Forced air cooling for cooling long steel products

Abstract

The present application relates to a heat treatment unit, in particular a cooling hood, comprising a chamber having an inlet opening through which a gaseous cooling medium can be supplied to the chamber and a gap-like outlet opening through which the gaseous cooling medium can be discharged at an increased velocity, the chamber comprising an intermediate chamber segment and first and second outer chamber segments extending from the intermediate chamber segment, both outer chamber segments having a cross-section that tapers proportionally towards their distal ends, and to an apparatus for heat treating hot rolled long steel products.

Description

[Technical Field]

[0001] The present invention relates to a heat treatment unit, in particular a cooling hood, and to an apparatus and method for heat treating hot rolled long steel products. [Background technology]

[0002] In order to adjust the mechanical properties of hot-rolled long steel products, in particular the yield point, tensile strength or hardness, these long steel products are cooled in a targeted manner by a cooling device during and / or after the hot-rolling process. For this purpose, in the prior art, water or a water / air mixture is usually used as a cooling medium, as disclosed, for example, in EP 1 412 543. However, such cooling media cause the so-called Leidenfrost phenomenon, which leads to deviations in the cooling rate over the length of the long steel product and thus to the formation of an inhomogeneous microstructure.

[0003] Further, a method and device for hardening rail heads with air or nitrogen is known from U.S. Pat. No. 4,913,747. In this document, the coolant is supplied via a pipe system to a collector with multiple nozzles. This known embodiment has the disadvantage that the large number of nozzles and holes makes the cooling device complex to design. Summary of the Invention [Problem to be solved by the invention]

[0004] It is therefore an object of the present invention to provide an improved apparatus and method for heat treating hot-rolled long steel products, as compared to the prior art. [Means for solving the problem]

[0005] According to the invention, this problem is solved by a heat treatment unit having the features of claim 1, an apparatus having the features of claim 9 as well as a method having the features of claim 12.

[0006] In a first aspect, the present invention relates to a heat treatment unit, in particular a cooling hood, for use in an apparatus for heat treating long, preferably hot-rolled steel products, comprising a chamber having an inlet opening through which a gaseous cooling medium can be supplied to the chamber, and a gap-like outlet opening through which the gaseous cooling medium can be discharged at an increased velocity, the chamber comprising an intermediate chamber segment and first and second outer chamber segments extending from the intermediate chamber segment, both outer chamber segments having a cross-section that tapers proportionally towards their distal ends.

[0007] The inventive design of the heat treatment unit, in particular the proportional reduction of the flow cross section over the length of each outer chamber segment, allows a uniform flow of a gaseous cooling medium, e.g., air or nitrogen, through the gap-shaped outlet openings over the entire length of the chamber. The use of such a heat treatment unit allows for homogeneous and uniform cooling of hot-rolled long steel products, thereby improving their mechanical properties. Furthermore, the gap-shaped design of the outlet openings results in less maintenance than conventional conical or flat-jet nozzles.

[0008] Further advantageous configurations of the invention are recited in several dependent claims. The features recited individually in these dependent claims can be combined with one another in a technically significant manner to define further configurations of the invention. Furthermore, the features recited in the claims are recited and explained in detail in the description, whereby further preferred configurations of the invention are indicated.

[0009] The term "cross section" within the scope of the present invention means cross-sectional area.

[0010] The term "long steel products" means within the scope of the present invention products made of metal, such as rails, in particular railway rails, H-shaped supports, U-shaped sections, angle sections, etc., which may have a length of up to 200 m.

