WO1995004622A1

WO1995004622A1 - Method and device for unplugging a molten metal discharge port

Info

Publication number: WO1995004622A1
Application number: PCT/GB1994/001623
Authority: WO
Inventors: Simon Augustus Beale
Original assignee: Foseco International Limited
Priority date: 1993-08-05
Filing date: 1994-07-28
Publication date: 1995-02-16
Also published as: ZA945838B; AU7234394A; GB9316297D0; TW401331B

Abstract

Method and apparatus to control the opening and closing of an outlet in a molten metal handling vessel, comprising a valve (6) having relatively moveable parts (7, 9 and 8, 11) to open and close the outlet (5a), means (13) to provide gas into the outlet (5a) and gas flow measurement means (22, 23) and control means (21, 24, 25) to monitor gas flow to detect a fall in flow as pressure builds up beneath any obstruction (15) in the outlet followed by an increase in flow when the obstruction is removed, and means (LT1) to indicate this increase in flow.

Description

Method and device for unplugging a molten metal di scharge port.

This invention relates to molten metal handling vessels and is particularly concerned to provide an improvement in the opening of the bottom of the vessel, e.g. a ladle. Under the tap channel of the vessel is positioned a valve which comprises movable valve parts with flow passages which, in the valve's closed position, are displaced from each other and in the valve's open position are essentially in line with each other so that the melt can flow from the vessel through the flow passages.

Valves of this type and their peripheral equipment are called sliding gate systems and are available in several designs, including those where the valve parts trace rectilinear translatoral relative movements and those where the valve parts trace relative rotary movements. Examples of valves of this type are described in WO/ 87/ 07306 among others.

The invention will be further described below with reference to a ladle.

In the bottom of the ladle there is a tap hole which leads to the sliding gate valve system. To prevent the melt running down into the valve, solidifying and blocking the tap channel, the tap hole is usually filled with sand. In spite of this it is a critical moment during the steel manufacturing process when a tap valve on a ladle filled with molten steel is to be opened to let the steel flow down into an ingot mould or tundish. What occurs in a proportion of cases is that the steel does not run out when the valve is opened due to some form of blockage in it or in the connection with the tap hole.

The absence of spontaneous flow of the molten metal when the valve is opened results in a series of economic, as well as work environmental, related problems. Normally, the melt flows from the ladle through a protective tube, which prevents air from coming into contact with the liquid steel. When blockage of the tap channel occurs this protective tube must be removed to allow access with oxygen burning equipment to remove the obstacle. A pipe lance connected to an oxygen-line is then fed manually up into the tap channel so that the blockage can be burned out.

During this operation, molten steel and slag splashes around the tap hole and as the obstacle is removed the steel flows in a violent stream down into the tundish close to the operator. The risks with this operation are quite obvious. Apart from the costs of the oxygen lance and oxygen, this operation can incur increased consumption of the refractory material of which the tap channel is constructed. Furthermore, since it takes time to open the blocked ladle, this can result in the optimal casting speed from the tundish to the mould not being achieved, which, in its turn, can cause deteriorated steel quality. In the worst case the casting must be stopped with subsequent preparations for the start of a new cast and reheating of the steel in the ladle.

It has been proposed to blow argon gas into the tap channel just before the sliding gate is opened, by which means the channel is pressurised so that the high temperature sintered sand shell or crust or possibly the solidified steel, which covers the mouth of the tap hole, is removed.

It is however, difficult to synchronise accurately the removal of the sintered sand shell (or solidified steel) with the desired opening of the valve and it is an object of the present invention to provide a control means to overcome this difficulty.

Accordingly, in one aspect the invention provides an apparatus to control the opening and closing of an outlet in a molten metal handling vessel which includes a valve communicating with the outlet and having relatively movable valve parts, the valve parts having openings which are displaced from one another to close the valve and, hence, the outlet and which are in communication with each other and with the outlet to open the outlet, whereby the molten metal can flow out of the vessel, and means to provide gas into the outlet characterised in that there is provided a gas flow measurement means and control means to monitor the gas flow to detect a fall off in flow as gas pressure builds up in the outlet beneath an obstruction of the outlet followed by an increase in gas flow when the obstruction is removed and means to indicate the occurrence of this increase in gas flow.

In another aspect the invention provides a method of opening and closing an outlet in a molten metal handling vessel in which a valve is positioned to communicate with the outlet, the valve having relatively movable valve parts, the valve parts having openings which are displaced from one another to close the valve and, hence, the outlet and which are positioned in communication with each other and with the outlet to open the outlet, and in which gas is supplied into the outlet to break a sintered shell of particulate material formed in the outlet, whereby molten metal can flow out of the vessel, characterised in that the flow of gas into the outlet is monitored to detect first a fall off in flow as gas pressure builds up in the outlet beneath the sintered shell and then an increase in gas flow when the sintered shell breaks.

