Patent Application
20080267251
The present invention relates generally to an induction melting furnace and, more specifically, to a stacked induction melting furnace constructed to promote a continuous melting process of a solid, substantially non-conductive material to recover precious metals therefrom.
Induction furnaces are a well-known system used in casting operations and reclamation processes for heating and melting metal and other materials containing amounts of metal therein, such as low grade ore or rock containing small quantities of metal therein. With previous designs, it has been difficult to continuously melt these materials without interruption for pouring and refilling. An intermittent melting method has been used in which material is first conveyed into the furnace, then raised in temperature until it is molten wherein the molten metal therein can then be discharged from the furnace. When the material has been melted and superheated to the desired pouring temperature, power to the induction furnace is typically either turned off or reduced in order to maintain the temperature of the material during a pouring operation. This pouring operation commonly involves at least tilting or tipping a crucible in which the molten material is held, but also can include moving the crucible to another location before the pour. When the desired amount of molten material has been removed from the furnace, the next batch of material is conveyed in and full power is once again applied to the furnace to begin the next melt cycle. Thus, the conventional induction melting furnace is of the type of which discharges the molten material intermittently and does not allow for a process in which material is continuously added, melted, and discharged.
As stated above, conventional induction furnaces do not allow for a continuous melting process. Such an intermittent melting operation is not only time consuming, but such intermittent melting can also lead to other problems. For example, “bridging” can occur during a melting process, in which the molten material solidifies on the top surface of the melt. When bridging occurs, gases can accumulate in the crucible as the material continues to melt therein. This trapping of gases can ultimately lead to sudden and unwanted discharge of the pent up gas.
To overcome the problems associated with an intermittent melting method, induction furnaces have been designed that allow for melting metal in a somewhat continuous melting process. However, these induction furnaces are limited in their use, as these existing designs are only able to accommodate melting of a primarily metal material. That is, these induction furnaces are not suitable for use in reclamation processes where the material to be melted is primarily non-conductive, such as slag, rock, or low grade ore, because the non-conductivity of these materials causes unique problems.
That is, problems arise when melting a substantially non-conductive material such as rocks in a standard induction furnace having a conductive crucible to heat and melt the material. In existing furnace designs, the crucible will be inductively heated and conduct heat to the material in direct contact with the crucible surface. Thus, an annular ring of molten material will rapidly form at the inner crucible surface. Unless the crucible is operated at a temperature much higher than the liquification temperature of the non-conductive material, the melting process will “stall” because of the poor thermal conductivity of the annular ring of molten material and the inability of heat to rapidly transfer inwardly toward the unmelted material.
If an induction furnace is operated to heat the crucible to a high temperature to improve melting of the substantially non-conductive material, the life of the crucible will be significantly shortened. The life of the conductive crucible can be further shortened by the erosion of the crucible caused by reactions that occur between the crucible and the molten material therein. Typically, the conductive crucible will contain carbon therein, and as such, will react with certain metallic oxides (e.g., iron) in the charge, producing liquid metal, carbon monoxide, and carbon dioxide. The liquid metal produced can further shorten the life of the crucible by pooling at the bottom thereof, which superheats in the bottom of the crucible.
Beyond the problems associated with efficiently heating the non-conductive material and maintaining crucible life, the implementation a continuous process for the melting of these substantially non-conductive materials is also problematic. Induction furnaces used for reclamation of small amounts of metal in a substantially non-conductive material require a construction that allows for separation and settling of the materials therein as well as a system/mechanism for removing an undesired material from the desired molten metal. Current induction furnaces that allow for a continuous melting of a metal lack such a capacity and construction. As such, induction furnaces for use in the reclamation of metal from substantially non-conductive materials such as rock or low-grade ore that allow for a continuous heating and melting operation are still not available.
Therefore, an induction furnace system designed to promote a continuous heating and melting operation of substantially non-conductive materials is desirable. Additionally, an induction furnace system that improves crucible life while efficiently melting the substantially non-conductive materials is also desired.
The present invention provides an induction furnace system constructed to heat and melt a solid material in a continuous melting operation. A stacked induction furnace includes a first furnace capable of continuously heating and melting a solid material and a second furnace in operable association with the first furnace to continuously receive molten material from the first furnace and maintain the material in a molten state until it is transferred as desired.
According to one aspect of the present invention, a stacked furnace system includes a first furnace having an induction coil to heat and melt a substantially non-conductive material contained in an upper crucible. The upper crucible has an opening in a bottom surface thereof to drain molten material therefrom. The stacked furnace system also includes a second furnace positioned below the first furnace having a lower crucible to receive the molten material drained from the opening, the second furnace constructed to maintain the molten material in a molten state in the lower crucible, and one or more power sources to power the first furnace and the second furnace.
