Externally cooled high efficiency induction coil system

Abstract

An externally cooled high efficiency induction coil system is formed from a substantially planar electrically conductive strip, machined or 3D printed from solid copper or a copper alloy defining a multiturn solenoidal induction coil. Each turn of the multiturn induction coil is separated by a separation gap dimensioned to produce a low-variance heating pattern in a magnetically coupled inductive load or workpiece when an alternating current is supplied to the induction coil. A cooling fluid is forced over the induction coil and through the gap width to externally cool the induction coil via forced convection. The substantially planar electrically conductive strip may further include a plurality of crests and troughs defining a wave structure to increase surface area in contact with the cooling fluid and thereby increase efficiency in heat transfer.

Description

EXTERNALLY COOLED HIGH EFFICIENCY INDUCTION COIL SYSTEMCross-Reference To Related Applications

[0001] This application claims the benefit of United States Provisional Application No. 63 / 547,557, filed November 7, 2023, which is hereby incorporated by reference in its entirety.Field of the Invention

[0002] The present invention generally relates to an induction coil structure and method of making the same, and in particular to an externally cooled induction coil formed from axially thin layers of a continuous electrically conductive strip, wherein each layer is separated by a separation gap width.Background of the Invention

[0003] In induction heating applications, a variable magnetic field is used to heat an electrically conductive object (induced object or workpiece). The variable magnetic field is produced by the electric current that is supplied by a power supply to an electrical conductor that is commonly called an inductor or an induction coil. When a conductive object is exposed to the variable magnetic field, eddy currents are induced in the electrically conductive object. The magnitude and direction of travel of the eddy currents depends on the geometry, electrical, and magnetic properties of the inductor and the induced object. The eddy currents produce Joule power losses that heat the induced object. The power losses in the induced object increase as the magnitude and frequency of the inductor's electric current increases. Typically, solenoidal inductors are implemented in induction heating systems to surround the induced object. Depending on the application, the shape and the size of the induction coil is adjusted to fit the geometry of the object, the desired heating result, and the electrical and cooling requirements of the power supply and the induction coil itself. In addition to losses in the induced object, there are resistive losses in the tubing of the induction coil. In general, the losses are greater the longer the coil is. The further away the coil turn is from the induced object, the higher the ratio of resistive losses in the coil to the losses in the induced object.

[0004] Solenoidal inductors are commonly implemented for the induction heat treatment of cylindrical or near-cylindrically shaped electrically conductive objects. Solenoidal inductors are typically constructed from a single or multiple turn layers by using 3D printing methods, computer numerical control (CNC) machined copper conduction paths with embedded machined water channels, or electrically conductive tubing pipe materials. Generally, flow of a coolingmedium, such as water, is injected into the hollow interior of the tubing pipe or other induction coil to avoid overheating and resultant damage to the inductor. A solenoidal inductor produces a heat pattern that can be limited to surround the induced object. The extension and distribution of the heat pattern depends on but is not limited to the length of the inductor, the diameter of the induction coil, and the spacing between adjacent turns of the induction coil in multiturn constructions. Similarly, the intensity of the induced power depends on but is not limited to the coupling distance between the induced object and the inductor, the number and space factor of the turns, as well as the magnitude and frequency of the supplied electric current. In order to conform to the energy requirements of the power supply, and to increase the amount of induced power, it is often necessary to tailor the impedance of the induction coil to better match the components of the power supply. This is often accomplished through varying the length of the inductor or the number of turns in a multiturn construction, and the number of layers of turns in order to achieve the desired impedance match and magnetic field magnitude and frequency.

[0005] However, frequently, the physical changes that are implemented to improve the power supply to inductor interaction, (for example, increasing the number of turns or the diameter of the inductor) lead to modifications of the induced heat distribution since the heat pattern that is produced by a solenoidal inductor is directly controlled by the turn spacing and inductor dimensions. Additionally, in high frequency and high electric current induction heating applications, higher cooling flow rates are required for cooling the inductor, requiring either high pressure pumps or larger diameter tubing pipe sizes to accommodate the increased flow rates, which in turn adds additional restrictions in the selection of the minimum bending radius of the coil, construction repeatability, the number of stacked layers of tubing and the proper selection of the electrical and thermal insulation to be taken into consideration when designing the inductor to achieve a desired heat pattern.