[0011] Advantageously, the intermediate chamber segment has a constant cross section along the longitudinal axis of the chamber. In this connection, it is specified that an inlet opening is preferably arranged in the intermediate chamber segment. The inlet opening may have a smaller inlet cross section compared to the cross section of the intermediate chamber segment. The larger cross section of the intermediate chamber segment allows the coolant entering the chamber through the inlet opening to first stabilize and then continue flowing in the direction of the gap-shaped outlet opening. Furthermore, the larger inlet cross section compared to the gap-shaped outlet opening ensures that the flow velocity of the coolant remains very low at the inlet of the chamber and high at the outlet. The change in cross section and the resulting change in flow velocity significantly reduce vortices, ensuring that the coolant exits very uniformly over the entire length of the gap-shaped outlet opening. The velocity change factor between the inlet and outlet of the chamber may preferably be between 3 and 20. The flow velocity at the inlet may be, for example, between 10 and 50 m / s. Correspondingly, the flow rate of the cooling medium at the outlet may then be 3 to 20 times that at the inlet, depending on the cross-sectional area ratio selected. It is therefore advantageously specified that the cross-sections located at the distal ends of both outer chamber segments are 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.

[0012] To further increase the uniformity of the flow at the outlet, each chamber segment preferably has a cross-sectional section that tapers conically in the direction of the gap-like outlet opening, which cross-sectional section may be symmetrically or alternatively asymmetrically configured.

[0013] The inlet openings can basically be formed directly in the middle chamber segment in the form of openings. However, in a preferred embodiment, the heat treatment unit comprises an inlet tube piece arranged in the inlet opening, the inlet tube piece being formed from a cup-shaped body and having one opening each aligned with the outer chamber segments. In this connection, it is preferred that each of the two openings has a cross section corresponding to at least half of the inlet cross section. This also prevents the formation of vortices inside the chamber and thus has a favorable effect on the flow characteristics. On the one hand, the bottom of the cup-shaped inlet tube piece ensures that the cooling medium flowing into the middle chamber segment is redirected into both outer chamber segments and thus cannot directly exit again through the gap-shaped outlet openings of the middle chamber segment. On the other hand, the pressure above the gap-shaped outlet openings can be kept constant over the entire length of the chamber.

[0014] In order to obtain the additional flexibility in adjusting the ratio between the inlet and outlet velocities, which can be achieved by adjusting the cross section as already explained, it is advantageously specified that the cross section of the gap-like outlet opening is adjustable. By adjusting the cross section of the gap-like outlet opening, the cooling rate of the hot-rolled long steel product can thus be adjusted in a stepless manner. Preferably, the gap-like outlet opening can be adjusted within a range of 0.5 to 50 mm depending on the required cooling width.

[0015] In a further aspect, the present invention relates to an apparatus for heat treating hot-rolled long steel products, comprising a receiving device for receiving the hot-rolled long steel products and at least one heat treatment unit according to the invention capable of supplying a gaseous cooling medium, in particular air or nitrogen, to the long steel products to be cooled.

[0016] To achieve this, for example, ambient air can be supplied as cooling medium to the heat treatment unit by a suitable blower device. By narrowing the cross section of the gap-like outlet opening, the cooling medium is accelerated through the gap-like outlet opening and acts on the surface of the hot-rolled long steel product to be cooled at a high speed, which can be, for example, 200 m / s. It is therefore advantageously specified that the device further comprises at least one blower device capable of supplying a gaseous cooling medium, for example air or nitrogen, to the heat treatment unit.

[0017] Since the cooling rate at the surface of the hot-rolled long steel product can be determined by the flow rate, the speed-adjustable blower device furthermore allows for stepless adjustment of the cooling rate, which may be, for example, between 1 and 20 K / s.

[0018] Advantageously, the at least one heat treatment unit is arranged in the device such that the gap-shaped outlet opening is positioned longitudinally parallel to the receiving device. In addition, it is further preferred that the distance between the gap-shaped outlet opening and the receiving device is adjustable, and it is particularly preferred that the distance between the outlet opening and the surface of the long steel product to be cooled is adjustable to between 5 and 300 mm.

[0019] In a particularly advantageous embodiment, the device for heat treatment is modularly configured so that one or more heat treatment units can be arranged around a longitudinal segment of the long steel product and / or one or more heat treatment units can be arranged along several longitudinal segments or the entire length of the long steel product.

