(a) Field of the Invention
The present invention relates to the art of continuous molten metal casting.
More specifically, the invention relates to a device for holding and replacing casting plates of a metallurgical vessel of a casting installation. This plate may be a calibrated plate or a casting tube. These types of plates are usually part of a nozzle comprising a plate connected to a tubular section of varying lengths depending on the applications.
(b) Description of Related Art
A device for replacing casting tubes, arranged facing a casting orifice of a metallurgical vessel of a continuous molten metal casting installation is known, particularly from the document EP 0 192 019 A1. Such a device comprises guiding means generally two rails whereon casting tubes can slide, to occupy firstly a standby position, followed by an operating position and finally an evacuation or exit position opposite the standby position. A drive also called actuator or pusher, actuated by a jack or cylinder, is used to push a casting tube from the standby station thereof to the operating station thereof, the tube moved expelling for this reason, to the evacuation station, the worn casting tube situated on the operating station.
The casting tube comprises a sliding face wherein a casting channel opens, which is in registry with the metallurgical vessel orifice when the casting tube is at the operating station. The metallurgical vessel orifice generally consists of the casting orifice of the upstream refractory element or the casting orifice of the upstream refractory elements which are in fluid communication. The upstream refractory element is generally rigidly connected to the metallurgical vessel, for example, it is cemented or mortared therein.
In the operating position, pushers also called thrusters are arranged extending from the guiding means or rails. These pushers are used to apply a substantially vertical force on two bottom faces of the plate of the casting tube such that the tube sliding face is in tight contact with the face of the upstream refractory element.
In some cases, as in WO2004/065041A1 (particularly paragraph 23), the casting tube sliding face is sufficiently large to form, next to the casting orifice, a sealing surface suitable for sealing or closing the metallurgical vessel casting orifice if the casting tube is moved over a distance at least equal to the diameter of the metallurgical vessel orifice. The sealing surface is also called shut-off surface or closure surface.
The casting tube present on the operating station can thus adopt two positions:                a casting position, wherein the casting channel thereof is facing the metallurgical vessel casting orifice, and        a sealing position, wherein the sealing surface thereof is facing the metallurgical vessel casting orifice.        
In this case, the casting tube may be used not only for casting the molten metal, but also for stopping (interrupting) the casting in the event of an emergency, which is useful for example if another upstream shutdown device is defective.
The movement of the casting tube on the guiding means, for instance the rails, thus needs to be controlled selectively, according to whether it is to be moved to the casting position or the sealing position on the operating station, requiring the use of one or more double-stroke jacks. However, such jacks are bulky, heavy and costly. Furthermore, they require the presence of at least two separate hydraulic supplies on the continuous casting floor.
The present invention is intended to provide a technical solution for controlling the movement of the casting tube, and more generally of a casting plate, to the casting position or to the sealing position on the operating station, completely automatically, simply and reliably.
For this purpose, the present invention relates to a device for holding and replacing a casting plate facing a casting orifice of a metallurgical vessel of a continuous molten metal casting installation, the casting plate being of the type comprising a sliding face wherein a casting channel opens and wherein a sealing surface suitable for sealing the metallurgical vessel casting orifice is formed, said device being of the type comprising a pusher or drive suitable for pushing a casting plate to move it from a standby station to an operating station, a plate on the operating station being suitable for adopting a casting position, wherein the casting channel thereof is facing the metallurgical vessel casting orifice, and a sealing position, wherein the sealing surface is facing the metallurgical vessel casting orifice, the pusher being provided with means for selectively moving same along two strokes:                a short stroke pushing a casting plate to the casting position on the operating station, or        a long stroke pushing a casting plate to the sealing position on the operating station,        
said device being characterised in that it comprises:                a casting plate passage detector between the standby station and the operating station,        a pusher limit switch, controlled by the passage detector and suitable for adopting:        a replacement position corresponding to a casting position, adopted when the detector detects the passage of a casting plate, wherein the limit switch limits the pusher stroke to the short stroke, and        a sealing position, in the other cases, wherein the limit switch allows the pusher to move over the long stroke.        
By means of the plate passage detector, if the pusher is actuated and a replacement plate is situated on the standby station, the detector controls the limit switch which is set to the replacement position and limits the stroke of the pusher such that the casting plate is moved to the casting position on the operating station, whereas, if no plate is situated on the standby station, the limit switch allows the pusher to cover the long stroke thereof to push the plate present on the operating station to the sealing position.
