EP2698588B1 - Furnace for the removal of impurities from metal melts - Google Patents

Description

The invention relates to a furnace for removing impurities from molten metal, preferably based on aluminum or copper, by means of purge gas.

In foundries, in furnaces, metals such as e.g. Copper or aluminum, melted and then processed the melt by shaping to a semi-finished product. During the melting of the metal, there is the absorption of gases, in particular hydrogen, and the formation of undesirable inclusions in the melt. In addition, it can lead to impurities of the melt.

Such inclusions cause voids or porous spots during cooling of the melt to a semi-finished product, which adversely affect the quality of the product. To solve this problem, it is already known to subject the molten metal to a purge gas treatment, wherein purge gas, for example argon, is injected into the molten metal and the rising purge gas bubbles absorb dissolved gases in the melt and other foreign substances still contained in the melt are flushed to the surface , For this purpose, different methods are known for purge gas treatment in an intermediate furnace, for example, on the EP 1 132 487 B1 is referenced.

The disadvantage of known ovens is that they cause a high consumption of purge gas (amount of purge gas / t molten metal) and are limited in their capacity.

In the WO2005 / 031234A1 discloses an industrial furnace for melting and gas treating non-ferrous metals comprising a steel shell, a refractory lining disposed on the inside of the steel shell enclosing a free interior space, at least one device for supplying gas into the interior and at least one burner for firing the interior, wherein the furnace is rotatably supported by a rotation angle of at least 40 ° about a horizontally extending axis of rotation, and the interior has a non-circular cross-sectional area.

Furthermore, in the EP 1 132 487 discloses an apparatus for degassing molten aluminum having a naturally-draining open-ended trough having a depth of 50 cm or less and a gas injection structure in the trough.

The invention has for its object to provide a furnace for removing impurities from molten metal, preferably based on aluminum or copper, by means of purge gas, which is characterized by an improved purge gas treatment of the molten metal and is suitable for treating larger amounts of molten metal.

According to the invention the object is achieved by the features specified in claim 1. Advantageous embodiments and further developments are the subject matter of claims 2 to 13.

The heatable furnace vessel has an oven interior with a U-shaped cross-sectional shape. The furnace vessel is arranged from a vertical starting position (90 ° position) about an axis of rotation in a horizontal position (0 ° position) and pivotable back into the starting position. It has on one of the two narrow sides an inlet or inlet opening for the molten metal to be supplied and on the other, opposite narrow side an outlet opening for the discharge of the purified molten metal. These two openings are equal to the rotational or pivot axis of the furnace vessel. The furnace interior is divided in the initial position by means of at least one weir arranged in two sections, wherein the weir in the lower region has a passage opening for the melt and in his Height at least over the axis of rotation of the furnace vessel extends beyond. In the furnace interior, along one of the longitudinally extending side walls, a trough-shaped channel for the passage of the molten metal is disposed in the refractory lining, which is used when the furnace vessel is in the 0 ° position. In the bottom region of the furnace vessel means, such as purging stones or Spüllanzen, provided for supplying purge gas. In the cover or in the lid of the furnace vessel means for heating and degassing of the furnace are installed.

The oven can be used both in 90 ° position and in 0 ° position in continuous operation. In the 90 ° position, batch operation is also possible.

When the oven is in the 0 ° position, the molten metal can flow through the oven via the channel. The channel-shaped channel thus acts as a connection between two adjacent furnaces or a furnace and the associated casting plant. To treat the molten metal, each purging plug or rinse lance is charged with a precisely defined amount of reaction gas. When the oven is rotated 90 ° clockwise, the U-shaped opening faces up and the bottom where the gas purging devices are installed points downwards. The interior of the furnace is filled with molten metal up to the height of the outlet opening.

Since the center line between the inlet and outlet openings is arranged at least one meter above the floor, the furnace vessel fills up to this center line, on which the axis of rotation of the furnace vessel is located. This relatively high level, due to the U-shape of the furnace interior, allows a particularly efficient purge gas treatment, since the reaction gas supplied to the bottom to the surface of the molten metal a relatively long distance through the Melt must cover. As a result, an intensive mass transfer is ensured in order to bind or dissipate gas dissolved in the melt by means of reaction or inert gases (or floatable particles).

If the treatment of the melt to be stopped with purge gas, the furnace vessel is pivoted to the 0 ° position.

