GB2534231A

GB2534231A - Slag shield

Info

Publication number: GB2534231A
Application number: GB1500877.4A
Authority: GB
Inventors: John Woolley Peter; Scott Chadwick Robert; Payne Mark
Original assignee: Monocon International Refractories Ltd
Current assignee: Monocon International Refractories Ltd
Priority date: 2015-01-19
Filing date: 2015-01-19
Publication date: 2016-07-20
Anticipated expiration: 2035-01-19
Also published as: GB2534231B; GB201500877D0

Abstract

A shield device, for occluding a tap hole of a furnace, may have an elongate shaft 400 with a shield 403 (extending transverse to the shaft) and retaining means 405. The retaining means 405 can hold at least a portion of the shaft 400 in the tap channel, e.g. using outwardly extending barbs (409, fig 6) to retain the shield device in the tap channel against the force of gravity. The shield 403 may have a circular disc and/or a frusto-conical plate, which may tilt and have limited movement along the shaft (figs 9/10). The shield device can be loaded onto a robotic placement machine (figs 7/8) and inserted into the tap channel from inside the converter. The shield device may melt when in contact with molten metal, unblocking the tap hole. A shield device may have a deformable plug 2302 which blocks the tap hole when a heat expandable material 2309 (e.g. heat activated expanding graphite) pushes on deformable material 2306 (e.g. clay), expanding it out radially (figure 23). A telescopic piston 2307, 2308 may house the graphite, urging upper and lower plates 2304, 2305 towards each other to compress the clay, blocking the hole.

Description

SLAG SHIELD

Field of the Invention

[0001] The present invention relates to a shield device for a furnace, and a method of shielding a furnace tap hole.

Background of the Invention

[0002] Steel and other metal alloys are produced in large heated vessels known as converters or furnaces, which convert iron to steel or another alloy.

Typically, steel is produced as a batch process, in quantities of up to 10 m3 or 60 m3, or quantities of 65 to 400 tonnes at a time in a single converter. The converter comprises a large robust vessel, suspended on a pivotal axis so that the vessel can be tilted in order to drain molten metal from a tap hole or tap channel in the side of the converter.

[0003] When producing steel in a heated converter, a layer of impurities (slag) floats on top of the molten steel. In the sidewall of the converter, there is provided the tap hole through which the molten metal can be discharged or emptied when the furnace is tilted about its pivotal axis. When the converter is in a heating phase, the metal fills the converter to a level below the tap hole, such that the tap hole is above the level of the molten metal and above the layer of slag resting on top of the molten metal.

[0004] Conventionally, the tap hole is plugged using a plug which stops the layer of slag from draining out of the tap hole when the converter is tilted. This allows the converter to tilt to a position where the tap hole is in the molten metal, before the metal is drained and avoids any slag contaminating the metal drained from the tap hole.

[0005] Known plugs can be made of clay, refractory material, Burlap bags, old cloths or rags, cotton waste, wood, or fibrous material, or may comprise metallic plugs with a layer of refractory material. In general the known plugs are all inserted into the tap hole from a position outside the converter using an applicator tool.

[0006] In one conventional method using a known clay pre-tap plug, prior to tilting the converter, an operative places the plug on an applicator comprising a long pole which is adapted to hold the plug at one end, which is inserted into the tap hole from a position outside the converter. The clay plug has a substantially circular cylindrical solid layer of compressible clay or refractory material between two circular metal discs. An outer metal disc at the distal end can be pulled back towards the inner metal disc nearer the operator's end of the pole, so as to compress the layer of clay, squeezing it outwardly. This means that the clay plug can be inserted through the tap hole, and then manipulated by an operative by pulling on a rod which runs inside the pole of the applicator, to squeeze the clay outwards to increase its diameter and block the tap hole. The applicator is then removed from the plug, leaving the plug behind in the tap hole.

[0007] Referring to figure 1 herein, there is illustrated schematically a conventional method of inserting a pre-tap plug into a tap hole of a converter 101, using a plug insertion tool 102. The converter 101 is rotated to allow insertion of a pre-tap plug 100 on the end of a long applicator tool 102. The operative must stand adjacent the converter to perform this operation. In some converter installations the operative is typically partially shielded from the converter by an intermediate barrier wall 103, but not all converters have such walls or barriers. Since the converter can operate at temperatures in the region of 1500°C to 1700°C, the operative wears protective clothing. Some, but not all, converter installations have a heat reflective barrier wall 103 in front of the converter to partially protect the operatives from heat.

[0008] Referring to figure 2A herein, there is shown in perspective view from a distal end and one side, a known tap hole plug for blocking a tap hole of a converter.

[0009] Referring to figure 2B herein, there is shown in perspective view from the rear and one side, the plug of figure 2A herein.

[0010] The tap hole plug comprises a substantially circular cylindrical block of refractory material 201, having a circular channel centrally there through. The channel is lined with a metal tube 202, which protrudes at a proximal end of the plug. At a distal end of the plug there is provided an end plate 203 having a conical/funnel-shaped indentation around the central circular channel. At a proximal end of the plug, there is provided a circular/annular backplate 204. A distal end of the inner tube 202 is rigidly secured to the end plate 203, whilst the backplate 204 is slidable relative to the inner tube 202 in an axial direction to allow for squeezing of the refractory material.

[0011] Referring to figure 3A herein, there is illustrated schematically in cutaway view the end of a known tap hole plug device 200 fitted to the end of a known insertion tool 300, at a position of initial insertion into a tap hole of the converter. From a position outside of the converter, an operative manually lifts the insertion tool, having a tap hole plug fitted on the distal end, and inserts the distal end of the insertion tool through the tap hole, to a position near the internal opening of the tap hole inside the converter.

[0012] The insertion tool 300 comprises an outer tube 301 and an inner rod 302, the inner rod being slidable axially through a central channel of the outer tube 301. At a distal end of the outer tube 301, there is provided a laterally extending circular plate 303 of a diameter approximately the same as the uncompressed outer diameter of the tap hole plug device 200, which abuts the rear of the plug device. The circular plate 303 is supported by a plurality of buttress members 304 attached to the end of the outer tube 301, there being a centrally located space through which the inner rod 302 can pass, and into which one end of the cylindrical tube of the plug locates.

[0013] At a distal end of the inner rod 302, there is provided a radially extending member 305 which extends transversely to the main length direction of the inner rod 302. Between the first circular plate 302 and the radially extending member 305, is located the plug device 200.

