Heating Element Assembly

Abstract

An electric heating assembly for a moving air system is described in which heating elements include thin strips of apertured, foil-like material. These elements are supported in linear reaches and arranged for an efficient element-to-space occupation ratio. The foil of the elements is a mesh that is supported in linear reaches by a plurality of insulators which are adjustably connected to a support rod. When the insulators are fixed in position, they rigidly immobilize the foil relative to the rod. According to one aspect of the invention, the linear reaches are flat. According to another aspect of the invention, the linear reaches are provided with a longitudinal fold to thereby stiffen the reach and minimize the number of supporting insulators along the reach.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to an electric resistance heating assembly and, more particularly, to an electric resistance heating assembly which includes thin strips of foil-like material and which is adapted to be employed in moving air systems.

Prior art electric resistance heating elements are commonly constructed either by utilizing a flat, self-supporting, expanded metal strip which is secured between two supporting members, or by using a coiled wire arrangement which is supported at intermediate locations by means of ceramic bearing mounts surrounding the coiled wire.

The conventional coiled wire construction, however, has a low surface area and a high mass compared to a foil-like material. The high mass leads to a relatively high raw material cost, while the low surface area contributes to reduced heating and cooling efficiency. As a consequence of the high raw material cost, a constant effort is made to minimize the amount of material used by deliberately operating the element at as high a temperature as possible, often well into the red heat range. The operation of the element at the high temperature level has at least two detrimental consequences. The areas of restricted air flow (inside the ceramic bushings) become overheated and are prone to failure; secondly, the efficiency of convective air heating is decreased as a significant amount of the energy is spent in radiant heating the solids surrounding the element. The low surface area-to-mass ratio also causes a slow heat-up and cooling rate.

Prior art self-supporting expanded metal strips comprising long reaches which are secured between only two supporting members are subject to excessive sagging at operating temperatures.

To overcome these disadvantages found in the prior art, an expanded metal heating element has been proposed which is composed of corrugations establishing a wavy pattern to provide at least the same electrical characteristics as prior art devices but with a considerable saving in raw material. Such a device is set forth in U.S. Pat. No. 3,651,304. A heating element which has these wavy corrugations and which is supported by skewering a rod through the resistive foil presents other potential problems. Since the strip is skewered by the support rod, it may have a tendency to rotate about the rod and/or to move axially relative to the rod. Axial displacement may tend to collapse some of the corrugations into contact with adjacent corrugations, thereby shorting out a portion of the circuit, while any rotational movement of the element relative to the support rod may cause the element to contact the surrounding housing structure.

Other considerations that raise problems with wavy or sagging conductors are space requirements. It is often necessary to install the resistive foil element as close as possible to the containing structure to ensure a close packing of elements, or to meet design limitations on space. A corrugated or sagging conductor may contact other closely packed elements or the containing structure, and requires a substantially wider space than does a linear, supported conductor.

SUMMARY OF THE INVENTION

The invention overcomes these prior art problems by providing an assembly with a plurality of elements, with each element being formed by linear reaches or strips of a foil-like resistive conductor immobilized along the length of a supporting rod by adjustable insulating bars at substantially regular intervals. These immobilizing insulating bars prevent axial or rotational movement of the conductive strips of foil to ensure that separate conductors neither short together nor come in contact with the supporting structure or the assembly's containment.

By the regular placement of the insulating bars along the support rod, sagging along the linear reaches is minimized in order to present a moving air stream with a plane of resistive heating foil that is substantially perpendicular to the direction of its movement. This orientation allows substantially uniform heat transfer to the air as it passes through the mesh openings in the foil.

When a plurality of these elements are combined in a heating assembly, a spacing plate is provided to immobilize the supporting rod of each element. The spacing plate adds durability and rigidity to the entire assembly, and prevents electrical contact between adjacent elements.

Another embodiment of the invention provides for the immobilization of more than one linear reach on each side of the insulating bars. The space requirements for a heater element of this kind are minimal, while the element has a significantly greater amount of resistive foil area with which to heat.

