WO2015110984A1

WO2015110984A1 - Method and appartus to maintain a homogenized melt and controlled fields of a molten metal

Info

Publication number: WO2015110984A1
Application number: PCT/IB2015/050493
Authority: WO
Inventors: Rajneesh CHAUDHARY; Ravi Kumar KANDASAMY; Jan-Erik Eriksson; Martin SEDEN; Bengt Rydholm
Original assignee: Abb Technology Ltd.
Priority date: 2014-01-22
Filing date: 2015-01-22
Publication date: 2015-07-30

Abstract

The present invention provides a method for maintaining a homogenized melt and controlled fields of a molten metal, by regulating the reciprocal combination of non‐intrusive electromagnetic members, which are connected to a heat loss compensator. The molten metal from the tundish is supplied to a caster, at uniform melt flow rate and temperature to a caster. The present invention also provides an apparatus and system for maintaining a homogenized melt and controlled fields of a molten metal in a tundish so as to facilitate an optimum melt superheat and melt flow rate at tundish outlets.

Description

METHOD AND APPARTUS TO MAINTAIN A HOMOGENIZED MELT AND CONTROLLED FIELDS OF A

MOLTEN METAL

Technical Field

[001] The present invention relates to an improved technology of continuous casting of a metal, particularly relates to a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, in the presence of a reciprocal combination of a non-intrusive electromagnetic members and a heat loss compensator. The present invention also provides an apparatus and system to maintain a homogenized melt and controlled fields of a molten metal in a tundish.

Background of the invention

[002] Continuous casting of steel is an energy intensive process and used to solidify 90% of steel worldwide. During continuous casting of steel, tundish is an important link between ladle and continuous casting mold. Tundish acts as a reservoir and distributor to maintain a continuous supply of molten metal to the caster. Tundish plays several key roles related to quality, productivity and efficiency of continuous casting process. To improve the quality of the metal, productivity and efficiency of the continuous casting process, tundish should supply the molten metal to the caster at optimum degree of melt superheat and at uniform flow rate. Usually, it is always difficult to maintain tundish outlet temperature at the desired level due to flow fluctuations and thermal losses occurring during continuous operation and ladle change sequences. Apart from that, in case of multi-strand tundish, it is always a challenge to get uniform superheat at all outlets.

[003] A closed loop control process has been extensively used in the continuous casting process for control of molten metal flow rate, level and temperature in the tundish.

[004] Similarly, it is conventionally known to controlling of temperature of a molten metal in a tundish, where the temperature is controlled based on predetermined or historically measured temperature or through a feedback control and induction heating. The temperature control in a tundish is also performed by using various techniques and looping the temperature measurement data with a tundish heater.

[005] Homogenization of molten metal temperature in a tundish is also performed by controlling temperature of a molten metal using bulk and outlet melt temperature data. Hhomogenization of molten metal temperature can be performed by using an inert gas injection in a tundish. However, the usage of inert gas for temperature homogenization in a tundish may not result in complete mixing of molten metal in all the areas the tundish, resulting in a non-uniform spread of superheat across various strands of the molten metal. Another disadvantage of using inert gas for temperature homogenization may also result in the creation of slag eye in the tundish, leading to the oxidation of molten metal. Oxidation of molten metal may also result in a disturbance of slag-steel interface leading to slag entrapment making steel dirty.

[006] Further, in a continuous casting process, the molten medium flows through different metallurgical vessels, for example ladle, tundish, caster etc. It is therefore, desirable to maintain molten metal in these vessels, at a desired rate and temperature, in order to prevent contamination in the form of inclusions. An optimum operation of every vessel is necessary to achieve high production rate and efficiency of the continuous casting process. In order to achieve this, non-intrusive mixing or stirring of molten medium is necessary to remove inclusions. Inclusions are formed mainly due to re-oxidation of the molten metal by air, mixing of slag and emulsification of these slags into the molten medium. These inclusions are required to be made to float during the flow of the molten metal through the vessels. Accordingly, it is preferred to bring such inclusions to the slag surface by maintaining homogenous temperature of molten metal, optimum degree of superheat, uniform free surface and avoiding short circuiting and vortexing. This is achieved by using either electromagnetic stirring or braking, along with heaters at various locations in the vessel. The current methods use physical barriers in the vessel to ensure increased residence time and improved mixing of flow of the molten medium. These barriers might sometimes cause formation of dead zones in the vessel which hinder the flow of molten medium. Therefore, there is a need to overcome the formation of dead zones in the vessel.

[007] Electromagnetic Stirrer (EMS) is used to stir the molten metal in the tundish to achieve thermal and compositional homogenization of molten metal, to some extent, while encouraging inclusion floatation by increasing the residence time of molten metal. However, particularly in case of a multi- strand tundish, the maintenance of thermal homogenization at various locations of the tundish, becomes a challenge, in view of the associated issues such splashing of molten metal at the inlet(s) of the tundish and vortexing at the outlet(s), which also require concurrent handling. Whereas, the issue of short-circuiting of the molten metal in the tundish, is only controlled to some extent by EMS.

[008] Electromagnetic Brake (EMBR) is used to brake or retard molten metal flow in the tundish. Brakes are normally used to avoid splashing at the inlet and vortexing at the outlet(s). However, the adoption of EMBR alone may not able to maintain the thermal homogeneity at the desired level. In addition, the adoption of EMBR may not help to encourage inclusion floatation at a desired level. [009] The adoption of EMBR tundish furniture such as dams and weirs help avoiding short circuiting of molten metal in the tundish. Dams and weir to some extent increase the residence time to increase the non-metallic inclusion separation. However, dam and weir may not able to reduce the splashing at the inlet and vortexing at the outlet(s). Further, EMBR tundish furniture may not able to maintain the thermal homogeneity of the molten metal at the desired level.

[0010] Tundish heater is to maintain the melt temperature at desire level in the tundish, particularly because it dumps the heat at specific locations where they are placed. However, tundish heater, when used alone, particularly in a multi-strand tundish, it may not able maintain the thermal homogeneity in the larger areas whole tundish.

