CA1276244C - Induction heating apparatus - Google Patents
Induction heating apparatusInfo
- Publication number
- CA1276244C CA1276244C CA000537772A CA537772A CA1276244C CA 1276244 C CA1276244 C CA 1276244C CA 000537772 A CA000537772 A CA 000537772A CA 537772 A CA537772 A CA 537772A CA 1276244 C CA1276244 C CA 1276244C
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- CA
- Canada
- Prior art keywords
- workpiece
- heating coil
- conductors
- transverse
- longitudinal
- Prior art date
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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- General Induction Heating (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An induction heating apparatus for utilizing electromagnetic induction to heat a workpiece. The apparatus includes a pair of heating coil units disposed in spaced-parallel relation to permit transportation of the workpiece between the heating coil units. Each of the heating coil units includes a main heating coil and an auxiliary heating coil disposed at a position adjacent to the main heating coil. The main heating coil has a plurality of spaced-parallel transverse conductors connected in series and produces magnetic field crossing the workpiece, causing heating when supplied with a high-or intermediate-frequency alternating current. The auxiliary heating coil includes a pair of series connected longitudinal conductors placed at positions facing to the workpiece at a small distance inside from the respective opposite side edges of the workpiece. The auxiliary heating coil is supplied with a high- or intermediate-frequency alternating current to heat the workpiece in a manner to compensate the temperature ununiformity provided by the main heating coil so as to provide good temperature uniformity over the width of the workpiece.
An induction heating apparatus for utilizing electromagnetic induction to heat a workpiece. The apparatus includes a pair of heating coil units disposed in spaced-parallel relation to permit transportation of the workpiece between the heating coil units. Each of the heating coil units includes a main heating coil and an auxiliary heating coil disposed at a position adjacent to the main heating coil. The main heating coil has a plurality of spaced-parallel transverse conductors connected in series and produces magnetic field crossing the workpiece, causing heating when supplied with a high-or intermediate-frequency alternating current. The auxiliary heating coil includes a pair of series connected longitudinal conductors placed at positions facing to the workpiece at a small distance inside from the respective opposite side edges of the workpiece. The auxiliary heating coil is supplied with a high- or intermediate-frequency alternating current to heat the workpiece in a manner to compensate the temperature ununiformity provided by the main heating coil so as to provide good temperature uniformity over the width of the workpiece.
Description
INDUCTION HEATING APPARATUS
BACKGROUND OF THE INVENTION
This invention relates to an induction heating apparatus for utilizing electromagnetic induction to heat a workpiece and, more particularly, to an induction heating apparatus of the transverse flux heating type which is used to heat a workpiece transported through the induction heating apparatùs by producing magnetic flux crossing the workpiece in a direction substantially perpendicular to the surface of the workpiece. It will be appreciated that the term "workpiece" as used throughout this invention is intended to include metal strips, metal sheets, metal plates, and other conductive thin members.
Induction heating apparatus have been employed in drying, hardening, annealing, preheating, and other heating processes whereby heat is generated within the part to be treated by electromagnetic induction. A
rapidly alternating magnetic field is produced in a pair of specially designed heating coil units between which a workpiece i8 transported at a predetermir,ed speed. The magnetic field induces an electric potential in the workpiece, causing heating because of I2R losses. For !: ~
this purpose, the heating coil units are supplied with a high- or intermediate-frequency alternating current from a suitable power source. High frequency is generally used for shallow heating, while intermediate frequency is used :
, ~ , ~276244 for applications requiring deeper heating.
One example of the heating coil unit used in conventional induction heating apparatus includes a pair of heating coil units disposed in spaced-parallel relation to permit transportation of the workpiece in a direction between the heating coil units, each of the heating coil units including a plurality of spaced-parallel transverse conductors extending in a direction substantially perpendicular to the direction of transportation of the workpiece. The transverse conductors are connected in series and supplied with a high- or intermediate-frequency alternating current to produce a rapidly alternating magnetic field crossing the workpiece in a direction perpendicular to the surface of the workpiece.
One problem associated with such conventional induction heating apparatus is that the heated workpiece has a temperature not uniform over its width.
Particularly, the workpiece temperature has troughs at positions somewhat inner from the opposite side edges of the workpiece, causing undesirable effects in the following workpiece processing steps. It is very difficult to provide uniform temperature over the full width of the workpiece even with adjustments of the length - , .
of the transverse conductors.
SUM~ARY OF THE IDVBNTION
A main object of the invention is to provide an improved induction heating apparatus which can heat a ', ' ~ ; - 2 -, : , . , ~.276244 workpiece with good temperature uniformity over the full width of the workpiece.
It is another object of the invention to provide an inuction heating apparatus applicable to workpieces of different widths.
There is provided, in accordance with the invention, an induction heating apparatus of a transverse flux heating type for utilizing electromagnetic induction to heat a workpiece transported through the apparatus in a direction. The apparatus comprises a power source unit for supplying alternating current at a predetermined frequency. The apparatus also includes at least one sets of a main heating coil unit having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main heating coils, and an auxiliary heating coil unit having a pair of auxiliary heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the auxiliary heating coils. Each of the main heating coil has a plurality of transverse conductors extending in a longitudinal direction substantially perpendicular to the direction of transportation of the workpiece. The transverse conductors have a length longer than the width of the workpiece. The transverse conductors are connected in series with the power source unit for producing magnetic field crossing the workpiece. Each of the auxiliary heating coil has first and second longitudinal ~276244 conductors extending in a transverse direction substantially the same as the direction of transportation of the wo~kpiece with a transverse distance shorter than the width of the workpiece. The first longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from one of the side edges of the workpiece. The second longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from the other side edge of the workpiece.
The first and second longitudinal conductors are connected in series with the power supply unit for producing - magnetic field crossing the workpiece.
BRIFF DESCRIPTION OF T~F DRUWINGS
This invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawings, in which like numerals identify like elements in the several figures and in which:
Fig. l is a schematic plan view showing one embodiment of an induction heating apparatus made in accordance with the invention;
Fig. 2 is a fragmentary perspective view showing a water-cooled coil conductor used in the induction " :
heating apparatus;
Figs. 3A to 3C are graphs used in explaining the operation of the induction heating apparatus;
Fig. 4A is a schematic plan view showing a :
: ~
modified form of the induction heating apparatus;
Fig. 4B is a schematic side view of the modification of Fig. 4A:
Fig. 5 is a fragmentary perspective view showing a water-cooled coil conductor with a magnetic shield used in the induction heating apparatus;
Fig. 6 is a schematic plan view showing another modified form of the induction heating apparatus;
Fig. 7 is a fragmentary plan view showing coupling mechanisms which may be used in the induction heating apparatus;
Fig. 8 is a sectional view taken along the lines 8-8 of Fig. 7;
Fig. 9 is a sectional view taken along the lines 159~9 of Fig. 7;
Fig. 10 is a sectional view showing a modified form of the coupling mechanism;
Fig. 11 is a schematic plan view showing still another modification of the induction heating apparatus;
20Fig. 12 is a schematic plan view showing a second embodiment of the induction heating apparatus;
Fig. 13 is a fragmentary perspective view showing a water-cooled coil conductor used in the induction heating apparatus;
25- Figs. 14A to 14C are graphs used in explaining the operation of the induction heating apparatus;
Fig. 15A is a schematic plan view showing a , .
