GB2179573A

GB2179573A - Metal-pouring equipment modified for protective gas injection

Info

Publication number: GB2179573A
Application number: GB08620664A
Authority: GB
Inventors: Edward Alexander Campbell
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1985-08-29
Filing date: 1986-08-26
Publication date: 1987-03-11
Also published as: GB8521536D0; GB8620664D0

Abstract

A composite sliding plate/collector nozzle for a slide gate valve, has bores (10, 12) for the passage of a gas injected therein through an exposed inlet port (14), the bores having (a) outlet orifices (15) in the lower outer sidewall of the nozzle which are sited to be in sealing engagement with an associated refractory shroud tube (17), and, optionally, (b) outlet orifices (6) in the upper surface of the sliding plate which is sited to be in sealing engagement with an associated fixed plate (18). Additional outlet orifices (16) may be sited in the bottom face of the nozzle. The nozzle may be used without the associated shroud tube (17), in which case a protective gas curtain from the orifices (15, 16) surrounds the melt stream. <IMAGE>

Description

SPECIFICATION Improvements in Molten Metal Teeming Practice This invention relates to teeming practice and in particular relates to teeming molten metal through a slide gate valve mounted on the bottom of a melt-containing ladle, the valve having a 'collector' nozzle in sealing engagement with an elongated refractory tube below it. The tube, known as a shroud and which extends into the tundish in a continuous casting process, reduces the reaction of the atmosphere with the ladle stream, minimises temperature fall in the (steel) stream and generally makes the casting environment more tolerable from the presence of flying droplets etc.

A good seal, as is desired, between the collector nozzle and the shroud causes a vacuum to be created in the area of the shroud below the nozzle and the negative pressure thus created will tend to draw in gas from any atmosphere art a higher pressure. In the event therefore of a perfect seal not being obtained air will be drawn into the stream resulting in nitrogen pick up and oxidation of dissolved elements such as aluminium etc.

adversely affecting steel cleanliness. Additionally, airwill be drawn in between the fixed and sliding plates in the gate valve.

Hitherto, attempts have been made to introduce an inert gas into or around the nozzle/shroud seal see e.g. UK Patent No. 2094454 and "Metals and Minerals" May 1985 p. 292 but this former does not introduce the protective gas into the sealing faces themselves and the latter requires a separate argon line to the shroud as distinct from the slide gate assembly. Additionally a protective gas has been introduced between the fixed and sliding plates, see e.g. UK Patent No. 1472 532 but this has required a discrete connection to one of these plates for that purpose only.

It is an object of this invention to mitigate these drawbacks.

From one aspect the present invention provides a collector nozzle for a slide gate valve, the nozzle having bores for the passage of a gas injected therein through an exposed inlet port, the bores having outlet orifices in the lower outer sidewall of the nozzle which are sited to lie in sealing engagement with an associated refractory tube.

From another aspect the invention provides a composite refractory sliding plate/collector nozzle assembly for a slide gate valve, the composite body having bores for the passage of a gas injected therein through an exposed inlet port, the bores having outlet orifices in (a) and lower outer sidewall of the nozzle which are sited to be in sealing engagement with an associated refractory tube, and (b) the upper surface of the sliding plate which are sited to be in sealing engagement with an associated fixed plate.

Additionally the bores may have outlet orifices in the bottom face of the nozzle.

The outlet in the sliding plate may be into a groove formed in the upper surface of the plate extending around the central aperture through which the molten metal is teemed through the valve.

in accordance with this invention then, the slide gate valve components are designed to enable gas, that is, an inert gas (e.g. argon) to be injected into the areas where air is drawn from the surrounding atmosphere by the vacuum created. Thus, in creating an atmosphere of argon around the collector/shroud in the event of an imperfect seal argon will be drawn into the stream preferentially to the external atmosphere (air), thus avoiding or minimising any re-oxidisation in the steel stream, and likewise the same situation will apply to the sliding contact between the plates.

In order that the invention may be fully understood one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic sectional side elevation of a composite plate/collector nozzle in a slide gas valve; Figure 2 is a sectional end elevation on Figure 1; and Figure 3 is a plan view.

Referring now to the drawings, a refractory plate 1 and a refractory collector nozzle 2 are cemented within a metal case 3 to form a composite body. An aligned aperture 4 for the teeming stream extends through the body and a refractory insert 5 is mounted within this aperture at the lower end of the nozzle 2.

