Abstract
A heater element including: a primary conductor formed from a single sheet of metal, wherein the primary conductor is capable of radiating heat within 5 seconds and has a DeLuca Element Ratio of less than 2 ohms/m2; and primary conductor bars that are not welded to the primary conductor.
Claims
1. A heater element comprising: a primary conductor formed from a single sheet of metal, wherein the primary conductor is capable of radiating heat within 5 seconds and has a DeLuca Element Ratio of less than 2 ohms/m.sup.2; and primary conductor bars that are not welded to the primary conductor.
2. The heater element of claim 1 wherein the single sheet of metal comprises two or more thicknesses.
3. The heater element of claim 1, wherein the primary conductor is shaped into a U shape.
4. The heater element of claim 3 wherein the U-shape comprises ends and a curve, the ends of the U are connected to an electrical circuit, and the curve is tensioned with a tensioner.
5. The heater element of claim 3 wherein a portion of the curve comprises multiple pathways for a current to flow.
6. The heater element of claim 1 wherein the heater element is adapted to increase in temperature during operation at a rate of greater than 100 degrees C. per second.
7. The heater element of claim 1 wherein the single sheet of metal comprises a mesh or lattice structure.
8. The planar element per claim 1 wherein the single sheet of metal comprises planar sections having a thickness greater than 0.001 inches.
9. The heater element per claim 1 wherein the single sheet of metal comprises ends and a middle part to radiate disposed between the ends, and a thickness of each of the ends is greater than a thickness of the middle part.
10. The heater element per claim 1 wherein the single sheet of metal is a portion of a roll or continuous sheet.
11. A process for making a heating element from a single sheet of metal comprising providing a sheet having two or more thicknesses formed either singularly or sequentially.
12. The process per claim 11 further comprising installing said heater element within an oven cavity.
13. The process of claim 11 further comprising welding the two or more sheet parts.
14. The process of claim 11 further comprising supplying electrical power from a power supply to the multi-planar heating element.
15. The process of claim 14 wherein the power supply delivers AC or DC current to the multi-planar heating element.
16. The process of claim 14 further comprising storing electrical energy to operate the multi planar heating element.
17. The process of claim 14 wherein said power supply delivers power to said heater element through a switch.
18. The process of claim 14 further comprising cycling on and off the electrical energy supplied to the multi-planar element is turned.
19. The process of claim 14 further comprising controlling electrical energy supplied to the multi-planar heating element with a feedback loop comprising input from a sensor.
20. The process of claim 11 further comprising providing an oven cavity; and monitoring a temperature rise in the oven cavity when the multi-planar heating element is in use.
21. The process of claim 11 further comprising cycling the multi-planar heating element on and off.
22. The process of claim 11 further comprising cycling the multi-planar heating element in association with a pre-set program.
23. The process of claim 11 further comprising submerging the multi-planar heating element in a liquid.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0019] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention.
[0020] FIG. 1a is an isometric view of a single wire mesh heating element formed with an integrated primary conductor and having a DER of less than 2.
[0021] FIG. 1b is an isometric view of a single mesh heating element made from ribbon formed with an integrated primary conductor and having a DER of less than 2.
[0022] FIG. 1c is an isometric view of a flat mesh heating element made from a single flat sheet incorporating primary conductor bars and having a DER of less than 2.
[0023] FIG. 2 is a cross sectional view of FIG. 1c illustrating the transition zone from the primary to the heating element.
[0024] FIG. 3 is an isometric view of a segmented mesh formed from the mesh in FIG. 1c.
[0025] FIG. 4 is an isometric view of a tensioning system used to hold the mesh of FIG. 3.
[0026] FIG. 5 is an isometric view of a roll of sequentially formed elements such as that in FIG. 1c so as to create a continuous string of elements.
[0027] FIG. 6 is an isometric view of the manufacturing process used to make the element of FIG. 1c further including a coating process.
[0028] FIG. 7 is a table describing various thickness of mesh and their appropriate mesh size to maintain a DER less than 2 and operate at various sizes.
