US2729692A - Rotary field stirring device with independently driven fan - Google Patents

Description

Jan. 3, 1956 Filed Aug. 14, 1952 T W. RATCLIFFE ROTARY FIE LD STIRRING DEVICE WITH INDEPENDENTLY DRIVEN FAN 3 Sheets-Sheet l INVEN TOR.

ATTORNEY Jan. 3, 1956 T. w. RATCLIFFE 2,729,692

ROTARY FIELD STIRRING DEVICE WITH INDEPENDENTLY DRIVEN FAN Filed Aug. 14, 1952 3 Sheets-Sheet 2 ATTORNEY Jan. 3, 1956 T w. RATCLIFFE 2,729,692

ROTARY FI EILD STIRRING DEVICE WITH INDEPENDENTLY DRIVEN FAN Filed Aug. 14, 1952 5 Sheets-$heet 3 FIG?) INVENTOR ATTOR N EY United States Patent ROTARY FIELD STIRRING DEVICE WITH INDEPENDENTLY DRIVEN FAN Temple W. Ratclitie, Beaver, Pa., assignor to The Bab cock 8; Wilcox Company, New York, N. Y., a corporation of New Jersey Application August 14, 1952, Serial No. 394,254 Claims. (Cl. 13-26) This invention relates to arrangements for the inductive stirring of fluid material and, more particularly, to a novel and simple arrangement for cooling an inductive stirring device associated with a container for molten metal.

While inductive stirring is applicable to any type of electrically conductive fluid material, it has found more particular application in the fields of molten metal founding and handling. In the art of founding metals and alloys, it is desirable to stir the molten metal to assure equalization of temperature throughout the molten metal body, acceleration of the reactions, particularly of the slag to base metal bath type, and, in alloy metals, to mix the bath in order to achieve a uniform product. When the heat is transmitted to the bath or molten metal body, through its surface, as when the bath is heated by an electric arc, the stirring action is necessary in order to avoid an over heating of the part of the charge below the electrodes, and to allow, when holding a heat of molten metal, an economy of operation. With stirring, at deep metal bath may be prevented from freezing with a minimum heat input to a localized zone, the stirring providing proper distribution of the heat input by virtue of the motion of the bath and thus offsetting the heat losses occurring at all bounding surfaces of the bath. The term bath, as used herein, refers to a body of molten metal and its slag cover, if any.

Various arrangements have been suggested to provide inductive stirring of molten metal in a container. These arrangements include those in which an electric flux is applied to the bath at a predetermined zone in order to circulate the metal through this zone, the zone generally comprising a restricted passage or the like in communication with the main bath of metal. Coils are used to provide the flux, being mounted in predetermined patterns on the ladles or furnaces and suitably energized with single or polyphase A. C., or sometimes with progressively switched D. C.

This stirring is particularly important in the case of continuous metal casting operations wherein, while molten metal is being poured into the mold from one ladle, one or more additional ladles of molten metal are kept in stand-by relation so that the available melting capacity may be effectively utilized by correlating the batch melting operations with the continuous casting operations. it is necessary to supply heat to the baths in the stand-by ladles at least to compensate for heat losses therefrom. This can be accomplished by electric arc heating arrangements provided at holding stations adjacent the pouring station as described in the copending application of Isaac Harter, J12, Serial No. 304,251, filed August 14, 1952. For the foregoing reasons, it is desirable to circulate or stir the molten metal both at the holding stations and at the pouring station. The electric arc heating may desirably be continued during pouring of the metal into the mold, thus maintaining the metal at optimum temperature. In addition, the arc blast, particularly with a single phase arc, acts as a slag dam to hold back surface slag from the ladle pouring lip.

