U.S. patent application number 13/392403 was filed with the patent office on 2012-06-21 for electric arc melting facility and method for producing molten metal by using the electric arc melting facility.
This patent application is currently assigned to JP STEEL PLANTECH CO.. Invention is credited to Takato Matsuo, Yasuki Mikami.
Application Number | 20120152057 13/392403 |
Document ID | / |
Family ID | 43628077 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120152057 |
Kind Code |
A1 |
Mikami; Yasuki ; et
al. |
June 21, 2012 |
ELECTRIC ARC MELTING FACILITY AND METHOD FOR PRODUCING MOLTEN METAL
BY USING THE ELECTRIC ARC MELTING FACILITY
Abstract
An electric arc melting facility includes a melting chamber
configured to melt a source iron therein by electric arc discharge
generated from an electrode, and a source iron feeder configured to
continuously feed the source iron to the melting chamber. The
facility further includes a state change detector configured to
detect a state change of the melting chamber when the electric arc
discharge is generated from the electrode, and a controller
configured to adjust a feed rate at which the source iron feeder
feeds the source iron to the melting chamber, based on a detection
result of the state change detectors.
Inventors: |
Mikami; Yasuki; (Kanagawa,
JP) ; Matsuo; Takato; (Yokohama-shi, JP) |
Assignee: |
JP STEEL PLANTECH CO.
Yokohama-shi
JP
|
Family ID: |
43628077 |
Appl. No.: |
13/392403 |
Filed: |
August 23, 2010 |
PCT Filed: |
August 23, 2010 |
PCT NO: |
PCT/JP10/64659 |
371 Date: |
February 24, 2012 |
Current U.S.
Class: |
75/10.12 ;
266/90 |
Current CPC
Class: |
Y02P 10/20 20151101;
Y02P 10/256 20151101; C21C 2005/5288 20130101; Y02P 10/25 20151101;
C21C 5/5211 20130101; F27D 21/00 20130101; H05B 7/144 20130101;
H05B 7/148 20130101; Y02P 10/216 20151101; F27B 3/28 20130101; F27D
19/00 20130101; F27D 13/002 20130101; Y02P 10/259 20151101 |
Class at
Publication: |
75/10.12 ;
266/90 |
International
Class: |
C22B 4/00 20060101
C22B004/00; C22B 4/08 20060101 C22B004/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2009 |
JP |
2009-196451 |
Claims
1. An electric arc melting facility comprising: a melting chamber
configured to melt a source iron therein by electric arc discharge
generated from an electrode; and a source iron feeder configured to
continuously feed the source iron to the melting chamber, wherein
the electric arc melting facility further comprises: a state change
detector configured to detect a state change of the melting chamber
when the electric arc discharge is generated from the electrode;
and a controller configured to adjust a feed rate at which the
source iron feeder feeds the source iron to the melting chamber,
based on a detection result of the state change detector, wherein
the state change detector is configured to detect a variation in at
least one of amounts of harmonics contained in current and voltage
applied to the electrode, as the state change of the melting
chamber.
2. The electric arc melting facility according to claim 1, wherein
the state change detector is configured to detect a variation in
harmonic distortion ratio as the variation in at least one of
amounts of harmonics.
3-6. (canceled)
7. A method for producing molten metal while melting the source
iron by using the electric arc melting facility according to claim
1, the method comprising: a state change detecting step of
detecting a state change of the melting chamber when the electric
arc discharge is generated; and a feed rate adjusting step of
adjusting a feed rate at which the source iron is fed to the
melting chamber, based on a detection result of the state change
detecting step.
8. The method for producing the molten metal, according to claim 7,
wherein the method further comprises a feed-power adjusting step of
adjusting an electric power applied to the electrode, in addition
to the feed rate adjusting step of adjusting the feed rate, based
on a detection result of the state change detecting step.
9. The method for producing the molten metal according to claim 7,
wherein the source iron feeder includes a preheating chamber
directly connected to the melting chamber and configured to preheat
the source iron therein, and a pushing device disposed at a lower
side of the preheating chamber and configured to move the source
iron from the preheating chamber toward the melting chamber, and
the method further comprises: a source iron feeding step of driving
the pushing device to feed the source iron from the preheating
chamber to the melting chamber; a source iron preheating step of
introducing exhaust gas generated in the melting chamber into the
preheating chamber to preheat the source iron in the preheating
chamber; and a source iron melting step of melting the source iron
with heat generated by the electric arc discharge in the melting
chamber while feeding the source iron to the preheating chamber so
as to maintain a state in which the source iron is present in the
preheating chamber and the melting chamber.