In accordance with another aspect of the present invention, a stacked induction furnace includes a melting chamber to heat a melt therein that is composed of a substantially non-conductive material, a settling chamber positioned below the melting chamber to maintain the melt, and at least one induction coil at least partially surrounding the melting chamber and the settling chamber to generate a magnetic flux to heat the melt. The melting chamber includes an opening in a lower portion thereof to transfer the melt from the melting chamber to the settling chamber.
In accordance with yet another aspect of the present invention, a continuous process for heating and melting a material in an induction furnace system includes the steps of depositing a substantially non-conductive material into a melting crucible of a top induction furnace and inductively heating and melting the substantially non-conductive material in the melting crucible by way of a first induction coil positioned at least partially about the melting crucible. The process also includes the steps of transferring the melted material to a holding crucible of a bottom furnace by way of a passage formed in a bottom surface of the melting crucible and removing the melted material from the holding crucible at a controlled flow rate.
Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.
The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention.
In the drawings:
Referring to
Induction furnace system 10 can also include an optional third development furnace 16. Development furnace 16 allows an operator to perform small trial experiments and melting operations on a chosen material to determine temperature and time for heating, as well as composition and chemistry of the material. Such information is useful in then performing a full-scale heating and melting operation of that material in the upper and lower furnaces 12, 14 of the induction furnace system 10. That is, trials performed in development furnace 16 provide information on a time required to melt the material, temperature needed, how long to let the melted material settle, and a suitable rate at which to transfer the melted material from the upper furnace 12 to the lower furnace 14.
Also shown in
Referring now to
Lower furnace 14 includes a settling crucible 24 (i.e., settling chamber) and a second set of induction coils 26 at least partially surrounding the settling crucible 24. Preferably, the settling crucible 24 is also composed of a suitable conductive material. It is also envisioned that lower furnace 14 comprise an electric furnace or other suitable high temperature furnace rather than an induction furnace and that the electric furnace could be separately powered from the upper furnace 12.
The first and second induction coils 22, 26 at least partially surround the exterior of the melting crucible 20 and the settling crucible 24 respectively. The induction coils 22, 26 are connected to one or more suitable high frequency power supplies 28 so that the magnetic field generated from AC current flowing through the coils 22, 26 inductively heats the melting crucible 20 and the settling crucible 24 respectively. It is envisioned that the first induction coils 22 and the second induction coils 26 are separately powered and that the amount of AC current flowing through the coils can be individually controlled to reflect heating requirements in the upper and lower furnaces 12, 14. Depending on the material being melted, a power supply frequency will range from an AC power frequency of 50-60 Hz up to 10 kHz. The induction coils 22, 26 may be air-cooled or water-cooled and may be comprised of solid or stranded conductors configured in what is commonly known as a Litz wire configuration. In the embodiment of
To begin a melting operation, melt 30 (i.e., the material to be heated and melted) is placed within melting crucible 20 and is heated to a desired temperature. The melt 30 can be a substantially non-conductive material such as rock, slag, or low grade ore. While generally composed of a substantially non-conductive material, the melt 30 also includes an amount of conductive metal therein, such as metallic iron or a semi-precious metal such as silver, copper, platinum, manganese, or another similar metal that is to be reclaimed therefrom. In order to reclaim the metal contained in melt 30, the melt 30 is heated to a molten state in upper furnace 12 to separate the waste material from the metal. That is, as the slag/rocks are heated to a melting state, conductive metal contained therein is melted to a liquid/viscous form. The melted conductive metal is drawn to the bottom of the melting crucible 20, as it is denser then the melted material from which it is separated.
Still referring to
As part of the melting operation, it is also envisioned a filtering operation can be performed on the melt 30 that is in a molten state and drains down to the bottom of melting crucible 20. That is, a blast of high frequency AC current can be applied from upper furnace 12 to first induction coils 22 and be directed to the bottom of melting crucible 20 to separate a precious metal from the molten melt 30. In this manner, small particles of a waste material could be separated from melt 30 (and the molten precious metal) before it drains out of melting crucible 20.
As stated above, melt 30 from melting crucible 20 is drained or transferred into settling crucible 24 in lower furnace 14 by way of passage 32. Melt 30 is held in settling crucible 24, which maintains temperature of the melt 30 by way of second induction coils 26 positioned at least partially around the settling crucible 24. The melt 30 delivered to settling crucible 24 may, in some cases, be slightly conductive in the molten state, having an amount of conductive material 34 (i.e., molten metal) therein, as shown in
The holding of melt 30, and the maintaining of a desired temperature thereof, allows for certain chemical and physical processes to be completed in the melt 30 that enables the desired removal of molten metal 34 therefrom. As melt 30 is held in the settling crucible 24, it further settles and separates into somewhat distinct regions composed of differing materials. That is, once melt 30 is melted and allowed to settle in settling crucible 24, it separates into two constituents having different densities. As shown in the embodiment of
As shown in
While use of connecting passage 42 and gate 46 has been described for removing molten metal 34 from settling crucible 24, it is also envisioned that molten metal 34 could be removed by other alternative methods and mechanisms. That is, induction furnace system 10 could be configured to allow for upper furnace 12 to swing out and away from lower furnace 14. Settling crucible 24 in lower furnace 14 could then be tipped and dumped to remove molten metal 34 therefrom in a manner known in the art.