,~ ~ - 5 -.~ ~
,. . ..
~276244 modified form of the induction heating apparatus;
Fig. 15B is a schematic side view of the modification of Fig. 15A; and Fig. 16 is a fragmentary perspective view showing a water-cooled coil conductor with a magnetic shield used in the induction heating apparatus.
DETAILED DESCRIPTI~N OF T~E INVENTION
With reference to tbe drawings, wherein like numerals refer to like parts in the several views, and in particular to Fig. 1, there is shown a schematic diagram of an induction heating apparatus embodying the invention for utilizing electromagnetic induction to heat a workpiece such as a metal strip, a metal sheet, a metal plate, or other conductive thin plates.
The induction heating apparatus includes a pair of heating coil units, one of which is shown at 10 in Fig.
l, disposed in speced-parallel relation to each other so that the workpiece WP can be transportated between the heating coil units lO. Each of the heating coil units lO
includes a main heating coil 20 and an auxiliary heating coil 30 placed at a position adjacent to the main heating coil 20. The auxiliary heating coil 30 is connected in series with the corresponding main heating coil 20 through an electrical connection 28. A power source 40 is connected through wires 42 and 44 to supply a high- or intermediate-frequency alternating current to the series connections of the main and auxiliary heating coils 20 and ~L276244 30 to produce magnetic field crossing the workpiece wP.
The main heating coil 20 includes a plurality of (in the illustrated case six) spaced-parallel transverse conductors 22 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S, of transportation of the workpiece WP. The transverse conductors 22 are shown as having a length L
longer than the width W of the workpiece WP. The transverse conductors 22 are connecte~ in series by means of electrical connections 24 so that the directions of the AC current flow through adjacent two transverse conductors 22 are opposite, as shown in Fig. l. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
The auxiliary heating coil 30 includes a pair of spaced-parallel longitudinal conductors 32 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 32 are spaced a distance U from each other, the distance U being shorter than the width W of the workpiece WP. One of the longitudinal conductors 32 is placed at a position facing to the workpiece WP at a slight distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a slight distance inside from the other side edge of the workpiece WP. The 127~244 longitudinal conductors 32 are connected in series with each other by electrical connections 34 so that the directions of the AC current flow through the two longitudinal conductors 32 are opposite, as shown in Fig.
l. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 2, each of the transverse conductors 22 is taken in the form of a water-cooled conductor having a coolant passage 22b extending axially thereof. Although the transverse conductor 22 is shown as having a rectangular cross section, it is to be noted that its cross section may have a circular or other suitable shape. The longitudinal conductors 32 and the electrical connections 24 and 34 may have the same structure as the transverse conductors 24. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the heating coils 20 and 30.
The main heating coils 20 arranged in pair have such a heating characteristic as shown in Fig. 3A which shows an illustration of the temperature distributed widthwise on the workpiece WP. It can be seen from a study of Fig. 3A that the temperature curve has two troughs at points B and D. These two trough points B and D appear at positions adjacent to or at a small distance inside from the respective opposite side edges of the workpiece WP. The auxiliary heating coils 30 arranged in pair have such a heating characteristic as shown in Fig.
3B which shows an illustration of the temperature distributed widthwise on the workpiece wP. As can be seen from Fig. 3B, the temperature curve has two crests at points G and I. These two crest points G and I appear at respective positions at which the longitudinal conductors face to the workpiece WP. The distance U between the longitudinal conductors 32 may be set in such a manner that the crest points G and I of Fig. 3B correspond to the respective trough points B and D of Fig. 3A to obtain a uniform temperature distribution over the full width w of the workpiece WP, as shown in Fig. 3C.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. l at a predetermined speed, the workpiece WP
passes the space between the main heating coils 20 where it is heated to have a temperature curve, as shown in Fig.
3A, and then it passes the space between the auxiliary heating coils 30 where heat is generated to compensate for the temperature ununiformity so as to provide a uniform temperature distribution over the full width of the workpiece WP, aæ shown in Fig. 3~.
Experiments were conducted for a metal sheet having a thickness of 0.5 mm and a width of 400 mm. In an experimental induction heating apparatus similar to the illustrated one, the metal sheet was heated at about _ g _ 600C. The difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 20C or less.
Referring to Figs. 4A and 4B, there is illustrated a modified form of the induction heating apparatus. In this modification, each of the main heating coils 20 includes a plurality of (in the illustrated case eight) spaced-parallel transverse conductors 21 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 4A, of transportation of the workpiece WP. Except for the two outermost transverse conductors 21, the transverse conductors 21 are arranged to form a plurality of pairs each including two transverse conductors 21 placed in close proximity with each other. The transverse conductors 21 are shown as having a length h longer than the width W of the workpiece WP. Each of the transverse conductors 21 has a magnetic shield 25 mounted thereon.
The magnetic shield 25 extends almost the full length of the transverse conductor 21 and has a U-shaped cross section to cover the transverse conductor 21 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The numeral 23 designates electrical connections connected to establish a series connection of the transverse conductors 21 so that the directions of the 12'762A4 AC current flow through adjacent two transverse conductors 21 placed in pair are the same, as shown in Fig. 4A. 5uch an AC current flow produces rapidly altenrating magnetic field ~, as shown in Fig. 4B, to induce an electric potential in the workpiece WP, causing heating therein.
Each of the auxiliary heating coils 30 includes a pair of spaced-parallel longitudinal conductors 31 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 31 are spaced a distance U from each other, the distance U being shorter than the width W
of the workpiece WP. One of the longitudinal conductors 31 is placed at a position facing to the workpiece WP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP. Each of the longitudinal conductors 31 has a magnetic shield 35 mounted thereon. The magnetic shield 35 extends almost the full length of the longitudinal conductor 31 and has a U-shaped cross section to cover the longitudinal conductor 31 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 31 are connected in series with each other by an electrical connection 25 and is connected to the ~2762A4 transverse conductors 21 through electrical connections 37 and 39 so that the directions of the AC current flow through the two longitudinal conductor 31 are opposite, as shown in Fig. 4A. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 5, each of the transverse conductors 21 is taken in the form of a water-cooled conductor having a coolant passage 21b extending axially thereof. Although the transverse conductor 21 is shown as having a rectangular cross section, it is to be noted that its cross section may have a curcular or other suitable shape. In addition, the magnetic shield 25, which has a U-shaped cross section, covers the corresponding transverse conductor 21 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 31 may have the same structure as the transverse conductors 21. The electrical connections 23 and 33 may have the same structure as described in connection with Fig. 2.