10. The method for producing the molten metal according to claim 8,
wherein the source iron feeder includes a preheating chamber
directly connected to the melting chamber and configured to preheat
the source iron therein, and a pushing device disposed at a lower
side of the preheating chamber and configured to move the source
iron from the preheating chamber toward the melting chamber, and
the method further comprises: a source iron feeding step of driving
the pushing device to feed the source iron from the preheating
chamber to the melting chamber; a source iron preheating step of
introducing exhaust gas generated in the melting chamber into the
preheating chamber to preheat the source iron in the preheating
chamber; and a source iron melting step of melting the source iron
with heat generated by the electric arc discharge in the melting
chamber while feeding the source iron to the preheating chamber so
as to maintain a state in which the source iron is present in the
preheating chamber and the melting chamber.
11. The electric arc melting facility according to claim 1, wherein
the controller is configured to adjust an electric power applied to
the electrode, in addition to the feed rate, based on a detection
result of the state change detector.
12. The electric arc melting facility according to claim 1, wherein
the source iron feeder includes a preheating chamber directly
connected to the melting chamber and configured to preheat the
source iron therein, and a pushing device disposed at a lower side
of the preheating chamber and configured to move the source iron
from the preheating chamber toward the melting chamber.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electric arc melting
facility that produces molten metal by continuously feeding a
source iron, such as iron scrap or direct-reduced iron, and melting
the source iron by means of an electric arc, and also relates to a
method for producing molten metal by using the electric arc melting
facility.
BACKGROUND ART
[0002] A batch type electric furnace that melts and refines a
source iron, such as scrap, uses a method of opening a furnace roof
arranged on an upper side of the furnace and charging the scrap to
be processed into the furnace by using a basket. When the furnace
roof is opened, melting work may be temporarily interrupted.
Further, opening the furnace roof may cause a large heat loss and
raise dust that adversely affects environment. On the other hand,
another type electric furnace has been proposed, which is capable
of continuously feeding scrap to a furnace without opening a
furnace roof when charging the scrap (see Patent Document 1 and
Patent Document 2, for example).
[0003] FIG. 8 is a schematic diagram showing a configuration of a
scrap-continuous-feed type electric furnace (electric arc melting
facility 22) as proposed in Patent Document 1. A scrap charge port
is formed on a side surface of an electric furnace (melting
chamber) 1 and is connected to a scrap feeder (source iron feeder)
8 to continuously feed scrap (source iron) 15 into the furnace.
[0004] FIG. 9 is a schematic diagram showing a configuration of
another scrap-continuous-feed type electric furnace (electric arc
melting facility 22) as proposed in Patent Document 2. A preheating
chamber 16 is directly connected to a side surface of an electric
furnace 1 and is equipped with a pusher (pushing device) 17 to be
inserted into and retracted from the preheating chamber 16 to feed
scrap 15 into the electric furnace 1.
[0005] The electric furnace of the type that continuously feeds the
scrap keeps molten metal in its inside to melt the fed scrap by the
energy of the molten metal. Energy to be applied from outside is
used for maintaining the temperature of the molten metal, so that
the temperature of the molten metal is adjusted to be held at a
temperature higher than a melting point of the scrap. Therefore, an
important factor of the electric furnace that continuously feeds
the scrap is to keep balance between the scrap feed rate and the
molten metal temperature, i.e., the energy supplied for
melting.
[0006] In light of this factor, there is known a method for
operating an electric furnace that continuously feeds scrap, as
follows (see Patent Document 3, for example): In a
scrap-continuous-feed type electric arc furnace, a total amount of
in-furnace molten metal is calculated from a cumulative amount of
charged scrap, and is used along with a measured temperature value
of the molten metal to accurately estimate the temperature of the
molten metal after the scrap is charged. Based on this estimation,
the scrap feed rate is controlled so that the temperature of the
molten metal falls within a proper temperature range.
PRIOR ART DOCUMENT
[Patent Document]
[0007] [Patent Document 1]
[0008] Jpn. Pat. Appln. KOHYO Publication No. 61-502899
[0009] [Patent Document 2]
[0010] Jpn. Pat. Appln. KOKAI Publication No. 11-257859
[0011] [Patent Document 3]
[0012] Jpn. Pat. Appln. KOKAI Publication No. 7-286208
SUMMARY OF INVENTION
Technical Problem
[0013] According to the method described in Patent Document 3, the
in-furnace molten metal amount can be estimated with accuracy to a
certain degree, and the speed of a scrap transfer device can be
controlled in accordance with the estimated in-furnace molten metal
amount. However, this method has a drawback such that, the state in
the electric arc furnace is not actually observed, and so the
source iron feed rate and the energy supplied to an electric
furnace may not be optimally adjusted.