[0014] Referring to figure 3B herein, there is illustrated the known tap hole plug 200 in an intermediate stage of insertion into the tap hole, under compression of the insertion tool 300. With the plug located near the internal opening of the tap hole on the inside of the converter, from a position outside the converter, an operator pulls the inner rod 302 relative to the outer tube 301, using a lever on the insertion tool, so as to compress the deformable plug 200. The plug 200 is compressed between the first plate 302 and the radially extending member 305 on the end of the inner rod. The channel plug 200 deforms laterally and radially outwards until its further deformation is restricted by the inner walls of the tap hole, and the plug blocks the tap hole. The plug is retained in the tap hole by virtue of the friction between the internal wall of the tap hole channel and the deformed plug material.

[0015] Referring to figure 3C herein, there is illustrated a removal of the known insertion tool after compression of the plug 200. The radially extending member 305 is collapsible such that it can be withdrawn through the circular cylindrical tube at the centre of the plug device 200, when the inner rod 302 is withdrawn axially along the centre of the outer tube 301. This allows the radially extending member 305 to pass through the central cylindrical channel of the plug member, thereby releasing the insertion tool from the plug member and leaving the plug member in situ, blocking the tap hole.

[0016] The known tap hole plug performs its function as follows. When it is required to tap molten metal from the tap hole, the converter is rotated or tilted.

During heating, the opening of the tap hole on the inside of the converter is located above the layer of slag. However during tilting, the layer of slag moves over the tap hole opening. The purpose of the tap hole plug is to stop the slag draining through the tap hole as the slag layer moves over the tap hole opening. Once the tap hole opening is underneath the slag layer and covered by molten metal, the plug disintegrates or washes away, by a combination of melting and fragmentation, allowing the molten metal to drain out of the tap hole. Once the plug breaks and is washed away, molten metal travels down the tap hole and out of the converter. To prevent the floating slag layer following the molten metal down the tap hole as the last parts of the molten metal flow though the tap hole, it is known to introduce a slag stopper device into the converter using a robotic arm. The slag stopper floats on the surface of the metal and settles into the tap hole to block the tap hole. Known types of slag stopper include darts having a conical stopper part, spheres or cylinders.

[0017] Another type of known tap hole plug comprises a conical or frustoconical concrete plug surrounded by a layer of fibrous material. At one end of the plug there is a hole for fitting the end of a lance applicator tool. To fit this plug, an operator has to manipulate the applicator tool, with the plug on the end, to a position adjacent the side of the furnace, and push the plug into the outer facing aperture of the tap hole.

[0018] Using this type of prior art tap hole plug, since the aperture on the inside of the vessel is not covered, then slag can pass into the tap hole. Further, the operator needs to approach the high temperature furnace in order to fit the prior art plug from the outside of the furnace.

[0019] During continuous steel production, which involves repeated charging of a converter with batches of scrap metal and molten iron, followed by conversion to steel and emptying of the converter, the refractory lining of the converter and the metal converter vessel itself have a thermal latency and store heat, so that the converter remains at a temperature in the range 1400°C to 1700°C and does not have time to cool down between successive batches of.

Steel. Therefore, plugs need to be fitted in a high temperature environment which is highly dangerous.

[0020] In addition to the hazard of radiative heat from the converter, slag may fall from the side of the vessel causing the molten metal to splash. Liquid steel at around 1700°C has a viscosity similar to that of water at room temperature. Any contact with a splash of liquid steel can result in severe injury or death for a human operator.

[0021] An object of the embodiments disclosed herein is to provide a safer method of blocking a tap hole of a furnace which is less hazardous to operators of the furnace.

[0022] US 3, 776, 532 discloses a device for plugging the tap hole of a reactor for a metallurgical process, comprising an elongate shaft member, a frusto -conical plug portion, and a member for locking the plug into the tap hole, the locking member being located outside the vessel of the reactor. This type of device must be fitted when the reactor is cool, and therefore can only be used for the first batch of steel production of a repeating batch process. It is not suitable for continuous batch operation of a steel converter, because fitting the outer locking member on the outside of the converter cannot be done when the converter is at full operating temperature, and to maintain productivity and retain energy efficiency, once the converter is heated up it needs to be kept working continuously on successive production batches.

Summary of the Invention

[0023] According to an aspect of the present invention, there is provided a shield device for occluding a tap hole of a furnace, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said shield member along a length of said shaft, for retaining at least a portion of said elongate shaft in a tap hole of said furnace.

[0024] The shield device occludes a tap hole of the furnace. In use, the shield device is inserted mechanically into the tap hole from a position inside the furnace, so that it occludes the open aperture of the tap hole in the inside of the furnace wall. When tilting the furnace, the shield device remains intact long enough to avoid a layer of slag on top of the molten metal from passing down the tap hole, and to allow the furnace to be tilted to a position where the aperture of the tap hole is underneath the slag layer and adjacent the body of molten metal, before the shield device washes away or melts, and then allows molten metal to flow through the tap hole. The shield device itself washes away through the tap hole as when it comes into contact with the molten metal inside the furnace.

[0025] The shield device is capable of being fitted into a hot converter at a temperature in the region of 1400°C -1500°C or thereabouts, using a robotic arm, and does not require access to the outside of the vessel to secure the device in the tap hole. The device is self -retaining in the tap hole when the vessel is rotated, and once fitted, retains itself in the tap hole even when inverted.

[0026] Other aspects are as set out in the claims herein, which are incorporated into the summary by reference.

