GB2311947A

GB2311947A - Sliding gate valve

Info

Publication number: GB2311947A
Application number: GB9605223A
Authority: GB
Inventors: Colin Ian Mcnair
Original assignee: Flogates Ltd
Current assignee: Flogates Ltd
Priority date: 1996-03-12
Filing date: 1996-03-12
Publication date: 1997-10-15
Also published as: GB9605223D0; WO1997033712A1; ZA972117B; AU1933597A

Abstract

A sliding gate valve having a fully open position, a shut-off position and a throttling position, the valve comprising: a fixed refractory plate having a first orifice disposed therein, a sliding refractory plate having a second, teeming orifice disposed therein, and a control system adapted to move the sliding plate in a controlled manner between the fully open position, the shut-off position and the throttling position, wherein, the shut-off position and the throttling position of the sliding plate are on opposed sides of the fully open position. An elongate refractory plate for a sliding gate valve having specified relative dimensions relative to the bore diameter is also disclosed. The sliding plate of the sliding gate valve may be biased into face to face contact with the fixed plate by biasing means.

Description

IMPROVEMENTS IN OR RELATING TO SLIDING GATE VALVES This invention relates to sliding gate valves for controlling the flow of molten metal through the tap hole of a vessel, and more particularly to a sliding gate valve having an improved performance and/or improved working lifetime.

Sliding gate valves for liquid metal-containing vessels, for example, ladles and tundishes, are well known and widely used in the steel industry. The valves typically comprise a refractory sliding gate plate having at least one teeming orifice, biased upwardly against a refractory top plate containing an orifice which communicates via a taphole with the interior of a vessel to which it is fixed. Illustrative of such valves are those disclosed in British Patents Nos 1602716, 1602717 and 2110342, the entire disclosures of which are incorporated herein by reference for all purposes.

Molten metal flow from the vessel is controlled by sliding the sliding gate plate against the top plate, usually by means of a reciprocating ram. The orifice in the fixed top plate which communicates with the interior of the vessel cooperates with the teeming orifice of the sliding gate plate when the two orifices are slid into register. In this configuration (the fully open position) fluid communication between the interior of the vessel and the teeming orifice in the sliding gate plate is established allowing molten metal to flow out of the vessel. The sliding gate plate usually bears a collector nozzle (or bushings for the attachment of a collector nozzle) to permit controlled pouring of molten metal in a compact stream.

When the teeming orifice of the sliding gate plate is slid completely out of register with the orifice in the fixed top plate (the closed position), the interface between the plates is such that molten metal should not flow between them, and in this configuration fluid communication between the taphole and the teeming orifice is shut off by the seal produced at the sliding plate/top plate interface. Shut off is necessary, for example, to prevent slag from entering a continuous casting mould, tundish, or ladle at the end of a heat.

Metal flow can therefore be turned on or off by sliding the teeming orifice in the sliding gate plate into or out of register with the orifice in the top plate, respectively. During teeming, the molten metal flow can also be throttled by bringing the sliding plate orifice partly into registry with the stationary top plate orifice, adjustment being provided by sliding the sliding gate plate to give greater or lesser metal flow (the throttling position). In this manner, the rate of flow of the metal stream issuing from the collector nozzle can be controlled.

In order to maintain the seal between the plates, the sliding plate is biased towards the fixed top plate.

The magnitude of the biasing force is determined to be a balance between being low enough so that the sliding plate can slide over the fixed plate without excessive wear, whilst being high enough to prevent molten metal ingress between the plates. Spring weakening, plate wear and other operational factors can, however, cause some plate separation to occur thereby allowing molten metal ingress between the plates.

The high temperatures, mechanical abrasion and chemical erosion to which the refractory plates are subjected also result in rapid erosion of the regions around the orifices in conventional operation, and the refractory plates accordingly need to be replaced on a frequent basis.

In steel manufacture, a significant proportion of the cost arises from time spent in maintaining and/or replacing sliding gate valve components, plus the production down-time this involves. Accordingly, the rate of replacement of sliding gate valve parts and the time used therefore must be kept to a minimum.

It is also desirable to maximize the number of heats which sliding gate valves can accommodate while minimizing down time.

The present invention seeks to provide a sliding gate valve with a relatively long working life which is suitable for applications where down time must be minimized.

