US2996773A

US2996773A - Method of casting squirrel cage rotors

Info

Publication number: US2996773A
Application number: US681519A
Authority: US
Inventors: Erwin R Summers
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1957-09-03
Filing date: 1957-09-03
Publication date: 1961-08-22
Anticipated expiration: 1978-08-22

Description

E. R. SUMMERS METHOD OF CASTING SQUIRREL CAGE ROTORS Aug. 22, 1961 5 Sheets-Sheet 1 Filed Sept. 3, 1957 Inventor: EFW/n f? Summers, by )O-AM W H/s fitter/76y Aug. 22, 1961 E. R. SUMMERS METHOD OF CASTING SQUIRREL CAGE ROTORS 5 Sheets-Sheet 2 Filed Sept. 3, 1957 fnl/fltaff': Erwin A. Summ arms; y wow 2 M k His Attorney 1961 E. R. SUMMERS 2,996,773

METHOD OF CASTING SQUIRREL CAGE ROTORS Fild Sept. 5, 195'! 5 Sheets-Sheet s [HI/EUtO)": Erw/h R Summers,

by yawulw /7/'5 Attorne 1961 I E. R. SUMMERS 2,996,773

METHOD OF CASTING SQUIRREL. CAGE ROTORS Filed Sept. 5, 1957 5 Sheets-Sheet 4 3/ [)7 mend-0r.- I EdW/I? fl? Summers,

[a 2 W y W5 Attorney Aug. 22, 1961 E. R. SUMMERS METHOD OF CASTING SQUIRREL. CAGE ROTORS 5 Sheets-Sheet 5 Filed Sept. 5, 1957 ///ls Attorney 2,996,773 METHOD OF CASTING SQL CAGE RGTORS Erwin R. Summers, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Sept. 3, 1957, Ser. No. 681,519 '8 Clairns. (Cl. ZZZ-400.5)

The invention described herein relates to dynamoelectric machines and more particularly to an improved method of casting a winding including conductor bars, end rings and fan blades in a squirrel cage rotor.

The casting of conductor bars in rotors is an old art and many different processes have been practiced to achieve a uniform distribution of cast material therein to provide a squirrel cage winding having the desired electrical characteristics, mechanical strength and capable of being manufactured with economy. Commonly known practices include casting by gravity, pressure, vacuum and centrifugal methods, but all of these processes are subject to the disadvantage that occasionally, shrink holes are formed in the cast aluminum material which disturb the mechanical and electrical balance, mechanical strength and current carrying capacity of the rotor.

These shrink holes take the form of voids or cavities in the end rings, and basically are caused by an improper sequence in the freezing of the cast material in the different parts of the cast structure. It has been found that changing the relative initial temperatures of the rotor and mold parts is sometimes helpful, but in other cases this merely shifts the location of the shrink holes in-the end rings. Reference to FIGURE 1 shows how inadequacies in the structure are produced. The apparatus illustrated is a view in elevation, partly in section, showing a rotor placed in molds and the casting process has been completed. The rotor is of well known construction having laminations or punchings 12 provided with the usual conductor slots 14. Upper and

lower plates

16 and 18 are held against the laminations with an arbor 19 and are arranged for coaction with upper and lower molds 2-0 and 22 for exerting force on the laminations to tightly pack them together and to provide pockets and cavities for shaping the end rings, also cast fan blades when used, on the rotor in the usual manner. Gates 24 located in the upper portion of the mold provide access for the molten aluminum material. The parts are preheated prior to casting such that the punchings 12. and assembled plates 16 and it; are usually made hotter than the lower mold surfaces at X and Y to accelerate freezing of the lower end ring. When the aluminum is cast through gates 24, it flows downwardly through the slots to cavities provided by the lower plate 18 and mold 22 to form the conductors, and fan blades, if used, and end rings.

