Method and apparatus for supporting electric heating elements in a furnace insulated with ceramic fiber

© Beginning of patent period: 1983 11 15

Longest possible duration:

© Issued ·. 1984 07 © inventor:

1984 07 10 © Dependence:

Q / .T CAP Τ V © References which have been taken into consideration for the purpose of distinction from the prior art: OE-OS 2242780 OE-OS 2648542 GB-PS 683559 GB-PS 743935

Nr.375176

The invention relates to a device for supporting electrical heating elements in an electric furnace whose walls are thermally insulated by means of insulating material consisting of fiber material, with supports, at whose ends facing the furnace inside the heating elements are supported.

In a known device of this type (DE-OS 2648542), the supports are often formed integrally with a block to be inserted into the insulation of the furnace, so that the arrangement of the supports must already be established when building the furnace wall. A subsequent change of this arrangement 'is not possible or only after extensive intervention in the structure of the insulation.

In other known such devices (eg DE-OS 2242780, GB-PS 683 559), the supports are in direct or indirect contact with the outer wall of the furnace, so that high heat losses through conduction are unavoidable.

In connection with the use of solid insulating goat in it has also become known (GB-PS No. 743,935) to insert bricks in the insulation, which have special recesses for receiving the supports. On the one hand, such a design is not possible with the use of insulating fiber material, on the other hand, the geometric arrangement is determined according to the structure of the furnace wall here. It can be subsequently changed only with great effort.

The object of the invention is to provide a device for supporting electrical heating elements in an electric oven, which allows a quick and easy replacement of the heating elements with minimal heat loss. Also, a change in the geometric arrangement of the supports and a replacement of the supports should be possible easily and without modification of the furnace wall.

This object is achieved in that an anchor is provided within an insulating element, at a distance from both its outer and inner wall, on which the inner end of at least one support can be fastened.

Thanks to the features of the invention, a thermal bridge through the insulation can be seen avoided and the use of a separate anchorage for the supports takes into account the nature of the insulation (fiber material) consideration.

If the anchoring is embedded in the insulating element, there is the advantage that the anchoring is completely surrounded by the insulation, so that heat losses are further reduced.

When using elastic fiber material as insulation, it is expedient if the inner end of the support has a shape which allows a displacement of the fiber material located between the inner wall and the anchoring means of the inner end. By this means a simple fastening of the supports after piercing the insulation to anchorage is possible.

A development of the invention is characterized in that the anchorage is elongated and extends substantially parallel to the inner surface of the insulating element, wherein the inner end of a support can engage at any point of the anchorage. In this way one is narrowed in the choice of the geometric arrangement of the supports in any way.

The anchors can be brought into place by simply inserting, if the insulating consists of superimposed strips of insulating material, these strips are approximately perpendicular to the inner surface of the insulating element and the anchoring between the individual strips is embedded.

An embodiment with the lowest possible heat loss is obtained when a fixed to the furnace wall bolt is provided at a distance from the anchor in the insulating.

It has been found in practice to be optimal in terms of low heat losses with high strength, when the anchorage is located at a distance from the inner surface of the insulating element, which is 25 to 50% of its thickness.

If the anchorage is designed as a rod made of ceramic material, particularly low heat loss is obtained.

If the anchorage is designed as an elongated profile part with a substantially U-shaped cross section, a secure fit of the anchorage in the insulation at low

Guaranteed cost of materials. In addition, the hanging of supports is facilitated.

Nr.375176

The formation of the supports essentially as S-hooks is not only very simple but also very useful, since both the support easily in the anchorage and the heating elements can be easily hung in the supports.

If the heating elements are to be held against the inner furnace wall, it is expedient if the planes of the hook ends are rotated relative to one another by approximately 90 °.

It is also advantageous if the inner end of the support has a cutting edge which facilitates the piercing of the material located between the anchoring and the inner side of the insulating element.

The use of a cutting edge facilitates the installation of the supports considerably, since the forces are lower for the introduction of the supports.