[0011] Usage of combination of an electromagnetic stirrer and a tundish heater for maintaining a desired melt temperature by adding heat and stirring molten metal to distribute heat based on historical casting process has been conventionally known. This arrangement is shown to achieve homogenization of melt temperature of the molten metal. However, such an arrangement alone may not be in position to control the events such as short-circuiting, vortexing, slag entrapment, melt splashing at a tundish inlet, during the course of continuous casting process, which may result in damaging the tundish refractory. Particularly, during ladle opening and tundish emptying the electromagnetic stirrer a tendency to add more perturbation or swirl to the flow of molten metal thus leading to detrimental splashing during initial ladle opening. Further, the adoption of an electromagnetic stirrer with fixed intensity in a tundish may also contribute to increase in vortex phenomena, particularly, during the emptying of tundish and when the level of molten metal in the tundish is below a desirable threshold.

[0012] In addition, the combined use of electromagnetic stirrer and heater, has the tendency to add more perturbation/swirl to the flow of the molten metal leading to detrimental splashing during initial ladle opening. In such an arrangement, where the stirring is with a fixed intensity, especially during the course of emptying of the tundish, vortexes are likely to be formed, whenever the molten metal level in tundish falls below a certain threshold.

[0013] It is therefore, preferred to have a reciprocal combination of electromagnetic and heating devices for a tundish, which are controlled dynamically to render a homogenized melt and controlled fields of a molten metal in a tundish so as to facilitate an optimum melt superheat and melt flow rate at tundish outlets.

Objects of the present invention [0014] The primary object of the present invention is to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, by actuating and regulating reciprocal combination of a non-intrusive electromagnetic members and furniture, in conjunction with a heat loss compensator.

[0015] An object of the present invention is to provide an apparatus and system to maintain a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish and to discharge the molten metal, from the tundish, at uniform melt flow rate and temperature.

[0016] Another object of the present invention is to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, by maintaining an optimum melt superheat and melt flow rate at the tundish outlets, by measuring either bulk or outlet melt temperatures.

[0017] Yet another object of the present invention is to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, in which ladle is brought to tundish at lower melt super heat temperatures and the required heat and flow dynamics are supplied at the tundish to attain desired superheat of the molten steel.

[0018] Still another object of the present invention is to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, to remove inclusions during the process of continuous casting.

[0019] Further object of the present invention is to provide a method of maintaining a maintaining a homogenized melt and controlled fields of a molten metal in a tundish of a molten metal in a tundish, particularly in a multi-strand tundish, while mitigating turbulence, short-circuiting, dead zones and vortexing of the molten metal in a tundish.

[0020] Yet another object of the present invention is to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, in which slag entrainment of the molten metal in the tundish is prevented by regulating the intensity of the electromagnetic stirrer to impart soft and intense stirring of the molten metal.

[0021] It is also an object of the present invention to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, in which outlet nozzles of the tundish are controlled precisely to prevent freezing of the molten metal and heat loss. [0022] It is also an object of the present invention to provide a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, in which the mixing of molten melt is sufficient to ensure homogeneous concentration and temperature distribution on one hand and a high residence time for of melt and high separation rate for non-metallic inclusions on the other.

[0023] It is also an object of the present invention to provide an apparatus and system to maintain a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, by actuating and regulating reciprocal combination of a non-intrusive electromagnetic stirrer and electromagnetic furniture, in conjunction with a heat loss compensator.

Summary of the invention

[0024] The present invention provides a method of maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi-strand tundish, by regulating the reciprocal combination of non-intrusive electromagnetic members, which are connected to a heat loss compensator. The molten metal from the tundish is supplied to a caster, at uniform melt flow rate and temperature to a caster. The present invention also provides an apparatus and system for maintaining a homogenized melt and controlled fields of a molten metal in a tundish.

Brief description of the drawings

[0025] FIG.l is a flow drawing depicting a method of the present invention for maintaining a homogenized melt and controlled fields of a molten metal in a tundish.

[0026] FIG.2 is a plot output of melt temperature at various time intervals and various tundish outlets in the presence of an electromagnetic stirrer.

[0027] FIG.3 is an exemplary graphical depiction of a maximum and average velocity of molten steel metal in the tundish at different heights from steel-slag interface as a function of EMS intensity.

[0028] FIG.4 is an exemplary graphical depiction of comparison of dimensionless energy of a steel molten metal both in the absence and presence of electromagnetic stirring.

[0029] FIG.5(a) and FIG.S(b) depict temperature maps of a tundish in the absence and presence of reciprocal combination of electromagnetic devices, furniture and heat loss compensator, respectively.

[0030] FIG.6 is an exemplary graphical depiction of a tundish with molten steel demonstrating a tundish inlet flow rate and temperature along with the time response of various process parameters (outlet temperatures and flow rates) in the presence of electromagnetic devices, furniture and heater as used in the method of the present invention.

[0031] FIG.7 is a side sectional view illustration of the apparatus of the present invention during normal operation of a closed loop continuous metal casting, showing the reciprocal arrangement of electromagnetic device and a heat loss compensator,

[0032] FIG.8(a) and FIG.8(b) depict a multi-strand tundish with an arrangement of non-intrusive electromagnetic stirrers.

[0033] FIG.9 is a side sectional view illustration of the apparatus of the present invention, depicting a reciprocal arrangement of combination of non-intrusive electromagnetic devices, furniture and a heat loss compensator.

[0034] FIG.10 is a side sectional view of the system of the present invention during normal operation of a closed loop continuous metal casting, showing the arrangement of controllers that are connected to the apparatus of the apparatus of the present invention.

Detailed description of the invention

[0035] Accordingly, the present method provides a method of maintaining a maintaining a homogenized melt and controlled fields of a molten metal in a tundish, particularly, in a multi-strand tundish. As shown in FIG.l, initially a molten metal is transported from a ladle into a tundish, particularly, a tundish with a multi-strand arrangement, at temperature range (T_meit, in) and at a flow rate (Qmeit). The molten metal that can be advantageously used in the method of the present invention can be derived from metals such as iron, steel, aluminum, copper and alloys of these metals.

