EP0875304B1 - Method and cooling aggregate for cooling rolling stock at rolling-temperature, especially hot wide strip - Google Patents

Abstract

Cooling of a rolled product (1) is by forced convection, with pressurised water stream in a pressure space (10) and a convection space (13). The intensity of forced convection is controlled by individually adjustable parameters such as the duration of stay of the product in the spaces (10, 13), as well as the amount, pressure and flow velocity of the cooling medium. The amount of heat taken from the product is preferably such that a safe distance from the boiling point is attained, and unstable film evaporation is avoided. The corresponding apparatus includes an amount and pressure controllable nozzle gap (11) for entry of the cooling medium into the pressure space (10), and diffusor (12) with means (16) for extraction of the cooling medium. A constriction (33) is located between the pressure and convection spaces.

Description

The invention relates to a method for cooling hot rolled rolling stock, in particular For cooling hot broadband on both sides, using forced convection when exchanging heat between the rolling stock and the cooling medium using a Pressurized water flow made in a pressure room and convection room and the rolling stock by specifically controlling the intensity of the forced convection is cooled, which is independent of one another by relative coordination adjustable parameters, such as dwell time of the rolling stock as it passes through the Pressure room and the subsequent convection room as well as quantity, pressure and Controlled flow rate of the cooling medium and heat from this from the rolling stock up to a safety distance from the boiling point for avoidance unstable film evaporation is recorded. The invention relates also an apparatus for performing the method.

The knowledge gained when cooling hot rolled rolling stock is based on many years of practical experience. These show that, for example, wire and bar steel can achieve significantly higher cooling intensities in water cooling sections than in water cooling sections of hot wide strip mills. In cooling sections of wire and steel bars, the heat transfer coefficients are approx. 20,000 to 40,000 W / m ² K, while in a laminar cooling section behind the finishing stand for hot broadband, heat transfer coefficients are approx. 800 to 1,500 W / m ² K, i.e. approx. 10 to 15 times lower cooling intensity can be achieved. As a result, a significantly longer cooling distance is required for the same temperature reduction in hot wide strip compared to wire and bar steel.

New technologies in ferritic rolling of hot wide strip mean that between the final stands are cooled intensively to low final rolling temperatures if the distances between the scaffolds are not too large. When rolling thin Dimensions at which the hot strip reel to avoid restless conveyor belt must be arranged closer to the finishing stand water cooling sections with higher cooling intensity are also required.

DE 39 27 276 A1 discloses a method for hardening steel with the aid of liquid cooling media. It follows from this that with the previously known methods for hardening steel with the aid of liquid cooling media, only a small hardening depth, based on the edge zone, is achieved even with rods with small rod diameters. In contrast, the method according to DE 39 29 276 A1 not only enables a considerable increase in the hardening depth, but also a complete hardening, in particular of rod-shaped rolled products up to 70 mm in diameter, in a particularly simple manner in that the rolled product made of steel immediately after the rolling process supplied with cooling media cooling section and exposed to high flow velocities, expediently the flow velocities in the cooling section are so high that heat transfer numbers greater than or equal to 50,000 W / m ² K are generated and the rolling stock is cooled therein until the average temperature of the rolling stock cross section is below the MS temperature, so that after leaving the cooling section through the temperature compensation over the cross section, the austenite still present in the core is converted into intermediate stage structure bainite, while at the same time in the martensitic n A large part of the overlapping thermal and transformation stresses is reduced by the temperature rising again to a maximum of MS temperature.

