Device and method for thermal treatment of a metal strip

Abstract

The invention relates to a strip treatment system for the continuous thermal treatment of a metal strip (6), comprising an annealing furnace and a heatable overageing chamber (11) downstream thereof. In the overageing chamber (11), the metal strip (6) is guided over a plurality of vertically spaced deflecting rollers (12, 12', 13, 13') so that the metal strip meanders through the overageing chamber (11). According to the invention, at least one deflecting roller (12', 13') is movable in the vertical direction, thus allowing the strip length or the residence time of the metal strip (6) in the overageing chamber (11) to be adjusted. The invention also relates to a method for the thermal treatment of a metal strip (6).

Description

[0001] The subject of this invention is a strip treatment system for the continuous heat treatment of a metal strip, comprising an annealing furnace and a subsequent heated aging chamber. The metal strip is guided in the aging chamber over several vertically spaced rollers, so that it meanders through the chamber.

[0002] Conventional strip processing plants consist of several chambers in which the metal strip is first heated to annealing temperature and held at this temperature for a specific period. It is also possible to follow a defined temperature curve. Such annealing furnaces are well-known. Afterward, the metal strip is cooled down according to a predetermined cooling rate to a defined over-aging temperature and held at this temperature for a predetermined period. So-called over-aging chambers thus serve to maintain a metal strip at a specific temperature for a precisely defined time (over-aging temperature). These chambers are also frequently referred to as "holding chambers," "soaking chambers," or "partitioning chambers." The temperature within the over-aging chamber should be as constant as possible and, depending on the metal strip alloy, ranges between 150°C and 500°C.These aging chambers typically contain a protective gas atmosphere or a reducing atmosphere, such as a hydrogen-nitrogen mixture. The metal strip can then be cooled to room temperature or, for example, heated to the coating temperature in electroplating plants, such as galvanizing plants.

[0003] All these heat treatment steps influence the mechanical properties of the metal strip. It is important that the metal strip is not only heated to a certain temperature, but also maintained at a defined temperature in the aging chamber for a precisely determined period of time. The heating and cooling rates also affect the strip properties. Furthermore, metal strips of varying thicknesses or compositions require different heat treatment parameters.

[0004] The residence time of the metal strip in the aging chamber is determined by the strip speed and the strip length within the aging furnace. In conventional aging chambers, the strip length is predetermined by the arrangement of the deflection rollers, meaning the residence time can only be controlled via the strip speed. However, the strip speed can only be varied to a very limited extent, as any change in speed naturally also affects the production capacity, the heating rate, and the cooling rate.

[0005] DE 10 2015 001 438 A1 describes a heat treatment plant through which the strip is guided in the form of loops. The upper roller bridge is vertically movable to adjust different strip transit times.

[0006] US patent 2020 / 0131598 A1 describes a vertical belt storage system, which can optionally be heated and is located between two annealing furnaces.

[0007] KR 101 951 945 B1 describes a vertical belt storage unit that can be arranged before or after a furnace and has a device that prevents the belt from touching itself in the belt storage unit.

[0008] The object of the present invention is to provide a strip treatment line in which the residence time of the metal strip in the aging chamber can be adjusted over a wider range, so that completely different metal strips can be treated with the same strip treatment system, whereby an optimal residence time in the aging chamber can always be set.

[0009] This problem is solved by a belt treatment system according to claim 1. In the aging chamber, at least one deflection roller is movable in the vertical direction, thus allowing the length of the metal belt in the aging chamber to be adjusted. This also allows the dwell time of the metal belt in the aging chamber to be adjusted.

[0010] This allows the dwell time to be set independently of the belt speed by changing the belt length in the chamber. As a result, one and the same belt processing system can meet different production requirements and be flexibly adapted to new conditions.

[0011] According to the invention, one or more movable deflection rollers are supported or fixed in a specific position to which they have been moved to achieve a predetermined belt length. The roller support is housed in a casing and can be retracted into the aging chamber.

[0012] For the processing of a specific metal strip, the guide rollers remain in this defined position anyway. Supporting or fixing them relieves the lifting mechanism for the guide rollers.

[0013] Ideally, for a given strip format (strip thickness, strip composition, strip width) and a given heating cycle (annealing temperature, cooling temperature, cooling rates, etc.), the strip speed is determined with regard to maximum production capacity. Based on this strip speed, the required strip length in the aging chamber is set so that the optimal residence time of the metal strip in the aging chamber, as determined by the heating cycle, is achieved.

