U.S. patent application number 12/092471 was filed with the patent office on 2009-09-10 for apparatus for melting metal and method for manufacturing metal.
Invention is credited to Masayasu Ito, Takeshi Shiraki, Norio Yamamoto.
Application Number | 20090223646 12/092471 |
Document ID | / |
Family ID | 38005587 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090223646 |
Kind Code |
A1 |
Yamamoto; Norio ; et
al. |
September 10, 2009 |
APPARATUS FOR MELTING METAL AND METHOD FOR MANUFACTURING METAL
Abstract
An apparatus for melting metals comprises a hearth for melting a
metal raw material, a mold for forming an ingot by cooling the
molten metal therein, the mold having a bottom, and a base unit for
pulling down the ingot and provided at the bottom of the mold. The
base unit has a surface provided with a concave portion at an
optional location, and the surface of the base unit surrounding the
concave portion is inclined toward the concave portion.
Inventors: |
Yamamoto; Norio; (Kanagawa,
JP) ; Ito; Masayasu; (Kanagawa, JP) ; Shiraki;
Takeshi; (Kanagawa, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
38005587 |
Appl. No.: |
12/092471 |
Filed: |
September 29, 2006 |
PCT Filed: |
September 29, 2006 |
PCT NO: |
PCT/JP2006/319490 |
371 Date: |
January 13, 2009 |
Current U.S.
Class: |
164/47 ;
164/335 |
Current CPC
Class: |
B22D 11/083 20130101;
B22D 11/11 20130101 |
Class at
Publication: |
164/47 ;
164/335 |
International
Class: |
B22D 23/00 20060101
B22D023/00; B22D 41/00 20060101 B22D041/00; B22C 9/00 20060101
B22C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2005 |
JP |
2005-319312 |
Claims
1. An apparatus for melting metals comprising: a hearth for melting
a metal raw material; a mold for forming an ingot by cooling the
molten metal therein, the mold having a bottom; and a base unit for
pulling down the ingot and provided at the bottom of the mold,
wherein the base unit has a surface provided with a concave portion
at an optional location, the concave portion comprises a bottom and
a side wall portion that is inclined from the perpendicular
direction so as to form an acute angle with the bottom, and the
surface of the base unit surrounding the concave portion is
inclined toward the concave portion.
2. The apparatus for melting metals according to claim 1, wherein
the surface of the base unit inclined toward to the concave portion
has an inclination angle of 2 to 10.degree..
3. (canceled)
4. The apparatus for melting metals according to claim 1, wherein
another concave portion is provided further to the concave portion
at the bottom.
5. The apparatus for melting metals according to claim 4, wherein
the concave portion provided at the bottom of the concave portion
has a bottom surface, and the bottom surface is inclined in any
direction with respect to a horizontal surface.
6. The apparatus for melting metals according to claim 1, wherein
the base unit for pulling down the ingot has a separable structure
so as to allow the ingot formed thereon to be pulled out.
7. The apparatus for melting metals according to claim 1, wherein
the base unit comprises a water-cooled copper.
8. The apparatus for melting metals according to claim 1, wherein
the apparatus for melting metals comprises one of an electron-beam
melting furnace and a plasma-arc melting furnace.
9. The apparatus for melting metals according to claim 1, wherein
the metal is selected from the group consisting of titanium,
zirconium, and tantalum.
10. A method for producing metals by using the apparatus for
melting metals according to claim 1.
11. The method for producing metals according to claim 10, wherein
the metal is selected from the group consisting of titanium,
zirconium, and tantalum.
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus for melting
metal materials and relates to a method for producing metals using
the apparatus. Specifically, the present invention relates to a
technique for preventing melting failure and surface defects, which
may form on an ingot portion at the initial melting stage for the
production of an ingot of the metal material in an electron-beam
melting furnace or a plasma-arc melting furnace.
BACKGROUND ART
[0002] It is known, as a technique for producing an ingot, that a
melting furnace provided with a water-cooled copper crucible may be
used, and that a perpendicularly movable water-cooled base unit may
be disposed at the bottom of the crucible. While an electron beam
is emitted on a metal material in a vacuum atmosphere, and a molten
metal material is poured or is dropped into the water-cooled base
unit, the water-cooled base unit is continuously or intermittently
pulled down so as to produce an ingot of the metal material.
