U.S. patent application number 12/138892 was filed with the patent office on 2009-12-17 for electrical servo driven rollover melt furnace.
This patent application is currently assigned to ZIMMER, INC.. Invention is credited to Steven Allen, James Rackley, Brad L. Rauguth.
Application Number | 20090308562 12/138892 |
Document ID | / |
Family ID | 41413693 |
Filed Date | 2009-12-17 |
United States Patent
Application |
20090308562 |
Kind Code |
A1 |
Rauguth; Brad L. ; et
al. |
December 17, 2009 |
ELECTRICAL SERVO DRIVEN ROLLOVER MELT FURNACE
Abstract
An apparatus and method for melting metal and casting molds. The
apparatus includes a rollover melt furnace having a crucible and a
mold. The apparatus also includes an electrical servomotor that
drives rotation of the crucible about an axis of rotation. This
rotation of the crucible causes molten metal to flow from a pour
opening in the crucible into a fill opening in the mold. The
apparatus may further include a controller to carry out a pouring
process in compliance with a pour profile and a melting process in
compliance with a melt profile.
Inventors: |
Rauguth; Brad L.; (North
Webster, IN) ; Rackley; James; (Warsaw, IN) ;
Allen; Steven; (Winona Lake, IN) |
Correspondence
Address: |
ZIMMER TECHNOLOGY - BAKER & DANIELS
111 EAST WAYNE STREET, SUITE 800
FORT WAYNE
IN
46802
US
|
Assignee: |
ZIMMER, INC.
Warsaw
IN
|
Family ID: |
41413693 |
Appl. No.: |
12/138892 |
Filed: |
June 13, 2008 |
Current U.S.
Class: |
164/121 ;
164/133; 164/47; 266/240; 266/78; 266/87 |
Current CPC
Class: |
B22D 41/04 20130101;
B22D 35/04 20130101; B22D 23/00 20130101; B22D 35/06 20130101 |
Class at
Publication: |
164/121 ;
266/240; 266/78; 266/87; 164/47; 164/133 |
International
Class: |
B22D 23/00 20060101
B22D023/00; B22D 23/06 20060101 B22D023/06; B22D 46/00 20060101
B22D046/00; B22D 35/06 20060101 B22D035/06; B22D 35/04 20060101
B22D035/04 |
Claims
1. An apparatus for melting metal and casting molds comprising: a
rollover melt furnace comprising a rotating shaft and a crucible
connected to the rotating shaft for rotation therewith, the
crucible having an exterior surface that includes a pour opening;
and an electrical motor connected in driving relationship to the
rotating shaft of the rollover melt furnace.
2. The apparatus of claim 1, further comprising a motion feedback
loop that controls the electrical motor, the motion feedback loop
comprising a controller and a feedback device, wherein: the
feedback device is capable of sending a plurality of feedback
signals to the controller; and the controller is capable of
receiving the plurality of feedback signals from the feedback
device, comparing the plurality of feedback signals to a pour
profile, and sending a plurality of command signals to the
electrical motor, the command signals comprising attempts to
minimize a difference between the feedback signals and the pour
profile.
3. The apparatus of claim 2, wherein: the crucible has an actual
position, an actual velocity, and an actual acceleration, about an
axis of rotation; and the plurality of feedback signals correspond
to at least one of: the actual position of the crucible, the actual
velocity of the crucible, and the actual acceleration of the
crucible about said axis of rotation.
4. The apparatus of claim 2, wherein the plurality of command
signals correspond to at least one of: a velocity of the electrical
motor and an acceleration of the electrical motor.
5. The apparatus of claim 1, further comprising a temperature
feedback loop that controls a temperature of the crucible.
6. An apparatus for melting metal and casting molds comprising: a
rollover melt furnace comprising a rotating shaft, a crucible
connected to the rotating shaft for rotation therewith, the
crucible having a pour opening into an interior cavity, and a mold
having an exterior surface that includes a fill opening, the fill
opening being sized to accommodate a flow from the pour opening of
the crucible; an electrical motor connected in driving relationship
to the rotating shaft of the rollover melt furnace; and a
controller, the controller being capable of sending a plurality of
command signals to the electrical motor.
7. The apparatus of claim 6, further comprising a feedback device
capable of sending a plurality of feedback signals to the
controller.
