SLAG detection unit

Abstract

Slag detection unit (10) configured to detect the occurrence of slag (6a) in a molten metal stream (6) guided in a direction (60) through a passageway (1) of a refractory part (50, 50a, 51a), such as a casting channel (2) of a well block (51a), the slag detection unit (10) comprising: a refractory part (50, 50a, 51a) with a passageway (1), preferably a well block (51a) with a casting channel (2); a transmitter (20) positioned at a first side of the passageway (1), preferably at a first side of the casting channel (2); a receiver (30) positioned at a second side of the passageway (1), preferably at a second side of the casting channel (2); wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the passageway (1), more preferably the second side is opposite from the first side with respect to the casting channel (2); the transmitter (20) being configured to direct a magnetic field (B) at least partially through the passageway (1), preferably through the casting channel (2); the receiver (30) being configured to receive at least a part of the magnetic field (B) emanating from the transmitter (20) and passing through the passageway (1), preferably passing through the casting channel (2); wherein the transmitter (20) comprises at least three transmitter coils, namely a first transmitter coil (22), a second transmitter coil (23) and a third transmitter coil (24), wherein the first transmitter coil (22), the second transmitter coil (23) and the third transmitter coil (24) are configured such that when an alternating current is provided to the transmitter (20), the magnetic field (B) emanating from the second transmitter coil (23) is of opposite direction than the magnetic field (B) emanating from the first transmitter coil (22), and the magnetic field (B) emanating from the second transmitter coil (23) is of opposite direction than the magnetic field (B) emanating from the third transmitter coil (24); and method for detecting the occurrence of slag.

Description

[0001] SLAG DETECTION UNIT

[0002] Description

[0003] The invention relates to a slag detection unit configured to detect the occurrence of slag in a molten metal stream and a method for detection of slag in a molten metal stream.

[0004] A metallurgical vessel is used for containing and / or treating liquid metal. The liquid metal often comprises a slag layer on its surface. The metallurgical vessel has an outer shell, e.g., made of steel, and an inner lining, e.g., made of refractory material and may further comprise (functional) refractory parts having passageways for guiding a molten metal stream to pour out the contained liquid metal and / or slag. Various types of refractory parts having such passageways are known, e.g., tapholes, nozzles etc. Upon pouring out the contained liquid metal, the liquid metal level in the metallurgical vessel lowers, until at a certain point in time, slag is entering the passageway I casting channel. In many metallurgical processes such an outflow of slag together with the liquid metal is to be avoided, as slag entrainment is detrimental to the quality of the end product of the metallurgical process. One way to avoid this slag outflow is to detect the moment, when slag enters into the respective passageway and to immediately stop the pouring process, e.g., by closing a slide gate mechanism or by stopping the flow by a stopper rod or by tilting an electric arc furnace to stop drainage of molten metal. The precise and early detection of the occurrence of slag in a molten metal stream is therefore an ongoing topic of research.

[0005] One known way of such detection of slag outflow is done by electromagnetic measurements, where an electromagnetic field is used to detect changes in a stream of molten metal. One problem regularly encountered in such electromagnetic slag detection is the significant interference from surrounding metallic I ferromagnetic parts, especially under changing temperature conditions. One way to account for this interference is the use of reference signals, such as,e.g., in EP 0300150 A1 , which discloses a device for detecting slag flowing with molten metal through an outlet opening (passageway) in a metallurgical vessel, including a sending coil and a receiving coil associated with a reference coil, wherein the coils run around the outlet opening. This disclosure aims at reducing the signal drift due to temperature changes in the ferromagnetic material of the base plate of the metallurgical vessel, which can create measurement problems. US 2004 / 0169502 A1 and EP 2366474 A1 also disclose a sending coil and a receiving coil having an annular shape, running around the outlet opening.

[0006] CA 1 235771 A discloses a sending coil and a receiving coil mounted on a carrier element which surrounds the refractory body. US 2006 / 0219052 A1 discloses a sending coil and a receiving coil mounted on a forked coil holder.

[0007] JP 2000256726 A discloses an electromotive force measurement sensor embedded outside a nozzle refractory.

[0008] So, one challenge in electromagnetic slag detection is to reduce or fully prevent interference to the measurement signal. Additionally, the detection of the occurrence of slag in a molten metal stream should be as fast as possible, to prevent or minimize the outflow of slag.

[0009] It is an object of the current disclosure to provide a slag detection unit configured to detect the occurrence of slag in a molten metal stream, wherein the slag detection unit provides a high signal quality (i.e. , a high absolute signal strength and / or a high signal to noise ratio) and a fast response time.

[0010] The object is achieved by a slag detection unit according to claim 1 and a method according to claim 14.

[0011] An angle is defined as the smaller angle between two lines, in case of skew lines, the smaller angle between any two intersecting lines parallel to said two lines. A direction is to be understood as a line along or parallel to that direction. A longitudinal axis is to be understood as an imaginary line spanning the length of a body.In a first embodiment, the object is achieved by providing a slag detection unit configured to detect the occurrence of slag in a molten metal stream guided in a direction through a passageway of a refractory part, such as a casting channel of a well block, the slag detection unit comprising:

[0012] - a refractory part with a passageway, preferably a well block with a casting channel;

[0013] - a transmitter positioned at a first side of the passageway, preferably in contact with the refractory part, such as the well block, more preferably in contact with an outer surface of the refractory part, such as the well block;; - a receiver positioned at a second side of the passageway, preferably in contact with the refractory part, such as the well block, more preferably in contact with an outer surface of the refractory part, such as the well block; - wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the passageway; - the transmitter being configured to direct a magnetic field (B) at least partially through the passageway, preferably through the casting channel; - the receiver being configured to receive at least a part of the magnetic field (B) emanating from the transmitter and passing through the passageway, preferably passing through the casting channel,

[0014] - wherein the transmitter comprises at least three transmitter coils, namely a first transmitter coil, a second transmitter coil and a third transmitter coil; - wherein the first transmitter coil, the second transmitter coil and the third transmitter coil are configured such that when an alternating current is provided to the transmitter, the magnetic field emanating from the second transmitter coil is of opposite direction than the magnetic field emanating from the first transmitter coil, and the magnetic field emanating from the second transmitter coil is of opposite direction than the magnetic field emanating from the third transmitter coil.

