Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 022~463 1998-12-1~
METHOD AND APPARATUS FOR JOINING METAL PIECES
This is a divisional application of Canadian Patent
Application Serial No. 2,156,195 filed on December 15, 1994.
TECHNICAL FIELD
The present invention relates to a metal piece join-
ing method useful for continuous hot rolling, by which a
preceding metal piece and a succeeding metal piece are heated
and joined with each other at their ends to continuously carry
out hot finishing rolling, and also to a joining apparatus
which is directly used for carrying out the method.
The subject matter of this divisional application is
directed to a method and apparatus for joining metal pieces
wherein a plurality of spaced-apart inductors are arranged in
the width direction and a synchronous control of phase is
performed, described more in detail hereinunder. Other
divisional applications have also been filed for further
inventions described herein. The subject matter of the parent
application was restricted to a method and apparatus for join-
ing metal pieces using reverse alternating magnetic fields,
disclosed herein. However, it should be understood that the
expression ~-the invention-- or the like encompasses the subject
matter of both the parent and the divisional applications.
BACKGROUND ART
Conventionally, in a hot rolling line for metal
pieces (for example, steel, aluminum or copper), since the
metal pieces have been extracted one by one from a heating
furnace, there occurred various problems particularly in the
finishing rolling process, as follows.
64881-439F
CA 02255463 1998-12-15
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As means for solvlng the above-mentloned
problems, there has been proposed a so-called endless
rolling ~n whlch metal pieces to be rolled are jolned at
their rear and front ends before the finlshing rolling,
and continuously 8upplied to the fi~ishing roll~ng line
to carry out the hot rolling.
As prior documents ~n thls regard, a number of
propositions can be found, for example, ~n Jàpanese
Patent Laid-open Publication Nos. 60-244401, 61-144203,
62-234679, 4-89109, 4-89115 and 4-89110.
When carrylng out the endless rolllng of metal
pleces, the following process has been generally
performed. That is, firstly, on the entry ~ide of a
roll~ng equipment, a small gap ~g provided between a
precedlng metal piece and a succeedlng metal piece at
the ends thereof and these metal pleces are opposed
substantially in parallel wlth each other. ~urther t a
portlon ~n the viclnlty of the end of each metal piece
18 clamped and supported by clamps, and the end regions
on the opposed faces of the metal pleces, which are
port~ons to be joined, are heated by a heating meang.
The both metal pieces are then pressed against each
other to be ~oined. In the ~oinlng method for metal
pieces using such a process, varlous disadvantages which
will be described below have stlll remained and an
improvement in this regard has been des;red.
64881-439
CA 022~463 1998-12-1~
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1) In the joining form of this type, there is
provided an inductor having a pair of magnetic poles
vertically sandwiching the portions to be joined in the
metal pieces. With the inductor, an alternating
magnetic field running through the metal pieces in the
thickness direction thereof is applied, and a surface
layer at the portions to be joined, or on the opposed
surfaces in particular is intensively heated by the
induced current generated at this time. The induced
current is, however, hard to flow at corners of the
front and rear ends of the metal pieces, and the heating
t~mp~rature at the portions to be joined thus gradually
lowers toward the wide ends. Thus, there is such a
disadvantage that the portions to be joined cannot be
joined over the full width thereof when pressing the
metal pieces against each other.
In this case, the wide ends having a low
temperature function as a resistance when pressing the
metal pieces against each other, if the temperature at
the portions to be joined does not reach a target
heating temperature, so that a pressing apparatus having
a capacity above a necessary level must be installed.
Also, since a sufficient joining strength cannot be
secured, the joined portions are gradually separated as
the rolling proceeds and the metal plate are ruptured so
that a serious accident may occur. In order to solve
CA 022~463 1998-12-1~
such a problem, it is most effective to continue the
heating until the temperature at the corners of the
steel pieces reaches a target value. However, since the
temperature in regions other than the corners (i.e.,
central regions in the plate width direction) reaches a
melting temperature and the metal pieces are melted down
in these regions, excellent joined portions cannot be
obtained. In addition, such a heating may deteriorate
the surface quality of the plate at the portions after
rolling which correspond to the joining portions or
other portions close thereto, and the input electrical
power has to be increased as well.
2) In the induction heating method using the
inductor, since a variation rate of magnetic fluxes (a
variation rate of the number of magnetic fluxes) is
proportional to the current to be induced, the variation
rate becomes large as the number of magnetic fluxes
running through the metal pieces is large at the peak of
the alternating current which flows in a coil of the
inductor, thus increasing the scale of the current.
Further, since a vertical component in the magnetic flux
generated by the inductor for the surface of the
magnetic pieces advantageously contributes to the
generation of the induced current, the induced current
can be increased as the magnetic flux running through
the magnetic pieces becomes vertical.
CA 022~463 1998-12-15
However, in the metal piece heating and joining
to which the induction heating method is applied, if the
positional relationship between the inductor and the
ends of the respective metal pieces (the position of the
inductor in the longitudinal direction of the metal
pieces in particular) is inadequate, the number of
magnetic fluxes running through the metal pieces is
insufficient and the vertical component of the magnetic
flux is also disadvantageously reduced. Further, for
example, in a conventional method disclosed in Japanese
Patent Laid-open Publication No. 62-234679 mentioned
above, this kind of disadvantage is not considered
therein, and the satisfactory heating speed cannot be
obtained depending on the positional relationship
between the inductor and each metal piece, involving a
prolongation of the heating time. Also, since the
preceding metal piece and the succeeding metal piece are
not uniformly and equally heated, an excellent joining
cannot be realized.
3) When heating the metal pieces, if the
preceding metal piece and the succeeding metal piece are
different in the initial temperature or in the plate
thickness, or if the metal pieces having different
melting points are heated, an appropriate heating cannot
be performed in accordance with each metal piece, and a
sufficient strength cannot be given to the joined metal
CA 022~463 1998-12-1~
pieces. In such a case, the plates may be ruptured from
their joined portions during rolling, resulting in a
serious accident.
4) There is proposed a joining method employing
a so-called non-contact heating in which the preceding
and succeeding metal pieces are heated with a space
therebetween and the up-setting is then performed for
joining (Japanese Patent Laid-open Publication No. 60-
244401). According to this method, although the uniform
magnetic flux must be given to the metal pieces over the
full width thereof, the uniform magnetic flux is
restrictedly given to the width of not more than 1000 mm
mainly from a viewpoint of design in the power supply of
the inductor. In the case of a larger width, for
example, a width of 1900 mm, a pair of inductors are
required (the limit in the capacity of one inductor is
2000 through 3000 kW, and practical use of an inductor
which has a capacity of not less than 4000 kW and can
deal with the width of 1900 mm is difficult). It is
therefore difficult to give a uniform magnetic flux
running through the metal piece over the full width
thereof.
5) For heating the preceding and succeeding
metal pieces in a relatively short time for joining,
there is an induction heating rolling method, as a
heating means, in which air-core type coil is used to
CA 022~463 1998-12-1~
induction-heat the rear end of the preceding metal piece
and the front end of the succeeding metal piece and the
both ends of these metal pieces are then pressed against
each other for joining (Japanese Patent Laid-open
Publication No. 60-244401). In this method, however,
since the metal pieces to be joined are inserted into
the coil and heated, this method cannot be applied to a
metal piece whose dimension is larger than the inner
dimension of the coil. On the other hand, in the case
where both metal pieces have a small width, such a
problem does not occur though a part of the magnetic
fluxes does not contribute to heat the metal pieces,
thereby deteriorating the heating efficiency for the
input power. Further, in connection with the above item
4), in the case where the metal pieces are heated using
a plurality of inductors, since the magnetic flux is not
generated from a portion corresponding to a part between
inductors adjacent to each other, the magnetic flux
running through the metal piece is locally decreased and
the temperature rise at this portion is insufficient.
It is therefore important to make a space between the
adjacent inductors as small as possible, but the space
between the adjacent inductors cannot be reduced at a
stage of securing facilities. Thus, the temperature
distribution of the metal pieces in the width direction
thereof inevitably becomes uneven.
CA 022~463 1998-12-1~
...
6) Although a preferred temperature at the
opposed faces (the end faces) of the metal pieces can be
usually within a range of approximately 1350 to 1400~C,
in the case where the metal pieces joined at such a
temperature are rolled by a finishing rolling mill
composed of a plurality of stands which functions after
joining with a draft percentage increased by 10 times or
more, all kinds of steel cannot be rolled without
causing rupture at the joining portions until the
completion of rolling.
In the endless rolling of the metal pieces,
since the timing of the processing for joining the metal
pieces must match with that of the rolling process, it
is general to provide a movable joining apparatus placed
on the entry side of a group of finishing rolling mills
so that it can follow the movement of the steel pieces,
or to provide an apparatus such as a looper having a
timing buffer function between the joining apparatus and
the rolling facilities. This involves an extension of
the line or provision of new apparatuses, thereby
disadvantageously increasing the facility cost.
However, in regard of this problem, a proposition
disclosed, e.g., in Japanese Patent Laid-open
Publication No. 4-89120 has been given and the problem
has been already improved.
The present invention intends to achieve the
CA 022~463 1998-12-1
following objects.
1) On the entry side of the hot finishing
rolling facilities, the preceding metal piece and the
succeeding metal piece are uniformly heated over the
full width thereof and, when pressing the metal pieces
against each other, the joining is carried out until a
sufficient strength can be obtained (until such a
strength that the plates are not ruptured during rolling
can be secured), thereby performing a stable rolling
operation.
2) The both metal pieces are heated in an
appropriate range of temperature and joined with a
sufficient strength being given thereto irrespective of
temperature or thickness of the metal pieces to be
joined or kinds of the plates.
3) Even if a plurality of inductors for
generating magnetic fluxes are used, a stable heating
and joining are realized by making uniform phases of
currents to be supplied to the respective inductors.
4) The metal pieces are heated and joined with
a good efficiency in a short time irrespective of
difference in sizes of the metal pieces and widths of
the same in particular.
5) Irrespective of the kinds of the metal
pieces to be joined, an excellent joining is realized by
giving such an advantageous heating condition that
CA 022~463 1998-12-1
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problems such as rupture of the plates do not occur in
the succeeding finishing rolling process.
DISCLOSURE OF THE INVENTION
The above-mentioned objects which are tasks to
be solved by the invention can be attained by adopting
the following measures.
1) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated at end regions of the opposed faces
of the respective metal pieces to perform heating; and
another alternating magnetic field reverse with respect
to the former alternating magnetic field is partially
generated in the end regions of the opposed faces of the
metal pieces and in either a region where the metal
pieces exist or a region outside width ends of the metal
pieces (the outside of the width ends of the metal
pieces), thereby adjusting a temperature distribution in
the end regions of the opposed faces of the metal pieces
in the width direction thereof.
CA 022~463 1998-12-1
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2) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated at end regions of the opposed faces
of the respective metal pieces to perform heating,
wherein another alternating magnetic field reverse with
respect to the former alternating magnetic field is
partially generated in either a region where the metal
pieces exist or a region outside width ends of the metal
pieces, by arranging reverse magnetic field generation
portions of a plurality of reverse magnetic field
generation circuits each having the reverse magnetic
field generating portion and a switch connected to the
reverse magnetic field generating portion in the end
regions of the opposed faces of the metal pieces in the
width direction thereof and controlling so as to open
and/or close the switch of each reverse magnetic field
generation portion, thereby adjusting a temperature
distribution in the end regions of the opposed faces of
the metal pieces in the width direction thereof.
CA 022~463 1998-12-1
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3) The region for generating the reverse
alternating magnetic field preferably comprises at least
one of a region in which a temperature rapidly reaches a
target heating temperature in the width direction of the
metal pieces as compared with other regions, and a
region outside a central region of the metal piece in
the width direction thereof or the width ends of the
metal piece.
4) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with an interval of
space therebetween, and an alternating magnetic field
running through the metal pieces in the thickness
direction thereof is generated at end regions of the
opposed faces of the respective metal pieces to perform
heating, wherein conductive members are provided to the
both width ends of at least one of the rear end of the
preceding metal piece and the front end of the
succeeding metal piece with a space between the
conductive member and the metal piece, thereby improving
the heating efficiency in the width ends of the metal
piece by this member.
CA 022~463 1998-12-1
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S) The members set forth in 4) are preferably
arranged over both the preceding metal piece and the
succeeding metal piece.
6) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated at end regions of the opposed faces
of the respective metal pieces to perform heating,
wherein the both width ends of at least one of the rear
end of the preceding metal piece and the front end of
the succeeding metal piece are brought into contact with
conductive members, thereby improving the heating
efficiency in the width ends of the metal piece by these
members.
7) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
CA 022~463 1998-12-1
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succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated in an end region on the opposed
faces of the respective metal pieces by an inductor to
perform heating, wherein members consisting of magnetic
substance whose depth is two to lO times as large as an
osmotic depth do of induced current which can be
expressed by the following equation are provided in a
gap between each of the metal piece and the inductor and
in a region which is not more than lO times as large as
the osmotic depth do and inside the width end of the
metal piece, thereby enhancing the density of the
magnetic flux of the alternating magnetic field to
improve the heating efficiency in the width ends of the
metal piece by these members.
do = {p x 107/(~ x f)}l/2/2~, where
do: osmotic depth of the induced current (m)
f : frequency of the alternating magnetic field (Hz)
p : electric resistivity (Q * m)
: relative magnetic permeability
8) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
CA 022~463 1998-12-1~
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the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated in an end region on the opposed
faces of the respective metal pieces by an inductor to
perform heating, wherein an overlap width L (m) of each
metal piece and a magnetic pole of the inductor in the
longitudinal direction of each metal piece is so
adjusted as to satisfy the following expression.