8. The apparatus of claim 7, wherein the feedback device is
incorporated within the electrical motor.
9. The apparatus of claim 7, wherein the feedback device is
remotely mounted on the rollover melt furnace.
10. The apparatus of claim 7, wherein: the crucible has an actual
position, an actual velocity, and an actual acceleration, about an
axis of rotation; and the plurality of feedback signals correspond
to at least one of: the actual position of the crucible, the actual
velocity of the crucible, and the actual acceleration of the
crucible about said axis of rotation.
11. The apparatus of claim 6, wherein the plurality of command
signals correspond to at least one of: a velocity of the electrical
motor and an acceleration of the electrical motor.
12. The apparatus of claim 6, further comprising at least one pour
profile, the at least one pour profile representing a set time
interval and at least one of: a set position of the crucible, a set
velocity of the crucible, and a set acceleration of the crucible
about an axis of rotation over the set time interval, wherein the
controller is further capable of: storing the at least one pour
profile; receiving a user command; accessing a desired pour profile
based on the user command; determining a command signal based on
the desired pour profile; and sending the command signal to the
electrical motor.
13. The apparatus of claim 12, wherein the controller is further
capable of: receiving a plurality of feedback signals from a
feedback device; and comparing the desired pour profile with the
plurality of feedback signals and determining a command signal
therefrom, the command signal comprising an attempt to minimize a
difference between the feedback signals and the desired pour
profile.
14. The apparatus of claim 6, wherein the controller is further
capable of: storing and accessing at least one melt profile, the at
least one melt profile representing a set time interval and a set
temperature of the interior cavity of the crucible over the set
time interval; and sending a temperature command to the
crucible.
15. The apparatus of claim 14, wherein the controller is further
capable of: receiving a plurality of temperature readings from a
temperature feedback device; and comparing the at least one melt
profile with the plurality of temperature readings and determining
the temperature command therefrom, the temperature command
comprising an attempt to minimize a difference between the
temperature readings and the at least one melt profile.
16. A method of melting metal and casting molds in a rollover melt
furnace comprising a rotating shaft and a crucible connected to the
rotating shaft for rotation therewith, the crucible having a pour
opening into an interior cavity, the pour opening being located on
an exterior surface of the crucible, comprising the steps of:
loading an ingot into the interior cavity of the crucible; melting
the ingot in the interior cavity of the crucible thereby forming a
molten metal; attaching a mold to the rollover melt furnace, the
mold having an exterior surface that includes a fill opening, the
fill opening being sized to accommodate a flow from the pour
opening of the crucible; and rotating the shaft using an electrical
motor to transfer the molten metal from the crucible to the
mold.
17. The method of claim 16, further comprising the step of
automatically positioning a clamp to receive the mold.
18. The method of claim 16, wherein the step of melting the ingot
comprises controlling a temperature of the crucible based on a melt
profile.
19. The method of claim 16, further comprising the steps of:
rotating the shaft so that the crucible reaches a wet lip position;
and after reaching the wet lip position, rotating the shaft so that
the crucible returns to the upright position before reaching an
inverted position.
20. The method of claim 16, wherein the step of rotating the shaft
using an electrical motor comprises accelerating rotation of the
shaft until the crucible reaches a set velocity.
21. The method of claim 16, wherein the step of rotating the shaft
using an electrical motor comprises: rotating the shaft so that the
crucible reaches a fill position, in which molten metal flows from
the crucible to the mold; and after reaching the fill position,
decelerating rotation of the shaft until the crucible reaches an
inverted position.
22. The method of claim 16, wherein the step of rotating the shaft
using an electrical motor comprises controlling rotation of the
shaft based on a pour profile.
23. The method of claim 16, further comprising the step of
inputting a command into a controller to automatically control
rotation of the shaft.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to rollover melt furnaces for
melting metals and casting metals in molds. More specifically, the
present invention relates to an electrical servo driven rollover
melt furnace and method for utilizing the same.
[0003] 2. Description of the Related Art
[0004] Casting is a manufacturing process by which molten metal is
poured into a mold, allowed to solidify within the mold, and then
removed from the mold, resulting in a solid fabricated part.
[0005] A rollover melt furnace is a device typically used to
perform the casting process. A typical rollover melt furnace has a
heated crucible that is connected to a rotating shaft. As the shaft
rotates, the crucible also rotates about a horizontal axis. When
the crucible is in an upright, or rest, position, a top surface of
the crucible faces upward. The top surface of the crucible includes
a pour opening.