[0014] More specifically, there are various types of scrap to be
fed to the electric furnace, as they may contain many different
components other than iron. When such various types of scrap are
charged and melted, the amounts of molten metal produced therefrom
may differ depending on the type of scrap. Therefore, the amount of
the in-furnace molten metal estimated by the calculation from the
amount of the charged scrap may greatly differ from the actual
amount of molten metal in refining. Thus, the estimated temperature
of the molten metal may also differ from the actual
temperature.
[0015] Further, for example, in a case where scrap pieces different
in shape or in bulk density are fed, the amount of the scrap fed
over a long period of time can be estimated, but the amount of the
scrap actually fed into the furnace may vary in a short period of
time. If a large amount of scrap is fed in a short period of time,
the balance with respect to the feed energy for melting may be
disordered, and the scrap may be stacked in the furnace. In order
to melt the stacked scrap, it is necessary to supply a large amount
of energy and also to prolong a melting time. It is thus important
to control the scrap charge rate in an appropriate balance with the
scrap melting rate in the electric arc furnace so as to smoothly
perform melting.
[0016] Accordingly, it is preferable to continuously measure an
amount of source iron that has been fed to the electric furnace and
not yet melted and an amount of molten metal, from time to time,
and to adjust the source iron feed rate and the energy supplied to
the electric furnace, in accordance with the measured amounts.
However, if the state of the source iron varies with time as
described above, it is practically difficult to continuously
measure the amount of source iron and the amount of molten metal in
the electric furnace.
[0017] An object of the present invention is to solve the problems
of the conventional techniques described above for electric
furnaces, particularly in a case where an electric arc furnace is
used for a melting chamber. Specifically, an object is to provide
an electric arc melting facility and a method of operating the
electric arc melting facility configured to continuously feed a
source iron into the electric arc furnace and melt it therein,
while detecting a state change of the source iron fed in the
furnace to maintain the molten metal in the electric arc furnace in
a stable state.
Solution to Problem
[0018] According to an aspect of the present invention, there is
provided an electric arc melting facility comprising a melting
chamber configured to melt a source iron therein by electric arc
discharge generated from an electrode, and a source iron feeder
configured to continuously feed the source iron to the melting
chamber. The electric arc melting facility further comprises a
state change detector configured to detect a state change of the
melting chamber when the electric arc discharge is generated from
the electrode, and a controller configured to adjust a feed rate at
which the source iron feeder feeds the source iron to the melting
chamber, based on a detection result of the state change
detector.
[0019] With this aspect of the present invention, when the source
iron is continuously fed to an electric arc furnace that serves as
the melting chamber to produce molten metal, the state change of
the source iron in the furnace is quickly detected, and the feed
rate of the source iron can be adjusted in accordance with the
detection result. Accordingly, the molten metal in the electric arc
furnace can be maintained in a stable state.
[0020] Further, according to an aspect of the present invention,
the state change detector may be configured to detect a variation
in at least one of current and voltage applied to the electrode, as
the state change of the melting chamber.
[0021] In this way, as the state change of the melting chamber, a
variation in at least one of current and voltage applied to the
electrode is used to quickly and indirectly detect the state change
of the source iron in the furnace, so that the feed rate of the
source iron can be adjusted in accordance with the detection
result.
[0022] Further, according to an aspect of the present invention,
the state change detector may be configured to detect a variation
in at least one of amounts of harmonics contained in the current
and the voltage, as the variation in at least one of the current
and the voltage applied to the electrode.
[0023] In this way, as the state change of the melting chamber, or
as the variation in at least one of the current and the voltage
applied to the electrode, a variation in at least one of amounts of
harmonics contained in the current and the voltage is used to
quickly and indirectly detect the state change of the source iron
in the furnace, so that the feed rate of the source iron can be
adjusted in accordance with the detection result.
[0024] Further, according to an aspect of the present invention,
the state change detector may be configured to detect a value of or
a variation per unit time in at least one of the current and the
voltage, as the variation in at least one of the current and the
voltage applied to the electrode.
[0025] In this way, as the state change of the melting chamber, a
value of or a variation per unit time in at least one of the
current and the voltage applied to the electrode is used to quickly
and indirectly detect the state change of the source iron in the
furnace, so that the feed rate of the source iron can be adjusted
in accordance with the detection result.
