EP1607156B1 - Casting method and installation for casting aluminium or aluminium alloys - Google Patents

Abstract

Al and Al alloy casting process in which the Al melt is added to at least one casting station (33, 34) where the melt is cast to a semifinished product. In adding the Al melt to the casting station a number of ladles (25) are used, into which the melt is filled, transported and treated in a further step (32) and finally fed to casting stations 33 or 34 with removal of the ladles. An independent claim is included for a casting unit as described above.

Description

The invention relates to a casting method for aluminum or aluminum alloys according to the preamble of claim 1 and a casting installation for carrying out the method.

There are known casting and casting systems for aluminum or aluminum alloys (Prospectus, BAYSIDE Aluminum, Aluminum Manufacturing Process, 2003), in which solid or liquid aluminum is melted in a melting furnace and then held in a heat holding furnace, from which the melt through a long groove flows to a casting station and is subjected to different treatment. Thus, alloying additives are added to the melt flowing through the channel and an inert cleaning gas (argon) is injected before the melt passes through a filter to the casting station, where it is cast into semi-finished products (cf. Fig. 1 in which a conventional casting plant for aluminum is shown schematically). A Homogenization of the melt is limited. The treatment times are bound to the casting process and thus predetermined and limited in time.

The individual treatment stations must be perfectly coordinated. If one of the stages of this in-line system does not work, the entire casting plant must be shut down. The long channel through which the melt passes means a loss of temperature, so that the material in the heat-holding furnace must be overheated, so that a sufficient temperature can be reached at the casting station at start-up. Extensive casting times mean that the melting and holding furnace must be available for the entire casting time before the next melting rate is used. The energy consumption of the stove is correspondingly large. As a rule, flue furnaces ( reverberatory furnaces ) with hydrocarbon are used as fuel, which causes the disadvantage of rapid absorption of hydrogen from the burner flame. In addition, greenhouse gases and other pollutants polluting the atmosphere are produced. However, the long, open channel for the flow through the melt also means that the metal absorbs the hydrogen from the atmosphere and causes the formation of slag.

It is according to the document DE-A-37 36 117 However, a plant known for the production of steel, in which the steel is melted in an oven and filled into pans and with these a continuous casting takes place. The various treatment stations, which are formed by electric furnace or by pans, should be arranged spatially so that they are rectilinear to each other.

The present invention has for its object to provide a more economical and flexible casting process for aluminum or aluminum alloys and a casting plant for performing the To provide a method that allow optimal timing for the treatment and casting of the molten aluminum and with which an improved quality of the semi-products to be produced can be achieved.

This object is achieved according to the invention by a casting method having the features of claim 1 and by a casting installation having the features of claim 13.

Preferred refinements of the casting method according to the invention and the casting installation according to the invention form the subject of the dependent claims.

By the inventive use of pans for the treatment and feeding of Alauschmelze in controllable sequences to preferably several Giessstationen this process phase is decoupled from the actual casting process in time. The individual treatments are no longer fix fixed and limited in time, but they can be adjusted as needed until the desired quality of the melt to be poured in the respective pan is achieved.

The inventive method is much more efficient than the in-line method, since the need for large heat holding furnace is eliminated. If anything, the furnaces are used for melting and heating, but not for keeping heat for long periods of time. These can be designed as an energetically efficient and ecologically advantageous induction furnace.

Fig. 1

schematisch ein Ausführungsbeispiel einer dem Stand der Technik entsprechenden Giessanlage für Aluminium; und

Fig.2

schematisch ein Ausführungsbeispiel einer erfindungsgemässen Giessanlage für Aluminium.

The invention will be explained in more detail with reference to the drawing. Show it:

Fig. 1

schematically an embodiment of a prior art casting plant for aluminum; and

Fig.2

schematically an embodiment of an inventive casting plant for aluminum.

