MULTI-COIL ELECTRICAL INDUCTION HEAT TREATMENT SYSTEMS FOR SIMULTANEOUS HEATING OF MULTIPLE CHARACTERISTICS OF A BEARING COMPONENT.

Abstract

A main inductor circuit is connected to an AC power supply and a passive inductor circuit are assembled as a separable split inductor assembly to form at least one pair of a main heating inductor and a passive heating inductor wherein the main and passive inductor circuits are electromagnetically coupled without physical connection; a bearing component can be brought into the presence of the magnetic flux field created by the main and passive heating inductors to induction heat one or more bearing features in the bearing component with subsequent cooling of the austenitized bearing features in the bearing component.

Description

SPLIT MULTI-COIL ELECTRICAL INDUCTION HEAT TREATMENT SYSTEMS FOR SIMULTANEOUS HEATING OF MULTIPLE CHARACTERISTICS OF A BEARING COMPONENT CROSS-REFERENCE WITH RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 62 / 970,237, filed on February 5, 2020, which is incorporated herein by reference in its entirety. FIELD OF INVENTION The present invention relates in general to electrical induction heat treatment of bearing components with bearing features such as bearing raceways and bearing paths, and in particular to said heat treatment where a selected feature or features of the bearing raceways and bearing paths require metallurgical hardening. BACKGROUND OF THE INVENTION The present invention relates to an electrical induction heat treatment of inner and outer bearing raceways, as well as other bearing features, used, for example, in power train components, drive lines, and wheels. Bearings are critical machine elements that enable components to move relative to one another. Depending on the specific application, there are a number of variations in bearing raceway designs, many of which are standardized. These include, but are not limited to, radial ball and roller bearings, and ball and roller thrust bearings. There are also single-row and multi-row bearings, as well as single- and double-direction bearing designs.Regardless of the design specifications, the bearing's contact working surfaces must be treated to ensure wear resistance and robustness throughout the bearing's service life, as well as other mechanical properties, and electrical induction hardening is one of the most popular methods of such heat treatment. Figure 1A illustrates a cross-sectional perspective view of a type of inner bearing raceway configured as bearing component 100, commonly used in the automotive industry. Various grades of steel are used for the manufacture of most forged bearing raceways. In less frequent applications, powder metallurgy materials and castings are also used. Bearing raceways can also be produced using additive manufacturing techniques, such as 3D printing. Figure 1B and Figure 1C illustrate, in a flat elevation cross-section, two alternative examples of induction surface hardness patterns of the configured inner raceway of bearing component 100. Figure 1B shows a broken raceway hardness pattern containing two circumferential metallurgically hardened zones 101 and 102 (regions shaded in solid black or crosshatched) separated vertically by a circumferential unhardened region 103, as also shown in Figure 1A and Figure 1B. The hardened zones 101 and 102 are bearing features or regions where rolling elements (e.g., balls or rollers) move against inner raceways 101a and 102a, respectively. Depending on the particular application, the geometries of zones 101 and 102 may be identical or different.The hardness pattern shown in Figure IB is the most popular because it provides the necessary mechanical properties of bearing contact surfaces where they are needed without hardening a region, such as region 103, where no contact wear occurs. Hardening only bearing features or regions 101 and 102 helps not only to provide the necessary engineering properties and minimize distortion characteristics after heat treatment, but also reduces the amount of electrical energy required for the heat treatment. Figure 1C illustrates an alternative type of hardness pattern 104 (solid black shaded region or cross-section) used in some specific applications. In this type of hardness pattern, in addition to the induction-hardened inner bearing contact surfaces (bearing features or regions 101a and 102a), region 103, which separates the inner bearing contact surfaces, is also induction-hardened. Pattern 104 is generally associated with at least two undesirable workpiece and process factors: excessive distortion features and a significant increase in the electrical energy required to harden all three regions, i.e., regions 101, 102, and 103. There are several reasons why the hardness pattern shown in Figure 1B is more popular than the hardness pattern shown in Figure 1C. In order to inductively heat treat bearing raceways, in some processes, an induction heating coil is moved into a heating position (Method A); however, in other processes, an induction heating coil is stationary and a bearing raceway (i.e., a bearing feature or region of the bearing component (workpiece to be heat treated)) is moved into a heating position (Method B). The invention described herein can be used in an apparatus and processes for heat treatment by either Method A or Method B or a combination of Methods A and B, wherein the induction heating coil and bearing raceway are moved relative to each other. Conventional solenoid-type coils with one or more turns (e.g., conventional two-turn coils of the prior art) are commonly used for heat-treating bearing raceways. An induction coil is placed outside the bearing raceway (in a configuration surrounding the raceway) to heat-treat the outer raceway surfaces. An induction coil is placed inside the bearing raceway to heat-treat its inner bearing surfaces. For convenience, the present invention is generally described herein for induction hardening (heat-treating) of internal bearing features such as raceways and paths, but it is also applicable for heat-treating internal bearing features or surfaces of bearing components.For example, Figure 1D and Figure 1E illustrate representative perspective views of a typically configured bearing raceway component 100' where the outer (external) surface 100' is required to be hardened. Figure 1F, Figure 1G, Figure 1H, and Figure II illustrate planar cross-sections of an outer bearing raceway configured from the bearing component 400 having an inner surface region 401 that is not required to be induction hardened and the bearing feature or region comprising the outer (external) surface 402 that is to be induction hardened.Depending on a particular application, an entire area of ​​the outer (external) surface 402, as shown (in the hatched region 405) in Figure 1H, may require induction surface hardening; alternatively selective bearing features or regions (each selective region shaded with cross-hatching), for example, selective region 403 shown in Figure 1F; selective region 404 shown in Figure 1G; or the previously mentioned selective region 405 shown in Figure 1H; and selective regions 406 in Figure II, may require induction surface hardening. The hardness pattern shown in Figure II represents an example of an interrupted hardness pattern. The effectiveness of an internal cylindrical induction coil depends to a much greater degree on the magnetic field coupling gap between the coil and the workpiece (or bearing feature to be hardened) compared to similar coils used to heat external surfaces (or outside diameters) of a bearing. The electrical efficiency of an internal coil decreases rapidly with an increase in the field coupling gap. Therefore, in order to increase electrical heating efficiency and minimize energy consumption, it is imperative to keep the field coupling gap between the coil and the workpiece as small as possible. αηαΑηη / ζζηζ / Ε / γίΛΐ The reason solenoid-type inductors for heating internal surfaces are not as efficient as similar inductors (also referred to as an induction coil or induction coil) used to heat external surfaces of a bearing is related to the electromagnetic ring effect. According to the electromagnetic ring effect, the coil current concentrates on the inner diameter of the solenoid-type coil, which represents a low-impedance path, as further described, for example, in section 3.1.5 of the Induction Heating Handbook (second edition; CRC Press; Boca Raton, FL, USA). When internal diameter surfaces are heated, the inner diameter of the coil is the region farthest from the heated internal diameter surfaces.As a result, the electromagnetic coupling between the coil and the heated workpiece (i.e., the bearing feature to be heated) is greater than the actual air gap between the inner diameters of the workpiece and the outer diameter of the induction coil. This results in poor field coupling of the coil to the workpiece (also known as spatial proximity) and therefore causes a noticeable reduction in coil efficiency. Installing a magnetic flux concentrator within the internal inductor is often necessary to increase the coil's electrical efficiency and reduce coil current, particularly for heating internal surfaces of small to moderate diameters. The flux concentrator creates an electromagnetic slot effect that has a substantially stronger impact on the coil current distribution than the electromagnetic ring effect. This forces the coil current to shift toward the outer regions of the coil, placing it closer to the surface of the heated workpiece. This increases the magnetic field strength and heat intensity on the internal surfaces of the workpiece (bearing component) that need to be heated. In order to minimize distortion after induction heat treatment and achieve heat treatment properties for a long service life of the raceways, it is important that the heat treatment process achieves sufficient minimum hardness depth but avoids: (1) causing excessively deep localized case depths; (2) very high temperatures during austenitizing; and (3) disproportionately different case depths of hardness within each of the bearing contact surfaces (e.g., in zones 101a and 102a for the inner bearing raceway configured in Figure IB). These heat treatment characteristics are some of the reasons why obtaining the most uniform hardness patterns possible within each of the bearing contact surface regions 101a and 102a is often highly desirable. Several factors make it difficult to obtain sufficiently uniform hardness patterns in bearing features or regions 101a and 102a. This factor is related to the complexity of the workpiece (bearing component) geometry, for example, the workpiece geometries in Figure 1A to Figure 1C. Corner regions that tend to attract magnetic fields due to the electromagnetic edge effect can produce deeper hardness box depths.In addition to that, there are appreciably different masses of metal forming the workpiece (i.e., the bearing component) in proximity to the bearing features comprising surface regions 101a and 102a, which produce appreciably different cold-penetrating effects (axially and radially) from neighboring areas and result in a corresponding deviation of temperatures while the surface is induction-hardened by the internal bearing raceways (regions 101a and 102a). The second factor relates to the difficulty of using single-turn or multi-turn solenoid-type coils (e.g., conventional two-turn coils of the prior art) to obtain contour-like hardness patterns. In order to position a solenoid-style hardening coil in the heating position within the bearing raceway to harden its inner surfaces in bearing features or regions 101 and 102 (shown, for example, in Figure IB), there must be sufficient clearance to allow the smaller diameter area (region 103 in Figure IB) to pass through during loading (to the heating position) and unloading (from the heating position) of the bearing raceway in a solenoid-style induction hardening coil.This results in variable electromagnetic coupling (spatial proximity) between the coil regions where the electric current flows and the internal bearing race regions, producing a non-uniform hardness pattern. Figure 2A and Figure 2B illustrate an example of the variable electromagnetic coupling phenomenon with cross-sectional views of an inner bearing raceway. In the example shown in these figures, copper tubing with a circular cross-section (and coil turns 301 and 302) and hollow inner water-cooling passages are used to fabricate the induction coil. In other embodiments, the induction coil can be formed alternatively: (1) by computer numerical control (CNC) machining from a solid block of copper; (2) by brazing together suitable copper components; or (3) by profiled heating faces forming a coil-turn array to fit the geometry of inner bearing raceway regions 115a and 106a (Figure 2A) and inner bearing raceway regions 125a and 126a (Figure 2B).Conventional magnetic flux concentrators 203 and 204 can be used to improve heating efficiency and concentrate the magnetic field generated by each turn of coil 301 and 302 of the two-turn coil formed from copper tubing to heat the inner bearing races (regions 115 and 106) in Figure 2A, and to heat the inner bearing races (regions 125 and 126) in Figure 2B of the alternative geometries. The magnetic flux concentrators are typically fabricated from standard lamination packs, pure ferrites, or conventional iron- or ferrite-based powder materials containing pressed and / or sintered magnetic particles. As shown in Figure 2A, the coil turns 301 and 302 of the copper tubing of the two-turn solenoid-style inductor of the prior art are positioned to heat the corresponding bearing features comprising the surfaces (regions 115a and 106a) of the inner bearing race configured in bearing component lOOy. The longitudinal axis of symmetry 50 of the configured inner bearing race component lOOy coincides with the longitudinal axis of symmetry of the two-turn solenoid-type coil of the copper tubing. In the example of Figure 2A, the upper radial clearance 107 between the cross-shaded hardened region 106 and the tubing 301 is circumferentially the same (i.e., when comparing the radial clearances 107 on the left and right sides in the cross-section of the planar cross-sectional drawing shown in Figure 2A).Sufficient radial clearance 107 allows safe movement of the workpiece (inner bearing races configured) into and out of a heating position where the workpiece is shown in the heating position in Figure 2A or Figure 2B while the two-turn coil is raised (and / or the inner bearing race is lowered) in the heating position. The bearing raceway can be rotated (i.e., spun) about its longitudinal axis of symmetry using a suitable prior art rotating apparatus (not shown in the drawings) during the heating and cooling cycles to even out the radial temperature distribution of the circumferentially heated area. After the induction heating austenitizing stage is complete, cooling can be performed in place (in the heating position), for example, using a spray-cooling apparatus known in the art, to cool the austenitized regions and form the required martensitic structures. In other processes, cooling can be performed out of place (i.e., outside the heating position) at a separate cooling location (for example, with the heated workpiece (bearing component) moved to a position vertically above or below the heating position).The cooling process step can be achieved with the cooling apparatus known in the art. As can be seen in Figure 2A, due to differences in spatial proximity (electromagnetic coupling) between the current-carrying face of the coil and various regions of the lower inner bearing race surface, there will be a noticeable non-uniform heat distribution due to the uneven application of the electromagnetic proximity effect. Upon cooling, this results in corresponding non-uniform hardness patterns in regions 115 and αηαΑηη / ζζηζ / E / γίΛΐ 125. In some applications, a non-uniform hardness pattern is manifested by a gradually decreasing hardness box depth. In other applications, instead of a gradual change in the hardness pattern of a region, there are wave-like hardness pattern regions that exhibit a combination of deeper or shallower hardness box depths. For example, regions 115 and 125 exhibit a deeper hardness box depth in localized regions 115x and 115y in Figure 2A (and the elongated partial view in Figure 2C) and in localized regions 125x and 125y in Figure 2B (and the elongated partial view in Figure 2D). Conversely, regions 115 and 125 exhibit shallower hardness box depths in the localized region 115z in Figure 2A (and elongated partial view in Figure 2C) and in the localized region 125z in Figure 2B (and elongated partial view in Figure 2D).An attempt to ensure the minimum required case depth in the internal raceway regions, where generating sufficient heat sources is difficult, could inevitably lead to severely overheating the adjacent raceway regions. This negatively impacts the metallurgical characteristics of the hardened areas and the engineering properties of the raceways; therefore, overheating must be avoided. However, conventionally designed electrical coils can inevitably be associated with the formation of non-uniform hardness patterns and excessive localized heat generation. Figures 3A through 3C and Figure 4 are diagrammatic illustrations of alternative prior art induction coil configurations that can be used for induction heat treatment of internal bearing raceways. Figure 3A shows a diagrammatic top view of a loading (to a heating position) and unloading (from the heating position) arrangement of a workpiece (configured internal bearing raceway) from a conventional prior art solenoid-type inductor similar to the arrangement