Hitherto it has been customary to carry out throttling and shut off of the metal stream by moving the sliding plate to the same side of the fixed top plate orifice between heats.

In UK patent application no 9509013.0 there is described and claimed a sliding gate valve for controlling the flow of molten metal from a vessel, the valve comprising an orificed fixed plate and an orificed sliding plate slidingly mounted on a support frame, the frame being hingedly movable between an operating position where the sliding plate is in face to face contact with the fixed plate and another position moved therefrom, the sliding plate being biased into said face to face contact by spring means removable from the valve whilst the frame is in its assembled position.

In UK patent application no 9509014.8 there is described and claimed a sliding gate valve for controlling the flow of molten metal from a vessel, the valve comprising an orificed fixed plate and an orificed sliding plate slidingly mounted on a support frame, the support frame being hingedly movable between an operating position where the sliding plate is in face to face contact with the fixed plate along a contact plane and another position moved therefrom, the sliding plate being biased into said face to face contact by biasing means which exert biasing force directly onto the contact plane.

According to a first aspect of the present invention, a sliding gate valve is provided wherein the sliding plate can travel between both sides of the fixed plate orifice. This permits throttling to be carried out on one side only of the valve, leaving relatively unworn surfaces on the opposite side for shut off.

In another aspect, the invention provides a sliding gate valve wherein, in the shut off position, the area of contact of the fixed plate and sliding plate surfaces around the orifice in the fixed plate extends in all directions to a distance at least as great as the diameter of the orifice, for at least a substantial part of the service life of the valve.

In a further aspect, the present invention provides a sliding gate valve having a fully open position, a shut off (closed) position and a throttling position, the valve comprising: a fixed refractory plate having a first orifice disposed therein, a sliding refractory plate having a second, teeming orifice disposed therein, and a control system adapted to move the sliding plate in a controlled manner between the fully open position, the shut off position and the throttling position, wherein the shut off position and the throttling position of the sliding plate are on opposed sides of the fully open position.

In a still further aspect, the invention provides a method of operating a sliding gate valve, the valve comprising a fixed refractory plate having a first orifice disposed therein and a sliding refractory plate having a second, teeming orifice disposed therein, in which the sliding plate is moved between a fully open position, in which the first and second orifices are in register, a shut off (closed) position, and a throttling position, such that the shut off position and the throttling position are always on opposed sides of the fully open position.

In a yet further aspect, the invention provides a sliding gate valve having a fully open position, a shut off position and a throttling position, wherein the valve comprises: a fixed refractory plate having a first orifice disposed therein, and a sliding refractory plate having a second, teeming orifice disposed therein, at least one of the first and second orifices being asymmetrically disposed with respect to its respective plate in the direction of travel of the sliding plate so as to divide the length of the said respective plate into a greater portion and a lesser portion, and a control system adapted to move the sliding plate in a controlled manner between the fully open position, the shut off position and the throttling position, wherein the shut off position and the throttling position of the sliding plate are on opposed sides of the fully open position, and wherein the greater portion of the length of the plate with the asymmetrically disposed orifice, between the said orifice and the further end of the plate, is accommodated adjacent the shut off position side of the valve.

In still another aspect, the invention provides a refractory plate for a sliding gate valve, the plate being substantially elongate, with at least two elongate, substantially parallel sides and having an orifice with a bore diameter D disposed asymmetrically with respect to the length of the plate so as to divide the length into a greater portion and a lesser portion, the length of the greater portion, between the orifice and the further end of the plate, being at least 3.7D, and the width of the plate being at least 3D.

Preferably the sliding plate is slidably mounted on a support frame, the support frame being hingedly moveable between an operating position where the sliding plate is in face to face contact with the fixed plate and another position displaced therefrom. Embodiments of such a valve are described and claimed in UK Patent Applications Nos.9509014.8 and 9509013.0 the entire disclosures of which are incorporated herein by reference for all purposes.

In a preferred embodiment the sliding plate is biased into said face to face contact by biasing means which exert a biasing force directly onto the contact plane.

In another preferred embodiment the sliding plate is biased into said face to face contact by spring means removable from the valve whilst the frame is in its assembled position.

