Electric heating – Inductive heating – Specific heating application
Reexamination Certificate
2000-06-22
2001-09-04
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Specific heating application
C219S635000, C219S653000, C219S670000, C219S672000
Reexamination Certificate
active
06285015
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-179164, filed Jun. 25, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an induction heater for induction heating heated steel materials that are continuously carried.
In an iron and steel rolling line, generally, heated steel materials are heated to a predetermined temperature in advance, and the heated steel materials are continuously carried to a plurality of rolling mills. The rolling mills sequentially roll the heated steel materials into thin plates. In this rolling process, the heated steel materials radiate heat and are gradually cooled down during carrying. The rolling of the heated steel materials in this state has a quality problem. Therefore, the heated steel materials are heated again before the finish rolling. Thus, the heated steel materials are rolled after the whole heated steel materials have been heated to a high temperature.
For heating the steel materials, a whole heater (a coarse bar heater) formed in a solenoid coil is passed through the heated steel materials to increase the temperatures at all portions of the heated steel materials. Particularly, as the temperatures at both end portions of each heated steel material become lower than the temperature at the center of the heated steel material, a C-shaped inductor is used to locally heat both ends of the steel material. Thus, the temperatures at all portions of the heated steel material are made uniform. The rolling is carried out after this process.
As shown in
FIG. 1
, a C-shaped inductor
1
for locally heating both ends of the steel material has upper and lower iron core legs
3
,
3
formed to sandwich a gap
4
of a C-shaped iron core
2
, with heating coils
5
,
5
wound around both iron cores. An end portion of a belt-shaped steel material
6
is passed through the gap
4
of the C-shaped inductor
1
, and a current is flown through the heating coils
5
,
5
from a power source. Thus, a magnetic flux &PHgr; is generated in upward and downward the iron core legs
3
,
3
. This magnetic flux &PHgr; is interlinked to the heated steel material
6
, thereby to induce an eddy current. As a result, Joule heat is generated to heat both end portions of the heated steel material.
According to an induction heater using this C-shaped inductor
1
, the heated steel material
6
is supported by table rollers
9
and carried. These table rollers
9
are earth-connected via roller stands
10
respectively. Therefore, an induced current for contributing to the heating flows to the earth through the table rollers
9
of the rolling facility.
An equivalent circuit in this state will be explained with reference to
FIG. 2. A
magnetic flux &PHgr; interlinks to a loop circuit
7
formed by a resistor R
2
of the heated steel material
6
continuously carried and a resistor R
1
of an edge portion and to a loop circuit
8
formed by a ground resistor R
0
and the resistor R
1
of the edge portion. Thus, the alternating magnetic flux &PHgr; interlinks within the closed loop to generate electromagnetic induction. Based on this principle, electromotive force of E=−d&PHgr;/dt is generated. As a result, induced currents I
1
and I
2
flow through loop circuits
7
and
8
.
With the above arrangement, the current I
2
that flows to the earth via the table rollers
9
generates a spark at a contact point between the heated steel material
6
and the table rollers
9
. When the level of power applied to the heating coils
5
,
5
is high, an arc hurt is generated on the heated steel material
6
, which results in a poor finished product.
In order to solve this problem, there has been a method of interrupting a current that flows to the earth, by sandwiching an electric insulating material into the roller stands
10
that support the table rollers
9
and installing the table rollers on the floor.
However, the provision of the insulation processing in the roller stands
10
over the range of a few hundred meters of the rolling facility has had a problem that the introduction of this facility requires a large amount of cost. Further, there has been a problem that oxidized scales are dispersed and are adhered onto the surface of the insulation materials during the use of the facility. This causes an insulation failure.
Further, as another measure against the above problem, there has been a method of setting an electromotive force to zero as shown in FIG.
3
. According to this method, two C-shaped inductors
1
,
1
are installed in parallel within the closed loop between the roller stands
10
,
10
. Directions of the magnetic fluxes of the two C-shaped inductors
1
,
1
are inverted to set the electromotive force to zero.
However, according to this method, there is a limit to the size for installing the facility. It is not possible to employ this method at a place where the two inductors
1
,
1
cannot be installed in parallel.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an induction heater capable of preventing a generation of sparks and capable of manufacturing a high-quality rolled-product, without an increase in the size of the induction heater.
An induction heater of the present invention includes an inductor for induction heating a heated steel material that is carried via table rollers; and
an induced-current restricting unit made of an iron core, that is disposed near the inductor, for restricting inducted currents generated in the heated steel material.
According to the present invention, the induced-current restricting unit including an iron core can restrict in high impedance a current that flows to the earth via the table rollers, even at a place where only one inductor can be installed between the table rollers. Thus, it is possible to prevent a generation of sparks, and it is also possible to manufacture a high-quality rolled-product.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
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patent: 4300031 (1981-11-01), Reboux et al.
patent: 4447690 (1984-05-01), Grever
patent: 4708325 (1987-11-01), Georges
patent: 4795872 (1989-01-01), Higisawa et al.
patent: 4987281 (1991-01-01), Yao
patent: 5578233 (1996-11-01), Arvedi et al.
patent: 8-69866 (1996-03-01), None
patent: 8-069866 (1996-03-01), None
patent: 10-092561 (1998-04-01), None
patent: 11-251047 (1999-09-01), None
patent: 11-269538 (1999-10-01), None
Doizaki Tetsuji
Motoyashiki Yoichi
Nakano Kiyoshi
Sekine Hiroshi
Sonobe Manabu
Kabushiki Kaisha Toshiba
Leung Philip H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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