The indication that the sintered shell has broken may be a visual and /or audible warning, e.g. a warning light together with a buzzer. The operator then immediately manually opens the valve to let the molten metal flow out of the outlet. Alternatively, the indication that the sintered shell has broken may be automatically coupled to means to open the valve, e.g. a conventional hydraulic piston arrangement, so that opening is carried out automatically after the shell has broken. In this latter alternative it may still be desired to have the visual and audible warnings that the valve opening is about to take place.

The invention may be applied to any system of introducing gas into the outlet for the purpose of removing/ breaking a sintered shell to release melt flow. However, it is preferred to utilise the invention with a means of introducing the gas, which is preferably argon gas, relatively high up in the tap channel.

If the gas is introduced at the lower part of the tap channel in the valve's closed position it must, under great resistance, push its way up through the whole pillar of, e.g. sand, to reach the upper part. In these circumstances the sand may be blown away and steel may run down into the tap channel and solidify before the valve can be opened. A procedure for introducing the gas relatively high up in the tap channel has been described in international patent application WO/ GB92/ 00485 and the present invention is particularly useful for monitoring the gas flow in that procedure.

International application WO/GB92/00485 describes the use of a relatively frangible tube which is introduced into the tap channel so that when the outlet valve is in its closed position, the tube extends through both parts of the valve. The tube may extend up into the tap channel for a considerable way towards the sintered sand shell that forms at the top of the channel. Gas can therefore be introduced close to the sintered sand shell or any other obstruction, which is then more reliably removed. The valve is then opened which shears off the length of frangible tube in the outlet.

The present invention will, therefore, be more specifically described with reference to the use of a frangible gas tube.

The invention is therefore further described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows a section of the bottom part of a ladle with an applied sliding gate system and including a frangible tube;

Figures 2, 3 and 4 are similar sections showing subsequent stages when opening the valve;

Figure 5 shows on a larger scale a plan view of a suitable design for the gas tube; Figure 6 is a schematic arrangement showing a gas flow control mechanism of the invention for use with the sliding gate valve system shown in Figures 1 to 5; and

Figure 7 is a detailed control circuit for the arrangement of Figure 6.

In Figures 1 to 5 of the drawings, 1 denotes the bottom of a ladle, 2 the brick lining of the ladle and 3 a hole in the bottom of the ladle. A well block 4 is placed in hole 3 and is lined with a ceramic tube 5, (which is called the inner nozzle) and which defines the tap channel 5a of the ladle.

Fixed to the ladle bottom 1 is a sliding gate valve system 6 which comprises an upper housing 7 and a similar lower, movable housing part 8. The sliding gate system 6 is a unit which can be attached to and then separated from the ladle. It comprises an upper housing 7 containing a refractory valve plate 9 and having a flow passage opening 10 therethrough and a lower housing 8 containing a refractory valve plate 11 with an exit channel 12. The upper part of the sliding gate system 7 is arranged so that in the position shown in the figure it is immovable relative to the ladle, whereby the flow passage opening 10 is positioned coaxially under the opening defined by the inner nozzle 5, i.e. it is coaxial with the tap channel 5a. In Figure 1 where the sliding gate system is shown in the closed position, the lower movable valve part 8 is positioned to the left side so that the exit channel 12 in the valve plate 11 is offset to the side of the flow passage opening 10 in the valve plate 9 and the surface of the valve plate 11 lies across and closes the tap channel 5a. As the sliding gate system is described it corresponds to known similar systems.

A gas tube 13 runs through the lower housing 8 and the portion of the valve plate 11 that closes off the tap channel 5a. The upper end of the gas tube 13 extends into the upper part of the channel 5a and its lower end sits in a sealing connection piece 14 which abuts against the underside of the lower housing. A source, not shown, of gas can be connected to the gas tube via connection 14. The gas tube 13 is of a relatively frangible, i.e. a relatively brittle, refractory material. Alternatively, only a portion of the length of the tube need be frangible with the remainder of the length being of, e.g. metal.

In the ladle above the brick lining 2, the well block 4 and the inner nozzle 5 there is a melt, (not shown) and as known the tap channel 5a defined by nozzle 5 is filled with a good measure of sand (not shown) which in the contact area with the melt sinters to a dome-like crust 15.