[0006] For example, in a traditional solenoidal induction coil construction where low frequency and poor power factor are constraints, additional layers of coil turns are added to achieve a desired inductance to heat the induced object. However, adding further turns increases the overall length of the inductor and the increased distance of those additional layers from the load reduces the strength of magnetic coupling to the induced object at the outermost turns of the coil while still generating additional heat losses due the proximity effect and to the resistivity of the coil material (I2R losses), typically copper. As the temperature of the coil increases, the resistivity of the coil further increases, resulting in greater I2R losses. As such, increased cooling must be supplied to the coil which is limited primarily by cooling fluid flow rate and available waterpressure, and as a result tubing diameter. Increasing tubing diameter to accommodate increased flow rates to combat increased heat generation within the coil further extends the length of the coil due to the increased width of each turn and the spacing between adjacent turns, resulting in further reduced magnetic coupling at the outermost turns.

[0007] Reducing the spacing between adjacent turns to reduce the coupling distance between the outermost turns and the induced object improves the efficiency of the coil and produces a uniform heating pattern in the induced object by reducing the temperature differences between hot and cold spots produced by the spacing between adjacent turns of the coil. However, reducing the spacing between adjacent turns in the coil requires better electrical and thermal insulation between turns to avoid electrical short circuits produced by intense electric fields and high temperature gradients between consecutive turns due to the proximity effect.

[0008] In summary, the coil dimensions, the number of coil turns, and the space factor between coil turns can be modified to fit the electrical and cooling requirements of the power supply and the coil itself.

[0009] It is one object of the present invention to provide an externally cooled induction coil system that produces an improved heating pattern in the induced object and increased efficiency in magnetic coupling with the induced object by physically compressing the amp-turns and bringing the coil turns closer to the workpiece without compromising the rate of cooling necessary to keep the coil operation temperature under a desired limit.

[0010] It is another object of the present invention to increase the magnetic coupling to the load by reducing the average coupling distance of the current in the solenoidal coil to the load while maintaining the same inductance. That is, essentially move the turns of the exterior layers to a single layer which cannot be practically accomplished with induction coil turns comprised of water-cooled tubing.

[0011] It is another object of the present invention to provide a substantially higher efficiency induction coil system that reduces copper losses, water flowrate, and hydraulic pressure requirements relative to typical internally cooled induction coil structures via external cooling of an axially thin substantially planar strip multiturn coil structure.Brief Summary of the Invention

[0012] In one aspect the present invention is a substantially planar strip (flat spring) multitum solenoidal induction coil structure, wherein each adjacent turn of the coil is separated by a gapwidth dimensioned to produce a desired heating pattern in a magnetically coupled inductive load. The induction coil is externally cooled via forced convection of a fluid passing through the gap width between each turn of the induction coil.

[0013] In another aspect the present invention is a substantially planar strip defining a plurality of crests and troughs (wave spring), the crests and troughs following a defined amplitude and function (sinusoidal, triangular, or other wave), the substantially planar strip defining a multiturn solenoidal induction coil structure. Each adjacent turn of the coil is separated by a gap width dimensioned to produce a desired heating pattern in a magnetically coupled inductive load. The induction coil is externally cooled via forced convection of a fluid passing through the gap width between each turn of the induction coil. The wave structure increases the overall surface area in contact with the cooling fluid, thereby increasing the heat transfer characteristics of the induction coil relative to the flat spring embodiment. The wave structure also allows the tailoring and control of the heat transfer intensity to the load at the ends of the induction coil.

[0014] The above and other aspects of the invention are set forth in this specification and the appended drawings and claims.Brief Description of the Drawings

[0015] The appended 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 appended claims:

[0016] FIG. 1(a) is a perspective view of one non-limiting example of the induction coil of an externally cooled high efficiency induction coil system of the present invention utilizing a flat spring multiturn coil structure.

[0017] FIG. 1(b) is a side plan view of the induction coil of FIG. 1(a).

[0018] FIG. 2(a) is a perspective view of an alternate non-limiting example of the induction coil of an externally cooled high efficiency induction coil system of the present invention utilizing a wave spring multitum coil structure.

[0019] FIG. 2(b) is a side plan view of the induction coil of FIG. 2(a).

[0020] FIG. 3 is a perspective view of one non-limiting example of an externally cooled high efficiency induction coil system of the present invention.

[0021] FIG. 4(a) is a plan view of a heat profile induced into a workpiece using a traditional induction coil of the prior art.

[0022] FIG. 4(b) is a plan view of a heat profile induced into a workpiece using a non-limiting example of the induction coil of the present invention.

