FR2466166A1 - Electric heater with refracting base - has metallic heating elements with extensions at each end which are fused into base before firing - Google Patents

Abstract

Coiled electrical resistance wires (4) are laid between the short ribs (3) of a rod (1). Threaded connection rods (5, 6) are laid in the ends of the same channels (2) defined by the ribs, the wires being mechanically attached or preferably soldered to them. The ribs are then pressed over to completely enclose and secure both wires and rods prior to firing. The rod consists of a refractory ceramic compatible with the wire, normally alumina based. The rods may alternatively have a block at each end through which the threaded rods pass or may have an embedded rod providing a termination for the wire. The design provides a reliable and inexpensive connection method to the resistance wire. The heater is used for frying pans and hot plates.

Description

Electric heating bodies are known which consist of one or more heating elements fixed on a support as is the case, for example, of metal deposits added to a refractory support using self-hardening compounds, of cement refractory or others. This is the case for thin circuits that are flat, or shaped for household appliances such as plate warmers, frying pans, etc.

Heating bodies are also known which are formed by the combination of heating elements and an insulating coating mass, whether they are mineral refractories or so-called "fibrous" refractories.

These heating bodies are, for example, large section son, ribbons and strips coated in whole or in part to produce mittens or tubular elements. This technique is also used to manufacture so-called "shielded" elements constituted by a wire wound in a spiral to constitute an electrical resistance, this wire being integrally embedded in a refractory mass, for example powdery, inside a metal tube, the assembly being almost always compressed using a mechanical means (pressing, hammering, rolling, etc.).

Such coated and compressed elements are also used to manufacture hotplates for cookers, dish warmers, irons, etc.

Thus, the patent of the United States of America No. 2,091,107 describes a heating element which is entirely embedded in a refractory sheath in order to completely protect it from attack by the atmosphere in which the element must be located.

Note the particular connection of the interior heating element with the exterior electrical wires, according to which only one embedded in the refractory sheath (and therefore irremovable) exceeds the sheath.

It is also noted that there is no means for removably securing together described in an apparatus.

There is also known a method of manufacturing heating elements according to which a heating wire is partially introduced into a plastic mass, after which the assembly is baked to harden the plastic mass which becomes refractory and immobilizes the wire over its entire length.

Such a process is described, for example, in Belgian patent no. 464.026 and in Swiss patent no. 212.048.

It should be noted that neither of these two patents gives any indication concerning the electrical supply of the heating wire or the removable fixing of the assembly obtained in an apparatus.

U.S. Patent No. 1,481,869 describes an apparatus which includes a heating element itself composed of a wire partially embedded in a refractory support.

The electrical supply of the heating wire is obtained by freely engaging the ends of said heating wire in holes and by subjecting them to a terminal. The mechanical fixing of the assembly results from the very shape of the refractory support which is intimately connected to an outer jacket.

The present invention departs from these earlier provisions in that it relates to a heating body of the type called "candle" and is intended to equip an appliance such as a water heater.

It is well known that these heating bodies must be securely fixed to the appliance and must be capable of being dismantled.
In addition, it is good that the mechanical fixing and electrical connection members as well as the part of the device which receives the heating body are relatively sheltered from too high a temperature due to radiation or to the conduction of the body. heating proper.

These conditions are not met satisfactorily and economically in practice because, most of the time, the mechanical and electrical connections are complex and costly.

The present invention remedies these drawbacks and makes it possible to produce an effective connection, both mechanically and electrically, by means of Simple and inexpensive means.

The invention will be better understood from the detailed description below made with reference to the accompanying drawing. Of course, the description and the drawing are given only by way of an indicative and nonlimiting example.

Figure 1 is a partial schematic view of a heating body according to the invention.

Figures 2 and 3 are two partial sectional views showing two alternative embodiments of a heating body according to the invention.

The process according to the invention is intended for the manufacture of electric heating bodies which must include a refractory support, at least one metallic heating element and at least one element for fixing the assembly in an appliance. It is of the type providing that the metallic element is fixed to the support, pushing it into the plastic mass of the support, before baking.

The process according to the invention is characterized in that an protruding part is left at each end of the metallic element, in that this assembly is brought to a temperature such that the mass is cooked and becomes a rigid support including the protruding parts to fasteners by exerting a mechanical clamping force on the protruding parts themselves.

According to this procedure, it is therefore necessary to choose the components of the mass on the one hand and of the element on the other hand so that their treatment at high temperature dies gives the desired characteristics without depriving them of any.

It is, therefore, forced to eliminate certain metal alloys which, after treatment at high temperatures, would not withstand mechanical stress such as axial traction.

