Patent Publication Number: US-7594535-B2

Title: Twin roll caster, and equipment and method for operating the same

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to twin roll casters, and more particularly to casting rolls for a twin roll caster. 
   The twin roll method of continuous casting thin metal strip from molten metal between a pair of counter rotating casting rolls and through the gap between the rolls is known for directly producing strip from molten metal.  FIGS. 6 and 7  show an example of a prior art continuous casting machine, the casting rolls  2  are in contact with side dams  1  at the circumferential end surfaces of the casting rolls  2 , and having hollow stub shafts  3  that axially engage the two ends of the casting rolls  2  (see for example U.S. Pat. No. 6,241,002). 
   The two end portions of the casting rolls  2  are smaller than the central portions, and are shaped as to come into contact with the side dams  1 . In the continuous casting machine, the pair of casting rolls  2  are disposed lateral to each other in such a manner that the casting roll gap may be adjusted according to the thickness of the strip S that is to be manufactured. The side dams  1  are respectively in contact with the end surfaces of the central portion of greater diameter of the casting rolls  2  containing the molten metal M. The speed and direction of revolution of the casting rolls are set such that the outer circumferential surfaces should move towards the casting roll gap at the same speed. 
   Radially below and spaced from the position of the side dams, the casting rolls  2  have in the past had internally a plurality of axially extending cooling channels  4  positioned equidistantly circumferentially, and a plurality of radially extending cooling channels  5  connected with the ends of the cooling channels  4 . The cooling channels  4  extend from one end of the casting rolls to the other end of the casting rolls radially below the position of the side dams. Bolts  7  or plugs  6  in the ends served as plugs to close the ends of the cooling channels  4 . The radial cooling channels  5  extend from an inner circumferential surface of the casting roll at right angles to the cooling channels  4 . 
   Radial cooling channels  8  pass through the hollow shaft  3  to allow cooling water W to flow through one hollow shaft  3  into one radial cooling channels  5 , then into cooling channels  4 , corresponding radial cooling channels  5  at the other end of the casting roll  2 , and finally into the interior of the other hollow shaft  3 . 
   In such a continuous casting machine, heat is removed by cooling water W flowing through the radial cooling channels  5  and the longitudinal cooling channels  4  while molten metal M is poured into the space confined by the side dams  1  and the casting rolls  2  forming a pool of molten metal M above the nip between the casting rolls. As the casting rolls rotate, the metal that is being cooled on the outer circumferential surfaces of the casting rolls  2  forms solidified shells, and strip S is sent downwards from the casting roll gap. The rate of cooling of the molten metal is however limited by the heat conductivity from the circumferential surfaces to the cooling channels. 
   Thus, it is apparent that it would be advantageous to provide an alternative apparatus and method to provide more efficient casting of melt strip. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
   SUMMARY OF THE INVENTION 
   An apparatus and method are disclosed for casting metal strip having a pair of laterally positioned novel casting rolls forming a nip between them. A molten metal supply system delivers molten metal into the nip between the casting rolls and forms a casting pool of molten metal supported on the casting rolls immediately above the nip. A pair of side dams, one at each end of the pair of casting rolls, confine the pool of molten metal and abut the axial end surfaces of the casting rolls. 
   Each casting roll has a cylindrical body with axial end surfaces. Each casting roll has a stepped cylindrical body where a cylindrical central portion has a larger outer diameter than adjacent cylindrical end portions that extend axially from each end of the central portion at a stepped shoulder portion. A plurality of longitudinal cooling passages extends from one axial end to the other axial end of the casting roll of the central portion at the stepped shoulder portion. The shoulder surfaces between the cylindrical central portion and the adjacent end portions have a plurality of circumferentially spaced cooling apertures therein with longitudinal cooling passages extending through the cylindrical central portion and terminating in one of the cooling aperture in the shoulder surfaces. Each cooling aperture is sealed by an enclosure. Each shoulder surface with the cooling apertures therein is capable of engaging a pool confining side dam. 
   The longitudinal cooling passages are closed by plugs. Further, radial cooling passages extend from a casting roll inner periphery and connect to a longitudinal cooling passage. Part of a radial cooling passage may extend axially towards the longitudinal cooling passages 
   In one embodiment, the plugs have a closed end and a hollow interior that opens into the longitudinal cooling passages. The plugs may also have a side aperture that connects with the radial cooling passages. The plugs may be threaded into the cooling passages and may also have a heat-conducting grease between the plugs and the cooling passages. 