The furnace according to the invention is very suitable for continuously operated foundries, in which large quantities of molten metal per unit time must be treated continuously. About the number of purging bricks, which are installed in the oven, the reactive purge gas per unit time can be tailored to the amount of metal to be treated. The advantage that a purge stone only ever reaches an optimum effect with a certain amount of purge gas can thus be used effectively. When using several purging stones can be made via a cascade control a gradation in terms of the total amount of gas used. In this case, only as much purging stones are charged with reactive gas, as are required for each amount of metal to be cleaned. The remaining flushing stones are charged with inert gas.

The furnace can also be used as a pure continuous furnace if, due to special conditions, a purge gas treatment is not required.

In the oven interior, several weirs can be arranged, which divide the oven into a corresponding number of sections. For example, 3, 7 or 9 weirs can be arranged in the interior of the furnace. This divides the oven into 4, 8 or 10 sections. In each section at least one rinsing unit is arranged. This makes it possible to realize an increase in the amount of purge gas, whereby larger amounts of molten metal can be treated.

Preferably, the furnace vessel for carrying out the pivoting movement (up to 110 ° about the longitudinal axis) with at least two semi-circular runners, which are supported on arranged in the top frame front and rear bearing rollers connected. The bearing rollers are arranged at different distances to the mounting plane, such that in the operating state at 0 ° position of the furnace vessel, the furnace interior can be completely emptied and at 90 ° position of the furnace vessel, the level top below the filling opening. The inclination of the furnace vessel is about 10 to 15 °.

To realize the pivoting movement of the furnace vessel, a plurality of hydraulic cylinders are arranged on the attachment frame, whose retractable and retractable piston rods are in communication with the furnace vessel.

In the side wall of the furnace vessel, in which the channel-shaped channel is located, a Notabstichöffnung can still be provided in order to empty the furnace in case of obstruction of the outlet pipe can.

The oven can be used both as a treatment and continuous furnace. The switching time is very short (minutes).

It is advantageous that due to the U-shaped design of the furnace interior effective Spülgasbehandlung without additional aids, such as. Rotors, is made possible. The wear of the refractory lining of the furnace during Spülgasbetriebes is comparatively very low.

The purge gas treatment of the melt takes place in a closed treatment room (no contact with the open atmosphere), whereby unwanted chemical reactions during treatment are avoided.

The novel furnace is particularly well-suited for providing molten metal from the smelting process for continuous casting processes (continuous casting, strip casting) in high quality.

The furnace may be used for any such molten metal requiring purge gas treatment, e.g. also for the removal of oxygen from copper to produce so-called "oxygen-free copper".

The new furnace is also characterized by a particularly economical operation, in comparison with known solutions, a saving of reaction or inert gas in the amount of about 10% is achieved for the same amount of treated metal. Due to the fastest possible conversion from continuous operation to purge gas operation in a short time (within minutes), the production costs can be further reduced.

Fig. 1

den erfindungsgemäßen Ofen in 90°-Stellung als Querschnittsdarstellung gemäß der Linie B-B in Fig. 2,

Fig. 2

einen Schnitt gemäß der Linie A-A in Fig. 1 und

Fig. 3

eine Rückansicht des Ofens.

The invention will be explained in more detail below using an exemplary embodiment. In the accompanying drawing show

Fig. 1

the oven according to the invention in a 90 ° position as a cross-sectional view along the line BB in Fig. 2 .

Fig. 2

a section along the line AA in Fig. 1 and

Fig. 3

a rear view of the oven.

The in the FIGS. 1 to 3 shown furnace consists of a cross-sectionally U-shaped furnace vessel 1 as a steel housing design with a refractory and insulating acting lining 2 based on mineral building materials. The furnace vessel 1 has two parallel spaced longitudinal side walls 4 and 5, a semi-circular bottom part 6, two narrow side walls 7 and 8 (FIGS. Fig. 2 ) and a cover or Lid 9. The lockable lid 9 is also equipped with a refractory and insulating lining. The furnace vessel 1 is connected to two semi-circular curved runners 10, which are supported on bearing rollers 11. The bearing rollers are rotatably mounted in bearing blocks 12, which are connected to the attachment frame 13.

On the narrow side walls following carriers of the top frame 13 is a respective hydraulic cylinder 14 ( Fig. 3 ), whose pistons 15 engage the adjacent narrow side wall 7 and 8 of the furnace vessel 1.

By operating the hydraulic cylinder 14, the furnace vessel 1 from the upright position (initial position, 90 ° position) ( Fig. 3 ) in a horizontal position (0 ° position) about the longitudinal or rotation axis 17 (FIG. Fig. 1 ) and back to starting position. The 90 ° position (starting position) of the furnace vessel 1 is the working position and the 0 ° position, the flow position, ie the molten metal can flow through the furnace vessel 1 in the longitudinal direction.

