US3146289A

US3146289A - Cold mold arc furnace

Info

Publication number: US3146289A
Application number: US214249A
Authority: US
Inventors: Donald E Cooper; Elmer D Dilling
Original assignee: Titanium Metals Corp
Current assignee: Titanium Metals Corp
Priority date: 1962-08-02
Filing date: 1962-08-02
Publication date: 1964-08-25
Anticipated expiration: 1981-08-25

Description

Aug. 25, 1 D. E. COOPER ETAL COLD MOLD ARC FURNACE Filed Aug. 2, 1962 2 Sheets-Sheet l INVENTORS Donald E. Cooper Elmer D. Dillinq Agent Aug. .25, 1 4 D. E. COOPER ETAL cow MOLD ARC FURNACE Filed Aug. 2, 1962 2 Sheets-Sheet 2 VENTORS Don E. Cooper Elmer D. Dillinq United States Patent 3,146,289 COLD MOLD ARC FURNACE Donald E. Cooper and Elmer D. Dilling, Las Vegas, Nev., assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed Aug. 2, 1962, Ser. No. 214,249 2 Claims. (Cl. 13-14) This invention relates to an arc furnace and more particularly to a cold mold type of furnace for melting three consumable electrodes.

Cold mold type are furnaces are now relatively widely used for melting refractory metals. Commercial furnaces employ a consumable electrode which is progressively melted to form an ingot in the cold mold or crucible, the melting arc being maintained by direct current applied at high amperage between the consumable electrode and the metal in the cold mold. As the ingot is formed the electrode is gradually lowered as its length decreases to maintain the desired arc length and melting conditions.

Employment of direct current requires rectification of an original alternating current source. Considerable capital expense in power supply apparatus would therefore be saved if alternating current could be employed for melting power, and particularly if readily available threephase alternating current could be used.

Problems involved in handling, guiding and controlling the movement of a single electrode in a cold mold type furnace have been successfully solved. However, in a furnace containing three electrodes, these must be precisely positioned vertically, and uniformly spaced one from the other, and these positions and spacings maintained during the melting period. In a three-phase alternating current furnace, therefore, the mechanical design for handling the more complex electrode organization and insuring proper electrical operation is very important.

It is therefore an object of this invention to provide an improved cold mold type consumable electrode melting furnace. Another object of this invention is to provide an improved arc melting furnace employing three consumable electrodes. Another object of this invention is to provide a consumable electrode arc melting furnace in which the consumable electrodes are maintained in desirable uniform spaced relationship during melting. These and other objects of this invention will be apparent from the following description thereof and from the annexed drawings in which:

FIG. 1 shows a general side view, partially broken out, of a furnace embodying features of this invention.

FIG. 2 shows a top view of the furnace of FIG. 1.

FIG. 3 shows a horizontal section of the furnace of FIG. 1 taken along the line 33.

FIG. 4 shows a horizontal section of the furnace of FIG. 1 taken along the line 4'4.

FIG. 5 shows a horizontal section of the furnace of FIG. 1 taken along the line 55.

Referring now particularly to FIG. 1 the furnace for convenience of description is divided into three general sections (as indicated at the right hand side of FIG. 1); a lower crucible section 10, an intermediate throat section 12, and an upper electrode drive section 14.

Crucible section comprises (starting now at the bottom left hand portion of FIG. 1 and reading generally upward) a bottom 16 which is attached and sealed as by bolts 18 to shell 20 which forms the outer shell of a water jacket in which is disposed a cold mold or crucible 22. Cooling fluid such as water is circulated through the cooling jacket by means of pipe connections 24.

Supported by legs 26 is a heavy horizontal plate 28 having a central cut-out through which depends crucible 22. Over the rim of such cut-out is arranged gasket 30 and on top of this an extending flange 32 which forms part of the top of crucible 22. Bolts 34 hold the bottom flange 36 of throat 38 in firm juxtaposition with crucible flange 32, gasket 30 and plate 28.

Inside throat 38 are suspended three electrodes 40 which are preferably of sector-shaped cross section, each having a stub 42 attached to its top and by which it is deinountably attached as by a clamp 44 to the bottom of hollow electrode ram 46.

The top of throat 38 is provided with extending flange 48, on which is placed gasket 50 and on this is arranged throat cover plate 52, these elements being held firmly in juxtaposition by bolts 54. Cover plate 52 encloses the top of the furnace interior, that is, the part inside throat section 12 and crucible section 10 containing crucible 22. Electrode rams 46 which are equally spaced, one from the other, pass through plate 52, their passage being arranged through sliding seals 56 which are of insulating material to electrically isolate each of electrode rams one from the other, and from cover plate 52. Fixedly mounted on plate 52 are the bottoms of vertical guide bars 58.

