EP3623079B1 - Device for the thermal treatment of melts produced from non-ferrous metals using a heat exchanger - Google Patents

Description

The invention relates to a device for the temperature treatment of melts made of non-ferrous metals and a use of a heat exchanger.

Melts of non-ferrous metals are usually held in heated containers with crucibles, with the heating being carried out indirectly, e.g. with an electric or gas heating device over the crucible wall, or directly, e.g. using immersion heating rods that are introduced into the melt (e.g. US 2004/0107799 A1 ).

From the publication WO2 / 058862 A2 is an arrangement of a melting furnace and a holding furnace designed as a metering furnace, which are connected to one another via a supply line and a return line. In the bottom area of the melting furnace, a pump is provided that the Melt pump transported through a degassing chamber and a filtration area from the melting furnace into the holding furnace and from there back into the melting furnace. At the bottom of the holding furnace, heating elements in the form of thermally conductive blocks, for example made of graphite, are arranged, through which electrical elements penetrate and are heated. These heating elements in the form of blocks are used to heat the melt in the holding furnace.

The melting of non-ferrous metals, in particular magnesium alloys, is carried out in practice in furnaces with an open bath surface and can be divided into two phases. The non-ferrous metal is brought into the furnace directly into the melt, for example in the form of preheated pigs, strips, rods or piece goods and the material is heated until it liquefies, at which the solidus point of the alloy is reached. The energy required to melt the material comes mainly from the liquid melt in the immediate vicinity of the material. As a result, the melt in the environment cools down accordingly. The second phase is the overheating of the cooled material to the required target temperature. For this heating to the process temperature, energy must be supplied in order to restore the original temperature level.

As mentioned, the energy supply is usually implemented in the furnace via the heated crucible wall, via heating elements exchanged in the melt or via radiation that acts on the bath surface. For the heat exchange, the size of the heat transferring surface is decisive in order to achieve the required heat flow under realistic boundary conditions.

• Verstärkte Oxidbildung
• Größerer Schutzgasbedarf
• Erhöhte Wärmeabstrahlung durch schlechtere Isolierung
• Erhöhter Reinigungsaufwand.

With the size of the heated crucible surface, the bath or melt surface and the crucible volume also increase. Bath surfaces cause many problems with melt systems. A larger bathroom surface means:

• Increased oxide formation
• Greater shielding gas requirement
• Increased heat radiation due to poorer insulation
• Increased cleaning effort.

Basically, the risk potential increases with larger amounts of liquid material and larger bathroom surfaces.

The invention is based on the object of creating a device for the temperature treatment of melts made of non-ferrous metals which allows the melts to be heated or cooled even with smaller melt surfaces.

This object is achieved according to the invention by the features of claim 1.

The measures specified in the subclaims are advantageous Further training and improvements possible.

According to the invention, the device for temperature treatment of melts from non-ferrous metals comprises a container receiving the melt of the non-ferrous metal, a conveying device with transfer line and at least one heat exchanger, the conveying device with transfer line and the heat exchanger being designed to feed melt from the container into and through the at least one heat exchanger their heating or cooling and conveying back from the heat exchanger into the container or into another container. Because a heat exchanger is used, to which the melt is fed from the container via the transfer line, the melt can be heated up in a relatively short time without an additional bath surface and without oxide formation, but also cooled and can be returned to or into the container from the heat exchanger be directed to another container. The container can have small dimensions with a small volume, a small bath surface, little protective gassing with a smaller risk potential. The melting capacity is mainly determined by the size of the heat exchanger and is therefore independent of the container size (crucible size). Existing systems can be retrofitted with a higher melting capacity using the heat exchanger.

In an advantageous embodiment, the container or the further container can be designed as a melting and holding furnace, the crucible of the furnace being kept as small as possible by providing the heat exchanger, since the desired temperature of the melt is reached via the heat exchanger. In addition, the hazard potential of a fire is reduced. It is also possible to retrofit melting and holding furnaces in use without great effort.

The conveying device has a pump which protrudes into the melt, whereby the melt can be transported via the transfer line from the container through the heat exchanger and back into the container or into another container. The further container can be designed in the most varied of ways. For example, the term second container can also include a pipeline system for transporting the melt. It can also be another furnace in which filtering, alloying or cleaning is carried out. The melt can also be conveyed into an overflow system in which, for example, a level is kept constant and the overflow is fed back into the container.

According to the invention, the container or the further container, the transfer line with the inlet end immersed in the melt and the outlet end immersed in the melt and the heat exchanger form a closed pipe system, so that the melt can be heated without contact with the atmosphere and thus the formation additional oxides are avoided. In addition, the melt cannot burn in the closed pipe system. Furthermore, no protective gassing is required in the closed pipe system. The device according to the invention can thus also be used for overheating melt which is to be raised in a process step to a higher processing temperature in the closed pipe system.

The heat exchanger can advantageously be designed as a tube bundle heat exchanger in which the melt is guided on the inside of the tubes and energy is supplied on the outside of the tubes, whereby a high degree of heat transfer efficiency is achieved. Of course, other types of heat exchangers can be used, such as plate heat exchangers, spiral or U-tube heat exchangers, jacket-tube heat exchangers and others.