For this purpose, the side wall 4 pointing in the 0 ° position, downwards, in the direction of the ground, or the refractory lining thereof, is provided with a channel-shaped channel 18, which runs slightly inclined in the direction of flow. Via the channel-shaped channel 18, the molten metal flows in the direction of the outlet pipe 19, which is integrated into the furnace vessel 1 on the narrow side 8. In the opposite narrow side 7 is the inlet opening 29 for the molten metal.

The furnace interior 3 of the furnace vessel 1 is by arrangement of a weir 20 (FIG. Fig. 2 ) made of refractory material in two sections 21 and 22 separately.

The weir 20 has on its underside a passage opening 23 for the supplied via the inlet opening 29 melt and extends in height slightly above the height of the axis of rotation 17 addition, so that in the working position of the furnace (90 ° position) no liquid metal over the weir can flow ( Fig. 2 ).

Both before and after the weir 20 are in the oven floor 6 at least one sink 26, 27 or at least one rinse lance each embedded in the refractory masonry. So that in the operating state the purge gases introduced via the purge stones have sufficient time to rise in the melt, the perpendicular distance h (FIG. Fig. 1 ) between the top of the furnace floor 6 and the axis of rotation 17 at least one meter.

The lid 9 locked on the oven vessel 1 is equipped with two burners 24 and 25 for heating the oven vessel 1. Further, in the cover 9, an exhaust port 28 and other openings for introducing Spüllanzen and / or temperature sensors are provided, which are not shown in detail. In addition, an inspection opening is provided which can be closed with a cover 30 ( Fig. 2 ).

The cover 9 is attached to the furnace vessel 1 so that it does not change its position during the pivoting movement of the furnace vessel.

• Zur Behandlung der Metallschmelze bzw. zur Entfernung von Verunreinigungen befindet sich der Ofen in der 90°-Stellung (Figuren 1 und 2). Über die Einlassöffnung 29 fließt Metallschmelze in den ersten Abschnitt 21 des Ofeninnenraumes 3 und gelangt über die Durchtrittsöffnung 23 in den zweiten Abschnitt 22. Der Ofeninnenraum wird bis zu einem Füllstand in Höhe des Auslaufrohres 8 mit Metallschmelze gefüllt.

To the furnace vessel 1, a walk-in walkway or a stage 16 is arranged ( Fig. 1 ) .The operation of the stove is as follows:

• For the treatment of molten metal or for the removal of impurities, the furnace is in the 90 ° position ( FIGS. 1 and 2 ). Metal melt flows into the first section 21 of the furnace interior 3 via the inlet opening 29 and passes into the second section via the passage opening 23 Section 22. The interior of the furnace is filled to a level at the level of the outlet pipe 8 with molten metal.

During the filling process with molten metal is already started with the supply of purge gas through the purge stones 26, 27 and Spüllanzen.

Each purging plug is charged with a defined amount of purge gas. The pre-pressure of the purge gas must be higher than the maximum metallostatic pressure of the metal column in the furnace interior plus pressure loss of the purge stones or flushing lances. Purge gas flows into the molten metal only under these conditions.

Due to the U-shaped furnace construction, the reactive gas introduced near the bottom of the molten metal requires a relatively long flow path up to the metal bath surface. This has proven to be a decisive advantage, since thus a particularly effective mass transfer between purge gas and present in dissolved form in the melt gas can take place and at the same time still floatable particles or impurities are expelled in the melt.

At the end of the purge gas treatment, the furnace vessel 1 is pivoted counterclockwise to the 0 ° position (continuous position) about the axis of rotation 17. The cleaned molten metal now flows along the channel 18 in the direction of the outlet pipe 19, e.g. in a strip casting mold for the production of copper strip.

When all molten metal in the furnace has drained off, the purge gas supply is interrupted. Subsequently, the oven can be moved back to its original position (90 ° position) with a new treatment cycle. The pivoting movement of the furnace to its initial position (90 ° position) is limited by an end stop 31.

The furnace according to the invention is particularly well suited for a reducing treatment of liquid copper for a continuously operating continuous casting plant. In this case (continuous operation, 90 ° position) the furnace remains filled as long as the incoming melt, e.g. Copper melt, to be treated with reactive gas. The treated copper melt runs continuously over the outlet pipe 19 and passes e.g. in a downstream continuous casting plant.

