Abstract:
A coil/capacitor combination useable as an induction furnace includes a reactive capacitor bank directly bolted to the coil and protected from coil fields by shields and heat sink plates. The coil includes a selectively openable switch for placing the coil assembly on and off of a moving strip. The switch is operated by deflecting coil turns within the natural resiliency of the turns themselves.

Description:
BACKGROUND OF THE INVENTION 
     The subject invention relates to electric induction furnaces for heat treating a running length of metal, such as steel or aluminum, and more particularly, to an improved assembly facilitating a greater convenience of coil movement on and off of the continuous strip. 
     Heating of a continuous strip with an induction furnace is well known. Commonly assigned U.S. Pat. No. 4,761,530 shows such an assembly. To the extent that the teachings of this patent can clarify or supplement the disclosure of the subject invention in this application, it is hereby incorporated by reference. Such heating assemblies have particular application in galvanizing or galvannealing operations, and the workpiece being treated is usually a running continuous strip of metal. Practical problems with such an operation concern the separation or removal of the furnace coils from about the strip without cutting the strip, or disassembling the heating apparatus. The &#39;530 patent noted above discloses one way of avoiding cutting or disassembly is to construct the coil to have a sidewall segment comprised of a hinged door, which door may be selectively opened or closed by a piston and cylinder actuator. When the door is closed, the coil is formed into a closed loop and can function as a normal solenoidal coil about the workpiece. When the door is opened, the loop has an open segment which will allow the coil to be moved off the strip for adjustment, maintenance or the like. The coil can also be moved back onto the strip, and then the door closed to form the closed loop and resume the intended heating operation. The &#39;530 patent shows a wheeled carriage assembly which supports the coil and facilitates the translation of the coil on or away from the strip when the coil door is opened. 
     There are two particular problems in the design of a furnace for this intended purpose. First, a running strip is a very dangerous item particularly for coolant hoses and electrical cables in that any contact with the running strip will result in a sawing action that can quickly cut the contacting item. Accordingly, the furnace design must be very careful to space the furnace components to avoid any such contact. An even better solution is to minimize the need for coolant hoses or electrical cables, particularly in the area of the strip. 
     The other problem is that in most induction coil applications, the current in the load coil is higher than other power components and the current is largely reactive. As such, it is advantageous to supply the reactive portion of the coil current from a capacitor bank located as close as possible to the induction coil to minimize the losses between the bank and the coil. Apart from the cable connecting problems mentioned above, the proximity to the coil enhances the consequences of the field effects of the coil on the bank. When such effects can cause an unacceptable heating of the bank, the prior art suggests spacing the bank away from the coil. 
     Another problem with the system shown in the &#39;530 patent above apart from the complexity itself with a hinged door, is that the nature of the high frequency currents in such an assembly are that they run on the inside surfaces of the coil. In the switch assembly of the &#39;530 patent the switch blades are disposed so that the current, instead of running down the wide part of the knife blade, actually runs down the edge of the knife. It is better that the switch can emulate a piece of bus bar, i.e., by providing a surface area greater than the knife edge, the more efficient and the lower the losses will be, for the connection. 
     The present invention contemplates a new and improved apparatus which overcomes all of the above-referred to problems and others to provide a new induction heating assembly for preferably heating a running strip which is simple in design, economical to manufacture, readily adaptable to a variety of dimensional characteristics, is rugged and reliable in its operation, provides improved heating efficiency, increased reliability and reduced assembly cost. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an electric induction heating assembly comprising an induction coil for heating a workpiece passing therethrough and a capacitor bank for supplying a reactive portion of current to the coil wherein the bank is disposed adjacent the coil and includes a housing configured for shielding capacitors within the bank from a magnetic field of the coil. The bank is preferably fastened to the coil and includes a conduit in communication with a source of coolant for cooling the banks. 
     In accordance with another aspect of the present invention, the housing comprises an electrically and thermally conductive heat sink, and the bank comprises a plurality of capacitors, each configured as a toroidal roll pack disposed between a first and second of the heat sink. A collector bus is in electrical communication with the capacitors and the coil. In one embodiment a plurality of the roll packs are serially connected to the bus and each of the roll packs is interposed between a pair of the plurality of heat sinks for forming a stack. 
     In accordance with another aspect of the present invention, the coil includes a selectively openable switch and an actuator for deforming the coil to open the switch with a spacing sized for moving the assembly on and off of a running strip. A moveable carriage supports the coil and the capacitor bank. 
