Apparatus for producing a molten seal in a continuous casting furnace
A seal for a continuous casting furnace having a melting chamber with a mold therein for producing a metal cast includes a passage between the melting chamber and external atmosphere. As the cast moves through the passage, the cast outer surface and the passage inner surface define therebetween a reservoir for containing liquid glass or other molten material to prevent the external atmosphere from entering the melting chamber. Particulate material fed into the reservoir is melted by heat from the cast to form the molten material. The molten material coats the cast as it moves through the passage and solidifies to form a coating to protect the hot cast from reacting with the external atmosphere. Preferably, the mold has an inner surface with a cross-sectional shape to define a cross-sectional shape of the cast outer surface whereby these cross-sectional shapes are substantially the same as a cross-sectional shape of the passage inner surface.
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This application is a continuation of U.S. patent application Ser. No. 10/989,563, filed on Nov. 16, 2004; the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Technical Field
The invention relates generally to the continuous casting of metals. More particularly, the invention relates to the protection of reactionary metals from reacting with the atmosphere when molten or at elevated temperatures. Specifically, the invention relates to using a molten material such as liquid glass to form a barrier to prevent the atmosphere from entering the melting chamber of a continuous casting furnace and to coat a metal cast formed from such metals to protect the metal cast from the atmosphere.
2. Background Information
Hearth melting processes, Electron Beam Cold Hearth Refining (EBCHR) and Plasma Arc Cold Hearth Refining (PACHR), were originally developed to improve the quality of titanium alloys used for jet engine rotating components. Quality improvements in the field are primarily related to the removal of detrimental particles such as high density inclusions (HDI) and hard alpha particles. Recent applications for both EBCHR and PACHR are more focused on cost reduction considerations. Some ways to effect cost reduction are increasing the flexible use of various forms of input materials, creating a single-step melting process (conventional melting of titanium, for instance, requires two or three melting steps) and facilitating higher product yield.
Titanium and other metals are highly reactive and therefore must be melted in a vacuum or in an inert atmosphere. In electron beam cold hearth refining (EBCHR), a high vacuum is maintained in the furnace melting and casting chambers in order to allow the electron beam guns to operate. In plasma arc cold hearth refining (PACHR), the plasma arc torches use an inert gas such as helium or argon (typically helium) to produce plasma and therefore the atmosphere in the furnace consists primarily of a partial or positive pressure of the gas used by the plasma torches. In either case, contamination of the furnace chamber with oxygen or nitrogen, which react with molten titanium, may cause hard alpha defects in the cast titanium.
In order to permit extraction of the cast from the furnace with minimal interruption to the casting process and no contamination of the melting chamber with oxygen and nitrogen or other gases, current furnaces utilize a withdrawal chamber. During the casting process the lengthening cast moves out of the bottom of the mold through an isolation gate valve and into the withdrawal chamber. When the desired or maximum cast length is reached it is completely withdrawn out of the mold through the gate valve and into the withdrawal chamber. Then, the gate valve is closed to isolate the withdrawal chamber from the furnace melt chamber, the withdrawal chamber is moved from under the furnace and the cast is removed.
Although functional, such furnaces have several limitations. First, the maximum cast length is limited to the length of the withdrawal chamber. In addition, casting must be stopped during the process of removing a cast from the furnace. Thus, such furnaces allow continuous melting operations but do not allow continuous casting. Furthermore, the top of the cast will normally contain shrinkage cavities (pipe) that form when the cast cools. Controlled cooling of the cast top, known as a “hot top”, can reduce these cavities, but the hot top is a time-consuming process which reduces productivity. The top portion of the cast containing shrinkage or pipe cavities is unusable material which thus leads to a yield loss. Moreover, there is an additional yield loss due to the dovetail at the bottom of the cast that attaches to the withdrawal ram.
