U.S. patent number 3,861,449 [Application Number 04/821,680] was granted by the patent office on 1975-01-21 for method of casting metallic objects.
This patent grant is currently assigned to Howmet Corporation. Invention is credited to Robert J. Barbero.
United States Patent |
3,861,449 |
Barbero |
January 21, 1975 |
METHOD OF CASTING METALLIC OBJECTS
Abstract
The disclosure relates to a method of casting objects having
small, thin and narrow sections from alloys or other
metal-containing materials to produce completed objects properly
filled with materials that solidify with relatively fine and
uniform grain structures. The method includes the steps of
controlling the temperature of the mold within a relatively narrow
temperature range which range includes the melting temperature of
the metal-containing material to be cast prior to the pouring of
the molten material into the mold and also controlling the
temperature of the metal to be cast within as narrow a superheat
range above the melting temperature as practicable.
Inventors: |
Barbero; Robert J. (Wayne,
NJ) |
Assignee: |
Howmet Corporation (Muskegon,
MI)
|
Family
ID: |
25234026 |
Appl.
No.: |
04/821,680 |
Filed: |
May 5, 1969 |
Current U.S.
Class: |
164/65;
164/122 |
Current CPC
Class: |
B22D
27/04 (20130101) |
Current International
Class: |
B22D
27/04 (20060101); B22d 027/04 () |
Field of
Search: |
;164/65,66,121,122 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Juhasz; Andrew R.
Assistant Examiner: Roethel; John E.
Attorney, Agent or Firm: Pennie & Edmonds
Claims
I claim:
1. A method of casting a metal-containing material to form an
object consisting essentially of said metal-containing material,
said object having a thin section and a substantially uniform fine
grain structure throughout comprising:
a. placing a mold in a chamber that is capable of being
evacuated,
b. placing a charge of material to be poured into a heatable
crucible in the chamber,
c. evacuating the chamber,
d. heating the mold and controlling the mold temperature in the
chamber within a range having an upper limit of about 150.degree.F.
above the melting point of the metal-containing material to be
poured and a lower range of 200.degree.F. below that melting
point,
e. melting the charge in the crucible,
f. controlling the temperature of the melted charge in the range of
approximately 50.degree.F. to 100.degree.F. above the melting point
of the metal-containing material, and
g. pouring the charge into the mold.
2. The method of claim 1 in which the charge is a nickel alloy.
3. A method of casting a metal-containing material to form an
object consisting essentially of said metal-containing material,
said object having thin sections and a substantially uniform fine
grain structure throughout comprising:
a. heating a mold having thin pouring spaces of substantial
area,
b. transferring the heated mold to a vacuum casting furnace,
c. controlling the temperature of the heated mold in the casting
furnace within a temperature range of 150.degree.F. above to
200.degree.F. below the melting temperature of the metal to be
poured,
d. controlling the temperature of the metal to be poured within a
range of about 50.degree.F. to about 100.degree.F. above its
melting temperature,
e. pouring the metal into the mold, and
f. cooling the poured mold to solidify the casting therein under
controlled conditions.
4. A method of casting a metal-containing material to form an
object consisting essentially of said metal-containing material,
said object having a thin section and a substantially uniform fine
grain structure throughout comprising:
a. placing a mold in a chamber that is capable of being
evacuated,
b. placing a charge of the material to be poured into a heatable
crucible in the chamber,
c. evacuating the chamber,
d. heating the mold and controlling the mold temperature at
approximately 25.degree.F. below the melting point of the
metal-containing material to be poured,
e. melting the charge in the crucible,
f. controlling the temperature of the melted charge in the range of
approximately 50.degree.F. to 100.degree.F. above the melting point
of the metal-containing material, and,
g. pouring the charge into the mold.
5. A method of casting a metal-containing material to form an
object consisting essentially of said metal-containing material,
said object having a thin section and a substantially uniform fine
grain structure throughout comprising:
a. heating a mold having thin pouring spaces of substantial
area,
b. transferring the heated mold to a vacuum casting furnace,
c. controlling the temperature of the heated mold in the casting
furnace at approximately 25.degree.F. below the melting temperature
of the metal to be poured,
d. controlling the temperature of the metal to be poured within a
range of about 50.degree.F. to about 100.degree.F. above its
melting temperature,
e. pouring the metal into the mold, and
f. cooling the poured mold to solidify the casting therein under
controlled conditions.
Description
BACKGROUND OF THE INVENTION
Prior methods of casting objects in an evacuated atmosphere have
included removing the refractory mold from the furnace in which the
mold has been heated for the purpose of removal of wax or other
fusible pattern material and placing the heated mold in a vacuum
chamber where the mold commences to cool for a period of time prior
to being poured. The cooling period varies with the time required
for closing and evacuation of the chamber and readying the melting
and pouring crucible. The mold will cool hundred of degrees
Fahrenheit during this period and the temperature of the mold when
it is poured will vary substantially under commercial operating
conditions. Castings with thin sections and with proper grain
structure have not been made using these methods.
