U.S. patent application number 13/234377 was filed with the patent office on 2012-03-08 for process for producing semi-solidified slurry of iron alloy.
This patent application is currently assigned to Kogi Corporation. Invention is credited to Yasushi Fujinaga, Yoshihito Isshiki, Susumu Nishikawa, Minoru Sasaki, Syuichi Shikai.
Application Number | 20120055284 13/234377 |
Document ID | / |
Family ID | 45769682 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120055284 |
Kind Code |
A1 |
Shikai; Syuichi ; et
al. |
March 8, 2012 |
PROCESS FOR PRODUCING SEMI-SOLIDIFIED SLURRY OF IRON ALLOY
Abstract
A process for producing a semi-solidified slurry of an iron
alloy including the steps of pouring a melt of an iron alloy into a
semi-solidified slurry producing vessel 30 and cooling the melt
therein to obtain a semi-solidified slurry having a crystallized
solid phase and a residual liquid phase, wherein a hypereutectoid
or hypoeutectic cast iron composition containing 0.8-4.3 wt. % C is
used as a material, a melt of the composition is poured into the
semi-solidified slurry producing vessel in a predetermined amount
at a time, a temperature of the melt when poured into the
semi-solidified slurry producing vessel is controlled to be not
lower than a crystallization initiation temperature of the
composition and not greater than a temperature that is 50.degree.
C. higher than the crystallization initiation temperature, and a
cooling rate of the melt poured into the semi-solidified slurry
producing vessel is controlled not to exceed 20.degree. C. per
minute.
Inventors: |
Shikai; Syuichi;
(Himeji-shi, JP) ; Fujinaga; Yasushi; (Himeji-shi,
JP) ; Sasaki; Minoru; (Himeji-shi, JP) ;
Isshiki; Yoshihito; (Himeji-shi, JP) ; Nishikawa;
Susumu; (Himeji-shi, JP) |
Assignee: |
Kogi Corporation
Hyogo
JP
|
Family ID: |
45769682 |
Appl. No.: |
13/234377 |
Filed: |
September 16, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12449368 |
Aug 5, 2009 |
|
|
|
PCT/JP2007/051987 |
Feb 6, 2007 |
|
|
|
13234377 |
|
|
|
|
Current U.S.
Class: |
75/10.15 ;
75/584 |
Current CPC
Class: |
C21C 5/5241 20130101;
F27B 14/20 20130101; C21D 1/42 20130101; C22C 37/10 20130101; C21C
1/08 20130101; C21D 5/00 20130101; C22C 33/08 20130101; Y02P 10/25
20151101; Y02P 10/253 20151101; F27B 14/14 20130101 |
Class at
Publication: |
75/10.15 ;
75/584 |
International
Class: |
C21C 7/00 20060101
C21C007/00; C22B 9/00 20060101 C22B009/00 |
Claims
1. A process for producing a semi-solidified slurry of an iron
alloy comprising the steps of: pouring a melt of an iron alloy into
a semi-solidified slurry producing vessel; and cooling the melt in
the vessel to obtain a semi-solidified slurry having a crystallized
solid phase and a residual liquid phase; wherein a hypereutectoid
or hypoeutectic cast iron composition containing 0.8-4.3 wt. % C is
used as a material, a melt of the composition is poured into the
semi-solidified slurry producing vessel in a predetermined amount
at a time, a temperature of the melt when poured into the
semi-solidified slurry producing vessel is controlled to be not
lower than a crystallization initiation temperature of the
composition and not greater than a temperature that is 50.degree.
C. higher than the crystallization initiation temperature, and a
cooling rate of the melt poured into the semi-solidified slurry
producing vessel is controlled not to exceed 20.degree. C. per
minute.
2. The process for producing a semi-solidified slurry of an iron
alloy according to claim 1, wherein above the semi-solidified
slurry producing vessel, the melt poured from a ladle is once
received in a relay and damper vessel in a predetermined amount at
a time, and the melt received in the relay and damper vessel is
then poured into the semi-solidified slurry producing vessel via a
discharge port provided at a bottom of the relay and damper vessel,
a diameter of the discharge port is not less than 10 mm, a
temperature of the discharged melt at the discharge port is
controlled to be not lower than a temperature that is 20.degree. C.
higher than the crystallization initiation temperature of the
composition and not greater than a temperature that is 80.degree.
C. higher than the crystallization initiation temperature, a
preheating temperature of the semi-solidified slurry producing
vessel is not less than 400.degree. C. lower than the
crystallization initiation temperature of the composition and not
greater than a temperature that is 200.degree. C. higher than the
crystallization initiation temperature, and a height of the relay
and damper vessel from the semi-solidified slurry producing vessel
is not less than 100 mm.
3. The process for producing a semi-solidified slurry of an iron
alloy according to claim 2, wherein the melt is cooled by wind
while the melt is falling from the relay and damper vessel down
into the semi-solidified slurry producing vessel.
4. The process for producing a semi-solidified slurry of an iron
alloy according to claim 2, wherein energy caused by the melt
falling from the reply and damper vessel down into the
semi-solidified slurry producing vessel is used to stir the melt
within the semi-solidified slurry producing vessel.
5. The process for producing a semi-solidified slurry of an iron
alloy according to claim 2-4, wherein a semi-solidified slurry
produced is taken out in the state where the semi-solidified slurry
producing vessel is heated by high-frequency induction heating such
that part of the semi-solidified slurry that is in contact with the
semi-solidified slurry producing vessel is heated via the
semi-solidified slurry producing vessel.
Description
[0001] This application is a Continuation-in-part of pending U.S.
application Ser. No. 12/449,368, filed Aug. 5, 2009, which was a
national stage of PCT/JP2007/051987, filed on Feb. 6, 2007.