The heat exchanger advantageously has a heating device which comprises at least one burner and / or electrical heating elements or an inductor.

In addition, the heat exchanger can include a cooling device that can quickly cool the melt, which is particularly important in the case of a magnesium melt in order to reduce the risk of fire in the event of overheating and to quickly bring the melt into the safe temperature range.

Gas- and oil-heated burner systems can be used at least partially for cooling. To do this, the burner or burners are switched off and it is only over the combustion air fan blows air through the burner or burners, whereby the melt in the heat exchanger is cooled with air.

According to an advantageous embodiment, several heat exchangers in a modular design can be connected one after the other in series or in parallel between the transfer line, as a result of which a flexible increase in output is achieved.

Fig. 1

eine schematische Darstellung der erfindungsgemäßen Vorrichtung zur Temperaturbehandlung von Schmelzen,

Fig. 2

ein Ausführungsbeispiel der erfindungsgemäßen Vorrichtung zur Temperaturbehandlung von Schmelzen aus Nichteisenmetallen in einer teilweise geschnittenen perspektivischen Ansicht,

Fig. 3

a) eine teilweise geschnittene perspektivische Ansicht des in Fig. 1 verwendeten Wärmetauschers, b) eine Schnittansicht durch den Wärmetauscher, und

Fig. 4

ein weiteres Ausführungsbeispiel der erfindungsgemäßen Vorrichtung in einer teilweise geschnittenen perspektivischen Ansicht.

The invention is shown in the drawing and is explained in more detail in the following description. Show it

Fig. 1

a schematic representation of the device according to the invention for the temperature treatment of melts,

Fig. 2

an embodiment of the device according to the invention for the temperature treatment of melts made of non-ferrous metals in a partially sectioned perspective view,

Fig. 3

a) a partially sectioned perspective view of the in Fig. 1 heat exchanger used, b) a sectional view through the heat exchanger, and

Fig. 4

a further embodiment of the device according to the invention in a partially sectioned perspective view.

In the Fig. 1 The device shown for the temperature treatment of melts made of non-ferrous metals has a container 1 on which a melt receives. The container 1 is assigned a conveying device which comprises at least one pump 10, which is immersed in the bath of the melt, and a transfer line 3. A heat exchanger 2 is over the transfer line 3 connected to the container 1 in such a way that all of them together form a closed pipe system. Another container 200, which is connected to the outlet of the heat exchanger 2 via the transfer line 3, is shown in dashed lines. In this embodiment, too, container 1, transfer line 3, heat exchanger 2, transfer line 3 and further container 200 form a closed pipe system.

The melt is pumped by the pump 10 from the container 1 via the transfer line 3 into and through the heat exchanger 2, where the temperature of the melt is changed by heating or cooling, and the temperature-changed melt is returned by the pump 10 via the transfer line 3 transported back into the container 1 or passed into the further container 200.

In Fig. 2 a further embodiment of the device according to the invention is shown, which is designed as a device for melting and keeping warm non-ferrous metals, which can contain, for example, magnesium, zinc, lead, etc. It has a melting and holding furnace 1 and a heat exchanger 2 as a container, the heat exchanger 2 being connected to the interior of the furnace 1 via the transfer line 3. The furnace comprises a crucible 4 in which the melt is accommodated, heating devices 5 being attached to the furnace walls which, depending on its heating power, bring the melt in the crucible 4 to a temperature that keeps the melt in the liquid state. The crucible 4 is closed by a cover 6 in which at least one opening 7 (shown open here) for the introduction of solid metal material to be melted, for example in the form of pigs, is arranged.

The transfer line 3 comprises an inlet line 8 and a return line 9, which are each guided through the cover 6 of the crucible 4 and protrude into the melt and are connected to the heat exchanger 2. The pipe ends are below the surface of the bath. The transfer lines are heated by trace heating. Each pipe has a terminal box with a plug for the electrical connection.

Furthermore, the pump 10 is provided, which also passes through the cover 6 protrudes and is connected with its suction end 11 to the end of the supply line 8.

The in Fig. 2 The heat exchanger 2 shown is provided with a heating device which is designed as a gas burner 12 in the exemplary embodiment.

In Fig. 3a, b the heat exchanger 2 is shown in more detail and designed as a tube bundle heat exchanger. A flame tube 13 is provided in the center and is connected to the burner 12, the flames of the burner being directed into the flame tube 13. A tube bundle 14 is spirally wound around the flame tube 13, which is connected to the feed line 8 and the return line 9 and leads melt from the feed line 8 to the return line 9. A partition 19 divides the tube bundle 14 into a first tube bundle area 0 and a second tube bundle area 21.

A heat-insulating cylindrical wall 15 and a corresponding base 16 and cover 17 are provided around the tube bundle 14, the burner 12 reaching through the cover 17. Finally, an exhaust pipe 18 is also connected to the interior of the heat exchanger, via which the exhaust gases generated by the combustion process are discharged.

