EP0738334A1

EP0738334A1 - Magnesium melting furnace and process for melting magnesium

Info

Publication number: EP0738334A1
Application number: EP95937021A
Authority: EP
Inventors: Dominik Schroeder; Erich Rauch
Original assignee: Ing Rauch Fertigungstechnik GmbH; Schmitz and Apelt LOI Industrieofenanlagen GmbH
Current assignee: Ing Rauch Fertigungstechnik GmbH; Schmitz and Apelt LOI Industrieofenanlagen GmbH
Priority date: 1994-11-03
Filing date: 1995-10-27
Publication date: 1996-10-23
Anticipated expiration: 2015-10-27
Also published as: CA2180351A1; DE4439214A1; EP0738334B1; DE59509688D1; US5908488A; ATE206770T1; WO1996014439A3; AU3925895A; WO1996014439A2

Abstract

PCT No. PCT/EP95/04232 Sec. 371 Date Jul. 2, 1996 Sec. 102(e) Date Jul. 2, 1996 PCT Filed Sep. 27, 1995 PCT Pub. No. WO96/14439 PCT Pub. Date May 17, 1995The magnesium melting furnace (1) has a plurality of chambers. The material to be melted is fed into a melting chamber (2) through a charging chute (20), one end of which terminates under the surface of the melting bath. The melt is slowly transferred into a holding chamber (4) through a passage (3) situated in the lower third of a dividing wall (11) above a layer of impurities settling at the bottom (14) of the melting chamber (2). The melt slowly flows through the holding chamber (4), with impurities rising to the surface or settling on the bottom (15). The purified melt flows through a second passage (5) situated in the lower third of a second dividing wall (12) into a metering chamber (6). The melt can be removed from the metering chamber (6) through a transfer pipe (28) using a metering pump (27). The magnesium melting furnace (1) makes it possible to simultaneously melt, purify and remove the magnesium in metered quantities.

Description

Magnesium melting furnace and method for melting magnesium

The invention relates to a method for melting magnesium and a magnesium melting furnace with a first chamber for receiving the melt and a device for feeding material to be melted into the first chamber.

Magnesium is increasingly used as a material, especially for the production of castings. Similar to aluminum, magnesium is obtained from an electrolysis process and cast into bars, press bolts or ingots. These are melted down in special melting furnaces before further processing. Return scrap is added. The increasing proportion of return scrap leads to higher contamination (contamination) of the starting material fed to the melting furnace.

An arrangement for melting press bolts and ingots and for further processing the molten magnesium is known from DE 41 16 998 AI. Material to be melted is fed to a melting furnace through a refill opening located above the melt. The melt below the melt surface is removed from the melting furnace via a siphon-like connecting line and fed to a casting furnace. The melt in the casting furnace serves as a supply for further processing into castings. For further processing, the molten magnesium is removed from the casting furnace via a second siphon-like connecting line and fed to a mold.

A disadvantage of this known system is the high cost of commissioning due to the use of two ovens and the siphon-like connecting lines. The entire system including the siphon-like connecting lines must be heated above the melting point of the magnesium so that a liquid melt is present both in the casting furnace and in the melting furnace. The pressure in the casting furnace must then be increased with a special pressure line to such an extent that the siphon-like connecting lines are completely filled with liquid magnesium. After the pressure has been reduced again, the melt levels in the two furnaces balance each other out, so that when liquid magnesium is removed from the casting furnace, magnesium is fed out of the melting furnace for further processing via the siphon-like connecting line.

The use of two separate ovens is energetically unfavorable and leads to a relatively high level of structural complexity.

Furthermore, such an arrangement does not allow the use of contaminated return scrap, since the melt in the melting furnace, as it is removed from the siphon-like connecting line, must already be relatively pure, because no further cleaning takes place in the casting furnace.

The object of the invention is to reduce the energy loss during the melting of the magnesium and in the provision of a cleaned melt while reducing the structural complexity.

According to the invention, this object is achieved by a magnesium melting furnace with the features of claim 1 and a method with the features of claim 33.

The use of at least one second chamber makes it possible to combine melting and cleaning the melt in a melting furnace. Due to the melt cleaning, the use of a more contaminated starting material, for example the use of a higher proportion of old scrap, is possible. Due to the special guidance of the melt flow through a suitable arrangement of the passage or the outlet, a large part of the contaminants can rise to the surface of the melt or sink to the bottom of the chambers, from where the contaminants can be easily removed. Eddies, which are caused in the first chamber (the protective chamber) by the immersion of the material to be melted and by the convection currents generated by the burners, impede the settling or rising of impurities. This disadvantage is caused by the melt flowing over into the at least one second chamber ,

(the separation chamber) compensated. There is no swirling in this chamber; the impurities can rise or settle. The arrangement of the passage and that of the outlet are chosen so that as few impurities as possible pass through with the flow.

