TECHNICAL FIELD

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.

BACKGROUND

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 inFIG. 1and described in United States patent application US20100032455A1. As is apparent formFIG. 1, in the conventional casting apparatus, liquid metal is supplied from a reservoir via a flow path1(here shown in a sectional view and implemented as a launder) into the mold cavity2of a mold3. The flow path1comprises an outlet, here implemented as a nozzle,4through which the liquid metal exits the flow path1and flows into the mold cavity2. The driving force for the flow of the liquid metal is gravity. To control the flow of the liquid metal, there is provided a pin assembly5, that can increase or decrease the effective cross-sectional area available for the liquid metal to flow through the nozzle4by a vertical movement of the pin assembly to thereby control the volumetric flow rate of the liquid metal from the flow path1into the mold cavity2. The cast product exits the mold cavity2via a downwards movement of a starter block6.

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.

Short Description of the Invention

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 inFIG. 2) in the mold cavity and a laminar flow of the liquid metal when the liquid metal enters the mold cavity improve the quality, in particular the surface quality, of the cast product. In the conventional apparatus describe above, a precise control of the metal level in the mold cavity is difficult due to the movement of the pin assembly. Further, the conventional casting apparatus generates a turbulent flow of the liquid metal, because the effective flow cross section is reduced and a flow velocity increases according to the Venturi effect. The turbulent flow may result in oxidation of the liquid metal to be cast and quality problems of the cast product

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.

