Device for heating continuously cast and extruded round bars and round bolts

Abstract

The present invention relates to a device for heating continuously cast and extruded round bars and round bolts, in particular a device for laser-based heating of such elements by means of absorption of optical radiation via a heat transfer means. A device (100) according to the invention for heating continuously cast and extruded round bars and round bolts (S) comprises a bar guide (10) for transporting a bar (S) through the device (100); a laser device (20) for heating the bar (S) by means of absorption of optical radiation; and a heat transfer means (30) configured to absorb optical radiation emitted by the laser device (20) and convert it into heat, wherein the heat transfer means (30) is in contact with the bar (S) for heat transfer.

Description

[0001] The present invention relates to a device for heating continuously cast and extruded round bars and round bolts, in particular to a device for laser-based heating of such elements by absorption of optical radiation via a heat transfer means. State of the art

[0002] Some industrial manufacturing processes use continuously cast or extruded metallic round bars and round billets as the raw material for their respective products. Round billets are essentially shorter round bar sections. A typical material for these semi-finished products is aluminum, but other metals or plastics can also be used. Aluminum bars are usually produced using the so-called continuous casting process, which can be divided into vertical and horizontal continuous casting. Another manufacturing process for round bars is extrusion. Especially in the continuous casting of metals, the surface of the produced bars is typically relatively rough.

[0003] For further processing of round bars and round billets through forming, for example in extrusion presses and extrusion lines, the bars typically need to be heated to a material-specific forming temperature. Gas-fired furnaces are typically used for this purpose in the current state of the art. However, due to the expected steadily rising gas prices and the detrimental dependence on a single fossil fuel, alternative heating concepts will be needed in the future. In addition to providing the required temperatures and sufficient heat output for heating large volumes of material in conventional industrial systems, the focus in the future will be on the energy efficiency and climate neutrality of such systems.

[0004] In addition to switching the combustion gas used for heating to more resource-efficient alternatives (e.g., hydrogen, biogas), the use of electric heating elements in industrial furnaces is already known for this purpose. However, the electrical heating of a furnace volume comparable to that of conventional gas furnaces to the temperatures required for the forming processes is generally not a viable alternative to the use of fossil gas due to the higher costs per kW of heating output. Therefore, new ways of heating the materials more efficiently must be found. Localized and direct-acting heating concepts, in particular, offer significant savings and optimization potential. However, these concepts must be as easy to handle as possible for industrial use and must be characterized by a long service life and low operating and maintenance costs. Disclosure of the invention

[0005] It is therefore an object of the present invention to provide a device for heating continuously cast and extruded round bars and round billets (hereinafter referred to as bars for short), which is capable of heating even several meters long cylindrical bars of a corresponding material for subsequent processing (e.g. forging, extrusion) to a material-specific process temperature (e.g. for forming), which can in principle be operated in a climate-neutral and as energy-efficient manner as possible, has lower or potentially at least comparable operating and maintenance costs compared to conventional gas heating furnaces, and is suitable for industrial use. Potentially wear-prone moving components should be largely eliminated. In addition, many applications require highly precise and / or positionally accurate temperature control.

[0006] These objects are achieved according to the invention by the features of independent claim 1. Expedient embodiments of the invention are contained in the dependent claims. The features listed individually in the claims can be combined with one another in a technologically expedient manner and can be supplemented in many ways by explanatory facts from the description and / or details from the figures, whereby further embodiments of the invention are shown.

[0007] The present invention relates to a device for heating continuously cast and extruded round bars and round billets, comprising a bar guide for transporting a bar through the device; a laser device for heating the bar by absorbing optical radiation; and a heat transfer means configured to absorb optical radiation emitted by the laser device and convert it into heat, wherein the heat transfer means is in contact with the bar for heat transfer.

[0008] Before heating, the rods must first be inserted into the device. This can be done using a rod guide commonly used in the prior art. The rod guide can be designed for transport through the device from an inlet opening to an outlet opening. However, the rod guide can also be designed for insertion and removal of the rods through a single opening in the device by reversing the corresponding transport direction. Suitable rod guides for the directed transport of cylindrical round rods and round bolts through heating furnaces (e.g., gas furnaces) are well known in the prior art and can accordingly also be used in a device according to the invention.

