CA1295376C

CA1295376C - Induction heating apparatus

Info

Publication number: CA1295376C
Application number: CA000553367A
Authority: CA
Inventors: Yukio Sakimoto
Original assignee: Meidensha Corp
Current assignee: Meidensha Corp
Priority date: 1986-12-03
Filing date: 1987-12-02
Publication date: 1992-02-04
Anticipated expiration: 2009-02-04

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 full width of the workpiece. Each of the main heating coils is divided into a plurality of Portions arranged alternatively in a line with the auxiliary heating coil. In another aspect, the first and second longitudinal conductors of each of the auxiliary heating coils are inclined at an angle with respect to the direction of transportation of the workpiece.

Description

lZ5~376 INDUCTION HEATING APPARAT~S

BACRGROUND 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 apparatus 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 is transported at a predetermined 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 l~S3~6 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.

SUMMAR~ OF T~E INVENTION
A main object of the invention is to provide an improved induction heating apparatus which can heat a ~53 ~6 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 a plurality of main heating coil units each having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main heating coils, and a plurality of auxiliary heating coil units each 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 has a plurality oE transverse conductors extending in a transverse 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 j3~f~

heating coils has 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 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. The main heating coil units and the auxiliary heating coil units are placed alternatively in a line extending in the direction of transportation of the workpiece.
In another aspect of the invention, the induction heating apparatus includes at least one set 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 auxiliary heating coils has first and second longitudinal conductors extending in a longitudinal direction substantially the .

;3 ~6 same as the direction of transportation of the workpiece 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 slight 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 slight 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 1 o crossing the workpiece. Each of the main heating coils has a plurality of transverse conductors extending in a transverse direction substantially perpendicular to the direction of transportation 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 main heating coils is divided into first and second portions disposed on the opposite Sides of the auxiliary heating coil.
In another aspect of the invention, the first and second longitudinal conductors of each of the auxiliary heating coils are inclined at an angle with reSpect to the direction of transportation of the workpiece.

According to the invention there is also provided an induction heating appara-tus of a transverse flux heating type inductively heating a sheet-formed workpiece trans-ported through the apparatus in a direction, the workpiece having a substantially uniform width defined by opposed side edges, comprising:
a power source unit for supplying alternating current at a predetermined frequency; and at least one set 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 heatiny 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 pluralityof 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 heat.;.ng co:i.l.s hav:i.ng first and second longitudinal conduct:ors extendirlg i.n a longitudinal direction substantially -the same as the direction of transportation of the workpiece with a transverse distance shorter than the wid-th of the workpiece, the fi.rst 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 - 5a -2~3 ~6 being connected in series with the power supply unit for producing magnetic field crossing the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS:

This invention will be described in greater detail by reference to -the following description taken in ~

- 5b -1~9~37~

connection with the accompanying drawings, in which like numerals identify like elements in the several figures and in which:
Fig. 1 is a perspective view showing one embodiment of an indution heating apparatus made in accordance with the invention;
Fig. 2A is an enlarged elevational view showing heating coil unit shifting device used in the induction heating apparatus of Fig. l;
Fig. 2B is an enlarged side view showing the heating coil unit shifting device;
Fig. 3 is a side view showing a modified form of the heating coil unit shifting device;
Fig. 4A is a schematic plan view showing a first embodiment of the heating coil unit of the invention;
Fig. 4B is a schematic side view of the first embodiment of Fig. 4A;
Figs. 5A to 5C are graphs of temperature versus workpiece width;

Fig. 6 is a graph used in explaining the operation of the first embodiment of the heating coil unit;
Fig. 7A is a schematic plan view showing a modified form of the heating coil unit of Fig. 4A;

Fig. 7B is a schematic side view of the modification of Fig. 7A;
Fig. 8 is a schematic plan view showing another modified form of the heating coil unit of Fig. 4A;
Fig. 9 is a schematic plan view showing a second embodiment of the heating coil unit of the invention;
Figs. 10 and 11 are graphs used in explaining the operation of the second embodiment of the heating coil unit;
Fig. 12A is a schematic plan view showing a modified form of the heating coil unit of Fig. 9;
Fig. 12B is a schematic side view of the modification of Fig. 12A:
Figs.13 (appearing with Fig. 11) and 14 are graphs used in explaining the operation of the modification of Fig.
12A;
Fig. 15 is a schematic plan view showing another modified form of the heating coil unit of Fig. 9;
F'ig. 16 is a schematic plan view showing a third embodiment of the heating coil unit of the invention;
Figs. 17A to 17C are graphs used in explaining the operation of the heating coil unit of Fig. 16;
Fig. 18 (appearing with Fig. 16) is a schematic plan view showing a modified form of the heating coil unit of Fig. 16;
Fig. 19 is a schematic plan view showing another modified form of the heating coil unit of Fig. 16;
Figs. 20A to 20C (appearing w:ith F':igs. 17A to 17C) are graphs used in exp~a;n:ing the operation oE the modification of F'ig. 19;
Fig. 21 is a schematic plan view showing a fourth ernbodiment of the heating coil unit of the invention;
Fig. 22 is a fragmentary plan view showing the manner where the longitudinal conductors are coupled in the heating coil unit of Fig. 21;
Fig. 23 is a fragmentary sectional view showing the coupling mechanism;
Fig. 24A and 24B are graphs of temperature versus ;3o6 workpiece width;
Fig. 25 (appearing with Fig. 23) is a schematic plan view showing a modified form of the heating coil unit of Fig. 21:
Fig. 26 is a schematic plan view showing another modified form of the heating coil unit of Fig. 21;
Fig. 27A is a schematic plan view showing a fifth embodiment of the heating coil unit of the invention;
Fig. 27B is an enlarged fragmentary plan view showing the manner where the coil conductor is coupled; and Fig. 28 (appearing with Fig. 26) is a schematic plan view showing a modified form of -the heating coil unit of Fig. 26.