According to a further aspect of the invention, the linear reaches of resistance material are provided with a longitudinal corrugation or fold to thereby stiffen the reach and minimize the number of supporting insulators along the reach.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an assembly according to one aspect of the invention;

FIG. 2 is a side elevation view of the assembly of FIG. 1;

FIG. 3 is an enlarged, fragmentary, perspective view of a portion of the assembly illustrated in FIGS. 1 and 2;

FIG. 4 is a side elevational view of an assembly according to a further aspect of the invention;

FIG. 5 is a plan view of the assembly of FIG. 4;

FIG. 6 is an enlarged, fragmentary, perspective view of a portion of the assembly illustrated in FIGS. 4 and 5; and

FIGS. 7 through 9 are enlarged, fragmentary, perspective views of assemblies illustrating the mounting of straight but linearly corrugated foil conductors according to further aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the embodiment of FIGS. 1 through 3, there is shown an electric heating element assembly 10. The assembly 10 has a plurality of electrically connected elements 12a, 12b, and 12c spaced in a generally regular manner and forming three separate rows or circuits on a mounting plate 18. The rows formed on the mounting plate 18 by the elements 12a-12c present substantially parallel planes of heating element surface so that a source of moving air impinging perpendicularly on one such plane does so also on all elements in a row and on all such rows. The number of elements in a row and the number of rows depend upon the electrical and space requirements of the particular assembly.

Each element 12a-12c includes a support rod 14, a plurality of insulators 32 adjustably fixed along the length of the rod, and linear reaches of heating element foil strips 30 immobilized by the insulators. The support rods 14 are made of aluminized steel and have L-shaped feet welded to the mounting plate 18 to provide a strong and rigid support for the elements 12a-12c. The support rods 14 extend through openings 20 in a spacing plate 16.

The spacing plate 16 prevents the elements 12a-12c in each row from moving laterally and contacting each other, thereby shorting out part of their own circuit, and, equally important, it prevents elements in adjacent rows from contacting and shorting out other circuits.

Each row forms essentially a resistance circuit through which current flows to heat the foil strips 30, with each row having its own terminals 21 for the supply and return of A.C. current. This resistance circuit is formed by connecting the linear reaches of the foil strip 30 in series with each other across a row of elements by connecting conductors 31. Some of the connecting conductors 31 attach each element of a row in series circuit, while the others join the foil strips 30 of each element into the circuit.

The terminals 21 have ceramic bushings 22 to keep the mounting plate at zero potential, since the mounting plate, when installed into a working environment, usually will contact supporting structure that is at ground potential. A bolt conductor 24 passes through each bushing 22 and a hole in the mounting plate 18. Locking nuts 26 are provided on the bolt threads to hold the assembly together.

Each element 12a-12c of the assembly 10 has at least one linear reach of the foil strip 30 which has electric resistance characteristics. This foil material is more fully described in U.S. Pat. No. 3,651,305, the disclosure of which is incorporated herein by reference. In the embodiment illustrated in FIGS. 1 through 3, each element includes two foil reaches which are retained and supported by the insulators 32 spaced along each support rod 14. The insulators 32 are preferably made from a ceramic, such as steatite, and have strip attaching means on either side of the support rod 14. The foil strips 30 are immobilized along the rods 18 by wire clips 46 which extend through openings in the mesh of the foil strips 30 and insulator holes 48 to immobilize the strip of foil. Grooves 49 may be cut in the insulators 32 to act as guides, while the clip is pushed toward the insulator holes 48 to facilitate installation.

The strips are immobilized in substantially linear reaches by spacing the insulators 32 in generally parallel planes and by providing connecting means between the insulators and the support rod to prevent axial and rotational movement of the insulators. Each such connecting means comprises a V-shaped clip 34 having a pair of legs 36 which flare outwardly from a clamping portion 38 of the clip. The insulator has restraining projections 40 which prevent lateral movement of the insulator in the clamping portion 38 of the clip 34. The legs 36 of the clip 34 have apertures 42 which correspond to the cross section of the rod 14 so that the support rod may be passed therethrough.

