Forced air cooling for cooling long steel products

Abstract

The present invention relates to a heat treatment unit, in particular a cooling cowl, comprising a chamber with an inlet opening through which a gaseous cooling medium can be fed to the chamber and a slit-shaped outlet opening through which the gaseous cooling medium can be discharged faster, wherein the chamber comprises a central chamber segment and a first and a second outer chamber segment extending from the central chamber segment and both outer chamber segments have a cross-section tapering proportionally towards the distal ends of said chamber segments, and a device for heat treatment of hot-rolled long steel products.

Description

[0001] The present invention relates to a heat treatment unit, in particular a cooling hood, a device and a method for the heat treatment of hot-rolled long steel products.

[0002] To adjust the mechanical properties, such as yield strength, tensile strength, or hardness, of hot-rolled long steel products, these are selectively cooled during and / or after a hot-rolling process using cooling devices. In the prior art, water or a water-air mixture is generally used as the cooling medium, as disclosed, for example, in EP 1 412 543 B1. However, such cooling media lead to the formation of the so-called Leidenfrost phenomenon, which results in variations in the cooling rate along the entire length of the long steel product and thus in the formation of inhomogeneous microstructures.

[0003] US Patent 4,913,747 discloses a method and apparatus for hardening a rail head using air or nitrogen. In this method, the coolant is supplied via a piping system to a manifold comprising a multitude of nozzles. A disadvantage of this design is the complex construction of the cooling apparatus with its numerous nozzles and bores.

[0004] The object of the present invention is therefore to provide an improved device and a method for the heat treatment of hot-rolled long steel products compared to the prior art.

[0005] EP-A 2 535 431 discloses a cooling hood comprising a chamber with lateral chamber segments, wherein both chamber segments have a cross-section that tapers towards their distal ends, or is proportional to their diameter ( Fig. 1 ), wherein the cooling hood comprises several slot-like nozzles ( Figs. 2-4 ).

[0006] WO-A 2007 014 406 relates to a device for cooling a metal strip with at least two nozzle arrays arranged longitudinally. Description of the invention

[0007] According to the invention, the problem is solved by a heat treatment unit with the features of claim 1, by a device with the features of claim 9 and by a method with the features of claim 12.

[0008] In a first aspect, the present invention relates to a heat treatment unit, in particular a cooling hood, preferably for use in a device for the heat treatment of hot-rolled long steel products, comprising a longitudinally extending chamber with an inlet opening through which a gaseous cooling medium can be supplied to the chamber, and a slit-shaped outlet opening extending over the entire length of the chamber through which the gaseous cooling medium can be accelerated out, wherein the chamber comprises a central chamber segment as well as a first and second outer chamber segment extending from the central chamber segment, and both outer chamber segments have a cross-section that tapers proportionally towards their distal ends.

[0009] The inventive design of the heat treatment unit, in particular the proportional reduction of the flow cross-section along the length of the respective outer chamber segment, enables a uniform flow of the gaseous cooling medium, such as air or nitrogen, at the slit-shaped outlet opening along the entire length of the chamber. By using such heat treatment units, hot-rolled long steel products can be cooled homogeneously and uniformly, thus improving their mechanical properties. Furthermore, the slit-shaped outlet opening reduces maintenance requirements compared to conventional conical or flat jet nozzles.

[0010] Further advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined in a technologically meaningful manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are specified and explained in more detail in the description, which also presents further preferred embodiments of the invention.

[0011] For the purposes of the present invention, the term "cross-section" is understood to mean a cross-sectional area.

[0012] For the purposes of the present invention, the term "long steel product" means a metallic product which can have a length of up to 200 m, such as rails, in particular railway rails, H-shaped beams, U-shaped profiles, angles, etc.