As casting proceeds, centrifugal force throws the entering aluminum against the outer wall X and the fluid metal builds inward toward Z and upward from Y until the lower mold, rotor slots and upper molds are filled in that sequence. As metal is freezing in the slots 14, a layer of aluminum accordingly commences freezing adjacent all the contacting surfaces of the mold, with the highest rate of freezing occurring at the colder surfaces X and Y and progressing toward the hotter surface Z. The entrances from the small rotor slots to the large lower end ring cavity freeze solid at W while a portion of the lower end ring is still in a fluid state. As the freezing of the re maining portion of fluid aluminum progresses toward Z, the volume of the cast end ring decreases because there is no possibility of feeding in additional molten metal to compensate for the shrinkage that necessarily occurs. As freezing progresses further, metal is drawn from the unfrozen areas toward the surfaces where solidification is occurring. Also, centrifugal force assists in the movement of molten particles from Z and tends to throw any remaining fluid metal radially outward and this interrup tion of continuous contact reduces the rate of heat transfer from the aluminum to surface Z. Shrink holes therefore occur at or near the inner surface of the end ring at Z as illustrated.

Substantially the same action occurs in the upper mold cavities when gates 24 freeze before the upper end ring is completely solidified, thus resulting in the metal near surfaces W, X, and Y freezing before Z, thereby causing shrink holes to also form at or near Z in the upper end ring.

If the surface Z is made an integral part of the mold, such that surfaces X, Y, and Z are approximately the same temperature when the aluminum is poured, the shrink hole will be shifted away from Z toward the center of the end ring but will not be eliminated completely if the cross-section of the end ring is sufliciently large compared to that of a slot-conductor.

Various modifications of molds and casting procedures have been made to overcome the above described problems, and although they have been reasonably successful, certain basic improvements are necessary to obtain optimum rotor performance. The more serious objections however, are found in two-pole rotors which usually require end rings of very large cross-sectional area compared to that of a rotor bar. .Also, it is evident that shrink holes limit the current carrying capacity thus presenting the possibility of failure when operated under load condi tions. The shrink holes cause non-uniform current distribution in the end ring and also in the rotor bars which results in the motor running with increased noise and vibration. Also, when the holes are not uniform in size and spacing, difficulties are sometimes encountered in properly balancing the rotor mechanically, which may also result in excessive vibration. Concurrent with this, is the likelihood, although remote, of an end ring disintegrating when subjected to centrifugal force with possible injury to personnel or equipment. This could occur as a result of excessive weakening of the structure caused by cracks extending outwardly from the shrink holes formed during shrinkage of the aluminum. Other practical disadvantages include the necessity for providing more than one oven to heat various parts to desired different temperatures prior to casting, and casting through the bore instead of through the slots is not possible since an arbor is located therein for supporting the structure.

In View of the disadvantages and deficiencies inherent in rotors cast by the prior art processes described above, it is apparent that the need is great for an improved casting method capable of providing a rotor Winding having the cast material uniformly distributed throughout so as to provide a rotor having the most desirable electrical and mechanical characteristics. The primary object of my invention therefore is to provide such an improved casting process.

Another important object of my invention is to avoid development of shrink holes in rotor end rings by admitting cast conductive material from a common source directly through openings into both end rings without having oppositely moving streams of the cast material meet in the conductor slots.

A further object of my invention is to obtain more flexibility in design by making it possible to cast end rings without regard to the size of rotor slots.

Still another object is to utilize a rotor bore during casting to provide a molten sprue of material in an adequate amount available for feeding previously filled fan blade, end ring and conductor slots in the rotor, so as to account for shrinkage and to prevent premature freezing of the sprue and gates before the useful parts of the winding are frozen.