[0006] In operation, the crucible is first manually rotated to a
charge position. Once reaching this charge position, an ingot is
loaded into the crucible.
[0007] Next, the crucible is manually rotated to an upright
position. The crucible is heated in the upright position until the
ingot melts. After the molten metal reaches a desired temperature,
a mold is connected to the crucible with a bottom surface of the
mold facing downward. The bottom surface of the mold includes a
fill opening. The bottom surface of the mold is attached to the top
surface of the crucible, with a device such as a clamp, so that the
fill opening of the mold is in fluid communication with the pour
opening of the crucible.
[0008] Then, the crucible is rotated to an inverted position. Once
reaching this inverted position, the top surface of the crucible
faces downward, while the bottom surface of the mold faces upward.
The molten metal pours from the pour opening of the crucible into
the fill opening of the mold. Finally, the mold is removed from the
rollover melt furnace, and the molten metal inside the mold is
allowed to solidify before being removed from the mold.
[0009] Currently, rotation of the crucible is driven by a hydraulic
motor. Hydraulic rollover melt furnaces possess many disadvantages.
First, the pour cycle described above is not repeatable. Hydraulic
actuators are highly susceptible to process variability, especially
over time as the actuators wear out. For example, from pour to
pour, the pour cycle of a hydraulic rollover melt furnace may vary
up to several seconds. Particular molds require particular pour
cycles. If a pour occurs too quickly, inclusions may form within
the hardened metal. If a pour occurs too slowly, the molten metal
may not fill all areas of the mold, particularly those areas of
small cross-section. If a mold is filled incorrectly, the process
must be repeated.
[0010] Also, the pour cycle of a hydraulic rollover melt furnace is
not reproducible from furnace to furnace. Each hydraulic rollover
melt furnace has a single pour cycle setting that cannot be
efficiently or easily reprogrammed to account for various
molds.
[0011] Finally, the process of actually filling a mold using a
hydraulic rollover melt furnace presents several challenges. For
one, current devices provide one-directional rotation of the
crucible. More specifically, the motor drives the crucible from the
upright position to the inverted position, but the actuator is not
programmable to stop at discrete positions when pouring or when
driving the crucible from the inverted position back to the upright
position. Therefore, the crucible must be manually rotated from the
inverted position to a charge position to receive the next ingot,
and then must be manually rotated from the charge position to the
upright position to melt the ingot. In addition, the speed at which
current devices rotate is difficult to control, often resulting in
pours conducted at excessive speeds. As mentioned above, if a mold
is filled too quickly, inclusions may form within the hardened
metal. Finally, current devices do not allow for wetting the
crucible lip with molten metal before pouring. For one, the pour
speed is too fast to pause at a wet lip position, because molten
metal would slosh out of the crucible. Also, the one-directional
rotation prohibits the crucible from stopping at this discrete
position and from automatically returning to an upright position
after reaching the wet lip position.
SUMMARY
[0012] The present invention relates to an apparatus for melting
metal and casting molds. The apparatus includes a rollover melt
furnace having a crucible and a mold. The apparatus also includes
an electrical servomotor that drives rotation of the crucible about
an axis of rotation. This rotation of the crucible causes molten
metal to flow from a pour opening in the crucible into a fill
opening in the mold. The apparatus may further include a controller
to carry out a pouring process in compliance with a pour profile
and a melting process in compliance with a melt profile.
[0013] According to an embodiment of the present invention, an
apparatus includes a rollover melt furnace, having a rotating shaft
and a crucible, and an electrical motor. The crucible is connected
to the rotating shaft for rotation therewith. The crucible has an
exterior surface that includes a pour opening. The electrical motor
is connected in driving relationship to the rotating shaft of the
rollover melt furnace.
[0014] According to another embodiment of the present invention, an
apparatus includes a rollover melt furnace having a rotating shaft,
a crucible, and a mold. The crucible is connected to the rotating
shaft for rotation therewith and includes a pour opening into an
interior cavity. The mold has an exterior surface that includes a
fill opening, which is sized to accommodate a flow from the pour
opening of the crucible. The apparatus also includes an electrical
motor connected in driving relationship to the rotating shaft of
the rollover melt furnace. The apparatus further includes a
controller. The controller is capable of sending a plurality of
command signals to the electrical motor.