Referring to Fig. 6, there is illustrated another modified form of the induction heating apparatus which is substantially the same as described in connection with Fig. 1 except that coupling mechanisms are provided for use in adjusting the distance U between the longitudinal conductors. Accordingly, parts in Fig. 6 which are like those in Fig. 1 have been given like reference numerals. In this modification, a pair of coupling mechanisms Tl and T2 is provided to make mechanical and electrical couplings of one of the longitudinal conductors 32 between the electrical connections 34. The coupling mechanism pair permits movement of the one longitudinal conductor 32 with respect to the other longitudinal conductor along the electrical connections 34 in order to vary the distance U between the longitudinal conductors 32 so as to adjust the crest points G and I (Fig. 3B) to positions corresponding to the respective trough points B and D (Fig. 3A).
Referring to Figs. 7 to 9, the one longitudinal conductor 32 is provided at the opposite ends thereof with franges 32a each having two threaded holes. A mounting frange 50, which is secured on each of the electrical connections 34, is formed with an elongated slot 52 extending in parallel with the corresponding electrical connection 34. The frange 32a is secured on the corresponding mounting frange 50 by two bolts 54 which are threaded in the respective threaded holes to secure the corresponding mounting frange 50 between their heads and the frange 32a. Each of the electrical connections 34 is formed near its opposite ends with ports 56 through which its coolant passage 34b opens to the exterior and each of the longitudinal conductors 32 is formed near its opposite ends with ports 58 through which its coolant passage 32bopens to the exterior. Four coolant hoses 59 are provided to make hydraulic connections between ports 56 and 58 so as to form a series connected coolant conduit in each of the auxiliary heating coils 30. To move the one longitudinal conductor 32 with respect to the other longitudinal conductor, the bolts 54 may be loosened to such an extent that the flanges 32 can slide along the respective mounting franges 50. After the one longitudinal conductor 32 moves to a desired position with respect to the other longitudinal conductor, the bolts 54 are tightened again to fix the one longitudinal conductor 32 to the electrical connections 34. Although two coupling mechanisms Tl and T2 are illustrated and described, it is to be appreciated that four similar coupling mechanisms Tl to T4 may be provided, as indicated by the two-dotted lines of Fig. 6, to permit movement of both of the longitudinal conductors 32.
Referring to Fig. 10, there is illustrated a modified form of the coupling mechanism where the longitudinal conductor 32 has a frange 32c which mates with a frange 34c projecting from the electrical connection 34. A clamping device 60 is used to clamp the flanges 32c and 34c together.
Referring to Fig. 11, there is illustrated still another modified form of the induction heating apparatus which is substantially the same as described in connection ~76244 with Fig. 4A except that coupling mechanisms are provided for use in adjusting the distance U between the longitudinal conductors. Accordingly, parts in Fig. 11 which are like those in Fig. 4A have been given like reference numerals. In this modification, four coupling mechanisms Tl to T4 are provided to make mechanical and electrical couplings of one of the longitudinal conductors 31 between the electrical connections 33. The coupling mechanisms permit movement both of the longitudinal conductors 31 with respect to the corresponding longitudinal conductors along the electrical connections 33 in order to vary the distance U between the longitudinal conductors 31 so as to adjust the crest points G and I ~Fig. 3B) to positions corresponding to the respective trough points B and D (Fig. 3A). The coupling mechanisms Tl to T4 may be the same as described in connection with Figs. 7 to 9 or Fig. 10. The magnetic shields 35 are indicated by the two-dotted lines of Fig.
7.
Referring to Fig. 12, there is illustrated a second embodiment of the induction heating apparatus of the invention. The induction heating apparatus includes a pair of heating coil units, one of which is shown at 110 in Fig. 12, disposed in spaced-parallel relation to each other so that the workpiece WP can be transportated between the heating coil units 110. Each of the heating coil units 110 includes a main heating coil 120 and an ~LZ76;244 auxiliary heating coil 130 placed at a position adjacent to the main heating coil 120. A power source 142 is connected to supply a high- or intermediate-frequency alternating current to the main heating coils 120 to produce magnetic field crossing the workpiece WP. Another power source 146 is connected to supply a high- or intermediate-frequency alternating current to the auxiliary heating coils 130 to produce magnetic field crossing the workpiece wP.
The main heating coil 120 includes a plurality of (in the illustrated case six) spaced-parallel transverse conductors 122 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S, of transportation of the workpiece WP.
The transverse conductors 122 are shown as having a length L longer than the width W of the workpiece WP. The transverse conductors 122 are connected in series by means of electrical connections 124 so that the directions of the AC current flow through adjacent two transverse conductors 122 are opposite, as shown in Fig. 12. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
The auxiliary heating coil 130 includes a pair of spaced-parallel longitudinal conductors 132 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal : - 16 -conductors 132 are spaced a distance u from each other, the distance U being shorter than the width W of the workpiece WP. One of the longitudinal conductors 132 is placed at a position facing to the workpiece wP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP. The longitudinal conductors 132 are connected in series with each other by electrical connections 134 so that the directions of the AC current flow through the two longitudinal conductors 132 are opposite, as shown in Fig.
12. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 13, each of the transverse conductors 122 is taken in the form of a water-cooled conductor having a coolant passage 122b extending axially thereof. Although the transverse conductor 122 is shown as having a rectangular cross section, it is to be noted that its cross section may have a circular or other suitable shape. The electrical connections 124 may have ~- the same structure as the transverse conductors 124. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the main heating coils 120. The longitudinal ' ~ ~
~Z76Z44 conductors 132 and the electrical connections 134 may have the same structure as the transverse conductors 124. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the auxiliary heating coils 130.
A pair of coupling mechanisms Tl and T2 is provided to make mechanical and electrical couplings of one of the longitudinal conductors 132 between the electrical connections 134. The coupling mechanism pair permits movement of the one longitudinal conductor 132 with respect to the other longitudinal conductor along the electrical connections 134 in order to vary the distance U
between the longitudinal conductors 132 so as to adjust the crest points G and I ~Fig. 14B) to positions corresponding to the respective trough points B and D
(Fig. 14A). The coupling mechanisms Tl and T2 may be the same in structure as described in connection with Figs. 7 to 9 or Fig. 10. Although two coupling mechanisms have been described, it is to be noted that four similar Coupling mechanisms Tl to T4 may be provided, as indicated by the two-dotted lines of Fig. 12, to permit movement of both of the longitudinal conductors 132.
