Abstract:
A system for transferring a steel slab from a first roller table to a second roller table by lifting the top slab from a stack of slabs on the first table, and then transferring and lowering the slab onto the second table. Specifically, a gantry-type bridge trolley mechanism having suspended electromagnets is provided that is motor driven on a cantilevered runway over the slab unpiler table and the furnace table. A stabilizer system minimizes sway of the electromagnets and the slabs.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional application No. 60/271,601 filed Feb. 26, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a system for transferring objects. In particular, the present invention relates to a system for transferring steel slabs. 
     BACKGROUND OF THE INVENTION 
     Steel slabs are semi-finished products obtained in the steel industry. A typical slab may weigh between 20 and 50 tons. Subsequent to casting, slabs are sent to a hot stripmill to be rolled into coiled sheet and plate products. 
     In a prior arrangement, stacks of steel slabs of various lengths are received from an overhead crane at a slab receiving roller table in a slab receiving area of a hot strip mill. Typical stacks consist of five slabs. The stack is then transferred by roller tables to a slab unpiler roller table. The slab unpiler table is lowered so that the bottom of the top slab of the stack is approximately level with the top of a parallel furnace charging table. Each slab is transferred perpendicularly to the rolling direction from the slab unpiler table to the furnace charging table by a pushing mechanism. The pushing mechanism pushes each slab across the slab upon which it is resting (unless it is the bottom slab of the stack) and onto the furnace charging table. Often slabs are bowed and at ambient temperature can also be at 1000° F. when hot charging is required. 
     Problems arise in that pushing slab over slab or directly over the roller table causes marking, etching and deformation of the slabs, which in turn affects the quality of the end product. Also, the pusher system typically cannot maintain the production time required by the pre-heat furnaces. 
     Accordingly, an advantage exists for a system to transfer slabs efficiently while minimizing damage. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for transferring a steel slab from a first roller table to a second roller table by lifting the top slab from a stack of slabs on the first table, and then transferring and lowering the slab onto the second table. Specifically, in a presently preferred embodiment, the present invention provides a gantry-type bridge trolley mechanism that is motor driven on a cantilevered runway over the slab unpiler table and the furnace charging table. The cantilevered system provides a space-saving advantage by limiting the necessary supports to only one side of the roller tables. Alternatively, in situations where space is not a factor, a crane having supports on both sides of the roller tables could be provided. A lifting device on the trolley mechanism is powered by a self-contained hydraulic actuator with its own power source. The actuator is connected to a center lever arm that is mounted to a horizontal torsional shaft. Spaced on the horizontal shaft are at least two and preferably four additional lever arms. The lever arms are preferably but not necessarily spaced apart at an equal spacing (in instances using three or more arms). Spacing the lever arms unequally along the horizontal shaft ensures that the shortest slabs can be picked up. A vertical rod suspending an electromagnet is operationally connected to each additional lever arm. Each vertical rod and electromagnet combination is structurally designed to be able to support a slab. Although not required, it is desired to have at least two electromagnets pick up a slab for stability purposes. While in the most preferred embodiment four vertical arm and electromagnet combinations are provided, it should be apparent that other numbers are contemplated. Optionally, and preferably, each vertical rod includes a load cell which is operationally connected to a control unit to measure the weight of each slab. Each vertical rod is also provided with a stabilization system to eliminate sway of the vertical rods. While a single actuator preferably controls the vertical position of the electromagnets, each vertical rod and electromagnet combination may have independent actuators. 
     In operation, the trolley mechanism which is driven by powered wheels positions the electromagnets over the stack of slabs on the slab unpiler table. The hydraulic actuator lowers the electromagnets so that the electromagnets make magnetic contact with the top slab. The hydraulic actuator then causes the electromagnets to lift the slab. The trolley mechanism then positions the slab over the furnace charging table. The mechanism then lowers and releases the slab onto the furnace charging table. 
     A programmed control unit reads the slab&#39;s weight, lift and transfer path. 
     Lifting the slabs (as opposed to pushing them off the stack) minimizes marking and deformation of the slabs, enabling a higher quality end product. The present invention also provides increased production rates by transferring a 1000° F. slab in about 36 seconds as compared to the pushing mechanism transfer time of about 45 seconds. Production capacity is increased to 300 slabs in an 8-hour period. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention and its presently preferred embodiments will be better understood by way of reference to the detailed disclosure herebelow and to the accompanying drawings, wherein: 
     FIG. 1 is an elevational view of the slab handling transfer system of the present invention; 
     FIG. 2 is partial elevational view showing the lifting apparatus of the present invention; 
     FIG. 3 is a higher elevational view of the slab handling transfer system of the present invention; 
     FIGS. 4-9 are end views showing the sequence of movement of the system of the present invention; 
     FIG. 10 is a top view showing the system of the present invention having the electromagnets positioned over the slab transfer table; 
     FIG. 11 is a top view showing the system of the present invention having the electromagnets positioned over the furnace charging table; 
     FIG. 12 is a side elevational view of FIG. 10; and 
     FIG. 13 is a side elevational view of FIG.  11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 3, the general system  10  according to the invention is illustrated. Preferably the present system is provided to transfer steel slabs between a slab unpiler table  12  and a furnace charging table  14  spaced from and parallel to said slab unpiler table  12 . Furnace charging table  14  is positioned at the entrance of a pre-heat furnace (not illustrated). Slab unpiler table  12  and furnace charging table  14  are preferably conveyor roller tables. A cantilevered runway  16  extends from adjacent the furnace charging table  14  and across the furnace charging table  14 . A carriage or trolley mechanism  18  rides along the runway  16  and is supported by a pair of powered drive wheels  20 . A pair of lift wheels  22  on the trolley mechanism  18  provide additional support and also ride along the cantilevered runway  16 . When positioned at its most advanced position, the trolley mechanism  18  is positioned over the slab unpiler table  12  (FIGS.  6 - 9 ). When retracted, the trolley mechanism  18  is positioned over the furnace charging table  14 . When retracted further, the trolley mechanism  18  is positioned so that it is not above either table for maintenance purposes (FIGS.  4  and  11 ). 