The invention together with its further advantages and features is explained in more detail below with reference to exemplary embodiments, which are illustrated in the drawings. 2 shows, in section, a part of the furnace according to FIG. 1 with details of the support for the heating elements, FIG. 3 shows a cross section along the line 3-3 in FIG 4 shows diagrammatically, partly in section, a partial view for explaining another embodiment of the device according to the invention, FIG. 5 shows a detail of a heating element in cross-section, Figure 6 is a front view of an S-shaped support which can be used in the arrangement according to Figure 4 and is used in the arrangement according to Figure 5, Fig.7 a perspective view, partly in section, a partial view for explaining a further embodiment of the invention and Figure 9 in cross section an inventively designed furnace with a curved furnace body wall.

In all drawings, like reference numerals designate like parts. To explain the device according to the invention, Fig.l part of a furnace -10- is shown, whose outer wall -12- consists of metallic wall panels. In order to avoid heat loss and endangerment of people near the furnace as far as possible, the furnace shell is insulated.

To isolate a furnace, one can use a variety of methods and materials. In the context of the invention, an insulation is not provided on the outside of the furnace shell, but on the inside thereof.

It is preferable to use commercially available block-shaped insulating elements -14- with, for example, 300 × 300 mm lateral length and a thickness of 100 mm. The insulating elements 14 are preferably made of elastic ceramic fibers which extend normal to the furnace wall 12 or lie in planes normal to this wall. However, one can use rigid, non-compressible modules made by vacuum forming. In any case, such an element consists of electrically insulating and heat-insulating fiber material.

The block-shaped ceramic fiber insulating elements -14- can be attached to the furnace wall -12- or to a refractory wall -16- (Figure 4) in various ways. For example, one can fix the element -14- to a furnace wall made of steel by means of a weldable bolt -18-, which is inserted into the interior of the insulating element -14- (Figure 3). U.S. Patent No. 3,706,870 discloses a weldable metal stud suitable for mounting a ceramic fiber insulating module of the present type (see also U.S. Patent No. 3,993,236). With the help of such a bolt can be attached to the furnace wall -12- an expanded metal pad -20- attached, which in turn is attached to the back of the insulating element (Figure 2, 3). It is also possible to fix a ceramic fiber insulating element to the furnace wall -12- made of steel or to a fireproof wall -16- by gluing. An adhesive is commercially available which has such chemical and mechanical properties and heat resistance as to reliably bond the insulating member to a surface of a supporting structure.

Regardless of the type of insulating material used inside the furnace, it has a hot outer wall facing the furnace interior and a cold outer wall facing the furnace wall to which the insulating material is attached to the furnace wall. From the inner wall -22- of the insulating element -14- are from several S-shaped supports -26- from which support an electrical resistance heating element -28-, which is usually arranged meandering to achieve the highest possible efficiency.

- 4 No. 375176

To improve the thermal properties of the heating element -28- it may be appropriate to arrange this so that it does not touch the inner wall -22- of the insulating element -14- directly. Therefore, in Figs. 2 and 3, for example, an annular ceramic spacer -30- and a ceramic rod -32- are shown holding the heating element a short distance from the inner wall of the insulating element.

According to Fig.2 at least one anchoring -34- is arranged in the interior of the insulating element -14-. This preferably consists of a ceramic tube, for example of the same material as the rod -32-. It has proven to be expedient to arrange the anchoring at a distance of 25 to 50% of the thickness of the element from its inner wall. The length 10 of the anchorage -34- is preferably smaller than the width of the insulating element, so that the anchorage does not interfere with the mounting of the element -14- to the furnace wall -12-. Further, in this case, an insulating member made of elastic insulating fibers can be slightly compressed in its attachment to the furnace wall, without the anchoring projecting from an edge surface of the element. Also with regard to the thermal expansion of the anchorage is a small

Addition expedient, so that a strong Axialpressung is prevented.

