FR2720888A1 - Protective envelope for electric components esp, immersion heating elements used e.g. in aluminium@ prodn. - Google Patents

Abstract

An outer protective envelope is claimed for an electrical component. The protective envelope is fabricated from aluminium nitride in either the massive state or in a coated state. Its use as a protective envelope for an electric immersion heating element able to smelt materials at elevated temperatures is also claimed.

Description

 The present invention relates in particular to metallurgy and, more particularly, to the melting and maintaining at temperature of products capable of melting at high temperature.

 A more specific subject of the invention is an outer casing for an electrical component, in particular a long-line thermally immersed rod with an electrical supply for heating products capable of melting at high temperature, for example such as those used for melting aluminum.

 In many fields and in particular in metallurgy, use is made of electrical heating installations which use in particular elongated immersion heaters to ensure the melting and the temperature maintenance of products capable of melting and which are liquid at temperatures of around 800 "C such as aluminum, and whose molten baths are relatively aggressive at these temperatures with respect to the materials used for the rods, in particular near the free surface of the bath of molten products. this zone often manifests a notable oxidation of the molten metal and / or the rod material.

 A solution to this problem of electric heating is for example described in the document FR 92 14 783 filed by the Applicant. The solution set out in this document consists of a long, thermally heated, electrically powered cane for heating products capable of melting at high temperature, which in particular comprises an electrically conductive element with at least one external terminal for its electrical connection, a hollow sheath with a closed bottom and a mouth closed by a nozzle with a passage for the crossing of a part of the element and if necessary locally an external protective sheath. Such a rod has the particularity that the sheath and / or the sheath which form an external envelope, are made of a non-metallic material containing carbon or even a ceramic.

In particular, the materials used to make such a sheath or such a sheath are chosen from graphite, carbon / carbon composites, composites
C / SiC, SiC / SiC composites, solid ceramics.

To make such a sheath or such a sheath, it is also possible to use ceramics based on silicon nitride, boron nitride, silicon carbide,
SiAlON or A1203. These materials are used in the solid state or in the surface coating state.

 Depending on the nature of the material chosen and the composition of the bath in which the rod is intended to be immersed, the material may be relatively sensitive to corrosion of the molten bath or else has a relatively small coefficient of thermal conductivity, most often between 5 Wm - '"C-1 and 20 Wm-1" C-1.

 We understand that with such values of coefficient of thermal conductivity, we quickly arrive at a limitation of the power dissipable by a cane with, as a consequence, an increase in the unit cost of the immersion cane and therefore the whole of the installation which results in particular from the multiplication of rods to be used to reach the required power.

 According to the invention, to make an external envelope, a sheath and / or sheath of an electrical component, aluminum nitride (A1N) is used either in the solid state or in the coating state of an other constituent substance of the envelope itself.

 Aluminum nitride offers the advantage of having a relatively high coefficient of thermal conductivity of the order of 60 Wm10C1 to 100 Wm10C- and, moreover, of being relatively very stable with respect to substances such as magnesium, zinc, aluminum, lead and their respective alloys which are among the products to be melted.

 The use of this material makes it possible to make sheaths and / or immersion heater sheaths of dimensions at least equal to those of sheaths and / or sheaths already existing and manufactured using other materials.

 Aluminum nitride makes it possible to obtain shaped or coated parts which are very resistant to corrosion, which consequently increases the longevity of the rods and which, moreover, are very resistant to thermal shocks which improves their reliability. .

 Compared to the other materials already proposed for the manufacture of immersion rods, the use of aluminum nitride allows power gains of the order of 2 or 3, all other things being equal.

 Aluminum nitride has been indicated in connection with the manufacture of envelopes for immersion rods, but it is clear that it can be used to make protective envelopes for other electrical components such as thermocouples for example.

 The above clearly highlights the distinctive features of the invention, the interest it offers and the advantages it provides.

Claims (4)

 1 - Protective outer casing for an electrical component, characterized in that it is made of aluminum nitride.  2 - Casing according to claim 1 for a long, thermowellable rod with electrical power supply for heating products capable of melting at high temperature which comprises an electrically conductive element with at least one external terminal for its electrical connection, a hollow sheath with a closed bottom and a mouth closed by a nozzle with a passage for crossing a part of the element and if necessary a sheath, characterized in that this envelope constitutes this sheath and / or sheath.  3 - Casing according to claim 1 or 2, characterized in that the aluminum nitride is used in the solid state.  4 - Casing according to claim 1 or 2, characterized in that the aluminum nitride is used in the coating state.