Casting Method and Casting Installation for Aluminium or Aluminium Alloys

Abstract

The invention relates to a 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 metal is cast into semi-finished products or similar. A number of casting ladles (25) are used to treat and feed the molten aluminium to the respective casting station (33, 34). The ladles are filled with the molten metal and the latter is then transported to at least one additional stage (32), where it is treated. The molten metal is subsequently delivered in the ladles (25) to the casting station (33, 34), where the ladles (25) are emptied. The invention thus provides an efficient method that can be flexibly adapted to the time periods of the process, said periods altering according to the situation.

Description

The invention concerns a casting method for aluminium and/or aluminium alloys in accordance with the generic term of claim 1 and also a casting machine for implementation of the method.

Casting methods and casting machines for aluminium and/or aluminium alloys are known in the art, in which solid or liquid aluminium is melted in a smelting furnace and then retained in a refining furnace, from which the molten aluminium flows via a long channel to a casting station and is thereby exposed to different treatments. Thus, alloy additions are added to the molten aluminium flowing down the channel and an inert purging gas (argon) is injected, before the melt, via a filter, reaches the casting station, in which it is cast into semi-finished products (cf. FIG. 1 in which an ordinary casting machine for aluminium is shown diagrammatically). Only limited homogenisation of the molten aluminium is possible. The treatment times are tied to the casting process and thus predetermined and limited in terms of time.

The individual treatment stations have to be co-ordinated with each other perfectly. If one of the stages of this in-line machine does not function, then the entire casting machine has to be shut down. The long channel through which the molten aluminium flows means a loss of temperature so that the material has to be overheated in the refining furnace so that a sufficient temperature can be reached on arrival at the casting station. Extensive casting times mean that the smelting and refining furnace has to be available for the entire casting time, before the next batch of melt is used. The energy consumption of the furnaces is correspondingly high. Normally, reverbatory furnaces with hydrocarbon fuel are used, giving rise to the disadvantage of a rapid absorption of hydrogen from the burner flame. Furthermore, greenhouse gases and other pollutants which load the atmosphere are also created. The long, open channel through which the molten aluminium runs, however, also means that the metal absorbs hydrogen from the atmosphere and causes the formation of dross.

The present invention is based on the problem of proposing a more economical and more flexible casting method for aluminium and/or aluminium alloys and also of creating a casting machine to implement the method, enabling an optimal period for the treatment and casting of the molten aluminium and thereby achieving an improved quality of the semi-finished products to be produced.

This problem is solved according to the invention by a casting method with the characteristics of claim 1 and by a casting machine with the characteristics of claim 13.

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

By making use of ladles in accordance with the invention for the treatment and feeding of molten aluminium in controllable sequences, preferably to several casting stations, this phase of the method is decoupled in terms of time from the actual casting process. The individual treatments are no longer fixed and temporally restricted, but can if necessary be adapted until the desired quality of the molten aluminium to be cast is achieved in the relevant ladle.

The method according to the invention is considerably more efficient than the in-line method since there is no longer any need for large refining furnaces. If used at all, the furnaces are used for smelting and heating, but not for keeping warm over longer periods. These can be in the form of energy-efficient and ecologically advantageous induction furnaces.

The invention is next explained in more detail with the aid of the drawings, which show:

FIG. 1 diagram of an embodiment of a state of the art casting machine for aluminium; and

FIG. 2 diagram of an embodiment of an aluminium casting machine according to the invention.

FIG. 1 shows a state of the art casting machine 1 for aluminium and/or aluminium alloys. Liquid or solid aluminium is introduced as basic material in a first stage or station 2, which comprises a smelting furnace 3 and a refining furnace 4 attached thereto. For example, the aluminium can be supplied from a potroom by means of a transfer ladle 5 or as a scrap batch. The furnaces 3, 4 are usually large reverbatory furnaces using hydrocarbon fuel. The melt produced in the smelting furnace 3 is heated in the refining furnace 4 to the necessary temperature and partly homogenised by agitation.