[0023] FIG. 5(a) through FIG. 5(d) show a simplified diagrammatic partial cross-sectional view of an apparatus for induction heating of a workpiece utilizing the externally cooled high efficiency induction coil system of the present invention.Detailed Description of the Invention

[0024] FIGs. 1(a) and 1(b) illustrate one example of the externally cooled high efficiency induction coil system. The induction coil 12 comprises a substantially planar electrically conductive strip 14 in a multitum solenoidal construction, wherein the substantially planar electrically conductive strip 14 includes a width W disposed along a radial direction (Y-axis of FIG. 1(b)) of the induction coil 12 and a thickness T disposed along an axial direction (X-axis of FIG. 1(b)) of the induction coil 12. Each turn of the induction coil 12 is separated by a separation gap 16, wherein the separation gap 16 is minimized to present a reduced axial coil length L. The separation gap 16 can be determined via finite element analysis to optimize the axial coil length L and a heating profile produced in an associated workpiece. In some such embodiments, the heating profile is optimized to produce a substantially constant depth of thermal penetration across an entire surface of the workpiece. The substantially planar electrically conductive strip 14 may preferably comprise copper or a copper alloy either machined or 3D printed from solid copper or copper alloy, such that the substantially planar electrically conductive strip 14 comprises a solid construction having no internal openings or throughways contrary to traditional internally cooled induction coils. The strip array of the shown embodiment allows a turn density of 6 turns / inch without a compromise to the electrical and thermal insulations between consecutive turns. As the separation gap 16 is minimized, the heating pattern produced in a magnetically coupled inductive load is more consistent as the temperature differences between hot spots (corresponding to the location of turns of the induction coil 12) and cold spots (corresponding to the location of separation gaps 16 between turns of the induction coil 12) are reduced. Furthermore, the substantially planar electrically conductive strip 14 comprises a dielectric material coating, such as a varnish, wherein the dielectric material coating is adapted to electrically insulate adjacent turns of the multiturn solenoidal construction from each other. In this manner, turn-to-tum electrical shorts caused by the minimized separation gap are prevented.In some such embodiments, the dielectric material coating is disposed only on each radial face of the substantially planar electrically conductive strip 14, wherein each radial face comprises a surface parallel to and coplanar with the radial direction.

[0025] As illustrated in FIG. 4(a), in the prior art, typical internally cooled induction coil systems 46, due to larger separation gaps 16 caused by larger coil diameters and to avoid proximity effect, result in inconsistent heating profiles 40 having hot spots in proximity to the induction coil 46 and cold spots 42 positioned relative to the separation gap 16 between adjacent turns of the induction coil 46. For example, as shown in FIG. 4(a), when adjacent turns of the induction coil 46 are separated to ensure substantially even flow of current through the entire coil turn, the separation gap 16 is sufficiently large to introduce cold spots in the workpiece where the magnetic field fails to couple to the load. Alternatively, should the separation gap 16 of the traditional internally cooled induction coil 12 be reduced, proximity effect dominates, driving electrical current to opposing edges of adjacent turns, resulting in a similar magnetic field density and heating profile having significant cold spots. This inconsistent heating profile 40 can produce undesirable heating and / or heat treatment qualities in the workpiece 44 without additional considerations, such as rotating or moving the workpiece 44 to ensure a uniform heating profile 40, which may not be suitable for all heating applications. Alternatively, as shown in FIG. 4(b), the present externally cooled induction coil 12 facilitates more tightly packed turns relative to a traditional internally cooled induction coil 46 of FIG. 4(a), thereby resulting in a heating profile 40 with greater consistency over the length of the workpiece 44. As shown in FIG. 4(b), approximately four turns of the externally cooled induction coil 12 may occupy the same space as three turns of a traditional internally cooled induction coil 46, however alternate relative dimensions are also contemplated as necessary for a particular induction heating application.