[0015] In the first embodiment, the object is preferably achieved by providing a slag detection unit configured to detect the occurrence of slag in a molten metal streamguided in a direction through a casting channel of a well block, the slag detection unit comprising:

[0016] - a well block with a casting channel;

[0017] - a transmitter positioned at a first side of the casting channel, preferably in contact with the well block, more preferably in contact with an outer surface of the well block;

[0018] - a receiver positioned at a second side of the casting channel, preferably in contact with the well block, more preferably in contact with an outer surface of the well block;

[0019] - wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the casting channel;

[0020] - the transmitter being configured to direct a magnetic field (B) at least partially through the casting channel;

[0021] - the receiver being configured to receive at least a part of the magnetic field (B) emanating from the transmitter and passing through the casting channel - wherein the transmitter comprises at least three transmitter coils, namely a first transmitter coil, a second transmitter coil and a third transmitter coil; - wherein the first transmitter coil, the second transmitter coil and the third transmitter coil are configured such that when an alternating current is provided to the transmitter, the magnetic field emanating from the second transmitter coil is of opposite direction than the magnetic field emanating from the first transmitter coil, and the magnetic field emanating from the second transmitter coil is of opposite direction than the magnetic field emanating from the third transmitter coil.

[0022] It is understandable that the magnetic field received at the receiver will change during a casting operation, e.g., when the molten metal stream consists of steel, in a situation, when slag is present in the passageway I casting channel, as the magnetic field strength I the magnetic field lines will interact differently with the steel and the slag.Generally, a refractory part with a casting channel may be any part made of a refractory material, that comprises a passageway, where molten metal may flow through. Preferably, the refractory part may be a well block, where the passageway is the casting channel. Such a well block is regularly used in steel ladles. Positioning transmitter and receiver at the sides of a well block at its beginning (i.e. , top end) allows a fast signal response, as the measurement takes place when the molten metal flow only enters the passageway. Preferably, the magnetic field (B) and the direction of the molten metal stream in the passageway, form an angle (a); wherein the angle (a) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°. Preferably the magnetic field (B) and the direction of the molten metal stream in the casting channel, form an angle (a); wherein the angle (a) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°. This has shown to reduce external signal interference, e.g., caused by temperature changes of surrounding parts.

[0023] A transmitter driver is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to provide signals, or which are implemented partially or completely as a computer program in a computer.

[0024] Preferably, the slag detection unit further comprises a transmitter driver connected to the transmitter, the transmitter driver being configured to provide an alternating current to the transmitter. Preferably, the alternating current provided by the transmitter driver is in the range of 900 mA (0.9 A) to 1500 mA (1.5 A), more preferably in the range of 1000 to 1200 mA (1.0 A to 1.2 A). Preferably, the alternating current provided by the transmitter driver has a frequency in the range of 500 Hz to 1500 Hz, more preferably in the range of 700 Hz to 1000 Hz. This has shown to yield an increased relative signal response when slag is entering the passageway. The frequency range specifically showed an increased signal to noise ratio during the transition from (pure) molten steel to slag entrainment.

[0025] The transmitter comprises at least three transmitter coils, namely at least a first transmitter coil, a second transmitter coil and a third transmitter coil. It has beenfound that at least three transmitter coils are particularly suitable for achieving a high signal intensity and good signal to noise ratio.

[0026] More preferably, the transmitter comprises an odd number of at least three transmitter coils, namely at least a first transmitter coil, a second transmitter coil and a third transmitter coil. Even more preferably, the transmitter comprises three, five or seven transmitter coils, namely at least a first transmitter coil, a second transmitter coil and a third transmitter coil. Most preferably, the transmitter comprises exactly three transmitter coils, namely a first transmitter coil, a second transmitter coil and a third transmitter coil.

[0027] The first transmitter coil, the second transmitter coil and the third transmitter coil are configured such that when an alternating current is provided to the transmitter, the magnetic field (B) emanating from the second transmitter coil is of opposite direction than the magnetic field (B) emanating from the first transmitter coil, and the magnetic field (B) emanating from the second transmitter coil is of opposite direction than the magnetic field (B) emanating from the third transmitter coil. This has shown to increase signal strength and signal to noise ratio significantly.

[0028] A core is to be understood as a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets. In the course of this invention, a coil may be arranged around such a core. A core may have a general shape of a cylinder or any other elongated structure. Preferably, each of the first transmitter coil, the second transmitter coil and the third transmitter coil are arranged co-axially around a longitudinal axis (L) of a single core, wherein the second transmitter coil is arranged between the first transmitter coil and the third transmitter coil. Preferably, all transmitter coils are arranged co-axially around a longitudinal axis (L) of a single core, wherein the respective magnetic field (B) emanating from neighbouring transmitter coils are of opposite direction. A single core is to be understood as only one core. Thus, preferably the first transmitter coil, the second transmitter coil and the third transmitter coil share the single core as their common and only core. This has shown to increase signal strength andsignal to noise ratio significantly. The single core preferably comprises iron or ferritic stainless steel, more preferably the single core consists of iron or ferritic stainless steel. The single core is preferably made from a material with a relative magnetic permeability

[0029]

[0030] > 1000, more preferably with a relative magnetic permeability

[0031]

[0032] > 1500. This leads to an enhanced flux density within the passageway.

[0033] Preferably, the longitudinal axis (L) of the single core passes through the passageway, preferably through the casting channel. This has shown to increase signal strength and signal to noise ratio significantly.

[0034] Preferably, the longitudinal axis (L) of the single core and the direction of the molten metal stream in the passageway, preferably the casting channel, form an angle ( / ?); wherein the angle (3) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°. This has shown to reduce external signal interference, e.g., caused by temperature changes of surrounding parts.

[0035] A receiver unit is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to process signals, or which are implemented partially or completely as a computer program in a computer.

[0036] Preferably, the slag detection unit further comprises a receiver unit connected to the receiver, the receiver unit being configured to provide a signal from the induced current at the receiver. Preferably, the receiver unit comprises at least one receiver coil. Preferably, the receiver unit is configured to provide a signal from the induced current at the receiver coil. Preferably, the receiver unit detects the induced current at the receiver. Preferably, the receiver unit generates an amplified signal from the induced current at the receiver. Generally, the signal provided from the receiver unit relates to the magnetic field (B) emanating from the transmitter and passing through the passageway, preferably through the casting channel. Preferably, the signal provided from the receiver unit is a digital signal obtained by an analogue-to-digital conversion (ADC) of the induced current at the receiver.Preferably, the longitudinal axis (L) of the single core passes through the receiver. This has shown to reduce external signal interference, e.g., caused by temperature changes of surrounding parts and to increase signal strength and signal to noise ratio significantly.

[0037] A processing unit is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to process signals, or which are implemented partially or completely as a computer program in a computer.

