WO1991010525A1

WO1991010525A1 - Metal pouring method and apparatus

Info

Publication number: WO1991010525A1
Application number: PCT/GB1991/000062
Authority: WO
Inventors: William Albert Griffiths
Original assignee: Flogates Limited
Priority date: 1990-01-16
Filing date: 1991-01-16
Publication date: 1991-07-25
Also published as: GB2246533A; CS8891A2; GB9117659D0; IE910080A1; GB2246533B; ZW291A1; YU5991A; CN1053375A; CA2034235A1; AU7178491A

Abstract

Flow of molten steel from a tundish to a continuous casting mould is controlled by a sliding gate valve (10). The gate valve comprises a stationary refractory member (14) having a metal pouring orifice (18) and a slidable refractory member (37) also having a metal pouring orifice (42) and movable between an open condition in which its orifice (42) is aligned with the orifice (18) of the stationary member, and a closed condition in which the two orifices are out of alignment. Freezing of molten steel at the sliding gate valve when it is closed is prevented by imparting an incremental stepping motion to the slidable member (37) in its closed condition.

Description

METAL POURING METHOD AND APPARATUS

In, for example the continuous casting of steel, molten metal from a ladle flows into an intermediate tundish from where it flows via a pouring tube into a continuous casting mould.

Flow from the tundish into the continuous casting mould may be controlled by a sliding gate valve, as is well known in the art.

If casting has to be interrupted, for example to change the pouring tube, the sliding gate valve is closed and there is a danger of metal freezing at the sliding gate valve, which would prevent resuming the metal flow until any frozen metal had been cleared by e.g. oxygen lancing. European Patent 66118 of Metacon AG., seeks to minimize this risk of freezing by imparting an oscillation to the slidable member of the gate valve in its closed position. This may or may not be more or less effective but in any event rapid oscillation of the slidable member can have a detrimental effect on the life of the slidable member, and adjacent refractory components and also wear on the associated mechanical components. It is an object of the invention to provide an improved method of minimizing the risk of metal freezing during the interruption of metal pouring operations.

The invention provides a method of pouring molten metal, in which flow of molten metal is controlled by a sliding gate valve, the gate valve comprising a stationary refractory member having a metal pouring orifice and a slidable refractory member also having a metal pouring orifice and movable between an open condition in which its orifice is aligned with the orifice of the stationary member, and a closed condition in which the two orifices are out of alignment; wherein when the slidable member is in its closed condition an incremental stepping motion is imparted thereto to prevent freezing of molten metal at the sliding gate valve.

The incremental motion takes place for example in steps of 0.5 to 10mm e.g., 0.5 to 2mm; the dwell time between the steps of the incremental motion is e.g. 0.5 to

2 seconds; and for example each step of the incremental motion takes place in a period not exceeding 0.5 seconds.

The speed in each step is for example 5-lOOmm per second e.g., 5-20mm per second.

The time ratio between periods of dwell and periods of incremental motion is for example 20:1 to 5:1. The invention also provides a method according to the invention, wherein in the closed condition of the sliding gate valve, the slidable member is movable between a first closed position in which the two orifices are just out of alignment and a second, terminal, closed position in which the two orifices are further out of alignment, and the slidable member moves continuously with the incremental stepping motion between the first and second positions.

The distance between the first and second positions is for example 20 to 100mm, e.g. 25 to 85mm.

The incremental stepping motion may be unidirectional from the first to the second position and from the second position back to the first position. Alternatively, however, the incremental stepping motion may take place cyclically by a plurality of steps in the general direction of motion followed by a lesser number of reverse steps.

There may be for example 2 to 7 steps in the general direction of motion alternating with 1 to 4 reverse steps; e.g. 3 or 5 steps in the general direction of motion alternating with a single reverse step, which may however be longer in distance than a forward step, but still consistent with the general direction of motion being forwards.

The invention also provides apparatus constructed and arranged to carry out a method according to the invention, and comprising a sliding gate valve which comprises; (a) a stationary refractory member having a metal pouring orifice; (b) a slidable refractory member also having a metal pouring orifice; (c) means for moving the slidable member between an open condition in which its orifice is aligned with the orifice of the stationary member, and a closed condition in which the two orifices are out of alignment; and (d) means for imparting an incremental stepping motion to the slidable member when it is in its closed condition.

There now follows a description, to be read with reference to the accompanying drawings, of a method and apparatus embodying the invention. This description is given by way of example only and not by way of limitation of the invention.

