Apparatus and method for heating rod-shaped metallic workpieces

Abstract

The invention relates to a device for heating rod-shaped metal workpieces (1), in particular bolts made of aluminium or copper and alloys thereof, the device comprising an induction furnace (2) for inductive heating, the induction coils (3) of the induction furnace (2) being cooled by means of a cooling apparatus (5), and comprising a pre-heating apparatus (9) for pre-heating the workpieces (1). The invention also relates to a method for heating rod-shaped metal workpieces using such a device. To be able to dispense with a gas-heated pre-heating furnace for pre-heating the rod-shaped workpieces and to achieve an increase in energy efficiency during inductive bolt heating in order to minimise as much as possible or to completely avoid energy losses, according to the invention the cooling apparatus (5) uses a liquid temperature-control medium which is guided in a cooling circuit and the workpieces (1) are heated by the heated temperate-control medium in the pre-heating apparatus (9) before entering into the induction furnace (2).

Description

[0001] The present invention relates to a device and a method for heating rod-shaped metallic workpieces, in particular bolts made of aluminum or copper and their alloys, with an induction furnace for inductive heating, wherein the induction coils of the induction furnace are cooled by means of a cooling device, and with a preheating device for preheating the workpieces, as well as a corresponding method for heating such rod-shaped metallic workpieces.

[0002] Such devices are also known as "inductive bolt heating systems (IBE)." These are used to heat metallic press bolts and have proven their worth for decades for numerous reasons. A device of this type is known, for example, from WO 2010 / 031503 A1.

[0003] DE3425060 A1 relates to a method for recovering and utilizing waste heat generated in the coils of electric induction furnaces using a cooling medium, particularly during the inductive firing of pre-formed carbon anodes. DE3538151 A1 relates to a method and an apparatus for producing pre-formed, highly compressed synthetic carbon bodies, in particular carbon anodes for aluminum molten salt electrolysis. The very high

[0004] The high heat output enables high throughput with minimal space requirements. This high heat output allows for precise temperature control within the bolt, offering advantages in subsequent processing. The fact that the inductive heating is electrically powered makes the system particularly attractive in the current climate, as CO₂-free energy can be used when renewable electricity is employed.

[0005] Compared to press bolts made of ferritic materials, heating non-ferritic materials, especially aluminum and copper, as well as their alloys, results in lower efficiencies. This is due to the different magnetic coupling of the induction field. However, because of the advantages mentioned earlier, their use is quite common for materials such as aluminum and copper.

[0006] Magnetic coupling, and thus inductive heat transfer, leads to efficiency losses, particularly with non-ferritic materials. This necessitates cooling the induction coils of the induction furnace, usually implemented as water cooling. This cooling also dissipates the heat radiated from the preheated bolts onto the induction coil(s). A smaller amount of waste heat is also generated in the electrical control circuitry, which is likewise dissipated via the cooling water. The overall efficiency is on the order of approximately 60%, meaning that about 40% of the supplied electrical energy must be dissipated primarily via the cooling water.

[0007] To save primary energy, gas-fired preheating furnaces are often installed upstream of inductive billet heating systems. These furnaces preheat the billet to a base temperature level. Above this level, the inductive billet heating system then performs the necessary, very rapid final heating. It is important to note in current developments that gas-fired preheating results in CO₂ emissions, which can only be avoided by using regeneratively produced hydrogen as the fuel gas.

[0008] Based on this, the present invention aims to design and further develop the aforementioned and previously described device and the corresponding method in such a way that a gas-heated preheating furnace for preheating the rod-shaped workpieces can be dispensed with. In particular, the inductive bolt heating process is intended to be made more energy-efficient in order to minimize or completely avoid energy losses.

[0009] This problem is solved in a device with the features of the preamble of claim 1 by the fact that the cooling device uses a liquid temperature control medium circulated in a cooling circuit and that the workpieces are heated by the heated temperature control medium in the preheating device before entering the induction furnace. In this way, the unused residual heat from the induction furnace can be fully utilized for preheating the workpieces. Direct heating of the workpieces (bolts) by the temperature control medium of the cooling device is possible.

[0010] The problem is also solved procedurally by the fact that the cooling device uses a liquid temperature control medium circulated in a cooling circuit and that the workpieces are heated by the heated temperature control medium in the preheating device before entering the induction furnace.

