GB2094454A - Improvements in the pouring of molten metals - Google Patents

Abstract

In submerged teeming operations the extended pouring tube (17) which receives molten metal from a vessel via a nozzle (12) has gas admitted thereto for protecting it against molten metal attack. A union block (18) is sandwiched between the nozzle (12) and pouring tube (17), block (18) being surrounded by a metal jacket (20) spaced therefrom to form a gas manifold (21) to be fed with gas via a gas supply pipe (24). Gas admitted to the manifold (21) is ejected, around the lower end of the union block (18), by a surrounding annular orifice (28) into the pouring tube (17) and flows downwardly along the wall (16) thereof as a protective gas film. <IMAGE>

Description

SPECIFICATION Improvements in the pouring of molten metals The present invention relates to improvements in the pouring of molten metals.

It is often desirable during teeming to isolate as far as possible, molten metal streams from the ambient air to avoid excessive oxidation. In continuous casting, for example, submerged pouring techniques may be adopted. Thus, the molten metal from the teeming ladle may be conducted into the tundish, and/or from the tundish into the mould via an elongated pouring tube which has its lower end submerged beneath the melt surface in the tundish and/or the mould. In common with other tubes or nozzles through which the teeming metal passes, as well as gate valve plates, the elongated pouring tubes are made from refractory materials. Such components are costly in terms of the refractory materials and energy requirements needed to produce them, and attention is turning to production techniques which minimise or avoid the need for high firing temperatures.In the result, there has been a tendency to try material of rather low refractoriness, including silica, and special concretes. A drawback of such materials is that the molten metal erodes or chemically attacks them quite quickly, and if they are of high thermal conductivity impurities from the molten metal may build up thereon. Accretion of solids may become quite serious, depending on the metal or alloy to be teemed and the length of the pouring tube. in either event, the useful life of refractory items is undesirably limited.

Gas injection has been proposed as a means of protecting or isolating refractories from molten metal. What has hitherto been sought is a protective gas film between the metal stream and the bore of a nozzle. The present invention aimed to develop such a film in the elongated pouring tube to extend its useful life, and the invention provides a convenient assembly for introducing the gas. The gas will usually be inert, for example argon.

The invention is particularly advantageous for protecting pouring tube of low refractoriness, but is equally useful in protecting higher fired refractories in view of their greater costs and their own lack of immunity from molten metal attack.

According to the present invention, there is provided apparatus for use in the submerged pouring of molten metals, comprising a nozzle, an elongated submerged pouring tube downstream of the nozzle and an orificed refractory block forming a union therebetween, the union block having an annular manifold space therein and a gas supply pipe communicating therewith, the union block further having a gas discharge orifice or orifices at its downstream end for discharging gas fed into the manifold space, the union block forming a gas-tight joint with the upstream end of the pouring tube, and its orifice or orifices being arranged in use to eject gas in a downstream direction substantially along the inner wall of the pouring tube.

The union block can have a metal jacket and its manifold space, orifice or orifices and gas passage means connecting the manifold with the latter, are all located within the refractory mass of said block.

The refractory mass conveniently is a cast concrete material.

Alternativeiy, the union block has a surrounding metal jacket which is spaced therefrom to define the annular manifold with the block.

The union block and its jacket (where provided) can taper inwardly in the downstream direction, for gas-tight reception in a flared opening at the upstream end of the pouring tube.

In a preferred embodiment, the manifoldproviding metal jacket defines a single ringshaped orifice and the manifold space contains a filling of gas-porous material, which may comprise a fibrous ceramic substance or other porous packing.

The nozzle and union block may interfit by way of a stepped joint, when advantageously means will be provided to convey gas fed by the gas supply pipe to the region around the joint. By this means it is possible to minimise the sucking in of air through the joint.

Molten metal attack of the nozzle is often severe, especially if a flow control slide gate valve atop the nozzle is in a throttling setting. To lessen attack, the nozzle is often made of or lined with a costly highly refractory material such as fired zirconia. By means of the union block, the length of the costly nozzle may be minimised, the union block being a readily-replaceable nozzle extension.

The block can be made of inexpensive refractory material.

For some applications, the separate union block may be unnecessary, when the nozzle component itself will be arranged to receive and eject gas into the pouring tube.

Accordingly, the present invention further provides apparatus.for use in submerged pouring of molten metals, comprising a nozzle component leading downstream to an elongated submerged pouring tube, the nozzle component having, at least at its downstream end, means providing an annular manifold space, with which a gas supply pipe communicates, and a gas discharge orifice or orifices at the said end of the nozzle component, the nozzle components forming a gas-tight joint with the upstream end of the pouring tube, and its orifice or orifices being arranged to eject gas fed into the manifold space in a direction substantially along the inner wall of the pouring tube.

Most conveniently, the nozzle is attached to the downstream one of cooperating valve plates of a slide gate valve.