illustrated in Figures 2A and 2B and discussed above.In Figure 3A and Figure 3B, the dashed circle diagrammatically represents the inner circumferential boundary of the inner bearing race lia, and the solid circle represents the current-carrying face of coil 22, which is oriented to the inner circumferential boundary of the inner bearing race as shown in the cross-sectional view of Figure 3C. During a workpiece loading operation to the heating position, the rotational longitudinal symmetry axis lia' of the configured inner bearing race lia coincides with the longitudinal symmetry axis 22a of the solenoid-type induction coil 22 to form a circumferentially uniform space 23 (Figure 3A) between the configured inner bearing race lia and the induction coil 22.Before starting the heating step of the heat treatment process, the workpiece or the induction coil, or both the workpiece and the induction coil, are moved in a radial direction (perpendicular to the inner bearing race and the longitudinally symmetric induction coil axes) resulting in a smaller gap 24 on the right side and a larger gap 25 on the opposite left side as shown in Figure 3B between the inner bearing race and the induction coil.As a result of this movement, the improved electromagnetic coupling between the inner raceway and the coil is provided in a smaller gap 24 compared to a uniform gap 23, and concentrated heating occurs in the raceway regions around this smaller gap. Otherwise, there would be a heat generation deficit in these raceway regions due to poor electromagnetic proximity. However, after this movement, an opposite side will exhibit an enlarged gap 25. Therefore, in this method, the gap 24 is smaller than the gap 25, which helps produce a more uniform hardness pattern within the raceway region, as shown in Figure 3C, at the expense of producing poor electromagnetic coupling in the larger gap 25 on the opposite horizontal region of the raceway.The configured inner bearing raceway is rotated (i.e., spun with the rotating apparatus) during the heating step of the heat treatment process using a conventional rotating apparatus to equalize the circumferential temperature distribution regions llaa and llbb. After the austenitization step is completed, quenching (using a conventional quenching apparatus) can be applied in place (i.e., in the heating position) to cool the austenitized regions and form the required martensitic structures.In other heat treatment processes, cooling can be done off-site (i.e., with the hot workpiece moved out of the heating position) in a dedicated cooling location; for example, in a cooling tank that can be positioned below the heating position to lower the hot workpiece into the tank, or in a spray-cooling apparatus positioned in close proximity to the heating position to which the workpiece can be transferred with, for example, a suitable electromechanical transfer apparatus. Unfortunately, the heating method and apparatus illustrated in Figure 3A, Figure 3B, and Figure 3C are not without drawbacks. One drawback relates to the need for at least vertical movement of the components (e.g., during loading the workpiece into and unloading from the heating position) and radial movement (perpendicular to the vertical movement). Therefore, an auxiliary electromechanical transfer device for both vertical and radial movement is required, resulting in additional costs and complexity for the heat treatment system.The additionally improved spatial proximity (and the resulting improved electromagnetic coupling) on ​​one side with the smaller space 24 is related to the deteriorated electromagnetic coupling on the opposite side with the larger space 25 which worsens the sensitivity of the heat treatment process (with possible deviations from the hardness pattern) and reduces the electrical efficiency of the workpiece heating. Figure 4 is a diagrammatic illustration of an alternative prior art induction coil (inductor). In Figure 4, an arc-shaped inductor 40 (also known as a hairpin inductor in the art) is shown in three interconnected segments, which are shown in cross-shading. The inductor 40 comprises: a heating segment 41; a return current segment 43; and an interconnecting segment 42. The magnetic flux concentrator 44 (shown in dotted shading) is placed between the heating segment 41 and the return current segment 43. The three inductor segments are electrically connected in series and connected to an AC power supply (AC PS in the figure).The magnetic flux concentrator 44 provides electromagnetic decoupling between the heating segment 41 and the return current segment 43 to shift the maximum electrical current density flowing in the heating segment 41 towards the outer surface of the heating segment 41a, which would be opposite the configured inner bearing race region (not shown in the figure) that needs to be heated when the inner bearing race is in the heating position. The fork inductor design 40, shown in Figure 4, improves the electromagnetic coupling between the inductor and the inner bearing race of the workpiece and, in some applications, simplifies achieving a required hardness pattern.The workpiece (i.e., the bearing component with the bearing characteristic of the inner bearing race) is rotated during the heating process steps and the cooling process steps to level the circumferential temperature distribution around the inner bearing race. The arc-shaped inductor 40 provides some flexibility to the process. However, it is not free from known drawbacks of the earlier designs illustrated, for example, in Figures 3A to 3C, which include low energy efficiency and the need for the induction heating apparatus to be capable of providing two movements (vertical and radial) in order to position the coil sufficiently close to the bearing race during the heating process steps without obstructing complex geometries such as region 103 on the inner bearing race for the configured inner bearing race component 100 shown in Figure 1B.In addition, a magnetic flux concentrator 44 (Figure 4) that is inserted (interleaved) between two coil segments 41 and 43 carrying electric current flowing in opposite directions can act as an electrical load that has a tendency to magnetically saturate and overheat, which will reduce the overall reliability of the induction heating system. In view of the prior art, it is an objective of the present invention to provide an electric induction heating system and method for providing narrower electromagnetic coupling gaps between the induction heating coil and the bearing feature of a bearing component, such as a region of the bearing raceway surface when in a heating position for metallurgical hardening in an induction heating application, which will result in higher energy efficiency and superior hardness pattern control than in the prior art. Another objective of the present invention is to provide an electric induction heating system and method with contour-like hardness patterns on bearing features, including inner and outer bearing races, with minimal size and shape distortion and reduced peak and maximum temperatures during the austenitizing process steps to produce metallurgically sound microstructures with a reduced probability of bearing race cracking during the heat treatment process. Another objective of the present invention is to provide an electric induction heating system and method that provides simultaneous heat treatment of multiple bearing features in a bearing component where the different geometries of the multiple bearing features and the bearing component are not suited to the placement of the multiple bearing features adjacent to a single induction coil for the efficient simultaneous heat treatment of the multiple bearing features and / or multiple bearing components. BRIEF DESCRIPTION OF THE INVENTION In one aspect the present invention is an electrical induction heat treatment apparatus and method for metallurgically hardening one or more selected bearing features of a bearing workpiece, for example, a region or regions of an inner or outer bearing raceway,with a combined main inductor circuit connected to an AC power supply and a passive inductor circuit wherein the combination of the main and passive circuits are electromagnetically coupled to each other without physical and electrical connection to form at least one pair of complementary main inductor coil and passive inductor coil around which the selected bearing features are placed so that the selected bearing features are coupled with the magnetic flux field created by the pair of complementary coils to inductively heat to austenitize the selected bearing features with subsequent cooling to transform the metallurgical properties of the selected austenitized features. In another aspect, the present invention comprises an electrical induction heat-treating apparatus for a bearing workpiece and a method wherein a bearing workpiece has at least two bearing features for metallurgical heat treatment, which in some embodiments of the invention are separated from each other by means of a bearing feature not subjected to heat treatment. In some embodiments of the invention, a bearing workpiece with a single bearing feature is metallurgically heat-treated, for example, the bearing workpiece in Figure 1C with a single continuous bearing feature. The apparatus and method comprise a main inductor circuit and a passive inductor circuit, with the main inductor circuit and the passive inductor circuit physically separated from each other and without a physical electrical connection between them.The main inductor circuit is supplied with alternating current from a power source to a network of conductors within the main inductor circuit. This network includes at least one main heating inductor configured for initial induction heating of the bearing feature before cooling the bearing workpiece, and a main circuit electromagnetic coupler. The passive inductor circuit comprises a network of conductors within the passive inductor circuit. This network includes at least one passive heating inductor configured for a second induction heating of the bearing feature before cooling the bearing workpiece, and a passive circuit electromagnetic coupler. The main inductor circuit and the passive inductor circuit are positioned adjacent to each other for heating the workpiece.In a process application of the present invention with the main inductor circuit and the passive inductor circuit in the workpiece heating position, at least one main heating inductor and at least one passive heating inductor are configured respectively for simultaneous induction heating of the first bearing feature by a main circuit flow of the main circuit alternating current and the second bearing feature by a passive circuit current flow induced by a magnetic flux coupling of the main circuit alternating current between the main circuit electromagnetic coupler and the passive circuit electromagnetic coupler. After completing the induction heating of at least one first bearing feature and at least one second bearing feature, the bearing workpiece is cooled as required by a particular application, for example, alternatively in the workpiece heating position with a cooling apparatus integrated with at least one main heating inductor, at least one passive heating inductor, at least one main and passive heating inductor, or a cooling apparatus disposed in one or more locations of the cooling apparatus away from the workpiece heating position. οηαΑηη / ζζηζ / Ε / γίΛΐ The foregoing and other aspects of the invention are set forth in this specification and in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, as briefly summarized below, are provided for exemplary understanding of the invention, and do not limit the invention as further set forth in this specification and the accompanying claims. Figure 1A is a side perspective cross-sectional view of a type of bearing feature, primarily an inner bearing race configured in a bearing component described as the 100 bearing workpiece commonly used in heavy-duty bearings for power trains and automotive transmissions, and other heavy-duty applications. Figure IB is an elevation cross-sectional view of the inner bearing race configured on the bearing workpiece 100 in Figure 1A illustrating a longitudinally interrupted hardness pattern (along the longitudinal axis L), containing two circumferentially hardened longitudinal zones (or regions) 101 and 102 separated by a circumferentially unhardened longitudinal region 103. Figure 1C is an elevation cross-sectional view of a configured inner raceway in the bearing workpiece 100 illustrating a circumferentially uninterrupted longitudinal hardness pattern 104, which is an alternative to the longitudinally interrupted hardness pattern in Figure 1B. In Figure 1C, the bearing features, primarily the configured inner raceway zones 101 and 102 (i.e., the bearing roller contact surfaces), are induction hardened together with the circumferential longitudinal region 103 between the inner raceway zones. Figure ID and Figure 1E are perspective views of an outer bearing race configured on bearing workpiece 100'. Figure 1F, Figure 1G, Figure 1H and Figure II are cross-section views of a configured outer bearing race of bearing component 400 illustrating four alternative hardness patterns (zones or regions) 403, 404, 405 and 406 (shown shaded with cross lines) that can be formed in alternative electrical induction hardening processes as required for alternative applications. Figure 1J is a side perspective cross-sectional view of an inner bearing race configured in bearing workpiece 1001' commonly used in heavy-duty bearings for automotive powertrains and transmissions, and other heavy-duty applications exhibiting bearing raceway zones having identical geometries and uniform hardness patterns (which is highly desirable) 101 and 102. Figure 1K is a cross-sectional elevation view of the configured inner bearing race shown in Figure 1J illustrating an interrupted hardness pattern, containing two hardened zones 101 and 102 separated by an unhardened zone (or region 103). Figure 2A is a cross-sectional view of a configured inner bearing raceway illustrating a variety of hardness patterns (in areas shaded with cross lines 106 and 115) in a heating position with a prior art induction heating apparatus comprising a two-turn solenoid-style electric heating inductor with coil turns 301 and 302 and an associated flux concentrator 203 and 204. Coil turn 301 surrounds the region 106 to be heated and coil turn 302 surrounds the region 115 to be heated in Figure 2A. Each coil turn can be connected in series or in parallel with alternating current supplied to the coil from a suitably connected power supply with instantaneous current flowing in the same or opposite direction in the coil turns. Figure 2B is a cross-sectional view of a configured inner bearing raceway illustrating alternative inner bearing raceway geometries and hardness patterns (including areas shaded with cross lines 125 and 126) of those in Figure 2A in a heating position with a prior art induction heating apparatus comprising a two-turn solenoid-style electric heating inductor with coil turns 301 and 302 and associated flux concentrators 203 and 204. Each coil turn can be connected in series or in parallel with alternating current supplied from a suitably connected power supply with alternating current flowing in the same or opposite direction in the coil turns. Figure 2C and Figure 2D are elongated illustrations of selected hardness patterns shown in Figure 2A and Figure 2B respectively. Figure 3A and Figure 3B are diagrammatic illustrations of an induction heating process for heat-treating inner bearing races. They conceptually show uniform and non-uniform circumferential clearance distances between the inductor and an inner bearing race of the bearing workpiece, as represented diagrammatically by the circular boundary of the dashed line of the inner race being heated. Figure 3A illustrates an example of the mutual placement of the coil workpiece during the loading process step of the inner bearing race of the bearing workpiece within the inductor, with a uniform circumferential clearance distance between the inductor and the inner bearing race being heated.Figure 3B illustrates an example of the mutual placement of the workpiece to the coil during the process step of heating the inner bearing race of the workpiece within the inductor 22 with non-uniform circumferential electromagnetic coupling distances 24 and 25. Figure 3C illustrates the resulting circumferentially uniform hardness patterns llaa and llbb assuming sufficiently rapid rotation of the workpiece (i.e., spinning) about axis 50 during induction heating with a conventional workpiece rotation apparatus (not shown in the drawing). Figure 4 is a diagrammatic illustration of a prior art arc-shaped inductor 40 (also known as a hairpin inductor) that can be used to heat treat a configured inner bearing race. Figures 5A through 5D diagrammatically illustrate an embodiment of an electric induction heating system of the present invention, showing a main inductor circuit (Figure 5A) and a passive inductor circuit (Figure 5B). Figures 5C and 5D are alternative perspective views of a main inductor circuit and a passive inductor circuit in a heating position of the workpiece (bearing component). The internal bearing races (bearing features) and the cooling apparatus are not shown for clarity. The arrows indicate relative instantaneous current directions in the heating system. Figure 5C illustrates that this arrangement produces an instantaneous electric current flow direction in the passive inductor 220 that is oriented in the opposite direction compared to the instantaneous current flow in the main inductor 