[0036] In an aspect of the present invention the temperature (T_meit, in) of the molten metal is advantageously maintained at a melt temperature of the molten metal, which is marginally higher than the melting temperature of the desired molten metal. For instance, in case the molten metal is a steel molten metal, the temperature (T_mei_t, ,_n) of the molten metal in the ladle, is exemplarily maintained in the range of about 1550°C to 1650°C. The lowering of the temperature of the molten metal facilitates supply of molten metal into the tundish at lower temperatures and the required heat can be added in the tundish to attain the desired superheat, so that the energy losses that normally accrue while transferring the molten metal into the tundish, at higher temperatures, can be substantially minimized. The adoption of this molten metal temperature, in the ladle, also facilitates batch ladle operation, in a more convenient manner, even in the presence of heat loss that is normally suffered by the molten metal, during multiple ladle operation. In this aspect the transportation of the ladle to the tundish in which the molten metal is brought at a lower temperature is facilitated, thereby avoiding the additional heat losses, while compensating for heat in the tundish.

[0037] Accordingly, in this method of the present invention initially the molten metal is supplied to the tundish from the ladle, preferably at the preferred melt temperature and in controlled flow direction. The preferred melt temperature of the molten metal is maintained at higher than the melting temperature of the molten metal and in the range of 20-100°C higher than the melting temperature. The controlled flow direction is maintained by the operation of the ladle gate and homogenization of melt temperature is performed by an electromagnetic device. Once the molten metal is received in the tundish the temperature of the molten metal is measured at various locations of the tundish and at tundish outlets. The difference in the temperature is also measured at various locations of the tundish. Concurrently, the level of the molten metal in the tundish is measured to regulate a melt regulator stopper and a ladle frequency so an optimum level of molten metal is maintained in the tundish, particularly to prevent formation of vortex inside the tundish. A homogenized melt and controlled fields of a molten metal in the tundish is maintained by actuating and regulating the reciprocal combination of non-intrusive electromagnetic members, in conjunction with the heat loss compensator, as hereinafter described.

[0038] The flow of molten metal feed into the tundish is controlled by a ladle gate or a stopper rod, which is connected to a tundish inlet. The ladle gate is regulated by a level controller to maintain the desired flow rate of the molten metal in the tundish. The control on ladle gate facilitates in reducing splashing of molten metal and related slag entrapment during ladle opening. The ladle gate position is controlled to maintain the uniform or desired molten metal level in the tundish and to control casting speed. Apart from this, the desired value of uniform casting speed can also be achieved by measuring melt level in the tundish by controlling stopper rod or slide gate position and by varying ladle change frequency. The level of the molten metal in the tundish can also be maintained at the required range by controlling the ladle gate, so that an optimum level of the molten metal is maintained in the tundish to reduce or avoid vortexing or swirl flow of the molten metal, from the tundish outlet regions. By preventing vortexing or swirl flow in the tundish, the slag entrapment into the molten metal is minimized, which leads to supply of better quality of molten metal to a caster. The control on ladle gate also helps in reducing splashing of melt and related slag entrapment during ladle opening. By supplying uniform melt flow rate to the caster increases the productivity of the continuous casting process. The controlling ladle change frequency maintains the molten metal level in the tundish, which finally controls the casting speed/melt flow rate to the mold or caster. The aforementioned control features of the ladle may be controlled either individually or in unison with others, based on user requirements.

[0039] The ladle is also subjected to heating, as deemed necessary, in order to maintain the temperature (T_meit, m) of the molten metal in the ladle.

[0040] The flow rate (C it) of the molten metal from the ladle is maintained in an optimum manner. Flow rate (CWit) of molten metal from the ladle is controlled by regulating ladle slide gate and ladle change frequency. Therefore, by controlling melt flow from the ladle, uniform melt level in the tundish is attained, leading to the supply of molten metal to the caster with uniform melt flow rate. In doing so, splashing of the molten metal in the tundish is also controlled by regulating melt flow rate from the ladle into the tundish. Thus, the molten metal feed in the method of the present invention is transported into the tundish with a uniform flow and at a preferred temperature.

[0041] In further aspect of the present invention, once the feed of molten metal is received by the tundish, measurement of melt temperature (T_meit) of the molten metal in the tundish is performed, in a continual manner, at various locations of the tundish. It is to be noted here that since the flow of the molten metal in the tundish includes both vertical and horizontal flows and having variable flow field velocities. It is therefore, desirable to measure the melt temperature (T_meit) of the molten metal at various locations.

[0042] In addition, the measurement of tundish outlet temperature (T_mei_t, out) is also performed, at an outlet and at various outlets, in case of a multi-strand tundish. The melt temperature difference (Tmeit, diff), between and among the various locations of the tundish is also measured. Melt temperature difference (T_mei_t, diff) across the tundish domain is measured to observe the melt thermal homogeneity, to control the intensity of electromagnetic stirring and to analyze the melt flow and heat loss behavior. The molten metal melt level in the tundish (L_mei_t, tun) and the caster (L_mei_t, cast) is also measured, in a continual manner and at short intervals. For instance, the melt level in the tundish is measured at an interval as low as once in every minute.

[0043] The feed of molten metal into the tundish is controlled by the incorporation electromagnetic furniture such as weirs, baffles, dams and electromagnetic brakes, in the tundish. In case, a weir is preferred for performing an electromagnetic braking the location and intensity of the feed may be changed in accordance with an end user requirement. Weir is used in the tundish to control the flow pattern of the molten metal and to reduce the melt velocity or turbulence on the free surface of the molten metal. The adoption of weir also facilitates in redirecting the flow of the molten metal, to facilitate melt mixing and inclusion separation. Advantageously, in the present invention, the electromagnetic braking by means of weir is used in the tundish along with the electromagnetic stirring and heating, to enhance the melt flow control, thermal homogeneity and non-metallic inclusion separation.

[0044] In case, it is observed that the melt temperature (T_meit) and melt temperature at the tundish outlet (Tmeit, out) is less than the summation of liquidus temperature (T|_id) of the desired molten metal and degree of superheat (S), the molten metal is heated only till the temperature difference between (T_meit/ Tmeit, out) is greater or equal to the sum of liquidus temperature (T|_ici) and the degree of superheat (S). The values of liquidus temperature (T|_ici) of the desired molten metal and degree of superheat (S) are subject to the composition of the selected molten metal and are recorded from known sources.

