US1638660A - Electrothermic crucible - Google Patents

Description

Aug. 9, 1927.

4 c. B. FOLEY 'ELECTROTHERMIC CRUCIBLE Original Filed Nov. 1'7, 1915 Patented Aug. 9, 19 27 .UNITED STATES PATENT OFFICE.

GHARLESZB. FOLEY, OF DA YTON, OHIO, ASSIGNOR TO CHARLES B. FOLEY, INC", A.

CORPORATION OF NEW'YORK.

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Application filed November 17, 1913, Serial 1%. 801,474. Renewed-December 28, 1916. Serial 110. 139,487.

My invention relates to electric furnaces of the induction type- It relates specifically to crucible furnaces which have a channel of loop form opening-into the interior thereof and a suitable primary coil and core linked with the channel, the channel being adapted to receive molten metal and form it into a loop joined with the pool of metal held by the main body of the crucible, the

loop of metal together with the metal in the pool constituting a short-cirouited secondary conductor.

For operating furnaces of thiskind, an alternating voltage is impressed on the terminals of the primary winding, causing an alternating current therein and a resulting alternating magnetic flux in the core. This flux cutting the loop of molten metal induces secondary currents therein which heat the metal, the amount of heat produced being proportional to the product of the res stance of the secondary conductor. and the square of the current. Since the secondary consists.

of metal, a good conductor even at the high temperatures attained in the operation of the furnace, secondary currents of very large value must be used in order to generate sufficient heat to melt the charges and maintain the metal at the desired working temperatures.

It is obvious that. where the heat additions occur principally in a constricted loop of molten metal, provision must be made for driving the hot metal therefrom continuously and rapidly. Otherwise a zone of such intense heat would be created in the loop that the metal would be vaporized. My main object is to provide a furnace of the above type, capable of supplying the requisite heat addition, even where the charge consists of metal having great conductivity, such as copper, and having structural' provisions for automatically, continuously and vigorously driving the hot metal from the secondary channel up into the body ofthe pool, where it may communicate some of its heat to the colder metal. 7

Specifically, the furnace embodying my invention consists of a relatively deep receptacle adapted to hold a high hydraulic head of molten metal. Near the bottom of the receptacle there is a hollow cylindrical smallest dimensions at thelowest part. One

member of a vertically-arranged core passes through the bore of the tube and saidmember carries a primary winding with its axis substantially perpendicular to the plane of the loop. The furnace is adapted to receive molten metal and form it into a relatively deep pool with a. broad annular band of metal depending from opposite sides of the pool, having flaring portions joining the bottom thereofand a relatively thin lower portion. J

In the operation of my furnace there are at least three distinct forces tending to drive the metal out of the secondary channel into the bottom of the pool. First, the force ofgravity tending to cause displacement of the hotter and lighter metal in the lower zones by the colder and heavier metal in the upperzones. This force, of course, is not a factor except when there is a difference in density such as is due to differences in temperature and by reason of which heavier metal in upper parts of the molten mass displaces lighter metal below it. Second, the radially-acting electromagnetic forces created by the field of the secondary current, squeezing the molten secondary and tending to produce a flow of metal along the axis thereof. force is known in the art as pinch effect. It varies directly with the square of the secondary current and inversely with the cross-sectional area of the secondary con- "tube formed integrally or' otherwise with The manifestation of this ductor. Third, the force created by the reaction between the primary and secondary currents and acting along lines radiating from the axis of the primary coil, but effective to produce pressure perpendicular to the elemental lines of flow of secondary current tending to repel the metal "constituting the secondary conductor outwardly in the general direction of the planes of the secondary channel. The manifestation of this force is commonly known in the art as motor effect? It varies directly as the square of the secondary current and inversely as the length of leakage path between the primary and secondary conductors.

The structural features of my furnace outlined above utilize these forces to a very effective degree for producing circulation and stirring of the molten metal. Forming the secondary with its cross-sectional area progressively increasing from a minimum at the lowest point results in a maximum current density, and a correspondingly maximum heating effect, in the lowest part of the secondary with a progressively decreasing heating effect in the upper zones thereo It therefore follows that in general, In the operation of the furnace, the metal constituting the secondary will progressively 1ncrease in specific gravity from the lower to the upper zones, resulting in a constant and uniform tendency of the heavier metal above to displace the lightermetal below. 4

Since the current density is a maximum in the lower part of the secondary and progressively decreases in the upper zones, the pinching or squeezing force, exerted on the secondary by the field of the current flowing therein, progressively decreases from a maximum at the lowest or most constrict ed portion of the secondary. This radiallyactmg force tending to produce motion of the metal along the axis of the secondary will, therefore, have its greatest strength at the lower portion thereof, the strength progressively decreasing with. the increasing cross-section of the secondary.

