Suspension device for resistor elements in furnaces

Suspension device for electric resistor elements (5) in furnaces. A rod element (4) is horizontally arranged and is supported by consoles (2,3) at a distance from the furnace walls (1). The resistor element (5) is suspended on the rod element (4) and forms dense winding coils hanging freely from the rod element substantially in a flattened helical configuration.

FIELD OF THE INVENTION 
The invention relates to a suspension device for loop-shaped resistor 
elements in furnaces, particularly in furnaces insulated with ceramic 
fiber materials. Such fiber materials provide important advantages, such 
as effective insulation, low heat capacity and lower total costs than 
e.g., bricks. However, the ceramic fiber materials also have certain 
disadvantages, such as high porosity, low strength and a tendency to 
crumble. 
Various arrangements have previously been suggested on how to mount 
electrical resistor elements in furnaces insulated with ceramic fiber 
materials. Thus, U.S. Pat. No. 4,272,638 discloses a device for the 
suspension of meander-shaped element loops on horizontal ceramic rod 
elements being fixed to the furnace wall, which consists of fiber material 
blocks, by means of fasteners holding the rod element against the furnace 
wall. Along its length, the rod element is provided with grooves or 
recesses in which the upper end portions of the meander loops are secured. 
However, the assembly and dismounting of the rod elements are rather 
complicated. 
OBJECT OF THE INVENTION 
The object of the invention is to achieve an improved suspension device 
permitting a high heating power per unit area of the furnace wall and 
enabling a simple installation and dismounting of the resistor elements, 
e.g., in connection with repairs of the furnace lining. Another object is 
to permit the extensive use of standard parts. 
SUMMARY OF THE INVENTION 
These objects are achieved, according to the invention, in that the 
supporting means for the substantially horizontal rod element consist of 
consoles adapted to support the rod element at a distance from the furnace 
walls and that the resistor element loops form dense winding coils hanging 
freely from the rod element substantially in a flattened helical 
configuration. Hereby, one may easily and advantageously use helically 
wound or bent resistor elements, particularly of a metallic material, and 
preferably of Fe-Cr-Al alloys (e.g., of the type sold under the registered 
trade mark KANTHAL), which are resistant in most atmospheres even at 
temperatures as high as about 1300.degree. C. Owing to the fact that the 
resistor element loops are supported at the top by the rod element and 
hang freely therefrom at a distance from the furnace wall, the entire 
resistor element can easily be dismounted by mere lifting of the rod 
element with the resistor element supported thereby, e.g., in case the 
furnace walls need to be repaired or partly replaced. It is hereby a great 
advantage that the element loops are hanging freely at a distance from the 
furnace wall, since the resistance material may become rather brittle 
after a long period of operation and, thus, cannot withstand much 
mechanical strain or load.

DETAILED DESCRIPTION 
In FIG. 1 a furnace wall 1 is schematically shown, said wall being assumed 
to consist essentially of an insulating, ceramic fiber material, wherein 
consoles 2 and 3 are mounted at the furnace wall 1 and support a 
substantially horizontally oriented rod element 4 in the form of a ceramic 
tube. On the rod element 4 a loop-shaped resistor element 5 is suspended. 
The resistor element consists of a metallic material, namely a Fe-Cr-Al 
alloy of the type sold under the trade mark KANTHAL, having the shape of a 
flat band being wound into a helix and thereafter suspended in a flattened 
configuration from the rod element 4, so that each winding coil hangs 
freely from the rod element, preferably at a distance downwards 
corresponding to at least five times the diameter of the rod element, so 
that the resistor element loops together rather densely cover a relatively 
large surface area somewhat inside the furnace wall 1. In practice, the 
hanging loops can reach downwards about 200 to 1000 mm. However, when the 
operational temperature of the resistor elements is high, e.g., 
1100.degree.-1300.degree. C., the downwardly extension should not exceed 
about 500 mm (due to the self-dilatation under the influence of gravity). 
