US2788270A

US2788270A - Method and apparatus for melting metal under vacuum

Info

Publication number: US2788270A
Application number: US448904A
Authority: US
Inventors: James D Nisbet; Artemas H Perkins
Original assignee: Universal Cyclops Steel Corp
Current assignee: Universal Cyclops Steel Corp
Priority date: 1954-08-10
Filing date: 1954-08-10
Publication date: 1957-04-09
Anticipated expiration: 1974-04-09

Description

April 9, 1957 J. D. NISBET ET AL 2,788,270

METHOD AND APPARATUS FOR MELTING METAL UNDER VACUUM Filed Aug. 10, 1954 2 Sheets-Sheet l INVENTORS (Jane-I I? f/ SB T THE firTaRNE/S April 9, 1957 J. D. NISBET ET AL 2,788,270

METHOD AND APPARATUS FOR MELTING METAL UNDER VACUUM Filed Aug. 10. 1954 2 Sheets-Sheet 2 ,1, 7x 5 {any \INVENTORS 3 53 DNISEET 171/0 FYTMAJ TEE/m",

. T LL \I ber so that melting can take place under vacuum.

United States Patent METHOD AND APPARATUS FOR MELTING METAL UNDER VACUUM James D. Nisbet, Pittsburgh, Pa., and Artemas H. Perkins, Trenton, N. J., assignors to Universal-Cyclops Steel Corporation, Bridgeville, Pa., a corporation of Pennsylvania Application August 10, 1954, Serial No. 448,904

11 Claims. (Cl. 75-49) This invention relates to melting and casting meta while under vacuum, and more particularly to the charging of vacuum melting furnaces.

To obtain alloys that exhibit high strength, ductility and corrosion resistance at elevated temperatures, it has been found highly desirable to melt the metal in a furnace operating under vacuum and also to cast the metal while it remains under vacuum. The reasons for this are now well known and need not be repeated here. As it would waste a considerable amount of time to have to open the furnace to the surrounding atmosphere every time it is charged and then evacuate it again, it is important to be able to charge the furnace without breaking the vacuum. In this way melting can proceed as a continuous process until it is necessary to open the furnace for some other reason, such as for cleaning the inside of the furnace or for removing a number of ingots that have "been cast therein. Also, it is highly desirable to be able to exercise control over the order in which elements are added to the melt.

It is among the objects of this invention to provide a method and apparatus for melting metal in a vacuum which do not require restoration of atmospheric pressure to the furnace before it can be charged, but which allow charges to be added to the furnace in predetermined batches as needed, and in a predetermined order.

In accordance with this invention, an air-tight furnace is provided in its top with a charging opening, in which there is a normally open valve. Above the furnace there is an air-tight charging chamber that has an open bottom detachably connected with the valve. Means are provided for evacuating the furnace and the charging cham- In the charging chamber there is means for supporting one or more charges and for lowering them through the open valve into the furnace to be melted therein. Thissupporting means is removable from the furnace after the valve has been closed, whereby the vacuum is preserved in the furnace while a new charge is being attached to the supporting means for delivery to the furnace. Preferably, the supporting means is a hoist that is mounted in the upper part of a charging bell which is removable laterally from the furnace so that the hoist and bell always remain together. When several charges are suspended in the charging bell at one time, they preferably are connected together in series in a predetermined relationship by readily fusible elements or the like, so that as each charge is lowered into the furnace it will become separated from the charges above it.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which Fig. l is a perspective View of my melting apparatus;

Fig. 2 is an enlarged vertical section through the charging bell and valve;

Fig. 3 is a horizontal section through the valve, taken on the line III-III of Fig. 2;,and

2,788,270 Patented Apr. 9, 1957 Fig. 4 is a side view, partly in section, of modified furnace charges.

