Abstract:
An induction heating element includes a primary conductive portion and a secondary conductive portion. The primary conductive portion is connected to a power source, and conducts electric current from the power source to generate a magnetic field that inductively heats a portion of the workpiece. The secondary conductive portion is electrically insulated from the primary portion, and receives an induced electric current from the primary portion to affect the magnetic field generated by the primary portion.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an inductor assembly, and in particular, to an inductor assembly that is used for contour induction heat-treatment of workpieces. 
     BACKGROUND OF THE INVENTION 
     Induction heat-treatment is a widely used process for the surface hardening of steel workpieces. The workpieces are heated by producing a high-frequency alternating magnetic field, so that selected surface regions of the workpiece are heated to a temperature within or above the transformation range, followed by immediate quenching. The core of the workpiece remains unaffected by this treatment and its physical properties are those of the bar from which it was machined, while the treated regions of the workpiece are metallurgically hardened. 
     One such workpiece is a bearing sleeve having an internal bore with bearing support surfaces or races disposed along the interior surface. Selected portions of the interior surface can be heat treated and metallurgically hardened by magnetic induction, in which an inductor body is positioned within the bore and quickly energized to magnetically induce an electric current in selected regions of the workpiece and heat those portions to a high temperature before quickly quenching them. The region of heat-treating of the interior surface of the workpiece is defined by the contour of the magnetic flux pattern produced by the coil of the inductor body. 
     The inductor body is connected to an AC power source adapted for this purpose, so that AC current flowing through the inductor will create a magnetic field that penetrates the workpiece and induces an eddy current in the workpiece. The heating of the workpiece by this eddy current and the subsequent quench is used to metallurgically harden the workpiece, but only the region in which the current is magnetically induced is hardened in this process. The other portions of the workpiece remain unaffected. The contour of the heating pattern is accomplished by the shape of the inductor and/or the shape of the coils on the inductor body. 
     In the case of heating the interior bore of a workpiece that has a varying inner diameter profile, such as a bearing sleeve, the induction element must have an outer diameter that is no larger than the smallest inner diameter of the workpiece bore, so that the induction element can be inserted and removed from the bore. A typical bearing sleeve for two sets of bearings has a bearing separator or straddle between the two bearing surfaces. At the straddle the interior bore has a reduced inner diameter, and the inductor body must have a maximum outer diameter no greater than this minimum inner diameter. 
     These limitations on the configuration of the inductor may cause the magnetic field produced by the inductor to heat portions of the workpiece that do not need to be heated. A further problem can result if these portions should not be hardened for various reasons, such as the need to perform further machining operations on these portions. For example, in the case of a bearing sleeve, it may not be possible using conventional induction elements to avoid hardening substantial portions of the straddle, and it may be desirable to perform further machining operations on the straddle, such as to drill a port through this portion of the bearing sleeve. If the straddle has been inductively hardened, it becomes more difficult to drill through the straddle. 
     SUMMARY OF THE INVENTION 
     The disadvantages of the prior art are overcome by the present invention of an induction heating element that produces a contour heating pattern in a different manner than the prior art. The induction heating element of the present invention shapes the induction field without relying entirely upon the configuration of the element. 
     In accordance with the present invention, the induction heating element has a secondary induction coil that is not directly connected to the power source used to produce the field by the primary coil. This secondary coil is electrically insulated from the primary coil, so that the only current in the secondary coil is the result of induction from the primary coil. The secondary coil thus creates its own magnetic field that opposes the magnetic field produced by the primary coil. The field produced by the secondary coil thus shapes the field produced by the primary coil, resulting in contoured induction pattern. 