Due to the flow in the multi-chamber furnace according to the invention, sufficient cleaning of the melt is possible even without the addition of cleaning salts to the weld pool. By eliminating the addition of salt, the environmental impact is reduced and high costs for the disposal of residues are avoided.

In a preferred embodiment of the invention, a third chamber is provided downstream of at least one outlet of the second chamber for receiving the melt. The second and the third chamber have a common second partition, the outlet from the second chamber being designed as a second passage in this second partition. A device for removing the molten magnesium is connected to the third chamber. With this arrangement, it is advantageous that there is a sufficiently cleaned melt in the third chamber which can be fed directly for further processing. The third chamber thus contains a melt reservoir from which the magnesium can be removed intermittently.

In an advantageous development of the invention, the total area of the at least one first passage is larger than a first minimum area A _m i _n> ι. This minimum area is calculated from a maximum flow rate of the melt in the passage for a given material throughput of molten magnesium through the magnesium melting furnace. The limitation of the flow velocity in the passage serves to avoid turbulence in the flowing melt at the passage. This prevents entrainment of contaminants, for example from the melt sludge at the bottom of the chamber. Limiting the flow rate to below 0.1 / sec is advantageous. A significantly lower flow rate is preferably selected by selecting the passage to be sufficiently wide.

In order to reconcile the demands for a deep arrangement of the passage (in the lower third of the partition), for a sufficient height of the passage above the settling sludge sludge and for the largest possible cross-sectional area preferred exemplary embodiment provided that the at least one first passage is a gap which extends essentially over the entire width of the first partition.

It is advantageous if the first and the second chamber have a substantially rectangular base area and the first partition and the downstream wall of the second chamber, which has the outlet, are arranged flat and parallel to one another. This simplifies the flow conditions in the second chamber and reduces the work involved in manufacturing the melting furnace.

So that the time in which the melt flows through the second chamber is sufficient for a large portion of the impurities to settle or rise, the length of the second chamber must be chosen to be sufficiently long in the direction of flow.

In an advantageous development of the invention in the second chamber between the first partition and the wall having the outlet is arranged in the middle and parallel to these two walls, a central wall terminating with the bottom and the side walls, the height of which is greater than half the maximum fill level and is less than the minimum fill level of the melt in the second chamber. This central wall redirects the flow in the second chamber, so that even with a relatively short distance between the first partition and the wall having the outlet, ie with a relatively short second chamber, a flow short circuit between the first passage and the outlet is avoided. In a preferred exemplary embodiment, the distances between the first partition, the middle wall and the wall having the outlet and the height of the middle wall are dimensioned such that in the second chamber a meandering channel through which the melt flows has an essentially constant flow cross ¬ cut is formed. In other embodiments, further dividing and middle walls deflecting the flow of the melt are conceivable. The flow conditions are influenced in such a way that the settling or rising of contaminants is improved.

Furthermore, it is possible to arrange a sink in the second chamber directly below the passage through which the melt enters from the first chamber. The sink is gassed and the gases rising at the entrance to the second chamber improve the cleaning effect and the flow conditions in the second chamber.

In another advantageous development of the invention, the total area of the at least one outlet is chosen to be larger than a second minimum area A _m j_ _n . The minimum area ^A 2, min is calculated from a second maximum speed Strömungsge¬ v _{max /} 2 ° - ^it melt in the outlet with a gege¬ surrounded material throughput of molten magnesium through the furnace according to the equation

^A min, 2 = material throughput of the melting furnace,

P • v _maX 2

where p is the density of the molten magnesium. A maximum flow rate is preferably less than 0.05 m / sec. selected. By choosing the low flow rate of the melt in the outlet, entrainment of contaminants from the second chamber and transfer of the contaminants to the third chamber are avoided. Furthermore, it is It is advantageous to arrange the lower boundary of the at least one outlet at a height above the bottom of the second chamber which is greater than the maximum height of a layer of impurities, in particular melt-containing sludge containing heavy metals, which settles on the bottom of the second chamber.

