Patent Publication Number: US-2002011696-A1

Title: Tundish impact pad

Description:
[0001] This invention relates to the handling of molten metal, especially steel. In particular, the invention relates to a tundish impact pad, i.e. an article formed from refractory material to be placed on the floor of a tundish to receive an incoming stream of molten metal poured into the tundish from a ladle. The invention has particular utility in the continuous casting of steel.  
       [0002] International Patent Application No. WO 96/14951 (FOSECO) discloses a tundish impact pad comprising a body of refractory material capable of withstanding contact with molten steel in a tundish. The impact pad body comprises a base having an impact surface, an outer sidewall extending upwardly from the impact surface, and a top surface connected to the sidewall and defining an opening therein. The top surface has an inner annular portion substantially parallel to the impact surface, and there is a substantially right angled corner between the sidewall and the impact surface, and also between the sidewall and the inner annular portion of the top surface.  
       [0003] U.S. Pat. No. 4,468,012 discloses a device for removing inclusions from a molten metal which is poured into a casting tundish. The device comprises long blocks of heat-insulating material which is sinterable at the temperature of the molten metal and which comprises inorganic particles incorporated in an organic binder which is decomposable at the temperature of the molten metal so as to form pores in the heat-insulating material. A duct extends through each long block, for the supply of an inert gas which diffuses into the molten metal through the pores in the heat-insulating material.  
       [0004] U.S. Pat. No. 5,054,749 discloses a tundish for the continuous casting of steel, comprising a permanent refractory cast on a sheet metal frame defining an external wall of the tundish. In the bottom of the tundish there is a gas chamber and a porous refractory wear plate surmounting and extending over the chamber. A gas inlet duct extends from an upper edge of the tundish and down through the permanent refractory to the gas distribution chamber.  
       [0005] United Kingdom Patent Application No. 2164281A discloses a tundish used in a steel making process, which includes a replaceable refractory lining disposed on the inner surface of the bottom and side walls of the tundish. A porous refractory tile is supported upon the upper surface of the refractory lining and has a major axis extending substantially the entire width of the tundish. The porous tile encapsulates a perforated conduit for supplying inert gas which is allowed to emanate from the tile across the width of the tundish, to remove unwanted inclusions from the steel. The tile has a ramp-like surface for deflecting steel flowing towards it upwardly in the tundish. The tundish also includes an impact pad upstream of the tile.  
       [0006] According to a first aspect, the present invention provides a tundish impact pad formed from refractory material, the impact pad comprising a base having an impact surface which in use faces upwardly to receive molten metal poured onto the impact pad, and a sidewall extending upwardly from at least part of the periphery of the impact surface, characterised in that at least part of the interior, and a surface, of the sidewall are porous, and the impact pad includes means for supplying a gas to the porous interior of the sidewall, to enable the gas to be supplied to the molten metal from the porous surface of the sidewall.  
       [0007] According to a second aspect, the invention provides a kit of parts for assembly to form a tundish impact pad, comprising:  
       [0008] (a) a base part formed from refractory material and having an impact surface for receiving molten metal poured onto the impact pad in use; and  
       [0009] (b) a peripheral sidewall part formed from refractory material, for attachment directly or indirectly to the base part to form at least part of a sidewall around at least part of the periphery of the impact surface; characterised in that at least part of the interior, and a surface, of the sidewall part are porous, and the base part and/or the sidewall part include(s) means for supplying a gas to the porous interior of the sidewall part, to enable gas to be supplied to the molten metal from the porous surface of the sidewall part.  
       [0010] According to a third aspect, the invention provides a tundish for containing molten metal, the tundish comprising a floor and sidewalls formed from refractory material, and further comprising an outlet for the molten metal, characterised in that the tundish contains an impact pad according to the first aspect of the invention or assembled from a kit of parts according to the second aspect of the invention, placed on the floor of the tundish.  
       [0011] The gas is preferably an inert gas, e.g. argon or nitrogen, and is preferably supplied to the molten metal for the purpose of removing unwanted inclusions from the metal.  
       [0012] According to a fourth aspect, the invention provides a method of removing inclusions from molten metal in a tundish, by means of tundish impact pad according to the first aspect of the invention or assembled from a kit of parts according to the second aspect of the invention, the method comprising supplying a gas to the molten metal from the porous sidewall of the impact pad.  
       [0013] The expression “porous” is intended to include any arrangement in which at least part of the sidewall is able to supply gas to the molten metal from the interior of the sidewall. For example, pores, channels or other apertures in the sidewall may generally have any shape, for example they may be generally round, or elongate, in cross-section, thus appearing in the form of round holes or slits, respectively, on the surface of the sidewall. Furthermore, the porosity of the sidewall may be in the form of an irregular network of pores, or it may be in the form of a substantially regular structure of channels, for example.  