[0038] Preferably, the slag detection unit further comprises a processing unit; the processing unit being in communication with the transmitter driver and the receiver unit; the processing unit being configured to control the transmitter driver to provide an alternating current to the transmitter, such that a magnetic field (B) is directed at least partially through the passageway, preferably through the casting channel; the processing unit being configured to receive a signal from the receiver unit relating to the magnetic field (B) emanating from the transmitter and passing through the passageway, preferably through the casting channel; the processing unit being configured to detect an occurrence of slag in a molten metal stream guided in a direction through the passageway of the refractory part, preferably through the casting channel of the well block. The processing unit may detect the occurrence of slag by detecting sudden signal changes compared to a baseline signal. Generally, the signal provided from the receiver unit will increase, when slag is detected, as the shielding of the magnetic field B by the molten metal stream is reduced. This allows to monitor any occurrence of slag, e.g., for a quality control.

[0039] Preferably, the processing unit is configured to generate a warning signal in case the occurrence of slag is detected in the molten metal stream. Preferably, the processing unit is configured to detect the occurrence of slag in case the signal is outside a predefined range (e.g., above a predefined threshold value), and the processing unit is configured to generate a warning signal. This allows a user to interfere during a process of drainage of molten metal.Preferably, the processing unit is further configured to provide a signal to a slide gate system for controlling the position of a slide gate; wherein the processing unit and the slide gate system is configured to close the slide gate in case the occurrence of slag is detected in the molten metal stream. This allows an automated stopping of the drainage of molten metal in case a slag is detected. This allows to increase molten metal I steel quality.

[0040] In a second embodiment, the object is achieved by providing a method for detecting the occurrence of slag, the method comprising the following steps:

[0041] - Providing a metallurgical vessel containing molten metal;

[0042] - Providing a slag detection unit according to the first embodiment;

[0043] - wherein the passageway of the refractory part, such as the casting channel of the well block, is installed such, that molten metal can be drained from the metallurgical vessel through the passageway of the refractory part, preferably through the casting channel of the well block,

[0044] - Draining the molten metal from the metallurgical vessel through the passageway of a refractory part, such as a casting channel of a well block; - Providing an alternating current to the transmitter, preferably by the transmitter driver;

[0045] - Detecting a signal from the induced current at the receiver, preferably the signal is provided by the receiver unit;

[0046] - When the signal is outside a pre-defined range, preferably when the signal is above a predefined threshold level:

[0047] - generate a warning signal, preferably by the processing unit;

[0048] or

[0049] - stop draining of the molten metal, e.g., by closing the slide gate, preferably by providing a signal to a slide gate system, more preferably by the processing unit.

[0050] The metallurgical vessel may comprise a metallurgical vessel shell, and a refractory lining. The metallurgical vessel may be a steel ladle.In a third embodiment, the object is achieved by providing a slag detection unit configured to detect the occurrence of slag in a molten metal stream guided in a direction through a casting channel of an eccentric bottom taphole, the slag detection unit comprising:

[0051] - a transmitter positioned at a first side of the casting channel of the eccentric bottom taphole and preferably in contact with the eccentric bottom taphole, more preferably in contact with an outer surface of the eccentric bottom taphole;

[0052] - a receiver positioned at a second side of the casting channel of the eccentric bottom taphole and preferably in contact with the eccentric bottom taphole, more preferably in contact with an outer surface of the eccentric bottom taphole;

[0053] - wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the casting channel;

[0054] - the transmitter being configured to direct a magnetic field (B) at least partially through the casting channel;

[0055] - the receiver being configured to receive at least a part of the magnetic field (B) emanating from the transmitter and passing through the casting channel.

[0056] In the third embodiment, the object is preferably achieved by providing a slag detection unit configured to detect the occurrence of slag in a molten metal stream guided in a direction through a casting channel of an eccentric bottom taphole, the slag detection unit comprising:

[0057] - an eccentric bottom taphole with a casting channel;

[0058] - a transmitter positioned at a first side of the casting channel of the eccentric bottom taphole and preferably in contact with the eccentric bottom taphole, more preferably in contact with an outer surface of the eccentric bottom taphole;- a receiver positioned at a second side of the casting channel of the eccentric bottom taphole and preferably in contact with the eccentric bottom taphole, more preferably in contact with an outer surface of the eccentric bottom taphole;

[0059] - wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the casting channel;

[0060] - the transmitter being configured to direct a magnetic field (B) at least partially through the casting channel;

[0061] - the receiver being configured to receive at least a part of the magnetic field (B) emanating from the transmitter and passing through the casting channel.

[0062] Generally, an eccentric bottom taphole with a casting channel is used for draining molten metal from an electric arc furnace (EAF), where, by tilting the electric arc furnace, the molten metal may flow out of the electric arc furnace through the casting channel.

[0063] It is understandable that the magnetic field received at the receiver will change during a casting operation (e.g., when the molten metal stream consists of steel), in a situation, when slag is present in the casting channel, as the magnetic field strength I the magnetic field lines will interact differently with the steel and the slag. Preferably, the magnetic field (B) and the direction of the molten metal stream in the casting channel, form an angle (a); wherein the angle (a) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°. This has shown to reduce external signal interference, e.g., caused by temperature changes of surrounding parts.

[0064] A transmitter driver is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to provide signals, or which are implemented partially or completely as a computer program in a computer.

[0065] Preferably, the slag detection unit further comprises a transmitter driver connectedto the transmitter; the transmitter driver being configured to provide an alternating current to the transmitter. Preferably, the transmitter comprises at least one transmitter coil. Preferably the transmitter driver is configured to provide an alternating current to the least one transmitter coil.

[0066] Preferably, the transmitter comprises at least two transmitter coils, namely at least a first transmitter coil and a second transmitter coil, wherein at least the first transmitter coil and the second transmitter coil are arranged next to each other along a first direction, preferably the first direction has a component normal to the direction of the molten metal stream.

[0067] Preferably, the transmitter is configured such that a first alternating current 11 can be provided to the first transmitter coil and a second alternating current I2 can be provided to the second transmitter coil, such that by varying the first alternating current 11 and / or the second alternating current I2, the magnetic field (B) emanating from the transmitter can be spatially relocated. This allows the operator to shift / relocate the magnetic field in order to obtain an optimum signal to noise ratio.

[0068] Preferably, the transmitter comprises at least four transmitter coils, namely at least a first transmitter coil, a second transmitter coil, a third transmitter coil and a fourth transmitter coil, wherein at least the first transmitter coil and the second transmitter coil are arranged next to each other along a first direction and wherein at least the first transmitter coil and the third transmitter coil are arranged next to each other along a second direction, wherein the second direction is perpendicular to the first direction, preferably the first direction has a component normal to the direction of the molten metal stream. Preferably, at least the third transmitter coil and the fourth transmitter coil are arranged next to each other along the first direction, preferably at least the second transmitter coil and the fourth transmitter coil are arranged next to each other along the second direction.

