US20030129077A1

US20030129077A1 - Aluminium base alloy of scrap metal and casting alloy produced from this

Info

Publication number: US20030129077A1
Application number: US10/375,596
Authority: US
Inventors: Hubert Koch; Horst Schramm; Peter Krug; Gerhard Ost
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-12-24
Filing date: 2003-02-27
Publication date: 2003-07-10
Also published as: MXPA00012836A; NO20006644D0; EP1111077A1; US20010006606A1; NO20006644L; CA2329561A1; JP2001254128A; BR0006375A

Abstract

An aluminium base alloy for production of casting alloys with magnesium as the most essential alloy element contains at least 50% scrap metal on primary aluminium base and as the remainder primary aluminium and/or scrap metal on secondary aluminium base of known composition. For production of the aluminium base alloy mainly foodstuff and animal feed packings are used, separated with a pyrolysis process and then the aluminium contained in the packing recycled by melting. The casting alloys produced from the aluminium base alloy are suitable in particular for production of heat-resistant and/or corrosion-resistant parts in the engine area, in particular for production of engine blocks, cylinder heads and oil sumps, by means of sand casting, chilled casting, diecasting, thixocasting or thixoforging.

Description

The invention concerns an aluminium base alloy for production of casting alloys with magnesium as the most essential alloy element. The scope of the invention also includes a process for production of the aluminium base alloy, casting alloys produced from the aluminium base alloy and a process for their production.

For the production of heat-resistant and/or corrosion-resistant parts in the engine area of vehicles, today largely remelt alloys are used, also known as secondary aluminium alloys or scrap metal on a secondary aluminium base. Because of the composition of the standard secondary aluminium alloys, castings produced from this usually only have a slight elongation of less than 1%. For certain applications higher elongation values would be desirable without the alloys needing to be produced from relatively costly primary or virgin metal.

DE-C-1483229 discloses AlMgSi alloys made from secondary aluminium alloys or secondary metals for production of cylinder heads.

EP-A-0779371 and EP-A-0780481 disclose a process for preparation of aluminium-containing waste for recovery of aluminium from this waste. The essential core of this known process is the recovery of aluminium from materials contaminated with organic components, in particular from foodstuff and animal feed packing, in the form of printed and/or painted aluminium waste or aluminium/plastic compound material waste.

The invention is based on the task of preparing a low cost aluminium base alloy for production of casting alloys. Casting alloys made from the aluminium base alloy are suitable amongst others for production of heat-resistant and/or corrosion-resistant parts in engine areas.

The task according to the invention is solved by an aluminium base alloy which contains at least 50% scrap metal on a primary aluminium base and as the remainder primary aluminium and/or scrap metal on a secondary aluminium base of known composition.

The use of scrap metal on a primary aluminium base, i.e. primary alloys, leads to a relatively “pure” base material without high contents of generally undesirable accompanying elements.

If the content of undesirable accompanying elements is too high for a particular application, in this case the aluminium base alloy can be “diluted” with primary aluminium. In general, however, it should be noted that the scrap composition for production of an aluminium base alloy with a low content of undesirable accompanying elements is preselected accordingly before production of the scrap metal. Secondly, the aluminium base alloy can in principle contain, as well as the scrap metal on a primary aluminium base, also a certain proportion of scrap metal on a secondary aluminium base, but in this case the composition of the scrap metal should be known so that the quantity of undesirable accompanying elements introduced into the aluminium base alloy is not too great.

Preferably the proportion of primary alloys is at least 80% and ideally 100% of the scrap metal used.

Suitable scrap metal on a primary aluminium base is mainly recycling metal obtained from foodstuff and animal feed packaging.

For the production of a casting alloy from the aluminium base alloy according to the invention, magnesium can also be added up to a total content of 3.0 to 5.0 w. % and silicon up to a total content of 1.5 to 3.0 w. %. Further additional alloy elements are 0.5 to 1.2 w. % manganese and/or 0.5 to 1.2 w. % copper and max 0.2 w. % titanium, max 0.4 w. % cobalt, max 0.4 w. % cerium and max 1.2 w. % zirconium.