Referring to Fig. 1 of the drawings, a melting furnace 1 includes a large cylindrical shell 2 that is rigidly supported in any suitable manner. The shell has a cover 3 that seals its top, while the 'bottom is sealed by a ver' tically movable closure 4. The furnace can be evacuated by drawing the air out of the shell through. a large pipe 5 connected to suitable suction apparatus. llnside the shell there is a crucible 6 supported by trunnions 7 that are journaled on suitable bearings 8 on the shell. The crucible can be tilted from outside the furnace to pour molten metal into a stationary trough or spout 9 that directs the metal into different ingot molds 10 mounted on a turntable (not shown) supported by closure 4.

As shown in Fig. 2, the top of the furnace is provided with a charging opening 12, on which is tightly mounted the cylindrical lower end of a large valve housing 13. The central part of the housing is enlarged and opens at one side into a wide casing 14. Slidable back and forth in the valve housing and projecting casing is a pair of circular valve gates 15 that are spaced vertically from each other. These gates are large enough to close off the valve housing above and below them when they are in valve-closing position, as shown in Fig. 2. The gates are supported by inclined toggle links 17 pivot-ally connccted to them and to a piston rod 18 that extends out through casing 14 and into a cylinder 19 mounted in a chamber 21 supported by the casing. The gates are pressed vertically against circular gaskets 21 on their seats by the piston rod and toggle links, due to fluid pressure delivered to the outer end of the cylinder through pipe 22. When that pipe is connected toexhaust and the other pipe 23 is connected to pressure, the piston rod pulls on the links and the gates are pulled toward each other by coil springs 24 connecting them. As the rod continues to pull, the gates are drawn out into casing 14 to open the valve. T o prevent the gates from sliding on gaskets 21 and wearing them, there are arcuate shoulders 25 between the valve housing and casing 14. These shoulders prevent the gates from moving laterally until after they have cleared the shoulders and are out of contact with the gaskets.

The furnace is charged through the valve at its top, but it is a feature of this invention that this can be done without losing the vacuum in the furnace. To accomplish this, the open bottom of an air-tight charging chamber 26 is detachably connected with the valve, such as by bolts 27 that connect the flanged lower end of the chamber to the top of an extension 28 of the valve. The top of the charging chamber is closed by a cap 31, on top of which there is an eye 32 so that after bolts 27 have been removed the chamber can be lifted like a bell from the valve by means of a suitable overhead crane 33 (Fig. l) or the like.

, Also mounted on top of the charging hell is an electric motor 35 that drives a gear reduction unit 36, which is connected by a belt and pulley drive 37 with the outer end of a shaft 38. The shaft is journaled in sealed bearings 39 mounted in opposite sides of the cap 31, and carries a drum 41 on its central portion inside of the bell. Wound on this drum is a cable 42 that supports a pulley 43 which is raised and lowered as the hoist is operated. The pulley supports charges for the furnace, which are lowered through the open vaive and into the crucible.

After the furnace has been charged in this manner, the valve is closed and atmospheric pressure is admitted to the charging bell through a pipe 45 connected with valve extension 28. Bolts 27 then are removed and the bell is carried away by the crane to receive a new charge into place.

through its open lower end. The new charge is drawn up into the bell by means of the hoist and the bell is returned to the furnace, where it once again is bolted The pressure in thefbell then is reduced to that in the furnace by withdrawing air through pipe following which the valve is opened to permit the new charge to be lowered into the crucible after the latter has poured its previous charge into one or more of the ingot molds.

Another feature of this invention is that various alloying elements can be added to the melt as required and in the order desired. Accordingly, the main charge is placed in a large sheet metal bucket or can 50, such as a garbage can, and is hung from pulley 43 through the medium of fusible links 51. Suspended from the bottom of the can is a string of small batches of alloying or additive elements which may be carried in pails 52. These pails are connected by fusible links 53. Such an assembly of furnace charges is carried by the charging bell into position above the furnace after the crucible has received its first main charge. When that charge has been melted, the hoist in the bell lowers the string of charges until the lowest pail is in the crucible. The heat quickly melts the fusible link that connects that pail to the one above, and the remaining charges then can be raised up into the bell again until the batch that was left in the crucible has been thoroughly melted. Thereupon, the charges can be lowered again to deposit the next batch in the crucible. This is continued until all of the small batches have been added to the molten metal, and then the crucible is poured. While the last small charge is melting in the crucible, the next main charge, in bucket 50, can be left down in the furnace as far as possible so as to preheat it.