[0009] The rods are heated by absorbing optical radiation from a laser device. This heating process has the advantage that the heat can be applied very locally and directly to the rods, without having to heat the entire furnace volume to the required process temperatures. Although the furnace is also heated indirectly by heat radiation from the heated rods, the required energy consumption is nevertheless lower than if the entire furnace chamber were heated to the process temperature. Laser devices are now available in a cost-effective and durable manner, even for the high-performance range, and they also exhibit very high conversion efficiency for converting electrical energy into radiant energy.If the generated optical radiation is then absorbed as completely as possible by the heat transfer medium, there is an optimal heat input into the heat transfer medium and thus also into the rod in contact with it.

[0010] However, the rods typically available are not suitable for direct heating by absorbing optical radiation. In particular, the untreated surface of metal rods is generally more or less highly reflective, so that only a fraction of the incident optical power can be absorbed by the material due to surface reflections. Furthermore, due to manufacturing reasons, the surface of the rods is usually not smooth, but typically exhibits a relatively high degree of roughness. This surface roughness forms scattering points on the surface of the material, which can also greatly reduce the amount of energy that can be introduced into the material. In both cases, this leads to a reduction in absorption at the surface of the material, which is undesirable.

[0011] According to the invention, optical radiation is therefore not absorbed directly via the surface of the rods themselves, but rather an additional heat transfer means is used, which is designed to absorb optical radiation emitted by the laser device and convert it into heat, wherein the heat transfer means is in contact with the rod for heat transfer. The heat transfer means can, for example, be a lacquer or paint layer applied to the surface of the rod as an absorber layer. The heat transfer means can be specifically adapted to the wavelength of the optical radiation intended for absorption. In particular, the heat transfer means can contain specific absorber particles, photonic nanoelements or appropriately functionalized polymers (antenna molecules).Contact with the rod is required to effectively conduct the heat generated by absorption into the rod material.

[0012] Preferably, the heat transfer means can be designed as a heat transfer sleeve or cuff surrounding the rod. Such elements can be provided to surround the rods as closely as possible and thus enable largely direct, full-surface contact with the rod. The elements can be made of a material that strongly absorbs the incident optical radiation in the corresponding wavelength range and has high temperature stability. Alternatively, a lacquer or paint layer applied to the surface of said heat transfer means can be provided for absorption, in accordance with the previous exemplary embodiment, for the optical radiation emitted by the laser device. In this case, the heat transfer sleeve or cuff only needs to be made of a suitable temperature-stable material and does not itself need to be an effective radiation absorber.For example, this could be a metal or steel sheet that is blackened in the direction of incidence of the optical radiation (outside).

[0013] Preferably, the outer surface of the heat transfer means is smooth to avoid scattering centers. The heat transfer means can extend along the entire area of ​​the rod to be heated, or a plurality (at least two) of adjacent heat transfer means can be used for rod heating. The use of a combination of relatively short heat transfer means offers the advantage of simpler mechanical implementation and also allows for easy adaptation to different rod lengths.

[0014] A heat transfer sleeve can, for example, be designed as a cylindrical hollow element that largely matches the diameter of the rod to be heated and can be brought into contact with the rod before or during transport. To ensure that the heat transfer sleeve is in full contact with the rod for heat transfer in the event of possible fluctuations in the diameter of the rod, the heat transfer means can further comprise a contact medium for improved heat conduction (e.g., a thermally conductive gel or thermally conductive paste). This preferably completely fills a gap between the surface of the rod and an inner side of the heat transfer sleeve. However, a contact medium is not limited to use in heat transfer sleeves and can also be used in conjunction with other heat transfer means.

[0015] A heat transfer sleeve can, in principle, be designed similarly to the heat transfer sleeve described above and used accordingly. In contrast, however, it can be designed with an adjustable diameter so that rods of different or non-uniform diameters can be used. Such a sleeve can, for example, be equipped with a variably adjustable opening mechanism to adapt the diameter of the opening. One possibility for this is to design the sleeve with prong- or band-shaped tension elements around a support area, whereby the sleeve can be tightened around the rod by tensioning the tension elements after the rod has been inserted into the sleeve.Another possibility is to design a corresponding sleeve as a spiral arrangement, for example by arranging several windings of a sheet metal acting as a heat transfer means offset from one another along the rod direction. As in the example of the above-mentioned sleeve with the prong- or band-shaped tension elements, the diameter of the opening of the spiral arrangement can be reduced by tightening the tension elements arranged accordingly on the sheet metal, so that the sleeve can be tightened spirally around the rod. A sleeve whose diameter can be adjusted by means of a rotary drive is also possible, similar to the principle of a hose clamp whose size can be adjusted to suit the opening.