The casting alloys produced from primary aluminium alloys according to the invention achieve a higher elongation, which can be up to 6%, in relation to the casting alloys produced from secondary aluminium alloys according to the state of the art.

A process particularly suited for production of the aluminium base alloy according to the invention is characterised in that materials on a primary aluminium base contaminated with organic compounds are prepared separately according to their thermal value and their aluminium content, combined in measured quantities to achieve a nominal value, the organic compounds carbonised by pyrolysis with formation of pyrolysis gas and pyrolysis coke, the pyrolysis coke separated off, the materials pretreated in this way are where applicable bright annealed, and where applicable sorted to separate out foil constituents, and then melted.

Here, aluminium compound substances are suitably reduced to a unit size and after pyrolysis at least the iron parts are separated out.

In a suitable version of the process according to the invention, the separately prepared materials are combined to set the nominal value by way of a computer-controlled metering system, where in addition to the thermal value and the aluminium content of the materials, further parameters of the materials prepared can be taken into account, in particular their moisture, apparent density and grain size.

Depending upon the area of application of the casting alloy produced from the aluminium base alloy, with the known process by combining scrap or waste of various types, the composition of the aluminium base alloy can be set within certain limits i.e. the process allows in a simple manner the production of different aluminium base alloys for different applications. Tables 1 to 3 show as examples three mixtures of different scrap metals. The typical compositions of the individual scrap metals relate to 100% aluminium alloy. The tables also contain typical further compositions of aluminium base alloys produced from the three scrap mixtures. Here:

DSD material is combined packaging material provided by the system Duales System Deutschland

IGORA material is combined packing material produced by the Swiss collection point IGORA

mixed aluminium waste is presorted packing and other aluminium waste of various origins.

TABLE 1


Mixture I
50% DSD
Material

50% bottle	Composition in w. %

caps	Si	Fe	Cu	Mn	Mg	Cr	Ni	Zn

DSD material	0.20	0.60	0.10	0.40	0.30	0.01	0.01	0.05
Foreign	0.10	2.00	1.00	—	—	0.11	0.05	1.70
substances in
DSD material
Total DSD	0.30	2.60	1.10	0.40	0.30	0.12	0.06	1.75
material
Bottle caps	0.20	0.50	0.16	0.52	0.20	0.02	0.01	0.03
Aluminium	0.24	1.20	0.50	0.48	0.25	0.06	0.05	0.30
alloy 1

TABLE 2


Mixture II
40% IGORA
material
35% DSD
material

25% mixed	Composition in w. %

Al waste	Si	Fe	Cu	Mn	Mg	Cr	Ni	Zn

IGORA	0.28	1.00	0.14	0.35	0.18	0.012	0.01	0.05
material
Total DSD	0.30	2.60	1.10	0.40	0.30	0.12	0.06	1.75
material
Mixed	0.50	0.43	2.90	0.40	0.28	0.03	0.03	2.85
Al waste
Aluminium	0.37	1.13	1.10	0.40	0.30	0.03	0.03	0.60
alloy II

TABLE 3


Mixture III
50% DSD
Material

25% bottle
caps	Composition in w. %

25% cans	Si	Fe	Cu	Mn	Mg	Cr	Ni	Zn

DSD material	0.30	0.54	0.77	0.43	0.07	0.016	0.10	1.80
total
Bottle caps	0.20	0.50	0.16	0.52	0.20	0.02	0.01	0.03
Cans	0.20	0.40	0.16	0.77	0.83	0.01	0.01	0.02
Aluminium	0.20	0.49	0.50	0.55	0.32	0.02	0.05	0.45
alloy III

The following comments should be made on the composition of the scrap materials given in the table:

The relatively high proportion of zinc in the DSD material including the foreign substances is largely retained in the coke during pyrolysis so that the aluminium base alloy has a relatively low Zn content.

