Annealing furnace and method for annealing a steel strand

Abstract

An annealing furnace for annealing a strand of steel. The annealing furnace including a first heating apparatus for heating the strand during operation of the annealing furnace. A transport device advances the strand in a direction of transport through the annealing furnace during operation of the annealing furnace. The annealing furnace also includes a first cooling device for cooling the outer surface of the strand with a gas guide in the direction of transport behind the first heater, wherein the gas guide is arranged in such a manner that a gas flows along the outer surface of the strand during operation of the annealing furnace for cooling the strand.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic perspective view of an annealing furnace according to an embodiment of the invention.

(2) FIG. 2 shows a broken sectional view through two of the cooling devices of the annealing furnace from FIG. 1.

(3) FIG. 3 shows a schematic cross-sectional view through one of the cooling devices of the annealing furnace from FIG. 2.

(4) FIG. 4 shows a schematic view of a deforming system according to an embodiment of the present invention.

DETAILED DESCRIPTION

(5) In FIG. 1, an annealing furnace 1 is shown schematically in an embodiment of the present invention. In the annealing furnace 1 a stainless steel tube 2 is annealed as a strand within the meaning of the present application at a temperature of 400 C. To anneal the steel tube, the steel tube 2 is guided in the direction of transport (this is denoted in FIG. 1 by arrow 3) through the annealing furnace 1. Thus, the annealing of tube 2 takes place continuously in furnace 1.

(6) According to the present application, there are two pairs of motor-driven drive rollers 4, 5 and 6, 7 acting as a transport device for transporting tube 2 through the annealing furnace 1. These drive rollers are engaged with the stainless steel tube 2 to be annealed, so that a rotation of the rollers 4, 5, 6, 7 leads to a translational movement of tube 2 in the direction of transport 3 through the annealing furnace 1.

(7) A pair of sets of straightening rollers 8 are also provided in the inlet region of the annealing furnace 1, which help to straighten the cold-deformed, incoming tube in the X- and Y-direction in the annealing furnace 1, so that it is substantially straight before it is annealed in the furnace.

(8) The presented embodiment of the annealing furnace 1 comprises two heating apparatuses 9, 10. According to the present application, the heating apparatus 9 is a first heating apparatus and the heating apparatus 10 is a second heating apparatus. The second heating apparatus 10 comprises two heating radiators 11, 12.

(9) The first heating apparatus 9 in the direction of transport 3 of the annealing furnace 1 is an induction heating apparatus, in which the steel tube 2 is heated using a current induced by an induction coil in the tube 2 to be heated.

(10) Such an induction heating has the advantage of quickly heating the tube 2 in a very efficient way, but causes only a very small length expansion of the tube 2.

(11) The induction coil 30 surrounds tube 2 in a concentric manner, wherein the coil is wound on a hollow glass cylinder which extends between the turns of the coil and tube 2.

(12) In the case of radiators 11, 12, the second heating apparatuses, which are disposed in the direction of transport 3 of the tube 2 behind the first inductive heating apparatus 9, are conventional electrically operated resistance heaters. The inside of radiators 11, 12 is heated with the help of heating coils so that tube 2 does not cool or hardly cools on its way from the first inductive heating apparatus 9 to the cooling devices.

(13) The annealing furnace 1 in the embodiment shown in FIG. 1 has a total of four different cooling devices 13, 14, 15, 31.

(14) The core element for cooling the annealed tube 2 in the direction of transport 3 behind the second radiator 12 is a quenching or sudden cooling consisting of two cooling devices 13, 14, which are integrated with each other. According to the present application both these cooling devices 13, 14 are the first and second cooling devices.

(15) The first cooling device 13 is a gas flow cooling for cooling the outer surface, that is, the envelope surface of the tube 2. It uses a gas flow of hydrogen for cooling, which flows past the outer surface of tube 2 and thus cools the tube.

