Metal melting equipment

Abstract

The present invention relates to an apparatus for melting metals having a melting temperature below 1000°C. A device (2) for forming a plasma (8) is arranged in a melting furnace (1). The device (2) is connected to at least one first source of plasma gas and a voltage source capable of forming a plasma (8), and is designed, dimensioned, positioned, and / or aligned so that the formed plasma (8) is located away from the metal as a material (9) to be melted, where a hot gas stream can be formed by the plasma (8) and the hot gas stream is aligned toward the melting material (9). A melting tank or crucible (5) for receiving the molten metal is arranged in the melting furnace (1).

Description

[Technical Field]

[0001] The present invention relates to an apparatus for melting metals, in particular non-ferrous metals. In this context, the term metal should be understood to include, if possible, the corresponding alloys having a melting temperature below 1000°C. The invention is particularly suitable for melting aluminum and its alloys. [Background technology]

[0002] Until now, these metals have typically been melted in melting furnaces of different configurations using oil or gas burners, using high-temperature flames that can convert each metal into a liquid phase. The combustion of each hydrocarbon compound releases relatively large amounts of CO2, formed by chemical oxidation, into the Earth's atmosphere, which is extremely harmful from the perspective of climate change.

[0003] Furthermore, induction heating of metals as melting materials is also known. However, as a result of the AC electric field generated, a strong stirring effect occurs in the melt that is formed. This leads to a high oxide content in the metal, which has a strong negative effect on the quality of the components manufactured from the melt thus obtained. Induction melting furnaces are also generally not suitable for melting coarse recycled material or cast iron scrap due to the unfavourable bonding conditions.

[0004] Electric resistance furnaces are also known, which usually have a low power output and are therefore generally only suitable for keeping metals that are already liquid.

[0005] Attempts have also been made to melt metals using plasma. In these cases, an electric arc was used to create the plasma. To do this, the electrode was in contact with the unmelted molten material. However, this resulted in contamination of the individual molten metals, which cannot be avoided and is specifically affected. Loss of contact immediately stops the arc during deposition, which must be avoided by very sophisticated process control. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is therefore to provide the possibility of melting metals, which allows the complexity of the system to be kept within limits and which avoids, as far as possible, on-site CO2 emissions as well as contamination of the resulting melt. [Means for solving the problem]

[0007] According to the invention, this object is solved by an apparatus having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized by the features specified in the dependent claims.

[0008] In the melting apparatus according to the invention for melting metals, in particular non-ferrous metals with a melting point preferably below 1000°C, the free-gas torch and the device for forming a plasma in the form of heat transfer by radiation to the molten material are arranged on a melting furnace, which may be any familiar melting furnace with an otherwise identical configuration. Shaft furnaces, hearth-type furnaces, as well as crucible furnaces are preferred.

[0009] The device is connected to a voltage supply and further connected to at least a first source of plasma gas in which a plasma can be formed.

[0010] The apparatus is designed, dimensioned, positioned, and / or aligned so that the formed plasma is located away from the metal molten material, and in this case, the plasma can form a hot gas stream that is aligned toward the molten material. The plasma thus formed does not directly contact the unmelted molten material or the melt. This eliminates the need for such electrodes, and also avoids the use of electrodes that contact the molten material or the melt.

[0011] The formed plasma must function only as a heat source. As a result, heating of the metal melt can only be achieved by the thermal energy of the hot gas stream and the thermal radiation emitted by the plasma.

[0012] For this purpose, the generated plasma must be designed and arranged in the device in such a way that at least most of the free charged particles (especially ions, electrons) cannot come into direct contact with the metal to be melted. For this purpose, the volumetric flow rate and flow velocity of at least one further feed gas, from which a hot gas stream is essentially formed, can be set or controlled accordingly.