[0015] The present invention also relates to a method for melting
metal and casting molds. Advantageously, the present method may be
customized depending on the particular mold, the particular metal
being used, and any other relevant factors. Also, the present
method is repeatable and consistent from pour to pour, and is
reproducible from apparatus to apparatus. Finally, the present
method permits two-directional, electronically controlled rotation
of the crucible.
[0016] According to an embodiment of the present invention, a
method is provided for melting metal and casting molds in a
rollover melt furnace. The rollover melt furnace includes a
rotating shaft and a crucible connected to the rotating shaft for
rotation therewith. The crucible includes a pour opening located on
an exterior surface of the crucible into an interior cavity. The
method involves loading an ingot into the interior cavity of the
crucible; melting the ingot in the interior cavity of the crucible
thereby forming a molten metal; attaching a mold to the rollover
melt furnace, the mold having an exterior surface that includes a
fill opening, the fill opening being sized to accommodate a flow
from the pour opening of the crucible; and rotating the shaft using
an electrical motor to transfer the molten metal from the crucible
to the mold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention itself will be better understood by
reference to the following description of embodiments of the
invention taken in conjunction with the accompanying drawings,
wherein:
[0018] FIG. 1 is a front elevational view of an apparatus of the
present invention;
[0019] FIG. 2 is a side elevational view of the apparatus of FIG.
1, taken along line 2-2 of FIG. 1;
[0020] FIG. 3 is a cross-sectional view of the apparatus of FIG. 1,
taken along line 3-3 of FIG. 1;
[0021] FIG. 4 is a partial cross-section of the apparatus of FIG. 3
with a crucible in the charge position;
[0022] FIG. 5 is a partial cross-section of the apparatus of FIG. 3
with the crucible in the upright position;
[0023] FIG. 6 is a partial cross-section of the apparatus of FIG. 3
with the crucible in the wet lip position;
[0024] FIG. 7 is a partial cross-section of the apparatus of FIG. 3
with the crucible in the fill position;
[0025] FIG. 8 is a partial cross-section of the apparatus of FIG. 3
with the crucible in the inverted position;
[0026] FIG. 9 is a block diagram of a motion feedback loop and a
temperature feedback loop of the present invention;
[0027] FIG. 10 is graphical depiction of pour profiles of the
present invention; and
[0028] FIG. 11 is graphical depiction of a melt profile of the
present invention.
[0029] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate exemplary embodiments of the invention and such
exemplifications are not to be construed as limiting the scope of
the invention any manner.
DETAILED DESCRIPTION
[0030] Referring to FIGS. 1-8, apparatus 10 is provided for melting
metal and casting molds. Apparatus 10 includes rollover melt
furnace 12. Rollover melt furnace 12 includes frame 14, rotating
shaft 16, clamp 18, crucible 20, and mold 22. Frame 14 supports
rollover melt furnace 12.
[0031] As shown in FIG. 1, crucible 20 is connected to rollover
melt furnace 12 for rotation along with rotating shaft 16. In other
words, crucible 20 may be directly or indirectly connected to
rotating shaft 16. Crucible 20 includes exterior surface 24, which
may include top exterior surface 26 and bottom exterior surface 28.
Crucible 20 also includes interior cavity 30. Exterior surface 24
includes pour opening 32, which comprises an aperture in exterior
surface 24 that provides access into interior cavity 30 of crucible
20. In an exemplary embodiment, top exterior surface 26 includes
pour opening 32. Lip 34 is formed between exterior surface 24 and
interior cavity 30. Crucible 20 may be heated by any method known
in the art including, but not limited to, induction. In one form
thereof, interior cavity 30 of crucible 20 has a capacity of up to
approximately 50 pounds. In another form thereof, crucible 20 is
approximately 0.5 inches thick between interior cavity 30 and
exterior surface 24.
[0032] As shown in FIG. 5, mold 22 includes exterior surface 36,
which may include top exterior surface 38 and bottom exterior
surface 40. Mold 22 also includes interior cavity 42. Exterior
surface 36 includes fill opening 44, which comprises an aperture in
exterior surface 36 that provides access into interior cavity 42 of
mold 22. In an exemplary embodiment, bottom exterior surface 40
includes fill opening 44. Fill opening 44 should be sized to
accommodate a flow from pour opening 32, as discussed in more
detail below.