[0026] Further, according to an aspect of the present invention,
the state change detector may be configured to detect a variation
in vibration of the furnace body transmitted to the melting chamber
when the electric arc discharge is generated, as the state change
of the melting chamber.
[0027] In this way, as the state change of the melting chamber, a
variation in vibration of the furnace body transmitted to the
melting chamber when the electric arc discharge is generated is
used to quickly and indirectly detect the state change of the
source iron in the furnace, so that the feed rate of the source
iron can be adjusted in accordance with the detection result.
[0028] Further, according to an aspect of the present invention,
the state change detector may be configured to detect a variation
in position of the electrode as the state change of the melting
chamber.
[0029] In this way, as the state change of the melting chamber, a
variation in position of the electrode is used to quickly and
indirectly detect the state change of the source iron in the
furnace, so that the feed rate of the source iron can be adjusted
in accordance with the detection result.
[0030] Further, according to an aspect of the present invention,
there is provided a method for producing molten metal while melting
the source iron by using the electric arc melting facility
described above. The method comprises a state change detecting step
of detecting a state change of the melting chamber when the
electric arc discharge is generated, and a feed rate adjusting step
of adjusting a feed rate at which the source iron is fed to the
melting chamber, based on a detection result in the state change
detecting step.
[0031] With this aspect of the present invention, when the source
iron is continuously fed to an electric arc furnace that serves as
the melting chamber to produce molten metal, the state change of
the source iron in the furnace is quickly detected, and the feed
rate of the source iron can be adjusted in accordance with the
detection result. Accordingly, the molten metal can be produced
while the molten metal in the electric arc furnace is maintained in
a stable state.
[0032] Further, according to an aspect of the present invention,
the method for producing the molten metal may further comprises
adjusting an electric power applied to the electrode, in addition
to the feed rate, based on a detection result by the state change
detector.
[0033] In this way, the electric power applied to the electrode of
the electric arc furnace is adjusted in addition to the feed rate
of the source iron, so that the state of the molten metal can be
further stably controlled.
[0034] The method for producing the molten metal may further
comprises a source iron feeding step of driving a pushing device
disposed at a lower side of a preheating chamber, which is
configured to preheat the source iron therein, to feed the source
iron from the preheating chamber to the melting chamber, a source
iron preheating step of introducing exhaust gas generated in the
melting chamber into the preheating chamber to preheat the source
iron in the preheating chamber, and a source iron melting step of
melting the source iron with heat generated by the electric arc
discharge in the melting chamber while feeding the source iron to
the preheating chamber so as to maintain a state in which the
source iron is present in the preheating chamber and the melting
chamber.
[0035] Consequently, the productivity is further improved, while
the efficiency of heat recovery from the exhaust gas is increased
and the energy efficiency can be thereby sufficiently
increased.
Advantageous Effects of Invention
[0036] According to the present invention, when the source iron,
such as iron scrap, is continuously fed to the electric arc furnace
to produce the molten metal, the state change of the source iron in
the furnace can be quickly detected in an indirect manner. Further,
by adjusting an operation condition in accordance with the
detection, the molten metal in the furnace can be maintained in a
stable state. Accordingly, an operation with high energy efficiency
can be performed without prolonging the melting time of the source
iron.
BRIEF DESCRIPTION OF DRAWINGS
[0037] [FIG. 1] This is a flowchart showing a general operation of
a method for producing molten metal by using an electric arc
melting facility according to an embodiment of the present
invention.
[0038] [FIG. 2] This is an explanatory view showing detection of
current and voltage harmonics along with a scrap feeder control
circuit according to an embodiment of the present invention.
[0039] [FIG. 3] This is an explanatory view showing detection of
current and voltage along with a scrap feeder control circuit
according to an embodiment of the present invention.
[0040] [FIG. 4] This is an explanatory view showing detection of
scrap by using vibration of a furnace body along with a scrap
feeder control circuit according to an embodiment of the present
invention.
[0041] [FIG. 5] This is an explanatory view showing detection of an
electrode position along with a scrap feeder control circuit
according to an embodiment of the present invention.
[0042] [FIG. 6] This is a graph showing changes with time in scrap
feed rate and harmonic distortion ratio. (An example of the present
invention)
[0043] [FIG. 7] This is a graph showing changes with time in scrap
feed rate and harmonic distortion ratio. (A comparative
example)
[0044] [FIG. 8] This is a schematic diagram showing a conventional
scrap-continuous-feed type electric furnace.
[0045] [FIG. 9] This is a schematic diagram showing another
conventional scrap-continuous-feed type electric furnace.