     In accordance with the present invention, an induction heater is provided for heating a continuous strip wherein the heater is selectively moved on and off the strip. The heater comprises a closed loop coil disposed about the strip. An accessway is included within the coil for selectively opening the coil for the movement relative to the strip. The accessway comprises a switch supported by a turn of the coil. An actuator is associated with the turn for deflecting the turn to an extent to open the switch. 
     In accordance with another aspect of the present invention, the switch comprises a knife switch extending for a length of the coil. The actuator preferably comprises a piston and cylinder assembly supported on a base frame and fastened to the coil for the deflecting of the coil turn. 
     In accordance with another aspect of the present invention, the heater includes a flat pack capacitor bank in electrical communication with the coil. The bank and the coil are supported on a trolley for movement on and off the strip. 
     One benefit obtained by use of the present invention is an induction heating assembly comprising a carriage mounted coil wherein the coil and an associated capacitor bank are packaged in the assembly for reduced space consumption. 
     Another benefit is an assembly with a reduced number of coolant hoses and cable connections adjacent the coil and a running strip passing through the coil. 
     Another benefit is an openable coil including a knife switch wherein the coil has the advantages of lower losses, increased reliability, less sensitivity to alignment, lower switch costs, and which avoids end water and cooling hose connections. 
     Yet another advantage of the present invention is a flat pack capacitor pack which can be bolted directly to the coil, but which avoids harmful heating of the capacitor bank by appropriate shielding and cooling. 
     Another benefits and advantages of the subject new induction heating assembly will become apparent to those skilled in the art upon a reading and understanding of this specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, the preferred embodiments of which will be described in detail in the specification and illustrated in the accompanying drawings, which form a part hereof and wherein: 
     FIG. 1 is a perspective view of a single roll pack capacitor; 
     FIG. 2 is a perspective view of a set of capacitors assembled between opposed cooling and shielding heat sink plates; 
     FIG. 3 is an elevated perspective view of a single heat sink plate, particularly showing the coolant tubes extending from the end portions thereof; 
     FIG. 4 is a perspective view of a collector bus which is in electrical communication with the capacitor group and a coil; 
     FIG. 5 is a perspective view of a stacked assembly comprising the flat pack and capacitor bank; 
     FIG. 6 is a partial perspective view of a capacitor bank and induction coil assembled in accordance with the present invention; 
     FIG. 7 is a view similar to FIG. 6 except the wall housings have been removed for ease in illustrating internal componentry; 
     FIG. 8 is a side-elevational view showing a strip heating assembly including a coil capacitor apparatus formed in accordance with the present invention; 
     FIG. 9 is a side-elevational view showing the coil deflected into an open position for removal from the strip; and, 
     FIG. 10 is a partial cross-sectional view particularly illustrating the knife switch components of the coil. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, the Figures show an induction heating assembly  10  useful for heating a moving workpiece such as strip steel or aluminum  12  (FIG.  8 ). Since the strip  12  is continuous, assembly  10  must include some means for allowing the coil componentry surrounding the strip  12  to be opened so that the coil can be moved on and off of the strip. A wheeled trolley  14  is convenient for moving the coil assembly. A conventional frame  16  supports the trolley, and therefore the coil. A power supply  18  supplies the energy to the coil through a capacitor bank  20  as hereinafter will be more fully explained. 
     It is a principal purpose of the subject invention that the coil assembly  22 , capacitor bank  20 , opening and closing switch (FIG. 10) and associated shielding can be packaged so as to require a smaller space requirement than prior known assemblies, so that the coil/capacitor bank assembly can be placed with convenience on the trolley  14  in an area where the strip  12  is, i.e., where space is a premium in a fully operational assembly, while the power supply  18  can be disposed off the trolley  14  in less expensive space area within the overall system  10 . Effectively, the invention comprises the grouping of the switch, coil  22  and capacitor bank  20  as a single assembled entity, conveniently mounted on a trolley  14  for improved ease of application to and removal from the strip  12 . The close proximity of the bank and coil not only promotes improved electrical efficiencies, but also enhanced constructural safety and simplicity. 
