US1595970A - Induction furnace - Google Patents

Description

Aug. 10 1926. 1,595,970

' J. WEED I NDUCTI ON FURNACE! Filed 29, 1921 3 Sheets-$heet 1 Invemto'r: James Tfi. Weed,

H i s Attor'n ey.

Aug. 10, 1926. 1,595,970

J. M. .WEED

INDUCTION FUR'NAiE 5 5? .ssa sws Inventor: James TTLWeed,

His Attor neg.

Aug. 10 1926.

J. M. WEED INDUCTION FURNACE Fild D630.

Fig.7

Inventor: Jamesm .Weeczl b5 l His Attorney.

Patented Aug. 10, 1926.

UNITED STATES 1,595,970 PATENT OFFICE.

JAMES M. WEED, OF SCHENEC'IFADY NEW YORK, ASSIGNUR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NJElW YURK.

INIDUCETIQN FURNAGE.

application filed December 29, 1921.

(than 2. between the reservoir and .loo'ioiil portions of the rece jitarle than norotmoro obtained. For this purpose I utilize a prin ciple not previously used in induction 'furnacos, namely, the eloctrornagnetic roacoion between prin'iary and secondary, the 0 b6" ing so disposed as to give dilleronros of fluid pressure between different partra or regions of tho secondary. I make ilQylQllSl two Sllt'l'l regions of diil'oruni; prossnres, preforably those adjacent, to the two most. Widely Separated opposite bounding similar-cs of" ihe container for the serondary, to open into or roiinniinicate throiiglrreaper-tire din-its with dill'eront parts of tho rwiaoir. so that too PXORWHO (,lill'eronrc run art. in producing a. desired circulation of the rhar;

more detailed description of my iii-vention is given in the follmring riporii'ioali n taken in coiinorl'ion with the :iconipnnying drawin in whirl; Figs. 1 and are. vertirzil srriions taken at. right ann'lrs to 0 other ol a prolrrrod embodiment of my 1. 'rrntion; a modification illnsrratod in l I oy a horizontal nrrliion. and. in Fl 1 4 and iv vertical emtions talmn a. iif angles to .arh other; l igs. (i. 7 and S a 0 vertical norlions of other modilioz'il'ioi'is of my 111* naro; Fig. 9 a horizontal section othor n'n'idifiration; and Fig. 10 is a live 'VlifW ol'the form of my iiirnaco in Figs. 1, and

Tho iiirnam: shown in Figs. l. and :2 ornpriars a rrlraotory rouc itzirlo (OHSlll'lll'Wl i" a looprd portion .1. of reli'itivnly' small oros "'rlion. and a 'rewrroii' of qrvator Moss;

i'ioi'i adapird lo ronlain a, pool 2 iii fluid. vharg'r. n n'izignotir (Zillfllil. or (ore 33 mini- Serial No. 525,660.

soconoar i with newest to tho .rirnar Windins. Uonva iieiitlv the crucible or race rl u a taclo for the cliarq'e 1S constituted b no- :lorrned i ers 0i suitable retractory maenamplo, fused magnesia, which may be ill ed and tired before being assemhlrd in tho lllEBQ-CQ These refractory mem- .18 in. Z cemented together at onfined in the furnace.

Widely sepnratod opposite surfaces of the secondary l are at ljho ends; or the oylincler, designated a: J and ii illi tlio co-axial arrangement of primary and. aecondary illustrated in ll l and '12,.in which they are offset, or ilacod from each other in an axial limo lion, the n'iaximum fluid. pressure in the secondary due to the. repulsion 0f the pri- Inary is found near '5. tho encl of the cylinder most remote from the, primary, While iiiinin'nnn pressure is found near 6, the end nearer the primary. 7 and 8, res 'iectively. are therefore provided lK'lWBLll these regions of maximum and minimum {)ICSSUIG- and different parts of the reservoir to permit circulation of molten charge in tho direction. indicated. in Fig. 2 by tho arrows.

The oiiionnt o? the pressure ditloronco which prozihiros this cii nlation. and ronso i iioiitly tho rapidity oi. the circulation. may in varied or adjusted by changing tho geoniizi rio rolation oi the primary Windii with in "or- 1 to the Si('i'in(lfil'}". Assuming that the im. on of the priinary shown in Fig. 2 gives; maxin'iiim oirciilation. tluz circulation will he reduced by shifting lho primary to tho 'ight. IVhen primary and secondary an: of tho same axial length, as in the presonl. raw, and ar flush with each other in an axial direction, the circulation will pFLC- lllitlly roasn. if tho prin'iary is shifted still l'iirtl' r, resulting in tliaplaoonwnt in. the revorsr, direction, the direction of r'rciilation will he. reverse. it is thus possihle to control l'm'il' the strength and the direction of the ciri'rnlation of tho molten charge in the for naco of l. and 2 by adjusting" the poailion of t primary winding in an axial direction.

