Abstract:
Presented is a heating element, and method for producing same, comprised of strip material having a length, width and depth where the strip material is twisted at least once axially relative to its length and bent at least once across its width resulting in a generally flat profile. The twists and bends provide for expansion and contraction of the heating element and thereby provide stress relief during heating and cooling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of provisional patent application Ser. No. 61/905,949, filed on Nov. 19, 2013 by the present applicants, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present application is directed to a pancake style flat electrically powered heating element that withstands quick heating and cooling with maximized area of radiation surface. Also presented is a method to relieve stress related to rapid temperature change and exposure to liquids and vapor through the utilization of twists and bends in heating elements. 
         [0004]    2. Prior Art 
         [0005]    Flat heating elements bent to meet specific profiles are well known in the art. Often, such flat elements with bends are subjected to stresses upon rapid heat-up and exposure to liquids, such as water, or vapor, such as steam. These stresses may cause bowing, bending or failure of the elements. If a flat configuration is needed, the stresses may bow or warp the element from its initial flat condition. An element is needed that can withstand these stresses and retain an original configuration. It is also desirable that such elements have a maximized area of radiation surface. 
       SUMMARY 
       [0006]    This application consists of a heating element comprising a strip of heating element material, the strip comprised of at least one twist and at least one bend along the length of the strip. The strip may be rectangular in cross-section, but may also be other geometric shapes such as square, triangular, round, octagonal, etc. The at least one twist and at least one bend may be configured to provide any desired two-dimensional overall element shape or profile including, but not limited to, round, rectangular or square. The element may be generally flat on one side (the top or bottom face) but the twists and bends may also provide a depth and different three-dimensional configurations. 
         [0007]    The combination of twists and bends will help to relieve stresses caused by rapid heat-up, rapid cool-down and liquid or vapor contact. The twists and bends themselves expand and contract and may act to prevent overall deformation of the element. The twist and bend areas are provided by their geometry with room to contact or expand and may deform, but the flat surface of the element will not deform and the overall flatness and shape of the element will remain the same. Along with stress reduction or absorption, the twists also provide a surface that maximizes the radiation surface of the element. The disclosed element overcomes the common problem of breakage of heating element configurations having different section (leg) lengths. 
     
    
     
       DRAWINGS—FIGURES 
         [0008]      FIG. 1  is a top view of an embodiment of the flat heating element. 
           [0009]      FIG. 2  is a perspective view of an embodiment of the flat heating element. 
           [0010]      FIG. 3  is a side view of an embodiment of the flat heating element showing the twists. 
           [0011]      FIG. 4  is a side view 90° in relation to the side view if  FIG. 3  of an embodiment of the flat heating element showing the bends. 
       
    
    
     DRAWINGS—REFERENCE NUMERALS 
       [0012]      
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10. flat heating element 
                 20. strip material 
               
               
                   
                 30. initial twist 
                 35. return twist 
               
               
                   
                 40. bend 
                 50. return leg 
               
               
                   
                 55. terminal leg 
                 60. bottom face 
               
               
                   
                 70. top face 
                 80. terminal 
               
               
                   
