Abstract:
A transport path is defined by a plurality of consecutively arranged separately driven conveyor sections. A plurality of heat treating stations are spaced one from the other along the transport path. Coils are conveyed along the transport path through one or more of the heat treating stations. The speed at which the coils are conveyed on the separately driven conveyor sections is controlled to provide different transport and/or dwell times for the coils at different locations along the transport path.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from provisional patent application Ser. No. 60/831,874 filed Jul. 19, 2006. 
     
     BACKGROUND DISCUSSION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to continuous hot rolling mills producing coiled bar and rod products, and is concerned in particular with a coil handling system for centrally supporting and transporting the coils at variable rates of speed through successive stations where cooling is accelerated or retarded at controlled rates in order to impart selected metallurgical properties to the coiled products. 
         [0004]    2. Description of the Prior Art 
         [0005]    Conventional coil handling systems typically rely on continuous chain, walking beam or roller conveyors to transport upright coils through successive stations where cooling rates may either be accelerated or retarded. The coils are carried on pallets, and the conveyors operate at constant speeds. Transport times between stations, as well as the intervals during which the coils are exposed to thermally controlled station environments, are tied to the constant conveyor speeds. The conventional systems are thus incapable of accommodating thermal processes that require transport times between stations to vary independently of station dwell times that also may vary independently of each other. 
         [0006]    The stations of conventional coil handling systems also have been found to be unduly limited in their ability to cool the coils at the different rates required to achieve a wide range of metallurgical properties in the coiled products. 
         [0007]    Moreover, the upright coils are often somewhat unstable and as such are prone to toppling during transit. This is particularly the case with larger coils weighing two tons or more, and where the coiled product has a sulphur and lead content for use in automatic machines (so called “free cutting steels”). 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect of the present invention, a transport path is defined by a plurality of consecutively arranged separately driven conveyor sections. A plurality of heat treating stations are spaced one from the other along the transport path. Upright coils are conveyed along the transport path through one or more of the heat treating stations. The speed at which the coils are conveyed on the separately driven conveyor sections is controlled to provide different transport and/or dwell times for the coils at different locations along the transport path. 
         [0009]    According to another aspect of the present invention, one or more of the heat treating stations have tunnel enclosures with vented openings that are adjustable to achieve either retarded or accelerated cooling rates. Cooling rates may be accelerated still further by exposing the coils to forced air cooling as they progress through the tunnel enclosures. 
         [0010]    According to still another aspect of the present invention, the coils are formed around stems projecting upwardly from the supporting pallets. The stems provide stability for the coils as they progress along the transport path. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a plan view of an exemplary coil handling system in accordance with the present invention; 
           [0012]      FIGS. 2 and 3  are sectional views on an enlarged scale taken respectively along lines  2 - 2  and  3 - 3  of  FIG. 1 ; and 
           [0013]      FIG. 4  is a graph depicting cooling rates and transport and dwell times. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  depicts an exemplary layout of the delivery end of a rolling mill producing hot rolled steel bars. The hot rolled product is delivered from the rolling mill (not shown) along a path  10  leading to shears  12  which serve to crop and subdivide the product into customer lengths. The subdivided lengths are then subjected to cooling in a water box  14  before being alternately directed by a switch  16  to one or the other of two pouring reels  18  which form the product lengths into upstanding coils at a coil forming station A. A rotary table  20  then transfers the coils to the first leg  22   a  of a conveyor system  22  defining a transport path. 
         [0015]    The conveyor system comprises a series of individually driven conveyor sections indicated typically at  24  which preferably will comprise short roller tables. Because the conveyor sections are individually driven, their transport speeds can be adjusted to accommodate a wide range of thermal treatments for the product coils. 