TECHNICAL FIELD
[0002] The present invention relates to a process for producing a
semi-solidified slurry of an iron alloy. More particularly, the
present invention relates to a process for producing a
semi-solidified slurry of an iron alloy such as a cast iron, by
cooling the iron alloy from a molten state to obtain a
semi-solidified slurry in a solid-liquid coexisting state with a
solid phase developed in the melt.
BACKGROUND ART
[0003] A semi-solidified state refers to the state where a metallic
material cooled from a liquid (melt) state has attained a
solid-liquid coexisting state.
[0004] The metallic material in the solid-liquid coexisting state
may be obtained by a semi-solid process (rheometal process) or a
semi-melt process (thixometal process). For example, rheocasting is
a molding process using the semi-solid process, and thixocasting is
a molding process using the semi-melt process.
[0005] Processing the metal in the semi-solidified state or in the
semi-molten state is generally advantageous in that finer and more
homogenous crystal grains can be obtained.
[0006] Comparing the semi-solid molding process with the semi-melt
molding process generally, assuming a mass production, the
semi-solid molding process is more advantageous because less energy
is lost. In consideration of application to small-scale lots,
however, the semi-melt molding process may consume less energy
because the process can be made in a necessary quantity as
required. This means that it will be desirable to use both the
semi-solid molding process and the semi-melt molding process
depending on the circumstances.
[0007] Various processes for producing semi-solidified metallic
slurries according to the semi-solid molding process have been
proposed, which include: a process for producing a semi-solidified
metal by applying mechanical stirring during a cooling process
(Patent Document 1); rheocasting process and rheocasting apparatus
using an inclined cooling plate (Patent Document 2); and an
apparatus for producing a solid-liquid co-existing metallic slurry
by applying electromagnetic stirring (Patent Document 3). [0008]
Patent Document 1: Japanese Patent Application Laid-Open No.
6-297097 [0009] Patent Document 2: Japanese Patent Application
Laid-Open No. 10-34307 [0010] Patent Document 3: Japanese Patent
Application Laid-Open No. 2005-88083
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] With the process configured to apply mechanical stirring as
disclosed in Patent Document 1 above, however, in the case of a
material with a high melting point such as a cast iron, a stirrer 1
as shown in FIG. 7 of the present application may deteriorate
easily, or its components may melt in. There is essentially no
stirrer 1 that can be put into practical use. With the process
using the inclined cooling plate as disclosed in Patent Document 2
above, the inclined cooling plate may deteriorate easily again if
it is used for solidification of a high melting point material.
Furthermore, a molten metal coming into contact with the inclined
cooling plate may solidify and adhere thereto. This technique
requires subtle and delicate temperature control as well as
operation control of the inclined cooling plate.
[0012] Furthermore, with the process configured to apply
electromagnetic stirring as disclosed in Patent Document 3 above,
the viscosity of the melt needs to be kept low in order to realize
substantial stirring. The resultant slurry has a low solid fraction
of about 20% or less. When the slurry with such a low solid
fraction is subjected to die casting or other molding process,
defects including blow holes will increase.
[0013] In view of the foregoing, an object of the present invention
is to solve the conventional problems as described above, and to
provide a process for producing a semi-solidified slurry of an iron
alloy, wherein an iron alloy, particularly a cast iron, is used to
obtain a favorable semi-solidified slurry which will suffer fewer
blow holes when molded by die casting or the like, without
performing mechanical stirring requiring a stirrer, without using a
special facility for electromagnetic stirring, and without using
special contact flow-down means like the inclined cooling
plate.
Means for Solving the Problems
[0014] To achieve the above object, the present inventors have
diligently carried out various experiments and examinations. As a
result, they have found that a semi-solidified slurry of a given
solid fraction may be produced by appropriately controlling the
temperature during the process where a melt is solidified, without
the need of mechanical or electromagnetic stirring means, and they
have finally achieved the present invention.
[0015] A process for producing a semi-solidified slurry of an iron
alloy according to the present invention has a first feature that
the process includes the steps of pouring a melt of an iron alloy
into a semi-solidified slurry producing vessel and cooling the melt
in the vessel to obtain a semi-solidified slurry having a
crystallized solid phase and a residual liquid phase, wherein a
hypereutectoid or hypoeutectic cast iron composition containing
0.8-4.3 wt. % C is used as a material, a melt of the composition is
poured into the semi-solidified slurry producing vessel in a
predetermined amount at a time, a temperature of the melt when
poured into the semi-solidified slurry producing vessel is
controlled to be not lower than a crystallization initiation
temperature of the composition and not greater than a temperature
that is 50.degree. C. higher than the crystallization initiation
temperature, and a cooling rate of the melt poured into the
semi-solidified slurry producing vessel is controlled not to exceed
20.degree. C. per minute.
[0016] In addition to the first feature described above, the
process for producing a semi-solidified slurry of an iron alloy of
the present invention has a second feature that, wherein above the
semi-solidified slurry producing vessel, the melt poured from a
ladle is once received in a relay and damper vessel in a
predetermined amount at a time, and the melt received in the relay
and damper vessel is then poured into the semi-solidified slurry
producing vessel via a discharge port provided at a bottom of the
relay and damper vessel, a diameter of the discharge port is not
less than 10 mm, a temperature of the discharged melt at the
discharge port is controlled to be not lower than a temperature
that is 20.degree. C. higher than the crystallization initiation
temperature of the composition and not greater than a temperature
that is 80.degree. C. higher than the crystallization initiation
temperature, a preheating temperature of the semi-solidified slurry
producing vessel is not less than 400.degree. C. lower than the
crystallization initiation temperature of the composition and not
greater than a temperature that is 200.degree. C. higher than the
crystallization initiation temperature, and a height of the relay
and damper vessel from the semi-solidified slurry producing vessel
is not less than 100 mm.