[0014] The aging chamber described here should not be confused with a conventional belt storage unit (looper). Loopers also have movable rollers and can accommodate different belt lengths. However, their purpose is to compensate for different belt speeds within the system. For example, if a newly introduced belt needs to be welded to the end of the previous belt and the belt has to be stopped for this process, the belt storage unit ensures that the belt speed in subsequent processing units remains unchanged by dispensing stored belt. However, these types of loopers operate at ambient temperature in ambient air. They only serve to compensate for different belt speeds and do not perform any heat treatment.

[0015] It is advantageous if several deflection rollers are movable in the vertical direction in the aging chamber according to the invention. This allows the recorded belt length to be varied considerably.

[0016] Advantageously, one or more upper deflection rollers can be moved in a vertical direction.

[0017] The aging chamber is preferably heated electrically, for example with jet tubes. However, the gas in the aging chamber can also be extracted, heated electrically, and then reinjected.

[0018] The aging chamber according to the invention is, for example, arranged in front of a coating system.

[0019] It is advantageous to have a cooling section between the annealing furnace and the aging chamber, as such a cooling step is required for many heat treatments.

[0020] The invention relates not only to the device but also to a method for the continuous heat treatment of a metal strip according to claim 8.

[0021] In this process, a dwell time is set for the heat treatment of the metal strip in the aging chamber. The strip length, and thus the dwell time, is then adjusted by moving at least one deflecting roller. The movable deflecting roller(s) are then supported or fixed in a specific position by a roller support. The roller support is housed in a casing and can be retracted into the aging chamber.

[0022] It is advantageous if the metal strip is heat-treated in a hydrogen-nitrogen atmosphere in the aging chamber.

[0023] Several embodiments of the invention are described below with reference to the drawings. The drawings show: Fig. 1A schematic view of an aging chamber according to the state of the art. Fig. 2 an embodiment of an aging chamber according to the invention with a movable upper deflection roller; Fig. 3 another embodiment of an aging chamber according to the invention with a movable lower deflection roller; Fig. 4 an embodiment of an aging chamber according to the invention with several movable upper deflection rollers; Fig. 5 a schematic view of a possible roller motion system; Fig. 6 three different role positions in an aging chamber 11; Fig. 7 and Fig. 8 an embodiment of a roller motion system; Figs. 9 and 10 a schematic representation of the heating and cooling of the aging chamber 11;

[0024] The same reference symbols in the individual illustrations refer to the same parts of the plant.

[0025] In Figure 1An aging chamber 1 according to the prior art is depicted. A metal belt 6 is inserted into the aging chamber 1 from the left and deflected vertically upwards by a lower, stationary deflecting roller 2. In the upper region of the aging chamber 1, the metal belt 6 is then deflected downwards by 180° by an upper, stationary deflecting roller 3. The metal belt 6 thus meanders through the aging chamber 1 until it is finally deflected horizontally by the last lower deflecting roller 2 and exits the aging chamber 1. The interior of the aging chamber 1 is maintained at a predetermined temperature, which is typically between 150°C and 500°C. It is important that the interior of the aging chamber 1 is kept at a temperature that is as constant as possible. To reduce heat loss, the housing 4 of the aging chamber 1 is provided with insulation 5.The aging chamber is heated by electrically heated radiant tubes 7.

[0026] To achieve optimal material properties, the metal strip 6 should spend a defined period of time (dwelling time) in the aging chamber 1.

[0027] Since in the aging chamber 1 according to Figure 1 Since the lower and upper rollers 2 and 3 are stationary, the recorded tape length is always the same. Therefore, the dwell time can only be changed by altering the tape speed.

[0028] Figure 2Figure 1 shows an embodiment of the aging chamber 11 according to the invention. The housing 14 is also provided with insulation 15, and the metal belt 6 is guided through the aging chamber 11 in a meandering pattern over lower fixed guide rollers 12 and upper fixed guide rollers 13. However, in this case, an upper guide roller 13' is movable in the vertical direction. In the present example, it has been lowered to half its height. The aging chamber is heated in this example by electrically heated radiant tubes 17. These radiant tubes 17 are not arranged in the area of ​​the movable guide roller 13', as this would impede the movement of the guide roller 13'. Of course, it is also conceivable that this aging chamber 11 is heated by supplied hot gas, as described below.

[0029] Since the deflection roller 13' is now movable in the vertical direction, the length of the metal strip 6 in the aging chamber 11 can be changed. Thus, the dwell time of the metal strip 6 in the aging chamber 11 can be adjusted without having to change the strip speed.

[0030] The optimal dwell time for a specific metal strip 6 is generally determined in advance. Based on a specified strip speed, the required strip length in the aging chamber 11 is then calculated and adjusted by moving the upper deflection roller(s) 13'. Preferably, the movable upper deflection rollers 13' are no longer moved during the treatment of a specific metal strip 6, but rather fixed in their position.

