EP0756439B1 - Heating element and method for sealing such an element - Google Patents

Description

The present invention relates to the field of heating subassemblies used in electrical appliances and in particular in appliances appliances. The invention relates to heating elements of the shielded type and in particular a method of manufacturing and capping such elements heating.

It is already known to plug shielded heating elements using a liquid silicone resin in combination with an insulating bead mounted on the heating element and a possible steaming operation to polymerize said resin. It is also known to use a silicone adhesive deposited in cold, which seals a ceramic bead. Such methods of capping have the disadvantage of using well sized and shaped beads specially adapted to these methods. In addition the number of steps for implementing these methods as well as their complexity increase the manufacturing time and the cost of the heating elements thus produced. US 4,314,401 discloses a heating element according to the state of the prior art.

The object of the present invention is thus to remedy the disadvantages of the prior art and to achieve low cost of heating elements having a good behavior over time, especially at the level of the containment of the magnesia contained in said heating elements.

Another object of the present invention is to simplify the process shutter or plugging of the heating elements and in particular to automate in an extremely simple way all the steps of this process.

A complementary object of the present invention is to replace the ceramic beads of these heating elements by parts or means inexpensive and easily achievable industrially.

The objects assigned to the present invention are achieved with the aid of an element heating element, comprising a metal tube in which a wire is arranged resistive, magnesia providing electrical insulation of said wire and the transmission to the metal tube, a connection terminal attached to each end of said wire and protruding from the metal tube, as well as means for sealing the heating element made using a means electrical insulation of the connection terminal and a material based on silicone filling the inside of the metal tube in the available space between the connection terminal and said tube, characterized in that the isolation means electrical connection is associated with means for centering the connection terminal in the metal tube the arrangement of the electrical insulation means and the centering means not completely closing said tube.

According to an advantageous embodiment, the electrical insulation means of the connection terminal and the centering means of the connection terminal in the metal tube consist of one piece.

• à introduire dans un tube métallique un fil résistif muni de bornes de connexions à ses extrémités,
• à disposer un moyen d'isolation électrique de la borne de connexion et des moyens de centrage de la borne de connexion dans le tube métallique,
• à remplir le tube de magnésie pour assurer l'isolation électrique et la transmission thermique,
• à déposer un matériau à base de silicone dans le tube métallique de préférence autour de la borne de connexion afin de sceller le tube métallique contenant la magnésie.

The objects assigned to the present invention are also achieved by means of a method of sealing a shielded heating element consisting of:

• to introduce into a metal tube a resistive wire provided with connection terminals at its ends,
• disposing an electrical isolation means of the connection terminal and centering means of the connection terminal in the metal tube,
• to fill the magnesia tube for electrical insulation and thermal transmission,
• depositing a silicone material in the metal tube preferably around the connection terminal to seal the metal tube containing the magnesia.

• la figure 1 représente une vue partielle en coupe d'exemple de réalisation d'un élément chauffant conforme à l'invention,
• la figure la représente une vue en section selon la ligne A-A de la figure 1,
• la figure 2 représente une vue partielle en coupe d'une variante de réalisation d'un élément chauffant conforme à l'invention,
• la figure 3 représente une vue partielle en coupe d'une autre variante de réalisation d'un élément chauffant conforme à l'invention,
• la figure 3a représente une vue en section selon la ligne A-A de la figure 3,
• la figure 4 représente une vue en coupe d'une variante préférentielle de réalisation d'un élément chauffant conforme à l'invention,
• la figure 4a représente une vue en section selon la ligne A-A de la figure 4,
• la figure 5 représente une autre variante d'un élément chauffant conforme à l'invention et représenté à la figure 4.

Other features and advantages will emerge more clearly on reading the description given below with reference to the appended drawings given as illustrative but non-limiting examples in which:

• FIG. 1 represents a partial sectional view of an exemplary embodiment of a heating element according to the invention,
• FIG. 1a is a sectional view along line AA of FIG. 1,
• FIG. 2 represents a partial sectional view of an alternative embodiment of a heating element according to the invention,
• FIG. 3 represents a partial sectional view of another variant embodiment of a heating element according to the invention,
• FIG. 3a shows a sectional view along the line AA of FIG. 3,
• FIG. 4 represents a sectional view of a preferred embodiment of a heating element according to the invention,
• FIG. 4a shows a sectional view along the line AA of FIG. 4,
• FIG. 5 represents another variant of a heating element according to the invention and represented in FIG. 4.