Each insulator 32 is mounted on the rod 14 by first clamping it within the clamping portion 38. The clip 34 may then be positioned at a desired location on the rod 14 by pressing the legs 36 together and inserting the rod through the apertures 42. When the desired location is reached, the legs are released so that they spring back to their illustrated position, thereby preventing further axial movement of the insulator 32 along the rod. Clip-engaging serrations or notches 44 are provided to securely hold the edges of the apertures 42 in place. After all of the insulators are mounted on a support rod and after the strips 30 are attached thereto by the wire clips 46, any strip slack between adjacent insulators may be taken up by sequentially adjusting the insulators along the support rod in a direction away from the terminals.

In FIGS. 4 through 6 there is illustrated an electric heating element 60. The element 60 includes a mounting or base plate 61, a support rod 62 welded thereto at one end, a plurality of insulators 63 immobilized along the extent of the support rod and angularly related thereto, and straight reaches of heating element foil strips 64 and 65 immobilized on the insulators. As may be seen most clearly in FIG. 6, each insulator 63 is affixed to the support rod 62 by a V-shaped clip 66 which is similar to the clip 34 illustrated in FIGS. 1 through 3. The support rod is provided with serrations 67 to ensure immobilization of the clip, and therefore the insulator thereon. Each insulator 63 is provided with a V-shaped notch 68 which straddles the support rod 62 and is further provided with inwardly extending slots 69 and 70.

Each strip 64 and 65 is continuous and is associated with and immobilized by the insulator 63 in such a manner as to form three flat, parallel reaches 64a, 64b, 64c, and 65a, 65b, 65c, respectively. One end of the reach 64c is electrically connected to a terminal 70 and extends in a straight run along all of the insulators 63 and is attached to each insulator by wire clips 71 which extend through the foil mesh and through apertures 72 in the insulators. At the end of this run, the heating foil is wrapped about a portion of the last insulator 63 through its slot 69 and then continues as the straight reach 64b while passing through all of the remaining apertures 69 in the insulator 63. When the reach 64b reaches the last insulator 63, it is wrapped about a portion of that insulator and then continues as the straight reach 64a until it reaches the insulator most remote from the terminal 70. The reach 64a is attached to all of the insulators 63 by wire clips 71, which extend through the foil mesh and through aperture 72 in the insulators. At that end of the reach 64a, the strip 64 is electrically connected to the strip 65 by a conductor 75 which bridges the clip 66. The strip 65 is trained between the conductor 75 and a terminal 76 in a manner identical with the path of the strip 64 to form the reaches 65a-65b. Thus, it may be seen that when the terminals 70 and 76 are connected to a power source, a resistance circuit results.

Turning now to FIGS. 7 through 9, strip immobilizing and strip configuration techniques according to further aspects of this invention are illustrated. In FIG. 7, a portion of a heating element assembly includes a support rod 80 having an insulator 81 fixed thereto by a V-shaped clip 82 similar to the clips 34 and 66. Foil heating strips 83 and 84 are supported and immobilized by the insulator 81 and other insulators (not shown) are provided along the length of the rod 80 to support the strips 83 and 84 in straight reaches. It is to be noted, however, that while the strips 83 and 84 constitute straight reaches, they are axially bent or corrugated and are received in pockets 85 cut into the ends of the insulator. By providing a longitudinal corrugation in the straight reaches, the foil is thereby rigidified to minimize any tendency for the foil to sag between insulators. Furthermore, fewer insulators may be provided, if desired, by providing a greater spacing between insulators.

In FIG. 8, there is illustrated a portion of a heating element having a support rod 86 and an insulator 87 attached thereto by a V-shaped clip 88. Straight reaches of foil strips 89 and 90 are immobilized by the insulator 87. Although the strips 89 and 90 form straight reaches between adjacent insulators, they are longitudinally folded or corrugated and received in circular apertures 91 in the ends of the insulator to rigidify the straight reaches between insulators.

