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, with a cooling element made of a thermally highly conductive material, which cooling element has a cooling surface along which a strip-shaped workpiece can be guided and brought into thermal contact with this, and a cooling channel which is thermally connected to the cooling element and which is fluidly connected to a supply line connected to a source of a cold-liquefied gas for supplying cold-liquefied gas into the cooling channel and to an outlet line for discharging the supplied cold-liquefied gas from the cooling channel.

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

[0003] In particular, in the case of continuously produced workpieces, such as continuous material, metal strips, wires, profiles, pipes or the like, cooling devices are used for the purposes mentioned, through which the workpiece to be cooled continuously passes during the treatment.

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

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

[0006] EP 3 497 250 A1 discloses a cooling device, a hardening device, and a method for cooling continuous elements, in particular blade strips, in which the strip-shaped workpiece is cooled indirectly. For this purpose, the workpiece is guided along a thermally highly conductive metal plate that is thermally connected to a cooling channel through which a cooling medium in the form of a liquefied gas, in particular liquid nitrogen, is passed. The liquefied gas evaporates completely in the cooling channel. A portion of the evaporated gas is withdrawn via a gas line arranged at the outlet side 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 treatment.A disadvantage, however, is that the evaporation of the cooling medium in the cooling channel can lead to strong pressure fluctuations and thus also to fluctuations in the heat transfer and the flow of the gas, which can also impair the subsequent inerting process and cause an overall quite high consumption of cold-liquefied gas.

[0007] The object of the present invention is therefore to provide a cooling device for cooling strip-shaped workpieces, in particular following a 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 object is achieved by a device having the features of patent claim 1. Advantageous embodiments are specified in the subclaims.

[0009] A device of the type and purpose mentioned at the outset is therefore characterized according to the invention in that the device is equipped with a device for subcooling the cold-liquefied gas before it is fed to the cooling channel, which device has a heat exchanger surface arranged in the feed line and through which the cold-liquefied gas flows when the device is in use, which heat exchanger surface is accommodated within a container equipped with a feed line for a liquid cooling medium, in the upper region of which a gas outlet line for gas opens out, which evaporates in the container upon thermal contact with the cold-liquefied gas fed through the heat exchanger surface, which gas outlet line is fluidly connected to a nozzle arrangement directed towards the cooling surface of the cooling element.

[0010] According to the invention, the subcooling device therefore has a heat exchanger surface arranged in the supply line, upstream of the cooling channel and downstream of the source for the cold-liquefied gas, which heat exchanger surface is accommodated within a container in such a way that, when the device is in use, the heat exchanger surface is completely or partially bathed in a bath of a liquid cooling medium which is at a lower temperature than the cold-liquefied gas in 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 cold-liquefied gas flowing through the heat exchanger surface is subcooled, i.e. brought to a temperature which is lower than its boiling point at the pressure at which it is present in 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 fluidly connected to a nozzle arrangement directed toward the cooling surface of the cooling element. This nozzle 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 running along the cooling surface. This inertizes the cooling surface and / or the surface of the workpiece and simultaneously cools it; the inerting process is thus unaffected or only slightly 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 highly conductive metal plate which 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 or workpieces are continuously guided along the cooling surface and brought into contact with it. The cooling of the workpiece or workpieces takes place indirectly by passing the cold-liquefied gas, which has previously been subcooled by thermal contact with the cooling medium in the bath of the container, through the cooling channel thermally connected to the cooling element. During the cooling process on the cooling element, the cold-liquefied gas heats up. However, since it is in a subcooled state, it remains completely or at least partially in the liquid state despite the heat absorption.Pressure fluctuations due to the evaporating gas are therefore negligible, or nonexistent. This ensures a uniform heat transfer, allowing for precise metering of the liquefied 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 material that conducts heat well and is in turn thermally well connected to the cooling element.