However, experience shows that the number of alloys that can be used is large enough to meet the majority of practical needs in the industry.

To carry out the process which has been described above, one starts from a refractory mass whose composition can be variable depending on the desired goal but which, for reasons of compatibility with the metal alloy, generally has a minimum content of about 30% of alumina, a content all the more important as the temperature of the assembly thus constituted will be high taking into account the intended application.

The refractory mass can be prepared by known conventional means: kneader, mixer, kneader, etc., then then be shaped by molding or by extrusion.

 Or may recall that, according to the known technique, the refractory mass can be made more compact by degassing, which provides better workability of the mass.

The mass thus obtained is ready to receive the metal element (s) because it is sufficiently pliable, plastic and soft so that the metal element (s) can be inserted therein, and this, by partially driving them into the outer surface of the support.

When the metallic element is constituted, in a manner known per se, by a wire wound in a simple or complex spiral, this spiral is driven by a part of its periphery into the plastic mass.

The wire wound in a spiral can, for example, be placed around the mass obtained in the form of a cylinder and this by arranging the wire like the thread of a screw, this very simple operation being able to be carried out manually.

The wire wound in a spiral can also be arranged longitudinally.

This assembly is then subjected to the desired temperature to obtain the cooking of the refractory elements which make up the support and to give it the desired rigidity and mechanical strength.

Naturally, as is known per se, the cooking of the refractory dough can be preceded by a natural, forced or mixed drying phase.

The refractory components of the support can be chosen from those that are known because they do not present any particular disadvantages with regard to the technique of the invention.

On the other hand, as said above, the metal part cannot be arbitrary and we can, for example, cite among the metallic alloys which gave good results to the tests - nickel-chromium (80 - 20%), - nickel-chromium-iron, - iron-chromium-aluminum alloy, - metallic ceramics.

Metal ceramics, such as molybdenum bisilicide, silicon carbide, lanthanum chromite or others, can be inserted in a refractory mass to be fired later, but in this case, the expansion coefficients must be taken into account so that the removal after cooking is done without dislocation and without deterioration of the assembly.

Experiments have shown that the most easily usable alloys are those of nickel-chromium, nickel-chromium-iron and iron-chromium-aluminum. These alloys, in fact, support the baking operation required for the refractory support, this operation being carried out at a minimum of 1000 "C and a maximum of 1300 C. Iron-chromium-aluminum alloys are very particularly to be recommended.

As explained above, the spirally wound wire is partially embedded in the mass but not completely embedded.

Depending on the intended use, the wire wound in a spiral can be placed in different configurations as long as one part is embedded in the mass and the other outside.

According to a variant of the process according to the invention, the projecting part is formed by the end itself of the heating element and this possibly twisted end is subjected to a fixing element such as a threaded shaft.

According to another variant of the process according to the invention, a fastening element is fixed, such as a threaded rod at each end of the metal element, then one end of the fixing element is drowned in the plastic mass. of the uncooked body, then the whole is cooked.

The plastic mass of the body can conform to any desired shape: smooth, grooved, twisted, etc.

According to a variant of the invention, when the body conforms to an externally grooved and possibly hollow cylinder, for example by extrusion, the element is placed in a groove and the walls of the groove are brought together to embed said element on at minus part of its length.

 Thus in FIG. 1, it can be seen that the body 1 is cane longitudinally to present a plurality of channels 2 separated by ribs 3.

When the mass which constitutes the body 1 is still plastic, a spiral twisted wire 4 is placed in the channels 2 then, manually or mechanically, the two ribs 3 are separated separating two neighboring channels 2 so that the wire 4 is trapped and , therefore, immobilized and permanently connected to the body (or supportl).

Naturally, the spirally wound wire 4 must be connected to an electrical supply wire so that, finally, the body (or support) 1 must have at least two electrical connections with the ends of the heating element.

According to the invention, the metal elements to be connected to the support are of at least two kinds: the heating element and the connection element of the latter to the electrical supply wire.

In FIG. 1, it can be seen that the wire 4 can easily be connected by its two ends to the electric supply wires by means of two threaded rods 5 and 6 which are each placed in a channel 2 and which are each connected to a end of the wire 4 either by simple pressure, or by screwing the rods into the spiral of the wire 4, or by means of a weld or any other connecting element.

Whichever variant is used, contact is made between the wire 4 and the corresponding threaded rod 5 or 6, taking care that one end of these rods exceeds the end of the support 1. As explained above, we bring together the ribs 3 located on either side of the channel 2 in which a rod is engaged in such a way that the rod and the end of the spirally wound wire 4 are sealed at the same time, thereby obtaining two effects by the same operation: immobilization of the end of the wire 4 and fixing of the rods 5 and 6.

