Device for cooling strip-shaped workpieces

Abstract

A device for cooling strip-shaped workpieces is equipped with a cooling element made of a thermally conductive material. The workpiece to be cooled is continuously guided along this element. Cooling is achieved via a cooling channel thermally connected to the cooling element, through which a cryogenic cooling medium flows. To ensure uniform heat transfer, the cooling medium is supercooled before being fed into the cooling channel. This supercooling is accomplished by thermal contact with a partial flow of the same cooling medium, but at a lower pressure. This subcooled medium evaporates upon thermal contact with the cooling medium flowing into the cooling channel. The evaporated cooling medium is then used to inert the cooling element.

Description

[0001] The invention relates to a device for cooling strip-shaped workpieces, comprising a cooling element made of a thermally conductive material, which cooling element has a cooling surface along which a strip-shaped workpiece can be guided and brought into thermal contact with it, and a cooling channel thermally connected to the cooling element, which is flow-connected to a supply line connected to a source of a liquefied gas for supplying liquefied gas into the cooling channel and to an outlet line for removing the supplied liquefied gas from the cooling channel.

[0002] During production, metallic workpieces are frequently subjected to heat treatment to adjust specific material properties. Such heat treatment is regularly followed by a cooling process, which can either be part of the heat treatment itself or serve to make the workpiece available for subsequent processing as quickly as possible. For example, steel must be hardened for certain applications. In such a hardening process, the steel is first heated to austenitizing temperature and quenched, and then further cooled to adjust the retained austenite content.Cooling processes may also be necessary following various processing operations on metallic workpieces, in order to avoid deformation of the workpieces or increased tool wear, such as in continuous casting, welding, cutting, deep drawing and others.

[0003] Especially in the case of continuously manufactured workpieces, such as extruded material, metal strips, wires, profiles, pipes or the like, cooling devices are used for the aforementioned purposes, which are continuously passed through by the workpiece to be cooled during the treatment.

[0004] Cooling devices are already known in the art in which strip-shaped workpieces, such as blade strips, are continuously guided through a working area and cooled with water or a water / oil emulsion. However, these devices have the disadvantage that oxide layers and scale can form on the surface of the cooled workpieces due to cooling with water or a water / oil emulsion, requiring subsequent, costly cleaning.

[0005] It is also known to spray strip-shaped workpieces with a cooling medium in the form of a cryogenically liquefied gas, such as nitrogen, argon, or carbon dioxide, or in the form of carbon dioxide snow, after heat treatment in order to cool them to a desired temperature. Cooling methods of this kind are described, for example, in US 2018 031 29 38 A and DE 10 2011 109 534 A1. A disadvantage of these methods, however, is the relatively high consumption of the cooling medium used.

[0006] From EP 3 497 250 A1, a cooling device, a hardening device, and a method for cooling continuous elements, in particular blade strips, are known, in which the cooling of the strip-shaped workpiece is carried out indirectly. For this purpose, the workpiece is guided along a thermally conductive metal plate, which is thermally connected to a cooling channel through which a cooling medium in the form of a liquefied gas, in particular liquid nitrogen, is guided. The liquefied gas evaporates completely in the cooling channel. A portion of the evaporated gas is drawn off via a gas line arranged at the outlet of the cooling channel and used to inertize the material surface or the surface of the metal plate that comes into contact with the material during the treatment.However, a disadvantage is that the evaporation of the cooling medium in the cooling channel can lead to strong pressure fluctuations and thus also to fluctuations in heat transfer and gas flow, which can also impair the subsequent inerting process and cause a generally quite high consumption of liquefied refrigeration gas.

[0007] The object of the present invention is therefore to provide a cooling device for cooling strip-shaped workpieces, in particular following heat treatment, which operates efficiently and in which a uniform heat transfer from the workpiece to the cooling medium is ensured during the treatment.

[0008] This problem is solved by a device having the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0009] According to the invention, a device of the type and purpose mentioned above is characterized in that the device is equipped with a device for subcooling the liquefied gas before its supply to the cooling channel, which has a heat exchanger surface arranged in the supply line and through which the liquefied gas flows during use of the device, which is housed within a container equipped with a supply line for a liquid cooling medium, in the upper region of which a gas outlet line opens for gas which evaporates in the container upon thermal contact with the liquefied gas guided through the heat exchanger surface, which gas outlet line is flow-connected to a nozzle arrangement directed towards the cooling surface of the cooling element.