[0045] Furthermore, concurrently, the molten metal is stirred using an electromagnetic stirrer, in case the melt temperature difference (Tmeit, diff) in the tundish is higher than the set value (Tdiff, set) . The set value (Tdiff, set) is a desired melt temperature difference in the tundish. In case, the melt temperature difference (Tmeit, diff) is high, the electromagnetic stirrer is regulated to impart an intense stirring to the molten metal, till the desired melt temperature difference (Tmeit, diff) in the tundish is achieved. However, a very high intensity of EMS may increase the melt surface velocity and the increase in surface velocity thereby leads to slag entrapment into the molten metal. Accordingly, the slag entrapment into the metal is contained by proportionally reducing the intensity of the EMS. The molten metal is subjected to stirring, preferably a controlled stirring and heating, thereby an initial action of removal of inclusions, including metallic inclusions such as and non-metallic inclusions such as oxides, sulfides, nitrides and phosphides. The application of stirring and heating of the molten metal in the tundish, in this manner, also facilitates removal of the inclusions with smaller particle sizes.

[0046] Stirring of an exemplary molten steel metal in the tundish using the reciprocal combination of EMS, electromagnetic furniture and a heat loss compensator, is performed and the melt velocities of the molten metal are recorded and plotted in a graph as shown in FIG.3. FIG .3 depicts the melt velocity at different heights from the top molten metal layer (TMML). It is observed that the average velocity at 50 mm below the TMML is about 0.554 m/s, which is considered a very high for a tundish operation leading to the danger of shearing off slag into the steel even with small surface variations. Therefore, the desirable range of molten metal velocity near the slag surface is maintained typically at about 0.2 to 0.3 m/s. Accordingly, the stirring of the EMS is regulated with an intensity varying in the range of 10-20%, to maintain an optimum mixing of the molten metal in the tundish. It is understood here that the indicated molten velocities and intensities are exemplary in nature, which tend to vary and regulated depending on the configuration and capacity of the desired tundish and the nature of molten metal.

[0047] Therefore, the control of electromagnetic stirring is performed based on the melt temperature difference in the tundish, since the melt temperature difference in the tundish is directly proportional to the intensity of the electromagnetic stirring. For instance, if the temperature difference of the molten metal is very high, a strong electromagnetic stirring is implemented.

[0048] In the meanwhile, the melt level in the tundish (L_mei_t, tun) and caster (L_meit, cast) is continuously measured. If the melt level difference between the tundish and caster (Lmeit, tun - Lmeit, cast) is greater than the set level ( Lmeit, set), a stopper rod or a slide gate is regulated to control controls the melt flow to the caster.

[0049] If the difference between the tundish ( Lmeit, tun) and caster (Lmeit, cast) is less than ( Lmeit, set), the ladle change frequency is controlled in order to maintain the melt level in the tundish.

[0050] Inclusion floatation of the molten metal is enhanced by increasing residence time of the molten metal by better mixing, directing flow towards the top (slag) surface. This is achieved by combining electromagnetic stirrer (EMS) and electromagnetic tundish furniture. While doing so the EMS is positioned horizontally or in an inclined position, in order to achieve desired inclusion floatation. The residence time is achieved by mixing the molten metal in the tundish in an optimum manner as described above. The residence time of melt is increased by proportionately regulating the intense mixing of molten metal in tundish. The effect of regulating mixing of the molten metal in the tundish in the presence of the EMS and in conjunction with other EMDs and electromagnetic furniture on enhancing the residence time of the molten steel metal in the tundish is exemplarily shown in FIG. 4. FIG.4 depicts variation in dimensionless energy with time and in the absence of the EMS. The area under the curve is total dimensionless energy and spread of this curve is directly proportional to the residence time of molten metal in the tundish. It can therefore, clearly be seen that the residence time of melt increases with intense mixing of molten metal.

[0051] The aforementioned functions viz., melt temperature, melt temperature difference in the domain and melt level are simultaneously controlled to have uniform melt temperature and flow to the caster from the tundish, by operating flow, level and temperature controllers, respectively. [0052] Accordingly, in this method of the present invention initially the molten metal is supplied to the tundish from the ladle, preferably at the preferred melt temperature and in controlled flow direction. The preferred melt temperature of the molten metal is higher than the melting temperature of said molten metal. The controlled flow direction is maintained by the operation of the ladle gate and homogenization of melt temperature is performed by an electromagnetic device. Once the molten metal is received in the tundish the temperature of the molten metal is measured at various locations of the tundish and at tundish outlets. The difference in the temperature is also measured at various locations of the tundish and at tundish outlets. Concurrently, the level of the molten metal in the tundish is measured to regulate a melt regulator stopper and a ladle frequency so an optimum level of molten metal is maintained in the tundish, particularly to prevent formation of vortex inside the tundish. A homogenized melt and controlled fields of the molten metal in the tundish is maintained by actuating and regulating the reciprocal combination of a non-intrusive electromagnetic members, in conjunction with the heat loss compensator. The reciprocal combinations of non-intrusive electromagnetic members that are used in this method are stirrers, baffles, brakes, weirs and dams or any other suitable electromagnetic members such as impact pads.

[0053] In an exemplary aspect, temperature maps of a tundish having a molten steel in the absence and presence of reciprocal combination of electromagnetic devices and a heat loss compensator, such an electromagnetic stirrer and a heater, are obtained and shown as F!G.5{a) and FIG,5{b). RG,5{a) depicts the temperature difference of molten steel melt in the tundish that is not subjected to an electromagnetic stirring and arrangement, whereas RG,5(b) depicts the temperature difference of the molten steel in the tundish that is subjected to the electromagnetic stirring and heating. It can be observed here that in case where the molten metal is not subjected to the electromagnetic stirring and heating in the tundish, a temperature map with higher temperature difference across the various tundish locations, is obtained. Whereas, when the molten metal in the tundish is subjected to the electromagnetic stirring along with the application of desired heating parameters, a uniform temperature at the tundish outlets is observed, as shown in FIG.5(b), even though the inlet temperature of the tundish is varied with time.