L ~ 2 * do, where
do: osmotic depth of the induced current (m)
(do = {p x 107/(~ x f)}l/2/2~) where
f : frequency of the alternating magnetic field (Hz)
p : electric resistivity (Q * m)
: relative magnetic permeability
9) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated in an end region on the opposed
CA 022~463 1998-12-1
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faces of the respective metal pieces by an inductor to
perform heating, wherein a relative position of a
magnetic pole of the inductor and each metal piece in
the longitudinal direction is changed to adjust a
penetration quantity of the magnetic fluxes of the
alternating magnetic field for each magnetic piece.
lO) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated in an end region on the opposed
faces of the respective metal pieces by a plurality of
inductors arranged in the width direction of the metal
pieces to heat the respective metal pieces, wherein a
synchronous control of the phase is performed in such a
manner that the current having the same phase flows in a
coil of each inductor.
ll) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
CA 022~463 1998-12-1~
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finishing rolling, characterized in that the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposed with a space
therebetween, and an alternating magnetic field running
through the metal pieces in the thickness direction
thereof is generated in an end region on the opposed
faces of the respective metal pieces by a plurality of
inductors arranged in the width direction of the metal
pieces to heat the respective metal pieces, wherein the
space between magnetic poles of the inductors adjacent
to each other is set to not more than five times as
large as an osmotic depth do of the induced current
represented by the following expression.
do = {p x 107/(~ x f)}l/2/2~, where
do: osmotic depth of the induced current (m)
f : frequency of the alternating magnetic field (Hz)
p : electric resistivity (Q * m)
: relative magnetic permeability
12) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that a temperature T
(~C) in a heating region of the preceding metal piece
and the succeeding metal piece is adjusted to be within
a range of the following expression.
CA 022~463 1998-12-1
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TS ~ T ~ (TS + TL) /2, where
Ts: solidus line temperature of the metal piece (~C)
TL: liquidus line temperature of the metal piece (~C)
13) A method for joining metal pieces wherein a
rear end of a preceding metal piece and a front end of a
succeeding metal piece are heated and the metal pieces
are pressed against each other for joining before hot
finishing rolling, characterized in that a temperature
T (~C) in a heating region of the preceding metal piece
and the succeeding metal piece is adjusted to be within
a range of the following expression.
if Tc ~ Ts~
( TC + TS ) /2 ~ T ~ ( TS + TL ) /2, and
if Tc > Ts
TS ~ T ~ (TS + TL) /2
where Ts : solidus line temperature of the metal piece
( o C )
TL: liquidus line temperature of the metal piece (~C)
Tc: melt temperature of an iron oxide scale (~C)
14) An apparatus for joining metal pieces
comprising an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction thereof with a gap therebetween,
characterized in that a reverse magnetic field
generation portion of a circuit for generating an
alternating magnetic field whose direction is reversed
CA 022~463 1998-12-1
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from that of an alternating magnetic field generated by
the inductor is provided between the magnetic poles of
the inductor.
15) An apparatus for joining metal pieces
comprising: an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction with a gap therebetween; and a clamp
for vertically clamping a preceding metal piece and a
succeeding metal piece between the magnetic poles of the
inductor for fixing and holding the metal pieces,
characterized in that the clamp protrudes from a region
where the metal pieces are fixed and held toward the
ends of the metal pieces and has a plurality of notch
portions made by notching the clamp in the comb-like
form at an interval of space in the width direction of
the metal pieces, and a reverse magnetic field
generation portion of a reverse magnetic field
generation circuit for generating an alternating
magnetic field whose direction is reversed from that of
an alternating magnetic field generated by the inductor
is provided to each of the notch portions.
16) A plurality of reverse magnetic generation
portions are preferably provided along the width
direction of the inductor. Further, each of the reverse
magnetic generation portions is preferably composed of a
coil of one wind or of a plurality of winds or a
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20-
U-shaped conductive member and further has a member
consisting of magnetic substance.
17) The reverse magnetic filed generation
circuit has a switch for opening/closing the circuit and
preferably has a variable resistor.
18) An apparatus for joining metal pieces
comprising an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction thereof with a gap therebetween,
characterized by comprising a reverse magnetic field
generation circuit having: a reverse magnetic field
generation portion for generating an alternating
magnetic field whose direction is reversed from that of
an alternating magnetic field generated by the inductor;
a switch; a lead wire for connecting the switch and the
reverse magnetic field generation portion to each other;
and an open/close controller for opening and/or closing
the switch.
19) An apparatus for joining metal pieces
comprising an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction thereof with a gap therebetween,
characterized by comprising a member consisting of
magnetic substance which is provided between the
magnetic poles and increases a density of magnetic flux
of an alternating magnetic field generated by the
CA 022~463 1998-12-1~
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inductor at width ends of the metal pieces.
20) An apparatus for joining metal pieces
comprising an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction thereof with a gap therebetween,
characterized by comprising a conductive member which is
provided between the magnetic poles and outside width
ends of the metal pieces in the width direction with a
gap or provided contacting with the width ends.
21) An apparatus for joining metal pieces
comprising an inductor having at least a pair of
magnetic poles sandwiching the metal pieces in the
thickness direction thereof with a gap therebetween,
characterized by comprising a moving mechanism being
capable of moving the inductor in the longitudinal
direction of the metal pieces.
22) An apparatus for joining metal pieces
comprising at least two sets of inductors each having a
pair of magnetic poles sandwiching the metal pieces in
the thickness direction thereof, characterized in that a
power supply inverter is provided to each of the
inductors and each power supply inverter is connected to
a phase control circuit.
23) An apparatus for joining metal pieces
comprising at least two sets of inductors each having a
pair of magnetic poles sandwiching the metal pieces in
CA 022~463 1998-12-1
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the thickness direction thereof, characterized by
comprising projections provided on adjacent surfaces of
the magnetic poles of the inductors in such a manner
that the projections are brought into contact with each
other or decrease an interval of space therebetween.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an explanatory view showing the point
of heating according to the present invention;
Fig. 2 is an explanatory view showing the point
of heating according to a prior art;
Fig. 3 is an explanatory view showing the state
of heating metal pieces;
Fig. 4 is an explanatory view showing the state
where cracks are generated in a joined portion of metal
pieces;
Fig. 5 is a view typically showing a structure
of a circuit;
Fig. 6 is a view showing a structure of an
apparatus preferable for carrying out the present
invention;
Fig. 7 is a view showing the state of joining
metal pieces;
Fig. 8 is an explanatory view showing the state
where joined metal pieces are ruptured;
Fig. 9 is a view showing a structure of an
apparatus according to the present invention;
CA 022~463 1998-12-1
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Fig. 10 is a view showing a primary part of the
apparatus according to the present invention;
Fig. 11 is an explanatory view showing the point
of joining metal pieces according to the present
invention;
Fig. 12 is an explanatory view showing the point
of joining metal pieces according to the present
invention;
Fig. 13 is a view showing an example of a
conductive members;
Fig. 14 is a view showing an example of a member
consisting of magnetic substance:
Fig. 15 is a view showing an example of a member
consisting of magnetic substance;
Fig. 16 is a view showing an example of a member
consisting of magnetic substance;
Fig. 17 is a view showing an example of a member
consisting of magnetic substance;
Fig. 18 is a view showing a reverse magnetic
field generation portion of a circuit;
Fig. 19 is a view showing a reverse magnetic
field generation portion of a circuit;
Fig. 20 is a view showing a structure of an
equipment for performing continuous hot rolling to metal
pieces;
Fig. 21 is a view showing a structure of a
CA 022~463 1998-12-1
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primary part of a joining apparatus according to the
present invention;
Fig. 22 is an explanatory view showing the state
where metal pieces are heated;
Fig. 23 is a view showing a structure of a
primary part of a joining apparatus according to the
present invention;
Fig. 24 is an explanatory view showing a case
where metal pieces having different widths are joined;
Figs. 25(a), (b) and (c) are explanatory views
showing cases where metal pieces are heated and joined
in accordance with the present invention;
Figs. 26(a), (b) and (c) are explanatory views
showing cases where metal pieces are heated and joined
in accordance with the present invention;
Fig. 27 is an explanatory view showing the point
of joining metal pieces in accordance with the present
invention;
Fig. 28 is a view showing an example in which
metal pieces are heated using a single inductor;
Fig. 29 is a view showing an example in which
metal pieces are heated using a single inductor;
Fig. 30 is a view showing a distribution of a
temperature rising speed in end portion of a metal piece
in the width direction thereof;
Figs. 31(a) and (b) are views showing an example
CA 022~463 1998-12-1
25-
in which metal pieces are heated and joined by arranging
members consisting of magnetic substance;
Fig. 32 is a view showing an example in which
metal pieces are heated and joined by arranging members
consisting of magnetic substance;
Fig. 33 is a view showing the relationship
between the width dimension of a member consisting of
magnetic substance/osmotic depth of an induced current,
and the length of joining failure;
Fig. 34 is a view showing a structure of a
primary part of a joining apparatus to which members
consisting of magnetic substance are arranged;
Fig. 35 is an explanatory view showing the point
of movement of members consisting of magnetic substance;
Figs. 36(a), (b) and (c) are views showing a
structural example of an inductor;
Figs. 37(a), (b) and (c) are views showing a
structural example of an inductor;
Figs. 38(a) and (b) are views showing a
structural example of an inductor;
Fig. 39 is a view showing the state of
distribution of magnetic fluxes;
Fig. 40 is a view showing the state of
distribution of magnetic fluxes;
Fig. 41 is a graph showing the relationship
between L/do and the temperature rising speed;
CA 022~463 1998-12-1
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Fig. 42 is an explanatory view showing the state
in which metal pieces are heated;
Fig. 43 is an explanatory view showing a case
where a penetration quantity of magnetic fluxes is
adjusted;
Fig. 44 is an explanatory view showing a case
where a penetration quantity of magnetic fluxes is
adjusted;
Fig. 45 is view showing the relationship between
the temperature rising speed ratio and L/do (space g);
Fig. 46 is a view showing a structure of a
moving mechanism of an inductor;
Fig. 47 is a view showing a structure of a
moving mechanism of an inductor;
Fig. 48 is a view showing a structure of a
moving mechanism of an inductor;
Figs. 49(a) and (b) are explanatory views
showing the points of heating and joining metal pieces;
Fig. 50 is a view showing the state in which an
inductor is arranged;
Figs. 51(a) and (b) are views showing structures
in a case where a plurality of inductors are used;
Fig. 52 is a block diagram showing a control
system of inductors according to the present invention;
Fig. 53 is a view showing a structure in a case
where a plurality of inductors are used;
CA 022~463 1998-12-1
-27-
Fig. 54 is a view showing a structure of a
joining apparatus for metal pieces;
Fig. 55 is a view showing the state in which
metal pieces are heated;
Fig. 56 is view showing the state in which
inductors are arranged;
Fig. 57 is a graph showing the relationships
between Wl/do and such a length that a temperature
rising speed is not more than 9o%~ and between Wl/do and
a temperature rising speed ratio;
Fig. 58 is a view showing, especially, inductors
of an apparatus according to the present invention;
Fig. 59 is a graph showing the relationship
between the C content and the heating temperature;
Fig. 60 is a graph showing the relationship
between the C content and the heating temperature;
Fig. 61 is a view showing sections of ends of
metal pieces cut by a crop shear;
Fig. 62 is a view showing a structure of an
electric circuit;
Fig. 63 is a graph showing the relationship
between the plate width and the temperature at a joining
face;
Fig. 64 is a graph showing the relationship
between the plate width and the temperature rising speed
ratio;
CA 022~463 1998-12-1
-28-
Fig. 65 is a graph showing the relationship
between the distance from an end of a plate and the
temperature rising speed ratio;
Fig. 66 is a graph showing the relationship
between the distance in a width direction of a metal
piece and the temperature at a joining face;
Fig. 67 is a graph showing the relationship
between the distance in a direction of a metal piece
width and the temperature of a joining face;
Fig. 68 is graph showing the relationship
between the distance in a direction of a metal piece
width and the calorific power ratio at a joining face;
Fig. 69 is a view showing a state in which an
inductor is arranged;
Fig. 70 is a view typically showing inductors;
Fig. 71 is a graph showing the relationship
between the width dimension of a metal piece and the
rate of heating quantity;
Fig. 72 is a graph showing the relationship
between the length in a width direction of a metal piece
and the rate of heating quantity; and
Fig. 73 is a view showing an example o~ an
inductor which is preferable for embodying the present
invention.
CA 022~5463 1998-12-1
-29-
BEST MODE FOR CARRYING OUT THE INVENTION
In case of heating metal pieces to be joined by
generating an alternating magnetic field running through
the metal pieces in a thickness direction thereof, the
present invention partially generates another
alternating magnetic field reversed from the above
alternating magnetic field in either of a region where
the metal pieces exist or another region outside the
width ends of the metal pieces to adjust the temperature
distribution in the plate width direction. The present
invention will now be described in detail hereinafter
with reference to the drawings.
Fig. 1 shows a structure of a joining apparatus
preferable for adjusting the temperature distribution at
ends of metal pieces in the width direction thereof in
case of heating and joining the metal pieces. In the
drawing, reference numeral 1 denotes a metal piece
(referred to as a preceding metal piece hereinbelow)
precedently carried; 2, a metal piece (referred to as a
succeeding metal piece hereinbelow) carried after the
preceding metal piece l; 3, at least a pair of inductors
for heating composed of a coil c and a core t and
sandwiching the preceding metal piece 1 and the
succeeding metal piece 2 in the thickness direction
thereof with a gap D (although the gap D is a space, any
electrical insulator may be provided thereto)
t CA 022~463 1998-12-1
-30-
therebetween. An alternating magnetic field running
through the metal- pieces in the thickness direction
thereof is generated by the inductors 3 to heat the end
region of the opposed faces until the temperature in
this region reaches a predetermined value.
Further, reference numeral 4 designates a power
supply of the inductors 3; and 5, a reverse magnetic
field generation portion of a reverse magnetic field
generation circuit (an electric circuit). A lead wire
5a is connected to the both ends of the loop type
reverse magnetic field generation portion 5 to form a
closed circuit including these ends, and an alternating
magnetic field reversed from the alternating magnetic
field produced by the inductors 3 is generated by
flowing an induced current when heating by the inductors
3 or by positively flowing a current (from any other
power supply, for example). In addition, reference
numeral 6 represents a switch having an open/close
controller r; and 7, a variable resistor.
As shown in Fig. 2, the preceding metal piece 1
and the succeeding metal piece 2 are opposedly provided
with a gap g therebetween, which is a gap of
approximately a few to tens mm and may be an interval of
space, or any other electrical insulator may be provided
to this gap. When the alternating magnetic field
running in the plate thickness direction is generated by
CA 022~463 1998-12-1~
.