[0031] In Figure 3 An aging chamber 11 is shown, in which a lower deflection roller 12' is movable in a vertical direction.

[0032] Figure 4 Figure 1 shows an embodiment in which several upper deflection rollers 13' are movable in a vertical direction. The upper deflection rollers 13' are movable independently of each other.

[0033] In Figure 5 Figure 1 shows a possible embodiment of a mechanism by which the deflection rollers 12' and 13' can be moved in a vertical direction. The bearing housings 23 of the upper movable deflection roller 13' are each suspended from a chain 25, which is deflected by gears 21 in the upper region of the aging chamber 11. Counterweights 20 are attached to the other end of the chains 25. The two gears 21 are coupled to each other via a shaft 22 and connected to a drive 18. By rotating the shaft 22, the upper deflection roller 13' can be moved in a vertical direction. The arrangement would be analogous if a lower deflection roller 12' were to be moved in the same way.

[0034] Roller supports 19, 19' are provided laterally in the wall at different heights. The deflection roller 13' or 12' can be placed on or fixed to these roller supports. This relieves the chains 25 and the drive 18 during the heat treatment of a specific metal strip 6. The stationary lower deflection roller 12 and the shaft 22 are mounted outside the aging chamber 11. Therefore, these bearings 46 do not have to withstand high temperatures. The lower deflection roller 12 has a drive 45.

[0035] In Figure 6 Three different band lengths are shown in an aging chamber 11.

[0036] In the middle illustration, both upper deflection rollers 13' are in their uppermost position, the belt length in the aging chamber 11 is therefore at its maximum and the residence time at a given belt speed is at its longest.

[0037] In the left illustration, one of the two movable upper deflection rollers 13' was lowered slightly, thus shortening the belt length and consequently the dwell time at a given belt speed.

[0038] In the right-hand illustration, both upper deflection rollers 13' are in their lowest position. Here, the belt length in the aging chamber 11 is shortest, and thus the residence time at a given belt speed is also minimized.

[0039] In the Figures 7 and 8The adjustment mechanism for the movable deflection pulleys 12' and 13' is shown in more detail. Since the deflection pulleys 12' and 13' are located inside the heated aging chamber 11, where temperatures can reach up to 500°C, they are mounted on high-temperature bearings 31. A standard roller bearing 27, housed in a bearing casing 26, is sufficient to support the shaft 22. The bearing casing 26 is connected to the support structure 30 via a bearing support 29. The motor support 28 and the drive 18 also rest on this support structure 30.

[0040] To better compensate for any thermal expansion and as dust protection, an expansion bellows 24 is arranged between the housing 14 of the aging chamber 11 and the bearing housing 26.

[0041] In Figure 8The function of the roller support 19, 19' is shown. The roller support 19, 19' is housed in a casing 32 and can be retracted into the aging chamber 11. The casing 32 rests on a steel structure 44 via a substructure 33. Several roller supports 19, 19' are typically arranged at different heights along the chamber height, so that the deflection roller 12' or 13' can be supported at different heights.

[0042] In Figure 9Figure 1 shows one method for heating the aging chamber 11. The aging chamber 11 should maintain a constant internal temperature for the treatment of a specific metal strip 6; this temperature ranges between 150°C and 500°C, depending on the material and treatment. Since heat loss always occurs, the chamber must be heated to maintain a relatively constant temperature. Of course, minor temperature variations may exist within the aging chamber 11, but these are generally only a few degrees Celsius. For heating, hot gas, for example, an inert gas or a reducing gas such as a nitrogen-hydrogen mixture, is blown into the aging chamber 11 via a laterally arranged supply box 34 and extracted again on the opposite side by a blower 36 via an extraction box 35.The gas is then fed either to an electric heater 40 or a heat exchanger 39 and returned to the aging chamber 11 via a recirculation line 37. Valves 38 and 41 allow the hot gas to be directed either to the heat exchanger 39 or the electric heater 40. The electric heater 40 raises the gas temperature again. If the gas is routed through the heat exchanger 39, it can also be cooled. This is necessary, for example, when switching from one steel grade to another. If, for instance, the subsequent steel grade requires a lower aging temperature, the gas is cooled so that the optimal temperature in the aging chamber 11 is reached as quickly as possible. Simultaneously, the strip length in the aging chamber 11 can be adjusted by moving the deflecting rolls 12' and 13', ensuring optimal heat treatment of the subsequent steel grade.