Briefly stated, I carry out the above cited object by placing a ceramic or metallic sleeve in a rotor bore, preheating the rotor and placing it between hot upper and lower molds and rotating the assembled apparatus about a vertical axis at a predetermined speed. A funnel, supported by the top mold, or otherwise, extends downward below the upper end of the lamination stack and into the rotor bore. Molten current-conductive material is then poured through the funnel downwardly into the rotor bore and out radial gates provided in the bottom mold to fill the fan blade and end cavities provided therein. Centrifugal force causes the molten material to assume the shape of a paraboloid and this principle is utilized to advantage since it helps to cause the material to rise vertically in the conductor slots, forcing air upwardly, prior to filing the fan blades and end ring cavities formed by the upper mold surfaces. As the material fills the rotor and mold openings, air is vented from the rotating structure through special vents formed in the upper mold and through upper gates and past the funnel positioned in the bore. The lower mold, rotor slots, and part of the top mold are filled before any aluminum is thrown radially outward through the top gates, thereby preventing oppositely moving streams of aluminum from meeting within the rotor slots. When all the casting metal is poured, a large molten mass constituting a sprue is thus made available in the rotor bore for feeding, through large gates to each end ring individually, the additional amount of material necessary to compensate for shrinkage as the casting metal freezes. The mold elements are then removed and the remaining sprue thus formed in the rotor core is out free and driven outwardly so as to provide a smooth internal bore requiring only a minimum of machining prior to insertion of the rotor shaft.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein:

FIGURE 1 illustrates a prior art mold assembly showing the formation of shrink holes in an end ring of a cast rotor winding as described above;

FIGURE 2 is a view in elevation of an improved assembled mold apparatus prior to performing the casting process;

FIGURE 3 is a top view of the mold apparatus shown in FIGURE 2;

FIGURE 4 is an elevation view, partly in section, of the mold apparatus shown in FIGURE 2 and taken on lines 4-4 of FIGURE 3;

FIGURE 5 is a view of an upper plate for the mold and taken on lines 55 of FIGURE 4;

FIGURE 6 is a view taken on lines 6-6 of FIGURE 4;

FIGURE 7 is a view taken on lines 77 of FIGURE 4;

FIGURE 8 is a view taken on lines 8-8 of FIGURE 4;

FIGURE 9 is a perspective view illustrating the arrangement of parts on the top end of a rotor immediately after removing it from the mold and prior to driving the sprue out of the rotor bore;

FIGURE 10 is a similar view showing the opposite end of the rotor;

FIGURE 11 is a view in elevation of a sprue after removal from the rotor;

FIGURE 12 is a modification illustrating the arrangement employed for feeding cast material radially outward through gates from the bore into the slots at one or more intermediate points along the lamination stack between the end rings;

FIGURE 13 illustrates the different types of spacers utilized in separating the punchings near the outer periphery constituting the rotor shown in the rotor of FIG- URE 12; and

FIGURE 14 is a view taken through the rotor illustrating the disposition of spacers in the punching stack.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIGURES 2 through 6, a mold apparatus 28 comprising upper and

lower molds

29 and 30 enclosing a rotor core 31 into which a current conductive material, such as aluminum, is cast, to form the rotor winding. As is common practice, upper and

lower cover plates

32 and 33 are respectively positioned on opposite ends of the

molds

29 and 30. These cover plates are equipped with U-shaped slots 34 arranged to align with similarly shaped slots 35 provided in flanges 36 extending outwardly from the peripheral surface of the molds. The mold apparatus is then placed on a turntable 37 arranged for rotation by a motor 38 or other suitable mechanism. Arms 39 pivoted at one end to a hydraulic device 40 and terminating at their other ends in clamping members 41 are arranged for reception by the

slots

34 and 35 and assume the position shown in FIGURE 2 during the casting process. Aligning of the apparatus 28 on the turntable is obtained by an upwardly projecting pin 42 designed to engage an aperture located in lower plate 33 of the mold. The rotor core 31 comprises a plurality of laminations 44 equipped with a central bore 46 and conductor slots 48 in the usual manner. A ceramic sleeve 50 is cemented or otherwise secured in the rotor bore to insulate the sprue thermally and mechanically from the laminations, and to provide a ledge for cutting off the inner end of gates 58 at YY at a point inside the rotor bore to facilitate removal of the sprue after the winding is cast.