An effective design of ladle for use in a continuous metal casting arrangement is a relatively deep ladle provided with a sloping bottom wall which has inductive stirring devices associated with the sloping wall to effect circulation of the metal upwardly along the sloping Wall. In the usual manner, the ladle comprises a refractory lining supported in a metal casing. In order to assure the maximum possible stirring field being effective on the molten bath, the metal casing is so constructed as to minimize dissipation of the stirring field in the casing. To this end, all parts of the casing within the etlfective magnetic field of the inductive stirring devices are made of suitable non-magnetic metal, such as one of the stainless steels. In addition, the continuity of electrical and magnetic paths is broken up by constructing the bottom of the casing as a series of separate, preferably parallel slats supported in electrically insulated relation on the casing walls and forming slots along the casing bottom. The slotted bottom also provides cooling channels for the inductive stirring coils or the like to prevent overheating of the same due either to proximity to the hot ladle or the flow of electric current through the inductive devices, particularly when the slats are tubular elements. This type of ladle is shown and described in the copending application of Maurice P. Jones, Isaac Harter, J11, and Temple W. Ratcliffe, Serial No. 304,252, filed August 14, 1952, for Fluid Material Container With Inclined Slotted Bottom Having Inductive Stirring Device Adjacent Thereto.

With this type of ladle, the most effective controlled stirring of the metal with the least power requirements is provided when a rotary inductor is mounted adjacent the sloping bottom wall, such an inductor being shown and described in the copending application of Maurice P. Jones, Serial No. 304,253, filed August 14, 1952, for Rotary Electric Field Fluid Stirring Apparatus, now Patent No. 2,686,823, issued August 17, 1954. The inductor comprises an axially elongated magnetic pole structure rotatable on an axis substantially parallel to the sloping bottom wall of the ladle and preferably extending transversely of such sloping wall. Energizing windings are provided on the pole structure, being supplied with current through a suitable commutator.

To provide the inductive stirring of the metal, the inductor is so positionally related to the sloping bottom wall that the lines of field force produced by the pole structure pass through the molten metal adjacent the sloping bottom wall and reversely acting fields are ineffective on the bath along the sloping ladle bottom. The inductor is slowly rotated in a direction to cause the field lines to move upwardly along the sloping bottom. The thus moving field lines effect a movement of the metal upwardly along the sloping bottom of ladle and thus a circulation of the metal in the oath.

However, due to the desired slow rotation of the inductor, it is difficult to provide adequate ventilation of the inductor by natural circulation of air therethrough. Accordingly, the present invention is directed to a novel forced air circulating arrangement integrated with the inductor and its drive. More specifically, a fan is freely rotatably mounted on the inductor axle adjacent one end of the pole structure and is driven at a relatively high speed, and preferably in the same rotational direction as the inductor, either by an independent drive or through suitable gearing driven from the driving means for the inductor. When used at a pouring station, the entire arrangement, including the ladle and the electric are heating means, is mounted in a supporting cradle which is tiltable about an axis passing transversely through the pouring lip of the ladle so that the heating and stirring may continue even while metal is being poured from the ladle. The latter is disengageably mounted in the cradle so that, when it is empty of molten metal, a fresh ladle of molten metal from a melting furnace, metal holding st... n, or melting shop may be readily substituted for the empty ladle.

For understanding of the invention principles, reference is to the following description to a typical embodiment thereof as illustrated in the accompanying d a in the drawings:

a side elevation view, partly in section, of a a1 holding, pouring, heating and stirring arement ccordance with the present invention;

is a plan View of the inductor, its driving arrangean driving arrangement; and

at elevation view, partly in section, of

Fig. l of the drawing, a ladle 1% is shown an outer metal casing 11 supporting suitactory lining The ladle is formed with a lip or outlet 13 through which passes transversely 1 (not shown) tiltably supporting a ge 16. T .e latter is supported on s ch as l? by means of which the cradle in may be adjustably positioned horizonc to a continuous casting mold, for example. 'ith la le ill removably supported therein is tilted by ans of upwardly extending rotatable screws driven by suitable mechanism 19 and each threadably engaged a nut 21 pivotally secured in a bracket 22 on the rear .vall 23 of cradle 15. As screws 18 are rotated by mechanism 1?, nuts 21 travel longitudinally along the screws to tilt the cradle about the transverse through the pouring lip 13. Thereby, ladle 2-3 r be tilted to pour molten metal through lip 13. he ladle it? is removably supported in cradle 15, and can be lifted therefrom by a crane or the like and replaced by another similar ladle, all as described and claimed in said copending application, Serial No. 304,251. The ladle is preferably oval or circular in horizontal section and includes a relatively deep rear segment 24, which is continuous with a substantially horizontal bottom wall portion 26 continuing into an upwardly and forwardly sloping bottom wall portion 25. The latter merges smoothly with a relatively shallow, outwardly sloping forward or front segment 28 in which is formed the pouring lip 13. Segment 28 continues into a rearwardly extending shelf like portion 29 at the inner lower edge of which is a water-cooled metal lintel 34. This lintel acts to promote a slag dam, during pouring, by virtue of chilling and solidifying slag on the bath surface flowing toward lip 13. The outer surfaces of rear segment 24 and portion 29 are coplanar to receive a cover 36 of refractory material, and which is removably secured to the ladle.

