JPS6333351Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Summary An improved electrical heating element for a high temperature furnace is disclosed that includes a support structure and an electrical heating assembly. The support structure includes a plurality of thin, flat, non-conductive plates each having a plurality of spaced apart openings therethrough and a plurality of non-conductive spacers smaller than the plates, one spacer between each pair of adjacent plates. A spacer is placed. The electrical heating assembly includes a plurality of elongated electrical conductors, preferably U-shaped, with each leg extending radially outwardly of the spacer and through one opening in each plate. A conductor is supported by the plates and extends between the plates, the ends of the conductors being connected such that the connected conductors define a single tortuous electrical path radially outwardly of the spacer. Connections between the conductors maintain the support structure assembled.

This invention relates generally to heating elements for high temperature heat treatment furnaces, and more particularly to improved heating elements for use in radiant tube heaters in high temperature furnaces.

The use of radiant tube heaters located within high temperature heat treatment furnaces is, of course, well known. Typically, in the prior art, gas is combusted inside the tubular member to heat the tubular member. The tubular member then radiates heat outward into the furnace.

There are various problems with gas-fired radiant tube heaters, the most significant of which are the relatively high cost and low efficiency of gas heating.

It is also known to use electrical heating elements inside the radiant tube. However, various problems have been encountered with prior art electric heating elements.

Typically, these electrical heating elements include a support structure having a hollow core and an electrical heating assembly. When electrical current is passed through the electrical heating assembly, the heating assembly radiates heat to the radiant tube, which radiates heat into the furnace.

In prior art electric heating elements, the current return path from the distal end of the heating element (inside the furnace) to the proximal end of the heating element (outside the furnace) is within the hollow core of the support structure. Therefore, the heat generated by the current flowing through the return path conductor in the core is
There is virtually no utilization in the overall heat generation of the assembly within the radiant tube.

Another problem with prior art electric heating elements is aging of the electrical conductors. This aging manifests as oxidation, pitting, or corrosion of the conductor. As this condition progresses, small holes appear in the conductor, these holes enlarge, and finally, when the conductor is cut, it becomes useless and must be replaced.

Yet another problem with prior art electric heating elements is a lack of stability, ie, sag and growth. Sag is the deviation from the original longitudinal axis and growth is the axial elongation, both of which occur during high temperature use of the heating element.

This invention overcomes the aforementioned problems by providing a new and improved electric heating element.
The heating element of this invention has all its electrical circuits outside the central core, so that all electrical circuits generate heat that can be used to heat the radiant tube or furnace.

Additionally, the invention also includes providing an electrical conductor with a sufficiently thick cross section to reduce oxidation and corrosion. Additionally, the invention allows for the replacement of pitted, oxidized or corroded conductors without requiring replacement of the entire electrical assembly. Finally, the support structure avoids sag and axial growth.

Accordingly, one object of this invention is to have a plurality of thin, flat, non-conductive plates, each having a plurality of spaced apart openings therethrough, and a plurality of non-conductive spacers smaller than the plates, with each pair of adjacent a support structure with a spacer disposed between the plates; and an electrical heating assembly having a plurality of conductors each extending outside the spacer and through at least one opening in each plate. An object of the present invention is to provide an improved electric heating element for high temperature furnaces or the like. The conductors are supported by the plates and the ends of the conductors are connected such that the connecting conductors define a single electrical path radially outwardly of the spacer. Connections between the conductors maintain the support structure assembled.

Another object of this invention is to provide an improved electrical heating element for insertion into a radiant tube such as a high temperature furnace, the heating element having a plurality of spaced apart openings, each parallel to an axis. a plurality of axially spaced insulating disks, a plurality of insulating spacers disposed between adjacent disks to separate the disks from each other, and a plurality of conductive rods each having an elongated leg and a curved portion;
A leg of the rod is inserted through an alignment opening in each disk and extends radially outwardly of the spacer in the axial direction of the disk spacer assembly, with a curved portion of each rod projecting from the end plate;
Additionally, the heating element includes a conductive member that holds the rods, disks and spacers assembled and connects the rods to provide a single continuous current path through each rod outside the spacer.

