U.S. patent application number 11/794609 was filed with the patent office on 2007-12-27 for method for melting magnesium and melting apparatus.
Invention is credited to Toru Kato, Toru Nakamura, Yuji Nomura, Hiroshi Sanui.
Application Number | 20070295166 11/794609 |
Document ID | / |
Family ID | 36692316 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295166 |
Kind Code |
A1 |
Sanui; Hiroshi ; et
al. |
December 27, 2007 |
Method for Melting Magnesium and Melting Apparatus
Abstract
An object of the present invention is to provide a melting
method for magnesium or a magnesium alloy which detects certainly
and immediately combustion of a magnesium melt and emits alarm
immediately based on the detection results, and extinguishes
immediately the magnesium combustion, in order to achieve the
object, the present invention provide a method for melting
magnesium while supplying a cover gas containing carbon dioxide and
a fireproof agent in a furnace for melting magnesium and obtaining
a magnesium melt to cover the surface of the magnesium melt,
wherein concentration of carbon monoxide in the furnace or gas
discharged from the furnace is measured and magnesium combustion in
the furnace is detected based on the concentration of carbon
monoxide.
Inventors: |
Sanui; Hiroshi; (Kai-shi,
JP) ; Nomura; Yuji; (Kai-shi, JP) ; Kato;
Toru; (Komaki-shi, JP) ; Nakamura; Toru;
(Nagoya-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
36692316 |
Appl. No.: |
11/794609 |
Filed: |
January 19, 2006 |
PCT Filed: |
January 19, 2006 |
PCT NO: |
PCT/JP06/00753 |
371 Date: |
July 3, 2007 |
Current U.S.
Class: |
75/602 ;
266/81 |
Current CPC
Class: |
Y02P 10/253 20151101;
C22B 26/22 20130101; C22B 9/003 20130101; C22B 9/006 20130101; B22D
21/007 20130101; Y02P 10/25 20151101 |
Class at
Publication: |
075/602 ;
266/081 |
International
Class: |
C22B 9/00 20060101
C22B009/00; C22B 26/22 20060101 C22B026/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 20, 2005 |
JP |
2005-012580 |
Claims
1. A method for melting magnesium or a magnesium alloy while
supplying a cover gas containing carbon dioxide and a fireproof
agent in a furnace for melting magnesium or a magnesium alloy and
obtaining a magnesium melt or a magnesium alloy melt to cover the
surface of the magnesium melt, wherein a concentration of carbon
monoxide in the furnace or gas discharged from the furnace is
measured and magnesium combustion in the furnace is detected based
on the concentration of carbon monoxide.
2. A method for melting magnesium according to claim 1, wherein the
magnesium combustion is prevented by increasing a flow rate of the
cover gas or concentration of the fireproof agent contained in the
cover gas when magnesium combustion is confirmed.
3. A method for melting magnesium according to claim 1, wherein the
fireproof agent is
1,1,1,2,2,4,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone.
4. A melting apparatus for magnesium comprising: a furnace for
melting magnesium and obtaining a magnesium melt; a cover gas
supplying portion for supplying a cover gas containing carbon
dioxide and a fireproof agent in the furnace; a carbon monoxide
concentration meter for measuring concentration of carbon monoxide
in the furnace or gas discharged from the furnace; and a control
portion for controlling a supply rate of the fireproof agent in the
furnace based on the concentration of carbon monoxide measured by
the carbon monoxide concentration meter.
5. A melting apparatus for magnesium comprising: a furnace for
melting magnesium and obtaining a magnesium melt; a cover gas
supplying portion for supplying a cover gas containing carbon
dioxide and a fireproof agent in the furnace; a carbon monoxide
concentration meter for measuring a concentration of carbon
monoxide in the furnace or gas discharged from the furnace; and a
control portion for controlling a supply rate of the cover gas in
the furnace based on the concentration of carbon monoxide measured
by the carbon monoxide concentration meter.