The operator thus no longer needs to determine whether it is necessary to actuate the pusher for a plate replacement or an emergency stop. The passage detector and the limit switch determine which stroke of the pusher is required automatically.
In particular, if the operator actuates the jack without having positioned a replacement plate on the standby station, an emergency stop is required. The device according to the invention thus automatically actuates the jack over the long stroke thereof so that it moves the plate to the sealing position.
Therefore, the invention provides, besides a simple and economical jack control device, improved safety on the casting site, both for the operator himself, who no longer needs to intervene in the vicinity of the molten metal, and for the entire site, in that the operator can respond more rapidly in the event of an emergency and does not risk to make a mistake.
The majority of known devices do not comprise double-stroke jacks, or casting tubes having a sealing surface. When an emergency stop is required, the operator needs to intervene in the vicinity of the molten metal, remove the tube in standby position, replace it by a blank plate and then actuate the jack to move the blank plate into the casting position. The devices equipped with a double-stroke jack and a casting plate comprising a sealing surface are already an improvement as the blank plate and its handling is not necessary anymore. However, they present the drawbacks mentioned above. Double-stroke jacks are bulky, heavy, costly and require the presence of at least two separate hydraulic supplies. These and other problems and disadvantages associated with the prior art are overcome by the invention disclosed herein by providing a simple, economical and safe method for actuating a device. The operator can actuate the jack remotely and very rapidly and seal the casting channel.
In one advantageous embodiment, the limit switch is arranged so as to retain the replacement position after detecting the passage of a casting plate, as long as the pusher has not moved back after covering the entire short stroke thereof.
For this purpose, a stabilizer is incorporated in the limit switch, so that said limit switch retains the position set by the passage detector, even after the passage detector has stopped detecting the presence of a plate.
In one particular embodiment of the invention, the passage detector is a lever which is actuated by the casting plate when it moves from the standby station to the operating station.
This means offers the advantage of being simple to produce and reliable in the operation thereof.
Advantageously, the limit switch comprises a movable abutment, the pusher or drive comprising a bearing surface suitable for resting on the abutment only when the limit switch is in the sealing position.
The lever and the movable abutment may be connected by a ball type connection, which converts the rotation of the lever into a translation movement of the movable abutment. Any other link suitable for transmitting the movement of the lever to the movable abutment could obviously be suitable.
In one particular embodiment of the invention, the pusher comprises a rod and the pusher bearing surface is formed by a recess provided in the rod.
This embodiment is advantageous in that it is simple to produce and reliable in the operation thereof.
In certain embodiments, the recess provided in the rod comprises, opposite the bearing surface, a bevel replacing the movable abutment in the replacement position when the rod moves back after the pusher has covered the entire short stroke thereof.
According to one advantageous embodiment, the device comprises an evacuation or exit station, whereto a worn plate is sent when pushed by a plate pushed to the operating position by the pusher.
The invention also relates to an assembly of a casting plate and a device for holding and replacing casting plates wherein the casting plate comprises at least one protrusion or protuberance for interacting with a plate passage detector of a device as described above.
Cladding refractory elements, casting plates or casting tubes by an element such as a metallic casing is known in the art. These casings are well known to those skilled in the art along with the types of materials used to produce said casings. The refractory is preferably contained or cemented into the metallic casing.
The invention also relates to a metallic casing for a casting plate of a continuous molten metal casting installation comprising at least one protrusion or protuberance for interacting with a plate passage detector of a device as described above.
The casings are generally metallic, particularly made of steel or cast iron. Obviously, any other materials capable of fulfilling the same function could be used. The same applies for the protrusion.
In one embodiment, the casing comprises:                a main surface comprising an opening and side edges extending to said main surface and defining the perimeter thereof;        two bearing surfaces substantially longitudinal and intended to slide along the guiding means of the device,        projecting from the main surface, a protrusion extending in the plate sliding direction, the sliding direction being substantially parallel with the longitudinal bearing surfaces.        
In one particular embodiment, the casing comprises:                two longitudinal bearing surfaces intended to slide along the rails of the device for guiding the plate,        longitudinal bottom edges parallel with said longitudinal bearing surfaces and,        projecting from at least one of said longitudinal bearing surfaces, a protrusion extending in the plate sliding direction, that is parallel with the longitudinal bearing surfaces.        
