The present invention relates to a casting apparatus for continuous or semi-continuous casting of metals using a pump to counter a metal flow induced by a gravitational force to control a flow of liquid metal more precisely and with less turbulence.
In continuous or semi-continuous casting, liquid metal is supplied into a mold cavity of a casting mold. In the mold cavity, the liquid metal at least partially solidifies into a cast product that exits the mold cavity via an open side of the mold cavity caused by a relative movement between the cast product and the mold. Semi-continuous casting is for example used to cast rolling ingots (ingots that are for example hot and cold rolled to produce rolled products such as sheet metal), forging ingots (ingots that are forged into forged products) or extrusion billets (billets that are for example extruded in an extrusion press to produce an extruded product). Continuous casting is for example used to continuously produce a rolled product without producing a rolling ingot that is hot rolled and cold rolled in separate production steps as an intermediate product.
A casting apparatus usually comprises a reservoir for holding and/or producing liquid metal such as a melting furnace or a melt tank for holding liquid metal that has been supplied to the melt tank from for example a melting furnace or an electrolysis process.
From the reservoir, the liquid metal is supplied into a mold cavity of the casting mold via a flow path that is for example implemented as a distribution launder. In the mold cavity, the liquid metal cools and at least partially solidifies. The cast product exits the mold cavity via an open side thereof caused by a relative movement between the mold and the cast product as mentioned above, for example by movement of a starter block.
A conventional casting apparatus is shown in
It is desirable to have a casting apparatus and a casting method that have a less turbulent liquid metal feeding system and allow production of cast products with improved properties such as improved surface quality.
The inventor has found that the quality of a cast product (also known as casted product) strongly depends on a precise control of the level of liquid metal in the mold cavity so the level of liquid metal in the mold cavity corresponds to a predetermined value despite the relative movement between the mold and the cast product during the continuous or semi-continuous casting operation. The inventor has found that a low metallostatic pressure (see p in
In this respect, in order to avoid or alleviate the afore-mentioned problems, an aspect of the present invention provides a casting apparatus for continuous or semi-continuous casting (e.g. vertical direct chill casting) of a cast product comprising a reservoir for supplying liquid metal, a direct chill casting mold having a mold cavity for at least temporarily holding liquid metal and to at least partially solidify the liquid metal into a cast product, wherein a flow path for the liquid metal is defined between the reservoir and the mold cavity, and wherein the casting apparatus is configured such that the liquid metal has a tendency to flow along the flow path from the reservoir into the mold cavity by gravity, wherein the liquid metal enters the mold cavity via a first vertically higher side of the mold, and wherein the cast product exits the mold via a second vertically lower side of the mold, and a pump disposed on the flow path between the reservoir and the mold cavity, wherein the pump is operable to generate a force in the liquid metal that is acting against the tendency of the liquid metal to flow along the flow path from the reservoir into the mold cavity by gravity to control a flow of the liquid metal from the reservoir into the mold cavity. The cast product may exit the mold in a rectilinear manner via the second side of the mold in a straight vertical direction. A longitudinal axis of the cast product may be continuously rectilinear from the at least partial solidification until the full solidification. The cast product may be an extrusion ingot or a rolling slab.
According to the invention, a larger cross-sectional area for the flow of liquid metal along the flow path can be provided than in the conventional casting apparatus while a controllability of the flow of the liquid metal is improved. The larger cross-sectional area may result in a less turbulent and more laminar flow of the liquid metal. For example, a minimum flow cross-sectional area at an outlet of the flow path according to the invention may be 2000 mm2 (square millimeter), which is significantly larger than in the conventional casting apparatus using a pin assembly to control the flow of the molten metal. According to the invention, the flow of the liquid metal from the reservoir into the mold cavity is driven by gravity and the pump is used to limit the flow by generating a force acting in a direction opposite to the flow direction without changing the flow direction. In other words, according to the invention, the pump may be used as a flow regulator. According to the invention, the pump may be used to completely stop the flow of liquid metal from the reservoir into the mold cavity.
According to embodiments of the invention, the casting apparatus may further comprise a sensor for detecting a level of liquid metal in the mold cavity and for outputting a level value indicative of the level of liquid metal in the mold cavity, and a controller, wherein the sensor and the pump may be operably connected with the controller, and wherein the controller may be configured to operate the pump based on the level value and a predetermined set value indicative of a desired level of the liquid metal in the mold cavity such that a difference between the level value and the set value is minimized.