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

[0014] For this purpose, the supply line for the container is fluidly connected to this source of the cold-liquefied gas, and a throttle valve (pressure reducer) is installed in the supply line, which reduces the pressure of the cold-liquefied gas flowing through the supply line, while still maintaining the pressure in the container at a value above ambient pressure (1 bar). Due to the expansion occurring at the throttle valve, the cold-liquefied gas is at a lower temperature downstream of the throttle valve, and thus also in the container bath, than upstream of it, i.e., within the source, and also lower than in the supply line.

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

[0016] In order to minimize heat loss, the cooling element is advantageously equipped with a housing made of a thermally insulating material, wherein a space remains between the housing and the cooling surface, into which the nozzle arrangement connected to the gas extraction line opens. The gas extraction line leading from the container of the subcooling device is preferably led through a wall of the housing that is on the outlet side, as seen in the transport direction of the workpieces. Arranged within the housing is the nozzle arrangement, which is fluidly connected to the gas outlet and by means of which the gas evaporated in the container is applied towards the cooling surface or the workpieces. The nozzle arrangement is a construction that has one or more nozzle openings that point towards the workpiece or workpieces.directed toward the workpieces, and / or extending within the enclosure over at least part of the cooling surface. 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 vent located near an inlet wall of the enclosure, thus flowing through the enclosure in countercurrent to the workpieces.

[0017] The cooling channel is preferably equipped with means for improving heat transfer, which enable particularly good heat absorption by providing the largest possible surface area available for heat transfer. For example, in a cooling channel designed as a pipe, the means can be equipped with fins or other means 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 manner on or within the cooling element, and / or the cooling channel can be divided in the region of the cooling element into a plurality of sub-channels arranged parallel to one another, each of which is thermally connected to the cooling element or passes through it.

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

[0019] The device according to the invention is particularly suitable for cooling during the production of blade strips, in particular 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. 1) shows schematically a cooling device according to the invention in a longitudinal section.

[0021] The Figure 1The embodiment of a device 1 according to the invention shown has a cooling element 2, for example a metal plate made of brass or another thermally stable material, the upwardly facing side surface of which, here called 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 a heat treatment for hardening, for example in a furnace not shown here, is continuously pulled over the cooling surface 3 in the direction indicated by the arrows 6, 7 by means of a transport device 5. For this purpose, the cooling surface 3 can be provided with a coating or the like in a manner not shown here, which promotes both the lowest possible friction feed of the workpiece 4 and the best possible heat transfer from the workpiece 4 to the cooling element 2.

[0022] In the embodiment shown here, a cooling channel 8 runs through a lower part of the cooling element 2. 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 guided along a side surface of the cooling element 2, for example the lower side surface 9, and 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 the heat transfer between the cooling element 2 and the cooling channel 8, such as ribs or a meandering course of the cooling channel 8. Furthermore, the device 1 has a housing 11 made of a material with good thermal insulation above the cooling surface 3.The housing 11 is arranged at a distance from the cooling surface 3, forming a spacing space 12, and, in order to promote the formation of an inert gas atmosphere in the manner described below, is designed to be closed both on the top side and on the front sides 13, 14, with the exception in particular of passage openings 15, 16 for the workpiece 4. Furthermore, it is advantageous, but not shown here for reasons 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 fluidly connected on the inlet side via a supply line 17 to a source of a cold-liquefied gas, in the embodiment shown here a tank 18. The tank 18 is pressure-resistant and equipped with thermally well-insulated walls.

[0024] In the supply line 17, a device 20 is arranged for subcooling the cold-liquefied gas fed 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, is passed, without there being a flow connection to the container 21. A supply line 23 opens into a lower region of the container 21 and is fluidly 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 region of the container 21. The gas exhaust line 25 is passed through the front side 13 of the housing 11 and ends within the space 12 at a nozzle arrangement 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 for cooling. To cool the cooling element 2 and thus the cooling surface 3, a cold-liquefied gas, for example liquid nitrogen, with 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 cold-liquefied gas is subcooled, i.e., brought to a temperature below its boiling point. For this purpose, a partial flow of the cold-liquefied gas taken from the tank 18 is passed through the feed line 23, where it is expanded at the throttle valve 24 and 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 cold-liquefied gas fed through the heat exchanger surface 22 to the feed line 17. As a result, heat is extracted from the cold-liquefied gas in the feed line 17, while at the same time the cold-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 via the nozzle arrangement 27, where it forms an inert atmosphere consisting largely of cold gaseous nitrogen, which simultaneously contributes to the cooling of the workpiece 4. If necessary, a partial flow of the vaporized gas can also be discharged via a branch line 29 and used for another purpose.

