EP0052840A1

EP0052840A1 - System of support or sustentation of electric heating elements in furnaces or equipment, insulated with ceramic fiber

Info

Publication number: EP0052840A1
Application number: EP81109656A
Authority: EP
Inventors: Jose Carlos Cazzoli; Roberto Piva
Original assignee: Kennecott Corp
Current assignee: Kennecott Corp
Priority date: 1980-11-24
Filing date: 1981-11-12
Publication date: 1982-06-02
Also published as: BR8007655A; DE52840T1; JPS57155084A

Abstract

This invention relates to a device of support or sustentation of electric heating elements in furnaces and equipment insulated with ceramic fiber which is fundamentally characterized by being consistuted of a structural material which is non-conducive to electricity in the form of pieces of complex construction and consisting of part of a free end in the form of a hook (1) and a part on the opposite end in the form of a wedge (2) to be anchored in the insulating lining or module or ceramic fiber (10) with the aid of a coupling piece whose hooks (1) cooperate for placing and/or holding the heating elements of the electric resistance (11) in the form of special spiralled or helicoidal wires, or of tape.

Description

Technical Field

This invention relates to an improved system used to support elements of electric heating in the form of tapes or wire conductors, applicable to the lining of ceramic fiber refractories.

Background Art

The petroleum crisis, from which the energy crisis in general has resulted, has determined with increasing pressure the development of systems of thermal insulation and of alternative sources of energy. The substitution of other higher cost sources of energy, for example, electric for the thermal energy from combustion of petroleum products has also increased the use of insulation.
For a case of better insulation, the applicable of ceramic fiber resolved the related problems with highly satisfactory performance. However, the application of electric energy in ceramic fiber lined furnaces has created difficulties and practical problems in the face of technical limitations or the cost of the systems of support of the elements of electric resistance, which are the "in-situ" generators of thermal energy required in furnaces and other equipment, and principally in industry.
The electric resistance supports used normally in this case are usually composed of several pieces, including refractory or stainless steels, of sophisticated manufacture, high cost and are not always available. Therefore, to obtain high temperatures "in-loco" of around 800°C, INOX 310.steel is used, and for 1100°C, INOX 310 or INCONVEL 601 is employed.
Systems for hanging electrical.heaters using metal hangers all suffer from the problem that the creep strength of the metal decreases with temperature increase leading to failure of the system.
Other methods of supporting hangers.for electrical heaters in systems using ceramic fiber are shown in U.S. Patent 4,272,638 and U.S. Patent 4,154,975. Both of these patents disclose complicated and expensive systems.
There remains a need for a system that is inexpensive, stable at high temperatures and easy to install in a variety of ceramic fiber wall systems.

Disclosure of the Invention

Such solution of the above problem consists essentially in providing electrically inert pieces of certain structure, proper for insertion into insulating linings of ceramic fiber. Normally such insulating lining is attached to the housing of ; the equipment or a hard refractory layer is applied intermediately or superficially to the walls of the housing with ceramic fiber overlaying the hard refractory.
For such purposes, the invention provides a supporting device and system applicable for heating elements of a certain form and structure, described later and illustrated in the attached drawings. Such supporting devices are firmly anchored in the ceramic fiber blankets covering the housing or in pre-molded modules of ceramic fiber, installed on the housing in a state of compression which on the average typically makes up 30% and may use batten strips to adjust for shrinkage between such modules in use.
The electrical support system of the invention utilizes a series of ceramic hanger elements having a generally wedge shaped pointed end adapted to be inserted into the ceramic fiber, a coupling member having a generally flat surface generally perpendicular to the axis of said wedge and a hook adapted to support an electrical heater element located at the opposite end of said hanger from said wedge shaped pointed end. The hanger further comprises a coupling portion joining the hook and wedge shaped portion.. The coupling member is generally planar and adapted to bear against the ceramic fiber when in use. The wedge shaped portion is composed of at least one planar member generally perpendicular to the plane of the hook and at least one planar member generally in the plane of the hook.
The structure and application of the.sustentation device and inventive electrical hanger system will be better understood when referred to in the drawings attached.

Brief Description of the Drawings

Figure 1 represents a type of support device in longitudinal vertical cut.
Figure 2 represents a type of support in longitudinal horizontal view.
Figure 3 represents a section along B_-B of Figure 1.
Figure 4 shows a type of anchorage of the support ; devices of electric resistance in the forms of a helicoid wire in which modules of ceramic fiber are used and hold the hanger elements.
Figure 5 shows the same type of anchorage in which the electric resistance is shown in the form of tape or ribbon.
Figure 6 shows the support device in two methods of suspension of electric resistance.
Figures 7 and 8 represent an alternative design of the support device of the invention.