Especially when using the above Middle wall in the second chamber, the outlet should be in the lower area of the partition to the third chamber. On the other hand, the outlet must be clearly above the maximum height of a layer of melt sludge which settles at the bottom of the second chamber. The size must also be sufficient to avoid excessively high flow speeds and thus turbulence. In an advantageous development of the invention, these requirements are brought into harmony in that the at least one outlet is a gap which extends essentially over the entire width of the wall.

In order to improve the flow conditions in the second chamber, an advantageous development of the invention has a weir projecting horizontally into the second chamber at the upper edge of the gap forming the outlet.

In a preferred embodiment, the bottoms of the first and second chambers have inclined surfaces which are arranged in such a way that a channel is formed, at the lowest point of which sinking contaminations of the melt, in particular melt sludge containing heavy metals, collect. This concentration of impurities at certain points in the chamber floors enables easy removal. Advantageously, a first and a second suction device are arranged in the first and in the second chamber, respectively, so that they can suck off the sunken impurities at the deepest point of the chamber floor. As a result, the 'axial height of the melt sludge in the chambers can be kept low, which permits a lower arrangement of the passages and thus leads to better utilization of the chamber volume. The gutter can are formed both by inclined flat floor slabs as well as by arching the floors. The suction device can have a tube inserted into the melt from above as well as a drain mounted on the chamber bottom from below.

In an advantageous further development of the invention, the spaces of the first and second chambers and possibly also the third chamber above the melt are isolated from one another by the first partition or further partition walls and can be filled separately with protective gas, different protective gas compositions and concentrations in the Spaces can be generated above the first and second (and possibly the third) chamber. This allows the shielding gas composition to be set as a function of the reaction parameters on the surface of the respective chambers. To avoid oxidation reactions, the protective gas usually contains an SFg component. The separation of the rooms above the chambers enables different SFg proportions above the melts in the chambers. In a preferred embodiment, a protective gas with a higher SFg content is present in the space above the melt in the first chamber than in the space above the melt in the second chamber. The proportion of SFg is chosen to be relatively high (0.5%) only where such a high concentration is required. The SFg content above the second chamber and possibly other chambers is only 0.2 to 0.3%. This reduces the corrosion effects of the sulfuric acid formed from SFg in these chambers, which leads to a longer service life of the melting furnace.

In a preferred embodiment, the outer walls of the first and second chambers are steel walls. Steel walls allow good heat transfer. It is advantageous to also design all chambers, partitions and partitions as steel walls. The use of outer walls made of steel allows an arrangement of burners for direct Heating the chambers via the outer walls of the first and the second chamber. It is also possible to use an electrical resistance heater which acts in the same way.

In a preferred exemplary embodiment of the invention, the device for removing the molten magnesium has a metering pump. With this dosing pump, a precise, demand-based removal of molten magnesium for further processing is possible. The metering pump takes the required amount of molten and cleaned magnesium from the third chamber. In a preferred embodiment, a transfer tube is coupled to the metering pump, through which the melt transported by the metering pump is laterally discharged. In an advantageous development, the transfer tube is also filled with protective gas. Flushing the transfer tube with protective gas prevents oxidation of the removed magnesium.

In an advantageous further development of the invention, the device for supplying material to be melted has a charging shaft immersed under the melt surface of the first chamber. The material to be melted which is fed through this shaft does not fall onto the surface of the melt bath and thus only carries very small dross portions on the surface inside the charging shaft into the bath. In addition, the charging shaft, which is immersed under the surface of the melt, enables a more targeted supply of the material to be melted with less swirling of the melt pool.

In an advantageous development of the invention, the device for supplying material to be melted has a charging device which is coupled to a measuring device for measuring the weight of the melting furnace in such a way that the material to be melted is supplied as a function of the furnace weight. The mass of the supplied material to be melted corresponds to the mass loss of the melting furnace due to take molten magnesium and / or remove impurities (suction of the sludge from the ground). In this way, the filling level of the chambers is kept approximately constant, so that the charging shaft always dips below the melt surface and the flow conditions in the chambers remain constant.

In a further advantageous development of the invention, the device for supplying the material to be melted has a descaling device which is arranged in such a way that the material to be supplied to the first chamber can be thermally pretreated when it passes through the descaling device, contaminants and / or evaporate. The material to be melted, for example magnesium scrap contaminated with oil, is fed to the melting furnace via an encapsulated conveying device. A section of the conveyor has a heating section, in which the material passing through is heated, the contaminants (e.g. oil residues) swelling and / or evaporating. The resulting gas (carbonization gas) is collected via the encapsulation of the conveying device and can be used for further purposes. The heated material is fed into the charging shaft via locks and immersed under the surface of the weld pool. The use of the decongestant reduces the proportions of the impurities in the material supplied to the melt pool and thus leads to less itching and to the avoidance of the otherwise necessary removal of the reactive low-temperature gases which would form above the melt in the first chamber. This enables the use of a higher proportion of return and old scrap.

