Field of the Invention

The present invention relates to a system for fall teeming under vacuum of liquid steel according to the preamble of claim 1.

Background of the Invention

During fall teeming under vacuum, liquid steel is teemed from a ladle into a receiving housing from which it is distributed via a distributor into at least one mould in which a vacuum is provided. As an example, by fall teeming under vacuum the amount of oxygen of an ingot is reduced to about 20 ppm at a vacuum of about -0.9 bar.

The ladle with liquid steel has a closable outlet opening in the bottom wall and is handled by a crane or is standing on a teeming car.

Before the teeming operation starts the closable outlet opening in the bottom wall of the ladle has to be aligned with an inlet of the receiving housing and is lowered against the receiving housing so as to abut against the same for achieving an airtight sealing between the closable outlet opening and the inlet of the receiving housing which should be maintained during the teeming operation.

Object of the Invention

An object of the invention is to provide an improved system for connecting the closable outlet opening in the bottom wall of the ladle with the inlet of the receiving housing in an airtight manner.

Thus, this object is achieved by the invention by providing a system for fall teeming under vacuum of liquid steel through a closable outlet opening in a bottom wall of a movable ladle into a liquid steel receiving apparatus vacuum sealed and fluidly connected to said closable outlet opening and therefrom into a distributor arranged on a distributor plate, to which distributor an upstream end of at least one distributor pipe is vacuum sealed and fluidly connected, an outlet end of which is placed in a mould sealingly arranged underneath said distributor plate and arranged to be filled with liquid steel and provided with vacuum by a vacuum pipe, characterized in that said liquid steel receiving apparatus comprises a housing having a through channel and an upper housing part movably and sealingly arranged inside said through channel, and that said at least one distributor pipe is provided with a flow restriction means enabling an upper end of said movable upper housing part to be forced upwardly by a static pressure from the liquid steel filling said liquid steel receiving apparatus and acting upon a lower end of said movable upper housing part whereby said upper end of said movable upper housing part is adapted to exert a force on said closable outlet opening in said bottom wall so as to provide a more powerful sealing between said upper end of said movable upper housing part and said closable outlet opening.

Brief description of drawings

The invention will now be described by way of a non-limiting example with reference to the accompanying drawing, in which

- Fig. 1 is a partial sectional side view of a system according to the invention for teeming under vacuum liquid steel from a ladle via at least one distributor pipe into at least one mould before the teeming operation has started and showing a vacuum valve of a liquid steel receiving apparatus in a closed position and with a meltable jet concentrating means discharging into a mould, the bottom of which is not shown,

- Fig. la is an enlarged sectional side view of a portion of the inventive system shown in figure 1,

- Fig. lb is an enlarged sectional side of an portion of the inventive system shown in figure 1,

- Fig. 1c is a view similar to the view shown in figure la in a further enlarged scale and without the vacuum valve,

- Fig. 2 is a view similar to the view shown in figure 1 but during teeming operation and showing the vacuum valve in an opened position and with the meltable jet concentrating means being melted at its lower end as the level of the liquid steel raises in the mould,

- Fig. 2a is a view similar to the view shown in figure lb but during the teeming operation and showing the vacuum valve in an opened positioned,

- Fig. 2b is an enlarged view of a part of a distributor plate and an upper portion of the mould during teeming operation and showing a jet of liquid steel leaving an end of the distributor pipe and diverging towards an inside of the meltable jet concentrating means,

- Fig. 3 is a view similar to the view shown in figure 2 but with a non-meltable jet concentrating means having a fixed length which ends above/at the level of the finished ingot, and

- Fig. 3a is a view similar to the view shown in figure 2ashowing how a jet of liquid steel diverge towards the inside of the non-meltable jet concentrating means.

Description of preferred embodiments

Figs. 1, la, lb, and 1c show the inventive system before the teeming operation has started, i.e. before the closable outlet opening 4a in a bottom wall la of a ladle 1 is opened so as to teem liquid steel into the inventive system. Fig. 1 is a partial sectional side view of a system according to the invention for teeming under vacuum liquid steel 2 from the ladle 1 into at least one mould 24. The ladle 1 has a bottom wall la in which preferably a potty 3 is arranged. The ladle 1 filled with liquid steel 2 is preferably handled by a crane (not shown) for placing said ladle 1 in contact with a liquid steel receiving apparatus A.