In a preferred embodiment of the device, two rod-shaped anchors -34- are provided, u.zw. a first upper anchorage -36- and a second lower anchorage -38- (Figure 3). When the insulating member has been fixed to the furnace wall by means of a welded bolt or adhesive, the S-shaped support -26- is inserted through the inner wall 20-22 into the element -14-. The support -26- may be made of alloy steel or other suitable material which has grown to the expected temperatures in the furnace room. For example, as shown in Fig. 3, at the inner end -40-, the support -26- has a downwardly directed hook which is inserted into the fibrous material insulating member so as to overlap the rod-shaped anchoring embedded therein. The support -26- is so long that after the embracing of the anchor -36- with the downwardly directed end hook the support -26- projecting from the inner wall -22- of the insulating element with an upwardly directed hook -42- which at an upper loop end - 44- of the heating element -28- attack.

The support -26- should be so long that between the inner wall -22- of the Isolier30 element -14- and the heating element -28- space for the spacer -30- is present. As mentioned above, this spacer -30- is preferably an annular disk of ceramic material; but you can also use spacers made of other materials and in other geometric shapes.

The heating element -28- supported in the center of its upper loop end -44- is located at its lower part -46- from the inner wall -22- of the insulating member at a distance substantially equal to the thickness of the spacer -30-. If, on the other hand, the heating element is to be arranged on an inclined wall or if a continuous space is required between the heating element and the inner wall of the insulating element, it may be expedient to provide support for the lower part 40 of the heating element 40 as well. Here one can similar procedure as for the support of the upper loop end of the

Heating element.

Through the inner wall of the insulating material made of fiber material in this a lower support -48- is introduced so that it engages over the embedded in the insulating, lower anchorage -38-. The lower support -48- is like the upper support -26- 45 formed at both ends with a hook. In the lower support -48-, however, these two end hooks are mutually rotated by 90 °, so that they can easily include the heating element -28- at the vertical distance of its lower part -46-. At this second, lower point of attack can be provided between the heating element -28- and the inner wall -22- of the insulating the already mentioned ceramic rod -32- as a spacer. While the spacer used at this location could be configured as well as the spacer associated with the top support, it has been found useful to use a ceramic spacer similar to the anchorage -38- as the bottom spacer. This ceramic rod is between the heating element -28- and the inner wall -22- of Isolier5

No. 375176 element directly above a protruding from the inner wall protruding part -50- the lower support -48-.

Since the insulating element -14- is made of elastic ceramic fibers, one can introduce the support in the element at any point of its inner wall, because the fibers dodge easily during insertion of the support. The insulating element may consist of a plurality of juxtaposed strips which are connected to one another in a known manner to form a module. It is not necessary to introduce the supports in the inner wall of the element at a certain point relative to 'the joints between these strips.

It can be seen in Fig. 9 that a meandering electrical resistance heating element -28- can be supported inside the furnace at a series of upper supports -26- fixed to the anchorage -36- in element -14-. The distances between the upper supports correspond to the center distances between the upper loop ends -44- of the heating element. On a sloping wall or ceiling, one can support the heating element -28- both at its upper loop end -44- or in the vicinity thereof, as well as at its lower loop end -52- or in the vicinity thereof. The skilled artisan recognizes that for supporting a heating element on an inclined wall or the ceiling of a furnace can suitably use S-shaped supports -26- and / or 90 ° S-shaped supports -48- with 90 ° from each other twisted end hook. An insulating element with two anchorages -36 and 38- is preferably used. In the context of the invention, however, it is also possible to use insulating elements with an anchoring, for example the elements 14 'in FIG. 9, or with three or more anchors. The length of the supports -26 and 48- can also be varied. The invention thus provides a very adaptable system for supporting heating elements in ovens of various geometric shapes.

4 to 7 another embodiment of the invention is explained. The ceramic fiber insulating element -54- shown in Figure 4 has been made by vacuum forming so that the element -54- is relatively rigid and its fibers are somewhat brittle. Therefore, it may be desirable to provide in the inner wall of the element -54- a series of notches or slots -56- so that a relatively flat support -58- can be easily inserted through the inner wall of the element into it, so that the support overlaps an anchorage. One can form these cuts or slits in the element before or after inserting the ceramic anchors -36 and 38-.