[0013] The central chamber segment advantageously has a cross-section that is constant along a longitudinal axis of the chamber, and in this context, it is preferably provided that the inlet opening is arranged in the central chamber segment. The inlet opening can have a smaller cross-sectional area than the central chamber segment. Due to the larger cross-section in the central chamber segment, the cooling medium flowing into the chamber through the inlet opening can initially settle before flowing further towards the slit-shaped outlet opening. Furthermore, the larger inlet cross-section compared to the slit-shaped outlet opening keeps the flow velocity of the cooling medium very low at the chamber inlet and high at the outlet.The change in cross-sectional area and the associated change in flow velocity significantly reduce turbulence, ensuring that the cooling medium flows out very uniformly along the entire length of the slit-shaped outlet opening. The velocity change factor between the inlet and outlet of the chamber can preferably be 3 to 20. For example, the flow velocity at the inlet can be 10 to 50 m / s. Correspondingly, the flow velocity of the cooling medium at the outlet can then be 3 to 20 times this, depending on the selected cross-sectional ratios. Advantageously, the cross-sections arranged at the distal ends of the two outer chamber segments are therefore at least 3 times, preferably at least 4 times, and even more preferably at least 10 times smaller than the cross-section of the middle chamber segment.

[0014] To further increase the uniformity of the flow at the outlet, each of the chamber segments advantageously has a cross-sectional section that tapers conically towards the slit-shaped outlet opening, which can be symmetrical or alternatively asymmetrical.

[0015] The inlet opening can, in principle, be formed directly in the central chamber segment as an opening. However, in a preferred embodiment, the heat treatment unit comprises an inlet nozzle arranged in the inlet opening. This nozzle is formed from a cup-shaped body and has an opening facing each of the outer chamber segments. In this context, it is preferred that each of the two openings has a cross-section that is at least half the cross-section of the inlet. This also prevents the formation of turbulence within the chamber and thus has a beneficial effect on the flow characteristics.The base of the cup-shaped inlet nozzle ensures, firstly, that the cooling medium flowing into the middle chamber segment is deflected into the two outer chamber segments and thus cannot exit directly through the slit-shaped outlet opening of the middle chamber segment. Secondly, the pressure above the slit-shaped outlet opening can be kept constant along the entire length of the chamber.

[0016] To achieve greater flexibility in adjusting the ratio between inlet and outlet velocity, which, as previously explained, can be accomplished by adjusting the cross-sections, it is advantageously provided that the cross-section of the slit-shaped outlet opening is adjustable. This allows the cooling rate for the hot-rolled long steel product to be continuously controlled by adjusting the cross-section of the slit-shaped outlet opening. Preferably, the slit-shaped outlet opening can be adjusted in the range of 0.5 to 50 mm, depending on the required cooling width.

[0017] In another aspect, the present invention relates to a device for the heat treatment of hot-rolled long steel products, comprising a receiving device for receiving the hot-rolled long steel product and at least one heat treatment unit according to the invention, via which the long steel product to be cooled can be supplied with a gaseous cooling medium, in particular air or nitrogen.

[0018] To achieve this, ambient air can be supplied to the heat treatment unit as a cooling medium by means of a suitable blower. The narrowing of the cross-section at the slit-shaped outlet accelerates the cooling medium to such an extent that it impacts the surface of the hot-rolled long steel product to be cooled at a high velocity, which can be, for example, 200 m / s. Advantageously, the device is therefore provided to also include at least one blower through which a gaseous cooling medium, such as air or nitrogen, can be supplied to the heat treatment unit.

[0019] Since the cooling rate on the surface of the hot-rolled long steel product can be determined by the flow velocity, a speed-controlled blower device also allows stepless adjustment of the cooling rate, which can be, for example, 1 to 20 K / s.

[0020] The at least one heat treatment unit is advantageously arranged in the device such that the slit-shaped outlet opening is positioned longitudinally parallel to the receiving device. Furthermore, it is preferably provided that the distance between the slit-shaped outlet opening and the receiving device is adjustable, particularly preferably such that the distance between the outlet opening and the surface of the long steel product to be cooled is 5 to 300 mm.

[0021] In a particularly advantageous embodiment, the heat treatment device is modularly designed, so that one or more heat treatment units can be arranged around a length segment of the long steel product and / or one or more heat treatment units can be arranged along several length segments or along the entire length of the long steel product.