The composition of the aluminium base alloy cannot be determined theoretically from the compositions of the individual scrap metals of a mixture because packaging waste in particular contains a lot of plastic and adhering foreign substances such as foodstuff residue, and therefore the aluminium proportion in this scrap material is considerably less than with practically pure metal scrap such as for example cans or bottle tops.

In a particularly preferred process for production of a casting alloy starting from an aluminium base alloy, to a melt of aluminium base alloy including, where applicable, added further alloy elements are 0.02 to 0.15 w. % vanadium, preferably 0.02 to 0.08 w. % vanadium, in particular 0.02 to 0.05 w. % vanadium and less than 60 ppm beryllium.

The addition of vanadium leads to a higher scabbing resistance of the casting alloy than is possible with a beryllium addition according to the state of the art. It has namely been observed that the beryllium content of an aluminium magnesium alloy in the melt diminishes with time. When the beryllium concentration falls below a critical level, evidently scabs rapidly begin to form on the melt. An increased beryllium addition to the metal melt is undesirable due to the carcinogenic property of beryllium and should therefore be avoided as far as possible.

By the addition of vanadium to the alloy, the scab-reducing addition of beryllium can take place in substantially lower quantities than without the addition of vanadium. For a content of more than 3.5 w. % magnesium, it is sufficient to add 10 to 50 ppm beryllium, preferably 10 to 35 ppm beryllium. If the content of magnesium in the melt is less than 3.5 w. %, less than 25 ppm beryllium is required to achieve a high scabbing resistance. For lower requirements for the scabbing tendency, the beryllium addition can even be omitted.

The preferred area of application of the casting alloys produced from the aluminium base alloy- according to the invention is the production of heat-resistant and/or corrosion-resistant parts in the engine area, in particular engine blocks, cylinder heads and oil sumps, by means of sand casting, chilled casting, diecasting, thixocasting or thixoforging.

