Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
  • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/06—Control, e.g. of temperature, of power
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/06—Control, e.g. of temperature, of power
  • H05B6/067—Control, e.g. of temperature, of power for melting furnaces
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
  • H05B6/101—Induction heating apparatus, other than furnaces, for specific applications for local heating of metal pieces

Definitions

• the present invention relates to induction heating, and in particular to an induction heating device and process for controlling the temperature distribution in an electrically conductive material during heating.
• a non- electrically conductive material can be heated with a controlled temperature distribution by placing it in d e vicinity of the electrically conductive material.
• Induction heating occurs in electrically conducting material when such material is placed in a time -varying magnetic field generated by an alternating current (ac) flowing in an induction heating coil. Eddy currents induced in the material create a source of heat in the material itself. Induction heating can also be used to heat or melt non-electrically conducting materials, such as silicon- based, non-electrically conductive fibers. Since significant eddy currents cannot be induced in non-electrically conductive materials, they cannot be heated or melted directly by induction. However, the non-electrically conductive material can be placed within an electrically conductive enclosure defined as a susceptor. One type of susceptor is a cylinder through which the non-electrically conductive material can be passed.
• an induction coil can be placed around a susceptor so that the electromagnetic field generated by the coil will pass through the susceptor.
• the susceptor is electrically conductive.
• a typical material for a susceptor is graphite, which is both electrically conductive and able to withstand very high temperatures. Since the susceptor is electrically conductive, an induction coil can induce significant eddy currents in the susceptor. The eddy currents will heat the susceptor and, by thermal conduction or radiation, the susceptor can be used to heat an electrically non-conductive workpiece placed within or near it.
• induction heating of non-electrically conductive materials such as artificial materials and silicon
• the susceptor can be surrounded with multiple induction coils along its length. Each coil, surrounding a longitudinal segment of the susceptor, could be connected to a separate high frequency ac power source set to a predetermined output level. The susceptor would be heated by induction to a longitudinal temperature distribution determined by the amount of current supplied by each power source to each coil.
• a disadvantage of this approach is that segments of the susceptor located between adjacent coils can overheat due to the additive induction heating effect of the two adjacent coils. Consequently, the ability to control the temperature distribution through these segments of the susceptor is limited.
• the multiple coils could be connected to a single high frequency ac power source for different time intervals via a controlled switching system. Since high electrical potentials can exist between the ends of two adjacent coils when using a single power supply, it may not be possible to locate the ends of the coils sufficiently close to each other to avoid insufficient heating in the segment of the susceptor between the ends of the coil without the increased risk of arcing between adjacent coil ends. Consequently, this approach also limits the ability to control the temperature distribution through these segments of the susceptor.
• a heating device having an induction coil in which the turns of adjacent coil sections allow induction power to be delivered in a controlled manner to preselected sections along the length of the susceptor and, consequently, to a workpiece placed within or near the susceptor, including segments between coil sections, thus eliminating cold or hot spots and permitting a desired preselected temperature distribution along the length of the susceptor.
• This will permit a non-electrically conductive workpiece placed within the susceptor to be heated at the preselected temperature distribution by t ermal conduction and radiation.
• the present invention fills that need.
• the present invention is an induction heating device for producing a controlled temperature distribution in an electrically conductive material or susceptor.
• the device includes a power source (typically comprising a rectifier and inverter), an induction coil that has multiple coil sections disposed around the length of the susceptor, a switching circuit for switching power from the power source between the multiple coil sections, and a control circuit for controlling the power duration from the power source to each of the coil sections.
• the coil sections may be of varying length and have a variable number of turns per unit length.
• the switching circuit can include SCRs connected between the power source and each termination of a coil section.
• the control circuit can also adjust the output of the power source to maintain a constant output when the switching circuit is switched between the coil sections.
• the control circuit can include sensing of a predetermined power set point for each coil section to preset average power to be supplied to each coil section.