DETAILED DESCRIPTION OF THE INVENTION:
With reference to the drawings, wherein like numerals refer to like parts in the several views, and in particular to Fig. 1, there is shown one embodiment of an induction heating apparatus made in accordance with the invention.
The induction heating apparatus includes a pair of heating coil units 10 carried on respective frames 10a ;376 disposed in spaced-parallel relation to each other so that a workpiece WP, which is transported by means of a plurality of feed rollers A, can pass 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.
A power source unit B is connected to a matching transformer E through flexible cables D covered by a protective duct C. The matching transformer E is connected to supply a high- or intermediate-frequency alternating current to the main and auxiliary heating coils 20 and 30 to produce rapidly alternating magnetic field crossing the workpiece, causing heating.
The induction heating apparatus is shown as including a control unit, generally designated by the numeral l, for adjusting the coil frame lOa to a target position with respect to the workpiece WP in response to a position sensor 2. The position sensor 2 has a U-shaped sensor frame which carries light-emission and light-recelpt elements 2a and 2b facing to each other for sensing the position of one side edge of the workpiece WP
with respect to the coil frames lOa. Although the position sensor 2 is shown as positioned on the upstream side of the heating coil units lO, it will be appreciated that it may be positioned on the downstream side of the heating coil units lO. In addition, the position sensor 2 may be of another type which can sense the workpiece ~Z~3~
position in a mechanical or acoustic manner.
Referring to Figs. 2A and 2B, the coil frames lOa are carried on a movable table 3 along with the matching transformer E. The movable table 3 has rollers 4 positioned on guide rails 5 provided on a platform 6 positioned on one side of the coil frames lOa so that the movable table 3 can move in a direction perpendicular to the direction of transportation of the workpiece WP. The movable table 3 has a piece 7 secured on its lower surface. The piece 7 is formed with a threaded through-hole extending in the direction of movement of the movable table. The numeral 8 designates a servo motor having an output shaft with a threaded portion 9 held in engagement with the threaded through-hole of the piece 7.

The servo motor 8 is controlled by a servo control circuit ~not shown) which receives the sensor signal from the position sensor 2, calculates an error between the sensed and target positions of the heating coil units, and drives the servo motor 8 so as to move the movable table 3 in a direction reducing the calculated error to zero. Such a servo control circuit is well known in the art and will not be described in detail. As best shown in Fig. 2B, the movable table 3 has a cutout 3a which is effective to avoid any direct contact of the movable table 3 with the Workpiece WP.

Referring to Fig. 3, there is shown a modified form of the movable table which is substantially the same lZ9~376 as the structure of Figs. 2A and 2B except for its application to the case where the workpiece WP is transported between the heating coil units lO in the horizontal direction. Accordingly, parts in Fig. 3 which are like those in Figs. 2A and 2B have been given like reference numerals.
Referring to Figs. 4A and 4B, the induction heating`apparatus includes a pair of heating coil units lO
disposed in spaced-parallel relation to each other so that the workpiece WP can be transported 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 connected in series with the main heating coil 20. A
power source 40 is connected to supply a high- or intermediate-frequency alternating current to the heating coil units lO to produce rapidly alternating magnetic field crossing the workpiece WP.
The main heating coil 20 is divided into a first portion Il and a plurality of ~in the illustrated case three) second portions I2. The main heating coil first portion Il includes a plurality of ~in the illustrated case three) spaced-parallel transverse conductors 22 extending in a direction substantially perpendicular to the direction of transportation of the workpiece WP. The transverse conductors 22 are connected in series by means of electrical connections 24 so that the directions of the AC current flow through adjacent two transverse conductors lZS~3~t~

22 are opposite, as shown in Figs. 4A and 4B. Each of the main heating coil second portions I2 has a transverse conductor 26 extending in a direction substantially perpendicular to the direction of transportation of the workpiece WP. The transverse conductors 22 and 26 have a length L longer than the width W of the workpiece WP.
The auxiliary heating coil 30 is divided into a plurality of (in the illustrated case two) first portions IIl and a plurality of (in the illustrated case two) second portions II2. Each of the auxiliary heating coil first portions IIl has a longitudinal conductor 32 extending substantially in the same direction as the direction of transportation of the workpiece WP, the longitudinal conductor 32 being placed at a position facing to the workpiece WP at a small distance inside from one of the side edges of the workpiece WP, and a pair of transverse conductors 34 connected respectively to the Opposite ends of the longitudinal conductor 32. Each of the auxiliary heating coil second portions II2 has a longitudinal conductor 36 extending in the same direction as the direction of transportation of the workpiece WP, the longit~dinal conductor 36 being placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP, and a pair of transverse conductors 38 connected respectively to the Opposite ends of the longitudinal conductor 36.
The main heating coil first portion Il is 37~

connected in series with one of the auxiliary heating coil first portions II1, which in turn is connected in series with one of the main heating coil second portions I2, which in turn is connected in series with one of the auxiliary heating coil second portions II2. This auxiliary heating coil second portion I2 is connected in series with another main heating coil second portion I2, which in turn is connected in series with the other auxiliary heating coil first portion IIl. This auxiliàry heating coil first portion IIl is connected in series with the other main auxiliary heating coil second portion I2, which in turn is connected in series with the other main heating coil second portion I2, which in turn is connected in series with the other auxiliary heating coil second portion II2.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 4A, the workpiece WP passes the space between the main heating coil first portions Il where it is heated to have a temperature curve having two low-temperature or trough points B and D, as sown in Fig. 5A, the space between the auxiliary heating coil first portions II1 where it is heated to have a high-temperature or crest point G ~see Fig. 5B), the space between the main heating coil second portion I2 where it is heated to have a temperature curve having two low-temperature or trough points B and D, as shown in Fig. 5A, and the space between 12~537~

the auxiliary heating coil second portions II2 where it is heated to have a high-temperature or crest point I (Fig.
5B) in this sequence. During this operation, the workpiece WP is heated to have uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 5C. A similar operation is repeated while the workpiece WP passes the space between the main heating coil second portions I2, the space between the auxiliary heating coil first portions IIl, the space between the main heating coil second portions I2, and the space between the auxiliary heating coil second portions II2 in this sequence.
Fig. 6 shows variations in the temperature on the center point C tsee Fig. 5A) of the workpiece WP and the temperature on point B or D (see Fig. 5A) while the workpiece WP passes the respective spaces. As can be seen from Fig. 6, the difference between the temperatures on the points C and B is relatively small. This stems from the fact that the main and auxiliary heating coil portions are disposed alternatively in the direction of transportation of the workpiece WP. Accordingly, there is Substantially no stains which may occur to curve the Workpiece WP during the heating operation. Therefore, the workpiece WP can be maintained at a constant clearance with respect to the heating coil units, which improves the temperature uniformity over the full width and full length of the workpiece WP. In addition, it is possible to 1, 12~7~;