-31-
the inductors 3, a current e as shown in Fig. 3 is
induced by the alternating magnetic field in the end
region of the opposed faces of the metal pieces which
will be joined to each otherl and this portion is heated
in a extremely short time by the heat produced at this
time.
Since the current e is difficult to flow at
corners f of the metal pieces 1 and 2, the degree of
temperature rise is small at the corners f. If the
heating and temperature rise are tried until the
temperature at which the joining is possible, the
central region in the plate width direction is likely to
be melted down. On the other hand, even if the joining
of the metal pieces only in the central region thereof
is tried, cracks such as shown in Fig. 4 may be
developed during rolling because of insufficiency of the
joining strength in the width end region, and there is
such a disadvantage that the rolling cannot be continued.
In the present invention, since portions to be
joined are heated by the inductors 3 and the alternating
magnetic field reversed from the alternating magnetic
field d produced by the inductors 3 is generated by such
a reverse magnetic field generation circuit as shown in
Fig. 5 (by flowing the induced current in the circuit by
main magnetic fluxes of the inductors 3 or positively
flowing such a current that the reverse magnetic field
CA 022~463 1998-12-1
-32-
is generated) in a region where the temperature largely
varies (a region which is located in the width direction
of the metal pieces and where the temperature reaches a
target heating temperature faster than in any other
regions) and in a central region in the plate width
direction where the temperature greatly raises in
particular to weaken the strength of the magnetic field
in the portions to be joined, an excessive heating in
these portions can be suppressed.
Although the heating time is prolonged to some
extent because the heating is carried out with such a
reverse magnetic field being generated, the corners of
the metal pieces at which the temperature rise is
difficult can be heated until the temperature reaches a
predetermined range without a fear of melt down in the
central region in the plate width direction. As a
result, the temperature distribution in the width
direction becomes substantially uniform, thereby
ensuring the satisfactory joining strength.
In a concrete structure of an apparatus for
adjusting the temperature, as shown in Fig. 6, a
plurality of reverse magnetic field generation portions
S are previously arranged in parallel with the plate
width direction of the metal pieces 1 and 2, and
switches 6 to be connected to the reverse magnetic field
generation portions 5 which are located in a region
CA 022~463 1998-12-1
-33-
where suppression of the temperature rise is desired
when heating are closed to generate a reverse magnetic
field.
Further, if the quantity of current flowing in
the reverse magnetic field generation circuit is varied
by adjusting a variable resistor 7 as shown in Fig. 1,
for example, the scale of the reverse magnetic field is
adjusted, thereby further accurately adjusting the
temperature. In the case where a plurality of reverse
magnetic field generation circuits are provided, it is
effective to provide a variable resistor 7 for each
circuit for adjusting an impedance of each circuit. It
is also possible to additionally provide a coil, a
capacitor or others, and at least one of these members
may be used to adjust the impedance of each reverse
magnetic field generation circuit. If a desired
impedance is given to each reverse magnetic field
generation circuit by a variable resistor 7, for
example, a desired strength of the reverse magnetic
field can be obtained. Also, phases of the respective
circuits are unified, thereby relatively freely
adjusting the temperature of the metal pieces in the
width direction thereof.
In the state of arrangement as shown in Fig. 6,
in the case where the reverse magnetic field generation
portions 5 are arranged outside the plate width ends of
CA 022~463 1998-12-1
-34-
the metal pieces and the reverse magnetic generation
circuits are closed to flow the induced current
therethrough, magnetic fluxes outside the width ends of
the magnetic pieces can be converged at the corners f of
the magnetic pieces, and it is hence extremely
advantageous to enhance the heating efficiency at the
corners f.
When heating the metal pieces, the metal pieces
may be pressed against each other tthe pressing may be
carried out while heating or after heating). In such a
case, the preceding metal piece 1 and the succeeding
metal piece may be joined being shifted from each other
(this state is referred to as dislocation). When the
dislocated portion is caught in a roller, an end of one
metal piece is bent toward an end of the other metal
piece. The dislocated portion deeply encroaches upon a
sound portion which will be a product as the number of
rolling passes increases as shown in Fig. 8, whereby a
thin portion is locally formed. On the other hand, the
plate is ruptured due to a variation in a tensile force
between stands during rolling, and the rolling may not
be continued.
In the present invention, therefore, a
dislocation preventing plate 8 having notches u whose
tips are opened along the width direction of the metal
pieces 1 and 2 is provided as shown in Fig. 9 to join
CA 022~463 1998-12-1
-35-
the metal pieces 1 and 2.
In Fig. 9, by connecting the dislocation
preventing plate 8 to each clamp 9 having a positioning
function for the metal pieces 1 and 2, vertical
dislocation of the metal pieces 1 and 2 which can be
caused during pressing can be suppressed, so as to
minimize the dislocation.
The dislocation preventing plate 8 can avoid the
temperature rise of itself during heating the metal
pieces 1 and 2 and has the notches u for securing the
strength as a pressure plate. When the reverse magnetic
field generation portion 5 is engaged with each notch u
and the reverse magnetic field is appropriately
generated by each reverse magnetic field generation
circuit including the reverse magnetic field generation
portion, the entire area of the portions of the metal
pieces which will be joined can be substantially
uniformly heated.
Fig. 10 shows a primary part in a state where
the reverse magnetic field generation portions 5 are
provided on the dislocation preventing plate 8. As
shown in Fig. 10, when loops are formed by closing the
switches 6 provided at positions where the suppression
of heating is desired, a current e' flows in each
reverse magnetic field generation portion 5 and each
lead wire 5a in such a direction that the magnetic flux
CA 022~463 1998-12-1
-36-
(reverse magnetic flux) which is directed to cancel out
the main magnetic flux is generated by the action of
electromagnetic induction. In this case, the main
magnetic flux is weakened by the reverse magnetic flux
to suppress the temperature rise of the metal pieces at
portions where the switches 6 are closed.
Fig. 11 shows a structural example of such an
apparatus that the degree of temperature rise in the
central region of the metal pieces 1 and 2 in the width
direction thereof is decreased and the magnetic flux
outside the width ends of the metal pieces is converged
at the corners f. Further, Fig. 12 shows a structural
example of an apparatus which can decrease the degree of
temperature rise only in the central region of the metal
pieces 1 and 2 in the width direction thereof.
As the dislocation preventing plate, SUS304 and
others can be adopted, though any other material having
a strength at a high temperature such as titanium,
tungsten and others may be used.
In this invention, although the U-shaped
conductive member (such as Cu) is exemplified as the
reverse magnetic field generation portion 5 of the
reverse magnetic field generation circuit, a coil type
member such as that shown in Fig. 13 can be adopted. In
this case, the effect is enhanced as the number of winds
increases, though the winds are not restricted to any
CA 022~463 1998-12-1~
-37-
particular number.
In order to increase a value of the current
flowing in each reverse magnetic field generation
circuit without additionally providing unnecessary
units, in this invention, as shown in Fig. 14 or 15, a
member M consisting of magnetic substance (a silicon
steel plate or others) may be provided within each
reverse magnetic field generation portion 5.
Further, in order to prevent the member M from
being heated, it is preferable to obtain a structure in
which a plurality of members M are superimposed one
above the other through insulating films as shown in
Figs. 16 and 17.
Note that such a plate type superimposed body
(magnetic substance) as shown in Fig. 16 may be provided
in each reverse magnetic field generation circuit having
a coil type reverse magnetic field generation portion 5
shown in Fig. 17, instead of a cylindrical superimposed
body (magnetic substance).
Figs. 18 and 19 show examples in which the
members M consisting of magnetic substance are assembled
in the reverse magnetic field generation portions 5 of
the reverse magnetic field generation circuits.
Fig. 20 shows an equipment for performing
continuous hot rolling to the metal pieces, and a
joining apparatus A preferable for embodying this
CA 022~463 1998-12-1
-38-
invention is provided, for example, between pinch rolls
11 and 12 on the delivery side of a cutting apparatus (a
shear or others) 10.
In Fig. 20, referénce numeral 13 denotes a
rewinder for rewinding a metal piece wound in a coil
form; 14, a pinch roll; 15, a leveler; 16, a scale
breaker; and 17, a group of finishing rolling mills. If
the joining apparatus A is of a fixed type in this
equipment, a looper is provided on the entry side of the
scale breaker 16.
Each reverse magnetic field generation circuit
constituted by the reverse magnetic field generation
portion 5 may be maintained closed (the switch 6 is
closed) by the open/close controller r from an initial
stage when heating the metal pieces, or may be closed
during heating. The usage of the circuit is not
restricted to a specific procedure.
Although the above has been described in
connection with the case where the degree of temperature
rise is suppressed especially in the region where the
temperature is locally increased when heating the metal
pieces, the temperature in this region can be
precedently increased by generating in the circuit the
alternating magnetic field whose direction is same with
that of the alternating magnetic field produced by the
inductors 3 (in this case, the current is positively
CA 022~463 1998-12-1~
-39-
supplied to the circuit).
The description will now be given as to a case
where an apparatus having such a structure as shown in
Fig. 21 is used to improve the heating efficiency at the
width ends of the metal pieces.
In Fig. 21, reference numeral 18 designates a
conductive member which has been described as an example
of the plate, and each member 18 is provided between
magnetic poles of the inductor 3 and provided outside
the ends of the metal pieces 1 and 2 in the width
direction thereof with a gap tl between the members 18
and the metal pieces 1 and 2. In this case, the gap t
between may be an interval of space, or any electrical
insulator may be provided herein.
The preceding metal piece 1 and the succeeding
metal piece 2 are clamped by clamps 19 and 20 with a
space g, namely, a small gap being provided between the
ends of the opposed faces of the metal pieces 1 and 2,
and are heated by generating the alternating magnetic
field running through the metal pieces 1 and 2 the
thickness direction thereof by the inductor 3 having a
pair of magnetic poles vertically sandwiching the metal
pieces 1 and 2. At this time, the induced current
caused due to the alternating magnetic field also flows
in each conductive member 18, and the temperature is
increased at the same speed with that in the central
CA 022~463 1998-12-1
-40-
region of the pieces 1 and 2 at the corners of the metal
pieces where the temperature is not likely to be
increased.
By providing each conductive member 18 in close
proximity to one side of the metal pieces, the entire
end region of the opposed faces to be joined can be
heated at the same speed (a uniform heating over the
full width). The reason thereof is as follows.
In the first place, in the conventional heating
and joining method in which the conductive members 18
are not provided, the quantity of magnetic fluxes is
small at ends of the metal pieces, which will be joined,
in the width direction thereof, so that the induced
current e flows in the circular ~orm as shown in
Fig. 22. Even if the skin effect of the induced current
flowing in each end of the metal pieces 1 and 2 can be
expected, the induced current is difficult to flow
through the end of each metal piece in the width
direction thereof, whereby the temperature rise is
insufficient. As a result, even though the rear end of
the preceding metal piece and the front end of the
succeeding metal piece are opposedly joined to each
other, the joining strength is low at the ends of the
joined portions in the width direction of the steel
pieces. In the rolling operation to be subsequently
performed, cracks produced at the ends propagate to the
- CA 022~463 l998- l2- l~
- 41 -
central portion in the width direction, resulting in the
rupture.
In the case where the conductive members 18 are
provided with a space tl between the both width ends of
at least one of the preceding metal piece 1 and the
succeeding metal piece 2 and the conductive members 18
in accordance with the invention as shown in Fig. 21,
however, the alternating magnetic field produced between
the magnetic poles of the inductor 3 also runs through
the conductive members 18, thereby generating the
induced current e in each member 18. Since this induced
current and the induced current generated in the metal
pieces 1 and 2 flow in opposed directions in the region
where these currents are in close proximity to each
other, they are attracted to each other. The induced
current produced in the metal pieces consequently flows
to be closer to the ends of the metal pieces in the
width direction thereof. The temperature rising speed
at the ends of the metal pieces in the width direction
thereof becomes closer to the temperature rising speed
in the central region of the same in the width direction
thereof, and hence the temperature can be substantially
uniformly increased to a value in the entire region of
the portions to be joined in the width direction.
Further, by securing the sufficient pressing force when
pressing the metal pieces against each other, the
CA 022~463 1998-12-1~
-42-
complete joining can be carried out over the full width
of the metal pieces including the ends of the metal
pieces in the width direction thereof.
As for the conductive member suitable for the
invention, the desired object can be attained only if
any member can generate the induced current having a
predetermined scale, the member is not thus restricted
to a specific type.
However, a copper plate produces less heat due
to the induced current and is inexpensive, and hence it
is preferable. Further, since a material having a high
melting point such as a tungsten plate or a graphite
plate has a durability against heat, such a material can
also be used. Furthermore, a steel plate or an Al plate
can be used for a long time if a cooling means is
additionally provided.
Although Fig. 21 shows an example in which each
conductive member 18 is provided over the preceding
metal piece 1 and the succeedin~ metal piece 2, the
invention is not restricted to the example in this
figure. The same effect can be obtained when separate
conductive members 18a and 18b are provided to the rear
end of the preceding metal piece and the front end of
the succeeding metal piece, respectively. In this case,
it is particularly advantageous when the metal pieces
having different widths are joined.
CA 022~463 1998-12-1
- 43 -
In regard of the width dimension of the
conductive member, when the dimension is too small,
generation of the induced current is difficult even
though the magnetic flux runs through the member from
the inductor, thereby requiring such a width that the
induced current can be produced. The width of the
conductive member can be appropriately changed only if
this condition is satisfied. The member is not
restricted to have specific thickness and length.
The space tl between each conductive member and
the metal piece must be provided so that the induced
current produced in the metal piece and the induced
current generated in the conductive member are attracted
to each other and the conductive member and the metal
piece are in close proximity to each other.
Specifically, the space tl may be over 10 mm, though it
may preferably be set to 3 through 5 mm.