     Because the inductor head of the present invention does not rely solely upon the exterior shape or configuration of the head to contour the induction field, the present invention makes it possible to create an inductor head that can fit into places previously not possible with prior art induction elements. In the case of hardening the interior bore of a workpiece such as a bearing sleeve, it is possible with the present invention to effectively harden the bearing surfaces without substantially hardening the bearing separator that is directly adjacent to the bearing surfaces, even though the bearing separator may extend substantially into the bore and create the minimum inside diameter. Although the inductor head of the present invention must be very close to the straddle, it can substantially avoid hardening the straddle by the positioning the secondary coil which will divert the induction field away from the straddle. 
     The principles of the present invention may be used in other applications in which it is desirable to shape the induction pattern away from certain portions of the workpiece. Specialized patterns can be created without relying upon the shape of the inductor head. Smaller induction regions can be created, resulting in reduced power requirements and cost savings. 
     These and other advantages are provided by the present invention of an induction heating element for treatment of a workpiece. The induction heating element comprises a primary conductive portion and a secondary conductive portion. The primary conductive portion is connected to a power source, and conducts electric current from the power source to generate a magnetic field that inductively heats a portion of the workpiece. The secondary conductive portion is electrically insulated from the primary portion, and receives an induced electric current from the primary portion to affect the magnetic field generated by the primary portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of an inductor assembly according to the present invention. 
         FIG. 2  is another side elevational view taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a detailed side elevational view of a portion of the inductor assembly of  FIG. 1  comprising the inductor head. 
         FIG. 4  is another side elevational view taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a side sectional view, similar to  FIG. 3 , showing the same portion of the inductor assembly in relation to a workpiece being induction heat-treated. 
         FIG. 6  is a side elevational view of another embodiment of the inductor assembly of the present invention. 
         FIG. 7  is another side elevational view of the second embodiment taken along line  7 - 7  of  FIG. 6 . 
         FIG. 8  is a detailed side elevational view of a portion of the inductor assembly of  FIG. 6  comprising the inductor head. 
         FIG. 9  is a sectional view of the portion of the inductor assembly of  FIG. 8  comprising the inductor head, taken along line  9 - 9  of  FIG. 6 . 
         FIG. 10  is a side sectional view, similar to  FIG. 9 , showing the same portion of the inductor assembly in cross section in relation to a workpiece being induction heat-treated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to the drawings, and initially to  FIG. 1 , there is shown an inductor assembly  10  according to the present invention. The assembly  10  comprises a cylindrical inductor body or head  12  and a cylindrical inductor contact body  11  attached at one end of the inductor head for mounting the inductor head in an induction heat treating apparatus. 
     The inductor head  12  of  FIGS. 1 and 2  is shown in more detail in  FIGS. 3 and 4 . The inductor head  12  comprises a primary conductive portion in the form of an inductor loop or coil  15  made of a highly electrically conductive material such as copper, with portions connected together so as to highly electrically conductive. The inductor coil  15  includes two loops  16  and  17 , a pair of jumper legs  18  and  19 . Each of the two inductor loops  16  and  17  is axially spaced apart from the other, and each extends almost completely circumferentially around the inductor head. A small gap is provided on one side of the inductor head so that the inductor loops  16  and  17  do not extend entirely around the inductor head. The two inductor loops  16  and  17  are electrically connected together at each end adjacent to this gap by the jumper legs  18  and  19 . The jumper legs  18  and  19  extend parallel to each other and axially with respect to the inductor head to connect each of the two inductor loops  16  and  17  together. The gap that separates each of the inductor loops  16  and  17  continues axially between the jumper legs  18  and  19  to provide an insulator  20  between the jumper legs. The jumper leg insulator  20  is preferably made of a suitable electrically insulating material such as polytetrafluoroethylene (PTFE) resin. The insulator  20  extends radially completely through the insulator head, and the top inductor loop  16  has a second gap on the side of the inductor head opposite the jumper legs  18  and  19 . First and second head jumpers extend upwardly from the ends of the top inductor loop  16  formed by this second gap containing the insulator  20 . The two head jumpers are each contacted to one of the first and second contact bodies  37  and  38  contained in the inductor contact body  11 . A fastener, extending through a jumper insulator bushing  34 , extends through the insulator head  12  to attach the jumper leg insulator  20 . 