[0022] The cooling intensity in each of the cooling modules can be individually adjusted based on the detected temperature of the long steel product. This allows for the compensation of different temperature profiles along the entire length of the long steel product through targeted cooling. To achieve appropriate temperature control, the device advantageously includes at least one temperature sensor with which the temperature of the long steel product can be detected, preferably during heat treatment. Preferably, the temperature sensor is a pyrometer or a thermal imaging camera. Other temperature sensors known to those skilled in the art at the time of filing can also advantageously be used.

[0023] Another advantage of the modular design is its versatility. By using multiple heat treatment units, different workpiece geometries can be cooled. Individual adaptation to the shape and required cooling capacity is possible by changing the number and redesigning the heat treatment unit or the cooling hood.

[0024] Additionally, electromagnetic sensors can be used to detect and monitor microstructural transformations in the long steel product directly during the cooling process. The cooling rate can then be adjusted accordingly based on the determined microstructures.

[0025] Depending on the design variant of the heat treatment unit, in particular the cooling hood, or the device, the following additional advantages arise: The cooling rate is reliably and stably adjustable and offers the flexibility to adapt the necessary cooling rates for the heat treatment process for all common and also special material compositions; the use of ambient air as a cooling medium is particularly resource-efficient compared to the currently used liquid cooling media, such as water, oil and / or water-air mixtures; by using a blower device, such as a fan, a large volume of air can be transported at a low pressure, preferably up to 1320 mbar, so that no compressor is required.

[0026] In a further aspect, the present invention relates to a method for the heat treatment of a hot-rolled long steel product, wherein, following a hot-rolling process, the product is directly fed into a device according to the invention and heat-treated. Depending on the desired cooling intensity, the gaseous cooling medium, in particular air or nitrogen, can be blown onto the hot-rolled long steel product at a speed of at least 25 m / s, preferably at a speed of at least 50 m / s, more preferably at a speed of at least 100 m / s, even more preferably at a speed of at least 125 m / s, and most preferably at a speed of at least 150 m / s.

[0027] Furthermore, the present invention relates to the use of the heat treatment unit or the device according to the invention for the formation of a pearlitic, a ferritic, a bainitic and / or a martensitic microstructure in a hot-rolled long steel product. Character description

[0028] The invention and its technical context are explained in more detail below with reference to the figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations explained in the figures and combine them with other components and findings from the present description and / or figures. It should be noted in particular that the figures, and especially the depicted proportions, are only schematic. The same reference numerals denote the same objects, so that explanations from other figures can be consulted as needed. The figures show: Fig. 1 shows an embodiment of the heat treatment unit according to the invention in a perspective view, Fig. 2 shows the in Fig. 1Figure 1 shows a side view of the embodiment of the heat treatment unit, Figure 3 shows a sectional view through the heat treatment unit shown in the preceding figures, Figure 4 shows a perspective view of the inlet nozzle, Figure 5 shows an embodiment of the device according to the invention for the heat treatment of long steel products, Figure 6 shows an embodiment of a control process, Figure 7 shows a photograph of a rail head with determined hardness values ​​without heat treatment, Figure 8 shows a photograph of a rail head with determined hardness values ​​with a heat treatment according to the invention, Figure 9 shows results of cooling using a water-air mixture, and Figure 10 shows results of cooling according to the process according to the invention.

[0029] In the Figures 1 to 4An embodiment of the heat treatment unit 1 according to the invention is shown, which is suitable for a device 2 for the heat treatment of hot-rolled long steel products (see Figure 5 ), such as rail 3, is suitable and intended.

[0030] The heat treatment unit 1, in particular a cooling hood, comprises a longitudinally extending chamber 4 with an inlet opening 5 through which a gaseous cooling medium, such as ambient air, can be supplied to the chamber 4, and a slit-shaped outlet opening 6 extending along the entire length of the chamber 4 through which the gaseous cooling medium can be accelerated out. The ambient air can preferably be drawn in by a blower (not shown), such as a fan, and supplied to the cooling hood 1 via a suitable duct system (not shown). The distance between the cooling hood 1 and the blower should be as short as possible.

[0031] As shown in the presentation in the Figure 1 and 2As can be seen, the cooling hood 1 is formed by a middle chamber segment 7, which includes the inlet opening 5, and a first and a second outer chamber segment 8, 9, which each extend from the middle chamber segment 7 and are connected to it via flange connections 10, 11.