[0017] In addition to the second feature described above, the
process for producing a semi-solidified slurry of an iron alloy of
the present invention has a third feature that the melt is cooled
by wind while the melt is falling from the relay and damper vessel
down into the semi-solidified slurry producing vessel.
[0018] In addition to any of the second through forth features
described above, the process for producing a semi-solidified slurry
of an iron alloy of the present invention has a fifth feature that
a semi-solidified slurry produced is taken out in the state where
the semi-solidified slurry producing vessel is heated by
high-frequency induction heating such that part of the
semi-solidified slurry that is in contact with the semi-solidified
slurry producing vessel is heated via the semi-solidified slurry
producing vessel.
Effects of the Invention
[0019] According to the process for producing a semi-solidified
slurry of an iron alloy recited in claim 1, a hypereutectoid or
hypoeutectic cast iron composition containing 0.8-4.3 wt. % C is
used as a material, and a melt of the composition is poured into a
semi-solidified slurry producing vessel at a temperature of not
lower than the crystallization initiation temperature and not
greater than a temperature that is 50.degree. C. higher than the
crystallization initiation temperature, and cooled at a cooling
rate of not greater than 20.degree. C. per minute to a temperature
equal to or lower than the crystallization initiation temperature
of primary crystals. As a result, it is possible to obtain a
hypereutectoid or hypoeutectic cast iron semi-solidified slurry
containing 0.8-4.3 wt. % C having its primary crystals in granular
form, rather than in dendritic form. Using the semi-solidified cast
iron slurry having the granular primary crystals for subsequent
casting or other processing leads to formation of a product which
has few defects, which is closely packed and excellent in
structure, and which has good mechanical properties. In this case,
the semi-solidified cast iron slurry does not need to be once
solidified, but can suitably be used as it is for casting or other
processing. Accordingly, it is possible to obtain a product which
is not only excellent in mechanical properties but also
advantageous in saving energy.
[0020] The cooling of the melt within the semi-solidified slurry
producing vessel starts at a temperature that is higher by only
50.degree. C. than the crystallization initiation temperature. This
can reduce the time required for the cooling, and accordingly, it
is possible to efficiently produce the semi-solidified cast iron
slurry.
[0021] According to the process for producing a semi-solidified
slurry of an iron alloy recited in claim 2, in addition to the
above-described effects obtained by the configuration recited in
claim 1, a ladle is used to deliver the melt from a melting furnace
or the like, and a relay and damper vessel receives the melt from
the ladle in a predetermined amount at a time. The melt received in
the relay and damper vessel is then poured into the semi-solidified
slurry producing vessel via a discharged port at a bottom of the
rely and damper vessel while being cooled and homogenized in the
relay and damper vessel.
[0022] Of the melt which flows from the ladle down to the relay and
damper vessel, the initially discharged melt is poured into the
semi-solidified slurry producing vessel at a relatively early stage
and cooled within the semi-solidified slurry producing vessel. By
comparison, the subsequently discharged melt remains in the relay
and damper vessel for a while during which it is cooled before
being poured into the semi-solidified slurry producing vessel. This
can reduce the temperature difference when all the melt is poured
into the semi-solidified slurry producing vessel. As the
temperature difference in the melt is reduced, dendritic
crystallization is prevented, and accordingly, it is possible to
obtain a favorable semi-solidified slurry made up of granular
crystals and the melt.
[0023] The amount of the melt acquired by the ladle from the
melting furnace or the like is much larger than a predetermined
amount of the semi-solidified slurry. Thus, it would be difficult
to pour the melt directly from the ladle into the semi-solidified
slurry producing vessel smoothly and in a stable manner.
Furthermore, it would be necessary to hold the melt in the ladle in
the state where the temperature of the melt is decreased to and
kept at a level near the crystallization initiation temperature,
while preventing initiation of solidification. According to the
invention recited in claim 2, the relay and damper vessel once
receives the melt from the ladle, and relays the melt to the
semi-solidified slurry producing vessel. This enables a smooth
melt-pouring operation with which the melt is poured in
predetermined, small quantities from the ladle having large
capacity. Further, as the melt is once received from the ladle into
the relay and damper vessel, the melt of the predetermined amount
received can be homogenized, and accordingly, the melt poured into
the semi-solidified slurry producing vessel can be more
homogenized. Still further, as the melt from the ladle is cooled as
it passes through the relay and damper vessel, the melt can be held
in the ladle at a relatively higher temperature, which facilitates
the temperature control.
[0024] Especially according to the invention recited in claim 2, a
diameter of the discharge port is less than 10 mm, a temperature of
the discharged melt at the discharged port is not lower than a
temperature that is 20.degree. C. higher than the crystallization
initiation temperature of the composition and not greater than a
temperature that is 80.degree. C. higher than the crystallization
initiation temperature, a preheating temperature of the
semi-solidified slurry producing vessel is not less than
400.degree. C. lower than the crystallization initiation
temperature of the composition and not greater than a temperature
that is 200.degree. C. higher than the crystallization initiation
temperature, and a height of the relay and damper vessel from the
semi-solidified slurry producing vessel is not less than 100 mm.
This really enables us to obtain a favorable semi-solidified cast
iron slurry with granular crystals more reliably and stably.
[0025] According to the process for producing a semi-solidified
slurry of an iron alloy recited in claim 3, in addition to the
above-described effects obtained by the configuration recited in
claim 2, the melt is cooled by wind while it falls from the relay
and damper vessel down into the semi-solidified slurry producing
vessel. As the melt falling down toward the semi-solidified slurry
producing vessel can forcibly be cooled, the melt which enters the
semi-solidified slurry producing vessel has a temperature closer to
its crystallization temperature, which can reduce the subsequent
cooling time. As the melt is cooled by wind, the melt may be poured
from the ladle at a higher temperature and the melt may also be
held in the relay and damper vessel at a higher temperature. This
facilitates the temperature control.