[0033] Returning to FIG. 1, apparatus 10 also includes electrical
servomotor 46. Electrical servomotor 46 is connected in driving
relationship to rotating shaft 16 of rollover melt furnace 12.
Electrical servomotor 46 is capable of rotating shaft 16 about axis
48. Crucible 20 is non-rotatably connected to rotating shaft 16, so
electrical servomotor 46 is also capable of rotating crucible 20
about axis 48.
[0034] Referring to FIGS. 9 and 10, to control the rotation of
crucible 20, apparatus 10 may further include controller 52.
Controller 52 controls the actual movement of crucible 20 about
axis 48 based on pour profile 58. Pour profile 58 is a set of
instructions for the operation of rollover melt furnace 12. Over a
set time interval 62, pour profile 58 indicates the desired
movement of crucible 20 about axis 48 in terms of a set position 64
of crucible 20, a set velocity 66 of crucible 20, and/or a set
acceleration 68 of crucible 20 about axis 48, for example.
[0035] In an exemplary embodiment of the present invention,
controller 52 may be capable of storing more than one pour profile
58 and accessing a desired pour profile 58 based on user command
70. Controller 52 may include an input device for receiving user
command 70 such as, but not limited to, a keyboard or a bar code
reader. A user may inform controller 52 of the particular job being
performed by, for example, entering a command on the keyboard or
scanning a bar code.
[0036] According to an embodiment of the present invention,
apparatus 10 may further include motion feedback loop 49, as shown
in FIG. 9. Motion feedback loop 49 includes electrical servomotor
46, motion feedback device 50, and controller 52. Motion feedback
device 50 may be incorporated within electrical servomotor 46, or
motion feedback device 50 may be remotely mounted on rollover melt
furnace 12, such as on rotating shaft 16. Motion feedback device 50
may be any device, such as a transducer, capable of monitoring at
least one output variable 54 of electrical servomotor 46 and
sending feedback signals 56 to controller 52. In an exemplary
embodiment, motion feedback device 50 includes a resolver or an
encoder which provides position and/or velocity feedback. Output
variable 54 to be measured by motion feedback device 50 depends on
the location of motion feedback device 50. Ultimately, output
variable 54 corresponds to the actual position, the actual
velocity, and/or the actual acceleration of crucible 20 about axis
48 at a given time.
[0037] The following two examples illustrate the function of motion
feedback device 50. If motion feedback device 50 is mounted on
rotating shaft 16, output variable 54 may be the velocity of
rotation about axis 48 of rotating shaft 16. The velocity of
rotation about axis 48 of rotating shaft 16 corresponds equally to
the velocity of rotation about axis 48 of crucible 20. If, on the
other hand, motion feedback device 50 is incorporated within
electrical servomotor 46, output variable 54 may be the position of
electrical servomotor 46. The position of electrical servomotor 46
corresponds to the position of rotating shaft 16, and in turn the
actual position of crucible 20 about axis 48. For example, a single
rotation of electrical servomotor 46 may correspond to a certain
degree of rotation of crucible 20 about axis 48, depending on the
gear reduction (if any) used between electrical servomotor 46 and
crucible 20.
[0038] Referring still to FIG. 9, after motion feedback device 50
measures and/or computes output variable 54, it then sends feedback
signal 56 to controller 52. Like output variable 54, feedback
signal 56 also corresponds to the actual position, the actual
rotation velocity, and/or the actual rotation acceleration of
crucible 20 about axis 48 at a given time. Controller 52 may be any
device, such as a computer, capable of receiving feedback signals
56 from motion feedback device 50, comparing those feedback signals
56 to pour profile 58, and sending command signals 60 to electrical
servomotor 46.
[0039] Referring again to FIG. 9, upon receiving feedback signal 56
from motion feedback device 50, controller 52 compares feedback
signal 56 to a desired pour profile 58. More specifically,
controller 52 compares the actual position, the actual velocity,
and/or the actual acceleration of crucible 20 about axis 48 at a
given time (based on feedback signal 56) to set position 64, set
velocity 66, and/or set acceleration 68 of crucible 20 about axis
48 at the corresponding time from set time interval 62 (based on
pour profile 58).
