Patent Application
20190210099
The present invention pertains to the field of continuous casting of molten metal. In particular, the present invention pertains to machines and methods for casting multiple billet sub-strands from a single continuous casting machine strand.
Continuous casting refers to the process whereby molten metal is solidified into a casting section, typically for subsequent rolling in finishing mills. Continuous casting machines (CCM, see
While the term “twin-casting” may refer to a number of different processes in the steel and metals industry, twin-casting, as used herein, refers to a process in which two or more (similar or) identical casting sections are produced simultaneously from a single strand of a CCM. As per the prior art, so defined twin-casting requires that the casting sections produced be withdrawn from the machine at the same casting speed because of the mechanical link provided to all of the sections by the common withdrawal and straightening unit. Currently, twin casting is typically applied for converting a single strand designed for slab casting into two bloom strands.
Considering one given casting section geometry, the main advantage in the application of twin casting to a CCM strand is that the productivity of the casting section is multiplied by the number of multiple sections which are grouped together as in the following Equation 1.
Productivity [ton/h]=N*K*CS*60 Equation 1
Where:
N=number of strands paired (or number of strands casting)
K=constant (e.g. product section linear weight in [ton/m])
CS=casting speed (e.g. [m/min])
Accordingly, given a fixed productivity target for the section, twin casting allows for meeting the target, while running the strand at a lower casting speed (as compared to single-section per strand CCM), thereby improving speed-dependent figures of quality and safety. In particular, the advantages include: (1) Increase of the strand productivity by 100% for each casting section paired above 1 (e.g. 2 casting section paired together on the same strand=+100% of productivity in ton/h/strand, 3 casting section paired=+200% and so on) without affecting the performances of quality, safety and process stability (2) Possibility of meeting the same targets of productivity than the conventional single-section per strand scenario, with a much lower casting speed, therefore improving process stability and other technological aspects with respect to the conventional single-section per strand scenario. (3) Possibility of meeting the same targets of productivity while improving safety with respect to risk of speed-dependent breakouts. (4) Possibility of meeting the same targets of productivity while improving the quality in particular for those figures related to casting speed. Examples of speed-dependent product quality properties, normally known to improve with lower casting speed are rhomboidity, Internal porosity and central segregation.
In the typical arrangement of a CCM suitable for the casting of different product section geometries, each strand can be considered composed by: (1) a group of inter-changeable modular systems whose sizing and geometry are influenced by the product section geometry, called “section-dependent casting equipment”, where said “section-dependent casting equipment” is comprising but not limited to: the mold, the containment roller aprons, the secondary cooling spray system, and (2) another group of modular systems which is shared during production among any of the different casting sections produced by the strand, say “fixed strand equipment”, comprising but not limited to: the mold oscillating table, the strand supporting structures, the withdrawal and straightening system, the product cutting system and the product transportation roller tables. It is understood that in the actual state of art, any multi-section CCM strand can be arranged for casting any different section of its design portfolio by selecting and installing a suitable “section-dependent casting equipment”, while using the same, unchanged “fixed strand equipment”. A twin-casting may therefore be arranged on a suitable CCM strand by installing a “section-dependant casting equipment” specifically designed for the “twin casting” of a product section, while using the same, unchanged “fixed strand equipment” than the conventional strands. A typical requirement of a “section-dependant casting equipment” for twin casting is to have a mold specifically designed for hosting the number of sub-strands to be cast in a twin arrangement. The mold itself provides the link (both technological, automation and mechanical) between the sub-strands and the oscillating bench. The oscillating bench is considered part of the fixed-strand equipment, therefore usually remains unchanged. A twin-mold features a number of vertical openings crossing all along its body, each one used for the processing of one sub-strand. Each opening is delimited by a number of heat-exchanging bodies deputed to produce the solidification of the product section external perimeter. The heat-exchanging bodies may form a “sub-strand”-dedicated unit or they can be part of a common unit among all of the twin-casting arrangement, in both case said unit(s) is known as the “crystallizer”(s).
