Patent Application
20100147484
The invention pertains to a method for manufacturing a metal strip by means of continuous casting and rolling, wherein a thin slab is initially cast in a casting machine and this thin slab is subsequently rolled in at least one rolling train by utilizing the primary heat of the casting process, wherein a continuous manufacture of the metal strip (continuous rolling) can be realized in a first operating mode by directly coupling the casting machine to the at least one rolling train, and wherein a discontinuous manufacture of the metal strip (batch rolling) can be realized in a second operating mode by decoupling the casting machine from the at least one rolling train. The invention furthermore pertains to a device for manufacturing a metal strip by means of continuous casting and rolling.
Continuous thin slab/thin strip casting and rolling systems of this type are known as CSP-systems. The continuous rolling out of the casting heat has been known for quite some time, but not yet prevailed in the market. The rigid connection between the continuous casting machine and the rolling train, as well as the march of temperature through the entire system, proved to be difficult to manage. The continuous rolling out of the casting heat is known from EP 0 286 862 A1 and EP 0 771 596 B1. The casting process and the rolling process are directly coupled in this case. The continuous strip is severed by means of shears shortly before the coiler.
Similar methods for the continuous manufacture of steel strips by coupling the casting machine and the rolling train to one another are disclosed in EP 0 415 987 B2 and EP 0 889 762 B1. In order to solve the temperature problems at the relatively slow transport speed, inductive heaters are provided upstream of and within the rolling train in these publications.
An alternative technology is the rolling of individual slabs and individual strips. In the discontinuous rolling of strips, the casting process and the rolling process are decoupled from one another. The casting speed is usually very slow and the rolling process is realized independently thereof with a high speed, namely in such a way that the temperature for the final forming process lies above the minimum temperature. Systems of this type are also referred to as CSP-systems and described, for example, in EP 0 266 564 B1, in which a high reduction is realized in the thin slab system.
A similar thin slab system is also disclosed in EP 0 666 122 A1, wherein strips are discontinuously rolled by utilizing inductive heating between the first finishing stands.
The advantage of discontinuous rolling can be seen in that the casting speed and the rolling speed can be adjusted independently of one another. When rolling thin strips, it is possible, e.g., to flexibly adjust higher rolling speeds, namely even if the casting machine operates with a slower speed or its speed is currently adjusted.
Both methods—namely the continuous casting and rolling on one hand and the discontinuous casting and rolling on the other hand—are difficult to combine due to the above-described circumstances.
The invention is based on the objective of additionally developing a method of the initially cited type and developing a corresponding device that make it possible to increase the flexibility of the method and the device. It should be possible, in particular, to continue the casting process without interruptions if a malfunction occurs or brief maintenance procedures are required in the rolling train or during other interruptions of the rolling process, wherein this ability provides significant economical advantages and advantages with respect to the process control.
With respect to the method, this objective is attained, according to the invention, in that cast slabs or preliminary strips are removed from the main transport line downstream of the casting machine referred to the strip transport direction in the discontinuous manufacture (i.e., rolling) of the metal strip, stored and subsequently transported back into the main transport line, wherein the removed slabs or preliminary strips are heated to a desired temperature or maintained at a desired temperature prior to the transport back into the main transport line.
In this case, a special shuttle system consisting of two or more partial systems is preferably used in succession.
In this case, it is particularly preferred that slabs cast during the continuous operation of the casting machine are removed from the main transport line during a roll exchange in the rolling train and transported back into the main transport line at a later time. This makes it possible to exchange a roll without having to forgo the continuous operation of the casting machine.
One proposed device for manufacturing a metal strip by means of continuous casting and rolling features a casting machine, in which a thin slab is initially cast, and at least one rolling train that is arranged downstream of the casting machine and in which the thin slab is rolled by utilizing the primary heat of the casting process. The invention is characterized in that a shuttle system is arranged downstream of the casting machine referred to the strip transport direction and designed for transporting cast slabs out of and into the main transport line. A heating means is preferably arranged on or in the shuttle system in order to heat the slabs to a desired temperature.
This heating means is advantageously realized in the form of an inductive heater and/or a furnace that is heated with fuel (e.g., gas, oil). The shuttle system may comprise transport elements for moving the slabs transverse to the strip transport direction. These transport elements may comprise movable carriages. Alternatively, the transport elements could also consist of walking beam transport elements.
According to one additional development of the invention, the shuttle system consists of two or more (e.g., 3 or 4) partial systems that are arranged in succession in the strip transport direction. These partial systems can be displaced transverse to the strip transport direction jointly or independently of one another. Within these partial systems of the shuttle system, it is possible to realize a longitudinal transport from one partial system to another partial system in the strip transport direction or opposite thereto (i.e., forward or backward).