As indicated by dashed lines, a guiding rod 6 could possibly be arranged 
to guide the lower portions of winding coils. If desired, the guiding rod 
could be provided with recesses or means to maintain the winding coils at 
a uniform distance from each other. 
In accordance with the invention, the rod element 4 is supported at a 
distance from the furnace wall 1 by means of the consoles 2 and 3. In this 
case, the consoles are located adjacent to the terminal portions 7, 7' of 
the element 5. FIG. 2 shows how the terminal portion 7 extends inside a 
lead-through means in the form of a ceramic tube 30 through the furnace 
wall 1 and into the furnace through the console 2. For this purpose, the 
latter is constituted by two bent plate members 8,9, preferably also of a 
Fe-Cr-Al alloy, each such member having a leg 8a and 9a, respectively, 
abutting flat against the furnace wall 1, and a leg 8b and 9b, 
respectively, extending perpendicularly thereto. Each leg 8b, 9b is 
provided with a substantially semi-cylindrically bent portion 8c and 9c, 
respectively, which are connected to each other, e.g., by welding, while 
enclosing the terminal portion 7', within the complementary portions 8c, 
9c. Hereby, the entire console 2 will be supported by the terminal portion 
7', and no separate fasteners between the respective console 2, 3 and the 
furnace wall 1 are therefore needed. Adjacent to the outer, free end 
portions of the legs 8b and 9b, respectively, a recess 10 is provided in 
their upper edges. The recess 10 has an upward V-shape and is dimensioned 
to form a bearing surface for the tubular rod element 4, so that the 
latter rests in a well defined position at a distance from the furnace 
wall 1. This distance should correspond to at least one tube diameter (for 
the tube 4), so that the loop portions of the element 5 located closest to 
the furnace wall hang freely inside the furnace wall 1. When dismounting 
the resistor element 5, the consoles 2,3 are pulled straight out from the 
inside of the furnace wall 1 (upon disconnecting the terminal portions at 
the outside of the furnace wall 1), so that both the terminal portions 
7,7', the rod element 4 as well as the resistor element 5 supported 
thereby will follow along as one unit. In this way, damage to the element 
loops is avoided and the element can be used again, e.g., after 
reconstruction or repair of the furnace lining. 
At temperatures where the plate material gets deformed e.g., above 
1000.degree. C., it may be desirable to make the consoles 2, 3 entirely or 
partly of a ceramic material, e.g., Sillimanit or Mullit. 
The embodiment according to FIGS. 1 to 3 with consoles resting on the 
terminal portions of the resistor element is also very advantageous in 
existing furnaces with linings of brick material since, only through holes 
need to be made, and specific fasteners are not needed. In FIGS. 1 to 3 
the resistor element 5 is made from a flat-wound band. As possible 
alternatives hereto, FIGS. 4 and 5 show a part of a likewise flat band 5' 
(FIG. 4) wound or bent edgeways and a wire 5" of circular cross section 
(FIG. 5), respectively, wherein in both cases only the connection to the 
terminal portion 7 is shown. 
FIGS. 6 and 7 show an alternative embodiment of the consoles supporting the 
rod element 4, here generally denoted by the numeral 11. The consoles 11 
are separately arranged in relation to the terminal portions 7, the 
lead-through tube 30 and each console 11 thus being located at some 
distance from each other in the longitudinal direction of the rod element. 