DE 36 33 423 C2 describes a heat exchange part for a pressure cooling tube for cooling strip or flat material from the rolling heat, using cooling water fed in at the cooling pipe inlet and removed again from the rolling stock at the cooling pipe outlet becomes. The document discloses that such pressure cooling tubes e.g. on continuously working rolling mills with high wagering speeds can be. Under flat or strip material, rolled profiles with a understood rectangular or approximately rectangular cross-section, its width corresponds to at least twice the height of the rolled profile. In this document is state of the art DE-OS 25 43 750 with a device for Cooling of section steels and flat material mentioned by arrangement of spray nozzles, with which only relatively low cooling intensities can be achieved, and frequent constipation these nozzles for irregular cooling above the length and width of the flat material with the consequence of warpage of the material and disturbances run in rolling operation. The state of the art in this document DE-AS 22 35 063 mentioned is a slot nozzle with adjustable across the rolling direction Inner wedge is provided, thus avoiding blockages Cooling water quantity and thus the cooling intensity can be controlled. The suggestion according to DE 36 33 423 C2 is now that the heat exchange part consists of a tube with a rectangular cross-section, with wear-resistant guide elements is lined, the opposite of the broad sides of the rolling stock Inner surfaces of the guide elements over the length of the heat exchange part have a variable clear height, while the Narrow sides of the rolling stock opposite inner surfaces of the guide elements a constant clear width over the length of the heat exchange part exhibit.

EP 0 266 302 B1 discloses a method for cooling hot rolled rolling stock, with / without direct patenting, for pressurized water within a pressurized room is pressed onto the hot rolled surface of the rolling stock between the accumulation edges. The cooling unit is pressurized with a quantity of pressurized water, which is preferably in balance with the amount of heat to be extracted from the rolling stock stands to with the removal of heat by heating pressurized water in the pressure chamber a convection refrigerator and by removing heat from the on Pressurized water-steam mixture, evaporative heat given off, preferably up to the boiling point of the pressurized water, the desired cooling temperature of the To achieve rolling stock while cooling in pressurized water as well as in one Control pressurized water-steam mixture. Accordingly, the cooling unit exists from the pressure chamber of a convection refrigerator, the so-called convection pressure chamber between damming edges, in the warm rolling stock, mainly by convection, from inflowing and onto the hot rolled surface of the rolling stock Pressed water under pressure, preferably up to the boiling point of the pressurized water is withdrawn. The cooling unit also consists of the pressure chamber of an evaporative cooling section, the so-called evaporative pressure chamber between the stowage edges, in which the rolling stock primarily by heat of vaporization, from the flowing through and onto the rolling stock surface pressed heat-steam mixture further heat is removed.

EP 0 287 503 B1 relates to a method and a cooling unit for cooling of a continuous product and contains characteristics through which the suggestions be further developed according to EP 0 266 302 B1, specifically with the process engineering Features that heat extraction in the convection refrigerator and in the evaporative cooling section of the pressure chamber in the pressure cooling unit except with the predetermined inflow of cooling pressure water and the regulated inflow Amount of pressure water in the convection cooling section, with an additional, regulated inflow of guide pressure water into the evaporative cooling section and further with one, in the area of the high steam content in the the hot water-steam mixture flowing through the evaporative cooling section inflowing proportion of condensation water is guided. The device is described in such a way that in addition to the cooling and guiding pressure water inflow in the convection cooling section in the evaporative cooling section further inlet pressurized water inflows and further condensation pressurized water inflows are arranged.

Document EP-B-0 266 302 discloses a method for cooling hot wide strip, in which forced convection during heat exchange between Rolled stock and cooling medium with the help of a pressurized water flow in a pressure room and convection space and the rolling stock by targeted control the intensity of the forced convection is cooled, the intensity of the Forced convection can be set independently of one another by relative coordination Parameters such as the dwell time of the rolling stock as it passes through the pressure chamber and the subsequent convection space as well as the quantity, pressure and flow velocity controlled by the cooling medium and heat from this the rolling stock is picked up.

The object of the present invention is compared to this prior art based, a significantly simplified process for cooling warm whale Rolling stock and a corresponding device to specify at largely reduced cooling section length for flat material, especially for hot wide strip with thin dimensions, better through high intensity of cooling To achieve cooling results.

To solve this problem, a method according to the generic term is used to claim 1 a technical teaching with the characteristic Features of claim 1 proposed.

