Cable comprising a fire-resistant ceramic layer

Abstract

A cable, in particular a power and/or telecommunication cable, has at least one elongated electrically conductive element, and at least one fire-resistant layer surrounding said elongated electrically conductive element. The fire-resistant layer is a ceramic layer in direct physical contact with the elongated electrically conductive element.

Claims

1. A 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 a ceramic layer in direct physical contact with said elongated electrically conductive element, and said ceramic layer is obtained by heat treatment of a liquid ceramic composition, and wherein the solid ceramifiable composition comprises at least one silicon oxide and at least one aluminium oxide.

2. The cable according to claim 1, wherein the heat treatment is carried out at a temperature of at most 1100° C.

3. The cable according to claim 1, wherein the heat treatment is carried out at a temperature of at least 700° C.

4. The cable according to claim 1, wherein the ceramic layer is an inorganic layer.

5. The cable according to claim 1, wherein the liquid ceramic composition comprises at least one ceramic material.

6. The cable according to claim 5, wherein the liquid ceramic composition further comprises water.

7. The cable according to claim 5, wherein the liquid ceramic composition further comprises at least one plasticizer.

8. The cable according to claim 5, wherein the liquid ceramic composition further comprises at least one first anti-flocculation agent.

9. The cable according to claim 5, wherein the ceramic material is obtained from a solid ceramifiable composition comprising at least 15% by weight of metal oxide(s), based on the total weight of said solid ceramifiable composition.

10. The cable according to claim 1, wherein the liquid ceramic composition has a viscosity ranging from 5×10.sup.−5 to 7×10.sup.−5 m.sup.2/s (50 to 70 centistokes), said viscosity being measured according to the Ford viscosity cup.

11. The cable according to claim 1, wherein the elongated electrically conductive element has a melting temperature of at least 900° C.

12. The cable according to claim 1, wherein said cable further comprises at least one polymer layer surrounding the fire-resistant layer.

13. The cable according to claim 12, wherein the polymer layer is an electrically insulating layer.

14. A process for manufacturing a cable as defined in claim 1, wherein said process comprises at least the following steps: i) applying the liquid ceramic composition directly around at least one elongated electrically conductive element of the cable, and ii) heat treating the liquid ceramic composition to obtain the ceramic layer.

15. The process according to claim 14, wherein the heat treatment is carried out at a temperature of at most 1100° C. and at atmospheric pressure.

16. The process according to claim 14, wherein the method further comprises prior to step i), a step in which the elongated electrically conductive element is subjected to a surface treatment.

17. A liquid ceramic composition for a cable as defined in claim 1, wherein said composition comprises: at least one ceramic material comprising aluminium, silicon and oxygen, at least one first anti-flocculation agent, at least one plasticizer, and water.

18. A method for improving the fire resistance of a power and/or telecommunication cable, said method comprising the step of: applying said ceramic composition according to claim 17, to said power and/or telecommunication cable.

Description

DETAILED DESCRIPTION

Example

(1) A ceramic material in the form of a powder was prepared as follows:

(2) 300 g of silicon oxide was mixed with 100 g of aluminium oxide, 110 g of lead oxide and 440 g of dehydrated boric acid as fluxing agents, 220 g of magnesium oxide and 10 g of sodium hexafluorosilicate as second anti-flocculation agents, 90 g of titanium dioxide as a densifying agent, 140 g of calcium carbonate as a stabilizing agent, and 10 g of manganese dioxide as a binder, to form a solid ceramifiable composition.

(3) The resulting solid ceramifiable composition was then heat treated at 1200° C. (melting process), poured into a glass mould and then cooled to room temperature to form a solid ceramic material. The solid ceramic material was ground to form a ceramic powder.

(4) 1000 g of the ceramic powder was then mixed with 1000 g of water, 30 g of bentonite as plasticizer, and 50 g of magnesium oxide and 30 g of sodium hexafluorosilicate as first anti-flocculation agents, to form a liquid ceramic composition.

(5) An elongated electrically conductive copper element of 0.2 mm.sup.2 cross-section was dipped in a bath comprising the liquid ceramic composition, and then the dipped elongated electrically conductive element was heat treated by sintering with a tubular furnace at a temperature of 850° C., in order to form a fire-resistant ceramic layer around the elongated electrically conductive element of the cable.

(6) The ceramic layer thus formed meets the requirements of the following standards: NF C 32070 cat. CR1, EN 50200 (IEC 60331-2) 2h, and IEC 60331-11-23.