The simulat on Within thoso portions of tho r ioron lary which are not on the same" side of the i 'lindor with. the ducts i and 8, is laoilitalwl my the annular enlargements 9 and H ends of the cylinder 1 c0n- Communicating ducts stituting the secondary. The enlargement 10 in Fig. 2 distributes the molten material coming in through duct 8 more or less uniformly around the left hand end of the cylinder 1, while the enlargement 9 re-collects the material and leads it to the outgoing duct '2'. Within the body of the cylinder 1, between its two ends, the general trend of the circulation will be in an axial direction, from left to right. A free continuous circulation is thus maintained between the secondary and the reservoir, which passes throughout the entire secondary cylinder, thus avoiding all danger of hot spots; and thus maintaining an almost uniform temperature throughout the molten charge within the entire crucible. The refractory crucible 1, 2 is surrounded by a layer '36 of suitable heat insulating materiahfor example. the commercial product known as Sil- O-Cel, and an outer shell 37 of steel or other suitable metal, so constructed to avoid a conductive circuit about the core in which a secondarv current would be induced.

In ig. 10 is shown in side elevation 21 complete furnace of the form shown in section by Figs. 1 and 2. The furnace is mounted upon a pedestal 38 in such a way as to rmit tilting for pouring the charge. This 18 done by means of the hand-wheel 39. The charge is introduced by a door 40 and poured from the spout 41. A pivoted cover 42. permits access to the furnace interior for various urposes. The furnace as a whole can be li ted by eye bolts 43. Air for cooling the primary winding is, supplied by a ipe 4:4.

The modihed furnace illustrated in Figs. 3, t and 5 differs from that in Figs. 1 and 2, chiefly, first, in the relative positions of the reservoir and the annular secondarycontaining portions of the crucible, and second, in replacement of the ducts 7 and 8 by a single opening or channel of communication. In the form of furnace shown '11 Figs. 1 and 2 the secondary is beneath the reservoir with its axis horizontal, while in the modification shown in figs. 3, 4 and 5, they are beside each other, the axis of the mcondary being vertical. The circulation of the molten charge is controlled in the latter case by movements of the primary winding in a vertical direction. With the primary winding positioned as shown in Fig. 4, maximum pressure due to the repulsion of the primary will be found at the ottom of the secondary, and minimum pressure at the top. This difirence in pressure will result in a flow of the molten char e from the bottom of the secondary to t e reservoir, and from the reservoir back to the top of the secondar as indicated by the arrows. Parts in hi 3 to 9 coms ending to similar or i entical parts of igs. 1 and 2 have been indicated by the same numerals with the addition of n. prime mark.

Assuming that the primary winding in Fig. 4c is in a osition giving maximum velocity of circu ation, the circulation will be reduced by lowering the position of the primary relative to the secondary, and will be reversed in direction when the primary passes through the position of symmetry with respect to the secondary cylinder. The position of the primary coil 4 may be ad justed to vary the circulation by turning the nuts upon the frame 13.

With a tree passage 11 between the sec ondary and the reservoir, extending from the point of maximum pressure to that of minimum pressure, a flow will naturally be produced rom the secondary to the reservoir at the point of maximum pressure and from the reservoir tothe secondary at the point of minimum pressure, while the charge will be stagnant in that part of the channel opening into the secondary at points of neutral pressure. it is clear, therefore, that the principle of operation, so far as the production of circulation is concerned, is the same whether separate ducts are used for connecting the secondary with the reser. voir, as in the furnace in Figs. 1 and 2, or whether the wall between these ducts is eliminated, forming one common channel, as in the furnace of Fi s. 3, 4 and 5.

Since there is no de.nite limit to the width or thickness of the channel ll, it is clear that it might be increased if desired. to the full diameter of the secondary, or full width of thereservoir, thus causing the reservoir to become, in effect, a mere enlargement of one side of the secondary, as illustrated for instance at 12, in Fig. 9.

My invention may be embodied in various other forms of furnaces, all involving the same general principle. Three other modifications have been lllllfilililtfithlfl simplified form in Figs. 6, 7 and 8, respective y.