increase the heating efficiency by reducing the clearance between the heating coil units through which the workpiece is transported.
Referring to Figs. 7A and 7B, there is illustrated a modified form of the induction heating apparatus. In this modification, the main heating coil 50 includes a plurality of ~in the illustrated case two) spaced-parallel transverse conductors 52 extending in a direction substantially perpendicular to the direction of the transportation of the workpiece WP. The transverse conductors 52 have a length L longer than the width W of the workpiece WP. The auxiliary heating coil 60 is divided into a first portion IIl and a second portion II2.
The auxiliary heating coil first portion IIl has a longitudinal conductor 62 extending in the same direction as the direction of transportation of the workpiece WP, the longitudinal conductor 62 being placed at a position facing to the workpiece WP at a small distance inside from one of the side edges of the workpiece WP, and a pair of transverse conductors 64 connected respectively to the opposite encls of the longitudinal conductor 62. The auxiliary heating coil second portion II2 has a longitudinal conductor 66 extending in the same direction as the direction of transporation of the workpiece WP, the longitudinal conductor 66 being placed at a position facing to the workpiece WP at a small distance inside from the other side edge of the workpiece WP, and a pair of 129~ 6 .

transverse conductors 68 connected respectively to the opposite ends of the longitudinal conductor 66.
The main and auxiliary heating coils 50 and 60 are connected in series so that the directions of the AC
current flow through the adjacent two transverse conductors 52 and 64 are the same and the directions of the AC current flow through the adjacent two transverse conductors 64 and 68 are the same, as shown in Fig. 7A.
This connection is effective to increase the magnetic flux density. In addition, a magnetic shield 70 is provided to cover each of the transverse and longitudinal conductors 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. Coupling mechanisms may be provided to permit movement of each of the longitudinal conductors 62 and 66 with respect to the corresponding side edge of the workpiece in order to adjust the crest points G and I
~see Fig. 5B) in coincience with the trough points B and D

~see Fig. 5A).
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 7A, the workpiece WP passes the space between the main heating ciols 50 where it is heated to have a temperature curve having two low-temperature or trough points B and D, as shown in Fig. 5A, the space between the auxiliary heating coil first portions IIl where it is 33~7f~

heated to compensate for the trough point D, and the space between the auxiliary heating coil second portions II2 where it is heated to compensate for the trough point B.
During this operation, the workpiece WP is heated to have uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 5C.
Referring to Fig. 8, there is illustrated another modified form of the induction heating apparatus.
In this modification, the main heating coil 80 includes a plurality of (in the illustrated case two) spaced-parallel transverse conductors 82 extending in a direction substantially perpendicular to the direction of the transportation of the workpiece WP. The transverse conductors 82 have a length L longert than the width W of the workpiece WP. The auxiliary heating coil 90 is divided into two first portions IIl and two second portions II2. Each of the auxiliary heating coil first portions IIl has a longitudinal conductor 92 extending in the same direction as the direction of transportation of the workpiece WP, the longitudinal conductor 92 being placed at a position facing to the workpiece at a small distance inside from one of the side edges of the workpiece WP, and a pair of transverse conductors 94 Connected respectively to the opposite ends of the longitudinal conductor 92. Each of the auxiliary heating coil second portions II2 has a longitudinal conductor 96 extending in the same direction as the direction of 12~.~376 transportation of the workpiece WP, the longitudinal conductor 96 being placed at a position facing to the workpiece at a small distance inside from the other side edge of the workpiece WP, and a pair of transverse conductors 98 connected respectively to the opposite ends of the longitudinal conductor 96.
The main and auxiliary heating coils 80 and 90 are connected in series so that the directions of the AC
current flow through the adjacent two transverse conductors 98 and 94 are the same and the directions of the AC current flow through the adjacent two transverse conductors 82 and 94, 98 are the same, as shown in Fig. 8.
This connection is effective to increase the magnetic flux density. Coupling mechanisms may be provided to permit movement of each of the longitudinal conductors 92 and 96 with respect to the corresponding side edge of the workpiece in order to adjust the crest points G and I (see Fig. 5B) in coincidence with the trough points B and D
~see Fig. 5A).
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 8, the workpiece WP passes the space between the auxiliary heating coil first portions IIl, the space between the auxiliary heating coil second portions II2, the space between the main heating coils I, the space between the auxiliary heating coil first portions IIl, and the space between the auxiliary heating coil second - 18 - ?

537~

portions II2 in this order. During this operation, the workpiece WP is heated to have uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 5C.
Referring to Fig. 9, 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 100 disposed in spaced-parallel relation to each other so that the workpiece WP can be transported between the heating coil units 100. Each of the heating coil units 100 includes a main heating coil 120 and an auxiliary heating coil 130 connected in series with the main heating coil 120. A power source 140 is connected to supply a high- or intermediate-frequency alternating current to the heating coil units 100 to produce rapidly alternating magnetic field crossing the workpiece WP.
The main heating coil 120 is divided into a first portion Il and a second portion I2. The main heating coil first portion Il includes a plurality of ~in the illustrated case two) spaced-parallel transverse Conductors 122 extending in a direction substantially perpendicular to the direction of transportation of the Workpiece WP. The transverse conductors 122 are connected in scries 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 FigO

12~i37~

9. The main heating coil second portion I2 includes a plurality of (in the illustrated case two) space-parallel transverse conductors 126 extending in a direction substantially perpendicular to the direction of transportation of the workpiece WP. These transverse conductors 126 are connected in series by means of electrical connections 128 so that the directions of the AC current flow through the two transverse conductor 126 are opposite, as shown in Fig. 9. The transverse conductors 122 and 126 have a length L longer than the width W of the workpiece WP.
The auxiliary heating coil 130 is disposed between the main heating coil first and second portions Il and I2 and it has 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 conductors 132 being placed at positions facing to the workpiece WP at a slight distance inside from the respective opposite side edges of the workpiece WP. The longitudinal conductors 132 are connected in series with each other by means of transverse conductors 134.
The main and auxiliary heating coils are Connected in series so that the directions of the AC

