US1453097A - Multiple-unit induction furnace - Google Patents

Description

. Apr.24, 1923. 1,453,097

' C. B. FOLEY MULTIPLE UNIT INDUCTION FURNACE Original Filed D 28, 1916 2 Sheets-Sheet 1 C. B. FOLEY MULTIPLE UNIT INDUCTION FURNACE Apr. 24, 1923.

Original F $1916 2 Sheets-Sheet 2 d D 20. 28 N w I Wyn/r0? 6197/ 345? 5/5 Patented Apr. 24, 1923.

UNITED STATES PATENT OFFICE.

CHARLES B. FOLEY, OF BRISTOL, CONNECTICUT, ASSIGNOR TO CHARLES B. FOLEY, INC., 0]? NEW YORK, N. Y., A CQRPORATION OF NEW YORK.

MULTIPLE-UNIT INDUCTION FURNACE.

Original application filed December 28, 1916, Serial No. 139,437. Divided and this application filed March 13, 1920. Serial No. 365,636.

T 0 all whom it may concern:

Be it known that I, CHARLES B. FOLEY, a citizen of the United States, and a resident of Bristol, in. the county of Hartford and State of Connecticut,'have invented certain new and useful Improvements in Multiple-U nit Induction Furnaces, of which the following is a specification.

This application is a division of my copending application, Serial Number 139,437, filed Dec. 28, 1916.

My invention relates to electric induction furnaces of the'crucible type; and my object, generally, is to provide a compact furnace of simple and cheap construction, which will operate at a higher efficiency thanhas heretofore been attained in furnaces of the same t 'pe.

1 provide a crucible furnace in which the current-inducing means are located within the outlines of the crucible body and in which the induced secondary is formed by the metal within the crucible, in contradistinction to the structures found in the prior art, wherein the heat is generated in a narrow thread-like loop of metal confined in a separate channel communicating with the interior of the receptacle proper. Where the heat is generated in a loop of metal of small cross section, not only is it difficult to drive the heated metal out of the loop into the body of thejpool with sufficient rapidity to prevent vaporization of the metal constituting the loop, but the heat losses through com ection and radiation from the loop are excessive. By locating the current-inducing means within the outlines of the crucible and producing the heat addition in the metal contained in the crucible body, I minimize the heat losses and make very effective provisions for automatically, continuously and thoroughly stirring the pool of molten metal held by the crucible.

It is a further object of my invention to provide a plurality of current-inducing means associated with a receptacle of the crucible type, in conjunction with circuitcontrolling means for changing the relative polarities of the current-inducing means, for the purpose of varying the current density and, consequently, the heating effect in different portions of the metal.

Other objects of my invention will be apparent from the following description.

In the drawings:

Fig. l is a vertical section of a crucible embodying my invention;

Fig. 2 is a section taken on line 2-2 of Fig. l;

Fig. 3 is a diagram of the electric circuits;

Fig. 4 is a similar view showing how the polarities of the currentrinducing means may be controlled, and,

Fig. 5 is a vertical section of a crucible having several current-inducing means.

Referring to Figs. 1 and 2, the crucible is composed of a body of refractory material 16, adapted to hold a pool of molten metal 17. Located near the bottom of the crucible are cylinders 17 preferably formed integrally with the side walls of the crucible. The cylinders are exteriorly open and form chan nels or bores, extending transversely through the receptacle but completely isolated from the interior thereof. The bottom of the crucible is defined by a horizontal plane surface up to points about vertically beneath the centers of cylinders 17 and by cylindrically curved surfaces from these points to points about in line with the centers of the cylinders. From the latter points the crucible walls extend upwardly and substantially tangentially to the curved portion. The curved portions of the crucible have a larger radius than the outer radius of the cylinders and the axes of said portions are located substantially in the vertical planes containing the axes of the cylinders. This construction results in the formation of chan nels defined by the outer peripheries of the cylinders and the interior walls of the crucibles, the channels having a generally elongated cross section with minimum dimensions at the lowest parts, 22, 22.