[0069] Preferably, the transmitter is configured such that a first alternating current 11 can be provided to the first transmitter coil, and a second alternating current I2 can be provided to the second transmitter coil, and a third alternating current I3 can beprovided to the third transmitter coil, and a fourth alternating current I4 can be provided to the fourth transmitter coil, such that by varying the first alternating current 11 and / or the second alternating current I2, and / or the third alternating current I3, and / or the fourth alternating current I4, the magnetic field (B) emanating from the transmitter can be spatially relocated. Preferably, the transmitter driver is configured to provide a first alternating current 11 to the first transmitter coil, and a second alternating current I2 to the second transmitter coil, and a third alternating current I3 to the third transmitter coil, and a fourth alternating current I4 to the fourth transmitter coil. This allows to shift / relocate the magnetic field in two directions to determine an optimum signal to noise ratio by the user.

[0070] Preferably, the transmitter driver is configured such that the first alternating current 11 , the second alternating current I2, the third alternating current I3, and the fourth alternating current I4 can be varied in a range of -3 A to +3 A (wherein throughout this specification a negative current is to be understood as a respective current in the counter-clockwise direction of the coil, while a positive current is to be understood as a respective current in the clockwise direction of the coil), preferably in the range of -1 A to 1 A. Preferably, the first alternating current 11 , the second alternating current I2, the third alternating current I3, and the fourth alternating current I4 provided by the transmitter driver has a frequency in the range of 500 Hz to 1500 Hz, more preferably in the range of 700 Hz to 1000 Hz. This has shown to allow a certain tunability I change of direction of the magnetic field, which allows e.g. to better target the occurrence of slag at its relative position within the passageway. The frequency range specifically showed an increased signal to noise ratio during the transition from (pure) molten steel to slag entrainment.

[0071] Preferably, the transmitter is configured such that the spatial relocation of the magnetic field is possible at least along a component normal to the direction of molten metal flow through the casting channel. This has shown to allow to better detect the occurrence of slag at its relative position within the passageway.A receiver unit is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to process signals, or which are implemented partially or completely as a computer program in a computer.

[0072] Preferably, the slag detection unit further comprises a receiver unit connected to the receiver; the receiver unit being configured to provide a signal from the induced current at the receiver. Preferably, the receiver unit comprises at least one receiver coil. Preferably, the receiver unit is configured to provide a signal from the induced current at the receiver coil. Preferably, the receiver unit detects the induced current at the receiver. Preferably, the receiver unit generates an amplified signal from the induced current at the receiver. Generally, the signal provided from the receiver unit relates to the magnetic field (B) emanating from the transmitter and passing through the passageway, preferably through the casting channel. Preferably, the signal provided from the receiver unit is a digital signal obtained by an analogue-to-digital conversion (ADC) of the induced current at the receiver.

[0073] A processing unit is understood to mean one or more devices for carrying out the respective method steps described below, and which, for this purpose, comprise either discrete electronic components in order to process signals, or which are implemented partially or completely as a computer program in a computer.

[0074] Preferably, the slag detection unit further comprises a processing unit; the processing unit being in communication with the transmitter driver and the receiver unit; the processing unit being configured to control the transmitter driver to provide an alternating current to the transmitter, such that a magnetic field (B) is directed at least partially through the casting channel; the processing unit being configured to receive a signal from the receiver unit relating to the magnetic field (B) emanating from the transmitter and passing through the casting channel; the processing unit being configured to detect an occurrence of slag in a molten metal stream guided in a direction through the casting channel of the eccentric bottom taphole. The processing unit may detect the occurrence of slag by detectingsudden signal changes compared to a baseline signal. This allows to monitor any occurrence of slag, e.g., for quality control purposes.

[0075] Preferably, the processing unit is configured to generate a warning signal in case the occurrence of slag is detected in the molten metal stream. This allows a user to interfere during a process of drainage of molten metal.

[0076] Preferably, the eccentric bottom taphole comprises surrounding blocks, channel bricks, and one end brick; wherein the channel bricks and the end brick are preassembled and glued together to form a preassembled eccentric bottom taphole insert for a casting channel, wherein the surrounding blocks and the preassembled eccentric bottom taphole insert are configured such that the preassembled eccentric bottom taphole insert can be inserted into the surrounding blocks when the surrounding blocks are installed in an electric arc furnace, preferably if the surrounding blocks are embedded in an electric arc furnace hearth, such that the preassembled eccentric bottom taphole insert allows to drain molten metal through the casting channel. This allows simplified exchange I maintenance of the eccentric bottom taphole insert, while also having a high signal quality (i.e. , high absolute signal strength and / or high signal to noise ratio) for slag detection.

[0077] Preferably, the transmitter is positioned at a first side of the casting channel of the eccentric bottom taphole such that the transmitter is in contact with at least one of the surrounding blocks. Preferably, the receiver is positioned at a second side of the casting channel of the eccentric bottom taphole such that the receiver is in contact with at least one of the surrounding blocks. Preferably, the transmitter is positioned at a first side of the casting channel of the eccentric bottom taphole such that the transmitter is in contact with an outer surface of at least one of the surrounding blocks. Preferably, the receiver is positioned at a second side of the casting channel of the eccentric bottom taphole such that the receiver is in contact with the outer surface of at least one of the surrounding blocks. This allows increased accessibility to the transmitter and receiver while simultaneously having a high signal quality.Preferably, the transmitter is an integral part of the preassembled eccentric bottom taphole insert, preferably the transmitter is rigidly connected to the preassembled eccentric bottom taphole insert. Preferably, the receiver is an integral part of the preassembled eccentric bottom taphole insert, preferably the receiver is rigidly connected to the preassembled eccentric bottom taphole insert. This allows fast installation of the receiver while simultaneously having a high signal quality (i.e., high absolute signal strength and / or high signal to noise ratio).

[0078] Preferably, the transmitter is positioned at a first side of the casting channel of the eccentric bottom taphole such that the transmitter is in contact with at least one of the channel bricks. Preferably, the receiver is positioned at a second side of the casting channel of the eccentric bottom taphole such that the receiver is in contact with at least one of the channel bricks. This has shown to yield low interference from surrounding parts.