[0011] A further aspect of the invention provides that the cooling circuit includes a heat exchanger. A treatment medium circulating in a second circuit can be indirectly heated via the heat exchanger by the temperature control medium of the induction furnace's cooling unit and used for the direct heating of the bolts supplied to the preheating unit. Another preferred embodiment of the invention provides that an intermediate heating unit is provided between the preheating unit and the induction furnace. This is advantageous whenever a sufficient temperature level of the workpieces / bolts cannot be achieved through preheating alone.

[0012] The preheating device according to the invention comprises either a basin for preheating the bolts by means of the temperature control medium or a spray / shower chamber for preheating the bolts. Devices for mixing the temperature control medium and / or for increasing heat transfer may be arranged in the basin. Such mixing devices may include nozzles or circulation units.

[0013] In an alternative embodiment, a spray / shower chamber can also be provided as a preheating device for preheating the bolts, which causes intensive contact of the treatment medium with the bolt surface.

[0014] In any case, according to a further preferred embodiment of the invention, it is advantageous if the preheating device includes means for cleaning and / or descaling the bolts. The cleaning of the bolts can be carried out mechanically, and for this purpose, for example, driven brushes can be provided within the preheating device.

[0015] A further teaching of the invention provides that devices for drying or blowing off the tempering medium from the bolts are provided between the preheating device and the induction furnace, so that they can be supplied to the induction furnace as dry as possible.

[0016] Water is preferably used as the temperature control medium and / or treatment medium; the water may contain chemical additives.

[0017] It is also possible to use a thermal oil instead of water as a temperature control medium and / or treatment medium, which can increase the temperature level.

[0018] According to a further teaching of the invention, it is provided that the cooling circuit of the cooling device is separated into different circuits and only one circuit, or several individual circuits, are used for preheating the bolts.

[0019] According to a preferred embodiment of the invention, fuel-heated heating can be connected upstream and / or downstream of the inductive heating of the bolts. Such fuel-heated heating can be gas-heated, in particular using hydrogen or natural gas. However, it is also possible for the fuel-heated heating to be carried out with liquid fuel.

[0020] The inductive heating of the bolts can also be preceded and / or followed by electrical (resistance-heated) heating, whereby the heat can be transferred to the bolts by means of convection or radiation.

[0021] In another alternative, the inductive heating of the bolts can also be preceded and / or followed by exhaust gas-heated heating.

[0022] In any case, it is advantageous to control the preheating of the billets using a mathematical model. Such a mathematical model records the preheating temperature and optimally adjusts the inductive heating in the inductive billet heating system to the desired target temperature based on a model of the entire heating process. This is also referred to as a "digital twin." Optimization for maximum performance or maximum energy savings is possible. Environmental influences (such as air or cooling water temperature) or process influences (such as shutdown of the downstream press line) can also be taken into account.

[0023] The invention is explained in more detail below with reference to a drawing illustrating only preferred embodiments of the invention. In the drawing, all schematic representations are shown, Fig. 1 shows a schematic representation of an inductive bolt heating system according to the prior art, Fig. 2 shows a first embodiment of a device according to the invention using a heat exchanger, Fig. 3 shows a second embodiment of the device according to the invention, and Fig. 4 shows a further embodiment of the invention.

[0024] Fig. 1 Figure 1 schematically shows the setup of an inductive billet heating system (IBE) in which a metallic, non-ferritic press billet (e.g., made of aluminum or copper) is inductively heated in an induction furnace 2 (indicated only). The schematically depicted induction coil of the induction furnace 2 and the necessary electrical control unit 4 are visible. A cooling device 5 (indicated only) uses a liquid temperature control medium circulating in a cooling circuit, which dissipates the unused heat (approximately 40% of the supplied electrical energy) from the induction coil 3 in the induction furnace 2. A smaller amount of waste heat is also generated in the electrical control unit 4, which is likewise dissipated via the temperature control medium and fed to a heat exchanger 7.It is not shown that the subsequent circuit extracts the heat supplied to the heat exchanger and can be used, for example, for heating buildings or for domestic hot water. A pump 6 ensures that the temperature control medium is returned to the induction furnace 2 or the electrical control unit 4 for cooling purposes after leaving the heat exchanger 7.

[0025] In Fig. 2 A first embodiment of the device according to the invention is now shown schematically, wherein the further circuit downstream of the heat exchanger 7 has a line 8 which feeds into a preheating device 9. This preheating device can have a basin 10 for receiving the treatment medium circulated in the second circuit, whereby the supplied bolts 1 come into complete contact with the treatment medium in order to heat them. Alternatively or additionally, it is also possible to provide a spray / shower chamber 11 or a sprinkler system (shown only schematically) in the area of ​​the preheating device 9. A pump 12 ensures that the treatment medium, cooled during preheating, is fed back to the heat exchanger 7 to complete the second circuit.