The invention will now be described in more detail by way of example with reference to the sole accompanying drawing, in which: Fig. 1 is a longitudinal sectional view of a nozzle and submerged pouring tube combination constituting a first embodiment of the invention, and Fig. 2 is a view similar to Fig. 1 but showing a second embodiment of the invention.

The embodiment illustrated in Fig. 1 will now be described.

The pouring apparatus 10 is shown attached to the lowermost or downstream valve plate 11 of a sliding gate valve. In a two plate valve, plate 11 is of course the sliding gate. The various forms of sliding gate valve are by now well known and no description thereof need be given here.

Apparatus 10 includes a nozzle 12 having its bore 14 in registry with the plate orifice 1 5. Nozzle bore 14 leads downstream to the passage 16 of an elongated submerged pouring tube 17..

An orificed union block 18 is sandwiched between nozzle 12 and pouring tube 1 7. Orifice 1 9 of the block 1 8 is coaxial with bore 14 and passage 16.

Nozzle 12, union block 1 8 and pouring tube 17 are made from refractory materials and at least the nozzle and union block are encased in metal jackets. Desirably the pouring tube 17 is metal jacketed too.

The metal jacket 20 encasing the union block 18 is spaced therefrom to define a surrounding annular manifold space 21. The spaced relationship between jacket 20 and union block 18 is maintained by a ring of cement 22 uniting the two around the top or upstream end of the union block. To feed gas to the manifold space 21, there is a gas supply pipe 24 which is borne by an attachment ring 25 disposed outwardly of the jacket 20. As will be described, the attachment ring secures the union block 18 & to the downstream end of the nozzle 12. In use, gas enters the manifold space 21 through a plurality of circumferentially-spaced openings 26 distributed about the jacket 20.

At the downstream end, the jacket 20 and union block 18 defines an annular gas-ejecting orifice 28. If desired, the jacket 20 could have internal ribs or other inward projections to maintain its lower end uniformly spaced from the union block. Such ribs or projections can result in the formation of a ring of gas-ejecting orifices.

The manifold space 21 can contain a filling of gas-porous material 29 such as a fibrous ceramic substance or porous cementitious mass. The filling will aid uniform distribution of gas to the orifices 28.

The union block 18 and its jacket 20 form a gas tight joint with the upstream end of the passage 1 6 of the pouring tube 1 7. Gas tightness is most easily attained if the block 18 and jacket 20 are frustoconically tapered at their lower ends, and the pouring tube 1 7 has a matingly-flared mouth opening or 30 at its upstream end. In use, it is likely that the tube 1 6 will fill substantially completely with molten metal, which may cause the jacket 20 to fuse to the mouth 30 and thereby ensure gas tightness.

When gas is admitted under pressure to the manifold space 21, it is ejected from the orifice(s) 28 in a direction which is along the wall of the passage 1 6. The gas tends to hug the wall and provides a protective film between the wall and metal flowing down the passage 1 6.

The joint 31 between the nozzle 12 and the union block 18 is of conventional stepped form, Air tends to be aspirated through such a joint and to mitigate this means is provided to convey gas fed through the pipe 24 to the joint 31. The said means comprises an annular space 32 between metal jacket 20 and an encircling downward extension 34 of the metal jacket 35 of the nozzle 12. The annular space 32 encircles the joint 31 and some of the gas fed by the pipe 24 flows into this space, the remainder flowing into manifold space 21. Gas in use traversing the joint 31 may provide a protective film about the wall of orifice 1 9.

The downward extension 34 is welded to jacket 35 and serves a second purpose which is in securing the union block 1 8 to the nozzle 12.

Thus, extension 34 is one haff of a coupling means, the other half of which is the attachment ring 25. The latter has an inturned lip 36 which engages an external shoulder 37 around the union block. Coupling of the parts 34 and 25 may rely on screw threads or preferably a bayonet connection.

As drawn, a substantial clearance appears between the attachment ring 25 and the extension 34. In practice, this clearance will be small and leakage of gas fed into the region between the ring 25 and jacket 20 will be minimal. A sealant could be utilised to prevent leakage via the said clearance.

Tube 17 will be supported beneath the nozzle in any convenient manner.

If desired, apparatus 1 0 can be associated with a stopper rod flow control system instead of a sliding gate valve, and in some tundish teeming operations need not be associated with any flow control system.

The second embodiment 40 shown in Fig. 2 differs from the first embodiment as follows.

Instead of coacting with its metal jacket 41 to define the manifold space, in this instance the refractory body 42 of the union block 43 has the manifold space 45 formed within its mass by means of an internal, encircling passage. Gas is fed to the manifold space 45 by a gas inlet pipe connection 46. The union block 43 has a plurality of discharge orifices 48 at its lower end and a corresponding number of passages 49 for conveying gas from the manifold to the orifices.

There can be eight such orifices 48 and passages 49.