The lower mold is of circular configuration and is equipped with

cavities

52 and 54 for respectively forming the lower fan blades 53, if desired, and end ring 55 during casting. Centrally disposed pocket 56 is also shaped in the lower mold and communication between the latter and the end ring is made through a plurality of gates 58 through which the molten aluminum, or other current conducting material, flows to fill the fan blade and end ring cavities, as illustrated in FIGURES 4 and 8. Reference to these figures will show that the rotor rests on a plurality of spaced projections 60 and shoulder 62, and the recesses provided between the projections constitute the gates 58 for providing an unimpeded flow of aluminum during the casting process. Lower plate 33 serves to close cavities 52 to confine the aluminum therein and to facilitate assembly of the mold apparatus. Obviously, molds of different configuration can be used. In some instances it is preferable not to provide for cast fan blades on a cast rotor, such as when the rotor is adapted or used in high speed applications. In such cases, the molds will not include the fan blade cavities as shown and described herein. The following description and the claims include fan blade structure although it is to be understood that they may or may not be formed during casting of the rotor.

The upper mold 29 is of substantially the same configuration and is likewise equipped with cavities 64 and 66 for forming the upper fan blades and end ring 67. Gates 68 likewise are formed in the same manner as lower gates 58 for providing communication between the rotor bore and the end ring. The upper gates 68 perform dual functions in that in addition to permitting molten aluminum to flow therethrough near the end of casting cycle, they also serve to vent the major part of the air inwardly and then vertically upward between the outer surface of a funnel and the bore of upper mold and cover plate as the rotor slots fill with aluminum. In order to provide for complete venting of air from the upper fan blade, balance weight lug and end ring cavities, special vents are provided between the lower surface of top cover 32 and upper surface of mold 29.

It will be evident that as molten aluminum is poured into the mold apparatus, air therein will be displaced upwardly through the conductor slots 48 and a part of it would normally be trapped in the fan blade and end ring cavities 64 and 66 and thus preclude complete casting in these areas if venting means in addition to the gates were not provided in the structure. Such venting means are illustrated in FIGURES 5, 6 and 7. Referring first to FIGURE 5, it will be seen that the bottom surface of upper plate 32 is of circular configuration and is equipped either with circular grooves or with a spiral groove '78 which progresses outwardly from the center. Referring now to FIGURE 6, the upper surface of upper mold 29 is equipped with radially extending slots 80 arranged to terminate at the outer edge of the upper surface of the mold body. When assembled, the grooved surface of upper plate 32 is arranged to overlie the surface of the upper mold containing the slots 80. Reference to FIGURES 4 and 6 will show that as the fan blade cavities 64 fill with molten aluminum, the air initially therein is permitted to escape through the coacting spiral grooves '78 and slots 80 to the atmosphere, thus preeluding any possibility of not obtaining a complete casting as a result of non-vented air pockets.

This additional venting of the upper end ring cavity 66 must be accomplished since the cavity extends above the upper gates. Portion 84 of upper mold 29' is utilized for providing the recesses which form the gates 68. Referring to FIGURES 4 and 7, it will be seen that cavities 86 are formed immediately above the end ring at points spaced between the fan blades. The purpose of these cavities is to form lugs 88 for supporting balance weights. This area is vented by a cylindrical member 90 having a central aperture 92. The bottom, top and side surfaces of the member 90 are equipped with

grooves

94 and 96 for permitting air from cavity 86 to escape from the mold. These

grooves

94 and 96 are of a size sufiicient to permit venting of air but prohibit flow of aluminum therethrough. A set screw 98 having a central opening 100 which serves as a vent, and which also receives an Allenhead wrench, completes the air passageway to slots 80 and also prevents the cylindrical member 90 from becoming dislodged when the mold apparatus 29 is handled or rotated. The air which would otherwise be trapped in the cavities 86 for balancing lugs 88 is thus permitted to escape through aperture 92 and

grooves

94 and 96 in member 90, to opening 1% in the set screw and finally into slots 80 through which it flows for discharge to the atmosphere. The air thus vented through this device precludes the formation of defective appurtenances on the rotor.