[0032] The middle chamber segment 7 is designed such that it has a cross-section of the same size along the longitudinal axis of the chamber 4, which in this case is designated by the reference numeral 12 in the Figure 3This is illustrated in the sectional view shown. In contrast, the two outer chamber segments 8, 9 have a cross-section that tapers proportionally towards their distal ends, resulting in a cross-sectional area 13 that is 2 to 6 times smaller at each distal end of the outer chamber segments 8, 9. It becomes apparent that each of the chamber segments 7, 8, 9 has, in addition to a quadrilateral cross-sectional section 14, a cross-sectional section 15 that tapers conically towards the slit-shaped outlet opening 6.

[0033] Furthermore, in the embodiment shown here, the cooling hood 1 includes an inlet nozzle 16 arranged in the inlet opening 5. This nozzle is formed from a cup-shaped body 17 comprising a base 18 and a cylindrical wall 19, with the inlet nozzle opening 20 serving as the inlet for the gaseous cooling medium. To allow the gaseous cooling medium to flow through the entire chamber 4, at least two openings 21 are provided in the cylindrical wall 19, each oriented towards the outer chamber segments 8 and 9. Each of the two openings 21 has a cross-section that is predominantly half the cross-section of the inlet nozzle opening 20.

[0034] The design according to the invention ensures that the cooling medium, despite being fed centrally into the cooling hood 1, has a constant air pressure at the outlet 6 over the entire chamber length or cooling hood length, so that a constant outflow velocity over the cooling length can be ensured.

[0035] In Figure 5 An embodiment of the device 2 according to the invention for the heat treatment of long steel products 3 is shown, comprising a receiving device 22 for receiving the hot-rolled long steel product 3 and, in this case, three heat treatment units 1, via which the long steel product 3 to be cooled can be supplied with the gaseous cooling medium and thus cooled in a targeted manner.

[0036] The device 1 further comprises a transport device 23 and a lifting table 24, via which the long steel product, shown in the form of a rail 3, can be lifted and fed to the receiving device 22. The receiving device 22 comprises a clamping device 25 by means of which the rail 3 can be clamped. The clamping device 25 can be designed such that the rail 3 is longitudinally movable in the device 2 by means of roller conveyor rollers 26.

[0037] In an alternative design variant, the rail 3 can be fixed stationary on a table and the cooling system can be moved longitudinally back and forth over the rail 3 during cooling.

[0038] In Figure 6Figure 3 shows a variant of a control process for the heat treatment of a long steel product or rail 3. Each of the three cooling hoods 1 is equipped with a temperature sensor 27, designed as a pyrometer, and positioned so that the temperatures of the rail end faces TOP, SIDE-LEFT, and SIDE-RIGHT can be measured during the cooling process. The recorded temperatures T_TOP, T_SIDE-LEFT, and T_SIDE-RIGHT are transmitted to a computer unit 28 and compared with a target temperature (T_target) of a technological model. If one of the detected temperatures is higher than the target temperature, the cooling capacity can be individually adjusted by increasing the speed of a corresponding fan 29, thus minimizing the temperature difference. Examples Example 1:

[0039] In the Figure 7The figures show hardness measurements on the cross-sectional area of ​​a rail head that has not undergone any heat treatment. Figure 8 Figure 1 shows a rail that has been heat-treated according to the inventive method. As can be seen from the values, the hardness in the rail head is on average up to 22% higher due to the cooling process according to the invention. Example 2:

[0040] Several hot-rolled rails were cooled to a temperature of 900 °C to achieve the desired microstructure. The rails were cooled using a prior art method employing a water-air mixture (comparative example; Fig. 9 ) and secondly, by means of the inventive method using pure ambient air ( Fig. 10The rails were cooled. The cooling parameters remained unchanged in every cooling process. After heat treatment, the Brinell hardness of the rails was determined at defined points in the cross-section of the rail head according to DIN 13674.

