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EP-4735192-A1 - DEVICE FOR VERTICAL CONTINUOUS CASTING

EP4735192A1EP 4735192 A1EP4735192 A1EP 4735192A1EP-4735192-A1

Abstract

The invention relates to a device for vertical continuous casting, having a casting pit (1) which, together with a die (2), forms an outlet region (3) for a metal strand (4) forming a liquid metal column. In order to design such a device in such a way that, despite simple design measures, undesired segregation effects in the edge regions or on the surface of the cast metal are effectively reduced even below the solidification point (20), it is proposed that the outlet region (3) is closed off in a gas-tight manner and in order to reduce the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point (20) of the metal strand (4), and the pressure in the outlet region (3) is provided with a fresh gas supply (8) and an exhaust gas discharge (9) for setting a casting pit pressure and for discharging a coolant.

Inventors

  • Berrer, Manuel
  • Fellsner, Christian Karl

Assignees

  • Hertwich Engineering GmbH

Dates

Publication Date
20260506
Application Date
20250221

Claims (11)

  1. 1. Device for vertical continuous casting, with a casting pit (1) which, together with a mold (2), forms an outlet area (3) for a metal strand (4) forming a liquid metal column, characterized in that the outlet area (3) is sealed in a gas-tight manner and, in order to reduce the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point (20) of the metal strand (4), and the pressure in the outlet area (3), is provided with a fresh gas supply (8) and an exhaust gas discharge (9) for setting a casting pit pressure and for discharging a coolant.
  2. 2. Device according to claim 1, characterized in that the outlet area (3) is sealed gas-tight by a housing (7).
  3. 3. Device according to claim 2, characterized in that the housing (7) has a viewing window, the inside of which is arranged in the flow path of the fresh gas and/or exhaust gas device.
  4. 4. Device according to one of claims 1 to 3, characterized in that the mold (2) has a casting gas supply (21) for sealing the mold outlet opening from the outlet region (3).
  5. 5. Method for vertical continuous casting with a device according to one of claims 1 to 4, characterized in that after filling the mold (2) to a minimum filling level, the pressure in the outlet region (3) is regulated via the fresh gas supply (8) and the exhaust gas discharge (9) to an overpressure compared to the ambient pressure in such a way that the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point (20), and the pressure in the outlet region (3) is reduced.
  6. 6. Method according to claim 5, characterized in that the pressure in the outlet region (3) is regulated via the fresh gas supply (8) and the exhaust gas discharge (9) to an overpressure relative to the ambient pressure such that the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point (20), and the pressure in the outlet region (3) is less than 20 mbar.
  7. 7. Method according to claim 6, characterized in that the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point (20), and the pressure in the outlet region (3) is less than 5 mbar.
  8. 8. Method according to one of claims 5 to 7, characterized in that the overpressure set in the outlet region (3) is more than 10 mbar.
  9. 9. Method according to claim 8, characterized in that the overpressure set in the outlet region (3) is more than 30 mbar.
  10. 10. Method according to one of claims 5 to 9, characterized in that at least 50 m 3 of exhaust gas is removed from the casting pit (1) per 1 t of cast metal.
  11. 11. Method according to one of claims 5 to 10, characterized in that the overpressure in the casting pit (1) is reduced when the minimum filling level in the at least one mold (2) falls below.

Description

Device for vertical strand casting Technical area The invention relates to a device for vertical continuous casting, comprising a casting pit which, together with a mold, forms an outlet area for a metal strand forming a liquid metal column. State of the art In vertical continuous casting of molten metals, particularly aluminum, a fundamental difficulty is preventing the formation of material defects on the surface of the solidified metal. During the casting process, a material zone with an increased concentration of alloying elements can develop in the edge region, i.e., the area directly beneath the surface of the solidified metal. This can lead to significantly different properties in this edge region than in the material further inside. This effect, known in casting technology as "exudation," "edge zone segregation," or "inverse segregation," is caused by metallostatic overpressure in the liquid metal column during the casting process. This metallostatic overpressure can subsequently lead to undesirable dendrite-like grain structures or cold runs in the edge region, as well as to surface defects in the solidified metal. In US20220062973A1 a “hot-top” process is presented which is frequently used in connection with vertical continuous casting, whereby needle valves are used to regulate the overpressure of the The gas cushion formed by the pouring gas supply is provided above the solidification point of the liquid metal column. This allows the increased pressure buildup above the solidification point, which would otherwise escape intermittently due to gas escaping between the mold wall and the solidified melt, to be diverted via these valves, thus preventing any impact-related microstructural anomalies. However, the disadvantage is that the pouring gas can flow freely into the outlet area, meaning that material defects can continue to occur in the edge area or on the surface of the solidified metal below the solidification point. Description of the invention The invention is therefore based on the object of designing a device of the type described above in such a way that, regardless of the overall height of the mold, undesirable segregation effects in the edge areas or on the surface of the cast metal are effectively reduced even below the solidification point, despite simple design measures. The invention achieves the stated object in that the outlet region is sealed in a gas-tight manner and, in order to reduce the difference between the metallostatic pressure of the liquid metal column, in particular at the level of the solidification point of the metal strand, and the in particular atmospheric pressure in the outlet region, is provided with a fresh gas supply and an exhaust gas discharge for setting a casting pit pressure and for discharging a coolant, in particular converted into the gaseous phase. The invention is based on the finding that the metallostatic pressure acting as a driving force for the formation of undesirable segregation effects can be effectively compensated by applying a gas pressure directly to the surface of the solidified metal strand or ingot in the outlet area. In this case, the casting pit pressure, i.e. the air or gas pressure present in the outlet area and immediately surrounding the metal strand, is reduced to an overpressure compared to the The ambient pressure prevailing outside the casting pit is regulated in such a way that the difference between the metallostatic pressure of the liquid metal column, in particular at the solidification point of the metal strand, and the atmospheric pressure in the outlet area is reduced. To achieve high surface and edge zone quality of the solidified metal strand, it is recommended that this differential pressure is less than 20 mbar, in particular less than 10 mbar. Particularly good results can be achieved with a differential pressure of less than 5 mbar. As a key prerequisite for enabling reliable gas pressure control in the outlet area to reduce segregation effects, it is necessary that the outlet area is sealed gas-tight. However, this gives rise to the problem that the coolant, for example water-based, initially partially evaporates as the metal column surface cools, and the resulting coolant vapor cannot escape from the gas-tight outlet area. Consequently, not only the sudden increase in vapor pressure in the outlet area but also, particularly in connection with aluminum melts, the unstoppable exothermic reaction of the water vapor with the aluminum leads to surface defects and, in the worst case, to a risk of bursting of the mold or casting table. Against this background, the exhaust gas discharge according to the invention offers the additional effect that the coolant converted into the gas phase, in particular water vapor, can be discharged from the outlet area. This prevents the water vapor from escaping unhindered into the environment outside the outlet area of the casting pit, thus also preventing unwanted moisture from