[0013] The plasma may also be mixed with another gas (secondary gas) to form a stable plasma or gas torch, which also emits radiant energy in the direction of the molten material, which can be used with the hot gases of the plasma or gas torch and the radiant energy to further transfer heat and melt the molten material in the furnace chamber of the melting furnace.

[0014] The melting furnace contains a melting tank or crucible for receiving molten metal.

[0015] In an alternative embodiment of the present invention, the device can be designed with a microwave generator and a resonator connected thereto, formed as a waveguide, with at least one reflector for the generated microwaves. Additionally, an electric ignition device with an ignition electrode electrically isolated from the housing should be part of the device. The ignition device is dedicated to igniting the plasma and can be switched on once a sufficient amount of plasma has been formed after free charge carriers in the plasma gas used are formed by the generated microwaves.

[0016] The plasma is formed in the region of the standing microwaves in the resonator, in front of at least one reflector through which the plasma gas flows. This largely avoids translational motion of the formed plasma, and allows for a stationary heat source to be formed for the formation of the high-temperature gas stream.

[0017] In this alternative, the plasma is formed within the housing of the apparatus, and the hot gas stream is directed toward the molten material in the melting furnace through at least one flow guide element. Tubular or channel-shaped elements can be used as the flow guide element, allowing the hot gas to flow toward the molten material. The flow guide element can be made of glass, glass ceramic, or pure ceramic material. At least two flow guide elements can be present. In this case, the flow guide element can be positioned in an area of ​​the interior of the flow guide element with at least a large inner diameter or a large free cross-sectional area, forming a heat shield there. The flow guide elements do not come into direct contact with each other.

[0018] In another alternative, the device is formed by two spaced apart electrodes between which plasma gas flows toward the molten material, generating an arc discharge. This device can be designed similarly to known plasma torches, such as those used for cutting and welding materials. In this case, the electrodes are usually made of tungsten, hafnium, or their alloys. The counter electrode can form a housing through which the plasma gas flows. Only the dimensions and operating parameters should be adapted to the application of melting metal. However, even in this case, the formed plasma should not come into direct contact with the molten material but should only function as a heat source for heating a gas that can be used as a hot gas stream for melting or as a free-gas torch.

[0019] At least one additional source of plasma gas or another gas (secondary gas) can be connected to the housing. This additional feed can be located at a distance from the first feed. Preferably, the additional feed can be located in the region of the formed plasma or downstream in the direction of flow.

[0020] Advantageously, the power of the microwave generator or the arc discharge of the device, the volumetric flow rate of the plasma gas and / or the volumetric flow rate of the further gas can be controlled. For example, the measured temperature can represent the control variable. This can be the temperature of the hot gas stream, the plasma, the molten material or the melt. The temperature is preferably measured contactlessly, for example by means of a thermograph or a pyrometer. However, it is also possible to regulate the temperature. Depending on the process control, this can be done, for example, to melt or to keep the melt warm.

[0021] It is also possible to adjust the length of the plasma-forming gas torch or the length of the plasma-forming torch in the direction of the molten material, and as a result, in particular, the microwave generator so that the proportion of available radiant energy can be influenced.

[0022] Advantageously, the plasma gas can be swirled tangentially into the enclosure before being subjected to the microwaves, resulting in extended contact time and more effective promotion of free charge carriers (ions, electrons) to higher energy levels, increasing efficiency.

[0023] However, other gases may also flow tangentially into the enclosure, either alone or in addition. The plasma gas can be introduced into the enclosure parallel to the longitudinal axis of the device enclosure or the direction of flow of the hot gas stream. This allows the gas to flow into the device enclosure through an inlet, which may be located immediately next to the ignition device.

[0024] Plasma gas inlets can be located around the periphery of the housing through which plasma gas can flow from the feed into the housing.

[0025] Advantageously, argon can be used as the plasma gas and / or other gases, as it is completely inert to the molten material and the melt. Nitrogen as a plasma or other gas should be avoided, especially when melting aluminum or its alloys. Oxygen or air is harmful in this respect, as it promotes oxidation.