[0028] The subcooled, cold-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. The workpiece is thereby cooled, while the cold-liquefied gas is heated in the cooling channel 8. Due to the subcooling of the cold-liquefied gas, evaporation of the cold-liquefied gas in the cooling channel 8 does not occur, or only partially occurs. The heated cold-liquefied gas is discharged via an outlet line 30 and can be used for further purposes, for example for producing an inert gas atmosphere in a furnace (not shown here), in which the workpiece 4 was subjected to heat treatment before being transported to the device 1, or for quenching the workpiece 4 after passing through such a furnace.

[0029] The cooling capacity of device 1 can be controlled by controlling the flow of liquefied refrigeration gas to cooling channel 8. For this purpose, a control valve 31 is provided in supply line 17, which is connected to a control unit 32. Control unit 32 determines a control parameter, for example, the temperature inside enclosure 11 measured by a probe 33, and automatically controls control valve 31 according to a predefined program. In the event of a significant withdrawal of liquefied refrigeration gas, the pressure in tank 18 can also be adjusted as needed by a pressure buildup arrangement 34, which is equipped, in particular, with an air evaporator 35. List of reference symbols

[0030] 1 device 19 - 2 Cooling element 20 Device for subcooling 3 Cooling surface 21 container 4 workpiece 22 Heat exchanger surface 5 Transport device 23 supply line 6 Arrow 24 throttle valve 7 Arrow 25 Gas exhaust line 8 cooling channel 26 Gas nozzle 9 side surface 27 Nozzle arrangement 10 - 28 bathroom 11 Enclosure 29 Branch management 12 Distance space 30 Outlet 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, with a cooling element (2) made of a thermally highly conductive material, which cooling element (2) has a cooling surface (3) along which a strip-shaped workpiece (4) can be guided and brought into thermal contact with the cooling element (2), and a cooling channel (8) which is thermally connected to the cooling element (2) and which is fluidly connected to a supply line (17) connected to a source (18) for a cold-liquefied gas for supplying cold-liquefied gas into the cooling channel (8) and to an outlet line (30) for discharging the supplied cold-liquefied gas from the cooling channel (8), characterized by thatthe device is equipped with a device (20) for subcooling the cold-liquefied gas before it is fed to the cooling channel (8), which has a heat exchanger surface (22) arranged in the feed line (17) and through which the cold-liquefied gas flows when the device is in use, which heat exchanger surface is accommodated within a container (21) equipped with a feed line (23) for a liquid cooling medium, in the upper region of which a gas discharge line (25) opens out, which is fluidly connected to a nozzle arrangement (27) directed towards the cooling surface (3) of the cooling element (2).

2. Device according to claim 1, characterized in that the supply line (23) of the container (21) of the device (20) for subcooling is fluidly connected to the source (18) for the cold-liquefied gas and is equipped with a throttle valve (24) for reducing the pressure.

3. Device according to claim 1 or 2, characterized in thata tank is used as the source (18) for the cold-liquefied gas, in which the cold-liquefied gas is stored at a pressure 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 to form a spacing space (12), and the nozzle arrangement (27) connected to the gas discharge line (25) opens out within the spacing space (12).

5. Device according to claim 4, characterized in that the gas extraction line (25) is guided through an outlet-side wall (13) of the housing (11) - seen in the transport direction of the workpiece (4).

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

7. Device according to one of the preceding claims, characterized in that Liquid nitrogen is used as a cold-liquefied gas.