US2607969A - Spacer for casting squirrel cage rotors - Google Patents

Description

Aug. 26, 1952 w.' M. EVANS ET AL 2,607,969

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed Nov. 19. 1948 s Sheets-Sheet 1 7P 2pm 5. mam 5e $.32 JNVENTORS BY f4,

. HTTOIQA/E y Aug. 26, 1952 w. M. EVANS ETAL ,5

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed Nov. 19. 1948 s Sheets-Sheet 2 flrroems'x 26, 19 w. M. EVANS ETAL 2,607,969

SPACER FOR CASTING SQUIRREL CAGE ROTORS Filed NOV. 19. 1948 3 Sheets-Sheet 5 MILL/44M M. EVfl/VS PHLPH 5'. THRCKEQ IN V EN TOR5 UTTOENEV Patented Aug. 26, 1952 UNITED STATES PATENT OF I SPACER FOR GAS TING SQUIRREL CAGE ROTORS William M. Evans, La Habra *Heights, and'Ral'ph S. -Tha'cker, Lo's Angeles, Calif., 'assigiiors to U. S. Electrical Motors, Inc., Los Angeles, Calif;, 'a corporation of California Ap lication November 19, 194.8,Se'ria1No. 61,092

2 Claims. (01. 22-116) This invention relates to the casting of metal- 110 conductors to form a'squirrelc'age of an induction motor rotor.

Rotors of this character are formedof'a stack of laminations having slots at the periphery for the reception of conductor bars. These bars are joined at their ends by rings of conducting material. v

It is common "to cast snch conductors to form the completed squirrel cage including the end rings, by pouring molten i'netal'into a mold that accommodates the assembled stack of lamina tions. Copper, aluminum, or other conducting metal may be used; and often the entire mold and the laminations are rotated to cause the metal to be cast 'centrifugally.

One form of apparatus-for centrifugally casting the squirrel cage is described in Patent 2,381,616, granted August 7, 1-945, t0 George T. Pfleger.

It is often required to provide airvents or duets at intervals along the stack of laminations; these provide passages'for ventilation when the motor is operating, and aids'in maintaining the temperature of the motor at a desired low value.

To ensure that these ventilating ducts will be left intact during the casting operation, spacers are utilized that can beremoved afterthe-cast ing is completed. These spacers have a thickness corresponding to the space to be left between the sections of the stack.

It is one of the objects -"of this invention to provide a spacer-such that it can be veryreadily removed after the casting operation is completed.

It is another object of this invention generally to improve the process of casting the squirrel cage conductors in the stack of laminations.

In order to maintain the spacing between the sections of the laminaticns, the 'cast bars are preferably provided with enlargements operating as spacers between thes'ections. It is another object of this invention to 'providesuch enlargements, the dimensions of whichniay be keptto close tolerances. In this way, it is assured that the enlargements, while adequate to provide the abutments. yet offer onlya slightre'sistanc'eto the how of cooling air. Furthermore, theexterior surface of the spacerportions can bearranged to provide increased heatradiating surfaces.

This invention posesses many other advantages, and has other objects which'may be made more clearly apparent-froma consideration of several forms in 'which'it may be embodied. Such forms are shown in the drawings accompanying and forming part of thelpresent-s15edification. Thesero'r'mswnrnow bedesc'ribed in de tail, illustrating the general principles of-the invention; but it-is to be understood that sueh detailed description is n'ot'to be takenin a limiting'sense, since the s'cope of the' inventio'n is best defined by theappended claims.

Referrin'g'to the drawing-s:

Figure 1' is aside elevation of a 's'teick 'of laminations utilizing the invention, and sho'wi-ng'zthe squirrel cage conductors;

Fig.-2 is a pictorial'viewof oneof the spacers utilized in 'connection with the casting operation;

Fig. 3 is a sectional'=view,{taken-generally along a surface corresponding to tne-1me- 3 s of Fig.1

Fig. 4 15a fragmentary plan viewor tne'spacer shown in Fig.2 I v Fig. 51s a fragmentary"sectional"newsman along a plane corresponding to line 5-5 of Fig. 3;

Fig. 6 is a sectional view. taken generally-along a plane corresponding -to'line6'-'-6 of Fig.4

Fig. 7 is a view similar to'Fig. 4 of a modified formof the spacer incorporating the invention;

Fig. 8 is an enlarged fragmentary view,'partl'y in section, of the spacer shown'in'Fig. 7;

Fig. 9 is a'view,similar to Fig.-4,-of a further modified form of the spacer;

Fig. 10 is an enlarged sectional view, taken along a plane corresponding to line Hi H) of Fig.9;

Figs. 11 and 12 are views similar to Figs. 4 and 5, and illustrating afurther modified form of the spacer; and V n Figs. 13, 14, and 15 are fragmentary sectional views, similar'to Fig. 3, of modified forms of the invention. p

In Figs. 1 and'3 there are-illustrated the sections I, 2, 3, 4,5, and S pt laminations comprising the core-of aninduction motor squirrel cage rotor. This core, it is understood, is arranged to be mounted on a spider or a shaft.