[0079] In a fourth embodiment, the object is achieved by providing an electric arc furnace comprising:

[0080] - a slag detection unit according to the third embodiment;

[0081] - an electric arc furnace shell;

[0082] - wherein the eccentric bottom taphole is installed such, that molten metal can be drained through the casting channel of the eccentric bottom taphole; - wherein the transmitter is positioned at a first side of the casting channel of the eccentric bottom taphole at a distance of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, to the electric arc furnace shell;

[0083] - wherein the receiver is positioned at a second side of the casting channel of the eccentric bottom taphole at a distance of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, to the electric arc furnace shell.

[0084] Preferably, the electric arc furnace further comprises:- An electric arc furnace hearth and optionally an electric arc furnace permanent lining;

[0085] - Wherein the eccentric bottom taphole is embedded in the electric arc furnace hearth;

[0086] - And wherein the transmitter is positioned at a first side of the casting channel of the eccentric bottom taphole at a distance of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, to the electric arc furnace shell and within the electric arc furnace hearth;

[0087] - wherein the receiver is positioned at a second side of the casting channel of the eccentric bottom taphole at a distance of at least 50 mm, preferably at least 100 mm, more preferably at least 150 mm, to the electric arc furnace shell and within the electric arc furnace hearth.

[0088] - Preferably, the transmitter and the receiver are positioned at such distances to the electric arc furnace shell, which defer by at most 50 mm, preferably by at most 20 mm, most preferably the distances are the same.

[0089] Preferably, the processing unit is configured to generate a warning signal in case the occurrence of slag is detected in the molten metal stream. Preferably, the processing unit is configured to detect the occurrence of slag in case the signal is outside a predefined range (e.g., above a predefined threshold value), and the processing unit is configured to generate a warning signal. This allows a user to interfere during a process of drainage of molten metal.

[0090] Preferably, the processing unit is further configured to control the tilting system of the electric arc furnace; wherein the processing unit is configured to stop drainage of the molten metal in case the occurrence of slag is detected in the molten metal stream. This allows an automated stopping of the drainage of molten metal (i.e., the tapping process) in case slag is detected. This allows to reduce unwanted slag carry-over into the steel and therefore to increase steel quality.

[0091] In a fifth embodiment, the object is achieved by providing a method for detecting the occurrence of slag, the method comprising the following steps:- Providing an electric arc furnace containing molten metal, preferably providing an electric arc furnace according to the fourth embodiment containing molten metal;

[0092] - Providing a slag detection unit according to the third embodiment;

[0093] - wherein the eccentric bottom taphole is installed such, that molten metal can be drained through the casting channel of the eccentric bottom taphole;

[0094] - Draining the molten metal from the electric arc furnace through the eccentric bottom taphole;

[0095] - Providing an alternating current to the transmitter, preferably by the transmitter driver;

[0096] - Detecting a signal from the induced current at the receiver, preferably the signal is provided by the receiver unit;

[0097] - When the signal is outside a pre-defined range, preferably when the signal is above a predefined threshold level:

[0098] - generate a warning signal;

[0099] and / or

[0100] - stop draining the molten metal.

[0101] Exemplary embodiments of the invention are explained in more detail by means of illustrations:

[0102] Fig. 1 shows a schematic part of a metallurgical vessel with a slag detection unit. Fig. 2 shows a schematic sequence, wherein an occurrence of slag is detected by the slag detection unit.

[0103] Fig. 3 shows a schematic preferred embodiment of a transmitter in a slag detection unit.

[0104] Fig. 4a shows an exemplary signal during an occurrence of slag from an embodiment of a transmitter in a slag detection unit.

[0105] Fig. 4b shows an exemplary signal during an occurrence of slag from a preferred embodiment of a transmitter in a slag detection unit.Fig. 5 shows a schematic sketch of an electric arc furnace with a slag detection unit.

[0106] Fig. 6a shows a schematic eccentric bottom taphole (EBT) with a slag detection unit.

[0107] Fig. 6b shows a schematic eccentric bottom taphole (EBT) with a preassembled eccentric bottom taphole insert and with a slag detection unit.

[0108] Fig. 7 and 8 show the spatial relocation of a magnetic field (B) emanating from a preferred embodiment of the transmitter.

[0109] Fig. 1 shows a slag detection unit 10 configured to detect the occurrence of slag 6a in a molten metal stream 6 guided in a direction 60 through a passageway 1 of a refractory part 50, in this example a casting channel 2 of a well block 51a. The figure shows a part of a metallurgical vessel 5 (here: a steel ladle 5) which comprises a metallurgical vessel shell 5a, and a refractory lining 51 , where a refractory part 51a with a passageway 1 is present, here a well block 51a with a casting channel 2. Through the casting channel 2 molten metal 6 can be drained out of the metallurgical vessel 5. Here, a transmitter 20 is positioned at a first side of the passageway 1 in contact with the outer side of the well block 51a, and a receiver 30 is positioned at a second side of the passageway 1 in contact with the outer side of the well block 51a, the second side here is opposite the first side with respect to the passageway 1. The transmitter 20 is configured to direct a magnetic field B at least partially through the casting channel 2, and the receiver 30 is configured to receive at least a part of the magnetic field B emanating from the transmitter 20 and passing through the casting channel 2. The magnetic field B and the direction 60 of the molten metal stream 6 in the passageway 1 , form an angle a wherein the angle a in this example is 90°. A transmitter driver 21 is connected to the transmitter 20, the transmitter driver 21 is configured to provide an alternating current to the transmitter 20. A receiver unit 31 is connected to the receiver 30, the receiver unit 31 being configured to provide a signal 32 from the induced current at the receiver 30. A processing unit 40 is in communication with the transmitter driver 21 and the receiver unit 31 ; the processing unit 40 isconfigured to control the transmitter driver 21 to provide an alternating current to the transmitter 20, such that a magnetic field B is directed at least partially through the casting channel 2; the processing unit 40 is configured to receive the signal 32 from the receiver unit 31 relating to the magnetic field B emanating from the transmitter 20 and passing through the casting channel 2; the processing unit 40 is configured to detect an occurrence of slag 6a in a molten metal stream 6 guided in a direction 60 through the casting channel 2 of the well block 51a. Here, the processing unit 40 is configured to generate a warning signal 41 in case the occurrence of slag 6a is detected in the molten metal stream 6 and is further configured to provide a signal to a slide gate system 7a for controlling the position of a slide gate 7 (here the slide gate 7 is mounted between the slide gate mounts 71, 71’); wherein the processing unit 40 and the slide gate system 7a is configured to close the slide gate 7 in case the occurrence of slag 6a is detected in the molten metal stream 6.