For this purpose, the invention provides that to control the dwell time of the rolling stock in the printing room at a given rolling speed the length of the in the printing room trained cooling section is set changeable in the rolling direction. there can the cooling medium in the pressure chamber in the rolling direction or transversely to it become. To avoid unstable film evaporation there is a safety margin to the boiling point of the cooling medium (e.g. Δ T> 25 ° C).

Furthermore, the invention provides that the amount of per unit time coolant flowing into the pressure chamber through a variable cross-section Nozzle gap is set, which is also the speed and determined the direction of the incoming cooling medium. additionally the amount can be changed by varying the inlet pressure.

The forced convection by flow cooling according to the invention a known pressure and convection room, but between an adjustable nozzle gap and one adjoining the convection room Diffuser is designed to remove the cooling medium. It can be targeted the parameters that can be set independently of one another are thus coordinated be that the cooling medium heat up to the boiling point is withdrawn without evaporation occurring. Then you can the cooling medium after absorbing heat from the rolling stock in the area of Pressure increase is subtracted from the diffuser through the existing openings become.

It is further provided that the cooling medium in front of the terminal diffuser Convection area with increased speed and reduced flow pressure flows through, which also limits the length of the pressure chamber and is preferably set to be variable in the axial direction. By an appropriate The point can quickly pass through the length setting of the pressure chamber at which the unstable film evaporation begins and the so-called suffering frost point is achieved. When the flow cross section is narrowed and thus Increasing the flow velocity then becomes a higher one in the convection space Heat transfer achieved through increased forced convection. After that the cooling medium after absorbing heat from the rolling stock in the area of Pressure increase withdrawn from the diffuser and discharged.

Furthermore, use can advantageously be made of the measure that the Flow cross section of the pressure chamber by changing the distance between the surface of the rolling stock and at least one wall of the pressure chamber is set.

In an embodiment essential to the invention, the invention can also be used be that the pressure chamber is transverse to the flow direction of the cooling medium using parallel guide elements into individual, side by side Channels is divided. So far, this has not resulted or only with great Possibility achievable by applying different amounts to the individual Flow channels cooling over the bandwidth, for example, to influence flatness and especially peripheral cooling or subcooling control while minimizing the consumption of cooling medium. there can in the present case, each cooling channel with regard to exposure to The pressure and quantity of the cooling medium can be controlled individually. The setting of the The cooling temperature is adjusted by adjusting the nozzle gap and also with the cooling medium pressure.

In addition, use can also be made of the measure that the flow cross section in the pressure chamber in the channels in it Flow direction is set wedge-shaped in some areas. This allows the Flow rate and thus the cooling effect varies locally become.

To avoid the effect of streaking when cooling the surface of the rolling stock, is advantageously a either oblique or tortuous arrangement of the Channels formed between the guide elements of considerable advantage.

Another advantage of this invention is that between surfaces of the rolling stock and walls of the pressure chamber formed gap-shaped flow areas and are pressed by this cooling medium at high pressure, such that the Rolled material is guided between liquid films formed by the cooling medium.

A device for cooling hot rolled rolling stock, in particular of Hot wide strip with one for heat exchange between rolling stock and cooling medium preferably pressure and convection space formed by forced convection with means for forming a pressure medium flow and for controlling the intensity of forced convection, with the pressure chamber on the inlet side of the rolling stock an inflow for the cooling medium in the form of a quantity and pressure-adjustable nozzle gap and a terminal diffuser with means for Pull off the cooling medium and in the rolling direction in front of the diffuser Damming element delimiting the pressure space is arranged, which is the beginning of the convection space is characterized in that the baffle element under Changing the length of the pressure chamber and convection space in the rolling direction is designed to be longitudinally adjustable and that the nozzle gap acts as an actuator Has wedge.

Further configurations of the device are in accordance with the subclaims intended.