6. A melting apparatus for magnesium according claim 4, wherein the
control portion has signal generation function which emits a signal
showing magnesium combustion when magnesium combustion is
confirmed, and a display portion for showing magnesium combustion
based on the signal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and a melting
apparatus for melting magnesium or a magnesium alloy and obtaining
a magnesium melt or a magnesium alloy melt, in which combustion at
the surface of the magnesium melt or the magnesium alloy melt is
detected and rapidly extinguished.
[0002] Priority is claimed on Japanese Patent Application No.
2005-012580 filed on Jan. 20, 2005, the contents of which are
incorporated herein by reference.
BACKGROUND ART
[0003] When magnesium or a magnesium alloy (hereinafter "magnesium"
means both magnesium and a magnesium alloy in the present
invention) is melted in a furnace to obtain a magnesium melt, the
vicinity of the surface of the melt has been covered with a cover
gas in order to prevent combustion of magnesium at the melt
surface.
[0004] Examples of the cover gas include a gas in which a fireproof
agent such as sulfur hexafluoride, and sulfur dioxide is diluted
with an inactive gas such as nitrogen.
[0005] A reaction between the fireproof agent in the cover gas with
the melt magnesium produces a protective film at the melt surface.
The protective film blocks contact between the melt magnesium and
oxygen in air, and thereby combustion of the magnesium melt is
prevented.
[0006] If the magnesium melt bums by any chance, not only the
furnace is damaged, an amount of the magnesium melt itself
decreases and economical damage is caused, but also safety problem
due to a fire hazard is caused. The combustion of a magnesium melt
has been detected by detecting white smoke of magnesium oxide which
is generated by combustion, or a temperature increase of the
magnesium melt. In addition, combustion of a magnesium melt is also
detected by detecting a temperature increase in a furnace as
disclosed in Japanese Unexamined Patent Application, First
Publication No. 2001-234253.
[0007] However, it is difficult to detect combustion of magnesium
within a short time from combustion starts by detecting white
smoke, temperature increase of the melt, or temperature increase in
a furnace, and this has poor reliability.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Present Invention
[0008] The problems to be solved by the present invention is to
detect certainly and immediately combustion of a magnesium melt
during magnesium melting, to extinguish immediately the magnesium
combustion based on the detection results, and to set off an
alarm.
Means for Solving the Problem
[0009] In order to solve the problems, the present invention
provides a method for melting magnesium while supplying a cover gas
containing carbon dioxide and a fireproof agent in a furnace for
melting magnesium and obtaining a magnesium melt to cover the
surface of the magnesium melt, wherein concentration of carbon
monoxide in the furnace or gas discharged from the furnace is
measured and magnesium combustion in the furnace is detected based
on the concentration of carbon monoxide.
[0010] In the method for melting magnesium, it is preferable that
the magnesium combustion can be prevented by increasing a flow rate
of the cover gas or concentration of the fireproof agent contained
in the cover gas when magnesium combustion is confirmed.
[0011] In the method for melting magnesium, it is preferable that
the fireproof agent be
1,1,1,2,2,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone.
[0012] In addition, in order to solve the problems, the present
invention provides a melting apparatus for magnesium comprising a
furnace for melting magnesium and obtaining a magnesium melt; a
cover gas supplying portion for supplying a cover gas containing
carbon dioxide and a fireproof agent in the furnace; a carbon
monoxide concentration meter for measuring concentration of carbon
monoxide in the furnace or gas discharged from the furnace; and a
control portion for controlling a supply rate of the fireproof
agent in the furnace based on the concentration of carbon monoxide
measured by the carbon monoxide concentration meter.
[0013] Furthermore, in order to solve the problems, the present
invention provides another melting apparatus for magnesium
comprising a furnace for melting magnesium and obtaining a
magnesium melt; a cover gas supplying portion for supplying a cover
gas containing carbon dioxide and a fireproof agent in the furnace;
a carbon monoxide concentration meter for measuring concentration
of carbon monoxide in the furnace or gas discharged from the
furnace; and a control portion for controlling a supply rate of the
cover gas in the furnace based on the concentration of carbon
monoxide measured by the carbon monoxide concentration meter.