current flow through the adjacent two transverse conductors 122 and 134 are the same and the directions of the AC current flow through the adjacent two transverse conductors 126 and 134 are the same. This connection is effective to increase the magnetic flux density. In addition, a magnetic shield 170 is provided to cover each of the transverse and longitudinal conductors except for its one side facing to the workpiece WP in order tominimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. Coupling mechanisms may be provided to permit movement of each of the longitudinal conductors 132 with respect to the corresponding side edges of the workpiece in order to adjust the crest points G and I (see Fig. 5B) in coincidence with the trough points B and D ~see Fig.
5A).
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S

of Fig. 9 at a constant speed, the workpiece WP passes the space between the main heating coil first portions Il, the space between the auxiliary heating coils II, and the space between the main heating coil second portions I2 in this sequence. During this operation, the workpiece WP is heated to have uniform temperature distribution over the full width of the workpiece WP, as shown in Fig. 10.
Fig. 11 shows variations in the temperature on the center point C ~see Fig. 5A) of the workpiece WP and the temperature on the point B or D ~see Fig. 5A) while the workpiece WP passes the respective spaces. As can be seen from Fig. 11, the difference between the temperatures 3 ~ ~i on the points C and B (or D) is relatively small. This stems from the fact that the main and auxiliary heating coil portions are disposed alternatively in the direction of transportation of the workpiece WP. Accordingly, there is substantially no stress which may occur to deform or curve the workpiece WP during the heating operation.
Therefore, the workpiece WP can be maintained at a constant clearance with respect to the heating coil units, which improves the temperature uniformity over the full width and full length of the workpiece WP. In addition, it is possible to increase the heating efficiency by reducing the clearance between the heating coil units through which the workpiece is transported.
Referring to Figs. 12A and 12B, there is illustrated a modified form of the induction heating apparatus. In this modification, the main heating coil is divided into three portions Il, I2 and I3 each having two spaced-parallel transverse conductors 152 extending in a direction substantially perpendicular to the direction of the transportation of the workpiece WP. The transverse Conductor5 152 have a length L longer than the width W of the workpiece WP. The auxiliary heating coil is divided into two portion IIl and II2 each having a pair of spaced-parallel longitudinal conductor 162 extending substantially in the same direction as the direction of tranSportation of the workpiece WP, the longitudinal Conductors being placed at respective positions facing to ~2~3~i the workpiece WP at a small distance inside from the respective opposite side edges of the workpiece WP, and a pair of transverse conductors 164 connecting the longitudinal conductors 162 in series.
The main and auxiliary heating coil portions are disposed alternatively and connected in series with each other. A magnetic shield 170 is provided to cover each of the transverse and longitudinal conductors 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.
Coupling mechanisms may be provided to permit movement of both of the longitudinal conductors 162 widthwise of the workpiece in order to adjust the distance between the longitudinal conductors 162 of the auxiliary heating coil first portion IIl at a value 11 which is equal to the distance between a position somewhat outer from the trough B and a position somewhat outer from the trough D, as shown in Fig. 13, and the distance between the longitudinal conductors 366 of the auxiliary heating coil second portion II2 at a value 12 which is equal to the distance between a position somewhat inner fro~ the trough B and a position somewhat inner from the trough D, as shown in Fig. 13.
Assuming now that the workpiece WP is transported in the direction indicated by the bold arrow S
of Fig. 12A, the workpiece WP passes the space between the ~Z~3~76 main heating coil first portions Il, the space between the auxiliary heating coil first portions IIl, the space between the main heating coil second portion I2, and the space between the auxiliary heating coil second portions II2, and the space between the main heating coil third portions I3. During this heating operation, the workpiece WP is heated to have uniform temperature distribution over the full width of the workpiece WP.
Fig. 14 shows variations in the temperature on the center point C (see Fig. 13) of the workpiece WP and the temperature on the point B or D (see Fig. 13) during the heating operation. As can be seen from Fig. 14, the difference between the temperatures on the points C and B
~or D) is relatively small. This stems from the fact that the main and auxiliary heating coil portions are disposed alternatively in the direction of transportation of the workpiece WP. In addition, the difference between the temperatures on the points C and B (or D) can be smaller than obtained in the second embodiment of Fig. 9 since the main and auxiliary heating coils are divided in a greater number of portions in this embodiment. Accordingly, there is substantially no stress which may occur to deform or curve the workpiece WP during the heating operation.
Therefore~ the workipece WP can be maintained at a constant clearance with respect to the heating coil units, which improves the temperature uniformity over the area of the workpiece WP. In addition, it is possible to increase ~$~7~

the heating efficiency by reducing the clearance between the heating coil units through which the workpiece WP is transported.
Referring to Eig. 15, there is illustrated another modification of the induction heating apparatus which is substantially the same as the modification of Figs. 12A and 12B except that the first, second and third main heating coils Il, I2 and I3 are connected in series and are supplied with a high- or intermediate-frequency alternating current from a power source 142 and the first and second auxiliary heating coils IIl and II2 are connected in series and are supplied with a high- or intermediate-frequency alternating current from another power source 144. This modification is effective to adjust the alternating current to the auxiliary heating coils independently of the alternating current to the main heating coils 120.
Referring to Fig. 16, there is illustrated a third embodiment of the induction heating apparatus of the invention. The induction heating apparatus includes a pair of heating coil units 200 disposed in spaced-parallel relation to each other so that the workpiece WP can be transported between the heating coil units 200 in a direction indicated by the bold arrow S. Each of the heating coil units 200 includes a main heating coil 220 and an auxiliary heating coil 230 disposed on the upstream side of the main heating coil 220. A power source 242 is - 12~5376 connected to supply a high- or intermediate-frequency alternating current to the main heating coils 220 to produce rapidly alternating magnetic field crossing the workpiece WP. Another power source 246 is connected to supply a high- or intermediate-frequency alternating current to the auxiliary heating coils 230 to produce rapidly alternating magnetic field crossing the workpiece WP.
The main heating coil 220 includes a pair of spaced-parallel transverse conductors 222 extending in a direction substantially perpendicular to the direction of transportation of the workpiece WP. The transverse conductors 222 are connected in series so that the directions of the AC current flow through adjacent two transverse conductors 222 are opposite. The transverse conductors 222 have a length L longer than the width W of the workpiece WP.
The auxiliary heating coil 230 is disposed on the upstream side of the main heating coil 220 and it has a pair of spaced-parallel longitudinal conductors 232 extending substantially in the same direction as the direction of transportation of the workpiece WP, the longitudinal conductors 232 being placed at positions facing to the workpiece WP at a slight distance inside from the respective opposite side edges of the workpiece WP. The longitudinal conductors 232 are connected in series with each other.

