EP0347662B1 - Strip steel casting installation with a rotating hearth furnace - Google Patents

Abstract

The invention relates to a method and an installation for the manufacture of hot-rolled strip steel from continuously cast input stock in successive working steps, in which the input stock is brought to hot-rolling temperature after solidification and is introduced into a rolling mill for rolling out to form finished strip, the input stock being wound into coils after reaching the hot-rolling temperature, temporarily stored in a rotating hearth furnace and retrieved as required, unwound and rolled out to form finished strip. The temporary storage is particularly advantageously carried out directly before the entrance to the finishing train. In this case, the coils are preferably temporarily stored in a horizontal position or with a horizontal winding axis. During temporary storage a reheating operation can be performed.

Description

The invention relates to a strip caster with a downstream first furnace to bring continuous cast material after solidification to hot rolling temperature, and with a finishing train designed as a continuous rolling mill downstream of the first furnace, with a coil winder and a second furnace arranged as a storage furnace between the first furnace and the finishing train and a bundle settler is subordinate to it. Such a belt caster is already known from JP-A-62-187 505.

Known belt casting systems mostly use tunnel ovens to bring the primary material to the desired hot rolling temperature, but the material strands are not wound up. Compared to tape winding, much less energy is required. With multi-strand systems, heating furnaces must be used in any case due to the long transport routes involved.

Warming furnaces are primarily bogie car continuous furnaces, lifting hearth or car hearth furnaces, but they have various disadvantages. When a bogie hearth furnace is used, loading and unloading of coils at different times is not possible, since when a bogie hearth is removed without another bogie wagon moving up, a gap is created that prevents heat radiation is not protected. The loading and unloading must therefore always take place simultaneously. The empty bogie wagons must also be returned from the removal side to the loading side. It is necessary to reheat the trolleys, in any case the ceramic benches, in order to avoid black spots (so-called SKID MARKS). In the event of malfunctions in the rolling mill, the bundles at the bundle winding station cannot be picked up by the furnace. An additional storage oven must be available to store the bundles. During the loading and unloading of a bogie wagon, both doors are open at the same time, which leads to higher heat losses.

A lifting hearth furnace requires several separately driven lifting hearth beam systems in order to enable the loading and unloading of bundles independently of one another. In the event of a malfunction in the rolling mill, no coils can be picked up from the furnace for storage. A second furnace system is also required here if bundles are to be stored.

A hearth hearth can accommodate one or more bundles according to the design. If the storage capacity is to be equal to the contents of the pan, several hearth hearths are required. The disadvantage of several furnaces is that the routes to the bundle unwinder are different and consequently the bundles do not have the same temperature.

GB-A-2 129 723 discloses a method and a plant for the production of hot-rolled steel strip from continuously cast starting material in successive working steps.

After solidification, the primary material is brought to the hot rolling temperature and introduced into a finishing train for rolling out to finished strip, whereby after the hot rolling temperature has been reached, it is wound into bundles, temporarily stored in a storage furnace, called up if necessary, unwound and rolled out into finished strip. It is proposed to use a rotary hearth furnace as the storage furnace.

GB-A-2 167 170 shows a rotary hearth furnace in which the bundles are temporarily stored in a horizontal position or with a horizontal winding axis. This is advantageous because the bundles are then temporarily stored on the same level as they are to be wound up and unwound.

JP-A-62-187 505 discloses a belt caster with a downstream first furnace to bring the continuously cast primary material to hot rolling temperature after solidification, and a finishing train downstream of the first furnace, designed as a continuous rolling mill, with a coil winder between the first furnace and the finishing train and a second oven and a coil unwinder are arranged. The second furnace is designed as an elongated intermediate store.

The invention has for its object to provide a strip caster of the type mentioned with downstream compensation and storage ovens, which are comparatively much shorter in design compared to conventional furnace arrangements and consequently significantly reduce the investment and operating costs of the entire system including the hall construction.

The task is solved with a belt caster of aforementioned type with the invention in that a transverse dividing device (2) is provided between the belt caster and the first furnace (6), that the first furnace is a shortened roller hearth furnace without a compensation zone with upstream induction heating and that the second furnace is designed as a rotary hearth furnace.