Intruding into the hollow interiors of drive rams 46 are lower ends of screw shafts 60 on which are threaded nuts 62, which are themselves fixedly mounted in suitable bores in triangular cross plates 64 and aligned with the electrode rams 46 attached thereto. Cross plates 64 are each provided with a connector 66 for attachment of a flexible electrical cable. Insulating bushings 68, preferably of fiuorinated hydrocarbon, insulate cross plates 64 from guide rods 58 which pass through cross plates 64 and on which they are slidably mounted. Cross plates 64 are of generally triangular shape, the attachment of the electrode ram 46 to each being near an inner part, i.e., the inner corner of the cross plate, and the mounting on guide bars 58 being near an outer part, i.e., the outer corners thereof.

The upper ends of guide bars 58 are fixedly attached to top plate 70 which is vertically aligned with cover plate 52 and through which pass the upper, unthreaded ends of screw shafts 60, their passage through top plate 7 0 being arranged through suitable thrust bearing 72 which supports the upper ends of screw shafts 60 and which are attached to, but insulated from, top plate 70 by bushings 74. Guide bars 58 connect cover plate 52 and top plate 70 and are arranged as shown in spaced pairs, disposed outwardly from electrode rams 46 but adjacent thereto, and with one of each pair on either side'of one of rams 46. At the tops of screw shafts 60 are fixedly attached horizontal spur gears 76 each of which meshes with a central pinion 78 driven by motor 80 mounted on overhanging bracket 82. Spur gears 76 and pinion 78 are fabricated of fiber or other insulating material so that screw shafts 60 remain electrically insulated from each other.

Bail S4 is fixedly attached to top plate 70 to enable the electrode drive section 14 to be lifted off throat section 12 after loosening bolts 54, or the electrode drive section 14 and throat section 12 to be lifted oif crucible section 10 after loosening bolts 34.

Valved pipe connector 86, communicating with the interior of throat section 12, is provided (indicated on the right hand side of the furnace) for connection to a suitable vacuum pump or inert gas supply if it is to be evacuated for operation under vacuum or filled with an atmosphere of inert gas, if this is desired.

In operation the furnace of FIG. 1 is first disassembled in order to set in place the electrodes to be melted. Bolts 34 are loosened so that the electrode drive section 14 and throat section 12 may be removed temporarily from the crucible section 10 and lifted off by means of bail 84. Three electrodes 40, preferably of sector shape as shown, are attached by means of their stubs 42 and clamps 44 to the bottoms of electrode drive rams 46. It will be seen in FIG. 5 that the sector shaped electrodes 40 are arranged in flat-face to flat-face relationamazes ship. A clean crucible 22 is placed inside outer shell 20. Preferably, in order to help initiation of the arc, some loose chips or small bodies of the metal similar to that of the electrodes 40 are placed in the bottom of crucible 22.

Electrode drive section 14 and throat section 12 are then replaced with the electrodes 40 and their attachment to drive rams 46 inside throat in the interior of the furnace. Bolts 34 are tightened to provide a tight seal between plate 28, gasket 30 and the crucible and throat bottom flanges. The furnace is now charged with electrodes and ready for melting. Cooling water flow is arranged through pipe connections 24. to provide adequate circulation of cooling water around crucible 22. Each of triangular cross plates 64 is connected by means of a connector 66 to one phase of a three-phase alternating current power supply. Connection of the power lead to cross plate 64 in each case provides a flow of current through drive ram 46, electrode stub 42, to each electrode 40. Motor 8i), which drives electrode rams 46 up and down, is connected to a suitable source of electric current, which will generally be direct current, and the current supplied to motor 80 is controlled by suitable, conventional mechanism so that the travel up and down of electrodes 40 maintains the proper spacing and arc conditions while electrodes 40 are being melted to form a solid ingot in crucible 22. Such mechanisms are well-known and may be based on voltage or current characteristics of the arc, or both; such control mechanism in and of itself forms no part of this invention.

The interior of the furnace, that is, the throat section 12 and the crucible section It), is first evacuated by connecting valve pipe connector 86 to a suitable vacuum pump. If the melt is to be made under an inert gas atmosphere, then a simple connection may be made to a source of such inert gas, for example, helium or argon, and the furnace interior may be back-filled to provide an atmosphere of the desired pressure.

With the proper furnace atmosphere obtained, cooling water supplied to the jacket surrounding the crucible and the electrode and ram assemblies ready for operation, power is turned on to the electrodes 40 and motor 80 is actuated to lower the electrode drive rams 46 until an arc is struck between the bottoms of at least two of electrodes 40 and the loose starting charge placed in the bottom of crucible 22. It will be understood that with three-phase electric current supplied to electrodes 40, the arc will strike from one electrode to the metal in the bottom of crucible 22 and then back to another electrode and that this arcing sequence will be progressive around each of the three electrodes in turn as the cycles of the three-phase current provide their characteristic wave type potential.