210.This current flow orientation is normally preferred to obtain the interrupted hardness pattern shown in Figure IB. Figure 5E is a diagrammatic illustration of an alternative passive inductor circuit that can be used with the main inductor circuit shown in Figure 5A to produce an instantaneous current flow direction in the passive inductor 220' that is oriented in the same direction as the instantaneous current flow in the active coil 210 (Figure 5C) in the main inductor circuit. This orientation of the electric current flow is typically desirable to obtain an uninterrupted hardness pattern, as shown in Figure 1C. Figure 5F and Figure 5G illustrate alternating instantaneous alternating current directions achieved in the passive inductor coil when the main inductor circuit in Figure 5A is combined with the passive inductor circuit in Figure 5B in one embodiment of the present invention compared to when the main inductor circuit in Figure 5A is combined with the passive inductor circuit in Figure 5E in another embodiment of the present invention. In some embodiments of the invention, the main heating inductor and the passive heating inductor are configured for an instantaneous current flow opposite to the alternating current of the main circuit and the alternating current of the passive circuit. αηαΑηη / ζζηζ / Ε / γίΛΐ Figure 6A illustrates primary electromagnetic coupling regions 230 of a primary inductor circuit and passive electromagnetic coupling regions 240 of a passive inductor circuit when the primary inductor circuit is separated from the passive inductor circuit, for example, when a bearing workpiece to be heat-treated is loaded into a heating position or unloaded from a heating position within a complementary pair of primary and passive inductors, respectively. The primary electromagnetic coupling regions and the passive electromagnetic coupling regions are alternatively referred to as the primary magnetic flux coupler and the passive magnetic flux coupler, respectively. Figure 6B illustrates the primary electromagnetic coupling regions 230 of a primary inductor circuit and the passive electromagnetic coupling regions 240 of a passive inductor circuit when the primary inductor circuit is brought into a workpiece heating position. The active and passive electromagnetic coupling regions are separated by a gap 205 to electrically isolate the active inductor circuit from the passive inductor circuit. The primary and passive inductor circuits are electromagnetically coupled when alternating current is supplied to the primary inductor circuit. In the workpiece heating position (bearing component), the primary magnetic flux coupler is placed adjacent to and physically separated (by a gap 205 in the example in Figure 6B) from the passive magnetic flux coupler. Figure 7A and Figure 7B illustrate alternative cross-sectional arrangements of the shape and composition of the master and passive electrical bus networks. Figure 7A illustrates each bus network comprising the copper tubing, and Figure 7B illustrates a rectangular copper bar sandwiched between the master and passive electromagnetic coupling regions, separated by corresponding gaps 205a (Figure 7A) and 205b (Figure 7B) when in the workpiece heating position. The gaps may be air gaps or filled with a dielectric material. The arrangement shown in Figure 7B is generally preferable to that in Figure 7A due to the improved electromagnetic coupling between the active and passive circuits.The main electrical conductor network and the passive electrical conductor network are alternatively referred to as the main inductor circuit bus network and the passive inductor circuit conductor network, respectively. Figure 8A to Figure 8D diagrammatically illustrate an embodiment of a method of the present invention for inductively heating a bearing feature of the bearing component, such as an inner or outer race, wherein the cooling process steps are performed when the induction heating apparatus remains with the bearing features in the heating position of the apparatus after completing the heating of the bearing features. Figures 9A through 9D illustrate diagrammatically another embodiment of a method of the present invention for inductively heat-treating a bearing feature of a bearing component, such as an inner or outer raceway, wherein the cooling process steps are performed by immersing at least the passive inductor coil of the passive inductor circuit with the bearing features in the cooling tank. In this embodiment, a corresponding section of the passive inductor coil circuit is used as a support (nest) to hold the heat-treated bearing features in place during the cooling process steps. Figures 10A to 10D illustrate diagrammatically another embodiment of a method of the present invention for inductively heat-treating the bearing features in a bearing workpiece, such as an inner or outer bearing race, wherein the cooling process steps commence when the bearing workpiece remains in the induction heating apparatus after the bearing features in the bearing workpiece have been inductively heated with the apparatus in the assembled (heating) position (Figure 10B), and the cooling process continues as the bearing workpiece with the heated bearing features is transferred (Figure 10C) with the passive heating inductor coil 220 in the passive inductor circuit to a cooling tank (Figure 10C) where the cooling process is completed. Figure HA and Figure 11B illustrate diagrammatically another embodiment of a method of the present invention for inductively heat-treating a bearing feature of the bearing component, such as an inner or outer bearing race, wherein the bearing features on at least two separate bearing components (workpieces) are heated simultaneously and combined with subsequent cooling process steps after completion of the simultaneous heating. Figure 12A illustrates an induction heating apparatus of the present invention wherein two separate bearing components (workpieces) can be heated simultaneously and used in the method illustrated in Figure HA and Figure 11B. Figure 12B partially illustrates in elongated detail one end of the induction heating apparatus shown in Figure 12A. Figure 13 is an embodiment of the present invention wherein the induction heating apparatus is placed adjacent to a vertically oriented rotary table where multiple separate workpieces can be loaded, for example, after preheating; rotated to a heat treatment location and loaded into the induction heating apparatus for heat treatment of bearing features; and rotated to a quenching treatment location. Figure 14A is a perspective view of the configured 800b passive inductor assembly of the configured 800 induction heat treatment apparatus shown in a heating position of the bearing component (workpiece) in Figure 16A and Figure 16B. Figure 14B is a top plan view of the passive inductor assembly shown in Figure 14A. Figure 14C is a side cross-sectional view of the passive inductor assembly shown in Figure 14A. Figure 15A is a perspective view of the configured main inductor assembly 800a of the induction heat treatment apparatus 800 shown in a bearing component (workpiece) heating position in Figure 16A and Figure 16B. Figure 15B is a top plan view of the main inductor assembly shown in Figure 15A. Figure 15C is a side cross-sectional view of the main inductor assembly shown in Figure 15A. Figure 16A and Figure 16B are alternate perspective views of an example of the 800 electric induction heat treatment apparatus with the passive inductor assembly 800b (Figure 14A) and the main inductor assembly 800a (Figure 15A) configured in the workpiece heating position for electric induction heating of the workpiece bearing features, such as the inner bearing races. Figure 17A illustrates diagrammatically an alternative split-coil electric induction heat treatment system for simultaneously heating one or more features of a bearing component configured with two separate main inductor circuits fed by separate phase-locked outputs from a single power supply. Figure 17B and Figure 17C illustrate both in-phase and out-of-phase output currents, respectively. Figure 18 illustrates diagrammatically an alternative split-coil electric induction heat treatment system for simultaneously heating one or more features of a bearing component configured with two separate main inductor circuits powered by a single single-output power supply feeding the primary of a transformer with two secondary outputs, each of which feeds a separate main inductor circuit. αηαΑηη / ζζηζ / Ε / γίΛΐ DETAILED DESCRIPTION OF THE INVENTION With regard to the drawings, where similar numbers indicate similar elements, Figures 5A through 5D illustrate diagrammatically an embodiment of the present invention comprising a main inductor circuit 200a and a passive inductor circuit 200b that can be assembled for inductively heat-treating an inner raceway, an outer raceway, or other bearing features of a bearing component used, for example, in heavy-duty applications utilizing rolling elements, bearings, raceways, or rings, including powertrain applications, transmission line applications, and wheel assemblies where the bearing component is of complex construction. The bearing component is alternatively described herein as the bearing workpiece. The main inductor circuit and the passive inductor circuit form an electrical induction heat treatment apparatus for the assembled bearing workpiece 200, as illustrated in Figure 5C or Figure 5D, wherein selective bearing features can be heat treated simultaneously with the main heating inductor and the passive heating inductors configured separately in the main inductor circuit and the passive inductor circuit for each of two or more different bearing features when the main inductor circuit in the main inductor assembly and the passive circuit in the passive inductor assembly are in the bearing component heating position illustrated, for example, in Figure 5C or Figure 5D.Therefore, the apparatus 200 can also be described as a split multiple coil (main heating inductor and passive heating inductor) with a split inductor assembly for simultaneously heating a plurality of bearing features in a bearing component, wherein the split inductor assembly is formed by means of the main inductor circuit in a main inductor assembly and the passive inductor circuit in a passive inductor assembly. In the illustrated embodiment of the invention, the main inductor circuit 200a comprises a main heating inductor 210 formed from: a first single-turn induction coil configured for induction heating of a first bearing feature to be heat-treated simultaneously in the bearing component; one or more main circuit magnetic flux coupling regions 230 forming a main magnetic flux coupler; and main inductor circuit power terminals 6a and 6b. All main circuit components are electrically interconnected by a network of main inductor circuit conductors 201 to form a main circuit in series, with all main circuit components physically and electrically connected in series, except for the main magnetic flux coupler, which is not physically connected in the circuit.The main inductor is separated by an air gap or a gap filled with dielectric material. The main magnetic flux coupler is positioned adjacent to and physically separated from the conductor network of the main inductor circuit 201 to couple the magnetic flux of the main inductor circuit when alternating current flows in the main inductor circuit. The main inductor circuit power supply terminals 6a and 6b connect the main inductor circuit 200a to a suitable AC power supply (designated AC POWER SUPPLY in the drawings). The AC power supply can be selected for a particular application from medium- or high-frequency power supplies known in the art for selective heat treatment of bearing characteristics and can be supplied with input power from the electrical grid where the treatment apparatus is located.with induction heating. The typical power supply rating is on a scale of 30kW to 500kW with an operating frequency of 1 kHz to 180 kHz as required for specified hardness case depths; geometry of the heat-treated bearing features; mass of heated metal material forming the bearing workpiece; and production rate (cycle time per heat-treated bearing feature). The two-wire, single-phase output of the selected power supply is connected to the main inductor circuit's power terminals 6a and 6b either: directly; via a power supply bus network; or via a load-matching transformer, depending on the power supply configuration and load-matching capability. In the embodiment of the invention illustrated in Figures 5B to 5D, the passive inductor circuit 200b comprises a passive heating inductor 220 formed by: a second single-turn induction coil configured for induction heating of a second bearing feature to be heat-treated simultaneously in the bearing component; and one or more passive circuit magnetic flux coupling regions 240 forming a passive magnetic flux coupler. The passive heating inductor 220 forms a series passive inductor circuit physically and electrically closed-loop with a passive inductor circuit conductor network 202.When the apparatus 200 is in a heating position or assembled as in Figure 5C or Figure 5D, the passive magnetic flux coupler is placed adjacent to and physically separated from the passive circuit conductor network 202 and the main inductor circuit conductor network 201 by means of air gaps or gaps with dielectric material so that when a main alternating current flows in the main inductor circuit, a passive alternating current flow is induced in the passive inductor circuit. While the primary and passive heating inductors are configured as single-turn solenoid coils in the figures, other inductor configurations may be used in other instances of the invention as required for a particular configuration of the bearing features to be heated by means of the primary heating inductor or the passive heating inductor, for example, if the internal or external bearing features will be heat treated. In other embodiments of the invention, the active heating inductor or the passive heating inductor may have different configurations, such as a multi-turn coil. Furthermore, in other embodiments of the invention, more than one bearing feature may be heated by the main heating inductor or the passive heating inductor, such that a plurality of more than two bearing features may be heated simultaneously. One or more main circuit magnetic flux coupling regions 230 forming the main magnetic flux coupler and one or more passive circuit magnetic flux coupling regions 240 forming the passive magnetic flux coupler can be alternatively formed from: standard lamination packs; pure ferrites; or conventional iron- or ferrite-based powder materials, including magnetic composites containing pressed and sintered magnetic particles as known in the art. In one embodiment of the invention, the main inductor circuit 200a and the passive inductor circuit 200b are selectively joined (also called the electrical induction heat treatment apparatus assembly in the heating position) from opposite longitudinal side ends of a bearing workpiece (e.g., a bearing workpiece 100 in Figure IB with multiple selected bearing features such as internal bearing races requiring heat treatment) in a step of the heat treatment process of loading the bearing workpiece for heat treatment with the apparatus.This step in the process of assembling the apparatus into the heating position is illustrated in Figure 5C, where the LL axis represents the central inner longitudinal axis LL of the exemplary bearing workpiece 100 in Figure 1B, which is not shown within the main heating inductor 210 and the passive heating inductor 220 for clarity. The main heating inductor descends from the top onto the upper longitudinal side end LL of the bearing workpiece, as indicated by the direction-of-movement arrow MC, and the passive heating inductor rises from below onto the lower longitudinal side end of the bearing workpiece, as indicated by the direction-of-movement arrow PC. Reference is made to FIG.Figure 12A and Figure 12B, where the bearing workpiece 100 is shown placed in the heating position of the heating apparatus 245 within the main heating inductor 210a1' and the passive heating inductor 220b. This configuration of the apparatus assembly in the heating position from opposite longitudinal side ends of the bearing workpiece eliminates the possibility that the geometry of the main circuit inductor or the passive circuit inductor, respectively, will create a physical interference with the feature of the bearing workpiece to be heated by the passive circuit inductor, or the feature of the bearing workpiece to be heated by the active circuit inductor.Similarly, the step in the heat treatment process of unloading (removing) the bearing workpiece after heat treatment from the heat treatment apparatus when the main inductor circuit 200a and the passive inductor circuit 200b is achieved by separating the main inductor circuit and the passive inductor circuit through the opposite longitudinal side ends of the bearing workpiece, as illustrated by the direction of the unloading movement arrow of the main heating inductor MO in Figure 5C in the direction of the unloading movement arrow of the passive heating inductor PO in Figure 5C.The process steps of joining and separating the main inductor circuit with the main heating inductor 210 and the passive inductor circuit with the passive heating inductor 220 from the opposite longitudinal side ends of the bearing workpiece LL allow the proximity (typically 0.5 mm to 6 mm) of the main heating inductor 210 and the passive heating inductor 220 to the bearing features to be heat treated respectively by the main heating inductor