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] Preferred embodiments of the present invention will be
described below in detail. The embodiments described below are not
intended to improperly limit the scope of the present invention
described in the claims. It is not always necessary to include all
of the features described in each of the embodiments to provide the
solution according to the present invention.
[0047] As described above, when a source iron is continuously fed
into an electric arc furnace (a melting chamber) to produce molten
metal, it is difficult to directly observe a state of the source
iron and a state of the molten metal in the electric arc furnace.
In order to address the above-described problems, close attention
has been paid to the following phenomenon in the present invention:
When an amount of source iron in the furnace is increased and the
source iron comes into a state where part of the source iron is
present on the surface of the molten metal near an electrode, an
electric arc is generated from the electrode to the part of the
source iron present on the surface of the molten metal near the
electrode. At this time, noticeable changes appear in state factors
that affect a state of the melting chamber, wherein the state
factors include amounts of harmonics contained in current, amounts
of harmonics contained in voltage, a variation in current, a
variation in voltage, a variation in position of the electrode, and
vibration of the furnace body. Further, in the process of
developing the present invention, the following matters have been
found: When a source iron is excessively fed into the electric arc
furnace and so the source iron is not completely melted but partly
remains on the surface of the molten metal near the electrode,
generation of electric arc discharge from the electrode of the
electric arc furnace to the part of the source iron remaining on
the surface of the molten metal can be indirectly detected by
detecting the above-described state changes of the melting chamber.
Then, the feed rate of the source iron to the electric arc furnace
can be adjusted in accordance with the presence or absence of the
detection of the electric arc discharge, so that the state in the
furnace is maintained stable. It should be noted that, in this
specification, changes in state factors that affect changes in the
state of the melting chamber are each described as the "a state
change of the melting chamber", wherein the state factors include
amounts of harmonics contained in current, amounts of harmonics
contained in voltage, a variation in current, a variation in
voltage, a variation in position of the electrode, and vibration of
the furnace body.
[0048] A method for producing molten metal by using an electric arc
melting facility according to the present invention is described
with reference to the drawings. FIG. 1 is a flowchart showing a
general operation of a method for producing molten metal by using
an electric arc melting facility according to an embodiment of the
present invention.
[0049] A source iron is continuously fed to a melting chamber (a
source iron feeding step S11), and the source iron is melted by
electric arc discharge generated from an electrode (a source iron
melting step S12). Then, a state change of the melting chamber when
the electric arc discharge is generated is detected (a state change
detecting step S13). As described above, if the state of the source
iron is changed every moment, it is practically difficult to
continuously measure the amounts of source iron and molten metal in
the electric furnace. Accordingly, this embodiment is made to
detect a state change of the melting chamber so as to indirectly
detect generation of the electric arc discharge to the source iron
remaining on the surface of the molten metal. When occurrence of a
state change is detected in the state change detecting step S13,
the feed rate for feeding the source iron to the melting chamber is
adjusted (a feed rate adjusting step S14).
[0050] With respect to detection of the generation of the electric
arc discharge from the electrode of the electric arc furnace to the
source iron remaining on the surface of the molten metal in the
furnace, the state change detecting step S13 measures, as the state
change of the electric arc furnace (the melting chamber), at least
one of vibration of the furnace body, a variation in position of
the electrode, a variation in current, a variation in voltage,
amounts of harmonics contained in current, and amounts of harmonics
contained in voltage, and detects a change of such a measured
value. Then, the feed rate adjusting step S14 adjusts the feed rate
of the source iron by using at least one of a plurality of state
changes, or a combination thereof, of the melting chamber detected
by the state change detecting step S13. Specifically, the feed rate
adjusting step S14 stops the feed of the source iron to the melting
chamber when the state change detecting step S13 detects, on the
basis of a variation in amounts of harmonics, the electric arc
discharge generated to the source iron remaining on the surface of
the molten metal due to the excessively fed source iron.
Alternatively, in order to resolve the state in which the source
iron excessively remains in the melting chamber, the feed rate of
the source iron may be controlled to be decreased. Further, in
order to accurately detect the state change of the melting chamber,
the detection may preferably be made based on a plurality of
detection results from among the above-described respective state
changes of the melting chamber. Particularly, the amount of a
harmonic contained in current or voltage is preferably used because
detection is easily carried out and a change is detected properly.
Specifically, the amount of a harmonic is given based on harmonics
obtained through frequency analysis on a result of measurements of
current or voltage fed to the electric arc furnace, and may be used
in a form of a harmonic distortion ratio.
