METHOD OF FILLING A BUFFER RESERVOIR OF A CONTINUOUS CASTING MACHINE AND CASTING PIPE USED THEREWITH

The invention relates to a method of filling a buffer reservoir of a continuous casting machine from a ladle in which a liquid metal is cast from the ladle through a casting pipe in the buffer reservoir.

In this respect the term liquid metal is to be interpreted as a liquid pure metal or liquid metal alloy. Furthermore the term metal, when it concerns the content of the ladle or the buffer reservoir, is to be interpreted as the liquid metal as defined above.

With the known method of filling a buffer reservoir of a continuous casting machine one end of a casting pipe is positioned against an outlet of the ladle, after which a shut-off valve of the outlet of the ladle is opened, allowing the liquid metal to flow out of the ladle and through the casting pipe, and finally the opposite end of the casting pipe is brought below the level of the liquid metal in the buffer reservoir. After the ladle has been emptied the ladle is lifted, therewith lifting the casting pipe out of the buffer reservoir, after which the casting pipe is removed from the ladle and the empty ladle is replaced by a full ladle and the procedure is repeated with the same or a new casting pipe. With this known method the liquid metal or metal alloy from the ladle is supplied initially through the slag layer floating on the metal in the buffer reservoir taking the slag beneath the casting pipe and of the surrounding area into the metal therewith contaminating the metal in the buffer reservoir. Another problem is that with the initial flow from the ladle the metal is in contact with the oxygen in the air and said oxygen may also be brought into the content of the buffer reservoir giving rise to oxidation of at least part of the metal. If the metal contains aluminium, at least part of the aluminium will react with the oxygen in the air into AI ₂ O ₃ .

The casting pipe is only lowered into the reservoir after it has been filled with metal because, as has turned out in practice, if the casting pipe is first lowered into the buffer reservoir and then the outlet of the ladle is opened, the casting pipe is bound to be knocked away from its position and collapse. This is believed to be caused by the filler sand that is used in the outlet of the ladle. Filler sand is used to prevent that molten steel comes into the outlet before the shut-off valve is opened, because otherwise the molten steel would cool down in the outlet, solidify and block the outlet. If the casting pipe is first lowered into the

buffer reservoir and then the outlet is opened the filler sand drops down and comes to rest on the slag or on the metal that fills the bottom end of the casting pipe, therewith clogging the casting pipe. Since the weight of the metal in the ladle resting on the filler sand clogging the casting pipe is far greater than the force with which the casting pipe is held against the ladle, the casting pipe will be knocked out of its position. Also if the casting pipe is only partially clogged by the filler sand the casting pipe may still be swept away due to the load of the molten metal in the ladle, possibly in combination with varying flow patterns in the buffer reservoir. It is an object of the invention to provide an improved method to fill a buffer reservoir of a continuous casting machine from a ladle.

It is a further object of the invention to provide a method in which less contamination of the metal occurs due to the inclusion of slag in the metal flowing from the ladle into the buffer reservoir. It is still a further object of the invention to provide a method in which less oxidation of the metal occurs due to contact of the metal with ambient air and taking ambient air along with the flow of the metal into the buffer reservoir.

It is still a further object of the invention to provide a method in which the outflow of the metal from the ladle is improved. It is still another object of the invention to provide a casting pipe that is suitable to start the flow of the metal from the ladle after the casting pipe is lowered into the metal in the buffer reservoir.

According to a first aspect of the invention one or more of the objects are reached with a method comprising the steps of positioning one end of the casting pipe against an outlet of the ladle, opening a shut-off valve of the outlet allowing the metal to flow out of the ladle and bringing an opposite end of the casting pipe below the level of the metal in the buffer reservoir, wherein after positioning the one end of the casting pipe against the outlet of the ladle, successively the opposite end of the casting pipe is lowered below the level of the metal in the buffer reservoir, the air present in the casting pipe is removed until at least a predetermined pressure in the casting pipe is reached and the shut-off valve of the outlet of the ladle is opened.

By reducing the pressure inside the casting pipe to a predetermined level, which is a predetermined level below ambient pressure, there will be less air in the casting pipe and the metal from the buffer reservoir will rise in the casting

pipe up to a level above the level in the buffer reservoir. It is believed that the lack of a considerable column of air in the casting pipe will allow for a more continuous flow from the moment the shut-off valve of the ladle is opened therewith preventing that the filler sand clogs the casting pipe. Instead of lowering the pressure to a predetermined level according to a further aspect of the invention it is provided that the pressure in the casting pipe is reduced to such an extent that the metal of the buffer reservoir rises in the casting pipe up to at least a predetermined height in the casting pipe or up to a predetermined level above the metal in the buffer reservoir. According to a further embodiment of the method it is provided that the pressure in the casting pipe is reduced such that the level of the metal rises in the casting pipe over at least 20% of the length of the casting pipe, more preferably over at least 40%, more preferably over at least 60%, more preferably over at least 70% and even more preferably over at least 80% of the length of the casting pipe.

