BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates generally to a furnace for melting metals and other materials in which a solid feed material is preheated. More particularly, the invention relates to such a furnace wherein the solid feed material is preheated by heated gas from within the melting chamber. Specifically, the invention relates to such a furnace in which a plasma torch used for melting the material produces the heated gas and wherein the gas is cooled and recycled for re-use by the plasma torch.
2. Background Information
Furnaces for melting metal and other materials typically have a melting chamber with a melting hearth disposed therein in which the metal or other material is melted. Various types of heat sources provide the heat in order to melt the material within the melting hearth. It would be helpful to preheat the solid feed material which is fed into the melting hearth in order to reduce the total melting time, thereby increasing productivity. An increased melt rate can also increase the depth and size of the molten pool, the super heat of the molten material, liquid metal mixing and the capability for chemistry control. The increased melt rate would also increase the probability of removing defects such as high density inclusions (HDIs) and improve the surface quality in continuously casting ingots or slabs. The present invention provides such preheating and the above-listed benefits.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method comprising the steps of preheating solid feed material; moving the heated solid feed material into a melting hearth disposed within a melting chamber; and melting the solid material in the melting hearth.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a sectional view taken from the side of the furnace showing the preheating system of the present invention.
FIG. 2 is similar to FIG. 1 and shows an alternate feeding mechanism.
Similar numbers refer to similar parts throughout the specification.
DETAILED DESCRIPTION OF THE INVENTION
The furnace and preheating system of the present invention is indicated generally at 10 in FIG. 1; and a second embodiment is indicated generally at 100 in FIG. 2. While furnace 10 is configured as a plasma arc melting furnace, various concepts of the invention are applicable to other types of furnaces as well. Furnace 10 includes an insulated melting chamber 12 with a withdrawal chamber 14 disposed therebelow and in fluid communication therewith, and an insulated feed chamber 16 which is disposed beside melting chamber 12 and in fluid communication therewith. A melting hearth 18 which defines a melting cavity 20 and a continuous casting mold 22 are disposed within melting chamber 12. A lift 24 is disposed below mold 22, is partially within withdrawal chamber 14 and is movable up and down as shown by Arrow A into and out of melting chamber 12. First and second heat sources which are preferably in the form of first and second plasma torches-26 and 28 extend from above melting chamber 12 through an upper wall thereof and into chamber 12 for respectively providing heat above mold 22 and melting hearth 18. More particularly, second torch 28 provides heat to melt pieces 30 of solid feed material which are moved into melting cavity 20 as indicated at Arrow B to form molten material 32 within cavity 20 which is subsequently poured or otherwise moved as indicated at Arrow C into mold 22 to produce a molded body in the form of an ingot 33 as lift 24 is lowered. First torch 26 provides heat to molten material 32 within mold 22 in order to control the solidification rates and so forth. While pieces 30 of feed material are typically metal, other materials are contemplated as well. Furnace 10 is suitable for melting titanium alloys or superalloys.
With continued reference to FIG. 1, feed chamber 16 has a first end 34 adjacent which it is connected to melting chamber 12 and a second opposed end 36 distal melting chamber 12. Feed chamber 16 defines an entrance opening 38 adjacent second end 36 for receiving pieces 30 of solid feed material from outside feed chamber 16. Furnace 10 includes a feed assembly 40 comprising an input mechanism in the form of an actuator 42 which is disposed external to feed chamber 16 and includes a piston 44 which is moveable back and forth as indicated by Arrow D. Feed assembly 40 also includes a conveyor assembly 46 disposed within feed chamber 16 and extending partially into melting chamber 12. Conveying assembly 46 includes a conveyor belt 48 which is revolvingly mounted on a pair of rotatable members 50A and 50B disposed at respective opposed ends of conveying assembly 46. Input mechanism 42 includes a substantially horizontal platform 45 which is aligned with a substantially horizontal upper portion 52 of conveyor belt 48. Feed chamber 16 includes a heating passage 54 through which pieces 30 of solid feed material are moved as indicated by Arrows E from entrance opening 38 to melting hearth 18. More particularly, piston 44 of actuator 42 is operated to move pieces 30 of solid feed material from a top platform 45 onto upper portion 52 of conveyor belt 48 whereby operation of conveying assembly 46 moves pieces 30 as indicated at Arrows E along upper portion 52 to feed pieces 30 into melting cavity 20 of hearth 18.