Fig. 24 illustrates an example in which the
metal pieces having different width dimensions are
joined with the centers of the metal pieces in the width
directions thereof being matched. When the alternating
magnetic field generated by the inductor 3 runs through
each conductive member 18, the induced current is
produced in the member 18. The induced currents
produced in the metal pieces 1 and 2, therefore, flow in
the vicinity of the ends of the metal pieces in the
CA 022~463 1998-12-1~
-44-
width direction thereof by the interaction of the
induced current in the member 18 and the induced
currents generated in the metal pieces, enabling a
uniform heating over the entire area in the plate width
direction.
Although the desired object can be attained by
providing the conductive members 18 only at the both
width ends in the end portion of the narrow metal pieces
as shown in Fig. 24, the effect can be further enhanced
by additionally providing the conductive members at the
both width ends of the wide metal piece as indicated by
a two-dotted line in Fig. 24.
As apparent from the above-mentioned action and
effect of the conductive member 18, in the invention,
the magnetic field generated by the inductor having at
least a pair of magnetic poles must run through the
conductive member 18. That is, the conductive member 18
must be provided in such a region that the magnetic flux
produced between the magnetic poles of the inductor 3
runs therethrough.
As viewed from the relationship between the
width of each metal piece and the width of the inductor,
in this invention, it is preferable to provide the
inductor in such a manner that the inductor overlaps on
the metal pieces and the magnetic flux generated by the
inductor runs through the metal piece and at least a
CA 022~463 1998-12-1
-45-
part of the conductive member. Specifically, it is
preferable that the inductor (core) having a width
dimension larger than that of the metal pieces to be
joined is used so as to protrude from the metal pieces
at the width ends thereof, and the opposed magnetic
poles of the inductor face to the metal pieces and the
conductive members provided to the width ends of the
metal pieces. This means that the metal pieces are
provided inside the ends in the width direction at which
the quantity of magnetic fluxes is apt to be decreased,
and this arrangement is extremely effective for
uniformly heating the metal pieces in the width
direction thereof.
In the case where the width direction of the
metal pieces used for joining is larger than that of the
inductor, a plurality of inductors are preferably
aligned in the width direction of the metal pieces so as
to protrude from the metal pieces at their width ends.
Figs. 25(a), (b) and (c) show an example in
which a current whose phase is substantially same with
that of the induced current generated in the metal
pieces positively flows in the conductive members from
outside.
Fig. 25(a) is a top plan view showing a region
in which the rear end of the preceding metal piece and
the front end of the succeeding metal piece are opposed
CA 022~463 1998-12-1
-46-
to each other; Fig. 25(b), a sectional view taken along
the A-A line in Fig. 25(a); and Fig. 25(c), a sectional
view taken along the B-B line in Fig. 25(a).
The inductor 3 shown in Fig. 25 is obtained by
winding coils c around a core t constituting a pair of
magnetic poles sandwiching the metal pieces and has a
width larger than those of the preceding metal piece 1
and the succeeding metal piece 2. According to the
inductor having such a structure, since the entire area
of the metal pieces in the width direction are
positioned between the magnetic poles, the magnetic
field generated by the inductor 3 can effectively act on
the metal pieces. Note that such an inductor is also
disclosed in Japanese Patent Laid-open Publication No.
4-89109.
In Fig. 25, when the (alternating) current whose
phase is the same with, but whose direction is reversed
from, those of the induced current is supplied from an
external power supply 22 to the conductive members 18,
the induced current circulating in the metal pieces
flows to the width ends thereof, enabling heating the
entire region in the width direction.
As similar to Fig. 25, Figs. 26(a), (b) and (c)
show an example in which the current is supplied from
outside to the conductive members 18 to uniformly heat
the metal pieces in the full width direction.
CA 022~463 1998-12-1
-47-
Figs. 26 shows the case where the metal pieces
each having a width larger than that of the inductor 3
are heated. In the example illustrated herein, a pair
of inductors 3 shown in Figs. 25 are prepared and
arranged along the width direction of the metal pieces
to carry out heating.
Fig. 26(a) is a top plan view showing an
apparatus; Fig. 26(b), a sectional view taken along the
A-A line in Fig. 26(a); and Fig. 26(c), a sectional view
taken along the B-B line in Fig. 26(a).
In the example shown in Fig. 26, as similar to
Fig. 25, the inductors 3 each having a substantially
C-shaped core t are provided at the ends of the metal
pieces to be joined, and the conductive members 18 are
provided at the both ends of the metal pieces at an
interval of space. Also, the current whose phase is
same with that of the induced current generated in the
metal pieces is supplied from the external power supply
22 to the members 18.
In Figs. 25 and 26, although the description has
been given to the case where the inductor having a
larger width dimension than those of the metal pieces to
be joined is used or the case where at least a pair of
inductors are used to heat the metal pieces, the present
invention is not restricted to the illustrated examples.
Since the scale of the current supplied from the
CA 022~463 1998-12-1
-48-
external power supply to the conductive members i5 not
limited, it is possible to flow the current which is
sufficiently large for uniformly heating the ends of the
metal pieces in the full width direction, and there is
no problem if an inductor whose width is smaller than
those of the metal pieces i5 used.
In the present invention, the metal pieces are
heated and joined in accordance with the above-mentioned
points. As a combination of these points, there is
adopted a method by which the rear end of the preceding
metal piece and the front end of the succeeding metal
piece are positioned in close proximity with a space
(small gap) therebetween and, after heating is performed
until the temperature reaches a target value, the power
input to the inductor is stopped to carry out the
pressing, or a method by which the input power is
lowered to such a level that no spark is produced if the
temperature at the portions to be joined reaches the
target value, and pressing is started while continuing
heating.
The description will now be given as to the case
where the conductive members are brought into contact
with the both width ends of either the rear end of the
preceding metal piece or the front end of the succeeding
metal piece and the heating efficiency at the width ends
of the metal pieces is improved by the members.
CA 022~463 1998-12-1
- 49 -
Referring to Fig. 27, in case of heating the
preceding steel piece 1 and the succeeding steel piece
2, when the conductive members 23 are previously pressed
against the both width ends of at least one of the metal
pieces in the vicinity of the end thereof, the induced
current generated in the preceding metal piece 1 and the
succeeding metal piece 2 also flow in the members 23.
The temperature at the both width ends, i.e., the
corners of the metal pieces increases at the same speed
with that in any other regions by the Joule heat
generated at this time, and the problems that the
joining failure occurs or the strength in the joining
portions is insufficient due to the resistance at the
heat defective portion are eliminated.
Since each conductive member 23 shown in Fig. 27
is likely to be melted and fused during heating the
metal pieces if its melting point is same with or lower
than that of the metal pieces, it is preferable to use a
material having a higher melting point than that of the
metal pieces, for example, tungsten or carbon.
Further, in regard of a size of each conductive
member, the thickness of the member is preferably equal
to that of the metal pieces to be joined, and it is
preferable to adapt such a width that the temperature
rise at the ends of the metal pieces in the width
direction thereof is not insufficient when heating is
CA 022~463 1998-12-1~
-50-
carried out without the conductive members. Further,
the length of the member is preferably not less than a
lapping length as viewed from the top plan of the core
of the inductor and the metal pieces to be heated.
In case of heating the metal pieces, the spark
is likely to be generated between the conductive members
and the metal pieces, Thus, it is particularly
preferable to increase the bearing to or above 2 kg/mm2
and push the conductive members against the metal pieces
in advance.
Although Fig. 27 shows the example in which the
metal pieces are heated by using a pair of inductors, it
is needless to say that the same effect can be obtained
by using a single inductor such as that shown in Fig. 28
to perform heating.
Fig. 30 shows for reference a distribution of
the temperature rising speed (which is measured at a
point spaced apart from the end face by 1.5 mm and
positioned in the center in the plate thickness
direction on the metal piece) in the plate width
direction in the case where two metal pieces each
consisting of stainless steel of SUS304 and having a
thickness of 30 mm are heated by using the inductor
having a core whose size is 240 x 1000 mm as shown in
Fig. 29 under such conditions that distances between the
metal pieces and the core is 90 mm on the upper side and
CA 022~463 1998-12-1
-51-
90 mm on the lower side and the input power is 980 kW.
The degree of the temperature rise is particularly small
at the corners of the metal pieces as compared with any
other regions. Therefore, even when the metal pieces
are subjected to continuous rolling after being joined
by the inductor having such a heating characteristic,
cracks are developed in the joined portion as the
rolling proceeds, and it is obvious that the joined
portion is inevitably ruptured over the full width.
The description will now be given as a case
where, when heating the metal pieces, the density of
magnetic fluxes of the alternating magnetic field is
increased and the heating efficiency at the width ends
of the metal pieces is improved by members each
consisting of magnetic substance provided between each
metal piece and the inductor to uniformly heat the
entire region in the width direction with reference to
Figs. 31(a) and (b) and Fig. 32.
In case of heating the metal pieces by the
inductor 3, members 24 consisting of magnetic substance
are provided at corners where the degree of temperature
rise is small and the magnetic influx density at the
corners is increased by the members 24. The induced
current then flows closer to these portions, and the
degree of heating is also increased. A satisfactory
joining strength can thus be secured at the both width
CA 022~463 1998-12-1
-52-
ends without a fear that the metal pieces are melted
down in the central region thereof in the plate width
direction.
In this invention, each of the members 24
consisting of magnetic substance must be provided at a
position in a region which is extending from the width
end of each metal piece and whose length is not more
than ten times as long as the osmotic depth do of the
induced current. That is because the temperature rise
is insufficient in the region and, if each member 24
consisting of magnetic substance is inwardly provided
beyond this region, the degree of temperature rise of
the metal piece becomes too large in such a region where
the member 24 is provided, causing such a problem as
melt down.
A width dimension W of the member 24 is set to
be two to ten times as long as the osmotic depth do.
That is because the effect obtained by placing the
magnetic substance is reduced when the rangé in which
the degree of heating and temperature rise can be
increased is small, if the width dimension W is not more
than two times as long as the osmotic depth do. On the
other hand, if it is more than 10 times as long as the
osmotic depth do, the temperature rising speed is
extremely increased in the portion extending beyond the
depth do, thereby causing melt down. In order to
CA 022~463 1998-12-1~
.
-63-
perform heating in such a manner that the temperature
rising speed similar to that in the central region of
the metal pieces in the width direction thereof can be
obtained and the temperature distribution is
substantially uniform in the entire area in the width
direction, the width W of each member 24 consisting of
magnetic substance is restricted to a width which is two
to ten times as long as the osmotic depth do.
Fig. 33 shows the relationship between the width
dimension of the member 24 consisting of magnetic
substance/the osmotic depth do and a length of defective
.
~olnlng .
As an example of a continuous hot rolling
equipment to which the joining apparatus having the
structure shown in Fig. 31 is incorporated, it is
possible to adopt one shown in Fig. 20 by which the
metal pieces are joined while matching with a timing for
rewinding a coil type metal piece provided between the
pinch rolls and a timing for effecting the rolling
process.
A dimension Lm of the member 24 consisting of
magnetic substance along the longitudinal direction of
the metal pieces may preferably be 2do + g + ~ (~ is a
clearance and set to be approximately 100 to 200 mm), in
the case where a space between the metal pieces which is
firstly formed when joining the metal pieces is
CA 022~463 1998-12-1
-54-
represented as g.
Further, when heating the metal pieces 1 and 2,
in order to prevent the temperature rise of the member
24 consisting of magnetic substance itself, the member
24 may be obtained by superimposing a plurality of
insulated thin plates one above the other. As the
member 24, simple substance such as iron, nickel, cobalt
or others, alloys thereof or non-crystallized substance
can be used in addition to silicon steel.
Fig. 34 shows an example in which the members 24
consisting of magnetic substance are adapted in the
notches u in the joining apparatus provided with the
dislocation preventing plates 8 each having the
notches u.
In the apparatus having such a structure, the
metal pieces are uniformly heated over the entire region
in the width direction. Also, it is extremely
advantageous for completely preventing fluctuations in
the vertical direction which are likely to be caused
during pressing the metal pieces 1 and 2 against each
other.
In the case where there is provided such
dislocation preventing plates 8 as shown in Fig. 34, if
there is provided such a structure as shown in Fig. 35
that each member 24 consisting of magnetic substance can
be temporarily removed from each notch u and shifted in
CA 022~463 1998-12-1~
parallel with the width direction of the metal pieces 1
and 2 to be again inserted in each notch u at a
predetermined position, it is possible to easily cope
with joining of metal pieces having different widths,
thereby performing the effective continuous hot rolling.
The explanation will now be given as to a case
where the overlap width of the preceding and succeeding
metal pieces and the magnetic poles of the inductor in
the longitudinal direction of the metal pieces are
adjusted to improve the heating efficiency at the
portions to be joined.
As an inductor used for joining the metal
pieces, those having the structure shown in Figs. 36
through 38 are typical examples. The state of magnetic
flux distribution when the electric power is supplied to
these inductors to generate magnetic fluxes is as shown
in Fig. 39 or 40.
As apparent from Figs. 39 and 40, magnetic
fluxes generated between the magnetic poles can be
roughly classified into three types irrespective of
difference between the structures of the inductors.
1) Magnetic fluxes running through the metal
pieces in the vertical direction thereof (region (I)).
2) Magnetic fluxes passing a space between the
preceding metal piece and the succeeding metal piece
(region (II)).
CA 022~463 1998-12-1
-56-
3) Magnetic fluxes dispersing without running
through the metal pieces and the space therebetween
(region (III)).
Among these types of magnetic flux, one
contributing to heat the metal pieces is the magnetic
flux in (I) and also having a vertical component. In
this type of heating method (induction heating method),
it is therefore important to secure a large number of
magnetic fluxes in (I).
The induced current generated by the magnetic
flux vertically running through the metal pieces,
namely, the magnetic flux running in the thickness
direction intensively flows along the ends of the metal
pieces, and this is known as the skin effect. The
region in which the induced current flows is generally
defined by a distance from the end of the metal piece
toward the inside of the metal piece (depth), namely, a
so-called osmotic depth do (m) and can be represented by
the following expression.
do = {p x 107/(~ x f)}l/2/2~
f: frequency of the alternating magnetic field (Hz)
p: electric resistivity (Q * m)
~: relative magnetic permeability (-)
Here, in order to find the influence of the
osmotic depth determined by a frequency of the
alternating magnetic field and the overlap width L
CA 022~463 1998-12-1
-57-
(smaller one of two dimensions Ll and L2 shown in
Figs. 36 through 38) of the respective metal pieces and
the magnetic poles of the inductor in the longitudinal
direction of the metal pieces upon heating, the
experiment was carried out as follows. The inductor
shown in Fig. 36 was used, and the metal pieces of SUS
304 each having a thickness of 30 mm were opposedly
arranged with a space of 5 mm therebetween. Also, gaps
D between the metal pieces and the magnetic poles were
made uniform, and heating was carried out while varying
the overlap width L of the magnetic poles and the metal
pieces. Variations in the temperature rising speed at
that time were observed.