     With reference to FIGS. 1 and 2, a reactive capacitor bank is well known as a component of an induction heating coil. The bank is comprised of a plurality of single roll-pack capacitors which are wound in a hockey puck type of shape. As shown in FIG. 2, the single roll packs  24  are assembled in parallel as a group and then are soldered to opposed copper plates  26 ,  28  forming sidewalls of each associated group. A plurality of such a group of assemblies are connected in electrical series and then the entire assembly forms the capacitor bank. FIG. 5 shows two such capacitor groups so assembled. It also shows a plurality of multi-capacitor water cooled heat sink plates  30  adjacent the groups. Keeping in mind that it is a design objective of the subject invention to dispose the capacitor bank in a position so close to the coil  22 , that field effects from the coil can reach the capacitor bank, the sinks  30  are electrically and thermically conductive and thus serve to facilitate cooling of the capacitor banks as well as enhanced shielding from field effects. Cooling conduit  31  draws heat from the plate  30 . 
     Turning to FIGS. 5 and 7, it can be seen that the capacitor bank further includes an additional shielding plate  34  located on both the top and bottom of the assembled group. Plate  34  serves as an end or pressure plate for holding the assembly together. In the commercial embodiment illustrated in FIG. 7, actually four capacitor groups are illustrated. In effect, the embodiment of FIG. 3 is duplicated on both sides of an insulating plate  36 , a collector bus  38  communicates electrical energy to the capacitors of the group supported on bus  39  pegs. It is an important feature of the invention to facilitate the direct bolting of the capacitor bank assembly directly to the coil  22  to locate the coil and bank immediately adjacent one another. Housing shield  34  and heat sinks  30  cooperate to permit the disposition of the capacitors so close to the coil. 
     With continued reference to FIG. 7, it can be seen that the collector bus  38  is connected at one end to power supply  18  through appropriate connection cables, while at the other end  40  is directly bolted to the coil  22 . Shield plate  42  is disposed intermediate the capacitor bank  20  and the coil  22 . 
     FIG. 6 illustrates a perspective view of the coil and bank assembly and it is important to note that the bank and coil are directly adjacent one another so that conventional connecting arrangements of cables, cooling hoses and multiple connectors are avoided. The capacitor and the coil are single assemblies with just one contact, comprising the bolting arrangement between the collector bus  38  and the coil. 
     With continued reference to FIGS. 6,  7  and  9 , another feature of the subject invention is that the coil construction includes a selectively openable knife switch  50  at the coil end opposite the capacitor bank to facilitate opening and removal of the coil  22  upon the moving strip  12 . As opposed to prior art systems which require hinges and doors, the subject invention comprises a switch  50  which is operated by deforming the coil  22  to open the switch with a spacing sized for removing the assembly on and off of the strip  12 . Thus, when the switch is closed, the coil comprises a closed loop coil including a plurality of turns disposed about the strip. In order to open the coil, the turns operate as a pivot arm to facilitate separation of switch components. Thus, the turn acting also as a pivot arm, comprises an integral and resilient conductor, and the opening of the switch comprises a resilient arcing of the pivot arm to an extent necessary to open the switch to allow the coil to be removed from about the strip. The resilient arcing of the turn must be less than a yielding bending of the conductor for avoiding fatiguing over a plurality of openings and closings of the switch  50 . FIG. 9 illustrates the deflection of the coil affected by opposed actuators  60  essentially comprising piston and cylinder assemblies which pull the ends  62 ,  64  of the coil away from each other. 
     With additional reference to FIG. 10, it can be seen that the switch  50  preferably comprises a knife switch extending over a cross-sectional length of the coil. By “length” is meant the approximate dimension of the coil that the strip passes through. A male part  70  is associated with the first end  62  of the coil and the female part  72  is associated with second end  64  of the coil. In operation, as the actuators  60  are fixedly supported on the base frame  80 , deflection of the coil causes the male and female components to mate or separate. The forks of the female component  72  are slightly spread upon reception of the male component  70  for enhanced electrical contact. 
     Another feature of the invention to note is that the alignment of the switch assembly  50  is disposed to allow the current, which runs on the inside surface (i.e., on the inside of the coil opening) to run along a more expansive dimension of the switch than if the switch were aligned otherwise to cause the current to run along merely the knife edge. Accordingly, only a single contact switch would be possible, but the double contact assembly of the preferred embodiment provides enhanced structural strength. The switch is water cooled as can be seen with coolant passageways  80 ,  82 . 
     The invention is described with reference to the preferred embodiments obviously, modifications and alterations will occur to others upon the reading and understanding of this specification. It is our intention to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.