• the control circuit can also include sensing of the temperature of the susceptor along its longitudinal points to adjust the power output to all coil sections in order to achieve the desired temperature distribution in the susceptor.
• the induction heating device includes a power source, an induction coil that has one or more overlapped multiple coil sections disposed around the length of the susceptor, a switching circuit for switching power from the power source between the overlapped multiple coil sections, and a control circuit for controlling the power duration from the power source to each of the coil sections.
• the coil sections may be of varying length and have a variable number of turns per unit length.
• the switching circuit can include pairs of anti-parallel SCRs connected between the power source and each termination of a coil section.
• the control circuit can also adjust the output of the power source to maintain a constant output when the switching circuit is switched between the coil sections.
• the control circuit can include sensing of a predetermined power set point for each coil section to preset average power to be supplied to each coil section.
• the control circuit can also include sensing of the temperature of the susceptor along its longitudinal points to adjust the power output to all coil sections in order to achieve the desired temperature distribution in the susceptor.
• the induction heating device includes a power source, an induction coil that has multiple coil sections disposed around the length of the susceptor, with the multiple coil sections connected to a power source by switching circuits that can apply varying power to selected multiple coil sections at the same time in a cascaded manner, and a control circuit for controlling the duration from the power source to each of the multiple coil sections.
• the coil sections may be of varying length and have a variable number of turns per unit length.
• the switching circuits can include pairs of anti-parallel SCRs connected between the power source and each termination of a coil section, except for one coil termination, which is connected to the power source.
• the control circuit can also adjust the output of the power source to maintain a constant output when the switching circuit is switched between the coil sections.
• the control circuit can include sensing of a predetermined power set point for each coil section to preset average power to be supplied to each coil section.
• the control circuit can also include sensing of the temperature of the susceptor along its longitudinal points to adjust the power output to all coil sections in order to achieve the desired temperature distribution in the susceptor.
• the induction heating device includes a power source and an induction coil disposed around the length of the susceptor with multiple coil sections. Adjacent multiple coil sections are counter-wound to each other and connected to form a coil pair.
• the device further includes a switching circuit for switching power from the power source between the coil pairs.
• a control circuit controls the power duration from the power source to each of the coil pairs.
• the coil sections may be of varying length and have a variable number of turns per unit length.
• the switching circuit can include pairs of anti-parallel SCRs connected between the power source and the end terminations of each coil pair.
• Application of varying power to each coil pair induces varying levels of eddy currents in the susceptor, which causes sections of the susceptor surrounded by different coil pairs to be heated to different temperatures as determined by the control circuit. Consequently, a controlled temperature distribution is achieved along the length of the susceptor.
• a non-electrically conductive material placed close to the susceptor will be heated by thermal conduction and radiation in a controlled fashion.
• the control circuit can also adjust the output of the power source to maintain a constant output when the switching circuit is switched between the coil sections.
• the control circuit can include sensing of a predetermined power set point for each coil section to preset average power to be supplied to each coil section.
• the control circuit can also include sensing of the temperature of the susceptor along its longitudinal points to adjust the power output to all coil sections in order to achieve the desired temperature distribution in the susceptor.
• FIG. 1 is a diagram showing a power source, switching circuit, control circuit, and a multi-section induction coil of an induction heating device for controlling temperature distribution in an electrically conductive material.
• FIG. 2 is a diagram of an alternate embodiment of the present invention having a multi-section induction coil with overlapping coil sections and switching circuits for each coil section.
• FIG. 3 is a diagram of an alternate embodiment of the present invention having a multi-section induction coil and switching circuits for each coil section.
• FIG. 4 is a diagram of an alternate embodiment of the present invention having a multi-section induction coil with counter-wound coil sections and switching circuits for each coil section.
• FIG. 5 is an illustration of typical controlled temperature distributions achieved in an electrically conductive material using the present invention.
• FIG. 1 a diagram for an induction heating device 10 for producing a controlled temperature distribution in an electrically conductive material or susceptor 60.