Brief Description of the Drawings

[0027] For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which: Figure 1 herein shows a prior art method of inserting a known pre-tap plug of the clay type into the tap hole of a converter; Figure 2A herein shows in perspective view from one end, a known tap hole plug device; Figure 2B herein, shows in perspective view, the known tap hole plug device from the opposite end; Figure 3A herein shows a known pre-tap plug positioned in the tap hole of a converter, prior to fixing the plug in the tap hole of a converter; Figure 3B herein shows the known pre-tap plug under compression using a known insertion tool; Figure 3C herein shows the known pre-tap plug located in situ in a tap hole of the converter, with the insertion tool retracted; Figure 4 herein shows a first specific embodiment slag shield device; Figure 5 herein shows a shield member component of the slag shield 20 device; Figure 6 herein shows a retaining portion of the slag shield device, for retaining an end of the slag shield device in a tap hole; Figure 7 herein shows a first stage of insertion of a slag shield device into a vertically oriented tap channel of a converter, with the converter in a 90° tilted orientation; Figure 8 herein shows the slag shield device fitted into a tap hole of a converter, with the converter in a 90° tilted orientation; Figure 9 herein shows a modification of the first slag shield device to allow the shield member to adapt its position relative to the elongate shaft so that the shield member can adapt to closely fit over the open end of a tap hole inside a converter; Figure 10 herein shows schematically the modified first slag shield device in cutaway view located in a tap hole of a converter, where the inside face of the converter wall is at a non-perpendicular angle to the main length of the tap hole; Figure 11 herein shows a converter having a fitted slag shield device in an orientation in which the converter is charged with raw materials for making steel; Figure 12 herein shows the converter in an upright orientation for blowing using an oxygen lance; Figure 13 herein shows the converter in a tilted orientation during a turn 15 down stage; Figure 14 herein shows the converter during a further stage of the turning down operation, in which the slag shield and tap hole of the converter are covered by molten metal; Figure 15 herein shows a tapping or metal pouring operation of the converter, with the converter in a tilted / turned down orientation; Figure 16 herein shows the metal pouring operation, in which a known refractory dart is dropped into the interior of the converter; Figure 17 herein shows a final stage of pouring or tapping of steel from the converter, in which the slag stopping dart locates in the tap hole of the converter; Figure 18 herein shows an end of a metal pouring operation, with the converter vessel is rotated back to a vertical orientation, and the dart and residual slag fall to the base of the vessel interior; Figure 19 herein shows the converter inverted, for removal of slag and the refractory dart, which are dumped out of the open end of the inverted converter vessel; Figure 20 herein illustrates schematically a human operator visually checking for clearance of a tap hole, with the emptied converter vessel in a tilted orientation, ready to start a subsequent batch of metal production; Figure 21 herein illustrates schematically the converter vessel in a tilted substantially horizontal position, in which a slag shield device is inserted into a tap hole using a mechanical robotic arm; Figure 22 herein shows a novel slag shield device in place in a tap hole, after removal of the mechanical robotic arm, and prior to loading the converter with raw materials for metal production: Figure 23 herein shows schematically a second slag shield device according to a second specific embodiment, being held on the end of a robotic arm for fitment into a tap hole of a converter furnace; and Figure 24 shows the second slag shield device inserted into the tap hole of a converter furnace.

Detailed Description of the Embodiments

[0028] There will now be described by way of example a specific mode contemplated by the inventors. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to

unnecessarily obscure the description.

[0029] In the following description, there is described embodiment slag shield devices made of steel, and used in production of steel. However it will be understood by the skilled person that the slag shield device could be used in the production of other metals, and the slag shield device itself can be made of steel or other metals, including refractory materials.

[0030] In this specification the term "furnace" is used to mean any heated vessel used to heat metal to liquid state and includes converters such as Bessemer converters, electric arc furnaces, and any like furnaces having a heated vessel with a refractory lining.

[0031] Referring to figure 1 herein, there is illustrated schematically a shroud manipulator according to a specific embodiment of the present invention.

[0032] Referring to figure 4 herein, the first slag shield for insertion into the tap hole of a furnace comprises an elongate shaft, rod or tube 400 having a first end 401 and a second end 402; a laterally extending shield member 403 located between said first and second ends of the rod or tube; a ballast member 404 located at the second end of the rod or tube 400; and one or a plurality of retention means 405 for preventing the slag shield from falling out of the tap hole once located.

[0033] In the embodiment shown, the shield portion comprises a circular or annular disc 406, supported by a frusto -conical shaped plate 407, the circular plate or disc extending laterally in a plane transverse to a main length axis of said elongate shaft, rod or tube. In some embodiments the shield may comprise a refractory component, such as a refractory shield component. The purpose of the frusto-conical portion is to centralise the top plate or shield member 403 in the tap hole.

[0034] The ballast member 404 in the embodiment shown comprises a conical solid metal body attached at the distal end of the rod or tube.

[0035] In the embodiment shown, the retention means comprise a plurality of outwardly extending barbs or rods, which together form the edges of a pyramid shape, having its apex coincident with an apex of the ballast member 404. In the embodiment shown, there are four individual outwardly extending barbs, however in the general case there may be one or a plurality of barbs.

[0036] In the embodiment shown, typically the dimensions of the shield components may be in the following ranges: Length of elongate shaft, tube or /rod 400: Diameter of elongate shaft, tube or rod 400: Outside diameter of circular/annular plate: Thickness of circular/annular plate: Angle of barbs relative to main length axis: Length of barbs: Distance of circular/annular plate from lower end: 250mm to 1500mm 15mm to 50mm 150mm to 600mm 2mm -30mm 25° to 55° 200mm to 400mm 400mm to 800mm [0037] Figure 5 herein shows a shield component of the slag shield device. The shield component 403 comprises a flat circular or annular plate 406; and a frusto-conical shaped member 407 having its pointed end pointing in a direction of the lower end of the slag shield device, towards the retaining means and ballast member. The frusto-conical shaped member and the circular/annular plate are each arranged concentrically with the rod or tube 400, so that the rod or tube 400 passes coaxially through the centre of the circular or annular plate, and concentrically through a circular aperture in the pointed nose portion of the frusto-conical member.

[0038] In the embodiment shown, there is an annular plate fitted to the wider end of the frusto-conical member 407. However the annular plate 406 could extend across the top of the hollow frusto-conical member to meet the outer surface of the central rod 400. In other embodiments, the frusto-conical member 407 may be a solid frusto-cone, and may be made of metal, a refractory material, or other bulk material such as wood.

[0039] Figure 6 herein shows the lower end of the slag shield device, showing the retaining means 405, for retaining an end of the slag shield device in a tap hole. The retaining means comprise a plurality of outwardly extending rods or barbs 409 which are angled relative to a main length axis of the central rod or tube 400. In the embodiment shown, four rods or barbs 409 lie on the edges of a four -sided virtual pyramid. However, in other embodiments, a plurality of rods may lie on the surface of a three -sided pyramid, or on the surface of a virtual cone. In other embodiments, the plurality of outwardly extending rods or barbs may extend radially outwards from a main length axis of the central rod 400. A further embodiment with only one such barb is possible.