   In another embodiment, the plugs are disked-shaped. Snap-rings may be used to retain the plugs in place. 
   The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       FIG. 1  is a schematic drawing showing a vertical cross section of one embodiment of a continuous casting machine; 
       FIG. 2  is a schematic drawing showing an axial view of the casting rolls and stub shafts shown in  FIG. 1 ; 
       FIG. 3  is a schematic drawing showing a vertical cross section of a further embodiment of a continuous casting machine; 
       FIG. 4  is a schematic drawing showing a vertical cross section of an additional embodiment of a continuous casting machine; 
       FIG. 5  is a schematic drawing showing the relative positions of the longitudinal cooling channels, radial cooling channels and plugs shown in  FIG. 4 ; 
       FIG. 6  is a schematic drawing showing a vertical cross section of a prior art continuous casting machine; and 
       FIG. 7  is a schematic drawing showing an axial view of the casting rolls and stub shafts of the prior art continuous casting machine shown in  FIG. 6 . 
   

   DETAILED DESCRIPTION 
   Shown in  FIGS. 1 through 5  are cylindrical casting rolls with a central portion and shoulder portions adjacent side dams. The casting rolls have longitudinal cooling channels extending through each of the central portions of the casting rolls from one shoulder portion where the side dam is positioned to the other shoulder portion where the other side dam is positioned. Radial cooling channels pass through each of the casting rolls from inner circumferential surfaces of the casting rolls at positions that are close to the surfaces of the shoulder portions of the casting rolls to communicate with the longitudinal cooling channels. Cylindrical plugs, with closed base ends, engage the ends of longitudinal cooling channels with an open interior end of the plugs facing inwards towards the centers of the longitudinal cooling channels. The plugs include through orifices linking the longitudinal cooling channels and the radial cooling channels, whereby cooling water flows sequentially through a radial cooling channel, a longitudinal cooling channel, and another radial cooling channel at the opposite end of the casting roll. 
   Also disclosed are cylindrical casting rolls with axial end surfaces contacting the side dams, having longitudinal cooling channels that extend through the casting roll from the surface at the end of the casting roll in contact with the side dams to the surface of the casting roll at the other end also in contact with the side dams. Radial cooling channels extend through each of the casting rolls from an inner circumferential surface of the casting rolls close to the end surfaces of the casting rolls and connect with the longitudinal cooling channels. Cylindrical plugs engage the end parts of the longitudinal channels, whereby cooling water flows sequentially through a radial cooling channel, a longitudinal cooling channel, and another radial cooling channel at the opposite end of the casting roll. 
   Furthermore, also disclosed are cylindrical casting rolls whose shoulder portions are adjacent side dams, and having longitudinal cooling channels extending through the end surface adjacent the side dam at one end of the casting roll to and through the end surface at the other end of the casting rolls adjacent the side dam. Radial cooling channels extend through each of the casting rolls from the inner circumferential surfaces in the vicinity of the casting roll end towards the casting roll end surfaces and communicate with the longitudinal cooling channels. Plugs with end surfaces formed into concave hollowed out portions and with the concave portions being directed inwards towards the centers engage the end parts of the longitudinal cooling channels, whereby cooling water flows in sequence through a radial cooling channel, a longitudinal cooling channel, and another radial cooling channel at the opposite end of the casting roll. 
   In other words, the longitudinal cooling channels are formed to extend from the first end surface of the shoulder portion of the casting rolls, adjacent a first side dam, to the second end surface of the shoulder portion of the casting rolls, adjacent a second side dam, allowing the distance between the outer circumferential surface of the casting rolls and the longitudinal cooling channels to be less than with cooled casting rolls in the past. As a result, the heat can be much more efficiently transferred from the molten metal in a casting pool to the cooling water in the casting roll. 
   Moreover, the radial cooling channels that extend from the inner circumferential surfaces of the casting rolls to the longitudinal cooling channels are positioned near the end surfaces of the casting rolls, with cooling water flowing through orifices in the cylindrical plugs and into the interior of the cylindrical plugs engaged with the ends of the longitudinal cooling channels. 
   Alternatively, cooling water may be introduced through cylindrical plugs attached to the end of the longitudinal cooling channels. As a further alternative, cooling water may flow through hollowed out portions of the plugs. 
   The novel casting rolls of the present invention provide the following effects.