Further advantages, features and details of the invention arise from the following exemplary description of scrap preparation and the drawings, which show diagrammatically: [0029]
FIG. 1 a diagram of the main structure of a recycling plant; [0030]
FIG. 2 a basic flow diagram of the plant in FIG. 1; [0031]
FIG. 3 a block circuit diagram of the plant in FIG. 1; [0032]
FIG. 4 a process flow diagram of the plant in FIG. 1; [0033]
FIGS. [0034] 5-7 enlarged sections of FIG. 3.
A plant for recovery of aluminium from aluminium scrap contaminated with organic compounds according to FIGS. [0035] 1 to 7 has the three operating units:
BE1 Material preparation [0036]
BE2 Decoating plant [0037]
BE3 Melting plant. [0038]
The material preparation BE1 includes the material delivery, storage until charging and mechanical preparation and retention (buffering) of prepared material for the decoating plant BE2. [0039]
Materials to be processed in the plant are usually delivered by road or rail. The incoming materials are weighed. The nature, provenance and quantity of the materials supplied are recorded and documented. A reception test may be performed depending on the material type. [0040]
The material preparation BE1 in principle serves for preparation of two fundamentally different material types: [0041]
Chippings S[0042] 1 from metalwork. These are sieved, the coarse fraction reduced in size, and ferrous metals separated out.
Aluminium compound substances S[0043] 2. These are reduced to a unit size, for example 30×40 mm, and the ferrous metals removed. Materials used here are therefore e.g. DSD (Duales System Deutschland) material, painted plates and metal goods, painted extrusion profiles, painted tubes and aerosol cans, flexible packs of aluminium combined with plastic or paper, used aluminium cans, cooling radiator scrap, pipes, fins, cuttings, offset panels, cables stripped with grease, bottle caps, number plates, road signs and window profiles.
Aluminium compound substances S[0044] 2 are intermediate-stored in the case of immediately processing in a preparation room before coarse size reduction. The aluminium compound substances S2 for coarse size reduction are supplied by way of a delivery conveyor 10 and a subsequent further delivery conveyor 14 into a slow-running cutter 16. The first delivery conveyor 10 is supplied by way of a delivery shaft 12 by means of a forklift truck 18. It is also possible to supply the cutter 16 directly using the forklift truck 18.
The use of the slow-running [0045] cutter 16 for size reduction generates a specific low proportion of fine grains. Aluminium chips are mixed into the process later.
The coarsely reduced material falls from the rotor shears [0046] 16 onto a belt conveyor 20 which also has a delivery well 22 for optimum delivery of batch material. Arranged above the belt conveyor 20 is a magnetic separator 24 with separating aid. At this point the coarse iron constituents S3 are removed from the material flow.
The [0047] belt conveyor 20 is fitted with an integral strong field magnetic roller or magnetic drum 26. Here further iron constituents S3 including stainless steel are removed.
Alternatively the iron constituents S[0048] 3 can be separated first after pyrolysis.
The preferred aluminium compound substances S[0049] 2 are transferred by a steep belt conveyor 28 and distribution conveyor 30 into one of for example five buffer containers 32 a-e each with a capacity of for example 40 m³.
The [0050] buffer containers 32 are designed closed i.e. with encapsulated input and output and venting to an extraction system. The material stored is output as required by way of metering conveyors 34 a-e onto a belt conveyor 36; this passes the material to the distribution conveyor 38 for the decoating plant BE2.
As an alternative to delivery of the aluminium compound substances S[0051] 2 prepared after separation of the iron constituents S3 to the steep belt conveyor 28, these can for example be divided further in a cross-flow separator 29 according to the aluminium content or thermal value H_u. Separation into aluminium-rich constituents with a low thermal value H_u, e.g. profile sections, and low-aluminium constituents with a high thermal value H_u, e.g. coated foils, takes place in the cross-flow separator 29 on the basis of the different weight and specific contact section. The various fractions with different aluminium content or different thermal value H_uare then intermediate-stored separately in the buffer containers 32.
Aluminium chips S1 are taken by wheel loader from chip boxes in the supplier room and deposited by way of a [0052] delivery shaft 40 into a delivery conveyor 42 to a sieve 44. The sieve 44 separates the coarse and fine chippings.
The fine chippings travel by way of a [0053] belt conveyor 46 and a subsequent further belt conveyor 48, with an overhead magnetic separator 50 to separate the iron constituents S3, into a buffer container 52 with for example a capacity of 20 m³.
Any coarse material occurring e.g. bushy chips, are caught in a [0054] collection container 54 and transferred by the forklift truck 18 to the size reduction line for the aluminium compound substances.
Before the delivery of the fine chippings to the [0055] distribution conveyor 38, the material flow can pass through a metal detector 31 for detection and subsequent separation of undesirable non-ferrous metals.