As soon as pouring has been completed, the main charge in bucket 50 is lowered into the crucible, where links 51 are melted so that the can is left in the furnace. During the time it requires for the main charge to melt, the charging bell is disconnected from the furnace and carried away from it by the overhead crane to a point where a new string of charges can be picked up. The refilled charging bell then is returned to the furnace and bolted into place, ready to repeat the cycle. Of course, before the bell is removed from the furnace the valve is closed so that the vacuum in the furnace will be preserved, and before the valve is reopened the bell is evacuated through pipe 45.

The apparatus is shown in Fig. 2 just before the valve is opened after the charging bell has been bolted in place. In Fig. 1 the small batches suspended from the main charge have all been deposited in the furnace and the crucible is being poured. As soon as pouring has been completed, the preheated main charge will be lowered into the crucible and the charging bell then will be carried away as indicated in broken lines. The furnace is recharged repeatedly until all of the molds inside of it have been filled, whereupon atmospheric pressure is restored to the furnace and the filled molds removed from it through the bottom.

Instead of suspending the alloying agents from the bottom of the next main charge as just described, they can be hung inside the large bucket that holds the main charge to which they are to be added. Thus, as shown in Fig. 4, a large can or bucket 56 is suspended from the ends of a chain 57 by S-shape hooks 58. A horizontal bar 59 is fastened to the chain, and suspended by fusible links 61 from the center of the bar is a string of pails 62 which carry the elements that are to be added to the main charge carried in the surrounding bucket. When the bucket is lowered from the charging bell into the crucible, the slack chain will slip off the hooks 58 and then the pails can be lifted out of the bucket so that the main charge 63 can melt by itself. As in the first embodiment, the agents in the pails then are added to the melt at intervals, each successive pail separating from the one above as soon as the connecting link melts.

After the last pail has been added to the melt, the main valve is closed and the charging bell is removed for refilling with a new series of charges for the next melt.

According to the provisions of the patent statutes, we have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. Apparatus for melting metal under vacuum, comprising an air-tight furnace provided in its top with a charging opening, a normally open valve for said opening, an air-tight charging chamber above the furnace having an open bottom detachably connected with said valve, means for evacuating the furnace and charging chamber, and means in said chamber for supporting a charge and including a vertically movable member for lowering the charge through the valve into the furnace to be melted therein, means for closing the valve after said member has been raised above it, said supporting means being removable from the furnace after said valve has been closed, whereby a new charge can be attached to said supporting means for delivery to the furnace.

2. Apparatus in accordance with claim 1, in which said supporting means includes a hoist mounted in the upper part of the charging chamber.

3. Apparatus in accordance with claim 1, in which said charging chamber is a hollow vertical cylinder closed at its upper end.

4. Apparatus for melting metal under vacuum, comprising an air-tight furnace provided in its top with a charging opening, a normally open valve for said opening, an air-tight charging bell above the furnace having an open bottom detachably connected with said valve, means for evacuating the furnace and charging bell, and means in the upper part of said bell for supporting a charge and including a vertically movable member for lowering the charge through the valve into the furnace to be melted therein, means at the side of the bell for closing the valve after said member has been raised above it, the charging bell being removable laterally from the furnace after said valve has been closed, whereby said bell can receive a new charge through its open bottom for delivery to the furnace.

5. Apparatus for melting metal under vacuum, comprising an air-tight furnace provided in its top with a charging opening, a normally open valve for said opening, an air-tight charging chamber above the furnace having an open bottom detachably connected with said valve, means for evacuating the furnace and charging chamber, a hoist in the upper part of said chamber, a string of vertically spaced furnace charge receivers below the hoist, and releasable elements connecting said charge receivers to one another and the hoist so that the receivers can be lowered through the valve into the furnace for delivering charges thereto in succession fo. melting therein, said hoist being removable from the furnace after said valve has been closed following release of the uppermost receiver from the hoist, whereby a new string of furnace charge receivers can be hung from the hoist for delivery to the furnace.