When tapping from the ladle is to take place, gas is blown in, preferably argon gas, through the connection piece 14 to break up the obstruction in the tap channel, i.e. the sintered sand crust 15, which in Figure 2 is shown in the broken up state. Due to the gas tube extending a considerable way up into the tap channel 5a (approximately three quarters of the nozzle height, measured from the bottom, has been shown to give good results), gas pressure is introduced just below the obstruction which is to be removed. Furthermore, most of the sand will be left in the nozzle and consequently prevents the melt from pushing down the nozzle with the attendant risk of solidification and blocking of the tapping channel. Also, the remaining sand gives a downward back pressure resulting in a decreased risk of leakage. However, if desired, a suitable gasket (not shown) may be positioned at the bottom of opening 10 surrounding tube 13 and sealing between plate 9 and movable plate 11. The gasket should be of compressible, non-porous, temperature-resistant material, e.g. a ceramic fibre material with a covering mica layer. As the gas pressure system does not effect the drive unit, (not shown) for the valve opening, such as a hydraulic piston and cylinder unit, the movable lower housing part 8 can be moved to the right as Figure 1 to open the nozzle hole unit. In this connection the gas tube 13 meets the inner nozzle 5 inner wall and is cut off against the latter's lower edge. This position is shown in Figure 3. In practice, however, the gas tube will break earlier due to its inserted part being fixed by the sand in the inner nozzle 5. It is possible that the inserted part of the gas tube 13 above valve plate 11 will, in the meantime, be pushed away to the position shown in Figure 3. Continued opening movements uncover the whole of the tapping channel so that the melt can flow through the inner nozzle 5, through the flow passage opening 10 and then lower valve plate exit channel 12. Here the sheared off part of the gas tube 13 follows along. The remaining part of the gas tube 13 in the lower housing part 8 can, after completed tapping, be removed by releasing the (not shown) agent, which holds the connection piece 14 against the lower housing part 8.

In Figure 5 an example is shown of a preferred design for the gas tube 13. Suitably, the gas tube is made of ceramic material which can withstand temperatures equivalent to the melting temperature of steel and, in addition, easily breaks off when the valve opens. The tube is provided with several - in the shown example four - holes or channels 13a extending axially throughout its length. When the valve opens the gas tube breaks as mentioned and a piece of it is left in the movable valve plate 8. If the sliding gate unit has to be closed during ongoing tapping, the remaining piece of tube will form a plug and the remaining accessible outflowing area is defined by the hole in the tube. Therefore, it is advantageous instead of one relatively large hole, to have several smaller holes which let the gas through freely but impede the melt from passing through by its solidifying and thereby blocking its own passage.

The flow of gas is monitored by the arrangement shown in Figures 6 and 7. Referring particularly to Figure 6, a source of gas 20 is connected via a manual valve 21 to a flow switch 22. From flow switch 22 the gas flows to a pressure gauge 23 with a pressure regulator 24. The gas then flows via a solenoid-activated valve 25 to the gas tube 13 of Figures 1 to 5 shown schematically in the slidegate outlet valve 6 of a ladle (not shown).

To operate the control system, manual valve 21 is opened and the gas flow line is connected into the frangible tube in the slide gate valve. At this stage the outlet tapping channel of the ladle will be full of sand, the ladle full of molten metal and a sintered sand shell (15 in Figure 1) will have formed in contact with the molten metal. The ladle will be positioned over a tundish to receive the molten metal. Solenoid valve 25 is then opened to allow gas into the tapping channel via the frangible tube. An initial gas pressure of say 10 bar from source 20 may be reduced, as desired, e.g. to 8 to 9 bar, by the pressure regulator 24 and the initial and reduced pressures are indicated on pressure gauge 23. As pressure of the gas builds up underneath the sintered sand shell, the gas flow rate as monitored by flow switch 22 will fall off. When the pressure has built up sufficiently, the sand shell breaks and there is a surge in gas flow. This surge is detected by the flow switch and after a predetermined delay, say of 1 or 2 seconds, the control circuit operates a visual signal 26 to indicate that the slide gate valve is to be opened. (Alternatively, as indicated above, the control circuit may automatically cause the opening of the valve after the predetermined delay.)

Referring now to Figure 7, the power supply is a single phase, for example, 110 volts AC.

An emergency stop ESI is provided.

