U.S. patent number 3,911,997 [Application Number 05/425,951] was granted by the patent office on 1975-10-14 for magnetic apparatus for metal casting.
This patent grant is currently assigned to Sumitomo Metal Industries, Ltd., Sumitomo Shipbuilding and Machinery Co., Ltd.. Invention is credited to Kantaro Sasaki, Kiyoshi Sugazawa, Kiyoto Ushijima.
United States Patent |
3,911,997 |
Sugazawa , et al. |
October 14, 1975 |
Magnetic apparatus for metal casting
Abstract
Apparatus for metal casting using a magnetostatic field
generator having at least one superconducting solenoid magnet
disposed on at least one side of a mould or metal shell for setting
up a heterogenious magnetostatic field of intensities at least in
excess of 10,000 gauss in the liquid metal retained within the
mould or metal shell to thereby agitate the liquid metal. The
mageto-static field generator is accommodated within a cryostat,
which is always held cool at a predetermined temperature by a
special auxiliary cooling means.
Inventors: |
Sugazawa; Kiyoshi (Kobe,
JA), Ushijima; Kiyoto (Kobe, JA), Sasaki;
Kantaro (Ashiya, JA) |
Assignee: |
Sumitomo Metal Industries, Ltd.
(JA)
Sumitomo Shipbuilding and Machinery Co., Ltd.
(JA)
|
Family
ID: |
14987643 |
Appl.
No.: |
05/425,951 |
Filed: |
December 19, 1973 |
Foreign Application Priority Data
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Dec 20, 1972 [JA] |
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47-128555 |
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Current U.S.
Class: |
164/504; 164/468;
505/914; 505/912 |
Current CPC
Class: |
B22D
11/122 (20130101); Y10S 505/914 (20130101); Y10S
505/912 (20130101) |
Current International
Class: |
B22D
11/12 (20060101); B22D 027/02 () |
Field of
Search: |
;164/49,82,146,147,250 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Annear; R. Spencer
Attorney, Agent or Firm: Watson, Cole, Grindle &
Watson
Claims
What is claimed:
1. An apparatus for casting metals comprising means for holding
non-solidified metal, means for generating a heterogenious
magneto-static field in said non-solidified metal, said generating
means being disposed in the vicinity of one side of said holding
means, and means for causing relative movement of said holding
means and generating means to each other.
2. The apparatus according to claim 1, wherein said magneto-static
field generating means includes at least one super-conducting
solenoid magnet.
3. The apparatus according to claim 2, wherein said solenoid magnet
is hollow and formed by winding a wire containing very fine
super-conducting filaments sealed therein and has a resin coating
provided after the winding of the wire.
4. The apparatus according to claim 1, wherein said holding means
is a mold.
5. The apparatus according to claim 4, wherein said moving means
includes means for vertically move said generating means.
6. The apparatus according to claim 4, wherein said moving means
includes wheels carried by a wagon supporting said mold and rails
to guide and support said wheels.
7. The apparatus according to claim 1, wherein said holding means
is a shell formed as a result of solidification of said
non-solidified metal.
8. The apparatus according to claim 7, wherein said moving means is
a mechanism for continuously withdrawing said shell.
9. The apparatus according to claim 8, wherein the speed of
withdrawal of said shell ranges from 0.5 to 3 meters per
minute.
10. The apparatus according to claim 1, wherein said magneto-static
field generating means can generate a magneto-static field of
intensities above 10,000 gauss in said non-solidified metal.
11. The apparatus according to claim 1, wherein said magneto-static
means includes a plurality of super-conducting solenoid magnets
disposed on opposite sides of said holding means with opposite
poles directed toward the opposite sides of said holding means.
12. The apparatus according to claim 1, wherein said magneto-static
means includes a plurality of super-conducting solenoid magnets
disposed on opposite sides of said holding means with like poles
directed toward the opposite sides of said holding means.
Description
This invention relates to metal casting and, more particularly, to
a process and apparatus for metal casting, which makes it possible
to prevent or reduce macro- or micro- or micro-metallographic
heterogenity resulting chiefly at the center of ingots or
continuously casted billets from the gradual cooling, cooling or
rapid cooling of liquid metal poured into the mould or liquid metal
core remaining within the solidified metal shell. This is
accomplished by applying magneto-static field at least in excess of
10,000 gauss to the liquid metal or liquid metal core during the
solidification thereof, thereby to obtain an ingot or billet having
a homogenious metallographic structure.
It is well known in the art that when liquid metal is solidified,
the center of the resultant body or casting center is prone to a
sort of heteroneious structure usually termed center porosity,
center-segregation or inner-crack, this trend being particularly
pronounced where the metal liquid is cooled in a still state
through rapid cooling, as is disclosed in Japanese Patent
Publication No. 33025/1972. It has also been known that this
heterogenity may be eliminated or reduced only by agitating the
liquid metal until the solidification thereof, and there have been
proposed various types of means for causing the flow of the liquid
metal by means of electromagnetic force.