Also after separation of the iron constituents, even for a lumpy part fraction of the [0056] cross-flow separator 29, the material flow can pass through metal detector 31 for detection and subsequent separation of undesirable non-ferrous metals.
The fine chippings are passed from the [0057] buffer container 52 by way of a metering conveyor 56 onto the belt conveyor 58 and thus reach the preparation line of the aluminium compound substances on the distribution conveyor 38 for the decoating system BE2.
The material from the compound and chip lines first reaches a buffer container or [0058] material store 60 in which the material is moistened where applicable. From here it reaches the input system of a pyrolysis drum 70. Instead of moistening in the buffer container 60, a pyrolysis delivery head can spray water, water vapour and/or an inert gas, e.g. CO₂.
At the treatment plant at various points such as the size reduction unit, transfer points and material buffer, extraction air is collected in order to prevent a diffuse release of emissions of foreign particles such as dust. The individual extraction air flows are combined and passed by way of a [0059] cyclone separator 62 and subsequent fan 64 to a combustion chamber 78 for afterburning. Solids separated out in the cyclone separator 64 are discharged into a container 68 by way of a cellular wheel sluice 66 and for example charged into the delivery well 22.
The decoating plant BE2 consists of the pyrolysis drum, a bright annealing machine, a foil separator, a pyrolysis gas combustion and a flue gas cleaning system with quench, heat exchanger, two-stage washer etc. [0060]
The material is supplied from the material preparation BE1 by way of the [0061] material delivery 60 and a sluice system consisting of two sealed pushers 72, 74 to the pyrolysis drum 70, which has a length L of approximately 25 m.
To avoid the emission of pyrolysis gas from the delivery area and to minimise undesirable air ingress into the [0062] pyrolysis drum 70, a reduced pressure is applied to the sluice system. Here, inert gas e.g. CO₂is flushed into this room and the gas between the two pushers 72, 74 is simultaneously extracted by means of a fan 76 and passed to the heating jacket exhaust gas S8 from the combustion chamber 78.
The sealed [0063] pushers 72, 74 are designed to be tightly closed. The material is added to the pyrolysis drum 70 in cycles by way of this pusher system. To avoid undesirable air ingress into the drum, in each case only one of the two pushers can be opened, which is guaranteed by means of an end position monitoring. A further seal is applied by way of the material presentation by way of the first double pusher 72, between the two sealed pushers 72, 74, and in an inlet screw 80 which can be liquid-cooled.
The pyrolysis process takes place at around 550° C. Because of the conditions of temperature and holding time conditions, it is guaranteed that on reaching the pyrolysis discharge head after around 50 minutes, the material is completely pyrolysed. Extensive degasification of the materials takes place in the [0064] pyrolysis drum 70.
The energy required for the pyrolysis process is supplied by way of a [0065] heating jacket 82 surrounding the pyrolysis drum 70. The heating jacket 82 is refractory-lined and designed without burners; the necessary hot gas S8 is supplied from outside the combustion chamber 70 to the heating jacket 82 and there evenly distributed along the pyrolysis drum wall. After flowing through the heating jacket 82, the hot gas S8, cooled to around 580° C. is guided by means of the fan in the heating jacket 84 of the pyrolysis gas lines 86 and then returned to the combustion chamber 78. It is returned to the combustion chamber 78 with a view to a closed circuit design and consequent emission reduction.
The [0066] heating jacket 82 consists of a boiler plate construction with refractory lining. To avoid the emission of hot gas between the heating jacket 82 and the rotary passage through the pyrolysis drum 70, cable seals are installed. Sealing occurs by mutually overlapping casting segments which are pressed against the rotating sealing surface of the rotary furnace by means of a surrounding cable over locking clamping pins. Because of the pressure conditions in the heating jacket 82, i.e. the slight pressure reduction, the fan arrangement on the suction side also prevents, by design, the emission of hot gas to the environment.
To start the [0067] pyrolysis drum 70, until sufficient pyrolysis gas is being produced, natural gas is used as the energy carrier. It is heated in the same manner i.e. by provision of heating energy from the combustion chamber 78.
The [0068] pyrolysis drum 70 is driven on the output side by way of a crown gear by means of a hydraulic drive, the drum also has an auxiliary drive. The drum rotation speed is for example 5 rotations per minute and can be varied.
The [0069] pyrolysis drum 70 is sealed on the input and output sides by means of a rotating mechanical seal and CO₂barrier gas supply.
The pyrolysis gas and the solids are separated at the pyrolysis discharge head. The pyrolysis gas is extracted under pressure control. The pressure control and subsequent [0070] pyrolysis gas line 86 are designed redundant for operating security.
At the pyrolysis discharge head the [0071] pyrolysis drum 70 projects with its end part 71 by a dimension a into an outlet housing 88. This end part 71 is designed as a sieve for separating the solids discharged from the pyrolysis drum 70 into a sieved fine fraction and a coarse fraction emerging from the open end part 71.