The shuttle system is preferably arranged between the casting machine and the rolling train. However, it may also be advantageous to arrange the shuttle system between a roughing train or a roughing stand and a finishing train.
The shuttle system may furthermore be realized such that it can be connected to a roller table for storing slabs. In this case, the roller table may be provided with heat insulation. A heating means may be arranged between the roller table and the shuttle system.
At least one auxiliary storage means, e.g., in the form of a holding pit or a similar device, may be arranged adjacent to the roller table in order to store slabs or preliminary strips. This makes it possible to expand the storage capacity or to realize a prolonged storage time so as to influence the microstructure. This may also be advantageous for metallurgic reasons, namely if prolonged storage times should be realized in the holding pit that acts as a storage means.
Slab shears or preliminary strip shears may be arranged upstream of the shuttle system referred to the strip transport direction.
The advantages of the continuous technique, i.e., the continuous operation of the proposed casting and rolling system, in connection with the CSP-technology can be seen in the following characteristics: the structural length of the system is reduced such that the investment costs are lowered. Energy savings can be achieved due to the consequent direct use. In addition, the yield strength is reduced due to the slower rolling speed. It is possible to manufacture products that are difficult to roll and, e.g., very thin (ultrathin) strips (strip thickness approximately 0.8 mm) in large quantities. It is furthermore possible to process special materials (high-strength materials). A combination of wide and thin strips can also be processed. Rolling defects on the strip ends and therefore damages to the rolls can be prevented or at least reduced. The malfunction rate of the system can be reduced and upstrokes can be prevented.
Embodiments of the invention are illustrated in the drawings. In these drawings:
The continuous casting and rolling system also features various other elements that are generally known in systems of this type. A descaling sprayer 12 is arranged downstream of the casting machine 2 referred to the strip transport direction F in order to clean the slabs. Strip shears 11 are positioned directly downstream of the roughing train 4. The shears are used for separating the dummy bar at the gate, for severing the slabs (usually individual slabs or half slabs) and for cutting the strip during malfunctions.
A shuttle system 7 arranged downstream thereof is described in greater detail below.
A furnace 13 is arranged downstream of the shuttle system 7 and preferably realized in the form of an induction furnace; however, this furnace may also consist of a roller hearth furnace. It is furthermore possible to divide the induction heater shown. It would even be conceivable to provide an induction heater upstream and downstream of the shuttle system. Additional strip shears 14 and an additional descaling sprayer 15 are arranged downstream thereof. The shears 14 serve as emergency shears or for profiling the shape of the slab ends.
A cooling section 16 is arranged downstream of the finishing train 5. The coiler 17 is situated downstream thereof. The finishing train 5 frequently comprises three to eight stands, preferably six stands. In this finishing train, the preliminary strip is rolled down to a final thickness of, for example, approximately 0.8 to 16 mm.
The following should be noted with respect to the shuttle system 7: in the solution according to
These figures also show that two partial shuttle systems 7′ and 7″ are provided in succession referred to the strip transport direction F. These partial systems may advantageously have a total length that corresponds to the length of a slab with maximum weight of coil plus a slight allowance for pendulum motions. Consequently, the shuttle or furnace zone is realized relatively short.
In the embodiment according to
In
These slabs or preliminary strips can then—as shown in FIG. 11—be optionally stored in holding pits 10 and subsequently reinserted into the transport line and rolled out as indicated in
Depending on the system variation, it is possible to operate with or without a rigid furnace section upstream of the shuttle 7. This also applies to the induction heater or the roller hearth furnace 13 arranged downstream of the shuttle. A pendulum motion of the slab 3 may take place between the roller table 9 and the shuttles 7 situated adjacent thereto on the right side in order to heat the slab 3 by means of the induction heater 8. The roller table 9 can be encapsulated for heat insulation purposes.
The subsequent reheating can be optionally realized in an inductive fashion with a heating means 8, e.g., a gas-fired or oil-fired roller hearth furnace.
According to
The heating means 19 (in
Furthermore, the heating means 8, 13 and 19 make it possible to realize homogenous temperatures over the length of the thin slabs and to compensate possible temperature non-uniformities by means of a varying introduction of energy over the length.
If the system is operated with a relatively slow casting speed and therefore rolling speed in the rolling train in the continuous mode, the induction heater is required for adjusting a sufficiently high rolling temperature. The induction heater arranged upstream of the finishing train may optionally be supplemented with induction heaters within the finishing train. The induction heater upstream of the finishing train is optionally realized such that it can be transversely displaced or pivoted upward in order to replace the induction heater with a (passive or heated) roller table cover or a conventional furnace section, if so required.
