Patent Publication Number: US-2022226872-A1

Title: Device for cooling a steel strip

Description:
BACKGROUND 
     The present invention relates to a device for cooling a metallic strip. Particularly, this invention is aimed at improving the rapid cooling of an annealing process. 
     During its manufacture, a metallic strip undergoes several thermal treatments, notably after its cold rolling where it is annealed. Through the annealing process, the metallic product is rapidly heated at a temperature generally comprised between 700 and 850° C. and maintained at the maximal temperature for about one minute. Then the metallic product undergoes a cooling treatment where it is cooled at a controlled cooling rate. Ultimately, the overaging and the final cooling take place. 
     In the case of a steel strip, thanks to the thermal treatments, several phenomena occur such as the recrystallisation and the carbides precipitation. All those treatments allow a desired structure improving the resistance and the formability of the strip to be obtained. 
     For particular steels such as: the (TRIP) TRansformation Induced Plasticity, the multiphase steels, the high-specific strength steel; the annealing generally comprises two coolings, a first slow one and then a second rapid one. 
     As illustrated in  FIG. 1 , the two coolings can be done in a device  1  combining a cooling in a tank  2  containing a coolant  3  and a faster cooling in a consecutive cooling device  4  containing a coolant. The arrows represent the flat metallic product moving direction. As illustrated in  FIG. 2 , U.S. Pat. No. 7,645,417 B2 discloses a cooling device, comprising a tank  5  in which two series ( 6  and  6 ′) of immersed tubes  7  are vertically stacked on both sides of a strip  8 . Said tubes projects onto the strip a coolant in the form of essentially horizontal turbulent jets. 
     SUMMARY OF THE INVENTION 
     Even though a high cooling rate is achieved, greater than 1000° C., this device is not satisfactory because the cooling is not homogeneous in the strip width direction leading to flatness defects. Consequently, there is a need to improve the product flatness of the exiting metallic flat product. Thus, the cooling device  4  needs to be improved. 
     Moreover, sealing means  9  usually isolates the tank  2  and the cooling device  4  to limit the influence of the coolant  3  onto the cooling device  4 . Furthermore, the coolant temperature in the cooling device  4  is generally inferior to the one of the tank  2  coolant. Any leakage from one space to another would create temperature gradient negatively impacting the cooling homogeneity. EP 1 300 478 B1 extensively describes a sealing means  9  and its advantages. 
     One purpose of this invention is to solve the aforementioned problem. 
     The present invention provides a cooling device ( 10 ) for a cooling operation of a flat metallic product (S), said cooling device being located in an essentially vertical, ascending or descending, path comprising:
         a tank ( 15 ) filled with a coolant bath ( 17 ) defining a coolant surface ( 11 ),   said tank comprising at least two openings, one on the upper surface ( 16 ) and one on the bottom surface ( 16 ′), through which said flat metallic product (S) can go, describing a path,   said opening on the bottom surface ( 16 ′) being equipped with a sealing means ( 9 ),   two series ( 18  and  18 ′), of projecting devices ( 13 ) comprising at least an aperture ( 13 E) being immersed in said coolant bath, facing each other on each side of said path   said projecting devices ( 13 ) being at least partly immersed in said coolant bath ( 17 ),   any two vertically successive projecting devices of a series being separated by a gap ( 19 ),   each series ( 18  and  18 ′) of projecting devices ( 13 ) having an uppermost projecting device ( 20  and  20 ′) being defined as the closest projecting device to the coolant surface ( 11 ),   at least the uppermost projecting device ( 20  and  20 ′) on both sides being downwardly inclined of an angle of 20° to 40° compared to the horizontal.       

     The present invention also provides a cooling method wherein a flat metallic product moving essentially vertically, ascendingly or descendingly, is cooled in a device as described above, wherein said series of projecting devices eject a coolant flux between 250 m 3  and 2,500 m 3  per hour per surface of flat product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention. 
       To illustrate the invention, various embodiment of non-limiting example will be described, particularly with reference to the following figures: 
         FIG. 1  exhibits an embodiment of a device  1  comprising a tank  2  and a cooling device  4 . 