The present invention eliminates or substantially reduces these problems with a sealing apparatus which permits continuous casting of the titanium, superalloys, refractory metals, and other reactive metals whereby the cast in the form of an ingot, bar, slab or the like can move from the interior of a continuous casting furnace to the exterior without allowing the introduction of air or other external atmosphere into the furnace chamber.
BRIEF SUMMARY OF THE INVENTIONThe present invention provides a casting furnace for manufacturing a metal cast, the furnace comprising: an interior chamber having a sidewall; a passage wall having an inner periphery which defines a passage extending through the sidewall of the interior chamber for communicating with the interior chamber and with atmosphere external to the interior chamber; a circumferential space within the passage; a metal cast pathway extending from the interior chamber through the passage and adapted for moving the metal cast from the interior chamber to the external atmosphere; a source of solid particulate coating material; a heat source for melting the particulate coating material to form molten coating material within the circumferential space; and a dispenser for dispensing the solid particulate coating material in a solid state from the source directly into the circumferential space adjacent the pathway.
The present invention also provides a casting furnace for manufacturing a metal cast, the furnace comprising: an interior chamber having a sidewall; a passage wall having an inner periphery which defines a passage extending through the sidewall of the interior chamber for communicating with the interior chamber and with atmosphere external to the interior chamber; a metal cast pathway extending from the interior chamber through the passage and adapted for moving the metal cast from the interior chamber to the external atmosphere; a molten bath bounding the pathway along at least a portion of the passage and adapted to prevent the external atmosphere from entering the interior chamber; a source of particulate coating material; a dispenser for dispensing the particulate coating material in a solid state from the source to adjacent the molten bath; and a heat source adjacent the molten bath for melting the particulate coating material to form molten coating material for the molten bath.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The seal of the present invention is indicated generally at 10 in
Furnace 12 further includes a lift or withdrawal ram 32 for lowering a metal cast 34 (
Seal 10 is configured to prevent reactive atmosphere 44 from entering melting chamber 16 during the continuous casting of reactionary metals such as titanium and superalloys. Seal 10 is also configured to protect the heated metal cast 34 when it enters reactive atmosphere 44. Seal 10 includes a passage wall or port wall 46 having a substantially cylindrical inner surface 47 defining passage 48 therewithin which has an entrance opening 50 and an exit opening 52. Port wall 46 includes an inwardly extending annular flange 54 having an inner surface or circumference 56. Inner surface 47 of port wall 46 adjacent entrance opening 50 defines an enlarged or wider section 58 of passage 48 while flange 54 creates a narrowed section 60 of passage 48. Below annular flange 54, inner surface 47 of port wall 46 defines an enlarged exit section 61 of passage 48.
As later explained, a reservoir 62 for a molten material such as liquid glass is formed during operation of furnace 12 in enlarged section 58 of passage 48. A source 64 of particulate glass or other suitable meltable material such as fused salt or slags is in communication with a feed mechanism 66 which is in communication with reservoir 62. Seal 10 may also include a heat source 68 which may include an induction coil, a resistance heater or other suitable source of heat. In addition, insulating material 70 may be placed around seal 10 to help maintain the seal temperature.
The operation of furnace 12 and seal 10 is now described with reference to
As cast 34 continues to move downwardly as indicated in
Once cast 34 has exited furnace 12 to a sufficient degree, a portion of cast 34 may be cut off to form an ingot 80 of any desired length, as shown in
Thus, seal 10 provides a mechanism for preventing the entry of reactive atmosphere 44 into melting chamber 16 and also protects cast 34 in the form of an ingot, bar, slab or the like from reactive atmosphere 44 while cast 34 is still heated to a temperature where it is still reactive with atmosphere 44. As previously noted, inner surface 24 of mold 20 is substantially cylindrical in order to produce a substantially cylindrical cast 34. Inner surface 47 of port wall 46 is likewise substantially cylindrical in order to create sufficient space for reservoir 62 and space between cast 34 and inner surface 56 of flange 54 to create the seal and also provide a coating of appropriate thickness on cast 34 as it passes downwardly. Liquid glass 76 is nonetheless able to create a seal with a wide variety of transverse cross-sectional shapes other than cylindrical. The transverse cross-sectional shapes of the inner surface of the mold and the outer surface of the cast are preferably substantially the same as the transverse cross-sectional shape of the inner surface of the port wall, particularly the inner surface of the inwardly extending annular flange in order that the space between the cast and the flange is sufficiently small to allow liquid glass to form in the reservoir and sufficiently enlarged to provide a glass coating thick enough to prevent reaction between the hot cast and the reactive atmosphere outside of the furnace. To form a metal cast suitably sized to move through the passage, the transverse cross-sectional shape of the inner surface of the mold is smaller than that of the inner surface of the port wall.