The result is as shown in Fig. 41. Values in
Fig. 41 were obtained as follows. A plurality of double
bevel sheath thermometers were embedded in the metal
pieces from the front and rear ends thereof in the
longitudinal direction at a pitch of 3 mm, and the
temperature rising speed was obtained when the current
was supplied to the coils of the inductor for three
seconds at various alternating magnetic field
frequencies (100 Hz through 10 kHz). The temperature
rising speed ratio (represented as a mean value of
results obtained with frequencies of 100 Hz, 500 Hz, 1
kHz and 10 kHz) was arranged with L/do = 4.0 as a
reference. Note that the osmotic depth is approximately
CA 022~463 1998-12-1
-58-
49 mm at 100 Hz, 22 mm at 500 Hz, 15 mm at lkHz and 5 mm
at 10 kHz.
As apparent from Fig. 41, the heating efficiency
prominently lowers when the overlap width L is 2.0 time
as long as the osmotic depth do of the induced current
and thereafter becomes shorter.
That is because, if the overlap width L is not
more that 2.0 times as long as the osmotic depth do, it
can be considered that the direction of flow of the
current induced to the metal is reversed with respect to
that of the current flowing at an inner portion and
these currents weaken their flows each other. Further,
the fact that the ratio of magnetic fluxes (III) which
do not relate to heating of the metal pieces becomes
large and the quantity of effective magnetic fluxes (I)
is relatively decreased can be regarded as another
reason.
On the other hand, when the overlap width L is
not less than 2.0 times as long as the osmotic depth do,
the substantially same temperature rising speed can be
obtained in any case. In the present invention,
therefore, it is determined to satisfy L 2 2.0 * do, or
more preferably, L 2 3.0 * do in the relationship
between the overlap width L and the osmotic depth do.
As described above, in case of heating and
joining the metal pieces, if the overlap width L (m) of
CA 022~463 1998-12-1
-59-
the rear and front ends of the respective metal pieces
and the magnetic poles of the inductor in the
longitudinal direction of the metal pieces satisfies L
2 2.0 x do in the relationship with the osmotic depth do
of the induced current, an effective heating can be
carried out.
Referring to Fig. 42, the preceding metal piece
1 and the succeeding metal piece 2 are opposed to each
other with a space g therebetween, and two inductors 3
each having a pair of magnetic poles vertically
sandwiching the metal pieces are provided thereto to
generate an alternating magnetic field running through
the metal pieces in the thickness direction thereof.
The induced current then flows at the ends of the
respective metal pieces 1 and 2, and the end region of
the opposed faces which will be joined is heated to
increase the temperature therein by heat generated due
to flow of the induced current. In the case where there
is, for example, a temperature difference between the
preceding metal piece 1 and the succeeding metal piece
2, however, since the both metal pieces are heated to
increase their temperatures at a substantially equal
speed, the temperature difference remains. The pressing
operation may be started while the temperature in one of
the metal pieces does not reach a target joining
temperature range or, conversely, one of the metal
CA 022~463 1998-12-1
-60-
pieces may be excessively heated to be fused or melted
down. Thus, an excellent joining portion may not be
obtained.
In the case where the thickness of the preceding
metal piece 1 is different from that of the succeeding
metal piece 2, the quantity of magnetic fluxes running
through the metal pieces in the thickness direction
thereof can be equal in the both metal pieces, but the
temperature rising speed is faster in the metal piece
having a large thickness and slow in the metal piece
having a small thickness. In this case, the metal
pieces are also brought to the above-described state,
and an excellent joining state cannot be obtained.
Therefore, in this invention, in case of heating
the ends of the preceding metal piece 1 and the
succeeding metal piece 2 to increase the temperature
thereof, the temperatures of the respective metal pieces
are first measured to grasp the temperature difference
therebetween.
Then, as shown in Fig. 43, in order that the
temperatures may reach the same temperature range in the
same heating time, the positions of the metal pieces 1
and 2 or the position of the inductor 3 are adjusted
(the adjustment of the space g or the positional
adjustment of the metal pieces in the longitudinal
direction) so that the penetration quantity of the
CA 022~463 1998-12-1
-61-
alternating magnetic field is controlled. In this
state, the alternating magnetic field running through
the metal pieces in the thickness direction thereof is
generated and the metal pieces are induction-heated and,
at the same time with or after this heating, at least
one of the clamps 9 moves toward the opposed metal piece
to press the metal pieces l and 2 against each other for
.
~olnlng .
In the case where the rear end of the preceding
metal piece and the front end of the succeeding metal
piece move toward each other and the alternating
magnetic field running through the metal pieces in the
thickness direction thereof is generated to perform
induction heating, the rate of temperature rise on
heating can be individually controlled in each metal
piece when the penetration quantity of magnetic flux is
adjusted for each metal piece. Thus, even when the
preceding metal piece is different from the succeeding
metal piece in temperature, thickness or melting point,
the both metal pieces are heated to increase their
temperature to a range suitable for joining the metal
pieces in substantially the same time, and the joining
having the substantially sufficient strength is
possible, eliminating such a problem that the plates are
ruptured during rolling.
In the case where the inductor 3 such as that
CA 022~463 1998-12-1
-62-
shown in Fig. 42 is used, since the density of the
magnetic flux generated by the inductor is substantially
constant, the penetration quantity of the magnetic
fluxes running through each metal piece can be obtained
form the product of the magnetic flux density and the
area in which the core of the inductor laps over the
metal pieces (which can be calculated from the positions
of inductors 3a and 3b and the space g).
For example, in Fig. 43, when heating is carried
out assuming that: the area of the core of the inductor
is 76 mm x 300 mm = 0.0228 m2; the magnetic flux density
when generating the alternating magnetic field by this
inductor is 0.5 T; the distance between the vertical
magnetic poles of the inductor is 150 mm; the space g
between the preceding metal piece 1 (extremely-low
carbon steel having a thickness of 28 mm and C of 0.004
wt%) and a succeeding metal piece 2 (extremely-low
carbon steel having a thickness of 28 mm and C of 0.004
wt%) is 5 mm; the lap area a of the magnetic poles in
the preceding metal piece 1 is 0.01065 m2; the lap area
b of the magnetic poles in the succeeding metal piece 2
is 0.01065 m2; and the power supply frequency of the
alternating magnetic field is 1000 Hz, the temperature
rising speed of the respective metal pieces is equally
70~C/sec.
In the state of Fig. 44 where the succeeding
CA 022~463 1998-12-1
-63-
metal piece 2 is moved back during heating while the
preceding metal piece 1 and the inductors 3 are fixed,
when the gap g between the preceding metal piece 1 and
the succeeding metal piece 2 is changed in a range of O
through 30 mm (when the lap area of the inductors is
changed), the temperature rising speed ratio of the
metal pieces shows such a relationship as shown in Fig
45. If such a relationship is previously grasped, an
appropriate penetration quantity of magnetic flux can be
determined in accordance with a difference between the
temperatures of the metal pieces or types of steel.
Further, it can be considered that the temperature
rising rate of the metal piece is inversely proportional
to the thickness of the same and, if the preceding metal
piece 1 is different from the succeeding metal piece 2
in thickness, the heating and temperature rise may be
carried out taking such a relationship into account.
In the present invention, although the
penetration quantity of magnetic flux in each metal
piece is adjusted by moving the metal piece or the
inductor, inductors may be individually provided for the
respective metal pieces to adjust the magnetic flux
density of the alternating magnetic field itself. It
is, however, realistic that the penetration quantity of
magnetic flux is adjusted by relatively moving the metal
piece and the inductor while maintaining the space g
.. . .. . .
CA 022~463 1998-12-1
- 64-
between the metal pieces to be constant.
Figs. 46 through 48 show a specific example of
an apparatus having a moving mechanism for adjusting the
penetration quantity of magnetic flux by moving the
inductor.
In Figs. 46 to 48, reference number 25 denotes a
frame movable along the longitudinal direction of the
metal pieces 1 and 2; 26, a carrier roller supporting
the metal pieces 1 and 2; 27 and 28, subframes movable
along the width direction of the metal pieces within the
frame 25; 29 and 30, clamps which are provided in the
subframes 27 and 28 for clamping and supporting the
metal pieces 1 and 2; 31, a rod which suspends and
supports the inductor S provided with a C-shaped core so
as to be capable of sliding along the axial direction
thereof and which can move on a rail 1 provided along
the width direction of the metal pieces together with
the inductor 5; and 32, a moving mechanism for moving
the inductor 5 in the longitudinal direction of the
metal pieces separately from the frame 25. As shown in
Fig. 47 illustrating the primary part of the moving
mechanism 23, the moving mechanism 23 is constituted by
fixed wedges 32a and 32b held by a suspending/supporting
portion of the inductor 5, and movable wedges 32e and
32f having hydraulic cylinders 32c and 32d and provided
between the fixed wedges 32a and 32b and between the
CA 022~463 1998-12-1
-65-
rails 1 to face different directions.
There is exemplified the joining apparatus
having the above-mentioned arrangement in which the
clamps 29 and 30 and the inductor 5 can be easily
removed from the carrier line of the metal pieces during
maintenance or in an emergency. The adequate heating is
enabled by appropriately moving the inductor 5 in the
longitudinal direction of the metal pieces by the moving
mechanism 32 and adjusting the penetration quantity of
magnetic fluxes.
In Figs. 47 and 48 showing the primary part of
the inductor 5, the movable wedges 32e and 32f are first
opposedly moved by the hydraulic cylinders 32c and 32d
to shift the inductor 5. At this time, the
suspending/supporting portions slide on the rails 1,
whereby the position of the inductor 5 is adjusted in
the longitudinal direction of the metal pieces.
In Figs. 46 and 48, although there is shown the
case where the movement is carried out by using the
movable wedges 32e and 32f of the moving mechanism 32,
one of the movable wedges may employ a spring or a
balance cylinder having a function similar to that of
the spring. On the other hand, the inductor 5 may be
directly moved by using the hydraulic cylinders instead
of the wedges, or the rails 1 themselves may be moved in
the longitudinal direction of the metal pieces to shift
CA 022~463 1998-12-1
- 66-
the inductor 5.
In this invention, the description has been
given as to the case where a pair of inductors, each of
which has a pair of magnetic poles vertically
sandwiching the metal pieces and which can cover the
metal pieces over the full width thereof, are provided
to perform heating and increase the temperature.
However, in the case where a target is metal pieces each
having a larger width than that of the inductor, two
pairs of, i.e., four inductors may be provided in the
plate width direction of each metal piece to perform
heating and increase the temperature. In such a case,
the heating means is not restricted to a specific form.
Further, although the clamps are employed as means used
when pressing the metal pieces, pinch rolls may also be
adopted.
The explanation will now be give as to a case
where a plurality of inductors are used to heat and join
the metal pieces.
In the joining operation which is as shown in
Figs. 49(a) and (b) and by which the preceding metal
piece 1 and the succeeding metal piece 2 are opposedly
provided with a space therebetween to perform heating
and increase the temperature, after the rear end of the
preceding metal piece 1 and the front end of the
succeeding metal piece 2 are heated by the current e
CA 022~463 1998-12-1
- 67-
induced to the metal pieces by the alternating magnetic
field of the inductors 3, the metal pieces are joined by
adding the pressing force thereto along the longitudinal
direction of the metal pieces. However, the area in
which the induced current flows is decreased as the
width of the respective metal pieces increases,
resulting in the reduction in the temperature rising
efficiency at end portions.
As a countermeasure, turning on the electricity
for a long time or increase in the quantity of heat
input can be considered. When the time for turning on
the electricity is prolonged, however, the portion
directly below the inductor is heated for a long time,
whereby a burn-through is caused due to an excessive
heating. On the other hand, when the quantity of heat
input is tried to be increased, a maximum value of the
input power for one inductor is 2000 through 3000 kW
which is the limit at a stage of manufacturing the
inverter, and there is hence a limitation.
Accordingly, in order to solve the above-
mentioned problems, as shown in Fig. 50, it is required
to provide a plurality of inductors along the portions
which will be joined in the metal pieces and, for
example, two inductors must be provided on a working
side (WSj and a driving side (DS).
As a power supply of the inductor, since an
CA 022~463 1998-12-1
-68-
inverter whose oscillation frequency depends on a load
impedance as viewed from the inverter side, namely, a
self-controlled inverter is frequently adopted, when the
load impedance on the WS is different from the load
impedance on the DS as viewed from the inverter, the
oscillation frequency varies.
In the actual joining operation, the joining
state on the WS is often different from that on the DS.
In the case where the load impedance is changed
depending on the joining state (the frequency actually
varies at the time of occurrence of an arc), the
oscillation frequency of the inverter on the WS is thus
different from that on the DS.
If the oscillation frequency of the inverter on
the WS is different from that on the DS, phases of the
WS and DS are inverted (for example, in case of 500 Hz
and 510 Hz, the phases are inverted after approximately
0.98 second), and the induced currents induced to the
metal pieces cancel out. As a result, the temperature
rising efficiency is decreased, and a desired heating
performance cannot be obtained.
In the invention, as shown in Figs. 51(a) and
(b), inverters are exclusively connected to inductors
L10 and L20 for use, respectively, and phases are
synchronously controlled so that the currents having the
same phase flow in the inductors L10 and L20. Eddy
CA 022~463 1998-12-1
-69-
currents Lll, L21, L12 and L22 induced to the metal
pieces have the same phase to realize the effective
heating by the induced currents.
Fig 52 is a block diagram showing a control
system in the case where a pair of inductors 3 for
generating the magnetic field are provided in the width
direction of the metal pieces.
In the drawing, reference numeral 33 denotes an
electric power command apparatus; 34 and 35, inverters;
and 36, a phase control circuit.