[0026] According to the process for producing a semi-solidified
slurry of an iron alloy recited in claim 4, in addition to the
above-described effects obtained by the configuration recited in
claim 2, energy caused by the melt falling from the relay and
damper vessel down into the semi-solidified slurry producing vessel
is used to stir the melt within the semi-solidified slurry
producing vessel. This means that the melt within the
semi-solidified slurry producing vessel can be stirred by the
stirring effect of the falling melt itself, without the need of a
stirrer such as a stirring rod, or an expensive, sophisticated
device such as electromagnetic stirring means. Accordingly, the
temperature of the melt can be made sufficiently uniform, and thus,
the nucleation is promoted, and fine and granular primary crystals
are obtained.
[0027] For adjusting the falling energy so as to obtain a desired
degree of stirring effect, the falling height may be determined in
advance through experiments, according to the amount of the melt
and the capacity of the semi-solidified slurry producing
vessel.
[0028] According to the process for producing a semi-solidified
slurry of an iron alloy recited in claim 5, in addition to the
above-described effects obtained by the configuration recited in
any of claims 2 to 4, a semi-solidified slurry produced is taken
out in the state where the semi-solidified slurry producing vessel
is heated by high-frequency induction heating such that part of the
semi-solidified slurry in contact with the semi-solidified slurry
producing vessel is heated via the semi-solidified slurry producing
vessel. This allows the semi-solidified slurry to be taken out of
the semi-solidified slurry producing vessel easily, without causing
temperature variation in the semi-solidified slurry. That is, when
the semi-solidified slurry produced is taken out of the
semi-solidified slurry producing vessel to be introduced into a
mold or other molding means, even if the temperature of the slurry
is adjusted to the level suitable for a molding process, the part
of the slurry in contact with the vessel will be low in
temperature, making it difficult to take out the slurry from the
vessel. On the other hand, high-frequency induction heating is
suitable for quickly heating the outer periphery of the slurry.
However, in the case of using the high-frequency induction heating
means for a semi-solidified slurry of a cast iron, although the
cast iron may be heated efficiently, the temperature will increase
locally due to the poor thermal conductivity, in which case the
slurry will suffer temperature variation and an unstable solid
fraction. It will also be difficult to measure the temperature,
hindering accurate temperature control.
[0029] According to the process recited in claim 8, the
semi-solidified slurry producing vessel itself is heated quickly by
high-frequency induction heating. This allows only the part of the
semi-solidified slurry in contact with the vessel to increase in
temperature quickly, so that the semi-solidified slurry can readily
be taken out of the vessel. At the same time, the semi-solidified
slurry would not suffer temperature variation, and it can be
subjected to a molding process at a stable solid fraction. While
there is a conventional art using high-frequency induction heating
means in semi-solid die casting of an aluminum alloy, it is used
for the purpose of causing the semi-solidified slurry to have a
uniform temperature, not for the purpose of taking the
semi-solidified slurry out of the vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a cross-sectional view schematically illustrating
an apparatus for producing a semi-solidified slurry of an iron
alloy according to an embodiment of the present invention.
[0031] FIG. 2 is a photograph showing a structure of the
semi-solidified slurry which is produced with the producing process
and the producing apparatus according to an embodiment of the
present invention.
[0032] FIG. 3 is a photograph showing, as a comparative example, a
structure of a semi-solidified slurry with dendrites crystallized
therein.
[0033] FIG. 4 is a table showing the conditions for producing
semi-solidified slurries according to examples of the present
invention.
[0034] FIG. 5 is a table showing the results of experiments in the
examples of the present invention.
[0035] FIG. 6 is a table showing the results of experiments in the
examples of the present invention.
[0036] FIG. 7 is a cross-sectional view illustrating a conventional
art.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0037] 10 ladle [0038] 11 heat insulating means [0039] 12
temperature measuring means [0040] 20 relay and damper vessel
[0041] 21 discharge port [0042] 22 vessel pre-heating means [0043]
23 temperature measuring means [0044] 30 semi-solidified slurry
producing vessel [0045] 31 heat insulating vessel [0046] 32
preheating means [0047] 33 temperature measuring means [0048] 40
blower fan
BEST MODES FOR CARRYING OUT THE INVENTION
[0049] Hereinafter, embodiments of the process for producing a
semi-solidified slurry of an iron alloy according to the present
invention will further be described with reference to the
drawings.
[0050] Referring to FIG. 1, the apparatus using for the present
invention at least includes: a ladle 10 for receiving and
delivering a melt from a melting furnace (not shown): a relay and
damper vessel 20; and a semi-solidified slurry producing vessel 30.
It may further include a blower fan 40 adapted to cool the melt
while the melt is being poured down into the semi-solidified slurry
producing vessel 30.
[0051] The ladle 10 and the relay and damper vessel 20 constitute
melt pouring means P for pouring the melt into the semi-solidified
slurry producing vessel 30.
[0052] The melt pouring means P takes charge of pouring the melt of
a predetermined amount into the semi-solidified slurry producing
vessel 30 under a melt pouring temperature condition of not lower
than the crystallization initiation temperature of the melt and not
greater than a temperature that is 50.degree. C. higher than the
crystallization initiation temperature. This melt pouring
temperature condition means that, in the case where the
crystallization initiation temperature (liquidus temperature) of
the melt being poured is 1300.degree. C. for example, the
temperature of the melt when entering the semi-solidified slurry
producing vessel is regulated such that it is not lower than
1300.degree. C. and not higher than 1350.degree. C.