[0003] The molten metal contacts the water-cooled base unit and is
solidified from the portion at the start of melting of the metal
material. The molten metal is piled up and is solidified on the
approximately entire surface of the water-cooled base unit after
the molten metal is fed for a certain time. Then, an electron beam
is emitted on the metal material piled up on the water-cooled base
unit so as to melt the entire surface, and the water-cooled base
unit is pulled down. Since the level of the molten metal is lowered
according to the pulling down of the water-cooled base unit, a
molten metal melted by an electron beam is further fed into the
water-cooled cooper crucible. Thus, by pulling down the
water-cooled base unit and continuously feeding a molten metal,
ingots may be successively produced.
[0004] The water-cooled base unit has a flat surface, and the
molten metal that is poured thereinto is solidified in a short time
at the location at which the molten metal falls. When more molten
metal subsequently falls on the solidified metal, the molten metal
flows in any direction and is solidified in a short time. In the
initial stage of the melting, the falling of the molten metal into
the water-cooled base unit and solidification of the molten metal
as described above occur repeatedly. Therefore, a bottom portion of
the ingot produced in the initial stage of the melting (hereinafter
called an "initial molten metal portion"), specifically, an ingot
portion contacting the water-cooled base unit, is formed with
portions that are insufficiently melted and have surface defects.
Since there may be a case in which the portions that are
insufficiently melted and have surface defects will be an obstacle
in the subsequent working process, the portions that are
insufficiently melted and that have surface defects are removed in
advance by machining or cutting. This process reduces the process
yield of the ingot and thereby requires improvement.
[0005] A technique for preventing the melting failure and the
surface defects is known. In this technique, an electron beam is
emitted on a molten metal immediately after the molten metal falls
on the water-cooled base unit so as to maintain the initial molten
metal portion in a melted state. In this case, the electron beam is
emitted on a location in which the molten metal fell on the
water-cooled base unit so as to form a molten metal and to maintain
the melted state. Therefore, the fallen molten metal solidifies
while an irradiation location of the electron beam thereto is
adjusted.
[0006] Regarding this problem, a technique for preventing the
solidification of the initial molten metal portion has been
proposed. In this technique, an electron beam is emitted on a wide
surface including the fallen molten metal on the water-cooled base
unit, thereby temporarily preventing a part of the initial molten
metal from solidifying. In this case, the electron beam is emitted
on the surface of the water-cooled base unit which is not covered
with the molten metal, and there may be a case in which the surface
of the water-cooled base unit is damaged by melting. Therefore,
this technique requires improvement.
[0007] As a method for solving the above problems, a technique is
disclosed in Japanese Unexamined Patent Application Publication No.
2000-274957, for example. In this method, a metal block material
having the same grade as that of a metal to be melted is disposed
on the water-cooled base unit, and melting is started after the
metal block material is irradiated with an electron beam so as to
form sufficient molten metal surface. According to this method, the
charged molten metal does not solidify before an electron beam is
emitted thereon, and the water-cooled base unit is not damaged even
when the electron beam is emitted on an area including the fallen
molten metal. The patent document discloses only a method in which
feeding of a molten metal into a mold is started after a molten
metal surface is formed on the top of the metal block that is
previously disposed on the water-cooled base unit. On the other
hand, the patent document does not disclose a method for forming an
initial molten metal portion. Accordingly, the portion
corresponding to the metal block disposed on the water-cooled base
unit should be removed, whereby the resultant yield is decreased,
and the additional costs are incurred for the removal.
[0008] Moreover, a technique for continuously casting an ingot is
disclosed in Japanese Unexamined Patent Application Publication No.
2000-153345, for example. In this technique, a water-cooled base
unit having a wedge-shaped portion that is engageable with an ingot
is provided on the bottom of a mold. The wedge-shaped portion and
an initial molten metal portion of an ingot are engaged when the
molten metal falls on the water-cooled base unit, and the
water-cooled base unit is pulled down after the ingot is
solidified.