An embodiment of the device according to the invention provides that the diffuser in the area of increased cooling medium pressure heated outlets for pulling off Has cooling medium. In an embodiment essential to the invention, the Device above or below and above and below the rolling stock to form a be box-shaped channel with connections for cooling medium and consist of flat plates into the flow channels on the sides facing the rolling stock are incorporated or trained using attached strips. And finally, an embodiment essential to the invention provides that the device a scraper with a nozzle gap, for example in the form of a screw is which coolant collects.

Figur 1

eine Kühlvorrichtung in Seitenansicht und im Längsschnitt,

Figur 2

die Vorrichtung im Querschnitt entlang einer Schnittebene II-II in Fig. 1,

Figur 2a

verschiedene Strömungskanäle der Kühlvorrichtung in schematischer Darstellung.

Figur 3

eine bekannte Vorrichtung zum Kühlen von Flachprodukten mit Hilfe einer Zwangskonvektion, quer zur Walzrichtung, im Schnitt einer Ebene III-III in Fig. 4,

Figur 4

die bekannte Vorrichtung gemäß Fig. 3 in Draufsicht.

Further details, features and advantages of the invention result from the following explanation of some exemplary embodiments, a hot broadband in a pressure convection space being cooled to the desired temperature by specifically controlling the intensity of the forced convection. To avoid unstable film evaporation, a safety distance from the boiling point of the cooling medium should be maintained. Show it

Figure 1

a cooling device in side view and in longitudinal section,

Figure 2

the device in cross section along a section plane II-II in Fig. 1,

Figure 2a

different flow channels of the cooling device in a schematic representation.

Figure 3

a known device for cooling flat products by means of forced convection, transverse to the rolling direction, in the section of a plane III-III in Fig. 4,

Figure 4

the known device of FIG. 3 in plan view.

The device for cooling hot rolled rolling stock 1, in particular from Hot wide strip with a for heat exchange between rolling stock 1 and cooling medium preferably designed to raise the suffering frost temperature 10 and the subsequent pressureless convection chamber 13 with means to form a pressure medium flow and to control the intensity The forced convection is designed so that the pressure chamber 10 on the entry side of the rolling stock 1, an inflow 32 for the cooling medium in the form of a adjustable quantity and pressure nozzle gap 11 and a terminal diffuser 12 with means 16 for withdrawing the cooling medium. Furthermore, in Rolling direction in front of the diffuser 12 a damming element delimiting the pressure chamber 10 33 arranged, which forms the beginning of the convection space 13.

By the interaction of the adjustable nozzle gap 11 with the in the Length adjustable pressure chamber 10 and the subsequent pressureless convection room 13 and the final diffuser 12 and with removal 16 of the Cooling medium can by adjusting the dwell time of the rolling stock 1 at Pass through the pressure chamber 10 and convection chamber 13 (e.g. by changing the length of the cooling section) as well as quantity, pressure and flow velocity the intensity of forced convection is controlled in a reproducible manner are and the cooling medium heat from the rolling stock preferably with a sufficient distance to the boiling point limit to avoid the unstable Film evaporation are transmitted. The heat transfer is therefore exact adjustable. To control the dwell time of the rolling stock 1 in the pressure chamber 10 The predetermined rolling speed can be the axial length of the pressure chamber 10 trained cooling section can be set changeable, for example by a length adjustable Damming element 33, which is also the beginning of the convection space 13.

The cooling device, which is shown only once above the hot strip 1 in FIG. 1 is, can also be mirror-symmetrically advantageous from the bottom of the rolling stock 1 be arranged in an identical manner.

The nozzle gap 11 has a wedge 34 as an actuator. By setting it According to arrow 38, the amount and / or pressure of the inflow 32 conveyed cooling medium can be set. The well-known Disadvantages of spray nozzles that tend to become blocked are completely avoided.

As shown in Fig. 2, the cooling device consists of a flat plate 23 which on the side facing the rolling stock 1 has flow channels 22. The size and The number of these channels 22 varies according to the width of the rolling stock. Corresponding the illustration shows the flow channels 22 between rectangular band guide rails 21 arranged with a flat surface to the rolling stock 1. So that at a cooling between these channels 22 and the rolling stock 1 at the same time The rolling stock 1 is guided.

