Roll casting method with cryogenic cooling of casting rolls
Molten metal poured into a mold region, delimited by a first casting roll that rotates about a first rotational axis, produces a metal strand upon solidification which is conveyed out of the mold region. A liquid coolant is applied to the surface of the first casting roll by a first cooling device via first coolant lines and first coolant applying devices. The coolant is inert with respect to the molten metal and has a standard boiling point below 20° C., e.g., −20° C., at normal air pressure, and an operating temperature at or below an operating boiling point at an operating pressure at which the coolant is supplied. A control device automatically controls the first cooling device by ascertaining a control state of the first cooling device using a target property for an actual property of the first casting roll or the metal strand detected by at least one sensor.
1. A roll casting method, comprising:
casting molten metal in a mold region delimited on a first side by a first casting roll rotating around a horizontal first axis of rotation;
conveying a metal strand, created by solidification of the molten metal, out of the mold region;
applying a liquid coolant to a surface of the first casting roll by a first cooling device via first coolant applying devices receiving the liquid coolant via first coolant lines, the liquid coolant being inert in respect of the molten metal and having a standard boiling point at normal air pressure of below 20° C. and an operating temperature at or below an operating boiling point related to an operating pressure applied to the liquid coolant;
detecting an actual property of the first casting roll by a first sensor configured to observe a section of the first casting roll before the section makes contact with the molten metal and after the section has received the coolant in a rotation cycle of the first casting roll; and
controlling the first cooling device by a control device determining, for each of a plurality of periodic cycles of a clock cycle time, a proportion of activation time of the first cooling device in the clock cycle time, as a function of the actual property and a corresponding target property, and activating the first cooling device accordingly throughout the cycles, the control device controlling the first cooling device such that the liquid coolant, after being applied to a surface portion of the first casting roll, is substantially entirely vaporized from the casting roll prior to the surface portion making next contact with the molten metal.
2. The roll casting method as claimed in claim 1 ,
wherein the mold region is delimited on a second side by a second casting roll rotating around a second horizontal axis of rotation parallel to the first axis of rotation,
wherein the first and the second casting rolls have a casting gap therebetween, and
wherein the metal strand is conveyed downwards out of the mold region and an angle of between 60° and 180° is formed through the first axis of rotation from a casting gap of the mold region to an application location at which the liquid coolant is applied to the surface of the first casting roll.
3. The roll casting method as claimed in claim 2 ,
wherein the first casting roll has a diameter, and
wherein the first coolant applying devices are disposed below a lowest point of the first casting roll in an area extending over the diameter the first casting roll.
4. The roll casting method as claimed in claim 2 , wherein the angle is between 90° and 180°.
5. The roll casting method as claimed in claim 3 , further comprising thermally screening at least one of the metal strand against the liquid coolant and the first coolant applying devices from the metal strand by a screening device disposed between the metal strand and the first coolant applying devices.
6. The roll casting method as claimed in claim 5 , wherein the first coolant lines are jacketed with a thermal insulation.
7. The roll casting method as claimed in claim 6 , wherein gas separators are disposed in the first coolant lines.
8. The roll casting method as claimed in claim 7 , wherein controllable switching valves are disposed in the first coolant lines.
9. The roll casting method as claimed in claim 8 , wherein the first coolant applying devices are distributed over the diameter of the first casting roll and are activated one of individually and in groups.
10. The roll casting method as claimed in claim 9 , further comprising setting at least one of a gap between the first coolant applying devices and the first casting roll and an orientation of the first coolant applying devices relative to the first casting roll.
11. The roll casting method as claimed in claim 10 , further comprising setting, by the control device during operation, at least one of a distance and an orientation of the first coolant applying devices relative to the first casting roll.
12. The roll casting method as claimed in claim 11 , wherein the liquid coolant is selected from the group consisting of liquid nitrogen, a liquid noble gas and an organic coolant.
13. The roll casting method as claimed in claim 12 , wherein the liquid coolant is liquid argon.
14. The roll casting method as claimed in claim 1 , wherein the standard boiling point of the liquid coolant at normal air pressure is below −20° C.