EP0726113B1 - Inflow system for a continuous aluminium casting installation - Google Patents

Abstract

In an Al continuous casting plant, a feeding nozzle (2) is provided in launder (1) and a stopper (3) regulates the flow of molten Al, such that the stopper at its narrowest portion is always spaced from the nozzle wall. The nozzle cross section decreases continuously from the entry to the middle, such that the angular difference between the side wall of the nozzle annular space (D) and the stopper is 1-3 degrees . At the end of the stopper adjacent to the nozzle entry, a sealing edge is formed, so that the nozzle is closed when the stopper enters it fully.

Description

The invention relates to inlet systems for continuous aluminum casting plants, consisting of a gutter, one inserted into the gutter Inlet nozzle into which a plug for regulating the Melt feed is used and optionally a control system, with which the immersion depth of the stopper within a predetermined Limits are controllable.

The regulation of the melt feed with the help of nozzle and plug is known from various publications. For example by the German Society for Metallurgy e.V. a symposium entitled "Continuous Casting - Melting - Casting - Monitor "was organized, in which the principle of the mold level control was explained according to the eddy current principle. At the lecture texts published in 1986 can be found on page 331 the illustration of a control system using Nozzles and plugs. The nozzle is attached to the bottom of a gutter and protrudes with its lower end into the mold.

The speed changes under certain conditions the molten aluminum in the inlet nozzle also changes the static pressure. At very high speeds of the aluminum melt are at the then occurring negative pressure on Nozzle inlet or nozzle outlet oxide and dirt particles from the metal surface of the channel or ingot into the melt sucked in, which is disadvantageous in the bar quality produced noticeable.

The object of the invention is therefore the inlet system in aluminum continuous casting plants optimize so that while maintaining of the essential installations the negative pressure at the nozzle inlet and is minimized at the nozzle outlet and the flow conditions be optimized in the inlet nozzle. A procedure for Operation of the inlet system is intended to create vortex formation in the melt reduce so that both on the melt surface in the There is no channel or on the melt surface in the mold Vortex formation occurs.

This object is achieved by the claims specified features solved. It has been shown that through a special shape of the inner contour of the nozzle and the Adherence to certain immersion depths in the above the swamp developing melting zone the entrainment of oxide and others Dirt particles from the metal surface can be avoided. Furthermore, for a sufficient metal level in the gutter The first step is the one at the nozzle outlet Minimized negative pressure and then measured the immersion depth so that a metal column of at least 2 cm the remaining Negative pressure compensated.

The nozzle contour according to the invention provides that in the middle of the Inlet nozzle has the narrowest cross section and thus the highest Speed is generated in the middle of the nozzle. Through the The shape of the nozzle becomes a stall, which is the cross-section through which the air flows could reduce avoided. The nozzle is thus flows evenly over the entire cross section, whereby an optimal volume flow can be set.

With the conventional channel arrangements, the infeed system results different flow conditions, depending on which Nozzle side of the melt flowing in the gutter first is flowed to. Under certain conditions, this leads with conventional infeed systems to an uneven distribution the liquid flow on the inner wall of the nozzle with which As a result, very high flow velocities at certain nozzle cross sections and in other places a flow shadow arises. These conditions have previously disturbed uniformity the flow and also affected the inlet and Flow conditions at the feed nozzle.

1. Ausbildung der Düse derart, daß am Düseneintritt und am Düsenaustritt nur geringe Unterdrucke entstehen.

2. Ausbildung der Düsenkonfiguration derart, daß die Düse über den Querschnitt gleichmäßig durchströmt wird und die Strömung an keiner Stelle abreißt.

3. Drosselung der Strömung im mittleren Bereich der Düse, sodaß die vorhandene Strömungsenergie vermindert wird und an den Ein- und Austrittsenden der Düse praktisch keine Turbulenz auftritt.

4. Vermeidung des Einfrierens von Düse und Stopfen im Bereich des Düseneintritts durch Abdichtung mittels eines umlaufenden Absatzes am Stopfen, der im geschlossenen Zustand am Rand des Düseneintritts anliegt.

5. Durch einen Spalt zwischen Stopfen und Düsenwand auch am engsten Querschnitt der Düse kann beim Schließen des Stopfens noch im Zwischenraum vorhandenes Metall abfließen.