[0040] Also at the lower end of the rod 400 is provided the ballast member 404. The purpose of the ballast member is to assist the rod in travelling downwards through the tap hole, and for helping the slag shield device orientate in a vertical manner, when held by a robotic arm during installation of the slag shield into a tilted converter, with the tap hole orientated in an upright orientation.

[0041] In the embodiment shown, the retaining means are attached to the elongate rod 400 by means of the ballast member 410 which is in the form of a second hollow frusto -conical member 410. The ballast member therefore provides the multiple function of serving to attach the barbs to the elongate shaft 400, guiding the lower end of the shaft into the tap hole, by virtue of its shape, and providing a weight or ballast to orientate the shield device in an upright orientation to direct the lower end of the shield device downwardly.

[0042] Use of the slag shield device shall now be described with reference to figures 7 to 20 of the accompanying drawings, throughout a full melting operation to produce a batch of metal, for example steel.

[0043] Figure 7 herein shows a first stage of insertion of a slag shield device into a vertically oriented tap hole of a converter, with the converter in a 90° tilted orientation. At the start of a melting operation for producing steel or other similar metal, an empty converter vessel is tilted, such that the upper open end of the vessel is presented substantially vertically, allowing access to the interior of the vessel by a robotic arm 700 located adjacent and outside the converter. Such machines are already known in the art, for introducing refractory darts into a converter.

[0044] With the converter in a substantially horizontal attitude and the tap hole 701 in a substantially upright attitude, the robotic arm is controlled automatically or remotely to locate the slag shield device with the retaining means end of the device positioned immediately adjacent the tap hole at the end of the hole, which opens into the interior of the converter. The robotic arm is manipulated to insert the retaining means end of the slag shield device into the open tap hole, so that the end of the slag shield enters the tap channel. The slag shield can then be either released to fall under its own weight, or pushed down towards the converter wall to insert the slag shield device into the tap hole.

[0045] Figure 8 herein shows the slag shield device fitted into a tap hole of a converter, with the converter in a 90° tilted orientation. When placed in the tap hole, a portion of the rod 400 protrudes into the vessel interior. The shield or cover plate portion 403 extends outwardly either side of the open end of the tap hole, in contact with the refractory material of the vessel lining, covering the opening of the tap hole. The frusto-conical shaped member underneath the cover plate or shield portion 403 helps the device locate centrally and coaxially within the tap hole. The lower end of the slag shield device is retained within the tap hole, by virtue of the barbs of the retaining means, which may be bendable when the slag shield device is dropped or pushed into the tap hole, and which contact the walls of the tap hole. This enables the device to move in one direction along the channel of the tap hole, but to encounter resistance in the opposite direction by engaging the walls of the tap hole channel, so that the slag shield device does not fall out of the tap hole once in situ in the tap hole. The length, dimensions, and resilience of the barbs may be selected to suit the internal diameter of the tap hole. In various embodiments, the radial distance between opposite barbs may be designed to be slightly less than or slightly greater than the internal diameter of the tap hole, to provide the optimum amount of retention of the slag shield device in the tap hole once fitted. Similarly, the springiness or resilience of the barbs may be selected to optimise the amount of tension on the barbs when within the tap hole.

[0046] Figure 9 herein shows a modification to the first slag shield device in which the frusto-conical funnel shaped plate 407 can slide over a limited extent of travel axially along a main length axis of the elongate shaft, and allowing the annular or circular plate 406 freedom of movement to adopt a variety of tilted positions transverse to the main axial direction of the elongate shaft, thereby allowing the flat circular or annular plate 406 to adopt a position where it is flush against a surface of the refractory lining of the converter inside the vessel of the converter.

[0047] The frusto-conical funnel shaped portion 407 has a circular central aperture located at its apex, which has a dimension slightly larger than the outer dimension of the elongate shaft, thereby allowing the funnel shaped portion to move both axially along the shaft, and angularly so that the direction of the main central axis of the frusto-conical funnel shaped portion can move relative to a direction parallel to the main central axis of the elongate shaft. Movement along the axial direction of the shaft is limited by a lower stop member 408 and an upper stop member 409, which are fixed to the elongate shaft, such that the apex end of the frusto-conical portion is restricted in movement between the upper and lower stop members. The stop members may comprise annular rings welded to the elongate shaft, bolts extending transversely through the shaft, or each stop member may simply comprise a single blob of weld.

[0048] Referring to figure 10 herein, there is illustrated schematically in cutaway view the modified first slag shield device located in situ in a tap hole, where the main length of the tap hole is not perpendicular to the surface of the refractory material surrounding the tap hole. In this case, the modified first slag shield device adapts to the angle between the surface of the refractory material and the main length axis of the tap hole by the circular or annular shield device tilting away from the perpendicular relative to the main length axis of the elongate shaft. As the elongate shaft drops into the tap hole, the shaft may move axially relative to the open aperture in the apex end of the frusto-conical portion.

[0049] Figure 11 herein shows a converter having a fitted slag shield device in an orientation in which the converter is charged with raw materials for making steel. The converter is tilted such that the tap hole is above the chamber inside the converter. The slag shield device is retained within the tap hole by the retaining means, which prevent the slag shield device falling out of the downwardly facing channel of the tap hole under gravity. The converter is charged by introducing scrap metal and / or molten iron into the converter through the open mouth of the converter. Since the tap hole and slag shield is on the upper roof of the converter with the converter tilted in this orientation, the slag shield device is out of the way of the materials being loaded into the converter. The protruding first end of the elongate shaft of the slag shield device is out of the way of the ladle, and the path of the scrap metal being introduced.

[0050] Figure 12 herein shows the converter in an upright orientation for blowing using an oxygen lance inserted into the upright open end of the converter in order to blow oxygen into the converter. This oxidises carbon and turns the metal into steel. The oxygen raises the temperature in the molten metal from 1400°C -1500°C to nearer 1700°C. In this orientation, metal is heated into a molten mass at the bottom of the vessel chamber, and slag appears on the surface of the molten metal. The slag shield and tap hole are located above the layer of molten metal and above the layer of slag which floats on top of the molten metal.

[0051] Figure 13 herein shows the converter in a tilted orientation during a turning down operation. In the turning down operation, the vessel is tilted so that the molten steel lays on the same side of the converter as the tap hole. At this stage shown in figure 13, the slag shield and the opening to the tap hole still lies above the layer of molten steel, and above the slag layer which floats on top of the molten steel.