The material to be melted is preferably heated to a temperature of about 300 ° C. to 450 ° C. in the decongesting device.

In a preferred exemplary embodiment, the carbonization gases produced in the descaling device are collected and either a burner for heating the material to be melted. rials in the descaling device (indirect heating; jet pipes) or a burner to melt the material. Alternatively, the carbonization gases collected can be fed to a burner coupled to a heat exchanger, the heat exchanger being able to preheat the combustion air.

Advantageous further developments of the invention are characterized in the subclaims.

The invention is described in more detail below with reference to exemplary embodiments shown in the drawing. The drawing shows:

1 shows a preferred exemplary embodiment of the magnesium melting furnace according to the invention; Figure 2 shows a device for suctioning melt sludge from a channel located at the bottom of a chamber. and FIG. 3 shows an exemplary embodiment of a device for supplying the material to be melted, with a decongesting device and charging shaft. 1 shows a magnesium melting furnace 1 according to the invention with three chambers, which enables the magnesium to be melted, cleaned and dispensed in a metered manner. The material to be melted is fed to a first chamber, the melting chamber 2. The molten magnesium flows through a passage 3 into a second chamber, the stand-off chamber 4, in which contaminants can rise or fall during the period of residence of the molten magnesium. The cleaned molten magnesium passes through a second passage 5 into a metering chamber 6, in which it is made available for removal.

The chambers 2, 4 and 6 of the magnesium melting furnace 1 are surrounded by steel walls 10. The steel walls ensure a relatively good heat transfer. A first partition 11 is arranged between the melting chamber 2 and the stand-off chamber 4 and one between the stand-off chamber 4 and the dosing chamber 6 second partition 12. The first and second partition 11 and 12 are also made of steel. The three chambers are surrounded by a heat-insulating jacket 13. The bottoms 14, 15 and 16 of the three chambers rest on the casing 13, while a combustion chamber 9 is formed between the side walls 10 of the chambers and the lateral parts of the casing 13. An arrangement is also conceivable in which the furnace chambers are placed on a steel frame, so that heating of the steel wall is also possible from below. For heating the melting chamber 2, two burners 17 and 18 are arranged in the casing 13 on the front side and on both lateral outer walls such that their flames and heat radiation are directed onto the outer wall 10 of the melting chamber 2. The burners 17 heat the end face of the melting chamber 2 and the burners 18 the side walls. A further burner 21 is arranged on each side wall of the holding chamber 4 and additionally heats the melt located in the holding chamber 4. In addition, a burner 21a can be provided for heating the metering chamber 6. This burner 21a takes over in particular the additional heating of the melt to be removed in the chamber 6 when the burners 17, 18 and 21 are not active because no material is supplied and melted. In other exemplary embodiments, the number, size and distribution of the burners can be varied.

The hot exhaust gases introduced into the combustion chamber 9 through the burners 17, 18, 21 and 21a flow along the outer walls 10 to the exhaust gas outlet 19, which is arranged in the casing 13 behind the metering chamber 6. If the furnace chambers were arranged on a steel frame, the exhaust gases could also be extracted below the chambers. This could provide additional heating surface and thus melting performance.

The material to be melted is fed to the melting chamber 2 via a charging shaft 20. The charging shaft 20 dips with its lower end under the melt surface in the melting chamber 2.

The material immersed in the melt of the melting chamber 2 is melted, impurities being absorbed into the melt. Some of the impurities, in particular melt sludge containing heavy metals, sink to the bottom 14 of the melting chamber 2. Another part of the impurities, especially magnesium oxide, rises to the surface of the melt. The contaminants accumulate in the form of scabies on the surface of the molten pool. The melt flows through the first passage 3 to the holding chamber 4. The first passage 3 is formed in the first partition 11 as a horizontal gap. The lower edge of the gap 3 is at a sufficient height above the layer of contaminants which settles on the bottom 14 of the melting chamber 2, in order to prevent contaminants from being entrained or transferred from the melt sludge into the standing chamber 4. In the preferred embodiment, the passage is approximately 150 mm above the bottom 14. The gap 3 is sufficiently large to achieve a low flow rate of the melt passing through at a given maximum throughput of the magnesium melting furnace 1. In the case of a furnace with a throughput of approximately lt / h, the size of the gap 3 is approximately 50 mm × 500 mm.