The console 11 consists of a ceramic body having a substantially circular 
base portion 12 and an outer portion 13 shaped as a hook, said portion 13 
forming a hook opening 14 for supporting the rod element 4. Even in this 
case, the hook opening 14 is located at a distance of at least one 
diameter of tube 4 from the inside of the furnace wall 1, so that the 
loops of the resistor element 5 hang freely downwards from the rod 
element. The hook body 11 is detachably coupled by means of bayonet 
coupling members 15, 16, to holder 17, in the form of a bowl or a pot, 
anchored to the furnace wall 1, the bottom of the holder being secured by 
a metallic pin 18 having a metal washer 19 and the edge portion thereof 
being formed as a circumferential flange 20. This flange 20 abuts and 
holds a ceramic disc 21 located at the inside of the furnace wall 1. The 
pin 18 extends through a hole in the bottom of the pot, and the disc 19, 
being screwed thereon as a nut or secured by welding, anchors the pot 17, 
the ceramic disc 21 and the hook body 13, the other end of the pin 18 
being fixed to the outer plate mantle 22 of the furnace wall 1 in a 
suitable manner. Between said outer plate mantle 22 and the inner ceramic 
disc 21 as well as inside the pot 17, a ceramic fiber material is disposed 
for heat insulation of the furnace wall. The hook body 11, the pot 17 and 
the ceramic disc 21 may be made of a suitable refractory material, e.g., 
Sillimanit or Mullit. 
The hook body 11 also serves as a lid to the pot 17 and contributes to the 
temperature reduction of the metallic anchoring means 18,19. The hook body 
can easily be detached from the holder pot 17 by rotation of, e.g., 
90.degree., so that the bayonet coupling members 15,16 are freed. It is 
preferable to turn the pot 17, so that the hook body can maintain its 
position and support the rod element 4. 
Instead of a hook body, the modification shown in FIG. 8 is provided with 
an eye body 11' with a through-hole 14' for the rod element. In this case, 
it is necessary that the eye body maintain its position when dismounting, 
e.g., by turning the pot 17 in the manner mentioned above. As appears from 
FIG. 9, the eye body 11' can also be divided into two halves 11'a and 
11'b, whereby the mounting is further facilitated. When the eye body is 
divided, it can be provided with recesses for the terminal portions of the 
resistor elements, which terminal portions then can be combined with the 
anchoring pin 18 (FIG. 6). 
FIGS. 10 and 11 show modified embodimemts of the rod element 4 in the form 
of a reserved U-profile (FIG. 10) and a T-profile (FIG. 11), respectively, 
of a ceramic material. The supporting means of the consoles (not shown) 
are of course adjusted to each profile, respectively, so that the rod 
element is fixed at a desired distance from the furnace wall. 
The profile member 4' according to FIG. 10 is in the central web portion 
provided with transversal slot 23 in the region of each element loop, 
which in this case consists of a flat band 5' bent edgeways (compare FIG. 
4). Upon introducing the upper portions of the loops from underneath 
through the slots 23 (the width of which only slightly exceeds the band 
thickness), the band loops are bent somewhat sideways, as shown at 24, so 
that the bent out band portions 24 rest on the top side of the profile 
member 4' adjacent each respective slot 23. 
In FIG. 11, the T-shaped profile member 4" is provided with recesses 25 on 
the longitudinal edges of the horizontal profile leg for securing each 
resistor element loop 5". In this case the resistor element consists of a 
helically wound wire having a circular cross section (compare FIG. 5). 
FIG. 12, finally, shows an example of a fixedly arranged console 26 
consisting of a ceramic body, which is mounted already when manufacturing 
the furnace wall blocks by vacuum forming of a ceramic fiber material. For 
additional anchorage and positioning of each console 26, a tube 27 is 
inserted through a hole 28 in the inner end portion of the console and is 
embedded into the wall insulation as well as, if necessary, connected to 
one or several additional consoles 26. At its free end portion located 
inside the furnace wall 1, the console 26 has a hook opening 29 facing 
obliquely inwards/upwards towards the interior of the furnace, into which 
opening 29 a rod element 4 can be inserted and suspended together with a 
corresponding resistor element 5. In this case as well, the terminal 
portions 7 are led through separate openings (not shown) in the furnace 
wall. 
The rod element as well as the consoles and the other parts can be modified 
in different ways within the scope of the invention. For example, the 
consoles can be adapted to be secured to the ceiling of the furnace. The 
essential idea is to provide for substantially horizontal suspension of 
the rod element 4 in the consoles, so that the resistor element loops hang 
freely at a distance from the furnace wall substantially in a flattened 
helical configuration.