The refractory body 42 can be a cast concrete shape, as shown at the right of the sectioned arrangement seen in Fig. 2. Alternatively, the refractory body can be a composite structure as shown at the left in Fig. 2. The composite comprises an inner refractory lining tube 50 embedded in a cast concrete outer portion 51. The composite structure enables the block 42 to be tailored to suit the teeming conditions. Thus, this structure may be preferred if aggresive metals or alloys are to be teemed through the apparatus, when a suitable erosion-resistant liner e.g. of zirconia may be employed.

In the second embodiment, the union block 42 is firmly and gas-tightly seated in the flared opening 30 of the pouring tube 17. The construction is again such that gas fed into the manifold 45 is ejected downwardly substantially along the inner wall of the pouring tube.

The union block 42 can be sealed to the bottom end of the nozzle 12 by cement or mastic sealants to prevent entry of air. The union block 42 has its upper surface shaped to interfit with the nozzle 12 by way of a stepped joint.

As shown, the metal jackets 35 and 41 are crimped together; they could also be welded or brazed together. Jacket 35 could be extended downwardly in the manner shown in Fig. 1 , when it could form one part of a demountable coupling (e.g. a bayonet coupling) for securing the union block to the nozzle 1 2. A ring element engageable with the tapered outer surface of the union block will form the other part of the coupling.

For some applications it may be preferred to integrate the nozzle 12 and union block 18or42 into a unitary nozzle component. This component is provided with the manifold space and orifices at its downstream end. Foilowing the teaching illustrated in Figs. 1 and 2, the manifold space of such a unitary nozzle component can be formed between the refractory body thereof and an encircling metal jacket (Fig. 1) or within the refractory body (Fig. 2).

Claims (14)

1. Apparatus for use in the submerged pouring of molten metals, comprising a nozzle, an elongated submerged pouring tube downstream of the nozzle and an orificed refractory block forming a union therebetween, the union block having an annular manifold space therein and a gas supply pipe communicating therewith, the union block further having a gas discharge orifice or orifices at its downstream end for discharging gas fed into the manifold space, the union block forming a gas-tight joint with the upstream end of the pouring tube, and its orifice or orifices being arranged in use to eject gas in a downstream direction substantially along the inner wall of the pouring tube.

2. Apparatus according to claim 1, wherein the union block tapers inwardly in the downstream direction, and its downstream end is gas-tightly received in a flared opening at the upstream end of the pouring tube.

3. Apparatus according to claim 1 or claim 2, wherein the union block has a metal jacket and its manifold space, orifice or orifices, and gas passage means connecting the manifold with the latter, are all located within the refractory mass of said block.

4. Apparatus according to claim 3, wherein the refractory mass comprises a cast concrete material.

5. Apparatus according to claim 3 or claim 4, wherein the nozzle is metal encased and its encasement is crimped, welded or brazed to the metal jacket of the union block.

6. Apparatus according to claim 1 or claim 2, wherein the union block has a surrounding metal jacket which is spaced therefrom to define the annular manifold with the block.

7. Apparatus according to claim 6, wherein the metal jacket defines a single ring-shaped orifice and the manifold space contains a filling of gasporous material.

8. Apparatus according to claim 7, wherein the said material comprises a fibrous ceramic substance.

9. Apparatus according to any of claims 1 to 8, wherein the nozzle and union block interfit by way of a stepped joint, and means is provided to convey gas fed by the said pipe to the stepped joint.

10. Apparatus according to any of claims 1 to 9 wherein an encircling, downward extension of a metal encasement of the nozzle forms one part of a coupling means with which a separate ring part coacts to secure the union block to the downstream end of the nozzle.

11. Apparatus according to claim 10, wherein the coupling means comprises a bayonet connection.

12. Apparatus for use in submerged pouring of molten metals, comprising a nozzle component leading downstream to an elongated submerged pouring tube, the nozzle component having, at least at its downstream end, means providing an annular manifold space, with which a gas supply pipe communicates, and a gas discharge orifice or orifices at the said end of the nozzle component, the nozzle component forming a gas-tight joint with the upstream end of the pouring tube, and its orifice or orifices being arranged to eject gas fed into the manifold space in a direction substantially along the inner wall of the pouring tube.

13. Apparatus according to claim 12, wherein the nozzle component tapers inwardly in the downstream direction, and is gas-tightly received in a flared opening at the upstream end of the pouring tube.

14. Apparatus according to claim 12 or claim 13, wherein the nozzle component comprises a metal-jacketed orificed refractory member, the metal jacket being spaced from the refractory member to provide the manifold space.

1 5. Apparatus according to any one of the preceding claims, wherein the nozzle component is attached to the downstream one of the cooperating valve plates of a sliding gate valve.

1 6. Apparatus for use in the submerged pouring of molten metals, substantially as herein described with reference to and as shown in Fig. 1 or Fig. 2 of the accompanying drawings.