[0051] An example of the electric arc melting facility used in the
present invention comprises an electric arc furnace, a source iron
feeder that continuously feeds a source iron to the electric arc
furnace, a detector for a state change of a melting chamber, and a
controller that adjusts the feed rate of the source iron feeder by
using an output from the detector. The detector for a state change
of the melting chamber is a device that can detect a generation of
the electric arc discharge from an electrode of the electric arc
furnace to the source iron fed into the electric arc furnace.
[0052] Alternatively, the electric power applied to the electric
arc furnace may be adjusted instead of the control on the feed rate
of the source iron. However, if the arc electric power is increased
without the feed rate being changed, a source iron newly fed needs
to be melted in addition to melting of the source iron already
present in the furnace. In this case, a large electric power is
required, and thereby makes it impossible to attain an operation
with high energy efficiency, which is an object of the present
invention. However, it is possible to control both the feed rate of
the source iron and the electric power applied to the electric arc
furnace by using the detected state of the source iron.
[0053] For example, the present invention may be applied to an
electric arc melting facility of the type as described in Patent
Document 2, which comprises a melting chamber configured to melt a
source iron therein, a shaft-type preheating chamber directly
connected to the melting chamber and configured to preheat the
source iron to be fed to the melting chamber, an electrode disposed
in the melting chamber to melt the source iron fed in the melting
chamber, and a pushing device disposed at a lower side of the
preheating chamber and configured to move the source iron, fed from
the preheating chamber, toward the electrode. In this facility, the
present invention can be applied to an operation of melting the
source iron by electric arc heating in the melting chamber, while
introducing exhaust gas generated in the melting chamber into the
preheating chamber to preheat the source iron in the preheating
chamber, and feeding the source iron to the melting chamber so as
to maintain a state in which the source iron is present in the
preheating chamber and the melting chamber. Such an application is
particularly preferable, because it is possible to sufficiently
improve the energy efficiency without deteriorating the
productivity. In this case, a control mechanism is provided to a
driving device of the pushing device to control the feed rate of
the source iron.
[0054] If the above-described electric arc melting facility is
used, the source iron is fed by using the pushing device, and so
the pushing device needs to be returned to the pushing start
position each time when the pushing operation is completed. That
is, the feed is not necessarily performed in a completely
continuous manner. However, even when the feed is not necessarily
performed in a completely continuous manner but repeatedly
performed at predetermined intervals, the feed of the source iron
to the electric arc furnace is regarded as a continuous operation.
A not-continuous-feed means a feed performed in a manner that the
source iron is, for example, collectively dropped by using a basket
etc. like a batch feed, and the feed cannot be stopped in the
middle of a single feed of the source iron to the electric arc
furnace after it is once started.
[0055] The source iron is an object, such as iron scrap or
direct-reduced iron, to be subjected to the melting process in the
electric arc melting facility. The iron scrap includes, for
example, stainless steel scrap, pig iron, mill scales, or
rerollable scrap. The iron scrap is generated, for example, when
steelmaking or other processes are performed by steelmakers, when
processes using iron products are performed in factories, or when
buildings, automobiles, electrical appliances, bridges, etc., are
knocked down.
[0056] Next, respective embodiments according to the present
invention will be described in detail with reference to the
drawings. In the specification and drawings, constituent elements
having substantially the same functional structures are denoted by
the same reference numerals, and redundant explanations thereof are
thus omitted.
First Embodiment
[0057] FIG. 2 is an explanatory view showing a general
configuration of an electric arc melting facility according to a
first embodiment of the present invention, and shows a case in
which the state of scrap inside a furnace is detected by using
harmonics in current or voltage applied to electric arc melting. In
this embodiment, an electric sensor 12 (12a, 12b, and 12c) serving
as a state change detector for detecting a state change of a
melting chamber 1 is connected to a power feed line 11 (11a, 11b,
and 11c) extending to an electric arc furnace 1, to measure a
current waveform or a voltage waveform of the power feed line 11.
The measured waveform is subjected to Fourier transform by a signal
processor 13 to calculate harmonics contained therein, and the
result is input to a controller 6 as a signal-processed state
signal 14 (14a, 14b, and 14c). If the source iron is excessively
fed in the furnace and comes to be present near an electrode, an
electric arc is generated from the electrode to the source iron,
and the harmonics in current or voltage are caused to vary. If the
signal-processed state signal 14 has a value or a variation per
unit time not smaller than a predetermined value, the controller 6
sends a control signal 7 to a scrap feeder 8, which serves as a
source iron feeder, to decrease the scrap feed rate or to stop the
feed. Then, if the measurement value is decreased to another
predetermined value, the controller 6 sends a control signal 7 to
the scrap feeder 8 to increase the scrap feed rate to a
predetermined rate.