[0026] However, it is also possible to use a mixture of gases as the plasma gas or other gases. In this process, the proportions of each gas in the mixture can be adapted to the specific metal to be melted. For example, argon can be mixed with air, but the air content must be less than the argon content.

[0027] There may also be a recirculation system for the hot gases recovered from the melting furnace, allowing this gas to be reused as plasma gas and / or further gas during the cycle, or to utilize the residual heat in other ways. Closed-loop operation allows for a reduction in the amount of plasma gas and other gas additions required, particularly reducing the cost of argon.

[0028] However, the residual heat of the extracted hot gases can also be used, for example, inter alia, to keep the resulting melt warm or to preheat further gases.

[0029] In the present invention, microwaves with frequencies in the range of 500 MHz to 5000 MHz and powers in the range of 5 kW to 3000 kW can be used.

[0030] The total volumetric flow rate of the plasma gas and / or other gases must be selected to be at least large enough so that the hot gas stream entering the melting furnace reaches or at least approaches the unmolten molten material, causing the molten material to melt as a result of thermal radiation.

[0031] It is also advantageous to arrange the ignition electrode of the ignition device for the microwave-generated plasma in the radiation trap. For this purpose, the ignition electrode can be arranged in a tubular or channel-like element whose inner diameter or inner free cross-sectional area is smaller than the housing of the device in which the plasma is formed. It is particularly advantageous if the tip of the electrode is recessed into the tubular or channel-like element, i.e., if the tip is arranged in the radiation trap. This design allows for a long service life of the ignition electrode and completely avoids contamination of the melt with the electrode material.

[0032] The plasma-forming device can be advantageously mounted in the furnace body in a swiveling device, allowing for targeted and variable directing of a gas torch, a plasma torch, or a hot gas stream in the furnace chamber. This allows the direction of the gas torch or plasma torch to be changed to achieve localized and targeted heating of each molten material in the furnace chamber. For example, the outer edge or the center of the molten material placed in the furnace chamber can be heated more or less at any given moment, as needed.

[0033] In accordance with the invention, the housing can be cooled in at least some areas, and it may be advantageous to temperature-condition in particular the flow guiding element(s) in order to advantageously reduce the effects of strong temperature variations in this area, and in particular to avoid large temperature differences occurring in a short time.

[0034] As already explained, the present invention allows for a significant reduction in the amount of CO2 emitted; existing melting furnaces can be converted or retrofitted with little effort; the quality of the molten metal is at least equivalent to that achieved with conventional gas or oil burners; contamination and oxidation of the molten metal can be avoided, if not completely, at least to a large extent.

[0035] The present invention will now be described in detail by way of examples, and the features can be combined with one another regardless of the specific example or corresponding figure in the drawings, and the individual features are not limited to the specific example or figure. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a schematic diagram of an example of an apparatus according to the invention; [Figure 2] 1 is a cross-sectional view through a portion of an example apparatus for forming a plasma using microwaves. DETAILED DESCRIPTION OF THE INVENTION

[0037] 1 shows a schematic diagram of an example of an apparatus having a melting furnace 1 according to the present invention. On one side of the melting furnace 1 there is a door (not shown) through which unmelted molten material 9 can be introduced into the melting furnace 1. The unmelted molten material 9 can be deposited onto an inclined melting platform 4, in the example shown at an angle of 10°, so that the molten metal can drip from the melting platform 4 into a crucible 5 or melting tank (not shown).

[0038] The device 2 for forming plasma is flange-mounted to the housing 6 of the melting furnace 1, and at least one flow guiding element for a hot gas stream, not shown in the figure, is guided through the housing wall of the melting furnace 1 into the interior of the melting furnace 1, so that at least one hot gas stream can be directed onto the unmelted molten material 9. The housing is pivotally mounted, so that the hot gas stream formed by the gas, plasma torch or plasma 8 can be followed during melting.