[0041] As shown by the results in Figure 9 As can be seen, the hardness varies greatly from rail to rail. In contrast, the hardness of the rails cooled using the inventive method is very stable ( Fig. 10 ). Reference symbol list

[0042] 1 Heat treatment unit / Cooling hood 2 Device 3 Long steel product / Rail 4 Chamber 5 Inlet opening 6 Slit-shaped outlet opening / Slit nozzle / Outlet 7 Middle chamber segment 8 First outer chamber segment 9 Second outer chamber segment 10 Flange connection 11 Flange connection 12 Cross-section of middle chamber segment 13 Cross-section at the distal ends of the outer chamber segments 14 Cross-sectional section 15 Cross-sectional section 16 Inlet nozzle 17 Body 18 Bottom 19 Cylindrical wall 20 Inlet nozzle opening 21 Opening 22 Receiving device 23 Transport device 24 Lifting table 25 Clamping device 26 Roller conveyor rollers 27 Temperature sensor / Pyrometer 28 Computer unit 29 Blower device / Fan

Claims

1. Thermal treatment unit (1), particularly cooling hood, comprising a longitudinally extending chamber (4) with an inlet opening (5) by way of which a gaseous cooling medium can be fed to the chamber (4), and a slot-shaped outlet opening (6) which extends longitudinally over the entire length of the chamber (4) and by way of which the gaseous cooling medium can be let out under acceleration, wherein the chamber (4) has a middle chamber segment (7) as well as a first and second outer chamber segment (8, 9) extending from the middle chamber segment (7) and the two outer chamber segments (8, 9) have a cross-section proportionally tapering towards the distal ends thereof.

2. Thermal treatment unit (1) according to claim 1, wherein the middle chamber segment (7) has a constant cross-section along a longitudinal axis of the chamber (4).

3. Thermal treatment unit according to claim 1 or 2, wherein the inlet opening (5) is arranged in the middle chamber segment (7).

4. Thermal treatment unit (1) according to any one of the preceding claims, wherein each of the cross-sections (13) arranged at the distal ends of the outer chamber segments (8, 9) is smaller by comparison with the cross-section (12) of the middle chamber segment (7) at least by the factor 3, preferably by the factor 4.

5. Thermal treatment unit (1) according to any one of the preceding claims, wherein each of the chamber segments (7, 8, 9) has a cross-sectional section (15) conically tapering in the direction of the slot-shaped outlet opening (6).

6. Thermal treatment unit (1) according to any one of the preceding claims, further comprising an inlet stub pipe (16) which is arranged in the inlet opening (5) and formed from a cup-shaped body (17) and which has a respective opening (21) oriented towards each of the outer chamber segments (8, 9).

7. Thermal treatment unit (1) according to claim 6, wherein each of the two openings (21) has a cross-section corresponding with at least half the inlet cross-section.

8. Thermal treatment unit (1) according to any one of the preceding claims, wherein the cross-section of the slot-shaped outlet opening (6) is configured to be adjustable.

9. Device (2) for thermal treatment of hot-rolled elongate steel products (3), comprising a receiving device (22) for reception of the hot-rolled elongate steel product (3) and at least one thermal treatment unit (1) according to any one of the preceding claims 1 to 8, by way of which the elongate steel product (3), which is to be cooled, can be acted on by a gaseous cooling medium, especially air.

10. Device (2) according to claim 9, further comprising at least one temperature sensor (27), by way of which the temperature of the elongate steel product (3) is detectable, preferably during thermal treatment.

11. Device (2) according to claim 10, wherein the temperature sensor (27) is a pyrometer.

12. Method for thermal treatment of a hot-rolled elongate steel product (3), wherein the elongate steel product (3) subsequently to a hot-rolling process is fed directly to a device (2) according to any one of the preceding claims 9 to 11 and thermally treated.

13. Method according to claim 12, wherein the gaseous cooling medium, especially air, is blown onto the hot-rolled elongate steel product (3) at a speed of at least 25 m / s, preferably at a speed of at least 50 m / s, more preferably at a speed of at least 100 m / s, still more preferably at a speed of at least 125 m / s and most preferably at a speed of at least 150 m / s.

14. Method according to claim 12 or 13, wherein the elongate steel product (3) is an H-beam, a U-section, an angle steel and / or a rail.

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