and the passive heating inductor, for example, the bearing raceway regions 101 and 102 in Figure IB, when the bearing workpiece 100 has been loaded for heat treatment in the apparatus.In this example, the intermediate track region with the smaller diameter 103 of the bearing workpiece between the heat treatment regions 101 and 102 shown in Figure IB will not obstruct (interfere with) the joining of the main heating inductor (coil) and the passive heating inductor (coil) to the loaded position of the workpiece (heating) since it is not required to have a sufficiently large radial separation 107 illustrated in Figure 2A during the workpiece loading and unloading process steps. In some embodiments of the invention, the split-coil electric induction heating system includes a split-inductor assembly positioning apparatus configured to bring together the main inductor circuit and the passive inductor circuit in the assembled (heating) position and to separate the main inductor circuit and the passive inductor circuit from the assembled (heating) position together with the movement of the main and passive magnetic flux coupler as indicated by the arrows in Figure 5C, which may represent linear actuators for movements shown by the arrows.In the assembled (heating) position, the main heating inductor of the main inductor assembly is longitudinally aligned with the passive heating inductor of the passive inductor assembly, and the placement of the passive magnetic flux coupler is adjacent to the main magnetic flux coupler and physically separated from it when the first bearing feature is positioned for inductive heating with the main heating inductor and the second bearing feature is positioned for inductive heating with the passive heating inductor for simultaneous heating of the first bearing feature and the second bearing feature.In the non-heating position, the main heating inductor of the main inductor assembly is separated from the passive heating inductor of the passive inductor assembly for the placement of the bearing component in the heating position of the bearing component for inductive heating of the first bearing feature and the second bearing feature or removal of the bearing component after inductive heating of the first bearing feature and the second bearing feature in the heating position of the bearing component. Figure 5C and Figure 5D show perspective views of the main inductor circuit 200a and the passive inductor circuit 200b after they are joined in a bearing workpiece heating position with a loaded bearing workpiece placed inside the main circuit inductor and the passive circuit inductor. The bearing workpiece is not shown (with an optional post-heating cooling apparatus) in these figures for clarity of the assembled main heating inductor and passive heating inductor circuit. In the embodiment of the invention illustrated in Figure 5A to Figure 5D, the conductor network of the passive inductor circuit 201 and the conductor network of the passive inductor circuit 202 are illustrated as copper pipe buses arranged respectively between the magnetic flux coupling regions of the main U-shaped circuit 230 and the magnetic flux coupling regions of the passive circuit 240. There is no physical contact or electrical circuit contact between the main inductor circuit components 200a and the passive inductor circuit components 200b when they are in the workpiece heating position as shown, for example, in Figure 5C or Figure 5D, and when one or more heat treatment process steps are performed to heat the bearing features of a bearing workpiece placed adjacent to the main and passive heating inductors.The magnetic flux coupling regions of the main inductor circuit 230 are positioned adjacent to, but physically separated from, the magnetic flux coupling regions of the passive inductor circuit 240 by a separation distance 205 as illustrated by the cross-sectional detail in Figure 5C or Figure 5F to transfer the magnetic flux established by the alternating current flow in the conductor network of the main inductor circuit to the passive inductor circuit. Figure 16A and Figure 16B illustrate in alternative perspective views an embodiment of an induction heat treatment apparatus configured 800 of the present invention using an assembled induction heat treatment apparatus 200 similar to that shown in Figure 5C and Figure 5D. The induction heat treatment apparatus configured 800 is shown in Figure 16A and Figure 16B in the bearing component (workpiece) heating position with an exemplary bearing workpiece 900 loaded into the apparatus for simultaneous heating of two bearing features in the bearing workpiece.In this non-limiting example, the bearing component has an upper inner bearing race (also referred to as the first bearing feature of the workpiece to be heated by the main heating inductor) that requires heat treatment and a lower inner bearing race (also referred to as the second bearing feature of the workpiece to be heated by the passive heating inductor) that requires simultaneous heat treatment, with axial separation between them by the workpiece feature of the central bearing that is not heat treated.The interior of the bearing workpiece 900, which is not visible in Figure 16A and Figure 16B because the workpiece is loaded in the heating position of the bearing component of the apparatus 800, may be, for example, similar to the interior of the bearing workpiece 100 in Figure 1A and Figure 1B, where the upper inner bearing race is inner bearing race 101a; the lower inner bearing race is 102a; and the feature of the unheated center bearing workpiece is region 103 in Figure 1A and Figure 1B. The configured induction heat treatment apparatus 800 comprises a configured main inductor assembly or section 800a and a configured passive inductor assembly or section 800b. Figures 14A through 14C are various views of the passive inductor assembly configured 800b when separated from the active inductor assembly configured 800b, for example, in an unheated position of the bearing workpiece. Figures 15A through 15C are various views of the main inductor assembly configured 800a when separated from the passive inductor assembly configured 800b, for example, in an unheated position of the bearing workpiece. In this example of the invention, the passive inductor assembly configured 800b is referred to alternatively as the lower inductor assembly and the main inductor assembly configured 800a is referred to alternatively as the upper inductor assembly for convenient descriptive orientation, and not to limit the orientation of the passive inductor assembly and the main inductor assembly forming an induction heat treatment apparatus 800. The configured main inductor circuit 800a comprises: a main heating inductor 710 formed from a first induction coil of one turn in this non-limiting example, mounted around or near the lower end of the mandrel 420a; main circuit magnetic flux coupling regions 730a and 730b forming a main circuit magnetic flux coupler; and main inductor circuit power terminals 6a and 6b separated by electrical insulating material 7; all of which components are associated with the main inductor circuit conductor network 701. The main inductor circuit power terminals 6a and 6b connect the main inductor circuit 800a to a suitable AC power supply (designated AC POWER SUPPLY in the drawings).The main heating inductor is configured for induction heating of the first bearing feature of the workpiece to be heat-treated. In some embodiments of the invention, mandrel 420a is referred to as the cooling mandrel, as described below. The configured main inductor circuit 800a further comprises an optional upper main magnetic flux concentrator 203a that is ring-shaped and positioned above the main heating inductor 710 around the cooling mandrel 420a, and an optional lower main magnetic flux concentrator 204a positioned below the main heating inductor to direct the inductive heating flux to the first bearing workpiece feature heated by the main heating inductor 710. The configured main inductor circuit 800a further comprises components of an auxiliary main inductor circuit forced liquid cooling medium system with main inductor circuit cooling medium provided by supply cooling tube 425a and return cooling tube 425b and is circulated in an internal gap through passage in the main inductor circuit conductor network 701. In this non-limiting example, the configured main inductor circuit 800a includes an optional integrated cooling apparatus, mainly the cooling mandrel 420a with cooling passages not shown in the figures that supply temper to the heat-treated features of the bearing workpiece in the workpiece heating position with temper supplied through temper supply ports 421a and 421b near the top end of the cooling mandrel. The configured main inductor circuit 800a further comprises one or more main inductor circuit support structures as required for a particular arrangement of a configured main inductor circuit. In this example shown in the figures, the configured induction heat treatment apparatus 800 includes, but is not limited to, a support clamp block 420b that retains the cooling mandrel 420a in position; a support riser 420c; and an adjustable support bridge 420d. The passive inductor circuit configured 800b comprises: a passive heating inductor 720 formed from a second induction coil of one turn in this non-limiting example, mounted around and near the upper end of the support post 410a (also referred to as the vertically oriented support structure); passive circuit magnetic flux coupling regions 740a and 740b forming a passive circuit magnetic flux coupler; all of which components are associated with the passive inductor circuit conductor network 702, also referred to as the passive inductor bus network, forming an electrically closed-loop passive bus network. The passive heating inductor is configured for induction heating of the second bearing feature of the workpiece to be heat-treated. The configured passive inductor circuit 800b further comprises an optional upper passive magnetic flux concentrator 203b that is ring-shaped and positioned above the passive heating inductor 720 around the support post 410a, and an optional lower passive magnetic flux concentrator 204b disposed below the main heating inductor to direct the inductive heating flux to the bearing workpiece feature being heated by the passive heating inductor 720. The passive inductor circuit configured 800b in the illustrated embodiment of the invention further comprises components of a forced liquid cooling system for the auxiliary passive inductor circuit with cooling medium for the passive inductor circuit provided by the supply cooling tube 406a and a return cooling tube 406b and is circulated in an internal cavity through the opening in the passive inductor circuit conductor network 702. The configured passive inductor circuit 800b further comprises one or more passive inductor circuit support structures as required for a particular arrangement of a configured passive inductor circuit. In the example shown in the figures, the configured induction heat treatment apparatus 800 includes, but is not limited to, a support post 410a (also referred to as the vertically oriented support structure); the passive circuit inductor mounting base 410b; and the passive circuit support cradle 410c. The configured main inductor circuit 800a and the passive inductor circuit 800b can be joined (also referred to as the electric induction heat treatment apparatus assembly) from opposite longitudinal side ends of a bearing workpiece (e.g., bearing workpiece 900) with selected multiple features of internal bearing races requiring heat treatment) in a heat treatment process step of loading the bearing workpiece for heat treatment with the apparatus.The assembly of the apparatus at opposite lateral ends of the bearing workpiece eliminates the possibility that the geometry of the main circuit inductor or the passive circuit inductor, respectively, will create physical interference with the feature of the bearing workpiece to be heated by the passive circuit inductor, or the feature of the bearing workpiece to be heated by the active circuit inductor. Similarly, the step in the heat treatment process of unloading (removing) the bearing workpiece after heat treatment from the heat treatment apparatus is achieved by separating the configured main inductor circuit and the configured passive inductor circuit from each other by means of opposite longitudinal lateral ends of the bearing workpiece.In some embodiments of the invention (for example, as illustrated in Figures 9A to 9D and 10A to 10D), the passive inductor circuit configured 800b is separated from the main inductor circuit configured 800a but not from the bearing workpiece (Figures 9C and 10C), with the bearing workpiece seated in the passive inductor with the dielectric insulation of the passive inductor in a structure known in the art as a dielectric nest. Only after the cooling cycle is completed is the bearing workpiece finally removed from the passive inductor circuit configured 800b.The steps of the process of joining and separating the main inductor circuit and the passive inductor circuit from opposite longitudinal side ends of the bearing workpiece allow the main heating inductor 710 and the passive heating inductor 720 to be placed in close proximity to the bearing features to be heat-treated, respectively, by the configured main heating inductor and the configured passive heating inductor. In the embodiment of the invention illustrated in Figures 5A to 5D, the conductor network of the passive inductor circuit 201 and the conductor network of the passive inductor circuit 202 are illustrated as copper pipe buses arranged between the magnetic flux coupling regions of the U-shaped main circuit 230 and the magnetic flux coupling regions of the passive circuit 240. There is no physical contact or electrical circuit contact between the components of the main inductor circuit configured 800a and the components of the passive inductor circuit configured 800b when they are in the workpiece heating position as shown, for example, in Figure 16A or Figure 16B, and when one or more steps of the heat treatment process are performed.The magnetic flux coupling regions of the main inductor circuit configured 730a and 730b are positioned adjacent to, but physically separated from, the magnetic flux coupling regions of the passive inductor circuit configured 740a (hidden in the drawing views) and 740b by the separation distance 705, as illustrated in Figure 16A and Figure 16B, to transfer the magnetic flux established by the alternating current flow in the conductor network of the main inductor circuit 701 to the conductor network of the passive inductor circuit 702. In some embodiments of the invention, an electrical insulator is positioned between the magnetic flux coupling regions 730a and 730b, and / or between the magnetic flux coupling regions 740a (hidden in the drawing views) and 740b, and / or between the networks of the main inductor 701 and the passive inductor 702. An electrical induction heating apparatus for the bearing workpiece of the present invention, for example, the configured induction heat treatment apparatus 800, can be moved between a workpiece heating position as shown in Figure 16A or Figure 16B by moving the configured main inductor circuit or the configured passive inductor circuit or both, the configured main and passive inductor circuits relative to each other in a direction (or directions) away from each other so that they are separated from each other and the loaded bearing workpiece (for example, the bearing workpiece 900 in Figure 16A or Figure 16B).By way of example and not limitation, the separation movement between the main and passive inductor circuits configured for loading or unloading the bearing workpiece from the workpiece heating position shown in Figure 16A or Figure 16B (with the suitable electromechanical workpiece transport apparatus not shown in the figures) can be achieved with one or more suitable electromechanical linear or rotary actuators configured for directional movement as required for a particular application. After completing a cycle of heating and austenitizing the selected bearing workpiece features with the 800 electric induction heat treatment apparatus illustrated in Figure 14A to Figure 16B, the cooling of the heat-treated bearing workpiece features can be achieved with a cooling apparatus integral with the heating apparatus or placed in a remote location from the heating apparatus as described herein, or as otherwise known in the art. Figure 7A and Figure 7B illustrate in cross-sectional views the magnetic flux coupling regions of the main and passive circuit 230 and 240 (magnetic flux concentrators) shown in Figure 6B when used alternately in an application where: (1) the main and passive inductor bus networks are formed from the electrically conductive pipe 201a and 202a (such as a copper composition) inserted between (also referred to as interleaved) electromagnetic coupling regions 230a and 240a in Figure 7A; or (2) the main inductor and passive bus networks are formed by electrically conductive rectangular bars 201b and 202b (like a copper bus bar) or rectangular-shaped tubing (not shown) inserted between electromagnetic coupling regions (also called interleaved) 230b and 240b in Figure 7B in air gaps or dielectric material gaps.The use of rectangular copper buses illustrated in Figure 7B is most commonly used. The air gaps spaced in the hot position, illustrative 205a in Figure 7A and 205b in Figure 7B, are sufficiently large to prevent arcing or short-circuiting between the main inductor circuit elements 200a and the passive circuit elements 200b. Although