A purging stone 22, which is gassed with a protective gas (2 with 0.2 to 0.5% SFg), can optionally be arranged behind the passage 3 in the holding chamber 4. The emerging protective gas rises to the surface in the stand-off chamber and entrains contaminants.

An overflow weir 23 is arranged in the middle of the holding chamber 4 between the first partition 11 and the second partition 12. The height of the overflow weir is approximately 50% to 80%, preferably 70% of the melt level. The introduction of this overflow weir 23 prevents, inter alia, that the melt entering through the first passage 3 leads directly to the flows through the second passage 5 straight ahead and so stays too short a time in the holding chamber. This improves the cleaning of the melt in the stand-off chamber 4.

During the flow through the holding chamber 4, some of the impurities, in particular melt sludge containing heavy metals, sink to the bottom 15 of the chamber 4. Another part of the contamination rises to the surface of the melt and forms a layer (dross) there.

Through the second passage 5 located in the second partition 12, the melt cleaned in the holding chamber 4 enters the metering chamber 6. The second passage 5, like the first passage 3, is arranged at a low height above the floor 15 in order to allow a melt which is as pure as possible to pass through. In order to avoid entrainment of the contaminants that have sunk to the bottom 15 of the stand-off chamber 4, the lower edge of the second passage 5 is arranged above the maximum height of the layer of contaminants that settles on the bottom 15 of the stand-off chamber 4. In the preferred embodiment shown in FIG. 1, the second passage 5, like the first passage 3, is designed as a horizontal gap. The second passage is at a height of approximately 100 mm above the floor 15.

Furthermore, on the upper edge of the second passage 5 there is a weir 24 projecting horizontally into the second chamber 4, which improves the flow conditions when the melt flows over into the third chamber 6.

A ceramic filter 25 can be attached directly behind the second passage 5 in the metering chamber 6. The ceramic filter 25 is used for further cleaning of the melt entering the metering chamber 6.

Before the molten and cleaned magnesium is removed, a metering pump 27 is arranged in the metering chamber 6. This lifts the molten magnesium to be removed over the melt surface and transfers the melt into a transfer tube 28. The transfer tube 28 is guided laterally outwards under the cover insulation 29. In order to cause the molten magnesium to flow out, the transfer tube 28 is inclined slightly downward. The part of the transfer tube 28 emerging from the casing 13 is provided with a heater 30, for example an electric heater. The magnesium melt removed is fed to a die casting machine or a transport container.

In order to avoid oxidation of the removed melt in the transfer tube 28, the transfer tube in the preferred embodiment is filled with a protective gas. The protective gas is passed through the transfer tube 28, pulse gas being provided in order to save protective gas.

The spaces above the melt surface in the three chambers 2, 4 and 6 are filled with protective gas to avoid oxidation. In the preferred exemplary embodiment, the partition walls 11 and 12 extend up to the cover insulation 29 in order to achieve a separation of the spaces filled with inert gas. The protective gas is supplied via a system 31 of pipes and valves. The valves are controlled in such a way that the compositions of the protective gas atmospheres located above the three chambers can be set separately. A staggered protective gassing is thus possible in such a way that a protective gas atmosphere with a higher SFg content in the space above the melt in the melting chamber 2 and a lower SFg in the rooms above the melt in the stand-off and metering chamber (4 and 6) - Share can be set. In the preferred exemplary embodiment, the SFg content above the melt of the melting chamber 2 is approximately 0.5% and above the melt of the standing chamber 4 and the metering chamber 6 is approximately 0.2 to 0.3%. This staggered protective gassing saves SFg; In addition, the corrosion caused by the SFg in the stand-off and in the dosing chamber is reduced. Protective gassing of the charging shaft 20 and the transfer pipe 28 is also possible via the system 31 of pipes and valves. In normal operation, ie with closed lids, the spaces above the melt in the chambers are gassed via the valves 33. If the lids above the respective chambers are opened for the purpose of cleaning the molten bath surface, the sudden increase in protective gas requirement is covered by the automatic opening of bypass valves 34. The bypass valves 34 deliver in the open state at the same gas pressure about a 5-10 times larger volume flow than the valves 33. The use of the bypass valve arrangement has the advantage over the regulation of a single valve that a quick reaction to a surge in demand is possible is.