The main precondition required to a strand-equipment for the application of twin-casting principle is to have the sufficient room for hosting the paired sections, plus their equipment, in a parallel layout. This translates into a requirement for a big-enough CCM fixed-strand mutual distance and a suitable geometry of the oscillating table hosting the mold. Said table hosting the mold exerts the function, thanks to its oscillating movement towards the casting direction, to prevent product sticking on the crystallizer walls.
In one existing method for twin casting, a slab mold is kept and adapted to cast 2 or more smaller sections by the insertion of a system of additional crystallizer walls (“mold divider”), to the original slab mold-plate-assembly, in order to separate the original slab section into 2 blooms with same section thickness.
In other versions of twin casting application, the original slab mold is modified to host 2 or more independent assemblies of plate-type molds, each one delimiting a smaller casting section, and the original slab mold plates are not kept.
U.S. Pat. No. 4,291,747 discloses a cooler (it can be considered equivalent to the mold) for twin strand continuous casting. Said cooler includes a steel jacket surrounding a cooling member having a pair of die receiving passages for respectively receiving the dies utilized to form the twin strand or products. Coolant introduced into the jacket is circulated about the periphery of the cooling member and through the cooling member itself in the area between the die receiving passages.
To accommodate the change from a conventional slab to the twin casting, dedicated containment and cooling systems are applied also downstream to the mold, since those systems are organized as interchangeable spare devices according the afore mentioned logic of a “section-dependant casting equipment”. During processing of the casting products into the “section-dependant casting equipment”, said products are driven out of the machine by means of a strand withdrawal system, being part of the “fixed-strand equipment” and providing the same withdrawal speed to all of the twin-cast products (say “sub-strands”) included in the strand arrangement.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
An object of the present is to provide a method of continuous casting two or more long products using a single continuous twin casting strand. In accordance with an aspect of the present invention, there is provided a method of continuous casting two or more long products using a single continuous casting machine's strand, said method comprising: providing at least one continuous, twin-casting strand comprising two or more sub-strands, wherein each of said sub-strands comprises a mold which casts a long product; pouring liquid metal into each of said molds and allowing said metal to partially solidify; and withdrawing long product from each of said two or more sub-strands, wherein process control of said method is automatic and comprises master/slave logic, wherein one sub-strand of said twin casting strand is a master sub-strand and remaining sub-strand(s) are slave sub-strand(s), wherein said master strand has non-controlled metal flow and liquid metal level in said master sub-strand is regulated by adjusting casting speed; and wherein liquid metal level in said slave sub-strand(s) is regulated by adjusting the liquid metal pouring rate at each slave sub-strand.
These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings.
Continuous casting, as used herein, refers to the process whereby molten metal is solidified into a casting section for subsequent rolling processes in finishing mills, or for other suitable processes of grane-refinement.
CCM, as used herein, refers to a continuous casting machine or a plant for continuous casting.
Strand, as used herein, refers to a sub-unit of the CCM which allows for parallel continuous casting. In the conventional casting, each strand casts one single product section.
Long product, as used herein, refers to a continuously-cast metal product shaped by a CCM with moderate width and moderate ratio width/height (e.g. w/h<3.5; width <1300 mm).
Billet, as used herein, refers to a long product characterized by square-shaped cross section with sides smaller than 200 mm.
Bloom, as used herein, refers to a long product characterized by square or rectangular cross section with at least one side greater than 200 mm.
Beam blank, as used herein, refers to a long product whose cross-shape constitutes a “near-net” shape of a beam. Its typical use is for rolling into (but not limited to) structural profiles (e.g. beams and columns)
Slab, as used herein, refers to a profiled product produced by Continuous Casting and characterized by a rectangular cross-section shape with very high ratio width/height (e.g. w/h>4) and typical width: w>800 mm.
Slab and its variant “thin slab” are usually identified as “Flat products”, to distinguish them from afore mentioned “long products”, whose are characterized by a different shape ratio of the cross-section.