[0054] In the method of the present invention, advantageously the electromagnetic braking is performed at the inlet area(s) of the tundish, during the opening of the slider gage of the ladle and is switched off. Thereafter, the electromagnetic stirring is performed to homogenize and remove inclusions and the stirring is paused when the level of the molten level reaches below a desirable threshold level. At this juncture, the electromechanical braking is performed to prevent the formation of vortexes in the tundish. This sequence of steps are repeated during every ladle change in order to maintain a clean and homogenized melt, at desired temperature and flow rates across the several strands of the tundish, while avoiding detrimental issues such as slag entrapment of the molten metal.

[0055] In yet another exemplary aspect of the present invention, as shown in FIG.6, the method of present invention is implemented in closed loop control of tundish. The variations of molten metal temperature and flow rate at the inlet with time as per ladle change cycle are analyzed by making closed loop between the ladle change frequency, outlet melt flow rate, outlet melt temperature, tundish level, tundish heater, and stopper rod/slide gate position. In this example, EMS intensity or frequency is maintained at a desired optimum level. The typical tundish inlet flow rate and temperatures in a ladle change cycle are shown as curves in FIG.6. In a ladle change sequence, the inlet flow cycle primarily has 5 stages, initially when a fresh ladle is opened the flow coming in tundish ramps up, this ramp-up overshoot before stabilizing to a steady flow rate which corresponds to steady casting condition. After this, when the ladle level drops the inlet flow to tundish reduces to zero and stays there until a fresh ladle is brought in. This fresh ladle again follows same path. In FIG.6, a total of four such ladle change cycles are implemented. During the ladle sequence, the ladle loses heat to the atmosphere and temperature of steel follows a close to a linear drop to lower value depending on the time taken in transferring steel from furnace to tundish. Since, ladle is also fitted with electromagnetic devices; the temperature in ladle is almost uniform. With these inlet flow rate and temperature conditions, the desirable target is to maintain outlet(s)/bulk temperature of 1890 K with outlet flow rates of 32.5 kg/s from each strands/outlets. In the present example, the tundish inlet flow rates (65 kg/s constant casting flow rate, peak flow rate is 10% more than constant casting flow rate) and temperature (temperature falls linearly by 40K from 1995 K during ladle change sequence, opening to emptying) with typical profile (ladle opening, flow ramp-up, flow stabilization, steady casting, ladle emptying etc.), is considered (FIG.6). The heat is added through the volumetric tundish heater (a surface heater may also be considered) to achieve desired optimum degree of superheat at the outlet. The EMS is used to stirrer the molten metal and maintains the molten metal temperature uniformly in the tundish as well as at the outlet(s). These transient simulations have been performed with accurate computational fluid dynamics model. FIG.6 depicts a substantially uniform molten metal temperature and flow rate at the outlets with the change in temperature and mass flow rate at the inlet. These results clearly demonstrate the maintenance of optimum degree of superheat across all strands having desired flow rates, while avoiding quality and process related issues and also saving on thermal energy. [0056] Finally, the molten metal from the tundish is supplied to a cast, at uniform melt flow rate and temperature. The temperature of the molten metal that is received by the caster substantially corresponds to the temperature of the molten metal in the tundish and at tundish outlets. The outlet nozzles of the tundish are controlled precisely to prevent freezing of the molten metal and heat loss.

[0057] The resultant solidified metallic product from the caster 103 as obtained using the method of the present invention is with suitable grain morphology, preferably having equiaxed grain structure, at various degrees of super heat, ranging from 5°C to 40°C.

[0058] Accordingly, the method for maintaining a homogenized melt and controlled fields of the molten metal is performed by transporting a molten metal into the tundish from the ladle, preferably at a preferred melt temperature and with a controlled flow direction and intensity, in the presence of an inlet electromagnetic brake. The temperature and temperature difference of the molten metal, is measured dynamically, at plurality of locations of the tundish and at tundish outlets. The level of the molten metal in the tundish is measured to regulate the melt regulator stopper and the ladle frequency. Homogenized melt and controlled fields of the molten metal in the tundish, is maintained by actuating and regulating a reciprocal combination of the plurality of non-intrusive electromagnetic members that are operably connected to the heat loss compensator. The molten metal from the tundish is supplied at uniform melt flow rate and temperature to a caster, where the temperature of the molten metal substantially corresponds to the temperature of the molten metal in the tundish and at tundish outlets.

[0059] In yet another aspect of the present invention, the method in which preferred melt temperature of said molten metal is higher than the melting temperature of the molten metal and the melt temperature is in the range of 20-100°C higher than the melting temperature.

[0060] In further aspect of the present invention the method in which the reciprocal combination of non-intrusive electromagnetic members are stirrers, baffles, brakes, weirs and dams.

[0061] In still another aspect of the present invention, the method in which the intensities of the reciprocal combination of non-intrusive electromagnetic members are variable.

[0062] It is also an aspect of the present invention, in which the heat loss compensator is one of plasma torch, induction heater, oxy-fuel heater, surface heater or a combination thereof.

[0063] In yet another aspect of the present invention, the method in which the maintenance of a homogenized melt and controlled fields is performed by an electromagnetic stirring of the molten metal, by inducing an electromagnetic field that is normal to the direction of flow of the molten metal. [0064] In further aspect of the present invention, the method wherein the maintenance of a homogenized melt and controlled fields is performed by applying an electromagnetic braking of the molten metal, by inducing an electromagnetic field that is normal to the direction of the flow of the molten metal.

[0065] It yet another aspect of the present invention, an apparatus 100 for controlling a homogenized melt and controlled fields of a molten metal and to supply the molten metal to a castor, at uniform melt flow rate and temperature, is now described. Referring now to the drawings, there is shown in FIG.7, a ladle 101. The ladle 101 is a vessel that is used to transport and pour out molten metal, into moulds to produce the casting. The ladle 101 is substantially an enclosed molten metal pouring vessel to pour the molten metal 101a into a tundish 102. The ladle 101 is responsible for grade change activities as well as removing of non-metallic inclusion separation, while maintaining minimum heat loss from the molten metal 101a. The tundish as exemplarily shown is FIG.7 is trough-type single-strand tundish, which is rectangular having sloping walls. However, in order to enhance an effective volume of the molten metal tundishes of other geometries such as B-Type, T-Type, L-Type, C-Type, H-Type tundishes etc., that are adapted to produce slab, bloom and billet castings can be suitably incorporated. The flow of molten metal 101a into the tundish 102 is controlled by a ladle gate 111, which is connected to a tundish inlet 104. A heating environment including a heat loss compensator can also be optionally connected to the ladle 101, to maintain the temperature of the molten metal 101a in the ladle 101. The heat loss compensator in this arrangement can be one of plasma torch, induction heater, oxy-fuel heater, surface heater or a combination thereof.