air is not a preferred dielectric material, in alternative embodiments of the invention, an air gap may serve as a sufficient dielectric, or the hot position separation spaces 205a or 205b may be filled with a conventional dielectric material known in the art for electrically insulating the electrical conductors. Such conventional dielectric materials include dielectric tapes, ceramic coatings, or other electrical insulating materials known in the art. The separation air gap 205a in Figure 7A and the separation air gap 205b in Figure 7B should not be too large so as to adversely affect the electromagnetic coupling between the main inductor circuit 200a and the passive inductor circuit 200b. Normally, but not by way of limitation, the size of the separation air gaps 205a and 205b (Figure 7B) is within a range of 0.5 mm to 6 mm depending on the electrical frequency, the magnitude of the electrical current, and the condition of the working environment (such as, but not limited to, humidity, dew, and the presence of electrically conductive dust). Reference is made to the teachings of U.S. Patent No. 6,274,857 and U.S. Patent No. 6,859,125 for the manufacturing features of the main and passive circuit magnetic flux coupling regions 230 and 240 for a particular application, including the selection of an appropriate geometry of the magnetic flux couplings and methods for retaining them in place, as well as the selection of an appropriate size of the separation air gap 205. In one embodiment of a process of the present invention, after loading a workpiece with one or more features to be inductively heated and placing the main and passive induction coils of an apparatus of the present invention in the heating position as shown in Figure 5A and Figure 5B, the alternating current power supply connected to the power terminals of circuit 6a and 6b is energized to initiate the flow of alternating current in the main inductor circuit. The magnetic flux coupling regions of the main and passive circuits 230 and 240 provide electromagnetic coupling between the powered main inductor circuit and the short-circuited passive inductor circuit, electrically similar to the effect between the core windings of a transformer.The alternating current flowing in the main circuit inductor will instantly (in practical terms) generate electric currents flowing within the closed-loop passive circuit thanks to the magnetic flux coupling regions of the main and passive circuits, similar to the flow of electric current in the primary and secondary windings of a power transformer. The instantaneous alternating current induced in the passive inductor circuit 200b will be oriented in the opposite direction to that of the source current flowing in the main inductor circuit, as illustrated, for example, by the arrows in Figure 5C. However, depending on the connections of the alternative circuit, the alternating currents flowing in the main inductor coil 210 of the main circuit 200a and in the passive inductor coil 220 of the passive inductor circuit 200b can be oriented in opposite directions or in the same direction. For example, the main and passive circuit connections illustrated in Figure 5A to Figure 5C produce an alternating current flow in the passive inductor coil 220 of the passive inductor circuit that is instantaneously oriented in the opposite direction to the coil current flowing in the main inductor coil 210 of the main circuit.This opposite current direction is beneficial for obtaining a hardness pattern shown, for example, in Figure 1B, Figure 1J, and Figure 1K, which are the most commonly desired hardness patterns for most internal bearing races used, for example, in automotive applications. In contrast, if the desired hardness pattern is as illustrated, for example, in Figure 1C, then it may be beneficial to change the circuit arrangement of the passive inductor circuit to orient the instantaneous coil current flowing in the passive inductor coil 220 in the same direction as the main inductor circuit current supplied by the connected power supply and flowing in the main inductor coil 210. A possible example of such a connection is illustrated in Figure 5E.Figure 5F and Figure 5G illustrate alternating instantaneous current flows in the passive inductor coil of a passive inductor circuit. Figure 5F illustrates an instantaneous direction of alternating current flow for the passive inductor circuit 200b with passive inductor coil 220 for the electrical circuit shown in Figure 5B and Figure 5C. Figure 5G illustrates an instantaneous direction of alternating current flow for the passive inductor circuit 200b' with passive inductor coil 220' shown in Figure 5E. Despite having the same instantaneous orientation of electric current flowing in the passive circuit 202 shown in Figure 5F and Figure 5G, the electric current flowing in passive inductor coil 220' (Figure 5G) is oriented in the opposite direction to the electric current flowing in passive coil 220 (Figure 5F). For a typical design application of a modality of the induction heat treatment apparatus of the present invention, with sufficient electromagnetic coupling between the main inductor circuit 200a and the passive inductor circuit 200b, the difference between the current flowing in the main induction coil 210 of the main inductor circuit 200a supplied to the power terminal connections 6a and 6b from an AC power supply and the current induced in the passive induction coil 220 of the passive inductor circuit 200b can be less than 10 percent, and the difference can be further compensated by profiling the coil heating face geometry (e.g., profiling the copper geometry) of the active induction coil 210 and the passive induction coil 220.In some embodiments of the invention, it is sufficient to provide a space between the passive induction coil and the workpiece that is 0.25 mm to 2 mm smaller than the space between the main induction coil and the workpiece to compensate for the difference in magnitudes of currents flowing in the main induction coil 210 and the passive induction coil 220. In other embodiments of the invention, it is advantageous to strategically position the bearing race in the heating position so that the lower mass region of the bearing race area will be heated by a passive induction coil located in the passive inductor circuit.For example, region 115 in Figure 2A has a smaller mass of metal that is required to be heat treated compared to region 106 in Figure 2A; thus in the heating position it is beneficial to place the passive induction coil 220 of the passive inductor circuit (lower current magnitude) to heat the smaller mass region 115 and to place the main induction coil 210 of the active inductor circuit (higher current magnitude) to heat the larger mass region 106. In the example shown in Figure 2A, for illustrative purposes only, water-cooled round copper tubing is used for coil fabrication. In other cases, the coil may be formed alternatively by: CNC machining of a solid copper block; brazing suitable copper components; or stamping profiled heating faces of the coil turns to match the geometry of the internal bearing raceways 115; or the coil may be manufactured using an additive manufacturing technique, such as 3D printing. Conventional magnetic flux concentrators 203 and 204 can be applied to improve heating efficiency and concentrate the magnetic field generated by each turn 301 and 302 of a two-turn coil for heating the inner bearing raceways. Magnetic flux concentrators are typically manufactured from standard lamination packs, pure ferrites, or conventional iron- or ferrite-based powder materials (such as magnetic compounds) containing pressed and / or sintered magnetic particles. The coil configurations of the present invention illustrated in Figure 5A to Figure 5D allow for minimal possible gaps between the induction coil and the workpiece without any restriction associated with obstruction of the smaller diameter region 103 (e.g., as shown in Figure 1B) during charging and discharging.The present invention results in providing substantially narrower coupling gaps between an induction coil and the workpiece surface compared to prior known techniques, resulting in high energy efficiency, better control of the hardness pattern, and also enabling contour-like hardness patterns with minimal size and shape distortion, reduced peak and maximum temperatures during austenitizing, and production of metallurgically sound microstructures with a reduced probability of bearing race cracking during heat treatment and operation. Depending on the requirements of a particular application, the induction heat treatment apparatus and method of the present invention are arranged alternatively in a vertical or horizontal orientation. In vertical arrangement applications of the apparatus and method, a passive circuit 200b (including an induction coil 220) can be provided in combination with a support pedestal (e.g., a workpiece support structure (nest)) on which the bearing race to be heat-treated is placed. In this vertical arrangement, the bearing race resting on the pedestal can be lifted (raised) into the heating position and held in the heating position for the heat-treating cycle, as illustrated in Figures 8A to 10D. According to a possible design of the present invention, an induction coil of the main circuit 200a (Figure 5A) is held stationary, and the bearing track 100 (Figure 1A), after being placed on the pedestal (or in the resting nest that forms part of the passive circuit 200b, which includes an induction coil 220), moves into and out of the heating position. Since the passive circuit 200b represents a closed-loop electrical system and can move freely into and out of the heating position, it is not necessary to move electrical power connection cables carrying high electrical current to the passive circuit 200b. The mechanism for moving the workpiece into and out of the heating position can be hydraulic, pneumatic, or electric. According to another design concept of the present invention, the induction coil 210 of the main circuit 200a moves in and out of the heating position, but the bearing race 100 does not move in the axial direction. Depending on the hardness pattern specification and the essential geometry of the bearing surface, the bearing can be rotated during the heating cycle using standard means. The conventional lift-and-rotate configuration, as known in the art for small and medium-sized workpieces, can provide a low-cost machine option. A cylinder raises the workpiece bearing to the working position, and an electric motor begins rotating the workpiece. As an option, an adjustable hard stop can be used for workpiece positioning. In this case, a clamping mandrel or clamping block can hold the bearing in a heating position while simultaneously allowing it to rotate during heating without needing to rest statically on a pedestal during rotation. In other embodiments of the invention, the bearing race of the workpiece 100 is held static during heating as described herein. Conventionally designed single-turn coils have an area where an unavoidable distortion of the magnetic field occurs, leading to a certain reduction in heat intensity. This area corresponds to the region where the copper busbars that transmit the electrical current from the power supply connect to an induction coil (the so-called polarized coil power wire region). The physical phenomenon responsible for this reduction in heat intensity is known as the electromagnetic field edge effect (also called the fishtail effect) and has been explained in the literature, for example, the Induction Heating Handbook. Rotating the workpiece during heating helps to eliminate (practically speaking) the heat deficit in the divided area.If the workpiece bearing raceway is heated statically (without rotation), it is still possible to minimize the heat intensity deviation. The industry has developed a variety of standard means to effectively control and compensate for the field edge effect in static induction heating applications using single-turn coils with a suitable copper coil profile. The enhanced electromagnetic coupling (proximity effect) in the split region of the single-turn coil compensates for the magnetic field edge, eliminating the need to rotate the heated workpiece. These field intensity compensation techniques in the vicinity of the coil's split region have been described in numerous publications, including U.S. Patent No. 6,274,857, and can be used in the present invention when the bearing raceway 100 is heated statically without rotation. After completing the heating cycle and appropriate austenitizing, the bearing raceway can be cooled in place or out of place by applying conventional quenching techniques suitable for a selected liquid quench or, in cases of sufficient hardenability of the steel, by applying an alternative cooling medium to the liquid quenching medium, such as forced air quenching or gas quenching. Figures 8A to 8D illustrate diagrammatically one embodiment of a method of the present invention for heat treatment of a bearing raceway. The electrical induction heating apparatus used in the illustrated method is formed, for example, from a main inductor circuit 200a (Figure 5A) and a passive inductor circuit 200b (Figure 5B).After loading a bearing raceway for heat treatment onto a pedestal or loading and unloading mounting device (not illustrated in the figures) that places the unheated bearing raceway inside or around the outside (depending on whether the bearing raceway is an inner or outer raceway) of the main inductor coil 210 of the main inductor circuit 200a with the separate heating apparatus (track loading position) in Figure 8A, the complete passive inductor circuit 200b (including passive coil 220, passive circuit magnetic couplers 240 and passive bus network 202) is raised to the track heating position shown in Figure 8B.In the track heating position, the main circuit and passive circuit electromagnetic couplers 230 and 240 are placed in close proximity to each other and surround the corresponding segments of the main bus network 201b and the passive bus network 202b (see Figure 5A to Figure 5C) which is formed from copper electrical conductors to create an electromagnetic link 250 (illustrated as a discontinuous elliptical region in Figure 8B when power is applied to the main inductor circuit 200a by means of a connection to an AC power supply (AC PS).In the process step shown in Figure 8B, coils 210 and 220 are located in their respective heating positions to initiate the heat cycle for the desired bearing race regions, for example, bearing race regions 101 and 102 in Figure IB if the bearing race being heated is bearing race 100 shown in Figure IB.After the heating cycle is complete, power is removed from the main inductor circuit 200a, and the main and passive inductor circuits are de-energized. At this point, a spray cooling cycle begins either instantly or after a short delay (also known as a soak time) to cool the bearing raceway regions loaded into the heating apparatus, as shown in Figure 8C. A conventional spray cooling device 71 (e.g., a spray cooling block or a liquid cooling sprayer) can be used. Depending on the bearing raceway geometry specifications and the required hardness pattern, a short delay in the cooling time may help achieve a suitable heat profile. The cooling delay typically does not exceed 5 seconds.After the spray cooling cycle is complete, the heat-treated bearing raceways (not shown in the figures) and the complete passive inductor circuit 200b are lowered, as shown in Figure 8D, to a bearing raceway unloading position where the heat-treated bearing raceway is unloaded from the pedestal. In a sequential, continuous bearing raceway heat treatment process, a subsequent unheat-treated bearing raceway is loaded onto the pedestal, and the induction heat treatment process described in Figures 8A through 8D is repeated. Figures 9A to 9D illustrate diagrammatically another embodiment of a method for heat treating the bearing raceway of the present invention, similar in some process steps to the method described in Figures 8A to 8D. In the method of Figures 9A to 9D, the first two process steps are as described above for the steps of the method illustrated in Figures 8A and 8B, except for the positioning of the cooling tank 70 below the bearing raceway heating apparatus.Once the heating cycle is complete, the power supply to the main inductor circuit 200a is removed, and the power supply to the main and passive inductor circuits is discontinued. At this point, the bearing raceway with the heated and austenitized regions and the complete passive inductor circuit 200b are transferred from the bearing raceway heating position to the cooling tank 70 below the surface level of a fluid quencher 70a, where the cooling cycle begins as illustrated in Figure 9C. Preferably, but not necessarily, the fluid quencher is agitated (e.g., by stirring) in the cooling tank to improve cooling uniformity and other preferred cooling characteristics.Once the cooling cycle is complete, the heat-treated and cooled bearing raceway 100 (not shown in the figures) is lifted into position for unloading from the passive inductor coil via its pedestal or mounting device and is then removed from the pedestal or mounting device. In a sequential, continuous bearing raceway heat treatment process, a subsequent, unheat-treated bearing raceway is loaded onto the mounting pedestal, and the induction heat treatment process described in Figures 9A through 9D is repeated. Some steels that can be used to form bearing raceways have poor metallurgical hardenability and, therefore, may be sensitive to a cooling delay during the time it takes to transport the bearing raceway to a cooling