Abstract:
Discrete billets are rolled through a plurality of roll stands arranged along a rolling mill pass line to produce successive product lengths having reduced cross sections and front and tail ends. At a selected location along the pass line, the tail end of each product length is joined to the front end of the next successive product length to thereby permit uninterrupted continuous rolling through the remainder of the mill.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority of provisional application Serial No. 60/378,757 filed May 8, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to the production of bar and rod products in continuous rolling mills by hot rolling discrete billets through roughing, intermediate and finishing mill sections, and is concerned in particular with a method and apparatus for the end-to-end welding of separate product lengths at a selected location along the rolling line, thereby making it possible to continue rolling uninterruptedly throughout the remainder of the mill.  
           [0004]    2. Description of the Prior Art  
           [0005]    In conventional bar and rod rolling mills currently in operation, the accepted practice is to begin the process with individual billets that are heated in a furnace and then discharged for separate rolling into product lengths having reduced cross sectional areas and front and tail ends. A number of drawbacks are associated with this practice. For example, the gap time between billets can account for as much as 10% lost production time.  
           [0006]    Also, the front and tail ends of each product length are dimensionally and/or metallurgically unacceptable and must therefore be trimmed and discarded, resulting in considerable scrap losses. The front ends are also prone to cobbling, particularly at the higher speeds reached in the finishing section of the mill.  
           [0007]    In an effort at avoiding these problems, technology has been developed to weld the billets end-to-end before they are introduced in the mill. However, this too has proven to be somewhat problematical. Welding of the large billet cross sections requires massive equipment and a heavy consumption of electrical energy. Excessive electrical energy is additionally required to inductively reheat the billet segments that have been chilled by contact with the heavy clamping devices required to force the billet ends together.  
           [0008]    A further drawback with billet welding stems from the fact that the fused metal at the welded joint is subsequently rolled into a substantial length of the finished product. For example, when billets having a typical cross sectional area of 22,500 mm 2  are welded and then rolled into 5.5 mm rod, the fused metal of the welded joint will extend through approximately 94 meters of the finished product. If the billets are metallurgically dissimilar, this length may well have to be scrapped, at a considerable loss to the mill operator.  
           [0009]    The present invention applies welding technology to the rolling process in a manner and at a location along the rolling line that avoids or at least significantly minimizes the problems and disadvantages associated with current practices. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a plan view of one embodiment of an apparatus in accordance with the present invention;  
         [0011]    FIGS.  2 A- 2 J are diagrammatic views showing successive stages in the operation of the apparatus depicted in FIG. 1;  
         [0012]    [0012]FIG. 3 is a plan view of an alternative embodiment of an apparatus in accordance with the present invention; and  
         [0013]    [0013]FIG. 4 is an enlarged cross section taken along line  4 - 4  of FIG. 3 and schematically depicting the stacked storage capacity of the accumulator. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    With reference initially to FIG. 1, first and second vertical and horizontal roll stands  10  and  12  are shown positioned along a mill pass line “P”. Roll stand  10  may, for example comprise the last roll stand of the mill&#39;s roughing section, and stand  12  may comprise the first roll stand of the mill&#39;s intermediate section. The delivery speed of roll stand  10  will exceed the take-up speed of roll stand  12 . Thus, in an exemplary operation, with a mill rolling a 2000 kg billet at a rate of 150 metric tons per hour, roll stand  10  would produce a bar having a cross sectional area of 57.4 mm at a delivery speed of 2052.5 mm/sec. The take up speed of roll stand  12  would be 1642 mm/sec.  
         [0015]    Switches  11  are arranged to direct successive product lengths exiting from roll stand  10  away from the mill pass line P and along an entry path  14  leading to a welding station  16 , and from the welding station along a delivery path  15  back to the mill pass line for continued rolling in the roll stand  12  and all subsequent roll stands (not shown). Alternatively, the switches  11  may be operated to bypass the entry path  14  and to thereby allow discrete product lengths to continue along the pass line P.  
         [0016]    A first storage means in the form of a repeater  18  is located along the delivery path  15 , and a second storage means, also in the form of a repeater  20  is located along the entry path  14 . The repeaters  18 ,  20  may be of conventional design well known to those skilled in the art.  
         [0017]    The welding station  16  includes a welder  22  configured to weld abutting trailing and leading ends of product lengths. The welded joints are deburred by a deburring device  24  before continuing along delivery path  15 . The welded joints and adjacent product segments may, if necessary, be reheated in advance of roll stand  12  by an induction heater  26 . Driven pinch rolls  28 ,  30 ,  32  and  34  are strategically positioned to control the forward movement of the product lengths being processed.  
         [0018]    The operation of the apparatus will now be described with reference to FIGS.  2 A- 2 J.  
         [0019]    [0019]FIG. 2A 
         [0020]    A first product length A is being rolled through roll stand  10  at a rate of 150 tons per hour and a speed of 2052.5 mm/sec. The product length A has passed along entry path  14 , through the welding station  16  and along delivery path  15 , and its front end A FE  has arrived at pinch roll unit  34  where it has been temporarily stopped. A first portion of the first product length has begun to accumulate in the form of a loop A L  in repeater  18 .  