       [0014] The invention has the advantage that because the gas is supplied to the molten metal in the tundish from the sidewall of the impact pad, it may provide a kind of “curtain” of gas bubbles surrounding the impact surface of the pad (or at least part of the impact surface). This means that molten metal poured into, and subsequently flowing out of, the impact pad will normally flow through the gas curtain, and furthermore the gas will come into contact with the molten metal very soon after the metal has been poured into the tundish. The gas therefore has substantially the longest possible contact time with the molten metal, and will generally be carried with the metal as it flows away from the impact pad. This generally leads to a more efficient incorporation of the gas into the metal, and therefore a more efficient removal of unwanted inclusions, for example.  
       [0015] In some preferred embodiments of the invention, the sidewall of the impact pad is porous at least in an upper portion thereof. Preferably, at least part of an upper surface of the sidewall is porous.  
       [0016] The sidewall may include an inwardly projecting ledge, which is preferably located substantially at the top of the sidewall (but which may, alternatively, project from the side of the sidewall). By “inwardly projecting” is meant projecting over at least part of the impact surface of the impact pad. At least a central region of the impact surface is preferably substantially planar, and substantially horizontal in use. In such embodiments, the ledge is preferably substantially parallel to the planar region of the impact surface.  
       [0017] For embodiments of the invention which include an inwardly projecting ledge, at least part of the porosity of the sidewall may advantageously comprise at least part of the ledge, and preferably at least an upper surface thereof. For example, substantially the entire upper surface of the sidewall, including the upper surface of an inwardly projecting ledge, may be porous. The inwardly projecting ledge may, for example, comprise an upper portion which is porous and a lower portion which is substantially non-porous. Alternatively, the ledge may comprise upper and lower porous portions and a substantially non-porous intermediate portion.  
       [0018] Additionally or alternatively, at least part of the porosity of the sidewall may be provided by a portion of the sidewall located between the base and an upper portion of the sidewall (e.g. a ledge)—i.e. the main body of the sidewall may provide at least part of the porosity of the sidewall. At least part of the inner and/or outer surface(s) of the sidewall may be porous, and therefore supply gas to the molten metal in use.  
       [0019] As mentioned above, the second aspect of the invention is a kit of parts for assembly to form a tundish impact pad. When reference is made in this specification to the base or sidewall of the impact pad according to the first aspect of the invention, it is to be understood that the reference also applies to the base part or sidewall part, respectively, of the kit of parts. Furthermore, as mentioned above, in some preferred embodiments of the impact pad, the sidewall includes an inwardly projecting ledge. When such embodiments of the impact pad are provided as a kit of parts, in accordance with the second aspect of the invention, the inwardly projecting ledge may comprise an integral part of the sidewall part, or it may comprise a further separate part, i.e. a further sidewall part of the kit.  
       [0020] The means for supplying a gas to the interior of the sidewall preferably comprises one or more conduits. The term “conduit” is intended to include “pipe”, “channel”, “duct” and the like. The or each conduit is preferably perforated along at least part of its length, in order to release the gas. The gas is therefore preferably supplied to substantially the entire porous region or regions of the sidewall (or the entire sidewall for embodiments in which the entire sidewall is porous). The impact pad therefore preferably includes one or more conduits (e.g. a network of conduits) for supplying the gas to the porous sidewall. For embodiments of the invention in which the sidewall extends around the entire periphery of the impact surface, the sidewall preferably includes at least one gas supply conduit extending through the entire length thereof (e.g. an endless conduit).  
       [0021] The tundish preferably includes one or more gas supply conduits for supplying the gas to the impact pad. In use, at least one conduit in the tundish is preferably connected to a respective conduit in the impact pad. The connection between a tundish gas supply conduit and an impact pad conduit may, for example, be made at the base of the impact pad, or at the sidewall of the impact pad, depending upon the design of the tundish and the arrangement of the impact pad within the tundish. For arrangements in which part of the sidewall of the impact pad is located adjacent to a sidewall of the tundish, the conduit connection may conveniently be made at the impact pad sidewall for example, whereas for arrangements in which the impact pad is located a distance from the sides of the tundish, it may be more convenient for the conduit connection to be made at the base of the impact pad. In the latter case, the conduit connection may be underneath the base of the impact pad, but it is generally preferred for the connection to be made at a side of the base of the impact pad, the tundish conduit for example lying on the floor of the tundish and provided in a refractory block or under a refractory cover. The tundish conduit(s) is/are preferably connected to a gas source located to the exterior of the tundish. 
     