tank, as illustrated in the method described above in relation to Figures 9A to 9D. The temperature of such steels after heating and austenitizing can potentially fall below the minimum required temperature level, and metallurgically undesirable structures can form with slow cooling. Figures 10A to 10D diagrammatically illustrate another embodiment of a method of the present invention for heat-treating a bearing raceway. The heat-treating method illustrated in Figures 10A to 10D is a modification of the method illustrated in Figures 9A to 9D.The process steps identified in Figure 9A, Figure 9B, and Figure 9D are performed in the same way in the process steps identified in Figure 10A, Figure 10B, and Figure 10D. The process step identified in Figure 10C is modified from the process step in Figure 9C in that spray cooling block 72 cools (as indicated by the cooling spray arrows) the heated and austenitized bearing race that is fixed relative to the passive inductor coil 220 as the entire passive inductor circuit 200b with the fixed heated and austenitized bearing race is lowered into the fluid cooling 70a in the cooling tank 70 to complete the cooling process. The method illustrated in Figure 10A to Figure 10D is particularly useful when immediate and / or uninterrupted cooling is required after austenitization due to the metallurgical properties of the heat-treated bearing raceway. Based on common industrial practice with electric induction heat treatment processes, the cooling time for a workpiece is typically 2 to 4 times longer than the heating and austenitizing time. Consequently, the heat treatment production rate of the heat-treated bearing raceways and the power supply utilization may be lower than desired in certain applications with any of the methods described in Figures 8A to 8D, 9A to 9D, and 10A to 10D. αηαΑηη / ζζηζ / Ε / γίΛΐ Figure 11A and Figure 11B illustrate diagrammatically another embodiment of a method of the present invention for heat treating the bearing raceway, which is an alternative for increasing the production speed of heat treating bearing raceways using the improved power supply. The electrical heating apparatus used in the illustrated method is formed, for example, from the main inductor circuit 200a with multiple main inductor coils 210a and 210b and the passive inductor circuit 200b with multiple passive inductor coils 220a and 220b to form an electric induction heating apparatus 245 shown in the bearing raceway heating position in Figure 12A.The heating apparatus 245 in Figure 12A illustrates a method of the present invention for increasing the production of the heat-treated bearing raceway and raising the utilization of the applied feed. In the method illustrated in Figure HA and Figure 11B, two bearing raceways (one on each of the two pairs of main and passive induction coils) can be simultaneously heat-treated and then simultaneously cooled using a suitable spray-cooling device (such as the device 73 in Figure HA or Figure 11B) as known in the art or with alternative, but not limited to, cooling process steps described in the methods of Figure 8A to Figure 8D; Figure 9A to Figure 9D; and Figure 10A to Figure 10D. Figure 12A illustrates an alternative arrangement of an electric induction heating apparatus of the present invention in a heating position while using multiple induction coils in the main and passive circuits, primarily two coils 210a” and 210b in the main inductor circuit and two coils 220a and 220b in the passive inductor circuit, to simultaneously heat raceways in two bearing workpieces. Only one bearing workpiece is illustrated in Figure 12A for convenience. Figure 12B is an enlarged view of the left end of the heating apparatus shown in Figure 12A. As shown in Figure HA through Figure 11B, multiple coils 210a and 220b of a main inductor circuit 200a are electrically connected in series. In an alternative arrangement of an electric heating apparatus of the present invention, multiple coils 210a and 220b of a main inductor circuit 200a may be electrically connected in parallel or in a combination thereof. Similarly, multiple coils 220a and 220b in the passive circuit 200b may also be electrically connected in parallel or have a combination of series / parallel connections. A rotary table can be used to increase production speed, where cooling can be performed in multiple locations outside the heating position. This type of system can also be used if the component requires hardening different areas on the same workpiece. The rotary table can be positioned horizontally, vertically, or at an angle. Figure 13 illustrates an example of an induction heating system of the present invention comprising a vertically oriented rotary table 330 having three stations for the heat treatment of two workpiece bearings simultaneously. With the table rotating counterclockwise as indicated by the arrow, two workpiece bearings 100x to be heat treated are loaded onto the rotary table at station 333, which may be referred to as the pre-heating loading and post-heating unloading station; two workpiece bearings 100y are loaded into a double workpiece heating apparatus of the present invention (e.g.,The exemplary heating apparatus 245 shown in Figure 12A) adjacent to table station 331 (bearing workpiece heating station) where the bearing raceways are loaded into apparatus 245; induction heated; austenitized and unloaded from apparatus 245; and two heated and austenitized workpiece bearings 100 are in cooling table station 332 where they are cooled in cooling 70a (shown as a dotted cooling surface area in the drawing) in cooling tank 70. The rotary table indexes two workpiece bearings at a time from table station 331,to table station 332 to table station 333. In some embodiments of the invention, an additional spray-cooling device (not shown in the drawing) is installed between the heating table station 331 and the cooling table station 332 to cool the austenitized bearing race features of the workpiece during transport between these two stations. The additional spray-cooling device may be similar to the spray-cooling block 72 in Figure 10C to provide stationary or agitated liquid quenching. In other embodiments of the invention, a plurality of table stations are provided for heating or cooling, or alternatively heating or cooling. In other embodiments of the invention,The rotary table is oriented horizontally or at a skew angle from the horizontal or vertical. The bearing raceway features can be heated while stationary on the rotary table's heating devices or rotated by a conventional rotating apparatus, such as a rotary actuator, as known in the art. In other embodiments of the invention, a shuttle apparatus is used to perform the function of the rotary table for transporting the workpiece bearings between different process positions (e.g., from heating to cooling and loading and unloading positions). Figure 17A illustrates diagrammatically another aspect of the present invention comprising a split multi-coil electrical induction heating system having a split inductor assembly for simultaneously heating a plurality of bearing characteristics in a bearing component and the alternating current (AC) power supply 160a containing at least two phase-blocking outputs 161 and 162. Any AC power supplies known in the art, including but not limited to electrical devices fabricated based on semiconductor technology (e.g., AC power supplies based on thyristors or transistors), are suitable for use as the AC power supply 160a provided they have at least two phase-blocking outputs 161 and 162. The split inductor assembly comprises two separable main inductor assemblies in a bearing component heating position. The first main inductor circuit conductor network 6a and 6b connects the first phase-lock output 161 of the AC power supply 160a to the first main heating inductor 210 (as illustrated in Figure 17A). The second main inductor circuit conductor network 6c and 6d connects the second phase-lock output 162 of the AC power supply 160a to the second main heating inductor 220. Thanks to the phase-locking capability of the 160a AC power supply outputs, the instantaneous inductor current flow in the first main heating inductor 210 and the instantaneous inductor current flow in the second main heating inductor 220 can be oriented in opposite directions, as illustrated by the current waveforms in Figure 17B, or the instantaneous inductor current flow in the first main heating inductor 210 and the instantaneous inductor current flow in the second main heating inductor 220 can be oriented in the same direction, as illustrated by the current waveforms in Figure 17C.Therefore, depending on the hardness pattern requirements for the bearing features (e.g., the interrupted bearing race hardness pattern illustrated in Figure 1B or the uninterrupted bearing race hardness pattern illustrated in Figure 1C), this phase-locking capability of the AC power supply outputs according to an alternative embodiment of the present invention will provide a desirable orientation of the instantaneous electric current flow in the first main heating inductor 210 and the second main heating inductor 220 (similar to those shown in Figure 5C, Figure 5F, or Figure 5G). The electrical power supplied by each of the two phase-locked outputs 161 and 162 of the AC power supply 160a (and therefore the power supplied to each of the heating inductors 210 and 220) is controlled independently, allowing compensation for possible differences in the masses of the heated metal, as illustrated in Figure IB (compare the characteristic zones 101 and 102 or bearing regions where the rolling elements (e.g., balls or rollers) move against internal bearing raceways). 101a and 102a respectively). As an alternative approach to using a single 160A AC power supply with multi-output phase-lock capability 161 and 162, a person skilled in the art and benefiting from the teachings of a previously described specification may use two different AC power supplies with output phase-lock capability instead of using the single 160A AC power supply described above. This modification does not depart from the scope of the present invention. Throughout the main passive design concept (e.g., Figure 5C or Figure 12A), a more cost-effective approach is used because it requires a conventional and less complicated AC power supply 160, compared to the more complex AC power supply 160a. Under certain conditions, using the AC power supply 160a, which contains at least two phase-locked outputs 161 and 162, could be beneficial and preferable, exhibiting certain process advantages. These conditions include, but are not limited to, higher frequency applications (e.g., frequencies ranging from 70 kHz to 600 kHz).Alternatively or in addition to these conditions, this includes applications where there are significant differences in the masses of metals required to be heated simultaneously (the differences in masses discussed above may be associated with corresponding differences in the geometries of the bearing features to be hardened (compare zones 101 and 102 of the bearing features or the regions where the rolling elements move against the internal bearing raceways 101a and 102a respectively, as shown in Figure IB)). Alternatively or in addition to these conditions, this includes applications where a bearing component consists of more than two bearing features required to be heat-treated simultaneously and having substantially different geometries.Alternatively or in addition to these conditions, it includes applications where the bearing component consists of a plurality of bearing features exhibiting a combination of uninterrupted or interrupted hardness patterns. These are just a few exemplary cases where the use of an induction heating system having multiple main inductors (such as Figure 17A, for example) may be preferable. Figure 18 diagrammatically illustrates another aspect of the present invention comprising a split-coil electric induction heating system having a split inductor assembly for simultaneously heating a plurality of bearing features in a bearing component comprising a conventional AC power supply 160 having a single output connected to a main winding 222a of an output transformer 222 having at least two secondary windings 222b and 222c. The secondary windings 222b and 222c are connected by means of corresponding outputs. 161a and 162a of an output transformer 222 and corresponding main inductor circuit conductor networks 6a - 6b and 6c - 6d to two corresponding main inductors 210 and 220. The main inductor circuit conductor network 6a and 6b connects the first output 161a of a transformer 222 and the first main heating inductor 210. The second main inductor circuit conductor network 6c and 6d connects the second output 162a of a transformer 222 and the second main heating inductor 220 (see figure 18). Each of the two conductor networks of the corresponding main inductor circuit 6a - 6b and 6c - 6d may consist of standard power supply control devices (not shown in Figure 18) such as thyristor-based AC regulators or thyristors known in the art and commonly used in industry that allow regulation of the power supplies delivered to each of the heating inductors 210 and 220 independently. By changing the relative configuration of the secondary windings 222b and 222c of transformer 222, it is possible to orient the instantaneous electric currents flowing in the heating inductors 210 and 220 in the same direction or in opposite directions (whichever is desirable to obtain the required hardness patterns). In applications where the interrupted hardness pattern is required (as shown in Figure IB, for example), it is advantageous to configure the secondary windings 222b and 222c of transformer 222 so that the instantaneous electric currents flowing in the heating inductors 210 and 220 can be oriented in opposite directions.In contrast, if an uninterrupted hardness pattern is required (as shown in Figure 1C, for example), it is advantageous to configure the secondary windings 222b and 222c of the transformer 222 in such a way that the instantaneous electric currents flowing in the heating inductors 210 and 220 can be oriented in the same direction. The primary passive design concept (Figure 5C and Figure 12A, for example) is more cost-effective and is a relatively simple design that eliminates the need for a 222 transformer with at least two secondary windings of a specific configuration. However, under certain conditions, the circuit assemblies shown in Figure 18 can offer some advantages. These conditions include, but are not limited to, low- and mid-frequency applications (e.g., a range of 500 Hz to 6 kHz). Alternatively, or in addition to these conditions, it includes applications requiring significantly deeper enclosures (e.g., enclosure depths of 3 mm to 9 mm).As an alternative or in addition to these conditions, it includes applications that exhibit substantial differences in the masses of the metals to be heated simultaneously (which are associated with corresponding differences in the geometries of the bearing features to be hardened, such as zones 101 and 102 of the bearing features or the regions where the rolling elements run against the inner raceways 101a and 102a respectively, as shown in Figure 1B). These are just a few exemplary cases where the use of an induction heating system, as shown in Figure 18, can be beneficial. A single-turn inductor is used in the preceding embodiments of the invention. In alternative embodiments of the invention, induction coils of two or more turns are used (for example, depending on a particular application, a single-turn active coil and a single-turn passive coil may also be used instead of a single-turn inductor). The round copper coil tubing is used for the main and passive coils in the preceding embodiments of the invention. In alternative embodiments of the invention, other coil configurations are used in particular applications, including a profiled copper coil. The magnetic flux concentrators identified above as having a specific geometric shape, for example, U-shaped or ring-shaped magnetic flux compensators, may have alternative geometric shapes or be assembled from flux concentrators of other shapes as required for a specific application. When the inner surface (inner raceway) of a thin-walled bearing component is heated for austenitizing, spray quenching of the outer surface can be applied for a full heat cycle or a fraction thereof. This helps prevent (if required) full hardening or excessive hardening depth when heat-treating thin-walled bearing components. Similarly, to prevent (if necessary) full or excessive hardening when heating the outer surface (outer ring), spray quenching of the inner surface can be applied. Alternative embodiments of the induction heat treatment apparatus and method apply to applications where the bearing raceway surface or raceway regions to be heat treated are different from the inner bearing raceways, by way of example and without limitation, for example, ball bearing raceways and outer bearing raceways 100' as illustrated in the bearing raceways of Figure 11 and Figure 1E. In other embodiments of the invention, for example, the outer bearing raceways, the complementary main inductor coil, and the passive inductor coil can be configured to be positioned externally around the outer bearing in the heating position. The present invention has been described in terms of the examples and preferred embodiments. Equivalents, alternatives, and modifications, other than those expressly stated, are possibly within the scope of the invention. Persons skilled in the art, benefiting from the teachings of this specification, may make modifications to it without departing from the scope of the invention.

