GB2065850A - Sliding gate valve refractories - Google Patents

Abstract

In controlled molten metal pouring via a sliding gate valve, the metal is teemed through a collector nozzle (32) integrally mounted on a valve plate (31). The nozzle has an expendable discharge tip (33) of lower thermal conductivity mounted internally therein, a shoulder (42) extending around the tip being seated on an internal ledge (40) in the nozzle. The tip (33) may be surmounted by a nozzle liner sleeve (44) which isolates the nozzle upstream of the tip from contact with the metal. A frangible cement secures the nozzle (32), liner (44) and tip (33) together. When the top and/or the liner have worn undesirably, they are forced upwardly through the nozzle and valve plate - rupturing the cement - and are replaced via the valve plate. The internal mounting of the nozzle tip ensures that molten metal cannot leak through the nozzle-tip joint. <IMAGE>

Description

SPECIFICATION Sliding gate valve refractories The present invention relates to sliding gate valve refractories.

In the controlled pouring of molten metals, e.g.

steel, using sliding gate valves, it is common to teem through a "collector" nozzle. Such a nozzle is a refractory tube integrally mounted on and dependent from a valve plate; in the case of a twoplate valve this is the sliding plate or gate. The purpose of a collector nozzle is to produce a welldefined stream of metal as it exits the valve into a receiver vessel.

Since molten metal streams are extremely erosive, collector nozzles are commonly made from chemically and erosion-resistant refractories such as high-alumina refractories. With such refractories, molten metal tends to freeze thereon, especially in the region of the nozzle exit. Frozen droplets can adversely affect the quality of the metal stream exiting from the collector nozzle.

Even if erosion-resistant refractories are employed, the nozzle exit of a collector nozzle is still vulnerable to erosion. An eroded nozzle exit tends to encourage a flaring stream and hence also adversely affects stream quality.

Metal solidification and/or exit erosion can render collector nozzles prematurely unserviceable.

Since the most vulnerable region of a collector nozzle is adjacent its exit, it has been proposed to furnish the collector nozzle with a separate exit tip which is replaced when it has become defective.

Such an exit tip is undermounted, in abutment with the downstream or bottom end of the collector noule, using interfitting clamping elements. A problem has been encountered with this arrangement in that molten metal may break out through the junction between the nozzle and the tip. Not only could break out be dangerous, it could also result in the clamping elements being non-releasably welded together, and in damage to parts of the sliding gate valve. Repair may well be impossible and hence costly parts may have to be scrapped.

The invention aims to provide, inter alia, an arrangement in which the foregoing break out problem is avoided.

Accordingly, the present invention provides a refractory member, for a sliding gate valve for controlling molten metal flow, which comprises a refractory collector nozzle furnished with a terminal discharge tip, together defining a flow passage, the tip being an expendable, replaceable refractory item, lower in thermal conductivity than the collector nozzle, which tip is positioned within a downstream end portion of the nozzle and protrudes outwardly from the downstream end portion, the nozzle having an internal, inwardlyextending ledge in its downstream end portion and the tip having a peripheral shoulder seated on the ledge whereby installation and removal of the tip is via the upstream end of the nozzle.

Break out is effectively impossible with the internally-disposed tip seating. Since stream quality may degrade somewhat in the course of a teem, through metal build up or erosion, the tip protrudes outwardly from the downstream end of the nozzle so that any flaring of the stream can occur out of harm's way downstream of the valve parts. The protruding tip takes the brunt of knocks e.g. when, as is commonplace, the user drops the refractory assembly on the foundry floor at those times when tip replacement for instance becomes necessary. Hitherto such handling has resulted in irreparable damage to otherwise reusable collector nozzles. The protruding tip offers advantageous protection to the nozzle.

Advantageously, the nozzle has an internal, replaceable tubular refractory liner to prevent molten metal from contacting the material of which the nozzle is made. The main body of the nozzle can be made from an inexpensive, low duty refractory while the liner is made from a more expensive, high duty refractory, thereby minimising the material costs.

If desired for special purposes, the tip can be a composite body having inner and outer portions made from different refractory formulations.