12~376 A magnetic shield 270 is provided to cover each of the transverse and longitudinal conductors 222 and 232 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 erficiency.
The workpiece WP passes the space between the auxiliary heating coils 230 where it is heated to have a temperature curve, as shown in Fig. 17C. As can be seen from Fig. 17C, the temperature curve has two crests which appear at positions adjacent or at a small distance inside from the respective opposite side edges of the workpiece WP. It is to be noted that the temperature at the opposite side edges of the workpiece WP is relatively low in this initial stage of the heating process.
Subsequently, the workpiece WP passes the space between the main heating coils 220, which has a heating characteristic as shown in Fig. 17B, where it is heated to compensate for the temperature crests so as to provide temperature uniformity over the full width of the workpiece WPr as shown in Fig. 17A. For this purpose, the distance between the longitudinal conductors 222 is set in such a manner that the temperature crest points (Fig. 17C) correspond6 to the respective temperature trough points ~Fig. 17B).
If a considedrable thermal expansion difference Occurs between a high temperature point and a low ?~376 temperature point during a heating process, strong stresses will occur to compress the part between the high and low temperature points, causing deformations or creases. This is true particularly for workpieces made of carbon steel or the like which is subject to Al transformation at a temperature around 726C, causing discontinuous thermal expansion. Although such an undesirable deformation can be avoided to some extent by reducing the difference between the low- and high-temperature portions A and B or E and D ~see Fig. 13) in such a manner as described previously, curves and creases would appear at the opposite side edge portions of the workpiece if the opposite side edges, which are free edges subjective to deformation, are heated first to such a high temperature as to lost the material rigidity. This embodiment can avoid such an undesirable deformation by heating the workpiece between the auxiliary heating coils 230 in the initial stage of the heating process and then heating it between the main heating coils 220 in the subsequent stage of the heating process.
Referring to Fig. 18, there is illustrated a modified form of the induction heating apparatus. This modification is substantially the same as the heating coil unit of Fig. 16 except that the main heating coil is divided into two portions each having a pair of Spaced-parallel transverse conductors 222 connected in series with each other. These main heating coil portions ;376 are supplied with high- or intermediate-frequency alternating currents from respective separated power SQUrCes 242 and 243. Accordingly, parts in Fig. 18 which are like those in Fig. 16 have been given like numerals.
With this modification, it is possible to reduce the possibility of such undesirable deformation of the workpiece by decreasing the rate at which the opposite side edges of the workpiece WP are heated.
Referring to Fig. 19, there is illustrated another modified form of the induction heating apparatus which is substantially the same as the heating coil unit of Fig. 18 except for that the auxiliary heating coil 230 is disposed between the main heating coil first and second portions 220. Accordingly, parts in Fig. 19 which are like those in Fig. 18 have been given like numerals.
The workpiece WP passes the space between the main heating coil first portions 220 where it is heated to have a temperature curve, as shown in Fig. 20C, the temperature curve having two troughs which appear at a small distance inside from the respective opposite side edges of the workpiece WP. It is to be noted that the temperature at the opposite side edges of the workpiece WP
is held at a temperature sufficiently lower than a value above which its rigidity is lost in this first stage of the heating process. Substantially, the workpiece WP

passes the space between the auxiliary heating coils 2300 As a result, the workpiece has a temperature curve, as 12~5;376 shown in Fig. 20B. Subsequently, the workpiece WP passes the space between the main heating coil second portions where it is heated to provide temperature uniformity over the full width of the workpiece WP, as shown in Fig. 20A.
With this embodiment, it is, therefore, possible to reduce the temperature difference between the low- and high-temperature portions of the workpiece during the heating process and also to prevent the opposite side edges of the workpiece from being heated to a high temperature before the inner portion of the workpiece.

This is effective to avoid curves and creases which may appear at the opposite side edge portions of the workpiece.
Referring to Fig. 21, there is illustrated a fourth 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 310 in Fig. 21, disposed in spaced-parallel relation to each other so that the workpiece WP can be transported between the heating coil units 310. Each of the heating coil units 310 includes a main heating coil 320 and an auxiliary heating coil 330 placed at a position adjacent to the main heating coil 320. A power source 342 is Connected to supply a high- or intermediate-frequency alternating current to the main heating coils 320 to produce magnetic field crossing the workpiece WP. Another power source 346 is connected to supply a high- or 12~?~;376 intermediate-frequency alternating current to the auxiliary heating coils 330 to produce magnetic field crossing the workpiece WP.
The main heating coil 320 includes a plurality of (in the illustrated case six) spaced-parallel transverse conductors 322 extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 21, of transportation of the workpiece WP. Except for the two outermost transverse-conductors 322, the transverse conductor 322 are arranged to form a plurality of pairs each including two transverse conductors 322 placed in close priximity with each otherO
The transverse conductors 322 are shown as having a length L longer than the width W of the workpiece WP. Each of the transverse conductors 322 may have a magnetic shield 325 mounted thereon. The magnetic shield 325 extends almost the full length of the transverse conductor 322 and has a U-shaped cross section to cover the transverse Conductor 322 except for its one side facing to the workpiece WP ln order to minimize the magnetic flux leakage and increase the magnetic flux concentration so as to improve the heating efficiency. The transverse Conductors 322 are connected in series so that the directions of the AC current flow through adjacent two tranSverse conductors 322 placed in pair are the same, as shown in Fig. 21. Such an AC current flow produces rapidly alternating magnetic field to induce an electric 12~3 ~6 potential in the workpiece WP, causing heating therein.
The auxiliary heating coil 330 includes a pairof spaced longitudinal conductors 332 extending substantially in the same direction as the direction of transportation of the workpiece WP. One of the longitudinal conductors 332 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 332 are spaced at a distance U from each other, the distance U being shorter than the width W of the workpiece WP. The longitudinal conductors 332 are connected in series with each other by electrical connections 334 and 336 so that the directions of the AC
current flow through the two longitudinal conductors 332 are opposite, as shown in Fig. 21. Such an AC current flow produces rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein. Each of the longitudinal conductors 332 may have a magnetic shield 335 mounted thereon. The magnetic shield 335 extends almost the full length of the longitudinal conductor 332 and has a U-shaped cross section to cover the longitudinal conductor 332 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. Both of the longitudinal conductors 332 are coupled between the electrical connections 334 and 336 in such a manner that one longitudinal conductor can move with respect to the other longitudinal conductor to vary the distance U between the longitudinal conductors 332 and also each of the longitudinal conductors can rotate to vary the angle of the longitudinal conductor with respect to the direction of transportation of the workpiece WP.