To avoid the effect of streaking when cooling, one can be advantageous oblique or winding arrangement of the channels 22 is provided in the longitudinal direction his. (Fig. 2a)

The adjustability of the flow channels provides a further advantageous design in the longitudinal direction in height, which can also be wedge-shaped. Thereby can target the flow velocity and consequently the cooling effect can be varied or adjusted.

The cooling device shown and described can be above or below or on both sides of the rolling stock 1 and with a short guide, for example between two roll stands are used.

Fig. 1 also shows the arrangement of a wiper 36 for cooling medium and its deduction according to arrow 39. This scraper member 36 has a collecting space preferably in the form of a snail, the excess cooling medium catches safely.

A design of the cooling device with guidance of the cooling medium across Rolling direction, which are not embodiments of the invention but is the state of the art that facilitates understanding of the technology, show the figures 3 and 4. The device consists of a number of Water boxes 35, which are arranged above or below the flat product 1. she have inflows 32 for cooling medium to be introduced under high pressure and have mushroom-shaped or wedge-shaped outlet control members 34. they form also circular at its periphery or straight in another variant Nozzle column 11, from which the cooling medium under high pressure in the convection pressure chambers 10 exits.

If the exits of the cooling medium in Fig. 4 with directed to both sides Arrows is indicated, it must not be overlooked that that Cooling medium from the circular nozzle gaps 11 radially in all directions exit. For the sake of clarity, this was symbolized by the straight arrows indicated.

Cooling also below the wedge-shaped outlet regulating members 34 takes place, the shafts are provided with short central holes and have an inlet hole across it, so that pressurized water from the holes emerges below the wedges 34 and in the pressure chambers 10 under forced convection has a cooling effect.

It is important, as is clear from FIGS. 3 and 4, between the upper and lower water boxes 35 provided a lateral offset to to avoid overcooling the rolling stock 1 in the middle of the device.

It should also be noted that when two water boxes 35 are connected each the resulting gap in the rolling direction by a correspondingly to be trained Connection member 37 is bridged. This prevents the cooling medium the shortest way between two water boxes or escape below without full use of its heat absorption capacity and thus can cause uneven cooling of the rolling stock.

The cooling medium under pressure in the water tank flows through adjustable Nozzle gaps 11 depending on the setting of the rotationally symmetrical wedges 34 or of the straight wedge 38 in each of the flat product 1 and the box wall formed channel 10 at high speed transverse to the rolling direction and takes one by forced convection depending on the setting of the cooling parameters large amount of heat. So that between the rolled product 1 and the box wall a high pressure can develop in the area of the rolled ends the walls of the water boxes 35 directed towards the rolling stock 1 optionally adjustable labyrinth seals 40 attached.

Claims (17)