[0040] Referring still to FIG. 9, after comparing feedback signal
56 to pour profile 58, controller 52 determines a command signal 60
and sends command signal 60 to electrical servomotor 46. Command
signal 60 may correspond to the desired velocity and/or the desired
acceleration of electrical servomotor 46. More generally, command
signal 60 controls the movement of electrical servomotor 46.
[0041] In operation, controller 52 conforms the actual movement of
crucible 20 about axis 48 to pour profile 58. If feedback signal 56
does not conform to pour profile 58, controller 52 sends command
signal 60 to electrical servomotor 46 to alter the behavior of
electrical servomotor 46. For example, if, at a given time within
set time interval 62, crucible 20 has not yet reached set velocity
66, controller 52 may send command signal 60 to electrical
servomotor 46 directing electrical servomotor 46 to accelerate.
Motion feedback loop 49 between electrical servomotor 46, motion
feedback device 50, and controller 52 may include any closed-loop
control devices known in the art, such as a resolver or an encoder
which provides position and/or velocity feedback, and may operate
throughout the pouring process, as described in more detail
below.
[0042] According to another embodiment of the present invention, an
open-loop control system may be utilized during a portion of or the
entire pouring process. Without necessarily receiving feedback
signals 56 from motion feedback device 50, controller 52 may send
command signals 60 to electrical servomotor 46 based on pour
profile 58. In this embodiment, pour profile 58 may indicate the
amount of power to be supplied to electrical servomotor 46 over set
time interval 62, such that controller 52 sends command signals 60
to electrical servomotor 46 in the form of power inputs to rotate
electrical servomotor 46 at a desired rate. The open-loop control
system may be less precise than the closed-loop control system of
motion feedback loop 49.
[0043] Referring to FIGS. 9 and 11, controller 52 may also control
the melting of metal within crucible 20 based on melt profile 74.
Melt profile 74 is a set of instructions for the heating of
crucible 20 of rollover melt furnace 12. Over a set time interval
80, melt profile 74 indicates, for example, the desired set
temperature 82 of crucible 20 or of its contents within interior
cavity 30 and/or the power supplied to heat crucible 20.
Ultimately, set temperature 82 should reach melting point 83 of the
particular material being poured.
[0044] In an exemplary embodiment of the present invention, as with
pour profile 58, controller 52 may be capable of storing more than
one melt profile 74 and accessing a desired melt profile 74 based
on user command 70. Controller 52 may include an input device for
receiving user command 70 such as, but not limited to, a keyboard
or a bar code reader. A user may inform controller 52 of the
particular job being performed by, for example, entering a command
on the keyboard or scanning a bar code. In another exemplary
embodiment, controller 52 will access both a desired pour profile
58 and a desired melt profile 74 based on a single user command
70.
[0045] According to an embodiment of the present invention,
apparatus 10 may further include temperature feedback loop 72, as
shown in FIG. 9. Temperature feedback loop 72 conforms the actual
temperature of crucible 20, or its contents, to a melt profile 74.
Temperature feedback device 75 measures the temperature of crucible
20, or its contents, and sends temperature reading 76 to controller
52. Temperature feedback device 75 may include an infrared
pyrometer or an immersion thermocouple, for example. Controller 52
may be capable of receiving temperature readings 76 from
temperature feedback device 75, comparing those temperature
readings 76 to melt profile 74, and sending temperature commands 78
to crucible 20. In an exemplary embodiment, controller 52 receives
temperature readings 76 from temperature feedback device 75 and
sends temperature commands 78 to crucible 20 by controlling the
power output to crucible 20.
[0046] In operation, temperature feedback loop 72 conforms the
actual melting process to melt profile 74. If a temperature reading
76 at a given time does not conform to set temperature 82 of melt
profile 74 at the corresponding time, controller 52 sends
temperature command 78 to crucible 20 to alter the temperature of
crucible 20. For example, if, at a given time within set time
interval 80, crucible 20 has not yet reached set temperature 82,
controller 52 may send temperature command 78 to crucible 20
directing crucible 20 to increase its temperature. Temperature
feedback loop 72 may include any closed-loop control devices known
in the art, such as an infrared pyrometer, and may operate during
the melting process, as described in more detail below.