In or below the bottom wall la a closable outlet opening 4a is provided, possibly in the form of a slide gate having a slide 5 for opening and closing the closable outlet opening 4a. The closable outlet opening 4a of the ladle 1 is shown placed in the centre of and connected to the liquid steel receiving apparatus A.

More particularly, as can be inferred from figures la and lb, the liquid steel receiving apparatus A comprises a housing 9 placed on a distributor plate 25 and having a through channel 9a in which an upper housing part 6 is movably and sealingly arranged. The upper housing part 6 can move in the longitudinal direction of the through channel 9a and is sealed against an inner wall 9b of the through channel 9a by sealings 8. The sealings 8 provide necessary friction so that the upper housing part 6 will not sink down in the through channel 9a by gravity. At the bottom of the housing 9 a vacuum valve 10 is arranged. Said vacuum valve 10 is adapted to in its opened position provide vacuum, via a distributor 14, at least one distributor pipe 17, and at least one mould 24, in the housing 9 from a vacuum pipe 27 connected to a suitable vacuum pump (not shown) . The distributor 14 is preferably sealed to the housing 9 by a distributor sealing 15. At least one distributor pipe 17 is connected to the distributor 14.

In figures 1, la, and lb the vacuum valve 10 is shown in its closed position. The distributor pipe 17 is arranged at said distributor plate 25 and extends from said distributor 14 to an upper portion of a mould 24 in which it discharges via a meltable jet concentrating means 20.

Moreover, in figure 1 the closable outlet opening 4a of bottom wall la of the ladle 1 is shown placed in contact with the upper housing part 6 via a sealing 7 arranged at an upper end 6a of the upper housing part 6.

Fig. lb shows, in enlarged scale, a portion of the distributor plate 25 and an upper portion of the mould 24 together with preferred piping components.

More particular, the distributor plate 25 is placed on top of the mould 24 via an intermediate part 30 having a sealing 26 against an upper end 24a of the mould 24. The vacuum pipe 27 is in communication with the interior of the mould 24 for providing a suitable vacuum of at most -0.9 bar, for example, in the mould 24, the distributor 14, and the piping components 17, 20. The vacuum is maintained in these parts since the vacuum valve 10 is in its closed position. Said vacuum pipe 27 by the vacuum pump (not shown) is arranged to suck out gas (air) from said liquid steel receiving apparatus A when the vacuum valve 10 is in its opened position and thus the mould 24 at least until a surface of an ingot in the mould has frozen .

A vacuum duct 11 (see particularly figures 1, la and lb) can be provided parallel to the vacuum valve 10 enabling vacuum to act on the space inside the liquid steel receiving housing A even in case said vacuum valve 10 is in its closed position.

Furthermore, a flow restriction means 18 is arranged in the at least one distributor pipe 17 close to an outlet end 17b thereof . In the embodiment shown in figures 1, la, lb, 1c, 2, 2a, and 2b a meltable jet concentrating means 20 extends to close to a bottom (not shown) of the mould 24 and is arranged to melt off as the liquid steel 2 fills the mould, i.e. it is adapted to melt progressively at its end immersed into the liquid steel at the same rate as the level of the liquid steel raises in the mould 24. This is made possible by making the meltable jet concentrating means 20 of a steel grade having a lower melting point that the melting point of the liquid steel 2 to be teemed .

Figures 2, 2a, and 2b show similar views as figures 1, la, and lb except that said figures show the teeming operation in progress, i.e. the liquid steel receiving housing A, the distributor 14, the at least one distributor pipe 17 and the mould 24 are filled with liquid steel 2.

After centring the closable outlet opening 4a of the bottom wall la of the ladle 1 relative to the liquid steel receiving apparatus A and lowering the ladle 1 until the closable outlet opening 4a of the bottom wall la is in contact with the upper housing part 6 via the sealing 7 arranged at the upper end 6a of the upper housing part 6, the ladle 1 being preferably lowered a bit further, a few centimetres, for example, so that good contact is established between the ladle 1 and the upper end 6a of the upper housing part 6, then vacuum is applied through the vacuum pipe 27 to the system via the vacuum duct 11, if provided, with the vacuum valve 10 closed and the teeming operation starts by opening the slide 5. It is of cause possible to apply vacuum to the vacuum pipe 27 also just before the closable outlet opening 4a of the bottom wall la has established contact with the upper housing part 6.