Referring to Fig. 22, each of the longitudinal conductors 332 is provided at the opposite ends thereof with first and second extensions 352 and 354. The first extension 352 is formed with a hole for insertion of a bolt 356. The second extension 354 is formed with a slot 355 for insertion of a bolt 358. A mounting frange 360, which is secured on the electrical connection 334, is formed with a slot 361 extending in parallel with the electrical connection 343. Another mounting frange 360, which is secured on the electrical connection 336, is formed with a slot 363 extending in parallel with the electrical connection 336. The first extension 352 is seCured on the mounting frange 360 by the bolt 356 and a nut ~not shown) fastened on the bolt 356. The second extensiOn 354 is secured on the mounting frange 360 by the bolt 358 and a nut ~not shown) fastened on the bolt 358.
Referring to Fig. 23, each of the electrical connections 334 and 336 is taken in the form of a i3~6 water-cooled conductor having a coolant passage 335 or 337 extending axially thereof. Although the electrical connection 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 332 may have the same structure as the electrical connections 334 and 336. 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 320. The transverse conductors 332 may have the same structure as the electrical connections 334 and 336 for dissipating the heat in the main heating coils 320.
The electrical connection 334 is formed near its Opposite ends with ports 362 through which its coolant passage 335 opens to the exterior, the electrical connection 336 is formed near its opposite ends with ports 360, and each of the longitudinal conductors 332 is formed near its opposite ends with ports 364. Coolant hoses 368 are provided to make hydraulic connections between ports 362 and 364 so as to form a series connected coolant conduit in each of the auxiliary heating coils 330.
To move and/or rotate each of the longitudinal conductOrs 332, the bolts 356 and 358 may be loosened to such an extent that the first and second extensions 352 and 354 can slide on the respective mounting franges 360.

lZg~3 f ~

After the longitudinal conductor 332 is set at a desired position, the bolts 356 and 358 are tightened again to fix the longitudinal conductor to the electrical connections 334 and 336.
In this embodiment, each of the longitudinal conductors 332 can move with respect to the other longitudinal conductor to vary the distance U between the longitudinal conductors 332 so as to adjust the crest points G and I ~Fig. 24B) to positions corresponding to the respective trough points B and D (Fig. 24A). In addition, each of the longitudinal conductors 332 can rotate to vary the angle of inclination of the longitudinal conductor with respect to the direction of transportation of the workpiece WP in such a manner that the width W2 of the crest G or I (see Fig. 24B) of the temperature curve provided by the auxiliary heating coils arranged in pair can be equalized to the width Wl of the trough B or D ~see Fig. 24A) provided by the main heating coils arranged in pair, thereby adjusting the density of energy inducted in the workpiece WP teansported between the auxiliary heating coils 330. The greater then angle at which the longitudinal conductor is inclined with respect to the direction of transportation of the Workpiece~ the samller the induced energy per unit area and the lower the temperature, indicated by the height of the crest G or I of Fig. 24B, of the workpiece heated between the auxiliry heating coils 330. It is, therefore, 12~537~

possible to provide uniform temperature distribution over the full width of the workpiece WP by adjusting the width W2 and height of the crests G and I provided by the auxiliary heating coils 330 arranged in pair.
Referring to Fig. 25, there is illustrated a modified form of the induction heatlng apparatus which is substantially the same as shown and described in connection with Fig. 21 except for the heating coil connection. Accordingly, parts in Fig. 25 which are like those in Fig. 21 have been given like reference numerals.
In this modification, the main heating coil 320 are divided into first and second portions between which the auxiliary heating coil 330 is disposed. The main and auxiliary heating coils 320 and 330 are connected in series, as shown in Fig. 25, and are supplied with a high-or intermediate-frequency alternating current from a single power source 148. ~he longitudinal conductors 332 are coupled between the electrical connections 334 substantially in the same manner as described in connection with Figs. 22 and 23 so that each of the ~ongitudinal conductors 335 can be inclined at a desired angle with respect to the direction of transportation of the workpiece WP.
Referring to Fig. 26, there is illustrated another modified form of the induction heating apparatus which is substantially the same as shown and described in connection with Fig. 21 except for the heating coil 3 t ~i connection. Accordingly, parts in Fig. 26 which are like those in Fig. 21 have been given like reference numerals.
In this modification, the auxiliary heating coil 330 is connected in series with the main heating coil 320 and is supplied with a high- or intermediate-frequency alternating current from a single power source 148.
Although the auxiliary heating coil 330 is shown as positioned on the downstream side of the main heating coil 320, it is to be noted that it may be positioned on the upstream side of the main heating coil 320.
Referring to Fig. 27A, there is illustrated a fifth 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 410 in Fig. 27A, disposed in spaced-parallel relation to each other so that the workpiece WP can be transported between the heating coil units 410. Each of the heating coil units 410 includes a main heating coil 420 and an auxiliary heating coil 430.
The main heating coil 420 is divided into first and second portions each having a plurality of (in the illustrated case three) spaced-parallel transverse conductors extending in a direction substantially perpendicular to the direction, indicated by the bold arrow S of Fig. 27A. The transverse conductors have a length L longer than the width W of the workpiece WP. The numeralS 424a to 424d indicate connection conductors used 3~6 to connect the transverse conductors 422a to 422f in series, as shown in Fig. 27A. A power source 442 is connected to supply a high- or intermediate-frequency alternatinq current to the main heating coils 420 to produce magnetic field crossing the workpiece WP. Such magnetic field induces an electric potential in the workpiece WP, causing heating therein. A magnetic shield 425 is provided on each of the transverse conductors 422a to 422f. The magnetic shield 425 extends almost the full length of the transverse conductor and has a U-shaped cross section to cover the transverse conductor 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.
Referring to Fig. 27B, each of the connection conductors 424a to 424g is formed with a slot 450 extending in parallel with the direction of transportation of the workpiece WP. A bolt 452 is used to secure one end of the transverse conductor to the corresponding connection conductor. The bolt 452 is inserted into the slot 450 from one side of the connection conductor and it engages with a nut ~not shown) on the other side of the connection conductor.
Returning to Fig. 27A, the auxiliary heating coil 430 is disposed between the first and second portions of the main heating coil 420 and it includes a pair of spaced-parallel longitudinal conductors 432a and 432b extending substantially in the same direction as the direction of transportation of the workpiece WP. One of the longitudinal conductors 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 432 are spaced at a distance U from each other, the distance U being shorter than the width W of the workpiece WP. The longitudinal conductors 432a and 432b are connected in series with each other by means of an electrical connection 443a and is connected in series with a power source 446 by means of connection conductors 434b and 434c. The power source 446 supplies a high- or intermediate-frequency alternating current to produce rapidly alternating magnetic field to induce an electric potential in the workpiece WP, causing heating therein.
Each of the connection conductors 434a, 434b and 434c has the same structure as shown in Fig. 27B, so that the distance U between the longitudinal conductors 432a and 432b can be adjusted to a desired value. Each of the longitudinal conductors 432a and 432b may have a magnetic Shield 435 mounted thereon. The magnetic shield 435 extends almost the full length of the longitudinal conductor and has a U-shaped cross section to cover the 12~3~37~;