[0058] When the in-furnace scrap state is detected by using the
harmonics in current or voltage applied to the electric arc
melting, a harmonic distortion ratio is preferably used as the
signal-processed state signal 14. Specifically, the harmonic
distortion ratio is continuously measured, and two threshold values
(harmonic judgment values) are set such that a higher threshold
value serves as a harmonic judgment value H and a lower threshold
value serves as a harmonic judgment value L. The harmonic judgment
value H is set to such a value that the harmonic distortion ratio
exceeds the harmonic judgment value H if an abnormal event occurs
during melting of the source iron in the electric arc furnace such
that the source iron comes to be present near the electrode. The
harmonic judgment value L is set to such a value that the harmonic
distortion ratio falls below the harmonic judgment value L if
melting of the source iron progresses and the furnace comes to have
a flat bath state therein. In this way, the source iron feed rate
is controlled to be decreased if the harmonic distortion ratio
exceeds the harmonic judgment value H, and increased if the
harmonic distortion ratio falls below the harmonic judgment value
L. Consequently, even if an abnormal event occurs such that the
source iron is excessively fed into the furnace, the state is
immediately restored to a normal state, and the production of
molten metal can be continued in a stable state.
Second Embodiment
[0059] FIG. 3 is an explanatory view showing a general
configuration of an electric arc melting facility according to a
second embodiment of the present invention, and shows a case in
which the state of scrap inside a furnace is detected by using
current or voltage applied to electric arc melting. In this
embodiment, an electric sensor 12 (12a, 12b, and 12c) serving as a
state change detector for detecting a state change of a melting
chamber 1 is connected to a power feed line 11 (11a, 11b, and 11c)
extending to an electric arc furnace 1, to measure current or
voltage of the power feed line 11. If the source iron is
excessively fed in the furnace and comes to be present near an
electrode, an electric arc is generated from the electrode to the
source iron, and the current or voltage is caused to vary. A state
signal 5 (5a, 5b, and 5c) of the electric sensor 12 is input to a
controller 6. If the current or voltage of the power feed line 11
has a value or a variation per unit time not smaller than a
predetermined value, the controller 6 sends a control signal 7 to a
scrap feeder 8, which serves as a source iron feeder, to decrease
the scrap feed rate or to stop the feed. Then, if the measurement
value is decreased to another predetermined value, the controller 6
sends a control signal 7 to the scrap feeder 8 to increase the
scrap feed rate to a predetermined rate.
Third Embodiment
[0060] FIG. 4 is an explanatory view showing a general
configuration of an electric arc melting facility according to a
third embodiment of the present invention, and shows a case in
which the state of source iron inside a furnace is detected by
using vibration of a furnace body. In this embodiment, an
acceleration sensor 4 (a state change detector) serving as a state
change detector for detecting a state change of a melting chamber 1
is attached to an electric arc furnace body (a melting chamber) 1.
The acceleration sensor 4 continuously measures vibration of the
furnace body, and inputs a state signal 5 of the vibration to a
controller 6. If the source iron is excessively fed into the
furnace and comes to be present near an electrode, an electric arc
is generated from the electrode to the source iron, and vibration
of the furnace body is caused to vary. If the measurement value of
the acceleration sensor 4 exceeds a predetermined value, the
controller 6 sends a control signal 7 to a scrap feeder 8, which
serves as a source iron feeder, to decrease the scrap feed rate or
to stop the feed. Then, if the measurement value is decreased to
another predetermined value, the controller 6 sends a control
signal 7 to the scrap feeder 8 to increase the scrap feed rate to a
predetermined rate. Consequently, the state in which the source
iron is excessively fed into the furnace is immediately resolved
and a stable operation can be continued.
Fourth Embodiment
[0061] FIG. 5 is an explanatory view showing a general
configuration of an electric arc melting facility according to a
fourth embodiment of the present invention, and shows a case in
which the state of scrap inside a furnace is detected by using a
variation in position of an electrode. In this embodiment, an
electrode position detector 9 serving as a state change detector
for detecting a state change of a melting chamber 1 is attached to
a movable portion of an electrode elevator 3 for the electrode. The
electrode position detector 9 continuously measures an electrode
position, and inputs a result signal to a controller 6. If the
source iron is excessively fed into the furnace and comes to be
present near the electrode, an electric arc is generated from the
electrode to the source iron, and variations in current and voltage
become large. At this time, the variation in the position of the
electrode is increased so as to change the current value to a set
value. If the variation in the position of the electrode per unit
time exceeds a predetermined value, the controller 6 sends a
control signal 7 to a scrap feeder 8, which serves as a source iron
feeder, to decrease the scrap feed rate or to stop the feed. Then,
if the measurement value is decreased to another predetermined
value, the controller 6 sends a control signal 7 to the scrap
feeder 8 to increase the scrap feed rate to a predetermined
rate.