[0053] The ladle 10 receives the melt at the position where the
melting furnace is located, and moves to the position above the
semi-solidified slurry producing vessel 30. The capacity of the
ladle 10 is much greater than the amount of a semi-solidified
slurry to be produced in the semi-solidified slurry producing
vessel 30 at one time, allowing the ladle 10 to supply the melt to
the semi-solidified slurry producing vessel 30 a plurality of
number of times, or to a plurality of semi-solidified slurry
producing vessels 30.
[0054] The ladle 10 may be provided with heat insulating means 11.
With this heat insulating means 11, the ladle 10 can keep the melt
received from the melting furnace at an appropriate temperature
during the melt pouring operation.
[0055] Further, the ladle 10 may be provided with temperature
measuring means 12 for measuring the temperature of the melt. The
temperature measuring means 12 may be an immersion thermometer, for
example, which can measure the temperature of the melt within the
ladle 10. The temperature of the melt may be measured, e.g., prior
to pouring of the melt from the ladle 10. The melt is poured out
only when the temperature of the melt measured falls within a
predetermined temperature range.
[0056] With the temperature measuring means 12 and the heat
insulating means 11, the temperature of the melt which is to be
poured from the ladle 10 down to the relay and damper vessel 20 can
be adjusted to an appropriate level.
[0057] The relay and damper vessel 20, which is placed above the
semi-solidified slurry producing vessel 30, receives the melt from
the ladle 10 and relays the melt to the semi-solidified slurry
producing vessel 30, while dampening the impact of the falling melt
as appropriate. The relay and damper vessel 20 is adapted to have
the capacity at least sufficient enough to receive the melt poured
at one time, which is much smaller than the capacity of the ladle
10.
[0058] The relay and damper vessel 20 may be a graphite crucible,
for example.
[0059] The relay and damper vessel 20 is provided with a discharge
port 21 at its bottom. The discharge port 21 may be provided, e.g.,
at the center of the bottom.
[0060] The diameter of the discharge port 21 is determined through
experiments such that it satisfies at least the condition that the
flow rate of the melt which is poured from the relay and damper
vessel 20 to the semi-solidified slurry producing vessel 30 is
smaller than the flow rate of the melt which is poured from the
ladle 10 to the relay and damper vessel 20. In practice, the
diameter of the discharge port 21 is preset to an optimum diameter
through experiments, taking into consideration the capacity and the
area of base of the relay and damper vessel 20, the flow rate of
the melt which flows down from the ladle 10, and the amount of the
melt to be poured at a time, so that the melt received from the
ladle 10 is pooled and retained as appropriate within the relay and
damper vessel 20, cooled as appropriate in the vessel, and mixed
and homogenized as appropriate by the melt flowing down from the
ladle 10, and further, poured from the discharge port 21 provided
at the bottom down into the semi-solidified slurry producing vessel
30 smoothly and continuously.
[0061] Using the relay and damper vessel 20 with the discharge port
21 as described above is advantageous in that the relay and damper
vessel 20 serves substantially as a funnel to introduce the melt
from the ladle 10 into the semi-solidified slurry producing vessel
30 reliably and smoothly with ease, without causing turbulence.
Further, it can appropriately promote and adjust the decrease in
temperature of the melt while it flows out of the ladle 10 and down
to the semi-solidified slurry producing vessel 30, and at the same
time, it can prevent the melt from acquiring too much energy as it
falls down to the semi-solidified slurry producing vessel 30.
[0062] It is noted that the discharge port 21 may be provided with
open/close means such as an openable lid or an openable shutter, so
that the melt can be received from the ladle 10 and discharged via
the discharge port 21 at regular intervals. This enables more
accurate control of homogenization as well as temperature decrease
of the melt in the relay and damper vessel 20.
[0063] The relay and damper vessel 20 may be provided with vessel
pre-heating means 22. The vessel pre-heating means 22 is provided
to prevent the undesirable event that the melt which is initially
supplied from the ladle 10 suffers a rapid temperature decrease
and, hence, starts to solidify. Further, it is provided such that
the temperature of the melt which flows from the relay and damper
vessel 20 down to the semi-solidified slurry producing vessel 30 is
stabilized in a certain temperature range which is suitably higher
than the crystallization initiation temperature.
[0064] The relay and damper vessel 20 may be provided with
temperature measuring means 23. The temperature measuring means 23
may be made up of a thermocouple, for example, which may be
arranged in contact with the outer wall surface of the relay and
damper vessel 20 to measure the temperature of the relay and damper
vessel 20. This can adjust the pre-heating temperature of the
vessel 20 to a predetermined level.
[0065] The semi-solidified slurry producing vessel 30 may be
arranged in a heat insulating vessel 31 in such a manner that it
can be freely taken in and out of the same. In the present
embodiment, the heat insulating vessel 31 is provided with
pre-heating means 32, to allow pre-heating of the semi-solidified
slurry producing vessel 30. For the semi-solidified slurry
producing vessel 30, electrically conductive ceramics may be used,
for example, as a material which has a heat-resistant temperature
of at least higher than the crystallization temperature of the melt
and which can withstand high-frequency induction heating.
Specifically, a composite material of carbon and ceramics such as
silicon carbide, boron carbide and the like may be used.
[0066] In the present embodiment, the pre-heating means 32 is
configured with high-frequency induction heating means. The
pre-heating means 32 which is the high-frequency induction heating
means heats the semi-solidified slurry producing vessel 30
itself.
[0067] The reference numeral 33 denotes temperature measuring
means. For the temperature measuring means 33, a radiation
thermometer may be used, for example, to measure the temperature of
the semi-solidified slurry producing vessel 30. Alternatively, the
temperature measuring means may be the one which can directly
measure the temperature of the slurry within the semi-solidified
slurry producing vessel 30, in which case the temperature of the
slurry would be kept at a predetermined level more accurately.