         [0016]    A rotary roller table  26  serves to transfer the coils from the conveyor leg  22   a  to a second perpendicular leg  22   b  leading through a heat treating station B. With additional reference to  FIG. 2 , it will be seen that station B includes a tunnel enclosure  28  internally provided with a series of forced air cooling installations  30 . At each installation  30 , a motor driven fan  32  serves to drive ambient air through a duct  34  upwardly into the interior of a coil  36 . At station A, each coil is formed around a central stem  36  projecting upwardly from a pallet  40  on which the coil is supported. The stem  36  provides a central support which lends stability to the coil as it progresses along the transport path. A vertically adjustable louvered cap  42  serves to redirect the air flow radially outwardly through the coil, and external louvers  44  in the tunnel walls and roof serve to further control air flow. An external drive  46  serves to manipulate the louvers over a range of adjustments between fully open and fully closed positions. With the louvers  44  fully open and the fans  32  in operation, the coils  36  are subjected to cooling at an accelerated maximum rate. Conversely with the fans  32  shut down and the louvers  44  closed, the coils undergo retarded cooling at a greatly reduced minimum rate. A myriad of cooling rates are possible between these two extremes. 
         [0017]    With reference again to  FIG. 1 , side shift transfer cars  48  receive the coils from station B and serve either to transfer them to any one of several processing lines  50   a ,  50   b ,  50   c , and  50   d  at a second heat treating station C, or to bypass station C and transfer the coils to a conveyor leg  22   c  which leads to remote hook carriers and packaging equipment (not shown). Side shift transfer cars  49  receive coils from the process lines  50   a ,  50   b ,  50   c , and  50   d  and also serve to convey them to the conveyor leg  22   c.    
         [0018]    It will be seen from  FIG. 3  that the processing lines  50   a ,  50   b ,  50   c , and  50   d  each comprise louvered tunnel enclosures of the type provided at station B, but without associated cooling stations fed by forced air fans. For illustrative purposes, the louvers of processing line  50   a  are shown fully open, those of processing line  50   b  are shown partially open, and those of processing lines  50   c  and  50   d  are shown fully closed. These different adjustments respectively achieve progressively slower cooling rates. 
         [0019]    By subdividing the conveyor system into individually driven segments, transport times between heat treating stations can be different from and beneficially faster than the transport times through the stations, the latter times being selected to coact with the rate of cooling at each station in order to achieve desired metallurgical properties in the coiled products. 
         [0020]    Thus, as shown in  FIG. 4 , the transport time t 1  between heat treating stations A and B can be relatively brief in order to limit uncontrolled cooling during that interval. The transport time t 2  through station B can be selected to achieve the desired metallurgical objective, and transport time t 3  between stations B and C can again be beneficially brief. Transport time t 4  at station C can be prolonged to again achieve the desired metallurgical objectives, and transport time t 5  can be selected to dovetail with prior process steps and to insure that the coils are delivered in a timely and coordinated sequence to the downstream hook carriers and packaging equipment. 
         [0021]    In a typical mill environment, and by way of example only, hot rolled steel bar products are received along path  10  at temperatures on the order of 1000° C. The products are formed into coils at station A at temperatures ranging from 800°-1000° C., and are cooled to temperatures of about 600°-700° C. at station B. Retarded cooling at rates of between 0.2° to 0.5° C./sec. may then take place at station C for extended periods of up to twenty four hours. 
         [0022]    In light of the foregoing, it will be understood by those skilled in the art that the layout shown in  FIG. 1  is merely exemplary and is not intended to be limiting in the number and type of equipment components, the manner in which they are arranged, or their method of employment. Although the conveyor system has been shown as a series of individually driven roller tables, other individually driven segments such as short chain conveyor sections and short carryover beam sections could serve as equivalents. Similarly, although the tunnel enclosures have been shown with louvered openings, other mechanisms for adjusting the openings could serve as equivalents, non limiting examples being slidable doors, mutually slidable foraminous plates, etc. Also, for certain metallurgical treatments, heat may be added to the tunnel enclosures, either to further retard cooling rates or to maintain a desired soaking temperature for prolonged periods.