[0110] Thus, a method is shown for detecting the occurrence of slag, where in a first step a metallurgical vessel 5 is provided which contains molten metal 6, and in a further step a slag detection unit 10 as shown in Fig. 1 is provided, wherein a casting channel 2 of a well block 51a is installed such, that molten metal 6 can be drained through the casting channel 2 of a well block 51a. In a further step the molten metal 6 is drained from the metallurgical vessel 5 through the passageway 1 of the casting channel 2 of the well block 51a. By further providing an alternating current to the transmitter 20, a signal 32 from the induced current at the receiver 30 is detected. In case the signal 32 is outside a pre-defined range, a warning signal 41 is generated and, by closing the slide gate 7, the draining of the molten metal 6 is stopped.

[0111] In an alternative to the example shown in Fig. 1 , the transmitter 20 can be positioned at a first side of the passageway 1 in contact with the outer side of a nozzle 50a, such as the upper or lower nozzle 50a, and a receiver 30 is positioned at a second side of the passageway 1 in contact with the outer side of the nozzle 50a, such as the upper or lower nozzle 50a, the second side here is opposite the first side with respect to the passageway 1.Fig. 2 shows a schematic sequence, wherein an occurrence of slag 6a is detected by the slag detection unit 10. Here, a stream of molten metal 6 is guided in a direction 60 through a casting channel 2 of a well block 51a (which is a refractory part 50). The transmitter 20 generates a magnetic field B which is directed through the passageway 1 and received by the receiver 30. Now Fig. 2 (a) shows a situation, where slag 6a is starting to be dragged into the passageway 1 , but the slag 6a has not yet reached the height of the transmitter 20 and the receiver 30. Thus, the magnetic field B is still passing through the stream of molten metal 6, which will relate to a certain signal 32 at a receiver unit 31 connected to the receiver 30 (not shown in this Fig. 2, see Fig. 1). Now, when slag 6a is further drained into passageway 1 , the magnetic field B will now partially pass through slag 6a and the molten metal 6, which influences signal 32 at a receiver unit 31. Fig. 2 (b) shows the moment, where signal 32 will first be impacted, while Fig. 2 (c) shows a situation where signal 32 will already be influenced strongly.

[0112] Fig. 3 shows an exemplary embodiment of a transmitter 20 in a slag detection unit 10, where the transmitter 20 comprises a first transmitter coil 22, a second transmitter coil 23 and a third transmitter coil 24. Here, the first transmitter coil 22, the second transmitter coil 23 and the third transmitter coil 24 are configured such that when an alternating current is provided to the transmitter 20, the magnetic field B emanating from the second transmitter coil 23 is of opposite direction than the magnetic field B emanating from the first transmitter coil 22, and the magnetic field B emanating from the second transmitter coil 23 is of opposite direction than the magnetic field B emanating from the third transmitter coil 24. Here, each of the first transmitter coil 22, the second transmitter coil 23 and the third transmitter coil 24 are arranged co-axially around a longitudinal axis L of a single core 29, the second transmitter coil 23 is arranged between the first transmitter coil 22 and the third transmitter coil 24. Here, the longitudinal axis L (which is shown in Fig. 3 as a dashed line) of the single core 29 passes through the passageway 1 , preferably through the casting channel 2 in a configuration as shown in Fig. 1, wherein the longitudinal axis L of the single core 29 and the direction 60 of the molten metal stream 6 in the casting channel 2, form an angle ?; wherein the angle is 90° andwherein the longitudinal axis L of the single core 29 passes through the receiver 30.

[0113] Fig. 4a shows a signal 32 over time during a sequence as described in connection with Fig. 2. At the beginning of the sequence, the signal 32 is normalized to 100%, here the signal 32 relates to the situation in Fig. 2 (a), where only molten metal 6 is detected in the casting channel 2. At a certain time, there is a kink in the graph, when the signal abruptly rises, this is when slag 6a is first drained into the casting channel 2, as shown in Fig. 2 (b). The peak of the signal 32 relates to the situation, when slag 6a is now influencing the signal 32 heavily. In this setup, a signal rise time of about 15 to 20 seconds was obtained. While Fig. 4a shows the signal obtained with a transmitter 20 made from only one transmitter coil 22, Fig. 4b shows the results when employing a transmitter 20 as shown in Fig. 3 comprising three transmitter coils 22, 23, 24. Here the setup of the transmitter 20 shows a huge increase in signal strength and quality, and the signal rise time was very short (approximately 2 to 5 seconds), which allows more precise and faster response in situation, where slag 6a is detected. In case the signal 32 shown in Fig. 4a or Fig. 4b are outside a pre-defined range, a warning signal 41 is generated and the draining of the molten metal 6 is stopped, by closing the slide gate 7. A pre-defined range for Fig. 4a might be, e.g., defined by a threshold level of 101% or in Fig. 4b, e.g., by a threshold level of 102%, where the warning signal 41 or the stopping of the draining of the molten metal 6 is initiated, when the signal 32 of Fig. 4a or Fig. 4b exceeds the pre-defined threshold level. It is evident from a comparison of Fig. 4a and 4b that the setup used in obtaining Fig. 4b with the three-coil setup of Fig. 3 allows to set up a more robust threshold level, such that in operation, false initiations of warning signal 41 or stopping of the draining of the molten metal 6 are prevented.

[0114] Fig. 5 shows a schematic sketch of an electric arc furnace 5.1 having a slag detection unit 10 with an eccentric bottom taphole 50’ comprising a casting channel 2. Thus, the metallurgical vessel 5 is an electric arc furnace 5.1 , which comprises an electric arc furnace shell 5.1a, an electric arc furnace permanent lining 5.1 b, and an electric arc furnace hearth 5.1 c and is designed for an electricarc furnace sill level 5.1d. In use, molten metal 6 is covered with a layer of slag 6a. The molten metal 6 can be drained from the electric arc furnace 5.1 through an eccentric bottom taphole 50’.

[0115] The slag detection unit 10 is further shown in Fig. 6a. Here, the detection unit 10 is configured to detect the occurrence of slag 6a in a molten metal stream 6 guided in a direction 60 through a casting channel 2 of an eccentric bottom taphole 50’. A transmitter 20 is positioned at a first side of the casting channel 2 of the eccentric bottom taphole 50’, a receiver 30 is positioned at a second side of the casting channel 2 of the eccentric bottom taphole 50’, wherein the second side is opposite from the first side with respect to the casting channel 2. The transmitter 20 is configured to direct a magnetic field B at least partially through the casting channel 2, the receiver 30 being configured to receive at least a part of the magnetic field B emanating from the transmitter 20 and passing through the casting channel 2. Here, the magnetic field B and the direction 60 of the molten metal stream 6 in the casting channel 2, form an angle a of 90°. As shown in Fig. 5, a transmitter driver 21 is connected to the transmitter 20, the transmitter driver 21 is configured to provide an alternating current to the transmitter 20.