[0068] The decrease in temperature of the slurry within the
semi-solidified slurry producing vessel 30 is restricted such that
it does not decrease below the level between the liquidus and the
solidus for the composition of the melt, and the temperature of the
semi-solidified slurry producing vessel 30 is adjusted such that
the slurry is kept at that temperature level.
[0069] The blower fan 40 is for blowing the air onto the melt which
is falling down from the relay and damper vessel 20 so as to cool
the same.
[0070] The melt pouring means P having the ladle 10 and the relay
and damper vessel 20 is provided with melt-pouring-temperature
adjusting means TC for pouring the melt into the semi-solidified
slurry producing vessel 30 under the melt pouring temperature
condition of not lower than the crystallization initiation
temperature and not greater than a temperature that is 50.degree.
C. higher than the crystallization initiation temperature.
[0071] Specifically, the melt-pouring-temperature adjusting means
TC is made up of a combination of the following elements: the heat
insulating means 11 and the temperature measuring means 12 for the
ladle 10, the relay and damper vessel 20, its discharge port 21,
the vessel pre-heating means 22, the blower fan 40, and the height
relation between the ladle 10, the relay and damper vessel 20, and
the semi-solidified slurry producing vessel 30.
[0072] Of the elements of the melt-pouring-temperature adjusting
means TC, the heat insulating means 11 and the temperature
measuring means 12 for the ladle 10 constitute first temperature
adjusting means TC1. The heat insulating means 11 and the
temperature measuring means 12 for the ladle 10 constituting the
first temperature adjusting means TC1 adjust the temperature of the
melt which is held in the ladle 10.
[0073] Further, of the elements of the melt-pouring-temperature
adjusting means TC, the material, shape, thickness, and capacity of
the relay and damper vessel 20, the size and position of the
discharge port 21, and pre-heating conducted by the vessel
pre-heating means 22 constitute second temperature adjusting means
TC2. The second temperature adjusting means TC2 adjusts the
decrease in temperature of the melt which flows through the relay
and damper vessel 20, and adjusts the temperature of the melt which
flows out via the discharge port 21.
[0074] Still further, of the elements of the
melt-pouring-temperature adjusting means TC, the blower fan 40
constitutes third temperature adjusting means TC3. This third
temperature adjusting means TC3 adjusts the decrease in temperature
of the melt which falls down from the relay and damper vessel
20.
[0075] The semi-solidified slurry producing vessel 30 is provided
with cooling-rate adjusting means SC for cooling the melt received
in the semi-solidified slurry producing vessel 30 at a cooling rate
of not greater than 20.degree. C. per minute.
[0076] Specifically, the cooling-rate adjusting means SC is made up
of the material, shape, thickness, and capacity of the
semi-solidified slurry producing vessel 30 itself, the heat
insulating vessel 31, and the pre-heating means 32. That is, the
cooling rate of the melt is adjusted by the material, shape,
thickness, and capacity of the semi-solidified slurry producing
vessel 30, and also by the material, shape, thickness, and capacity
of the heat insulating vessel 31. Particularly, the cooling rate of
the melt can be adjusted considerably freely depending on the
temperature to which the semi-solidified slurry producing vessel 30
is pre-heated by the pre-heating means 32. Accordingly, the
cooling-rate adjusting means SC can adjust the cooling rate of the
melt within the semi-solidified slurry producing vessel 30 not to
exceed 20.degree. C. per minute.
[0077] It is noted that the temperature of the melt within the
semi-solidified slurry producing vessel 30 is decreased to and kept
at a predetermined level between the liquidus and the solidus of
the melt, so that the ratio between the solid phase and the liquid
phase becomes a predetermined ratio.
[0078] For taking the semi-solidified slurry out of the
semi-solidified slurry producing vessel 30, the pre-heating means
32 constituted by the high-frequency induction heating means may be
used to quickly heat the semi-solidified slurry producing vessel 30
to thereby heat only the part of the semi-solidified slurry that is
in contact with the semi-solidified slurry producing vessel 30.
This facilitates taking out the semi-solidified slurry, and further
prevents occurrence of temperature variation in the semi-solidified
slurry. Accordingly, the slurry can reliably be taken out at a
desired solid fraction.
[0079] An embodiment of the process for producing a semi-solidified
slurry of an iron alloy using the apparatus as described above will
now be described.
[0080] As a raw material for producing a semi-solidified slurry, a
material of a hypereutectoid or hypoeutectic cast iron composition
containing 0.8-4.3 wt. % C is used. The material is melt in a
melting furnace to obtain a melt of a given hypereutectoid or
hypoeutectic cast iron composition.
[0081] The melt melted in the melting furnace is received by the
ladle 10 in an appropriate amount each time, which is moved to the
position above the relay and damper vessel 20.
[0082] The ladle 10, while keeping the melt within a predetermined
temperature range, discharges the melt down to the relay and damper
vessel 20 in a predetermined amount at a time (which amount
corresponds to the amount of the semi-solidified slurry to be
produced at a time).
[0083] The melt flowing down from the ladle 10 once enters the
relay and damper vessel 20, and further flows down via the
discharge port 21 provided at the bottom into the semi-solidified
slurry producing vessel 30. The melt poured into the
semi-solidified slurry producing vessel 30 is cooled therein,
whereby a semi-solidified slurry composed of a primary crystal
solid phase and a residual liquid phase is produced. The
semi-solidified slurry in this state is taken out of the
semi-solidified slurry producing vessel 30, which is then subjected
to rheocasting or other molding process.
