CONTINUOUS CASTINGS DIE WITH COOLANT CHANNEL

Abstract

In a continuous casting chill (1) with a coolant duct (2), which is formed by a chill inner wall (3), facing the molten metal, as the hot side, a chill outer wall (4) as the cold side and a right side wall (5) and a left side wall (6), the coolant duct (2) is constructed with turbulence-generating elements (7, 9, 10).

Description

The invention relates to a continuous casting chill with a coolant duct, which is formed by a chill inner wall facing the molten metal, as the hot side, a chill outer wall as the cold side and a right and a left side wall.

From DE 198 26 522 A1 a chill wall of a continuous casting chill is known, which consists of a chill inner plate and a water compartment connected to the chill inner plate by screw connections, with the chill inner plate having on its side facing the water compartment webs with grooves running therebetween, in which fillers are arranged. The grooves serve here as cooling ducts for a coolant, generally water. The fillers serve to reduce the duct cross-section, so that the speed of flow of the coolant in the cooling duct is increased.

DE 198 42 674 A1 describes similar fillers.

Continuous casting chills with cooling ducts are additionally known from the documents DE 101 22 618 A1, DE 100 35 737 A1 and DE 101 38 988 C2.

From DE 102 53 735 A1 a chill is known for the continuous casting of molten metals, particularly of steel, with cooling ducts such as cooling grooves, cooling slits or cooling bores in the contact surface lying opposite the chill hot side. The heat transmission of the chill is improved in that the geometric shapes of the heat-transmitting surfaces of a cooling duct or of a group of cooling ducts is adapted in form, cross-sectional area, circumference, boundary surface quality, orientation to the contact surface, arrangement and/or arrangement density with respect to the contact surface of the local formation of heat flow density and/or temperature of the contact surface in the casting operation, and in particular in the region of the casting level.

During continuous casting, the fluid melt flows out from a continuous casting distributor through an immersion tube into an oscillating, water-cooled copper chill. As a result of the heat dissipation, the melt temperature falls below the solidus temperature and a thin strand shell is formed which is withdrawn in the casting direction. With increasing cooling, the thickness of the strand shell increases until the strand is completely solidified. Depending on the format and number of strands, casting speeds of 6 m/min and above are nowadays achieved. Typical local heat flow densities lie in the order of up to 12 MW/square metre.

The heat flow which is carried off by the coolant is, inter alia, dependent on the geometry of the coolant ducts, the roughness of the walls and the through-flow speed and hence also on the degree of turbulence. The higher the degree of turbulence on the coolant side, the more intensive is the intermixture and all the more heat is carried off. The heat-transmitting area can in fact be increased, but close limits are set for this increase. Particularly in the case of very high heat flow densities, a contamination frequently takes place of the heat-transmitting surfaces by deposits, which is known as fouling. As the deposits have a very low thermal conductivity, fouling in the case of chill cooling leads to an intensive increase in the copper temperature and hence to a reduced service life of the chill.

Conventional continuous casting chills are formed with rectangular coolant ducts which are flowed through at speeds of flow of approximately 10 m/s. In these coolant ducts, with Reynolds numbers of approximately 250,000 a turbulent flow forms with a main component in the axial direction. The basic turbulence leads to an increased exchange or mass, impulse and energy between the individual coolant layers. Close to the wall, flow- and temperature boundary layers form which can be described by so-called logarithmic wall laws. The turbulence is attenuated with increasing proximity to the wall. The main disadvantage of conventional cooling lies in the directed turbulence with predominant components in the axial flow direction and lower components in the radial flow direction.

The invention is based on the problem of providing a continuous casting chill in which the recrystallization process of the chill material or the material of the walls of the coolant duct which is dependent on the operating temperature and the duration of operation, is decelerated, the service life of the chill and the turbulence are increased and a homogeneous intermixture of the coolant is achieved.

This object is achieved according to the invention in that in a continuous casting chill with a coolant duct which is formed by a chill inner wall facing the molten metal as the hot side, a chill outer wall as the cold side and a right and a left side wall, the coolant duct is formed with elements which generate turbulence. Through the introduction of turbulence-generating elements, generally a more intensive intermixture of the coolant is achieved. At the same time, the turbulence-generating elements increase the heat-transmitting area of the coolant duct or of the chill walls. The cooperation of the two measures, i.e. turbulence generation and increase of the heat-transmitting area, improves the local heat transmission from the walls of the coolant duct or from its walls to the coolant, which then carries off the heat.

The fundamental principle of all turbulence-generating elements is based on the turbulence-induced transportation of mass, impulse and energy. The thermal transmission in the coolant duct of continuous casting chills is improved in accordance with the invention. As a result of the more intensive intermixture, the turbulence generators lead to higher local heat flow densities, i.e. the heat which is carried off per unit of area is increased. The turbulence, both in the vicinity of the wall and also in the region of the core flow is increased and a homogeneous intermixture is achieved. Through the turbulence-generating elements, a better intermixture of the cooling water is achieved and the temperature level in the copper is reduced, with the recrystallization process of the chill material or of the material of the walls of the coolant duct, which is dependent on the operating temperature and duration, being decelerated. This leads to an increase in the service life of the chill. The material of the chill or of the chill walls is, for example, copper, partially copper or another material. In addition, the contamination and the tendency to deposits are reduced by the increased turbulence and the greater shear forces on the hot side of the cooling duct.