[0026] Fig. 3 Figure 1 shows only a schematic representation of a second embodiment of the invention, in which no heat exchanger is present. The heat extracted from the induction furnace 2 and also from the electrical control unit 4 in the temperature control medium is supplied directly to the preheating device 9 via a heat pump 6' and a line 8. The preheating device 9 has the same design as the device according to Figure 1. Fig. 2 . The temperature control medium is then supplied from basin 10 to the cooling unit 5 in its cooled state by means of pump 6, as described previously.

[0027] Finally, in Fig. 4 a modification of the device according to Fig. 2 The figure shown depicts an intermediate heating device, only indicated, that may be provided between the preheating device 9 and the induction furnace 2. This intermediate heating device can be heated with different forms of energy, as described in the dependent claims.

Claims

1. Apparatus for heating bar-shaped metallic workpieces (1), in particular bolts made of aluminium or copper and their alloys, comprising an induction furnace (2) for inductive heating, wherein the induction coils (3) of the induction furnace (2) are cooled by means of a cooling device (5), and comprising a preheating device (9) for preheating the workpieces (1), wherein the cooling device (5) uses a liquid heat transfer medium circulated in a cooling circuit, and the workpieces (1) are heated by the heated heat transfer medium in the preheating device (9) before entering the induction furnace (2), wherein the preheating device (9) comprises a tank (10) for preheating the bolts (1) by means of the heat transfer medium, or wherein a spray / shower chamber (11) is provided for preheating the bolts.

2. Apparatus according to claim 1, characterised in that the cooling circuit comprises a heat exchanger (7) and that a treatment medium circulating in a second circuit is heated indirectly via the heat exchanger (7) by the heat transfer medium of the cooling device (5) of the induction furnace (2) and is used for the direct heating of the workpieces (1) fed to the preheating device (9).

3. Apparatus according to claim 1 or 2, characterised in that an intermediate heating device (13) is provided between the preheating device (9) and the induction furnace (2).

4. Apparatus according to any one of claims 1 to 3, characterised in that devices for mixing the heat transfer medium and / or for increasing heat transfer are arranged in the tank (10).

5. Apparatus according to claim 4, characterised in that the devices for mixing comprise nozzles or circulation units.

6. Apparatus according to any one of claims 1 to 5, characterised in that the preheating device comprises means for cleaning and / or descaling the bolts.

7. Apparatus according to claim 6, characterised in that the cleaning of the bolts is carried out mechanically and that driven brushes are provided within the preheating device for this purpose.

8. Apparatus according to any one of claims 1 to 7, characterised in that means are provided between the preheating device and the induction furnace for drying or blowing the heat transfer medium off the bolts.

9. Apparatus according to any one of claims 2 to 8, characterised in that the heat transfer medium and / or the treatment medium is water.

10. Apparatus according to claim 9, characterised in that the water is mixed with chemical additives.

11. Apparatus according to any one of claims 1 to 8, characterised in that the heat transfer medium and / or the treatment medium is thermal oil.

12. A method for heating rod-shaped metallic workpieces, in particular bolts made of aluminium or copper and their alloys, by means of an apparatus according to any one of claims 1 to 11, wherein the cooling device uses a liquid heat transfer medium circulated in a cooling circuit, and the workpieces are heated by the heated heat transfer medium in the preheating device before entering the induction furnace.

13. Method according to claim 12, characterised in that the cooling circuit of the cooling device is separated into different circuits and only one circuit or several individual circuits are used for preheating the bolts.

14. Method according to claim 12 or 13, characterised in that the inductive heating of the bolts is preceded and / or followed by fuel-fired heating.

15. Method according to claim 14, characterised in that the fuel-fired heating is gas-heated, in particular using hydrogen or natural gas.

16. Method according to claim 14, characterised in that the fuel-fired heating is liquid-fuel-fired.

17. Method according to claim 12 or 13, characterised in that the inductive heating of the bolts is preceded and / or followed by electric resistance heating.

18. Method according to claim 16, characterised in that the heat is transferred to the bolts by means of convection.

19. Method according to claim 16, characterised in that the heat is transferred to the bolts by radiation.

20. Method according to claim 12 or 13, characterised in that the inductive heating of the bolts is preceded and / or followed by exhaust-gas-heated heating.

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