Mold, as used herein, is a device in a CCM in which the very early solidification of hot metal is promoted, by shaping a solidified product skin with the final geometry of the casting product's cross-section. The operation is done by removal of the superheat and the latent heat from the liquid metal facing the walls of the crystallizer, which is part of the mold assembly. The mold itself is an inter-changeable spare between the strands, in order to allow a proper maintenance of the crystallizer and to its other functional parts. As per afore mentioned logic, the mold is part of the “section-dependant casting equipment”.
Crystallizer, as used herein, is a high-conductivity solid-metal body deputed to exchanging heat with the liquid metal. Its function is to obtain the metal skin solidification by transferring the latent heat and the superheat of the hot metal to another liquid media (e.g. Water). The crystallizer is the main part of the mold, and the mold itself is its interface with the rest of the machine, automation and utility plants (e.g. water plant) to which the crystallizer interacts in order to allow the solidification process.
Tubular-type crystallizer, as used herein, is a CCM crystallizer type normally applied for production of small casting sections (e.g. cross section biggest dimension <450 mm), therefore this technology is applied to most of the small-size long-products casting equipment. This crystallizer is shaped as a tube with a closed, seamless section-perimeter, surrounding the product during the early phase of solidification process. The internal surface of the tube shapes the product during its solidification. The thickness of the crystallizer (or part of its thickness) exerts the thermal exchange (by conduction) from the steel to the cooling media (e.g. water), therefore the crystallizer is fabricated with high-thermal-conductivity material (e.g. Copper or special purpose Copper Alloys). One typical (but not necessary) feature of this crystallizer morphology is its coupling of it with water-jacket cooling systems.
Water jacket, as used herein, refers to a mold cooling method typically applied for cooling of the tubular crystallizers. The method consists in a thin layer of water flowing on the external surface of the tubular crystallizer, for cooling it in a forced-convection arrangement whereas water speed is approximately parallel to the product casting direction.
Breakout, as used herein, refers to hot-metal spread-around, due to product-skin perforation while the product core is still liquid. Breakout may occur due to lack of cooling in some part of the process and is an unwanted, hazardous event.
Meniscus, as used herein, refers to the freeboard level of the liquid metal inside a continuous casting mold.
Casting speed, as used herein, refers to the speed at which the solidified section exits from the mold. Typically expressed in meters per minute [m/min], and regulated by controlling the rotation speed of the withdrawal & straightening unit driven rollers. Considering that in any modern CCM, every strand is equipped with independent withdrawal and straightening unit, it is therefore understood that the casting speed is an independent, peculiar value of each strand, at any time of the process.
Oscillation bench (OB), as used herein, refers to a strand-dependent device that supports and oscillates the mold to prevent the product sticking on its crystallizer walls. In the prior art, each long-product CCM casting strand is normally equipped with a dedicated oscillation system.
Withdrawal and Straightening Unit (WSU), as used herein, refers to a strand-dependent system providing the straightening of cast products (from as-cast bowed shape, to straight) and the withdrawal (or supporting) force to control the product extraction from the mold bottom. Normally this system includes a modular assembly of driven roller couples (pinch rolls) plus a number of optional idle rollers aligned in suitable mutual positions in order to address properly the straightening, according a designed pattern. In the prior art, every strand of a long-product CCM is equipped with its own WSU.
Open/Closed casting, as used herein, refers to methods for the automatic control of the liquid metal level in the mold (say the meniscus position along the mold) during the continuous casting process. The meniscus position along the mold length can be controlled by the automatic flow-rate regulation of the liquid-metal stream (“closed casting” method) or by the automatic regulation of the casting speed (“open casting” method), being the steel-flow fixed, or non-controllable. The “open casting” normally applies when the liquid steel flow is not regulated by a proportional regulation system. Open casting is therefore normally associated with hot-metal pouring equipment based on usage of calibrated nozzles (which does not allow automatic control of steel flow), while closed casting is usually done by means of automatic control of a tundish stopper-rod system or a tundish slide-gate system, as those systems are well-known to allow continuous regulation of the liquid metal pouring rate.