[0020] The cooling intensity in each cooling module can be individually adapted based on the detected temperature of the long steel product. This allows different temperature distributions over the length of the long steel product to be compensated for by targeted cooling. Therefore, in order to carry out the corresponding temperature adjustment, the device preferably comprises at least one temperature sensor capable of detecting the temperature of the long steel product, preferably during the heat treatment. This temperature sensor is preferably a pyrometer or a thermal imaging camera. It is also advantageous to use other temperature sensors known to those skilled in the art at the time of filing.

[0021] A further advantage of the modular design is its usability: By using multiple heat treatment units, workpieces of different geometries can be cooled. Individual adaptation to a given shape and required cooling power is possible by changing and modifying the number of heat treatment units or cooling hoods.

[0022] Additionally, electromagnetic sensors can be used to detect and monitor structural transformations in the long steel products directly during the cooling process. Based on the determined structure, the cooling rate can be adapted accordingly.

[0023] Furthermore, depending on the embodiment of the thermal treatment unit, in particular the cooling hood, or the device, - the cooling rate can be reliably and stably adjusted, providing flexibility for adapting the cooling rate required for the heat treatment process to any conventional and special material composition; The use of ambient air as a cooling medium is particularly resource-saving compared to currently used liquid cooling media, such as water, oil and / or water / air mixtures; By using a blower device, e.g. a ventilator, a large air volume can be conveyed at a low pressure, preferably down to 1320 mbar, thereby eliminating the need for a compressor. Further advantages can be obtained.

[0024] In a further aspect, the present invention further relates to a method for heat treating a hot rolled long steel product, wherein the long steel product is fed directly into an apparatus according to the present invention following the hot rolling step for heat treatment. A gaseous cooling medium, in particular air or nitrogen, may be sprayed onto the hot rolled long steel product at a speed of at least 25 m / s, preferably at least 50 m / s, more preferably at least 100 m / s, even more preferably at least 125 m / s and most preferably at least 150 m / s, depending on the desired cooling intensity.

[0025] Furthermore, the invention relates to the use of a heat treatment unit according to the invention or an apparatus according to the invention for producing pearlitic, ferritic, bainitic and / or martensitic microstructural structures in hot rolled long steel products.

[0026] The present invention and related technologies will be described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the illustrated embodiments. Unless otherwise specified, partial aspects of the actual embodiments illustrated in the drawings may be extracted and combined with other elements and findings based on this specification and / or the drawings. It should be noted that the drawings, particularly the size ratios shown, are merely schematic. Since the same reference numerals are used for the same objects, a supplementary explanation based on other drawings may be used in some cases. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a perspective view of an embodiment of a thermal processing unit according to the present invention; [Figure 2] 2 is a side view of the embodiment of the thermal processing unit shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the heat-treating unit shown in FIGS. 1 and 2. [Figure 4] FIG. 12 is a perspective view of an embodiment of an inlet fitting. [Figure 5] 1 shows an embodiment of an apparatus according to the invention for heat treating long steel products; [Figure 6]FIG. 1 illustrates an embodiment of a reconciliation process. [Figure 7] 1 is a photograph of a rail head without heat treatment including the determined hardness values. [Figure 8] 1 is a photograph of a rail head with heat treatment according to the invention, including the determined hardness values. [Figure 9] FIG. 1 shows the results of cooling with a water / air mixture. [Figure 10] FIG. 1 illustrates the results of cooling by a process according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] 1 to 4 show an embodiment of a heat treatment unit 1 according to the present invention. The heat treatment unit 1 is suitable for and is provided for an apparatus 2 for heat treating hot-rolled long steel products (see FIG. 5), for example rails 3.

[0029] The heat treatment unit 1, in particular the cooling hood, comprises a longitudinally extending chamber 4 with an inlet opening 5 through which a gaseous cooling medium, for example, in particular ambient air, can be supplied, and a gap-like outlet opening 6 extending longitudinally over the entire length of the chamber 4, through which the gaseous cooling medium can be discharged at an increased speed. The ambient air can preferably be drawn in via a blower device (not shown), for example a ventilator, and supplied to the cooling hood 1 via a corresponding piping system (not shown). The distance between the cooling hood 1 and the blower device should be chosen as short as possible.