         (1) Because the longitudinal cooling channels extend through each of the casting rolls from the positions at the end of the shoulder portions, adjacent the side dams, to the positions at the other end of the shoulder portions, adjacent the other side dam, the distance between the longitudinal cooling channels and the outer circumferential surfaces of the casting rolls is small, and the outer circumferential surfaces of the casting rolls are more efficiently cooled.   (2) Because the cylindrical plugs engage the end parts of the longitudinal cooling channels and the cooling water is caused to flow continuously through the interiors of the plugs, the end portions of the outer circumferential surfaces in the vicinities of the plugs, the casting rolls are more efficiently cooled.   (3) Because the cylindrical plugs engage the end parts of the longitudinal cooling channels and the cooling water may be, if desired, in direct contact with the inner circumferential surfaces of the end portions of the longitudinal cooling channels, the end portions of the outer circumferential surfaces in the vicinity of the ends of the casting rolls are more efficiently cooled.   (4) Because hollowed out portions are formed in the plugs that engage the ends of the longitudinal cooling channels, and the radial cooling channels that extend from near the ends of the inner circumferential surfaces of the casting rolls to the end surfaces of the casting rolls, and cooling water is caused to flow through the hollowed out portions of the plugs, the end portions of the outer circumferential surfaces of the casting rolls are more efficiently cooled through the plugs.   (5) Because of the enhanced cooling of the outer circumferential surfaces of the casting rolls, the speed of the casting rolls may be increased and the productivity of cast strip may be increased.   (6) In addition, because of the enhanced cooling of the outer circumferential surfaces of the casting rolls, additional thickness of metal between the longitudinal cooling channels and the outer circumferential surfaces of the casting rolls can be provided for casting roll maintenance. Periodically, the surfaces of the casting rolls require machining to maintain the surfaces. The additional thickness of metal over the longitudinal cooling channels allows the casting roll described hereinto be re-machined more times, thereby extending the casting roll life. In one embodiment, the thickness of the casting roll available for machining increased from about 7.5 mm to about 8.5 to 10 mm while maintaining the increased cooling efficiency of the disclosed casting rolls.       

     FIGS. 1 and 2  show a continuous caster with the disclosed novel casting rolls disclosed herein. Such casting machines having casting rolls  12 , the outer diameters of which are greater at the central portions than at the shoulder portions  28  at the ends. The end surfaces of the central portions whose outer diameters are greater at the shoulder portions  28  may be in contact with side dams  11 . The hollow stub shafts  13  axially engage the two end portions of the casting rolls  12  have diameters similar to the outer diameters of the two end portions of the casting rolls  12  at the shoulders. 
   Longitudinal cooling channels  14  pass through the casting roll  12  from the end surface  28  of the larger diameter portion of one casting roll end adjacent the first side dam  11  to the other end surface (not shown) of the larger diameter portion of the casting roll end adjacent the other side dam  11 . Radial cooling channels  15  extend radially through the casting roll  12  from an inner circumferential surface of the casting roll near the end surface or shoulder  28  of the casting roll  12  and connect with the longitudinal cooling channels  14 . 
   The longitudinal cooling channels  14  may be disposed substantially equidistantly circumferentially in the casting roll  12   
   Furthermore, cylindrical plugs  16 , with a closed outer end  16   a  close both ends of the longitudinal cooling channels  14 . A hollow open end  16   b  of the plugs  16  faces towards the center of the longitudinal cooling channels  14 . 
   Apertures  17  are formed diametrically through side of plugs  16  and connect with the longitudinal cooling channels  14  via hollow open ends  16   b . The outer surface of the plugs  16  can be threaded to attach plugs  16  to the longitudinal cooling channels  14 . O rings or other sealing materials may be used to seal plugs  16  to the longitudinal cooling channels. 
   When the plugs  16  are threaded into cooling channels  14 , they may be coated with heat-conducting grease, such that heat-conducting grease is interposed between the outer circumferential surfaces of the plugs  16  and the inner circumferential surfaces of the longitudinal cooling channels. 
   Plug  16  is hollow and a radial cooling channel  18  extends from an inner circumferential surface of stub shaft  13  in such a manner that cooling water W flows continuously in sequence of through first radial cooling channel  18 , into hollow plug  16  through aperture  17 , then into longitudinal cooling channel  14 , into hollow plug  16  at the opposite end of cooling channel  14 , through aperture  17  and into the other radial cooling channel  18  and back to the hollow interior of stub shaft  13 . 