(16) However, in the second cooling device 14, there is a contact cooling, which provides thermal contact between the tube and a water cooling for heat dissipation in the annealed tube 2.

(17) The broken sectional view of FIG. 2 shows the two cooling devices 13, 14 in detail. The gas flow cooling of the first cooling device 13 mainly consists of a housing 16 concentrically surrounding tube 2 to be cooled as gas guide within the meaning of the present application. This gas guide ensures that the cooling gas is conducted past the outer surface 17 of tube 2 to be cooled.

(18) The housing 16 surrounding tube 2 to be cooled as a gas guide comprises a gas inlet 18 for supplying the cooling gas and a gas outlet 19 for discharging the gas. The gas inlet 18 is connected to a gas reservoir for hydrogen (H.sub.2) during the operation of the annealing furnace.

(19) The housing 16 of the gas guide has one gas restrictor 20 at its front and one gas restrictor at its rear end to ensure that as little gas as possible can escape from the gas guide. In the region of the restrictor 20, the distance of the housing 16 to tube 2 to be cooled is significantly less than the distance between the inner walls of both the tube portions 21, 22 of the housing 16 and tube 2 to be cooled. The resulting radial clearance between the restrictor 20 and tube 2 to be cooled therefore has a substantially higher flow resistance for the cooling gas than the tube sections 21, 22 of the housing 16 and the housing flanges 37, 38 so that the gas escapes primarily through gas outlet 19 from the cooling device. In one embodiment the restrictors 20 are made of graphite in order to avoid damage to tube 2 in case of an engagement between restrictors 20 and the stainless steel tube 2 to be cooled.

(20) The gas inlet 18 of the first cooling device 13 is, in the direction of transport 3 of tube 2 to be annealed, behind the gas outlet 19. This facilitates the flow of cooling gas, in operation of the furnace, counter to the direction of transport 3 on the outer surface 17 of tube 2.

(21) The housing 16 of the gas guide of the first cooling device 13 is not a continuous tube, but consists of three segments (21, 22, 23). The first segment 21 is a tube section 21 concentrically surrounding tube 2 to be cooled, which is connected to flange 37 as gas inlet 18. A second section 22 is also configured as a tube section concentrically surrounding tube 2 to be cooled. The latter is in turn connected to a flange 38 as a gas outlet 19.

(22) The tubes 21, 22 of housing 16 are lined from inside with a liner 31 made of graphite. This prevents damage to the tube 2 to be cooled in case it is engaged with the housing 16.

(23) Between the two tubular segments or sections 21, 22 of the gas guide there is another section 23 of the gas guide, in which the second cooling device 14 is extended. In this section 23, the gas guide is provided with a substantially cylindrical body 24 which has a much larger inner diameter as compared to both the tube portions 21, 22 of the housing 16. This body 24 is sealed with tubes 21, 22 connected to the other two sections of the gas guide. The gas flows through the designated channels within the body 24 which channels extend up to tube 2 to be cooled or up to its outer surface 17.

(24) The contact cooling of the second cooling device 14 is also arranged within the body 24. The cooling effect of this contact cooling is based on the four cheeks 25 made of graphite that engage with tube 2 to be cooled inside the body 24 and thus a thermal contact between tube 2 and the graphite cheeks 25 is established, which is used for removing the heat from the tube. The design of the contact elements 25 made of graphite has the advantage that they have a comparatively high thermal conductivity and at the same time demonstrate a low sliding friction between tube 2 and cheeks 25. The graphite cheeks 25 must be hydraulically pressed using a combination of hydraulic cylinders and pistons against the tube 2 in order to achieve a good thermal contact between the graphite cheeks 25 and the tube 2.

(25) The cheeks 25 are subject to wear by friction against the tube 2. However, this wear is automatically compensated by the hydraulic pressing against the cheeks 25. To facilitate this compensation, the cheeks 25 are designed conically in cross section, wherein the four cheeks together do not cover a full 360 ring, but a clearance is provided in each case between the cheeks 25. There is a schematic cross sectional view through cheeks 25 and tube 2, in which the formed clearances 26 can be clearly identified as shown in FIG. 3. This clearance is not only a possibility of compensating the wear of the cheeks, but also indicates that the cooling gas can at least flow past in sections along tube 2.

