Abstract:
A method and apparatus is disclosed for temporarily interrupting the passage of a long product between upstream and downstream paths in a rolling mill. Product passing along the upstream path is delivered onto a cylindrical drum. The drum is rotated in one direction to accumulate the product thereon in a series of windings. The direction of drum rotation is then reversed to unwind and deliver the accumulated product to the downstream path.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from provisional application Ser. No. 60/478,520 filed Jun. 13, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to rolling mills in which billets are continuously hot rolled into long products, and is concerned in particular with a method and apparatus for temporarily interrupting the passage of such products between upstream and downstream paths within the mill.  
         [0004]     2. Description of the Prior Art  
         [0005]     As herein employed, the term “long products” includes bars, rods and the like, and does not include flat products, examples being slabs and strips.  
         [0006]     The present invention may be employed to solve problems existing in both nonferrous and ferrous rolling mill environments. For example, in a nonferrous mill employing “up casting” systems, the cast product is delivered upwardly from the casting wheel. This has the advantage of producing high quality products containing minimum amounts of oxides. However, this advantage is, to some extent, offset by slow delivery speeds on the order of 3-10 feet/minute. Problems relating to product heat loss and fire cracking of work rolls preclude the introduction of such slow moving cast products directly into a rolling mill.  
         [0007]     There exists a need, therefore, for a method and apparatus that makes it possible to operate upcasting systems with relatively slow delivery speeds in direct sequence with rolling mills having higher take in speeds.  
         [0008]     Different problems are encountered in ferrous rolling mills, where typically, billets are heated to an elevated rolling temperature in a furnace. The heated billets are then subjected to continuous rolling in successive roughing, intermediate and finishing sections of the mill, with each mill section being comprised of multiple roll stands. For larger finished products, the entire mill can usually be operated at or close to the maximum capacity of the furnace. However, when the rolling schedule calls for smaller finished products, e.g., 5.5 mm rounds, the capacity of the finishing section is often reduced to well below that of the furnace and the roughing and intermediate mill sections. Under these circumstances, the roughing and intermediate sections can be slowed to match the capacity of the finishing section, but there are limits beyond which this becomes impractical. This is again because acceptable rolling procedure dictates that the heated billets should be introduced into the first stand of the roughing section at a minimum take in speed below which excessive heat loss and fire cracking of the work rolls can occur.  
         [0009]     In other cases, for example when rolling high speed tool steels or nickel based alloys, a higher take in speed is required to avoid excessive cooling of the billet, while lower finishing speeds are required to avoid excessive heat generation, which can cause core melting and surface cracking of the product.  
         [0010]     The size of the billet can be reduced in order to accommodate rolling at the maximum delivery speed of the mill and at a safe take in speed. However, this would require a new pass design for the roll stands, different guides, a lowering of the coil weight of the finished product, and a reduced production rate. The necessity to store different size billets would create further problems.  
         [0011]     Thus, in ferrous mills there also exists a need for a method and apparatus that will make it possible to roll smaller size products while maintaining the mill take in speeds at or above acceptable minimums, without having to reduce the size of the billets being processed, and preferably while continuing to roll at or close to the mill&#39;s maximum tonnage rate.  
       SUMMARY OF THE INVENTION  
       [0012]     In accordance with the present invention, a method and apparatus is provided for temporarily interrupting the passage of long products between upstream and downstream paths in a rolling mill. The products are delivered from the upstream path to a coil box having a cylindrical drum, and the drum is rotated in one direction to accumulate the product in a series of windings. The rotational direction of the drum is then reversed to unwind and deliver the accumulated product to the downstream path.  
         [0013]     In the nonferrous mill environment described above, multiple up casting systems are coupled to a single rolling mill. The output of each up casting system is received by a coil box of the present invention at the up casting system&#39;s relatively slow casting speed, and is temporarily accumulated before being delivered to the rolling mill at its higher take in speed. Operations of the casting systems are sequentially staggered to provide the rolling mill with a substantially constant supply of cast products.  
         [0014]     In the above described ferrous rolling mill environment, products emerging from the intermediate section of the mill are alternately switched to multiple coil boxes of the present invention. Each coil box feeds a separate mill finishing section. Products received at the relatively high delivery speed of the intermediate mill section are temporarily accumulated, alternately, by the multiple coil boxers, before being delivered at slower speeds to their respective finishing sections.  