One lamination I2 is shown in Fig. 5 and illustrates the slots 1 adjacent the'periphery of the lamination. These slots, intl 1'e"-r' re's'ent instance, areshow'n as neanymosed, there beingp'ripher r'mrmw slots Bcommiinicatin'g respectively with the slots '1. As shown mostclearlyinFig. 1, the laminations may bes'tacked'in'suchrnanher that the squirrel csgeeondu ctors intheslots are oblique to the axis, "producing "the desired skew' arrangement. k I

Cast within the slots"! and fi'arethe squirrel cage bars '9. These bars are integrally J'Qined with the endrings Mandi l. rneseend rings ma -carry the rim blades l ram [5.

In order to cast the bars 9 and the end rings Ill and II as a unit and to form the air spaces between the stacks of laminations, use is made of spacers 16 that are disposed between the sections of the stack and that may readily be disintegrated afterthe casting operation is completed. Thesespacers'are shown in Figs. 1 and 3; but, since the bars 9 and the end rings l and II have already been cast, these spacers are to be removed in order to complete the manufacture of the rotor.

To prepare the laminations for the casting operation, they are carefully stacked with the slots 1 and 8 of the laminations properly aligned. As shown in Figs. 1 and 3, the sections l to 6 inclusive are spaced apart by the spaced rings IS. The complete stack is clamped in proper assembled relation, and then the entire stack assembly is preheated at a temperature neighboring l100- F. The assembly is then transferred to a casting mold which may be made of metal, and the mold is rotated during the process of casting. Molten metal, such as aluminum or copper, is then poured intqthe revolving mold.

The cast rotor maythen. be removed from the mold for proper machining of the cast metal bars and end rings However, before this is accomplished, the spacer rings iii are removed, forming the vents or ducts between the sections of the laminations.

In order that these spacer rings l6 may be readily disintegrated, they are made from a special plaster materiaL-or plaster composition, which, uponthe application of heat, changes its characteristics and will disintegrate upon contact with water. The disintegrated spacers may then be completely removed by washing or brushing as, for example, by a stream of water flowing from anozzle; V 7

Plaster compositions capable of being thus disintegrated include gypsum and crystobalite. The composition is in the form ,of a fine powder. When heat is applied to a casting of this material, it expands, and disintegrates readily when plunged into Water. a

Since the plaster material is quite brittle; provisions are made for reinforcingthese plaster spacers. This is essential because of the handling of these spacers; after they are once in the stack, they are properly maintained in place by the reinforcing effect-of the adjacent sections. In the form shown in Figs. 2, 4, and 6, metal reinforcing wires I! may be embedded in the plaster composition near the periphery thereof. Furthermore, in this instance, the slots I8 of the spacer are shown as skewed (Fig. 6) to correspond with the skew formation of the slots defined by the laminated stack. These slots may be entirely closed to provide additional strength. They may be made somewhat larger than slots 1 of the laminationaso as to overlap them. In this way they provide for the formation of the enlarged portions [3 ofthe bars 9. Furthermore, in order to assist in aligning the slots 18 of the spacer IS with the slots 1, marks in the form of small depressions l9 (Fig. 4) may be provided on the outer periphery of the spacer [6,

The enlarged ends 13 can be precisely cast, and their "dimensions are maintained with small tolerances, because the plaster spacers [6 are not affected by the high temperatures during the casting operations. Sharp and smooth surfaces are therefore formed on. these enlargements, and there is no dangerthat the metal'willflow, so as 1 to block the air duct substantially entirely. A free flow of cooling air is maintained.

The forms of the bars between the sections I to 6 may be difierent. In Fig. 13, the enlarged parts 36 are substantially spherical. In Fig. 14, the enlargements are in the form of narrow flanges 31; andin Fig. 15, corrugations 38 are formed to increase the radiation of heat while the motor is in operation.