     The inductor coil  15  thus provides a continuous electrical path for electrical potential traveling between the first contact body  37  and the second contact body  38 . The path travels from the contact body  37  through a portion of the top loop  16 , though the first jumper leg  18 , through the bottom loop  17 , through the second jumper leg  19 , through the other portion of the top loop  16 , and finally to the second contact body  38 . The electrical energy traveling in this path creates an induction field or flux field around the inductor head  12  that essentially has two radially outwardly extending areas of energy, one portion adjacent to each of the inductor loops  16  and  17 . 
     A pair of intensifier rings  24  and  25  is provided, one adjacent to each of the inductor loops  16  and  17 , positioned axially away from the other inductor loop. Top intensifier core  23  is also provided inside the top loop  16 , and an interlocking intensifier core  29  is provided inside the bottom loop  17 . The intensifier cores  23  and  29  and the intensifier rings  24  and  25  are made of a known material for this purpose, such as Ferrotron. Ferrotron is a non-conductive magnetic material consisting of pure iron powder uniformly dispersed in an insulating plastic binder such as PTFE. The small iron particles form very small paths which, coupled with the insulating properties of the binder, result in high permeability low hysteresis losses and temperature resistance up to 300° C. This combination of properties makes Ferrotron an ideal intensifying material for induction hardening, particularly of difficultly shaped parts, such as gear wheels, bearing sleeves and dovetailed slides. The use of intensifier elements, such as the rings  24  and  25  adjacent to rings of the inductor coil, is well known and need not be described in further detail. The intensifier cores  23  and  29  and the intensifier rings  24  and  25  may be made together in the form of a single integral body. 
     An insulating bottom cap  27  is provided on the end of the inductor head next to the intensifier ring. An insulating top cap  28  is also provided on the other end of the inductor head  12  between the intensifier ring  24  and the contact body  11 . The bottom cap  27  and the top cap  28  are each made of a suitable non-conductive material such as Delrin. 
     In accordance with the present invention, a secondary conductive portion formed by an inductive coil or loop is also provided by means of a diverter ring  30  extending circumferentially around the inductor head  12  between the inductor loops  16  and  17 . The middle diverter ring  30  is electrically insulated from both loops  16  and  17  of the primary inductor coil by means of an intensifier ring  31  made of the same material as the intensifier rings  24  and  25 . Since the diverter ring  30  is insulated from the electrical path through the primary inductor coil  15 , it is not directly energized when the inductor head is connected to the power supply. However, since the diverter ring  30  is highly conductive, a current is induced in the diverter ring  30  when the primary coil  15  is energized, so that the diverter ring forms a secondary coil. The current that is induced in this secondary coil travels around the outer edges of the ring  30  in a direction directly opposite to the direction of current travel in the primary coil  15 . The induced current in the secondary coil reshapes the induction field or flux field produced by the primary coil, pushing the field away from the axial position of the middle diverter ring  30  and more towards the axial ends of the inductor head  12 . 
     Another diverter ring  26  is also provided at the bottom end of the assembly, separated from the bottom loop  17  by the bottom intensifier ring  25 . The bottom diverter ring  26 , like the middle diverter ring  30 , is made from a conductive material, and is insulated from the externally energized inductor coil  15  by the bottom intensifier ring  25 . The bottom diverter ring  26  is also indirectly energized when a current is inducted in the ring by the current in the bottom loop  17  of the inductor coil  15 . The bottom diverter ring  26  further shapes the flux field produced by the primary coil in the area at the bottom of the inductor assembly. 