The strip shears 18 in
The arrangement of the shuttle system 7 may be realized directly downstream of the casting machine 2 (as illustrated in
The holding furnace 13 arranged downstream of the casting machine 2 may also be realized in the form of a conventional gas-fired furnace.
According to the embodiment shown in
The strip shears 11 are used for severing the thin slabs 3 in the discontinuous mode and the strip shears 14 are used for severing the strips in the continuous rolling mode. The shears 11 serve, in particular, for cropping the strip head or strip end during the start or the outward transport in the continuous mode or in the discontinuous mode.
The utilization of the proposed system types makes it possible to selectively realize a coupled, fully continuous casting/rolling process (continuous rolling) and a decoupled, discontinuous processing of individual slabs (batch rolling).
In continuous rolling, the level of the casting speed defines the march of temperature through the entire system. Depending on the casting speed, a computer model dynamically controls the heating power of the furnaces arranged upstream and within the rolling train in such a way that the rolling train outlet temperature reaches the target temperature.
If the casting speed falls short of a certain predefined threshold value (when problems occur in the casting system, when processing materials that are difficult to cast, during the starting process, etc.), the system is automatically switched over from the continuous mode to the discontinuous rolling mode, i.e., the thin slab 3 is severed by means of the shears 11 and 14 and the rolling speed is increased such that the desired final rolling temperature is reached. During this process, the slab segments or strip segments are tracked within the train 4, 5 and the transport and rolling speeds, as well as the inductive heating power, are dynamically adapted over the strip length depending on the temperature distribution.
Once the casting process has stabilized again and the casting speed exceeds the predefined minimum value, the system is analogously switched back from the discontinuous mode into the continuous mode.
The option to randomly adjust or switch over between the continuous mode and the discontinuous mode provides a high degree of flexibility that represents an improved process reliability. This applies, in particular, to the startup of a production system.
The continuous processing mode is not generally used; the batch mode is primarily used during casting speed problems or during the starting process.
In order to realize an energy optimization, it is possible to roll, in particular, thinner strips or strips that are difficult to produce in the continuous mode and strips with a thickness that exceeds a critical thickness in the batch mode at faster speeds and therefore with a low heating power consumption. The correct combination of the production type optimizes the energy balance of the continuous/batch CSP-system for the entire product range.
The utilization of the proposed system types makes it possible to selectively realize a coupled, fully continuous casting/rolling process (continuous rolling) and a decoupled, discontinuous processing of individual slabs in the batch mode. The system has a very space-saving design. The system length (approximately 250 m) only amounts to approximately half the length of a conventional CSP-system. However, the proposed system still makes it possible to exchange a working roll without having to interrupt the casting process.
The following should be noted with respect to the possible operating modes of the proposed system:
1. Batch-Mode in the Rolling Train:
At the beginning of the casting process, during the startup of the system, during general casting problems or when processing steels that are difficult to cast, the casting speed is adjusted relatively slow. At slow casting speeds, the continuous rolling with this low mass flow from the casting system to the finishing train is not possible or uneconomical for temperature reasons. The batch mode is preferably used in order to reduce the energy losses. In the batch mode, the casting process and the finish rolling are respectively decoupled and therefore take place with a different speed (i.e., mass flow). After the casting process begins, the dummy bar is initially disposed and the thin slab is cropped in the region of the slab head. After the desired coil weight is reached, each slab is cropped with the shears downstream of the continuous casting system or the roughing train, respectively. Subsequently, the slabs are rolled in the finishing train with an individually adjustable rolling speed, transported through the cooling section and ultimately coiled up.
2. Continuous Mode (i.e., Casting Machine and Rolling Train are Coupled)
The system is switched over into the continuous mode as the casting speed increases and in dependence on the final thicknesses to be rolled. In this operating mode, the shears upstream of the coiler are used for severing the strips. Before the thin slab is introduced into the finishing train, it is inductively heated such that a sufficiently high rolling temperature is adjusted and the rolling takes place in the austenitic range. During the subsequent finish rolling, the inductive heaters within the finishing train are usually also utilized in order to supplement the inductive heaters upstream of the finishing train. However, in the discontinuous mode or during the starting process on the strip head, they are situated in a safe waiting position far above or adjacent to the strip.