Additional changes may be made to seal 10 and furnace 12 which are still within the scope of the present invention. For example, furnace 12 may consist of more than a melting chamber such that material 72 is melted in one chamber and transferred to a separate chamber wherein a continuous casting mold is disposed and from which the passage to the external atmosphere is disposed. In addition, passage 48 may be shortened to eliminate or substantially eliminate enlarged exit section 61 thereof. Also, a reservoir for containing the molten glass or other material may be formed externally to passage 48 and be in fluid communication therewith whereby molten material is allowed to flow into a passage similar to passage 48 in order to create the seal to prevent external atmosphere from entering the furnace and to coat the exterior surface of the metal cast as it passes through the passage. In such a case, a feed mechanism would be in communication with this alternate reservoir to allow the solid material to enter the reservoir to be melted therein. Thus, an alternate reservoir may be provided as a melting location for the solid material. However, reservoir 62 of seal 10 is simpler and makes it easier to melt the material using the heat of the metal cast as it passes through the passage.
The seal of the present invention provides increased productivity because a length of the cast can be cut off outside the furnace while the casting process continues uninterrupted. In addition, yield is improved because the portion of each cast that is exposed when cut does not contain shrinkage or pipe cavities and the bottom of the cast does not have a dovetail. In addition, because the furnace is free of a withdrawal chamber, the length of the cast is not limited by such a chamber and thus the cast can have any length that is feasible to produce. Further, by using an appropriate type of glass, the glass coating on the cast may provide lubrication for subsequent extrusion of the cast. Also the glass coating on the cast may provide a barrier when subsequently heating the cast prior to forging to prevent reaction of the cast with oxygen or other atmosphere.
While the preferred embodiment of the seal of the present invention has been described in use with glass particulate matter to form a glass coating, other materials may be used to form the seal and glass coating, such as fused salt or slags for instance.
The present apparatus and process is particularly useful for highly reactive metals such as titanium which is very reactive with atmosphere outside the melting chamber when the reactionary metal is in a molten state. However, the process is suitable for any class of metals, e.g. superalloys, wherein a barrier is needed to keep the external atmosphere out of the melting chamber to prevent exposure of the molten metal to the external atmosphere.
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 casting furnace for manufacturing a metal cast, the furnace comprising:
- an interior chamber having a sidewall;
- a passage wall having an inner periphery which defines a passage extending through the sidewall of the interior chamber for communicating with the interior chamber and with atmosphere external to the interior chamber;
- a circumferential space within the passage;
- a metal cast pathway extending from the interior chamber through the passage and adapted for moving the metal cast from the interior chamber to the external atmosphere;
- a source of solid particulate coating material;
- a heat source for melting the particulate coating material to form molten coating material within the circumferential space; and
- a dispenser for dispensing the solid particulate coating material in a solid state from the source directly into the circumferential space adjacent the pathway.
2. The furnace of claim 1 in combination with the metal cast; and wherein the heat source comprises heat radiating from the metal cast.
3. The combination of claim 2 wherein the heat radiating from the metal cast is sufficient for melting the particulate coating material.