• the induction heating device 10 includes a power source 20 which is connected to a multi-section induction coil 40 via a switching circuit 30.
• Multi-section induction coil 40 is segmented into coil sections 41, 42 and 43 which extend along t e length of the susceptor 60.
• Each coil section extends between two terminations. Terminations for the coil sections are: 44 and 45 for coil section 41; 46 and 47 for coil section 42; and 48 and 49 for coil section 43. Although three or six coil sections are shown in the disclosed embodiments of the invention for purposes of illustration, any number of coil sections can be used without departing from the scope of the invention.
• the coil sections in all embodiments of the invention may be of different lengths, and each coil section may have a variable number of turns per unit length to achieve a particular temperature distribution in the susceptor 60.
• the selection of coil length, number of turns per unit length, and other features of the coil sections are based on factors that include, but are not limited to, the size and shape of the susceptor that is to be heated, the type of susceptor temperature distribution desired, and the type of switching circuit.
• the duration of power provided by the power source 20 via switching circuit 30 to each one of the three coil sections is controlled by control circuit 50.
• control circuit 50 By varying the duration (duty cycle) to each of the three coils sections in a predetermined manner, temperature distribution 70 with uniform longitudinal heating, temperature distribution 71 with increased heating at one end, or temperature distribution 72 with increased middle section heating, as shown in FIG. 5, can be achieved in the susceptor 60 by the induction of eddy currents in the susceptor.
• Temperature distributions 70, 71 and 72 are typical distribution profiles for all embodiments of the invention that can be achieved by application of the present invention.
• One type of power source 20 for supplying the high frequency ac in all embodiments of the invention is a solid state power supply which utilizes solid-state high-power thyristor devices such as silicon-controlled rectifiers (SCRs).
• SCRs silicon-controlled rectifiers
• a block diagram of a typical power source used with induction heating apparatus, and an inverter circuit used in the power source, is described and depicted in Figures 1 and 2 of U.S. Pat. No. 5,165,049. That patent is herein incorporated by reference in its entirety.
• the power source in the referenced patent is used with an induction furnace (melt charge), an artisan will appreciate its use with a susceptor 60 in place of an induction furnace.
• the RLC circuit shown in Figure 1 of the referenced patent represents a coil section, or load, in the present invention.
• a suitable switching circuit 30 for switching power to each of the three coil sections 41, 42 and 43, in FIG. 1 is circuitry including SCRs for electronic switching of power from the power source 20 between coil sections.
• the control circuit 50 can be used in all embodiments of the invention to adjust commutation of the SCRs used in the inverter of the power source
• inverter output power level is controlled when switching among a number of inductive loads.
• the coil sections 41, 42 and 43 represent the switched inductive loads.
• the power set potentiometer associated with each switched inductive load in the referenced patent can be used to set a desired average power level defined by the duration of power application to each of the coil sections 41, 42 and 43.
• control circuit 50 and power source 20 of the present invention are also applicable to the control circuit 50 and power source 20 of the present invention.
• one or more temperature sensors can be provided in or near the susceptor 60.
• the sensors can be used to provide feedback signals for the control circuit 50 to adjust the output of the power source 20 and the duration of the source's connection to each coil section by the switching circuitry, so that the temperature distribution along the length of the susceptor 60 can be closely regulated.
• FIG. 2 shows another embodiment of the present invention.
• coil sections 81, 82 and 83 of the multi-section induction coil 80 partially overlap along longitudinal segments 61 of the susceptor 60.
• the number of overlapping longitudinal segments 61 will depend upon the number of coil sections used. Depending upon the desired temperature distribution, not all segments need to be overlapped.
• the segments 61 may be of different lengths to achieve a particular temperature distribution.
• Each coil section has a pair of terminations: 84 and 85 for coil section 81; 86 and 87 for coil section 82; and 88 and 89 for coil section 83. As shown in FIG. 2, one termination of each coil section is connected to switching circuit 31. The other termination of each coil section is connected to the second switching circuit 32.
• the switching circuits 31 and 32 include pairs of anti-parallel SCRs 31a, 31b, 31c, 32a, 32b and 32c.
• Each coil section has one termination connected to a pair of anti-parallel SCRs in switching circuit 31, and the other termination is connected to a pair of anti-parallel SCRs in switching circuit 32.
• termination 84 is connected to the pair of a i -parallel SCRs 31a
• termination 85 is connected to the pair of anti-parallel SCRs 32a.
• Power source 20 is connected to all pairs of anti-parallel SCRs as shown in FIG. 2.
