US20070163387A1

US20070163387A1 - Method and apparatus for preheating and feeding material

Info

Publication number: US20070163387A1
Application number: US11/333,430
Authority: US
Inventors: Frank Spadafora; Michael Jacques; Kuang-O Yu
Original assignee: RMI Titanium Co
Current assignee: RMI Titanium Co
Priority date: 2006-01-17
Filing date: 2006-01-17
Publication date: 2007-07-19

Abstract

A casting furnace for preheating and melting solid feed material includes a melting chamber with a melting hearth therein and a feed chamber in fluid communication with the melting chamber for conveying the solid material into the melting chamber. A heat source melts the feed material within the melting hearth and produces surplus heat used to preheat the solid feed material. Preferably, gas is heated by the heat source and moved into the feed chamber to preheat the feed material while it is conveyed toward the melting hearth. The heated gas is recycled back into the melting chamber to be re-heated therein and reused to preheat additional feed material in the feed chamber. Where the heat source in the melting chamber includes a plasma torch, the gas is recycled via the plasma torch, which ionizes the gas to create a plasma plume for melting the solid material.

Description

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.

Claims

1. A method comprising the steps of:

preheating solid feed material by moving the solid feed material within a melting chamber in a first direction and moving heated gas within the melting chamber along the feed material in a second direction generally opposite the first direction;

moving the heated solid feed material into a melting cavity of a melting hearth disposed within the melting chamber; and

melting the solid material in the melting cavity of the melting hearth.

2-20. (canceled)

21. The method of claim 1 further comprising the step of feeding solid feed material into the melting chamber through a feed entry port formed in a sidewall bounding the melting chamber; and wherein the step of preheating comprises the step of preheating solid feed material by moving the solid feed material in the first direction from the feed entry port toward the melting hearth and moving the heated gas in the second direction from adjacent the melting hearth to adjacent the feed entry port.

22. The method of claim 21 wherein the step of preheating comprises the step of preheating solid feed material by moving the solid feed material in the first direction from the feed entry port to the melting hearth atop a conveyor assembly disposed in the melting chamber and having a first end adjacent the feed entry port and a second opposed end adjacent the melting hearth.

23. The method of claim 22 wherein the step of preheating comprises the step of preheating solid feed material by moving the solid feed material atop an upper surface of the conveyor assembly onto an upper surface of the melting hearth adjacent the melting cavity and the upper surface of the conveyor assembly.

24. The method of claim 23 wherein the step of moving the heated solid feed material comprises the step of sliding the heated solid feed material along the upper surface of the melting hearth to move it into the melting hearth.

25. The method of claim 22 wherein the step of moving the solid feed material in the first direction comprises the step of moving the solid feed material in the first direction from the feed entry port to the melting hearth atop one of a conveyor belt assembly and a walking table disposed in the melting chamber.

26. The method of claim 22 further comprising the step of pushing solid feed material through the feed entry port onto the first end of the conveyor assembly.

27. The method of claim 26 wherein the step of pushing comprises the step of pushing solid feed material through the feed entry port on a platform extending from outside the chamber into the entry port and adjacent the first end of the conveyor assembly.

28. The method of claim 21 wherein the step of moving the heated gas comprises the step of moving the heated gas in the second direction from adjacent the melting hearth to a gas exit port formed in the sidewall adjacent the feed entry port; and further comprising the step of moving the gas out of the melting chamber through the gas exit port.

29. The method of claim 28 further comprising the step of recycling the gas which exited through the gas exit port back into the melting chamber adjacent the melting hearth and distal the feed entry port.

30. The method of claim 29 wherein the step of melting comprises the step of melting the feed material in the melting hearth with a first plasma torch positioned above the melting hearth distal the feed entry port; and wherein the step of recycling comprises the step of recycling the gas back into the melting chamber through the plasma torch.

31. The method of claim 28 further comprising the steps of pouring molten material from the melting hearth into a mold disposed in the melting chamber distal the feed entry port; and recycling the gas which exited through the gas exit port back into the melting chamber adjacent the mold.