By equipping the oven with seven sinks in the bottom of the oven, very good results can be achieved.

For purge gas supply a gas pressure control station and a flow control are provided, each purging plug can be acted upon separately with a defined amount of pure CO gas. In the working position (90 ° position) and during the continuous operation (0 ° position), each purging plug can be purged with nitrogen instead of reactive gas. The admission pressure for the gases is set, for example, to 3.5 bar.

By equipping the oven with seven sinks in the bottom of the oven, very good results can be achieved.

With continuous supply of reactive gas, the following results can be achieved:

Treatment of 55 t / h molten copper (Cu PHC)

• Four purging stones, purge gas 100% CO
• Oxygen content of the incoming copper: 60-80 ppm
• Oxygen content of the effluent copper: 30-40 ppm.

Treatment of 55 t / h copper melt (Cu OFHC)

• Seven purging stones, purge gas 100% CO
• Oxygen content of the incoming copper: 60-80 ppm
• Oxygen content of the effluent copper: <10 ppm.

Claims (13)

1. A furnace for removing impurities from metal melts, preferably aluminum or copper-based, wherein the heatable furnace vessel (1) is equipped with a refractory lining, has a U-shaped cross-section as well as a furnace inner space (3) and the furnace vessel (1) is disposed so as to be pivotable from a vertical starting position (90° position) around a rotational axis (17) to a horizontal position (0° position) and back to the starting position, characterized in that the furnace vessel (1) comprises an inlet opening (29) at one of the two narrow sides (7) and an outlet opening (19) for the cleaned melt at the other opposite narrow side (8), which are disposed at the height of the rotational axis (17), and in its starting position the furnace inner space (3) is divided into two sections (21, 22) by means of at least one provided weir (20), wherein the weir (20) comprises a passage opening (23) for the melt in its bottom area and extends in height at least beyond the rotational axis (17) of the furnace vessel (1), and a gutter-shaped channel (18), which is configured for the flow of the metal melts in the horizontal position of the furnace vessel (1), is arranged in the inner space (3) of the furnace along one of the longitudinal sides (4) in the refractory lining (2), and means (26, 27) for supplying purge gas are disposed in the bottom area in the starting position of the furnace vessel (1).
2. The furnace according to claim 1, characterized in that both in its 90° position and in its 0° position, it can be used in continuous operation.
3. The furnace according to claim 1, characterized in that in its 90° position, it can be used in discontinuous operation.
4. The furnace according to one of the claims 1 to 3, characterized in that several weirs (20) are disposed in the inner space (3) of the furnace so that they divide the furnace into corresponding sections.
5. The furnace according to one of the claims 1 to 4, characterized in that at least one purge plug (26, 27) or a flushing lance is disposed in each of the furnace sections (21, 22).
6. The furnace according to one of the claims 1 to 5, characterized in that the rotational axis (17) of the furnace vessel (1) is disposed at a distance of at least one meter from the deepest point of the inner space (3) of the furnace, when the furnace vessel is in its starting position (90° position).
7. The furnace according to one of the claims 1 to 6, characterized in that the amount of purge gas supplied through the purge plugs or flushing lances is controllable by means of a cascade control.
8. The furnace according to one of the claims 1 to 7, characterized in that a reactive gas or an inert gas is useable as a purge gas.
9. The furnace according to one of the claims 1 to 8, characterized in that the furnace vessel (1) is connected with at least two semicircular blades (10) that are supported by front and rear bearing rollers (11) disposed in the mounting frame (13).
10. The furnace according to one of the claims 1 to 9, characterized in that the front and rear bearing rollers (11) are respectively disposed at different distances from the installation plane, so that during operation, in a 0° position of the furnace vessel (1), the inner space (3) of the furnace can be completely emptied and in a 90° position, the upper edge of the fill level lies below the inlet opening (29).
11. The furnace according to one of the claims 1 to 10, characterized in that for implementing the pivoting movement of the furnace vessel (1), several hydraulic cylinders (14), whose extendable and retractable piston rods (15) are connected with the furnace vessel (1), are disposed on the mounting frame (13).
12. The furnace according to one of the claims 1 to 11, characterized in that an emergency discharge aperture is provided in the lateral wall (4) of the furnace vessel (1) in which the gutter-shaped channel (18) is arranged.
13. The furnace according to one of the claims 1 to 12, characterized in that means for heating (24, 25) and degassing the furnace are provided in the cover (9) of the furnace vessel (1).

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