• Control circuit 50 controls the duration of power provided by the power source 20 to each of the three coil sections 81, 82 and 83, by the switching circuits 31 and 32. As indicated above, the control circuit 50 can also be used to adjust commutation of the SCRs used in the inverter of the power source 20 to maintain a constant inverter power output when the load impedance changes due to the switching between coil sections by the switching circuits 31 and 32.
• each of the three coil sections is connected to the power source 20 for a preselected time, or duty cycle, via its associated pair of anti-parallel SCRs in the switching circuits 31 and 32. Consequently, the associated SCRs conduct full coil section current and must withstand full coil voltage when in the open state.
• a typical uniform temperature distribution 71 shown in FIG. 5 can be achieved in the susceptor 60 by the induction of eddy currents in the susceptor 60.
• FIG. 3 Another embodiment of the present invention.
• a separate switching circuit, 33, 34 or 35 is provided for each of the three coil sections 91, 92 and 93 of the multi-section induction coil 90.
• the terminations of the coil sections can be coil taps on a continuous coil wound around the length of the susceptor 60. As shown in FIG. 3, coil tap
• switching circuit 94 is connected to switching circuit 33; coil tap 95 is connected to switching circuit 34; and coil tap 96 is connected to switching circuit 35.
• Each switching circuit includes a pair of anti-parallel SCRs.
• Power source 20 is connected to switching circuits 33 through 35, and power source coil tap 97.
• Control circuit 50 controls the duty cycle of power provided by the power source 20 to each of the three coil sections 91, 92 and 93, by the switching circuits 33, 34 and 35.
• switching circuit 33 provides controlled power to coil sections 91, 92 and 93; switching circuit 34 provides controlled power to coil sections 92 and 93; and switching circuit 35 provides controlled power to coil section 93.
• a typical temperature distribution 71 shown in FIG. 5 with cascaded increase in heating of the susceptor 60 from the end associated with coil section 91 to the end associated with coil section 93 can be achieved by the induction of eddy currents in the susceptor 60.
• FIG. 4 shows an alternative embodiment of the present invention having a multi-section induction coil 120 with coil sections 121 through 126.
• Coil sections 121, 123 and 125 are counter-wound to coil sections 122, 124 and 126.
• coil sections 121, 123 and 125 are shown wound in an upward direction, and coil sections 122, 124 and 126 are shown wound in the downward direction. Terminations of the coil sections are as shown in FIG. 4.
• terminations 111 and 114 are connected to power source 20 and terminations 112 and 113 are connected to switching circuit 36.
• the power source 20 is also connected to the three switching circuits 36, 37 and 38.
• Each switching circuit can include two sets of anti-parallel SCRs that are connected to the two inner terminations of each coil pair.
• termination 112 is connected to the pair of anti- parallel SCRs 36a and termination 113 is connected to pair of anti -parallel SCRs 36b.
• Control circuit 50 controls the duty cycle of power provided by the power source 20 to each of the coil sections.
• each coil pair is provided with controlled power from the power source 20 via one of the switching circuits 36, 37 or 38.
• Counter- winding the coil pairs can provide a parabolic temperature distribution in the segment of the susceptor that the coil pair is wound around. Consequently, by applying power over a longer time period (or longer duty cycle) for one or more of the pairs of coil sections, an increased heating of a segment of the susceptor can be achieved. For example, by applying power for a longer duty cycle to the coil pair defined by coil sections 123 and 124 in FIG. 4, the temperature distribution 72 shown in
• FIG. 5 with increased heating in the center length of the susceptor can be achieved.
• the uniform temperature distribution 70 can be achieved. Numerous types of temperature distributions can be produced by selecting the power cycle and sequence in which power is applied to the pairs of coil sections as described herein.
• the material can be heated in a controlled manner.
• the present invention provides a flexible and adaptable induction heating device for controlling temperature distribution.
• the control circuit of the invention and the construction of the multi-section induction coil greatly reduces the complexity and cost of the power source while providing greater efficiency and productivity.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Induction Heating (AREA)

Priority Applications (5)

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Cited By (9)

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Citations (2)

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• 1998
  • 1998-11-05 US US09/187,562 patent/US6121592A/en not_active Expired - Lifetime
• 1999
  • 1999-10-25 DE DE69939284T patent/DE69939284D1/de not_active Expired - Lifetime
  • 1999-10-25 JP JP2000581857A patent/JP4450999B2/ja not_active Expired - Lifetime
  • 1999-10-25 DE DE69933432T patent/DE69933432T2/de not_active Expired - Lifetime
  • 1999-10-25 CA CA002317649A patent/CA2317649C/en not_active Expired - Fee Related
  • 1999-10-25 EP EP06117255A patent/EP1718117B1/en not_active Expired - Lifetime
  • 1999-10-25 AU AU12298/00A patent/AU1229800A/en not_active Abandoned
  • 1999-10-25 EP EP99971998A patent/EP1046321B1/en not_active Expired - Lifetime
  • 1999-10-25 WO PCT/US1999/024980 patent/WO2000028787A1/en not_active Ceased

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