FIG. 1, representing a heating element according to the invention, shows a metal tube 1, more particularly in the vicinity of an end 1a metal tube 1. Figure 1 also shows magnesia 2 inside of the tube 1 and a connection terminal 4 associated with an isolation means electrical connection terminal 4. The latter is intended for connect the heating element to a power source.

The shutter means of the shielded heating element according to the invention advantageously consist on the one hand, of a means of electrical insulation of the connection terminal 4 and secondly, a centering means of the terminal connection. When assembling, the tube is definitely clogged using of a silicone-based material deposited inside the metal tube 1 and spreading on the surface of magnesia 2, which does not completely fill the metal tube 1. The silicone material, not shown in the figures, is a cross-linked or polymerized silicone resin to effectively cover magnesia 2 and thus plug the heating element. The connection terminal 4 is advantageously immersed in magnesia 2 inside the tube metal 1 on the one hand and protrudes out of the metal tube 1 on the other.

The electrical insulation means is for example made of a material ceramic or polymer. Preferably the electrical insulation means is a piece threaded and fixed on the connection terminal 4. The isolation means electric is for example as shown in Figures 1, 3, 4 and 5, a sleeve 6 preferably comprising a tubular central portion 10 and provided with means for centering the connection terminal 4 in the tube metal 1, said centering means not completely closing said tube 1. This arrangement makes it possible to maintain communication between the interior and the outside of the metal tube 1 after the insertion of said sleeve into said tube 1.

The sleeve 6 is advantageously made of a plastic material resistant to high temperatures. These high temperatures correspond on the one hand to the operating temperatures of the elements according to the invention and on the other hand at the stoving temperatures magnesia 2 contained in the metal tube 1. The latter, once compacted and dehydrated using a steaming operation, immersed advantageously at least partially the electrical insulation means of the connection terminal 4 while not completely filling the tube metallic 1; there is therefore a free space 1b delimited by the metal tube 1, the magnesia 2 and the connection terminal 4 associated with the insulation means electric. This space 1b free is used to spread the silicone resin. The connection terminal 4 serves to connect a resistive wire 3, embedded in the magnesia 2 and constituting the source of heat, on a power supply. The electrical insulation means makes it possible in particular to avoid a short circuit between the connection terminal 4 and the metal tube 1. Such a risk can come from example of the accidental presence or not of drops of liquids or other products on the heating element.

The connection terminal 4 is advantageously provided with at least one deformation 5 or a shoulder 5a as shown in FIGS. 3, 4 or 5 to retain in translation the electrical insulation means. The deformations 5 are obtained for example by crushing the terminal of connection 4 or in any other known manner keeping ears. According to an alternative embodiment of the connection terminal 4 shown in FIG. 3, the deformations 5 are replaced by the shoulder 5a obtained directly by construction of the connection terminal 4. In this embodiment, the sleeve 6 providing the insulation of the connection terminal 4 is also partially embedded in the magnesia 2 and abuts at its other end against the shoulder 5a.

The centering means of the connection terminal 4 in the metal tube 1 advantageously consist of at least one branch 8 connected to the part tubular central unit 10 of the sleeve 6 and having a peripheral portion 11 ensuring contact with the metal tube 1.

Figure la shows a cross section along the line A-A of Figure 1 of the sleeve 6. In this embodiment, the sleeve 6 has a branch 8 ending in a peripheral portion 11 of tubular form covering at least 180 ° so as to maintain said sleeve 6 in the metal tube 1.

Figure 3a shows a cross section along the line A-A of Figure 3 of the sleeve 6. In this other embodiment, the sleeve 6 presents two branches 8 each terminating in a peripheral portion 11.

FIG. 4 represents a sectional view of a preferred variant of realization of a heating element according to the invention. In this variant, the electrical insulation means is a sleeve 6 having a configuration at least three branches 8 distributed symmetrically with respect to an axis of x-x 'symmetry of the metal tube 1.