[0116] Fig. 7 and 8 show the spatial relocation of a magnetic field B emanating from a preferred embodiment of the transmitter 20. Here, the transmitter 20 comprises coils 22, 23, 23, 24, namely a first transmitter coil 22, a second transmitter coil 23, a third transmitter coil 24 and a fourth transmitter coil 25, here the first transmitter coil 22 and the second transmitter coil 23 are arranged next to each other along a first direction 26, and the first transmitter coil 22 and the third transmitter coil 24 are arranged next to each other along a second direction 27, wherein the second direction 27 is perpendicular to the first direction 26. Also, here the third transmitter coil 24 and the fourth transmitter coil 25 are arranged next to each other along the first direction 26, and the second transmitter coil 23 and the fourth transmitter coil 25 are arranged next to each other along the second direction 27. In this example, the transmitter 20 is configured such that a first alternating current 11 can be provided to the first transmitter coil 22, and a second alternating current I2 can be provided to the second transmitter coil 23, and a third alternating current I3 can beprovided to the third transmitter coil 24, and a fourth alternating current I4 can be provided to the fourth transmitter coil 25, such that by varying the first alternating current 11 and / or the second alternating current I2 and / or the third alternating current I3 and / or the fourth alternating current I4, the magnetic field B emanating from the transmitter 20 can be spatially relocated. Here, the spatial relocation of the magnetic field B is possible along a component normal to the direction of molten metal flow 60 through the casting channel 2 (compare Fig. 7b and Fig. 8b, where the magnetic field B is shifted along the vertical direction, which aligns in its use position with the direction of the flow of molten metal).

[0117] Furthermore, as shown in Fig. 5, a receiver unit 31 is connected to the receiver 30, the receiver unit 31 is configured to provide a signal 32 from the induced current at the receiver 30. A processing unit 40 is in communication with the transmitter driver 21 and the receiver unit 31 , the processing unit 40 is configured to control the transmitter driver 21 to provide an alternating current to the transmitter 20, such that a magnetic field B is directed at least partially through the casting channel 2. The processing unit 40 is also configured to receive a signal 32 from the receiver unit 31 relating to the magnetic field B emanating from the transmitter 20 and passing through the casting channel 2. The processing unit 40 is further configured to detect an occurrence of slag 6a in the molten metal stream 6 guided in a direction 60 through the casting channel 2. Here, processing unit 40 is configured to generate a warning signal 41 in case the occurrence of slag 6a is detected in the molten metal stream 6, and processing unit 40 is further configured to control the tilting mechanism (not shown) of the electric arc furnace 5.1. Here, processing unit 40 is configured to tilt the electric arc furnace 5.1 such that the drainage of molten metal 6 is stopped in case the occurrence of slag 6a is detected in the molten metal stream 6.

[0118] As shown in Fig. 6a, the eccentric bottom taphole 50’ comprises surrounding blocks 53’, channel bricks 5T, and one end brick 52’. In this example, as shown in Fig. 6b, channel bricks 5T and end brick 52’ are preassembled and glued together to form a preassembled eccentric bottom taphole insert 55’ for a casting channel 2. Here, surrounding blocks 53’ and preassembled eccentric bottom taphole insert55’ are configured such that preassembled eccentric bottom taphole insert 55’ can be inserted into surrounding blocks 53’, when surrounding blocks 53’ are installed in an electric arc furnace 5.1 , especially when surrounding blocks 53’ are embedded in an electric arc furnace hearth 5.1c, such that preassembled eccentric bottom taphole insert 55’ allows to drain molten metal 6 through the casting channel 2.

[0119] The transmitter 20 is positioned at a first side of the casting channel 2 of eccentric bottom taphole 50’ such that transmitter 20 is in contact with at least one of the surrounding blocks 53’, as shown in Fig. 6a. Receiver 30 is positioned at the second side (here: opposite with respect to the casting channel 2) such that receiver 30 is in contact with at least one of the surrounding blocks 53’.

[0120] As shown in Fig. 6b, transmitter 20 may form an integral part of the preassembled eccentric bottom taphole insert 55’, as here transmitter 20 is rigidly connected to the preassembled eccentric bottom taphole insert 55’. Receiver 30 is an integral part of preassembled eccentric bottom taphole insert 55’, as here receiver 30 is rigidly connected to preassembled eccentric bottom taphole insert 55’. Here, transmitter 20 is positioned at a first side of casting channel 2 of eccentric bottom taphole 50’ such that transmitter 20 is in contact with at least one of the channel bricks 5T, and receiver 30 is positioned at a second side (here: opposite) of casting channel 2 of eccentric bottom taphole 50’ such that receiver 30 is in contact with at least one of the channel bricks 5T.

[0121] In this example, as shown in Fig. 6a and 6b, transmitter 20 is positioned at a first side of casting channel 2 of eccentric bottom taphole 50’ at a distance 20d of 200 mm to electric arc furnace shell 5.1a, wherein receiver 30 is positioned at a second side of casting channel 2 of eccentric bottom taphole 50’ at a distance 30d of 200 mm to electric arc furnace shell 5.1 a.

[0122] List of reference numerals and factors:

[0123] 1 Passageway

[0124] 2 Casting channelMetallurgical vessel

[0125] a Metallurgical vessel shell

[0126] .1 Electric arc furnace

[0127] .1a Electric arc furnace shell

[0128] .1b Electric arc furnace permanent lining

[0129] .1c Electric arc furnace hearth

[0130] .1d Electric arc furnace sill level

[0131] Molten metal

[0132] a Slag

[0133] Slide gate

[0134] a Slide gate system

[0135] 0 Slag detection unit

[0136] 0 Transmitter

[0137] 0d Distance of transmitter to metallurgical vessel shell I electric arc furnace shell

[0138] 1 Transmitter driver

[0139] 2 First transmitter coil

[0140] 3 Second transmitter coil

[0141] 4 Third transmitter coil

[0142] 5 Fourth transmitter coil

[0143] 6 First direction

[0144] 7 Second direction

[0145] 9 Core

[0146] 0 Receiver

[0147] 0d Distance of receiver to metallurgical vessel shell I electric arc furnace shell