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0013]    According to  FIGS. 1-4  the heating element of an embodiment  10  comprises flat strip material  20  having a length, width and depth. At a desired point from the end of the strip  20 , the strip  20  is twisted counter-clockwise axially along its length at a specific angle relative to an original position)( 0 ° of the width of the strip forming an initial twist  30 . The strip is than bent across its width at a radius greater than the width of the strip  20  in a manner so that the strip forms a bend  40  and returns toward the initial twist  30 . The twists and bends of the strip  20  may be performed when the strip  20  has been heated or when it is at room temperature depending on the material comprising the strip  20 . After heating, the strip  20  may be allowed to air cool or may be quenched depending on the material comprising the strip  20 . Jigs may be used to hold and position the strip  20  during twisting and bending. At a point in the length of the strip  20 , opposite of the initial twist  30  as the strip returns towards it (at 180°), the strip  20  is twisted again, but clockwise axially along the length of the strip  20  in a return twist  35  at an angle opposite of the angle of the initial twist  30  forming a return leg  50 . (For example, in a preferred embodiment, the initial twist  30  is at 90° relative to the width of the strip  20  and the return twist  35  is at −90° relative to the width of the strip  20 .) Alternatively, the initial twist  30  may be clockwise and the return twist  35  may be counter-clockwise. Due to the radius of the bend  40  being greater than the width of the strip  20  and the initial twist  30  being opposite to the return twist the return leg  50  of the strip will be roughly parallel to the original terminal leg  55  without touching it and within the same plane to give a roughly flat bottom surface  60 . The nearer the twists are to 90°, the flatter the bottom surface  60  will be. This bottom surface  60  may be placed upon a ceramic plate or other surface or material for support. 
         [0014]    At a designated point past the end of the strip  20 , the strip  20  is twisted again at the same angle of the initial twist  30 . Then a bend  40  of a like radius is made, returning the strip  20  towards the preceding initial twist  30  where another return twist  35  at an opposite angle is made. The flat strip  20  then returns parallel to the first and second flat sections (return leg  50  and terminal leg  55 ) of strip  20 . This process is repeated a specified number of times and with the lengths of flat strip  20  being at different lengths until the desired shape or profile is created such as the generally round profile of  FIG. 1 . As can be seen with  FIGS. 3 and 4 , the side of the element in contact with a bottom face  60  is roughly flat. The alternating initial twists  30  and return twists  35  (at 180° to each other) provide this configuration. When the twists are at 90°, the face of the element opposite the ceramic or other support surface, or top face  70 , has a non-flat surface with edge, or depth face of the strip  20  at the bends  40  being above the flat width surface of the strip  20 . 
         [0015]    The element  10  is connected to a power source near each end, or terminal leg  55 , by a terminal  80 . The terminals  80  are connected to an appropriate electric power source not pictured. Direct connection of a power source to the terminal legs  55  is also anticipated by the applicants. As explained above, the twists  30  and bends  40  will expand and contract and relieve the stress and subsequent deformation normally suffered by the element geometry as a whole. 
         [0016]    While the embodiment of  FIG. 1  discloses a flat sided element with parallel strips in the same plane and opposing twists and 180° return radii in a round overall configuration it is anticipated that other orientations are possible and anticipated. The twists may be 90° in the same direction to create a non-flat surface on both sides. Any twist angle over 5° is anticipated. The radii may be over 180° to allow the strips to splay out and not be parallel. The radii may also be less the 180° if desired. Other two-dimensional geometrical shapes or profiles may be formed by appropriate leg lengths. Such profiles are designed to cover and provide a heat zone for a specific two-dimensional area, such as a circle as in the case of the embodiment present in  FIG. 1 . Three-dimensional configurations including elliptical and spherical may be created by altering the twist angles and bending the strip legs out of flat. The element may also be expandable at the bends by increasing the radius thus further splaying out the legs. 
         [0017]    The flat surface defined by the bottom face  60  may be placed upon a ceramic or other surface to support the heating element. In other embodiments a support surface may not be necessary. A flat surface is obtained by each twist being in an opposite direction from the preceding twist (90° and −90°). In such a configuration the opposite side will not be flat. 
         [0018]    It is anticipated, as well, that the disclosed heating element may be composed of any appropriate material capable of being formed (bent, twisted or cast, etc.) in such configurations. The flat strip material may be heated or not before twisting or bending depending on the specific material. Anticipated materials include all grades and types approved for medical use such as stainless steel, steel, T91, 304H, CC or Inconel. Other anticipated element materials include, but are not limited to, nickel-chrome (NiCr), iron-chromium-aluminum (Fe—Cr—Al), silicon carbide (SiC), molybdenum, tungsten, zirconium and molybdenum disilicide (MoSi 2 ) or any coated with colloidal alumina or Al—O or Al—O—H compounds. 
         [0019]    The above descriptions provide examples of specifics of possible embodiments of the application and should not be used to limit the scope of all possible embodiments. Thus, the scope of the embodiments should not be limited by the examples and descriptions given, but should be determined from the claims and their legal equivalents.