According to embodiments of the invention, the first side of the mold may be sealed and a gas atmosphere between the liquid metal in the mold cavity and the first side may be controlled such as to control oxidation of the liquid metal in the mold cavity.
According to embodiments of the invention, the sensor may be a radar sensor that emits electro-magnetic radar radiation having for example a frequency of 80 GHz or higher that may be incident on the liquid metal in the mold cavity in a radar radiation area. According to embodiments, the sensor may be a laser distance sensor, a capacitive distance sensor or an ultrasonic distance sensor. Particularly good results may be achieved with the radar sensor having a radar frequency of 80 GHz or higher, as the electromagnetic radar radiation having such a radar frequency may penetrate through smoke and dirt that may be present in the mold cavity between the sensor and the surface of the liquid metal.
According to embodiments of the invention, there may be provided an at least partially radar radiation transparent body in a radar beam path between the radar sensor and the liquid metal in the mold cavity, wherein the at least partially radar radiation transparent body may have two outer surfaces that each may have a normal vector that is not parallel to a straight line between the sensor and the liquid metal in the mold cavity in the radar radiation area to avoid or reduce detection of radar radiation reflected by the at least partially radar radiation transparent body with the radar sensor.
According to embodiments of the invention, the at least partially radar radiation transparent body may be provided integrally with the closed first side of the mold.
According to the invention, the pump is an electromagnetic pump, in particular a direct current electromagnetic pump. An electromagnetic pump is particularly efficient as it allows a precise and delay-free control of the flow of the liquid metal due to the lack of moving mechanical parts.
According to embodiments of the invention, the controller may be configured to change the predetermined set value during a casting operation of the cast product.
According to embodiments of the invention, the controller may be configured to change the predetermined set value from a value indicative of a higher level of the liquid metal in the mold cavity earlier in the casting operation of the cast product to a value indicative of a lower level of the liquid metal in the mold cavity later in the casting operation of the same cast product.
According to embodiments of the invention, the mold may comprise means for active cooling of the cast product such as a cooling water nozzle for spraying water on the cast product that is exiting the direct chill casting mold cavity via the second side.
According to the invention, the liquid metal isliquid aluminium or aluminium alloy and the cast product is an aluminium or aluminium alloy product.
According to the invention, a flow diverter is provided on the flow path downstream of the pump to direct at least a portion of the liquid metal in a predetermined direction in the mold cavity. The flow diverter may be configured such that the portion of the liquid metal is directed into a direction that is not the vertical direction. For example, the flow diverter may comprise a tubular structure having a cross-section (through which the liquid metal may flow into the mold cavity) defining a flow path for the liquid metal that has a longitudinal central axis that has a direction that deviates from the vertical direction. Said cross-section may change, e.g. continuously change, along the flow path in an upstream-downstream direction from a rectangular, e.g. quadratic, cross-section towards a rectangular cross-section neighboring the outlet of the flow diverter. This is particularly useful if the cast product is a rolling slab. The cross-section may change, e.g. continuously change, along the flow path in an upstream-downstream direction from a rectangular, e.g. quadratic, cross-section to a circular cross-section neighboring the outlet of the flow diverter. This is particularly useful if the cast product is an extrusion billet. The flow diverter may be configured such that at least a portion of the liquid metal is directed into a direction that has a horizontal component.
According to a further aspect of the invention, there is provided a method for continuous or semi-continuous casting of a cast product using the apparatus described above, the method comprising supplying liquid metal from a reservoir into a mold cavity of a direct chill casting mold along a flow path defined between the reservoir and the mold cavity by using, for example exclusively, a gravitational force, and generating a force acting on the liquid metal using a pump that acts against the flow of the liquid metal along the flow path caused by the gravitational force to control supply of the liquid metal into the mold cavity to thereby control a level of liquid metal in the mold cavity.
According to embodiments of the invention, the method may further comprise calculating a set value indicative of a desired level of the liquid metal in the mold cavity, measuring an actual value indicative of the actual level of liquid metal in the mold cavity, and controlling generating the force using the pump such that a difference between the set value and the actual value is minimized during a casting operation.