By forming the secondary as a relatively broad band of annular outline and linking therewith the iron core with its central plane substantially bisecting the annular secondary and locating the primary coil on the core in a position within the loo of the secondary with its. axis substantially perpendicular to the plane of the latter, it is possible to bring the secondary in close inductive relation with the primary and to apply the motor forces created by the oppositely-flowing primary and secondary currents to repel the metal constituting the molten secondary loop outwardly in the general direction of the planes of the loop, said forces acting with substantially equal intensity on all corresponding elements of the molten metal within the secondary channel. mean elements equidistant from the transverse plane bisecting the secondary and passing through the axis of the primary coil. The intensity of the motor effect is a maximum, at the lowest part of the secondary, since the current center or medial line of the current flow in this part is closest to the primary coil, and since the reluctance of the leakage path between primary and sec- By corresponding elements, I

ondary is a minimum in the space including the planes of lamination of the iron core.

In order to increase the effectiveness of the motor forces, I locate the axis of the primary coil a substantial distance below the axis of the cylindrical bottom of the crucible. It results from this arrangement that the medial current line or path is nearest to the primary winding at the bottom and that its distance from the primary winding increases progressively along the path of current travel toward the main body of metal in the crucible as distinguished from the secondary loop.

It will be noted that the cross section of the secondary loop increases progressively from the bottom upwardly toward the main body of metal in the crucible so that both the motoreffect and pinch effect reduce progressively in the illustration from thepoint of smallest cross section in both directions toward the main body of metal in the crucible.

In the operation of the furnace, therefore, the outwardly-acting motor forces in conjunction with the axially-acting pinching or squeezing forces and the forces of gravity, acting upwardly on. the hotter and lighter metal, combine to produce a resultant movement of the metal upwardly along a path located between the medial current path and the outer wall of the channel, the metal being forcibly injected into the bottom of the down from the pool through the flaring mouths of the secondary channel about the upwardly flowing streams and largely inwardly of the hotter metal streams. The circulation thus represents a diversion of the pinch circulation toward the outer channel Wall. It follows from the distribution of the forces involved that the secondary is under a resultant pressure (independent of the pressure produced by hydrostatic head), having a maximum value at the lower portion thereof and decreasing progressively therefrom with the increasing cross-section of the secondary. This eliminates the possibility of the creation in the secondary of a stagnant zone; for the metal in the secondary will always flow from the lower points of greater, to the upper points of less pressure.

The pinch effect, as is well understood in this art, places a limit on the secondary current which it may not exceed without causing rupture of the secondary and consequent vaporization of the metal and injury to the furnace structure. It is therefore desirable to eliminate any objectionable result from this force, so far as possible,,wherc large secondary amperage is required in a constricted conductor, as it is in the opcration of my furnace. I therefore utilize in my furnace a high head of molten metal pool, and colder metal flowing which these forces must overcome, in addi-' tion to the atmospheric pressure, before they can cause rupture of the Secondary.

I rely primarily upon pinch effect and motor effect for the circulation in my furnace, combiningthem advantageously by making each a maximum at the point of smallest cross section, shown at the bottom of the furnace, and progressively decreasing both on each side of the point ofsmallest cross section so as to afford progressively reducing pressures as the distance from the point of smallest cross section increases. With the proportions shown the pinch effect pressure considerably exceeds the motor effect pressure, giving a circulation which might be described generally as a distorted pinch circulation. Its advantage lies in the fact that the two pressures combine nicely to effect a strong outward flow of hot metal.

While I have outlined the structural features of my furnace in considerable detail, I would have it distinctly understood that my invention is not limited to a furnace having all of the structural features specified. Some of these features may be modified or discarded without essentially affecting the mode of operation or the results attained, and I therefore do not intend to limit my invention other than as defined in the claims appended to this specification.

In the drawings:

Figure l is a central vertical section of my crucible, showing one electro-magnetic current inducing means associated therewith;

Fig.2 is a similar section taken at right angles to Fig. 1;

Fig- 3 is a plan view;

Fig. 4 is a section through the magnetic core of a current inducing means taken on the line H of Fig. 2.

My invention is best adapted for use in connection with a substantially rectangular crucible from which the metal may be poured, these devices being suspended on trunnions 11 and 12, as usual, when metal is to be poured from the crucible. The invention may be similarly applied to other forms of crucibles.

The crucible is composed of an outside metal jacket 13 and an inside lining 14, the former being split, at 15, to prevent induced electric current from circulating within the jacket. The bottom of the crucible is rounded or semi-cylindrical in shape, the center of curvature being located in a vertical line passing through the center of curvature of the cylindrical portion surrounding the current inducing means.