[0066] In the present invention, as an exemplary embodiment a bottom-pour ladle is shown in order to advantageously enable a uniform pour rate of self-skimming and clean molten metal from the bottom of the ladle 101 through the ladle gate or a stopper rod 111. This arrangement also helps in preventing floating surface dross and contaminants of the molten metal 101a from entering into the tundish 102. The control on ladle gate 111 also helps in reducing splashing of melt and related slag entrapment during ladle opening. The ladle gate position is controlled to maintain the uniform or desired melt level in the tundish 102 and to control casting speed. Controlling ladle gate position also leads to minimizing the splashing of molten metal 115 and damaging the refractory lining in the tundish 102 during ladle opening. Apart from this, the desired value of uniform casting speed can also be achieved by measuring melt level in the tundish 102 by controlling stopper rod or slide gate position and by varying ladle change frequency. The level of the molten metal 115 can is maintained at the required range by controlling the ladle gate 111, so that an optimum level of the molten metal 115 is maintained in the tundish 102 to reduce or avoid vortexing or swirl flow of the molten metal 115, from the tundish outlet regions. By preventing vortexing or swirl flow in the tundish 102, the slag entrapment into the molten metal is minimized, which leads to supply of better quality of molten metal to a caster 103. The control on ladle gate 111 also helps in reducing splashing of melt and related slag entrapment during ladle opening. By supplying uniform melt flow rate to the caster increases the productivity of the continuous casting process. The controlling ladle change frequency maintains the molten metal level in the tundish 102, which finally controls the casting speed/melt flow rate to the mold or caster 103. The aforementioned control features of the ladle 101 may be controlled either individually or in unison with others, based on user requirements.

[0067] In the present invention the molten metal 101a that is transported by the ladle 101 for the production of casting by using the apparatus of the present invention, is formed from one of iron, steel, aluminum, copper or a combination thereof.

[0068] A tundish 102, which is a vessel, is connected to the ladle 101 through the tundish inlet 104, as shown in FIG.8. The tundish 102 receives a feed of the molten metal 101a from the ladle 101, in a controlled manner with a uniform flow and advantageously at a marginally higher temperature than that of the melting temperature of the molten metal, at various ladle frequencies.

[0069] A heat loss compensator 109 is connected to the tundish 102. The heat loss compensator 109 is a heating device adapted to supply a regulated heat to the molten metal 115 in the tundish 102. The heat loss compensator 109 is arranged to provide a regulated heat to the molten metal 115, which can preferably be a plasma torch, an induction heater, an oxy-fuel heater, a surface heater.

[0070] Temperature sensors 118 are incorporated in the tundish 102 to measure and record, dynamically, the temperature of the molten metal 115 at various locations, including at the tundish outlets. In addition, the temperature sensors 118 also facilitate the recording of the temperature difference between or among the locations of the tundish 102.

[0071] A molten level indicator 110 is arranged in the tundish 102 to measure the changing levels of the molten metal 115. The molten level indicator 110 is also used to regulate the ladle gate 111 and to alter ladle frequency.

[0072] Now, turning to the arrangement of a reciprocal combination of non-intrusive electromagnetic members in the tundish 102, initially, the arrangement of an electromagnetic stirrer 108 is described. The electromagnetic stirrer 108 is connected to the tundish 102 as exemplarily shown in FIG.8. The electromagnetic stirrer 108 is a non-contact type electromagnetic device, which is arranged in proximity to the tundish 102 and external to the tundish 102 so that does not come into direct contact with the molten metal 115, even during the operation of the apparatus. The electromagnetic stirrer 108 is an electromagnetic device having an inductor, to induce a moving magnetic field on the application of an AC voltage (3-phase voltage). The moving magnetic field in turn generates an electromagnetic force in the molten metal 115 and causes the movement of the molten metal 115, in the direction of the magnetic field. Furthermore, the an electromagnetic stirrer 108 is arranged in a manner such that the magnetic field is induced in both horizontal and vertical vector fields in the tundish 102 so as to regulate the control the fluid dynamics of the molten metal 115.

[0073] The electromagnetic stirrer 108 is equipped to function at variable current and frequency. The frequency and current are varied suitably to achieve the desired intensity of the electromagnetic stirrer. The electromagnetic stirrer 108 is arranged to operate at variable intensities, which correspond to the maintenance of uniform molten metal temperature, at all the locations of the tundish, by non- intrusively mixing the molten metal. The intensity and stirring speed of the electromagnetic stirrer is varied based on the melt temperature difference and required degree of temperature uniformity of the molten metal in the tundish.

[0074] In further aspect of the present invention as shown in FIG.8 (a) and FIG.8 (b), a tundish 102 having multiple strands or outlets 105, is provided with an arrangement where electromagnetic stirrers 108 are arranged at various locations on the tundish. In this exemplary aspect, electromagnetic stirrers 108 are arranged both in proximity to and away from the multiple strands 105, of the tundish 102 so that the thermal uniformity of the molten metal in the tundish 102 is achieved at various locations. The functional arrangement of the electromagnetic stirrers 108 are reciprocal in nature and their actuation is synchronized or asynchronised with time to facilitate a controlled stirring of the molten metal.