     At the upper distal end of the trolley mechanism  18 , a horizontal mounted shaft  24  is provided having at least two and preferably four spaced lever arms  26 . A vertical rod  28  is connected to each lever arm and an electromagnet  30  is suspended at the lower end of each vertical rod. Preferably, the lever arms  28  are spaced apart at unequal intervals. Ideally, the two lever arms  28  positioned at the end of the horizontal shaft  24  nearest the furnace are spaced closer together than the other lever arms. This ensures the shortest slabs will be picked up by at least two electromagnets  30 . 
     A single hydraulic actuator  32  (as best seen in FIG. 2) is connected to a center lever arm  34  that is mounted on the horizontal shaft  24 . Actuation of the hydraulic actuator  32  causes the center lever arm  34  to pivot, thus, causing the horizontal shaft  24  to rotate which in turn causes the unequally spaced lever arms  26  to pivot. Pivoting of the unequally spaced lever arms  26  raises and lowers the vertical rods  28  and thus, the electromagnets  30 . 
     Each electromagnet  30  is suspended by at least one and preferably three chain linkages  36  to a horizontal disk  38  which is pivotally connected to the lower end of the vertical rod. This allows the electromagnet  30  to adjust its orientation to the slab. 
     A stabilization system  40  to eliminate sway of the vertical rods  28  is preferably provided. The stabilization system comprises a stabilization arm  42  connected to each vertical rod  28 . 
     Each stabilization arm  42  is pivotally connected at one end to a vertical post  44  which is connected to the underside of the trolley mechanism  18 . The opposite end of each stabilization arm  42  includes a curved down-turned portion  46  which is pivotally connected to the vertical rod  28  above the horizontal disc. The stabilization arm  42  limits the movement of the electromagnet  30  in the vertical plane and minimizes movement in the horizontal plane. 
     Each vertical rod  28  is also provided with a commercially available load cell  48  to weigh the slabs. The load cells  48  are operationally connected to a control unit (not illustrated). The force and timing of each electromagnet is set on the control unit to pick up only the top one slab at a time. 
     In operation, an overhead crane (not illustrated) deposits a stack of slabs S upstream of the unpiler table  12  (FIGS.  1  and  3 ). The stack is transferred to the unpiler table  12  by conveyor roller tables (FIGS.  1  and  3 ). The trolley mechanism  18  propelled by the power drive wheels  20  positions the electromagnets  30  over the slab stack on the unpiler table  12  (FIG.  6 ). The hydraulic actuator  32  advances causing the center lever arm  34  to pivot, thus, causing the horizontal shaft  24  to rotate which in turn causes the lever arms  26  to pivot downwardly. Pivoting of the lever arms  26  lowers the vertical rods  28  and thus, the electromagnets  30  so that at least two are in magnetic contact with the topmost slab on the stack (FIGS.  7  and  10 ). The number of electromagnets  30  in magnetic contact with the topmost slab depends on the length of the slab (and the number and arrangement of the electromagnets). It is not necessary for the electromagnets  30  to come in physical contact with the slab in order for the slab to be transferred by the electromagnets  30 . The hydraulic actuator  32  then retracts causing the center lever arm  34  to pivot, thus, causing the horizontal shaft  24  to rotate which in turn causes the lever arms  26  to pivot. Pivoting of the unequally spaced lever arms  26  raises the vertical rods  28  and thus, the electromagnets  30  so that the topmost slab is lifted off of the stack. Meanwhile the load cells  48  weigh the slab and transmit the weight data to the control unit. The trolley mechanism  18  then retracts and positions the slab over the furnace charging table  14  (FIG.  5 ). The electromagnets  30  now lower and release the slab onto the furnace charging table  14 . 
     If not otherwise stated herein, it may be assumed that all components and/or processes described heretofore may, if appropriate, be considered to be interchangeable with similar components and/or processes disclosed elsewhere in the specification, unless an indication is made to the contrary. It should be appreciated that the apparatus and methods of the present invention may be configured and conducted as appropriate for the application.