These forms are merely examples capable of being produced by appropriate shaping of discs I6.

The plaster discs or spacers l6 are conveniently formed by a molding operation. A master mold of plastic material, such as a rubber mold, can be formed by pouring the molten plastic material over a master pattern corresponding to the disc I6. The molten plastic, when it cools, is sumciently flexible so that it can be stripped from the master pattern. This plastic mold can then be used for the casting of the plaster discs or spacers l6. r I V The material used for casting these discs, as heretofore stated, is a plaster mixture, preferably including cristobalite, having an ingredient that permits the plaster material to be readily disintegrated in water. i 1

The plaster discs-or spacers [6 are preferably coated on each side with a graphite and oil mixture. In this way leakage or flash of the molten metal at the joint between the spacer-and the laminations is prevented. When the plaster spacers I6 are removed from the stack, as shown in Fig. 3, the enlarged portions [3 of the bars 9 are recessed below the outer periphery of the rotor. The effect of this is to reduce windage noise while the motor is operating.

The spacers [6, being made from brittle cast plaster material, must be carefully handled when assembling the stack of laminations. Just as soon as the stack is completed with the spacers interposed between the sections of laminations, it is not important to keep the plaster discs from cracking. In order to ensure that the plaster discs can be handled without premature cracking or breaking, the reinforcements I! are provided.

After the molding operation is completed, the entire rotor is immersed in water, and the plaster spacers are removed.

Other forms or reinforcements may be used.

In the form shown in Figs. 7 and 8, the plaster spacer '20 is shown as having the open slots 2! and a reinforcing band 22 of metal at the outside periphery. This band of metal is so arranged that it presents no radial protuberances. Thus, where the edges 23 and 24 overlap, they are arranged to form a substantially continuous circular form. Furthermore, if desired, the metal band 22 can be attached to the plaster disc as by appropriate fastening means, such as the nails 25. These nails 25 are cast into the plaster between the slots 2!. Recesses are formed in the band '22 to accommodate the heads of these nails.

In the form shown in Figs. 9 :and 10, reinforcement is provided by the aid of either the outer band 26 or the inn-er band 27, or both. In this case these bands may be formed of thin micarta, or equivalent materials. As shown most clearly in Fig. '10, apertures 28 in the bands may provide for the keying in of the plaster disc 29. The micarta bands are thus keyed firmly in place.

Duringthe step of preliminary heating the assembled stack utilizing the micar-ta reinforced r ngs or spacers 29, these micarta bands 26 and are burned away, leaving merely the plaster discs 29. These, in turn, are readily disintegrated by the aid of Water after the casting operation.

In the form shown in Figs. 11 and 12, metal bands 30 and 31 on the inner and outer peripheries of the plaster spacer 32 are utilized. Here the metal bands are held in place by the nails 33 and 34, embedded when the spacers 32 are molded. The heads of these nails are appropriately recessed within the bands.

After the plaster materials are disintegrated, the reinforcing metallic elements, such as the nails 33 and 34 and the bands 30 and 32, are easily removed from the completed rotor.

The inventors claim:

1. A spacer for use between sections of laminations of a dynamo-electric machine for providing ventilating spaces in the stack of laminations, said spacer being made from a composition of gypsum and cristobalite.

2. A spacer for use between sections of laminations of a dynamo-electric machine for providing ventilating spaces in the stack of laminations, said spacer being made from a composition of gypsum and cristobalite, and having a general WILLIAM M. EVANS. RALPH S. THACKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 371,176 Coleman Oct. 11, 1887 481,295 Black 'Aug. 23, 1892 976,465 Hunty Nov. 22, 1919 1,932,292 Coleman et al. Oct. 24, 1933 2,163,373 Cooper June 20, 1939 2,313,672 Salzberg Mar. 9, 1943 2,352,083 Detjen June 20, 1944 2,968,296 Goran Jan. 30, 1945 2,369,067 Mayer Feb. 6, 1945 2,474,186 Marks June 21, 1949 2,594,823 George Apr. "18, 1950

Claims (1)

1. A SPACER FOR USE BETWEEN SECTIONS OF LAMINATIONS OF A DYNAMO-ELECTRIC MACHINE FOR PROVIDING VENTILATING SPACES IN THE STACK OF LAMINATIONS, SAID SPACER BEING MADE FROM A COMPOSTION OF GYPSUM AND CRISTOBALITE.

Images