The main heating coils 120 arranged in pair have such a heating characteristic as shown in Fig. 14A which shows an illustration of the temperature distributed widthwise on the workpiece WP. It can be seen from a ~276244 study of Fig. 14A that the temperature curve has twotroughs at points B and D. These two trough points B and D appear at positions adjacent to or somewhat inner from the respective opposite side edges of the workpiece WP.
The auxiliary heating coils 130 arranged in pair have such a heating characteristic as shown in Fig. 14s which shows an illustration of the temperature distributed widthwise on the workpiece WP. AS can be seen from Fig. 14B, the temperature curve has two crests at points G and I. These 0 two crest points G and I appear at respective positions at which the longitudinal conductors face to the workpiece WP. The distance U between the longitudinal conductors 132 may be adjusted in such a manner that the crest points G and I of Fig. 3B correspond to the respective trough points B and D of Fig. 3A to obtain a uniform temperature distribution over the full width W of the workpiece WP, as shown in Fig. 14C.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 12 at a predetermined speed, the workpiece WP
passes the space between the main heating coils 120 where it is heated to have a temperature curve, as shown in Fig.
14A, and then it passes the space between the auxiliary heating coils 130 where heat is generated to compensate for the temperature ununiformity so as to provide a uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 14C.
~2'76244 Experiments were conducted for a metal sheet having a thickness of 0.5 mm and a width of 400 mm. In an experimental induction heating apparatus similar to the illustrated one, the metal sheet was heated at about 600C. The difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 20C or less. In an experimental induction heating apparatus similar to the conventional one described herein previously, the difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 150C.
In this embodiment, the main and auxiliary heating coils 120 and 130 are separated and supplied independently with a high- or intermediate-frequency alternating current from the respective power sources 142 and 146. This arrangement is effective to adjust the alternating current to the auxiliary heating coils 130 independently of the alternating current to the main heating coils 120.
Referring to Figs. 15A and 15B, there is illustrated a modified form of the induction heating apparatus. In this modification, each of the main heating coils 120 includes a plurality of ~in the illustrated case eight) spaced-parallel transverse conductors 121 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 15A, of transportation of the workpiece WP. Except for the two ~276244 outermost transverse conductors 121, the transverse conductors 121 are arranged to form a plurality of pairs each including two transverse conductors 121 placed in close proximity with each other. The transverse conductors 121 are shown as having a length L longer than the width W of the workpiece WP. Each of the transverse conductors 121 has a magnetic shield 125 mounted thereon.
The magnetic shield 125 extends almost the full length of the transverse conductor 121 and has a ~-shaped cross section to cover the transverse conductor 121 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The numeral 123 designates electrical connections connected to establish a series connection of the transverse conductors 121 so that the directions of the AC current flow through adjacent two transverse conductors 121 placed in pair are the same, as shown in Fig. 15A. Such an AC current flow produces rapidly alternating magnetic field ~, as shown in Fig. 15B, to induce an electric potential in the workpiece WP, causing heating therein.
Each of the auxiliary heating coils 130 includes a pair of spaced-parallel longitudinal conductors 131 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 131 are spaced a distance U from ~276244 each other, the distance u being shorter than the width wof the workpiece WP. One of the longitudinal conductors 131 is placed at a position facing to the workpiece wP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from the other side edge of the workpiece WP. Each of the longitudinal conductors 131 has a magnetic shield 135 mounted thereon. The magnetic shield 135 extgends almost the full length of the longitudinal conductor 131 and has a U-shaped cross section to cover the longitudinal conductor 131 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 131 are connected in series with each other by electrical connections 125 so that the directions of the AC current flow through the two longitudinal conductor 31 are opposite, as shown in Fig.
15A. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 16, each of the transverse Conductors 121 is taken in the form of a water-cooled conductor having a coolant passage 121b extending axially thereof. Although the transverse conductor 121 is shown as having a rectangular cross section, it is to be noted ~L276244 that its cross section may have a circular or other suitable shape. In addition, the magnetic shield 125, which has a U-shaped cross section, covers the corresponding transverse conductor 121 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 131 may have the same structure as the transverse conductors 121. The electrical connections 123 and 133 may have the same structure as described in connection with Fig. 13.
It is, therefore, apparent from the foregoing that there has been provided, in accordance with the invention, an improved induction heating apparatus which can heat a workpiece with good temperature uniformity over the full width of the workpiece. The induction heating apparatus includes auxiliary heating ciols disposed at a position adjacent to respective main heating coils fQr ccmpensating the temperature ununiformity provided by the main heating coils. In addition, at least one of the longitudinal conductors of each of the auxiliary heating coils is adapted to move with respect to the other longitudinal conductor. This is effective to adjust the distance between the longitudinal conductors for applications to another workpiece having a different width.
It is to be noted that the induction heating ~2~7624~
apparatus shown and described in connection with the above embodiments is of the transverse flux heating type where the main heating coils included in the respective heating coil units constitute a main heating coil unit, the transverse conductors included in one of the main heating coils being disposed at positions facing to the corresponding transverse conductors included in the other main heating coil to produce magnetic flux crossing the transported workpiece in a direction substantially perpendicular to the surface of the workpiece when the main heating coil unit is powered by the power source.
Similarly, the auxiliary heating coils included in the respective heating coil units constitute an auxiliary heating coil unit, the longitudinal conductors included in one of the auxiliary heating coils being disposed at positions facing to the corresponding longitudinal conductors included in the other auxiliary heating coil to produce magnetic flux crossing the transported workpiece in a direction substantially perpendicular to the surface of the workpiece when the auxiliary heating coil unit ispowered by the power source.
Although the auxiliary heating coils have been shown and described as disposed on the downstream side of the respective main heating coils, it will be appreciated that they may be disposed on the upstream side of the respective heating coils.
While the invention has been described in ~276Z44 conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art.
Accordingly, it is intended to embrace all alternatives, modifications and variatlons that fall within the scope of the appended claims.
BACKGROUND OF THE INVENTION
This invention relates to an induction heating apparatus for utilizing electromagnetic induction to heat a workpiece and, more particularly, to an induction heating apparatus of the transverse flux heating type which is used to heat a workpiece transported through the induction heating apparatùs by producing magnetic flux crossing the workpiece in a direction substantially perpendicular to the surface of the workpiece. It will be appreciated that the term "workpiece" as used throughout this invention is intended to include metal strips, metal sheets, metal plates, and other conductive thin members.
Induction heating apparatus have been employed in drying, hardening, annealing, preheating, and other heating processes whereby heat is generated within the part to be treated by electromagnetic induction. A
rapidly alternating magnetic field is produced in a pair of specially designed heating coil units between which a workpiece i8 transported at a predetermir,ed speed. The magnetic field induces an electric potential in the workpiece, causing heating because of I2R losses. For !: ~
this purpose, the heating coil units are supplied with a high- or intermediate-frequency alternating current from a suitable power source. High frequency is generally used for shallow heating, while intermediate frequency is used :
, ~ , ~276244 for applications requiring deeper heating.