As shown in Fig. 52, the inverter 34 is of a
self-controlled type, and its oscillation frequency is
determined by a circuit constant (this frequency varies
depending of the joining state such as a joining length
of the metal pieces). In addition, the phase control
circuit 36 has a function for detecting an oscillation
frequency and a phase of the inverter 34 and generating
ignition pulses which are given to the inverter 35.
Note that the inverter 35 is of an externally-controlled
type and its oscillation frequency is determined by the
ignition pulses supplied from the phase control circuit
36.
In Fig. 51(b), assuming that the inductance is
Li when the loads are viewed from capacitors C, each
inverter oscillates by a resonance frequency fi
represented by the succeeding expression:
CA 022~463 1998-12-1
-70-
fi = 1/{2~ (LiC)1/2}
Li is determined by the shape of the metal
pieces, the distance between the inductors and the metal
pieces and the space between the metal pieces, and thus
determined by Li = LiO + (Mil2/Lil) + (Mi22/Li2) from
LiO of the inductors, Lil of the preceding metal piece,
Li2 of the succeeding metal piece, and inductances Mil
and Mi2 between the inductors and the preceding and
succeeding metal pieces.
In this case, when the electricity is turned on
for five seconds, a difference between the oscillation
frequencies such that there may be no problem is O.l Hz.
In order to synchronize the oscillation
frequencies and the phases of the inverters on the WS
and DS, such a structure as that shown in Fig. 53 may be
adopted. That is, the self-controlled inverters are
used as power supplies on both the WS and the DS, and
the inverters are connected on the secondary sides. The
impedances viewed from the inverters thus become common,
thereby synchronizing the oscillation frequencies and
the phases of the inverters on the WS and DS.
In connection with the above-described case
where a plurality inductors are used, a point in
arranging each inductor will now be mentioned.
In order to simply and rapidly heat and join the
preceding metal piece and the succeeding metal piece
CA 022~463 1998-12-1
-71-
without consuming unnecessary energy, it is particularly
preferable to adopt a so-called transverse induction
heating method by which the preceding and succeeding
metal pieces are opposed with a gap of a few or tens mm
at their ends (the front end and the rear end), and the
inductor 3 having such a structure as that shown in
Fig. 54 is disposed herein to perform heating.
According to this method, as shown in Fig. 55 which is a
top plan view of a joining region of the metal pieces,
the induced current e flows at the end of each metal
piece, and the temperature in the portions which will be
joined in the metal pieces is precedently increased by
heating due to this current e, thereby enabling easy
joining of the metal pieces by the pressing operation
which is subsequently performed. In such a joining
method, however, there is no problem in particular when
the width of the magnetic poles of the inductor is
larger enough than that of the metal pieces, though in
the case where the metal pieces having a width larger
than that of the magnetic poles of the inductor are
joined, the penetration quantity of magnetic fluxes are
decreased at the width ends of the metal pieces, and
hence the induced current cannot flow in the entire end
region of the opposed face of the metal pieces. As a
result, the temperature distribution in the width
direction becomes uneven, thereby making it difficult to
CA 022~463 1998-12-1
-72-
realize the secure joining. On the other hand, in the
case where the width of the magnetic poles is made large
in correspondence with the width of the metal pieces, it
is necessary to increase the current supplied to the
inductors in order to obtain a satisfactory quantity of
magnetic fluxes running through the metal pieces per
unit area. Further, the current supplied to the
inductors must be restricted to be within such a range
that coils or cores constituting the inductors or the
metal pieces and in particular the central region
thereof cannot be melted down by Joule heat, and the
electric power which can be input to the inductors
therefore has a limitation. After all, even though the
width of the magnetic poles is enlarged, the quantity of
magnetic fluxes per unit area becomes uneven, and the
entire area at the ends of the metal pieces cannot be
heated at the same speed.
In order to eliminate such a problem, it is
extremely effective to use a plurality of inductors as
shown in Fig. 50.
However, if a plurality of inductors are only
provided along the width direction of the metal pieces
at their portions which will be joined, when the space
provided between the magnetic poles of the inductors
adjacent to each other is large, the temperature rising
speed in the metal piece at its portion corresponding to
CA 022~463 1998-12-1~
this space is slow as compared with that in any other
region. Therefore, there is a disadvantage that even
when the heating temperature reaches a target value, the
temperature at this portion is lower than this value.
When heating is continued until the temperature
in the region which corresponds to the space between the
magnetic poles and where the temperature rising speed is
lowered reaches a temperature at which joining is
possible, any other potion is melted down,
disadvantageously affecting on the joining operation for
the metal pieces.
In order to eliminate the above-mentioned
problems when heating the metal pieces by using a
plurality of inductors, the space is preferably set to
be not more than 5 times as long as the osmotic depth do
(m) of the induced current which can be represented by
do = {p x 107/(~ x f)}l/2/2~ (it is preferable to provide
no space between the magnetic poles of the inductors,
namely, the space should be 0, but a protective cover
and others are actually disposed to each inductor and
the space cannot be set to 0). Here, f represents the
frequency of the alternating magnetic field (Hz); p, the
electric resistivity of the metal pieces (Q * m), and ~,
the relative magnetic permeability.
Fig. 56 shows an example in which a pair of
inductors 3a and 3b are arranged at the ends of the
CA 022~463 1998-12-1
-74-
metal pieces 1 and 2 along the width direction thereof.
When the inductors 3a and 3b are provided as shown in
the drawing and a space w1 between the adjacent magnetic
poles is set within the above-described range, the
induced currents generated by the respective inductors
3a and 3b are united to have a large value. The uniform
heating is consequently realized in the full width
direction.
A pair of inductors are provided in the width
direction of the metal pieces and only the space between
the magnetic poles of the inductors adjacent to each
other is varied, and Fig. 57 shows the result of
research of influences by a ratio of the space to the
osmotic depth do, the research having been carried out
in accordance with the succeeding points:
1) Assuming that the portions which will be
joined and correspond with the magnetic poles are 100 %~
a ratio of the temperature rising speed in the portion
corresponding to the space between the magnetic poles;
and
2) In the width direction of the portions to be
joined, a length of a region where the temperature
rising speed is not more than 90 % with respect to that
in the portion corresponding with the magnetic poles.
In this case, the joining conditions are such
that: the width of the metal pieces is 1500 mm; the
., CA 022~463 1998-12-1
- 75-
width of the magnetic poles, 1000 mm x 2; the applied
power, 1000 KW; and the alternating magnetic field
frequency, 1 KHz.
As apparent from the drawing, if the space
between the magnetic poles is not less than five times
as long as the osmotic depth do, the temperature rising
speed in a portion corresponding with the space lowers
below 90 % of the temperature rising speed of the
portion corresponding with the magnetic poles, and a
problem may be caused in the actual operation. On the
other hand, the region in which the temperature rising
speed is not more than 90 ~ gradually increases from 0.
Therefore, in the case where a plurality of inductors
are used to heat the metal pieces and increase the
temperature for joining, it is preferable to set the
space between the magnetic poles adjacent to each other
to be not more than five times as large as the osmotic
depth do in connection with the frequency of the
alternating magnetic field.
Fig. 58 shows a structure of an apparatus for
carrying out such a heating operation.
Fig. 58 shows an example in which two inductors
are arranged along the width direction of the metal
pieces 1 and 2, and projections 37 are provided to the
respective inductors 3a and 3b on the adjacent faces of
the magnetic poles adjacent to each other so that the
CA 022~463 1998-12-1
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respective inductors 3a and 3b can be brought into
contact with each other or a space provided therebetween
can be narrowed.
The description has been given as to how to
uniformly heat the entire area of the metal pieces in
the width direction thereof. As to the above-mentioned
various conditions, even if they are satisfied, when the
metal pieces joined at a heating temperature of
approximately 1350 through 1400~C are rolled by a
finishing rolling mill composed of a plurality of stands
with a draft percentage increased by ten times or more,
it may not be said that rolling with respect to all
kinds of steel can be performed without causing a
rupture at the joined portion until the completion of
rolling.
For example, in regard of extremely-low carbon
steel of SS400 or that having a carbon content of not
more than 100 ppm, there sometimes occurs a problem that
the plate is ruptured during rolling.
Irrespective of types of steel, it is necessary
to provide a heating condition that such a problem as
rupture of plate during finishing rolling which is
thereafter performed is not caused, and such a heating
condition will be described hereinbelow.
In order to realize an excellent joining of the
metal pieces, when carrying out joining, the temperature
CA 022~463 1998-12-1~
of the portions to be joined must be increased to a
value such that the oxidized scale on the surface can be
melted and removed, or the base metal can be melted at
least on the opposed end faces of the portions which
will be joined. Either of them must be satisfied.
The present inventors, therefore, researched
about the joining conditions that the metal pieces can
withstand rolling with the draft percentage increased by
not less than five times after joining, and particularly
about a preferable range of heating temperature, for
various kinds of carbon steel having a carbon content of
1.3 wt~ or 5 ppm.
The quality of joining was judged in accordance
with existence/absence of rupture in the plate during
finishing rolling after joining and the joined state
obtained after rolling. In the judgment of quality,
there was actually no problem when finishing rolling was
carried out without any problem or even when a crack at
a joined portion was partially generated after rolling,
and the joining can be hence said to be excellent.
The obtained result is illustrated in Fig. 59.
As shown in the drawing, it was found that the
preferable range of heating temperature largely varied
in accordance with the carbon content and was extending
with values of temperature higher than 1350 through
1400~C, values of which were conventionally good, when
CA 022~463 1998-12-1~
the carbon content was small and, on the other hand, the
preferable range of heating temperature was extending
with lower values when the carbon content was large.
In this case, it was discovered that the
preferable range of heating temperature would be
excellently appeared when a melting temperature of the
scale of iron oxide, a solidus line temperature of the
metal pieces and a liquidus line temperature of the
metal pieces were used as parameters.
Fig. 60 shows the relationship between the
carbon content of the metal pieces and the liquidus and
solidus line temperatures of the metal pieces (this
figure is drawn by using computational expressions
described in "Handbook of Iron and Steel", 3rd edition,
Basic I, P. 205 (Maruzen Co., Ltd.)). Further, the
drawing also shows the melting temperature of the
oxidized scale and the rolling state obtained in
Fig. 59.
As apparent from a comparison between Figs. 59
and 60, an optimum range of heating temperature was able
to be excellently appeared by using the solidus line
temperature of the metal pieces (Ts) and the liquidus
line temperature of the metal pieces (TL), and finishing
rolling was carried out without any problem if the
temperature (T) at the portions which will be joined
satisfied a range represented by the succeeding
CA 022~463 1998-12-1
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expression:
Ts ~ T ~ (Ts + TL ) /2
where Ts indicates a solidus line temperature of the
metal pieces (~C), and
TL represents a liquidus line temperature of the
metal pieces (~C).
Although the above range of temperature is the
optimum range of heating temperature having no problem,
the preferable range of heating temperature actually
having no problem can be represented as follows.
That is, the range can be precisely expressed by
using the solidus line temperature of the metal pieces
(Ts), the liquidus line temperature of the metal pieces
(TL) and the melting temperature of the scale of iron
oxide (Tc) as parameters, and the following preferable
ranges of heating temperature were found out. Namely,
if the solidus line temperature of the metal pieces (Ts)
is equal to or above the melting temperature of the
scale of iron oxide (Tc), the temperature in the
portions to be joined (T) is in such a range that is
higher than an intermediate temperature of the melting
temperature of the scale of iron oxide (Tc) and the
solidus line temperature of the metal pieces (Ts) and
lower than an intermediate temperature of the solidus
line temperature (Ts) and the liquidus line temperature
(TL) of the metal pieces, namely, a range represented by
CA 022~463 1998-12-1
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the succeeding expression:
( TC + TS ) /2 ~ T ~ ( TS + TL ) /2
On the other hand, if the solidus line
temperature of the metal pieces (Ts) is lower than the
melting temperature of the scale of iron oxide (Tc), the
temperature in the portions to be joined (T) is in such
a range that is higher than the solidus line temperature
of the metal pieces (Ts) and lower than an intermediate
temperature of the solidus line temperature (Ts) and the
li~uidus line temperature (TL) of the metal pieces,
namely, a range represented by the succeeding
expression:
TS ~ T ~ ( TS + TL ) /2
It was confirmed that Ts and TL were changed to
some extent depending on a main component, but the
excellent joining was realized irrespective of types of
steel if the above temperature conditions were
satisfied.
Accordingly, in the present invention, in the
case where the both metal pieces are joined by heating
and pressing the rear end of the preceding metal piece
and the front end of the succeeding metal piece in a hot
rolling line, the pressing operation is effected under
such a temperature condition that at least the
temperature T (~C) at the portions to be joined
satisfies the succeeding expression:
CA 022~463 1998-12-1
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TS ~ T ~ ( TS + TL ) /2
or under such a temperature condition that the same
satisfies the succeeding expressions:
(1) if Tc ~ Ts,
(Tc + Ts) /2 ~ T ~ (TS + TL) /2, and
(2) if Tc > TS
Ts ~ T ~ (Ts + TL ) /2
Pressing operation for joining the preceding
metal piece and the succeeding metal piece needs to be
performed to such an extent that the sufficient strength
can be obtained. In the case where cutting is carried
out using a crop shear, the vertical cross section of
the metal pieces in the longitudinal direction thereof
is as shown in Fig. 61, and it is preferable to secure a
pressing quantity of approximately 8 through 10 mm in
order that the preceding metal pieces and the succeeding
metal pieces having such a cross section may be
induction-heated to be firm.
BEST MODE FOR CARRYING OUT THE INVENTION
EMBODIMENT 1
Embodiment (1)
Sheet bars (low carbon steel) each having a
width of 1000 mm, a thickness of 30 mm and a temperature
of 1000~C were joined by using an equipment (provided
with dislocation preventing plates of SUS304 each having
a thickness of 40 mm and 20 notches each having a width
CA 022~463 1998-12-1~
of 30 mm and a length of 900 mm (a width at a portion
for suppressing deformation of the plate is 20 mm), and
a finishing roller mill group having seven stands) such
as shown in Fig. 20 under the succeeding conditions, and
hot finishing rolling for obtaining a finished plate
width of 3 mm was carried out. Further, the temperature
distribution of the sheet bars in the width direction
thereof at the time of completion of joining and the
state of rupture of the plates during rolling were
examined.