The solids discharged from the [0072] pyrolysis drum 70 which consist of aluminium and coke as the residue of organic adhesions of the materials introduced, are discharged from the outlet housing 88 by means of two sluice systems.
To separate the pyrolysis coke R1 the material is first guided on output from the [0073] pyrolysis drum 70 by way of a swivelling sieve 90. Fine material, i.e. pyrolysis coke R1, falls into a well 92 below and from there is discharged downwards in timed cycles by way of a sealed pusher 94, according to the material introduction.
The position of the [0074] sieve 90, which is designed as an adjustable flap, can be used to set the fraction size of discharge material allocated to the two sluice systems.
The pyrolysis coke R1 is cooled in a water-cooled [0075] cooling screw 96 with double casing and indirect cooling. From the screw the cooled coke falls into a cellular wheel sluice 98; this discharges into a transport container 100. The heat is dissipated through a cooling water circuit to which the quench water circuit is also connected, by way of a total of three cooling towers 102 a-c.
The composition of the pyrolysis coke allows a quantitative use in the production of carbon products e.g. anodes for aluminium electrolysis. [0076]
The remaining material—as the sieve residue of the [0077] sieve 90 —is discharged by way of a sluice system consisting of two sealed pushers 104, 106, according to the material input. The sealed pushers 104, 106 are in each case designed to be tightly sealed. The material is output in cycles by way of these pushers. To avoid undesirable air ingress into the pyrolysis drum 70, in each case only one of the two pushers can be opened, which is guaranteed by means of an end position monitoring.
The material is discharged from the sluice system onto a [0078] sieve 108 on which the free pyrolysis coke R1 remaining in material flow is discharged separately as sieve passage (fine goods) from the aluminium fraction by way of a cellular wheel sluice 110 into the cooling screw 96; as described above this empties by way of a cellular wheel sluice 98 into the transport container 100. The pyrolysis coke can for example be used in production of carbon anodes for electrolysis for aluminium production.
The hot aluminium main flow containing the pyrolysis coke R1 is supplied by way of a [0079] hot goods conveyor 112 and a cellular wheel sluice 114 to a bright annealing device 116. In this bright annealing device 116 the pyrolysis coke residue is burnt in a targeted fashion on an oscillating bed through which flows oxygen-regulated hot gas. A proportion of melt furnace extraction gas S19 is used as a hot gas, to which air is added depending on the oxygen content, on the extraction gas side of the annealing device 116. The hot gas is supplied by way of a hot gas fan 118. The resulting flue gases are supplied to the combustion chamber 78.
Ash R3, which is contaminated with aluminium particles, is separated from the aluminium main flow as sieve passage from the [0080] bright annealing device 116 and ejected by way of a cellular wheel sluice 128 into a collection container 130.
The annealed material i.e. bright aluminium, is discharged from the [0081] bright annealing device 116 as sieve residue by way of a cellular wheel sluice and then output, by means of two hot goods conveyors 122, 124 connected in succession to the foil separator, into a buffer container 126. Here, the material is supplied to a sieve 134 by way of a constant conveyor 132. Here, by means of melt furnace exhaust gases S19 and air at a mixing temperature of approximately 400° C., foil is removed from the material flow by air separation, and subsequently precipitated from the separated air in a hot gas cyclone 136 and discharged by way of a cellular wheel sluice 138 into a collection container 140. The hot gas leaves the hot gas cyclone 136 by way of a hot gas fan 137. The separated foil residue can be passed to separate recycling.
The heavy goods from the air separation, i.e. the remaining aluminium fraction, from the [0082] separator 134 reaches a hot goods conveyor 144 by way of a cellular wheel sluice 142. This opens into an alternating flap 146 which divides the material flow, i.e. bright aluminium S13, into two lines. One part is output directly to the buffer container 148, the other part reaches a further buffer container 154 by way of two hot goods conveyors 150, 152 connected in succession.
Both buffer containers or [0083] silos 148, 154 supply an attached melting plant BE3 by means of constant conveyors 156, 158.
The pyrolysis gas S[0084] 7 is taken from the pyrolysis drum 70 by way of a redundant pressure control on the outlet housing 88. The extraction quantity of gas depends on the pressure inside the drum.
The separated pyrolysis gas is transported in the shortest route by means of the, also redundant, double jacket heated [0085] pyrolysis gas line 86 to the combustion chamber 78. The heating jacket 84 of the pyrolysis gas line 86 here receives the heating jacket exhaust gas from the pyrolysis drum 70.
The [0086] combustion chamber 78 is a lined, high temperature-resistant combustion chamber (burner muffle) into which the pyrolysis gas is discharged by way of a ring line protected against backfire. As well as pyrolysis gas, into the combustion chamber 78 are fed the extraction gases from the bright annealing furnace (S18), the air separator (S20), the remaining flue gas quantities from the melt plant (S19), extraction air from the treatment plant (S22) and also fresh air. The combustion air is supplied, stepped at various levels, to achieve combustion as low in NO_Xas possible.