In order to compress the outer periphery of the punchings together to prevent aluminum from escaping from the conductor slots 48, and to firmly anchor the mold apparatus to the turntable, the hydraulic device 40 is actuated to supply the necessary pressure to the laminations and to provide rigidity to the complete mold apparatus. This device is of a well known construction and such pressure is applied through arms 39 and clamping members 41 on the upper cover 32. It will be noted that the

shoulders

62 and 118, see FIG. 12, shaped in the mold bodies are arranged to contact a small area adjacent to the peripheral surface of the rotor so that when the hydraulic device is actuated the pulling force thus applied to the clamping members 41 causes them to impart a compressing force of several tons between the upper mold and the turntable, thereby compressing the laminations together and providing a firm unit capable of being rotated at a predetermined speed without leakage of molten metal.

Operation In operation, the rotor laminations are stacked and welded at 46 and ceramic sleeve 50 cemented in place as previously described. The rotor and molds are then placed in an oven for heating and upon withdrawal therefrom are assembled to form the structure illustrated in FIGURE 4. Insertion of clamping members 41 in the U-shaped slots and actuation of the hydraulic device 40 completes the action necessary for preparing the rotor for casting. A funnel 120, either supported externally, or else resting on cover plate 32 and having intermittent outer beads 122 arranged to space the funnel from the bore of cover plate 32 and thereby assure air vents, is placed therein, and, preferably, the lower end 124 thereof terminates below the upper gates 68 to prevent premature feeding of aluminum therethrough before the rotor slots are filled and thereby avoid two streams of aluminum meeting in the slots. Motor 38 is then energized to cause rotation of the mold apparatus 28. Molten aluminum is poured into the rotor bore and when the metal finally reaches the top end of the bore of upper plate 32, the funnel is removed and the casting permitted to cool, with the mold assembly continuing to rotate. As the casting process commences, the first aluminum poured will bypass the upper gate 68 and drop from the funnel into pocket 56 in the lower mold. Centrifugal force throws the molten aluminum outwardly into

cavities

52 and 54 and as these cavities fill the aluminum commences to move upwardly in the conductor slots 48 while simultaneously displacing the air therein. Since rotation occurs about axis KK, the upper surface of the fluid metal in the partly filled rotor will assume the shape of a paraboloid of revolution, such as CDE, with the steepness of the paraboloid depending on the speed of rotation. During this time, most of the air is vented through the upper gates and outward between the bore of upper plate 32 and the funnel which is spaced therefrom by the beads formed on its outer surface.

Continued pouring of aluminum moves the paraboloid surface upward from CDE to some higher point, FGH, by the time that the middle of the bore is filled to the level G. At this time, the conductor slots are full but the upper fan blade and end ring cavities may be only partially filled. As pouring continues the remaining air in the fan blade and end ring cavities 64 and 66 is then vented to the atmosphere through grooves 78 and slots 80 as previously described; also, any remaining air in the balancing lug cavities 86 is likewise vented to the atmosphere through openings 92, 9'4, 96, and 80 in the manner mentioned above. Pouring is continued further until the aluminum reaches point I at which time the funnel is removed and the aluminum then drops to level M.

Many different casting methods are known, as mentioned above, and although centrifugal casting is specifically disclosed herein, it will be evident that the teachings apply to such other casting processes, such as static casting through the bore.