Best Mode for Carrying Out the Invention

Illustrated in Figures 1 and 2 is the support device, made by molding and/or sinterization of an electric insulating ceramic material. The device is here shown in the form of a molded device, with an end in the form of hook 1 and the opposite end in the form of a wedge 2.
As illustrated in Figures 7 and 8, there are alternate embodiments of the hanging elements of the invention. These elements generally indicated as 20 differ from the embodiments of Figures 1 and 2 in that they do not have barbs 21, 23 and 25. They further differ as on the flat surface of 7' there are formed a series of ridges 27 and valleys 29 which act to increase the surface area of the hanger element.
In a particularly preferred form of installation utilized in the invention, the hanging elements are coated with a refractory cement prior to insertion into the insulating ceramic fiber. The ceramic fiber is at least partially slit with a knife prior to insertion and then the hanging element coated with the refractory cement is inserted into the cut. The series of ridges and valleys increases the surface area for bonding of the ceramic cement to the ceramic fibers. It further inhibits withdrawal of the hanging element.
The materials forming the hanging elements of the invention-may be any material which is generally non-conductive and also temperature resistant at the intended'use temperature of the furnace. Typical of materials suitable for the hanger elements of the invention are silicon carbide and alumina.
Alumina while having very desirable temperature proporties is expensive. Preferred materials for the system of the invention are mullite for applications up to about 2300°F and cordierite for applications up to about 1600°F as these materials are easily formed, chemically stable and heat shock resistant.
The refractory cement utilized in mounting the hangers of the invention may be any material which is operable at -the anticipated temperatures and is suitable for easy application onto the hanger element. Preferred materials are air drying water base refractory cements, such as fire clay refractory cements.
As may be observed in Figures 1, 4, 5 and 6, the hook part is placed externally from the lining, sometimes in modules of ceramic fiber and in the form of body 3 of a pyramid trunk or similar shape, of a trapezoidal transversal section, pointed outward and on whose end is formed a shoulder of rectangular transversal section of a relatively small height, forming a straight hook 4, leaving a space 5 for placing the electric. resistance in the form of wire or tape.
The opposite end 2 has a general shape of a tapered wedge, with point 6 slightly rounded and with projections 7 and 7', to reinforce its anchorage in the insulation or in the respective module of ceramic fiber 10. Projection 7 serves to provide structural'support for the hook 1 and also minimize side movement of the sustentation member. The projections of 7' serve to supply support or bearing surface to support the hangers and electrical heating elements without breaking down the fiber.
The hangers of the invention may be any desired size that will provide sufficient anchorage in a particular wall to support the electrical device to be used. A'typical size is about 6-1/2" overall length. The length and thickness will also vary depending on the ceramic material forming the hanger.
The coupling piece 9 represented in Figure serves to hold support 1 jointed to wedge 2 which is anchored inside the insulation of ceramic fiber. The coupling piece 9 in contact with the ceramic fiber stabilizes the hook 1 and helps prevent its sagging into the fiber so as to hang down and become dislodged.
As illustrated in Figure 4, the devices of support 1, 2 are anchored in the module of ceramic fiber 10, with part 2 firmly fitted under compression and fastened inside insulation 10, with the aid of projections 7, 7' and 31, 33 and 35 serving for sustentation of the electric resistances in the form of wire 11, as is well shown in Figure 4.
As illustrated in Figure 4, the supports 1, 2 are found placed in two horizontal rows, with hooks 4 of the upper row turned upward and those of the lower row turned downward, so as to hold wire 11, and to prevent it from slipping. To make holding better for wire 11, held in sine wave or in zig-zag alternately around the upper and the lower supports, the supports of the lower row are found separated from those of the upper row to the right, as seen in Figure 4 by the observer.
Figure 5 is an illustration similar to Figure 4 except that the electric resistance 37 is shown as a ribbon or tape, adapted to space 5 of support 1. In this case it is anchored in the ceramic fiber module 10, also two rows of supports 1 and 2, and in both their hooks are turned outward. As may be seen, in relation to the upper row, the electric resistance 37 in a spiral or helicoid form, rests on the | respective spaces 5. The tape 37 may be fastened to the supports, for example, by a wire of the resistance itself, or another adequate one in case this becomes necessary.
In Figure 6 in the lower row, the case of application of spiralled or helicoid resistances of a larger gauge 39 is illustrated. The element 4l is a heater of smaller gauge that may be placed on hook 5. In this case supports of larger dimensions are avoided, with more difficult anchorage in the mass of ceramic fiber, by pieces in the form of a joint double-L forming a type of hanger 12. The upper branch of the junction of pieces in L is simply placed in the space 5 of support 1 and the lower branches of the L will hold the larger size resistance. To provide for possible differences in the gauges of the electric resistances for each specific case, these parts 12 can be prepared in the form of an L, with dimensions of the lower branch, each of which adapted to each case. Parts 12 can be prepared of any thermal resistant material, which does not need to be properly insulated electrically because of the refractory nature and the insulation of supports 1 and 2.
The heating elements of Joule effect of electric resistance are supported on supports 1 and may be fastened to this by a wire of the same material or may be suspended. The fastening of the elements is of interest especially for these heating elements comprising spiral wires on a ceramic core.
The type of fastening of the invention eliminates any ; necessity of using refractory or stainless steels, and I generally substitutes a large variety of parts with one piece only with large economy of material and labor. As may be easily deduced from the illustration of Figures 4, 5 and 6, the electric resistance system is very easily assembled, and may be completed in a short period of time even by non- specialized personnel, and therefore at a greatly reduced cost.
Although described with reference to certain preferred embodiments, it would be clear to people skilled in the art that there are other variations in the hanger device and system of the invention which are obvious and are intended to be included by the present specification and claims. Further the hanger device could be formed with a.somewhat differently shaped wedge-shaped surface or with more than one planar member parallel to the plane of the hook. While the hangers and mounting system of the invention have been illustrated as installed in a ceramic fiber module, it is also within the invention to install the system in ceramic fiber wall systems of other construction or to insert the devices into the folded fiber blanket which may be inserted between the modules.