[0014] In these melting apparatus for magnesium, it is preferable
that the control portion have signal generation function which
emits a signal showing magnesium combustion when magnesium
combustion is confirmed, and a display portion for showing
magnesium combustion based on the signal.
Effects of the Present Invention
[0015] The present inventors found that when carbon dioxide is
added in a cover gas, and a magnesium melt bums, concentration of
carbon monoxide in the cover gas immediately is increased. It is
possible to detect and judge the combustion immediately and
certainly by measuring the concentration of carbon monoxide.
Therefore, if a magnesium melt bums by any chance, the combustion
is promptly extinguished.
[0016] In addition, since combustion was prevented by constantly
supplying excess flow rate of the cover gas or the fireproof agent
in the cover gas, conventional methods required a high cost. In
contrast, it is possible to increase the flow rate of the cover gas
or the fireproof agent to extinguish immediately after combustion
is detected. Therefore, it is not necessary to supplying supply an
excess amount of the cover gas or the fireproof agent, and thereby
it is possible to decrease cost.
[0017] Furthermore, it is also possible to extinguish
automatically, and control automatically the flow rate of the cover
gas and supply rate of the fireproof agent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] [FIG. 1] FIG. 1 is a schematic diagram showing an embodiment
of the melting apparatus according to the present invention.
[0019] [FIG. 2] FIG. 2 is a schematic diagram showing another
embodiment of the melting apparatus according to the present
invention.
[0020] [FIG. 3] FIG. 3 is diagram showing variation with time of
concentration of carbon monoxide in Experimental Example.
EXPLANATION OF REFERENCE SYMBOLS
[0021] TABLE-US-00001 1: furnace 2: crucible 3: heater 4: sensor 5:
carbon monoxide concentration meter 6: control portion 9: flow
regulating valve 11 and 14: on-off valve 7, 8, 10, and 15: pipe 13:
display portion M: melting
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] FIG. 1 is a schematic diagram showing an embodiment of the
melting apparatus according to the present invention. In FIG. 1, a
reference symbol 1 denotes a furnace. The furnace 1 is made of
heat-resistant bricks, etc., and a crucible 2 for melting magnesium
made of graphite, etc. is positioned therein. Magnesium in the
crucible 2 is heated and melt by a heater 3 and becomes a magnesium
melt.
[0023] A sensor 4 for measuring the concentration of carbon
monoxide contained in the furnace 1 is positioned in the upper
portion of the crucible 2 in the furnace 1. Signals from the sensor
4 are input to a carbon monoxide concentration meter 5.
[0024] The signals for the concentration of carbon monoxide output
from the carbon monoxide concentration meter 5 are input to a
control portion 6. At the control portion 6, the input signals are
handled in a PID controller to output control signals. When the
concentration of carbon monoxide excesses an upper limit which is
previously fixed, the control portion 6 receives signals for carbon
monoxide concentration from the carbon monoxide concentration meter
5, and sends an alarm signal to a display portion 13 such as a
warning light and a warning buzzer.
[0025] A cover gas is supplied in the furnace 1 through a pipe 7,
and thereby at least the vicinity of the surface of the melt in the
crucible 2 in the furnace 1 is covered with the cover gas.
[0026] The cover gas contains a fireproof agent and a diluent gas.
Examples of the fireproof agent include organic fluorine-containing
compounds which are gaseous materials reacting with melted
magnesium and forming a protective film at the surface of the melt
such as sulfur hexafluoride, sulfur dioxide, FREON.RTM. 113a, or
1,1,1,2,2,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone.
Among these,
1,1,1,2,2,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone is
preferable because it has a low global warming potential.
[0027] Examples of the diluent gas include a gas containing at
least carbon dioxide such as carbon dioxide, a mixture containing
carbon dioxide, and air. The content of carbon dioxide in the
diluent gas is preferably 0.1% or more, and more preferably 1% or
more, in volume.
[0028] The fireproof agent is sent to a flow regulating valve 9
through a pipe 8 from a fireproof agent supplying source which is
not shown in FIG. 1, and the flow rate of the fireproof agent is
controlled based on the control signals from the control portion 6,
and then the fireproof agent is sent to a pipe 7 at the controlled
flow rate.