4. The furnace of claim 1 wherein the furnace is free of a melting chamber for melting the solid coating material at a location external to the interior chamber.
5. The furnace of claim 4 wherein the circumferential space is the only location of the furnace for melting the particulate material.
6. The furnace of claim 1 wherein the passage has a transverse cross-sectional shape adapted to be substantially the same as and larger than a transverse cross-sectional shape of the metal cast.
7. The furnace of claim 1 further comprising a continuous casting mold in the interior chamber; an inner surface on the mold defining a transverse cross-sectional shape adapted to define a transverse cross-sectional shape of the metal cast; and a section of the inner periphery of the passage wall defining a narrowest portion of the passage having a transverse cross-sectional shape substantially the same as and larger than the transverse cross-sectional shape defined by the inner surface of the mold.
8. The furnace of claim 1 in combination with the metal cast; and further comprising a molten bath at least a portion of which is disposed in the circumferential space; and wherein the metal cast has an outer periphery; and the circumferential space is defined between the outer periphery of the metal cast and the inner periphery of the passage wall.
9. The combination of claim 8 wherein the molten bath is in contact with the outer periphery of the metal cast to form a protective barrier thereon as the metal cast moves from the interior chamber to the external atmosphere.
10. The combination of claim 9 wherein the passage wall comprises an inwardly projecting annular flange which defines a narrower portion of the passage; the passage wall above the flange defines a wider portion of the passage; and the inner periphery of the flange is spaced from and adjacent the outer periphery of the metal cast as it moves through the passage to define a thickness of the protective barrier.
11. A casting furnace for manufacturing a metal cast, the furnace comprising:
- an interior chamber having a sidewall;
- a passage wall having an inner periphery which defines a passage extending through the sidewall of the interior chamber for communicating with the interior chamber and with atmosphere external to the interior chamber;
- a metal cast pathway extending from the interior chamber through the passage and adapted for moving the metal cast from the interior chamber to the external atmosphere;
- a molten bath bounding the pathway along at least a portion of the passage and adapted to prevent the external atmosphere from entering the interior chamber;
- a source of particulate coating material;
- a dispenser for dispensing the particulate coating material in a solid state from the source to adjacent the molten bath; and
- a heat source adjacent the molten bath for melting the particulate coating material to form molten coating material for the molten bath.
12. The furnace of claim 11 further comprising an exit end on the dispenser adjacent the metal cast pathway and above the molten bath.
13. The furnace of claim 12 in combination with the metal cast; and further comprising an outer periphery on the metal cast; and wherein the exit end is adjacent the outer periphery of the metal cast when moving through the passage via the pathway.
14. The furnace of claim 11 further comprising an exit end on the dispenser adjacent the inner periphery of the passage wall.
15. The furnace of claim 11 further comprising an exit end on the dispenser adjacent the passage wall and above the molten bath.
16. The furnace of claim 15 wherein the passage wall has an upper end; and the exit end of the dispenser is adjacent the upper end of the passage wall.
17. The furnace of claim 11 further comprising a continuous casting mold in the interior chamber adapted for producing the metal cast; and an exit end on the dispenser below the mold.
18. The furnace of claim 11 wherein the furnace is free of a melting chamber for melting the solid coating material at a location external to the interior chamber.
19. The furnace of claim 11 in combination with the metal cast; and wherein the heat source comprises heat radiating from the metal cast.
20. The combination of claim 19 wherein the heat radiating from the metal cast is sufficient for melting the particulate coating material.
Type: Application
Filed: Oct 31, 2007
Publication Date: Mar 13, 2008
Applicant: RMI Titanium Company (Niles, OH)
Inventors: Michael Jacques (Canton, OH), Frank Spadafora (Niles, OH), Kuang-O Yu (Highland Heights, OH), Brian Martin (North Canton, OH)
Application Number: 11/981,135
International Classification: B22D 11/106 (20060101);