A metal jacket can encase at least part of the tip to reinforce the latter.

The invention embraces a two or three plate valve provided with a refractory member as defined hereinbefore.

The present invention will now be described in more detail by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a partial cross-sectional view through a ladle having a sliding gate valve, and Figs. 2 to 6 are similar cross-sectional views through five embodiments of the invention.

The ladle 10 shown in part in Fig. 1 is a bottompour vessel having a well 11 and an inner nozzle 12 through which molten steel in the ladle 10 can flow. Metal flow is controlled by a known type of sliding-gate valve 13. The valve has a stationary top plate 14 mounted on a valve body 1 5 which is secured to the underside of the ladle. An orifice 1 6 in the top plate 14 is in registry with the lower end of the bore of inner nozzle 12.

Within the valve body 1 5 is a reciprocal slide plate 20 which is slidable to and fro under the top plate 14 by actuation of a push/pull rod 21. The push/pull rod 21 is movable by a hydraulic actuator, not shown. The slide plate 20 is biased into face-to-face engagement with the underside of the top plate 14 by a plurality of springs 22. The slide plate is apertured and includes a.depending collector nozzle 23, which projects away from the underside or non-sliding surface of the plate 20; the illustrated nozzle is conventionai and, in practising this invention, is substituted for by the nozzles shown in Figs. 2 to 6 to be described hereafter.

The parts of the valve 1 3 which come into contact with the molten steel, namely the top plate 14, the slide plate 20 and the collector nozzle 23, are made from refractory materials. A high density alumina refractory containing 8590% Awl203 is suitable for the top plate 14 and for the upper portion 24 of the slide plate 20, the latter portion being in sliding engagement with the top plate 14.

it will be understood that the valve 13 is shown closed in Figure 1, the passage 25 through the slide plate 14 and collector nozzle 23 being out of registry with the orifice 1 6 of the top plate. The valve is fully open when the passage 25 is moved into exact registry with the orifice 1 6. The slide plate 20 serves to meter the flow of molten steel when it is in an intermediate position partially covering the orifice 16.

Reference is now made to Figs. 2 to 6 of the drawings. The same reference numbers are used throughout these Figures to denote the same or equivalent parts.

In accordance with the invention, the refractory members 30 are all composite articles each including a valve plate 31, a collector nozzle 32 and a discharge tip 33. The composite articles will all perform the roles of slide plate 20 and nozzle 23 in the valve 13 of Fig. 1. The composite articles could of course be used in a three plate valve, in which case valve plates 31 will be stationary. In such a valve, the slide plate will move in a space between the plate 31 and a stationary top plate.

Following common practice, the plate 31 and the upstream end of nozzle 32 in each embodiment are shaped to form an interfitting stepped joint 34 consisting of a socket 36 and spigot 37, the former being provided in the nozzle.

The discharge tip 33 is cemented into the nozzle 32 using a weak or frangible cement (not shown) to enable the tip to be separated from the nozzle, and projects downwardly, terminating beneath the bottom end of the collector nozzle 32.

In each of the embodiments shown in Figs. 2 to 6, the collector nozzle 32 has a stepped inner wall 38. Towards the lower, discharge end of the nozzle 32, wall 38 forms an inwardly-directly encircling step or ledge 40 which as shown is perpendicular to the flow axis of the nozzle.

The discharge tips 33 are all located within the downstream end portions of their respective nozzles and are seated on the ledges 40. Each discharge tip 33 is a tubular element having an enlargement at its upstream end, and is snugly received in its nozzle 32. The enlargement 41 forms a radia lly-outwardly-projecting, peripheral shoulder 42 which seats on the ledge 40. In all but the embodiment of Fig. 6, the shoulders 42 are coplanar with the ledges 40. In Fig. 6, however, the shoulder 42 is arcuate.

The ledges 40 need not be perpendicular to the nozzle flow axes. Thus, they could converge downwardly and the shoulders 42 could be shaped to match.