[0029] In contrast, the diluent gas passes through a pipe 10 from a
diluent gas source which is not shown in FIG. 1 to an on-off valve
11, and this is further sent to the pipe 7. The diluent gas is
mixed with the fireproof agent in the pipe 7 to be a cover gas, and
then sent in the furnace 1.
[0030] In other words, a cover gas supplying portion comprises the
pipes 7, 8, and 10, the flow regulating valve 9, and the on-off
valve 11.
[0031] The operations of the melting apparatus will be explained
below.
[0032] Magnesium in the crucible 2 is heated and melt to obtain a
melt. At this time, the cover gas containing at least carbon
dioxide and the fireproof agent is constantly supplied in the
furnace 1 by supplying the fireproof agent from the pipe 8 and the
diluent gas from the pipe 10.
[0033] The concentration of the fireproof agent in the cover gas
varies depending on the kinds of the fireproof agent, the surface
area of the melt magnesium, melting conditions, etc. However, when
the fireproof agent is
1,1,1,2,2,4,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone,
the concentration of the fireproof agent in the cover gas is
commonly in a range from 100 to 400 ppm in volume (below, ppm means
ppm in volume without special note). When the concentration of
1,1,1,2,2,4,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone in
the cover gas is adjusted to this range, it is possible to prevent
the combustion of magnesium.
[0034] While the cover gas is continuously supplied in the furnace
1, the concentration of carbon monoxide in the furnace 1 is
measured by the sensor 4 and the carbon monoxide concentration
meter 5, and the signal for the concentration is sent to the
control portion 6.
[0035] When the magnesium melt in the furnace 1 does not burn, the
concentration of carbon monoxide in the furnace 1 is almost
maintained at low values, for example, less than 10 ppm.
[0036] If the magnesium melt in the crucible 2 burns by any chance,
the concentration of carbon monoxide in the furnace 1 is suddenly
increased, for example, to 15 to 20 ppm. The increase of the
concentration of carbon monoxide is caused by forcibly reacting
oxygen constituting carbon dioxide in the cover gas with magnesium
as oxygen needed to burn, as shown in the following chemical
formula. Mg+CO.sub.2.fwdarw.MgO+CO
[0037] The control portion 6 judges that magnesium melt burns based
on the rapid increase of the concentration of carbon monoxide, and
sends a signal to the flow regulating valve 9 to increase the flow
rate of the fireproof agent while sending an alarm signal to the
display portion 13.
[0038] When the display portion 13 receives the alarm signal, an
alarm light blinks or a speaker beeps.
[0039] In addition, when the flow regulating valve 9 receives the
signal, this increases the open level to increase the flow rate of
the fireproof agent and thereby a large amount of the fireproof
agent is sent to the pipe 7. Due to this, the cover gas containing
the fireproof agent with high concentration such as 500 to 20,000
ppm is sent in the furnace 1 to extinguish the combustion of
magnesium.
[0040] The extinguishing of the combustion is confirmed by the
decrease of the concentration of carbon monoxide by the carbon
monoxide concentration meter 5. Specifically, when the
concentration of carbon monoxide is 10 ppm or less, it is judged
that the combustion is extinguished. When the control portion 6
judges that the combustion has been extinguished based on the
decrease of the concentration of carbon monoxide, the control
portion 6 stops sending the alarm signal to the display portion
13.
[0041] In addition, the control portion 6 sends a signal to the
flow regulating valve 9 to decrease of the flow rate of the
fireproof agent. The flow regulating valve 9 decreases the open
level to decrease the flow rate of the fireproof agent, and
supplies the cover gas having a normal concentration via the pipe 7
in the furnace 1.
[0042] As explained above, it is possible to detect rapidly the
combustion of the magnesium melt by measuring the concentration of
carbon monoxide in the furnace 1. When the combustion of the
magnesium melt is confirmed, it is possible to extinguish the
combustion by increasing immediately the amount of the fireproof
agent contained in the cover gas.