Claims

1. A split-coil electric induction heating system having a split inductor assembly for the simultaneous heating of a plurality of bearing features in a bearing component, the split inductor assembly comprising a main inductor assembly and a passive inductor assembly separable from a heating position of the bearing component, the split-coil electric induction heating system comprising: a main inductor circuit placed in the main inductor assembly,The main inductor circuit comprises: a main heating inductor for heating at least one first bearing feature; a main magnetic flux coupler; main inductor circuit power terminals; and a main inductor circuit conductor network connecting the main inductor circuit power terminals to the main heating inductor, the main magnetic flux coupler positioned adjacent to and physically separated by an air gap or a dielectric material gap from the main inductor circuit conductor network; and a passive inductor circuit positioned in the passive inductor assembly.The passive inductor circuit comprises: a passive heating inductor for heating at least a second bearing feature; a passive magnetic flux coupler; and a passive inductor circuit conductor network forming a closed series electrical circuit with the passive heating inductor, the passive magnetic flux coupler positioned adjacent to and physically separated from the passive inductor circuit conductor network, the passive magnetic flux coupler positioned adjacent to and physically separated by an air gap or a dielectric gap from the main magnetic flux coupler,so that when the main inductor circuit and the passive inductor circuit are in the bearing component heating position to inductively heat at least a first bearing characteristic and at least a second bearing characteristic, and an alternating current from the main circuit is applied to the power supply terminals of the main inductor circuit, a magnetic field from the main inductor circuit couples with the passive inductor circuit through the passive magnetic flux coupler magnetically coupled with the main magnetic flux coupler to generate an alternating current from the passive circuit in the conductor network of the passive inductor circuit.