In order to remove the air present in the casting pipe, the casting pipe is provided with air passage means. These air passage means allow the removal of the air present in the casting pipe after the opposite end of the casting pipe is lowered below the level of the metal in the buffer reservoir. According to a further embodiment the air present in the casting pipe is removed by suction. To this end the casting pipe is provided with connecting means to connect a suction duct with the interior of the casting pipe, the connecting means being positioned such that the suction duct is in connection with the air passage means. As to be able to remove the suction duct after the pressure in the casting pipe has been lowered to a predetermined pressure or that the level of the metal in the casting pipe has risen to a predetermined level a shut-off valve is provided with which the inside of the casting pipe can be shut off from the suction duct and/or the surrounding air. The shut-off valve can be mounted in the air passage means or in the connecting means. Accordingly a further embodiment of the method provides that the suction duct is connected to the casting pipe after the casting pipe has been positioned with respect to the outlet of the ladle. Still a further embodiment provides that the suction duct is connected to the casting pipe after positioning the casting pipe against the ladle and before the opposite end of the casting pipe is lowered below the level of the metal in the buffer reservoir.

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The suction duct is disconnected from the casting pipe after the pressure in the casting pipe has been lowered to a predetermined level or the level of the metal from the buffer reservoir has risen in the casting pipe up to at least a predetermined level. Preferably the suction duct is disconnected from the casting pipe before the shut-off valve of the outlet of the ladle is opened. With these connecting and disconnecting measures it is realized that the suction duct is not longer connected to the casting pipe than necessary, therewith increasing the working life of the suction duct.

According to a further aspect of the invention a casting pipe is provided for filling a buffer reservoir of a continuous casting machine from a ladle, wherein the casting pipe is provided with air passage means to be used in removing air present in the casting pipe. According to a further embodiment the casting pipe is provided with connecting means to connect a suction duct to the casting pipe. These connecting means are provided such that the suction duct connects through the air passage means to the inside of the casting pipe. According to another embodiment a shut-off valve is provided in the air passage means or in the connecting means, which enable to shut-off the air passage and therewith the inside of the casting pipe from the suction duct or the surrounding air.

To be able to remove the air from the casting pipe to such extent that the level of the metal in the casting pipe can rise to the highest possible level in the casting pipe the air passage means and connecting means are provided at an accordingly height of the casting pipe. Casting pipes are provided with a shaped part complementary to at least a part of the outside surface of the outlet of the ladle, the air passage means and connecting means being provided directly adjacent to said shaped part of the casting pipe or directly adjacent to the level the outlet of the ladle will reach in said shaped part. In this respect directly adjacent means directly below with the casting pipe in use.

The invention will be explained further by means of the example shown in the drawing. In the drawing a lower part of ladle 1 is shown having an outlet 2 provided with a shut-off valve 3 and a tapered connecting part 4. At the inside the ladle 1 is provided with a layer of refractory material 5. The outlet 2 above the shut-off valve 3 is filled with sand S or the like to prevent that the valve 3 is burned by the liquid metal 6 in ladle 1.

The shut-off valve 3 comprises a slide valve or a rotary valve to open and close the passage of outlet 2 of ladle 1.

Casting pipe 7 has a first part 8 with a first cross-section and a second part

9 with a second larger cross-section, a shoulder 10 forming the transition between first and second part 8,9. The second part 9 has a lower annular part

11 and an upper part 12 with at the inside thereof a tapered connecting part 13 complementary to tapered connecting part 4 of outlet 2 of ladle 1.

In annular part 1 1 of second part 9 of casting pipe 7 a passageway 16 is provided connecting the inside of casting pipe 7 to the outside thereof. The passageway 16 at the outside of the casting pipe 7 is provided with connecting means 17 to connect a suction duct 18 to casting pipe 7. In the passageway 16 a shut-off valve 19 is provided to close the passageway after air is removed from inside of casting pipe 7 to a predetermined level or the metal has risen to a predetermined level. Instead of in the passageway as shown the shut-off valve 19 could also be mounted in the connecting means 17 at the outside of casting pipe 7.

During use casting pipe 7 is supported at shoulder 10 by a forked or annular member 14, which is part of a positioning device not shown in the drawing. The shut-off valve 19 could be designed to be operated by the difference in pressure inside and outside casting pipe 7 or further means can be provided to be able to close and open the shut-off valve at any chosen moment. With the first embodiment the shut-off valve 19 is closed after the air inside casting pipe 7 is removed up to a predetermined level and suction duct 18 is removed, with a slight loss of the reduced pressure inside casting pipe 7. With the second embodiment the shut-off valve 19 can be closed first before the suction duct 18 is removed, with no loss of the reduced pressure inside casting pipe 7.

The method works as follows. A casting pipe 7 is picked up from a storage with the forked or annular member 14 of the positioning device and is brought by means of the positioning device in the right position in relation to outlet 2 of ladle 1 , after which casting pipe 7 is moved upward and pressed with tapered connecting part 13 against the tapered connecting part 4 of outlet 2. With forked or annular member 14 sufficient force is exerted to keep casting pipe 7 during use against outlet 2 of ladle 1 , for which a relatively low force will be sufficient.

After casting pipe 7 is rightly positioned with respect to ladle 1 and the tapered connecting parts 4, 13 butt against each other, suction duct 18 is connected to casting pipe 7. Subsequently ladle 1 and casting pipe 7 are lowered to a position in which the opposite end 22 of casting pipe 7 is in the liquid metal 15 in the buffer reservoir 20, that is below the slag 21 floating on the liquid metal 15. Next the air inside casting pipe 7 is removed through suction duct 18 until a predetermined pressure inside the casting pipe is reached or that the metal in the casting pipe has risen up to a predetermined level. Thereafter the shut-off valve 19 is closed and the suction duct 18 is disconnected from casting pipe 7, or in reverse order depending on how shut-off valve 19 is operated. Finally, the shut-off valve 3 of outlet 2 of ladle 1 is opened and the metal from the ladle flows through casting pipe 7 in buffer reservoir 20.