One example of the heating coil unit used in conventional induction heating apparatus includes a pair of heating coil units disposed in spaced-parallel relation to permit transportation of the workpiece in a direction between the heating coil units, each of the heating coil units including a plurality of spaced-parallel transverse conductors extending in a direction substantially perpendicular to the direction of transportation of the workpiece. The transverse conductors are connected in series and supplied with a high- or intermediate-frequency alternating current to produce a rapidly alternating magnetic field crossing the workpiece in a direction perpendicular to the surface of the workpiece.
One problem associated with such conventional induction heating apparatus is that the heated workpiece has a temperature not uniform over its width.
Particularly, the workpiece temperature has troughs at positions somewhat inner from the opposite side edges of the workpiece, causing undesirable effects in the following workpiece processing steps. It is very difficult to provide uniform temperature over the full width of the workpiece even with adjustments of the length - , .
of the transverse conductors.
SUM~ARY OF THE IDVBNTION
A main object of the invention is to provide an improved induction heating apparatus which can heat a ', ' ~ ; - 2 -, : , . , ~.276244 workpiece with good temperature uniformity over the full width of the workpiece.
It is another object of the invention to provide an inuction heating apparatus applicable to workpieces of different widths.
There is provided, in accordance with the invention, an induction heating apparatus of a transverse flux heating type for utilizing electromagnetic induction to heat a workpiece transported through the apparatus in a direction. The apparatus comprises a power source unit for supplying alternating current at a predetermined frequency. The apparatus also includes at least one sets of a main heating coil unit having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main heating coils, and an auxiliary heating coil unit having a pair of auxiliary heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the auxiliary heating coils. Each of the main heating coil has a plurality of transverse conductors extending in a longitudinal direction substantially perpendicular to the direction of transportation of the workpiece. The transverse conductors have a length longer than the width of the workpiece. The transverse conductors are connected in series with the power source unit for producing magnetic field crossing the workpiece. Each of the auxiliary heating coil has first and second longitudinal ~276244 conductors extending in a transverse direction substantially the same as the direction of transportation of the wo~kpiece with a transverse distance shorter than the width of the workpiece. The first longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from one of the side edges of the workpiece. The second longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from the other side edge of the workpiece.
The first and second longitudinal conductors are connected in series with the power supply unit for producing - magnetic field crossing the workpiece.
BRIFF DESCRIPTION OF T~F DRUWINGS
This invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawings, in which like numerals identify like elements in the several figures and in which:
Fig. l is a schematic plan view showing one embodiment of an induction heating apparatus made in accordance with the invention;
Fig. 2 is a fragmentary perspective view showing a water-cooled coil conductor used in the induction " :
heating apparatus;
Figs. 3A to 3C are graphs used in explaining the operation of the induction heating apparatus;
Fig. 4A is a schematic plan view showing a :
: ~
modified form of the induction heating apparatus;
Fig. 4B is a schematic side view of the modification of Fig. 4A:
Fig. 5 is a fragmentary perspective view showing a water-cooled coil conductor with a magnetic shield used in the induction heating apparatus;
Fig. 6 is a schematic plan view showing another modified form of the induction heating apparatus;
Fig. 7 is a fragmentary plan view showing coupling mechanisms which may be used in the induction heating apparatus;
Fig. 8 is a sectional view taken along the lines 8-8 of Fig. 7;
Fig. 9 is a sectional view taken along the lines 159~9 of Fig. 7;
Fig. 10 is a sectional view showing a modified form of the coupling mechanism;
Fig. 11 is a schematic plan view showing still another modification of the induction heating apparatus;
20Fig. 12 is a schematic plan view showing a second embodiment of the induction heating apparatus;
Fig. 13 is a fragmentary perspective view showing a water-cooled coil conductor used in the induction heating apparatus;
25- Figs. 14A to 14C are graphs used in explaining the operation of the induction heating apparatus;
Fig. 15A is a schematic plan view showing a , .
,~ ~ - 5 -.~ ~
,. . ..
~276244 modified form of the induction heating apparatus;
Fig. 15B is a schematic side view of the modification of Fig. 15A; and Fig. 16 is a fragmentary perspective view showing a water-cooled coil conductor with a magnetic shield used in the induction heating apparatus.
DETAILED DESCRIPTI~N OF T~E INVENTION
With reference to tbe drawings, wherein like numerals refer to like parts in the several views, and in particular to Fig. 1, there is shown a schematic diagram of an induction heating apparatus embodying the invention for utilizing electromagnetic induction to heat a workpiece such as a metal strip, a metal sheet, a metal plate, or other conductive thin plates.
The induction heating apparatus includes a pair of heating coil units, one of which is shown at 10 in Fig.
l, disposed in speced-parallel relation to each other so that the workpiece WP can be transportated between the heating coil units lO. Each of the heating coil units lO
includes a main heating coil 20 and an auxiliary heating coil 30 placed at a position adjacent to the main heating coil 20. The auxiliary heating coil 30 is connected in series with the corresponding main heating coil 20 through an electrical connection 28. A power source 40 is connected through wires 42 and 44 to supply a high- or intermediate-frequency alternating current to the series connections of the main and auxiliary heating coils 20 and ~L276244 30 to produce magnetic field crossing the workpiece wP.
The main heating coil 20 includes a plurality of (in the illustrated case six) spaced-parallel transverse conductors 22 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S, of transportation of the workpiece WP. The transverse conductors 22 are shown as having a length L
longer than the width W of the workpiece WP. The transverse conductors 22 are connecte~ in series by means of electrical connections 24 so that the directions of the AC current flow through adjacent two transverse conductors 22 are opposite, as shown in Fig. l. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
The auxiliary heating coil 30 includes a pair of spaced-parallel longitudinal conductors 32 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 32 are spaced a distance U from each other, the distance U being shorter than the width W of the workpiece WP. One of the longitudinal conductors 32 is placed at a position facing to the workpiece WP at a slight distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a slight distance inside from the other side edge of the workpiece WP. The 127~244 longitudinal conductors 32 are connected in series with each other by electrical connections 34 so that the directions of the AC current flow through the two longitudinal conductors 32 are opposite, as shown in Fig.
l. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 2, each of the transverse conductors 22 is taken in the form of a water-cooled conductor having a coolant passage 22b extending axially thereof. Although the transverse conductor 22 is shown as having a rectangular cross section, it is to be noted that its cross section may have a circular or other suitable shape. The longitudinal conductors 32 and the electrical connections 24 and 34 may have the same structure as the transverse conductors 24. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the heating coils 20 and 30.
The main heating coils 20 arranged in pair have such a heating characteristic as shown in Fig. 3A which shows an illustration of the temperature distributed widthwise on the workpiece WP. It can be seen from a study of Fig. 3A that the temperature curve has two troughs at points B and D. These two trough points B and D appear at positions adjacent to or at a small distance inside from the respective opposite side edges of the workpiece WP. The auxiliary heating coils 30 arranged in pair have such a heating characteristic as shown in Fig.