3. Roll Exchange in the Finishing Train During Active Casting Process
The casting process preferably should not be interrupted or disturbed during an exchange of the working rolls or during malfunctions in the rolling train. It is therefore sensible to install a buffer for the slabs. For this purpose, a short roller hearth furnace is provided downstream of the casting machine in a compact CSP-system, wherein said roller hearth furnace can accommodate four (or six) slabs depending on the process. The furnace is realized in the form of the proposed shuttles as illustrated, in particular, in
According to the figures, to shuttle groups 7′, 7″ are arranged in succession referred to the transport direction, wherein both shuttle groups can be transversely displaced independently of one another. Alternatively, the front shuttle group 7′ may be rigidly installed downstream of the casting machine 2 or the roughing train 4 in the form of a furnace section. For example, a total of four full or half thin slabs can be accommodated in these two shuttle groups. Storage capacities are optionally provided in short furnace sections. The fields drawn with broken lines in
If the shuttles (furnaces) are full, e.g., because the interruption of the rolling process lasts for an extended period of time, the slabs can be pushed off on a roller table 9 (see
The storage of half slabs (i.e., a compromise during a roll exchange) simplifies the filling of gaps between two strips at a short structural length such that slabs can be easily transported out of or into the transport line 6 with a shuttle. In the normal mode, however, the overall length of both shuttles makes it possible to maintain a slab warm over its entire length.
During the roll exchange, the casting speed is optionally reduced in order to increase the buffer time.
It is preferred to provide a 1-strand casting system with pendulum-type or transverse shuttles in order to store a thin slab or formed thin slab in a shuttle and/or parallel furnaces, e.g., during a roll exchange.
In order to carry out the roll exchange, the system is previously switched over from the continuous mode into the batch mode.
Within the shuttles that stand adjacent to the main transport line 6, it is also possible to realize the longitudinal transport of slabs from one shuttle to another shuttle (in this context, see the double arrow in the direction of the strip transport direction F in
Consequently, the proposed invention makes it possible to utilize the advantages of a continuous casting and rolling process, as well as those of a batch rolling process.
The transformation costs (rolling energy, heating energy) can be lowered, and the structural length of the system can be reduced by approximately 40% to 50% in comparison with the CSP-technology. The investment costs and the operating costs are also lowered accordingly.
Continuous rolling reduces the number of initial passes in the finishing train, wherein this is particularly advantageous when rolling thin final thicknesses. The cast slab passes, for example, through two inline roll stands, in which it is reduced to a suitable preliminary strip thickness for producing the final product with the smallest possible number of finishing stands.
The preliminary strip temperature can be maintained at the level of the outlet temperature of the inline-stands in a roller hearth furnace. An inductive heater upstream and, optionally, within the finishing train increases this temperature to the required rolling temperature.
It is advantageous to provide inductive heating systems upstream and within the finishing train because only relatively slow rolling speeds can be realized in the continuous mode. In this case, the temperature loss without inductive heating system would be greater than that permitted up to the end of the finishing train in order to observe the finish rolling temperature.
The proposed method also allows the rolling of individual strips known from the CSP-process. For this purpose, the preliminary strip is divided into the desired lengths downstream of the inline stands by means of pendulum shears. This makes it possible to manufacture a multitude of steel qualities that need to be cast with a slower casting speed due to metallurgic requirements. At these slow casting speeds, a continuous rolling process is not economical. The reheating power required for observing the finish rolling temperature is excessively high. In addition, the advantages of the continuous rolling process do not apply to steel qualities manufactured with this method because these products are manufactured in conventional finished strip thicknesses.
The continuous casting process preferably should not be disturbed during a roll exchange in the finishing train. This is the reason why it is necessary to install the proposed system for buffering the preliminary strips, wherein this system makes it possible to provide the required buffer time without impairing the quality of the preliminary strip. The uniformity of the preliminary strip temperature is one distinguishing characteristic of the CSP-technology and a prerequisite for a multitude of advantages during the subsequent finish rolling process. The roller hearth furnace is a suitable solution in this respect. In the present instance, the roller hearth furnace is essentially designed for accommodating approximately four half preliminary strip lengths and provides a buffer in the length of the required roll exchange time if the preliminary strips are transversely displaced and stored therein.
The described concept represents a one-strand concept. It would be possible to expand the system to two casting strands. If the system is designed in the form of a one-strand system, the capacity of the system components is utilized. This generally results in favorable investment and operating costs.
Typical data for the proposed concept are casting thicknesses between 60 and 100 mm, casting speeds between 4 m/min and 8 m/min, preliminary strip thicknesses between 25 mm and 60 mm and finished strip thicknesses between 1.0 and 16 mm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102007040072.3 | Aug 2007 | DE | national |
| 102007048117.0 | Oct 2007 | DE | national |
| 102008020412.9 | Apr 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/006867 | 8/21/2008 | WO | 00 | 2/18/2010 |