A cylindrical portion 17 composed preferably of the same integral material as the lining 14. extends from the side wall 18 of the crucible to the side wall 19 thereof. The cylindrical portion 17 is extcriorly open, as

at 20, its lower portion 20 approaching very close to the lower portion of the curved wall 14 of the crucible, the axis of the cylindrical portion 17 being located somewhat nearer the bottom of the crucible than is the axis from which the bottom is curved. This leaves a small space 22, between the bottom of the cylindrical portion 17 and the bottom wall of the crucible and this channel having a cross section of slightly increasing but always substantially rectangular cross Section extends around on either side of the cylinder 17, as indicated in Figs.

1 and 3. All cross sections of this passage taken on planes passing through the axis of the cylinder 17, would be of substantially rectangular cross section similar to that 7 shown at 22 in Fig. 2, but of varying area. The corners would usually in practice for structural reasons be somewhat rounded off as shown at 22, in Fig. 2.

' The cylindrical portion 17 may contain an interior supporting sheet metal cylinder 23. which, for the purpose of practical operation, is split longitudinally as at 24, to prevent induction of the electric current in said metal cylinder.

It will be observedthat the cylindrical portion provides an exterior opening 20,

which does not communicate with the interior of the crucible.

\Vithin the cylindrical opening 20, I place electro-magnetic induction elements 25, consisting of a preferably closed magnetic cir cuit 26, upon one or both limbs of which is located an electric conducting coil 27. The magnetic circuit consists of a series of laminated horse-shoe plates 27 constituting a closed core with the removable end piece 28. The plates of the main body part may be held together in any suitable fashion, but the replaceable end part 28, constituting the removable portion of the core, consists of a series of parallel plates 29 held together by insulated bolts 30, and placed between the limbs 31 and 32 of the major portions of the magnetic core. A very small part of the limbs3l and 32 may. be cut away for accommodating the insulating cylinder 33 thereby to hold the end part 28 in place. It is evident that the part 28 must be removed in order to place the coil 27 in position and to insert the coil and one of the limbs of the magnetic core within the hollow cylinder 17.

While I have shown herein a single embodiment of my invention in a situation in which it may be advantageously employed, it is evident that changes within the scope of the appended claims may be made, without departing from the principl of my invention.

Throughout the specification and in the claims, I have used the terms crucible and crucible type in the ordinary sense in which they are used in chemical and metallurgical operations.

Having thus fully described and illustrated my invention, and the means by which it is to be carried out, what I claim, is

1. An electric induction furnace, comprising a crucible provided with a refractory channel extending through the crucible from side to side and opening cxteriorly thereof, said channel being so located as to produce the greatest heating effect at the bottom of the crucible and having its sides so arranged relatively to the sides of the crucible as to leave a passge between themwhich increases in cross-section upwardly, in combination with induction means passing through said channel.

2. An electric induction furnace comprising a crucible adapted to hold a high hydraulic head of molten metal and provided near the bottom with a hollow refractory cylinder opening outwardly througl1,opposite sides of the crucible and so located as to produce the greatest heating effect at the bottom of the crucible, in combination with current inducing means passing through the cylinder.

3. An electric induction furnace, comprising a crucible havin its bottom and two sides defined by a cylindrically curved surface joined with upwardly extending tangential plane surfaces, and having its other two sides connected by a hollow cylinder opening outside the crucible, the axis of the cylinder being coplanar with and located a substantial distance below the axis of said cylindrical bottom, in combination with current inducing means passing through the cylinder.

4. An electric induction furnace compris ing a receptacle having a closed channel of loop form opening into the'interior thereof through flarlng mouths, said receptacle having a transverse opening formed within thechannel loop and a primary winding located in the opening with its axis transverse to the plane of the loop.

5. An electric induction furnace having a closed channel of loop form opening into the interior thereof, said furnace having a trans verse opening within-the loop, and a pri-' band, in combination with current inducing means passing through the opening.

7. An electric induction furnace having a closed annular channel opening into the 1nterior thereof, said furnace having an opening extending substantially at right angles to the plane of the channel and located with-,

in the embrace thereof, in combination with a magnetic core surrounding the channel and having a member passing through the opening and a coil on said member, the central plane of Said core substantially bisecting said channel and located substantially at right angles to the plane thereof.

8. An electric induction furnace comprising a receptacle havin a closed annular channel opening upwardly into the interior thereof, adapted to form a mass of molten metal into a pool having an annular'loop depending from the bottom thereof with its outer periphery'merging with the periphery of the pool, the annular loop of metal and the pool constituting a short-circuited secondary conductor, in combination with a magnetic core linked with the loop and having a primary coil thereon within the loop.

9. An electric induction furnace having a pool, a submerged loop channel connected with the pool at its outer ends and pro ressively increasing in transverse section rom a portion of minimum section at a distance from the pool toward the pool, a transformer whose core is enclosed by the channel, and a primary winding on the core and within the channel, whereby pinch effect is produced in the channel, the pressure from which effect progressively reduces from the portion of minimum section toward the pool.