[0010] According to the invention, the subcooling device comprises a heat exchanger surface arranged in the supply line, upstream of the cooling channel and downstream of the source of the liquefied gas, which is housed within a container. During operation, the heat exchanger surface is wholly or partially surrounded by a bath of liquid cooling medium, which is at a lower temperature than the liquefied gas within the heat exchanger surface. The cooling medium enters the container via the supply line, which preferably opens into a lower region of the container. Upon thermal contact with the cooling medium, the liquefied gas flowing through the heat exchanger surface is subcooled, i.e., brought to a temperature lower than its boiling point at the pressure at which it exists within the heat exchanger surface.Upon thermal contact, the cooling medium evaporates from the surrounding bath and is discharged via the gas exhaust line. The gas exhaust line is connected to a nozzle arrangement directed towards the cooling surface of the cooling element. This arrangement serves to blow at least a portion of the cooling medium evaporated in the container onto the cooling surface of the cooling element and / or onto the workpiece moving along the cooling surface. This inertizes and simultaneously cools the cooling surface and / or the surface of the workpiece; the inerting effect is therefore unaffected, or only minimally affected, by possible fluctuations in the gas flow through the cooling channel.

[0011] The cooling element of the device according to the invention is, for example, a thermally conductive metal plate that has a flat surface (cooling surface) on one side, for example, on a horizontally arranged, upward-facing side, for contact with one or more strip-shaped workpieces. For cooling, the strip-shaped workpiece(s) are continuously guided along the cooling surface and thereby brought into contact with it. The cooling of the workpiece(s) occurs indirectly by passing the liquefied gas, which has been previously supercooled by thermal contact with the cooling medium in the container bath, through the cooling channel thermally connected to the cooling element. During the cooling process at the cooling element, the liquefied gas warms up. However, since it is in a supercooled state, it remains completely or at least partially liquid despite the heat absorption.Therefore, pressure fluctuations due to the evaporating gas do not occur, or only to a negligible extent. This results in a uniform heat transfer, which allows for precise metering of the liquefied refrigeration gas used for cooling.

[0012] The cooling channel is, for example, a pipe that is milled into the cooling element or is otherwise thermally connected to the cooling element, for example embedded in a highly thermally conductive material that is itself thermally well connected to the cooling element.

[0013] Preferably, a liquefied gas is used as the cooling medium in the subcooling device, which is taken from the same source as the liquefied gas used for cooling in the cooling channel.

[0014] For this purpose, the supply line to the container is connected to this source of the liquefied gas, and a throttle valve (pressure reducer) is installed in the supply line. This valve reduces the pressure of the liquefied gas flowing through the supply line, while the pressure in the container still remains above ambient pressure (1 bar). Due to the pressure reduction at the throttle valve, the liquefied gas is at a lower temperature downstream of the throttle valve, and thus also in the bath of the container, than upstream, i.e., within the source, and also lower than in the supply line.

[0015] The source of the liquefied gas is preferably a tank in which the liquefied gas is stored at a pressure significantly higher than ambient pressure, for example, between 2 bar and 20 bar. The partial flow of liquefied gas supplied to the tank can thus be significantly expanded and cooled at the throttling valve.

[0016] To minimize heat loss, the cooling element is advantageously equipped with an enclosure made of a thermally insulating material, with a space remaining between the enclosure and the cooling surface, within which the nozzle assembly connected to the gas exhaust line opens. The gas exhaust line leading from the container of the subcooling device is preferably routed through an outlet wall of the enclosure – viewed in the direction of workpiece transport. The nozzle assembly, connected to the gas exhaust flow, is located within the enclosure and applies the gas vaporized in the container towards the cooling surface or the workpieces. The nozzle assembly is a design comprising one or more nozzle openings directed towards the workpiece or workpieces.The workpieces are oriented within the enclosure, and / or the cooling surface extends over at least part of the enclosure. The enclosure promotes the formation of a largely homogeneous, inert gas atmosphere above the cooling surface. The gas preferably exits the enclosure via a gas outlet located in the area of ​​an inlet wall of the enclosure; thus, the gas is guided through the enclosure in counterflow to the workpieces.

[0017] The cooling channel is preferably equipped with means for improving heat transfer, which enable particularly good heat absorption by maximizing the usable surface area for heat transfer. For example, in a cooling channel designed as a pipe, these means can be equipped with fins or other features that increase the surface area of ​​the pipe. Alternatively or additionally, the cooling channel can also be designed as a curved flow path that extends in a meandering fashion along or within the cooling element, and / or the cooling channel can divide in the area of ​​the cooling element into a plurality of parallel sub-channels, each of which is thermally connected to or passes through the cooling element.