It will be understood that in the embodiment described and illustrated the three electrodes 40 will be moved downwardly (or upwardly when required to maintain arcing conditions) simultaneously, because each is connected through the drive ram operating screw shaft 60 and its attached gear 76 and these gears are all operated by central pinion 78. Uneven burn-oif of electrodes 40 will be compensated during the melting operation by the fact that when one electrode becomes substantially shorter than the others, will thereby result in an increased arc length and less power in that are so that melting on that particular electrode will be temporarily slower than on the other two. This eifect and more or less automatic method of controlling the burnofl rates in a three-electrode assembly connected to threephase alternating current, is more particularly described and claimed in application Serial No. 181,407, filed March 21, 1962, in which Donald E. Cooper, one of the co-inventors of this application, is the inventor. The sector shaped electrodes themselves with their stubs and assemblies are more particularly described and claimed in Patent No. 3,080,499, issued March 5, 1963.

After melting has progressed to a point where the electrodes 4d are substantially entirely consumed and have been progressively melted to form a solid ingot in crucible 22, the power supply to cross plates 62 and motor is shut down and if the furnace has been operated under vacuum, the interior is preferably back-filled with inert gas through valve connector 86. The furnace is then disassembled by loosening bolts 34 to separate the electrode drive section 14 and the throat section 12 from crucible section It Crucible 32 is then lifted out of shell 20 and the ingot formed therein removed from it and the residual short ends of electrodes 40 attached to stubs 42 are removed from drive rams 46 by loosening clamps 44. The furnace may now be recharged and reassembled as previously described, and is ready for another melting operation.

The arrangement of the guide bars and cross plates is eflective to provide steady accurate positioning and control of the electrode rams and their attached electrodes during the melting operation. This is important because with three electrodes connected to a threephase alternating power source, uniform and proper spacing must be maintained between these electrodes to prevent short circuiting. It is obvious that best use must be made of the cross sectional area of the crucible to provide as much as possible electrode area otherwise the electrodes become too long for convenient handling, and arcing and melting will be confined to a more limited portion of the melt area. Therefore, the spacing between electrodes and between the electrodes and the crucible side wall will normally be the minimum or close to the minimum necessary to prevent short circuiting and each electrode and electrode ram must be precisely aligned vertically and accurately spaced one to the other.

The screw shaft drive arrangement provides a convenient and elfective method of producing vertical motion of the electrode ram. Disposal of the bottom of the screw shaft within the hollow electrode ram makes a compact organization, reducing head room requirements for a furnace installation.

The guide bars are arranged in spaced pairs, each pair being disposed outwardly from its adjacent electrode drive ram attachment to the cross plate. Preferably, as illustrated the cross plates are of generally triangular configuration with the electrode ram attached near the inner corner of the cross plate and the guide bar mountings located near the outer corners. A pair of guide bars is necessary to properly steady each cross plate and to obtain accurate positioning. The two guide bar mountings near the outer corners of the triangular cross plates could be considered to form brace points at the base of a triangular structure to give utmost rigidity to the electrode ram position near the apex corner, and to counteract any torque effects from the nut on the driving screw shaft.

Additionally, location of the guide bars outwardly from the electrode rams and associated mechanisms provides strong connection and Wide base bracing between the top plate and the furnace interior cover plate so that these elements are maintained in proper vertically aligned relationship.

Solution of problems associated with electrode alignment and spacing makes possible successful and efficient use of three electrodes connected to a three-phase alternating current power supply. This provides an improved type of cold mold consumable electrode melting furnace useful for melting refractory metals.

We claim:

1. In a consumable electrode arc melting furnace having an interior containing a crucible, the improvements which comprise in combination:

(a) a cover plate enclosing the top of said furnace interior,

(1)) three equally spaced hollow electrode rams passing through sliding seals in said cover plate, each electrode ram adapted to be attached at its bottom to a consumable electrode in the interior of said furnace,

(c) a top plate vertically aligned with and spaced apart from said cover plate,

(d) six guide bars fixedly attached to and connecting said cover plate and said top plate, said guide bars being disposed outwardly from said electrode rams and arranged in spaced pairs adjacent each of said electrode rams,

(e) three generally triangular cross plates each fixedly attached to the top of one of said electrode rams and slidably mounted on a pair of said guide bars, the attachment of said electrode ram being near an inner corner of said cross plate and the mounting on said guide bars being near outer corners of each of said cross plates,

(7'') a threaded nut fixedly attached in a bore in each of said cross plates aligned with the electrode ram attached thereto,

(g) a screw shaft passing through each of said cross plates engaging said nut, with its upper end supported by a bearing attached to said top plate and with its lower end disposed within one of said electrode rams, and I (/1) means for rotating each of said screw shafts thereby to raise and lower the said cross plates with electrode rams attached thereto, while said electrode rams are maintained in individual vertical alignment and relative spacing one to the other by the pair of guide bars on which each is slidably mounted.

