WO1994007628A1

WO1994007628A1 - Continuous casting mould

Info

Publication number: WO1994007628A1
Application number: PCT/GB1993/002067
Authority: WO
Inventors: David Alan Preshaw; Timothy Reynolds
Original assignee: Davy Mckee (Sheffield) Limited
Priority date: 1992-10-06
Filing date: 1993-10-05
Publication date: 1994-04-14
Also published as: GB9221006D0

Abstract

A continuous casting mould for generally rectangular metal slabs comprises two metal plates with end wall assemblies between them, a portion of the mould passage from the outlet end to a position inwards of the outlet end has a substantially uniform dimension, and each end-wall assembly has a heated region at the inlet end of the mould and a cooled region at the outlet end.

Description

CONTINUOUS CASTING MOULD

This invention relates to a continuous casting mould for producing elongate metal slab of generally rectangular cross-section normal to its length.

A continuous slab caster mould usually consists of two generally plain and rectangular wide faces separated at each end by two generally plain and rectangular narrow faces, thereby creating a box within which liquid metal, usually steel can be contained and solidified. The mould faces are made from copper or copper alloy plates which are water cooled. The purpose of the mould plates is to bring about the solidification of the molten metal adjacent to them to create a shell of thickness sufficient (with assistance from casting plant elements present after the mould) to contain and support the internal liquid core.

Conventional moulds usually produce slabs thicker than 150mm, however recent trends have resulted in the development of "Thin Slab Casting" in which moulds produce slabs less than 150mm, typically 50 to 90mm thick. To maintain casting output it is necessary to provide a means of pouring metal into the inlet end of the mould passage at conventional caster rates and to achieve this, variously shaped moulds and feed tubes have been developed.

All of the existing commercially applied techniques utilise water cooling outside of the entire internal surface area of the casting mould and the end walls of these moulds are of regular cross section equal to that of the thin slab being produced at the mould exit.

An object of the present invention is to provide a continuous casting mould for producing elongate metal slab, particularly thin slab, which is simpler in construction than prior art moulds. According to the present invention a continuous casting mould for producing an elongate metal slab of generally rectangular cross-section normal to its length, comprises two metal plates spaced apart with two end-wall assemblies located between and abutting the plates; the plates and the end-wall assemblies together defining the mould passage; each of the plates having a width dimension, a depth dimension extending from the inlet end to the outlet end of the mould passage and being shaped such that between the outlet end of the mould passage and a position intermediate the inlet and outlet ends of the mould passage, the dimension of the mould passage transverse to the width dimensions of the metal plates is substantially uniform and is less than the corresponding dimension at the inlet end of the mould passage; and the depth dimension of each end-wall assembly from the inlet end to the outlet end of the mould passage is made up of two regions, the first of which extends from the outlet end of the mould passage at least to the intermediate position and has cooling means associated with it and the second region extends from the first region to the inlet end of the mould passage and has heating means associated with it whereby in use, solidification of the molten metal is encouraged in contact with the first region and is discouraged in contact with the second region.

The thickness of the thin slab exiting the mould can be such that it can be used directly in the finishing stands of a hot strip rolling mill.

The second region of each end-wall assembly may be produced from any refractory material suitable for continuous contact with liquid steels. It may comprise one part or be made up of two or more parts. Heating may be by means of electrical resistance elemen (s) or fuel gas and may be applied prior to as well as during the casting operation.

The or each part of each end-wall assembly which constitutes the second region may have a working face which is flat or profiled, such that good contact is maintained with the end faces of the thin slab being cast.

The first region of each end-wall assembly is of metal and is conveniently water cooled and may be produced from one or more parts each of which may be articulated so as to be able to follow the position of the end-wall assemblies which may change due to deformation and or thermal contraction, thereby maintaining good physical contact with them.

The first region of the end-wall assembly may be produced from any high conductivity alloy suitable for use as mould walls when casting liquid steels i.e., Alloy Steel, Copper or copper alloys.

The or each part of the region may have a working face which is flat, or profiled such that good support contact is maintained with the end faces of the thin slab being cast.

The end-wall assemblies may extend beyond the outlet end of the mould passage by such an amount as may be necessary to ensure adequate thin slab end wall shell thickness to minimise the possibility of detrimental bulging or liquid metal breakout.

The parts making up the regions of each end wall assembly are mounted on ct common rigid support system which may be moved towards or away from the centreline of the mould assembly during the casting process, thereby varying the width of the thin slab being produced.

Temperature measuring devices, conveniently thermocouples, may be built into the parts of the end wall assemblies for the purpose of end-wall condition monitoring and control and monitoring of the primary solidification process.