[0062] In the above-described embodiments, the melting state of the
source iron is controlled by changing the source iron feed rate,
but the state of molten metal can be controlled in a more stable
manner by further adjusting the electric power applied to the
electric arc furnace in addition to the feed rate.
[0063] Further, as described above, each of amounts of harmonics
contained in current, amounts of harmonics contained in voltage, a
variation in current, a variation in voltage, vibration of the
furnace body, and a variation in position of the electrode can be
individually used for detecting the state of the source iron.
However, a combination of two or more of them may be used, so that
the scrap state is figured out more correctly and the state in the
furnace can be stabled more reliably. For example, a variation in
the electric arc current is used along with the amount of harmonics
contained in the electric arc current to detect the scrap
state.
EXAMPLE 1
[0064] A melting test for iron scrap was performed by using the
electric arc melting facility shown in FIG. 2.
[0065] FIG. 6 shows an example in which the harmonics in current
fed to the electrode were measured and the scrap feed rate was
changed in the method for producing molten metal by using the
electric arc melting facility according to the first embodiment
described above. The scrap was fed to the electric arc furnace at a
constant rate and a harmonic distortion ratio was obtained by a
harmonic analyzer disposed at each measurement point of the
electric arc current. It should be noted that the harmonic
distortion ratio represents a percentage of the sum of effective
values of all generated harmonics with respect to an effective
value of a reference frequency.
[0066] The present example is configured to determine that scrap
comes to be present near the electrode inside the furnace, when the
harmonic distortion ratio exceeds a predetermined value (the
harmonic judgment value H), and to stop the scrap feed. As the
scrap inside the furnace is increased, the harmonic distortion
ratio is also increased. If the scrap feed is stopped when the
value exceeds the harmonic judgment value H (time "a" in FIG. 6),
the scrap melting progresses and the harmonic distortion ratio is
caused to be gradually decreased. The decrease in harmonic
distortion ratio represents a state in which an electric arc is
generated to molten metal and the scrap is not present near the
electrode any more.
[0067] When the harmonic distortion ratio is detected as being
decreased to a predetermined value (the harmonic judgment value L)
(time "b" in FIG. 6), the scrap feed is restarted at a
predetermined rate. In this way, the state change inside the
furnace was quickly detected, and the state was immediately
restored to a normal state, so that the scrap melting was
continued.
[0068] FIG. 7 shows a comparative example relative to the present
invention, and shows a case in which the scrap feed rate is not
changed even if a harmonic distortion ratio of the electric arc
current is increased. If the present invention is used, the scrap
feed is stopped or decreased in feed rate at a time "a" in FIG. 7.
However, since the scrap was continued to be fed, the scrap amount
in the furnace was increased, and the harmonic distortion ratio was
increased, so that this state was being continued. That is, the
scrap was not completely melted and kept remaining. Since the
operation was continued under this condition, an excessive amount
of energy was required, and a melting time was also greatly
prolonged. Consequently, the energy efficiency was lowered, and the
productivity was deteriorated.
[0069] Although various preferable embodiments of the present
invention have been described above with reference to the
accompanying drawings, the present invention is not limited to the
above-described embodiments. It is obvious to those skilled in the
art that various alterations and modifications can be made within
the scope described in the claims, and that such alterations and
modifications also belong to the technical scope of the present
invention, as a matter of course.
REFERENCE SIGNS LIST
[0070] 1 electric arc furnace (melting chamber)
[0071] 2 (2a, 2b, 2c) electrode
[0072] 3 electrode elevator
[0073] 4 acceleration sensor (state change detector)
[0074] 5 (5a, 5b, 5c) state signal
[0075] 6 controller
[0076] 7 control signal
[0077] 8 scrap feeder (source iron feeder)
[0078] 9 electrode position detector (state change detector)
[0079] 10 power supply
[0080] 11 (11a, 11b, 11c) power feed line
[0081] 12 (12a, 12b, 12c) electric sensor (state change
detector)
[0082] 13 signal processor
[0083] 14 (14a, 14b, 14c) signal-processed state signal
[0084] 15 scrap (source iron)
[0085] 16 preheating chamber
[0086] 17 pushing device
[0087] 20 molten metal
[0088] 21 electric arc
[0089] 22 electric arc melting facility
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