Patent GB-742251-A (GB)
Title: Electric resistance heating devices
Inventor: EISLER PAUL
IPC: H05B3/78
Filed: 1952-08-08
Abstract: 742,251. Electric resistance heaters. TECHNOGRAPH PRINTED CIRCUITS, Ltd. July 16, 1953 [Aug. 8, 1952]. No. 20053/52. Class 39(3). A heater for use as immersion heater, a spaceheating device of the radiation or convection type, as a wall of a water tank, as a booster heater for liquid-filled radiators or for cooking vessels, comprises an electric resistance element 16 of metal foil spaced by layers of liquidpermeable material within and parallel to the walls of a jacket at least part of which is heat conductive and forms the heating surface, the jacket being filled with a liquid which is an electric insulator and which transmits heat from the resistance to the walls of the jacket. The liquid may be transformer oil or a silicone oil and may be highly viscous or a gel at room temperature. The resistance comprises a thin metal foil formed with slots by stamping or by a "printed circuit" technique. The slots are formed transversely of the strip 16 and are staggered as in Fig. 4, the edges 16c of the strip being finally removed to form short slots 16b at the edges. Thin layers of porous or waterpermeable insulating material, e.g. porous paper, woven or felted glass wool or other insulating fibres, are wrapped round or sewn to the resistance. When one wall of the jacket does not form a heating surface, it is heatinsulated by lagging on the inner or outer surface of the wall or by forming it as a double wall enclosing a dead air space. In Fig. 1 a washing machine has a wide strip of metal 12 bent to a U to form the bottom and two sides of a tub, and the edges of the strip are bent at 13 to form shallow flanges to which a U-shaped metal strip 15 is welded to form the outer wall of the jacket containing the foil heater 16 sandwiched between glass cloth layers 17 covered by porous glass wool mats 18 further covered by outer glass cloth layers 19. The insulating layers are sewn together at 22 above the element 16. The inner layers of glass cloth are continued up to form a loop 23 which carries a rod 24 and fits into a recess in a sealing neoprene strip 25 set firmly between a groove 26 in the outer wall 15 and the inner wall 12. The element is held under tension by resilient strips 27 of neoprene or the like sewn at 28 between the inner cloth layers. The leads to the resistance pass through a flexible grommet.sealed in one corner of the jacket. Heat lagging is placed on or a further U-shaped strip is spaced from the outer wall of the jacket to prevent heat loss outwards. The heater may be mounted on the inner surface of a tank or may be a flat immersion heater. The resistance may be in two parts for connection in series or parallel. The heater may be formed as a dish or pan with a wholly metal jacket for use as a cooking vessel or as a wholly or partly immersed immersion heater. The insulation may be thicker towards the outer side of the outer pan and a layer of glass cloth may be bonded to the inner side of the outer wall. The resistance may be connected through an insulating lug to a terminal plug, which may be connected to a detachable lifting handle. The device may be of such form as to be inserted into the liquid space of a radiator. According to the Provisional Specification the resistance comprises many thin wires connected in parallel.