The bearing surfaces may have various shapes, for example be planar, inclined, or convex. It is simply necessary for them to serve as a support for the casting plate and enable the movement thereof from a standby station to an operating station.
In general, the bearing surface is parallel with the plate sliding or replacement direction. In this case, the term “parallel” should be understood in the broad sense, i.e. the bearing surface comprises at least one line segment or generating line parallel with the plate replacement direction. Similarly, an edge or a protrusion is parallel with the bearing surfaces if the edge or protrusion comprises a line segment parallel with the plate replacement direction.
In certain embodiments, the casing further comprises one or any combination of any of the following features:                the casing comprises two pairs of opposed side edges as follows: two longitudinal edges and two transverse edges        the two segments respectively parallel to the transverse edges and the longitudinal edges of the casing and comprising the centre of the opening divide the casing into four quadrants; two quadrants being larger        the casing comprises a tubular portion matching and extending from the opening of the main surface        the casing has an overall rectangular outline.        the casing comprises longitudinal bottom edges parallel with said longitudinal bearing surfaces and, projecting from at least one of said longitudinal bearing surfaces, a protrusion extending in the plate sliding direction, the sliding direction being parallel with the longitudinal bearing surfaces        the bearing surfaces are planar        the bearing surfaces are not comprised in the same plane        the casing comprises a pair of opposed side edges, one of which has a first thickness and the second of which has a second thickness greater than said first thickness        the casing is made of cast iron        
The protrusion of the casing may be situated on only one side of the metallic casing.
In certain embodiments the casing comprises two protrusions wherein each protrusion is situated on either side of the metallic casing, symmetrically in relation to the longitudinal axis of said casing. This configuration is particularly interesting. As explained above, the means for selecting the stroke is located on the pusher. Depending on the casting installation and the space available in the vicinity of the metallurgical vessel, the pusher can be connected on the left side or the right side of the device. In case the vessel comprises a plurality of casting lines each equipped with a device, some may have the pusher on the left side and some others on the right side. Having two protrusions located symmetrically on each side of the plate permit the use of the plate equivalently on all the casting lines, this way, ensuring in all cases the interaction with the passage detector and the correct selection of the stroke.
In certain embodiments, the metallic casing protrusion is tapered in the plate sliding direction.
Advantageously, the protrusion or each protrusion comprises one or any combination of any of the following features:                the protrusion is formed by a ramp comprising an inclined portion, the inclination being in the plate sliding direction        the protrusion comprises a portion parallel with the bearing surfaces or the bottom longitudinal edges        the protrusion is located outside of the bearing surface        the protrusion is located adjacent the bearing surface        the protrusion is located on the longitudinal sides of a rectangle or outside of a rectangle, the rectangle being formed by the transverse side edges of the casing and the two tangents to the tubular opening parallel to the longitudinal side edges of the casing        the protrusion is located in the two larger quadrants        
In view of the high mechanical stress generated on the casing during use as well as the risk of damage of the protrusion(s) or ramp(s) during transport or handling, the casing is in certain embodiments relatively thick and obtained by moulding, e.g. by casting into a mould.
The invention also relates to a casting plate for a continuous molten metal casting installation, of the type comprising a sliding face wherein a casting channel opens and wherein a sealing surface capable for sealing a metallurgical vessel casting channel is formed, consisting of:                a refractory defining the casting channel and forming the sliding face,        a metallic casing encasing the refractory in the vicinity of the sliding face,        
characterised in that the metallic casing comprises a protrusion for interacting with a plate passage detector of a device as described above. In certain embodiments, the casting plate comprises a metallic casing as described above.
Advantageously, the casting plate comprises one or any combination of any of the following features:                the protrusion of the casting plate projects in the direction opposite the casting plate sliding surface.        the protrusion or each protrusion (30) of the casting plate is formed by a ramp comprised in a plane orthogonal to the sliding face and comprising an inclined portion (30a) and optionally a portion (30b) substantially parallel with the sliding face (19a, 20a).        the plate comprises a refractory tubular extension opposite the sliding face, to extend from the casting channel. The tubular extension may be sufficient to immerse the lower portion thereof in the molten metal mould.        
The invention also relates to a method for producing a plate according to the invention comprising the step of assembling a metallic casing and a refractory element. Assembly is performed using known means. In certain embodiments, the refractory is cemented into the metallic casing or assembled by casting a refractory concrete between the refractory element and the casing (cast around). It can also be considered to recover the metallic casing after use and assemble it with a new refractory element.