[0039] A viewing window embedded in the housing wall 6 of the melting furnace 1 allows the melting process to be observed from the outside, and also allows the temperature inside the melting furnace 1 to be measured through the viewing window.

[0040] In Figure 1, the melting furnace 1 also has an exhaust port 7 for hot exhaust gases, through which the hot exhaust gases can be extracted from the melting furnace 1. The hot exhaust gases can be recycled and regenerated, for example as plasma gas or other gases.

[0041] The extracted hot exhaust gases can be used to keep the molten metal warm or for other uses where thermal energy can be utilized.

[0042] The hot exhaust gases may also be passed through a heat exchanger.

[0043] The essential elements of the device 2 for forming the plasma are shown in Figure 2. The microwave generator, which can be a commercially available product but is not shown, is flange-mounted to the resonator 10.

[0044] The microwaves 11 generated by the microwave generator can be obtained as standing waves in the resonator 10. For this purpose, a reflector 10.1 is arranged on the flange of the housing 13 of the device 2 opposite the second flange 21. The microwave generator is connected to the second flange 21.

[0045] The reflector 10.1 may be made of glass. Near the microwave reflector 10.1, a cooling gas feed 17 is provided in the housing 13 of the device 2. In addition to the cooling effect, the cooling gas flows along the surface of the reflector 10.1 in the housing 13, which also cleans and keeps it free of particles.

[0046] In Figure 2, an ignition device with a rod-shaped ignition electrode 12 can be seen to the left of the housing 13 of the device 2. The ignition electrode is connected to one pole of a voltage source (not shown). If a voltage is applied to this ignition electrode 12 for a short time, the energy of the supplied plasma gas can be further increased, which ignites a plasma 8 in the region of the resonator 10, where standing microwaves 11 are formed. After the plasma 8 has been ignited, the ignition device can be switched off.

[0047] The housing 13 can be designed in the region of the ignition device with the ignition electrode 12 as a radiation trap, as explained in the general part.

[0048] The plasma gas can enter only through the radiation trap or only through the inlets 18 distributed around the periphery of the enclosure 13, although combinations of these are also possible.

[0049] Preferably, the swirl effect can be achieved and utilized by tangential entry through several inlets 18 .

[0050] In the example shown, further feeding of another gas is omitted, but at least one additional gas can be introduced into the housing 13 of the device 2, preferably into the region of the formed plasma gas 8. The further gas can then be used, at least in large part, for the hot gas stream.

[0051] A hot gas stream leaves the device 2 in the direction of the arrow shown. For this purpose, in this example, there are three tubular flow-guiding elements 14, 15, and 16. The quartz glass tube 14, which has the smallest diameter, encloses the formed plasma 8. In the area facing the melting furnace 1, this is enclosed by a further tubular flow-guiding element 15, which is located opposite the ignition device and can simultaneously form a shield against thermal radiation.

[0052] A tubular third flow guiding element 16 with the largest diameter is arranged in the flange part of the housing 13 facing the melting furnace 1. The third flow guiding element 16 can be guided at least up to the wall of the housing 6 of the melting furnace 1, so that the hot gas stream can be guided through an opening in the wall of the housing 6 to the molten material 9 arranged in the melting furnace 1. However, the length can also be selected so that it extends into the interior of the melting furnace 1.

[0053] The tubular third flow guiding element 16 may be guided and held in a flange 19 of the housing 13 of the device 2. The flow guiding elements 14, 15, 16 are inserted into one another, although they should not come into contact with one another.

[0054] In addition to the supply 17 for cooling gas, other areas of the housing 13 of the device 2 may be designed and used for cooling. For this purpose, a cooling medium (gas or liquid) can flow through these areas. These areas should be located at least in the vicinity of the formed plasma 8.