[0030] 1 and 2, cooling hood 1 is formed by a middle chamber segment 7 having an inlet opening 5 and first and second outer chamber segments 8, 9. The first and second outer chamber segments 8, 9 extend from middle chamber segment 7 and are connected to middle chamber segment 7 via flange connections 10, 11, respectively.

[0031] The middle chamber segment 7 is configured to have a uniformly sized cross-section along the longitudinal axis of the chamber 4. In this embodiment, this cross-section is clearly indicated by the reference numeral 12 in the cross-sectional view shown in FIG. 3. In contrast, both outer chamber segments 8, 9 have cross-sections that taper proportionally toward their distal ends. This results in a cross-section 13 at the distal end of each of the outer chamber segments 8, 9 that has a smaller value in the range of 2 to 6 times. In this case, it becomes clear that each chamber segment 7, 8, 9 has, in addition to the rectangular cross-section section 14, a cross-section section 15 that tapers conically toward the gap-like outlet opening 6.

[0032] Furthermore, the cooling hood 1 comprises, in the illustrated embodiment, an inlet stub 16 arranged in the inlet opening 5. In this embodiment, the inlet stub 16 is formed from a cup-shaped body 17 with a bottom 18 and a cylindrical wall 19. An inlet stub opening 20 in the body 17 forms the inlet for the gaseous cooling medium. To enable the gaseous cooling medium to flow through the entire chamber 4, the cylindrical wall 19 is provided with at least two openings 21 aligned with the outer chamber segments 8, 9, respectively. Each of these openings 21 has a cross-section that essentially corresponds to half the cross-section of the inlet stub opening 20.

[0033] The configuration according to the invention ensures that the cooling medium, despite its central supply into the cooling hood 1, always has a constant air pressure at the outlet 6 over the entire length of the chamber or cooling hood, thereby ensuring a constant outflow velocity over the cooling length.

[0034] 5 shows an embodiment of an apparatus 2 according to the invention for the heat treatment of long steel products 3. The apparatus 2 comprises a receiving device 22 for receiving the hot-rolled long steel products 3 and, in this embodiment, three heat treatment units 1, via which a gaseous cooling medium can be supplied to the long steel products 3 to be cooled, and thus the long steel products 3 to be cooled can be cooled in a targeted manner.

[0035] The device 2 further comprises a conveying device 23 and a lifting platform 24, by means of which a long steel product, shown in the form of a rail 3, can be raised and fed to the receiving device 22. The receiving device 22 comprises a clamping device 25 capable of clamping the rail 3. The clamping device 25 may be configured such that the rail 3 can be moved longitudinally within the device 2 by means of roller table rollers 26.

[0036] In an alternative embodiment, the rail 3 may be fixedly fixed to the platform and the cooling system may be moved back and forth longitudinally across the rail 3 during cooling.

[0037] 6 shows an embodiment of the conditioning process for the heat treatment of long steel products or rails 3. Each of the three cooling hoods 1 is assigned one temperature sensor 27 in the form of a pyrometer, which is positioned so that it can measure the temperature of the rail head surfaces TOP, SIDE-LEFT, SIDE-RIGHT during the cooling process. ist ,T_SIDE-LEFT ist ,T_SIDE-RIGHT ist is transmitted to the calculation unit 28 as a signal to calculate the target temperature (T soll ) If one of the sensed temperatures is higher than the target temperature, the cooling output can be individually adapted by increasing the speed of the corresponding ventilator 29, thereby minimizing the temperature difference. [Example]

[0038] Example 1: Figure 7 shows hardness measurements on a cross section of a rail head that was not subjected to heat treatment, while Figure 8 shows a rail that was heat treated by the method according to the invention. As can be seen from the values, the hardness at the rail head is increased by an average of up to 22% by the cooling process according to the invention.