The modification shown in vertical section in Fig. 6 is similar to the one of Figs. 1 and 2 except for the form and position of the primary winding. This windin 14 is disc shaped instead of cylindrica in shape, and is located at one end of the secondary cylinder. The circulation of the molten char e in this furnace will be similar to that of t e furnace illustrated in Fig. 2, entering the reservoir by a duct 15 and leaving by a. duct 16.

n the modification illustrated in Fi t, the prime winding 17 is cylindrica in shape, whi e the secondary-containing annular part 18 of the crucible is disc shaped. The two most widely separated, opposite bounding surfaces of: this secondary are the inner and outer circumferential surfaces 19 and 20. With the symmetrical concentric shown, the secondary surrounding the primary, the maximum fluid pressure in the secondary due to the repulsion of the rimary, is found nearer its outer circum erential surface 20, while minimum pressure is found near the inner circmnferential surface 19. Communicating ducts are therefore provided between these regions and different parts of the reservoir. Duct 21 serves the region of maximum pressure, while for purposes of symmetry, the region of minimum pressure is here served-by two distinct ducts 22 and 23.

In the modification shown in Fig. 7, both the primary winding 24 and the secondary 25 are disc shaped, and they are located in parallel planes perpendicular tov their common axis. The secondary communicates with th reservoir through ducts 26 and 27, the former leading from a region near the outer, periphery and the letter from a regionnear the inner periphery of the secondary 25. The total primary winding is of greater radial exte ie than the secondary, its internal diameter being smaller and its external diameter being larger. This winding, however, is provided with terminal leads 28 and 35, and in addition with tap leads 29 to 34, making it possible to excite one portion of the wind mg, while other portions are left unexcited. If now primary connection is made to leads 31 and 35, exciting an inner portion of the primary winding, the outer portion being unexcited, circulation will occur from the secondary to the reservoir through duct 26, and from the reservoir to the secondary throu h duct 27. If connection is made to lea s 30 and 34 instead of 31 and 35, the circulation will be in the same. direction as before, but with reduced velocit If connection is made to leads 29 an 33, the direction of the circulation will be reversed. And finally, if connection is made to leads 28 and 32, this reverse circulation will be increased in velocity. The modification shown in Fig. 7 thus differs from those shown in the other figures, not only in the fact that both primary and secondary are disc shaped, but also in its modification of the method illustrated in somev of the other figures for controlling the direction and the velocity of the circulation. Where. in other cases, this control is effected by shifting the physical position of the primary winding without changing its excitation, in this case it is effected by a change in the portion of the winding Which is excited, the position of the winding as a whole being unchanged,

A. better understanding (if tBe origin and location of the pressure difference producing circulation in my furnace [nay be ob tained as follows: Concentrating attention upon the particular form shown in Fig. 6,

we will consider the contents of the cylindrical secondary in this furnace as subdivided into a number of annular parts by parallel planes, which are perpendicular to the common axis of primar and secondary.

The magnetic leakage fied between primary and secondary in this case is in a generally radial direction, and parallel to the above-mentioned planes. The density of this field is maximum within the region "gles to the direction of the field. The magnitude of this stress at any point is proportional to the field density at that point. \Vithin any section of the field at right angles to its direction, the magnetic stresses at different points react upon each other, and only make themselves felt mechanically between points of different density, Where the opposing magnetic stresses ar unequal.

Considering now the action of the magnetic leakage field which has been described upon a given annular portion of the sec ondary, we find that the pressure upon the left-hand side of the annular portion (nearest to primary) is greater than the opposing )ressure upon the right-hand side (farthest from the primary). The dillerence between these pressures will therefore be transmitted mechanically as a fluid pressure from the portion of the secondary under consideration to the next adjacentpart on the right (further from the primary). Going from the end of the secondary cylilr der nearest to the primary to the end farthest away, this unbalanced pressure in each part is added to that which is transmitted to it from the preceding portion.

.The maximum fluid pressure, therefore, is

found at the end of the secondary farthest from the primary, where the density of the magnetic leakage field is minimum, while "minimum fiuid pressure is found at the end nearest to the primary where th density of the field is maximum.

The considerations thus outlined with respect to the form shown in Fig. 6 may be applied directly to the form of Fig. 8 by merely observing that the magnetic leakage field between primary and secondary is in a generally axial direction in the latter case instead of radial. Maximum pressure in this case is found near the outer periphery of the secondary, which is farthest from the primary, and where the density of the magnetic leakage field is minimum, while minimum pressure is found to one another along their longitudinal. axes thereby rausitlg circulation oi. charge be tween the annular portion and the reservoir by the repulsive force between primary and secondary currents.