         [0015]     The alternate use of multiple mill finishing sections, each fed by a coil box of the present invention, makes it possible to roll smaller sized products without having to reduce the furnace output or the size of the billets being rolled.  
         [0016]     These and other features and advantages of the present invention will now be described in greater detail with reference to the accompanying drawings, wherein:  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a plan view of a nonferrous mill layout embodying coil boxes of the present invention;  
         [0018]      FIG. 2  is a side sectional view of one of the up casting systems and its connection to the rolling mill;  
         [0019]      FIG. 3  is an enlarged plan view of one of the coil boxes spooler shown in  FIGS. 1 and 2 ;  
         [0020]      FIG. 4  is a vertical sectional view taken through the coil box shown in  FIG. 3 ;  
         [0021]      FIG. 5  depicts an exemplary timing sequence for the mill layout shown in  FIGS. 1-4 ;  
         [0022]      FIG. 6  is a plan view of a ferrous mill embodying the concepts of the present invention; and  
         [0023]      FIG. 7  depicts an exemplary timing sequence for the mill layout shown in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]     With reference initially to  FIGS. 1 and 2 , a mill layout includes a plurality of up casting systems  10 A,  10 B and  10 C respectively connected by delivery lines generally indicated at  12  to a common single strand rolling mill  14 .  
         [0025]     The up casting systems  10 A,  10 B and  10 C may be of any known type, such as that marketed by International Metals &amp; Chemical Group of Jenkintown, Pa. Each up casting system is configured to direct the cast product upwardly along a curved track  16  for delivery past the operative range of a shear  18  to a discharge table  20  at the entry end of a respective delivery line.  
         [0026]     As shown in  FIG. 2 , the discharge table  20  is pivotally adjustable between a horizontal position, as shown by the solid lines, and a raised position  20 ′ shown in dotted. When in its horizontal position, the table is aligned to deliver product to an “upstream” path  22  defined by a series of rollerized troughs. When in its raised position, the discharge table is configured to allow the cast product to pass downwardly via chute  24  to scrap bins  26 . The downwardly directed product is cut into scrap lengths by the shear  18 .  
         [0027]     Each upstream path  22  leads to a coil box  28 . As can be seen by further reference to  FIGS. 3 and 4 , each coil box includes a cylindrical drum  30  mounted on an elevator platform  32  for rotation about a vertical axis A. An externally toothed circular collar  34  on the base  36  of the drum  30  is engaged by a drive pinion  38  on the output shaft of a gear reducer  40 , which in turn is driven by a hydraulic motor  42  or the like. Motor  42  may be operated to rotate the drum  30  in either a clockwise and counterclockwise direction.  
         [0028]     The elevator platform  32  is vertically adjustable by any known mechanism, such as for example a scissor lift table  44  of the type supplied by Southworth of Falmouth, Me.  
         [0029]     Each coil box  28  additionally includes a pinch roll unit  46  mounted on a carriage  48  moveable around the drum axis A on curved guide rails  50 . The pinch roll unit  46  has driven pinch rolls  52  configured and arranged to grip and propel the cast product.  
         [0030]     A downstream path  54  defined by another series of rollerized troughs leads from each coil box  28  to the operative range of a receiving switch  56 . The switch  56  is pivotally adjustable to selectively communicate with and to direct product received from any one of the downstream paths  54  to the rolling mill  14 .  
         [0031]     Using as an example the operation of one of the up casting systems  10 A,  10 B or  10 C, during start up and until the cast product has stabilized dimensionally, the respective discharge table  20  is elevated to allow scrap pieces subdivided by the shear  18  to be directed downwardly into the bins  26 . When acceptable product is achieved, the discharge table is lowered to its horizontal operative position, and the cast product is directed along the upstream path  22  to the coil box  28  for winding on the drum  30 . The associated pinch roll unit  46  insures a constant feed of the product to the drum, and the drum is rotated at a peripheral speed matching the delivery speed of the caster while being gradually lowered during the winding process, with the rate of descent being approximately one product diameter per drum revolution.  