[0052] Figure 14 herein shows the converter during a turning down operation, in which the slag shield and tap hole of the converter are covered by molten metal. In this position, the converter is almost horizontal with the open end of the converter being presented upright or substantially vertical. The slag shield and the internal facing aperture of the tap hole are now within the mass of molten steel. During tilting of the converter from the position shown in figure 13 to the position shown in figure 14, the layer of slag which floats on top of the molten steel passes over the slag shield. The slag shield functions to stop any slag passing into the tap hole during turning down.

[0053] Figure 15 herein shows a tapping operation of the converter, with the converter in a substantially horizontally tilted orientation. Leaving the converter in the orientation as shown in figure 15, with the slag shield device and tap hole underneath the slag layer and in contact with the molten steel, the slag shield device itself starts to melt and disintegrate, and once sufficiently melted, the slag shield washes away and the interior channel of the tap hole becomes unblocked, and the molten metal starts to flow through the tap hole. Once the slag shield device has washed away, the molten steel flows through the tap hole, into a ladle placed there to catch the molten metal. The slag shield device itself is washed away through the tap hole.

[0054] The thickness of the shield plate 403 and / or the material composition of the slag shield device is designed so that the shield plate survives immersion in the hot molten steel long enough for the slag layer to travel over the end of the tap hole without slag draining through the tap hole, thereby performing the equivalent function of a prior art pre-tap plug.

[0055] Melting and disintegration of the slag shield device, and subsequent opening of the tap hole requires no intervention from operators, and there is no need for human operatives to approach the side of the converter, which can be at temperatures in the range up to 1700° C, in order to unblock the tap hole and commence tapping. The human operators simply have to wait until the slag shield device melts and washes away, and tapping starts automatically. Since the tap shield device is itself made of metal, e.g. steel, the initial flow of molten metal includes the metal of the melted slag shield device itself.

[0056] Figure 16 herein shows a stage of a metal pouring operation. In order to stop the flow of molten metal before any slag can pass through the tap hole, a known refractory tap hole closure device or "slag stopper" is inserted into the converter interior using a known slag stopper placement machine, and is dropped on top of the slag layer at a position above the interior aperture of the tap hole, so that its lower end locates in the tap hole. Known slag stoppers can include a variety of types such as refractory darts, spherical balls, or other shapes. In the case of a known dart, this comprises a frusto-conical portion of dimension larger than the diameter of the tap hole, so that as the conical portion submerges under the slag layer, due to its higher density, it acts as a plug to block the interior aperture of the tap hole before any slag can flow through the tap hole. Such tap hole closure devices are known in the art, for example in GB 2,236,837, GB 2,377,747 B and EP 0,605,560 B1. The tap hole closure device (dart) is inserted using a robotic arm of a dart placing machine, as is known in the art. The dart is introduced to stop vortex slag carryover and to stop final carryover through the tap hole.

[0057] Figure 17 herein shows a final stage of draining of steel from the converter. There is shown the plug component of the dart tap hole closure device above the slag layer, ready to block the tap hole as soon as the remaining amount of steel has drained through the tap hole. The dart self-locates at the tap hole due to the vortex in the molten steel.

[0058] Figure 18 herein shows the converter at the end of the metal pouring stage, with the converter vessel rotated back to a vertical orientation.

Between the final draining of figure 17, and the position shown in figure 18, the dart dislodges itself under gravity as the vessel is rotated. A residual amount of slag, plus the tap hole closure dart remain in the base of the upright vessel.

[0059] Figure 19 herein shows an inversion of the converter, for removal of residual slag and the refractory dart, which are dumped out of the end of the inverted open converter by rotation of the converter. After dumping any residual slag and the dart, the converter is rotated around again for checking that the tap hole is clear.

[0060] Figure 20 herein illustrates schematically a human operative visually checking for clearance of a tap hole, with the converter vessel in a tilted orientation, ready to start a subsequent batch of metal production. At this stage, the converter is still at high temperature, although all molten metal and slag have been emptied from the converter. Provided the tap hole is visually clear, the converter is ready for a further batch of metal production. This stage may be automated by providing a camera to view the tap hole remotely, rather than have a human operator looking through the tap hole to check if it is clear.

[0061] The converter is tilted into a position with its main axis horizontal, so that a new slag shield can be inserted into the tap hole.

[0062] Figure 21 herein illustrates schematically the converter vessel in a tilted substantially horizontal position, in which a further slag shield device is inserted into the tap hole using a mechanical robotic arm, as previously described herein, to commence a further batch process of steelmaking. As described previously, the mechanical robotic arm of a known dart placement machine holds the slag shield device above the internal open aperture of the tap hole, and locates the lower end of the slag shield device in the end of the tap hole. The arm drops or places the device into the channel and the slag shield device self retains in the channel of the tap hole, by virtue of the retention means at the end of the elongate rod 400.

[0063] Figure 22 herein shows the slag shield device inserted into a tap hole, after removal of the mechanical robotic arm, and prior to the next stage of rotating the vessel 180° and loading the converter with raw materials for metal production. The converter is then ready to commence the stages as shown in figures 11 to 20 herein including charging of the converter with scrap and/or ladle iron; heating and blowing of the scrap to form a molten mass using an oxygen lance; turning down the vessel, and waiting for the slag shield device to melt, so that tapping can commence; using the dart placement machine to place a dart over the tap channel to stop vortex slag carryover and to stop final carryover of slag through the tap channel, final draining of steel and termination of tapping, and final cleaning out of the converter by dumping residual slag and residual dart components from the converter prior to checking for clearance of the tap hole prior to commencing a new batch of steelmaking.

[0064] The material of the slag shield device may be selected so as to be of an identical or similar composition to the batch of metal being processed. For example if steel is being processed, the slag shield device may be fabricated from steel, so that when the device melts, the composition of molten metal initially flowing out of the tap hole is consistent with the main mass of metal being produced. In other embodiments, the slag shield device may include components made from refractory materials. For example, the shield member including shield plate 406 and frusto-conical portion 407 may be made of refractory materials, including clays or ceramic materials.

[0065] Referring to figure 23 herein, there is illustrated schematically a second embodiment slag shield device. The second embodiment device comprises an elongate shaft 2300, a shield portion 2301; a plug portion 2302; and a lower portion 2303.