The upper surface of the plate has an elliptical groove 6 formed in it and two holes 8,9 are cast in the plate to align with cast-in bores 10, 11, respectively, which in turn communicate with an arcuate bore 12 and twin recesses 13 formed around the lower sidewall of the nozzle 2. Additionally, a series of holes 16 are cast into the collector nozzle communicating with the recesses 13 and which issue from the lower face of the collector around the inner periphery of the metal case. A screw-threaded nipple 14 communicates with a gas line (not shown) for injecting gas through the bores. A series of holes 15 are drilled into the lower end of the metal case 3 into the recess 13 beyond.

The associated shroud (17) and the fixed plate (18) of the gate valve are shown in Figure 1 to illustrate their relationship.

In operation, in a continuous casting process the slide gate valve is mounted on the bottom of the melt-containing ladle and the refractory shroud is mounted in sealing engagement with the collector nozzle 2 (a ring seal may be introduced at the shroud/nozzle interface--see UK Patent No.

2144662). Immediately before the gate is opened for teeming, argon is injected through the nipple 14 and this gas is forcibly ejected through the outlet orifices, i.e., via the channel 6 and the recesses 13/holes 15 and 16. Thus any vacuum which tends to be created within the shroud by the teeming process is destroyed by the argon sucked into this area and any air ingress is therefore prevented.

Although the invention has been described with reference to the particular embodiment illustrated, it will be understood that various modifications may readily be made without departing from the scope of this invention. For example, the two recesses shown are only exemplary, three could well be adopted; the particular disposition and relationship of the drilled and cast-in bores does not need to be specifically as illustrated and some of the cast bores in the refractory may alternatively be drilled.

Further, the concept of injecting an inert gas between the nozzle/shroud interface from within the nozzle, as distinct from injection through or around the shroud, may be utilised alone without the gate plate injection. The invention is moreover not restricted to metal encased refractory sets.

The invention could alternatively be adopted for conventional ingots pouring through a slide gate valve, that is, without the refractory tube (shroud), the argon ejected then acting as a shield or curtain by which the teeming stream is shielded from the surrounding atmosphere.

Claims

1. A collector nozzle for a slide gate valve, the nozzle having bores for the passage of a gas injected therein through an exposed inlet port, the bores having outlet orifices in the lower outer sidewall of the nozzle which are sited to lie in sealing engagement with an associated refractory tube.

2. A collector nozzle according to claim 1, comprising a metal clad refractory body, in which the bores couple the inlet port with a circumferential recess in the said lower outer sidewall and additionally extend through the metal cladding and communicate with the recess to complete the gas passage.

3. A collector nozzle according to claim 1 or claim 2, in which the bores additionally have outlet orifices in the bottom face of the nozzle.

4. A collector nozzle substantially as herein described and illustrated in Figure 1 and Figure 2 in the drawings.

5. A composite refractory sliding plate/collector nozzle assembly for a slide gate valve, the composite body having bores for the passage of a gas injected therein through an exposed inlet port, the bores having outlet orifices in (a) the lower outer sidewall of the nozzle which are sited to be in sealing engagement with an associated refractory tube, and (b) the upper surface of the sliding plate which are sited to be in sealing engagement with an associated fixed plate.

6. A composite plate/nozzle assembly according to claim 5, in which the outlet orifices in the upper surface of the sliding plate issue into a groove formed in said surface which extends around a central aperture through which the molten metal is discharged through the valve.

7. A composite plate/nozzle assembly according to claim 5 or claim 6 which is clad within a common metal casing extending around the outer surfaces of the refractory components.

8. A composite plate/nozzle assembly according to claim 7, comprising at least one circumferential recess in the lower outer sidewall of the refractory nozzle, the bores extending through the refractory nozzle to communicate with said recess and additionally extending through the metal cladding in alignment with said recess thereby to complete the gas passage, the outlet orifices in the lower sidewall lying in said cladding.

9. A composite plate/nozzle assembly according to claim 8, in which the bores additionally extend via the said recess to the bottom face of the nozzle.

10. A composite plate/nozzle assembly according to any one of claims 5 to 9, in which at least some of the bores are cast into the refractory components.

11. A composite plate/nozzle assembly substantially as herein described and illustrated in the drawings.