DE102021212523A1 - Forced air cooling for cooling long steel products - Google Patents

Abstract

The present application relates to a heat treatment unit, in particular a cooling hood, comprising a chamber with an inlet opening, through which a gaseous cooling medium can be supplied to the chamber, and a slot-shaped outlet opening, through which the gaseous cooling medium can be discharged in an accelerated manner, the chamber having a central chamber segment and a first and second outer chamber segment extending from the middle chamber segment and both outer chamber segments having a proportionally tapering cross section towards their distal ends, and an apparatus for heat treating hot rolled long steel products.

Description

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.

In order to set the mechanical properties, such as in particular the yield point, the tensile strength or the hardness, of hot-rolled long steel products, these are cooled in a targeted manner by means of cooling devices during and/or after a hot-rolling process. For this purpose, water or a water-air mixture is used as a cooling medium in the prior art as a rule, as is the case, for example, in EP 1 412 543 B1 is revealed. However, such cooling media lead to the development of the so-called Leidenfrost phenomenon, which leads to deviations in the cooling rate over the entire length of the long steel product and thus to the formation of inhomogeneous microstructures.

From the U.S. 4,913,747 a method and a device for hardening a rail head by means of air or nitrogen is also known. Here, the coolant is fed via a line system to a collector that includes a large number of nozzles. A disadvantage of this embodiment variant is the complex construction of the cooling apparatus with the many nozzles and bores.

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

Description of the invention

According to the invention, the object is achieved by a heat treatment unit having the features of patent claim 1, by a device having the features of patent claim 9 and by a method having the features of patent claim 12.

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 chamber with an inlet opening, via which a gaseous cooling medium can be fed to the chamber, and a gap-shaped outlet opening, via which the gaseous cooling medium can be carried out in an accelerated manner, the chamber comprising a middle chamber segment and a first and second outer chamber segment extending from the middle chamber segment and both outer chamber segments having a cross section which tapers proportionally towards their distal ends.

The construction of the heat treatment unit according to the invention, in particular the proportional reduction of the flow cross section over the length of the respective outer chamber segment, enables a uniform flow of the gaseous cooling medium, such as air or nitrogen, at the gap-shaped outlet opening over the entire length of the chamber. By using such heat treatment units, the hot-rolled long steel products can be cooled homogeneously and evenly, so that their mechanical properties are improved. Due to the fact that the outlet opening is designed in the form of a slit, the maintenance effort is also lower in contrast to conventional conical or flat jet nozzles.

Further advantageous refinements of the invention are specified in the dependently formulated claims. The features listed individually in the dependent claims can be combined with one another in a technologically meaningful manner and can define further refinements of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred configurations of the invention being presented.

In the context of the present invention, the term “cross section” means a cross-sectional area.

In the context of the present invention, the term “long steel product” is understood to mean 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.

The middle chamber segment advantageously has a constant cross-section along a longitudinal axis of the chamber, it being preferably provided in this connection that the inlet opening is arranged in the middle chamber segment. The inlet opening can have an inlet cross section that is smaller than the cross section of the middle 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 first calm down before it flows further in the direction of the gap-shaped outlet opening. Through the compared to the slit-shaped outlet opening With a larger inlet cross-section, the flow rate of the cooling medium is kept very low at the inlet of the chamber and high at the outlet. The turbulence is significantly reduced as a result of the change in cross section and the associated change in flow speed, so that it can be ensured that the cooling medium flows out very evenly over the entire length of the slot-shaped outlet opening. The speed 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 rate of the cooling medium at the outlet can then be 3 to 20 times this, depending on the selected cross-sectional ratios. It is therefore advantageously provided that the cross sections arranged at the distal ends of the two outer chamber segments are smaller by a factor of at least 3, preferably at least a factor of 4, even more preferably at least a factor of 10 compared to the cross section of the central chamber segment.

In order to further increase the uniformity of the flow at the outlet, each of the chamber segments advantageously has a cross-sectional section which tapers conically in the direction of the slot-shaped outlet opening and which can be embodied symmetrically or alternatively also asymmetrically.

In principle, the inlet opening can be formed directly in the middle chamber segment in the form of an opening. In a preferred embodiment variant, however, it is provided that the heat treatment unit comprises an inlet connection which is arranged in the inlet opening and is formed from a cup-shaped body and has an opening in each case aligned with the outer chamber segments. In this context, it is preferably provided that each of the two openings has a cross section that corresponds at least to half the inlet cross section. This also prevents the formation of turbulence within the chamber and thus has an advantageous effect on the flow properties. The bottom of the cup-shaped inlet connector ensures that the cooling medium flowing into the middle chamber segment is deflected into the two outer chamber segments and thus cannot exit directly via the gap-shaped outlet opening of the middle chamber segment. On the other hand, the pressure above the gap-shaped outlet opening can be kept constant over the entire length of the chamber.