Conditions:
a. The distance between a preceding sheet bar and a
succeeding sheet bar: 5 mm.
b. The size of a core of an inductor: width =
1000 mm, dimension along the longitudinal
direction of the sheet bars = 240 mm.
c. The power supplied to the inductor: 1000 kw, and
a frequency: 650 Hz.
d. Ten constitutive members having a size of a =
200 mm, b = 20 mm and c = 20 mm (see Fig. 62)
are disposed to a space between the inductor and
the sheet bars at an interval of 50 mm along the
plate width direction, and each reverse magnetic
field generation circuit positioned at a central
portion in the plate width direction (the
circuit inwardly positioned from the width end
CA 022~463 1998-12-1~
by 250 mm) is closed to perform heating for 12
seconds and increase the temperature.
e. The pressing force: 2 kg/mm2 (pressed after
heating and increasing the temperature).
As a result, it was confirmed that the
temperature distribution in the plate width direction
was improved as shown in Fig. 63 and the stable hot
rolling was enabled without causing rupture of the
plates during rolling.
Embodiment (2)
Sheet bars (low carbon steel) each having a
width of 1000 mm, a thickness of 30 mm and a temperature
of 1000~C were joined by using an equipment (provided
with dislocation preventing plates of SUS304 each having
a thickness of 40 mm and 20 notches each having a width
of 30 mm and a length of 900 mm (a width at a portion
for suppressing deformation of the plate is 20 mm), and
a finishing roller mill group having seven stands) such
as shown in Fig. 20 under the succeeding conditions, and
hot finishing rolling for obtaining a finished plate
width of 1.2 mm was carried out. Further, the
temperature up speed ratio in the width direction of the
sheet bars at the time of heating and the state of
rupture of the plates during rolling were examined.
Conditions:
CA 022~463 1998-12-1~
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a. The distance between a preceding sheet bar and a
succeeding sheet bar: 5 mm.
b. The size of a core of an inductor: width =
1000 mm, dimension along the longitudinal
direction of the sheet bars = 240 mm.
c. The power supplied to the inductor: 1000 kw, a
current: 6120 A, a frequency: 650 Hz, and a
magnetic flux density: 0.21T.
d. Constitutive members each including magnetic
substance (formed by superimposing 70 thin
plates of silicon steel having an insulating
film one on another) and having a size of a =
200 mm, b = 1 mm and c = 20 mm (see Fig. 62) are
provided to notches of the dislocation
preventing plate (see Fig 11) at a space between
the inductor and the sheet bars, and all the
reverse magnetic field generation circuits are
opened for eight seconds from the start of
heating, and a circuit positioned at a central
portion in the plate width direction (the
circuit inwardly placed at a position distanced
from the width end by 250 mm) is closed to
perform heating for 2 seconds.
e. The pressing force: 50 tons (pressed after
heating and increasing the temperature).
CA 022~463 1998-12-1
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Fig. 64 is a graph in which the temperature
rising speed ratios are compared, and it was confirmed
that the effective heating was enabled and no rupture of
the plates occurs during rolling in the case where the
members consisting of magnetic substance were provided
as the constitutive members.
EMBODIMENT 2
Embodiment (1)
An apparatus such as shown in Fig. 21 was used
on the entry side of the rolling equipment for hot
rolling, and joining of metal pieces having the same
width dimension was tried. Both the preceding metal
piece and the succeeding metal piece are extremely-low
carbon steel and have a thickness of 30 mm, a width of
800 mm and a length of 6000 mm.
These preceding and succeeding metal pieces were
opposed with a space of 5 mm being formed therebetween,
and copper plates as conductive members were provided at
the both width ends of the metal pieces in close
proximity with each minute gap of 4 mm therebetween.
Further, the alternating current was supplied to such an
inductor as shown in the drawing, and the alternating
magnetic field running through the magnetic pieces in
the width direction thereof was generated to perform
heating.
A temperature of the metal pieces before heated
CA 022~463 1998-12-1~
-86-
is 1000~C; a thickness, a width and a length of each
copper plate extending over the preceding metal piece
and the succeeding metal piece are 30 mm, 200 mm and
600 mm, respectively; and a length and a width of each
core of the inductor in cross section parallel with the
metal pieces are 240 mm and 1000 mm, respectively.
A distance between each magnetic pole and the
metal pieces is 90 mm on the upper side and 90 mm on the
lower side; a frequency of the alternating magnetic
field is 1000 Hz; and an input power is 980 kW.
After the induction heating was carried out for
ten seconds under these conditions, the preceding and
succeeding metal pieces were opposed to and pressed
against each other using the clamps with the pressing
force of 40 t applied to complete the joining. As a
comparative example, the metal pieces were joined under
the same conditions with those of the embodiment except
that the copper plates were not provided to the sides of
the both metal pieces.
Fig. 65 shows a result of measuring the
temperature rising speeds at the portions to be joined
in the embodiment and the comparative example (the
temperature was measured by embedding double bevel
thermometer at a position inwardly distanced from the
end of each metal piece by 1.5 mm in the longitudinal
direction thereof).
CA 022~463 1998-12-1
-87-
Fig. 65 illustrates the temperature rising speed
ratio in the vicinity of the end of each metal piece in
the width direction thereof assuming that a central
portion of the metal piece in the width direction is 1.
As obvious from the drawing, when the conductive
member was provided to the side of each metal piece in
close proximity according to the present invention, the
temperature up speed at the end in the width direction
approximated the temperature rising speed at the central
portion. That is because the induced current generated
directly below a core of the inductor flows to the end
of the metal pieces in the width direction. Thus, the
end of each metal piece in the width direction was
heated and softened at a temperature such that the
joined portion having a sufficient strength was able to
be obtained without causing the melt down in the central
region in the width direction. Thereafter, when the
rolling was carried out, it was confirmed that no cracks
were developed at the joined portion to bring about the
rupture and the excellent rolling was enabled.
Embodiment (2)
As shown in Fig. 23, individual copper plates
were provided to the both width ends of the preceding
metal piece and the both width ends of the succeeding
metal piece in close proximity. A thickness, a width
and a length of each copper plate were 30 mm, 200 mm and
CA 022~5463 1998-12-1
-88-
300 mm, respectively, and a gap between the respective
metal pieces and the respective copper plates was all
4 mm. In regard of other conditions, the type and size
of steel used as the preceding and succeeding metal
pieces, the size of an inductor, an input power, a
frequency and other were all the same with those in
Embodiment (1).
When the temperature rising speed in the
vicinity of the portions of the metal pieces which will
be joined was measured during heating and the
temperature rising speed ratio of the both width ends
with respect to that of the central portion in the width
direction was calculated, the result equal to that of
Embodiment (1) was obtained. No cracks was generated
and developed by the rolling thereafter performed, and
the plates were excellently joined.
Embodiment (3)
In this embodiment, an examination was carried
out about a case where the current whose phase is the
same with that of the induced current was supplied to
the conductive members.
By using such an inductor as shown in Fig. 25,
the preceding and succeeding metal pieces both having a
width of 800 mm were joined. At the time of heating,
the inductor having a substantially-C-shaped core (a
sectional dimension parallel with the metal pieces: a
~ . ,. .~ ~
CA 022~463 1998-12-1
-89-
length = 1000 mm, a width = 240 mm) was used so that the
copper plates which are the conductive members overlap
on the magnetic poles of the inductor.
The preceding metal piece and the succeeding
metal piece were of SUS 304 steel type and had a
temperature of 900~C before heating, and the copper
plates were provided to the both width ends of the metal
pieces in close proximity so as to connect the rear end
of the preceding metal piece to the front end of the
succeeding metal piece.
Each of the copper plates had a thickness of
30 mm, a width of 200 mm and a length of 600 mm.
Further, a frequency of the alternating magnetic field
in a range of 500 Hz to 10 kHz was set to 500 Hz, lkHz
and 10 kHz, and an input power was 780 kW. Under these
conditions, the induction heating was performed for ten
seconds and the preceding metal piece and the succeeding
metal piece were then pressed against each other with a
pressing force of 40 t by using clamps to complete the
joining.
The temperature rising speed in the vicinity of
the joining portion of the succeeding metal piece was
measured during heating in each frequency, and the
temperature rising speed ratio of the end portion in the
width direction with respect to that of the central
portion in the width direction was obtained as a mean
CA 022~463 1998-12-1
- 90 -
value.
As a result, the temperature rising speed at the
end portion in the width direction further approximated
to the temperature rising speed in the central portion
as compared to Embodiment (1).
Thus, the preceding metal piece and the
succeeding metal piece was able to be joined in the
entire region in the width direction thereof, and no
cracks were developed from the joined portion to lead to
rupture in the rolling thereafter performed.
EMBODIMENT 3
Embodiment (1)
In order to join the preceding metal piece and
the succeeding metal piece both having a plate thickness
of 30 mm and a plate width of 800 mm and being of low
carbon steel type, heating (conditions for heating and
increasing the temperature: a longitudinal dimension of
a core = 240 mm, a width dimension of the core =
1000 mm, a gap between upper and lower magnetic poles =
210 mm, an input power = 200 Kw and alternating magnetic
field frequency = 2000 Hz, a conductive member: material
= graphite, a thickness = 30 mm, a width = 200 mm and a
length = 250 mm, and four conductive members were
pressed against the preceding and succeeding metal
pieces at four width end portions) and pressing
(pressing condition: pressing force of 60 ton) were
. _ .. _, . . . .. . ... .. . . .. .
CA 022~463 1998-12-1
- 91 -
carried out in the state shown in Fig. 28 to join the
both metal pieces. The obtained metal piece was
supplied to a hot rolling equipment to be subjected to
finishing rolling, and rupture of the plate which might
be caused by rolling was checked.
As a result, it was confirmed that there was no
rupture of the plate caused due to cracks at a joined
portion.
EMBODIMENT 4
Embodiment (1)
After the sheet bars (low carbon steel) each
having a plate width of 1000 mm and a thickness of 30 mm
were joined by using an equipment provided with an
apparatus having such a structure as shown in Fig. 34
under the succeeding conditions, hot finishing rolling
for obtaining a plate having a finished plate thickness
of 3 mm was carried out, and examinations were made into
an existence/absence of rupture of the plate during
rolling and a temperature distribution in the plate
width direction immediately after joining of the sheet
bars.
Conditions for joining the sheet bars:
a. A temperature of the sheet bars before finishing
rolling is approximately 900 through 1000~C, and
an electric resistivity in this temperature
range is approximately 120 x 10-8 Qm.
.. . . .
CA 022~463 1998-12-1
- 92 -
Therefore, when the alternating magnetic field
was applied with a frequency of 500 Hz, the
osmotic depth do is approximately 25 mm. Each
member consisting of magnetic substance
(dimension: a width of 100 mm x a length of
150 mm x a height of 30 mm) was thus disposed at
a position distanced from the width end of the
plate by 10 to 110 mm.
b. A space between a preceding sheet bar and a
succeeding sheet bar: 10 mm.
c. Size of an inductor (core): an inductor having a
dimension along the width direction of the sheet
bars of 1000 mm and a dimension along the
longitudinal direction of the same of 240 mm was
used.
d. A power input to the inductor: 1500 kW, a
frequency : 500 Hz.
e. A heating time: 10 seconds.
f. A pressing force: 3 kg/mm2.
Fig. 66 shows the result of comparison between
the temperature distributions in the width direction of
the sheet bar before and after heating when the both
sheet bars were joined in accordance with the present
invention, and Fig. 67 shows the temperature
distributions when the usual heating was performed (a
comparative example: when members consisting of magnetic
CA 022~463 1998-12-1
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substance were not disposed).
As apparent from Figs. 66 and 67, it was
confirmed that the application of heat to the metal
pieces extremely reduced portions in which the
application of heat was insufficient which would lead to
an existence of non-joined portions.
Fig. 68 shows a comparison of calorific power
ratios on the joined face of the sheet bar.
EMBODIMENT 5
Embodiment (1)
Hot-roughed sheet bars (900~C) of extremely-low
carbon (C = 20 ppm) steel each having a width of 1000 mm
and a thickness of 40 mm were opposed to each other with
a space of 5 mm therebetween; inductors (a width and a
length of each magnetic pole opposed to the sheet bars
was 240 mm and 1000 mm, respectively) shown in Fig. 37
were arranged at the rear and front ends of the opposed
sheet bars with a distance D to the sheet bars being
120 mm and an overlap width L of the sheet bars and each
magnetic pole being 70 mm; and the alternating magnetic
field was generated by the inductors with an input power
of 1350 kW and a frequency of 650 Hz to perform heating.
In this case, the osmotic depth was 22 mm; the
temperature rising speed was 70~C/s; and a times
required to reach a target heating temperature was
approximately 10 seconds.
,
CA 022~463 1998-12-1
-94-
Embodiment (2)
Hot-roughed sheet bars (950~C) of high carbon (C
= 0.75 %) steel each having a width of 1000 mm and a
thickness of 30 mm were opposed to each other with a
space of 10 mm therebetween; inductors (a width and a
length of each magnetic pole opposed to the sheet bars
was 100 mm and 1200 mm, respectively) shown in Fig. 38
were arranged at the rear and front ends of the opposed
sheet bars with a distance D to the sheet bars being
60 mm and an overlap width L of the sheet bars and a
coil being 45 mm; and the alternating magnetic field was
generated by the inductors with an input power of 1000
kW and a frequency of 650 Hz to perform heating. In
this case, the osmotic depth was 22 mm; the temperature
rising speed was 70~C/s; and a times required to reach a
target heating temperature was approximately 7.5
seconds.