To assure the maximum eifect of the inductor field being exerted on the bath overlying sloping bottom wall portion 25, the casing 3-3 is so constructed as to minimize field dissipation therein, particularly those portions of the casing within the effective field of the inductor. Thus, the portion 25 of easing ll within or adjacent the inductor field, is made of suitable non-magnetic material such as one of the stainless steels. Additionally, the bottom support structure of easing it is formed as a plurality of separate, substantially parallel, spaced slats 27 extending forwardly and rearwarclly along ladle bottom wall portions 25, 26. Slats 27 may be bars or tubes, and the spaces between the slats form slots for the flow of a coolant, which latter may also flow through the slats when the latter are tubular. Slats 27 further are individually supported, in electrically insulated relation, on non-magnetic casing section 25, thus destroying the continuity of magnetic and electrical flow paths to further reduce field dissipation in the ladle lining supporting casing. The limits of the inductor field, within which limits all structural parts are desirably of non-magnetic material, are indicated by the circle 41.

Cover 30 is apertured to receive electrodes 31 between which and the bath an arc is maintained to supply heat to the molten metal 32 in the ladle, the are being preferably a single phase arc. Electrodes 31 are supported and adjusted by a suitable structure indicated at 33 and which is mounted on a mast (not shown) supported on cradle 15. This structure is shown and described in detail in said copending application Serial No. 304,251. Detailed description and illustration thereof is omitted in the present case because it forms no part of the invention arrangement. The arcing electrodes are not immersed in the bath, and the arc blast acts as a slag dam during pouring.

Cradle 15 includes a floor or platform 35 which serves as a support for a rotary inductor 49 of the type shown, described, and claimed in said copending application Serial No. 304,253. Platform 35 also supports the driving mechanism for rotating inductor 40, and the driving mechanism for the inductor ventilating fan, all described more fully hereinafter.

As shown by the dot and dash line 41 in Fig. 1, the effective field of inductor 40 extends in an arc immediately inward of the inner surface of sloping wall portion 25. As the inductor rotates, a moving field is thus provided in the molten metal adjacent wall portion 25, and the direction of rotation of inductor 40 is such that the resultant field in the molten metal 32 tends to move the molten metal upwardly along sloping wall portion 25. Thus, a circulating action is induced in the molten metal, providing effective stirring of the metal.

Referring to Figs. 2 and 3, the inductor 4b is mounted on a shaft 42 rotatably supported in bearings generally indicated at 43 which are supported on cradle 15 at a position which can be selected, by those skilled in the art, to provide the most effective stirring of the molten metal. The inductor includes a magnetic core structure involving a cylindrical sleeve 44 secured on shaft 42 and serving as a mounting for pole pieces 45. On the outer ends of pole pieces 45 are arcuate pole extensions 46 which extend both circumferentially and axially beyond the pole pieces. Studs 47 having their heads 48 recessed in extensions 46 secure the extensions and the pole pieces to sleeve 44. A cylinder shield 51), of nonmagnetic material, is mounted around the extensions as, being secured in position by studs or the like 51.

Shieldfii? acts as a protecting sleeve to prevent foreign material entering the pole structure. For example, tramp iron or other para-magnetic material may be drawn toward the inductor by the relatively strong magnetic field. Shield 5i} protects the inductor from damage by any such foreign objects. A scraper 49 may be provided to remove the foreign material from the smooth outer surface of shield 50. In addition, the shield serves as a cooling tunnel for air forced axially through the inductor by the invention ventilating arrangement.