Referring now to FIG. 9, there is illustrated a heating element according to a further aspect of this invention. The heating element includes a support rod 92, an insulator 93 affixed thereto by a V-shaped clip 94, and straight reaches of resistance foil strip 95 and 96 fixed to the ends of the insulator. The strips 95 and 96 extend in straight reaches between adjacent insulators, but are longitudinally corrugated to rigidify the strips and prevent sagging between insulators. One leg of each corrugated strip extends into slots 97 at the ends of the insulators and is immobilized by a wire clip 98 which passes through the foil mesh and through an aperture 99 in the insulator. Another leg of the foil is wrapped over the insulator and is affixed thereto by a wire clip 100 which passes through the foil mesh and through an aperture 101 in the insulator.

While there have been described what are at present considered to be the preferred embodiments and aspects of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed therefore, in the appended claims, to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

What is claimed is:

1. A resistance heating element comprising:

a. support rod means;

b. a plurality of insulators connected to said support rod means and angularly related thereto, said insulators being substantially symmetrical about said support rod means;

c. connecting means including clips between said support rod means and each insulator preventing axial and rotational movement of each insulator relative to said support rod means; and

d. thin strips of apertured, foil-like, electrical resistance material retained and supported by said insulators on either side of the support rod means in linear reaches between adjacent insulators.

2. A resistance heating element as set forth in claim 1, wherein said resistance material is attached to said insulators by clips extending through said material and through aperture means in said insulators to clamp said resistance material to said insulators.

3. A resistance heating element as set forth in claim 1, wherein each linear reach is defined by a plane parallel to the longitudinal axis of said support rod means.

4. A resistance heating element as set forth in claim 1, wherein said insulators are rectangular and are substantially perpendicular to said support rod means and the resistance material is immobilized in a plane along one edge of said insulators.

5. A resistance heating element according to claim 1 wherein each strip of said foil-like, electrical resistance material has at least one axially extending longitudinal corrugation along its length.

6. A resistance heating element as set forth in claim 5, wherein said insulators include inwardly extending slot means in at least one end thereof and wherein said resistance material is received within said slot means.

7. A resistance heating element according to claim 5, wherein said insulators include inwardly extending slot means in at least one end thereof and wherein a portion of said resistance material is received and immobilized within said slot means and another portion of said material is folded over and immobilized on one edge of said insulator to form said corrugation.

8. A resistance heating element according to claim 1 wherein each insulator has

inwardly extending slot means in at least one end thereof and wherein each strip of apertured, foil-like, electrical resistance material is trained in a first linear reach over one edge of each insulator, then in a second parallel linear reach through said slot means, and then in a third parallel linear reach over a second opposite edge of each insulator.

9. A resistance heating element assembly according to claim 1 wherein said support rod means includes a plurality of spaced, parallel support rods fixed at one end to a base plate, a plurality of said insulators connected to each support rod and angularly related thereto, connecting means including said clips between each support rod and its insulators preventing axial and rotational movement of each insulator relative to its support rod, said thin strips of apertured, foil-like, electrical resistance material being retained and supported by the insulators on each support rod in linear reaches, and including means electrically connecting a linear reach of resistance material retained and supported along the insulators of one support rod to a linear reach of resistance material retained and supported along the insulators of another support rod, and means for spacing and retaining the other ends of the support rods.

10. A resistance heating element assembly comprising:

a. support rod means;

b. a plurality of insulators fixed to said support rod means and angularly related thereto, said insulators being substantially symmetrical about said support rod means;

c. connecting means between said support rod means and each insulator preventing axial and rotational movement of each insulator relative to said support rod means, said connecting means comprising a V-shaped clip having apertures in each leg of the V through which said support rod passes, said legs being biased apart to grip said support rod; and

d. thin strips of apertured; foil-like electrical resistance material retained and supported by said insulators on either side of the support rod means.

11. A resistance heating assembly according to claim 10, wherein said support rod is serrated and wherein said legs engage said serrations.

12. A resistance heating assembly according to claim 10, wherein said insulator comprises an insulation block and wherein an extended apex portion of said V-shaped clip is clamped over said block to fix said insulator to said connecting means, and therefore to said support rod.

13. A resistance heating element as set forth in claim 10, wherein said electric resistance material is retained and supported by said insulators in linear reaches between adjacent insulators.