A further object of the invention is to provide a series of non-conductive plates each having a plurality of non-conductive, longitudinally aligned spacers and a plurality of axial apertures therethrough, the apertures in the plates being axially aligned. The spacers are placed between the plates in a directionally aligned manner to maintain a parallel spaced relationship between the plates, each formed into a U-shape with a short base and parallel elongated legs. a plurality of elongated conductive rods, each leg of each rod being inserted axially through an aligned opening in a series of plates and radially outwardly of a spacer; With the exception of two rod legs, the free end of each rod leg is connected to the free end of another rod leg to form the rod into a single electrical path, and the remaining two rod legs are connected to the power source. An object of the present invention is to provide an improved electric heating element comprising: a member adapted to be connected to a heating element;

The foregoing objects and advantages of this invention, as well as other objects and advantages achieved by its use, are:
It will become clearer from the following detailed description in conjunction with the drawings.

In FIG. 1, the electrical heating element 10 of the invention is placed within a hollow tube 11 having a closed end 12 and a flanged front end 13 for attachment to a furnace. Tube 11 is preferably made of a heat resistant alloy such as Inconel, but steel pipe can also be used in the case of a low temperature furnace. The support structure of the electrical heating element of this invention includes a plurality of thin, flat ceramic plates or disks 15, including a first plate 16 and a second plate 17 at the front end of the assembly and an end plate at the distal end of the assembly. second plate 18
and a final plate 19.

Each plate is preferably identical and has a central axial bore 20 surrounded by a circular groove 21 on each side of the plate. Each plate has a plurality of through openings parallel to the plate axes. These apertures are arranged in a plurality of rows, with a first circular row of apertures 22 and apertures 23 as shown in FIG.
a second circular row of holes, all openings being beveled at 24. The rows of apertures are radially spaced, and in the preferred embodiment, the apertures 22 are offset diagonally from the apertures 23 to provide maximum direct exposure of the surface of the conductor to the radiation tube. There is.

The support structure also includes a plurality of identical non-conductive spacers 25, made of ceramic material, preferably hollow and open at both ends. The diameter of the spacer 25 corresponds to the diameter of the circular groove 21 of each plate, the diameter of the spacer 25 is smaller than the diameter of the plate 15, and all openings 22,
It is important that 23 is radially outward of spacer 25. As shown, one spacer 25 is disposed between each pair of adjacent plates 15.
The spacer thus serves to separate adjacent plates.

Next, the electric heating assembly of this invention will be explained. The invention includes a plurality of electrical conductors 30, and in the preferred embodiment, the conductors are solid rods having a circular cross section, and the conductors or rods have a generally hairpin or U-shaped configuration. The use of circular cross-section rods maximizes the thickness to surface area ratio. This reduces the likelihood of oxidation, pitting or corrosion penetrating the entire rod, thereby increasing the life of the rod compared to prior art electric heating elements.

Each conductor or rod 30 includes two elongated parallel legs 31, 32 which are joined at a base or bend 33.

When the support structure is assembled, the apertures in each plate are aligned and each rod leg is inserted through the series of aligned apertures parallel to the axis of the plate. Rod begins with the penultimate plate 18.
Projecting from the plate 18 is a curved portion 33 which is inserted through and forms the junction of the legs 31, 32 of each rod. The rods thus extend from plate 18 through each plate 15 to second plate 17, with the distance between plates 17, 18 defining the effective heating length of heating element 10. Each plate supports a rod 30, and the curved portion 33 of each rod serves to maintain the distal end of the structure in the assembled condition.

Additional support members are provided at the distal end of the heating element 10 to support the assembly and prevent electrical contact between the bend 33 of the rod and the end 12 of the radiant tube. In a preferred embodiment, this support member includes one spacer 25 and the final plate 1.
Contains 9. A pin 35, such as an 18-8 stainless steel pin, is inserted inside the spacer 25.
The pin has an opening at each end for receiving a cotter pin 36. The cotter pin and the stainless steel pin prevent plates 18 and 19 from moving apart, and the spacer 25 prevents the plates from coming closer together.