[0066] The elongate shaft 2300 is typically made of a steel or iron circular cylindrical rod or the like. The shield portion 2301 comprises a circular flat plate extending transversely to the main central length axis of the shaft 2300.

[0067] The plug portion 2302 comprises a circular cylindrical mass of a deformable material 2306, for example clay having a flux component to help the clay deform, an upper plate 2304, and a lower plate 2305, the deformable clay mass being located between the upper and lower plates.

[0068] The lower portion 2303 comprises first and second steel tubes 2307, 2308 respectively; a mass of graphite material 2309 positioned within the steel tubes; and an end piece 2310.

[0069] Between the plug and the end member 2310, the two hollow circular cylindrical metal tubes, which are preferably made of steel, are filled with a heat activated expanding graphite material, which expands as the material is heated up towards the high temperatures experienced in a converter device. The lower plate 2305 of the plug portion of the device is moveable in an axial direction along a length of the elongate shaft 2300, so that as the graphite material expands, being contained within the inner and outer steel tubes 2307, 2308 respectively, the inner tube 2307 pushes the lower plate member 2305 towards the upper plate member 2304, pushing the clay material radially outwards, so that the clay material is "squashed" outwardly between the upper and lower plates 2304, 2305 respectively, and increases the diameter of the clay plug.

[0070] Referring to figure 24 herein, there is illustrated schematically the second embodiment shield device in situ, in a tap hole 2400.

[0071] Operation of the second embodiment slag shield device is as follows.

[0072] Installation and fitment of the second embodiment device is substantially as herein described with reference to figures 11 to 22 herein during a complete batch cycle for production of steel, using a robotic plug placement machine. An upper protruding part of the elongate shaft 2300 which extends from the larger diameter transverse plate 2302 is grasped by a robotic arm of the plug fitment machine 2311 as shown in figure 23. The shield device can either be positioned above the tap hole and released from the robotic arm, and drop into the tap hole by gravity, or can be placed in the tap hole using the robotic arm, using the upper end of the elongate shaft to grasp the shield device until it is in place. As with the first embodiment device herein, this can be done during batch production, when the converter is at an elevated temperature in the region of 1500°C or more.

[0073] The second shield device is positioned in the tap hole, such that the plug portion 2302 and the axially expanding portion 2303 are located within the channel of a tap hole. As the device heats up, the expanding graphite material expands. Since the material is constrained in the radial direction by the inner and outer steel tubes 2307, 2308, any expansion of the graphite material is accommodated in an axial direction along a main length of the elongate rod 2300. The upper tube 2307 which is welded or otherwise rigidly fixed to the lower plate 2305 is urged towards the first end of the shaft, and towards the larger diameter shield plate 2301, and the first plate 2304 of the plug portion, thereby pressing the block of clay material 2306 there between. The clay material expands outwardly in a radial direction, until as shown in figure 24 herein, the deformable clay material touches the inside walls of the tap hole channel, thereby lodging the second device in place in the channel. The wider shield plate 2301 rests on the surface of the refractory wall of the converter, and can accommodate sideways movement in a direction radial to the main length axis of the elongate shaft 2300, as the deformable clay plug locates itself and settles in the channel of the tap hole.

[0074] The slag shield device described herein may therefore enable a method of occluding a tap hole of a converter comprising loading a shield device onto an arm of a mechanical placement machine; manoeuvring the placement machine so as to locate the shield device adjacent said tap hole, using the placement machine to insert the shield device into a tap hole such that the retaining means retains the shield in the tap hole, and so that the shield member occludes an aperture of said tap hole. Once the shield is released from the placement device, the shield is self -retaining in the tap hole, and will not fall out of the tap hole when the converter is rotated. The shield performs its function of stopping slag passing through the tap hole, before melting and washing out of the tap hole.

[0075] In the embodiments described herein the shield plate member has been described as circular or annular with a frusto-conical portion. However in the general case, the shield plate member may be square, rectangular, elliptical or any other suitable shape when viewed in a direction along a main axial length of the shaft. In various embodiments, the shield plate may be movable enough on the shaft so that it can tilt in a range of planes transverse to a main axial direction of the elongate shaft, so as to accommodate tap hole is which are at angles other than 90° to the inwardly facing wall of the refractory material lining the furnace vessel. The shield plate member may be capable of free movement relative to the shaft, so as to align with the lining of the vessel. In some embodiments, the shield plate member may be joined to the shaft by a universal joint which allows movement of the shield plate relative to the shaft, so that a main plane of the shield plate can move in a range of transverse orientations relative to the main length of the shaft. In other embodiments, the shield plate may be loosely connected to the shaft, so that a main plane of the shield plate can adopt a range of orientations transverse to the main length of the shaft.

[0076] In use, the shield member locates over the inner aperture of the tap hole of the furnace, and stays there long enough such that a layer of slag can pass over the shield member, before the shield member is submerged in molten liquid metal, preventing the egress or evacuation of slag from the vessel. Once submerged, the shield member melts and/or disintegrates, and washes out of the tap hole, allowing the tap hole to be cleared for capping of molten metal from the furnace.

[0077] The embodiments disclosed herein may have the following advantages.

[0078] The tap hole is kept free of slag and steel during blowing of the converter.

[0079] The slag shield prevents slag entering the tap hole during the initial converter rotation/turndown.

[0080] The slag shield enables control of the initial surge of steel through the tap hole.

[0081] The slag shield may increase the usable life of the tap hole.

[0082] A significant advantage is that the slag shield device may enable a fully automated procedure where the human operators can be kept away from potentially fatally dangerous parts of the furnace, such as the outlet to the tap hole. There is no need for a human operator to approach the furnace to insert the

prior art pre-tap plug from outside the furnace.

[0083] Rather, insertion of the slag shield device can be done mechanically using an existing known dart placement machine, and removal of the slag shield device happens automatically by virtue of melting / disintegration of the device when submerged by molten metal.