[0029] FIG. 8 is an isometric and schematic drawing illustrating how the DER value is calculated.
[0030] FIG. 9 is an isometric view of the element of FIG. 3 with a modified union end to allow for an equal resistive value.
[0031] FIG. 10 is an isometric view of the element of FIG. 3 and similar to that in FIG. 9.
[0032] FIG. 11 is a table showing the equal resistance of the path lengths across the width of the element in FIG. 10.
[0033] Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.
DESCRIPTION
[0034] The present teachings disclose a novel heating element with a DER of less than 2 incorporating a primary element that does not require the need to weld or otherwise join the primary to the mesh.
[0035] FIG. 1a is an isometric view of a single wire mesh heating element 30 formed with an integrated primary conductor and having a DER of less than 2. The wire mesh 1 is formed with cross elements 2 across which a voltage is applied from one side of the oven to the other and wire elements 3 are normally woven orthogonally to 2. A typical wire mesh used in the application might have a wire diameter of 0.012″ and be spaced 0.055″ from each other so as to form a mesh with 18 strands crossed. In accordance with the present invention, wire elements 3 may be pressed closer together at space 4 or wire that is larger in diameter such as strand 5 may be woven into the mesh to create a primary conductor section 6 of the element that is integrated into the heating element. Such a primary conductor, having a significantly lower electrical resistance than the mesh heater section should help to lower the temperature of the mesh at the ends 7 and 8. As an example, by decreasing the spacing 4 between strands at the end by half (from 0.055″ to 0.0275″) and increasing the diameter of wires 10 by two fold (to 0.024″ and thus increasing the cross sectional area of the cross wire 3 by 4 times and together with wire 2, the overall cross sectional area is increased by 2.5 times), and the resistance is thus decreased by 40% in the end primary conductor bar section.
[0036] Similarly to element 30 in FIG. 1a, FIG. 1b is an isometric view of element 20 having flattened wire or ribbon 21 and 22 cross woven together to form a mesh 50. Also like mesh 30, the cross flat ribbon 22 is moved closer together in the primary conductor area 23 and a ribbon with twice the thickness is used so as to create a primary conductor that like element 30 has 40% less of the electrical resistance of the mesh in region 24.
[0037] In a preferred embodiment, element 40 in FIG. 1c is formed from a solid sheet 41 that is chemically or electrically etched so as to create a heater mesh region 42 and a primary conductor section 43. As illustrated, the primary conductor region 43 having an electrical resistance of 75% less than mesh area 42 as the material is twice as thick and has no perforations 44. Unlike ribbon mesh 20 in FIG. 1b, both the length direction 45 and cross direction 46 can be increased in thickness. In addition, the ability to connect a secondary conductor to the primary in area 43 is much easier as the material is flat and stiff.
[0038] FIG. 2 illustrates a cross sectional view 50 of element 40. At the interface step 51 between the mesh region 42 and the conductor section 43, the current flowing from the secondary conductor bar enters the mesh. The use of a step that increases the material thickness above the interface 51 helps to insure that residual heat can be absorbed by the added metal in order to keep the zone cool. In addition, various gradations of thickness in the mesh region 42 can be created using an etching process that can help to increase the overall life of the mesh by reducing fatigue or temperature in the zone. As an example, initial current flow from the primary conductor 43 may create areas in the mesh 42 that are initially hotter compared to the rest of the mesh. Over thousands of cycles of heat up and cool down, these areas may become more prone to stress fracture. Thus, thickness may be adjusted accordingly and variably over the mesh to increase thickness and thus decrease resistance, further increasing life of the mesh.
[0039] FIG. 3 is an isometric view of an element 40 such as that of FIG. 1c that has been segmented at line 60 into two equal zones 61 and 62 each with its own primary conductor 63 and 64 and an adjoining region 65 between the two to form element 70. Region 65 is designed to be used without a secondary conductor but further remain as cool as possible. By increasing the length of region 65 in direction 66, an additional reduction in the resistance is achieved. Region 66 may also be formed at a third thickness, different than the primary conductors at 63 and 64 and generally thicker. Holes 200 and 201 can be used for registration and location of the mesh within an oven.