[0047] According to another embodiment of the present invention, an
open-loop control system may be utilized during a portion of or the
entire melting process. Without necessarily receiving temperature
readings 76 from temperature feedback device 75, controller 52 may
send temperature commands 78 to crucible 20 based on melt profile
74. In this embodiment, melt profile 74 may indicate, for example,
the amount of power to be supplied to crucible 20 over set time
interval 80, such that controller 52 sends temperature commands 78
to crucible 20 in the form of power inputs to melt metal ingot 86
at a desired rate. At some point during the melting process, such
as when the metal ingot 86 is expected to approach melting point
83, temperature feedback loop 72 may take over for the open-loop
control system.
[0048] Referring to FIGS. 1-8, a method is provided for melting
metal and casting molds. In the following paragraphs, the rotation
of crucible 20 about axis 48 is described relative to a vertical
plane. As shown in FIG. 1, crucible 20 is in an upright position 84
when top exterior surface 26 of crucible 20 faces upward. Upright
position 84 is associated with an angle of 0 degrees from a
vertical plane. Although the drawings depict rotation of rotating
shaft 16 and crucible 20 in a clockwise direction, rollover melt
furnace 12 may permit rotation of rotating shaft 16 and crucible 20
in a counter-clockwise direction, or in both clockwise and
counter-clockwise directions.
[0049] As illustrated in FIG. 4, metal ingot 86 is loaded into
interior cavity 30 of crucible 20. In an exemplary embodiment of
the present invention, this loading step takes place at charge
position 88. At charge position 88, crucible 20 is positioned
approximately 90 degrees from a vertical plane. In other words, top
exterior surface 26 of crucible 20 faces sideways. Charge position
88 makes interior cavity 30 easily accessible to a user for loading
metal ingot 86.
[0050] As illustrated in FIG. 5, after loading metal ingot 86 (FIG.
4) into crucible 20, crucible 20 is heated to melt metal ingot 86.
Crucible 20 may be heated at an uneven rate to reduce spitting as
metal ingot 86 melts. Crucible 20 may be heated until metal ingot
86 is within approximately 5 degrees of melting point 83 or until
metal ingot 86 becomes molten metal 90. As discussed above, this
melting process may be carried out in compliance with melt profile
74 (FIG. 11), such as by using temperature feedback loop 72 (FIG.
9). Upon reaching the desired temperature, a user may be notified,
such as via an alarm or an indication on a monitor, that the
melting process is complete. Along with temperature feedback loop
72, the point at which metal ingot 86 becomes molten metal 90 may
be verified manually with an immersions thermometer.
[0051] After metal ingot 86 is melted, mold 22 is attached to
rollover melt furnace 12. Mold 22 is secured to rollover melt
furnace 12, and more specifically to crucible 20. Mold 22 may be
secured to crucible 20 by manually or automatically pressing clamp
18 against top exterior surface 38 of mold 22, by locking mold 22
and crucible 20 together, or by any other known method. Mold 22 is
positioned onto crucible 20 such that fill opening 44 of mold 22 is
in fluid communication with pour opening 32 of crucible 20. In
other words, mold 22 is positioned onto crucible 20 such that
interior cavity 42 of mold 22 is in fluid communication with
interior cavity 30 of crucible 20.
[0052] In an exemplary embodiment of the present invention, the
attachment of mold 22 to crucible 20 takes place in upright
position 84. Also, according to this exemplary embodiment, bottom
exterior surface 40 of mold 22, which includes fill opening 44, is
secured to top exterior surface 26 of crucible 20, which includes
pour opening 32.
[0053] In another exemplary embodiment of the present invention,
clamp 18 is automatically positioned to receive mold 22. More
specifically, clamp 18 is automatically positioned far enough away
from crucible 20 to receive mold 22 but near enough to crucible 20
to be automatically and quickly pressed against mold 22 once mold
22 is attached to rollover melt furnace 12. To facilitate even
filling of mold 22, mold 22 may be preheated, such as in a furnace,
before receiving molten metal 90. The preheated mold 22 should be
filled quickly to avoid significant cooling of mold 22. Based on
user command 70, controller 52 may automatically direct clamp 18 to
the desired receiving position by operating, for example, a
hydraulic cylinder. The positioning of clamp 18 may occur at or
near the time that controller 52 accesses a desired pour profile 58
and/or a desired melt profile 74. Once mold 22 is attached to
rollover melt furnace 12, controller 52 may again operate the
hydraulic cylinder to press clamp 18 against mold 22.