Fig. 1 shows a prior art casting plant 1 for aluminum or aluminum alloys. As starting material, liquid or solid aluminum is introduced into a first stage or station 2, which comprises a melting furnace 3 and a heat-holding furnace 4 connected to it. For example, the aluminum may be delivered from a filling space by means of a transporting pan 5 or as a scrapload. The furnaces 3, 4 are generally large flame furnaces with hydrocarbon as fuel. The melt produced in the melting furnace 3 is heated in the heat holding furnace 4 to the necessary temperature and partially homogenized by stirring.

After the aluminum melt has reached the required temperature, it is passed from the heat holding furnace 4 via a long channel 6 (channel) to a casting station 7, wherein it passes through various treatment stations 11, 12, which together with a casting station 7 upstream filter 13 a second Form 10 of the casting plant 1 generally known as gutter treatment. In the treatment station 11 the Alauschmelze various alloying additions are added. In the treatment station 12, a gas cleaning takes place.

The casting station 7, in which the molten aluminum is poured into semi-products, can be operated continuously or semi-continuously in a manner known per se and therefore not described in more detail.

The treatment times in the gutter stage 10 are bound to the casting process to be performed in the casting station 7 and thus predetermined and limited. The individual treatment stations 11, 12, 13 must be perfectly matched in their function in terms of time. If one of the stages of this in-line system does not work, the entire casting plant 1 must be shut down. The long channel or channel 6, through which the melt flows, means a loss of temperature, so that the material in the heat holding furnace 4 must be overheated (eg to 730 ° C), so that at the casting station 7 a sufficient temperature when starting (eg 700 ° C) can be achieved. Extensive casting times mean that the melting and holding furnace 4 must be available for the entire casting time before next melting rate is used. The energy consumption of the oven 3, 4 is correspondingly large.

In the case of the flame furnace with hydrocarbon as fuel, the disadvantage of rapid absorption of hydrogen from the burner flame arises. In addition, greenhouse gases and other pollutants polluting the atmosphere are produced. However, the long, open channel 6 (channel) for the flow of the molten metal also means that the metal absorbs the hydrogen from the atmosphere and causes the formation of slag.

In Fig. 2 an inventive casting plant 1 for aluminum or aluminum alloys is shown schematically. The first stage of the casting process according to the invention takes place in a filling station 21, in which hot aluminum melt is filled into a number of pans 25. The pans, for example, have a capacity of 15 t. It can either liquid, hot (temperature about 900 ° C) aluminum from a filling space by means of transport ladles are filled directly into the pans 25, or it is at least one, preferably more furnace 22, 23, 24 of the filling station 21 assigned and for the delivery responsible for the Alauschmelze, in addition to liquid aluminum also aluminum scrap or intended for remelting blocks can serve as starting material. For example, the melt can be filled into one of the pans 25 at half-hourly intervals. Advantageously, from the individual furnaces aluminum melt of different quality (with different degree of aluminum purity) are filled into the pans 25, wherein the filling of the pans 25 with Alauschmelze possibly even with mixed material from different furnace 22, 23, 24 may be computer controlled.

As furnace 22, 23, 24 can preferably be used electric induction furnace, which are much more efficient energy than flame furnace. This may be, for example, an induction furnace with a capacity of 20 t, from each of which the 15 t aluminum melt is filled into one of the pans 25 and the remaining 5 t are helpful in melting a further charge.

The casting installation 1 according to the invention has a cleaning and preparation station 30 from which cleaned and preheated pans 25a are transported for filling to the filling station 21 (pans 25 located on a transport route are in FIG Fig. 2 generally indicated by the letter T). By preheating the pans 25a to 900 ° C, for example, from the with a temperature of approx. 800 ° C operated oven 22, 23, 24 filled Alauschmelze longer in the pans 25 remain until it drops to the typical pouring temperature of 700 ° C, as it would be without preheating.

After filling the respective pan 25, the slag is skimmed off from the surface of the molten bath by bringing the pan 25 into an inclined position.