In order to obtain further flexibility in setting the ratio between entry and exit speeds, which can be achieved, as already explained, by setting the cross sections, it is advantageously provided that the cross section of the slot-shaped exit opening is designed to be adjustable. Thus, the cooling rate for the hot-rolled long steel product can be continuously controlled by adjusting the cross section of the slit-shaped outlet. The gap-shaped outlet opening can preferably be set in the range from 0.5 to 50 mm, depending on the required cooling width.

In a further 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 subjected to a gaseous cooling medium, in particular air or nitrogen.

In order to achieve this, for example, ambient air can be supplied to the heat treatment unit as a cooling medium by means of a suitable blower device. Due to the narrowing of the cross section at the gap-shaped outlet opening, the cooling medium is accelerated through the latter in such a way that the cooling medium 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 provided that the device also comprises at least one fan device, via which a gaseous cooling medium, such as air or nitrogen, can be supplied to the heat treatment unit.

Since the cooling rate on the surface of the hot-rolled long steel product can be determined by the flow rate, a speed-controlled blower device also enables the cooling rate to be steplessly adjusted, which can be 1 to 20 K/s, for example.

The at least one heat treatment unit is advantageously arranged in the device in such a way that the slit-shaped outlet opening is positioned longitudinally parallel to the receiving device. In addition, it is preferably provided that the distance between the gap-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.

In a particularly advantageous embodiment, the device for heat treatment is modular, so that one or more Heat treatment unit(s) can be arranged around a length segment of the long steel product and/or one or more heat treatment unit(s) can be arranged along several length segments or along the entire length of the long steel product.

The cooling intensity in each of the cooling modules can be adjusted individually based on the detected temperature of the long steel product. In this way, different temperature profiles over the entire length of the long steel product can be compensated for by targeted cooling. In order to carry out appropriate temperature regulation, the device therefore advantageously comprises at least one temperature sensor, via which the temperature of the long steel product can be detected, preferably during heat treatment. The temperature sensor is preferably a pyrometer or a thermal imaging camera. Other temperature sensors known to a person skilled in the art at the time of the application can also be used advantageously.

Another advantage of the modular design is its usability. Different workpiece geometries can be cooled by using a plurality of heat treatment units. An individual adaptation to the shape and the required cooling capacity is possible by changing the number and redesigning the heat treatment unit or the cooling hood.

In addition, structural changes in the long steel product can be detected and monitored directly in the cooling process using electromagnetic sensors. The cooling rate can be adjusted accordingly based on the determined microstructure.

• - die Kühlrate ist zuverlässig und stabil einstellbar und bietet die Flexibilität, die notwendigen Kühlraten für den Wärmebehandlungsprozess für alle gängigen und auch besonderen Werkstoffzusammensetzungen, flexibel anzupassen;
• - die Verwendung von Umgebungsluft als Kühlmedium ist besonders ressourcenschonend im Vergleich zu den derzeit verwendeten flüssigen Kühlmedien, wie Wasser, Öl und/oder Wasser-Luft-Gemischen;
• - durch den Einsatz einer Gebläseeinrichtung, wie eines Ventilators, kann viel Luftvolumen mit einem geringen Druck, bevorzugt bis 1320 mbar, transportiert werden, so dass kein Kompressor erforderlich ist.

Depending on the design variant of the heat treatment unit, in particular the cooling hood, or the device, there are also other advantages:

• - the cooling rate can be adjusted reliably and stably and offers the flexibility to flexibly 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-saving compared to the liquid cooling media currently used, 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.

In a further aspect, the present invention also relates to a method for the heat treatment of a hot-rolled long steel product, with this product being fed directly to a device according to the invention and heat-treated following a hot-rolling process. Depending on the desired cooling intensity, the gaseous cooling medium, in particular air or nitrogen, can flow 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 blown onto the hot rolled long steel product at a speed of at least 125 m/s, and most preferably at a speed of at least 150 m/s.

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

character list

• 1 eine Ausführungsvariante der erfindungsgemäßen Wärmebehandlungseinheit in einer perspektivischen Darstellung,
• 2 die in 1 gezeigte Ausführungsvariante der Wärmebehandlungseinheit in einer seitlichen Darstellung,
• 3 eine Schnittdarstellung durch die in den vorhergehenden Figuren dargestellte Wärmebehandlungseinheit,
• 4 eine Ausführungsvariante des Einlassstutzens in einer perspektivischen Darstellung,
• 5 eine Ausführungsvariante der erfindungsgemäßen Vorrichtung zur Wärmebehandlung von Langstahlerzeugnissen,
• 6 eine Ausführungsvariante eines Regelprozesses,
• 7 eine Aufnahme eines Schienenkopfs nebst ermittelten Härtewerten ohne Wärmebehandlung,
• 8 eine Aufnahme eines Schienenkopfs nebst ermittelten Härtewerten mit einer erfindungsgemäßen Wärmebehandlung,
• 9 Ergebnisse einer Kühlung mittels eines Wasser-Luft-Gemisches, und
• 10 Ergebnisse einer Kühlung gemäß dem erfindungsgemäßen Prozess.