Power is switched on and switch SI on line 101 is pressed to energise relay Rl. This effects closure of associated contact R'l on line 102 which in turn energises spring-loaded gas solenoid valve Yl, thereby opening Y 1 against the spring pressure to let inert gas flow to the slide gate valve 6 and frangible tube 13 of Figure 6. Gas flow effects closure of switch S3 on line 103 which energises the constant gas flow timer relay Tl on line 103. If this gas flow energisation is for greater than, say, seven seconds, contact Tl energises relay R2 on line 104 by closure of associated contact T'l. This effects closure of associated contact R'2 on line 105, causing gas flow light LTl to illuminate, and of associated contact R'2 on line 106, thereby energising gas solenoid valve close time relay T2. After a delay of, say, 10 seconds relay T2 breaks contact line 101 by opening associated switch T'2 thus resetting the control circuit and effecting shutting of the gas valve Y 1 by its spring. Gas flow light LTl then goes out.

It will be appreciated that the circuit is completed in a conventional manner at line 106 or, alternatively, further circuits may be added, for example to effect automatic opening and closing of the slide gate valve at the appropriate time.

Claims

1. An apparatus to control the opening and closing of an outlet

(5a) in a molten metal handling vessel which includes a valve (6) communicating with the outlet (5a) and having relatively movable valve parts (7, 9 and 8, 11), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet and which are in communication with each other and with the outlet to open the outlet, whereby the molten metal can flow out of the vessel, and means (13) to provide gas into the outlet (5a) characterised in that there is provided a gas flow measurement means (22, 23) and control means (21, 24, 25) to monitor the gas flow to detect a fall off in flow as gas pressure builds up in the outlet beneath an obstruction (15) of the outlet followed by an increase in gas flow when the obstruction (15) is removed and means (LTl) to indicate the occurrence of this increase in gas flow.

2. An apparatus according to Claim 1, characterised in that the means to indicate the increase in gas flow is a visual and/ or audible warning.

3. An apparatus according to Claim 1 or 2, characterised in that the means to indicate the increase in gas flow is coupled to the opening means for the valve, whereby opening may be effected automatically after the obstruction (15) is removed.

4. An apparatus according to Claim 1, 2 or 3, characterised in that the means to provide gas into the outlet comprises a frangible tube (13) extending through the relatively movable valve parts (7, 9 and 8, 11) into the outlet (5a), whereby when the valve (6, 7, 8) is opened the length of frangible tube (13) in the outlet is sheared off.

5. An apparatus according to Claim 4, characterised in that only a portion of the length of the tube (13) is frangible.

6. An apparatus according to Claim 4 or 5, characterised in that the tube (13) has a plurality of axially extending holes (13a).

7. An apparatus according to any preceding claim, characterised in that the gas flow measurement means and control means comprises a valve (21) connected to a source of the gas, a flow switch (22) to measure the flow of gas, a pressure gauge (23) and a pressure regulator (24).

8. An apparatus according to Claim 7, characterised in that a solenoid-activated valve (25) is provided between the pressure regulator (24) and the outlet (5a).

9. An apparatus according to any one of claims 4 to 7, characterised in that it includes a gasket surrounding the frangible tube (13) and positioned in the outlet to seal between the relatively movable valve parts (9, 11).

10. A method of opening and closing an outlet (5a) in a molten metal handling vessel in which a valve (6) is positioned to communicate with the outlet, the valve having relatively movable valve parts (7, 9 and 8, 11), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet and which are positioned in communication with each other and with the outlet to open the outlet, and in which gas is supplied into the outlet to break a sintered shell (15) of particulate material formed in the outlet, whereby molten metal can flow out of the vessel, characterised in that the flow of gas into the outlet (5a) is monitored to detect first a fall off in flow as gas pressure builds up in the outlet beneath the sintered shell (15) and then an increase in gas flow when the sintered shell breaks.

11. A method according to Claim 10, characterised in that the increase in gas flow when the sintered shell (15) breaks activates a visual and/or audible warning.

12. A method according to Claim 10 or 11, characterised in that the increasing gas flow when the sintered shell (15) breaks activates opening of the valve (7, 9 and 8, 11).

13. A method according to Claim 10, 11 or 12, characterised in that the gas is introduced in the upper part of the outlet (5a) via a frangible tube (13) extending through the relatively moveable valve parts (7, 9, and 8, 11) into the outlet (5a) and opening of the valve (6, 7, 8) shears the frangible tube (13).

14. A method according to Claim 13, characterised in that the outlet (5a) is filled with sand, molten metal is poured into the vessel with the outlet (5a) closed, the gas control means (25) is operated to allow gas into the outlet via the tube (13), gas pressure builds up beneath a sintered shell (15) of sand, a surge in the gas flow is detected by a flow switch f(22) after the shell breaks and after a predetermined delay the control means indicates that the valve (6) is to be opened.