With the design of the first furnace according to the invention, it is advantageously achieved that its total length in the production line is considerably shorter than a roller hearth furnace of the conventional type. In this way, the overall length of the system can be greatly reduced since the roller hearth furnace is only about 80 m long with a heating zone and a short buffer zone. The induction heater takes up little space and is a great advantage of bringing the missing amounts of heat into the belt in the shortest possible time. Another advantage of induction heating is that it can be started up in accordance with the lack of heat, the switch-on time being calculated. The data for this can be calculated from the measured strip temperature, the casting speed and the furnace chamber temperature. Individual inductors are switched off in sequence as soon as the end of the strip has passed them. In this way, the use of energy can be optimally controlled economically. Another advantage results from the combination of the furnaces upstream of the rolling mill in that the second furnace is designed as a rotary hearth furnace. With its advantageous ratio of storage capacity to size, this contributes to significantly reducing the overall length of the system. This reduces the investment costs of the plant accordingly, so that the limit of economy can be reached at comparatively lower production rates and considerable Investment costs can be saved.

One embodiment provides that hoods which allow the removal of residual band pieces are provided between the cross-section device and the induction heating.

Furthermore, the strip caster can advantageously be designed as a double-strand system with two shortened roller hearth furnaces with these downstream coil winders.

A plurality of bundles formed from parallel primary material strands can advantageously be buffered in only one rotary hearth furnace.

According to a further advantageous embodiment of the invention, the rotary hearth furnace is integrated into the production line and each has a loading and unloading point. This measure saves space and at the same time creates an emergency store in the event of operational disruptions.

In addition, it can also make sense if the rotary hearth furnace is arranged next to the production line and provided with only one loading and unloading point, which greatly reduces heat losses. The charging device is optionally arranged in the inner circle of the furnace, with the advantage of a further reduced space requirement.

In a special embodiment that is very suitable for many possible uses, the rotary hearth furnace has an outer diameter of approximately 13.5 m and is designed to accommodate 10 bundles. Other design data result in Depends on the ladle content of the belt caster. The belt caster is generally designed as a double-strand system / two-strand belt caster and equipped with two coil winders downstream of the furnaces.

Further advantages of the invention result from the explanation below.

• Fig. 1 eine Prinzipskizze einer Zwei-Strang-Bandgießanlage in Draufsicht, mit Rollenherdofen und Anordnung eines langen Drehherdofens in etwa in Gieß- und Walzlinie,
• Fig. 2 eine Prinzipskizze eines Ausführungsbeispiels der erfindungsgemäßen Anlage mit verkürztem Rollenherdofen und Anordnung eines Drehherdofens in etwa in Gieß- und Walzlinie,
• Fig. 3 eine Bandgießanlage in Draufsicht, mit Drehherdofen in senkrechter Anordnung zur Gieß- und Walzlinie,
• Fig. 3 a eine mittig im Drehherdofen angeordnete Chargiereinrichtung als Einzelheit aus Fig. 3, in schematisch geschnittener Seitenansicht,
• Fig. 4 eine Bandgießanlage in Draufsicht, mit Drehherdofen in der Querverbindung zwischen versetzter Walz- und Gießlinie,
• Fig. 5 eine Bandgießanlage in Draufsicht, mit Drehherdofen bei nur einer Chargier- und Dechargieröffnung.

Show it:

• 1 is a schematic diagram of a two-strand belt caster in plan view, with roller hearth furnace and arrangement of a long rotary hearth furnace approximately in the casting and rolling line,
• 2 is a schematic diagram of an embodiment of the system according to the invention with a shortened roller hearth furnace and arrangement of a rotary hearth furnace approximately in the casting and rolling line,
• 3 shows a strip caster in plan view, with rotary hearth furnace in a vertical arrangement to the casting and rolling line,
• 3 a a charging device arranged centrally in the rotary hearth furnace as a detail from FIG. 3, in a schematically sectioned side view,
• 4 is a top view of a strip caster with a rotary hearth furnace in the cross-connection between the offset rolling and casting lines,
• Fig. 5 shows a strip caster in plan view, with rotary hearth furnace with only one charging and decharging opening.

The systems according to FIGS. 1 and 3 to 5 are not exemplary embodiments of the invention, but rather they merely provide a better understanding of the invention, in particular possible developments of the rotary hearth furnace.