The invention and the technical environment are explained in more detail below with reference to the figures. It should be pointed out that the invention should not be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description and/or figures. In particular, it should be pointed out that the figures and in particular the proportions shown are only schematic. The same reference symbols designate the same objects, so that explanations from other figures can be used as a supplement if necessary. Show it:

• 1 a variant of the heat treatment unit according to the invention in a perspective view,
• 2 in the 1 shown variant of the heat treatment unit in a side view,
• 3 a sectional view through the heat treatment unit shown in the previous figures,
• 4 a variant of the inlet connector in a perspective view,
• 5 an embodiment variant of the device according to the invention for the heat treatment of long steel products,
• 6 an embodiment variant of a control process,
• 7 a photograph of a rail head together with determined hardness values without heat treatment,
• 8th a photograph of a rail head together with determined hardness values with a heat treatment according to the invention,
• 9 Results of cooling using a water-air mixture, and
• 10 Results of cooling according to the process of the invention.

In the 1 until 4 an embodiment variant of the heat treatment unit 1 according to the invention is shown, which is used for a device 2 for the heat treatment of hot-rolled long steel products (see 5 ), Such as rails 3, is suitable and provided.

The heat treatment unit 1, in particular a cooling hood, comprises a longitudinally extending chamber 4 with an inlet opening 5, via which a gaseous cooling medium, such as in particular ambient air, can be supplied to the chamber 4, as well as a slot-shaped outlet opening 6 extending longitudinally over the entire length of the chamber 4, over which the gaseous cooling medium can be executed in an accelerated manner. The ambient air can preferably be sucked in via a blower device (not shown), such as a fan, and fed to the cooling hood 1 via a corresponding line system (not shown). Here, the distance between the cooling hood 1 and the fan device should be as short as possible.

As shown in the 1 and 2 As 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 .

The middle chamber segment 7 is designed in such a way that it has a cross section of the same size along the longitudinal axis of the chamber 4, which is given the reference number 12 in FIG 3 shown sectional view is illustrated. In contrast to this, the two outer chamber segments 8, 9 have a cross section that tapers proportionally towards their distal ends, which at each of the distal ends of the outer chamber segments 8, 9 has a value in the range of 2 to 6 times smaller in the cross section 13 results. It can be seen here that each of the chamber segments 7 , 8 , 9 , in addition to a quadrangular cross-sectional section 14 , also has a cross-sectional section 15 that tapers conically in the direction of the slot-shaped outlet opening 6 .

Furthermore, the cooling hood 1 in the embodiment variant shown here comprises an inlet connection 16 arranged in the inlet opening 5. In the present case, this is formed from a cup-shaped body 17 which comprises a bottom 18 and a cylindrical wall 19 and whose inlet connection opening 20 is the inlet for the gaseous forms cooling medium. So that the gaseous cooling medium can flow through the entire chamber 4, at least two openings 21 are provided in the cylindrical wall 19, which are each aligned with the outer chamber segments 8, 9. Each of the two openings 21 predominantly has a cross section which corresponds to half the cross section of the inlet connector opening 20 .

The construction according to the invention ensures that the cooling medium, despite being fed into the cooling hood 1 in the middle, always has the same air pressure at the outlet 6 over the entire length of the chamber or cooling hood, so that a constant outflow speed can be ensured over the cooling length.

In 5 shows an embodiment variant of the device 2 according to the invention for the heat treatment of long steel products 3, which comprises a receiving device 22 for receiving the hot-rolled long steel product 3 and, in the present case, three heat treatment units 1, via which the long steel product 3 to be cooled can be subjected to the gaseous cooling medium and thus cooled in a targeted manner.

The device 1 also includes 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 raised and fed to the receiving device 22. The receiving device 22 includes a clamping device 25 by means of which the rail 3 can be clamped. The clamping device 25 can be designed in such a way that the rail 3 can be moved longitudinally in the device 2 by means of roller table rollers 26 .