Other prior techniques have used heating means to control the
temperature of a mold readied for pouring but none of these methods
has provided a casting method capable of producing castings with
thin sections in which the proper controlled relationship among the
mold temperature, temperature of the liquid metal and the melting
temperature of the metal maintained before the pouring of the metal
to provide complete filling and a fine uniform grain size
throughout the casting.
SUMMARY OF THE INVENTION
Broadly, the present invention includes a method for forming a
casting with at least one thin section of substantial size and
having a selected grain structure which comprises heating the mold,
maintaining the mold temperature within a range having an upper
temperature of approximately 150.degree.F above the melting
temperature of the metal-containing material to be formed and a
lower limit of approximately 200.degree.F below the melting
temperature, controlling the temperature of the liquid material
within as narrow a range of superheat as practicable and pouring
the liquid material into the mold. The optimum practical range of
superheat of the liquid material has been found to be about
50.degree. to 100.degree.F to produce complete filling and the
preferred fine grain structure with most alloys used in producing
engine parts and other objects having thin sections whether
stressed during use or not.
The method of the present invention is particularly applicable to
investment casting where refractory molds are poured in an
evacuated, inert gas or other non-atmospheric condition.
It has been found that the controlling of temperatures of the metal
and the mold within the ranges of this novel method can be
practicably accomplished under commercial production conditions by
using induction coil heating means. The practice of the present
method is also effective in controlling grain structure where the
patterns have been coated with a material which gives the mold
grain nucleating properties.
It is a feature of the invention that castings, such as turbine
wheel and impeller blade parts, which have thin sections may be
cast without formation of detrimental columnar grains at the thin
sections of the parts, such as in the outer rim of the wheel and
between the blades. Since during use these parts are highly
stressed especially at the above locations, the improved filling of
the thin sections during pouring and the improved grain structure
provides an acceptable part that resists the formation of
continuous cracks and their propagation during service.
It has also been found that parts having thin sections which are
not subject to stress may be made using the method, for example;
engine exhaust manifolds which are thin walled and have complex
intersections.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
The drawing illustrates apparatus that may be used in practicing
the invention, in which a refractory mold 1 is positioned on an
metal plate 2 which in turn is placed on an insulation base plate 3
made of any suitable insulating material.
A cylindrically-shaped section of graphite material or susceptor 4
is positioned on the plate 2 within an induction coil 6. The
susceptor may also be made of tantalum, molybdenum or other
suitable material. susceptor 4 is heated by the magnetic field
produced in induction coil 6 and the susceptor in turn through
radiation heats mold 1 positioned within it.
Refractory melting crucible 7, mold 1 and susceptor 4 are
positioned within a vacuum casting furnace (not shown) in a proper
relationship to each other, as shown, to permit heating of the mold
and metal and the pouring of the melted metal into the mold.
Pouring crucible 7 is heated by an independently operated induction
coil 8 and is tilted and rotated by conventional tilting means (not
shown) to pour the molten metal 9 into the mold 1. Other suitable
heating means such as resistance heaters may be used to heat the
mold and crucible provided that each is independently controllable
and capable of providing sufficient heat to produce readily the
required temperatures in varying sized molds and crucibles.
As an example of the practice of the method, a mold shaped for
casting a multi-blade turbine rotor was removed from a burnout
furnace in which it had been heated to about
1,800.degree.-2000.degree.F. The turbine blades to be formed had
thin sections that are only about .015 inch in thickness and had in
addition relatively thin blading sections having substantial length
and area. The mold was placed within a susceptor and susceptor and
mold were placed in a suitable vacuum chamber having facilities for
mounting and pouring a molten metal.
A charge of a nickel based alloy having a melting temperature of
about 2,300.degree.F was placed in pouring crucible 7 in the
chamber and the chamber was closed and evacuated. The charge was
then melted and superheated to a temperature of about
2,385.degree.F. The mold temperature was maintained through use of
the susceptor at approximately 2,275.degree.F. Mold temperatures as
low as 2,100.degree.F may be used but a temperature of about
25.degree. below the melting point is preferred.
Where a mold temperature in the upper end of the range of the
invention is used, it is preferred that it be close to the melting
temperature of the alloy and should not be more than 150.degree.F
above that temperature. It is preferred that the method be
commercially operated such that the temperature of the mold is most
likely to be just below the melting temperature of the charge.
Temperatures within the desired ranges were accomplished using
proper controls together with the judgment of experienced personnel
in the casting field. The pattern from which the mold had been made
was not coated with a material which imparted nucleating properties
to the mold; however, such coatings may be used if desired.
The mold was poured and after a suitable period for solidification
of the alloy the mold was removed from the chamber. The casting
formed was completely filled and had a fine equiaxed grain
structure.
The cooling rate of the casting after initial solidification may be
controlled to further influence the formation of grain structures
to provide the particular characteristics which are desired for the
part to be made.
* * * * *