[0018] Any liquefied gas with a positive Joule-Thomson coefficient can be used as the cryogenic gas, such as nitrogen, oxygen, argon, or a hydrocarbon suitable for the specific cooling task. Liquid nitrogen is preferred, which is stored in the tank at a pressure of, for example, 2 to 20 bar. For the subcooling according to the invention, a partial flow can be extracted from this, the pressure of which is reduced to a value of, for example, between 1 and 3 bar using a suitable throttling valve.

[0019] The device according to the invention is particularly suitable for cooling during the production of blade strips, especially those made of hardened steels, such as those used in the production of razor blades.

[0020] An embodiment of the invention will be explained in more detail with reference to the drawing. The only drawing ( Fig. 1Figure 1 schematically shows a cooling device according to the invention in a longitudinal section.

[0021] The in Figure 1The illustrated embodiment of a device 1 according to the invention comprises a cooling element 2, for example a metal plate made of brass or another thermally efficient material, the upward-facing side surface of which, referred to here as the cooling surface 3, serves to cool a strip-shaped workpiece 4, for example a blade strip. For this purpose, the workpiece 4, which has previously undergone heat treatment for hardening, for example in an oven (not shown here), is continuously drawn over the cooling surface 3 by means of a transport device 5 in the direction indicated by arrows 6 and 7. The cooling surface 3 can be equipped with a coating or the like (not shown here) that promotes both the lowest possible frictional feed of the workpiece 4 and the best possible heat transfer from the workpiece 4 to the cooling element 2.

[0022] In the lower part of the cooling element 2, a cooling channel 8 is traversed in the embodiment shown here. As an alternative to the example shown here of a cooling channel 8 milled through the cooling element 2, the cooling channel can also be routed along a side surface of the cooling element 2, for example, the lower side surface 9, and be thermally connected to the cooling element 2 via a suitable heat exchanger surface (not shown here). Also not shown here are further means for improving heat transfer between the cooling element 2 and the cooling channel 8, such as fins or a meandering course of the cooling channel 8. Furthermore, the device 1 has an enclosure 11 made of a thermally insulating material above the cooling surface 3.The enclosure 11 is arranged at a distance from the cooling surface 3, forming a space 12, and is closed both on the top and on the front sides 13, 14 in order to promote the formation of an inert gas atmosphere as described below, with the exception, in particular, of the openings 15, 16 for the workpiece 4. Furthermore, it is advantageous, although not shown here for the sake of clarity, that the cooling element 2 is equipped with thermally insulating walls on its sides facing away from the cooling surface 3.

[0023] The cooling channel 8 is connected at its inlet side via a supply line 17 to a source of a liquefied refrigeration gas, in the embodiment shown here a tank 18. The tank 18 is pressure-resistant and equipped with thermally insulating walls.

[0024] In the supply line 17, a device 20 is arranged for subcooling the liquefied gas supplied via the supply line 17 to the cooling channel 8.

[0025] The device 20 comprises a container 21 through which the supply line 17 with a heat exchanger surface 22, for example a cooling coil, passes without a flow connection to the container 21. A supply line 23 opens into a lower section of the container 21 and is flow-connected to the supply line 17 and thus to the tank 18. A throttle valve 24 for pressure reduction is arranged in the supply line 23. A gas exhaust line 25 opens into an upper section of the container 21. The gas exhaust line 25 passes through the front 13 of the housing 11 and terminates within the space 12 at a nozzle assembly 27 equipped with one or more gas nozzles 26.

[0026] During operation of the device 1, the workpiece 4 is guided along the cooling surface 3 by means of the transport device 5. To cool the cooling element 2 and thus the cooling surface 3, a liquefied gas, for example liquid nitrogen, at a pressure of, for example, between 2 bar and 10 bar, is taken from the tank 18 and fed to the cooling channel 8 via the supply line 17.

[0027] In the subcooler 20, the liquefied gas is supercooled, i.e., brought to a temperature below its boiling point. For this purpose, a partial flow of the liquefied gas taken from tank 18 is routed through the supply line 23, where it expands at the throttle valve 24 and is fed to the container 21 at a pressure of, for example, 1.1 bar. In the container 21, it forms a liquid bath 28 into which the heat exchanger surface 22 is completely immersed. Due to the lower pressure, the temperature of the bath 28 is lower than the temperature of the liquefied gas supplied to the supply line 17 via the heat exchanger surface 22. As a result, heat is extracted from the liquefied gas in the supply line 17, while simultaneously liquefied gas from the bath 28 evaporates.The vaporized gas is discharged via the gas exhaust line 25 and blown into the spacer chamber 12 at the nozzle assembly 27, where it forms an inert atmosphere consisting largely of cold gaseous nitrogen, which also contributes to cooling the workpiece 4. If required, a partial flow of the vaporized gas can also be discharged via a branch line 29 and used for another purpose.