6. Verkürzung des Regelweges durch Zuspitzung des Stopfens auf einen Radius von 7 mm.

7. Erhöhung der Winkeldifferenz auf 2° zur Verkürzung des Regelweges.

The features according to the invention can be summarized as follows:

1. Formation of the nozzle in such a way that only slight negative pressures arise at the nozzle inlet and outlet.

2. Formation of the nozzle configuration in such a way that the cross-section flows through the nozzle uniformly and the flow does not stop at any point.

3. Throttling the flow in the central area of the nozzle, so that the existing flow energy is reduced and practically no turbulence occurs at the inlet and outlet ends of the nozzle.

4. Avoiding freezing of the nozzle and stopper in the area of the nozzle inlet by sealing by means of a circumferential shoulder on the stopper which, in the closed state, lies against the edge of the nozzle inlet.

5. Through a gap between the stopper and the nozzle wall, even at the narrowest cross section of the nozzle, metal that is still in the space can flow out when the stopper is closed.

6. Shortening the control path by tapering the plug to a radius of 7 mm.

7. Increase the angle difference to 2 ° to shorten the control path.

Figur 1

Gesamtansicht eines erfindungsgemäßen Einlaufsystem,

Figur 2

Erfindungsgemäße Zulaufdüse mit Stopfen im Querschnitt,

Figur 3

Druckverlauf in einem erfindungsgemäßen Einlaufsystem (Wassermodell),

Figur 4

Düsen/Stopfensystem nach dem Stand der Technik,

Figur 5

Druckverlauf bei einem herkömmlichen Einlaufsystem im Wassermodell,

Figur 6

Schematische Darstellung einer elektronischen Gießspiegelregelung,

Figur 7

Gesamtansicht eines Einlaufsystems nach dem Stand der Technik,

Figur 8

Schematische Darstellung einer mechanischen Gießspiegelregelung,

Figur 9

Schematische Darstellung beim Öffnen der erfindungsgemäßen Zulaufdüse.

The invention is explained in more detail below with the aid of several exemplary embodiments. Show it:

Figure 1

Overall view of an inlet system according to the invention,

Figure 2

Inlet nozzle according to the invention with stopper in cross section,

Figure 3

Pressure curve in an inlet system according to the invention (water model),

Figure 4

State-of-the-art nozzle / plug system,

Figure 5

Pressure curve in a conventional inlet system in the water model,

Figure 6

Schematic representation of an electronic mold level control,

Figure 7

Overall view of an intake system according to the state of the art,

Figure 8

Schematic representation of a mechanical mold level control,

Figure 9

Schematic representation when opening the inlet nozzle according to the invention.

According to FIG. 1, the inlet system consists of a channel 1 used inlet nozzle 2, in which a plug 3 for regulation of the melt inlet 4 is used. Arrived through the pouring nozzle the melt into the mold 5, where it is formed into an ingot 6 is held on the sprue 7. By lowering a casting table 8 by means of lowering device 9 is the ingot 6 pulled down out of the mold 5.

The shapes of nozzles 2 and plugs 3 are shown in FIG remove. It can be seen that the cross sections X and Y at the nozzle inlet and nozzle outlet in relation to the other cross sections the inlet nozzle are selected large, so that there are low flow rates occur.

It can also be seen from FIG. 2 how the plug 3 enters the nozzle 2 dips. The one remaining between the nozzle 2 and the plug 3 Space is to be seen as an annular gap C and is designed to that the flow fills the entire cross-section evenly. Seen from the inlet side X, the annular gap tapers C, so that a dynamic pressure builds up in the flowing metal counteracts a reduction in the static pressure in the melt.

In the almost parallel part of the annular gap C is used for throttling generates the necessary friction. The annular gap C widens then slightly towards the plug 3, so that the flow better put on the plug 3 here. With a decreasing cross-section passes through the tapered nozzle 2 an equalization the flow across the cross section.

Expanded behind the narrowest point, for example in the middle of the nozzle the cross-section, so that the flow decelerated again without tearing becomes. In order to also stall the plug 2 avoid this is at the top to a radius of in the example 11.5 mm extended.

