Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1276244
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
-- 3 --
~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
:
- 4 -
: ~
1276244
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
- 8 -
1276244
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 _
1276244
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
- 10 -
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
-- 11 --
~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
- 12 -
76244
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
- 13 -
127624A
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
- 14 -
~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
- 15 -
~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 -
12762A4
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
- 18 -
~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.
-- 19 --
~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
- 20 -
~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
- 21 -
~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
- 22 -
~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
- 23 -
~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
- 24 -
~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.