1. Method of cooling rolled stock (1) hot from rolling, particularly for cooling hot wide strip at both sides, in which a forced convection with heat exchange between rolled stock (1) and coolant is carried out with the help of a pressurised water flow in a pressure space (10) and convection space (13) and the rolled stock (1) is cooled by selectively controlling the intensity of the forced convection, wherein this is controlled by relative matching of parameters which are settable independently of one another, such as dwell time of the rolled stock (1) during transit through the pressure space (10) and the adjoining convection space (13) as well as quantity, pressure and flow speed of the coolant, and heat is taken up from the rolled stock (1) by the coolant as far as a safety distance from the boiling point so as to avoid an unstable film evaporation, characterised in that for control of the dwell time of the rolled stock (1) in the pressure space (10) at a given rolling speed the length of the cooling path formed in in the pressure space (10) is variably set in rolling direction and for control of the dwell time of the rolled stock (1) in the convection space (13) at a given rolling speed the length of the cooling path formed in the convection space (13) is variably set in rolling direction.
2. Method according to claim 1, characterised in that the coolant in the pressure or convection space (10 or 13) is conducted in the rolling direction or transversely thereto.
3. Method according to claim 1 or 2, characterised in that the quantity of coolant flowing into the pressure space (10) unit of time is set by a nozzle gap (11) which is variable in cross-section and which at the same time determines the speed and direction of the inflowing coolant.
4. Method according to one of claims 1 to 3, characterised in that a baffle element (33) in the region of the pressure space (10) counteracts, through pressure increase in the coolant, the creation of steam or steam/water mixture and that the coolant after take up of heat from the rolled stock (1) is drawn off in the region of the pressure increase by way of a diffuser (12).
5. Method according to one of claims 1 to 4, characterised in that the coolant before the diffuser (12) at the end flows through a convection space (13) at increased speed and reduced pressure, which at the same time limits the length of the pressure space (10) and is variably set in rolling direction, wherein the flow cross-section of the pressure space (10) is set by changing the spacing between the surface of the rolled stock (1) and at least one wall (20) of the pressure space (10).
6. Method according to one of claims 1 to 5, characterised in that the pressure space (10) is subdivided transversely to the flow direction of the coolant into adjacently disposed channels (22) with use of parallel guide elements (21) and that the flow cross-section in the pressure space (10) or in the channels (22) present therein is regionally set to be wedge-shaped in flow direction.
7. Method according to one of claims 1 to 6, characterised in that gap-shaped flow regions are formed between surfaces of the rolled stock (1) and walls of the pressure space (10) and coolant is forced through these at high pressure in such a manner that rolled stock is conducted between liquid films formed by coolant.
8. Method according to one of claims 1 to 7, characterised in that the cooling over the strip width, particularly for influencing of planarity, as well as edge cooling and edge subcooling are controlled by different action of individual channels (22) and at the same time the consumption of coolant is set to a minimum.
9. Method according to one of the preceding claims, characterised by use thereof for the rolling out of thin slabs according to an endless rolling concept.
10. Method according to one of the preceding claims, characterised by use thereof as intermediate stand cooling, wherein the rolled stock temperature is so controlled that a ferritic rolling is made possible.
11. Device for cooling rolled stock (1) hot from rolling, particularly for cooling hot wide strip at both sides, with a pressure space (10) and convection space (13), which are constructed for heat exchange between the rolled stock (1) and coolant for forced convection, with means for forming a coolant flow as well as for controlling the intensity of the forced convection, wherein the pressure space (10) has at the inlet side of the rolled stock (1) an inflow port (32) for coolant in the form of a quantity-settable and pressure-settable nozzle gap (11) and a diffuser (12) at the end with means (16) for drawing off the coolant, and that a baffle element (33) bounding the pressure space (10) is arranged in front of the diffuser (12) in rolling direction and represents the beginning of the convection space (13), characterised in that the baffle element (33) is constructed to be adjustable in length with change in the length of the pressure space (10) and the convection space (13) in rolling direction and that the nozzle gap (11) has a wedge (34) as setting element.
12. Device according to claim 11, characterised in that the diffuser (12) has in the region of increased coolant pressure outlets (16) for drawing off heated coolant.
13. Device according to claim 11 or 12, characterised in that it is constructed with connections for coolant above or below and preferably above and below the rolled stock (1) while forming a box-shaped channel (35) and consists of flat plates (23), into which flow channels (22) are worked on the sides facing the rolled stock (1) or are formed by means of strips which are placed on.
14. Device according to one of claims 11 to 13, characterised in that a stripper element (36) with a nozzle gap, for example in the form of a helix, is arranged downstream thereof and catches coolant.
15. Device according to one of claims 11 to 14, characterised in that the diffuser (12) at the end has a further baffle element (40).
16. Device according to one of claims 11 to 15, characterised in that the cooling device and/or the baffle elements (23, 40) thereof and/or the flow channels (22) thereof or the flow strips thereof are adjustable in the direction of the rolled stock surface (1).
17. Device according to one of claims 11 to 16, characterised in that the flow channels (22) formed between the guide elements (21) have either an oblique arrangement or also twisted arrangement.

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