On the rear edge of the turbulence-generating elements, the water flow breaks off and a non-steady and eddied, ie. turbulent recirculation area forms. A first embodiment of turbulence-generating elements consists of horizontal stages in the coolant which are formed for example by rectangular profiles which extend over the entire width or partial regions of the coolant duct. A second and third embodiment of turbulence-generating elements has the form of tetrahedra and winglets. In these forms, inwardly turning vortex trains are induced which lead to an even more intensive intermixture of the coolant. Vortex trains can be seen for example at the end of an airfoil or behind motor vehicles, where they are basically undesired. The turbulence-generating elements are arranged on the hot side for example staggered one behind the other, with the spacing being determined applicably by the spatial extent of the recirculation area lying upstream. Alternatively, the turbulence-generating elements can also be installed on the cold side, because the effect of the recirculation extends up to the hot side. A combination of tetrahedra on the cold side and horizontally arranged stages on the hot side of the coolant duct is also possible. Likewise, it is conceivable to install the turbulence-generating elements only in the inlet of a coolant duct or only at the height of the casting level, in order to keep the expenditure as regards manufacturing technology within limits. In addition to the above-mentioned effects with regard to flow technology, the heat-transmitting area is increased somewhat by the turbulence elements, by approximately 6% with the described tetrahedra. In this way, the local heat flow density is also increased. The pressure loss can be kept low through the dimensions of the turbulence elements which are not selected to be too great.

The basic mode of operation of the coolant duct according to the invention can be verified by means of numerical flow simulations (CFD—Computational Fluid Dynamics).

Example embodiments of the invention are described in further detail by means of very diagrammatic drawings.

FIG. 1 a part of a continuous casting chill in three-dimensional illustration;

FIG. 2 the continuous casting chill in front view in section with turbulence-generating elements according to a first embodiment;

FIG. 3 the continuous casting chill in front view in section with turbulence-generating elements according to a second embodiment;

FIG. 4 the continuous casting chill in front view in section with turbulence-generating elements according to a third embodiment; and

FIG. 5 the continuous casting chill in side view in section with turbulence generating elements.

FIG. 1 shows in three-dimensional illustration a part of a continuous casting chill 1 with a coolant duct 2, which is formed by a chill inner wall 3 facing the molten metal as the hot side, a chill outer wall 4 as the cold side and right side wall 5 and a left side wall 6. Turbulence-generating elements 7, 9 and 10 are arranged in the direction of flow 8 on the chill inner wall 3, the hot side, and project into the coolant duct 2.

FIG. 2 shows in a front view in section the coolant duct 2, in which turbulence-generating elements 7 in the form of tetrahedra are arranged in two rows 11 on the chill inner wall 3. The tetrahedra point with their tip in opposition to the direction of flow 8. Through such an arrangement, an increasing resistance is produced. The coolant behaves in a turbulent manner behind the tetrahedron. The tetrahedra can also be arranged so as to be staggered.

In FIG. 3, turbulence-generating elements 9 are illustrated in the form of horizontal stages. The horizontal stages are formed for example by a rectangular bar (see FIG. 5) which extends over the entire width of the coolant duct 2.

A further form of the turbulence-generating elements 10 is illustrated in FIG. 4. These turbulence-generating elements have the form of winglets. These winglets, known for example from aeroplane wings, are either fastened on the chill inner wall 3 aligned in rows 11 one behind the other, or are fastened distributed on the chill inner wall, as indicated by the lowermost winglet.

All the turbulence-generating elements 7, 9 and 10 project from the chill inner wall 3 into the coolant duct 2 or vice-versa and influence the coolant when it flows in the flow direction 8 through the coolant duct 2.

LIST OF REFERENCE NUMBERS

1 continuous casting chill

2 coolant duct

3 chill inner wall

4 chill outer wall

5 right side wall

6 left side wall

7 tetrahedron

8 flow direction

9 horizontal stage

10 winglet

11 row

Claims

1. A continuous casting chill (1) with a coolant duct (2), which is formed by a chill inner wall (3), facing the molten metal, as the hot side, a chill outer wall (4) as the cold side and a right side wall (5) and a left side wall (6), and

the coolant duct (2) is constructed with turbulence-generating elements (7, 9, 10),

wherein

the turbulence-generating elements (7) are constructed in the form of tetrahedral and/or horizontal stages and/or winglets.

2. The continuous casting chill (1) according to claim 1,

wherein

the turbulence-generating elements (7, 9, 10) are constructed arranged on the chill inner wall (3).

3. The continuous casting chill (1) according to claim 1, wherein the turbulence-generating elements (7, 9, 10) are constructed arranged on the chill outer wall (4).

4. The continuous casting chill (1) according to claim 1, wherein the turbulence-generating elements (7, 10) are constructed arranged in rows (11).

5. The continuous casting chill (1) according to claim 1, wherein the turbulence-generating elements (7, 10) are constructed arranged staggered in rows (11).

6. The continuous casting chill (1) according to claim 1, wherein the turbulence-generating elements (7, 9, 10) are constructed arranged in the region of the casting level.