According to embodiments of the invention, generating the force using a pump may comprise generating an electromagnetic field acting on the liquid metal that results in a force having a direction opposing a flow of the liquid metal along the flow path.
All embodiments and features of the invention may be combined with each other. Features relating the apparatus also relate to the method and vice versa.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the invention.
Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention to those exemplary embodiments.
With reference to
The liquid metal 20 may be liquid aluminium, liquid aluminium alloy, liquid steel or any other liquid metal.
The casting apparatus 10 further comprises a direct-chill casting mold 25. The casting mold 25 comprises a mold cavity 30 for receiving the liquid metal 20, for at least temporarily holding the liquid metal 20 and to at least partially solidify the liquid metal 20 into a cast product 35. The mold cavity 30 may be surrounded on the lateral sides thereof by a mold frame 40 of the casting mold 25. The cast product 35 may for example be a rolling ingot, an extrusion billet, a T-bar, or any other cast product 35.
The casting mold 25 may have a first, vertically higher side 26 and a second, vertically lower side 27. The liquid metal 20 may enter the mold cavity 30 via/through the first side 26. The liquid metal 20 may at least partially solidify in the mold cavity 30 to produce the cast product 35.
The casting mold 25 may comprise means for active cooling of the liquid metal 20 in the mold cavity 30 and/or for active cooling the partially solidified metal 21 and/or for active cooling of the cast product 35. In
With further reference to
With reference to
The pump 60 may for example be an electromagnetic pump, in particular a direct current (DC) electromagnetic pump of the induction type without moving parts as schematically shown e.g. in
According to embodiments of the invention and with reference to
With reference to
The sensor 75 (not shown in
According to embodiments of the invention, in particular when the sensor 75 is implemented as a radar sensor (for example one with a radar frequency of 80 GHz or higher), and with reference to
With reference to
The controller 95 may be configured to change the predetermined set value from a value indicative of a higher level h of the liquid metal 20 in the mold cavity 30 earlier in the casting operation of the cast product 35 to a value indicative of a lower level h of the liquid metal 20 in the mold cavity 30 later in the casting operation of the cast product 35. That is, the set value may be changed, e.g. during an initialization phase of a casting operation of a cast product 35 before the casting operation reaches a steady state operation. It has been found that such a change of the predetermined set value may result in a better quality of the cast product, as a preset filling rate of the mold cavity during the initial phase of casting and a gradual reduction of the metal level as the casting speed is increased during the early phase of casting toward a steady-state situation where the casting parameters and the metal level is kept constant until the end of cast.
In light of the above, a method for continuous or semi-continuous casting of a cast product 35 according to the invention may comprise supplying liquid metal 20 from the reservoir 15 into the mold cavity 30 of the direct chill casting mold 25 along a flow path 55 defined between the reservoir 15 and the mold cavity 30 by using a gravitational force, and generating a force acting on the liquid metal 20 using the pump 60 that acts against the flow of the liquid metal 20 along the flow path 55 caused by the gravitational force to control supply of the liquid metal 20 to the mold cavity 30 to control a level h of liquid metal 20 in the mold cavity 30 during casting of the cast product 35.
The method may further comprise calculating a set value indicative of a desired level h of the liquid metal 20 in the mold cavity 30, measuring an actual value indicative of the actual level h of liquid metal 20 present in the mold cavity 30 using the sensor 75, and controlling generating the force using the pump 60, for example a direct current electromagnetic pump 60, such that a difference between the set value and the actual value is minimized. The generating the force using the pump 60 may comprise generating an electromagnetic field acting on the liquid metal 20 that results in a force having a direction opposing a flow of the liquid metal 20 along the flow path 55. The method described herein may be carried out using the casting apparatus 10 according to embodiments of the invention.
All embodiments described herein may be combined with each other unless specified otherwise. Features described with respect to the casting apparatus 10 also apply as corresponding method steps for the method described herein and vice versa.
Number | Date | Country | Kind |
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20171932 | Dec 2017 | NO | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/080941 | 11/12/2018 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2019/110250 | 6/13/2019 | WO | A |
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Number | Date | Country | |
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20210001394 A1 | Jan 2021 | US |