6. Apparatus as defined in claim 5, in which said string of receivers consists of a large main receiver suspended from the hoist, and a plurality of small batch receivers suspended from the main receiver.

7. Apparatus as defined in claim 5, in which said string of receivers consists of a large bucket suspended from the hoist, and a plurality of small batch receivers suspended from the hoist inside said bucket.

8. In the method of continuously melting metal in a furnace, the steps comprising connecting a string of vertically spaced furnace charges together by readily separable elements, supporting the string above a furnace by means of readily separable means, lowering the string of charges into the furnace as each successive charge is needed therein, and after the uppermost charge has been released by said separable means positioning a new string of charges above the furnace ready for lowering into it.

9. In the method of continuously melting metal in a furnace, the steps comprising connecting a string of vertically spaced furnace charges together by readily fusible elements, positioning the string of charges above a furnace, lowering the string by steps into the furnace as each successive charge is needed therein, and after the uppermost charge has been deposited in the furnace positioning a new string of charges above the furnace ready for lowering into it.

10. In the method of continuously melting metal in a furnace, the steps comprising evacuating the furnace,

connecting a string of vertically spaced furnace charges together by readily separable elements, positioning the string of charges above the furnace, removing the air from around the charges, lowering the string of charges by steps into the evacuated furnace as each successive charge is needed therein, and after the uppermost charge has been deposited in the furnace positioning a new string of charges above the furnace ready to be lowered into it.

11. Apparatus for melting metal under vacuum, comprising an air-tight furnace provided in its top with a charging opening, a normally open valve for said opening, an air-tight charging chamber above the furnace having an open bottom detachably connected with said valve, means for evacuating the furnace and charging chamber, a plurality of vertically spaced receptacles in said chamber adapted to hold furnace charges, fusible elements connecting the receptacles to one another to support them in a string, lowering means in the upper part of the chamber, and fusible means suspending the receptacles from said lowering means, whereby the receptacles can be lowered through the open valve into the furnace.

References Cited in the file of this patent UNITED STATES PATENTS 770,189 Schoellhorn et al. Sept. 13, 1904 1,132,376 Naylor et a]. Mar. 16, 1915 1,596,888 Pacz Aug. 24, 1926 2,252,808 Jung Aug. 19, 1941 2,477,406 Church July 26, 1949 2,595,292 Reece May 6, 1952 2,625,719 Moore Jan. 20, 1953 2,698,749 Fishell Jan. 4, 1955 FOREIGN PATENTS 692,050 Great Britain May 27, 1953

Claims

1. APPARATUSA FOR MELTING METAL UNDER VACUUM, COMPRISING AN AIR-TIGHT FURNACE PROVIDED IN ITS TO WITH A CHARGING OPENING, A NORMALLY OPEN VALUE FOR SAID OPENING, AN AIR-TIGHT CHARGING CHAMBER A BOVE THE FURNACE HAVING AN OPEN BOTTOM DETACHABLY CONNECTED WITH SAID VALUE, MEANS FOR EVACUATING THE FURNACE AND CHARGING CHAMBER, AND MEANS IN SAID CHAMBER FOR SUPPORTING A CHARGE AND INCLUDING A VERTICALLY MOVEABLE MEMBER FOR LOWERING THE CHARGE THROUGH THE VA LUE INTO THE FURNACE TO BE MELTED THEREIN, MEANS FOR CLOSING THE VALUE AFTER SAID MEMBER HAS BEEN RAISED ABOVE IT, SAID SUPPORTING MEANS BEING REMOVABLE FROM THE FURNACE AFTER SAID VALVE HAS BEEN CLOSED, WHEREBY A NEW CHARGE CAN BE ATTACHED TO SAID SUPPORTING MEANS FOR DELIVERY TO THE FURNACE.