1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
In operation, the crucible is first manually rotated to a charge position. Once reaching this charge position, an ingot is loaded into the crucible.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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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.
According to an embodiment of the present invention, apparatus 10 may further include motion feedback loop 49, as shown in
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.
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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.
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.
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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.
According to an embodiment of the present invention, apparatus 10 may further include temperature feedback loop 72, as shown in
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.
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.
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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.
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.
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.
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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.
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.
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.