   Alternatively, plug  16  may not include aperture  17  with the radial cooling channel  18  extending into cooling channel  14 . 
   Moreover, in the machining of the base end surface of the plug  16  and the end surface  28 , the plug  16  may be inserted with the closed end  16   a  recessed below surface  28 . Then the end surface  28  may be finished until it is flush with the base end surface  16   a . Or the plug  16  may be inserted such that the base end surface  16   a  protrudes from the longitudinal cooling channels  14 , and then the plug  16  and the end surface  28  are both machined until both are flush. 
   In the continuous casting machine, the pair of casting rolls  12 , stub shafts  13  and plugs  16  are positioned laterally to each other, and in such a manner that the casting roll gap may be adjusted according to the thickness of the strip S that is to be manufactured. The side dams  11  may be respectively in contact with the first end surface  28  and the other end surface  28  containing plugs  16 . 
   In such continuous caster, heat is removed from the casting rolls  12  by cooling water W flowing through the radial cooling channels  15  and the longitudinal cooling channels  14  while molten metal is poured into the space above the nip confined by the side dams  11  and the casting rolls  12  to form a casting pool of molten metal M. As the casting rolls rotated, the metal that has been cooled by the outer circumferential surfaces of the casting rolls  12  forming solidified shells, and forming strip S at the nip sent downwards from the casting roll gap. 
   The longitudinal cooling channels  14  extend from the first end surface  28  of the casting rolls  12  that may be in contact with the first side dam  11  to the second end surface  28  of the casting rolls  12  that may be in contact with the second side dams  11 . Hence it is possible to provide a small gap T 3  between the longitudinal cooling channels  14  and the outer circumferential surfaces of the casting rolls  12 , while maintaining contact T 4  of the side dams  11  with the end surfaces of the portions of casting rolls  12  that are of greater diameter at the shoulder portions. 
   Thus the cooling water W passes through the longitudinal channels of the casting rolls  12  can effectively cool the outer circumferential surfaces of the casting rolls  12 . 
   Furthermore, an embodiment is provided in which the cooling water W flows into the interiors of the cylindrical plugs  16  through apertures  17  from the radial cooling channels  15  positioned near the end surfaces  28 . The outer circumferential surfaces of the casting rolls  12  near end surfaces  28  are cooled more efficiently because heat conducting grease is interposed between the outer side surfaces of the plugs  16  and the inner side surfaces of the longitudinal cooling channels  14 . 
   In this manner, in the casting rolls shown in  FIG. 1  and  FIG. 2 , the surface temperature of the outer circumferential surfaces of the casting rolls  12  are reduced, and the speed of the casting rolls  12 , which is to say the speed of casting, can be increased and the productivity of strip S can be raised. 
     FIG. 3  is a second example of a continuous casting machine with similar casting rolls as shown in  FIG. 1 , and the same symbols in the drawings represent the same parts as in  FIG. 1  and  FIG. 2 . 
   In this embodiment, disc-shaped plugs  19  may engage each end of the longitudinal cooling channels  14 , such that the radial cooling channels  15  communicate with the longitudinal cooling channels  14  in place of the plugs  16  described above. 
   The plugs  19  are fixed to the casting rolls  12  by snap rings  20 , sealing members such as O rings and the like are inserted between the plugs  19  and the inner circumferential surfaces of the longitudinal cooling channels  14 . Cooling water W flows continuously in sequence through the first radial cooling channel  15 , the longitudinal cooling channel  14  and then into the other radial cooling channel  15  connected with the longitudinal cooling channel  14 . 
   The continuous casting machine employing the casting rolls described above efficiently removes heat from the casting rolls  12  through the cooling water W that flows into the radial cooling channels  15  and the longitudinal cooling channels  14 , while the molten metal is poured into the space above the nip formed by the side dams  11  and the casting rolls  12 . 
   The longitudinal cooling channels  14  extend from the first end surface  28  of the casting rolls  12  that may be in contact with the first side dams  11  to the second end surface  28  of the casting rolls  12  that may be in contact with the second side dams  11 . It is therefore possible to reduce the gap T 3  between the longitudinal cooling channels  14  and the outer circumferential surfaces of the casting rolls  12 , while maintaining the level of contact T 4  of the side dams  11  with the end surfaces  28  of the portions of casting rolls  12  at the shoulder portion. 