longitudinal conductor 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 applicants have found that the temperature at the center of the workpiece WP is lower than the temperature at the opposite side edges of the workpiece when the pitch Pl, P3 of the transverse conductors of the main coil is greater than a reference pitch or when the width W of the workpiece WP is shorter than a reference width and that the temperature at the center of the workpiece WP is higher than the temperature at the opposite side edges of the workpiece WP when the pitch of the transverse conductors of the main heating coil is smaller than the reference pitch or when the width W of the workpiece WP is longer than the reference width. In this embodiment, the transverse conductor pitch Pl, P3 can be changed freely. It is, therefore, possible to provide uniform temperature distribution over the full width of the workpiece WP by increasing the transverse conductor pitch for a broader workpiece in which longer induced current transverse paths appear and by decreasing the transverse conductor pitch for a narrower workpiece in which relatively shorter induced current transverse paths appear. It is to be noted, of course, that this invention may be used to adjust the temperature of the center of the workpiece at a value difference from the temperature at 3~76 the side edges of the workpiece. In addition, the longitudinal conductors 432a and 432b can be moved to vary the distance U between the longitudinal conductors.
To change the pitch of the transverse conductors or the distance between the longitudinal conductors, the bolts 452 may be loosened to such an extent that each of the transverse or longitudinal conductors can slide on the corresponding connection conductors. After a desired transverse conductor pitch or a desired longitudinal conductor distance is set, the bolts are tightened again to fix the transverse or longitudinal conductor to the connection conductors.
Referring to Fig. 28, there is illustrated another modified form of the induction heating apparatus which is substantially the same as shown and described in Figs. 27A and 27B except that the auxiliary heating coil 430 is disposed on the downstream side of the main heating Coil 420. Accordingly, parts in Fig. 28 which are like those in Figs. 27A and 27B have been given like reference numerals. In this modification, the auxiliary heating Coil 430 is shown as having a pair of longitudinal Conductors 432a and 432b movable to adjust the angle at which they are inclined with respect to the direction of transportation of the workpiece WP substantially in the same manner as described in connection with Figs. 22 and 23.
It is, therefore, apparent from the foregoing 3 ~ 6 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 for compensating 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 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 sourceO
Similarly, the auxiliary heating coils included in the ~Z~i376 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 perpendic~lar to the surface of the workpiece when the auxiliary heating coil unit is powered by the power source.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art.
For example, the control unit is optional and may be removed from the induction heating apparatus. The magnetic shield are also optional and may be removed~
Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the scope of the appended claims.

Claims

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;
a plurality of main heating coil units each having a pair of heating coils disposed in spaced-parallel relation to permit transportation of the workpiece between the main 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 produced magnetic field crossing the workpiece; and a plurality of auxiliary heating coil units each 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 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;
said main heating coil units and said auxiliary heating coil units are placed alternatively in a line extending in the direction of transportation of the workpiece.

2. The induction heating apparatus as claimed in claim 1, wherein one of the main heating coil units is disposed on the downstream side of the other main heating coil units and on the downstream side of the auxiliary heating coil units.

3. The induction heating apparatus as claimed in claim 1, wherein the power source unit includes first and second power sources, the first power source being connected to supply alternating current to the main heating coil units, the second power source being connected to supply alternating current to the auxiliary heating coil units.

4. The induction heating apparatus as claimed in claim 1, wherein each 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 each of the first and second longitudinal Conductors is inclined at an angle with respect to the direction of transportation of the workpiece.

6. The induction heating apparatus as claimed in claim 5, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

7. The induction heating apparatus as claimed in claim 1, wherein each the main heating coil has at least one pair of transverse conductors arranged at a pitch.

8. The induction heating apparatus as claimed in claim 7, wherein each the main heating coil includes means for manually adjusting the pitch provided between the adjacent two transverse conductors through which AC
current flows in opposite direction.

9. 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 set 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 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; and 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, each the main heating coil is divided into first and second portions disposed on the opposite sides of the auxiliary heating coil.

10. The induction heating apparatus as claimed in claim 9, wherein each the auxiliary heating coil includes means for manually adjusting the transverse distance between the first and second longitudinal conductors.

11. The induction heating apparatus as claimed in claim 9, wherein each the main heating coil and each the auxiliary heating coil are connected in series.

12. The induction heating apparatus as claimed in claim 9, wherein the power source unit includes first and second power sources each supplying alternating current, the first power source being connected in series with each the main heating coil, the second power source being connected in series with each the auxiliary heating coil.

13. The induction heating apparatus as claimed in claim 9, wherein each the auxiliary heating coil includes a pair of transverse conductors disposed in spaced-parallel relation to each other and connected to the first and second longitudinal conductors to form a one-turn coil connected in series with the power source unit.

14. The induction heating apparatus as claimed in claim 9, wherein the power source unit includes first and second power sources each generating alternative current at a predetermined frequency, the first power source being connected in series with each the main heating coil, the second power source being connected in series with each the auxiliary heating coil.

