WO1994021406A1

WO1994021406A1 - Improvements in molten metal handling vessels

Info

Publication number: WO1994021406A1
Application number: PCT/GB1993/000485
Authority: WO
Inventors: Gunnar Broms; Tore SÖDERBERG; Kevin J. Cook
Original assignee: Ifa Institutet For Produktions & Arbetsplatsutveckling Ab; Foseco International Limited
Priority date: 1992-03-11
Filing date: 1993-03-22
Publication date: 1994-09-29
Also published as: JPH08511729A; SE469969B; ZA931331B; FI954421A; AU3893893A; FI954421A0; BR9307841A; SE9200756L; EP0689486A1; SE9200756D0

Abstract

The invention provides a means of introducing gas into the outlet to remove an obstruction. Accordingly, the invention provides an apparatus to open and close an outlet in a molten metal handling vessel which includes a valve (6) communicating with the outlet (5a) and having relatively movable valve parts (7, 8), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet (5a) and which are in communication with each other and with the outlet (5a) to open the outlet, whereby the molten metal can flow out of the vessel, characterised in that there is provided a frangible tube (13) through which gas can be passed, the tube (13) being of sufficient length to extend through both valve parts (7, 8) and into the outlet (5a) of the vessel, whereby gas can be passed into the outlet and then opening of the valve (6) by relative movement of the valve parts (7, 8) breaks the tube (13) so that it does not obstruct opening.

Description

IMPROVEMENTS IN MOLTEN METAL HANDLING VESSELS

This invention relates to molten metal handling vessels and is particularly concerned to provide a procedure and an appliance to improve 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 of 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 eguipment 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/37/07306 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 and solidifying, blocking the tap channel as a result, 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 liguid steel. When blockage of the tap channel occurs this protective tube must be removed to allow access with oxygen burning eguipment 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 guite 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 entail deteriorated steel quality. In the worse case the casting must be stopped with subsequent preparations for the start of a new cast and reheating of the steel in the ladle.

Trials have been carried out to blow in argon gas into the tap channel just before the sliding gate is opened, by which the channel is pressurised so that the high temperature sintered sand shell or possibly the solidified steel, which covers the mouth of the tap hole, is removed. At these trials the argon gas has been introduced at the lower part of the tap channel in the valves^,s closed position and thus, under great resistance must push its way up through the whole pillar of sand to reach the upper part.

During some trials the sand has been blown away and steel has run down into the tap channel and had time to solidify before the valve could be opened. Even problems with sealing have been significant.

Thus, for many reasons, there is a wish to improve spontaneous tapping in conjunction with the opening of the ladle valve and the purpose of this invention is to design a method and an apparatus to accomplish this.

Thus, the invention is based on the utilisation of gas, preferably argon gas, with a means of introducing it relatively high up in the tap channel. During the procedure, according to the invention, a tube of relatively frangible material is introduced into the tap channel where the tube in the closed position of the valve extends through both parts of the valve. Thereafter, gas is blown through the tube, whereupon the valve is opened during which the tube is sheared off. The sheared off end of the tube follows the outflowing sand before a stream of molten steel then follows during tapping.

Accordingly, in one aspect the invention provides an apparatus to open and close 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, characterised in that there is provided a frangible tube through which gas can be passed, the tube being of sufficient length to extend through both valve parts and into the outlet of the vessel, whereby gas can be passed into the outlet and then opening of the valve by relative movement of the valve parts breaks the tube so that it does not obstruct opening.

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, whereby molten metal can flow out of the vessel, characterised in that a frangible tube is inserted through the valve parts into the outlet while the valve is in the closed position, gas is injected into the outlet through the tube to remove any obstruction to the outlet and the valve is opened thereby shearing off the length of tube in the outlet.

The relatively frangible tube may extend through a section of the movable valve part by the side of its flow passage and up through the passage in the fixed valve part.

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

Figure l shows a section of the bottom part of a ladle and with an applied sliding gate system set up in accordance with the invention;

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; and Figure 6 shows in a somewhat similar larger scale, a suitable design for the connection of the gas tube to the sliding gate assembly.

In 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.

According to the invention 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.

If desired, pre-manufacture may be carried out on an industrial scale of units comprising the connection piece 14 with gas tube 13 preassembled so <^■ that the gas tube can be positioned into the pre- manufactured hole in the valve plate 11. The connection piece 14 can be kept in place with help of an agent (not shown). One variation of the gas tube with a connection agent is described later with reference to Figure 6 but it will be appreciated that any suitable connecting means may be employed without departing from the scope and spirit of the invention. 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 for leakage. 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 connection of gas tube 13 to the sliding gate unit is shown in greater detail in Figure 6. To the underside of lower valve part housing 8 is welded, or otherwise attached, an annular connector 14' having a central bore 15 aligned co-axially with bore 16 in part 8. Connector 14' has a depending lower annular portion 14b which is externally threaded and whose central bore 17 is coaxial with bores 15 and 16 but is of larger diameter. Thus, a shoulder 18 is provided on the inside bore of connector 14'. Bores 15 and 16 are of larger diameter than the outer diameter of tube 13 so that the latter can be freely inserted through these two holes and up through the more exactly adapted hole in the valve plate 11, i.e. the hole in plate 11 is a closer fit around the tube. Thereafter tube 13 passes up through flow passage opening 10 in upper valve plate 9 (not shown in Figure 6). However, the annular gap between the gas tube 13 and the holes 15 and 16 should be so small that penetration by the melt is avoided as far as possible. As indicated above, coaxial with hole 15 in the connection piece 14', a bore hole 17 is arranged with a larger diameter than the hole 15, so that a shoulder 18 is formed. This shoulder serves as a seat for an annular sleeve 19, which is preferably cemented to the gas tube 13 just above its lower region 13'. For a given length of tube 13, the length of sleeve 19 determines how far tube 13 extends into the tap channel 5a.