         FIG. 2  exhibits an embodiment of a cooling device  4  as disclosed in the state of the art. 
         FIG. 3  exhibits an embodiment of the present invention, a cooling device  10 . 
         FIG. 4  exhibits a second embodiment of the present invention, a cooling device  10 . 
         FIG. 5  exhibits a coolant bath surface  11  and coolant streams  12  of an embodiment of a cooling device of the present invention. 
         FIG. 6  exhibits the influence of a gap between the projecting devices  13  on a coolant bath surface  11 ′ and coolant streams  12 ′ of a cooling device. 
         FIG. 7  exhibits a coolant bath surface  11 ″ and coolant streams  12 ′ of an embodiment as disclosed in the state of the art. 
         FIG. 8  exhibits a simulation of a coolant bath surface  4 ″ of an embodiment as disclosed in the state of the art. 
         FIGS. 9A and 9B  exhibit two other possible uses of the claimed device. 
         FIGS. 10A and 9B  exhibit two embodiments of tubes  14  of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 2 to 7  do not exhibit all the elements of the cooling device but the main elements permitting to understand the invention and its difference with the known state of the art. For example, the system permitting to flow the coolant into the projecting devices are not represented. 
     As illustrated in  FIG. 3 , the invention relates to a cooling device  10  for a cooling operation of a flat metallic product S, said cooling device being located in an essentially vertical, ascending or descending, path comprising:
         a tank  15  filled with a coolant bath  17  defining a coolant surface  11 ,   said tank comprising at least two openings, one on the upper surface  16  and one on the bottom surface  16 ′, through which said flat metallic product S can go, describing a path,   said opening on the bottom surface  16 ′ being equipped with a sealing means  9 ,   two series ( 18  and  18 ′), of projecting devices  13  comprising at least an aperture  13 E being immersed in said coolant bath, facing each other on each side of said path,   said projecting devices  13  being immersed in said coolant bath  17 ,   any two vertically successive projecting devices of a series being separated by a gap  19 ,   each series ( 18  and  18 ′) of projecting devices  13  having an uppermost projecting device ( 20  and  20 ′) being defined as the closest projecting device to the coolant surface  11 ,   at least the uppermost projecting device ( 20  and  20 ′) on both sides being downwardly inclined of an angle of 20° to 40° compared to the horizontal.       

     In the following specification, the flat metallic product S will be referred as a strip. However, said flat metallic product is not limited to a strip. 
     As illustrated in  FIGS. 3 and 4 , the fast cooling device  10  is used to cool and/or quench a flat metallic product, such as a steel strip. The sealing means are not represented in  FIG. 4 . 
     The cooling device is positioned in an essentially vertical, ascending or descending, path of the flat metallic product. It means that when the flat metallic product passes through the cooling device, its moving direction is essentially vertical as represented by the arrow D. 
     The cooling device comprises a tank  15  containing a coolant bath  17  which defines a coolant surface  11 . The primary role of the tank is to contain a coolant creating a coolant bath. The coolant is preferably a liquid and can be water. Its secondary role is to isolate the coolant bath from the exterior which permits to control the coolant parameters, such as the temperature, and the projected coolant fluxed. 
     Moreover, said tank comprises at least two openings, one on its upper side  16  and one on its bottom side  16 ′, through which said flat metallic product S can go, describing a path. The role of those openings is to let the flat metallic product pass through the cooling device  10 . They should also prevent the entrance of any external liquid into the coolant bath  17 . Said openings wherein the strip pass through should be essentially vertically aligned so the strip can have an essentially vertical path. The path described by said flat metallic product is essentially vertical. 
     Furthermore, the tank preferably comprises at least two lateral openings ( 21  and  21 ′) allowing the coolant discharge. 
     The opening on the bottom side is equipped with a sealing means  9  to improve the coolant bath isolation from the exterior. As illustrated in  FIG. 3 , the sealing means can comprise a double pair of rollers ( 22  and  22 ′) pressed against the strip S and positioned symmetrically relative to the latter. Moreover, a fluid can be injected with a controllable pressure and/or temperature between the rollers. 