8. An induction furnace con'iprising, a primary winding, and a crucible comprising a'rcscrvoir and a cylindrical chamber containing a portion of the charge constituting secondary, said chamber communicating at both ends with said reservoir and being so positioned with respect to the pri: m'ary winding't-hat one end is more remote from the primary than the other whereby the charge is caused to flow from the remote end of said chamber to the reservoir and from the reservoir to the other end. i

9. An induction furnace comprising the combination of a continuous annular refractory container elongated in an axial direc tion, a reservoir communicating therewith and a magnetic core extending tl'irough said annular container, a primary Winding on said core displaced in an axial direction with respect to said container to exert a re pulsive force on a conductive charge in said container whereby said charge is caused to circulate between said reservoir and said container.

10. An indljrction furnace comprisine the con'ibination of a magnetic core, a primary Winding thereon, and a refractory (.arucibie comprising a reservoir adapted to contain a pool and a communicating annular poi tion adapted to contain. a secondary, the primary Winding and the annular portion being geometrically arranged with respect to each other to cause circulation of charge between the reservoir and annular portion of the crucible by electromagnetic repulsion, and means for adjusting the ell'ectivep ition of the prin'iary to regulate said. circula- 11. An induction furnace comprising: the combination of a magnetic core, a crucible providing: an annular portion interlinked with said core and con'imunicatino reservoir, a primary winding interlinked with said core and surrounded at least in part by said annular portion of the crucible while being longitudinally displaced from the primary winding, as a whole to cause circulation of charge by electromagnetic repulsion, and means for adjusting the positionzof the primary winding to regulate the circulation. I

12. An induction furnace comprising the combination of an annular refractory container elongated in an axial direction, a magnetic core interlinked with said container, a primary winding on said core, said winding and container being relatively displaced in an axial direction, and. a reservoir communicating with said container at points spaced apart in an axial direction portion of the char whereby flow charge is caused in said chamber and return flow through saio reset your due to eiectromagnetic repulsion,

18, An induction furnace comprising the combination of a charge--containing rec/op tacle having looped portionand a reservoir in common? anion with each other, and a primary w' no; arranged to induce a heating cum in the charge in said looped portion, and to cause cirouiation through said looped portion of the receptacle with a unidirec nai flow by the expulsion 0t charge lEIOLi said iooped portion to the reservoir at one place of: communication and the admission of charge from the reservoir to, said looped portion at another place of c0mmunication.

14. An induction furnace comprising a containing crucible providing a chamber in which the charge constitutes a closed second ary, and a primary winding for inducing an electric current in said charge so positioned with relation to said secondary that fluid }'.)resr-: .1res are set up in said chamber due to electromagnetic repulsion between said primary and secondary producing flow of tin-(nigh e" chamber mainly in a direction trailer to the direction of the electric "r-"rcrn'; i,. cured t ,erein, and means :ittiinr returniiow external to said C0111}! rible providing a reservoir for and an annular chamber cointherew i in which a portion of constiti'ates a secondary, and a primary c ding so positioned n th rela tion to said secondary that fluid pressures varying in an axial direction are produced in said (liamber due to electromagnetic repulsion .wtween said primary and secondary causingum rirectional flow of charge in said chamber in an axial direction and retmn iiow through said reservoir.

16.1%] induction furnace comprising a magnetic core. a primary winding on said core, a crucil'ile comprising a reservoir and a looped chamber having oblong transverse sections intcrlinkingr said core containing a portion oi the charge constitilting a secondary, said chamber coinnxunicatingi with said rcser oir at opposite ends of such transverse f-Kft'iltlllfi a; llfil. {1 so positioned with respect tween imary and secondary is greater at one end or" said sections than the other, whereby :ircula'lion of charge is produced iictween said chamber and reservoir.

17. An indu tion furnace comprising a prime winding and a crucible providing a reservoir and a looped chamber having an oblong transrc section containing a I 2 constituting a secondary, said chamber" communicating with the reservoir at opposite ends of such transverse section and being so disposed with respect to the primary that one end of such section is farther from the primary than the other.

18. An induction furnace comprising a crucible roviding a reservoir for the charge and a ciihmber in which a portion of the charge constitutes a closed secondary, said chamber and reservoir comunicating with each other at their extremities, and a primary winding associated with said secondary producing unidirectional circuiation of charge through said chamber and reservoir.

19. An induction furnace comprising a crucible providing a reservoir for the charge and a chamber in which a portion of the charge constitutes a closed secondary, said chamber communicating with said reservoir at opposite sides of certain axially perpendicular transverse sections of said chamber, and a primary winding so disposed with relation to said seconda that one side of a transverse section of said secondary is more remote than the other from the fprimary whereby a charge is caused to flow om the side of said'section more remote from the primary to the reservoir and from the reservoir to the other side of said section.

In witness whereof, I have hereunto set my hand this 28th day of December, 1921.

JAMES M. WEED.

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