32. The method of claim 31 further comprising the step of heating material in the mold with a plasma torch positioned above the mold distal the feed entry port; and wherein the step of recycling comprises the step of recycling the gas back into the melting chamber through the plasma torch.

33. The method of claim 1 wherein the step of moving the heated solid feed material comprises the step of sliding the heated solid feed material along an upper surface of the melting hearth adjacent the melting cavity to move it into the melting hearth.

34. The method of claim 33 wherein the step of preheating comprises the step of preheating solid feed material by moving the solid feed material with a conveyor assembly disposed in the melting chamber on an upper surface of the conveyor assembly which is adjacent the upper surface of the melting hearth; and

further comprising the step of transferring the preheated solid feed material from the upper surface of the conveyor assembly onto the upper surface of the melting hearth.

35. The method of claim 34 wherein the step of transferring comprises the step of contacting both upper surfaces simultaneously with a piece of the preheated solid feed material.

36. The method of claim 1 further comprising the step of pouring molten material from the melting hearth into a mold disposed in the melting chamber.

37. The method of claim 36 further comprising the step of pouring molten material from the melting hearth into a continuous casting mold disposed in the melting chamber.

38. The method of claim 36 further comprising the steps of forming a molded body with the mold; and removing the molded body from the melting chamber.

39. The method of claim 38 wherein the step of removing comprises the step of lowering the molded body from the melting chamber on a lift.

40. The method of claim 36 further comprising the steps of heating material in the mold with a plasma torch positioned above the mold; heating gas within the melting chamber with the plasma torch to produce heated gas used in the step of preheating.

41. The method of claim 40 further comprising the steps of recycling the gas back into the melting chamber via the plasma torch; and generating a plasma plume with the gas.

42. The method of claim 1 wherein the step of melting comprises the step of melting the feed material in the melting cavity with a first plasma torch positioned above the melting hearth; and further comprising the steps of pouring molten material from the melting hearth into a mold disposed in the melting chamber; heating material in the mold with a second plasma torch positioned above the mold; heating gas within the melting chamber with the first and second plasma torches to produce heated gas used in the step of preheating.

43. The method of claim 42 further comprising the steps of recycling the gas back into the melting chamber via the first and second plasma torches; and

generating a plasma plume in each torch with the gas.

44. A method comprising the steps of:

preheating solid feed material by moving the solid feed material within a melting chamber from a feed entry port formed in a sidewall bounding the melting chamber toward a melting hearth disposed in the melting chamber and moving heated gas from adjacent the melting hearth out of the melting chamber through a gas exit port formed in the sidewall adjacent the feed entry port;

moving the preheated solid feed material into the melting hearth; and

melting the preheated solid feed material in the melting hearth.

45. The method of claim 44 wherein the step of preheating comprises the step of preheating by moving the solid feed material on a conveyor assembly in the melting chamber having a first end adjacent the feed entry port and a second opposed end adjacent the melting hearth and moving heated gas from the second end to the first end.

46. The method of claim 44 further comprising the step of pouring molten material from the melting hearth into a mold disposed in the melting chamber; and wherein the step of moving heated gas comprises the step of moving heated gas from adjacent the mold out of the melting chamber through the gas exit port.

47. A method comprising the steps of:

preheating solid feed material within a melting chamber in which a melting hearth is disposed;

sliding the preheated solid feed material along an upper surface of the melting hearth adjacent a melting cavity thereof to move it into the melting cavity; and

melting the preheated solid feed material in the melting cavity.

48. The method of claim 47 wherein the step of preheating comprises the step of preheating solid feed material by moving the solid feed material with a conveyor assembly disposed in the melting chamber on an upper surface of the conveyor assembly which is adjacent the upper surface of the melting hearth; and further comprising the step of transferring the preheated solid feed material from the upper surface of the conveyor assembly onto the upper surface of the melting hearth.

49. The method of claim 48 wherein the step of transferring comprises the step of contacting both upper surfaces simultaneously with a piece of the preheated solid feed material.