The stand-off chamber 4 has an additional shaft 32 through which material for re-alloying the molten magnesium can be introduced. The material introduced into the separation chamber 4 through this shaft 32 is relatively pure, so that it does not produce any further impurities in the holding chamber. The additional shaft 32, like the charging shaft 20, is immersed under the surface of the melt pool in order to avoid entrainment of contaminants and swirls when the parts to be melted are introduced. Furthermore, the additional shaft 32 can be filled with protective gas via the system 31 of pipes and valves.

FIG. 2 shows a device for suctioning off the impurities 45 which settle on the bottom 41 of a chamber 40. FIG. 2 shows a section perpendicular to the plane of the view according to FIG. 1 through the melting chamber 2 or the stand-off chamber 4, in FIG hereinafter generally referred to as chamber 40.

The bottom 41 of the chamber 40 has inclined surfaces 42 and 43 which are arranged such that a groove 44 is formed in the middle of the chamber 40 as the deepest point. Melt sludges 45 collect in this channel 44. - -

16

A tube 46 protrudes from above into the chamber 40 and into the melt, the tube 46 ending in the immediate vicinity of the channel 44 in the melt sludge 45. A line 47, which leads to a suction pump 48, is fastened to the upper end of the tube 46. With the aid of the suction pump 48, the melt sludge 45 is sucked off from the bottom 41 of the chamber 40 and conveyed into a container 49.

3 shows a device for feeding the material to be melted into the magnesium melting furnace 1.

The starting material 50, which contains both relatively pure magnesium raw material in the form of ingots and return scrap as well as old scrap contaminated with oil and other contaminants, is fed to a decarbonization device 51 via a filling opening 52. A transport device 53 with a slowly moving conveyor belt transports the supplied material through an obliquely upward, encapsulated shaft 54 to the upper opening 55 of the charging shaft 20 provided with locks 56. Inside the upward shaft 54, the material lying on the transport device 53 is Material heated by means of a heater 57 radiating from above onto the material. During heating to around 450 ° C, some of the contaminants (oily soiling) smolder and / or evaporate. The smoldering or evaporating contaminants form a smoldering gas which rises in the shaft 54 and enters a discharge channel 59 at the upper end 58 of the shaft 54. The heated magnesium material to be melted falls at the end 58 of the shaft 54 from the transport device 53 into the charging shaft 20 provided with locks 56 and further into the melting bath.

The exhaust duct 59 has a fan 60 for sucking in the carbonization gases. In the exemplary embodiment according to FIG. 3, the carbonized gases sucked in are burned by a burner 61. The hot exhaust gases reach a via a heat exchanger 62 Chimney 63. The heat energy obtained in the heat exchanger can be used to heat the combustion air for the burners 17.

The quantity of material to be melted fed to the magnesium melting furnace 1 is controlled by the drive of the transport device 53. The supply of the material to be melted is controlled as a function of the weight of the melting furnace 1. The magnesium melting furnace is rotatably mounted on one edge of the bottom of the casing 13. A bearing provided with a load cell is provided on the opposite edge. The force measured with the aid of this measuring cell is converted into a weight of the magnesium melting furnace 1. The required amount of the material to be fed to the furnace is determined from the determined time-dependent weight difference. By keeping the weight of the magnesium melting furnace constant, it is ensured that the melting level in the furnace chambers remains approximately constant. This ensures an uninterrupted immersion of the lower limit of the charging shaft 20 under the melt surface. In addition, the flow conditions in the furnace are kept approximately constant in this way.

Claims

Expectations

1. Magnesium melting furnace with a first chamber (2) for receiving the melt and a device (20) for supplying material to be melted into the first chamber, characterized in that at least one second chamber (4) is provided for receiving the melt, wherein between the First and second chamber a common first partition (11) is provided that at least one first passage (3) through which the melt flows is arranged in the first partition (11) in the lower third of the melt height, the lower boundary of which is at a height above the bottom (14) of the first chamber (2), which is greater than the maximum height of a layer of contaminants, in particular heavy metal-containing melt sludge, which settles on the bottom of the first chamber, and that in the lower third of a wall (12) arranged downstream of the second Chamber (4) is arranged at least one outlet (5) through which the melt flows.

2. Magnesium melting furnace according to claim 1, characterized gekenn¬ characterized in that downstream of the at least one outlet of the second chamber, a third chamber (6) is arranged for receiving the melt, the at least one outlet at least a second passage (5) in forms a second partition (12) arranged between the second and the third chamber, and that a device (27, 28) for removing the molten magnesium is connected to the third chamber.