2. The split multi-coil electric induction heating system according to claim 1, further characterized in that the main heating inductor comprises a single-turn solenoid coil and the passive heating inductor comprises a single-turn solenoid coil.

3. The split multi-coil electric induction heating system according to claim 1, further characterized in that at least a first bearing feature or at least a second bearing feature is positioned at least partially around an exterior of the main heating inductor or the passive heating inductor to inductively heat an inner bearing feature of the bearing component.

4. The split multi-coil electric induction heating system according to claim 1, further characterized in that at least a first bearing feature or at least a second bearing feature is positioned at least partially around an interior of the main heating inductor or the passive heating inductor to inductively heat an outer bearing feature of the bearing component.

5. The split multi-coil electric induction heating system according to claim 1, further characterized in that the main heating inductor and the passive heating inductor are configured for counter-instantaneous current flows.

6. The split-coil electric induction heating system according to claim 1, further characterized in that it additionally comprises a split-inductor assembly positioning apparatus configured to alternatively: (a) longitudinally align the main heating inductor of the main inductor assembly with the passive heating inductor of the passive inductor assembly and position the passive magnetic flux coupler adjacent to and physically separated from the main magnetic flux coupler when at least one first bearing feature is positioned for inductive heating with the main heating inductor and at least one second bearing feature is positioned for inductive heating with the passive heating inductor for the simultaneous heating of at least one first bearing feature and the at leasta second bearing feature; and (b) longitudinally separating the main heating inductor from the passive heating inductor assembly for placement of the bearing component in the heating position of the bearing component for inductive heating of at least a first bearing feature and at least a second bearing feature or removal of the bearing component after inductive heating of at least a first bearing feature and at least a second bearing feature in the heating position of the bearing component.

7. The split multi-coil electric induction heating system according to claim 1, further characterized in that it additionally comprises a rapid cooling system for quenching the austenitized regions of at least a first bearing feature and at least a second bearing feature after inductive heating, the rapid cooling system having a rapid cooling application apparatus for alternatively, or in combination, cooling in the heating position of the bearing component, in a transition from the heating position of the bearing component to a remote cooling station, in the remote cooling station.

8. The split multi-coil electric induction heating system according to claim 1, further characterized in that it additionally comprises a second main heating inductor in electrical series connection with the main heating inductor and a second passive heating inductor in electrical series connection with the passive heating inductor configured to heat respectively at least a first bearing feature and at least a second bearing feature in a second bearing component.

9. The split multi-coil electric induction heating system according to claim 8, further characterized in that the main inductor assembly and the passive inductor assembly are configured to be placed adjacent to a bearing workpiece heating station, the split multi-coil electric induction heating system further comprises: a rotary table comprising: a pre-heat loading and post-heat unloading station for a bearing workpiece rotary table to load the bearing component and the second bearing component onto the rotary table and unload the bearing component and the second bearing component from the rotary table;The bearing workpiece heating station loads the bearing component and the second bearing component into the main inductor assembly and the passive inductor assembly for inductive heating, and unloads the bearing component and the second bearing component from the main inductor assembly and the passive inductor assembly after induction heating; a bearing workpiece rapid cooling station cools the bearing component and the second bearing component after induction heating;and a rotary actuator to move the bearing component and the second bearing component from the loading station before heating and unloading after heating of the bearing workpiece rotary table, the bearing workpiece heating station, the bearing workpiece rapid cooling station and the loading station before heating and unloading after heating of the bearing workpiece rotary table.; 10. A split-coil electric induction heating system having a split inductor assembly for the simultaneous heating of a plurality of bearing features in a bearing component, the split inductor assembly comprising a main inductor assembly and a passive inductor assembly separable from a heating position of the bearing component, the split-coil electric induction heating system comprising: a main inductor circuit positioned in the main inductor assembly, the main inductor circuit comprising: a main heating inductor for heating a first bearing feature,The main heating inductor comprises a single-turn main solenoid coil positioned at a first end of the mandrel around an outer perimeter of a vertically oriented mandrel having a central longitudinal axis of the vertically oriented mandrel; a main magnetic flux coupler; main inductor circuit power terminals; and a main inductor circuit conductor network connecting the main inductor circuit power terminals to the main heating inductor, the main magnetic flux coupler being positioned adjacent to and physically separated from the main inductor circuit conductor network; and a passive inductor circuit positioned in the passive inductor assembly.The passive inductor circuit comprises: a passive heating inductor for heating a second bearing feature; the heating inductor comprising a single-turn passive solenoid coil positioned at a first end of the support structure around an outer perimeter of a vertically oriented support structure having a central longitudinal axis of a vertically oriented support structure; a passive magnetic flux coupler; and a passive inductor circuit conductor network forming a closed series electrical circuit with the passive heating inductor, the passive magnetic flux coupler positioned adjacent to and separated by an air gap or a dielectric material gap from the passive inductor circuit conductor network, the passive magnetic flux coupler positioned adjacent to and physically separated from the main magnetic flux coupler.so that when the main inductor circuit and the passive inductor circuit are in a position of heating the bearing component to inductively heat the first bearing characteristic and the second bearing characteristic and an alternating current from the main circuit is applied to the power terminals of the main inductor circuit, a magnetic field from the main inductor circuit is coupled with the passive inductor circuit through the passive magnetic flux coupler magnetically coupled with the main magnetic flux coupler to generate an alternating current from the passive circuit in the network of conductors of the passive inductor circuit.

11. The split multi-coil electric induction heating system according to claim 10, further characterized in that at least a first bearing feature or at least a second bearing feature is positioned at least partially around an exterior of the main heating inductor and the passive heating inductor to inductively heat an inner bearing feature of the bearing component.

12. The heating system of the split multi-coil electric inductor according to claim 10, further characterized in that it additionally comprises at least one main inductor magnetic flux concentrator positioned either above or below the main single-turn solenoid coil in the vertically oriented mandrel.

13. The heating system of the split multi-coil electric inductor according to claim 11, further characterized in that it additionally comprises at least one magnetic flux concentrator of the passive inductor positioned either above or below the single-turn passive solenoid coil in the vertically oriented support structure. 14 - The split multi-coil electric inductor heating system according to claim 10, further characterized in that the vertically oriented mandrel has a plurality of cooling openings to provide rapid cooling to the first bearing feature and the second bearing feature from an inner chamber of the vertically oriented mandrel.

15. The split multi-coil electric induction heating system according to claim 10, further characterized in that it additionally comprises a split inductor assembly positioning apparatus configured to alternatively: (a) longitudinally align the main heating inductor of the main inductor assembly with the passive heating inductor of the passive inductor assembly and position the passive magnetic flux coupler adjacent to and physically separated from the main magnetic flux coupler when the first bearing feature is positioned for inductive heating with the main heating inductor and the second bearing feature is positioned for inductive heating with the passive heating inductor for simultaneous heating of the first bearing feature and the second bearing feature;and (b) longitudinally separating the main heating inductor from the split inductor assembly of the passive heating inductor of the split inductor assembly to position the bearing component for inductive heating of at least a first bearing feature and at least a second bearing feature or the removal of the bearing component after inductive heating of at least a first bearing feature and at least a second bearing feature.; 16. A method for simultaneously heat-treating a plurality of bearing features in a bearing component, the method comprising: assembling a split inductor assembly of a main inductor assembly and a passive inductor assembly, a main inductor circuit placed in the main inductor assembly, the main inductor circuit comprising: a main heating inductor for heating at least a first bearing feature in the bearing component; a main magnetic flux coupler; main inductor circuit power terminals;and a main inductor circuit conductor network connecting the main inductor circuit power terminals to the main heating inductor, the main magnetic flux coupler positioned adjacent to and physically separated by an air gap or a dielectric gap from the main inductor circuit conductor network; and a passive inductor circuit positioned in the passive inductor assembly, the passive inductor circuit comprising: a passive heating inductor for heating at least a second bearing feature in the bearing component; a passive magnetic flux coupler;and a network of conductors of the passive inductor circuit forming a closed series electrical circuit with the passive heating inductor, the passive magnetic flux coupler placed adjacent to and physically separated by an air gap or a dielectric material gap from the network of conductors of the passive inductor circuit, the main magnetic flux coupler placed adjacent to and physically separated from the main magnetic flux coupler; locating the bearing component with an inner longitudinal shaft of the bearing component disposed within the main heating inductor and the passive heating inductor for induction heating of at least a first bearing feature with the main heating inductor and induction heating of at least a second bearing feature with the passive heating inductor;Apply a main alternating current to the power supply terminals of the main inductor circuit so that when the main inductor circuit and the passive inductor circuit are in an assembled position, a magnetic field from the main inductor circuit is coupled with the passive inductor circuit through the passive magnetic flux coupler to generate an alternating current from the passive circuit in the conductor network of the passive inductor circuit to inductively heat at least a first bearing characteristic and at least a second bearing characteristic.

17. The method according to claim 16, further characterized in that it additionally comprises locating an outer longitudinal surface of the bearing component at least partially within the main heating inductor or the passive heating inductor to heat an outer bearing feature in the bearing component.

18. The method according to claim 16, further characterized in that it additionally comprises locating an inner longitudinal surface of the bearing component at least partially within the main heating inductor or the passive heating inductor to heat an inner bearing feature in the bearing component.

19. The method according to claim 16, further characterized in that it further comprises separating the main inductor assembly and the passive inductor assembly in opposite extreme longitudinal directions of the bearing component to remove the bearing component from the assembled position after inductive heating of the bearing component and joining the main inductor assembly and the passive inductor assembly in opposite extreme longitudinal directions of the bearing component to place it in the assembled position.

20. The method according to claim 16, further characterized in that it additionally comprises cooling an austenitized region of at least a first bearing feature and at least a second bearing feature alternatively, or in combination, with the bearing component disposed in the assembled position of the split inductor assembly; in a remote cooling station; or in a combination of a transition from the assembled position of the split inductor assembly and the remote cooling station.

21. A split-coil electric induction heating system having a split inductor assembly for the simultaneous heating of a bearing feature in a bearing component, the split inductor assembly comprising a main inductor assembly and a passive inductor assembly separable from a heating position of the bearing component, the split-coil electric induction heating system comprising: a main inductor circuit placed in the main inductor assembly,The main inductor circuit comprises: a main heating inductor for partially heating the bearing feature; a main magnetic flux coupler; main inductor circuit power terminals; and a main inductor circuit conductor network connecting the main inductor circuit power terminals to the main heating inductor, the main magnetic flux coupler positioned adjacent to and physically separated by an air gap or a dielectric material gap from the main inductor circuit conductor network; and a passive inductor circuit positioned in the passive inductor assembly.The passive inductor circuit comprises: a passive heating inductor for partially heating the bearing feature; a passive magnetic flux coupler; and a passive inductor circuit conductor network forming a closed series electrical circuit with the passive heating inductor, the passive magnetic flux coupler positioned adjacent to and physically separated from the passive inductor circuit conductor network, the passive magnetic flux coupler positioned adjacent to and physically separated by an air gap or a dielectric material gap from the main magnetic flux coupler,so that when the main inductor circuit and the passive inductor circuit are in a position to heat the bearing component to inductively heat at least a first bearing characteristic and at least a second bearing characteristic, and an alternating current from the main circuit is applied to the power terminals of the main inductor circuit, a magnetic field from the main inductor circuit is coupled with the passive inductor circuit through the passive magnetic flux coupler magnetically coupled with the main magnetic flux coupler to generate an alternating current from the passive circuit in the conductor network of the passive inductor circuit.

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