[0009] Japanese Unexamined Patent Application Publication No.
2000-153345 does not disclose a method for forming an initial
molten metal portion and a method for preventing portions that are
insufficiently melted and have surface defects occurring on an
initial molten metal portion. As described above, there have been
no effective methods for solving the problem relating to the
formation of an initial molten metal portion in the production of
ingots.
DISCLOSURE OF THE INVENTION
[0010] The present invention has been completed in view of the
above circumstances. An object of the present invention is to
provide a method for solving the above problem remaining in the
conventional techniques and to produce ingots on the more superior
conditions of the process yields. That is, the present invention
provides a method for melting a metal material while preventing
melting failure and surface defects, which will form on an initial
molten metal portion at the start of melting.
[0011] The inventors performed intensive research so as to solve
the problem remaining in the above conventional techniques. As a
result, the inventors found the following, and the present
invention has thereby been completed. That is, a melting furnace
comprising a water-cooled copper mold is used, and the bottom of
the water-cooled copper mold is disposed with a water-cooled base
unit for pulling down an ingot that is produced. The water-cooled
base unit is provided with a concave portion on the surface thereof
and is provided with an incline on the surface surrounding the
concave portion of the base unit. Therefore, molten metal that
falls or drops into the mold can be collected at the concave
portion provided at the water-cooled base unit.
[0012] That is, the present invention provides an apparatus for
melting metals comprising a hearth for melting a metal raw material
and a mold into which a molten metal is poured so as to form an
ingot. The mold has a bottom and is provided with a base unit for
pulling down the ingot at the bottom. The base unit has a surface
and is provided with a concave portion at an optional location of
the surface, and the surface surrounding the concave portion of the
base unit is inclined toward the concave portion.
[0013] Moreover, in the present invention, another concave portion
is provided to the concave portion at the bottom on the surface of
the base unit. The base unit to be pulled down the ingot has a
separable structure so that the ingot formed thereon can be pulled
out.
[0014] According to the apparatus for melting metals of the present
invention having the above structure, the surface of the base unit
arranged at the bottom of the mold is provided with a concave
portion, and the surface of the base unit other than the concave
portion is inclined toward the concave portion. Therefore, a molten
metal, which is poured from the hearth and reaches the base unit at
the beginning, flows into the concave portion first according to
the incline. Then, the following molten metals fed are filled in
the mold in order from the concave portion and are solidified by
cooling. As a result, surface defects and the portions caused by
the insufficient melting conditions are effectively reduced and may
not occur on the initial molten metal portion of an ingot that is
produced.
[0015] The molten metal can be collected at the bottom of the
concave portion on the base unit surface, thereby further which
reduces the surface defects and the portions caused by the
insufficient melting conditions.
[0016] Moreover, since the base unit for pulling down the ingot has
a separable structure, the ingot produced on the base unit can be
easily pulled out after melting of the metal raw material is
completed.
[0017] In the conventional methods, the melting failure and the
surface defects of the initial molten metal portion are removed by
cutting. In contrast, in the present invention, the surface defects
and the portions that are insufficiently melted hardly occur on the
initial molten metal portion as described above. Therefore, the
process yield of the ingot can be improved compared to the
conventional methods.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 shows a schematic sectional view of an electron-beam
melting apparatus of the present invention.
[0019] FIG. 2 is a schematic sectional view showing a modification
example of a water-cooled base unit of the present invention.
[0020] FIG. 3 is a schematic sectional view showing another
modification example of a water-cooled base unit of the present
invention.
[0021] FIG. 4 is a schematic sectional view showing another
modification example of a water-cooled base unit of the present
invention.
[0022] FIG. 5 is a schematic sectional view showing another
modification example of a water-cooled base unit of the present
invention.
[0023] FIG. 6 is a schematic sectional view showing a conventional
water-cooled base unit.