3. Magnesium melting furnace according to claim 1 or 2, characterized ge indicates that the total area of the at least one first passage (3) is larger than a first minimum area (A _m -j_ _n ι_), the minimum area (A _m i _{n #} i ₎ from a first a- ximal flow velocity (v _maX i _{) of} the melt in the passage (3) for a given material throughput of molten magnesium through the magnesium melting furnace (1) according to the equation

Material throughput of the melting furnace

^A min, l ^~ n P • _v ^v max, 1-

where p is the density of the molten magnesium.

4. Magnesium melting furnace according to claim 3, characterized gekenn¬ characterized in that v _maX ι <0, lm / sec.

5. Magnesium melting furnace according to one of claims 1-4, characterized in that the at least one first passage (3) is a gap which extends essentially over the entire width of the first partition (11).

6. Magnesium melting furnace according to one of claims 1 to 12, characterized in that the first (2) and the second (4) chamber have a substantially rectangular base and that the first partition (11) and the downstream angeord¬ nete having the outlet Wall (12) of the second chamber are arranged flat and parallel to each other.

7. Magnesium melting furnace according to claim 6, characterized gekenn¬ characterized in that in the second chamber (4) between the first partition (11) and the wall having the outlet (12) substantially centrally and parallel to these two walls one with the bottom ( 15) and the side walls closing the middle wall (23) is arranged, the height of which is greater than half the maximum fill level and smaller than the minimum fill level of the melt in the second chamber (4).

8. Magnesium melting furnace according to claim 7, characterized gekenn¬ characterized in that the distances between the first partition (11), the central wall (23) and the outlet (5) having wall (12) and the height of the central wall are dimensioned so that in the second chamber (4) a meandering channel through which the melt flows and of essentially constant flow cross section is formed.

9. Magnesium melting furnace according to one of claims 1 to 8, characterized in that the total area of the at least one outlet (5) is larger than a second minimum area (A _m i _{n /} 2 ₎ , the minimum area (A _m i _n 2 ₎ from a second maximum flow velocity (v _{maX (} 2 _{) of} the melt in the outlet (5) for a given material throughput of molten magnesium through the melting furnace (1) according to the equation

Material throughput of the melting furnace

^A min, 2 ~ «.,

P ^{• v} max, 2

where p is the density of the molten magnesium.

10. Magnesium melting furnace according to claim 9, characterized gekenn¬ characterized in that v _maX 2 <0.05m / sec.

11. Magnesium melting furnace according to one of claims 1 to 10, characterized in that the lower limit of we¬ at least one outlet (5) is at a height above the bottom (15) of the second chamber (4) which is greater than the maximum The height of a layer of impurities, in particular melt sludge containing heavy metals, which settles on the bottom (15) of the second chamber (4).

12. A magnesium melting furnace according to claim 11, characterized in that the at least one outlet (5) is a gap which extends essentially over the entire width of the wall (12).

13. A magnesium melting furnace according to claim 12, characterized in that a weir (24) projecting horizontally into the second chamber (4) is arranged at the upper edge of the gap (5) forming the outlet.

14. Magnesium melting furnace according to one of claims 1 to 13, characterized in that the bottoms (14, 15; 41) of the first and the second chamber have inclined surfaces (42, 43) which are arranged such that a channel (44) is formed, at the lowest point of which sinking contaminations of the melt, in particular melt sludges containing heavy metals, collect.

15. Magnesium melting furnace according to claim 14, characterized gekenn¬ characterized in that a first and a second suction device (46- 48) in the first and in the second chamber are arranged so that they the sunken impurities at the deepest points (44) Can suction chamber floors (41; 14, 15).

16. A magnesium melting furnace according to one of claims 1 to 15, characterized in that the spaces of the first (2) and two (4) chambers above the melt are isolated from one another by the first partition (11) and can be filled separately with protective gas, wherein Different shielding gas compositions and concentrations can be generated in the rooms above the first and the second chamber.

17. Magnesium melting furnace according to claim 16, characterized gekenn¬ characterized in that in the space above the melt of the first chamber (2) a protective gas with a higher SFg content than in the space above the melt in the second chamber (4).

18. Magnesium melting furnace according to one of claims 1 to 17, characterized in that the outer walls (10) of the first and the second chamber are steel walls.

