Patent Publication Number: US-6216334-B1

Title: Electric heater and method of manufacture

Description:
This invention relates to a flexible electric heater and a method of manufacturing such a heater. 
     DESCRIPTION OF PRIOR ART 
     GB-A-1 569 588 (E.G.O. Elektro-Gerate Blanc u. Fischer) describes an electrical radiation heater for a glass ceramic plate in which anchoring tabs formed at the lower edge of a heating conductor strip pass entirely through an annular sheet and are bent over in a region below a notch formed in each tab in order to hold the heating conductor strip against the sheet. The annular sheet has the structure of a relatively strong cardboard material made from a high temperature-resistant insulating material. The material of the sheet is a fibrous insulating material which is combined with a ceramic binder to form an insulating board, such as that sold under the Registered trade Mark FIBERFRAX. The tabs are sufficiently strong to pierce the board-like material of the annular sheet and a rotary tool is then used to press down the lugs formed beyond the notches against the underside of the annular sheet. 
     The disadvantage of such a bound fibrous support is that it is brittle and lacks flexibility. Therefore the support tends to break if any attempt is made to flex the same. 
     OBJECT OF THE INVENTION 
     It is an object of the present invention to provide an electric heater which is relatively flexible. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention there is provided a flexible electric heater comprising a heat resistant support of sheet or tape form having at least one electrical resistance heating element secured thereto, the at least one heating element comprising a ribbon of electrical resistance material provided with a plurality of integral tabs extending therefrom, the tabs having been pressed through the support, wherein the support is flexible and comprises a woven fabric material or a non-fibrous material. 
     The tabs of the ribbon may protrude from a rear surface of the support and may be deformed at that rear surface, such as by being bent, twisted or buckled. 
     According to another aspect of the invention there is provided a method of manufacturing a flexible electric heater comprising: 
     providing a heat resistant support of sheet or tape form; 
     providing at least one electrical resistance heating element comprising a ribbon of electrical resistance material provided with a plurality of integral tabs extending therefrom; and 
     urging the tabs of the ribbon through the support to secure the heating element to the support 
     wherein the support is flexible and comprises a woven fabric material or a non-fibrous material. 
     The tabs may be urged through the support from a front surface thereof such that they emerge from a rear surface of the support and are deformed at the rear surface, such as by bending, twisting or buckling. 
     During urging of the tabs of the ribbon through the support, plate means may be provided in contact with the rear surface of the support, the emerging tabs being deformed against the plate means. 
     The plate means may comprise a substantially firm or hard material, such as metal, plastics or rubber. 
     The ribbon may be provided with the plurality of tabs extending edgewise therefrom. 
     The tabs may be arranged such that the ribbon is secured edgewise to the support. 
     The ribbon may be provided of corrugated form. 
     The support may be of any suitable flexible heat resistant sheet or tape form material, of woven fabric material or non-fibrous material, capable of having the tabs of the heating element pressed therethrough and capable of withstanding the operating temperature conditions of the heater. 
     The support may comprise flexible non-fibrous mica or may comprise woven glass fabric or woven ceramic fabric. 
     The invention is now described by way of example with reference to the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged perspective view of a portion of corrugated ribbon form electrical resistance heating element for use in a heater according to the invention; 
     FIG. 2 is a plan view of a heater according to the invention incorporating the heating element of FIG. 1; and 
     FIG. 3 is a side view of the heater of FIG.  2 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     A radiant electric heating element  1  for a flexible radiant heater according to the invention comprises a corrugated ribbon  2  of bare electrical resistance material, such as iron-chromium-aluminium alloy, provided along its length with a plurality of tabs  3 , the tabs extending edgewise from the ribbon and integral and substantially coplanar therewith. The tabs may be substantially rectangular or triangular in shape with each side of the tabs being continuous, that is without deformations such as notches. 
     A flexible support  4  for the heating element is provided of sheet or tape form and comprises a suitably heat resistant material such as flexible (non-fibrous) mica or woven glass fabric or woven ceramic fabric. An example of woven ceramic fabric is Nextel (Registered Trade Mark) 312, manufactured by 3M Co. 
     The corrugated heating element  1  is pre-formed into a meandered shape and located with the corrugated ribbon edgewise on the flexible support  4  and with the ends  5  of the tabs  3  in contact with a front surface of the support. Using a simple press tool, pressure is applied between the ribbon  2  and the support  4  to urge the tabs  3 , end  5  first, through the support  4 . The tabs  3  protrude from a rear surface  6  of the support and are bent over or twisted or caused to buckle, as shown in FIG. 3 whereby the heating element is secured to the support  4  with the corrugated ribbon  2  edgewise thereon. The press tool includes a plate  10  of a substantially firm or hard material, such as metal, plastics or rubber. During urging of the tabs  3  through the support  4 , the plate  10  is arranged to contact the rear surface  6  of the support and when the tabs  3  emerge from the rear surface they are deformed against the plate, i.e. bent over, twisted or buckled, thereby securing the heating element to the support. 
     For the sake of clarity, the portion of the heating element  1  shown in FIG. 1 is a detail of a section represented by reference numeral  7  in FIG.  2 . 
     The resulting heater may be flexed into any desired shape according to its required application, with the ends  8 ,  9  of the heating element arranged for electrical connection to an appropriate voltage source.