Magnetization of the magnetic structure is provided by windings, generally indicated at 52, embracing pieces 45 between sleeve 44 and extensions 46. These windings are energized through conductors 53 connected to slip rings 54 engaged by brushes 55 connected to 'a'suitable source of electric current, preferably D. C. The slip rings are supported in spaced concentric relation to shaft 42 by studs or bolts 56 extending through the hub 57 of. a driven'sprocket 58 mounted on a shoulder 59 of shaft 42.

Adjacent the end of shaft 42 opposite to that carrying sprocketfiil is secured a bearing 61 rotatably supporting a bearing sleeve 62 of a ventilating fan 60. Sleeve 62 is held axially fixed relative to hearing 61 by a ring 63 adjacent one end of the bearing and secured to bearing sleeve 62. The other end of sleeve 62 has secured thereto a driven sprocket 64 substantially smaller in diameter than sprocket 58. Sprocket 64 is held in place by a ring 66 secured to sleeve 62 by studs 67, sprocket 64 seating in a recess in the end of bearing sleeve 62.

Referring to Figs. 1 and 2, rotor tively slow rate bracket 66' drive shaft 40 is rotated at a relaby driving motor 65 mounted on a and the relative direlatively high speed 65 is converted to the very ameter of sprockets of the drive shaft of motor low speed of rotor shaft 42.

Desirably, the speed of motor 65 is correspondingly vary the rate of stirring the bath. For example, during pouring the stirring rate may be increased to impede flow of slag toward pouring lip 13.

power required to drive the fan.

The invention arrangement thus provides a for the draft produced by fan While a specific embodiment of the invention has been shown and described in detail to illustrate the ap- What is claimed is:

1. An inductive stirrer comprising a rotatable fieldmember, said field-member having a mounting shaft and a succession of peripherally disposed magnetic poles of opposite polarities; a cylindrical shroud, of non-magnetic material, surrounding said field-member; variable speed drive means for rotating said field-member at a relatially in excess of the speed of said field-member to force cooling air axially through the latter.

2. An inductive stirrer comprising a rotatable fieldmember, said field-member having a mounting shaft and a succession of peripherally disposed magnetic poles of opposite polarities; exciting means for said poles and including field coils operatively associated with said poles, current collector means, a source of electric power, and adjustable control means controlling flow of power from said source to said field coils; an open-ended cylindrical shroud, of non-magnetic material, surrounding said field-member; and variable speed drive means for rotating said field-member at a relatively low speed; a fan of said field member to force cooling air axially through the latter.

3. An electric field device for stirring fluid material comprising, in combination, a container for the fluid material; a rotatable field member supported outside said tained within the container; said field-member including a mounting shaft and a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral pole pitch sufficiently longer than the minimum distance from a peripheral pole face to the fluid material that a moving magnetic field of substantial strength will penetrate the fluid material; a cylindrical shroud, of non-magnetic material, surrounding said field field-member axially through the latter.

4. An electric field device for stirring fluid comprising, in combination, a container for the fluid material; a rotatable field-member supported outside said container in closely spaced relation thereto and material said field-member including a mounting shaft and a succession of peripherally disposed magnetic poles of opposite polarities having a peripheral trate the fluid material; an open-ended cylindrical shroud of non-magnetic material surrounding said field-member;

shroud. 5. An inductive stirrer comprising a rotatable fieldmember, said field-member having a mounting shaft and a succession of peripherally disposed magnetic poles of opposite polarities; an open-ended cylindrical shroud of non-magnetic material, surrounding said field-member; variable speed drive means for rotating said field-member References Cited in the file of this patent UNITED STATES PATENTS 1,068,558 Bally July 29, 1913 1,838,806 Cappa Dec. 29, 1931 1,884,637 Feehan Oct. 25, 1932 2,339,964 Tama Jan. 25, 1944 2,573,319 Dreyfus et a1. Oct. 30, 1951 2,686,823 Jones Aug. 17, 1954 FOREIGN PATENTS 999.012 ,France Sent. 26. 1951

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