Secondary cooling (or spray cooling), as used herein, refers to a strand-dependent cooling system used for the heat withdrawal from the continuously-cast product after its exit from below the mold. It is typically done by water-spray cooling, organized in distinct cooling zones to differentiate and control suitably the product cooling process.
Containment, as used herein, refers to a strand-dependent system located downstream the mold to counteract the tendency of the partially-solidified casting section to bulge in its edges, due to the static pressure of the hot metal liquid phase acting from inside the product shell. It is done typically by idle roller aprons acting on the product faces. Containment system may be organized together to secondary cooling spray nozzles, into inter-changeable devices named “sectors”.
Plate mold, as used herein, refers to a mold cooling system applied to big casting sections (e.g. cross section dimensions >450 mm), therefore applied to all of the flat products and many of the biggest long products casting sections (e.g. some of the beam blank sections whose width is widest than about 450 mm). Each one of such molds are made of an assembly of heat-exchanging bodies (in the most common arrangement it is made of 4 of said bodies) realized by high-conductive material (e.g.
Copper and/or its special alloys) whereas a coolant media (e.g. water) flows, at least partially, inside said exchanging bodies. One typical (but not necessary) feature of this cooling system is the split of the cooling water flow rate into 2 or more separate, flow-controlled circuits, in order to differentiate the coolant flow-rate control between the long faces of the cross section (flat plates) and the narrow faces (side plates).
“Fixed strand equipment”, as used herein, refers to a system composed by the group of fixed devices of a strand, i.e. those devices or parts which are not movable or not subjected to inter-changeability during the ordinary maintenance-stops of the machine. Also, no substitution of any of the “Fixed strand equipment” parts (e.g. with others having different geometrical characteristics) is required for changing the casting-section setup of the strand. Fixed strand includes but is not limited to: machine foundations, machine supporting beams, oscillating bench, withdrawal and straightening unit, cutting system and transport roller tables.
For simplicity, “Fixed Strand Equipment” will be occasionally referenced to as the “Strand” of a CCM.
Twin casting, as used herein, refers to the principle of grouping together 2 or more similar or identical casting sections for producing them simultaneously from one single “Fixed-Strand Equipment” of a CCM. This principle requires that the casting sections produced are being withdrawn from the machine at the same casting speed, due to the mechanical link provided to all of the sections by a unique withdrawal and straightening unit.
Sub-strand, as used herein refers, to one of the casting sections grouped into a twin casting arrangement
Sub-mold, as used herein refers to a sub-assembly or more generally a functional area inside of a twin-casting mold, comprising the sub-strand crystallizer and its main, sub-strand related devices for level control, water-cooling and mechanical supporting of its sub-strand (e.g. the sub-strand water-jacket conveyor, the meniscus-level detection system, the sealing flanges).
It is known, as per the actual state of art, that typically the CCMs designed to cast flat products has a different look with respect to long products CCM, in particular due to the more massive use of containment roller aprons, used to control the product skin-bulging that tends to occur due to the static pressure of internal liquid phase. The mold technology is also widely different in the flat product CCM, having typically additional features such as movable crystallizer walls to better accommodate the product shrinkage during cooling, and more detailed probes for prevention of break-out.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The present invention is based on the application of the twin-casting principle to a CCM strand. Accordingly, the present invention provides a method of continuous casting more than one long product, including but not limited to a billet, using a single CCM strand. In certain embodiments, the present invention provides a method of continuous casting of two or more long products using a single CCM strand. Also provided is a CCM strand for casting more than one long product including but not limited to casting two billets (i.e. twin casting strand) and a multi-strand CCM comprising at least one of the CCM strands of the present invention. In certain embodiments, the multi-strand CCM of the present invention comprises one or more twin casting strands of the present invention and one or more single casting strands. In other embodiments, each strand of the multi-strand CCM is a twin casting strand of the present invention.