The oxygen content and temperature in the [0087] combustion chamber 78 are monitored and recorded. A combustion chamber temperature of 1200° C. is maintained and an oxygen content above 6% ensured in principle. The combustion chamber geometry ensures a minimum flue gas holding time of 2 seconds. In plant start-up and shut-down mode, the combustion chamber is operated with natural gas.
The combustion chamber extraction gas, where not used as a part-flow for the pyrolysis drum heating (S[0088] 8), is passed to the quench 160. The combustion chamber extraction gas used for heating is returned to the combustion chamber 78.
In the [0089] quench 160 the flue gas S9 is shock-cooled to below 150° C. This prevents the reformation of polychlorinated p-dibenzodioxine and dibenzofurane (PCDD/PCDF) (prevention of de-novo synthesis). In connection with the combustion achievable in high temperature combustion, the best possible reduction of PCDD/PCDE emission should be achieved by primary measures.
The shock-cooling is achieved by spraying a very large quantity of water into the gas flow. This is recirculated by the quench sump pump or [0090] water circulation pump 162, evaporation losses are constantly replaced under level control in the quench sump. The heat extracted from the gas flow by way of the recirculated water is passed by way of a heat exchanger 164 to a second water circuit and output to the environment by way of the total of three cooling towers 102 a-c. To ensure a cooling effect, the quench 160 is fitted with an emergency spraying system; on failure of water circulation pump 162 water can still be sprayed into the quench 160 by way of an additional emergency water pump 163. On power failure this system remains in operation by way of the emergency power supply.
After the [0091] quench 160 the cooled extraction gas S10 first reaches a droplet separator 166 and then a two-stage gas washer 168 a,b. Liquid occurring at the droplet separator 166 is recirculated in the quench circuit.
The hot extraction gas emerging from the [0092] combustion chamber 78 can be supplied alternatively for energy use. Here, after emerging from the combustion chamber 78, the extraction gas enters a boiler with a cooling spiral. The cooled extraction gas is passed for cleaning. The water vapour, heated for example to 400° C. in the cooling spiral, is then passed at a pressure of 38 bar for example to a generator to generate power.
As a washing fluid additive in the gas washer, sodium lye S[0093] 17 is used; the supply is pH-controlled and takes place by way of a sodium lye metering pump 170 in the sump or washing lye container 170 of the two washer stages. In addition, level-controlled fresh water is added. Slurry water with washer slurry (R2) is continuously centrifuged out from the washer circuit and quench water circuit, and supplied by means of the washer sump pumps 172, 174 to an evaporation system designed as a thin layer vaporiser 176. The washing circuits of the two washer stages are operated by redundant circulation pumps 178, 180 (stage 1) and 182, 184 (stage 2).
The washed exhaust gas S[0094] 11 leaves the flue gas cleaning system at a temperature of around 85° C., saturated with water vapour. To achieve better extraction of the exhaust gas it is therefore raised to a temperature of approximately 105-110° C. by the supply of hot melt gases and then discharged by means of a redundantly designed exhaust gas fan by way of a chimney 189 into the free air flow.
After evaporation of the washer slurry, salts such as oxides (R[0095] 2) remain. These can be used, where applicable after recipe correction, as melt salts in the melt plant BE3.
The melt plant BE3 is a twin-chamber system (open well) and consists of an [0096] open charging chamber 190, 192 with vortex system, a pump 194, 196, an open hearth furnace as a heating chamber, and a conduit system.
From the [0097] open hearth furnace 198, 200, liquid metal is transported by a pump by way of a conduit into a specially designed charging chamber 190, 192, and there given a rotary movement, creating a vortex.
Solid aluminium is continuously added to the vortex in the rotating liquid metal by way of the [0098] metering conveyor system 156, 158. Due to the rotary movement and the delivery point, the solid aluminium is immediately drawn below the bath surface and moistened. Oxidation of the aluminium is largely avoided.
From the charging [0099] chambers 190, 192, the metal flow returns to the open hearth furnace 198, 200. There, the enthalpy applied in the melting process is compensated by gas heating. For this, natural gas air burners 202, 204 are used.
Oxides and salts from the melting process remain on the bath surface as metal-rich scabs. The scab is moved from the [0100] open hearth furnace 198, 200 in a rhythm determined by operation.
The melted liquid aluminium is supplied in batches to the foundry, either with [0101] liquid metal crucibles 206, 208 and transport trolleys, or cast to size by way of a casting device 210, 212.
The melt power of the system is designed for example so that in total max 5 t/h can be melted (2.5 t/h per melt device); this output is achieved only if material with few organic adhesions is pyrolysed. On average around 3.4 t/h are melted. [0102]
The metal produced is characterised and processed according to its alloy composition. [0103]