3B which shows an illustration of the temperature distributed widthwise on the workpiece wP. As can be seen from Fig. 3B, the temperature curve has two crests at points G and I. These two crest points G and I appear at respective positions at which the longitudinal conductors face to the workpiece WP. The distance U between the longitudinal conductors 32 may be set in such a manner that the crest points G and I of Fig. 3B correspond to the respective trough points B and D of Fig. 3A to obtain a uniform temperature distribution over the full width w of the workpiece WP, as shown in Fig. 3C.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. l at a predetermined speed, the workpiece WP
passes the space between the main heating coils 20 where it is heated to have a temperature curve, as shown in Fig.
3A, and then it passes the space between the auxiliary heating coils 30 where heat is generated to compensate for the temperature ununiformity so as to provide a uniform temperature distribution over the full width of the workpiece WP, aæ shown in Fig. 3~.
Experiments were conducted for a metal sheet having a thickness of 0.5 mm and a width of 400 mm. In an experimental induction heating apparatus similar to the illustrated one, the metal sheet was heated at about _ g _ 600C. The difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 20C or less.
Referring to Figs. 4A and 4B, there is illustrated a modified form of the induction heating apparatus. In this modification, each of the main heating coils 20 includes a plurality of (in the illustrated case eight) spaced-parallel transverse conductors 21 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 4A, of transportation of the workpiece WP. Except for the two outermost transverse conductors 21, the transverse conductors 21 are arranged to form a plurality of pairs each including two transverse conductors 21 placed in close proximity with each other. The transverse conductors 21 are shown as having a length h longer than the width W of the workpiece WP. Each of the transverse conductors 21 has a magnetic shield 25 mounted thereon.
The magnetic shield 25 extends almost the full length of the transverse conductor 21 and has a U-shaped cross section to cover the transverse conductor 21 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The numeral 23 designates electrical connections connected to establish a series connection of the transverse conductors 21 so that the directions of the 12'762A4 AC current flow through adjacent two transverse conductors 21 placed in pair are the same, as shown in Fig. 4A. 5uch an AC current flow produces rapidly altenrating magnetic field ~, as shown in Fig. 4B, to induce an electric potential in the workpiece WP, causing heating therein.
Each of the auxiliary heating coils 30 includes a pair of spaced-parallel longitudinal conductors 31 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 31 are spaced a distance U from each other, the distance U being shorter than the width W
of the workpiece WP. One of the longitudinal conductors 31 is placed at a position facing to the workpiece WP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP. Each of the longitudinal conductors 31 has a magnetic shield 35 mounted thereon. The magnetic shield 35 extends almost the full length of the longitudinal conductor 31 and has a U-shaped cross section to cover the longitudinal conductor 31 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 31 are connected in series with each other by an electrical connection 25 and is connected to the ~2762A4 transverse conductors 21 through electrical connections 37 and 39 so that the directions of the AC current flow through the two longitudinal conductor 31 are opposite, as shown in Fig. 4A. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 5, each of the transverse conductors 21 is taken in the form of a water-cooled conductor having a coolant passage 21b extending axially thereof. Although the transverse conductor 21 is shown as having a rectangular cross section, it is to be noted that its cross section may have a curcular or other suitable shape. In addition, the magnetic shield 25, which has a U-shaped cross section, covers the corresponding transverse conductor 21 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 31 may have the same structure as the transverse conductors 21. The electrical connections 23 and 33 may have the same structure as described in connection with Fig. 2.
Referring to Fig. 6, there is illustrated another modified form of the induction heating apparatus which is substantially the same as described in connection with Fig. 1 except that coupling mechanisms are provided for use in adjusting the distance U between the longitudinal conductors. Accordingly, parts in Fig. 6 which are like those in Fig. 1 have been given like reference numerals. In this modification, a pair of coupling mechanisms Tl and T2 is provided to make mechanical and electrical couplings of one of the longitudinal conductors 32 between the electrical connections 34. The coupling mechanism pair permits movement of the one longitudinal conductor 32 with respect to the other longitudinal conductor along the electrical connections 34 in order to vary the distance U between the longitudinal conductors 32 so as to adjust the crest points G and I (Fig. 3B) to positions corresponding to the respective trough points B and D (Fig. 3A).
Referring to Figs. 7 to 9, the one longitudinal conductor 32 is provided at the opposite ends thereof with franges 32a each having two threaded holes. A mounting frange 50, which is secured on each of the electrical connections 34, is formed with an elongated slot 52 extending in parallel with the corresponding electrical connection 34. The frange 32a is secured on the corresponding mounting frange 50 by two bolts 54 which are threaded in the respective threaded holes to secure the corresponding mounting frange 50 between their heads and the frange 32a. Each of the electrical connections 34 is formed near its opposite ends with ports 56 through which its coolant passage 34b opens to the exterior and each of the longitudinal conductors 32 is formed near its opposite ends with ports 58 through which its coolant passage 32bopens to the exterior. Four coolant hoses 59 are provided to make hydraulic connections between ports 56 and 58 so as to form a series connected coolant conduit in each of the auxiliary heating coils 30. To move the one longitudinal conductor 32 with respect to the other longitudinal conductor, the bolts 54 may be loosened to such an extent that the flanges 32 can slide along the respective mounting franges 50. After the one longitudinal conductor 32 moves to a desired position with respect to the other longitudinal conductor, the bolts 54 are tightened again to fix the one longitudinal conductor 32 to the electrical connections 34. Although two coupling mechanisms Tl and T2 are illustrated and described, it is to be appreciated that four similar coupling mechanisms Tl to T4 may be provided, as indicated by the two-dotted lines of Fig. 6, to permit movement of both of the longitudinal conductors 32.
Referring to Fig. 10, there is illustrated a modified form of the coupling mechanism where the longitudinal conductor 32 has a frange 32c which mates with a frange 34c projecting from the electrical connection 34. A clamping device 60 is used to clamp the flanges 32c and 34c together.
Referring to Fig. 11, there is illustrated still another modified form of the induction heating apparatus which is substantially the same as described in connection ~76244 with Fig. 4A except that coupling mechanisms are provided for use in adjusting the distance U between the longitudinal conductors. Accordingly, parts in Fig. 11 which are like those in Fig. 4A have been given like reference numerals. In this modification, four coupling mechanisms Tl to T4 are provided to make mechanical and electrical couplings of one of the longitudinal conductors 31 between the electrical connections 33. The coupling mechanisms permit movement both of the longitudinal conductors 31 with respect to the corresponding longitudinal conductors along the electrical connections 33 in order to vary the distance U between the longitudinal conductors 31 so as to adjust the crest points G and I ~Fig. 3B) to positions corresponding to the respective trough points B and D (Fig. 3A). The coupling mechanisms Tl to T4 may be the same as described in connection with Figs. 7 to 9 or Fig. 10. The magnetic shields 35 are indicated by the two-dotted lines of Fig.