[0016] The laser device preferably comprises a plurality of laser diode bar stacks arranged in a ring around the rod, preferably with an emission wavelength between 900 nm and 1 µm. Laser diode bars can provide very high optical output powers and exhibit high electrical conversion efficiency. To further increase the output power, the individual laser diode bars can be arranged in stacks. Emission wavelengths in the aforementioned range, for example, at 940 nm, are particularly well-suited for a radiant heater according to the invention and are available cost-effectively and in a wide range from a variety of suppliers. For example, optical outputs of typically approximately 100 W to 150 W per laser bar are currently available, with conversion efficiencies of 60-70%. This can provide optical output powers in the kW range for a laser stack with approximately 8 to 12 laser bars.The electrical energy not converted into optical radiation by the laser diode bars leads to heating of the laser diode bar stacks, whereby the resulting heat loss must be effectively dissipated by appropriate cooling devices. Active liquid cooling of the laser diode bar stacks is preferred, with the operating temperature generally stabilized at approximately 20 °C - 30 °C.

[0017] A rough estimate of the required system power can be made by comparing it with current industrial systems. For example, for aluminum rods with a diameter of 8 inches and a length of approximately 1 m, an optical power of several hundred kW would be required to heat them from the average ambient temperature to a typical process temperature of approximately 520 °C, a throughput typically achieved in industrial systems. While it is possible in principle to provide such high power levels using purely optical means, it places very high demands on the system design used. For practical reasons, a hybrid approach is therefore sensible, in which the rods are not heated purely by radiation from ambient temperature to the required process temperature, but rather the rods are preheated by another means before the heating according to the invention.For aluminum rods, for example, a preheating temperature of approximately 400 °C is a reasonable starting point. Under these assumptions, the required optical system power is reduced to just a few hundred kW.

[0018] Based on this rough estimate, it can therefore be assumed that one ring of said annular arrangement preferably comprises approximately 5 to 10 laser diode bar stacks (e.g., 6 laser diode bar stacks), the distance between individual rings is preferably approximately 5 cm - 15 cm (e.g., 8 - 10 cm), and the laser diode bars are preferably arranged approximately 50 mm to 100 mm (e.g., 60 mm - 80 mm) from the surface of the rod (assuming a typical aperture angle of 10° in the slow axis and 50° - 70° in the fast axis).

[0019] Preferably, the rod and the heat transfer means are insulated from the environment by a housing, and the optical radiation from the laser device is transmitted from the outside into the interior of the housing through entrance windows in the housing. The housing can, for example, be formed by an open or closable steel cylinder to form a largely enclosed furnace volume. The housing preferably has a diffusely scattering surface or coating on its inside. As a result, if optical radiation is reflected by the rod or the heat transfer means, this radiation can be diffusely backscattered, so that in particular hotspots cannot form on the inside of the housing (e.g., on the inside of said steel cylinder), and the incident optical radiation can be backscattered into the interior of the housing.The entrance windows can be made, in particular, of a temperature-resistant material (e.g., Duran) that is transparent to the coupled optical radiation. The laser device is preferably located outside the housing, separating the laser device from the heated area and enabling effective cooling.

[0020] The enclosure preferably has a thermal insulation layer on its exterior. The thermal insulation layer serves to prevent heat transfer from the interior of the casing element. The thermal insulation layer can be, for example, a temperature-resistant insulating material. In addition to heat transfer (heat loss) through convection, the enclosure is also intended to prevent indirect radiant heating of the exterior area through the emission of infrared radiation from the interior of the enclosure.

[0021] Preferably, a gap between the thermal insulation layer and the laser device is cooled by means of an air flow. This allows, on the one hand, residual heat dissipated into the air in the gap via the thermal insulation layer to be dissipated and, on the other hand, effective front-side cooling of the laser device to be achieved.

[0022] Preferably, waste heat generated by the laser device is used to preheat the rods. To increase the efficiency of the device, the heat emitted by the laser device should preferably not be released unused into the environment. Instead, the considerable amount of energy, despite the very high conversion efficiency of the individual laser diode bars, should be sensibly reused, preferably in a preheating process for the rods. For example, starting from an equilibrium temperature established in the environment of the laser device with respect to the waste heat dissipated by the laser device as a lower temperature level, an upper temperature level of approximately 150 °C can be achieved using industrial heat pumps known in the art.