Claims

1. Aluminium base alloy for production of casting alloys with magnesium as the most essential alloy element, characterised in that

it contains at least 50% scrap metal on a primary aluminium base and as the residue primary aluminium and/or scrap metal on a secondary aluminium base of known composition.

2. Aluminium base alloy according to claim 1, characterised in that it consists at least 80%, preferably 100%, of scrap metal on a primary aluminium base.

3. Aluminium base alloy according to claim 1 or 2, characterised in that the scrap metal on a primary aluminium base is mainly recycling metal obtained from foodstuff or animal feed packing.

4. Process for production of an aluminium base alloy according to any of claims 1 to 3, characterised in that materials on a primary aluminium base contaminated with organic compounds are prepared separately according to their thermal value and their aluminium content, combined in measured quantities to achieve a nominal value, the organic compounds carbonised by pyrolysis with formation of pyrolysis gas and pyrolysis coke, the pyrolysis coke separated off, the materials pretreated in this way are where applicable bright annealed, and where applicable are sorted to separate out foil constituents, and then melted.

5. Process according to claim 4, characterised in that aluminium compound substances are reduced to a unit size and the iron parts separated out after pyrolysis.

6. Process according to claim 4 or 5, characterised in that the materials which are prepared separately are combined to achieve a nominal value by way of a computer-controlled metering system, where as applicable in addition to the thermal value and aluminium content of the materials, further parameters of the materials treated can be taken into account, in particular their moisture, apparent density and grain size.

7. Casting alloy made from an aluminium base alloy according to any of claims 1 to 3, characterised in that it also contains 3.0 to 5.0 w. % magnesium and 1.5 to 3.0 w. % silicon.

8. Casting alloy according to claim 7, characterised in that it also contains 0.5 to 1.2 w. % manganese and/or 0.5 to 1.2 w. % copper.

9. Casting alloy according to claim 7 or 8, characterised in that it also contains max 0.2 w. % titanium.

10. Casting alloy according to any of claims 7 to 9, characterised in that it also contains max 0.4 w. % cobalt, max 0.4 w. % cerium and max 1.2 w. % zirconium.

11. Process for production of a casting alloy according to any of claims 7 to 10, characterised in that to a melt of the aluminium base alloy, including where applicable added further alloy elements, are added 0.02 to 0.15 w. % vanadium, preferably 0.02 to 0.08 w. % vanadium, in particular 0.02 to 0.05 w. % vanadium and less than 60 ppm beryllium.

12. Use of a casting alloy according to any of claims 7 to 10 produced from an aluminium base alloy according to any of claims 1 to 3 to produce heat-resistant and/or corrosion-resistant parts in the engine area, in particular for production of engine blocks, cylinder heads and oil sumps, by means of sand casting, chilled casting, diecasting, thixocasting and thixoforging.