[0026] In the illustrated example of FIGs. 1(a) and 1(b), the induction coil 12 comprises a 54- tum coil, wherein the width W of the substantially planar electrically conductive strip 14 is / i inch and the thickness T of the substantially planar electrically conductive strip 14 is 1 / 8 inch, producing an axial coil length L of 10 inches at a coil inner diameter of 8 inches. Adjacent turns of the coil in the shown embodiment include a separation gap 16 of 0.06 inches. These dimensions are contemplated as one potential embodiment of the induction coil 12 and should not necessarily be considered limiting, however the ratio between the dimensions of each element may be maintained in alternate embodiments to retain the benefits of the present invention. By maintaining the thickness T substantially smaller than a diameter of traditional internally cooled induction coil 12 as shown in FIG. 4(a), proximity effect is mitigated in combination with asubstantially reduced separation gap 16. In such embodiments, a relative distance between the concentration of current flowing in adjacent turns is substantially reduced compared to traditional internally cooled induction coil systems, thereby resulting in a more consistent heating profile in the workpiece. In alternate embodiments, the thickness T of the substantially planar electrically conductive strip 14 can be adjusted to improve the impedance of the induction coil 12 to produce equivalent heating patterns in the workpiece across varying operating frequencies. Alternatively, the thickness T may be variable along a length of the substantially planar electrically conductive strip 14 to improve temperature distribution across areas of the workpiece, for example, where the workpiece geometry is non-symmetrical at the surface, such that some areas of the workpiece require comparatively more induced heating than other areas to maintain an even heating profile. In such embodiments, the induction coil 12 comprises dimensions corresponding to the workpiece or a particular induction heating application.

[0027] The induction coil 12 is further cooled via cooling fluid flowing externally across the induction coil 12 and through the separation gaps 16 to maximize surface area in contact with the cooling fluid. As illustrated in FIG. 3, the externally cooled high efficiency coil system includes an enclosure 22 within which the induction coil 12 is submerged in flowing cooling fluid. The enclosure 22 comprises a series of external walls defining an interior volume. One or more fluid inlet ports 24 are disposed on a first external wall 28, and one or more fluid outlet ports 26 are disposed on a second external wall 30. The first external wall 28 is disposed directly opposite the second external wall 30, such that fluid flows through the enclosure 22 across the induction coil 12 oriented perpendicular to the direction of cooling fluid flow. In the illustrated embodiment, a transverse opening 36 extends through the interior volume between a third external wall 32 and a fourth external wall 34, wherein the transverse opening 36 defines an interior cylindrical wall 38. In alternate embodiments, the interior wall defines differing cross-sectional dimensions and is therefore not necessarily limited to cylindrical cross-sections. In some such embodiments, the interior wall conforms to the overall shape of the workpiece to be heated, such that the induction coil 12 defines a similar cross-sectional shape to minimize a coupling distance between the workpiece and the induction coil 12. The induction coil 12 is wrapped about the interior cylindrical wall 38, such that a workpiece inserted through into the transverse opening 36 can be inductively heated thereby. In this manner, the cooling fluid flows perpendicular to the transverse opening 36, flowing over the induction coil 12 and through the separation gap 16 between adjacent turns of the induction coil 12. In the illustrated embodiment, the enclosure 22 comprises a substantially cubic structure, however, alternate enclosure geometries that maintain the substantially perpendicular flow over the induction coil 12 are similarly contemplated by thepresent disclosure. The enclosure 22 can be made of any non-electrically conductive or electrically conductive materials such as but not limited to plastics with desirable mechanical properties or any metals provided that the distance between the enclosure and the induction coil 12 is sufficient to avoid the magnetic coupling between the induction coil 12 and the enclosure 22. The enclosure 22 may be sealed by any means, such as but not limited to, gaskets, epoxies, sealing tape, ceramics, glue, silicones, among other sealing solid state, liquid, or gas materials.

[0028] In this manner, due to the increased induction coil 12 surface area in contact with the cooling fluid respective to the volume of the induction coil 12, greater cooling efficiency can be achieved in comparison to internally cooled induction coils constructed from traditional electrically conductive tubing, as less cooling fluid is necessary to achieve the same temperature reduction. Furthermore, the external cooling of the present system provides reduced electrically conductive material use as induction coils of similar numbers of turns need not be manufactured in a tubular structure, as typically required to run cooling fluid through the interior of the electrically conductive coil, leading to a decrease in material costs and weight of the induction coil 12. In the illustrated embodiment, 60 gallons per minute of cooling fluid is provided at 1.3 pounds per square inch to maintain the induction coil 12 at a desired operating temperature, for example, a nominal operating temperature of 140 degrees Fahrenheit.