EMBODIMENT 6
Embodiment (1)
In order to join the preceding metal piece
having a width of 600 mm, a thickness of 28 mm and a
melting point of 1532~C (a type of steel: extremely-low
carbon steel having a carbon content of 0.002 wt%) and
the succeeding metal piece having a width of 600 mm, a
thickness of 28 mm and a melting point of 1485~C (a type
of steel: carbon steel having a carbon content of 0.7
CA 022~463 1998-12-1
_ 9~j _
wt%) to each other, after heating and increasing the
temperature under such conditions that: an area A of a
core of an inductor was 76 mm x 300 mm = 0.0228 m2; a
magnetic flux density of the alternating magnetic field
was 0.5 T; a distance between upper and lower magnetic
poles of the inductor was 150 mm; a temperature of the
preceding metal piece before starting heating was
1000~C; a temperature of the succeeding metal piece
before starting heatin~ was 1000~C; a space g between
the preceding and succeeding metal pieces was 5 mm; a
lap area a of each magnetic pole in the preceding metal
piece was 0.01050 m2; a lap area b of each magnetic pole
in the succeeding metal piece was 0.01080 m2; a
frequency of the alternating magnetic field was 1000 Hz;
two inductors were prepared and disposed at the both
width ends of the metal pieces; a heating time was 6.5
seconds; and a pressing force was 2 kgf/mm2 (bearing),
the both metal pieces were pressed against and joined to
each other, and an examination was made into a tensile
strength at the joined portion after completely cooled.
In regard of heating of the metal pieces under
the above-mentioned conditions, it was confirmed that
the temperatures of the preceding metal piece and the
succeeding metal piece after heating reached 1475~C and
1430~C which were lower than the respective melting
points by 55~C, respectively. Further, as to the
CA 022~463 1998-12-1
-96-
tensile strength of the joined portion, there was
obtained an excellent result, i.e., 28 kgf/mm2
corresponding to approximately 90 ~ of a tensile
strength (31 kgf/mm2) of the preceding metal piece.
EMBODIMENT 7
Embodiment (1)
An apparatus shown in Fig. 51 in which two
inductors (the size of a core of each inductor: a length
of 240 mm x a width of 1000 mm) for generating the
magnetic field were provided in the width direction of
the metal pieces was used; the electric power of 1000 kW
was input to each inductor while synchronously
controlling phases; and metal pieces (900~C) of regular
steel each having a width of 1000 mm and a thickness of
30 mm were heated and joined to each other.
As a result, in the conventional joining, since
the induction currents induced to the metal pieces
canceled out depending on the width dimension of the
metal pieces, the temperature rising efficiency was
lowered, whereby a desired heating efficiency might not
be obtained. In the case where two inductors were
synchronously operated in accordance with the invention,
however, it was confirmed that even when the width of
the metal pieces was large, the temperature rising
efficiency was not decreased, thereby enabling the
stable joining.
CA 022~463 1998-12-1
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EMBODIMENT 8
Embodiment (1)
In the hot rolling line shown in Fig. 20, after
the sheet bars (low carbon steel) each having a width of
1800 mm and a thickness of 30 mm were opposed to each
other as the preceding metal piece and the succeeding
metal piece with a space of 10 mm therebetween, heating
was carried out for 10 seconds and the temperature was
increased to 1500~C by a joining apparatus having
inductors whose structure is as shown in Fig. 58 (a
width of each magnetic pole was 800 mm; a length of each
magnetic pole was 250 mm; and a distance between
adjacent magnetic poles was 75 mm) under such conditions
that an input power was 1500 kW and a frequency was 500
Hz, and the metal pieces were pressed against each other
by a force of 3 kgf/mm2, thereby completing the joining
of the both metal pieces. The obtained metal piece was
then rolled by a hot finishing mill having seven stands
until the plate thickness of 3 mm was realized. At this
time, an existence/absence of rupture in the joined
region was checked, but the plate had no rupture and the
excellent continuous rolling was hence performed.
On the other hand, in the case where an
apparatus such as shown in Fig. 70 in which two
inductions each having a C-shaped core are arranged in
the width direction of the metal pieces was used, the
CA 022~463 1998-12-1
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succeeding facts were found out.
That is, since the temperature of the metal
pieces is usually in a range of 900 through 1000~C
during joining and the electric resistivity p of the
metal pieces is approximately 120 x 10-8 Q*m in this
range of temperature irrespective of types of steel,
when the induction heating was effected with a frequency
of the alternating magnetic field of 500 Hz, the
calculated osmotic depth do becomes approximately 25 mm.
In heating using the apparatus shown in Fig. 70, a limit
of a space between the magnetic poles is 150 mm (do x 6)
from a viewpoint of an insulating limit of two inductors
adjacent to each other and, as shown in Fig. 71
illustrating the heating quantity distribution in the
width direction of the metal piece, the heating quantity
at a space between the magnetic poles did not exceed
90 % of the that in the joining region corresponding
with the magnetic poles, resulting in the insufficient
joining at this region.
Fig. 72 shows a distribution of heating quantity
in the case where an apparatus having inductors shown in
Fig. 58 was used, it is obvious that the a rate of
decrease in the heating quantity at a portion between
the inductors is extremely low as compared to data shown
in Fig. 70.
Although this embodiment has been described as a
, . , . ~ . ,
CA 022~463 1998-12-1
99
case where a space (a dimension between two projections)
between magnetic poles adjacent to each other is 75 mm
(usually, a value of 150 mm is a lower limit even though
the space is narrowed as possible), any apparatus, for
example, one shown in Fig. 73 in which the space is 0 mm
can be applied if only a desired heating capacity can be
secured.
EMBODIMENT 9
Embodiment (1)
A joining apparatus utilizing heating by the
induced current was provided between a delivery side of
a roughing mill and an entry side of a finishing mill in
a hot rolling line; the rear end of the preceding metal
piece and the front end of the succeeding metal piece
were cut to obtain desired end shapes by a crop shear at
an earlier stage of operation in the joining apparatus;
heating was carried out at various temperatures by the
induced current; the metal pieces were pressed against
and joined to each other; and the thus-obtained metal
piece was then supplied to a finishing mill.
The temperature rising speed was previously set
to be 100~C/s, and the temperature of each roughed sheet
bar immediately before heating was also adjusted in
accordance with a heating furnace extract temperature
and a roughing speed to be 1000~C + 20~C.
In regard of a steel type, carbon steel having a
.
CA 022~463 1998-12-1
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carbon content of 20 ppm or 1.3 wt~ was used.
Rolling conditions were such that: a sheet bar
width after roughing was 700 to 1900 mm; a sheet bar
thickness was 25 to 50 mm, and a steel plate thickness
on a delivery side of a finishing mill on a seventh
stage was 0.8 to 3.5 mm.
The inductor for generating the alternating
magnetic field was disposed in such a manner that a pair
of magnetic poles would vertically sandwich the front
and rear ends of the metal pieces and the magnetic field
could act upon the entire region of the portions to be
joined. The electric power was supplied from the same
alternating power supply to the vertically extending
inductor, and a maximum input power capacity was
3000 kW.
In this case, the heating processing was carried
out under such a condition that a solidus line
temperature (Ts) and a liquidus line temperature (TL)
were obtained from components of the metal pieces and an
ultimate temperature of heating T satisfied Ts ~ T ~
(TS + TL) / 2. Note that a melting temperature Tc of
the scale in the embodiment was 1350~C.
The obtained result is shown in Table 1.
CA 022~463 1998-12-1~
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Table 1
Content Plate th~ k ~olidus T TS TL TS+TL Draft
No of C width nesS rat ~ (~C) (~C) ( C) /2 ~) ~f
1 1.3700 30 94 1310 1300 1460 1380 15.0 good
2 0.81000 30 43 1430 1375 1472 1423 10.0 good
3 0.21600 30 85 1470 1460 1525 1492 15.0 good
4 0.05700 30solid 1515 1510 1532 1521 10.0 good
0.051500 25 100 1510 1510 1532 1521 31.3 good
6 0.051500 40 77 1515 1510 1532 1521 15.0 good
7 0.002 1900 25 87 1522 1520 1535 1527 31.3 good
8 0.002 70050 53 1527 1520 1535 1527 20.0 good
As apparent from the table, when the heating/
joining processing was effected under the conditions
satisfying an optimum heating temperature range, good
finishing rolling was able to be performed in any case.
Embodiment (2)
A type of steel and rolling conditions are the
same with those in Embodiment (1).
Heating was carried out under such a condition
that a melting temperature of scales of iron oxide (Tc),
a solidus line temperature (Ts) and a liquidus line
temperature (TL) were obtained from components of the
metal pieces and an ultimate temperature of heating T
satisfied (Tc + Ts) / 2 ~ T ~ (TS + TL) / 2. However,
in case of Tc > Ts, the condition was such that T5 ~ T
(TS + TL) / 2 was satisfied.
The obtained result is shown in Table 2.
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Table 2
Plate
~ontent Plate thiCk_ T TC TS TL Draft Result of
( t%) ( ) ness (~C) (~C) (~C) (~C) (%) rolling
9 1.3 700 30 1375 1365 1300 1460 10.0 good
partially incom-
0.7 900 30 1372 1365 1377 1485 20.0 plete joining
after rolling
11 0.21300 30 1470 1360 1460 1525 10.0 good
partially incom-
12 0.06700 30 1440 1360 1510 1532 15.0 plete joining
after rolling
partially incom-
13 0.051500 25 1450 1360 1510 1532 31.3 plete joining
after rolling
14 0.051900 50 1512 1360 1510 1532 25.0 good
partially incom-
0.002 700 25 1450 1355 1520 1535 31.5 plete joining
after rolling
16 0.002 1900 30 1524 1355 1520 1535 15.0 good
17 0.002 1300 30 1526 1355 1520 1535 10.0 good
As apparent from the table, when the heating
processing was carried out under the conditions
satisfying the preferable range of heating temperature,
although a partially incomplete joining occurred,
excellent continuous rolling actually having no problem
was able to be performed.
Comparative example (l)
A type of steel and rolling conditions are the
same with those in Embodiment (l).
Heating was carried out under such a condition
that a melting temperature of scales of iron oxide (Tc),
a solidus line temperature (Ts) and a liquidus line
CA 022~463 1998-12-1
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temperature (TL) were obtained from components of the
metal pieces and an ultimate temperature of heating T
satisfied (Tc + Ts) / 2 > T.
The obtained result is shown in Table 3.
Table 3
Content Plate th k ~ TC TS TL Draft Result of
( t%) ( ) ness (~C) (~C) (~C) (~C) (~) rolling
partially incom-
18 0.5 1200 30 1415 1365 1475 150010.0 plete joining
after rolling
19 0.002 1000 25 1420 1355 1520 1535 31 3 rupture during
rupture during
20 0.002 1900 30 1430 1355 1520 1535 15.0
rolllng
As apparent from the table, when heating/joining
processing was not performed under the heating
conditions shown in the table, the excellent finishing
rolling was not possible in any case.
Although the embodiments has been described as
the cases where mainly the carbon steel is a target
material for joining, it is considered that the same
effect can be obtained when silicon steel or high alloy
steel is applied.
In addition, even if the sequence of joining is
changed so that pressing is carried out after heating or
heating is performed while pressing, the same effect can
be obtained, and the excellent result can be similarly
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obtained by using any other well-known means other than
induction heating.
In this invention, there has been explained
about the steel having a C content of not less than 20
ppm, but it is obvious that the temperatures Ts and TL
rarely show variations with value close to 20 ppm, and
it is thus understood that steel having a C content less
than 20 ppm can be also applied.
INDUSTRIAL APPLICABILITY
1) For heating and joining metal pieces, since
an alternating magnetic field whose direction is opposed
to that of an alternating magnetic field generated in
the metal pieces is produced, corner portions of the
metal pieces are sufficiently heated without a fear of
melting down in a central region of the metal pieces in
the plate width direction, and uniform heating over the
entire region in the width direction of the metal pieces
consequently enables a length of the incompletely-joined
portion of the metal pieces which may lead to rupture of
the plate during rolling to be extremely short, thereby
performing stable continuous hot rolling. Specifically,
each reverse magnetic field generation circuit for
generating a reverse magnetic field operates by only
opening and/or closing a switch provided thereto in the
joining apparatus, thus prominently simplifying
structure and control of the apparatus.
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2) By lapping the inductor over each conductive
member provided to each width end of the metal pieces,
the magnetic flux directly runs through the inductive
member to flow the induced current thereto, and a
heating efficiency at the width ends of the metal pieces
can be hence greatly improved.
3) Since the induced current can flow in the
vicinity of corners of the metal pieces more than ever
by positively flowing the current having the same phase
with that of the induced current generated in the metal
pieces from an external power supply to the conductive
members, a heating efficiency can be improved at the
width ends of the metal pieces.
4) Since an overlap width of the inductor
(magnetic poles) and the metal pieces can have an
appropriate value, the temperature can be increased to a
value required for joining in a short time of, e.g., lO
seconds. Further, the same effects can be obtained by
adequately securing a distance between the metal pieces
and coils for induction heating. These effects can
prevent the scale of the apparatus from being enlarged
and clarify a preferred positional relationship between
end portions of the metal pieces to be joined and the
inductor, and the uneven distribution of temperature
during heating can be extremely minimized.
5) For performing continuous hot rolling of the
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metal pieces, since temperature rising quantities at
portions of the preceding metal piece and the succeeding
metal piece where joining is desired can be individually
adjusted to perform heating and raise the temperature,
even when the both metal pieces are different from each
other in temperature or they are of a steel type having
different plate thicknesses or melting points, they can
be assuredly joined to each other, thus eliminating a
problem such that the plate is ruptured from a joined
portion during rolling to stop the production line;
6) Since phases of a plurality of magnetic
field generation inductors arranged in the plate width
direction are controlled, even in the case where widths
of the metal pieces are changed, the metal pieces can be
stably joined to each other.
7) In a method for joining metal pieces by
which induction heating is performed by magnetic fluxes
running through the metal pieces in the thickness
direction thereof, since a plurality of induction
heating coils are provided in the width direction of the
metal pieces and each space provided between induction
heating coils are set to be in a predetermined range,
even if the metal pieces having a large width are a
target of heating and joining the excellent heating is
possible over the entire area of the metal pieces in the
width direction. As a result, a good joined portion can
. .
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be obtained and stable continuous hot finishing rolling
is enabled.
8) Since the metal pieces are heated at
portions to be joined under predetermined conditions,
joining is assuredly enabled irrespective of types of
steel, and stable continuous hot rolling can be effected
while largely decreasing problems such as rupture during
finishing rolling which is carried out after joining.