     The inductor contact body  11  provides a means for mounting the inductor head  12  in an induction heating apparatus. The inductor contact body  11  comprises the two large contact bodies  37  and  38  each made of copper or other highly conductive material, separated by an insulator  39  made of PTFE. The contact insulator  39  extends the top of the jumper leg insulator  20  in the same general plane. The two contact bodies  37  and  38  and the intermediate contact insulator  39  are attached together by fasteners  40  and  41 . Insulator bushings  35  and  36  are provided around each of the fasteners  40  and  41 , respectively, to insulate the fasteners from the contact bodies  37  and  38 . Each of the contact bodies  37  and  38  provide a high current path for electrical energy flowing to and from the inductor head  12 . Each of the contact bodies has a cooling inlet quick disconnect  42  and  43  extending from the top end. Locator stop bolts  46  and  47  extend from each side of the inductor contact body, generally in the middle of each the contact bodies  37  and  38 , respectively. 
     One of two quench passages  49  and  50  extends through each of the contact bodies  37  and  38 , respectively, for the flow of quenching fluid from the induction heating apparatus to the workpiece. Each quench passage  49  and  50  extends generally axially through the one of the contact bodies, and includes a radial portion that communicates with the exterior of the inductor head through an inlet port  51  and  52 . 
     The quench passages  49  and  50  communicate with corresponding passages in the inductor head  12 . O-ring seals  55  and  56  are provided between the contact body passages  49  and  50  and the inductor head passages. The passages in the inductor head  12  are connected to a plurality of holes  61  provided on the exterior of the inductor head. The holes  61  are provided in each of the intensifier rings  24  and  25  and in the middle diverter ring  30 . The holes  61  allow for the quenching liquid, such as water, to be sprayed onto the workpiece at the end of the induction hardening process. 
     A suitable fastener  57 , such as a screw made of nylon, is used to secure the elements of the inductor head  12  together and the mount the inductor head onto the inductor contact body  11 . 
     The relationship of the inductor head with respect to a workpiece can be seen with reference to  FIG. 5 . There is shown a workpiece  72  in the form of a bearing sleeve having an interior bore  73 . The interior bore  73  includes a pair of bearing support races  74  and  75  with a straddle  76  separating the two bearing races surfaces. Because the straddle  76  has a smaller inner diameter than the rest of the interior bore  73 , the inductor head  12  must be made with a maximum outer diameter small enough to allow it to be moved through the straddle. This means that the inductor head  12  cannot be positioned any closer to the bearing races than is shown in  FIG. 5 . This would ordinarily make it difficult to provide a contoured heating pattern in which the straddle  76  is not heated to a substantial depth. In other words, an ordinary inductor head would necessarily provide a heating pattern that extends relatively deeply into the straddle due to the close proximity between the straddle and the inductor head. 
     In accordance with the present invention, however, the presence of the secondary coil formed by the middle diverter ring  30  creates a countering magnetic flux that shapes the heating pattern produced by the two loops of the primarily coil. The countering flux influence produced by the middle diverter ring tends to repel the flux field away from the location of the straddle. As a result the two loops of the primary coil produce heating patterns that are generally defined by the limits of the minimum heat pattern  78  and the maximum heat pattern  79  shown in  FIG. 5 . The resulting heating pattern, which ends somewhere between these minimum and maximum limits, does not extend substantially into the straddle. This allows the straddle to avoid substantial heat treatment, so that the straddle can be further processed as required. For example, if it is desired to machine an opening through the straddle for placement of a sensor or probe, the opening can be drilled through the straddle without difficulty, since this portion of the workpiece has not been substantially heat-treated. 
     In operation, the inductor assembly is mounted in apparatus for heat-treating a workpiece, such as the bearing sleeve shown in  FIG. 5 . The heating treating apparatus provides a fixture for holding the workpiece and provides for the high-speed rotation of the workpiece. The inductor assembly is mounted in the apparatus so that the contact bodies  37  and  38  are connected to a suitable power supply, and the quench liquid connections are connected to a supply of quench liquid. The power supply may be a 3 to 450 kHz, up to 500 kW suitable power unit used for contour induction hardening, as is known in the art. When the workpiece is inserted into the apparatus, the induction heat treating process can be initiated in which the workpiece is rotated at a high speed, such as 100 to 200 rpm, and the power supply is activated to supply power to the induction coil. 