Passing through the cylinders 17' are laminated iron cores 31, 31', each carrying a primary coil 27, 27'. The crucible may be provided with a metallic envelope 18, 19, transversely split to prevent induced electricity flowing therein.

Figs. 3 and 4: illustrate circuits and switch mechanism for controlling the relative polarities of the transformers. 52 designates pole-changing switches connected with a source of alternating current 53 and with the primary windings 27, 27'. With the switches in the position shown in Fig. 3 the transformers are of like polarity. By moving the left-hand switch to the position shown in Fig. 4, the polarity of transformer 27 is reversed with respect to that of transformer- 27. Either or both of the transformers may be, cut out of operation by moving the switches on to the dead contacts a, a.

When the transformers are connected so as to have like polarities, the electromotive forces induced in the metal located in the constricted portions 22, 22 of the secondary channels by the alternating flux in the iron cores, will have the same direction and the current will flow as indicated by the broken line, Fig. 1. As there is practically no difference of potential between the upper and lower zones of the metal between the cylinders, no appreciable current will flow in this part of the metal. The C 'B, or heating, effect will therefore be confined principally to the metal within the channels defined by the outer surfaces of cylinders 17 and the inner curved surfaces of the crucible, having maximum values in the constricted portions 22, 22 of these channels.

, the cylinders 17'. This circulatory action is brought about by the forces of gravity operating to displace the hotter and lighter metal in the lower zones by the colder and heavier metal in the upper zones, in conjunction with the dynamic forces created by the fields of the primary and secondary currents.

The tapering formation of the restricted channels between the cylinders 17 and the curved inner walls of the crucible with the minimum cross-section of the channel 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 thereof. Since there is no heat addition produced in the metal between the cylinders, the metal" there will be relatively cold with respect to the metal in the restricted portions of the channels 22, 22.

The motor forcescreated by the leakage fields between the primary and secondary channels act along lines radiating from the centers of the primary coils. These forces repel the metal constituting the secondary outwardly,and they vary progressively from the maximum values at the lower constricted portions of the secondaries to minimum values at the wide portions of the secondaries where the latter merge with the bottom of the pool.

It will be noted that since the axes of the outer walls of the channels are located above the axes of thecylinders the motor forces,

which act along lines radiating from the axes of the primary coils, have components directed up along the outer walls of the channels. These motor forces, therefore, will be effective in driving the metal out of the channels into the body of the pool.

There are further involved in the movement of the metal, the radially-acting forces created by the field of the secondary current and manifesting themselves in a fiow of metal generally along the axis of the secondary conductor. These forces vary directly with the square of the current and inversely with the cross section of the conductor. They will therefore have their maximum intenslty at the constricted portions 22, 22 of the sec ondary, and the metal will consequently tend to flow from these points axially up along the secondary channels. I do not depend upon these forces, to produce circulation in my furnace; for the forces of gravity and the motor reactions between the primary and secondary leakage fields are ample to produce the desired stirring of the metal. The effect of the radially-acting forces, which is commonly termed the pinch effect, is considerably reduced in a conductor of the form utilized in my furnace. The effect is a maximum in conductors of cir- (-ular cross section, since in a circular con- (luctor the average distance between the cur rent-bearing elements is a minimum, and the resultant attractive forces between said elements are focused and concentrated at the axis of the conductor. \Vhereas, in a broad and relatively thin conductor, such as I use, the average distance between the currentbearing elements is considerably greater than the average distance between the current-bearing elements of a circular conductor having the same cross-sectional area; and, furthermore, the attractive forces between said elements are not focused along an axial line, as they are in a circular conductor, but are dispersed in an axial plane.v However, whatever may be the movement of the metal produced in my furnace by the pinch effect, such movement will be in an upward direction from the constricted portions 22. 22, where the effect is most intense, and will therefore combine with the movements effected by the motor forces and the forces of gravity to expel the metal from the secondary channels up into the body ,of the pool.

