Industrial electric heating furnaces – Plural diverse heating means – Induction
Reexamination Certificate
1998-12-08
2001-09-11
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Plural diverse heating means
Induction
C219S651000, C373S008000, C373S141000
Reexamination Certificate
active
06289033
ABSTRACT:
BACKGROUND
Reactive metals such as titanium, zirconium, hafnium, molybdenum, chromium, niobium, high-temperature nickel-based super alloys, and other metals exhibit an intensive affinity towards oxygen and nitrogen, particularly when heated. In fact, titanium shows such an extreme affinity to oxygen that it is often employed as an oxygen “getter.” When heating such metals and metal alloys for forming purposes, it is therefore necessary to do so under an atmosphere free of oxygen and nitrogen.
The metallurgical art has for some time recognized the desirability of utilizing induction heating methods for the melting of reactive metals, such as titanium, as a replacement for known industrial-scale melting processes based on, for example, consumable electrode arc-melting techniques. In induction melting, an electric current is induced into the metal to be melted. Thus, by supplying an alternating current to a primary induction coil, a reverse alternating current is induced into any electrical conductor lying within the magnetic field of the coil, producing heating in the conductor.
Typical induction heating processes are carried out in an oxygen-containing environment such as air. The presence of oxygen results in the formation of scale on the heated metal parts. Scale is an abrasive, which significantly contributes to the wearing of the forming dies, reducing their useful life.
There have been prior efforts to introduce an inert gas into the enclosures of various induction-heating apparatuses to eliminate, or at least substantially reduce, the presence of oxygen. In induction-heating apparatuses, where the induction coils and molten metal are contained in separate housings, a cover has been placed over the space between the housings to provide an airtight enclosure. Multiple inlets have been provided in the cover to transport an inert gas from a source into the pathway contained within the cover. The inert gas then diffuses into the housing to provide a more acceptable gaseous environment for induction heating and subsequent forming.
Disadvantages of such induction systems include lack of control of the injection of the inert gas and the inability to provide a barrier against the infiltration of unwanted gases, such as air, due to drafting. More specifically, induction-heating devices never achieve complete protection against air leaks. For example, it is known that air enters the induction heating apparatus though the entryway where the cold metal parts enter the apparatus and the exit where the heated parts leave the apparatus. In addition, air leaks may be present where the cover is attached to the housing of the induction heating apparatus. The infiltration of such air into the heating areas produces scaling.
Thus, there is a need for an induction-heating system capable of heating reactive metals in an environment of inert gas. A system is needed that is capable of eliminating air leaks and drafts associated with the loading and unloading of the metal billets. A significant benefit could be derived from a system capable of controlling the atmosphere and heating rate of reactive metal billets in an heating system.
SUMMARY
The present invention is directed to an environmentally controlled heating system that satisfies these needs. An heating system having features of the present invention comprises a cold-billet load-chamber and means to place metal billets to be heated into the load-chamber. The billets travel through the heating system in ceramic crucibles on a trolley system. A crucible elevator lifts each crucible up from one end of a loading leg to the cold-billet load-chamber to receive the billet from the load-chamber. The loading leg is one of four legs comprising the main chamber. The other three legs include the heating leg, transfer leg, and return leg. The crucible elevator lowers the loaded crucible to the loading leg.
An actuator pushes the crucible through the loading leg to the entrance of the heating leg. An actuator is mounted on each leg of the heating system for advancing the crucible through a series of induction heating coils. When the crucible enters the heating leg, the billet is heated by advancing the crucibles through the heating system. Once the heating process is complete, the crucible leaves the heating leg on a transfer trolley and enters a hot-billet dump-chamber. A crucible dump actuator triggers inversion of the transfer trolley and crucible, thereby delivering the billet to a forming system. The empty crucible then enters the transfer leg and travels through the transfer leg to the return leg. The empty crucible travels through the return leg to the loading leg to receive another billet.
The heating system and the working relation of all subsystems is controlled by a computing device, preferably a programmable logic controller (PLC). The computing device monitors and controls the actuators, and it keeps track of the positions of all billets inside the heating system. The computing device also monitors output signals from an induction heating power supply, as well as signals from safety sensors that provide data to enable the computing device to know when it should shut down the system.
The heating system also comprises an environmental control system for evacuating air from and forcing an inert gas into the heating system. Prior to production startup, the heating system is run through a vacuum pump-down cycle to remove ambient air and other gaseous contaminants from the system. After this vacuum period, the heating system is back-filled with the inert gas. A gettering system mounted on the return leg continually cleans the inert gas, and a blower located between the return leg and the gettering system forces circulation of the gettered gas.
The environment within both the load and dump chambers is cycled for each billet. Each billet enters the cold-billet load-chamber through an outer cold-billet load-chamber vacuum gate. When the outer load gate is closed, a cold-billet load-chamber vacuum pump evacuates air from the load-chamber. After air evacuation, an inner cold-billet load-chamber vacuum gate opens to permit the billet to pass to a crucible and enter the load leg. After the billet has been heated, the loaded crucible moves from the heating leg into the dump-chamber through an inner hot-billet dump-chamber vacuum gate. After this gate closes, an outer hot-billet dump-chamber vacuum gate opens, permitting the billet to leave the dump-chamber when the crucible is inverted. After the outer dump gate closes, a hot-billet dump-chamber vacuum pump evacuates air from the dump chamber. After air evacuation, the inner dump gate opens, allowing the empty crucible to return to the main chamber.
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Alexion Chris C.
Corrente Russell S.
Creeden Thomas P.
Tipton Bryan P.
Waterbury Mark C.
Concurrent Technologies Corporation
Draughon P.A.
Hoang Tu Ba
Jreisat Mayen E.
Young Mark J.
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