Claims

Claims 1. A shield device for occluding a tap hole of a furnace, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said shield member along a length of said shaft, characterised in that said retaining means is capable of passing into said tap hole from a position inside said vessel into said tap hole, and of self -locating to hold at least a portion of said shaft in said tap hole.
2. The shield device as claimed in claim 1, further comprising a ballast member located at a distal end of said elongate shaft.
3. The shield device as claimed in any one of the preceding claims, wherein said retaining means comprises one or a plurality of arm members extending outwardly in a direction transverse to a main length axis of said elongate shaft.
4. The shield device as claimed in claim 3, wherein said one or plurality of outwardly extending arm members each have a length which allows said outwardly extending arm members to be more easily moved in a first direction along said tap channel, than in a second opposite direction along said tap channel.
5. The shield device as claimed in any one of the preceding claims, wherein said retaining means are capable of retaining said shield device in said tap channel, against the force of gravity on said shield device.
6. The shield device as claimed in any one of the preceding claims, wherein said shield member is attached to said elongate shaft at a position between a first end of said shaft and the second end of said shaft.
7. The shield device as claimed in any one of the preceding claims, wherein said shield member comprises a substantially circular plate member extending laterally outwards in a direction transverse to a main length axis of said elongate shaft.
8. The shield device as claimed in any one of the preceding claims, wherein said shield member comprises a substantially annular plate member extending around said elongate shaft.
9. The shield device as claimed in claim 8, wherein said shield member comprises a frusto-conical plate member and a circular annular plate 20 member.
10. The shield device as claimed in any one of the preceding claims, wherein said shield member is movable along a main length direction of said elongate shaft, over a limited range of movement, said range of movement limited by respective first and second stop members.
11. The shield device as claimed in any one of the preceding claims, wherein said shield member is movable such that a main plane of said shield member can adopt a range of attitudes, each being transverse to a main length axis of said elongate shaft.
12. The shield device as claimed in any one of the preceding claims, comprising a substantially frusto-conical member located around said elongate shaft, having a smaller end of said frusto-conical member facing towards said retaining means.
13. The shield device as claimed in any one of the preceding claims, which is adapted to be located in a tap hole of a furnace using a robotic arm, and which disintegrates upon contact with the molten metal so that the shield device washes away through said tap hole.
14. A method of occluding a tap channel of a furnace using a shield device, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said plate member along a length of said shaft, for retaining at least a portion of said elongate shaft in a tap channel of said furnace; said method comprising: loading said shield device onto an arm of a mechanical placement machine; manoeuvring said placement machine so as to locate said shield device adjacent said tap channel; using said placement machine to insert said shield device into said tap channel such that said retaining means retains the elongate shaft in said tap channel, and said shield member occludes an aperture of said tap channel; and releasing said shield device from said placement machine.
15. The method as claimed in claim 14, wherein said placement machine inserts said shield device into said tap channel, from a position inside said furnace.
16. A method of operation of a furnace for production of molten metal, using a shield device to occlude a tap channel of said furnace, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said plate member along a length of said shaft, for retaining at least a portion of said elongate shaft in a tap channel of said furnace; said method comprising: using a mechanical placement machine to insert said shield device into a tap channel in a wall of said furnace; rotating said furnace such that said shield device is positioned clear of a path through which material to be heated is loaded into said furnace; loading said material to be heated into said furnace; rotating said furnace such that said shield device is above said material to be heated; heating said material to produce molten metal; rotating said furnace such that said shield device is located adjacent and in contact with said molten metal, and underneath an upper surface of said molten metal; and melting said shield device such that said shield member no longer occludes said tap channel, thereby allowing molten metal to flow through said tap channel.
17. The method as claimed in claim 16, wherein said shield device is removed from the furnace via said tap channel as molten metal.
18. A shield device for occluding a tap hole of a furnace, said shield device comprising: an elongate shaft; a deformable plug member capable of deforming outwardly in a plain transverse to a main axial length direction of said elongate shaft; a heat expandable material, capable of expanding in response to increase in temperature, arranged such that said heat expandable material urges against said deformable plug material in order to urge said deformable plug material in said radially outward direction.
19. The shield device as claimed in claim 18, further comprising a telescopic chamber for containing said heat expandable material, such that as said heat expandable material expands, said telescopic chamber extends in a direction along a main axial length of said elongate shaft.
20. The slag shield device as claimed in claim 18 or 19, wherein said deformable material is located between first and second transverse plate members, such that said first plate member is fixed in relation to said elongate shaft, and said second plate member is slidable in a direction along a main length access of said elongate shaft.
21. The slag shield device as claimed in any one of claims 18 to 20, wherein said telescopic chamber comprises first and second concentric tubes, containing said heat expandable material therein.
22. A shield device for occluding a tap hole of a furnace, said shield device comprising: an elongate shaft; and a plug member connected to said elongate shaft, for blocking said tap hole; characterised in that said plug member is capable of passing into said tap hole from a position inside said vessel; and said plug member is automatically expandable in a direction transverse to a main length of said elongate shaft.
23. The shield device as claimed in claim 22, further comprising a heat expandable material operable so as to automatically expand said plug member 25 when said heat expandable material experiences temperatures above 1400°C.
24. The shield device as claimed in claim 22 or 23, further comprising wherein said plug member comprises a deformable material positioned between an upper and a lower plate member; such that when said upper and lower plate members are urged towards each other in a direction along a main axial length of said elongate shaft, said deformable material deforms outwardly in a direction transverse to said main axial length of said elongate shaft.
25. The shield device as claimed in claim 24, further comprising a heat expandable material confined within a telescopic piston arrangement, such that when said heat expandable material experiences an elevated temperature, it operates to expand within said telescopic piston arrangement, thereby pushing said piston arrangement in the length axial along a direction along a main length axis of said shaft, and thereby urging said upper and lower plates towards each other so as to compress said deformable material and core said deformable material to expand in a radially outward direction.