19. Magnesium melting furnace according to claim 18, characterized gekenn¬ characterized in that on the outer wall (10) of the first or the first and the second chamber burners (17, 18, 21) are arranged for heating the chambers.

20. Magnesium melting furnace according to one of claims 2 to 19, characterized in that the device for removing the molten magnesium has a metering pump (27).

21. A magnesium melting furnace according to claim 20, characterized in that a transfer tube (28) is coupled to the metering pump (27), through which the melt transported by the metering pump (27) over the melt surface of the third chamber (6) is under a cover insulation (29) is discharged laterally.

22. A magnesium melting furnace according to claim 21, characterized in that the transfer tube (28) can be filled with protective gas.

23. Magnesium melting furnace according to one of claims 1 to 22, characterized in that the device for supplying material to be melted in the first chamber (2) has a submerged under the melt surface of the first chamber Chargier¬ shaft (20) through which the to be melted Material can be introduced into the first chamber.

24. Magnesium melting furnace according to one of claims 1 to 23, characterized in that the device for supplying material to be melted comprises a charging device which is coupled to a measuring device for measuring the weight of the melting furnace (1) in such a way that the supply is to be melted Material depends on the weight of the furnace.

25. A magnesium melting furnace according to one of claims 1 to 24, characterized in that the device for supplying material to be melted (50) has a decarbonization device (51) which is arranged in such a way that the first chamber (2) is to be supplied Material can be pretreated thermally as it passes through the descaling device (51), with contaminants simmering and / or evaporating.

26. Magnesium melting furnace according to claim 25, characterized gekenn¬ characterized in that the material to be melted is heated in the Abschwelvor¬ direction (51) to a temperature of about 300 ° C to 450 ° C.

27. A magnesium melting furnace according to claim 25 or 26, characterized in that the smoldering gases in the de-smoldering device (51) can be collected, and in that the smoldered gases collected are either a burner for indirect heating of the material to be melted in the de-smoldering device (51 ) or a burner (17, 18) for melting the magnesium can be fed.

28. Magnesium melting furnace with a container (2) for receiving the melt and a device for feeding material to be melted into the container, wherein the device for feeding material to be melted has a charging shaft (20) immersed under the surface of the melt bath, through which the melting material in the A container (2) can be inserted, characterized in that the device for supplying material to be melted has a decarbonization device (51) which is arranged in such a way that the material to be supplied to the container can be thermally pretreated as it passes through the decarbonization device, contaminants decaying and / or evaporate.

29. A magnesium melting furnace according to claim 28, characterized in that the material to be melted can be heated in the deposition device (51) to a temperature of approximately 300 ° C to 450 ° C.

30. Magnesium melting furnace according to claim 28 or 29, characterized in that the smoldering gases arising in the de-smoldering device (51) can be collected, and that the smoldered gases collected can either be a burner for indirect heating of the material to be melted in the de-smoldering device (51 ) or a burner (17) arranged on the container (2) for melting the magnesium.

31. Magnesium melting furnace according to one of claims 28 to 30, characterized in that the device for supplying material to be melted has a charging device which is coupled to a measuring device for measuring the weight of the melting furnace in such a way that the supply of materials to be melted depending on the furnace weight.

32. A method for melting magnesium, characterized in that material to be melted is fed to a melting furnace and melted in a first chamber, - -

25

that the melt which arises in the first chamber is fed via a passage at a flow rate below 0.1 μm / sec to a second chamber, that the melt remains in the second chamber under slow flow, with contaminants settling or on the surface of the melt rise that the cleaned melt is transferred through an outlet at a flow rate below 0.05 m / sec into a third chamber and that the cleaned melt is removed from the third chamber for further processing.

33. A method for melting magnesium according to claim 32, characterized in that the material to be melted is thermally pretreated in a decarbonization device before being fed to the first chamber, contaminants decaying and / or evaporating.

34. A method for melting magnesium according to claim 33, characterized in that the material to be melted is heated to a temperature of about 300 ° C to 450 ° C in the desoldering device.

35. A method for melting magnesium according to claim 33 or 34, characterized in that the smoldering gases formed in the deposition device are collected and afterburned and that the energy thereby obtained either for heating the material to be melted in the deposition device or for melting of the material used in the first chamber.

36. Method for melting magnesium according to one of the

Claims 32 to 35, characterized in that the weight of the melting furnace is determined and that the material to be melted is supplied as a function of the furnace weight so that the

The furnace weight and thus the fill level of the melt remain approximately constant.