[0084] The temperature of the melt of the hypereutectoid or
hypoeutectic cast iron which is poured into the semi-solidified
slurry producing vessel 30 is regulated to the temperature range of
not lower than the crystallization initiation temperature for the
component composition and not greater than a temperature that is
50.degree. C. higher than the crystallization initiation
temperature.
[0085] For controlling this melt pouring temperature, the
temperature of the melt which comes out of the ladle 10 may be
adjusted (adjustment by the first temperature adjusting means TC1),
and further, the amount of temperature decrease may be adjusted by
the shape, thickness, and capacity of the relay and damper vessel
20, the diameter of the discharge port 21, presence/absence of
pre-heating, and the pre-heating temperature (adjustment by the
second temperature adjusting means TC2), and still further, the
amount of temperature decrease of the melt flowing down from the
relay and damper vessel 20 may be adjusted by the blower fan 40
(adjustment by the third temperature adjusting means TC3).
[0086] The amount of temperature decrease of the melt from when it
comes out of the ladle 10 until when it reaches the semi-solidified
slurry producing vessel 30 may of course be adjusted through
adjustment of the height relation between the ladle 10, the relay
and damper vessel 20, and the semi-solidified slurry producing
vessel 30, or put more simply, by adjusting the time (drop) during
which the melt is exposed in the air while it falls from the ladle
10 down to the semi-solidified slurry producing vessel 30. It is
assumed that the melt-pouring-temperature adjusting means TC
includes adjustment of this drop.
[0087] For the adjustment and control of the melt pouring
temperature as described above, it may be predetermined through
experiments how much the temperature of the melt will decrease from
when it is discharged from the ladle 10 until when it reaches the
semi-solidified slurry producing vessel 30, or how much temperature
decrease will be needed for the melt from when it flows out of the
ladle 10 until it reaches the semi-solidified slurry producing
vessel 30. Then, it is only necessary to control the temperature of
the melt that is discharged from the ladle 10 to fall within a
predetermined temperature range, so that the temperature of the
melt when it is poured into the semi-solidified slurry producing
vessel 30 is adjusted and controlled to a predetermined temperature
(of not lower than the crystallization initiation temperature and
not greater than a temperature that is 50.degree. C. higher than
the crystallization initiation temperature).
[0088] In the above configuration, increasing the drop from the
ladle 10 to the semi-solidified slurry producing vessel 30 can
increase the amount of temperature decrease, which is advantageous
in that the melt can be held at a higher temperature within the
ladle 10. However, it may cause excessive energy by the falling
melt and, hence, turbulence in the poured melt. In view of the
foregoing, according to the present invention, the relay and damper
vessel 20 is provided in the middle, for appropriately dampening
the energy caused by the falling melt due to the increased drop. As
a result, the melt can be poured into the semi-solidified slurry
producing vessel 30 with accuracy, involving not too much energy
(so that excessive stirring and spattering of the melt are both
suppressed).
[0089] By adjusting the height (drop) from the relay and damper
vessel 20 to the semi-solidified slurry producing vessel 30, the
melt can surely be poured smoothly and without spattering.
Furthermore, by virtue of the suitable stirring effect achieved by
appropriate energy of the falling melt, the melt within the
semi-solidified slurry producing vessel 30 can be homogenized.
Specifically, if the height of the relay and damper vessel 20 with
respect to the semi-solidified slurry producing vessel 30 is small,
the stirring effect by the falling melt cannot be obtained, in
which case the melt poured into the semi-solidified slurry
producing vessel 30 may not be homogenized sufficiently. As the
height of the relay and damper vessel 20 with respect to the
semi-solidified slurry producing vessel increases, the melt may be
homogenized more sufficiently by the stirring effect as described
above. If the height is too great, however, the melt may spatter
when it is poured into the semi-solidified slurry producing vessel
30, leading to an excessively stirred state. Accordingly, the
desired height of the relay and damper vessel 20 is predetermined
through experiments, taking into consideration the size of the
discharge port 21 provided in the relay and damper vessel 20, the
shape and capacity of the semi-solidified slurry producing vessel
30, and others.
[0090] The function of the relay and damper vessel 20 is to once
receive the melt from the ladle 10 and hold the same in the vessel
20, for homogenizing the melt and also for cooling the melt within
the vessel 20.
[0091] Another function of the relay and damper vessel 20 is to
continuously discharge the melt through the discharge port 21
provided at the bottom down to the semi-solidified slurry producing
vessel 30, to ensure smooth and stable pouring of the melt.
[0092] It is configured such that the melt which has been poured
into the semi-solidified slurry producing vessel 30 is cooled at a
cooling rate of not greater than 20.degree. C. per minute. The
cooling rate is controlled primarily by pre-heating the
semi-solidified slurry producing vessel 30. The cooling rate will
of course vary depending on the cooling properties specific to the
semi-solidified slurry producing vessel 30, according to its shape,
thickness, capacity, and the like. Therefore, it is predetermined
through experiments how much the semi-solidified slurry producing
vessel 30 will have to be pre-heated in relation to the temperature
of the melt being poured therein, so as to obtain a semi-solidified
slurry composed of favorable granular primary crystals and the
residual liquid phase within the prescribed cooling rate range.
[0093] The semi-solidified slurry producing vessel 30 may be
pre-heated by high-frequency induction heating. This can pre-heat
the vessel 30 as necessary, more quickly than in the case of using
an electric heater, thereby enabling finer temperature control.
Accordingly, the cooling rate can be controlled with accuracy, so
that a favorable semi-solidified slurry can be obtained, with
crystallization of dendrites being suppressed therein.