7.
Referring to Fig. 12, there is illustrated a second embodiment of the induction heating apparatus of the invention. The induction heating apparatus includes a pair of heating coil units, one of which is shown at 110 in Fig. 12, disposed in spaced-parallel relation to each other so that the workpiece WP can be transportated between the heating coil units 110. Each of the heating coil units 110 includes a main heating coil 120 and an ~LZ76;244 auxiliary heating coil 130 placed at a position adjacent to the main heating coil 120. A power source 142 is connected to supply a high- or intermediate-frequency alternating current to the main heating coils 120 to produce magnetic field crossing the workpiece WP. Another power source 146 is connected to supply a high- or intermediate-frequency alternating current to the auxiliary heating coils 130 to produce magnetic field crossing the workpiece wP.
The main heating coil 120 includes a plurality of (in the illustrated case six) spaced-parallel transverse conductors 122 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S, of transportation of the workpiece WP.
The transverse conductors 122 are shown as having a length L longer than the width W of the workpiece WP. The transverse conductors 122 are connected in series by means of electrical connections 124 so that the directions of the AC current flow through adjacent two transverse conductors 122 are opposite, as shown in Fig. 12. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
The auxiliary heating coil 130 includes a pair of spaced-parallel longitudinal conductors 132 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal : - 16 -conductors 132 are spaced a distance u from each other, the distance U being shorter than the width W of the workpiece WP. One of the longitudinal conductors 132 is placed at a position facing to the workpiece wP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP. The longitudinal conductors 132 are connected in series with each other by electrical connections 134 so that the directions of the AC current flow through the two longitudinal conductors 132 are opposite, as shown in Fig.
12. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 13, each of the transverse conductors 122 is taken in the form of a water-cooled conductor having a coolant passage 122b extending axially thereof. Although the transverse conductor 122 is shown as having a rectangular cross section, it is to be noted that its cross section may have a circular or other suitable shape. The electrical connections 124 may have ~- the same structure as the transverse conductors 124. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the main heating coils 120. The longitudinal ' ~ ~
~Z76Z44 conductors 132 and the electrical connections 134 may have the same structure as the transverse conductors 124. In this case, it is preferable to connect the coolant passages to form a series connected coolant conduit through which a coolant is circulated so as to dissipate the heat in the auxiliary heating coils 130.
A pair of coupling mechanisms Tl and T2 is provided to make mechanical and electrical couplings of one of the longitudinal conductors 132 between the electrical connections 134. The coupling mechanism pair permits movement of the one longitudinal conductor 132 with respect to the other longitudinal conductor along the electrical connections 134 in order to vary the distance U
between the longitudinal conductors 132 so as to adjust the crest points G and I ~Fig. 14B) to positions corresponding to the respective trough points B and D
(Fig. 14A). The coupling mechanisms Tl and T2 may be the same in structure as described in connection with Figs. 7 to 9 or Fig. 10. Although two coupling mechanisms have been described, it is to be noted that four similar Coupling mechanisms Tl to T4 may be provided, as indicated by the two-dotted lines of Fig. 12, to permit movement of both of the longitudinal conductors 132.
The main heating coils 120 arranged in pair have such a heating characteristic as shown in Fig. 14A which shows an illustration of the temperature distributed widthwise on the workpiece WP. It can be seen from a ~276244 study of Fig. 14A that the temperature curve has twotroughs at points B and D. These two trough points B and D appear at positions adjacent to or somewhat inner from the respective opposite side edges of the workpiece WP.
The auxiliary heating coils 130 arranged in pair have such a heating characteristic as shown in Fig. 14s which shows an illustration of the temperature distributed widthwise on the workpiece WP. AS can be seen from Fig. 14B, the temperature curve has two crests at points G and I. These 0 two crest points G and I appear at respective positions at which the longitudinal conductors face to the workpiece WP. The distance U between the longitudinal conductors 132 may be adjusted in such a manner that the crest points G and I of Fig. 3B correspond to the respective trough points B and D of Fig. 3A to obtain a uniform temperature distribution over the full width W of the workpiece WP, as shown in Fig. 14C.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 12 at a predetermined speed, the workpiece WP
passes the space between the main heating coils 120 where it is heated to have a temperature curve, as shown in Fig.
14A, and then it passes the space between the auxiliary heating coils 130 where heat is generated to compensate for the temperature ununiformity so as to provide a uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 14C.
~2'76244 Experiments were conducted for a metal sheet having a thickness of 0.5 mm and a width of 400 mm. In an experimental induction heating apparatus similar to the illustrated one, the metal sheet was heated at about 600C. The difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 20C or less. In an experimental induction heating apparatus similar to the conventional one described herein previously, the difference between the highest and lowest temperatures distributed widthwise on the metal sheet was about 150C.
In this embodiment, the main and auxiliary heating coils 120 and 130 are separated and supplied independently with a high- or intermediate-frequency alternating current from the respective power sources 142 and 146. This arrangement is effective to adjust the alternating current to the auxiliary heating coils 130 independently of the alternating current to the main heating coils 120.
Referring to Figs. 15A and 15B, there is illustrated a modified form of the induction heating apparatus. In this modification, each of the main heating coils 120 includes a plurality of ~in the illustrated case eight) spaced-parallel transverse conductors 121 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 15A, of transportation of the workpiece WP. Except for the two ~276244 outermost transverse conductors 121, the transverse conductors 121 are arranged to form a plurality of pairs each including two transverse conductors 121 placed in close proximity with each other. The transverse conductors 121 are shown as having a length L longer than the width W of the workpiece WP. Each of the transverse conductors 121 has a magnetic shield 125 mounted thereon.
The magnetic shield 125 extends almost the full length of the transverse conductor 121 and has a ~-shaped cross section to cover the transverse conductor 121 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The numeral 123 designates electrical connections connected to establish a series connection of the transverse conductors 121 so that the directions of the AC current flow through adjacent two transverse conductors 121 placed in pair are the same, as shown in Fig. 15A. Such an AC current flow produces rapidly alternating magnetic field ~, as shown in Fig. 15B, to induce an electric potential in the workpiece WP, causing heating therein.