During assembly of the heating element 10, the rods 30 are inserted into the openings 22, 23 of the penultimate plate 18.
inserted through. The support consisting of stainless steel pins 35, spacers 25 and final plate 19 is then assembled. Finally plate 1
The remaining support structure, including plates 5, 17 and spacers 25, is assembled, with rods extending through alignment openings 22, 23 in each plate.

A member is provided for electrically connecting the free ends of the rod legs 31, 32 and for maintaining the support, including the plate and spacer, in the assembled condition.

Referring to FIGS. 2, 5 and 6, all legs 31, 32 of rod 30 extend through openings in second ceramic plate 17. Referring to FIGS. A series of jumper rods 40 are shown in FIG. These jumper rods 40 have the same size and are made of the same material as the conductive rods 30 and extend from the free end of one leg 31 of one U-shaped conductor to one leg of another U-shaped conductor. Welded to the free end of the section. The connection of the free ends of the legs of the conductive rods is such that the four legs of the four different U-shaped rods remain unconnected, as shown in FIG. 5 by the four leg ends 41, 42. It is achieved by

The first ceramic plate 16 is then positioned so that the four leg ends 41, 42 pass through the plate. A crossover bar 43 of the same material as the jumper rod 40 and the conductor 30 is then welded to the two free ends 42. This leaves two free ends 41 unconnected, but at the same time one
A continuous electrical path is provided from one free end 41 through each U-shaped conductor and each jumper rod and crossover rod to the other free end 41. The entire electrical path is therefore radially outward of the spacer 25.

The remainder of the support assembly and electrical connections will now be described with reference to FIGS. It is preferable to reduce the distance between the two free ends 41 of the rod to a size suitable for connection to a supply source, and at the same time provide terminals of increased thickness for said connection. Furthermore, it may be desirable to provide additional support for this first end of the heating element. To achieve this, two rods 45 made of the same material as the conductor 30, but of a slightly larger diameter, are
It is welded to the free end 41 at 46. The upper end of the rod 45 is connected to the two terminal rods 4 at 47.
Welded to the end of 8. Rod 48 is preferably 35-15 stainless steel. These terminal rods 48 have a diameter of 0.625 inches. The terminal rods are inserted through the first insulating block 50, which has two through holes 51 and two vent holes 52 for receiving the terminal rods 48. Washers 53 are welded to the terminal rod on both sides of the first insulating block 50. A good insulating block is made by John Mansville Company.
It is a Marinite disk manufactured by.

Terminal rod 48 extends through a second marinite block 55 and has a washer 56 welded to the terminal rod inside second insulating block 55. Appropriate screws are attached to the terminal rod,
It is adapted to receive a lug 57 which secures the second insulating block 55 to the washer 56.

A heating element manufactured according to the principles of this invention was tested with the following results.
The insulating plate 15 was made to have a diameter of 4.875 inches (approximately 124 mm) and a thickness of 0.5 inches (approximately 13 mm), with 17 openings in each of the outer and inner rows. Then, 17 U-shaped conductors were inserted through the openings and the assembly was 6 in.
placed inside a pipe with an outside diameter of . The effective heated length of the assembly was 42 inches. Thermocouples were placed inside and outside the pipe. Power was applied at a voltage of 45-60 volts and a current of 30-45 amperes (the heating element is rated at 137 volts). The temperature of the pipe was maintained at 2200°C for 24 hours as part of the test.
Sometimes it exceeded 2300〓 (1260〓). A similar test was conducted on a larger pipe with a lower current rating, and the outside temperature of the pipe exceeded 1700°C.