         [0021]    [0021]FIG. 2B 
         [0022]    The loop A L  in repeater  18  has increased considerably, and the front end A FE  of the first product length has now passed through pinch roll unit  34  into roll stand  12 . The rolling rate of roll stand  12  is 120 tons per hour, with a take in speed of 1642 m/sec.  
         [0023]    [0023]FIG. 2C 
         [0024]    The loop AL in repeater  18  has reached its maximum. The tail end A TE  of the first product length is just clearing roll stand  10 , and the front end B FE  of the second product length B is approaching roll stand  10 .  
         [0025]    [0025]FIG. 2D 
         [0026]    The tail end A TE  of the first product length A is now moving into the entry path  14  as the front end B FE  of the second product length B enters roll stand  10 .  
         [0027]    [0027]FIG. 2E 
         [0028]    The tail end A TE  of the first product length A and the front end B FE  of the second product length B have arrived at the welding station  16  where they are held stationary in an abutting relationship by pinch roll units  32 ,  30 . Welding of the front and tail ends begins.  
         [0029]    [0029]FIG. 2F 
         [0030]    While welding of the front and tail ends takes place, the loop A L  of the first product length in repeater  18  is gradually depleted, and the second product length B accumulates in a loop BL form in repeater  20 .  
         [0031]    [0031]FIG. 2G 
         [0032]    The welded front and tail ends have progressed from the welding station  16  to roll stand  12 , and the loop B L  previously accumulated in repeater  20  is now being transferred by the pinch roll units  30 ,  32  to repeater  18 .  
         [0033]    [0033]FIG. 2H 
         [0034]    As transfer of the product loop B L  from repeater  20  to repeater  18  continues, the tail end B TE  of the second product length arrives at roll stand  10 .  
         [0035]    [0035]FIG. 21 
         [0036]    As described previously with reference to FIG. 2D, the tail end B TE  of the second product length is now moving into the entry path  14  as the front end C FE  of a third product length C enters roll stand  10 .  
         [0037]    [0037]FIG. 2J 
         [0038]    Welding of the tail end B TE  of the second product length to the front end CFE of the third product length has commenced, as described previously with respect to FIG. 2E.  
         [0039]    The pinch roll units  28 ,  30 ,  32  and  34  are individually driven and thus may be selectively controlled to accelerate, decelerate and stop the successive product lengths in order to effect the above described movements. Although welding is preferably accomplished with the front and tail ends arrested at station  14 , alternatively, the pinch roll units  30 ,  32  could be operated to simply slow the front and tail ends, with the welder  22  being movable at the same speed to effect welding on the fly.  
         [0040]    Once a lead product is fed to roll stand  12 , uninterrupted rolling continues thereafter in that stand and any subsequent stands throughout the remainder of the mill.  
         [0041]    Welding of front and tail ends with reduced cross sectional areas at station  16  can be achieved quickly, with minimum consumption of energy, and with smaller, less expensive welding equipment.  
         [0042]    [0042]FIGS. 3 and 4 illustrate an alternative embodiment of the invention, where components identical to those of the FIG. 1 embodiment have been identified by the same reference numerals. Here, the repeater  20  of the first embodiment has been replaced by a multilevel accumulator  40 .  
         [0043]    It will be seen from FIG. 4 that the accumulator comprises vertically stacked pairs of guide rollers  42  arranged around a circular footprint  44 . The guide rollers define a helical delivery path  46  configured and dimensioned to provide a product storage capacity comparable to that of the repeater  20  of the FIG. 1 embodiment.  
         [0044]    In light of the forgoing it will now be understood by those skilled in the art that the present invention operates to divert successive product lengths exiting from roll stand  10  away from the pass line P and along entry paths  14  (or  46 ) to the welding station  16 , and from the welding station along a delivery path  15  back to the pass line for continued rolling in roll stand  12 . Repeater  18  operates in conjunction with pinch roll units  32  and  34  on the delivery side of the welding station to temporarily store a first accumulation of one product length and to arrest or slow the trailing end of that product length at the welding station.  
         [0045]    Repeater  20  (or accumulator  44 ) operates in conjunction with pinch roll units  28  and  30  on the entry side of the welding station to arrest or slow the leading end of the next product length at the welding station, and to temporarily store a second accumulation of that product length.  
         [0046]    The first and second product accumulations allow sufficient time for welding the arrested or slowed tail and front ends at the welding station. Thus, a continuous product is fed to roll stand  12  from the discrete product lengths being received from roll stand  10 .  
         [0047]    The present invention is most advantageously employed to join product lengths having reduced cross sectional areas ranging from about 700-4400 mm 2 . Here, the fused metal of the welded joints will extend through relatively small lengths on the order of 3-18 meters. Thus, even when billet lengths having dissimilar metallurgy are being welded, scrap losses will be minimized in comparison to those experienced when welding billets prior to rolling.