   Consequently, the cooling water W passes through the longitudinal channels of the casting rolls  12 , and effectively cools the outer circumferential surfaces of the casting rolls  12 . 
   Furthermore, an embodiment is provided where the cooling water W flows into the ends of the longitudinal cooling channels  14  via radial cooling channels  15  from the inner circumferential surfaces of the casting rolls to the longitudinal cooling channels  14  near the end surfaces  28  of the central portions of the casting rolls  12 . Therefore, the outer circumferential surfaces at the end portions of the casting rolls  12  are more efficiently cooled. 
   In this manner, in the casting rolls shown in  FIG. 3 , the temperature of the outer circumferential surfaces of the casting rolls  12  are reduced, and the speed of the casting rolls  12 , which is to say the speed of casting, can be increased and the productivity of strip S (see  FIG. 2 ) can be raised. 
     FIG. 4  and  FIG. 5  are a third example of a continuous casting machine that employs the disclosed casting rolls, and the same symbols in the drawings represent the same parts as in  FIGS. 1 to 3 . 
   Longitudinal cooling channels  14  extend through the casting rolls  12  from one end surface  28  that may contact the side dam  11  to the other end surface  28  that may also contact the other side dam  11 . Radial cooling channels  21  extend radially from the inner circumferential surface of the casting rolls towards outer diameter of the central portion of the casting rolls  12  and connect with the longitudinal cooling channels  14 . 
   The longitudinal cooling channels  14  may be disposed substantially equidistantly circumferentially in the casting roll  12 , and the radial cooling channels  21  may extend radially in relation to the center portion of the casting roll  12 . 
   Furthermore, plugs  22  engage both ends of the longitudinal cooling channels  14 , and have concave hollowed out parts  23  that face towards the centers of the longitudinal cooling channels  14  formed in the end surfaces of the plugs  22 . 
   The outer circumferential surfaces of the end portions of the plugs  22  are threaded to screw into corresponding threads in the inner circumferential surfaces of the longitudinal cooling channels  14 . O rings or other sealing materials may also used to seal plugs  22  to cooling channels  14 . 
   Plugs  22  may be coated with heat-conducting grease such that the heat-conducting grease is interposed between the outer side surfaces of the plugs  22  and the inner side surfaces of the longitudinal cooling channels  14  that face towards the plugs. 
   In the continuous caster employing the novel casting rolls described above, cooling water W flows through the radial cooling channels  21  and into the longitudinal cooling channels  14 , which extracts heat from the casting rolls  12  as the molten metal is poured into the space enclosed by the side dams  11  and the casting rolls  12 . 
   The longitudinal cooling channels  14  extend from the first end surfaces  28  of the casting rolls  12  at the shoulder portions, adjacent the first side dams  11 , to the second end surfaces  28  of the casting rolls  12  at the opposite shoulder portion, adjacent the second side dams  11 . Therefore, it is possible to reduce the gap T 3  between the longitudinal cooling channels  14  and the outer circumferential surfaces of the casting rolls  12 , while maintaining the desired level of contact T 4  of the side dams  11  with the end surfaces  28  of casting rolls  12 . 
   Thus the cooling water W passes through the longitudinal channel near the surface layer parts of the casting rolls  12 , and effectively cools the outer circumferential surfaces of the casting rolls  12 . 
   Furthermore, an embodiment is provided in which the radial cooling channels  21  extend such that cooling channels  21  communicate obliquely with hollowed out parts  23  formed in the leading end surfaces of the plugs  22 , so that the cooling water W is conducted into and out of the hollowed out parts of the plugs  22  causing more efficient cooling of the end portions of the outer circumferential surfaces of the casting rolls  12 . To further improve the removal of heat, heat conducting grease may be used between the outer side surfaces of the plugs  22  and the inner side surfaces of the longitudinal cooling channels  14 . 
   Due to the increased cooling effect on the outer circumferential surfaces of the casting rolls  12  in the casting rolls shown in  FIG. 4  and  FIG. 5 , the speed of the casting rolls  12 , that is to say, the casting speed can be increased and the productivity of the strip S (see  FIG. 2 ) can be raised. 
   The generality of the casting rolls as claimed herein are not limited to the modes of implementation described above, and naturally modifications may be made thereto provided only that they do not breach the spirit of the invention. 
   The casting rolls disclosed herein may be employed for the continuous casting of various metals such as steel in particular.