[0023] Preferably, the rods are therefore first preheated to a temperature between 120 °C and 180 °C (e.g., approx. 150 °C), intermediately heated to a temperature between 360 °C and 440 °C (e.g., approx. 400 °C) using an intermediate heater, and finally heated to a temperature between 480 °C and 560 °C (e.g., a maximum of approx. 520 °C for aluminum rods) using the laser device. A heat pump heater as described in the above embodiment can be used as preheater. Conventional industrial gas and / or electric furnaces, for example, can be used as intermediate heaters. The rods can first pass through a preheating area along a common heating line before being further heated to the intermediate heating temperature in an intermediate heating area. The actual heating to a required target temperature (e.g.,Forming or process temperature) can then take place in a main heating area provided by the device according to the invention.

[0024] To set a temperature profile, the optical power of the laser device can preferably be regulated depending on the position. This is a particular advantage of the device according to the invention compared to conventional furnaces with a uniform temperature distribution. The direct and positionally precise heating of the rods by means of absorption of optical radiation achieved by the present invention enables the temperature profile along the rod to be specifically influenced. For example, a slightly higher temperature can be set at the beginning of the rod than at the end of the rod, which can be advantageous for some subsequent processes. However, when implementing a specific temperature profile, the heat conduction inside the rods must always be taken into account. In particular, strong temperature gradients can only be generated or maintained to a limited extent.Position-dependent control of the laser device can preferably be achieved by controlling the individual laser diode bar stacks via their own power electronics. A temperature profile can then be implemented via a simple control circuit for controlling the respective power electronics. The control circuit can preferably be implemented via appropriate control electronics or computer-implemented.

[0025] Further preferred embodiments of the invention result from the features mentioned in the respective subclaims.

[0026] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case. Brief description of the drawings

[0027] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. They show: FIG. 1 shows a schematic representation of a first exemplary embodiment of a device according to the invention in an isometric view; FIG. 2 shows a schematic representation of a second exemplary embodiment of a device according to the invention in a side view; FIG. 3 shows a schematic representation of an embodiment of a device according to the invention in a sectional view; and FIG. 4 shows a schematic representation of an embodiment of a heat transfer means according to the invention in various views. Detailed description of the drawings

[0028] Figure 1shows a schematic representation of a first exemplary embodiment of a device 100 according to the invention in an isometric view. The embodiment shown comprises a rod guide 10 for transporting a rod S through the device 100; a laser device 20 for heating the rod S by absorbing optical radiation; and a heat transfer means (not explicitly shown) configured to absorb optical radiation emitted by the laser device 20 and convert it into heat, wherein the heat transfer means is in contact with the rod S for heat transfer.

[0029] The laser device 20 shown comprises a plurality of laser diode bar stacks 22 arranged in a ring around the rod S, preferably with an emission wavelength between 900 nm and 1 µm. In this embodiment, one ring comprises, purely by way of example, exactly 6 laser diode bar stacks 22, wherein the distance between individual rings can be approximately 5 cm to 15 cm, and the laser diode bar stacks 22 should be arranged approximately 50 mm to 100 mm from the surface of the rod S. A total of 15 rings are shown, so that the total length of the heated region in this example is approximately 1 m to 2 m.

[0030] The rod S and the heat transfer means 30 are isolated from the environment by a housing 40, and the optical radiation of the laser device 20 is transmitted from the outside into the interior of the housing 40 through entrance windows (not shown) in the housing 40. To set a temperature profile, the optical power of the laser device 20 can be controlled depending on the position.

[0031] Figure 2 shows a schematic representation of a second exemplary embodiment of a device 100 according to the invention in a side view. The embodiment shown largely corresponds to the one in FIG. 1 The reference numerals and their respective assignment to individual features therefore apply accordingly. In contrast to the FIG. 1At least one additional heater 60 is further arranged in front of the area with the laser device 20. The additional heater 60 can preferably comprise a preheating area with a corresponding preheating area and an intermediate heating area with a corresponding intermediate heating area. The rods S can be initially preheated to a temperature between 120°C and 180°C in the preheating area, intermediately heated to a temperature between 360°C and 440°C in the intermediate heating area, and finally heated by the laser device 20 to a temperature between 480°C and 560°C. Preferably, waste heat generated by the laser device 20 is used to preheat the rods S. A heat pump heater as described above can be used as the preheating area. Conventional industrial gas and / or electric furnaces, for example, can be used as the intermediate heating area.