In order that the invention may be more readily understood it will now be described by way of example only, with reference to the accompanying drawings in which:-

Fig. 1 is a PERSPECTIVE VIEW of a continuous casting mould in accordance with the present invention and;

Fig. 2 is a SECTIONAL END ELEVATION of the mould on the line II-II of Fig. 1.

A continuous casting mould for producing an elongate metal slab less than 150mm thick, typically a thin slab of 50 to 90mm thick, comprises a pair of shaped metal plates (1) and a pair of end-wall assemblies (2, 4, 5) located between and abutting the plates (1) so as to separate the plates and together they define a mould passage P.

Each metal plate (1) is shaped so that at the inlet end of the mould passage the plates are spaced apart to accommodate the lower end of a feed tube (6) , and at a position approximately half way between the inlet and outlet ends of the mould passage, the two plates (1) come towards each other and are spaced apart by a distance "t" substantially equal to the thickness of the slab to be cast. This spacing "t" of the plates 1 extends to the outlet end of the mould passage. The outer faces of the plates (1) are provided with outer cover plates 1A to which they are sealed to accommodate liquid for cooling the plates.

The depth dimension of each end-wall assembly from the inlet end to the outlet end of the mould passage is made up of two regions 2 and 4. The region 2 at the inlet end of the mould passage comprises one part of refractory material and has an electrical heating element 3 embedded in it or on the outside of it. However, the region 2 could be made up of two or more parts, each of refractory material, but having different heating capacities so that the heating provided to the region can be adjusted over the depth of the region.

The region 4 of each end-wall assembly extends from the outlet end of the mould passage to at least a position where the depth "t" of the mould passage is reduced so that it becomes equal to the depth "t" at the outlet end of the mould passage. The region 4 shown in the figures is made up of one metal part having provision (not shown) by which water can be circulated through its interior, or alternatively on its outside, to cool it. However, the region 4 can be made up of two or more parts engaging each other and each provided with cooling means.

The end-wall assemblies extend beyond the outlet end of the mould passage by arranging for the region 4 of each end-wall assembly to have an extension portion 5.

Thermocouples (7) are located at various positions in the end-wall assemblies.

In use, molten metal is introduced by the feed tube (6) into the mould passage and a meniscus level M is formed just below the upper edges of the plates (1) and end- wall assemblies (2). Heat is supplied via the elements 3 to heat the regions (2) of the end-wall assemblies so that the molten metal does not commence to solidify whilst in contact with them.

Solidification of the molten metal is encouraged to occur against the mould wall of the mould passage where the depth of the passage transverse to the width of the metal plates is uniform. The regions 4 of the end-wall assemblies are cooled and the corresponding lower parts ofthe plates 1 are also cooled. The casting is withdrawn, by means not shown, from the outlet end of the mould and below the outlet end, the extensions (5) prevent bulging of the end walls of the rectangular casting or break-through of the molten metal through these walls.

The plates 1 may be arranged to include a low conductivity wall section locally at the metal meniscus region. This section could be unheated or heated by external means. The effect of these sections is to delay the onset of solidification around the entire metal meniscus to a position beneath the free liquid surface.

Claims

Claims :

1. A continuous casting mould for producing an elongate metal slab of generally rectangular cross-section normal to its length, comprising two metal plates (1) spaced apart with two end- wall assemblies (2,4) located between and abutting the plates; the plates and the end wall assemblies together defining the mould passage (P) ; each of the plates (1) having a width dimension, a depth dimension extending from the inlet end to the outlet end of the mould passage and being shaped such that between the outlet end of the mould passage and a position intermediate the inlet and outlet ends of the mould passage, the dimension (t) of the mould passage transverse to the width dimensions of the metal plates is substantially uniform and is less than the corresponding dimension at the inlet end of the mould passage; and the depth dimension of each end wall assembly from the inlet end to the outlet end of the aould passage is made up of two regions (2,4), the first of which extends from the outlet end of the mould passage at least to the intermediate position and has cooling means associated with it and the second region extends from the first region to the inlet end of the mould passage and has heating means (3) associated with it whereby in use, solidification of the molten metal is encouraged in contact with the first region and is discouraged in contact with the second region.

2. A continuous casting mould as claimed in claim 1 in which the second region of each end-wall assembly is of refractory material and the first region is of metal.

3. A continuous casting mould as claimed in claim 2 in which the first region and/or the second region is made up of two or more parts.

4. A continuous casting mould as claimed in claim 1, 2 or 3 in which the first region of each end-wall assembly extends beyond the outlet end of the mould passage.

5. A continuous casting mould as claimed in any preceding claim in which temperature measuring devices are associated with each of the first and second regions of each end-wall assembly.

6. A continuous casting mould as claimed in any preceding claim in which the depth dimension of each plate includes a part towards the inlet end of the mould passage against which, in use, the meniscus level is formed and the operating temperature of said part being such as to discourage solidification of molten metal in contact with said part.