[0029] FIG. 2(a) and FIG. 2(b) illustrate an alternate example of the externally cooled high efficiency induction coil system. Alternatively, in the shown embodiment, the substantially planar electrically conductive strip 14 comprises a plurality of crests 18 and troughs 20 of a particular amplitude defining a wave structure. In the illustrated embodiment, the plurality of crests 18 comprise a first amplitude and the plurality of troughs 20 comprise a second amplitude, wherein the first amplitude and the second amplitude are opposite in direction. In some such embodiments, the first amplitude and the second amplitude are equivalent in magnitude, however, in alternate embodiments, the first amplitude may comprise a different magnitude than the second amplitude as required to suit a particular induction heating application. In the illustrated embodiment, the wave structure comprises a substantially sinusoidal wave, however other wave structures, such as triangular waves, square waves, sawtooth waves, or the like are also contemplated. The various wave designs are also contemplated to address different power density distributions induced into each end of the workpiece, which typically overheat utilizing traditional solenoid induction coils. The wave structure is similarly configured in a multiturn solenoidal coil construction, such that the overall form factor of the wave structure of the shown embodiment is substantially similar to the form factor of the embodiment shown in FIG. 1(a). Forexample, in the exemplary embodiment, a 54-tum coil formed from the substantially planar electrically conductive strip 14 comprises a thickness T of approximately 1 / 8 inch having a separation gap 16 of 0.06 inches, such that an axial length L of the wave structure is effectively 10 inches at a coil inner diameter of 8 inches.

[0030] A primary benefit of the wave coil construction shown in FIGs. 2(a) and 2(b) is that the added curvature in the planar electrically conductive strip 14 increases the effective surface area of the induction coil 12 in contact with the cooling fluid, thereby further reducing cooling fluid requirements. As such, the magnitude of each of the first and second amplitudes can be dimensioned to reduce cooling water requirements for the system. However, as the wave structure effectively increases the absolute length of the substantially planar electrically conductive strip 14, the total I2R losses increase. In order to compensate for the greater resistance, the width W of the substantially planar electrically conductive strip 14 may be increased relative to the embodiment shown in FIG. 1(a). For example, in the shown embodiment of FIG. 2(a), the width W of the substantially planar electrically conductive strip 14 is % inches, as opposed to the ’A inch width W of FIG. 1(a). In this manner, the greater width further increases the surface area of the substantially planar electrically conductive strip 14 in contact with the cooling fluid, thereby enhancing convective cooling thereof. Generally, the selection of the width W of the substantially planar electrically conductive strip 14 at a desired operational frequency is a tradeoff between a skin depth of the current flowing through the substantially planar electrically conductive strip 14 and the amount of cooling required to maintain the induction coil 12 at a desired temperature. Ideally, the width W of the substantially planar electrically conductive strip 14 is selected to be less than four times the skin depth at a desired operational frequency, at which point the surface area and the associated cooling capacity of the substantially planar electrically conductive strip 14 can be determined, such that a flowrate of cooling fluid over the induction coil 12 can be adjusted to maintain a desired coil temperature. In such embodiments, as only the portions of the induction coil 12 most proximate to the workpiece effectively couple to the workpiece to induce heating therein, additional width W of the induction coil 12 contributes predominantly to I2R losses, and therefore reduces efficiency of the induction coil 12. As such, by limiting the width W to no more than four times the skin depth at the desired operational frequency, efficiency of the induction coil 12 can be maximized while limiting excess heating of the induction coil 12 caused by resistive losses. In the illustrated embodiment of FIG. 2(a), only 40 gallons per minute of cooling fluid at 1.5 pounds per square inch is required to achieve the same temperature reduction in the induction coil 12 as the embodiment illustrated in FIG. 1(a).As such, the coil structure of FIG. 2(a) represents a reduction of required cooling fluid flowrate requirements of approximately 30-35% relative to the coil structure of FIG. 1(a).

[0031] The present induction coil 12 as described may further be utilized in a scanning induction billet pre-heating system, such as the one disclosed in U.S. Patent Application Publication No. 2017 / 0094730 (the '730 application), hereby incorporated by reference in its entirety. The '730 application discloses an apparatus and method for induction heating of large billets (workpieces) to achieve a tapered heating profile along an axial length of the billet prior to extruding or forging (together referred to as hot working) the billet into an article of manufacture using a singular induction coil. The tapered heating profile ensures that the leading (hot) end of the billet has a higher cross-sectional temperature than an opposing (cooler) end of the billet to allow friction generated during the extrusion process to heat the trailing end and maintain an isothermal temperature of the length of the extrusion thereby improving extrusion precision as extrusion precision is hampered when an extrusion varies in temperature as the material expands and contracts. The tapered heating profile is contemplated to include linear and non-linear longitudinal heating profiles. Inclusion of the present induction coil 12 produced an significantly increased inductance and power density ratio per inch of axial length of the induction coil 12, such that more amp-turns of the induction coil 12 are devoted to heating the workpiece instead of internally circulated cooling water as with traditional internally cooled induction coil designs. In some such embodiments, the induction coil 12 of the present invention being incorporated into the scanning induction billet pre-heating system results in a 30-35% reduction in the capacity of the power supply to apply an equivalent amount of work to the workpiece.