[0055] In the illustrated example, a flange cooling 20 is provided in a part of the housing 13 of the device 2 . [Explanation of symbols]

[0056] 1 melting furnace 2 equipment 4 Molten Platform 5. Crucible 6. Housing 7. Exhaust port 8. Plasma 9 Molten Materials 10 Reflector 11 Microwave 12 ignition electrode 13. Cabinet 14 Guidance Elements 15 Guidance elements 16 Guidance elements 17 Source 18 Entrance 19 Flange 20 Flange cooling 21 flange

Claims

1. 1. Apparatus for melting metals, comprising: a device for forming a plasma is disposed in the melting furnace, said device being connected to a voltage supply source, and at least one first feed for a plasma gas capable of forming said plasma is connected to said device; The apparatus is designed, dimensioned, positioned and / or aligned so that the formed plasma is located at a position away from the metal as the material to be melted, in which case a hot gas stream can be formed by the plasma, and the hot gas stream is aligned in the direction of the material to be melted, so that the heating of the metal melting material is achieved only by the thermal energy of the hot gas stream and the thermal radiation emitted from the plasma, and therefore the formed plasma does not come into direct contact with the unmelted melting material or the melt; The apparatus includes a melting tank or crucible disposed within the melting furnace for receiving the molten metal.

2. 2. The apparatus according to claim 1, characterized in that the device is designed to form a free gas torch or a plasma torch in the furnace chamber of a melting furnace, in which the plasma gas and further gases of the plasma can use their hot gas and radiant energy for heat transfer and melting of the respective metals.

3. 2. The device according to claim 1, characterized in that the device comprises a microwave generator and a resonator connected to it, designed as a waveguide and having at least one reflector for the generated microwaves.

4. 4. The apparatus of claim 3, wherein the apparatus is formed with an electric ignition device, an ignition electrode being electrically isolated from the housing, the plasma being formed in a region of standing microwaves within the resonator in front of the at least one reflector through which plasma gas flows, and the plasma being formed within the housing.

5. 5. Apparatus according to claim 3, characterized in that the hot gas flow is directed towards the molten material via at least one flow-guiding element.

6. 5. The apparatus of claim 4, wherein the ignition electrode of the electrical ignition device for the plasma is arranged in a radiation trap.

7. 7. Apparatus according to any one of claims 1 to 6, characterized in that the power, length, temperature and / or length of the free gas or plasma flare can be varied by means of a controllable microwave generator.

8. 8. The apparatus according to claim 1, wherein the device comprises two electrodes arranged at a distance from each other, between which a plasma gas flows in the direction of the material to be melted, and an arc discharge occurs.

9. Apparatus according to any of the preceding claims, characterized in that at least one further source for plasma gas or a further gas is connected to the housing of the device.

10. 5. Apparatus according to claim 4, characterized in that the power of the microwave generator, the volumetric flow rate of the plasma gas and / or the volumetric flow rate of further gases can be controlled.

11. 5. Apparatus according to claim 4, characterized in that at least the plasma gas and / or the further gas flows tangentially into the housing in a spiral manner.

12. 12. Apparatus according to any of the preceding claims, characterized in that argon is used as the plasma gas and / or the further gas.

13. 11. The device according to any one of claims 3 to 10, characterized in that it uses microwaves with a power ranging from 5 kW to 3000 kW and a frequency ranging from 500 MHz to 5000 MHz.

14. 14. Apparatus according to any one of claims 1 to 13, characterized in that a gas mixture is used as plasma gas and / or further gas.

15. 15. An apparatus according to any one of claims 1 to 14, characterized in that a recirculation system for the hot gas extracted from the melting furnace is provided, so that this gas can be reused as plasma gas and / or as further gas in the circulation, or the residual heat can be used in other ways.

16. 16. The apparatus according to claim 1, wherein the device is fixed to the furnace body in a swivel device, thereby allowing for variable and targeted guidance of gas flares, plasma flares or hot gas flows in the furnace chamber.

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