    
    
     [0022] The invention will now be described, by way of example, with reference to the accompanying drawings, of which:  
     [0023]FIG. 1 is a schematic illustration in cross section of a one-piece impact pad according to the invention;  
     [0024]FIG. 2 is a schematic illustration in cross section of a two-piece impact pad according to the invention;  
     [0025]FIG. 3 is a schematic illustration in cross section of a three piece impact pad according to the invention; and  
     [0026]FIG. 4 is a schematic illustration in cross section of a tundish containing an impact pad according to the invention. 
    
    
     [0027]FIG. 1 shows in cross-section a one-piece tundish impact pad  1  formed from concrete. The impact pad comprises a base  3  having an upwardly facing impact surface  5  for receiving molten metal poured onto the impact pad, and a sidewall  7  extending upwardly from the periphery of the impact surface. The impact pad is generally square or rectangular in plan view (but other shapes are of course possible, e.g. other quadrilateral shapes, or round, e.g. circular). An upper portion  9  of the sidewall  7  is formed from a porous concrete material. In use, a gas supply conduit (not shown) in the impact pad supplies a gas to the interior of the porous portion  9 , and the gas permeates through the porous portion and is released as a “curtain” of gas bubbles emanating from the upper surface of the sidewall of the impact pad. The sidewall includes an inwardly projecting ledge  11 , and part of the porous upper portion  9  of the sidewall comprises an upper part of this ledge.  
     [0028]FIG. 2 shows an impact pad similar to that shown in FIG. 1, with a porous upper portion  9 , but this impact pad has been assembled from a kit of two main parts, namely a base part  13  comprising a base  3  and a lower region of sidewall  7 , and a sidewall part  15  which constitutes an upper region of the sidewall, comprising the porous upper portion  9  and a non-porous portion  16 . The two parts of the kit have been assembled and cemented together to form the impact pad.  
     [0029]FIG. 3 shows an impact pad similar to those shown in FIGS. 1 and 2, except that this impact pad has been assembled from a kit of three main parts, and it contains an additional porous portion in the sidewall. The kit comprised a base part  17 , a lower sidewall part  19 , and an upper sidewall part  15  (which is the same as that of FIG. 2), the parts having been assembled and cemented together to form the complete impact pad. The lower sidewall part  19  comprises a porous portion  23 , and the upper sidewall portion comprises an upper porous portion  9  and a lower non-porous portion  16 . The lower porous portion  23  releases the gas from its exterior and interior surfaces, i.e. the gas is released both into the interior of the tundish and to the exterior of the tundish. In combination with the upper porous portion  9  which releases the gas from the upper surface of the sidewall, the result is the production of a (radially) deeper “curtain” of gas bubbles surrounding the impact surface, compared to that produced by the impact pads shown in FIGS. 1 and 2.  
     [0030]FIG. 4 shows, schematically and in cross-section, a tundish  25  filled with molten steel  27  and containing an impact pad  1  according to the invention. The flow direction of the molten steel from a submerged entry shroud  29  onto the impact surface  5  of the impact pad, through bubbles of gas supplied by the impact pad and towards and through outlets  31  is indicated by the arrows. The gas supply conduits are not shown.