[0075] In yet another aspect of the present invention as shown in FIG.9, a reciprocal combination of reciprocal combination of the electromagnetic stirrer of variable intensity 108 and electromagnetic furniture, in conjunction with a heat loss compensator, is arranged at various locations of the tundish 102, to maintain a homogenized melt and controlled fields of a molten metal in a tundish. The electromagnetic furniture in this exemplary aspect, includes electromagnetic brakes 117 and dams 119. The reciprocal combination of electromagnetic stirrers, brakes, dams and heat loss compensators facilitate a homogenized melt and controlled fields of a molten metal in a tundish, particularly in a multi- strand tundish, by maintaining homogenized melt and controlled fields of a molten metal in a tundish, at various locations and thereby rendering an optimum melt superheat and melt flow rate at the tundish outlets. The reciprocal arrangement of the electromagnetic devices and furniture mitigates turbulence by maintaining a uniform flow rate and substantially minimizes dead zones and vortexing of the molten metal in a tundish. This reciprocal arrangement also facilitates removal of inclusions from the molten metal. The regulation of the frequency of the electromagnetic stirrer in the tundish mitigates the formation of slag entrainment in the tundish, by imparting a soft stirring of the molten metal. The reciprocal combination of the electromagnetic devices and furniture enables an optimal mixing of molten metal, which is sufficient to ensure homogeneous concentration and temperature distribution on one hand and a high residence time for fluid and high separation rate for non-metallic inclusions on the other.

[0076] In yet another aspect of the present invention, the variable intensities of the electromagnetic stirrer 108 is regulated in close coordination with the actuation of the heat loss compensator 109, so as to maintain uniform molten metal temperature in the tundish 102.

[0077] In further aspect of the present invention, electromagnetic flow retarder braking is effected by either using magnets or passing a direct current through the coils of the electromagnetic brakes. A steady magnetic field perpendicular to the flow of the molten medium is generated near corresponding one inlet and one outlet of the tundish. These brakes avoid slag entrapment due to sudden splashing at inlet during metal pouring and also control swirl and stirring effects at the outlet. Steady electromagnetic field or brake is also used to create electromagnetic furniture in order to achieve desired fluid flow pattern, avoid short circuiting, encourage inclusion removal, maintain uniform temperature, free surface and uniform residence time, thus replacing the physical usage of conventional tundish furniture and hence eliminating the formation of dead zones in the region. This is used to avoid issues such as slag entrapment by controlling surface waves, vortexing during empting of tundish, increasing life of tundish by avoiding damage to refractory lining etc.

[0078] In yet another aspect of the present invention a reciprocal combination electromagnetic stirrers and electromagnetic brakes are combined together in the tundish to enhance its performance by achieving the advantages of both electromagnetic stirring and electromagnetic braking. The challenge in achieving this is due to the fact that electromagnetic stirring requires alternating current and electromagnetic braking requires direct current besides their positioning with respect to each other in bringing about a combined effect. Desired pattern for the flow of the molten medium in the tundish can be achieved by varying the strength of the magnetic field generated. Electromagnetic stirring and electromagnetic braking can be customized as per requirements on stirring, braking and tundish furniture with the help of strong or weak electromagnetic stirring and electromagnetic braking as per requirements.

[0079] Accordingly, the present invention provides an apparatus for controlling homogenized melt and controlled fields, in which at least a non-intrusive electromagnetic stirrer is arranged in functional connectivity with a ladle having a molten metal, said ladle is in flow communication with a tundish to supply said molten metal at a preferred melt temperature. The apparatus also includes at least a non- intrusive electromagnetic stirrer, a magnetic furniture disposed in functional connectivity with the molten metal and operably connected to a heat loss compensator, to maintain a homogenized melt and controlled fields of the molten metal in the tundish and to discharge the molten metal, from the tundish, with a uniform melt flow rate and temperature.

[0080] In yet another aspect of the present invention the apparatus in which the electromagnetic furniture is a dam, weir, brake or a combination thereof.

[0081] In further aspect of the present invention the apparatus in which the heat loss compensator is one of plasma torch, induction heater, oxy-fuel heater, surface heater or a combination thereof.

[0082] In still another aspect of the present invention the apparatus in which a plurality of non- intrusive electromagnetic stirrers, electromagnetic furniture and heat loss compensators, tundish inlets and outlets, are operably connected to the tundish.

[0083] In yet another aspect of the present invention the apparatus in which the non-intrusive electromagnetic stirrers are with variable frequency.

[0084] In yet another aspect of the present invention a system for controlling for controlling homogenized melt and controlled fields of a molten metal, using the apparatus of the present invention is now described by referring to FIG.10. A molten metal flow controller 113 and at least non-intrusive ladle-melt flow altering member 119 are connected to the ladle 101 and a ladle-melt homogenizer 101a. A molten metal level controller 113 operably connected to a ladle gate 111 of the ladle 101. A tundish 102 with an inlet 104, a molten metal level detector 110 and an outlet 105 with a melt regulator 107, arranged in flow communication with said ladle 101 and including a reciprocal combination of non- intrusive electromagnetic members 109, 117 and 119. The non-intrusive electromagnetic members 109, 117 and 119 are connected to at least a heat loss compensator 109 as shown in FIG.10. The reciprocal combination of the electromagnetic members with the heat loss compensator is adopted in the system to maintain a homogenized melt and controlled fields of said molten metal in the tundish and to discharge the molten metal, with a desired uniform melt flow rate and temperature, into a caster 103. The melt regulator 107 is connected to the molten metal flow controller 114 and the molten metal level controller 113 as shown in FIG.10. The heat loss compensator 109 is also connected to a temperature controller 112. Accordingly, the system of the present invention is provided primarily with the three controllers 112, 113 and 114, to function in tandem in order to maintain the desired melt temperature and flow rate going across various strands. The Flow controller 114 controls the stopper-rod or slide- gate 107 movement based on the level in the tundish 102 and ladle change frequency and ladle slide- gate position 114. The level controller 113 along with the temperature controller 112 control the stirring and braking of electromagnetic devices 108 and furniture 117 and 119 based on melt homogenization and other geometry related parameters. The temperature controller 112 controls, the heater based on temperature measurements at strand inlets and in the tundish at several locations.

[0085] In the system of the present invention the exemplary non-intrusive electromagnetic members are include stirrers, brakes, dams, weirs. The melt regulator 107 in the system is a slide gate or a stopper rod.

[0086] The controllers 112, 113 and 114 of the system of the present invention for example may be a programmable logic controller (PLC), including an input/output (I/O) unit, a processing unit and a memory. The memory included computer-executable components, which can be loaded into the processing unit during operation. When the computer-executable components are run on the processing unit the controllers 112, 113 and 114 control the temperature, intensity of the electromagnetic stirrer, control of electromagnetic furniture, level of molten metal in a tundish, ladle flow control and tundish outlet flow control according to the method presented herein.

