Annealing furnace and method for annealing a steel strand

1. An annealing furnace for annealing a strand of steel with a first heating apparatus for heating the strand during operation of the annealing furnace, a transport device for the strand arranged to advance the strand in a direction of transport through the annealing furnace during operation of the annealing furnace, the annealing furnace, in the direction of transport, following the first heating apparatus, comprising:

a first cooling device for cooling the outer surface of the strand by gas flow cooling, the first cooling device including a gas guide, wherein the first cooling device is arranged to cool the strand during the operation of the annealing furnace as a gas flows over the outer surface of the strand, and

a second cooling device for cooling the outer surface of the strand by contact cooling, wherein the second cooling device cools the strand during the operation of the annealing furnace by thermal contact between the strand and a liquid cooled contact element,

wherein the first cooling device includes a first section and a second section, and

wherein, relative to the direction of transport, the first section of the first cooling device is arranged before the second cooling device and the second section of the first cooling device is arranged after the second cooling device.

2. The annealing furnace according to claim 1 , wherein the gas guide includes a housing surrounding the strand during operation of the annealing furnace, the housing being arranged concentrically to the strand, the housing having a gas inlet and a gas outlet for the gas.

3. The annealing furnace according to claim 2 , wherein the housing of the gas guide includes a seal both at a front end and a rear end for sealing the housing against the strand during operation of the annealing furnace.

4. The annealing furnace according to claim 2 , wherein the gas inlet of the gas guide is in fluid communication with a reservoir for the gas, wherein the reservoir during the operation of the annealing furnace contains hydrogen so that the outer surface of the strand can be cooled with the gas.

5. The annealing furnace according to claim 2 , wherein the gas outlet is arranged before the gas inlet in the direction of transport of the strand so that the gas flows counter to the direction of transport past the strand during operation of the annealing furnace.

6. The annealing furnace according to claim 1 , wherein the second cooling device includes a pneumatic or hydraulic device which is constructed and arranged in such a manner that it keeps the liquid cooled contact element in engagement with the strand during operation of the annealing furnace.

7. The annealing furnace according to claim 1 , wherein the contact element is made of graphite.

8. The annealing furnace according to claim 1 , wherein the second cooling device includes a fluid cooling system arranged to dissipate the heat transferred from the strand to the liquid cooled contact element during operation of the annealing furnace.

9. The annealing furnace according to claim 1 , wherein the liquid cooled contact element of the second cooling device is arranged within the first cooling device for cooling the outer surface of the strand.

10. The annealing furnace according to claim 1 , further comprising a third cooling device for cooling the outer surface of the strand, the third cooling device having a housing with a fluid cooling system, which surrounds the strand during operation of the annealing furnace.

11. The annealing furnace according to claim 9 , wherein the liquid cooled contact element of the second cooling device is arranged within the housing of the gas guide.

12. The annealing furnace according to claim 2 , wherein the gas inlet is located in the second section of the first cooling device and the gas outlet is located in the first section of the first cooling device.

13. The annealing furnace according to claim 1 , wherein the gas guide extends continuously from a first end associated with the first section of the first cooling device to a second end associated with the second section of the first cooling device.

14. The annealing furnace according to claim 1 , wherein the gas guide is incorporated into the second cooling device, and

wherein, in the second cooling device, an inner diameter of the gas guide is larger than an inner diameter of the gas guide in the first cooling device.

15. The annealing furnace according to claim 14 , wherein, in the second cooling device, the gas guide includes a plurality of flow channels.

16. The annealing furnace according to claim 15 , wherein the plurality of flow channels extend up to an outer surface of the strand of steel.

17. The annealing furnace according to claim 15 , wherein the plurality of flow channels connect the gas guide in the first section of the first cooling device with the gas guide in the second section of the first cooling device.

18. The annealing furnace according to claim 1 , wherein the second cooling device for cooling the outer surface of the strand includes:

a contact element in slideable contact with the strand during operation of the annealing furnace so that thermal contact is established between the strand and the liquid cooled contact element, and

a pneumatic or hydraulic device that maintains the slideable contact between the liquid cooled contact element and strand during operation of the annealing furnace.

19. The annealing furnace according to claim 18 , wherein the liquid cooled contact element has a conical cross section.

20. The annealing furnace according to claim 18 , wherein the liquid cooled contact element is made of graphite.

21. The annealing furnace according to claim 18 , wherein the second cooling device includes a fluid cooling system arranged to dissipate the heat transferred from the strand to the liquid cooled contact element during operation of the annealing furnace.