[0040] FIG. 4 is an illustration of element 70 that has been connected with a tensioning mechanism 71 at region 65 to create tension in direction 66 as the element is heated. The benefit of forming element 70 in this manner is that it helps to disassociate the current carrying ends 63 and 64 of element 70 from the tensioning mechanism 71 and thus simplifies the design mechanics of the secondary conductor bars.
[0041] FIG. 5 illustrates a continuous roll 80 of the element 40 of FIG. 1c with mesh sections 42 following primary conductors 43 which may be reused as the roll is indexed. US patent application U.S. Ser. No. 15/183,967 describes a continuous mesh system yet does not use the primary conductors that greatly facilitate the current transfer to the mesh.
[0042] FIG. 6 illustrates a manufacturing process for etching and forming element 40 in the etcher 90 from blank roll stock 100 and further applying a coating 91. A continuous roll 80 may be produced by winding the finished product 40 into a roll 80 or by individually parting each element 40.
[0043] In the process of designing a flat film element 40 with perforations, the thickness is of crucial importance in the effective resistance. The thicker the material, the lower the resistance and therefore the more power will be required to make the element emit in the 0.5-3 micron range. The following table of FIG. 7 illustrates various mesh opening sizes for various elements of various thicknesses. Note that all these elements have a DER of less than 2.
[0044] FIG. 8 Illustrates how to measure the DER as further described by De Luca in U.S. Pat. Nos. 8,498,526B2 and 9,500,374B2. In these calculations, the DER is calculated by considering a single mesh or element material covering an entire 0.25 m×0.25 m in an oven and further operating both elements simultaneously with energy applied in parallel to both a top and bottom element. By using this standardized approach to calculate the DER, the value will remain consistent and accurately reflect the properties of the material versus whether the material is made smaller or larger and whether it is used in various long or short configurations to obtain a different resistance.
[0045] Considering mesh 40 shown in FIG. 3, this mesh is 5″×8.375″ or 0.027 m2 on one side but with a 50% open area is 0.014 m2 of black body radiative area on one side or 0.027m2 per element. The single element 250 has a resistance of 0.14 ohms if measured end to end of the oven (across the 8″) or between edges 105 and 106. If 2 were placed in parallel with element 251 as shown in FIG. 8 to cover 0.25 m×0.25 m in the oven the resistance would drop to 0.07 ohms and the black body radiative area would increase to 0.055 m2. As explained in paragraph 25 of patent US20100166397 and beginning with line 43 of column 6 of U.S. Pat. No. 8,498,526B2 a typical oven with 0.25 m×0.25 m of area would have 4 surfaces or thus 2 more elements in parallel (253 and 254) powered through the same voltage source. Thus the resistance would again drop by 2 and the black body surface areas would increase by 2. So the total for a “standard” oven with this mesh would be 0.035 ohms and the black body radiative area would be 0.110 m2. Thus, the DER would equal 0.035/0.11=0.31
[0046] FIG. 9 illustrates the elements of FIGS. 3 and 4 where the element 70 made as element 700 has a modified region 65 of the element with a resistance that is equal across the intersection area 600 and 601 between the thinned section and the union and a hole 703. By creating a modified pathway 800 with equal resistance for the current to traverse between the positive end 704 and the negative end 705 through the union 65, the regions 701 and 702 remain cooler as the current passes more evenly throughout union 65.
[0047] Similarly, to FIG. 9, FIG. 10 illustrates a flat element 70 and 700 with a modified union end 65 formed with pathways 800.
[0048] The table of FIG. 11 shows the equal resistance of each of the pathways 800 across the union end of the elements in FIG. 10.
[0049] The examples presented herein are intended to illustrate potential and specific implementations. It can be appreciated that the examples are intended primarily for purposes of illustration for those skilled in the art. The diagrams depicted herein are provided by way of example. There can be variations to these diagrams or the operations described herein without departing from the spirit of the invention. For instance, in certain cases, method steps or operations can be performed in differing order, or operations can be added, deleted or modified.