In so doing, liquid steel 2 will flow into the liquid steel receiving housing A. At a certain level of the liquid steel in the liquid steel receiving housing A the vacuum valve 10 will open by floating due to density difference between the vacuum vale 10 and the liquid steel 2, and liquid steel 2 will thus flow through the distributor 14 into the at least one distributor pipe 17 and further through the flow restriction means 18 via the jet concentrating means 20 into the mould 24. A stop means 12 is arranged at a lower end 10a of the vacuum valve 10. In the open position of the vacuum valve 10 the stop means 10a is adapted to abut on a stop surface 12a arranged at a lower portion of the housing 9, thus preventing the vacuum valve from floating up too much. See figure la.

In an embodiment a flotation body of the vacuum valve 10 is provided with a cavity 10b so as to increase its floatability in the liquid steel receiving housing A when filled with liquid steel. See figures 1, la, and lb.

As the flow restriction means 18 restricts the flow of liquid steel through said at least one distributor pipe 17, the liquid steel 2 will thus totally fill up the liquid steel receiving housing A including the movable upper housing part 6. See figures 2 and 2a. When the liquid steel 2 reaches a lower end 6b of the movable upper housing part 6, the liquid steel will, by hydraulic action, act on said lower end 6b and thereby lift and force the movable upper housing part 6 upwards. This lifting force will press the upper housing part 6 with its sealing 7, further against the closable outlet opening 4a of the ladle 1 and thus improve the sealing between the liquid steel receiving housing A and the closable outlet opening 4a.

In a preferred embodiment the movable upper housing part 6 is made of a ceramic material having a density which is substantially lower that the density of the liquid steel and this will also assist, in addition to the hydraulic action, lifting the movable upper housing part 6 towards against the closable outlet opening 4a of the ladle 1.

The movable upper housing part 6 has, as an example, a shape, as seen in cross section, selected from the group consisting of a cylinder, oval, triangle and polygon.

The increase of lifting force of the upper housing part 6 has importance particularly at the end of the teeming operation in case the ladle is handled by a crane, for instance, since the weight of the ladle 1 is reduced at the end of the teeming operation, and the inherent flexibility of the crane and possible lifting equipment for lifting the ladle 1 will to some extent raise the ladle 1 away from the upper housing part 6 of the liquid steel receiving housing A.

Figure 2 shows, and in enlarged scale in figure 2a, how the flow of liquid steel 2 leaving the end 17b of the distributor pipe 17 diverge (is splitted) (at 22) towards the inside of the jet concentrating means 20. In said figures, a vacuum channel 21 is also shown enabling vacuum which reside where the flow of liquid steel diverges, at 22, to also reduce the pressure inside the jet concentrating means 20.

In case the jet concentrating means 20 is arranged to extend from an upper end 24a of said mould 24 to close to a bottom (not shown) of said mould 24 it is of a meltable type, and in case an outlet end 20a of said jet concentrating means 20 (figs. 3 and 3a) is positioned above a top of a finished ingot 23 in said mould 24 it is of a non-meltable type.

As the liquid steel fills the mould the jet concentration means 20 is adapted, in case of a meltable jet concentrating means 20, to melt progressively at its end immersed into the liquid steel at the same rate as the level of the liquid steel raises in the mould 24, as explained above. Preferably, the vacuum is applied to the system through the vacuum pipe 27 from the beginning of the ladle 1 being centre relative to the movable upper housing part 6 until the top/surface of the liquid steel has frozen in the mould 24.

The teeming of liquid steel from the ladle 1 is stopped when the level of liquid steel reaches an upper level of the putty 3. The purpose of the putty 3 is to reduce the risk of oxygen being sucked into the closable outlet opening 4a of the ladle 1 and thereby into the teemed liquid steel by formation of a vortex .

Each distributor pipe 17 is at its upstream end connected to the distributor 14 and at its downstream end provided with the flow restriction means 18, preferably in the form of a reduction of the diameter of the pipe. The purpose of the flow restriction means 18 is to ensure that the flow of liquid steel 2 is the same in all distributor pipes 17 so that all the moulds 24 will be filled evenly.

Figure 1c shows a further embodiment of the inventive system but without a vacuum valve arranged in the liquid steel receiving housing A. This embodiment will function in the same way as the embodiment first described, but vacuum to the liquid steel receiving housing A, the at least one distributor pipe 17 and the mould 24, etc. is only provide when the teeming is in operation and thus no vacuum in these parts after teeming to the ingot frozen.

It should be noted that the at least one distributor pipe 17 is arranged horizontally or with a slope towards the mould 24 so as to be free draining when teeming of liquid steel has stopped .