To check the actual flow conditions in the nozzle according to the invention was a water model in the manufacture of a rolling ingot prevailing condition. In the conditions in the channel, in of the nozzle and in the rolled ingot, with various nozzle-plug systems can be simulated. With this water model, the Pressure profiles examined in the optimized inlet system. The result is shown in Figure 3.

It can be seen that at the nozzle inlet (nozzle length = 0) there is a positive one or there is only slightly negative pressure. In the middle of the nozzle become very high due to the high flow velocities Negative pressure reached. The lowest cross section is high negative pressure measured, which show that the flow does not stop, but lies against the walls. After that it takes place within shortest Time to reduce the very high negative pressure, so that at the nozzle outlet with a nozzle length of about 17 cm only very small Negative pressures remain.

The pressure ratios are also shown by an enlarged level difference - in the example 26 cm and 34 cm - hardly changed. The closely spaced curves for different level differences show that the flow conditions are very stable and even in the case of high negative pressures, the flow in the nozzle is not tears off. It follows that the available cross section is flowed through relatively evenly and none Speed peaks occur.

The pressure profiles are better known in FIGS. 6a, b and 5a, b Inlet systems shown as examples. With one down closing inlet system according to Figure 4a, the vacuum on Nozzle outlet can no longer be dismantled because of the available Cross section at the nozzle outlet through the stall below the Stopper is reduced very much. This creates high negative pressures at the nozzle outlet, which is no longer due to an enlargement the immersion depth of the nozzle can be compensated (see Figure 5a).

FIG. 4b shows a known upward closing inlet system shown. Here the negative pressure increases with increasing Level difference strongly on (see Figure 5b). As a consequence, that the metal column above the nozzle inlet in the channel and the associated static pressure is not sufficient to To compensate for the negative pressure that arises at the nozzle inlet. Further there is a stall under the stopper, which is available standing cross section reduced. At a higher level difference this stall can occur up to the nozzle outlet effect, so that there is a strengthening of the underpressure with the above-mentioned adverse consequences.

The pressure curves used for the above considerations depend on the position of the measuring points. The Representations in Figure 5a, b are as two-dimensional representations to look at and therefore say nothing about uniformity the flow over the circumference of the inlet nozzle. As at the beginning shown, but can cause irregularities in conventional infeed systems occur over the circumference of the inlet nozzle, whereby Speed peaks arise, which in turn create the negative pressure increase.

In addition, in practice, crooked or crooked is often the case Stoppers influence the flow conditions even further, in such a way that the inhomogeneities are increased. Both known systems it happens that only a half of the nozzle circumference is flowed through. This also creates problems with the regulation of the volume flow, which is particularly the case with an automatic level control disadvantageous.

When changing the cross sections according to the invention, the Volume flow metered much more precisely and the occurrence of Instabilities can be avoided. It showed on the glass model, that an optimized nozzle is relatively even over the circumference is flowed through.

In contrast, the known inlet system tends to form turbulence. This is shown in FIG. 7 and is shown in following explained in more detail. The melt 4 arrives in the direction of the arrow through the channel 1 to the inlet nozzle 2. Through the nozzle inlet and emerges negative pressure is the melt surface dented by the air pressure, causing the oxide layer to tear open can and oxide or dirt particles sucked into the melt can be. The non-deformable impurities are in the solidification front installed. Arrive at the later rolling process They surface and cause the rolled strip to tear open or damage to the rollers.

In Figure 8 is a mechanical control of the mold casting system shown schematically for aluminum ingots. About one Float 14 positioned on the metal surface of the bar is, the plug is via a mechanical deflection 15 3 moved up or down by means of a push rod 16. Of the The term "float" stands for a piece of refractory material, that floats on the metal surface and a lever Metal level reports. In the present case, it becomes the annular gap between nozzle and stopper enlarged or reduced, each after in which direction the melt level deviates from the target value. The feed rate of the molten metal is thus determined by different plug heights regulated.

Other methods consist in laser scanning of the metal stand in the mold. The resulting signal is electronic here Paths processed and a manipulated variable for the stopper 3 remodeled (see Figure 6).