The pans 25 filled in the filling station 21 are transported to a treatment station 32, in which the second stage of the casting process runs. In this case, alloying additives are first introduced into the aluminum melt (compare the pans designated 25b in FIG Fig. 2 ). (However, at least some of the alloying additives can also be introduced into the cleaned pans 25a before the melt is introduced.) Thereafter, the aluminum melt is homogenized and cleaned (compare pans 25c). For this purpose, the pans are placed below an impeller immersed in the respective pan 25c for blowing an inert gas, for example argon or nitrogen, wherein a combined hydrogen removal, homogenization and / or thermal regulation of the aluminum melt can take place. The injection of argon eliminates the absorption of hydrogen from the moisture present in the atmosphere and reduces slag formation. To remove alkaline trace impurities, small amounts of chlorine may be added to the purge gas.

After treatment of the aluminum melt, the pans 25 can be stored in designated storage stations (in Fig. 2 are generally such storage stations with the letter S) are held until a casting station 33 and 34 is available. The casting plant 20 preferably has over several such casting stations (in Fig. 2 two shown), to which the pans 25 can be transported from the treatment or storage station, and in which the melt is poured into semi-finished products.

To maintain the Alauschmelze temperature, the pans 25 can be covered with a lid with advantage.

During the stay in the storage station S, the temperature in the pan 25 can be reduced by blowing argon through a porous plug in the pan bottom or maintained or increased by means of a small burner built into the pan lid.

The emptying of the pans 25d at the respective casting station 33, 34 takes place through the bottom of the pan with controllable opening of a sliding closure, wherein the outflowing aluminum melt is conducted into a collecting channel, preferably under sheath by an inert gas. Also during this phase argon can be blown through the porous plug in the pan bottom, whereby the melt is stirred and purified. By covering the pan 25d, inert atmosphere can be created in its upper region, which reduces the oxidation and absorption of hydrogen.

The casting stations 33, 34 are each equipped in a manner known per se with a filter system and are operated continuously or semi-continuously.

After emptying the pans 25d they are transported to the already mentioned cleaning and preparation station 30 and in this cleaned (see pan 25e) and prepared for reuse, in particular preheated (see pan 25a). The emptied pans can also be stored until reuse in designated storage stations S.

For the transport of the pans 25 from one station to the next or to the storage stations S multiple ways are provided, wherein the pans 25 can be transported on rails or by means of overhead cranes.

The casting plant according to the invention is equipped with a control system with which the batches to be filled from individual ovens 22, 23, 24 into the individual pans 25, the alloying additions, heating, cooling, gas supply and treatment times are controlled so that the aluminum melt in the desired quality, with desired Temperature and fully homogenized to the Giessstationen 33, 34 passes.

By the inventive use of pans 25 for the treatment and feeding of Alauschmelze in controllable sequences to preferably several Giessstationen 33, 34, this process phase is decoupled from the actual casting process in time. The individual treatments are no longer fix fixed and limited in time, but they can be adjusted as needed, until the desired quality of the molten aluminum to be poured in the respective pan is achieved. If, for example, a low hydrogen content is required, the gas purification time ( degassing ) can be extended. This possibility existed in the traditional in-line method Fig. 1 Not. The production capacity of the casting plant depends on the actual casting process at the casting stations alone, which can be continued until the feed the treated Alauschmelze is interrupted to the Giessstationen in a desired manner.

The inventive method is much more efficient than the inline method, since the need for large heat holding furnace is eliminated. If anything, the furnaces are needed for melting and heating, but not for keeping heat for long periods of time. These can be designed as an energetically efficient and ecologically advantageous induction furnace. By preheating the pans, the temperature of the melt which can be reached in the ovens can be a lower value.