[0043] In addition, after the combustion has been extinguished, it
is possible to decrease automatically the amount of the fireproof
agent in the cover gas to the normal amount. Therefore, if the
magnesium burns by any chance, it is possible to extinguish the
combustion automatically, and it is also possible to return
automatically to normal operations after extinction.
[0044] FIG. 2 is a schematic diagram showing another embodiment of
the melting apparatus according to the present invention. The
components shown in FIG. 2 which are the same as the components
shown in FIG. 1 have the same reference numerals as shown in FIG.
1. Thereby, explanations for those same components are omitted in
this embodiment.
[0045] In this embodiment, the carbon monoxide concentration meter
5 comprises an output device. The carbon monoxide concentration
meter 5 with an output device measures the concentration of carbon
monoxide in the furnace 1, and when the measured concentration
excesses the upper limit which is previously fixed, for example, 15
ppm, this sends an alarm signal the display portion 13 while
outputting a signal showing that the concentration of carbon
monoxide excesses the upper limit to the on-off valve 14. In
contrast, when the concentration is less than the upper limit, the
concentration meter 5 with an output device instructs the display
portion 13 to shut off the alarm while outputting a signal showing
that the concentration of carbon monoxide is less than the upper
limit to the on-off valve 14. The carbon monoxide concentration
meter 5 with an output device has the same functions as those of
the control portion 6 as well.
[0046] When the on-off valve 14 receives the signal showing that
the concentration excesses the upper limit from the carbon monoxide
concentration meter 5, the on-off valve 14 opens. In contrast, when
the on-off valve 14 receives the signal showing that the
concentration is less than the upper limit from the carbon monoxide
concentration meter 5, the on-off valve 14 closes. The on-off valve
14 allows or blocks the flow of the fireproof agent via the pipe 8.
At normal conditions, the on-off valve 14 blocks the flow of the
fireproof agent.
[0047] The cover gas containing carbon dioxide and the fireproof
agent is sent constantly from the pipe 15 in the furnace 1. The
concentration of the fireproof agent in the cover gas is adjusted
in a range from 100 to 400 ppm, and thereby the combustion of
magnesium is prevented.
[0048] In other words, the cover gas supplying portion comprises
the pipes 7, 8, 15, and the on-off valve 14.
[0049] In order to operate the melting apparatus, first, the cover
gas is constantly supplied from the pipe 15 in the furnace 1, and
the concentration of carbon monoxide in the furnace 1 is
continuously measured by the carbon monoxide concentration meter
5.
[0050] When the concentration of carbon monoxide in the furnace 1
is less than the upper limit, it is judged that the magnesium melt
is not burning, and the cover gas is continuously supplied in the
furnace 1 from the pipe 15.
[0051] When the concentration of carbon monoxide in the furnace 1
excesses the upper limit, it is judged that the magnesium melt is
burning, and a signal showing that the magnesium melt is burning is
sent to the on-off valve 14. When the on-off valve 14 receives the
signal, the on-off valve 14 immediately opens, and allows the
fireproof agent flow from the pipe 8 to the pipe 7 and allows the
concentration of the fireproof agent to be in a range from 500 to
20,000 ppm. Simultaneously, the carbon monoxide concentration meter
5 sends an alarm signal to the display portion 13.
[0052] When the concentration of carbon monoxide in the furnace 1
is less than the upper limit, it is judged that the combustion of
the magnesium has been extinguished, and the carbon monoxide
concentration meter 5 sends a signal showing that the combustion
has been extinguished to the on-off valve 14 and the display
portion 13. After that, the on-off valve 14 closes and the display
portion 13 stops warming notice.
[0053] Due to this, the cover gas containing the fireproof agent at
normal concentration is again sent in the furnace 1 from the pipe
15.
[0054] The melting apparatus of this embodiment obtains the same
effects as those of the melting apparatus in the previous
embodiment.
[0055] Below, experimental results obtained using the melting
apparatus will be shown.