[0087] In the system as shown in FIG.10, as an exemplary embodiment and single strand tundish is shown with a stirrer, brakes (metal flow retarder) and a dam. It is within purview of this invention to include a plurality of electromagnetic members and furniture and heat loss compensators, at various locations of the tundish, as exemplarily shown in FIGs.8(a), 8(b) and FIG.9, to cater to a multi-strand tundish arrangement.

[0088] Thus the system of the present invention therefore maintains a homogenized melt and controlled fields of a molten metal in the tundish, particularly in a multi-strand tundish, by actuating and regulating reciprocal combination of non-intrusive electromagnetic members such as a stirrer, brakes, dams, weirs, in conjunction with a heat loss compensator.

[0089] Accordingly, the system of the present invention for maintaining homogenized melt and controlled fields of a molten metal, as shown in FIG.10 is provided with a molten metal flow controller and at least non-intrusive ladle-melt flow altering member that are connected to a ladle. A molten metal level controller is connected to a ladle gate of the ladle. A tundish with at least an inlet, a molten metal level detector and an outlet with a melt regulator, is arranged in flow communication with the ladle and includes a reciprocal combination of non-intrusive electromagnetic members. The non- intrusive electromagnetic members are connected to at least a heat loss compensator, to maintain a homogenized melt and controlled fields of the molten metal in the tundish and to discharge the metal, with a desired uniform melt flow rate and temperature, into a caster. The melt regulator is connected to the molten metal flow controller and the molten metal level controller. A heat loss compensator is connected to a temperature controller.

[0090] In another aspect of the present invention, the system in which, the non-intrusive electromagnetic members are stirrers, brakes, dams, weirs.

[0091] In yet another aspect of the present invention, the system in which the melt regulator is a slide gate or a stopper rod.

[0092] In further aspect of the present invention the intensities of the electromagnetic members, electromagnetic furniture can be suitably altered in conjunction with the corresponding controllers.

[0093] Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

Claims

We Claim:

1. A method for maintaining homogenized melt and controlled fields of a molten metal, said method comprising the steps of:

(a) transporting a molten metal into a tundish from a ladle, preferably at a preferred melt temperature and with a controlled flow direction and intensity, by regulating an inlet electromechanical brake;

(b) measuring temperature and temperature difference of said molten metal, dynamically, at plurality of locations in said tundish and at tundish outlets;

(c) measuring level of said molten metal in said tundish to regulate a melt regulator stopper and a ladle frequency;

(d) maintaining a homogenized melt and controlled fields of said molten metal in said tundish, by actuating and regulating a reciprocal combination of plurality of non-intrusive electromagnetic members that are operably connected to at least a heat loss compensator; and

(e) supplying said molten metal, from said tundish, at uniform melt flow rate and temperature to a caster, said temperature of the molten metal substantially corresponds to said temperature of the molten metal in said tundish and at tundish outlets.

2. The method as claimed in claim 1, wherein said maintenance of homogenized melt and controlled fields is performed by an electromagnetic stirring of said molten metal, by inducing an electromagnetic field that is normal to the direction of flow of said molten metal.

3. The method as claimed in claim 1, wherein said maintenance of homogenized melt and controlled fields is performed by applying an electromagnetic braking of said molten metal, by inducing an electromagnetic field that is normal to the direction of the flow of said molten metal.

4. The method as claimed in claim 1, wherein the intensities of said reciprocal combination of non- intrusive electromagnetic members are variable.

5. The method as claimed in claim 1, wherein said preferred melt temperature of said molten metal is higher than the melting temperature of said molten metal and said melt temperature is in the range of 20-100°C higher than said melting temperature.

6. The method as claimed in claim 1, wherein said heat loss compensator is one of plasma torch, induction heater, oxy-fuel heater, surface heater or a combination thereof. A system for homogenized melt and controlled fields of a molten metal, comprising:

(a) a molten metal flow controller and at least a non-intrusive ladle-melt flow altering member, operably connected to a ladle;

(b) a molten metal level controller operably connected to a ladle gate of said ladle;

(c) a tundish with at least an inlet, a molten metal level detector and an outlet with a melt regulator, disposed in flow communication with said ladle and including a reciprocal combination of non-intrusive electromagnetic members, said non-intrusive electromagnetic members operably connected to at least a heat loss compensator, to maintain a homogenized melt and controlled fields of said molten metal in said tundish and to discharge said metal, with a desired uniform melt flow rate and temperature, into a caster;

(d) said melt regulator operably connected to molten metal flow controller and said molten metal level controller; and

(e) said heat loss compensator operably connected to a temperature controller.

The system as claimed in claim 13, wherein said non-intrusive electromagnetic members are stirrers, brakes, dams, weirs.

The system as claimed in claim 14, wherein said non-intrusive electromagnetic stirrers are with variable frequency.

The system as claimed in claim 13, wherein speed and intensities of said electromagnetic members are variable.

The system as claimed in claim 13, wherein said melt regulator is a slide gate or a stopper rod. An apparatus for homogenized melt and controlled fields of a molten metal, comprising:

(a) at least a non-intrusive electromagnetic stirrer disposed in functional connectivity with a ladle having a molten metal, said ladle is in flow communication with a tundish to supply said molten metal at a preferred melt temperature; and

(b) at least a non-intrusive electromagnetic stirrer and a electromagnetic furniture disposed in functional connectivity with said molten metal and operably connected to a heat loss compensator, to maintain a substantially uniform thermal and flow fields of said molten metal in said tundish and to discharge said molten metal, from the tundish, with a uniform melt flow rate and temperature.

The apparatus as claimed in claim 9, wherein said at least electromagnetic furniture is a dam, weir, brake or a combination thereof.

14. The apparatus as claimed in claim 9, wherein said heat loss compensator is one of plasma torch, induction heater, oxy-fuel heater, surface heater or a combination thereof.

15. The apparatus as claimed in claim 9, wherein plurality of non-intrusive electromagnetic stirrers, electromagnetic furniture and heat loss compensators, tundish inlets and outlets, are operably connected to said tundish.