In Figure 1 (1) denotes a strip caster with two strands (1 ', 1''), each of which is followed by a cross-cutting device (2), for example a flame cutting machine or scissors for separating the cast and the caster (1) with one Speed of about 6-7, maximum 8 m / min leaving belts (1 ′, 1 ′ ′) in sections of the same length, for example 65 m. The individual partial lengths of the strips are then temporarily stored in two roller hearth furnaces (6) of approximately 150 m in length and brought to a homogeneous hot rolling temperature of approximately 1050 to 1100 degrees Celsius. The roller hearth furnaces (6) have, for example, a 3 m long, unheated, hinged hood on the entrance side, followed by a 70 m long heating zone, a 65 m long compensation zone and a buffer zone of 12 m. The partial lengths leaving the furnaces (6) are wound into bundles or coils (11) in a bundle winder or two coilers (10). The coil winding speed is about 2 - 3 m / s. The bundles (11) then have, depending on the bandwidth, between 1100 and 1350 mm with a thickness of 40 mm and one Belt length of 65 m, a coil weight between 22 and 27 t. The bundles (11) are fed from the bundle transfer stations (12) via a transport system (14) to a charging or charging device (18) which brings the bundles (11) into a rotary hearth furnace (20).

The rotary hearth furnace (20) is advantageously arranged in the line between a two-strand strip casting machine (or several single-strand strip casting plants) and the hot wide strip rolling mill (40). It is essentially designed as a storage furnace or compensating furnace and has, for example, approximately 10 to 25 storage spaces distributed in a ring (21). The annular furnace (20) has fire-proof insulation on all sides, charging openings (24, 25) which can be closed preferably being provided in the outer and / or inner wall (22, 23), in the present case a loading opening (24) and a removal opening (25 ). The storage spaces (21) inside the furnace (20) can be moved in a circular path between the fixed outer and inner walls (22, 23) at any speed and direction. About the removal or
Decharging device (28) a bundle (11) is removed and fed to a bundle unwinder or decoiler (30) by means of a suitable bundle transfer device (29). The transfer can take place in any manner, for example also by means of a removal device (28) which is pivotable between the removal position and the decoiler (30). The unwound tape is then in a known manner conveyed via scissors (32) and a descaling system (34) to the finishing mill (40), the unwound strip being rolled out from the final rolling thickness to the finished strip (41) in the finishing mill (40). After leaving the last rolling stand of the finishing train (40) with an outlet temperature of approximately 860 degrees Celsius, the finished belt (41) passes through a cooling section in a known manner in order to be subsequently wound up by an underfloor reel at a temperature of approximately 560 degrees Celsius (not shown) .

The loading and unloading of bundles (11) can take place independently of one another. When the rolling mill (40) is in trouble-free operation, the coils (11) pass through only a partial area of the furnace (20), corresponding to the required dwell time between the loading and unloading station (18, 28). If faults occur in the rolling mill (40), additional bundles (11) can be buffered. After the rolling mill (40) has been put back into operation, it can be removed from the furnace (20) in any order. The bundles (11) are transported through the oven (20) on a stove prepared for this purpose. This has the furnace chamber temperature and prevents black spots, i.e. the so-called SKID MARKS. A temperature equalization takes place in the bund during the dwell time. The furnace (20) can advantageously be designed for low-scale heating.

The furnace combination according to FIG. 2 has the advantage that the total length of the furnaces (6, 20) in the production line is shorter than a roller hearth furnace (6) 1, since the compensation zone can be omitted. The length of the roller hearth furnaces (6) here is about 80 m with a belt length of 65 m, consisting of a heating zone of 68 m and a buffer zone of 12 m, which is required for the subsequent process steps. The belts (1, 1 ') run through the furnaces (6) during the reheating at the casting speed. When the end of the strip reaches the roller hearth furnace (6), it is conveyed out of the respective furnace (6) at winding speed, ie at about 2-3 m / s, and wound into bundles (11) in the coil winders (10). The dwell time of a strip in the roller hearth furnace (6) decreases continuously from the strip tip to the end of the strip. The front part of the belt remains in the furnace (6) during the entire casting time and therefore has a higher temperature. As the dwell time decreases, a partial length of the strip may not be brought up to the temperature level required for the subsequent rolling process. Hinged hoods (3) are provided for removing remaining pieces of tape and thereby reducing heat loss.

The induction heater (4) has the task of introducing the missing amount of heat into the belt. The heating power of the induction heaters (4) is increased according to the missing amount of heat, the switch-on time being calculated. The data for this are the measured strip temperature, the casting speed and the furnace chamber temperature. The individual inductors (4) are switched off when the end of the strip has passed them. A temperature compensation in the collar (11) to the required Temperature profile can take place in the downstream rotary hearth furnace (20). The arrangement and mode of operation of the rotary hearth furnace (20) and the upstream and downstream units correspond to the description of FIG. 1.