[0148] 1 Receiver unit

[0149] 2 Signal

[0150] 0 Processing unit

[0151] 1 Warning signal

[0152] 0 Refractory part

[0153] 0a Nozzle (Collector nozzle / outer nozzle / lower nozzle)51 Refractory lining

[0154] 51a Well block

[0155] 50’ Eccentric bottom taphole

[0156] 5T Channel bricks

[0157] 52’ End brick

[0158] 53’ Surrounding blocks

[0159] 54’ Annular gap mix

[0160] 55’ Preassembled eccentric bottom taphole insert 60 Direction of molten metal flow

[0161] 71, 71’ Slide gate mounts

[0162] B Magnetic field

[0163] L Longitudinal axis of core

Claims

1. Claims:

1. Slag detection unit (10) configured to detect the occurrence of slag (6a) in a molten metal stream (6) guided in a direction (60) through a passageway (1 ) of a refractory part (50, 50a, 51 a), such as a casting channel (2) of a well block (51a), the slag detection unit (10) comprising:- a refractory part (50, 50a, 51a) with a passageway (1), preferably a well block (51a) with a casting channel (2);- a transmitter (20) positioned at a first side of the passageway (1 ), preferably at a first side of the casting channel (2);- a receiver (30) positioned at a second side of the passageway (1 ), preferably at a second side of the casting channel (2);- wherein the second side is different from the first side, preferably the second side is opposite from the first side with respect to the passageway (1), more preferably the second side is opposite from the first side with respect to the casting channel (2);- the transmitter (20) being configured to direct a magnetic field (B) at least partially through the passageway (1), preferably through the casting channel (2);- the receiver (30) being configured to receive at least a part of the magnetic field (B) emanating from the transmitter (20) and passing through the passageway (1), preferably passing through the casting channel (2);- wherein the transmitter (20) comprises at least three transmitter coils, namely a first transmitter coil (22), a second transmitter coil (23) and a third transmitter coil (24);- wherein the first transmitter coil (22), the second transmitter coil (23) and the third transmitter coil (24) are configured such that when an alternating current is provided to the transmitter (20), the magnetic field (B) emanating from the second transmitter coil (23) is of opposite direction than the magnetic field (B) emanating from the first transmitter coil (22), and the magnetic field (B) emanating from thesecond transmitter coil (23) is of opposite direction than the magnetic field (B) emanating from the third transmitter coil (24).

2. Slag detection unit (10) according to claim 1, wherein the slag detection unit (10) is configured such that the magnetic field (B) and the direction (60) of the molten metal stream (6) in the passageway (1), preferably the casting channel (2), form an angle (a); wherein the angle (a) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°.

3. Slag detection unit (10) according to any of claims 1 to 2, further comprising a transmitter driver (21) connected to the transmitter (20), the transmitter driver (21) being configured to provide an alternating current to the transmitter (20).

4. Slag detection unit (10) according to any of claims 1 to 3, wherein the transmitter (20) comprises an odd number of at least three transmitter coils, preferably five or seven transmitter coils.

5. Slag detection unit (10) according to any of claims 1 to 4, wherein each of the first transmitter coil (22), the second transmitter coil (23) and the third transmitter coil (24) are arranged co-axially around a longitudinal axis (L) of a single core (29), and wherein the second transmitter coil (23) is arranged between the first transmitter coil (22) and the third transmitter coil (24).

6. Slag detection unit (10) according to claim 5, wherein the slag detection unit (10) is configured such that the longitudinal axis (L) of the single core (29) passes through the passageway (1), preferably through the casting channel (2).

7. Slag detection unit (10) according to any of claims 5 to 6, wherein the slag detection unit (10) is configured such that the longitudinal axis (L) and thedirection (60) of the molten metal stream (6) in the passageway (1), preferably the casting channel (2), form an angle ( / ?); wherein the angle (3) is in the range of 45° to 135°, preferably 60° to 120°, more preferably 80° to 100°.

8. Slag detection unit (10) according to any of claims 1 to 7 further comprising a receiver unit (31) connected to the receiver (30), the receiver unit (31) being configured to provide a signal (32) from the induced current at the receiver (30).

9. Slag detection unit (10) according to any of claims 5 to 8, wherein the longitudinal axis (L) of the single core (29) passes through the receiver (30).

10. Slag detection unit (10) according to any of claims 8 to 9, further comprising a processing unit (40); the processing unit (40) being in communication with the transmitter driver (21) and the receiver unit (31); the processing unit (40) being configured to control the transmitter driver (21) to provide an alternating current to the transmitter (20), such that a magnetic field (B) is directed at least partially through the passageway (1), preferably through the casting channel (2); the processing unit (40) being configured to receive a signal (32) from the receiver unit (31 ) relating to the magnetic field (B) emanating from the transmitter (20) and passing through the passageway (1), preferably through the casting channel (2); the processing unit (40) being configured to detect an occurrence of slag (6a) in a molten metal stream (6) guided in a direction (60) through the passageway (1) of the refractory part (50, 50a, 51a), preferably through the casting channel (2) of the well block (51a).

11. Slag detection unit (10) according to claim 10, wherein the processing unit (40) is configured to generate a warning signal (41) in case the occurrence of slag (6a) is detected in the molten metal stream (6).

12. Slag detection unit (10) according to any of claims 10 to 11 , wherein the processing unit (40) is further configured to provide a signal to a slide gate system (7a) for controlling the position of a slide gate (7); wherein the processing unit (40) and the slide gate system (7a) are configured to close the slide gate (7) in case the occurrence of slag (6a) is detected in the molten metal stream (6).

13. Method for detecting the occurrence of slag, the method comprising the following steps:- Providing a metallurgical vessel (5) containing molten metal (6), preferably the metallurgical vessel (5) is a steel ladle (5);- Providing a slag detection unit (10) according to any of claims 1 to 12;-wherein the passageway (1 ) of the refractory part (50, 50a, 51 a), such as the casting channel (2) of the well block (51 a), is installed such, that molten metal (6) can be drained from the metallurgical vessel (5) through the passageway (1) of the refractory part (50, 50a, 51a), preferably through the casting channel (2) of the well block (51 a),- Draining the molten metal (6) from the metallurgical vessel (5) through the passageway (1 ) of the refractory part (50, 50a, 51a), such as the casting channel (2) of the well block (51a);- Providing an alternating current to the transmitter (20);- Detecting a signal (32) from the induced current at the receiver (30); - When the signal (32) is outside a pre-defined range:-generate a warning signal (41), preferably by a processing unit (40);or-stop draining of the molten metal (6), e.g. by closing a slide gate (7), preferably by providing a signal to a slide gate system (7a), more preferably by the processing unit (40).

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