(26) Coming back to the presentation in FIG. 1, the structure of the downstream cooling devices 15 and 31 will now be described in detail. These cooling devices 15, 31 form a third cooling device 15 and a fourth cooling device 31 used for cooling the outer surface 17 of the tube 2 according to the claims of the present application.

(27) The cooling device 15 comprises two cooling registers 27, 28, which are formed by water-cooled tube sections 29, wherein the heat transfer takes place between tube 2 to be cooled and the cooled tube sections 29 through heat radiation and convection.

(28) Tube 2 is finally directly sprayed with cooling liquid, here water, in the last cooling device 31 in the direction of transport 3, a so-called water tank, which drips and is scraped with a scraper from the tube before the outlet of the tube from the water tank.

(29) The annealing furnace in FIG. 1 additionally comprises a flushing device used for flushing the inner surface of the annealed tube 2. For this, a gas outlet (not shown) of a reservoir is connected in a sealing manner to the beginning of the tube 2 to be annealed in the direction of transport 3 of the tube 2 in front of the annealing furnace 1 so that the gas can flow into the tube and flow through it.

(30) An embodiment of the invention schematically shown in FIG. 4 demonstrates a continuously working drawing bench 32 for cold deforming the tube 2 after the annealing furnace 1. During the cold deforming of the tube 2, the outside diameter of tube 2 is reduced by moving tube 2 through a drawing die 33. A flying saw 34, which is moved with the tube 2 in the direction of transport 3 of tube 2, is also provided behind the drawing bench 32, so that tube 2 can be cut into tube sections of a defined length during the drawing of the tube. In addition, a CO.sub.2-cleaning device 35 is provided between the drawing bench 32 and the flying saw 34 for cleaning the outer surface of the tube 2. The remaining lubricant can be removed from the outer surface of the tube 2 with the help of this cleaning device 35. The arrangement of annealing furnace 1, draw bench 32, cleaning device 35 and flying saw 34 is designated in the sense of the present application as deforming system 36.

(31) For purposes of the original application it should be noted that all features as they become apparent from the following description, the drawings and the claims for a person skilled in the art, even if they were described concretely only in connection with certain other features, can be combined both individually and in any combinations with other features disclosed herein or group of features, unless this has been expressly excluded or if technical factors make such combinations impossible or pointless. A comprehensive, explicit presentation of all conceivable combinations of features described here is omitted only for the sake of brevity and readability of the description. Although the invention was presented and described in detail in the drawings and the foregoing description, this presentation and description are merely exemplary and are not a limitation of the scope as defined by the claims. The invention is not limited to the disclosed embodiments.

(32) Modifications to the disclosed embodiments will be apparent to a person skilled in the art from the drawings, the specification and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain features are claimed in different claims does not exclude their combination. Reference numerals in the claims should not be construed as limiting the scope.

REFERENCE LIST

(33) 1 Annealing furnace 2 Stainless steel tube 3 Direction of transport 4, 5, 6, 7 Driver rollers 8 Straightening roller assembly 9 First heating apparatus 10 Second heating apparatus 11, 12 Radiators of the second heating apparatus 13, 14, 15, 31 Cooling device 16 Housing sections of the gas guide 17 Outer surface of the stainless steel tube 2 18 Gas inlet 19 Gas outlet 20 Seal 21, 22, 23 Gas guide housing 24 Cylindrical body 25 Graphite cheek 26 Clearance 27, 28 Cooling register 29 Water-cooled tube sections 30 Induction coil 31 Graphite liner 32 Drawing bench 33 Drawing die 34 Flying saw 35 CO2 cleaning device 36 Deforming system 37, 38 Flange