         [0032]     When one coil weight has passed by the shear  18 , the shear is activated to cut the product, and the rotational speed of the drum is accelerated to rapidly pull the remainder of the severed product length out of the upstream path  22 . Drum rotation is stopped when the tail end of the severed product length reaches the pinch roll unit  46 .  
         [0033]     The drum  30  is then rotated in the opposite direction through approximately 180°, with an accompanying travel of the carriage  48  around the guide rails  50  to thereby realign the pinch roll unit  46  with the downstream path  54 . The pinch roll unit is then operated in reverse to unwind the product from the drum at a speed matching that of the take in speed of the mill  14 , which typically will be about 60 feet per minute. The switch  56  will direct the unwinding product into the first mill stand.  
         [0034]     The troughs defining the upstream and downstream paths  22 ,  54  and the drums  30  may be heated, and an additional induction heater  58  and descaler  60  may be located between the switch  56  and the first roll stand of the mill  14 .  
         [0035]      FIG. 5  depicts an exemplary timing sequence for the sequential staggered operation of the mill layout shown in  FIGS. 1-4 . Assume that each casting system  10 A,  10 B,  10 C produces 10,000 lb of cast product having a 2.5″ diameter and a length of 529 feet during a 100 minute casting time. Assume further that the up casters have casting speeds of 5-8 feet/min., and that the take in speed of the rolling mill is 60 feet/min.  
         [0036]     After the shear  18  cuts the product, one minute and fifteen seconds is required to clear the severed product from the upstream paths  22 . Another one minute and forty seconds is consumed by reorientation of the drum  30  and carriage  48  to bring the pinch roll unit  46  into alignment with the downstream path  54 . Threading of the product into the mill takes twenty five seconds, and rolling of the coiled product takes eight minutes and forty five seconds. Another one minute and forty seconds is required to return the drum and pinch roll unit into position to receive the next product length. Thus, the total time elapsed between the cut of shear  18  and the return of the drum and pinch roll unit to the receiving position is thirteen minutes and forty five seconds. The time required for the lead end of the next product length to reach the pinch roll unit  46  is fourteen minutes and sixteen seconds.  
         [0037]     It will be seen, therefore, the by staggering the sequential operation of casting system  10 B by fourteen minutes and sixteen seconds, and casting system  10 C by twice this time, the rolling mill can be operated substantially continuously at its taking speed of 60 feet per minute, which is substantially higher than the 5-8 feet per minute delivery speed of the casting systems.  
         [0038]     In an exemplary ferrous rolling mill environment, as depicted in  FIG. 6 , a switch  56 ′ directs billet lengths of hot rolled product emerging from the last roll stand  62  of the intermediate mill section selectively along upstream paths  22 ′ to three coil boxes  28 A,  28 B and  28 C. Coil box  28 A is arranged to direct its output via path P 1  to mill finishing section  64 A, and alternatively to mill finishing section  64 B via path P 1 ′. Similarly, coil box  28 B is arranged to direct its output via path P 2  to mill finishing section  64 B, and alternatively to mill section  64 A via path P 2 ′. Coil box  28 C is arranged to feed finishing mill section  64 A via path P 2 ′, or finishing mill section  64 B via path P 1 ′.  
         [0039]     Typically, when the mill is set up to roll a small diameter product, e.g., 5.5 mm rod, the maximum delivery speed V 1  at roll stand  62  will exceed the maximum take in speed V 2  at the entry end of one mill finishing section, e.g., section  64 A. In order to avoid having to slow the mill down or switch to smaller billets, an additional mill finishing section  64 B is employed with three coil boxes  28 A,  28 B,  28 C. Each coil box can receive product from roll stand  62  at velocity V 1 , and deliver product to a selected one of the mill finishing sections at velocity V 2 . Assuming that V 1  is approximately twice V 2 , a typical timing sequence would be as shown in  FIG. 7 , where solid lines indicate time intervals for loading the coil boxes, and broken lines indicate the time intervals required to unload the coil boxes to the mill finishing sections. By appropriately staggering the delivery of billet lengths of product from roll stand  62  to the coil boxes  28 A,  28 B,  28 C, the entire mill, including the two finishing sections, can be operated substantially continuously.