In another separate aspect of the invention, the biasing means are so arranged that the biasing force is applied only over the area of face to face contact of the fixed and sliding plates, whatever the position of the sliding plate. This can be achieved, for example, by the use of spring means which exerts a biasing force against a load beam which is in contact with the sliding plate only over that area of the sliding plate which is always in face to face contact with the fixed plate.

Preferably the amount of throttling is restricted to no more than 70% of the full bore (the area of the first orifice in the fixed plate). We have found that when this throttling value is exceeded, multiple impingement of the steel stream and collector bore can occur, which may produce excessive erosion, stream deflection, and break up. As an example, with a sliding gate valve in accordance with the invention having a maximum bore size of 70 mm the 70% maximum throttling restriction equates to approximately 50 mm of sliding gate stroke.

Preferably at least the sliding refractory plate of the sliding gate valve of the present invention, is provided with a teeming orifice disposed asymmetrically therein, in order to provide a greater portion of the length of the plate, between the orifice and the further end of the plate, which is available for shut off of the metal stream. It will be apparent that throttling is a procedure which is likely to be carried out throughout the teeming stage, and is therefore more likely to lead to erosion of the sliding plate than shut off, which, in normal circumstances, will be required only occasionally.

Nevertheless, a clean shut off is more difficult to achieve if the surfaces have begun to erode and are no longer in contact. It can be seen, therefore, that the sliding plate of the present invention provides a greater proportion of its length which is available for shut off, thus leading to longer life overall.

Preferably both the fixed and the sliding plates of the sliding gate valve of the invention are provided with asymmetrically disposed orifices, which can, for example, each be situated at a distance equivalent to at least 3.7D from the further end of their respective plates, where D is the maximum bore diameter of the fixed plate orifice.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying Drawings in which: Figure 1 shows a sliding plate and a fixed plate of a sliding gate valve in accordance with the invention in sectional side elevation, in the shut off, teeming (open), and throttling positions; Figure 2 shows the fixed and sliding plates of Figure 1 in the shut off, teeming (open) and throttling positions, in plan view; Figure 3 shows a sliding plate for a sliding gate valve in accordance with the invention in sectional side elevation and in plan view; Figure 4 shows a side elevational view of the fixed and sliding plates and illustrates the position of the bias springs and the load beam; and Figure 5 is a block diagram of the control system for the sliding gate valve.

Referring to the drawings, Figure 1 shows a fixed plate 1, having an asymmetrically disposed orifice 2 therein, and a sliding plate 3 having a second asymmetrically disposed teeming orifice 4 therein. In the plates 1 and 3, the orifices 2 and 4 are disposed such that the distance between the centre of the orifice and the end of the greater length of the plate, and the centre of the orifice and the end of the lesser length of the plate are in the ratio of 1.0 to 0.52. It has been found, for practical purposes, that the preferred ratio of the greater to lesser lengths of the fixed and sliding plates lies in the range of 1.0 to 0.4, to 1.0 to 0.6.

The fixed and sliding plates 1 and 3 are arranged such that the greater length of the one is adjacent to the lesser length of the other, respectively.

In Figure la, the plates are shown in the shut off (closed) position, with the orifices 2 and 4 out of register. Areas of erosion of the fixed and sliding plates are indicated at 5 and 6 respectively.

In Figure 1b the plates are shown in the teeming (fully open) position, with the orifices 2 and 4 in register.

In Figure lc, the plates are shown in the maximum throttling position. In this position it can be seen that the orifice 4 is now on the opposite side of the orifice 2 compared with the shut off position in Figure la.

The valve as illustrated has a maximum bore of 70 mm and in the maximum throttling position the second orifice 4 in the sliding plate 3 is moved out of alignment of the first orifice 2 in the fixed plate 1 by a distance of approximately 50 mm.

It will be observed that, whilst the areas 5 and 6 will eventually become eroded by continual operation in the throttling position, when the valve is moved to the shut off position (Figure la) there are always contact areas of clean refractory on the fixed and sliding plates around the orifice 2 and the eroded region 5 in every direction, indicated, for example, at 8 and 9 respectively, which are available to make a seal and prevent liquid metal egress from the valve.

It will be appreciated that, for a sliding gate valve of maximum bore diameter D, the stroke necessary to obtain maximum throttling of not more than 70%, and shut off with at least one bore diameter D of contact area between the plates around the fixed plate orifice, is at least 2.7D. In Figure la, therefore, the lengths 8 and 9 are at least equal to D.