[0039] Example 2: In order to produce the desired microstructure, hot-rolled rails, each having a temperature of 900°C, were cooled. On the one hand, the rails were cooled using a water / air mixture (comparison example; Figure 9) according to a method known from the prior art, and on the other hand, the rails were cooled using pure ambient air (Figure 10) according to the method according to the invention. The cooling parameters remained constant during each cooling process. After the heat treatment, the Brinell hardness of the rails was determined at defined points in the cross section of the rail head in accordance with DIN 13674.

[0040] As can be seen from the results shown in Figure 9, the hardness of each rail varies greatly. In contrast, the hardness of the rail cooled by the method according to the present invention is very stable (Figure 10). [Explanation of symbols]

[0041] 1 Heat Treatment Unit / Cooling Hood 2 equipment 3 Long steel products / rails 4 chambers 5 Entrance opening 6 Gap outlet opening / gap 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 Transverse section at the distal end of the outer chamber segment 14 Cross section division 15 Cross section division 16 Inflow pipe piece 17 Main Unit 18 Bottom 19 Cylindrical Wall 20 Inflow pipe piece opening 21 Aperture 22 Receiving device 23 Conveyor equipment 24 Lift platform 25 Clamping device 26 Roller table roller 27 Temperature Sensor / Pyrometer 28 computing units 29 Blower / Ventilator

Claims

1. 1. A thermal treatment unit (1), in particular a cooling hood, comprising a longitudinally extending chamber (4) having an inlet opening (5) through which a gaseous cooling medium can be supplied to the chamber (4), and an interstitial outlet opening (6) extending longitudinally over the entire length of the chamber (4) through which the gaseous cooling medium can be discharged at an increased velocity, the chamber (4) comprising an intermediate chamber segment (7) and first and second outer chamber segments (8, 9) extending from the intermediate chamber segment (7), both outer chamber segments (8, 9) having a cross section that tapers proportionally towards their distal ends.

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

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

4. 2. The thermal treatment unit (1) according to claim 1, wherein the cross section (13) of each of the outer chamber segments (8, 9) located at the distal end is at least three times, preferably four times, smaller than the cross section (12) of the intermediate chamber segment (7).

5. 2. The thermal treatment unit (1) according to claim 1, wherein each of the chamber segments (7, 8, 9) has a cross-sectional section (15) tapering in the direction of the gap-like outlet opening (6).

6. 2. The heat treatment unit (1) according to claim 1, further comprising an inlet pipe piece (16) arranged in the inlet opening (5), the inlet pipe piece (16) being formed from a cup-shaped body (17) and having one opening (21) each aligned with the outer chamber segments (8, 9).

7. 7. A heat treatment unit (1) according to claim 6, wherein both openings (21) each have a cross section corresponding to at least half of the inlet cross section.

8. 2. The heat treatment unit (1) according to claim 1, wherein the cross section of the gap-like outlet opening (6) is adjustable.

9. 1. An apparatus (2) for heat treating a hot-rolled long steel product (3), comprising a receiving device (22) for receiving the hot-rolled long steel product (3) and at least one heat treatment unit (1) according to claim 1, capable of supplying a gaseous cooling medium, in particular air, to the long steel product (3) to be cooled.

10. The apparatus (2) according to claim 9, further comprising at least one temperature sensor (27) capable of sensing the temperature of the long steel product (3) during heat treatment.

11. The device (2) of claim 10, wherein the temperature sensor (27) is a pyrometer.

12. 10. A method for heat treating a hot rolled long steel product (3), wherein the long steel product (3) is fed directly to an apparatus (2) according to claim 9 following the hot rolling step for heat treatment.

13. 13. The method according to claim 12, wherein the gaseous cooling medium, in particular air, is blown onto the hot-rolled long steel product (3) at a speed of at least 25 m / s, preferably at least 50 m / s, more preferably at least 100 m / s, even more preferably at least 125 m / s, most preferably at least 150 m / s.

14. 14. A method according to claim 12 or 13, wherein the long steel products (3) are H-shaped supports, U-shaped members, angle members and / or rails.

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