Each of the auxiliary heating coils 130 includes a pair of spaced-parallel longitudinal conductors 131 extending substantially in the same direction as the direction of transportation of the workpiece WP. The longitudinal conductors 131 are spaced a distance U from ~276244 each other, the distance u being shorter than the width wof the workpiece WP. One of the longitudinal conductors 131 is placed at a position facing to the workpiece wP at a small distance inside from one of the side edges of the workpiece WP, while the other longitudinal conductor is placed at a position facing to the workpiece at a small distance inside from the other side edge of the workpiece WP. Each of the longitudinal conductors 131 has a magnetic shield 135 mounted thereon. The magnetic shield 135 extgends almost the full length of the longitudinal conductor 131 and has a U-shaped cross section to cover the longitudinal conductor 131 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 131 are connected in series with each other by electrical connections 125 so that the directions of the AC current flow through the two longitudinal conductor 31 are opposite, as shown in Fig.
15A. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Referring to Fig. 16, each of the transverse Conductors 121 is taken in the form of a water-cooled conductor having a coolant passage 121b extending axially thereof. Although the transverse conductor 121 is shown as having a rectangular cross section, it is to be noted ~L276244 that its cross section may have a circular or other suitable shape. In addition, the magnetic shield 125, which has a U-shaped cross section, covers the corresponding transverse conductor 121 except for its one side facing to the workpiece WP in order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The longitudinal conductors 131 may have the same structure as the transverse conductors 121. The electrical connections 123 and 133 may have the same structure as described in connection with Fig. 13.
It is, therefore, apparent from the foregoing that there has been provided, in accordance with the invention, an improved induction heating apparatus which can heat a workpiece with good temperature uniformity over the full width of the workpiece. The induction heating apparatus includes auxiliary heating ciols disposed at a position adjacent to respective main heating coils fQr ccmpensating the temperature ununiformity provided by the main heating coils. In addition, at least one of the longitudinal conductors of each of the auxiliary heating coils is adapted to move with respect to the other longitudinal conductor. This is effective to adjust the distance between the longitudinal conductors for applications to another workpiece having a different width.
It is to be noted that the induction heating ~2~7624~
apparatus shown and described in connection with the above embodiments is of the transverse flux heating type where the main heating coils included in the respective heating coil units constitute a main heating coil unit, the transverse conductors included in one of the main heating coils being disposed at positions facing to the corresponding transverse conductors included in the other main heating coil to produce magnetic flux crossing the transported workpiece in a direction substantially perpendicular to the surface of the workpiece when the main heating coil unit is powered by the power source.
Similarly, the auxiliary heating coils included in the respective heating coil units constitute an auxiliary heating coil unit, the longitudinal conductors included in one of the auxiliary heating coils being disposed at positions facing to the corresponding longitudinal conductors included in the other auxiliary heating coil to produce magnetic flux crossing the transported workpiece in a direction substantially perpendicular to the surface of the workpiece when the auxiliary heating coil unit ispowered by the power source.
Although the auxiliary heating coils have been shown and described as disposed on the downstream side of the respective main heating coils, it will be appreciated that they may be disposed on the upstream side of the respective heating coils.
While the invention has been described in ~276Z44 conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art.
Accordingly, it is intended to embrace all alternatives, modifications and variatlons that fall within the scope of the appended claims.
Claims (6)
1. An induction heating apparatus of a transverse flux heating type for utilizing electromagnetic induction to heat a sheet-formed workpiece transported through the apparatus in a direction, comprising:
a power source unit for supplying alternating current at a predetermined frequency; and at least one sets of a main heating coil unit having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main heating coils, and an auxiliary heating coil unit having a pair of auxiliary heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the auxiliary heating coils;
each of the main heating coils having a plurality of transverse conductors extending in a transverse direction substantially perpendicular to the direction of transportation of the workpiece, the transverse conductors having a length longer than the width of the workpiece, the transverse conductors being connected in series with the power source unit for producing magnetic field crossing the workpiece; and each of the auxiliary heating coils having first and second longitudinal conductors extending in a longitudinal direction substantially the same as the direction of transportation of the workpiece with a transverse distance shorter than the width of the workpiece, the first longitudinal conductor being placed at a position facing to the workpiece at a slight distance inside from one of the side edges of the workpiece, the second longitudinal conductor being placed at a position facing to the workpiece at a slight distance inside from the other side edge of the workpiece, the first and second longitudinal conductors being connected in series with the power supply unit for producing magnetic field crossing the workpiece.
a power source unit for supplying alternating current at a predetermined frequency; and at least one sets of a main heating coil unit having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main heating coils, and an auxiliary heating coil unit having a pair of auxiliary heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the auxiliary heating coils;
each of the main heating coils having a plurality of transverse conductors extending in a transverse direction substantially perpendicular to the direction of transportation of the workpiece, the transverse conductors having a length longer than the width of the workpiece, the transverse conductors being connected in series with the power source unit for producing magnetic field crossing the workpiece; and each of the auxiliary heating coils having first and second longitudinal conductors extending in a longitudinal direction substantially the same as the direction of transportation of the workpiece with a transverse distance shorter than the width of the workpiece, the first longitudinal conductor being placed at a position facing to the workpiece at a slight distance inside from one of the side edges of the workpiece, the second longitudinal conductor being placed at a position facing to the workpiece at a slight distance inside from the other side edge of the workpiece, the first and second longitudinal conductors being connected in series with the power supply unit for producing magnetic field crossing the workpiece.
2. The induction heating apparatus as claimed in claim 1, wherein a magnetic shield is provided to cover each of the transverse and longitudinal conductors except for its one side facing to the workpiece.
3. The induction heating apparatus as claimed in claim 1, wherein each of the transverse and longitudinal conductors is a water-cooled conductor for dissipating heat in the conductor.
4. The induction heating apparatus as claimed in claim 1, wherein the auxiliary heating coil includes means for manually adjusting the transverse distance between the first and second longitudinal conductors.
5. The induction heating apparatus as claimed in claim 1, wherein the main and auxiliary heating coils are connected in series.
6. The induction heating apparatus as claimed in claim 1, wherein the power source unit includes first and second power sources each supplying alternating current, the first power source being connected in series with the main heating coil, the second power source being connected in series with the auxiliary heating coil.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61118938A JPS62276786A (en) | 1986-05-23 | 1986-05-23 | Coil apparatus for induction heating of flat plate |
| JP61-118938 | 1986-05-23 | ||
| JP61-118934 | 1986-05-23 | ||
| JP61118934A JPS62274593A (en) | 1986-05-23 | 1986-05-23 | Flat plate induction heating coil apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1276244C true CA1276244C (en) | 1990-11-13 |
Family
ID=26456764
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000537772A Expired - Fee Related CA1276244C (en) | 1986-05-23 | 1987-05-22 | Induction heating apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1276244C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114525399A (en) * | 2022-03-02 | 2022-05-24 | 盐城市星凯环保科技股份有限公司 | Annealing conveying device for electrothermal alloy material |
-
1987
- 1987-05-22 CA CA000537772A patent/CA1276244C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114525399A (en) * | 2022-03-02 | 2022-05-24 | 盐城市星凯环保科技股份有限公司 | Annealing conveying device for electrothermal alloy material |
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