In the throttling position it is also preferable for there to be at least one bore diameter of clean contact between the fixed and sliding plates around the orifice 2 and any eroded areas associated therewith. In Figure lc it can be seen that lengths 7 and 9 are at least equal to D.

Referring now to Figure 2, the fixed and sliding plates 1 and 2 are illustrated in plan view with the area of overlap in hatched lines.

It will be seen that in the shut off position (Figure 2a) there is a large area of overlap 20, in this case equivalent to 109.85D, giving the maximum area of sealing contact.

In the teeming position (Figure 2b) the area of overlap 21 is reduced to 73.43D.

In the throttling position the area of overlap 22 is reduced to 54.14D, and it is this area which, in accordance with a further aspect of the invention, is designated as the area over which the spring bias force is applied.

By maintaining the spring force in the hatched area 22 shown in the throttling position (Figure 2c) it will be apparent that, as the area of contact is reduced, the biasing pressure increases. This has a beneficial effect of providing the maximum biasing pressure between the plates at the maximum throttling position, when there is the smallest degree of overlap. This improves the seal between the plates and reduces the risk of liquid metal egress along the contact plane between the plates during throttling.

A further advantage of providing the bias force only over the area of overlap is that there is no overhang load which could reduce the effective sealing load and/or result in cracking of the sliding plate around the fixed plate edge contact point.

Referring now to Figure 3, there is shown an embodiment of a sliding plate in accordance with the invention, with a collector nozzle mounted thereon. The sliding plate, illustrated generally at 10, comprises a sliding refractory plate 11 provided with an erosion resistant insert 12, having a teeming orifice 13, located asymmetrically with respect to the plate 11. Mounted on the plate 11 is a collector nozzle 14 having an orifice 15 aligned with the teeming orifice 13 in the insert 12.

The plate 11 and the base of the collector nozzle 14 are surrounded by a metal gate can 16.

In the lower drawing of Figure 3 (Figure 3b) the sliding plate is shown in plan view with the shut off 17 and maximum throttling positions 18 of the orifice 13 illustrated by broken lines. The maximum throttling position is arranged such that it falls within the outer diameter of the erosion resistant insert 12. The minimum diameter of the erosion resistant insert is greater than 2.4D. The width of the sliding plate (and of the fixed plate) is such that it is at least 3D, where D is the diameter of the orifice 13. This permits the orifice 13 to be disposed such that the width of plate contact 19 on each side of the orifice is at least equal to D.

Referring now to Figure 4, the sliding plate 30 is shown supported on a load beam 31. The sliding plate 30 is biased against the fixed plate 32 by means of bias springs 33. The load beam 31 has upper bearing surfaces 34 which are in contact with the sliding plate 30. The surfaces 34 apply the biasing force from the springs to that part of the sliding gate surface corresponding to the area of overlap 22 in Figure 2c. This ensures that the maximum biasing pressure is applied between the plates at the maximum throttling position. It will also be appreciated that there is no overhang load in this situation.

Figure 5 illustrates diagrammatically the control system for the sliding gate stroke mechanism. In the operation of the valve, the action of the programmable logic controller 40 on commencing teeming is to activate a hydraulic cylinder 41, connected to a hydraulic unit 42, to move the sliding gate to the fully open position.

This position can be accurately determined, for example, using a linear transducer, or similar means, fitted to the hydraulic cylinder 41. Should the teeming rate need reducing, the sliding plate is moved over centre by the hydraulic cylinder 41 and controlled by the programmable linear controller 40, resulting in a throttling action.

In accordance with one aspect of the invention, the amount of throttling is restricted to 70% of full bore, based on a maximum bore size of 70mm. As previously stated, this 70% throttling value equates to approximately 50mm of sliding gate stroke.

Air ingress in a sliding gate system is always a problem when any degree of throttling is undertaken.

However we have found that when excessive throttling is carried out the resultant turbulence mixes the air with the steel causing them to combine and thereby downgrading the steel quality. By limiting the extent of the throttling this mixing is reduced.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A sliding gate valve having a fully open position, a shut-off position and a throttling position, the valve comprising: a fixed refractory plate having a first orifice disposed therein, a sliding refractory plate having a second, teeming orifice disposed therein, and a control system adapted to move the sliding plate in a controlled manner between the fully open position, the shut-off position and the throttling position, wherein, the shut-off position and the throttling position of the sliding plate are on opposed sides of the fully open position.