To obtain good electrical continuity it is good to join the wires 4 to each of the rods 5 and 6 by means of a weld for example.

 After baking, the mass which constitutes the support 1 is hardened in the position which has been given when the mass is still plastic so that the ribs 3 energetically and rigidly trap the wire 4 and the rods 5 and 6.

The rods 5 and 6 can then serve as solid supports for the electrical connections and for the mechanical connections as will be explained a little later.

In Figure 1 we have shown a very punctual deformation of the ribs 3 so that the drawing remains clearly legible but, in practice, it is more advantageous to provide this deformation over a slightly longer length and located at least at the junction between the wire 4 and the corresponding rod 5 or 6 if a weld or other positive connecting element has not been provided.

In Figure 2, we see that the wire segment 4a is perpendicular to the rib 3 which separates the two channels 2a and 2b so that the segments 4b and 4c are correctly retained longitudinally even if by extraordinary their inlay in the channels 2 was not properly performed throughout their journey.

 In this FIG. 2, an embodiment has been represented according to which the end of the wire 4 is simply twisted while in FIG. 5, a different variant has been represented because here, as in FIG. 1, the end of the wire 4 is connected to a threaded rod 5.

We will describe how to use these two variants not only for electrical purposes but for mechanical purposes.

It is necessary to provide not only the electrical connection of the ends of the wire 4 but also the fixing of the support 1.

Up to now this has been achieved by relatively complex means intended to isolate the actual support (which is very hot) from the device on which it is fixed.

We are thus obliged to provide spacers, end bases, etc.

Here, it suffices to provide these parts directly in the constituent mass of the support itself, which is particularly easy when the support is obtained by extruding the dough in profile, by means of an automatic machine.

According to a particular embodiment of the method according to the invention, a base is placed at at least one of the ex hoppers of the refractory support, the protruding ends are engaged in holes which this base presents and the said base is maintained pressed against the refractory support with, possibly, the interposition of an insulating sheet, exerting a tensile force on the protruding ends.

In FIGS. 2 and 3, it can be seen that at at least one of the two ends of the support 1 is a base 7 which is placed at the end of the support 1 with the interposition of an insulating sheet 8, for example based on asbestos or other fibrous refractory.

The base 7 of FIG. 2 is crossed by holes 9 by two of which the ends 4d of the wire 4 are passed (only one is visible). The ends 4d are twisted on themselves two, three or four times if it is necessary to constitute a segment sufficiently solid and rigid to allow to exert a traction.

Furthermore, the base 7, of any known material and suitable for this use, is provided with fixed threaded rods 10 on which are placed nuts 11 and washers 12 so that the end 4d can be wound between the two washers 12 and tighten the assembly between the nuts 11.

It should be recalled that the cooking of the refractory material which constitutes the support 1 is carried out while the wire 4 is already in place and before the fixing of the base 7, so that the end 4d which exceeds the end of the support 1 is firmly anchored in the latter and that we can act on this 4d end safely. In other words, it is possible to exert a very strong traction thanks to which the base 7 is applied against the support 1 with the interposition of the insulation 8 by means of the only ends 4d which are wound around the threaded rods 10.

There is thus obtained the mechanical fixing of the base 7 and the material connection of the end 4d and of a rod 10 on which, then, one can have a terminal carrying the electric supply wire, in the known manner.

Referring to FIG. 3, we can see another embodiment according to which the wire 4 is connected to rods 5-6 as shown in FIG. 1.

In this case, the base 7 must be pierced with holes 13 corresponding to the holes 9 in FIG. 2, that is to say located opposite the channels 2 and, therefore, rods 5-6 made integral with the support 1.

The mounting of the base 7 on the body 1 is obtained by passing the sheet of insulating product 8 through the rods 5-6 then by placing a locking nut 14 acting on the base 7 by means of a washer 15.

In this position, the base 7 is mechanically fixed to the body 1 in an absolutely rigid, solid and energetic manner.

It suffices, then, to engage on the protruding end of the rods 5-6 a terminal clamped between two washers 15 and held by a locking nut 17. The terminal 16 receives a standard electric wire A.

The assembly which has just been described (FIG. 2 or FIG. 3) can be found at the other end (not shown) of the support 1.

There is thus a complete set which can be put in place by any known means.

Thus, for example, one can use the rods 10 or the rods 5-6 to fix tabs or brackets which will serve to secure the assembly and the receiving device.

It is also possible, according to the method according to the invention, to use the malleability of the dough constituting the support 1 to press in it, before cooking, fastening elements such as brackets or pins.

Among the most interesting applications of the invention are "candles" intended for electric water heaters.