[0094] Furthermore, as the semi-solidified slurry producing vessel
30 is heated quickly and with accurate temperature control by
high-frequency induction heating, it is possible to quickly heat
only part of the semi-solidified slurry that is in contact with the
semi-solidified slurry producing vessel 30 when taking the
semi-solidified slurry out of the vessel 30. Accordingly, the
semi-solidified slurry can readily be taken out of the vessel 30,
as it is only necessary to turn the vessel 30 over to take the
semi-solidified slurry out of the vessel. Furthermore, the
semi-solidified slurry can be taken out of the vessel 30 without
changing the solid-liquid ratio of the semi-solidified slurry and
without causing temperature variation therein.
EXAMPLES
[0095] A raw material of a hypoeutectic cast iron composition
containing 2.6 wt % of C (carbon) and 1.5 wt % of Si (silicon) as a
component composition was melted in a melting furnace to obtain a
melt. The hypoeutectic cast iron of this composition has a liquidus
temperature of about 1300.degree. C. and a solidus temperature of
1150.degree. C. Accordingly, a semi-solidified slurry can be
obtained by cooling the melt to a temperature between 1300.degree.
C. and 1150.degree. C. and keeping it at the temperature.
[0096] The melt in the melting furnace was received by the ladle 10
and poured therefrom. Specifically, the melt in the ladle 10 was
poured in a predetermined amount at a time, down to the relay and
damper vessel 20 made up of a graphite crucible which was
preheated. Further, the melt was discharged from the discharge port
21 provided at the bottom of the relay and damper vessel 20, down
to the semi-solidified slurry producing vessel 30 which was
preheated. The melt was cooled within the semi-solidified slurry
producing vessel 30, whereby the semi-solidified slurry was
produced.
[0097] The conditions for producing semi-solidified slurries were
as shown in FIG. 4.
[0098] For the semi-solidified slurry producing vessel 30, a
composite material of carbon and ceramics (silicon carbide and
boron carbide) was used as a material that can withstand
high-frequency induction heating. The slurry accumulated in the
semi-solidified slurry producing vessel 30 was cooled to
1200.degree. C., and then the vessel 30 was subjected to
high-frequency induction heating. When the vessel 30 was heated to
1300.degree. C., the vessel 30 was reversed to take out the
semi-solidified slurry, which was water-cooled and subjected to
structure observation.
[0099] The results of experiments are shown in FIGS. 5 and 6.
[0100] According to the results of experiments shown in FIGS. 5 and
6, under the conditions shown in FIG. 4 adopted this time, it was
possible to pour the melt from the ladle 10 via the relay and
damper vessel 20 down into the semi-solidified slurry producing
vessel 30 in the case where the temperature of the melt flowing out
of the ladle 10 was not lower than 1350.degree. C., the pre-heating
temperature of the relay and damper vessel 20 was not lower than
600.degree. C., and the discharge port 21 at the relay and damper
vessel 20 had a diameter of not less than 10 mm.
[0101] In the case where the temperature of the melt flowing out of
the ladle 10 was 1300.degree. C. (Sample 1), the melt remained and
solidified in the relay and damper vessel 20.
[0102] Even in the case where the temperature of the melt flowing
out of the ladle 10 was 1400.degree. C., when the diameter of the
discharge port 21 at the relay and damper vessel 20 was 5 mm
(Sample 26), the melt remained and solidified in the relay and
damper vessel 20.
[0103] Further, even in the case where the temperature of the melt
flowing out of the ladle 10 was 1400.degree. C., when the
pre-heating temperature of the relay and damper vessel 20 was as
low as 300.degree. C. (Sample 27), the melt remained and solidified
in the relay and damper vessel 20.
[0104] In the case where the temperature of the melt being poured
into the semi-solidified slurry producing vessel 30 exceeded
1350.degree. C. (Samples 29, 31, 32, 33, 34, 35, and 42), primary
crystals were in dendritic form, as shown in FIG. 3.
[0105] Further, in the case where the cooling rate in the
semi-solidified slurry producing vessel 30 exceeded 20.degree.
C./min (Samples 40 and 49), even if the melt pouring temperature
was not lower than 1300.degree. C. and not higher than 1350.degree.
C., primary crystals became dendrites, as shown in FIG. 3.
[0106] On the other hand, in the case where the cooling rate in the
semi-solidified slurry producing vessel 30 was not greater than
20.degree. C./min, primary crystals were in granular form, as shown
in FIG. 2.
[0107] However, even in the case where the cooling rate in the
semi-solidified slurry producing vessel 30 was not greater than
20.degree. C./min, when the height of the relay and damper vessel
20 from the semi-solidified slurry producing vessel 30 was less
than 100 mm (50 mm in the examples) (Samples 2 to 9, 28, and 30),
dendrites were found near the part coming into contact with the
semi-solidified slurry producing vessel 30, although the granular
crystals were found inside. This is presumably because, even though
the cooling rate was not greater than 20.degree. C./min at the
temperature-measuring position in this experiment (near the central
portion of the vessel 30), the cooling rate would have exceeded
20.degree. C./min near the above-described part contacting the
vessel at the outer periphery.
[0108] In the case where the cooling rate in the semi-solidified
slurry producing vessel 30 was not greater than 20.degree. C./min
and the height of the relay and damper vessel 20 from the
semi-solidified slurry producing vessel 30 was not less than 100 mm
(100 mm and 200 mm in the examples), the stirring effect by the
energy of the falling melt was obtained, and accordingly, the
resultant semi-solidified slurry had granular crystals suitable for
a molding process, not only inside the slurry, but also at the
outer periphery thereof (coming into contact with the vessel
30).
INDUSTRIAL APPLICABILITY
[0109] The process and the apparatus for producing a
semi-solidified slurry of an iron alloy according to the present
invention are favorably applicable to a rheocasting process and a
rheocasting apparatus, and also to other processes and apparatuses
using the semi-solidified slurries.
* * * * *