     As illustrated in  FIGS. 3 and 4 , two series ( 18  and  18 ′), of projecting devices  13  comprising at least an aperture  13 E, are facing each other. In other words, the two series ( 18  and  18 ′) are on both sides of said flat metallic product vertical path. Preferably, said two series of projecting device are positioned on two opposite tank sides. Each series is made of several projecting devices  13  essentially vertically aligned and positioned to homogeneously cool the strip in its width direction W. The projected coolant should be distributed along the strip width to achieve a homogeneous cooling in the strip width direction. 
     The coolant is projected through apertures  13 E in said projecting devices  13 . Said apertures  13  are among other possibilities: a slit, a hole or a series of holes. Said projecting devices apertures  13 E are completely immersed in the coolant bath. Such an immersion permits to suppress or at least lower the gas bubble or vapor formation (and presence) in the coolant bath close to the strip compared to non-immersed apertures. Preferentially said projecting devices are completely immersed in said coolant. 
     A gap  19  separates two vertically successive projecting devices (e.g.  13 A and  13 B) of a series ( 18  and  18 ′) of projecting devices. As illustrated in  FIG. 5 , such a gap permits to improve the cooling efficiency of the sprayed coolant by improving the renewal of the coolant in contact to the strip and heat exchange between the projected coolant and the strip. If there was no gap between the projecting devices, the coolant could only evacuate by flowing  12 ′ vertically along the strip thus reducing the cooling efficiency, as illustrated in  FIG. 6 . On the contrary, such a gap permits the discharge of the coolant perpendicularly to the strip surface. Moreover, absence of gap would also promote the creation of turmoil at the bath surface  11 ′. 
     The closest projecting device, of each series, to the coolant bath surface  11  comprised in the tank  15  is referred as the uppermost projecting device ( 20  and  20 ′). As illustrated in  FIGS. 3, 4 and 5 , at least the uppermost projecting device of a series is downwardly inclined of an angle comprised between  20 ° and  40 ° to the horizontal. Such an inclination of the uppermost projecting device permits to suppress or at least drastically reduce the turmoil generated by the uppermost projecting devices compared to horizontal projecting device as disclosed in U.S. Pat. No. 7,645,417 B2 and illustrated in  FIG. 7  wherein the bath surface  11 ″ is not flat but exhibits turmoil. Consequently, the cooling homogeneity in the width direction is increased. 
       FIG. 8  is a simulation a coolant bath surface  11 ″ of a cooling device having a series of projecting devices oriented essentially horizontally; i.e. having coolant sprayed essentially horizontally, wherein the strip is moving upward. This case corresponds to the one of patent U.S. Pat. No. 7,645,417 B2. One can observe that turmoil is generated on the coolant bath surface close to the strip. Consequently, the cooling is not uniform along the strip width and degrades the strip quality. 
     The use of such a claimed cooling device  10  is not limit to only one positioned at the strip exit from the cooling device as illustrated in  FIG. 1 . On the contrary, this claimed cooling device  10  can be positioned at the strip entry of the tank  2 , as illustrated in  FIG. 9A . Moreover, two claimed cooling devices can be installed on the entrance and exit of the strip of tank  2 , as illustrated in  FIG. 9B . Such a positioning of one or several claimed cooling devices permits to perform various cooling cycles when used in addition of a tank containing water. For example, the three following thermal cycles are possible if the coolant temperature in the cooling device  10  is lower than the one in the tank  2 :
         1) slow cooling then fast cooling ( FIG. 1 ),   2) fast cooling then slow cooling ( FIG. 9A ),   3) fast cooling then slow cooling then fast cooling ( FIG. 9B ),       

     wherein the fast cooling takes place in the claimed cooling device and the slow cooling is in a tank containing boiling water. 
     In the prior art, it seems that no solution permits to avoid the formation of turmoi leading to a heterogeneous cooling along the strip width. On the contrary, with the equipment according to the present invention, the cooling homogeneity is improved along the strip width. 