According to FIG. 3, the rotary hearth furnace (20) can also be arranged next to the production line of the belt casting system (1) and serves here as a purely bund storage furnace. The bundles (11) are loaded or removed at the same point via the charging opening (24). This makes it possible to keep the paths of the transport system (14) short. As can also be seen in particular from FIG. 3 a, closable openings, each with a door (24, 26), are provided in the outer and inner walls (22, 23) of the rotary hearth furnace (20) for the charging device (18) arranged in the inner circle of the furnace. In the furnace (20) there are also two slides (27) which close the rest of the furnace space during charging. As a result of this provision, the heat loss and atmosphere exchange are low when the doors (24, 26) are open. The bundles (11) are transported to and from the rotary hearth furnace (20) by means of a bundle transport system (14). The bundles (11) can be called up from the oven (20) in any order. Alternatively, the rotary hearth furnace (20) can be designed for a charging device (18) arranged on the outside.

The transport system (14) according to FIG. 4 is particularly useful for systems in which a greater distance has to be bridged between the strip casting machines (1) and the rolling mill (40). The main area of application is therefore the retrofitting of conventional rolling mills to strip casting systems with a subsequent continuous mill. Behind the coilers (10) and the coil transfer devices (12) are lifting stations (13) for lifting the bundles (11) to the level of the transport system (14), i.e. provided at the level of the trolley (15). The carriages (15) are equipped with removable thermal insulation hoods which prevent high heat losses during the movement of the bundles (11) to the rotary hearth furnace (20). Each car (15) has its own drive and can be moved independently. The rail guide (16) depends on the local conditions and project specifications. The thermal insulation hoods of the wagons (15) are equipped with burners, pilot burners etc. and a temperature measurement and can be heated or reheated at the places provided. The rotary hearth furnace (20), the charging openings (24, 25) of which lie opposite one another, is arranged in the transport direction following the rail path (16). The method of operation of the device and the following units essentially corresponds to the description of FIG. 1.

According to FIG. 5, the rotary hearth furnace (20) can also be arranged next to the production line of the strip casting system (1), similar to the system shown in FIG. 3 and in turn serves as a purely bund storage oven. The bundles (11) are loaded or removed at the same point via the charging opening (24). This in turn gives the possibility of keeping the paths of the transport system (14) short. The bundles (11) can be called up from the oven (20) in any order.

Claims (8)

1. Strip casting plant with a downstream first oven (6), in order to bring continuously cast starting material up to hot rolling temperature after hardening, as well as with a finishing train (40) arranged downstream of the first oven (6) and constructed as a continuous rolling mill, wherein a coil winding device (10) and a second oven (20) as storage oven, downstream of which is arranged a coil unwinding device (30), are arranged between the first oven (6) and the finishing train (40), characterised thereby that a cross-cutting equipment (2) is provided between the strip casting plant and the first oven (6), that the first oven (6) is constructed as an abbreviated roller furnace without an evening-out zone and with upstream induction heating (4) and that the second oven (20) is constructed as a rotary furnace.
2. Plant according to claim 1, characterised thereby that hinged hoods (3), which enable removal of residual strip pieces, are provided between the cross-cutting equipment (2) and the induction heating (4).
3. Plant according to claim 1 or 2, characterised thereby that the strip casting plant (1) is designed as a double strand plant with two abbreviated roller furnaces (6) and coil winding devices (10) arranged downstream thereof.
4. Plant according to claim 1, characterised thereby that a plurality of coils formed from parallel starting material strands are intermediately storable in only one rotary furnace (20).
5. Plant according to claim 1 or 2, characterised thereby that the rotary furnace (20) is integrated into the production line and has each of a loading station (18) and an unloading station (28).
6. Plant according to claim 1 or 2, characterised thereby that the rotary furnace (20) is arranged beside the production line and provided with only one loading and unloading station (18).
7. Plant according to one or more of claims 1 to 6, characterised thereby that the charging equipment (18, 28) is arranged in the oven inner circle.
8. Plant according to one or more of claims 1 to 7, characterised thereby that the rotary furnace (20) has an outer diameter of about 13.5 metres and is designed for the reception of ten coils (11).

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