To avoid the unwanted heat transfer through the cuts or slits as possible, it is expedient to use a relatively flat support -58-, as shown in Figures 6 and 7. There it is seen that this support is substantially S-shaped and formed at one end with a cutting edge -60-, which facilitates the import of the support -58- in the ceramic Isolierfasermaterial, especially in a rigid insulating, which may also without the previously formed cuts or slits -56-. But even with an insulating element with previously formed cuts or slits -56-, the cutting edge -60- facilitates insertion of the support -58- until it reaches over the rod-shaped anchors -36 or 38-.

It has already been pointed out above that the relatively rigid, block-shaped insulating element 54 can advantageously be fastened to the metal jacket of a furnace or to an existing refractory wall by means of adhesive 62. In this case, the adhesive -62- must be so strong that it is the additional weight of the heating element -28-, the anchorages -36 and 38- and supports -58- grown.

In a further embodiment, the device according to the invention according to Figure 8 has a ceramic fiber insulating element -64-, which consists of a single meandering folded mat of elastic insulating fibers. It is possible to hold such an element in its shape by means of a support or in other ways, not shown. During or after the fabrication of the element -64-, an upper and a lower ceramic anchorage -66 and 68- are inserted into each one fold -70- of the fiber mat. These anchors can be cylindrical or U-shaped. Again, it may be appropriate to provide in the element -64- cuts or slots -72-, so that a support easier through the inner wall

Nr.375176

- 6 -22- of the element can be inserted until it reaches over the anchors -66 or 68-. One can use either a support -26 or 48- of round material, as shown in Fig.3, or a relatively flat support -58-, as shown in Figures 6 and 7.

Of course, together with the insulating element -64- it is possible to use supports whose end hooks lie in the same plane, eg as upper supports, and supports rotated by 90 °, such as the lower support -48- in FIG. According to FIGS. 6 and 7, within the scope of the invention a relatively flat support 58 with a rotation of 90 ° can also be used. A twisted support is preferably twisted on its shaft at a location outside the insulating member.

In an insulating element -14 or 64- of elastic ceramic fibers spring back after insertion of the support into the element through the inner wall -22- the ceramic fibers into cavities formed during insertion of the support. In contrast, in a rigid ceramic fiber insulating module 54- in which a cut or slot 56 has been formed, these fibers do not spring back into the cut or slot. Therefore, it may be appropriate, in this case after attaching the support -0- some fibrous material od. Like. In the incision or slot to bring. In this way, as much as possible, one can avoid overheating which occurs when the insulation between the interior of the furnace and the furnace body has a smaller thickness in a small area.

By applying the device according to the invention important advantages are achieved. It is possible to support electric heating elements in a furnace chamber, without having to be attached to the furnace body bolts. In the context of the invention, electrical heating elements can be arranged in horizontal or vertical or any desired inclined orientation. Defective electrical heating elements can be quickly and easily renewed or repaired. If no heating element of the same dimensions is available as a replacement for a damaged or faulty heating element, the supports can be converted according to the dimensions of the new heating element. For example, it is relatively easy to move the supports on the anchorage so that they can support a heating element with other center distances between the upper loop ends.

The application of the invention requires no special tools and allows the installation of electrical heating elements without the involvement of skilled workers after minimal training time.

The parts in direct contact with the heating element are independent of metal parts which may be used to secure the anchoring-carrying insulating element to the furnace wall. In this way it is avoided that these metal parts are thermally stressed by the heat conduction between the heating element and the metal parts. When using parts that are in direct contact with both the furnace wall and the heating elements, the heat conduction may result in local overheating of the furnace wall, which may affect the strength of the support for the heating element and endanger persons in the vicinity of the furnace ,

You can also provide for the attack of the support to the anchorage in place of a hook and another device, for example, screw the support in the anchor. Anchors in different lengths and with different cross-sectional shapes can be used. For example, in the context of the invention, it is possible to use a leaf-shaped armature which extends only through part of the insulating element.