     Another embodiment of the present invention is shown in  FIGS. 6-10 . There is shown an inductor assembly  110 , which has an annular shape instead of cylindrical shape of the inductor assembly  10  of  FIGS. 1-5 . The inductor assembly  110  can be used to heat-treat a rod-shaped workpiece, such as a pump shaft or transmission shaft. The inductor assembly  110  comprises an inductor body or head  111  and inductor contact leads  112  by which the inductor head is mounted in an induction heat treating apparatus. 
     The inductor head  111 , as shown particularly in  FIGS. 8 and 9 , has a primary conductive portion formed by an inductor coil  115  comprising an annular inductor loop  116  which is made of a conductive material such as copper and is connected to the power source, so that an induction heating field is thus produced. Annular intensifier rings  124  and  125 , made of a suitable material such as Ferrotron, are provided on both sides of the inductor coil  115 . The inductor head  111  also has a secondary conductive portion in the form of two annular diverter rings  130  and  132  located on either sides of the intensifier rings  124  and  125 . The diverter rings  130  and  132  are both made of highly conductive material such as copper and are electrically insulated from the primary inductor coil  115  by the intensifier rings  124  and  125 , respectively. 
     The inductor head  111  is connected inductor contact leads  112  comprising a two symmetrical contact bodies  137  and  138  extending axially from one side of the inductor head. An insulator  139  is located between the contact bodies  137  and  138  to insulate them from each other. A gap is formed in the inductor loop  116  on one side of the inductor head, and the insulator  139  extends into this gap so that the loop  116  is open on one side and each end of the loop formed by the gap is connected to one of the contact bodies  137  and  138 . An insulator  139  is provided around the contact bodies  137  and  138 . Top and bottom straps  144  and  145  hold the contact bodies  137  and  138  together and secure the insulator  139  onto the contact bodies. Each of the straps  144  and  145  are secured to the contact bodies  137  and  138  by fasteners  140  and  141 . 
     A pair of cooling inlet quick disconnects  142  and  143  are located on the base of the contact bodies  137  and  138  for connection to a source of cooling liquid. Each of the contact bodies  137  and  138  has an interior passage  149  and  150 , respectively, connected at one end to one of the quick disconnects  142  and  143 , respectively, and connected at the other end an annular chamber in the inductor head  111 . Quench inlet nozzles  151  and  152  are also provided on opposite sides of the inductor head  111 . The quenching liquid is fed through the inlet nozzles  151  and  152 , through the quench passages in the quench assembly  113  and through the annular chamber in the quench assembly  113  formed below the bottom diverter ring  132  and through the quench opening  162 , where it is sprayed onto the workpiece in the direction  161  shown in  FIG. 9 . 
     The elements of the inductor head  111  are secured together by suitable fasteners, such as three nylon screws  157 . 
     As shown in  FIG. 10 , inductor assembly  110  is used to heat-treat a workpiece  172 . The workpiece  172  is in the form of a rod having a recessed bearing race  174 . When connected to the power source, the primary inductor coil  115  produces an induction heating field and, at the same time, induces a current flow in both of the diverter rings  130  and  132  that is the oppose or complementary to the current flow in the primary coil. The induced current flow in the diverter rings  130  and  132  shape the resulting induction field away from the workpiece  172  to produce a contoured field in which the bearing surface  174  is induction hardened, but the regions of the workpiece  172  on either side of the bearing surface are left unaffected so that they may be machined or otherwise further processed without additional difficulty. 
     It should be realized that the embodiment described herein is only representative of the invention and is not intended to limit the invention to one particular embodiment as the invention includes all embodiments falling within the scope of the appended claims. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.