EXPLANATION OF REFERENCE NUMERALS
[0024] 1 denotes a device for feeding raw materials, 2 denotes a
titanium sponge, 3 denotes a cold hearth, 4 denotes a molten metal,
5 denotes a water-cooled copper mold, 6 denotes an electron beam
gun, 7a to 7e denote water-cooled base units (examples of the
present invention), 7f denotes a water-cooled base unit (example
used in conventional techniques), 71 denotes an inclined portion of
a base unit, 72 denotes a concave portion of a base unit, 73
denotes an inverse tapered portion, 74 denotes a bottom of a base
unit, 75 denotes an inclined bottom portion, 76 denotes a
horizontal bottom portion, and 77 denotes an inclined bottom
portion.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] Preferred embodiments of the present invention will be
described in detail with reference to the figures.
[0026] FIG. 1 shows a preferred embodiment for producing a titanium
ingot from a titanium sponge, which is a raw material to be melted,
by using an electron-beam cold hearth melting furnace. The
reference numeral 1 indicates a device for feeding raw materials,
by which a titanium sponge 2 that is a raw material is fed. In
downstream of the device 1 for feeding raw materials, there is
provided a cold hearth 3 which is made of a water-cooled copper and
contains a molten metal 4 including molten titanium. A water-cooled
copper mold 5 is provided downstream of the cold hearth 3, and the
whole of the cold hearth 3 is obliquely arranged, whereby the
molten metal 4 can be poured from the cold hearth 3 into the
water-cooled copper mold 5. An electron beam gun 6 is provided over
the cold hearth 3 and the water-cooled copper mold 5, and an
electron beam is emitted therefrom so as to melt the titanium
sponge 2.
[0027] The water-cooled copper mold 5 is provided with a
water-cooled base unit 7a at the bottom. As shown in FIG. 1, a
concave portion 72 of the base unit is formed at the center of the
water cooled base unit 7a, and the periphery thereof is formed with
an inclined portion 71 of the base unit that is inclined toward the
concave portion 72 of the base unit. The concave portion 72 of the
base unit comprises an inverse tapered portion 73, which forms the
side wall of the concave portion 72 of the base unit, and a bottom
74 of the base unit. As shown in FIG. 1, the inverse tapered
portion 73 is inclined from the perpendicular direction so that the
inverse tapered portion 73 and the bottom 74 of the base unit form
an acute angle.
[0028] Then, operation methods of the hearth electron-beam melting
furnace will be described as follows. The bottom of the cold hearth
3 is disposed with a solid layer of a titanium called a "skull"
(not shown in the figure) before the melting of the titanium is
started, and an electron beam is emitted on the skull so as to form
a molten metal 4. Then, a titanium sponge 2 is fed into the cold
hearth 3 by the device 1 for feeding raw materials, and the
electron beam is emitted on the titanium sponge 2 so that the
titanium sponge 2 is melted and is mixed with the molten metal 4.
After the molten metal 4 is flown and is refined in the cold hearth
3, the molten metal 4 is poured into the water-cooled copper mold
5.
[0029] The molten metal 4 poured into the water-cooled copper mold
5 reaches the water-cooled base unit 7a that is disposed at the
bottom of the water-cooled copper mold 5. A portion of the molten
metal 4, which reached the water-cooled base unit 7a, reaches the
concave portion 72 of the base unit and is solidified after the
molten metal 4 is cooled by the bottom portion 74 of the base unit
for a while. The other portion of the molten metal 4, which reached
the water-cooled base unit 7a, reaches the inclined portion 71 of
the base unit and rapidly flows into the concave portion 72 of the
base unit according to the incline of the inclined portion 71 of
the base unit. Then, the molten metal 4 is solidified in the same
way as that of the above molten metal 4. Thus, the molten metal
that reaches any portion of the base unit flows into the concave
portion 72 of the base unit, thereby being solidified. The molten
metal 4 is further fed into the water-cooled copper mold 5 until
the molten metal 4 approximately covers the inclined portion 71 of
the base unit, and the molten metal 4 is solidified so as to form
an initial molten metal portion of titanium ingot. In this case,
the molten metal may be solidified in a short time immediately
after the molten metal is fed into the concave portion 72 of the
base unit at the beginning, because the water-cooled base unit is
not sufficiently heated by the heat of the molten metal itself and
is in a low-temperature condition. Therefore, the output level of
the electron beam for irradiation is preferably increased.