Figure 4a shows a cross section along the line A-A of Figure 4 of the sleeve 6. This cross section shows an example with four 8 branches symmetrical with respect to the x-x 'axis of the sleeve 6 or the element heating according to the invention. Figure 4a also shows a piercing 9 crossed by the connection terminal 4.

The sleeve 6 advantageously rests on the magnesia 2 inside the tube metal 1 and abuts with its other end against deformation 5 and the connection terminal 4. The sleeve 6 can also according to another mode of embodiment of the invention to be secured to the connection terminal 4 by means of any known means and in particular by a mounting force. Figure 4 shows also a syringe 15 intended to fill the space 1b between the branches 8 with a liquid silicone resin, which will be polymerized or cross-linked by the following. The dimensions of the sleeve 6 are advantageously chosen for allow its introduction with play inside the metal tube 1.

In the exemplary embodiment of the shielded heating element according to the invention and shown in FIG. 5, the branches 8 extend radially through relative to the symmetry axis x-x ', but have dimensions reduced by relative to the total axial length of the sleeve 6. The branches 8 are located so completely immersed in the metal tube 1 therefore in the liquid silicone resin spread in space 1b available above the Magnesia 2. The part of the sleeve 6 protruding out of the metal tube 1 has a cylindrical shape surrounding the connection terminal 4 and coming into stop against the deformation 5. Such a configuration of the sleeve 6 allows to spread more evenly the silicone resin in the space 1b delimited by the metal tube 1, the connection terminal 4 associated with the sleeve 6 and the magnesia 2.

In the embodiment of the heating element according to the invention and shown in FIG. 2, the electrical insulation means comprises a enamelled coating 7 projected over the entire periphery of the connection terminal 4. A sleeve not shown in said figure threaded on the connection terminal 4 makes it possible to center said terminal 4. This means of electrical insulation also allows to save near the end of the tube 1, the space 1b for receiving the silicone resin.

The method of sealing a shielded heating element in accordance with the present invention of introducing into a metal tube 1 the resistive wire 3 provided of connection terminals 4 at its ends, and to use magnesia 2 for ensure electrical insulation and heat transfer and to use a means for sealing the heating element further comprises steps complementary.

These consist on the one hand to use a means of electrical insulation of the connection terminal 4 in combination with the silicone material in as sealing means and secondly to deposit said material based on silicone in the metal tube 1, preferably around the terminal of connection 4 to confine the magnesia 2 inside the metal tube 1. In consequence any contact or communication between the magnesia 2 and the gaseous or liquid medium in which the heating element is used is stop. The insulation of the connection terminal 4 is done within the framework of the process according to the invention before using the silicone-based material resin type for plugging the heating element.

The method according to the invention also consists in using means of centering of the connection terminal 4 in the metal tube 1 arranged on the periphery of the electrical isolation means of the connection terminal 4 and not completely obturating said tube 1. Thus magnesia 2 can be introduced into the metal tube 1 after the isolation of the connection terminal 4 held in place relative to the inner walls of the metal tube 1.

The process according to the invention also consists in intimately binding the means of electrical insulation of the connection terminal 4 and introduce them in the metal tube 1 before the steps of filling the tube metallic 1 with magnesia 2, to compact and to dehydrate said magnesia 2. The realization of a heating subassembly consisting of a terminal of connection 4 having a means of electrical insulation and possibly deformations 5 makes it possible to simplify the capping process and consequently the method of manufacturing the shielded heating element according to the invention.

The process according to the invention also consists in using a piece of type sleeve to put it on the connection terminal 4 and thus to achieve less partially its electrical insulation. The latter is completed by the silicone-based material and magnesia 2 dehydrated and compacted to inside the metal tube 1.

According to a variant of the process according to the invention, the latter consists of project the enamelled coating 7 on the connection terminal 4 to obtain its electrical insulation. Such an operation is easily automatable and requires no manual intervention. It is the same for the threading of the sleeve-type part on the connection terminal 4. The method according to the invention also consists in deforming the connection terminal 4 after having threaded the sleeve 6 on the latter, so as to retain in translation said sleeve 6.

A considerable advantage of the process according to the invention lies in the insulation of the connection terminal 4 before any resinsing operation, thus simplifying said method.