In the melting operation, as melt 30 is transferred out from melting crucible 20 and settling crucible 24, melt 30 is also being added back into melting crucible 20 at a substantially similar rate to keep a desired quantity of melt therein. As the filling and draining of melting crucible 20 occurs on a continuous basis, no “bridging” of the melt 30 therein is allowed to occur. That is, no solidification of a top layer on melt 30 is allowed to occur as material is continuously being added. As such, gases do not accumulate in the melting crucible 20 and unwanted discharge of any pent-up gas is prevented.
Referring again to
A cover 50 can also be placed on melting crucible 20. The cover 50 joins with melting crucible 20 to retain heat and also to allow the control of the gaseous by-products inside the upper furnace 12 during operation. In processes which generate such gaseous by-products, the cover 50 may be provided with one or more outlets 52 to enable the gaseous by-products to either escape from the furnace 12 in a controlled manner or be recycled for other purposes. Cover 50 can also be configured to be raised manually or automatically from and lowered to melting crucible 20 as needed.
It is also envisioned that a rotatable support 53 can be attached to upper furnace 12. Rotatable support 53 allows for tipping of the melting crucible 20 to pour out the melt 30 therein. While passage 32 also serves to empty melt 30 from melting crucible 20, addition of rotatable support 53 can be used for cleaning or mass removal of melt 30 from melting crucible 20 in case of power failure or other malfunction.
Referring now to
Preferably, the susceptor 54 is comprised of a refractory material such as graphite, although it is also envisioned that other materials can be used that can be heated to the temperature of the melt without losing mechanical integrity. When composed of graphite, the temperature of the susceptor 54 can be taken up to the temperature limit of graphite (about 2600° C.), allowing heat to be driven to the melt 30 and resulting in faster processing times and higher yield. The temperature of susceptor 54 can be controlled via the current being run through first induction coil 22, thus controlling the temperature of the melt 30 as well.
As shown in
In addition to providing heat to the melt 30, the graphite susceptor 54 also prevents oxidation in the molten metal 34 contained in the melt 30 by stripping oxygen therefrom. That is, oxygen present in the melt 30 bonds with the graphite to form CO, which is then exhausted from the upper furnace 12. Over time, the conductive susceptor 54 degrades due to oxidation, and other possible chemical reactions, between the susceptor 54 and melt 30. Susceptor 54 is preferably cylindrical or rod shaped. Such a configuration degrades more evenly, therefore extending the life of the susceptor 54 beyond a susceptor of alternate configurations.
A graphite susceptor rod 54 of the type explained herein is generally not used in the prior art since most systems use conductive crucibles and because susceptor 54 occupies space in the melting crucible 20. Furthermore, it is generally believed that a close proximity of the conductive member to the induction coils is most efficient. However, since the induction heating system described herein is preferably used to separate metals, it is preferred to use a non-conductive crucible for even heat distribution. Also, the single graphite susceptor rod 54 of the described embodiment is sized so that a majority of the melting crucible 20 is available for a melt 30 to be placed therein. As shown in
As described above with respect to the embodiment of induction furnace system 10 set forth in
Referring now to
Therefore, according to one embodiment of the present invention, a stacked furnace system includes a first furnace having an induction coil to heat and melt a substantially non-conductive material contained in an upper crucible. The upper crucible has an opening in a bottom surface thereof to drain molten material therefrom. The stacked furnace system also includes a second furnace positioned below the first furnace having a lower crucible to receive the molten material drained from the opening, the second furnace constructed to maintain the molten material in a molten state in the lower crucible, and one or more power sources to power the first furnace and the second furnace.
In accordance with another embodiment of the present invention, a stacked induction furnace includes a melting chamber to heat a melt therein that is composed of a substantially non-conductive material, a settling chamber positioned below the melting chamber to maintain the melt, and at least one induction coil at least partially surrounding the melting chamber and the settling chamber to generate a magnetic flux to heat the melt. The melting chamber includes an opening in a lower portion thereof to transfer the melt from the melting chamber to the settling chamber.
In accordance with yet another embodiment of the present invention, a continuous process for heating and melting a material in an induction furnace system includes the steps of depositing a substantially non-conductive material into a melting crucible of a top induction furnace and inductively heating and melting the substantially non-conductive material in the melting crucible by way of a first induction coil positioned at least partially about the melting crucible. The process also includes the steps of transferring the melted material to a holding crucible of a bottom furnace by way of a passage formed in a bottom surface of the melting crucible and removing the melted material from the holding crucible at a controlled flow rate.
The present invention has been described in terms of the preferred embodiments, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.