Once the molten aluminium has reached the necessary temperature, it is guided out of the refining furnace 4 via a long channel 6 to a casting station 7, whereby it flows through various treatment stations 11, 12, which together with a filter 13 connected upstream of the casting station 7 form a second stage 10 of the casting machine 1. In the treatment station 11, various alloy additions are added to the molten aluminium. Gas purification occurs in the treatment station 12.

The casting station 7, in which the molten aluminium is cast into semi-finished products, can be operated continuously or semi-continuously in a way known in the art and therefore not described in more detail.

The treatment periods in the second stage 10 are tied to the casting process to be carried out in the casting station 7 and thus predetermined and restricted. The individual treatment stations 11, 12 must be perfectly synchronised with each other in their function. If one of the stages of this in-line machine does not function, then the entire casting machine 1 has to be shut down. The long channel through which the molten aluminium flows means a loss of temperature so that the material has to be overheated (e.g. to 730° C.) in the refining furnace 4 so that a sufficient temperature (e.g. 700° C.) can be reached on arrival at the casting station 7. Extensive casting times mean that the smelting and refining furnace 4 has to be available for the entire casting time, before the next batch of melt is used. The energy consumption of the furnaces 3,4 is correspondingly high.

In reverbatory furnaces with hydrocarbon fuel, the disadvantage arises of a rapid absorption of hydrogen from the burner flame. Furthermore, greenhouse gases and other pollutants which load the atmosphere are also created. The long, open channel 6 through which the molten aluminium runs, however, also means that the metal absorbs hydrogen from the atmosphere and causes the formation of dross.

FIG. 2 shows a diagram of a casting machine 1 according to the invention for aluminium and/or aluminium alloys. The first stage of the casting method according to the invention occurs in a filling station 21, in which hot molten aluminium is poured into a number of ladles 25. The ladles can for example have a capacity of 15 t. Either liquid, hot (temperature approx. 900° C.) aluminium from a potroom can be poured directly into the ladles 25 using transfer ladles or at least one, preferably several, furnaces 22, 23, 24 are assigned to the filling station 21 and are responsible for delivering the molten aluminium, whereby in addition to liquid aluminium, scrap aluminium or ingots provided for recasting can serve as basic material. The molten aluminium can for example be poured into one of the ladles 25 at half-hourly intervals. Advantageously molten aluminium of varying quality (with different degrees of aluminium purity) can be poured from the individual furnaces into the ladles 25, whereby the filling of the ladles 25 with molten aluminium, possibly also with mixed material from various furnaces 22, 23, 24, can be computer-controlled.

Preferably, electrical induction furnaces can be used as furnaces 22, 23, 24, which are considerably more efficient in energy terms than reverbatory furnaces. These can for example be induction furnaces with a capacity of 20 t, from each of which 15 t of molten aluminium can be poured into one of the ladles 25 and the remaining 5 t can serve when smelting a further charge.

The casting machine 1 according to the invention has a purification and preparation station 30, from which purified and pre-heated ladles 25a are transported to the filling station 21 for filling (ladles 25 on a transport section are generally designated in FIG. 2 by the letter T). By pre-heating the ladles 25 to, for example, 900° C., the molten aluminium poured from the furnaces 22, 23, 24 operated at a temperature of approx. 800° C. can remain for longer in the ladles 25 until it falls to the typical casting temperature of 700° C., as would be the case without pre-heating.

After the respective ladles 25 have been filled, the dross is skimmed off the surface of the melting bath (dedrossing) by tilting the ladle.