In the accompanying drawings:

Figure 1 shows a sliding gate valve in an open condition and shows diagrammatically hydraulic actuating and control equipment of the sliding gate valve; Figure 2 shows the sliding gate valve in its closed condition with its orifice just out of alignment with a stationary orifice;

Figure 3 shows the sliding gate valve also in its closed position but with its orifice further out of alignment with the stationary orifice; Figure 4 shows a graphical illustration of one mode o operation of apparatus embodying the invention; and

Figure 5 shows a graphical illustration of a alternative mode of operation. The apparatus embodying the invention comprises sliding gate valve 10 arranged to control flow of molte steel from a tundish (not shown) via a pouring tube (no shown) to a continuous casting mould, as is well known i the art. The sliding gate valve 10 comprises a stationary to plate assembly 12 which is mounted on the base of th tundish. The top plate assembly comprises a refractor plate 14, partially clad with metal at 16 and a refractor insert 17 in which is provided a stationary pouring orific 18. The gate valve 10 also comprises a complementar stationary bottom plate assembly 20 with a refractory plat 22, metal cladding 24, refractory insert 26 and stationar orifice 28. A metal clad refractory nozzle member 30 i mounted on the bottom plate assembly 20 and comprises a axial bore 32; the nozzle member 30 is arranged to exten into an upper end portion of the pouring tube (not shown)

The nozzles 18, 28 and the bore 32 are all axially aligned

A slidable plate assembly 34 is arranged for slidin movement between opposed refractory surfaces 36, 38 of th top and bottom plate assemblies 12, 20 respectively. Th slidable plate assembly 34 comprises a refractory plate 37 encased by annular metal cladding 39, and a refractory insert 40 in which is provided an orifice 42.

The apparatus embodying the invention also comprises hydraulic actuating and control equipment 44 for the sliding gate valve 10. This equipment comprises a piston 46 mounted in a cylinder 48 and connected to the slidable plate assembly 34 by a piston rod 50. The cylinder 48 is connected to hydraulic power supply means 52 by hydraulic lines 54; in the operation of the apparatus hydraulic fluid is supplied from the power supply means via the lines 54 to cause movement of the piston 46 in the cylinder 48 which is translated into movement of the slidable plate assembly 34 via the piston rod 50. The power supply means 52 is controlled by a microprocessor 55 which is in turn controlled by software 56.

In the operation of the apparatus the slidable plate assembly 34 is movable between an open condition as shown in Figure 1 in which the orifice 42 is aligned with the orifices 18 and 28 and molten metal can flow from the tundish through the orifices 18, 42, 28, and the bore 32 and then via the pouring tube to the continuous casting mould; and a closed condition as shown in Figures 2 and 3 in which the orifice 42 is out of alignment with the orifice 18, and the flow of molten metal is shut off.

Figure 2 shows a first closed position of the plate assembly 34 in which the orifice 42 is just out of alignment with the orifice 18; and Figure 3 shows a second, terminal, closed position in which the orifice 42 is further out of alignment with the orifice 18. When casting is interrupted by moving the plate assembly 34 to its closed condition the plate assembly 34 is kept moving between its first closed position and its second closed position to minimize the risk of metal freezing at the sliding gate valve, particularly but not exclusively between the surface 36 and the plate assembly 34.

To this end, the microprocessor 55 is programmed by the software 56 to impart continuously, via the hydraulic power supply means 52 and cylinder 48, an incremental stepping motion to the sliding plate assembly 34.

The incremental stepping motion for example comprises incremental steps of 1mm at a constant speed of 10mm per second (i.e. 1mm in 0.1 seconds) alternating with dwell periods of 1 second each.

The full stroke of the sliding gate valve 10 is from the axis A of the stationary orifice 18 to the axis B of the orifice 42 in the terminal position shown in Figure 3. This distance is for example 120mm for a diameter of the orifice 42 of 35mm. Thus the stroke between the first and second positions as shown in Figures 2 and 3 is 85mm but the second, terminal, position may be adjusted to reduce this stroke to less than the full stroke. Again, with bigger or smaller orifice bores the stroke may be increased or decreased accordingly. It will be realized that with a stroke of 85mm between the first and second closed positions, incremental steps of 1mm in 0.1 seconds and dwell periods of 1 second the time taken from the position of Figure 2 to that of Figure 3 is 93.5 seconds. If this period is sufficient for the pouring to be resumed the sliding plate assembly 34 can be returned rapidly to its open condition (Figure 1) from the terminal position of Figure 3, or indeed from some intermediate position if the apparatus is ready before the second position is reached. If on the other hand the apparatus is not ready for the resumption of pouring when the second position is reached then the incremental stepping motion is reversed, and it can again be reversed towards the position of Figure 3 when the position of Figure 2 is regained. Figure 4 illustrates one forward and one reverse stroke in an embodiment of the invention in which the incremental stepping motion is unidirectional from the first to the second position and from the second position back to the first position. The horizontal axis represents time and the vertical axis distance; thus an increment is represented by a vertical line of each step and a dwell by a horizontal line.