[0030] After an initial molten metal portion is formed so as to
cover the concave portion 72 of the base unit and the inclined
portion 71 of the base unit, the water-cooled base unit 7a is
pulled down so as to expand the space over the water-cooled copper
mold 5, and the molten metal 4 is further fed to the space. Thus,
the water-cooled base unit 7a is pulled down while the molten metal
4 is fed into the water-cooled copper mold 5, whereby the molten
metal is cooled and is solidified in order from the lower portion
to the upper portion of the mold. As a result, titanium ingots can
be successively produced. When the water-cooled base unit 7a is
pulled down, since the inverse tapered portion 73 in the concave
portion 72 of the base unit engages with the initial molten metal
portion of titanium ingot, the initial molten metal portion and the
water-cooled base unit 72 will not be separated, and the titanium
ingot can be pulled down.
[0031] Other preferred modification examples of the structural
member of the present invention will be described.
[0032] The inclined portion of the base unit on the water-cooled
base unit of the present invention is preferably inclined from the
periphery toward the center thereof.
[0033] The inclined portion of the base unit is preferably formed
to have an inclination angle of 2 to 10.degree. with respect to the
horizontal surface when a titanium is used as a molten metal. By
forming the inclined portion of the base unit to have an
inclination angle of the above range, the molten metal which is fed
can be uniformly poured into the center portion of the water-cooled
base unit. When the inclination angle is less than 2.degree., it is
difficult to rapidly pour the molten metal to optional locations of
the water-cooled base unit due to the viscosity of the molten
titanium. When the inclination angle is more than 10.degree., the
ratio of the initial molten metal portion to the ingot produced is
increased, whereby the process yield may be decreased. It should be
noted that the lower limit of 2.degree. of the inclination angle
range is effective when titanium is to be ingoted, and the lower
limit is selected according to the viscosity of a metal to be
ingoted.
[0034] As another preferred embodiment of the present invention,
the following steps may be used. Titanium sponge is previously
disposed on the water-cooled base unit, and an electron beam is
emitted thereon so as to melt the titanium sponge. Then, the molten
titanium sponge is poured into the concave portion of the base unit
so as to form an initial molten metal portion. According to this
embodiment, the titanium sponge covers the water-cooled base unit,
whereby the water-cooled base unit is not damaged by irradiation by
the electron beam in forming an initial molten metal portion.
[0035] FIG. 2 shows another preferred embodiment relating to the
present invention. That is, FIG. 2 shows a modification example of
the water-cooled base unit 7a of FIG. 1. In the water-cooled base
unit 7b, the concave portion 72 of the base unit is not provided
with a horizontal bottom, but is instead provided with an inclined
portion 75 that is inclined toward the center portion. According to
the water-cooled base unit 7b having such a structure, the molten
metal poured thereinto first is led to the center of the concave
portion of the base unit and can be solidified in sequence while
preventing the molten metal from solidifying at random
portions.
[0036] FIG. 3 shows another preferred embodiment of the
water-cooled base unit 7a. The water-cooled base unit 7c further
comprises an inclined portion 75 and a horizontal portion 76. By
forming such a concave portion, the bottom of the initial molten
metal portion of an ingot that is produced can be formed with a
convex portion having a gentle curve. Therefore, the initial molten
metal portion produced by using the water-cooled base unit 7c can
be handled more easily than that produced by using the water-cooled
base unit 7b shown in FIG. 2.
[0037] FIG. 4 shows a further preferable embodiment of the
water-cooled base unit 7a. The water-cooled base unit 7d comprises
a concave portion 72 of the base unit having a bottom 77, and the
bottom 77 is flat and is inclined toward the right of the paper
surface. According to the water-cooled base unit 7d having such a
structure, the molten metal that is poured from the hearth into the
base unit can be led along the inclination direction of the bottom
of the concave portion 72 of the base unit. As a result, the molten
metal is solidified in order from the lowest end portion of the
bottom 77, whereby macroscopic defects do not form on the
solidified portion of the molten metal, and an ingot with a good
quality can be produced.