The prior-art methods for electromagnetically causing the flow of
liquid metal include: a rotating electromagnetic field method as
disclosed, for instance, in Dukefriet Unkhans patent (Japanese
Patent Publication No. 9962/1956); one using an electromagnetic
field set up by three-phase alternating current as disclosed in
Japanese Patent Publication No. 32486/1972; and one using a
travelling electromagnetic field set up by alternating current as
disclosed in U.S. Pat. No. 3,656,537. All these prior-art methods
have resorted to a copper wire coil which is disposed to surround
or disposed in the close proximity of the mold or metal shell and
through which single or three phase alternating current is caused,
whereby the liquid metal is electromagnetically agitated due to
alternating magnetic field set up in it and eddy current induced in
it.
In the above prior-art method, which use alternating current for
obtaining the agitating force, very large current has to be passed
through the copper wire coil. Therefore, the ampere turns of the
copper wire coil has an extremely large value, so that water
cooling or oil cooling is necessary to remove the Joule's heat.
Also, the magnetic field generator coil as a whole is very large in
size. Particularly, where the coil surrounds a large casting body,
its operability will be limited due to the Joule's heat, and its
cost as a practical unit will be enormous.
According to the invention, unlike the afore-mentioned prior-art
techniques having resort to alternating magnetic field for
obtaining strong agitating force, a very intensive magnetic-static
field at least in excess of 10,000 gauss is set up in the liquid
metal by a single magnet.
Thus, the size and cost of the magnetic field generator may be
extremely reduced. While sufficient electromagnetic agitating
effect can be obtained with a single magnetic field generator or
magnet according to the invention, further strong electromagnetic
agitating effect may be given to the liquid metal by a combination
of a plurality of magneto-static field generators arranged such as
to provide the most effective magnetic flux distribution. Thus, it
is possible to obtain a strong agitating force that could not be
obtained by the prior-art alternating current method with an
extremely small and inexpensive apparatus as compared to the
prior-art one.
In accordance with the invention, the magneto-static field is set
up by direct current through a superconducting solenoid magnet. The
superconducting solenoid is made of a superconducting metal having
a character of offering zero electric resistance at the temperature
of liquid helium (-268.9.degree.C) such as a niobium-tin
intermetallic compound and a niobium-titanium alloy, and it is held
at the termperature of liquid helium when it carries direct
current. Since the solenoid offers zero electric resistance at the
working temperature, it may use a very fine wire or filament and
may be formed in a very small size with a large number of turns.
Also, since the solenoid as a whole may be readily held at the
liquid helium temperature, it is readily possible to produce a high
magneto-static field of 70,000 to 100,000 gauss at the center of
the solenoid.
The above and other objects, features and advantages of the present
invention become more apparent from the following description in
conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic representation of a set-up using
superconducting solenoid magnets according to the invention applied
to a still casting process;
FIGS. 2 to 4 are schematic representations of set-ups according to
the invention applied to a continuous casting process;
FIG. 5 shows a cryostat;
FIG. 6 shows a schematic liquid helium circulating system used for
a continuous casting process according to the invention; and
FIGS. 7A and 7B are graphs showing sulphur and carbon assay content
distributions in a billet obtained in accordance with the invention
and a billet obtained without using any agitating electromagnetic
field.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a set-up according to the invention with a
superconducting solenoid magnet disposed in the vicinity of one
side of a still mold for setting up an intensive magneto-static
field in the liquid metal within the mold. In FIG. 1 reference
numeral 1 designates a mould made from a non-magnetic material, and
numeral 2 a solid metal shell surrounding liquid metal 3. Numeral 5
designates the superconducting solenoid magnet, which is disposed
in the vicinity of one side of the mold 80 that the magnetic flux
generated by it may act upon the liquid metal. The solenoid magnet
5 is supported within a cryostat 7, and in this embodiment it is
held in position by a non-magnetic support 8. The cryostat 7 is a
high performance insulated vessel having an evacuated double-wall
insulating structure made of a non-magnetic metal. It is filled
with liquid helium, whose surface level 9 is held at a
substantially constant level. The liquid helium is replenished from
a feed pipe 10, and evaporated helium is recirculated through a
discharge pipe 11 to a helium liquifier. The cryostat has an upper
flange 21 provided with a power lead terminal 12 for supplying
power to the solenoid magnet 5. A heat insulator 15 is insterposed
between the cryostat and the mold for protecting the wall structure
of the cryostat. The magnetic flux 6 set up by the solenoid magnet
and acting upon the liquid metal may be moved relative to the
liquid metal by vertically oscillating the cryostat by means of a
vertically movable stand 13 or by horizontally moving the mould by
vertically movable stand 13 or by horizontally moving the mould by
means of wheels 16 and rails 17, so that the intensive
magneto-static field may efficiently act upon the liquid metal so
as to evoke the flow thereof in the desired direction. Of course,
it is desirous to this end to move both the cryostat and the mold
simultaneously. Also, it is possible to move the cryostat in the
horizontal direction and the mold in the vertical direction.
