An automatic electric controller put into and out of operation by push-buttons 76, 77 respectively, is described for effecting movement of the locking- latches 61, 62, 63 at the appropriate intervals. Red and green signal lamps 95, 98 are provided to indicate when the pusher 48 reaches its fully extended and retracted positions. The trays 28 are formed in two parts, of which the upper is filled with powdered heat-insulating material 29 and the lower formed with a groove 32 and a flat-bearing surface 31 for engagement by the rollers 25, 26. The charge 27 is supported on upwardly extending metallic pins 30 to one pair of which is fastened a plate 30<a> adapted substantially to close the passages 13a, 13<b>, and so prevent escape of heat. A pedal-operated stop 52a is provided on the lower roller-way 52 so that trays may be kept stationary during unloading and re-loading. An inert gas, such. as hydrogen or a mixture of hydrogen and nitrogen, is supplied to the furnace through a pipe 53. When pure hydrogen or an explosive mixture thereof is used, and it is desired to shut down temporarily the furnace for repairs, the explosive gas is displaced by nitrogen supplied at 103. This latter conduit may serve for the escape of the tunnel atmosphere when the nitrogen is supplied through the pipe 53.