[0032] As shown in FIGs. 5(a) through 5(d), the apparatus comprises a workpiece handling assembly 52 that lifts and holds workpiece 90 at opposing ends of the workpiece 90 for entry into the induction coil 12 via the transverse opening 36 defined through the enclosure 22. The enclosure 22 is disposed on a platform 54. The workpiece handling assembly 52 is adapted such that the workpiece 90 makes no contact with any part of the workpiece heating apparatus, including the transverse opening 36 about which the induction coil 12 is disposed. As such, the surface finish of the workpiece 90 is maintained after heating of the workpiece 90 is completed. The workpiece heating apparatus may further comprise a workpiece rotational apparatus configured to rotate the workpiece 90 during at least a portion of the induction heating process to promote a uniform circumferential temperature distribution.

[0033] In the illustrated embodiment, a flux extender 50 is provided at a fixed or variable position from the leading end of the workpiece 90. However, it should be noted that the fluxextender 50 is not necessary in all use cases of the present scanning induction heating system. The flux extender 50 is formed from an electromagnetically conductive material and is used to extend magnetic flux generated by the induction coil 12 beyond the leading end of the workpiece 90 to control the induced current along the axial length of the workpiece 90. For example, in the illustrated embodiment of FIG. 5(a) through 5(d), when workpiece 90 is at the initial entry of the transverse opening 36, the flux extender 50 is disposed at a distance Xi from the leading end of the workpiece 90. As the workpiece 90 progresses through the transverse opening 36, the distance between flux extender 50 and the leading end of the workpiece 90 varies, such as a smaller X2 distance as the workpiece 90 passes one-quarter of its axial length into the transverse opening 36 (as shown in FIG. 5(b)) until the workpiece 90 exits the transverse opening 36 (as shown in FIG. 5(d)). Alternatively, the flux extender 50 may remain at a fixed distance from the leading end of the workpiece 90 through the entire heating process.

[0034] A separate cooling fluid circuit (not shown) is defined and comprises a cooling fluid source operably connected to each of the fluid inlet ports and the fluid outlet ports of the enclosure 22. A pump or other means of circulation selectively circulates the cooling fluid through the enclosure 22 perpendicular to the transverse opening 36 at a desired flowrate and fluid pressure, as previously described with reference to FIG. 3. The fluid connections between the fluid inlet and fluid outlet ports and the cooling fluid source are contemplated to comprise flexible hose adapted to provide sufficient movement of the platform 54 to translate the enclosure 22 along a linear path in embodiments in which the platform 54 selectively moves during the heating process. Compared to the scanning induction workpiece pre-heating system disclosed by the '730 application, incorporating the induction coil 12 of the present invention reduces the horsepower requirement of the pump to cool the induction coil 12, as the pressure required to effectively cool the induction coil 12 is significantly reduced compared to a traditional internally cooled induction coil.

[0035] In some embodiments, induced power density changes can be made by changing the output power magnitude of the power source 56 operably connected to the induction coil 12 through the scan induction heating process. The power source 56 receives output control signals from a programmable logic circuit (PLC) or other control such as an industrial computer program to adjust the power level to create the desired heating profile. For example, the output power magnitude may initially comprise a maximum output power for the process as the leading end of the workpiece 90 passes through the transverse opening 36, and progressively or incrementally in discrete steps the output power magnitude may be decreased as the workpiece 90 progressesthrough the induction coil 12. In this manner, more energy is induced in the leading end than in the trailing end, leading to the desired tapered axial length or longitudinal heating profile. However, as this variable output power magnitude impacts the temperature of the induction coil 12 due to I2R losses, coil cooling needs vary over the course of operation as well. In such embodiments, the PLC is operably connected to the pump such that the flowrate and the fluid pressure are adjustably controlled by the PLC over the course of operation to maintain a temperature of the induction coil 12 at a consistent temperature. In this manner, as the power level provided to the induction coil 12 varies over the course of operation as previously discussed, the cooling fluid is delivered at a varying flowrate and pressure to account for the variable heating of the induction coil 12.