By increasing the number of long products produced per CCM strand, productivity may be increased as compared to conventional CCM strands. For example, replacement of one conventional casting strand in a 5 strand CCM with a twin casting strand of the present invention may increase productivity by up to 20%. Accordingly, in certain embodiments, the present invention provides a method of increasing the productivity of a CCM plant. Increasing productivity by increasing the number of casting strands rather than casting speed may result in increased operator safety. In particular, a worker skilled in the art would readily appreciate that increased casting speed may lead to increased steel meniscus level instability and/or increased risk of breakouts. Accordingly, in certain embodiments, the present invention provides a method of improving the safety of a CCM plant.
Moreover, when increasing productivity by increasing the number of casting strands rather than casting speed, the risk of high-speed related deleterious effects on the casting quality and/or on the machine reliability may be avoided.
The capital investment costs associated with using a multi-strand CCM comprising one twin casting strand of the present invention, as compared to the cost of the fixed-strand equipment (for one strand) of a conventional multi-strand CCM, may be minimal. As illustrated in
In certain embodiments, each of the molds in the twin-casting arrangement comprise a tubular crystallizer. In certain embodiments of the twin casting strand of the present invention, each of the molds in the twin casting are cooled by a conventional fluid jacket (such as a water jacket) system. In certain embodiments, as illustrated in
In certain embodiments, the present invention provides an internal “twin mold adapter” or “twin mold cartridge” to be installed inside a conventional, single-strand mold for its conversion into a twin-casting mold. In those embodiments, the use of such an adapter may allow for the utilization of existing long-product section mold-body without operating any permanent, mechanical modification. Accordingly, the internal mold adapter allows for the modification of pre-existing CCM strands and therefore, in certain embodiments, the present invention provides methods of modifying a conventional casting CCM strand to a twin casting strand. A non-limiting example of the internal mold adapter is provided in
In certain embodiments, the adapter provides technological and mechanical link (including connection for fluids such as cooling-water and lubrication-oil) of the sub-strands' crystallizers with the oscillating bench, as well as the automation to realize the mold meniscus position reading for each of the sub-strands (see
Typical plate-type mold bodies are designed to cool a plate-type mold with differentiated flow between the wide faces and the narrow faces (or between each single plate of the assembly) and as such are designed to interface with a suitable number of regulated-flow water lines. In certain embodiments, the internal mold adapter of the present invention interfaces with at least some of these separate waterlines, separately. This allows differentiated control of the water flow-rate for each of the sub-molds (see
In other embodiments, one waterline could be used for cooling of the sub-strands. See, for example, US20160082503, WO2014174445A1, EP 2988890.
In other embodiments of the present invention, a dedicated twin-casting mold instead of an internal mold adapter is used. For example, a dedicated twin-casting mold may be used instead of an internal mold adapter when a new CCM plant is being built or when the sub-strands equipment is too big to fit in a conventional mold body for flat or long products (e.g. in the case of application of Electro-Magnetical Stirrer “M-EMS” to each twin-arranged sub-strand). In such embodiments, the twin mold body is designed to accommodate all the necessary components for functioning of each sub-strand (including but not limited to water feeding, power connections, automation).
In certain embodiments of the present invention, the twin casting process is conducted automatically. In such embodiments, there is liquid metal level in both of the sub-strands of the twin casting strand during the continuous casting process. Optionally, in such cases where the casting process is conducted automatically, the friction between the solidifying product and the mold is counteracted, in all of the sub-strands, by means of automatically-fed lubricant, such as oil.
Automatic control of the liquid metal level in the mold during a continuous casting process may be done by an “open-casting” mode or a “closed-casting” mode. In certain embodiments, the automatic control of each of the sub-strands of the twin casting strand is independent of the other strand. Accordingly, in such embodiments, the casting mode for all the sub-strands of the twin casting strand may be same or different. For example, all of the sub-strands may be run in an open casting mode; all the sub-strands may be run in a closed casting mode; or some of the sub-strands may be run in an open casting mode and the other sub-strands in a closed casting mode. Accordingly, in certain embodiments where there is automatic adjustment of the mold level in the sub-strands of the twin casting strand, only one strand is run in open-casting mode.