The ladles 25 filled in the filling station 21 are transported to a treatment station 32, in which the second stage of the casting process occurs. Firstly alloy additions are added to the molten aluminium (cf. the ladles referred to as 25b in FIG. 2). (However, it is also possible first to place at least part of the alloy additions in the cleaned ladles 25a before pouring in the melt.) After that the molten aluminium is homogenised and purified (cf. ladles 25c). To this end, the ladles are placed beneath a rotary impeller immersible in the respective ladles 25c to inject inert gas, e.g. argon or nitrogen, whereby combined hydrogen removal, homogenisation and/or thermal regulation of the molten aluminium can occur. The injection of argon eliminates the absorption of hydrogen from the humidity present in the atmosphere and the formation of dross is reduced. To remove alkali trace contaminants, small amounts of chlorine can be added into the purge gas.

Following treatment of the molten aluminium the ladles 25 can be kept in storage stations provided for this purpose (in FIG. 2 such storage stations are generally designated by the letter S), until a casting station 33 or 34 is available. The casting machine 20 preferably has several such casting stations (two shown in FIG. 2), to which the ladles 25 can be transported from the treatment or storage station, and in which the molten aluminium is cast into semi-finished products.

The temperature of the molten aluminium is maintained advantageously by covering the ladles 25 with a cover.

During the time spent in the storage station S, the temperature in the ladles 25 can be reduced by the injection of argon through a porous plug in the base of the ladle or maintained or increased by means of a small burner built into the ladle cover.

The emptying of the ladles 25d at the respective casting station 33, 34 occurs through the base of the ladle by means of controllable opening of a sliding closure, whereby the outflowing molten aluminium is guided into a collector spout, preferably encased by an inert gas. During this phase, too, argon can be blown in through the porous plug in the ladle base, agitating and purifying the melt. By covering the ladles 25d, inert atmospheres can be created in their upper area, which reduces oxidation and absorption of hydrogen.

The casting stations 33, 34 are each equipped with a filter system in a way known in the art and are operated continuously or semi-continuously.

After emptying the ladles 25d, these are transported to the aforementioned cleaning and preparation station 30 where they are cleaned (cf. ladle 25e) and prepared for re-use, in particular pre-heated (cf. ladle 25a). The emptied ladles can also be stored until further use in the storage stations S provided for this purpose.

There are multiple routes provided to transport the ladles 25 from one station to the next or to the storage stations (S), whereby the ladles 25 can be transported on rails or by means of overhead hoists.

The casting machine according to the invention is equipped with a control system to control the charges to be poured out of the individual furnaces 22, 23, 24 into the individual ladles 25, the alloy additions, heating, cooling, gas supply and treatment times, so that the molten aluminium reaches the casting stations 33, 34 in the desired quality, at the desired temperature and fully homogenised.

By the use of ladles 25 according to the invention for the treatment and feeding of molten aluminium in controllable sequences to preferably several casting stations 33, 34, this process phase is decoupled in terms of time from the actual casting process. The individual treatments are no longer predetermined and limited in terms of time, but can be adjusted as required, until the desired quality of the molten aluminium to be cast is achieved in the respective ladle. If, for example, a lower hydrogen content is required, the gas purification period can be extended. This option did not exist in the traditional in-line process according to FIG. 1. The production output of the casting machine depends on the actual casting process, solely at the casting stations, which can be continued until the supply of the treated molten aluminium to the casting stations is interrupted as required.

The method according to the invention is considerably more efficient than the in-line process, since there is no longer any need for large refining furnaces. If used at all, the furnaces are used for smelting and heating, but not for keeping the melt warm over longer periods. These can be in the form of energy-efficient and ecologically advantageous induction furnaces. By pre-heating the ladles, the smelting temperature achievable in the furnaces can be lower.

Claims

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, 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 claim 1, characterised in that after filling the respective pan (25), the dross is skimmed off the surface of the melting bath (dedrossing) to which end the pan is brought into a tilted position.

6. Casting method according to claim 1, 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 claim 2, 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 claim 1, 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 claim 1, 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 claim 6, 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, homogenisation, 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 claim 1, 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, 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 claim 13, 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 claim 13, 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 claim 13, characterised in that the ladles (25) are equipped with a porous plug for injection of an inert gas.

19. Casting machine according to claim 13, 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).