[0036] The workpiece pre-heating system may further comprise one or more surface scanning pyrometers 94a and 94a' disposed at the entry and exit ends of the transverse opening 36 and one or more radial thermocouples. The one or more surface scanning pyrometers 94a and 94a ' verify workpiece surface temperatures along the length of the workpiece 90 and may further transmit temperature data, along with input signals from the one or more radial thermocouples to the PLC which in turn sends control signals to the workpiece handling apparatus, the flux extender 50 positioning apparatus, the power source 56, and the pump to selectively adjust the induction heating process. For example, the workpiece 90 and flux extender 50 may be moved at differing rates through the transverse opening 36, repeated heating cycles through the induction coil 12, or as previously discussed, the output power magnitude may be varied and the flowrate and pressure of cooling fluid varied to ensure the desired heating pattern is created within the workpiece 90. The collected temperature data for the workpiece 90 may further be recorded and stored for reference or to serve as the basis of future workpiece heating profile process programs. In this manner, preset induction heating programs may be used to heat workpieces 90 having similar properties, or alternatively, the input signals and temperature data may be utilized to execute a variable heating process accounting for present conditions of the workpiece 90.

[0037] Reference throughout this specification to "one example or embodiment," "an example or embodiment," "one or more examples or embodiments," or "different example or embodiments," for example, means that a particular feature may be included in the practice of the invention. In the description various features are sometimes grouped together in a single example, embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects.

[0038] The present invention has been described in terms of preferred examples and embodiments. Equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the invention. Those skilled in the art, having the benefit of the teachings of this specification, may make modifications thereto without departing from the scope of the invention.

Claims

Claims1. An externally cooled induction coil system, comprising: an induction coil comprising a substantially planar electrically conductive strip in a multitum solenoidal construction, the substantially planar electrically conductive strip comprising a solid construction and having a width disposed along a radial direction of the induction coil and a thickness disposed along an axial direction of the induction coil; a separation gap disposed between each turn of the induction coil, the separation gap dimensioned to minimize an axial length of the induction coil along a longitudinal axis thereof, such that variance in a heating pattern induced into a workpiece by the induction coil is minimized; an enclosure having a plurality of external walls defining a fluid impermeable internal volume; a transverse opening disposed through a center of the enclosure and defined by an interior wall extending through the enclosure, the transverse opening dimensioned to receive the workpiece therethrough; wherein the induction coil is disposed about the interior wall within the enclosure such that the induction coil is coaxial with the transverse opening and positioned to magnetically couple to the workpiece when an alternating current is provided to the induction coil; one or more fluid inlet ports disposed through a first external wall of the plurality of external walls; one or more fluid outlet ports disposed through a second external wall of the plurality of external walls; wherein the first external wall is disposed parallel and opposite to the second external wall; at least one pump operably connected to the one or more fluid inlet ports and the one or more fluid outlet ports, the at least one pump adapted to circulate a cooling fluid transversely across the longitudinal axis of the induction coil and through the separation gap between each adjacent turn of the induction coil at a desired flowrate and pressure.

2. The externally cooled induction coil system of claim 1, wherein a thickness of the substantially planar electrically conductive strip varies along a length thereof, such thatone or more adjacent turns of the induction coil comprise a different thickness than a remainder of the adjacent turns.

3. The externally cooled induction coil system of claim 1, wherein the substantially planar electrically conductive strip comprises a dielectric material coating across an entire exterior thereof.

4. The externally cooled induction coil system of claim 1, wherein the separation gap and the thickness are dimensioned to maintain a ratio of at least six turns per inch of axial length of the induction coil.

5. The externally cooled induction coil system of claim 1, wherein the width of the substantially planar electrically conductive strip is dimensioned to be less than four times a skin depth of the induction coil when the alternating current is provided at a desired operational frequency.

6. The externally cooled induction coil system of claim 1, wherein the substantially planar electrically conductive strip further comprises a plurality of crests disposed sequentially with a plurality of troughs, each of the plurality of crests having a first amplitude and each of the plurality of troughs having a second amplitude, wherein the first amplitude and the second amplitude are equivalent and opposite, defining a wave coil structure.

7. The externally cooled induction coil system of claim 6, wherein the wave coil structure is selected from a group consisting of: a sinusoidal wave, a triangular wave, a square wave, and a sawtooth wave.

8. The externally cooled induction coil system of claim 1, wherein the enclosure comprises a non-electrically conductive material.