15. The induction heating apparatus as claimed in claim 9, wherein each of the first and second longitudinal conductors is inclined at an angle with respect to the direction of transportation of the workpiece.

16. The induction heating apparatus as claimed in claim 15, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

17. The induction heating apparatus as claimed in claim 9, wherein each the main heating coil has at least one pair of transverse conductors arranged at a pitch.

18. The induction heating apparatus as claimed in claim 17 wherein each the main heating coil includes means for manually adjusting the pitch provided between the adjacent two transverse conductors through which AC
current flows in opposite direction.

19. The induction heating apparatus as claimed in claim 10, wherein each of the first and second longitudinal conductors is inclined at an angle with respect to the direction of transportation of the workpiece.

20. The induction heating apparatus as claimed in claim 19, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

21. 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 set 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 placed at positions facing to the workpiece, the first and second longitudinal conductors extending at an angle with respect to the direction of transportation 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.

22. The induction heating apparatus as claimed in claim 21, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

23. The induction heating apparatus as claimed in claim 21, wherein each the main heating coil is disposed on the downstream side of the auxiliary heating coil.

24. The induction heating apparatus as claimed in claim 21, wherein each the main heating coil is divided into first and second portions disposed on the opposite sides of the auxiliary heating coil.

25. The induction heating apparatus as claimed in claim 21, where each the auxiliary heating coil is disposed on the downstream side of the main heating coil.

26. An induction heating apparatus of a transverse flux heating type inductively heating a sheet-formed workpiece transported through the apparatus in a direction, the workpiece having a substantially uniform width defined by opposed side edges, comprising:
a power source unit for supplying alternating current at a predetermined frequency; and at least one set 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.

27. The induction heating apparatus as claimed in claim 26, wherein a magnetic shield is provided to cover each of the transverse and longitudinal conductors except for its one side facing to the workpiece.

28. The induction heating apparatus as claimed in claim 26, wherein each of the transverse and longitudinal conductors is a water-cooled conductor for dissipating heat in the conductor.

29. The induction heating apparatus as claimed in claim 26, wherein each the auxiliary heating coil includes means for manually adjusting the transverse distance between the first and second longitudinal conductors.

30. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil and each the auxiliary heating coil are connected in series.

31. The induction heating apparatus as claimed in claim 26, wherein the power source unit includes first and second power sources each supplying alternating current, the first power source being connected in series with each the main heating coil, the second power source being connected in series with each the auxiliary heating coil.

32. The induction heating apparatus as claimed in claim 26, wherein each the auxiliary heating coil includes a pair of transverse conductors disposed in spaced-parallel relation to each other and connected to the first and second longitudinal conductors to form a one-turn coil connected in series with the power source unit.

33. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil is divided into a plurality of portions, the auxiliary heating coil being divided into a plurality of portions disposed alternatively in the direction of transportation of the workpiece with the main heating coil portions.

34. The induction heating apparatus as claimed in claim 33, wherein the power source unit includes first and second power sources each generating alternative current at a predetermined frequency, the first power source being connected in series with each the main heating coil, the second power source being connected in series with each the auxiliary heating coil.

35. The induction heating apparatus as claimed in claim 33, wherein each the auxiliary heating coil is divided into first and second portions, the first portion having the first longitudinal conductor, the second portion having the second longitudinal conductor.

36, The induction heating apparatus as claimed in claim 26, wherein each the auxiliary heating coil is divided into first and second portions, the first portion having the first longitudinal conductor, the second portion having the second longitudinal conductor.

37. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil is divided into first and second portions disposed on the opposite sides of the auxiliary heating coil.

38. The induction heating apparatus as claimed in claim 37, wherein the power source unit includes first and second power sources each generating alternating current at a predetermined frequency, the first power source being connected in series with each the main heating coil, the second power source being connected in series with each the auxiliary heating coil.

39. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil is disposed on the downstream side of the auxiliary heating coil.

40. The induction heating apparatus as claimed in claim 39, wherein each the main heating coil is divided into first and second portions connected to individual power sources for supplying a high- or intermediate-frequency alternating current;

41. The induction heating apparatus as claimed in claim 26, wherein each of the first and second longitudinal conductors is inclined at an angle with respect to the direction of transportation of the workpiece.

42. The induction heating apparatus as claimed in claim 41, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

43. The induction heating apparatus as claimed in claim 41, wherein each the main heating coil is disposed on the downstream side of the auxiliary heating coil.

44. The induction heating apparatus as claimed in claim 41, wherein each the main heating coil is divided into first and second portions disposed on the opposite sides of the auxiliary heating coil.

45. The induction heating apparatus as claimed in claim 41, where each the auxiliary heating coil is disposed on the downstream side of the main heating coil.

46. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil has at least one pair of transverse conductors arranged at a pitch.

47. The induction heating apparatus as claimed in claim 46 wherein each the main heating coil includes means for manually adjusting the pitch provided between the adjacent two transverse conductors through which AC current flows in opposite direction.

48. The induction heating apparatus as claimed in claim 47, wherein each the main heating coil is divided into two portions disposed on the opposite sides of the auxiliary heating coil.

49. The induction heating apparatus as claimed in claim 47, wherein each the auxiliary heating coil unit including means for manually adjusting the transverse distance between the first and second longitudinal conductors.

50. The induction heating apparatus as claimed in claim 47, wherein each of the first and second longitudinal conductors is inclined at an angle with respect to the direction of transportation of the workpiece.

51. The induction heating apparatus as claimed in claim 50, wherein each the auxiliary heating coil includes means for manually adjusting the angle of inclination of each of the first and second longitudinal conductors with respect to the direction of transportation of the workpiece.

52. The induction heating apparatus as claimed in claim 26, wherein each the main heating coil is divided into a plurality of portions one of which is disposed on the downstream side of the other main heating coil portions and on the downstream side of the auxiliary heating coil.

53. The induction heating apparatus as claimed in claim 26, which comprises a control unit for adjusting the heating coil units to a predetermined position with respect to the workpiece.

54. The induction heating apparatus as claimed in claim 53, wherein the control unit includes a position sensor for sensing the position of the workpiece to generate a sensor signal indicative of the sensed workpiece position, means for generating a control signal indicative of a target position, means responsive to the sensor and control signals for determining an error between the sensed position and the target position, and means for moving the heating coil units to zero the error.