2. A sliding gate valve according to Claim 1, wherein at least one of the first and second orifices is asymmetrically disposed with respect to its respective plate in the direction of travel of the sliding plate so as to divide the length of the said respective plate into a greater portion and a lesser portion, and wherein the greater portion of the length of the plate having the asymmetrically disposed orifice, between the said orifice and the further end of the plate, is accommodated adjacent the shut-off position side of the valve.

3. A sliding gate valve according to Claim 1 or 2, wherein, in the shut-off position, the area of contact of the fixed plate and sliding plate surfaces around the first orifice in the fixed plate extends in all directions to a distance at least equal in length to the diameter of the first orifice.

4. A sliding gate valve according to Claim 2 or 3, wherein the length of the greater portion of the plate with the asymmetrically disposed orifice, between the orifice and the further end of the plate, is at least 3.7D, and the width of the plate is at least 3D, where D is the maximum bore diameter of the first and second orifices.

5. A sliding gate valve according to any of the preceding claims, which is provided with biasing means for biasing the sliding gate plate into face to face contact with the fixed plate, the biasing means being so arranged that the biasing force is applied only over the area of face to face contact of the fixed and sliding plates, whatever the position of the sliding plate, in use.

6. A sliding gave valve according to Claim 5, wherein the biasing means comprises spring means which exerts a biasing force against a load beam which is in contact with the sliding plate only over that area of the sliding plate which is always in face to face contact with the fixed plate.

7. A sliding gate valve according to any of the preceding claims, wherein at least the sliding plate is provided with a teeming orifice disposed asymmetrically therein.

8. A sliding gate valve according to any of the preceding claims, wherein both the fixed plate and the sliding plate are provided with orifices disposed asymmetrically therein.

9. A sliding gate valve according to any of the preceding claims, substantially as described with reference to and as illustrated in the accompanying Drawings.

10. A sliding gate valve substantially as hereinbefore described.

11. A method of operating a sliding gate valve, the valve comprising a fixed refractory plate having a first orifice disposed therein and a sliding refractory plate having a second, teeming orifice disposed therein, in which the sliding plate is moved between a fully open position, in which the first and second orifices are in register, a shut off position and a throttling position, such that the shut-off position and the throttling position are always on opposed sides of the fully open position.

12. A method according to Claim 11, wherein the amount of throttling is restricted to no more than 70% of the area of the first orifice in the fixed plate.

13. A method of operating a sliding gate valve according to Claim 11 or 12, wherein there is used a sliding gate valve according to any of Claims 1 to 10.

14. A method of operating a sliding gate valve substantially as hereinbefore described.

15. An elongate refractory plate for a sliding gate valve, the plate having at least two elongate substantially parallel sides and having an orifice with a bore diameter D disposed asymmetrically with respect to the length of the plate so as to divide the length into a greater portion and a lesser portion, the length of the greater portion, between the orifice and the further end of the plate, being at least 3.7D, and the width of the plate being at least 3D.

16. A refractory plate according to Claim 15, which is a sliding plate and is provided with a collector nozzle.

17. A refractory plate according to Claim 15 or 16, which is provided with an erosion resistant refractory insert.

18. A refracting plate according to Claim 17, in which the erosion resistant insert has a minimum diameter of greater than 2.4D.

19. A refractory plate according to any of Claims 15 to 18, substantially as hereinbefore described with reference to and as illustrated in the accompanying Drawings.

20. A refractory plate for a sliding gate valve substantially as hereinbefore described.

21. A sliding gate valve wherein the sliding plate can travel between both sides of the fixed plate orifice.

22. A sliding gate valve wherein, in the shut-off position, the area of contact of the fixed plate and sliding plate surfaces around the orifice in the fixed plate extends in all directions to a distance at least as great as the diameter of the orifice, for at least a substantial part of the service life of the valve.

23. A sliding gate valve wherein the sliding plate is biased into face to face contact with the fixed plate by biasing means, the biasing means being so arranged that the biasing force is applied only over the area of face to face contact of the fixed and sliding plates, whatever the position of the sliding plate.