FIGS. 2 to 4 show other forms of the invention applied to the
continuous casting process. In the Figures, the cryostat is not
shown but is implied. In FIGS. 2 and 3, numeral 1' designates a
bottomless water cooled mold, and numeral 2 a solidified metal
shell enclosing non-solidified or liquid metal 3. The billet
containing the liquid metal is withdrawn at a substantially
constant speed in the direction of arrow 4. In both these
arrangements, two solenoid magnets are provided with respectively
opposite poles (N and S poles) directed toward the shell. In the
example of FIG. 2, both the solenoid magnets 5 and 5-1 are disposed
on the same side of the shell and at different vertical positions.
With this arrangement, it is possible to vary the magnetic field
intensity or magnetic flux density by varying the distance between
the two magnets. In the example of FIG. 3, the two solenoid magnets
5 and 5-1 are disposed on opposite sides of the shell and at
different vertical positions. With the disposition of the solenoid
magnets with respect to the lateral direction of the billet as in
the example of FIG. 2, an extremely improved agitating effect may
be obtained.
In case of the continuous casting, the billet is withdrawn
substantially at a constant speed, and this means that the solenoid
magnet is always moved relative to the liquid metal. Thus, in this
case the cryostat oscillating means as has been mentioned in
connection with FIG. 1 is not needed. The agitating effect of the
magneto-static field upon the liquid metal is attributable not only
to the eddy current induced but also to the gradient of the
intensity or flux density of the field in the liquid metal. In
other words, the liquid metal about to solidify is subjected to the
combined effect of eddy current and gradient of the field. In
further detail, in case of FIG. 3 example, for instance, the billet
is continuously withdrawn, so that the liquid metal enclosed within
the solid shell proceeds usually at a speed of, for instance, 0.5
to 3 meters per minute. Due to its interaction with the
magneto-static field, the liquid metal experiences forces tending
to stop its movement. However, since there is a gradient of the
field in the liquid metal, there also results a gradient of the
intensity of the force acting upon the liquid metal, so that the
liquid metal is agitated. Although a gradient of the field is
formed solely with a single magnet, the magnetic flux pattern may
be changed to suit the type of casting and various specifications
of the ingot or billet to be produced by appropriately changing the
number and disposition of the solenoid magnets as typically shown
in the examples of FIGS. 2 to 4.
Also, the solenoid magnet for generating the magnetic field is
designed by taking various conditions such as the intensity of the
exerted force and the position of installation into
consideration.
FIGS. 5 and 6 show examples of apparatus required for the execution
of the invention. FIG. 5 shows an example of the cryostat. The
illustrated cryostat, generally designated at 7, essentially
consists of an upper part having a lower flange 22 and a lower part
accommodating a solenoid magnet 5. Its interior is in communication
with a vacuum pump not shown, through a pipe 23 and is held under a
pressure of 10.sup.-5 mm Hg. Numeral 24 designates a magnet case,
whose top communicates with a pipe 25. Liquid helium is supplied
from a liquid helium feed pipe 10 to fill the case 24 and pipe 25
to a constant level 9. Evaporated helium is recirculated through a
discharge pipe 11 to a helium liquifier as shown in FIG. 6. This
example uses liquid nitrogen having a vaporization temperature of
-195.8.degree.C as auxiliary cooling means to take up external heat
with respect to the cryostat for ensuring steady cooling effect of
the liquid helium. More particularly, a liquid nitrogen chamber 26
having a plurality of downwardly extending fine tubes 27 is
provided within the upper part of the cryostat. Liquid nitrogen is
supplied through a supply tube 29, and evaporated nitrogen is
exhausted through an exhaust tube to the outside. The cryostat used
for the invention is entirely made of such non-magnetic material as
stainless steel 304. Although not shown, the actual apparatus will
include a liquid level gauge, a thermometer, a vacuum gauge, power
lead terminals for the magnet 5, a magnet position adjuster, a
safety device and heat insulation means.