By way of example, it may be mentioned that a heating body of the type conforming to the invention has been tested and marked advantages have been obtained. Thus, one can use an iron-chrome-aluminum wire (which is cheaper than a nickel-chrome wire) in a diameter of 0.4 mm for a power of 1,800 Watts, 3x220 Volts, while with the known device the diameter should have been 0.53 mm, which represents a gain in Ohm.Kg in the ratio of 1 to 3 and a load of 6.15 W / cm2 instead of 2.7 W / cm2 , which is quite satisfactory.

The invention makes it possible to give a very exact position to the heating element, which makes it possible to completely remove the spacers which are sometimes used to move the heating part away from the porcelain or soapstone part since a base 7 (figures 2 and 3) mounted directly. Likewise, the invention makes it possible to remove on the one hand the central rod, which is necessary for fixing the usual "candles" and on the other hand an end piece serving to support this central rod.

Any means can be used to carry out the necessary mechanical and electrical assemblies at the ends of the support. One can, for example, use smooth rods (and no longer threaded) to which the ends of the wires are welded and which receive, at their other end, one or more welded lugs. This assembly makes it possible to weld said lugs in such a way that they block the base against the body. When a non-rigid insulating material is placed between the body and the base or when the base itself is made of this material, it is good to interpose only one elastic compensator between the base and the welded lugs. This element can, for example, consist of a hemispherical washer engaged on the rod.

According to a variant, a heating body according to the invention is characterized in that one end of at least one threaded rod is placed in contact with one end of a heating element while the other end of the rod protrudes one of the ends of the support, the rod being held in place by the material constituting the refractory support, as is described with reference to FIG. 1 while, according to the variant of FIGS. 2 and 3, a rod constitutes a part connecting, for example, a base.

As indicated with reference to FIGS. 2 and 3, at least one of the rods receives an organ, such as a terminal, which is placed so as to bear, possibly by means of an interposed element, against the refractory support in the purpose of opposing the relative displacement of the refractory support and the rod.

In addition, as explained above, the interposed element can be elastic in order to compensate for any longitudinal deformations due to the material constituting either an insulating sheet, or the base itself.

The invention is not limited to the embodiments described and shown but on the contrary embraces all of the variants

Claims (11)

 the protruding parts themselves.  fixing by exerting a mechanical clamping force on  subjects these protruding parts to elements of  the protruding parts are integral, then that one  that the mass cooks and becomes a rigid support of which  what we wear this set at such a temperature  mite of the metallic element a protruding part,  port, characterized in that one spares each time  pushing it into the still plastic mass :: of said sup  seeing that the metal element is fixed to the support in  fixing of the assembly in a device, of the pre-  a metallic heating element and at least one heating element  ques must include a refractory support, at least  CLAIMS 1 - Process for the manufacture of electric heating bodies 2 - Method according to claim 1, characterized in that  the protruding part is formed by the end  itself of the heating element and in that one assu  threw this possibly twisted end to an element  fixing such as a threaded rod. 3 - Method according to claim 1, characterized in that  a fastening element, such as a rod, is secured  threaded, at each end of the metal element,  then drown an end of the fastener  in the plastic mass of the uncooked body, and then  cook the whole thing. 4 - Method according to claim 1, characterized in that  the body is shaped into an externally grooved cylinder  and possibly hollow, for example by extrusion, in  what only metal is placed in a groove  and in that we bring the walls of the groove together  to embed said element on part of its length  cheerfully. 5 - Method according to any one of claims 1 to 4  above, characterized in that a base is placed at  at least one of the ends of the refractory support,  that we engage the protruding ends in steps  wise that this base presents and that we maintain said  base pressed against the refractory support with, even  tuellement, interposition of an insulating sheet, in exer  erasing a tensile force on the protruding ends  health. 6 - Heating body obtained by implementing the process  according to any one of claims 1 to 5  above. 7 - Heating body according to claim 6, characterized in that one end of at least one threaded rod is pla cee in contact with one end of a heating element  while the other end of the rod exceeds one of the ends of the support, the rod being held in  place by the material of the refractory support. 8 - Heating body according to claim 7, characterized in  what the rod constitutes a connecting piece, for example ple for a base or a power wire. 9 - Heating body according to claim 7, characterized in  that the rod receives an organ, such as a thimble, which is  placed so as to take support, possibly, by through an interposed element, against the sup  refractory port in order to oppose the move relative ment of the refractory support and the rod. 10 - Body according to claim 9, characterized in that The interposed element is elastic in order to compensate for possible longitudinal deformations due to the ma  making up either an insulating sheet or  pedestal itself. 11 - Device fitted with at least one body according to which one  conch of claims 1 to 10 above such that  water heater, infrared ray device  and the like.