Again, however, full stroke operation may not be required and the incremental stepping motion could be confined to a region nearer to the position of Figure 2, which is where the sliding plate assembly 34 is hotter and therefore metal freezing is less likely to occur.

Figure 5 illustrates one forward and one reverse stroke in an embodiment of the invention in which the incremental stepping motion between the first and second positions takes place serially by three steps in the general direction of motion followed by one step in the reverse direction, which, as shown in Figure 5, may be twice the length (in distance) of a forward step.

Claims

Claims :

1. A method of pouring molten metal, in which flow of molten metal is controlled by a sliding gate valve, the gate valve comprising a stationary refractory member having a metal pouring orifice and a slidable refractory member also having a metal pouring orifice and movable between an open condition in which its orifice is aligned with the orifice of the stationary member, and a closed condition in which the two orifices are out of alignment; wherein when the slidable member is in its closed condition an incremental stepping motion is imparted thereto to prevent freezing of molten metal at the sliding gate valve.

2. A method according to claim 1, wherein the incremental motion takes place in steps of 0.5 to 10mm e.g. , 0.5 to 2mm.

3. A method according to claim 1 or claim 2, wherein the dwell time between the steps of the incremental motion is 0.5 to 2 seconds.

4. A method according to any one of the preceding claims, wherein each step of the incremental motion takes place in a period not exceeding 0.5 seconds.

5. A method according to any one of the preceding claims, wherein the time ratio between the periods of dwell and periods of incremental motion is 20:1 to 5:1.

6. A method according to any one of the preceding claims, wherein the speed in each step of the incremental motion is 5-lOOmm per second e.g., 5-20mm per second.

7. A method according to any one of the preceding claims, wherein in the closed condition of the sliding gate valve the slidable member is movable between a first closed position in which the two orifices are just out of alignment and a second, terminal, closed position in which the two orifices are further out of alignment, and the slidable member moves continuously with the incremental stepping motion between the first and second positions.

8. A method according to claim 7, wherein in the closed condition the slidable member performs up to only two strokes, one from the first position to the second position and the other back to the first position.

9. A method according to claim 7, wherein in the closed condition the slidable member performs more than two strokes, one from the first position to the second position and the other back to the first position.

10. A method according to any one of claims 7, 8, and 9, where the second, terminal, position is adjustable.

11. A method according to any one of claims 7 to 10, wherein the distance between the first and second positions is 20 to 100mm.

12. A method according to any one of claims 7 to 11, wherein the incremental stepping motion is unidirectional from the first to the second position and from the second position back to the first position.

13. A method according to any one of claims 7 to 11, wherein the incremental stepping motion between the first and second positions takes place cyclically by a plurality of steps in the general direction of motion followed by a lesser number of reverse steps.

14. A method according to claim 13, wherein 2 to 7 steps in the general direction of motion alternate with 1 to 4 reverse steps.

15. A method according to claim 13 or claim 14, wherein the reverse steps are longer in distance than the forward steps.

16. A method according to any one of the preceding claims, wherein the metal is steel, the sliding gate valve is mounted on a tundish and is arranged to control flow of molten steel from the tundish to a continuous casting mould.

17. Apparatus constructed and arranged to carry out a method according to any one of the preceding claims, and comprising a sliding gate valve which comprises;

(a) a stationary refractory member having a metal pouring orifice; (b) a slidable refractory member also having a metal pouring orifice;

(c) means for moving the slidable member between an open condition in which its orifice is aligned with the orifice of the stationary member, and a closed condition in which the two orifices are out of alignment; and

(d) means for imparting an incremental stepping motion to the slidable member when it is in its closed condition.

18. Apparatus according to claim 17 also comprising a tundish on which the sliding gate valve is mounted and a continuous casting mould, the sliding gate valve being arranged to control flow of molten metal from the tundish to the continuous casting mould.