[0038] FIG. 5 is a plan view showing a water-cooled base unit that
relates to the present invention and is observed from the top, and
the water-cooled base unit has a rectangular shape. That is, an
ingot that is produced in this embodiment has a rectangular shape
in cross section. In this embodiment, the concave portion 72 of the
base unit is formed into a trapezoidal shape. The line L-L'
indicates a separation line of the mold. The water-cooled base unit
7e has a structure that can be separated into two portions (7e-a
and 7e-b) at the separation line. Specifically, the lower base unit
of the trapezoidal shape portion is preferably arranged at the side
of the separation line. In this case, the lower base unit is longer
than the upper base unit, and each side connecting the upper base
unit and the lower base unit preferably has an angle in a range of
30 to 60.degree. with respect to the horizontal line from a
practical point of view.
[0039] According to such an arrangement, after a predetermined
amount of an ingot is produced, the water-cooled base unit 7e-a is
separated from the water-cooled base unit 7e-b, and the ingot piled
up on the upper surface of the water-cooled base unit 7e is slid in
a direction perpendicular to the line L-L'. As a result, the ingot
formed with a fitting portion that corresponds to the concave
portion can be separated from the water-cooled base unit 7e.
[0040] The separable structure of the water-cooled base unit as
described above is preferably applied to the above water-cooled
base units 7a to 7d. Such a separable structure facilitates pulling
out of the ingot, which is produced, from the water-cooled base
unit.
[0041] The horizontal cross section of the water-cooled base units
7a to 7e may be formed into a circular shape as well as the above
rectangular shape so as to form an ingot having a circular
shape.
[0042] One of the water-cooled base units 7a to 7e as described
above is disposed in the water-cooled copper mold 5 before melting
of the metal raw material. Therefore, a molten metal poured from
the hearth is appropriately led to the concave portion, whereby the
initial molten metal portion and the water-cooled base unit can be
strongly engaged. Moreover, the formed ingot can be reliably pulled
out from the water-cooled base unit after the melting is
completed.
EMBODIMENTS
[0043] Hereinafter, the present invention will be specifically
described with reference to embodiments. The embodiments are
example of the preferred embodiment of the present invention, and
the present invention is not limited thereto.
First Embodiment
[0044] The water-cooled base unit 7c shown in FIG. 3 was mounted to
the water-cooled copper mold 5 of the electron-beam melting
apparatus in FIG. 1. Then, the cold hearth 3 was irradiated with an
electron beam and was fed with a titanium sponge 2 so as to form a
molten metal 4. The molten metal 4 was fed into the water-cooled
copper mold 5, and a titanium ingot was produced. The ingot
produced was cooled and was separated from the water-cooled base
unit 7c by cutting. The structure at the bottom of the ingot that
was cut had a good quality and had the same quality as that of a
material that can be used for a hot forging. The process yield of
the collected titanium ingot was 98% with respect to the
theoretical yield that was calculated from the input amount of the
raw material.
Second Embodiment
[0045] An ingot was produced under the same conditions as those of
the First Embodiment, except that the water-cooled base unit 7d was
used instead of the water-cooled base unit 7c. As a result, the
process yield of the collected titanium ingot was 98% with respect
to the theoretical yield that was calculated from the input amount
of the raw material.
Comparative Embodiment
[0046] An ingot was produced under the same conditions as those of
the First Embodiment, except that the conventional water-cooled
base unit 7f shown in FIG. 6 was used. The titanium ingot that was
produced was separated from the water-cooled base unit by cutting.
The cut surface of the separated titanium ingot was examined, and
there were portions which were not sufficiently melted, and the
portions were thereby cut off. As a result, the net process yield
of the titanium ingot was only 95%.
INDUSTRIAL APPLICABILITY
[0047] According to the method for melting a metal material by
using an electron beam of the present invention, melting failure
and surface defects of the initial molten metal portion of an ingot
can be reduced. Therefore, the process yield in producing an ingot
can be further improved.
* * * * *