[0043] In Figure 10 Is the heating or cooling system made of Figure 9 The diagram is shown again. It can be seen here that the heat exchanger 39 is supplied with cooling water 43. The motor 42 for the blower 36 is also shown. In this diagram, a hydrogen-nitrogen mixture (HNX) is used as the heating medium. Reference sign

[0044] 1. Aging chamber according to the state of the art 2. Lower fixed deflection pulley 3. Upper fixed deflection pulley 4. Housing 5. Insulation 6. Metal band 7. Jet tube 11 Aging chamber 12 Lower deflection pulley (fixed) 12' Lower deflection pulley (movable) 13 Upper deflection pulley (fixed) 13' Upper deflection pulley (movable) 14 Housing 15 Insulation 17 Jet tube 18 Drive 19 Roller support (extended) 19' Roller support retracted into aging chamber 11 20 Counterweight 21 Gear 22 Shaft 23 Bearing housing 24 Expansion bellows 25 Chain 26 Bearing housing 27 Roller bearing 28 Motor support 29 Bearing support 30 Support structure 31 High-temperature bearing 32 Housing for roller support 19 33 Substructure 34 Feed box 35 Extraction box 36 Blower 37 Recirculation line 38 Valve 39 Heat exchanger 40 Electric heater 41 Valve 42 Motor 43 Cooling water 44 Steel construction 45 Drive for the deflection roller 12 46 Bearing for the stationary deflection roller 12

Claims

1. Strip treatment plant for continuous heat treatment of a metal strip (6), with an annealing furnace and a subsequent over-ageing chamber (11) that can be heated, the metal strip (6) being guided over several rolls spaced vertically apart from one another (12, 12', 13, 13') in the over-ageing chamber (11) so that the metal strip (6) passes through the over-ageing chamber (11) in a meandering path, where at least one deflector roll (12', 13') can be moved in vertical direction in a way that allows the length of the metal strip (6) in the over-ageing chamber (11) and, as a result, also the retention time of the metal strip (6) in the over-ageing chamber (11) to be set, characterised in that the movable deflector roll (12', 13') or the movable deflector rolls (12', 13') are supported or secured in a certain position with a roll support (19, 19'), wherein the roll support (19, 19') is accommodated in a housing (32) and wherein the roll support (19, 19') can be run into the over-ageing chamber (11).

2. Strip treatment plant according to claim 1, characterised in that several deflector rolls (12'. 13') can be moved in vertical direction.

3. Strip treatment plant according to claim 1 or 2, characterised in that one or several top deflector rolls (13') can be moved in vertical direction.

4. Strip treatment plant according to one of claims 1 to 3, characterised in that the over-ageing chamber (11) can be heated electrically.

5. Strip treatment plant according to one of claims 1 to 4, characterised in that the over-ageing chamber (11) can be heated by spraying in heated gas.

6. Strip treatment plant according to one of claims 1 to 5, characterised in that the over-ageing chamber (11) is disposed ahead of a coating plant, preferably ahead of an electrogalvanizing plant.

7. Strip treatment plant according to one of claims 1 to 6, characterised in that a cooling section is disposed between the annealing furnace and the over-ageing chamber (11).

8. Method for continuous heat treatment of a metal strip, with an annealing furnace and a subsequent over-ageing chamber (11), the metal strip (6) being guided in a meandering path over deflector rolls (12, 12', 13, 13') spaced vertically apart from one another in the over-ageing chamber (11), where a retention time is defined for heat treatment of the metal strip (6) in the over-ageing chamber (11) and in that the length of the metal strip and thus also the retention time of the metal strip (6) in the over-ageing chamber (11) are set by moving at least one deflector roll (12', 13') in vertical direction in the over-ageing chamber (11), characterised in that the movable deflector roll (12', 13') or the movable deflector rolls (12', 13') are supported or secured in a certain position by a roll support (19'), wherein the roll support (19, 19') is accommodated in a housing (32) and where the roll support (19, 19') can be run into the over-ageing chamber (11).

9. Method according to claim 8, characterised in that the gas or gas mix in the over-ageing chamber (11) is removed by suction, heated and then fed into the over-ageing chamber (11) again.

10. Method according to claim 9, characterized in that the gas or gas mix is heated electrically.

11. Method according to one of claims 9 to 10, characterized in that the metal strip (6) in the over-ageing chamber (11) is heat-treated at a temperature of 150°C to 500°C, preferably at 400 to 500°C.

12. Method according to one of claims 9 to 10, characterized in that the metal strip (6) in the over-ageing chamber (11) is heat-treated in a hydrogen-nitrogen atmosphere.

Images