The metal level in the mold 5 can be for various reasons vary. For example, the melting furnace is inclined not continuously, so that gushing in the channel 1 occurs. The metal level in the gutter is also common regulated with a float, so that normally two control systems are coupled together. This leads to a dynamic Control behavior that is constant during the casting phase Correction of the respective plug height is required.

Fluctuations in the metal level change the thermal conditions, resulting in an unfavorable formation of the bar surface leads. The thickness of the edge shell, which is complete before rolling must be milled, increases.

In FIG. 9, the processes during Opened the stopper. In Figure 9.1 is the stopper 3 shown in the nozzle 2 in the closed position. Through the closing edge 21 of the plug 3, the nozzle opening 22 is closed.

In FIG. 9.2, the closing edge 21 is around a gap of approximately 2 up to 3 mm from the nozzle inlet opening 22. Thereby melt reaches nozzle 2 and flows at stopper 3 along to the narrowest point approximately in the middle of the nozzle. The Melt appears as a thin jet 23 at the lower end of the nozzle out.

Just as in Figure 9.2, there is a gap between the narrowest cross section of the nozzle 2 and the plug 3 can be seen. This means that even when the nozzle is closed about existing melt can flow out of the nozzle. This is special important for intermittent operation such as B. at one Casting carousel where the molten metal feed in sections he follows.

In Figures 9.3 to 9.5 the gap between the stopper 3 and the nozzle 2 steadily enlarged. To the same extent also increases the amount of runoff metal.

When the plug 3 moves in the opposite direction - that is when closing the nozzle - the amount of flowing off Metal steadily decreased. When the stopper is closed, liquid can Metal still in the gap between the nozzle and plug in the upper area between the nozzle inlet and the narrowest cross section the nozzle. Since the amount of metal due to the narrow gap is very small there is a risk that the Metal solidifies and the stopper does not come off afterwards can move.

To avoid this, the invention provides that the Nozzle is already sealed at the nozzle inlet. This is what the circumferential paragraph 21 on the plug, which in the closed state on Edge 22 of the nozzle inlet rests.

Because there is always a gap between the stopper and the nozzle, even when closed Condition of the inlet nozzle is present when closing Drain any metal still present in the space between the plugs.

Claims (5)

1. An inlet system for continuous casting plants for aluminium, consisting of a launder, a feeder nozzle (2) which is inserted into the launder (1) and into which there is inserted a stopper (3) for regulating the melt supply (4), and optionally of a control system for controlling the depth of immersion of the stopper within predetermined limits,
   characterised in

   that, at the narrowest cross-section of the nozzle, the stopper (3) is always held at a distance from the nozzle wall and that, even after the stopper (3) has been closed, there exists a space between the stopper and nozzle wall, which space allows the metal melt remaining therein to flow off;

   that the nozzle cross-section is reduced continuously from the nozzle entrance to approximately the nozzle centre, with an angular difference between the side wall of the annular nozzle chamber D and the stopper amounting to 1° - 3°;

   and that at the end of the stopper (3) adjoining the nozzle entrance, there is formed a sealing edge which, when the stopper (3) is inserted fully, seals the nozzle entrance relative to the melt.
2. An inlet system according to claim 1,
   characterised in

   that, from the narrowest cross-section of the nozzle to the nozzle entrance and nozzle exit, a distance A of a least 7 cm is observed.
3. An inlet system according to any one of the preceding claims,
   characterised in

   that, at the nozzle entrance, the space between the nozzle (2) and the stopper (3) becomes continuously narrower along a length B, with the length of the portion B ranging between 0 - 10 cm.
4. An inlet system according to any one of the preceding claims,
   characterised in

   that narrowing takes place along a length of 1 - 10 cm.
5. An inlet system according to any one of the preceding claims,
   characterised in

   that, above the narrowest nozzle cross-section, between the nozzle (2) and the stopper (3), there is formed a narrowing annular chamber C, D, whereas below the narrowest nozzle cross-section, the chamber between the nozzle (2) and stopper (3) is extended continuously, with the stopper point S, in the operating condition, maintaining a minimum distance relative to the nozzle exit Y, which minimum distance amounts to 1 to 1.5 times the diameter of the stopper point, with the stopper point preferably being rounded with a radius of 5 - 10 mm.

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