In the embodiments shown in Figs. 2 and 6, molten metal can contact the nozzle inner wall 38 upstream of the tips 33. Such contact may be undesirable, in which case a tubular liner will be provided to isolate wall 38 from the metal. The liner will be cemented in place by a weak, frangible cement for ease of replacement.

Exemplary lined structures are shown in Figs. 3 to 5.

The liner 44 in Fig. 3 has its bottom end received in an annular recess formed by a peripheral rebate 46 in the tip enlargement 41 and the adjacent wall 38. The liner in Fig. 4 however merely abuts or rests on the tip enlargement 41. In Fig. 5, the tip enlargement has a smaller outside dimension compared with Figs. 3 and 4, to enable the liner 44 to fit around the enlarged upstream portion of the tip. Thus, in this embodiment both the tip shoulder 42 and the liner 44 abut the ledge 40.

Removal and replacement of the tips 33 (and the liners 44 where used) is via the upstream end of the nozzles 32, and the dimensions of the plate orifices 48 are determined accordingly. The tip and liner arrangements shown in Figs. 3 and 4 are.

particularly convenient in that both tip and liner can be detached together by pushing the tip upwardly to rupture the frangible cement bond.

Where liners 44 are used, it is preferably for them to extend through the plate orifices 48 and to terminate flush with the sliding surfaces 50 of the plates 31.

The nozzle, tip and liner can all be of different refractory formulations suiting the conditions of service including the constitution and properties of the molten metal to be teemed. The tip however is a cheaper, lower duty refractory of lower thermal conductivity than the nozzle 32 and plate 31. For example, the latter may be 8095% alumina whilst the former may be a 60% alumina fireclay.

If a liner 44 is used, it could be a high duty alumina or zirconia refractory cemented into a low duty refractory nozzle body.

The low thermal conductivity nozzle tip 33 could be a composite structure for certain purposes or to minimise material costs where adverse teeming conditions may demand the use of expensive refractory materials for contact with molten metal. Fig. 6 shows a composite tip having dissimilar inner and outer portions 51, 52. The inner portion has a tapered inlet and can be a thin shell of a highly erosion-resistant material such as zirconia.

The plate 31 and nozzle 32 is metal encased for strength, as indicated by the chain-dotted lines in Figs. 2 to 6. The replaceable tip 33 could likewise be metal encased or jacketed at least in part, e.g.

around its lower end, if so desired.

Claims (11)

1. A refractory member, for a sliding gate valve for controlling molten metal flow, which comprises a refractory collector nozzle furnished with a terminai discharge tip, together defining a flow passage, the tip being an expendable, replaceable refractory item, lower in thermal conductivity than the collector nozzle, which tip is positioned within a downstream end portion of the nozzle and protrudes outwardly from the downstream end portion, the nozzle having an internal, inwardly-extending ledge in its downstream end portion and the tip having a peripheral shoulder seated on the ledge whereby installation and removal of the tip is via the upstream end of the nozzle.

2. A refractory member according to claim 1, in which there is an internal, replaceable tubular refractory liner to prevent molten metal from contacting the material of which the nozzle is made.

3. A refractory member according to claim 2, in which the liner abuts the upstream end of the tip.

4. A refractory member according to claim 2, in which the tip has an encircling rebate in its upstream end, and the liner is seated in the rebate.

5. A refractory member according to claim 2, in which the liner fits around an upstream portion of the tip, and both the liner and the shoulder of the tip are seated on the ledge of the nozzle.

6. A refractory member according to any preceding claim, in which the collector nozzle is secured to an orificed refractory valve plate, the orifice thereof being so dimensioned as to pass the tip (and the liner if provided).

7. A refractory member according to claim 6, in which a liner is provided and it extends through the plate orifice and terminates flush with an upstream surface of the plate.

8. A refractory member according to a preceding claim, in which at least part of the tip is encased in a metal jacket.

9. A refractory member according to any preceding claim, in which the tip is a composite body having inner and outer portions made from different refractory formulations.

10. A refractory member for a sliding gate valve substantially as herein described with reference to and as shown in any of Figs. 2 to 6 of the accompanying drawings.

11. A sliding gate valve which includes a refractory member as claimed in any of the preceding claims.