Another advantage of the present invention is obtained with a possible capillary rise of a silicone resin, during filling of the tube 1, between the connection terminal 4 and the part threaded on this last. Such a lift contributes to the maintenance and fixation of the said piece on the connection terminal 4. The resin can in this case realize the interface between the connection terminal 4 and its isolation means.

An advantage of the sealing method according to the invention lies in the implementation of successive steps, all easily automated to a lower cost.

Another advantage of the present invention lies in the possible use of a particular silicone resin capable of undergoing treatment with a ultraviolet radiation to obtain a polymerization of said resin. In effect the absence of beads closing the metal tube 1 allows the radiation to directly access the resin. Such an operation may replace an additional stoving.

Another advantage of the process according to the invention therefore lies in the automatic assembly of the part performing the electrical isolation of the terminal connection 4 and the removal of a manual installation of a bead on the tube 1. Such operations may be carried out before the heating elements according to the invention are formed, ie before that they do not have their final configuration, which in most case is not straight.

All these advantages lead to another significant advantage allowing substantially reduce the cost of manufacturing the armored heating elements according to the invention.

As a variant, it is possible to imagine that the electrical insulation means and the centering means of the connection terminal 4 consist of more than one element, for example that the electrical insulation means and the means of centering consist of two separate parts, or that the means of centering themselves by more than one piece.

Claims (12)

1. A metal-clad heater element comprising a metal tube (1) having arranged therein: a resistor wire (3); magnesia (2) serving to insulate said wire electrically and to transmit heat towards the metal tube (1); a connection terminal (4) fastened to each end of said wire and projecting out from the metal tube (1); and closure means for closing the heater element, the closure means being made with the help of electrical insulation means (6; 7) for each connection terminal (4) and a material based on silicone filling the inside of the metal tube (1) in the space (1b) available between the connection terminal (4) and said tube (1), the element being characterized in that the electrical insulation means is associated with means for centering the connection terminal (4) in the metal tube (1), the arrangement of the electrical insulation means and the centering means not completely closing said tube (1).
2. A metal-clad heater element according to claim 1, in which the electrical insulation means of the connection terminal (4) and the centering means for centering the connection terminal (4) in the metal tube (1) are constituted by a single part.
3. A metal-clad heater element according to claim 2, in which the means for centering the connection terminal (4) in the metal tube (1) are advantageously constituted by at least one branch (8) connected to the tubular central portion (10) of the sleeve (6) and presenting a peripheral portion (11) providing contact with the metal tube (1).
4. A metal-clad heater element according to claim 2, in which said part forms a sleeve (6).
5. A metal-clad heater element according to claim 4, in which the sleeve (6) presents a configuration having at least three branches (8) distributed about an axis of symmetry (x-x').
6. A metal-clad heater element according to any one of claims 1 to 5, in which the silicone-based material is a cross-linked or polymerized silicone resin for covering the magnesia (2) and thus plugging the heater element.
7. A metal-clad heater element according to any one of claims 4 to 6, in which the sleeve (6) is made out of a plastics material that withstands high temperatures.
8. A metal-clad heater element according to any one of claims 4 to 7, in which the connection terminal (4) is provided with deformations (5) for holding the sleeve (6) in translation.
9. A method of closing a metal-clad heater element, the method consisting in:

   · introducing a resistor wire (3) carrying connection terminals (4) at its ends into a metal tube (1);

   · disposing means for electrically insulating the connection terminal (4) and means for centering the connection terminal (4) in the metal tube (1);

   · filling the tube (1) with magnesia (2) to provide electrical insulation and heat transmission; and

   · disposing a silicone-based material in the metal tube, preferably around the connection terminal (4) in order to seal the metal tube (1) containing the magnesia (2).
10. A method according to claim 9, in which the electrical insulation means and the connection terminal (4) are intimately bonded together and are introduced into the metal tube (1) before the steps consisting in filling the metal tube (1) with magnesia (2), in compacting said magnesia (2), and in dehydrating said magnesia (2).
11. A method according to claim 9 or claim 10, in which a sleeve (6) is used for threading onto the connection terminal (4) and thus for providing at least part of its electrical insulation.
12. A method according to claim 11, in which the connection terminal (4) is deformed after the sleeve (6) has been threaded thereon, so as to hold said sleeve (6) in translation.

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