[0028] The supercooled liquefied gas in the supply line 17 comes into thermal contact with the cooling element 2 in the cooling channel 8, and thus indirectly also with the workpiece 4. This cools the workpiece, while the liquefied gas in the cooling channel 8 heats up. Due to the supercooling of the liquefied gas, it does not evaporate, or only partially evaporates, in the cooling channel 8. The heated liquefied gas is discharged via an outlet line 30 and can be used for other purposes, for example, to create an inert gas atmosphere in a furnace (not shown) in which the workpiece 4 was heat-treated before being transported to the device 1, or to quench the workpiece 4 after passing through such a furnace.

[0029] The cooling capacity of the device 1 can be controlled by regulating the flow of liquefied refrigerant to the cooling channel 8. For this purpose, a control valve 31 is provided in the supply line 17, which is in data communication with a control unit 32. The control unit 32 determines a control parameter, for example, the temperature inside the housing 11 measured by a probe 33, and automatically controls the control valve 31 according to a predefined program. In the event of a high demand for liquefied refrigerant, the pressure in the tank 18 can also be adjusted as needed by a pressure build-up device 34, which is equipped in particular with an air evaporator 35. Reference symbol list

[0030] 1 device 19 - 2 Cooling element 20 Hypothermia device 3 Cooling surface 21 container 4 workpiece 22 Heat exchanger surface 5 Transport equipment 23 supply line 6 Arrow 24 Throttle valve 7 Arrow 25 Gas exhaust pipe 8 Cooling channel 26 Gas jet 9 side surface 27 Nozzle arrangement 10 - 28 bath 11 Enclosure 29 Branch Management 12 Clearance space 30 Exit line 13 Front 31 Control valve 14 Front 32 control unit 15 Passage opening 33 Measuring probe 16 Passage opening 34 Pressure build-up arrangement 17 Supply line 35 Air evaporator 18 tank

Claims

1. Device for cooling strip-shaped workpieces, comprising a cooling element (2) made of highly thermally conductive material, said cooling element (2) having a cooling surface (3) along which a strip-shaped workpiece (4) can be led and with which the strip-shaped workpiece can be brought into thermal contact, and comprising a cooling channel (8) which is thermally connected to the cooling element (2) and is fluidically connected to a feed line (17), said feed line being connected to a source (18) of a cryogenically liquefied gas and being provided for feeding cryogenically liquefied gas into the cooling channel (8), and is fluidically connected to a discharge line (30) for discharging the fed cryogenically liquefied gas from the cooling channel (8), characterized in that the device is equipped with an apparatus (20) for subcooling the cryogenically liquefied gas before it is supplied to the cooling channel (8), said apparatus comprising a heat exchange surface (22) which is arranged in the feed line (17) and through which the cryogenically liquefied gas flows during use of the device and which is accommodated within a vessel (21) equipped with a supply line (23) for a liquid cooling medium, from the upper region of which vessel a gas withdrawal line (25) which is fluidically connected to a nozzle arrangement (27) directed at the cooling surface (3) of the cooling element (2) leads out.

2. Device according to Claim 1, characterized in that the supply line (23) of the vessel (21) of the apparatus (20) for subcooling is fluidically connected to the source (18) of the cryogenically liquefied gas and is equipped with a throttle valve (24) for reducing the pressure.

3. Device according to Claim 1 or 2, characterized in that the employed source (18) of the cryogenically liquefied gas is a tank in which the cryogenically liquefied gas is stored at a pressure of between 2 bar and 20 bar.

4. Device according to one of the preceding claims, characterized in that the cooling element (2) is equipped with a housing (11) made of a thermally insulating material, such that a distance space (12) is formed, and the nozzle arrangement (27) connected to the gas withdrawal line (25) discharges within the distance space (12).

5. Device according to Claim 4, characterized in that the gas withdrawal line (25) is led through a wall (13) of the housing (11) which - seen in the transport direction of the workpiece (4) - is on the exit side.

6. Device according to one of the preceding claims, that the cooling channel (8) is equipped with means for improving heat transfer, such as cooling ribs and / or a winding course of the cooling channel.

7. Device according to one of the preceding claims, characterized in that the cryogenically liquefied gas used is liquid nitrogen.

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