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

In 6 an embodiment variant of a control process for the heat treatment of a long steel product or a rail 3 is shown. Each of the three cooling hoods 1 is one Temperature sensor 27, which is in the form of a pyrometer, is assigned and positioned in such a way that the temperatures can be measured from the rail head sides TOP, SIDE-LEFT and SIDE-RIGHT during the cooling process. The recorded temperatures T_TOP _actual , T_SIDE-LEFT _actual and T_SIDE-RIGHT actual _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 greater than the target temperature, the cooling capacity can be individually adjusted by increasing the speed of a corresponding fan 29 so that the temperature difference is minimized.

examples

Example 1:

In the 7 shows hardness measurements in the cross-sectional area of a rail head which has not been subjected to heat treatment. In 8th 1 shows a rail that has been heat treated according to the method of the invention. As can be seen from the values, the hardnesses in the rail head are on average up to 22% higher as a result of the cooling process according to the invention.

Example 2:

In each case, several hot-rolled rails were cooled at a temperature of 900 °C in order to set the desired microstructure. On the one hand, the rails were made using a method known from the prior art using a water-air mixture (comparative example; 9 ) and on the other hand by means of the method according to the invention using pure ambient air ( 10 ) chilled. The cooling parameters were unchanged in each cooling procedure. After the heat treatment, the Brinell hardness of the rails was determined in accordance with DIN13674 at the defined points in the cross-section of the rail head.

As shown by the results in 9 As can be seen, the hardness varies greatly from bar to bar. In contrast, the hardnesses of the rails that have been cooled using the method according to the invention are very stable ( 10 ).

Reference List

1

Heat treatment unit / cooling hood

2

contraption

3

Long steel product / rail

4

chamber

5

entry opening

6

slit-shaped outlet opening / slit nozzle / outlet

7

middle chamber segment

8th

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 section

15

cross section

16

inlet port

17

Body

18

floor

19

cylindrical wall

20

Inlet port opening

21

opening

22

recording device

23

transport device

24

lifting table

25

clamping device

26

roller table rollers

27

Temperature sensor / pyrometer

28

computing unit

29

Blower device / fan

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 1412543 B1 [0002]
• US4913747 [0003]

Claims (16)

Heat treatment unit (1), in particular a cooling hood, comprising a chamber (4) with an inlet opening (5) through which a gaseous cooling medium can be fed to the chamber (4) and a slot-shaped outlet opening (6) through which the gaseous cooling medium can be discharged in an accelerated manner wherein the chamber (4) comprises a middle chamber segment (7) and first and second outer chamber segments (8, 9) extending from the middle chamber segment (7), and both outer chamber segments (8, 9) have a distal Ends have proportionally tapered cross-section. Heat treatment unit (1) after claim 1 , wherein the central chamber segment (7) along a longitudinal axis of the chamber (4) has a constant cross section. Heat treatment unit after claim 1 or 2 , wherein the inlet opening (5) is arranged in the middle chamber segment (7). Heat treatment unit (1) according to 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 at least a factor of 3 compared to the cross-section (12) of the middle chamber segment (7), is preferably smaller by a factor of 4. Heat treatment unit (1) according to one of the preceding claims, wherein each of the chamber segments (7, 8, 9) has a cross-sectional section (15) tapering conically in the direction of the gap-shaped outlet opening (6). Heat treatment unit (1) according to one of the preceding claims, further comprising an inlet connection (16) which is arranged in the inlet opening (5) and is formed from a cup-shaped body (17) and has an opening ( 21). Heat treatment unit (1) after claim 6 , wherein each of the two openings (21) has a cross section which corresponds at least to half the inlet cross section. Heat treatment unit (1) according to one of the preceding claims, in which the cross section of the slot-shaped outlet opening (6) is designed to be adjustable. Device (2) for the heat treatment of hot-rolled long steel products (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 one of the preceding ones Claims 1 until 8th , via which the long steel product (3) to be cooled can be acted upon with a gaseous cooling medium, in particular air. Device (2) after claim 9 , further comprising at least one temperature sensor (27) via which the temperature of the long steel product (3), preferably during a heat treatment, can be detected. Device (2) after claim 10 , wherein the temperature sensor (27) is a pyrometer. A method for the heat treatment of a hot-rolled long steel product (3), the long steel product (3) following a hot-rolling operation being fed directly to a device (2) according to one of the preceding ones claims 9 until 11 supplied and heat treated. procedure after claim 12 , wherein the gaseous cooling medium, in particular air, 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, onto the hot-rolled long steel product (3). procedure after claim 12 or 13 , wherein the long steel product (3) is an H-beam, a U-profile, an angle and/or a rail. Use of a heat treatment unit (1) according to one of Claims 1 until 8th or a device (2) according to one of claims 9 until 11 to form a pearlitic, a ferritic, a bainitic and/or a martensitic microstructure in a hot-rolled long steel product (3). use after claim 15 , wherein the microstructure is formed to a depth of 50 mm, preferably to a depth of 45 mm, more preferably to a depth of 40 mm, even more preferably to a depth of 35 mm.

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