Flat heating element comprising twists and bends and method thereby to relieve heating element stress

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.

BACKGROUND

Field

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.

Prior Art

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

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.

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.

DETAILED DESCRIPTION

According toFIGS. 1-4the heating element of an embodiment10comprises flat strip material20having a length, width and depth. At a desired point from the end of the strip20, the strip20is 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 twist30. The strip is than bent across its width at a radius greater than the width of the strip20in a manner so that the strip forms a bend40and returns toward the initial twist30. The twists and bends of the strip20may be performed when the strip20has been heated or when it is at room temperature depending on the material comprising the strip20. After heating, the strip20may be allowed to air cool or may be quenched depending on the material comprising the strip20. Jigs may be used to hold and position the strip20during twisting and bending. At a point in the length of the strip20, opposite of the initial twist30as the strip returns towards it (at 180°), the strip20is twisted again, but clockwise axially along the length of the strip20in a return twist35at an angle opposite of the angle of the initial twist30forming a return leg50. (For example, in a preferred embodiment, the initial twist30is at 90° relative to the width of the strip20and the return twist35is at −90° relative to the width of the strip20.) Alternatively, the initial twist30may be clockwise and the return twist35may be counter-clockwise. Due to the radius of the bend40being greater than the width of the strip20and the initial twist30being opposite to the return twist the return leg50of the strip will be roughly parallel to the original terminal leg55without touching it and within the same plane to give a roughly flat bottom surface60. The nearer the twists are to 90°, the flatter the bottom surface60will be. This bottom surface60may be placed upon a ceramic plate or other surface or material for support.

At a designated point past the end of the strip20, the strip20is twisted again at the same angle of the initial twist30. Then a bend40of a like radius is made, returning the strip20towards the preceding initial twist30where another return twist35at an opposite angle is made. The flat strip20then returns parallel to the first and second flat sections (return leg50and terminal leg55) of strip20. This process is repeated a specified number of times and with the lengths of flat strip20being at different lengths until the desired shape or profile is created such as the generally round profile ofFIG. 1. As can be seen withFIGS. 3 and 4, the side of the element in contact with a bottom face60is roughly flat. The alternating initial twists30and return twists35(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 face70, has a non-flat surface with edge, or depth face of the strip20at the bends40being above the flat width surface of the strip20.

The element10is connected to a power source near each end, or terminal leg55, by a terminal80. The terminals80are connected to an appropriate electric power source not pictured. Direct connection of a power source to the terminal legs55is also anticipated by the applicants. As explained above, the twists30and bends40will expand and contract and relieve the stress and subsequent deformation normally suffered by the element geometry as a whole.

While the embodiment ofFIG. 1discloses 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 inFIG. 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.

The flat surface defined by the bottom face60may 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.

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 (MoSi2) or any coated with colloidal alumina or Al—O or Al—O—H compounds.

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.