FR2681270A3 - Nozzle for the continuous casting of liquid metal, particularly steel - Google Patents

Abstract

The refractory wall (2) of the nozzle (1) has embedded in it a layer (3) impermeable to gases, capable of adhering to the material of the wall (2) and which prevents atmospheric oxygen from passing through this wall (2) in order to give rise to inclusions in the liquid metal, thus preserving its cleanliness (purity). If the refractory material (2) is graphitised alumina, the layer (3) may advantageously be a sheet of flake graphite.

Description

 The present invention relates to a nozzle for the continuous casting of liquid metal, in particular steel, the wall of which is made of a refractory material, such as graphite alumina.

 It is known that after preheating, the graphitized alumina is not free from a certain porosity, owing to the fact that part of the carbon has been oxidized, releasing carbon monoxide which leaves a hollow network adding to the natural porosity of the refractory. As a result, atmospheric oxygen inevitably crosses the wall of the nozzle and comes to form in the liquid metal inclusions of oxides which harm the cleanliness of the cast metal.

 In order to block possible air passages through the wall of the nozzle, it has already been proposed to coat it externally with a layer of vitreous enamel. Unfortunately, the nozzles thus coated with enamel are not satisfactory, the enamel losing during preheating its gas tightness properties.

 The object of the invention is therefore to propose a satisfactory solution to the above problem.

 According to the invention, a layer of a gas-impermeable material which can adhere to the material constituting the wall is embedded in the latter, in order to prevent atmospheric oxygen from passing through the wall towards the liquid metal.

 According to one embodiment of the invention, in which the wall is made of graphite alumina, the layer of gas-impermeable material is a sheet of lamellar graphite, a material which is particularly suitable for such use.

 According to a feature of the invention, the gas impermeable layer is advantageously inserted over the entire height of the wall and closer to the outer surface of said wall than to its inner surface.

 The invention will now be described with reference to the single appended figure which illustrates an embodiment thereof by way of non-limiting example.

 The single appended figure is a partial perspective view, on a reduced scale, of a nozzle for continuous casting of liquid metal according to the invention.

 The nozzle 1, shown in the drawing, is intended for the continuous casting of a liquid metal such as steel, and its wall 2 is made of an appropriate refractory material, such as graphite alumina.

In the wall 2 is embedded, by an operation carried out during the manufacture of the nozzle, a layer 3 of a material impermeable to gases and capable of adhering to the refractory material 2. The layer 3 must, in addition to its waterproofing characteristic gas, meet two other conditions: be compatible with graphitized alumina, that is to say have good adhesion characteristics therewith, and be able to undergo the operating conditions of the nozzle.

 If the refractory material 2 is graphitized alumina, an impermeable material which is particularly suitable for producing the layer 3 is a sheet composed of lamellar graphite, for example the product known under the brand PAPYEX marketed by the company "Le Carbone Lorraine.

 According to an advantageous embodiment, the impermeable sheet 3 is located at a distance dl from the outside surface of the wall 2 less than its distance d2 from the inside surface of this same wall. Thanks to the fact that consequently the sheet 3 is closer to the outer surface than to the inner surface of the wall 2, atmospheric oxygen, the displacement of which in the refractory material 2 is symbolized by the arrows carried on the drawing, is stopped very early in its progression inside the mass of the refractory. As a result, only the residual carbon found in the external part of the wall 2, of thickness d1, can be oxidized, the oxygen being stopped by the sheet 3.

This increases the life of the nozzle, by limiting the oxidation of the residual carbon, therefore by reducing the chemical corrosion of the wall 2.

 The cleanliness of the liquid metal poured into the nozzle 1 can no longer, practically, in these conditions, be affected by atmospheric air, prevented from passing through the wall 2.

 The invention is not limited to the embodiment described and may include variant embodiments. Thus other materials having the same properties as lamellar graphite could be used, in association with other refractories than graphitized alumina.

Claims (3)

 1 nozzle (1) for the continuous casting of liquid metal, the wall (2) of which is made of a refractory material, characterized in that a layer (3) of a material impermeable to gases and capable of adhering to the material constituting the wall is embedded in the latter, in order to prevent atmospheric oxygen from crossing the wall towards the liquid metal.  2. Nozzle according to claim 1, the wall (2) of which is made of graphite alumina, characterized in that the layer of gas-impermeable material is a sheet (3) of lamellar graphite.  3. Nozzle according to one of claims 1 and 2, characterized in that the layer (3) impermeable to gases is closer to the outer surface of said wall than to its inner surface.