2. In a consumable electrode arc melting furnace having an interior containing a crucible, the improvements which comprise in combination:

ing through sliding seals in said cover plate, each electrode ram adapted to be attached at its bottom to a consumable electrode in the interior of said furnace,

(c) a top plate vertically aligned with and spaced apart from said cover plate,

(e) three cross plates each fixedly attached to the top of one of said electrode rams and slidably mounted on a pair of said guide bars, the attachment of said electrode ram being near an inner part of said cross plate and the mounting on said guide bars being near an outer part of each of said cross plates,

(f) a threaded nut fixedly attached in a bore in each of said cross plates aligned with the electrode ram attached thereto,

(g) a screw shaft passing through each of said cross plates engaging said nut, with its upper end supported by a bearing attached to said top plate and with its lower end disposed within one of said electrode rams, and

(h) means for rotating each of said screw shafts thereby to raise and lower the said cross plates with electrode rams attached thereto, while said electrode rams are maintained in individual vertical alignment and relative spacing one to the other by the pair of guide bars on which each is slidably mounted.

References Cited in the file of this patent UNITED STATES PATENTS 2,848,524 McLaughlin et a1 Aug. 19, 1958 2,857,445 Mangin Oct. 21, 1958 2,900,556, Gifford Aug. 18, 1959

Claims

1. IN A CONSUMABLE ELECTRODE ARC MELTING FURNACE HAVING AN INTERIOR CONTAINING A CRUCIBLE, THE IMPROVEMENTS WHICH COMPRISE IN COMBINATION: (A) A COVER PLATE ENCLOSING THE TOP OF SAID FURNACE INTERIOR, (B) THREE EQUALLY SPACED HOLLOW ELECTRODE RAMS PASSING THROUGH SLIDING SEALS IN SAID COVER PLATE, EACH ELECTRODE RAM ADAPTED TO BE ATTACHED AT ITS BOTTOM TO A CONSUMABLE ELECTRODE IN THE INTERIOR OF SAID FURNACE, (C) A TOP PLATE VERTICALLY ALIGNED WITH AND SPACED APART FROM SAID COVER PLATE, (D) SIX GUIDE BARS FIXEDLY ATTACHED TO AND CONNECTING SAID COVER PLATE AND SAID TOP PLATE, SAID GUIDE BARS BEING DISPOSED OUTWARDLY FROM SAID ELECTRODE RAMS AND ARRANGED IN SPACED PAIRS ADJACENT EACH OF SAID ELECTRODE RAMS, (E) THREE GENERALLY TRIANGULAR CROSS PLATES EACH FIXEDLY ATTACHED TO THE TOP OF ONE OF SAID ELECTRODE RAMS AND SLIDABLY MOUNTED ON A PAIR OF SAID GUIDE BARS, THE ATTACHMENT OF SAID ELECTRODE RAM BEING NEAR AN INNER CORNER OF SAID CROSS PLATE AND THE MOUNTING ON SAID GUIDE BARS BEING NEAR OUTER CORNERS OF EACH OF SAID CROSS PLATES, (F) A THREADED NUT FIXEDLY ATTACHED IN A BORE IN EACH OF SAID CROSS PLATES ALIGNED WITH THE ELECTRODE RAM ATTACHED THERETO, (G) A SCREW SHAFT PASSING THROUGH EACH OF SAID CROSS PLATES ENGAGING SAID NUT, WITH ITS UPPER END SUPPORTED BY A BEARING ATTACHED TO SAID TOP PLATE AND WITH ITS LOWER END DISPOSED WITHIN ONE OF SAID ELECTRODE RAMS, AND (H) MEANS FOR ROTATING EACH OF SAID SCREW SHAFTS THEREBY TO RAISE AND LOWER THE SAID CROSS PLATES WITH ELECTRODE RAMS ATTACHED THERETO, WHILE SAID ELECTRODE RAMS ARE MAINTAINED IN INDIVIDUAL VERTICAL ALIGNMENT AND RELATIVE SPACING ONE TO THE OTHER BY THE PAIR OF GUIDE BARS ON WHICH EACH IS SLIDABLY MOUNTED.