     Advantageously, both series ( 18  and  18 ′) have the same number of projecting devices ( 13 ) downwardly inclined of an angle of 20° to 40° compared to the horizontal. In order to obtain a homogeneous in the strip width, the inclined projecting device of each series should be facing each other. 
     Advantageously, the two uppermost projecting devices of both series ( 18  and  18 ′) are downwardly inclined of an angle of 20° to 40° compared to the horizontal. The two uppermost projecting devices ( 20  and  20 A or  20 ′ and  20 ′A) of a series correspond to the two immersed projecting devices being the closer to the surface, as illustrated in  FIG. 4 . Such an arrangement permits to increase even further the cooling homogeneity in the strip width. 
     Advantageously, the three uppermost projecting devices on both series ( 18  and  18 ′) are downwardly inclined of an angle of 20° to 40° compared to the horizontal. 
     Advantageously, the four uppermost projecting devices on both series ( 18  and  18 ′) are downwardly inclined of an angle of 20° to 40° compared to the horizontal. 
     Advantageously, all projecting devices located up to a depth of 50 cm from the coolant surface are downwardly inclined of an angle of 20° to 40° compared to the horizontal. Such an arrangement permits to increase even further the cooling homogeneity in the strip width because the formation of gas bubble is reduced even more. Preferably, all projecting devices located up to a depth of 1 meter or 2 meters or 3 meters from the coolant surface are downwardly inclined of an angle of 20° to 40° compared to the horizontal. 
     Advantageously, said series of projecting devices comprises 10 to 40 devices. Such a quantity of devices permits to ensure a sufficient cooling capacity of the cooling device. More advantageously, each projecting device can spray at least 250 m 3 ·h −1  of coolant per m 2  of strip. 
     Advantageously, said projecting devices are tubes  14 . Preferably, as illustrated in  FIGS. 10A and 10B , said tubes are hollow rectangular cuboid. The coolant enters said tubes by opening on their two lateral faces  23 , which are preferentially their smallest faces. The coolant exits said tubes by a frontal face  24 , which is oriented toward the strip. Preferentially, said frontal face is equipped with a plate having at least an aperture such as rows of round holes, as illustrated in  FIG. 10A , and/or at least a slit, as illustrated in  FIG. 10B . 
     Advantageously, said projecting device apertures  13 E (See  FIG. 3  for example) are at a distance between 30 and 200 mm of said path. The path is referring to the path described by the flat metallic product. On one hand, if the distance between the apertures of the projecting device and the strip is smaller than 30 mm, the moving strip might contact the cooling device which can lead to scratch or damage the strip surface. On the other hand, if the distance is greater than 200 mm, the cooling performance is reduced. 
     Advantageously, the cooling device does not comprise rolls, such as restraining rolls, between said two openings. 
     The invention also relates to a cooling method wherein a flat metallic product moving essentially vertically, ascendingly or descendingly, is cooled in a device as described previously, said series of projecting devices eject a coolant flux between 250 m 3  and 2,500 m 3  per hour per surface of flat product. A coolant flux in that range is sufficient to obtain a cooling speed desired to achieve the desired product properties. 
     Preferably, said series of projecting devices eject a coolant having a speed between 0.25 m·s −1  and 20 m·s −1 . Such a speed permits to the ejected coolant to reach the strip surface and being reflected horizontally in the gap between the projecting devices which improves the coolant renewal and thus the cooling homogeneity. 
     Preferably, said series of projecting devices eject a coolant being at a temperature between 10 and 100° C. 
     Preferably, said cooling device permits to cool said flat metallic product of at least 200° C.·s −1 . More preferably, said cooling device permits to cool said flat metallic product of at least 500° C.·s −1 . Even more preferably, said cooling device permits to cool said flat metallic product of at least 1000° C.·s −1 . 
     The invention has been described above as to the embodiment which is supposed to be practical as well as preferable at present. However, it should be understood that the invention is not limited to the embodiment disclosed in the specification and can be appropriately modified within the range that does not depart from the gist or spirit of the invention, which can be read from the appended claims and the overall specification.