FIG. 6 shows an example of the liquid helium supply system employed
for a continuous casting process of curved strand type. In this
process, liquid metal is poured from a pouring system 31 into a
bottomless water cooled mold 1'. Solenoid magnets 5 and 5-2 are
arranged in a way as in the example of FIG. 3 on the path of the
strand 2 emerging from the mold 1' directly below or in the
secondary cooling zone. Liquid helium and liquid nitrogen are
supplied to the cryostat and evaporated gas is recovered in the
manner as described above. Only the recirculation of helium is
shown. Helium gas stored under a pressure of about 150 atm. in
helium gas bombs 33 and under a pressure of about 1 atm. in a
helium gas tank 34 is supplied to a helium gas compressor 35, and
pressurised helium gas from the compressor 35 is supplied to a high
pressure helium gas tank 36, and thence to a helium liquifier 37.
In the helium liquifier, the high pressure helium gas is subjected
to heat exchange with liquid nitrogen and then passed through a gas
expander, whereby it is rendered into liquid helium, which is
supplied through a liquid helium tank 38 to the cryostat 7. Also,
evaporated helium from the cryostat goes to the helium gas tank 34
either through the liquifier 37 or directly for recovery of liquid
helium for recirculation. Although liquid helium is expensive,
substantially no helium is lost in the course of the recirculation
involving evaporation and liquefaction since the processed helium
is recirculated through a closed loop. Also, in the iron making
plants provided with apparatus for producing oxygen, liquid
nitrogen is inexpensively and readily avialable as a by-product.
Thus, no debit factor is found from the standpoint of the running
cost.
The following experimental example demonstrates the effects
attainable according to the invention.
EXPERIMENT
A quantity of 2,000 kilograms of molten low carbon steel, which was
produced by a high frequency induction furnace, was casted with an
experimental vertical continuous casting apparatus provided with a
magneto-static field generator according to the invention. The
chemical composition of the steel was 0.15 percent carbon, 0.30
percent silicon, 0.71 percent manganese, 0.010 percent phosphor,
0.012 percent sulphur and 0.030 percent soluble aluminum, the rest
being iron. The resultant billet had a thickness of 130 millimeters
and a width of 260 millimeters. The magneto-static field generator
was disposed directly below the mold, with its magnets positioned
in the proximity of one broader side of the billet, that is as in
the arrangement in FIG. 2. The first half of the steel, namely
1,000 kilograms of steel, was casted without applying any magnetic
field, and the field was applied for the remaining half. The billet
obtained in this way, was sampled at its positions corresponding to
the feed of 400 kilograms and 1,600 kilograms respectively from the
start of the casting. From each of these samples assay test pieces
were cut out at intervals of 2 to 10 millimeters in the direction
of the thickness of the billet for examining the segregation of
component elements. The results of the tests are shown in FIGS. 7A
and 7B. It will be seen that the billet obtained by applying the
magneto-static field resulted in very little segregation of carbon
sulphur at the center compared to the billet obtained without any
field applied. Also, it was confirmed that the magneto-static field
applied is particularly effective in the refinement of the dendrite
grain structure and capable of reducing the segregation coefficient
down to well below 2.0. The specifications of the magnets used in
this experiment were as follows:
Number of magnets: 2
Type and size of the magnets: Solenoid type magnet with an inner
diameter of 50 mm, an outer diameter of 180 mm and a width of 50
mm
Number of turns of the solenoid: 22,000
Solenoid wire: Copper wire 0.4 mm in diameter and containing 40
sealed fine filaments of Nb-Ti alloy resin coating being provided
after winding the wire.
Current: 30 amperes
Field intensity: 70,000 gauss at the center of solenoid and 22,000
gauss at the end of solenoid
Initial liquid helium consumption: 25 liters
As has been shown, by using the superconducting solenoid magnet, a
magneto-static field of high flux density, namely in excess of
10,000 gauss which could never be attained by passing large current
through the conventional solenoid coil, may be obtained in a large
space inexpensively and with a very small unit to effectively exert
an agitating force to the liquid metal. Also, as has been verified
by experiments, it is possible to suppress segregation and
center-porosity and reduce the segregation coefficient down to 2.0
or below. Further, in addition to the fact that the growth of
dendrites can be repressed by the slight agitation of the metal
liquid, crystalline precipitates or ionized concentrates of higher
susceptibility than the original liquid metal are affected by the
very intense magnetic field and tend to be attracted toward the
higher flux density. While the above experimental results are
obtained by using the experimental continuous casting apparatus, it
may be readily understood that similar results may be obtained in
the case of the set-up of FIG. 1 provided the mold and magnet are
moved relative to each other, and application to large ingots is
possible. (In this case, the mold should be made of a non-magnetic
material such as stainless steel.)
From the above grounds, it is possible to rapidly cool the liquid
metal without resulting in defects attributable to the central
heterogenious structure. Thus, it is possible to adopt the rapid
cooling system so as to increase the billet withdrawal speed and
hence reduce the possibility of crack formation in the rolling
process, so that the invention will greatly contribute to the
betterment of the yield of products.
* * * * *