[0032] Figure 3shows a schematic representation of an embodiment of a device 100 according to the invention in a sectional view. In particular, the illustration shows a cross section through the laser device 20 perpendicular to the axis of the rod S in the region of the laser diode bar stacks 22 arranged in a ring around the rod. The embodiment shown corresponds largely to the Figures 1 and 2 shown device 100 according to the invention.

[0033] The reference symbols and their respective assignment to individual features therefore apply accordingly.

[0034] Additionally, this illustration particularly shows the heat transfer means 30. The heat transfer means 30 is shown here, by way of example, as a heat transfer sleeve surrounding the rod S. According to the invention, the heat transfer sleeve is designed to absorb optical radiation emitted by the laser device 20 and convert it into heat, wherein the heat transfer means 30 is in contact with the rod S for heat transfer (the small gap shown between the rod and the heat transfer means 30 is inserted for illustrative purposes). It can also be seen that the rod S and the heat transfer means 30 are insulated from the environment by a housing 40, and the optical radiation of the laser device 20 is transmitted from the outside into the interior of the housing 40 through entrance windows 42 in the housing 40.The housing 40 also has a thermal insulation layer 44 on its exterior. The space between the thermal insulation layer 44 and the laser device 20 can be cooled by means of an air flow.

[0035] Figure 4shows a schematic representation of an embodiment of a heat transfer means 30 according to the invention in various views. In particular, this is intended to be an exemplary embodiment of a heat transfer sleeve surrounding the rod S as a corresponding heat transfer means 30. The sleeve shown comprises a support area 32 and prong-shaped tension elements 34. By tensioning the tension elements 34 after inserting the rod S into the sleeve, the sleeve can be tightened around the rod S. The necessary contact between the heat transfer means 30 and the rod S for heat transfer is established via the support area 32, which rests firmly against the rod S as a result of the tensioning. List of reference symbols

[0036] 10Rod guide 20Laser device 22Laser diode bar stack 30Means for heat transfer 32Support area 34Tension elements 40Housing 42Entrance window 44Thermal insulation layer 60Additional heating (e.g., comprising a preheater and an intermediate heater) 100Device SS rod

Claims

1. A device (100) for heating continuously cast and extruded round bars and round bolts (S), comprising: a bar guide (10) for transporting a bar (S) through the device (100); a laser device (20) for heating the bar (S) by absorbing optical radiation; and a heat transfer means (30) configured to absorb optical radiation emitted by the laser device (20) and convert it into heat, wherein the heat transfer means (30) is in contact with the bar (S) for heat transfer.

2. Device (100) according to claim 1, wherein the heat transfer means (30) is designed as a heat transfer sleeve or cuff surrounding the rod (S).

3. Device (100) according to claim 1 or 2, wherein the laser device (20) comprises a plurality of laser diode bar stacks (22) arranged in a ring around the rod (S), preferably with an emission wavelength between 900 nm and 1 µm.

4. Device (100) according to claim 3, wherein a ring comprises 5 to 10 laser diode bar stacks (22), the distance between the individual rings is about 5 cm to 15 cm and the laser diode bar stacks are arranged about 50 mm to 100 mm from the surface of the rod (S).

5. Device (100) according to one of the preceding claims, wherein the rod (S) and the means for heat transfer (30) are insulated from the environment by a housing (40) and the optical radiation of the laser device (20) is transmitted through entrance windows (42) in the housing (40) from outside into the interior of the housing (40).

6. Device according to claim 5, wherein the housing (40) has a thermal insulation layer (44) on the outside.

7. The device (100) according to claim 6, wherein a gap between the thermal insulation layer (44) and the laser device (20) is cooled by means of air flow.

8. Device (100) according to one of the preceding claims, wherein waste heat generated by the laser device (20) is used to preheat the rods (S).

9. Device (100) according to one of the preceding claims, wherein the rods (S) are first preheated to a temperature between 120 °C and 180 °C, intermediately heated to a temperature between 360 °C and 440 °C with an intermediate heater and finally heated to a temperature between 480 °C and 560 °C by the laser device (20).

10. Device (100) according to one of the preceding claims, wherein the optical power of the laser device (20) can be regulated in a position-dependent manner in order to set a temperature profile.

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