With continued reference to FIG. 1 and in accordance with a feature of the invention, melting chamber 12 and feed chamber 16 are part of a recirculation pathway 56 which includes various conduits or ducts 58, a heat exchanger 60, a scrubber 62 for removing impurities from gas and a pump 64, all of which are in fluid communication with one another. Recirculation pathway 56 is configured to recirculate a gas 66 therethrough so that gas 66 is heated within melting chamber 12 and moved into feed chamber 16 in order to heat pieces 30 of solid feed material prior to entering melting cavity 20 to be melted by torch 28. Gas 66 is typically an inert gas and when used with plasma torches such as torch 28 is typically helium or argon or a mixture thereof.
With reference to FIG. 1, the operation of furnace 10 is further detailed. Pump 64 is operated to pump gas 66 through a segment of duct 58 as indicated at Arrows F into second torch 28. Gas 66 is then moved as indicated at Arrows G through torch 28, which heats and ionizes gas 66 to generate a plasma plume 68 for heating and melting pieces 30 and maintaining molten material 32 in melting hearth 18. Where other plasma torches such as torch 26 are used, gas 66 may also be circulated through such other plasma torches as indicated at Arrow G2. The core of plasma plume 68 typically has a temperature on the order of about 10,00° C. and gas 66 within chamber 12 has a temperature typically on the order of about 1,000° C. Thus, gas 66 becomes a heated gas within chamber 12 which moves as indicated by Arrows H into and through heating passage 54 of feed chamber 16 from first end 34 thereof to second end 36 thereof.
As the heated gas 66 is moved as indicated by Arrows H away from melting chamber 12, pieces 30 of solid feed material are moved toward melting chamber 12 in substantially the opposite direction. Due to the elongated nature of chamber 16, the invention thus takes advantage of a relatively lengthy heating passage 54 in order to allow substantial time for the heat exchange between heated gas 66 and pieces 30. The heated gas 66 will of course be substantially hotter adjacent first end 34 than adjacent second end 36 of feed chamber 16. The insulated walls of melting chamber 12 and feed chamber 16 help maintain heated gas 66 as hot as is feasible in order to better take advantage of the heat exchange between gas 66 and pieces 30.
Heated gas 66 reaches second end 36 of feed chambers 16 and exits through a vent or segment of duct 58 as indicated at Arrow J into heat exchanger 60 and then through another segment of duct 58 as indicated at Arrow K into scrubber 62 and finally through another segment of duct 58 as indicated at Arrow L back to pump 64 whereby gas 66 has been completely recirculated. Heat exchanger 60 cools gas 66 down to a temperature which is suitable for scrubbing of gas 66 via scrubber 62, typically at about room temperature.
With reference to FIG. 2, furnace 100 is described. Furnace 100 is similar to furnace 10 except that furnace 100 includes a feed assembly 102 which differs from feed assembly 40 of furnace 10 in that assembly 102 includes a conveying assembly 104 which is different than that of furnace 10. More particularly, conveying assembly 104 is a walking table suitable for receiving pieces 30 from platform 45 and delivering pieces 30 as shown by Arrows E into melting cavity 20 of hearth 18. Otherwise, the operation of furnace 100 is the same as furnace 10.
Thus, furnaces 10 and 100 provide systems that are configured to preheat solid feed material prior to placing the feed material in the melting hearth where it is melted. While the invention contemplates preheating solid feed material by any mechanism, it also advantageously utilizes the surplus heat produced by the primary heat sources which are used for melting the feed material within the melting hearth and melting chamber. It is contemplated that this surplus heat produced by the primary heat source within the melting chamber may be transferred to preheat the solid feed material by means of radiation, convection, conduction or any combination of these. However, the movement of the heated gas is a preferred mode of accomplishing this transfer of heat in a more efficient manner. While the exemplary embodiment preferably utilizes at least one plasma torch whereby the heated gas is recirculated for reuse by the plasma torch, it is also contemplated that gas which is heated by the surplus heat within a melting chamber may be transferred in other manners in order to preheat solid feed material. For example, in furnaces which are under a vacuum to eliminate or substantially eliminate gasses within the melting chamber, conduits may be configured to pass through a portion of the melting chamber so that gas passing through such conduits is heated within the melting chamber by the surplus heat and then transferred to a separate feed chamber or the like in order to preheat the solid feed material. Other variations which are within the scope of the present invention will be evident to one skilled in the art.
In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.
Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.
Patent Application
20070163387
