Patent GB-1427676-A (GB)
Title: Heating element and heater
IPC: D06F58/26
Filed: 1974-03-05
Abstract: 1427676 Resistance heating element NIPPON GAISHI KK 5 March 1974 [9 March 1973] 9869/74 Heading H5H A P.T.C. ceramic heating element 1 with a large surface to volume ratio between 10 to 60 cm.<SP>2</SP>/cm.<SP>3</SP> has a honeycomb structure i.e. it has a plurality of parallel channels 2 extending therethrough. As shown, the element 1 is cylindrical and the channels 2 extend between end faces provided with current supply electrodes 4, 5. The channels may be of triangular, hexagonal, any other polygonal, or circular cross-section. The heat element 1 may be rectangular or polygonal in cross-section. The supply electrodes may be mounted on surfaces of the element other than those in which the channels 2 terminate. The element may be made of BaCO 3 , TiO 2  SiO 2  and La 2 O 3  which are calcined, pulverized, screened and dried before being blended with methyl cellulose, polyvinyl alcohol water solution, polyethylene glycol and water. The mixture was extruded through a "honeycomb" nozzle of a de-airing pug mill, and the "green" body obtained was freeze dried before being finally fired. Various other ceramic compositions may be used. In an alternative method of fabrication the honeycomb structure was produced by firing a bundle of green P.T.C. pipes together, or by coating ceramic particles suspended in an organic binder on the surface of a sheet of paper, corrugating the coated sheet of paper, folding the corrugated paper to produce superposed corrugated layers, and firing the superposed layers to leave a ceramic honeycomb structure in the manner disclosed in U.S. Specification 3,112,184. The electrodes may be formed by flame sprayed aluminium, an indium amalgam, electroless nickel plating, fired silver, fired gold, ultrasonic soldering with indium amalgam, or with a hypoeutectic alloy of nickel and indium. A silver paste comprising silver, zinc, glass powder and an organic solvent is screen printed on to the resistor 1 and baked to form the electrodes. Aluminium is hot sprayed on to the resistor to form the electrodes, the spray direction being inclined by an angle of 10 to 60 degrees to the end surfaces through which the channels extend to prevent clogging. Similarly, in electroless nickel plating, the honeycomb structure is immersed in silicone resin or wax to mask it, the electrode surfaces are ground to remove the mask and, the body is placed in a nickel salt path to form the electrodes. A plate resistor having a honeycomb structure and supplied by annular terminal plates is incorporated in an air heater. In Fig. 7, a rectangular section honeycomb resistor 1 is spaced from a housing 22 by thermal insulation 21 and heats fluid passed therethrough by pipes 19, 23. The heating element 1 may be coated with corrosion resistant material, e.g. P.T.F.E., fluorine rubber, silicone resin, silicone rubber, or silicone varnish to enable it to be used with corrosive acids or alkalis. Alternatively each channel may be lined with a stainless steel pipe. The heater of Fig. 7 may be used for heating liquid fuel, for preheating oil, or in a beverage maker. In Fig. 8 (not shown) a humidifier comprises a disc shaped honeycomb resistor mounted on a water absorbing mat provided with a wick dipping in a bowl of water. A plurality of heating elements may be connected in series and/or parallel with conventional nickel chrome heaters. The heater may be incorporated in a hair dryer or a hot air hand drier.