The shape shown is similar to that of an oil heater. In the tube bundle 14 there is a large inner tube made of heat-resistant material with a refractory-lined bottom. The flame burns against the floor, the gases come back up the tube wall, flow over the upper edge back into the first tube bundle area 20. In the tube bundle 14, the gases flow downwards around the lower edge of the partition 19 in the second bundle area 21 and here from bottom to top to the side exhaust outlet. These exhaust gases can still be passed through the furnace. The temperature level is so high that the heating power is sufficient to compensate for the temperature losses in the crucible furnace.

In Fig. 4 FIG. 13 is a further exemplary embodiment in a view similar to that in FIG Fig. 1 shown, with this embodiment to the embodiment according to Fig. 1 The difference is that the heat exchanger is designed as an induction heat exchanger. The pipeline is run through an inductor and the melt is heated by the alternating magnetic field.

During the heating of the melt, preheated pigs, which for example consist of a magnesium alloy, are introduced into the crucible 4 through the opening 7 in the described furnaces, these pigs being heated and liquefied directly in the melt. This process cools the melt, particularly in the vicinity of the pigs. Therefore, as soon as pigs are to be melted, the pump 10 is activated, the melt is sucked in at a first temperature T1 and conveyed via the feed line 8 into the heat exchanger 2, in which the temperature of the melt is increased. After leaving the heat exchanger 2, the melt with the higher second temperature T2 is returned to the crucible 4 via the return line 9.

This process of conveying the melt into the heat exchanger 2, the heating in the heat exchanger 2 and its return to the crucible 4 can be controlled by temperature, process or manually. It is advantageous if the position of the pigs to be melted is arranged between the outlet opening of the return line 9 and the suction point of the pump.

For the forced cooling of the melt, the melt is conveyed into the heat exchanger 2, cooled in the heat exchanger and returned to the crucible 4. In this case, the intake temperature T1 is higher than the temperature T2 of the outlet opening of the return line 9. The process is started automatically or manually. The combustion air fan can be used for cooling with gas or oil heated heat exchangers. However, cooling air can also be passed through the heat exchanger 2 via an additional fan, with which the melt is cooled. With this process, thermal energy can be extracted from the melt. In the event of rapid shutdowns from the melting process or rapid temperature reductions in the melt, it is advantageous to quickly dissipate thermal energy from the system. In the case of rapid shutdowns, the overheated furnace lining can be pushed in, and the melt may overshoot and critical excess temperatures, at which the effectiveness of the protective gassing decreases and the risk potential increases significantly. With the cooling heat exchanger you can these situations can be avoided by forced cooling of the melt. The cooling process until the melt solidifies takes a long time with large amounts of melt in well-insulated furnaces. In the case of some alloys, the melt passes through mixed crystal phases during this time, which results in segregation, which impairs the quality of the melt and later requires more maintenance. With the cooling heat exchanger, these times can be reduced and the side effects described above can be significantly reduced.

It is possible to retrofit systems that are in use with the pump 10, the transfer line 2 and the heat exchanger 3, so that these systems that are already in use can be brought to a higher melting capacity.

Claims (10)

1. A device for heat treating melts made of non-ferrous metals, comprising a container (1) receiving the melt of the non-ferrous metal, a delivery device (10) including a transfer line (3) and at least one heat exchanger (2), the delivery device (10) including the transfer line (3) and the heat exchanger being designed to deliver melt from the container (1) into and through the at least one heat exchanger (2) for heating or cooling, and out of the heat exchanger (2) back into the container (1) or into a further container (200), characterized in that the transfer line (3), with the inlet end that is immersed into the melt and located beneath the bath surface and the outlet end that is immersed into the melt and located beneath the bath surface, and the heat exchanger (2) form a closed tube system passing through the heat exchanger.
2. The device according to claim 1, wherein the container (1) is a melting and holding furnace (100).
3. The device according to claim 1 or 2, wherein the delivery device comprises a pump (10) for pumping the melt through the heat exchanger (2) via the transfer line (3) out of the container (1), and back into the container (1) or into the further container (200).
4. A device according to any one of claims 1 to 3, wherein the heat exchanger (2) is designed as a shell-and-tube heat exchanger.
5. A device according to any one of claims 1 to 4, wherein the heat exchanger (2) comprises a heating device, which includes at least one burner (12), electric heating elements and/or an inductor.
6. A device according to any one of claims 1 to 5, wherein the heat exchanger (2) comprises an exhaust gas outlet (18).
7. A device according to any one of claims 2 to 6, wherein the melting and holding furnace comprises a feed opening (7) for feeding solid non-ferrous metal parts to be melted, such as pigs.
8. A device according to any one of claims 1 to 7, wherein the heat exchanger (2) comprises a cooling device.
9. The device according to claim 8, wherein the cooling device is designed in the form of a gas or air cooling system.
10. A device according to any one of claims 1 to 9, wherein a plurality of heat exchangers (2) are consecutively connected in series or in parallel to one another between the transfer line (3).

Images