An important result of these tests was that negligible element sag (change in longitudinal axis) and growth (change in axial length) occurred during the tests. Although these tests were not conducted under actual working conditions, the test results are
It is shown that the operating conditions necessary to heat the furnace to 2000°C (approximately 1093°C) can be obtained with this invention and that sag or growth of the electric heating element is negligible.

It must be recognized that many changes and modifications may be made without departing from the spirit and scope of the invention. The use of U-shaped rods, which can be easily replaced individually if one rod corrodes, has been described, but straight rods welded at both ends have been described.
It is equally possible to use rods. It is likewise possible to utilize the heating element of the invention without a radiant tube, depending on the atmosphere of the heat treatment furnace. Additionally, although the spacer of the present invention is hollow, this is not necessary and other structures may be used to secure the final plate 19 and the penultimate plate 18. Therefore,
The scope of this invention should be determined only by the scope of the claims for utility model registration.

[Brief explanation of the drawing]

FIG. 1 is a partially cut away view of the electrical heating element of the invention inserted into a radiant tube. Second
The figure is an enlarged view of the front end of the electric heating element.
FIG. 3 is an enlarged cross-sectional view taken along line 3-3 of the electric heating element of FIG. FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of the electric heating element of FIG. FIG. 5 is an enlarged cross-sectional view taken along line 5-5 of the electric heating element of FIG. FIG. 6 is an enlarged cross-sectional view taken along line 6-6 of the electric heating element of FIG. 10... Electric heating element, 11... Radiation tube, 15... Plate, 16... Plate, 17
... Plate, 18 ... Plate, 19 ... Plate, 22 ... Opening, 23 ... Opening, 25 ... Spacer, 30 ... Conductive rod, 31 ... Leg, 3
2... Leg, 33... Base, 35... Steel pin,
40... Jumper rod, 48... Terminal rod.

Claims (1)

[Claims for Utility Model Registration] 1. In an electric heating element for a high temperature furnace adapted to heat the furnace to a temperature of up to 2000㎓ (1093°C) having a longitudinal axis, a plurality of thin flat non-conductive plates are axially spaced apart along said longitudinal axis, each of said plates parallel to said longitudinal axis and spaced laterally outwardly from said axis. has a plurality of openings passing through the
The openings in each of the plates are arranged in a pair of laterally spaced circular rows including an inner circular row and an outer circular row, each of the circular rows of the plates having an equal number of openings, The openings in each circular row are adjacent to the openings in the outer circular row, the openings in each circular row are equally spaced apart, and the openings in each circular row of each plate are adjacent to the openings in the outer circular row. each vertically aligned with an aperture in a corresponding circular row, and a plurality of vertically aligned non-conductive spacers disposed on the vertical axis and laterally inward of the aperture. and each of the spacers is
cylindrical in shape and having a diameter smaller than the diameter of the inner circular row of apertures provided in said plates, and one between each pair of adjacent plates to maintain said plates parallel and spaced apart; opposite ends of the spacer abuttingly engage within circular grooves in opposing surfaces of said adjacent plates, and a plurality of elongated, straight, rigid electrical conductors extending parallel to said longitudinal axis and extending from said plates. an electrical heating element extending axially through longitudinally aligned apertures in the conductor and retained by the plate thereof to define a single continuous current path through the electrical conductor; An electric heating element characterized in that means are provided at each end for interconnecting the ends of said electrical conductors. 2 each of said electrical conductors is provided with two long legs joined by a base, each leg of said electrical conductor extending through one opening in each said plate; a base is positioned beyond the final plate to form said interconnection means at one end of the electric heating element, said interconnection means at the other end of the electric heating element comprising a plurality of jumper rods;
Each of the jumper rods interconnects the free ends of the legs of each of the electrical conductors with the free ends of the legs of another electrical conductor, and the legs of two other electrical conductors are connected to a power source without interconnecting the jumper rods. Electric heating element according to claim 1, characterized in that it is adapted to be coupled to. 3. The electric heating element according to claim 1, wherein the means for interconnecting the ends of the electric conductors connects a portion of each electric conductor in a U-shape.