Claims (19)

1. Casting method for aluminium or aluminium alloys, in which molten aluminium is treated and fed to at least one casting station (33, 34), in which the molten aluminium is cast into semi-finished products or similar, characterised in that
   a number of ladles (25) are used to treat and to feed the molten aluminium to the respective casting station (33, 34), the melt being poured into said ladles, transported to a further stage (32) and treated there, and is then delivered to the casting station (33, 34), in which the ladles (25) are emptied.
2. Casting method according to claim 1, characterised in that in a further stage (30) the emptied ladles (25) are cleaned and prepared for re-use, in particular are pre-heated.
3. Casting method according to claim 1 or 2, characterised in that in the first stage (21) the melt is poured from one or alternatively from several furnaces (22, 23, 24) into the ladles (25), whereby if there are several furnaces (22, 23, 24) molten aluminium of varying quality from the individual furnaces (22, 23, 24) can be poured into the ladles (25).
4. Casting method according to claim 3, characterised in that induction furnaces are used in the first stage (21).
5. Casting methods according to one of the claims 1 to 4, characterised in that after filling the respective ladle (25), the slag is skimmed off the surface of the melting bath to which end the ladle is brought into a tilted position.
6. Casting method according to one of the claims 1 to 5, characterised in that the second stage (32) includes the addition of alloying additions to the melt, their purification and homogenisation and also if necessary any temperature regulation.
7. Casting method according to claim 6, characterised in that in the second treatment stage (32), the ladles (25) can be placed underneath an immersible rotary impeller to blow in argon or nitrogen for combined removal of hydrogen, homogenisation and if necessary, thermal regulation, whereby additional small amounts of chlorine can be mixed into the purge gas to remove alkali trace contaminants.
8. Casting method according to one of the claims 2 to 7, characterised in that at least part of the alloy additions has been placed in the emptied and cleaned ladles (25) before the molten aluminium is poured in.
9. Casting methods according to one of the claims 1 to 8, characterised in that the ladles (25) run through the individual stations or stages on rails or by means of overhead hoists, whereby multiple routes lead to preferably several casting stations (33, 34), and to additional storage stations (S) to store ladles (25) filled with molten aluminium and/or empty ones until use.
10. Casting method according to one of the claims 1 to 9, characterised in that the emptying of the ladles (25) occurs at the respective casting station (33, 34) through the base of the ladles by controlled opening of a sliding closure, whereby the outflowing molten aluminium is guided into a collector spout preferably encased by an inert gas.
11. Casting method according to one of the claims 6 to 10, characterised in that the filling of the ladles (25) with molten aluminium, if necessary with mixed material from various furnaces (22, 23, 24), the addition of the alloy additions, the homogenisation, the thermal regulation and chronological sequence of treatment and feeding of the molten aluminium to the selected casting station (33, 34), is computer-controlled.
12. Casting method according to one of the claims 1 to 11, characterised in that the respective casting station (33, 34) operates continuously or semi-continuously and is equipped with a filter system.
13. Casting machine to carry out the process according to claim 1, with at least one casting station (33, 34) and with means of treating and feeding molten aluminium to the casting station (33, 34), characterised in that the means of treating and feeding molten aluminium comprise a number of ladles (25) fillable in a first filling station (21) with the molten aluminium, which are transportable to a second treatment station (32) and from there to the respective casting station (33, 34), whereby multiple routes for the transport are provided, and the ladles (25) are each fitted with a sliding closure or similar, by the opening of which they can be emptied.
14. Casting machine according to claim 13, characterised in that a further purification and preparation station (30) is provided for the emptied ladles (25), from which the ladles (25) are transportable to the filling station (21).
15. Casting machine according to claim 13 or 14, characterised in that additional storage stations (S) are provided for storage of ladles (25) filled with molten aluminium and/or emptied ladles (25) until use.
16. Casting machine according to one of the claims 13 to 15, characterised in that the filling station (21) is provided with a number of furnaces (22, 23, 24) which can be supplied with basic material, preferably induction furnaces, whereby the individual furnaces (22, 23, 24) can if necessary be supplied with aluminium material of varying quality.
17. Casting machine according to one of the claims 13 to 16, characterised in that the ladles (25) can be covered by a cover in which a burner can be installed to maintain or to increase the temperature of the molten aluminium.
18. Casting machine according to one of the claims 13 to 17, characterised in that the ladles (25) are equipped with a porous plug for injection of an inert gas.
19. Casting machine according to one of the claims 13 to 18, characterised in that rails or hoists are provided for the transport of the ladles (25) from one station to the next and to the storage stations (S).

Images