A vexing problem that must be contended with in casting aluminum is that it shrinks approximately 10% in volume upon conversion from a liquid at the pouring temperature to a solid at the freezing temperature, and if means are not provided to feed in additional molten metal to compensate for such contraction, shrink holes appear in the winding as described above in the discussion of the prior art. Accordingly the sprue formed in the middle bore represents a large mass of molten material available to perform the important function of remaining fluid and continuing automatically to serve as a source of supply to the material cast in the conductor slots and mold cavities. The aluminum is continuously fed through both the lower and upper gates 58 and 68 by centrifugal action to compensate for the shrinkage during the progressive freezing of the metal and these cavities are maintained full until the aluminum has completely solidified. Because of their thinner sections, the tips of the fan blades and the slot conductors solidify first with their shrinkage being fed from the end ring cavities, and the end rings subsequently freeze with solidification progressing from their outer periphery and end surfaces toward the gates, since the heat of fusion must be dissipated from the outer surfaces of the molds.

The above sequence meets the basic requirements for a good casting in that freezing starts at the points most remote from the gates and progresses toward them, with sufiicient makeup metal continuously flowing through the gates to feed the shrinkage as it occurs, and with the aluminum sprue remaining fiuid until after all parts of the useful winding are frozen. The gates can be made considerably smaller in cross-section than the end rings and still freeze thereafter, because the continuous flow of hot metal from the sprue through the gates helps to maintain the molten material in them in a fluid state until the winding is completely frozen. The gates then freeze immediately thereafter since there is a stoppage of flow of material to the winding.

Because of its larger section area, the sprue freezes last with a large shrink hole appearing in the upper central portion, as shown in FIGURE 11, which corresponds to the change in volume of all the metal poured during the casting process. There is no possibility for shrink holes to develop except in the main body sprue since this portion is the last to freeze. It is this improved sequence in freezing action which eliminates the shrink holes found in prior art rotors.

When the rotor winding and molds have cooled sufficiently to permit removal of the latter, rotation of the mold apparatus is concluded and the molds are knocked loose from the rotor body. The structure presented at this time is the same as that illustrated in FIGURES 9 and 10 which includes conductor bars embedded in the rotor slots, the fan blades, end ring, balance lugs integrally formed therewith and the sprue 130 including gates 58 and 68 which now appear as solid members. It will be noted that the outer end surface of the upper fan blades 65 and the balancing lugs 88 are serrated, as indicated at 89, as a result of the aluminum filling the grooves provided for venting air during casting. Also, the lower end of the sprue in FIGURE 10 resembles the shape of the bottom cavity 56 while the upper end in FIGURES 9 and 11 has a somewhat irregular internal appearance resulting from the feeding of the aluminum therein into the fan blades, slot conductors and end ring cavities during freezing of the winding and also due to the shrinkage of the sprue as it freezes. When the funnel was removed, the level of molten aluminum dropped to level M, and the large cavity 133 subsequently formed in the upper central portion of the sprue indicates the amount of aluminum fed to the fan blades, slot conductors and end rings during the freezing process, plus the shrinkage of the sprue itself.

In order to remove the sprue from the rotor bore, the gates on the upper or pouring end are cut with an air hammer at a point X-X adjacent to the bore of the upper end ring 67. The gates on the other end of the sprue having the conical frustum formed by cavity 56, are cut adjacent to the bore of lower end ring 55 at Z-Z in FIGURE 4. A second cut on each of the latter gates 58 is also made at Y--Y close to the surface of the lower end of sprue to permit its removal from the bore. The only member holding the sprue in position after the above cutting operations is the ceramic sleeve. Repeated sharp raps with a mallet or air driver hammer on the lower end of the sprue are sufiicient to break up the sleeve and thereby permit the sprue to be driven upward and removed from the top end of the rotor bore. Any remains of the ceramic sleeve can then be readily taken out of the rotor bore.

