Patent GB-1432377-A (GB)
Title: Heater devices
IPC: H05B3/18
Filed: 1972-10-19
Abstract: 1432377 Resistance heater J G BEDFORD 20 Dec 1973 [19 Oct 1972] 48193/72 Heading H5M A heater device comprises a metal sheathed mineral insulated heating cable embedded in a cementitious body and maintained in a preferred configuration by attachment to embedded metal reinforcement, the body being formed by hardening a mixture of water and "high" aluminium oxide hydraulic cement. The "high" aluminium oxide cement may be "CIMENT FONDUM" Registered Trade Mark or LIGHTNING Registered Trade Mark containing between 38-40% by weight of Al 2 O 3 . Alternative "high" aluminium oxide cements may contain between 40-80% by weight of Al 2 O 3 , e.g. SECAR 250 Registered Trade Mark. Aggregate of high thermal conductivity, e.g. marble chips or marble flour and a filler, e.g. unfine cement clinker may be incorporated. Fibrous reinforcement such as carbon, silica or glass fibres may be added. Magnesium, calcium and ammonium lignosulphate plasticizers and a wetting agent, e.g. sodium alkyl aryl sulphonates may be incorporated. A compatable synthetic resin, e.g. p.v.c. or acetate emulsion to improve flexibility may be added. Pigments may also be used. Preferably the mineral insulated metal sheathed cable, a resistance wire of copper, copper alloy or nichrome and a sheath of copper, aluminium, stainless steel or cupro-nickel. The cable is secured to an earthed metal reinforcement, preferably in the form of a grid or expanded metal sheet, by ties, and a similar sheet secured to it to sandwich the cable between the sheets. Such an assembly may be placed in a mould and embedded in a cement paste or in a dry cement mix to which water is later added from the bottom. Curing may be at ambient conditions, in an oven or preferably by passing current pulses through the cable. Cold tails are provided. These may be in the form of metal sheathed mineral insulated cable or double glass insulated flex. A junction box may be used, the cold tails then being connected directly to the mains. The joint between the heating cable and wiring cable may be silver soldered and covered with synthetic resin, e.g. silicone resin. The cable is preferably laid in the form of a rectangular spiral to the middle of the sheet, and then a concentric spiral from the middle to the outside of the sheet. Such an arrangement with a suitable switch enables three-heat operation. Overheating protection is provided by a thermal cut-out of the self resetting type inserted in one cold tail. A thermostat mounted on or adjacent a heater panel may be provided. Holes to take mounting bolts may be provided through the panels. A panel may be tiled with metal ceramic or glass. Decorative finishes of materials having incompatible thermal expansions may be provided for panels by enclosing the cement block in a box or tray of the decorative material and providing contact and heat transfer through a thin powder film of, e.g. marble flour or talc, to allow slipping to occur on expansion. Panels may be attached to the fabric of the building with a small space therebetween or incorporated in the fabric of the building. The panels may be formed as part of folding screens, as bath panels or as furniture. In the latter case the heater is shaped as a cylinder, cube or support column for a table lamp or the like.