9. A method of inductively heating a workpiece and externally cooling an induction coil, the induction coil comprising a substantially planar electrically conductive strip comprising a solid construction defining a multitum solenoidal coil structure, the induction coil defining a separation gap disposed between each turn of the induction coil, the separation gap dimensioned to minimize both an axial length of the induction coil along a longitudinal axis thereof and a variance in a heating pattern induced into the workpiece by the induction coil, the method comprising: providing a fluid impermeable enclosure having a plurality of external walls defining an interior volume, the fluid impermeable enclosure further comprising a centrally disposed interior wall having a transverse opening therethrough; securing the induction coil about the interior wall of the fluid impermeable enclosure; supplying an alternating current to the induction coil from an external power source to generate a magnetic field;feeding the workpiece through the transverse opening to inductively heat the workpiece via the magnetic field; circulating cooling fluid through the fluid impermeable enclosure via one or more fluid inlet ports disposed through a first external wall of the plurality of external walls and one or more fluid outlet ports disposed through a second external wall of the plurality of external walls, such that the cooling fluid is forced through the separation gap disposed between each adjacent turn of the induction coil to maintain the induction coil at a nominal operating temperature.

10. The method of claim 9, further comprising the step of adjusting an output pressure and a flowrate of the cooling fluid circulated through the fluid impermeable enclosure corresponding to variations in a power level provided to the induction coil to consistently maintain the induction coil at the nominal operational temperature.

11. The method of claim 9, further comprising positioning the one or more fluid inlet ports directly opposite the one or more fluid outlet ports, whereby the cooling fluid is circulated transversely across a longitudinal axis of the induction coil.

12. The method of claim 9, further comprising selecting a width of the substantially planar electrically conductive strip to be less than four times a skin depth of the alternating current flowing through the substantially electrically conductive strip at a desired operational frequency.

13. The method of claim 9, further comprising determining the separation gap by finite element analysis to optimize a heating profile in the workpiece.

14. The method of claim 9, further comprising coating the substantially planar electrically conductive strip with a dielectric material adapted to electrically insulate adjacent turns of the induction coil from each other.

15. A scanning induction workpiece heating system having an externally cooled induction coil, comprising: an induction coil comprising a substantially planar electrically conductive strip in a multitum solenoidal coil structure, the substantially planar electrically conductive strip having a solid construction, wherein each turn of the multitum solenoidal construction comprises a separation gap therebetween, the separation gap dimensioned to minimize both an axial length of the induction coil and a variance in a heating pattern induced into a workpiece by the induction coil; an enclosure having a plurality of external walls defining a fluid impermeable internal volume, the enclosure having one or more fluid inlet ports disposed through a first external wall of the plurality of external walls and one or more fluid outlet portsdisposed through a second external wall of the plurality of external walls, wherein the first external wall is disposed parallel and opposite the second external wall; a transverse opening disposed through a center of the enclosure and defined by an interior wall extending through the enclosure, the transverse opening dimensioned to receive the workpiece therethrough; wherein the induction coil is disposed about the interior wall within the enclosure such that the induction coil is coaxial with the transverse opening and positioned to magnetically couple to the workpiece when an alternating current is provided to the induction coil; at least one pump operably connected to the one or more fluid inlet ports and the one or more fluid outlet ports, the at least one pump adapted to circulate a cooling fluid transversely across the induction coil and through the separation gap between each adjacent turn of the induction coil at a flowrate and pressure; a workpiece handling assembly for holding the workpiece and moving the workpiece through the transverse opening; a workpiece heating process controller for execution of a workpiece heating process algorithm, the workpiece heating process controller having a workpiece movement output signal to the workpiece handling assembly to move the workpiece handling assembly through the transverse opening at a variable workpiece induction heating velocity and a power command output signal to the external power source to set a power magnitude supplied from the external power source to the induction coil as determined by the workpiece heating process algorithm to produce a desired heating profile in the workpiece.

16. The scanning induction workpiece heating system of claim 15, wherein the power command output sets the power magnitude supplied to the workpiece at a variable power magnitude level.

17. The scanning induction workpiece heating system of claim 16, wherein a pump command output signal is supplied to the at least one pump, the pump command output adapted to set the flowrate and pressure of cooling fluid supplied to the enclosure at a variable flowrate and variable pressure corresponding to the variable power magnitude level.

18. The scanning induction workpiece heating system of claim 15, further comprising one or more workpiece surface scanning sensors at an entry end and an exit end of the transverse opening.

19. The scanning induction workpiece heating system of claim 15, wherein the substantially planar electrically conductive strip further comprises a plurality of crests disposedsequentially with a plurality of troughs, each of the plurality of crests having a first amplitude and each of the plurality of troughs having a second amplitude, wherein the first amplitude and the second amplitude are equivalent and opposite, defining a wave coil structure.

20. The scanning induction workpiece heating system of claim 15, wherein the separation gap and the thickness are dimensioned to maintain a ratio of at least six turns per inch of axial length of the induction coil.

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