EXPERIMENTAL EXAMPLE
[0056] In this Example, the melting apparatus shown in FIG. 1 was
used. The inner diameter of the furnace 1 was 300 mm, and the
height was 670 mm. The inside of the furnace 1 could be watched
through the heat-resistant glass in the furnace cover.
[0057] The crucible 2 having an inner diameter of 200 mm and a
height of 300 mm was positioned in the furnace 1. A magnesium melt,
which was obtained by melting 4.7 kg of magnesium alloy (AD91D),
was put in the crucible 2. The temperature of the magnesium melt
was maintained at 680.degree. C.
[0058] A diluted gas, which was obtained by diluting
1,1,1,2,2,4,4,5,5,5,-nonafluoro-4-(trifluoromethyl)-3-pentanone
which is a fireproof agent with carbon dioxide such that the
concentration be 200 ppm, was used as a cover gas. The cover gas
was supplied to the furnace 1 from the pipe 7 at a rate of 7.5
litter/min. The concentration of carbon monoxide in the furnace 1
was measured by the sensor 4 and the carbon monoxide concentration
meter 5.
[0059] The variation of the concentration of carbon monoxide with
time is shown in FIG. 3.
[0060] When combustion of magnesium in the crucible 2 was not
confirmed visually through the heat-resistant glass, the
concentration of carbon monoxide remained constant at about 7
ppm.
[0061] When combustion of a part of the magnesium melt was observed
(point A), the concentration of carbon monoxide increased suddenly
to 17.5 ppm.
[0062] After immediately the combustion of the magnesium melt was
confirmed, the open level of the flow regulating valve 9 was
increased in order to decrease the supply rate of the fireproof
agent, and the concentration of the fireproof agent in the cover
gas was increased to 800 ppm. Thereby, the concentration of carbon
monoxide was decreased, and after 90 seconds, the concentration
returned to 7 ppm which was the normal concentration. It was
confirmed that the combustion was extinguished by visual
observation.
[0063] It was judged from the results that when the concentration
of carbon monoxide in the furnace 1 was suddenly larger than the
normal concentration, combustion of the magnesium happened. Then,
it was also confirmed that the combustion was extinguished by
increasing the concentration of the fireproof agent in the cover
gas.
[0064] In Experimental Examples, when the concentration of carbon
monoxide increased and the combustion of the magnesium was
confirmed, the concentration of the fireproof agent in the cover
gas increased. However, it is also possible to increase the supply
rate of the cover gas itself to the furnace. For example, it is
also possible to increase the supply rate of the cover gas to the
furnace by replacing the on-off valve 11 in FIG. 1 to a flow
regulating valve, and sending the signal from the control portion 6
to the flow regulating valve.
[0065] In addition, the concentration of carbon monoxide in the
furnace 1 was measured. However, the concentration of carbon
monoxide is also measured by forming a discharge pipe for
discharging gas in the furnace 1, and measuring the concentration
of carbon monoxide in the discharged gas.
[0066] Furthermore, the concentration of carbon monoxide may be
measured continuously or intermittently, for example, each 10 to 20
seconds by the concentration meter 5.
INDUSTRIAL APPLICABILITY
[0067] The present inventors found that when carbon dioxide is
added in a cover gas, and a magnesium melt burns, concentration of
carbon monoxide in the cover gas immediately increases. It is
possible to detect and judge the combustion immediately and
certainly by measuring the concentration of carbon monoxide.
Therefore, if a magnesium melt burns by any chance, the combustion
is promptly extinguished.
[0068] In addition, since combustion was prevented by supplying
constantly excess flow rate of the cover gas or the fireproof agent
in the cover gas, conventional methods required a high cost. In
contrast, it is possible to increase the flow rate of the cover gas
or the fireproof agent immediately after a combustion is detected
and to extinguish it. Therefore, it is not necessary to supply
constantly an excess amount of the cover gas or the fireproof
agent, and thereby it is possible to decrease the cost.
[0069] Furthermore, it is also possible to extinguish
automatically, control automatically the flow rate of the cover
gas, and the supply rate of the fireproof agent.
* * * * *