Around the region 13' of gas tube 13 an 0-ring 20 is placed. A connection nipple 21 is provided for a gas pipe (not shown), the nipple having a gas channel 22 therethrough and an outwardly directed flange 23. The gas channel 22 is widened to provide larger bore 24 in the region of flange 23. Bore 24, with some free play, houses the bottom 13' of gas jtube 13. In the transition between the bore 24 and the upper surface of connection nipple 21, an annular groove 25 is formed with a lesser depth than the thickness of 0-ring 20 and an inside diameter corresponding to the outer diameter of the 0-ring. After the gas tube 13 has been positioned through the holes 15 and 16 until sleeve 19 contacts the shoulder 18 and with the 0-ring mounted around lower end 13' of the gas tube, the connection nipple 21 is then fitted so that its bore 24 surrounds lower end 13', so that the 0-ring seats in the groove 25. Thereafter a clamp bolt 26 is screwed on the threaded portion 14b of connection piece 14. Bolt 26 has an inward flange 27 which contacts the flange 23 which, under compression of the 0-ring, pushes the sleeve 19 against the shoulder 18. After opening of the valve and shearing off of the gas tube 13 the remaining part of the gas tube can be easily removed after unscrewing the clamp bolt 26 and removal of the connection nipple 21.

Claims

1. An apparatus to open and close an outlet in a molten metal handling vessel which includes a valve (6) communicating with the outlet (5a) and having relatively movable valve parts (7, 8), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet (5a) and which are in communication with each other and with the outlet (5a) to open the outlet, whereby the molten metal can flow out of the vessel, characterised in that there is provided a frangible tube (13) through which gas can be passed, the tube (13) being of sufficient length to extend through both valve parts (7, 8) and into the outlet (5a) of the vessel, whereby gas can be passed into the outlet and then opening of the valve (6) by relative movement of the valve parts (7, 8) breaks the tube (13) so that it does not obstruct opening.

2. An apparatus according to Claim 1, in which the vessel is a ladle and the outlet (5a) is in the base (1) of the ladle.

3. An apparatus according to Claim 1 or 2, in which the valve (6) has a stationary part (7) attached to the underside of base (1) of the vessel and a moving part (8) attached beneath the stationary part (2) .

4. An apparatus according to Claim 3, in which the tube (13) is attached to the moving part (8) so that when the moving part (8) is positioned to close the outlet (5a) the tube (13) extends through the opening (10) in the stationary part (7) and into the outlet (5a).

5. An apparatus according to any one of the preceding claims, in which the tube (13) is of sufficient length to extend for a major proportion of the length of the outlet (5a).

6. An apparatus according to Claim 3, 4 or 5, in which the tube (13) is mounted adjacent one of its ends (13') in a connection unit (14) which is fastenable to the moving valve part (8).

7. An apparatus according to Claim 3, 4, 5 or 6, in which the tube (13) is engaged through a hole (16) through the moving valve part (8).

8. An apparatus according to any one of the preceding claims, in which a sleeve unit (19) is provided on the tube (13) to define the length of the tube (13) insertable into the outlet (5a).

9. An apparatus according to any one of the preceding claims, in which tube (13) contains a multi¬ plicity of longitudinally-extending gas channels (13a).

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 (5a), the valve (6) having relatively movable valve parts (7, 8), the valve parts having openings (10, 12) which are displaced from one another to close the valve (6) and, hence, the outlet (5a) and which are positioned in communication with each other and with the outlet (5a) to open the outlet, whereby molten metal can flow out of the vessel, characterised in that a frangible tube (13) is inserted through the valve parts (7, 8) into the outlet (5a) while the valve (6) is in the closed position, gas is injected into the outlet 5a through tube (13) to remove any obstruction (15) to the outlet (5a) and the valve (6) is opened thereby shearing off the length of tube (13) in the outlet (5a).

11. A method according to Claim 10, in which the vessel is a ladle and the outlet (5a) is in the base (1) of the ladle.

12. A method according to Claim 10 or 11, in which the valve has a stationary part (7) which is attached to the underside of base (1) of the vessel and a moving part (8) attached beneath the stationary part (7) .

13. A method according to Claim 12, in which the tube (13) is attached to the moving part (8) so that when moving part (8) is positioned to close outlet (5a) the tube (13) extends through the opening (10) in the stationary part (7) and into the outlet (5a).

14. A method according to any one of Claims 10 to 13, in which the tube (13) is inserted into the outlet (5a) for a distance of up to approximately three guarters of the length of the outlet (5a).

15. A method according to any one of Claims 10 to

14, in which the obstruction removed by the gas injected through the tube (13) is the sintered crust (15) of a deposit of sand in the outlet (5a).

16. A method according to any one of Claims 10 to

15, in which the gas is argon.

17. A frangible tube (13) having at least one longitudinal gas passage (13a) and connectable to a source of gas, for use in the apparatus or method of any one of the preceding claims.