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSClaims 1. A shield device for occluding a tap channel of a furnace prior to tapping a flow of metal from said tap channel, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said shield member along a length of said shaft, characterised by said retaining means being attached to said shaft; said retaining means being capable of being fitted into said tap channel from a position inside said furnace, without the need for access to the outside of the furnace to secure the shield device in the tap channel; and said retaining means being capable of self -locating to hold at least a portion of said shaft in said tap channel; and said retaining means being capable of retaining said shield device in said tap channel against the force of gravity.2. The shield device as claimed in claim 1, further comprising a ballast member located at a distal end of said elongate shaft. * * * * * * * * * * *3. The shield device as claimed in any one of the preceding claims, wherein said retaining means comprises one or a plurality of arm members extending outwardly in a direction transverse to a main length axis of said elongate shaft.4. The shield device as claimed in claim 3, wherein said one or plurality of outwardly extending arm members each have a length which allows said outwardly extending arm members to be more easily moved in a first direction along said tap channel, than in a second opposite direction along said tap channel.5. The shield device as claimed in any one of the preceding claims, wherein said shield member is attached to said elongate shaft at a position between a first end of said shaft and the second end of said shaft.6. The shield device as claimed in any one of the preceding claims, wherein said shield member comprises a substantially circular plate member extending laterally outwards in a direction transverse to a main length axis of said elongate shaft.* * * 20 7. The shield device as claimed in any one of the preceding claims, * * * 25 wherein said shield member comprises a substantially annular plate member extending around said elongate shaft.* * * . 30 8. The shield device as claimed in claim 8, wherein said shield * * member comprises a frusto-conical plate member and a circular annular plate member.* * * 9. The shield device as claimed in any one of the preceding claims, * * * wherein said shield member is movable along a main length direction of said elongate shaft, over a limited range of movement, said range of movement limited by respective first and second stop members.* * * * * * * * * * * ** * * * ** ** * * * 10. The shield device as claimed in any one of the preceding claims, wherein said shield member is movable such that a main plane of said shield member can adopt a range of attitudes, each being transverse to a main length axis of said elongate shaft.11. The shield device as claimed in any one of the preceding claims, comprising a substantially frusto-conical member located around said elongate shaft, having a smaller end of said frusto-conical member facing towards said retaining means.12. The shield device as claimed in any one of the preceding claims, 10 which is adapted to be located in a tap channel of a furnace using a robotic arm, and which disintegrates upon contact with the molten metal so that the shield device washes away through said tap channel.13. The shield device as claimed in any one of the preceding claims: wherein said shield device comprises: a deformable plug member capable of deforming outwardly in a plane transverse to a main axial length direction of said elongate shaft; and * * * a heat expandable material, capable of expanding in response to increase in temperature, arranged such that said heat expandable material urges against said deformable plug material in order to urge said deformable plug material in said radially outward direction. * * * 14. The shield device as claimed in claim 13 or 14, wherein said * * * * deformable material is located between first and second transverse plate * * * members, such that said first plate member is fixed in relation to said elongate shaft, and * * * * * * * * * * * * * * * * * * * * * * * * * * * said second plate member is slidable in a direction along a main length access of said elongate shaft. * ed0* * * 000 * 15. The shield device as claimed in claim 14, further comprising a telescopic chamber for containing said heat expandable material, such that as said heat expandable material expands, said telescopic chamber extends in a direction along a main axial length of said elongate shaft.16. The shield device as claimed in claim 15, wherein said telescopic chamber comprises first and second concentric tubes, containing said heat expandable material therein.17. The shield device as claimed in claim 1, comprising: a plug member connected to said elongate shaft, for blocking said tap channel, said plug member being capable of passing into said tap channel from a position inside said vessel; wherein said plug member is automatically expandable in a direction transverse to a main length of said elongate shaft. ** * 18. The shield device as claimed in claim 17, further comprising a heat * 1.41 * * *400 * *8 * * 0 Ink * * * expandable material operable so as to automatically expand said plug member.19. The shield device as claimed in claim 18 or 19, wherein said plug member comprises a deformable material positioned between an upper and a lower plate member; such that when said upper and lower plate members are urged towards each other in a direction along a main axial length of said elongate shaft, said deformable material deforms outwardly in a direction transverse to said main axial length of said elongate shaft.20. The shield device as claimed in claim 19, wherein said heat expandable material is confined within a telescopic piston arrangement, such that when said heat expandable material experiences an elevated temperature, it operates to expand within said telescopic piston arrangement, thereby pushing said piston arrangement in the length axial along a direction along a main length axis of said shaft, and thereby urging said upper and lower plates towards each other so as to compress said deformable material and cause said deformable material to expand in a radially outward direction.21. A method of occluding a tap channel of a furnace using a shield device prior to tapping metal from said tap channel, said shield device comprising: an elongate shaft; a shield member attached to said elongate shaft and extending transverse to a main length of said elongate shaft; and a retaining means spaced apart from said plate member along a length of said shaft, said retaining means being attached to said shaft; . Ile * said retaining means being capable of being fitted into said tap channel from a position inside said vessel without the need for access to the outside of the furnace to secure the shield device in the tap channel; and * . . * * * * * . * * * * . * * * said retaining means being capable of self -locating to hold at least a * * * portion of said elongate shaft in said tap channel; and * * * * * * * * * said retaining means being capable of retaining said shield device in said tap channel against the force of gravity; said method comprising: loading said shield device onto an arm of a mechanical placement machine; manoeuvring said placement machine so as to locate said shield device adjacent said tap channel; using said placement machine to insert said shield device into said tap channel such that said retaining means retains the elongate shaft in said tap channel, and said shield member occludes an aperture of said tap channel; and releasing said shield device from said placement machine.22. The method as claimed in claim 21, wherein said placement machine inserts said shield device into said tap channel, from a position inside said furnace.23. A method of operation of a furnace for production of molten metal, using a shield device to occlude a tap channel of said furnace, said shield device comprising: an elongate shaft; *** 20 a shield member attached to said elongate shaft and extending transverse * * *** * to a main length of said elongate shaft; and * * * * ** * * * **** * said shaft; ** * a retaining means spaced apart from said shield member along a length of * said retaining means being attached to said shaft; said retaining means being capable of being fitted into said tap channel from a position inside said vessel without the need for access to the outside of the furnace to secure the shield device in the tap channel; and if * . * * * ** * said retaining means being capable of self locating to hold at least a portion of said elongate shaft in a tap channel; and said retaining means being capable of retaining said shield device in said tap channel against the force of gravity; ** * said method comprising: . . * using a mechanical placement machine to insert said shield device into a tap channel in a wall of said furnace; * *** rotating said furnace such that said shield device is positioned clear of a path through which material to be heated is loaded into said furnace; loading said material to be heated into said furnace; rotating said furnace such that said shield device is above said material to be heated; heating said material to produce molten metal; rotating said furnace such that said shield device is located adjacent and in contact with said molten metal, and underneath an upper surface of said molten metal; and * * * * * * * **** melting said shield device such that said shield member no longer occludes * *** * said tap channel, thereby allowing molten metal to flow through said tap channel. * * * * * * ** * * * * The method as claimed in claim 23, wherein said shield device is washed from the furnace via said tap channel by the flow of molten metal.