In certain embodiments, master/slave logic is used for the casting process control. Among those cases, in a specific embodiment, to perform the process control one sub-strand of the twin group is run in open-stream mode (e.g. is equipped with a calibrated-nozzle pouring system) and the open-stream controlled sub-strand is elected as the “master” sub-strand. The master strand has a non-controlled metal flow and the position of liquid metal level in the sub-mold is regulated by adjusting the casting speed of the whole strand. In this embodiment, other sub-strands are equipped with proportional hot-metal flow-control system (e.g. slide-gate or tundish stopper-rod) and are defined “slave” (see
In certain embodiments, a fork-type dummy-bar is used to extract simultaneously the sub-strands during machine starting (
To gain a better understanding of the invention described herein, the following example is set forth. It will be understood that this example is intended to describe an illustrative embodiment of the invention and is not intended to limit the scope of the invention in any way.
The twin casting machine described below has been manufactured and has been hot-tested successfully.
A comparison of the conventional billet and the “twin” casting billet is provided in Table 1 below.
Table 2 provides mold data
Table 3 provides level control data.
Table 4 provides manufacturing and testing details of a conventional CCM and an embodiment of the present invention.
Mold:
In order to pair 2 billet sections into a TWIN arrangement, the 2 products were placed at a mutual inter-distance of 800 mm, realizing a total encumbrance of about 950 mm between the external faces of the sub-sections. Each strand of the CCM described in this example is suitable for managing both tubular and plate-type mold equipment. The biggest casting section produced by the machine conventional arrangement is the beam-blank “BB5”, 1050 mm wide.
In order to host the twin-casting system, a BB5 mold body was used as the interfacing-body with the machine. The mold body of BB5 (section dimension encumbrance of 1050×460 mm) was filled with 2 sub-molds, each one including a billet tubular crystallizer, fully compatible with any other (conventional) billet strand equipment of the CCM. The 2 sub-strands are cooled by a water-jacket system using the same parts (crystallizer+conveyor jacket) of the conventional billet equipment. Means that the new equipment engineered and produced for the mold (the “Twin cartridge” or “Twin mold adapter”) has the function of bridging the BB5 mold body with the two billet crystallizer and conveyor parts (
Foot Rollers
The twin-cartridge described in this example is designed to host the installation of 2 foot rollers' assembly from the conventional billet mold equipment. The foot rollers spray-cooling collectors require only little modification to avoid interference in the feeding manifolds
Mobile Sector
The mobile sector for billets in the CCM described in this example is a spray-cooling collector fixed to the foot-rollers assembly. There was no mutual interference when pairing 2 original-design mobile sectors in the twin-arrangement chosen. Accordingly, existing conventional parts were used without any modification.
Fixed Sector
To host the twin-casting arrangement a newly designed fixed-sector to perform and spray-cooling and guidance of the product was required. One solution which reduced time and investment cost was found in modifying one existing sector into a dedicated solution for twin-casting (
Straightening Unit
No changes were needed since the maximum casting section width (BB5) exceeds the encumbrance of the twin-casting products (950 mm).
Cutting Machine
The cutting machine was originally equipped with double torch for cutting wide-section long products (such as Beam Blanks) from both sides. A dedicated automatic program was implemented for cutting the twin-billets simultaneously. A minor mechanical modification can be planned to stabilize the billet mutual distance during clamping.
Evacuation
A conventional evacuation system to dispatch billets from the roller tables was used with no modification.
Tundish Area
A dedicated set of tundish-bottom adaptation plates was engineered and installed in order to accommodate the correct sub-strand mutual distance (800 mm) and distance from strand tangent vertical line.
Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims.
This is application claims benefit of U.S. Provisional Application No. 62/568,378 filed Oct. 5, 2017, the contents of all of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62568378 | Oct 2017 | US |