Singe'the motor forces act to press the metal away from the tubes towards and against the inner curved surfaces of the crucible; there will be local whirls formed by the upwardly flowing metal in the outer portions of the secondary and the downwardly-flowing metal along the inner portions thereof; in addition to the downward flow indicated by the arrow 36 between the tubes.

When the transformers are connected so as to have opposite polarities, the electromotive forces generated in the metal in the constricted portions of the channels. will means. The same principles are involved in the operation of this furnace as in the furnace illustrated in Figs. 1 and 2, and need not be restated. With the transformers connected so as to have the relative polarities shown, the currents producing stirring of the pool will be along the paths indicated generally by the arrows. I

In the operation of the furnace shown in Fig. 5, I may tap out the metal to the line 40 through the tap hole 41 by removing the plug of refractory material 42. This will take out the lighter metal within the crucible, which in some cases may be desired, or the metal may be drawn down to the line 43 by removing the plug 44 from the tap hole 45. The slag 46 which is located above the line 47 will, as it accumulates, pass out through the mouth 48 of the crucible. I prefer to retain the body of the metal 49, which extends to the line 43, permanently within the crucible, but when it becomes necessary .to remove this metal, in order to make repairs upon any-portion of the crucible, the plug 50 may be removed from the tap hole 51 and the entire content of the crucible may then be withdrawn.

Having fully described my invention, I claim:

1. An electric furnace, comprising a re ceptacle of refractory material, having interior walls forming channels, and independent current-inducing means linked with said channels said current inducing means being so connected asto produce secondary electromotive forces of the same direction.

2. An electric furnace comprising a receptacle having a substantially flat bottom oined with the side walls by cylindricallycurved portions and having its other two sides formed integrally with exteriorly open cylinders, the peripheries of the cylinders cooperating with said curved portions to form channels having minimum cross sections at the lower parts, and current-inducing means located in said cylinders.

33. An electric furnace comprising a cruelble having interior channels formed wholly" within the outline of the crucible, and a. plurality of current-inducing means linked with the channels and switches for controlling the relative polarities of said current inducing means.

4. An electric furnace comprising a crucible having interior channels formed wholly within the outline of the crucible, a plurality of independent current-inducing means linked with the channels, and means for controlling the relative polarities of said ourrent-inducing means.

5. An electric induction furnace, comprisin a receptacle of the crucible type, a plura ity of current-inducing means located near the bottom of the crucible, said receptacle adapted to hold a mass of molten material forming the secondary circuit and surrounding the current-inducing means, in combination with means for controlling the relative polarities of the current-inducing means and producing zones of different temperature on opposite sides of said inducing means.

6. An electric induction apparatus comprising a refractory receptacle of the crucible type, adapted to contain a mass of molten metal forming the secondary circuit, a plurality of current-inducing means so arranged as to produce the greatest heating effect near the bottom of the crucible, the inducing means being so located that the space between the inducing means is greater than that between the mducing means and the walls of the crucible, in combination with means for varying the relation of the temperatures existing in the-space between the inducing means and the inner wall of the receptacle.

7 An electric induction furnace, comprising a crucible, a plurality of current-inducing means so located as to produce the greatest heating efi'ect near the bottom of the crucible, and means for varying the relative polarities of said inducing means. 8. In an electric induction furnace, the combination of a crucible, a plurality of current-inducing means near the bottom of the crucible and so located as to leave a space between the inducing means and the crucible walls which is wider at the top than at the bottom, and is narrower than the space between the inducing means, in combination with means for so controlling the currentinducing means as to produce the hottest zone at the bottom of the crucible, a relatively cooler zone between the walls of the crucible and the inducing means and the coolest zone between the current-inducing means.

CHARLES B. FOLEY.

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