FR2590188A1 - CONTINUOUS CASTING LINGOTIERE WITH HOT HEAD - Google Patents

Abstract

In their upper part the walls comprise an insert (3) consisting of a thin deposit of a refractory material of low heat conductivity, which has a good resistance to thermal shocks and intended to slow down the heat exchanges, at the meniscus, between the cast metal and the ingot mould. The deposit of refractory material is obtained by spraying with a detonation gun and is made of alumina, zirconia, boron nitride or chromium carbide.

Description

CONTINUOUS CASTING LINGOTIERE WITH HOT HEAD

  The invention relates to a continuous casting ingot mold, made of copper or copper alloy, with a hot head, that is to say in which the heat exchanges, at the meniscus, between the cast metal and the ingot mold are slowed down so to mitigate

  oscillation wrinkles on the cast product.

  We know, for example from documents FR-A-2 528 738 and FR-A-2 540 409, such an ingot mold, the walls of which have at their upper part a metal insert of stainless steel, the thermal conductivity of which is lower. to that of the metal constituting the walls of the mold. In this way, the metal is less cooled in the vicinity of the meniscus, which makes it possible to reduce the depth of the oscillation wrinkles and the length of the solidified horn which accompanies their formation. It is known that such wrinkles constitute sensitive points where preferential surface cracks are created which are detrimental to the

quality of the finished product.

  The installation of this metal insert, the average thickness of which can be a few millimeters (the thickness can be uniform, or even decrease from top to bottom of the insert), is done using an expensive technique (generally plating by explosion) due to the need to obtain perfect contact between the metal insert and the wall of the mold. This necessity results in particular from the fact that any non-zero contact thermal resistance introduces non-predetermined and non-reproducible data into the overall thermal resistance of the mold. On the other hand, these ingot molds often include a surface wear coating of nickel intended to avoid the formation of star cracks in the cast product: the addition of a thermal contact resistance risks bringing the nickel to a close temperature. its use limit around 600 C (temperature of the metal near the wall: approximately

1540 C).

  The object of the invention is to propose a new type of insert for a hot-headed ingot mold, which does not have the

aforementioned drawbacks.

  According to the invention, the insert consists of a thin deposit of a refractory material with low thermal conductivity,

  having good resistance to thermal shock.

  In the field under consideration, refractory materials resist temperatures of around 1800 C. Their thermal conductivity is preferably less than Wm 1l 1, to be compared to conductivities of the order of, 100 and 300 Wm 1K-1 respectively for inserts in

  stainless steel, nickel and copper-silver alloy.

  The small thicknesses envisaged are advantageously between 2 and 5/10 of mm, to compare with the few

  millimeters of thickness of the metal inserts.

  The refractory materials are in particular alumina (melting temperature: 2040aC; thermal conductivity ranging between 2 Wm- 1K1 and higher values depending on the treatment undergone), zirconia (melting temperature: 27000C; thermal conductivity: I Wm- l K), boron nitride, or, preferably, chromium carbide (melting temperature: 1800; thermal conductivity: 7.5

W.m 1K1).

  The deposition of the material is obtained by spraying hot powdery material, for example by means of a plasma torch or preferably a detonation gun (according to the technique marketed by the company "Union Carbide Corporation"), followed polishing. This technique provides excellent bonding between the support and the filler material, and a

  homogeneous coating free of roughness.

  The deposit is made in a recess in the wall of the ingot mold, of depth equal to the thickness of the deposit, made either in the copper of the wall, or in the coating

  surface of nickel or chromium if one is provided.

  The accompanying drawings illustrate two particular embodiments of the invention. Figures 1 and 2 show partial sections through a mold wall according to

  the invention, respectively without and with surface coating.

  In FIG. 1, the copper wall I has a recess 2 3 / 10th mm thick and about fifteen centimeters high covering the region of the meniscus taking into account the oscillations on the one hand and possible level variations way. The recess 2 is filled with a deposit 3 of Cr3C2 obtained by projection with a detonation gun, followed

polishing.

  In Figure 2, the recess 2 'is made from the chrome coating 4, 0.3 mm thick, covering the wall 1' of the mold. The material 3 'is flush with the internal surface

of the mold.

Claims (7)

  1. Continuous casting ingot mold, of copper or copper alloy, the walls of which have at their upper part an insert, made of a material with thermal conductivity lower than that of copper or copper alloy, intended to slow down exchanges thermal, at the meniscus, between the cast metal and the mold, characterized in that said insert is constituted by a thin deposit of a refractory material (3, 3 ') with low thermal conductivity, having good impact resistance thermal.   2. Ingot mold according to claim 1, characterized in that the thickness of the deposit is approximately 2 to 5 tenths of a millimeter.   3. Ingot mold according to any one of claims   above, characterized in that the refractory material (3, 3 ') has a melting temperature above about 18000 C.   4. Ingot mold according to any one of claims   above, characterized in that the refractory material (3, 3 ') has a thermal conductivity of less than about 10 W.m -1-1   5. Ingot mold according to any one of claims   above, characterized in that the refractory material (3, 3 ') is chosen from the following group: alumina, zirconia, nitride boron, chromium carbide.   6. Ingot mold according to any one of claims   above, characterized in that the deposit of refractory material (3, 3 ') is obtained by spraying material hot powdery.   7. Ingot mold according to claim 6, characterized in   that the deposit is made by means of a detonation cannon.