[0054] Referring to FIGS. 6-8, the present method involves pouring
molten metal 90 to cast mold 22. As discussed above, this pouring
process may be carried out in compliance with pour profile 58 (FIG.
10), such as by using motion feedback loop 49 (FIG. 9). In an
exemplary embodiment, the pouring process is initiated after molten
metal 90 forms within crucible 20 (FIG. 5).
[0055] As illustrated in FIG. 6, crucible 20 is rotated to wet lip
position 92. Wet lip position 92, as used herein, is the position
of crucible 20 at which molten metal 90 contacts lip 34 of crucible
20 just before exiting interior cavity 30 of crucible 20 through
pour opening 32. Depending on the amount of molten metal 90 within
crucible 20, the position of crucible 20 relative to a vertical
plane may vary between 0 and 90 degrees. For example, as shown in
FIG. 6, crucible 20 is positioned approximately 45 degrees from a
vertical plane. If interior cavity 30 of crucible 20 contained a
smaller amount of molten metal 90, crucible 20 would have to be
rotated further before reaching wet lip position 92. Contacting lip
34 of crucible 20 with molten metal 90 promotes even pouring by
preheating lip 34 and by cleaning residue from lip 34. Crucible 20
may pause at wet lip position 92 to more fully achieve these
benefits.
[0056] In an exemplary embodiment of the present invention, shown
graphically in FIG. 10, crucible 20 may be rotated back to upright
position 84 after reaching wet lip position 92. Crucible 20 may
then return to and pause at wet lip position 92 once again before
undergoing the rest of the pouring process. This motion between wet
lip position 92 and upright position 84 may be repeated any number
of times before undergoing the remainder of the pouring
process.
[0057] As illustrated in FIG. 7, crucible 20 is rotated to fill
position 94. At fill position 94, crucible 20 is positioned
approximately 160 degrees from a vertical plane, and mold 22 is
located at least partially beneath crucible 20. Because fill
opening 44 of mold 22 is positioned in fluid communication with
pour opening 32 of crucible 20, molten metal 90 flows into interior
cavity 42 of mold 22.
[0058] In an exemplary embodiment of the present invention, shown
graphically in FIG. 10, crucible 20 briefly pauses at wet lip
position 92. From this stopped position, crucible 20 may rotate
about axis 48 with increasing velocity until reaching fill position
94.
[0059] As illustrated in FIG. 8, crucible 20 is rotated to fully
inverted position 96. At inverted position 96, crucible 20 is
positioned 180 degrees from a vertical plane such that top exterior
surface 26 of crucible 20 faces downward and bottom exterior
surface 40 of mold 22, which is located beneath crucible 20, faces
upward. Molten metal 90 continues to flow into interior cavity 42
of mold 22 until interior cavity 30 of crucible 20 is essentially
empty.
[0060] In an exemplary embodiment of the present invention, shown
graphically in FIG. 10, crucible 20 reaches a maximum velocity at
fill position 94, and then crucible 20 rotates about axis 48 with
decreasing velocity until reaching inverted position 96. By slowing
the rotation of crucible 20 at the end of the pour cycle, the rate
at which molten metal 90 flows into mold 22 is reduced.
[0061] A remaining step of the present method involves loosening
clamp 18 and removing mold 22 from crucible 20. Molten metal 90
inside mold 22 should be allowed to solidify before being removed
from mold 22. Finally, crucible 20 is returned to charge position
88 in preparation for receiving another metal ingot 86.
[0062] Advantageously, the method described above may be customized
depending on the particular mold 22, the particular metal being
used, and any other relevant factors. For example, melt profile 74
and pour profile 58 may be customized based on these factors to
minimize the presence of inclusions and gaps in a solid fabricated
part. Also, the method described above is repeatable and consistent
from pour to pour, and is reproducible from apparatus 10 to
apparatus 10. Finally, the method described above permits
two-directional, electronically controlled rotation of crucible
20.
[0063] While this invention has been described as having preferred
designs, the present invention can be further modified within the
spirit and scope of this disclosure. This application is therefore
intended to cover any variations, uses, or adaptations of the
invention using its general principles. Further, this application
is intended to cover such departures from the present disclosure as
come within known or customary practice in the art to which this
invention pertains and which fall within the limits of the appended
claims.
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