Claims

1. A support or sustentation method for elements of electric heating in furnaces and in equipment insulated with ceramic fiber comprising a structural material resistant to electricity in the form of pieces of complex construction, comprising a part at the free ends in the form of hooks, parts at the opposite end in the form of wedges anchored in the insulating lining or module of ceramic fiber with the aid of coupling pieces joining said hooks and wedges wherein the hooks of said pieces cooperate to hold the heating elements of the electric resistance heaters.

2. A support or sustentation method in accordance with claim 1, wherein the parts in the form of hooks have a body of a general form of a trunk or pyramid or similar of a transversal trapezoidal section where a wire or tape of electrical resistance is placed.

3. A support or sustentation method, in accordance with claim 2, wherein the parts in the form of wedges have a tapered point with projecting shoulders of the wedge, respectively, upward and toward the sides to reinforce the anchorage of the device in the insulation.

4. A support or sustentation method, in accordance with claim 3, characterized by its alternate arrangement in horizontal rows, with coupling and anchorage in the insulation, with hooks in position of the upper row, turned upward and those of the lower row turned downward, to assure a firm positioning of the elements of the electric resistance in the form of wires or tapes in a sine wave development.

5. A support or sustentation method, in accordance with claim 3, further comprising arrangement in horizontal rows for direct reception of the heating elements in the form of tapes or spiralled or helicoidal wires in the respective spaces of the hooks turned upward in alignment, with eventual fastening with the same material as these elements.

6. A support or sustentation method, in accordance with claim 5, characterized by the fact that, for applying spiralled wires of a larger diameter, complementary pieces are placed in the respective hooks in the form of adouble-L hanger, joined in the upper part by a horizontal transversal branch supported in the open space and where the lower free branches have a width corresponding to the mentioned wire..

7. A high temperature hanger for use in ceramic fiber furnace walls comprising a wedge shaped pointed end adapted to be inserted into the ceramic fiber, and a hook located at the opposite end of said hanger from said wedge shaped pointed end.

8. The hanger of claim 7 wherein said wedge shaped end comprises at least one generally planar member generally transverse of the plane of said hook.

9. The hanger of claim 8 wherein said wedge shaped end further comprises at least one planar support element generally in the plane of the hook.

10. The hanger of claim 9 wherein said hook is planar.

11. The hanger of claim 7 wherein a coupling member having a generally flat surface joins said wedge shaped pointed end and said hook and said flat surface is adapted to bear against said ceramic fiber during use.

12. The hanger of claim 8 wherein said wedge shaped end comprises a series of ridges and valleys on its surface.

13. The hanger of claim 8 wherein said wedge shaped end comprises barbs.

14. The hanger of claim 7 wherein it has an overall length of about 6.5".

15. A method of sustentation of electrical heating elements comprising inserting a plurality of hangers into the ceramic fiber lining of a furnace, said hangers comprise a wedge shaped pointed end adapted to be inserted into the ceramic fiber and a hook located at the opposite end of said hanger from the pointed end and suspending electrical heating elements from said hooks.

16. The method of claim 15 wherein said hangers are in a plurality of rows with said hangers of each row offset vertically from said hangers in rows parallel to it.

17. The method claim 16 wherein electrical ribbon heaters are suspended from said hooks.