Cable comprising a fire-resistant layer

Abstract

A cable including at least one elongated conductive element and at least one fire-resistant insulating layer in direct physical contact with the elongated electrically conductive element, the fire-resistant layer is obtained by heat treatment of a liquid inorganic composition.

Claims

1. Cable comprising: at least one elongated electrically conductive element; and at least one fire-resistant layer surrounding said elongated electrically conductive element, wherein said fire-resistant layer is in direct physical contact with said elongated electrically conductive element, and in that said fire-resistant layer is obtained by heat treatment of a liquid inorganic composition.

2. Cable according to claim 1, wherein the fire-resistant layer is obtained by solidification of the liquid inorganic composition.

3. Cable according to claim 1, wherein the heat treatment is performed at a temperature of at most 300 C.

4. Cable according to claim 1, wherein the liquid inorganic composition comprises at least one transition metal oxide, at least one aluminosilicate and at least one solvent.

5. Cable according to claim 4, wherein the liquid inorganic composition comprises at least 10% by weight of at least one transition metal oxide relative to the total weight of said composition.

6. Cable according to claim 4, wherein the transition metal oxide is zirconium oxide.

7. Cable according to claim 4, wherein the liquid inorganic composition comprises at least 2% by weight of at least one aluminosilicate relative to the total weight of said composition.

8. Cable according to claim 4, wherein the liquid inorganic composition comprises at least 10% by weight of at least one solvent relative to the total weight of said composition.

9. Cable according to claim 8, wherein the solvent is water.

10. Cable according to claim 4, wherein the liquid inorganic composition also comprises at least one other silicate different from said aluminosilicate.

11. Cable according to claim 4, wherein the liquid inorganic composition also comprises at least one plasticizer.

12. Cable according to claim 1, wherein the liquid inorganic composition has a viscosity ranging from 10.sup.3 to 210.sup.3 m.sup.2/s (1000 to 2000 centistokes), said viscosity being measured at a temperature of 25 C., using a No. 4 Ford viscosity cup, according to the standard ASTM D1200.

13. Cable according to claim 1, wherein the fire-resistant layer comprises at least one transition metal oxide and at least one aluminosilicate.

14. Cable according to claim 1, wherein the thickness of said fire-resistant layer ranges from 20 to 500 m.

15. Cable according to claim 1, wherein the elongated conductive element is made of copper, aluminium, a copper alloy or an aluminium alloy.

16. Cable according to claim 1, wherein said cable further comprises a plurality of elongated electrically conductive elements, each of the elongated electrically conductive elements being individually surrounded with at least one fire-resistant layer, and in that each of said fire-resistant layers is in direct physical contact with each of said elongated electrically conductive elements.

17. Cable according to claim 1, wherein said cable also comprises at least one polymer layer (4) surrounding said fire-resistant layer.

18. Process for preparing a cable as defined in claim 1, wherein said method comprises at least: i) a step of applying a liquid inorganic composition to the surface of at least one elongated electrically conductive element of said cable, and ii) a step of heat treatment of said liquid inorganic composition to form said fire-resistant layer.

19. Process according to claim 18, wherein steps i) and ii) are repeated several times.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The attached drawings illustrate the invention:

[0083] FIG. 1 schematically represents a structure, in cross section, of a cable in accordance with the invention according to a first embodiment.

[0084] FIG. 1 shows a cable (1) in accordance with the invention comprising an elongated electrically conductive element (2) and a fire-resistant layer (3) surrounding said elongated electrically conductive element (2), and being in direct physical contact with the elongated electrically conductive element (2). The elongated electrically conductive element (2) is notably a copper wire.

[0085] FIG. 2 schematically represents a structure, in cross section, of a cable in accordance with the invention according to a second embodiment.

[0086] FIG. 2 shows a cable (10) in accordance with the invention comprising the elongated electrically conductive element (2) and the fire-resistant layer (3) as described in FIG. 1, and also an electrically insulating layer (4) surrounding the fire-resistant layer (3). The electrically insulating layer (4) may be, for example, a layer of a polyethylene-based polymer material, formed notably by extrusion.

[0087] FIG. 3 schematically represents a structure, in cross section, of a cable in accordance with the invention according to a third embodiment.

[0088] FIG. 3 shows a cable (100) in accordance with the invention comprising several elongated electrically conductive elements (2), each elongated electrically conductive element (2) being successively surrounded with the fire-resistant layer (3) and the electrically insulating layer (4), each elongated electrically conductive element, fire-resistant layer and electrically insulating layer being as described in FIG. 2. The cable (100) also comprises a protective sheath (5) surrounding all of the constituent elements of the cable. The protective sheath (5) may be, for example, a layer of HFFR type polymer, formed notably by extrusion. The protective sheath may also surround a metal shield (not shown), said metal shield surrounding all of the constituent elements of the cable. The metal shield may be, for example, one or more metal strips, notably made of galvanized steel.

DETAILED DESCRIPTION

[0089] Other characteristics and advantages of the present invention will emerge in the light of the examples that follow with reference to the annotated figures, said examples and figures being given for illustrative purposes and not being in any way limiting.

EXAMPLES

Example 1: Preparation of a Cable in Accordance with the Invention Including a Fire-Resistant Layer 150 m Thick

[0090] A copper wire with a diameter of 1.2 mm was dipped in an aqueous solution with a viscosity of about 1.210.sup.3 m.sup.2/s (1200 centistokes) (measured at a temperature of 25 C., using a No. 4 Ford viscosity cup, according to the standard ASTM D1200), sold by the company Aremco under the reference Pyropaint 634-ZO, and then subjected to a heat treatment at a temperature of 250 C. for a time of 30 seconds, using a ceramic radiant heating system.

[0091] After the heat treatment, a cable covered with a fire-resistant white layer 50 m thick was obtained.

[0092] The steps of dipping the copper wire in the Pyropaint 634-ZO solution and of heat treatment were then repeated twice under the same conditions.

[0093] A cable covered with a fire-resistant white layer 150 m thick was obtained.

Example 2: High-Temperature Resistance Test

[0094] The cable obtained above in Example 1 was placed in a vertical oven heated at 830 C. for 30 minutes in order to test the resistance of the layer applied to the copper wire to exposure to a very high temperature.

[0095] After this test, it was observed that the fire-resistant layer had not suffered any degradation (no cracking) and that it thus efficiently protects the copper wire against the harmful effects of exposure to a very high temperature.