10. An electric induction furnace comprising walls forming a furnace pool and a channel of progressively variant section connecting at its ends with the bottom of the pool, and having the smallest cross section of the channel at approximately the middle .of the length of the channel, a transformer core passing through the channel and a winding on the core, said winding being surrounded by the channel.

11. An electric induction furnace comprising a receptacle holding a furnace pool and walls'forming a channel lying beneath the pool and connected at both ends with the furnace pool, a transformer core threaded through the channel and a winding on that portion of the core which pases through the channel, so that the winding is surrounded by the channel.

12. An electric induction furnace having a pool, a submerged loop channel of progressively variant section connected at its ends with the furnace pool, and means for inducing current in the loop,- including a primary coil within the loop, the relation of the primary coil and the loop being such that there is maximum reaction of primary current upon, secondary current at the point of minimum section.-

13. An electric induction furnace comprising walls forming a furnace pool and'a an opening within the channel and a .winding on the core, said winding being sur' rounded by the channel.

14. An electric induction furnace comprls- I ing walls forming afurnace pool and a channel of progressively variant sect-ion connecting at both ends with the bottom of the pool, having the smallest cross section of the channel and the closest approach of the medial current line of secondary current in the channel to the primary. winding at the same part of the length of the channel, a transformer core passing through an opening within the channel and a primary winding on the core, said winding being surrounded by the channel.

15. An electric induction furnace having a pool: and asubmerged secondary channel loop connected with the pool, a transformer core passing through the secondary and a primary coil u on the core, said primary eing surroun ed by the secondary and spaced farther from one part of the secondary than from another part of the secondary for the purpose of providing reaction of primary current upon secondary current to cause circulation.

16. The method of heating and stirring the pool of molten metal in an electric induction furnace, which comprises forming by suitable refractory walls a pool of molten metal and'a loopof molten metal depending from the bottom of the pool, heating the metal by induced electric currents, and

simultaneously subjecting the loop of molten metal to electromotor forces acting out- 'wardly thereon in the general direction of the planes of the loop-and acting with maximum intensity on the metal in the outer or lower part of the loop.

17. The method of heating and stirring the pool of molten metal .in an electric induction furnace, which comprises forming by suitable refractory walls a pool of molten metal and a loop of molten metal connectedwith the bottom of the pool, heating the metal b induced electric currents and slmult-aneous ydrivin the hot metal from the loop by the app ication of electromagnetic pressure acting with maximum intensit on {he metal' in the outer or lower part 0 the oop.

18. The method of heating and stirring the pool of molten metal in an electric induc-' metal in an electric induction furnace, which comprises forming by suitable refractory walls a relatively deep pool of molten metal and a loop of molten metal connected with the bottom of the pool, inducing electric currents in the loop and pool to heat the metal, and simultaneously subjectin the molten loop to electro-motor forces acting outwardly ofthe loop in the general direction of the planes thereof.

20. The method of heating and stirring the metal in an electric induction furnace, which comprises forming by suitable refractory walls a relatively deep pool of molten metal and a symmetrical loop of molten metal depending from the bottom of the pool, threading a core and winding through l the loop with the winding embraced by the loop and having its axis substantially peroutwardly of the loop in the general direct-ion of the planes thereof.

21. The method of heating and stirring the pool of molten metal inan electric in duction furnace, which comprises heat-in the metal b induced currents in a close continuous c annel communicating with the bottom of the pool through flaring mouths, and simultaneously subjecting the hot metal to gutwardly acting electro-motor forces, whereby streams of hotter metal'are injected into the bottom of the pool along channel lines outside of the center lines of the channels, relatively colder metal being withdrawn through theflaring mouths to a greater extent mside than outside the paths of the hotter streams. 7

22. The method molten metal in an electric induction furnace by the application of electromagnetic drive to fluid metal confined in a continuous channel opening into the bottom of the pool' at opposite sides thereof, which consists in injecting into the bottom of the pool upwardly-directed streams of hotter metal enof stirring the pool of tering the pool at opposite sides adjacent its periphery and withdrawing from the pool relatively colder metal to a greater expressure to the tent inside than outside the paths of the hotchannel loop at a distance from the pool to ter metal streams. cause the metal to flow from said portion 23. The process of stirring a pool of upward outside the center lines along both 6 molten metal in an' electric induction fursegments of the loop into the bottom of the nace by applying electromagnetic pressure to pool. 15 molten metal in' a closed channel ofloop In testimony whereof I hereunto set my form communicating with the bottom of the hand. pool, which consists in applying a maximum metal'in a portion of them CHARLES B; FOLEY.

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