The use of a ceramic sleeve over the full length of the bore of the punching stack is especially adaptable for use with short rotors, or where greater thermal insulation is needed to give more delay in freezing of the sprue. However, in larger sizes, or in rotors of great length, it is preferable to use a short ceramic ring of approximately one-half inch in length in lieu of the full length sleeve shown in FIGURE 4. Even though larger rotor windings are cast using such a short sleeve, the aluminum sprue does not adhere to the laminations or become locked on irregularities in the bore because the sprue, having a greater temperature coefiicient of contraction than the laminations, shrinks radially inward by an amount sufficient to clear the walls of the bore such that the sprue, after it cools, can be readily driven out of the rotor. In lieu of the ceramic sleeve, sleeves of other materials can also be employed. It has been found for example that a steel ring of even lesser length such as /s to 4 inch, is especially effective and economical and many rotor windings have been cast using metallic rings. The sprue in FIGURE 11 illustrates the use of a short ceramic sleeve 131 of approximately /2 inch in length during the process. The outer portion of this sleeve was sheared off as the sprue was driven out of the rotor bore. One function served by the ring is to permit cutting off the lower gates at a point inside the punching bore after casting, and thereby facilitate removal of the sprue from the rotor. The long ceramic sleeve 50 also serves to thermally insulate the sprue from the rotor laminations so as to delay freezing of the sprue. The dotted lines represent the void created in the sprue resulting from the feeding of aluminum to compensate for the shrinkage in the slot conductors, end rings, and fan blades and in the sprue itself, during the freezing of these parts. Since the aluminum filling the upper gates is cut adjacent to the end ring bore, protruding members 68 remain attached to the sprue when it is driven upward from the rotor core. The bottom end of the sprue must be of a diameter smaller than that of the rotor bore to permit passage therethrough, and this view illustrates the extent to which the members 58 are cut back to permit such passage.

The casting process previously described has application to rotors of conventional length and design. However, in some instances, rotor windings of great length or those with small or unusual shapes of conductor slots for example, may not be successfully cast by the process described above because the aluminum may freeze before it completes its course of travel up the conductor slots, or the air may not be completely vented therefrom. In such cases, the same principles of casting through the bore and permitting the aluminum to rise in the conductor slots may be carried out, but additional openings connecting the bore with the conductor slots must be provided so as to permit the introduction of molten aluminum and/or the venting of air at preselected points along the punching stack. Many different arrangements may be provided to which the casting principles disclosed herein may apply. For example, in the modification shown in FIGURES 12, 13 and 14, spacers consisting of small steel blocks are welded to one or more of the duct punchings or laminations which are then located at preselected points along the punching stack. The spacers serve to provide gates 142 through which the hot aluminum flows from the molten sprue 130 to supplement the colder fluid metal rising in the conductor slots 144. Since the spacers are located adjacent the bore and are substituted for laminations, the outer peripheral surface of the rotor must likewise be equipped with either a continuous ring 146 such as in FIGURE 13a or with a stack of punchings or laminations such as FIGURE 13d of a thickness equal to that of the spacers and having an internal diameter greater than that at the outer end of the spacers, and aranged such that aluminum passing through gates 142 can enter conductor slots 144. Various other types of spacers may be employed at the outer periphery of rotor, several different embodiments of which are shown in FIGURES 13b and 130. The molds employed and the steps carried out during the casting process are the same as that described above with the exception that an additional step consisting of feeding molten aluminum through the slots 142 formed by the spacers 140 is included in the process. When molten material flows therethrough to the conductor slots 144, it serves to maintain the aluminum in the slots in a fluid state and thus precludes freezing in the slots until they are completely filled. It will be evident that the spacers 140 may be extended to a point adjacent the slots to confine the aluminum to a plurality of parallel paths, or to use staggered punchings for achieving this purpose. The molds employed and the steps carried out during casting are otherwise the same, except that a short sleeve such as 131 should be used which does not block or extend over the gates 142, and it is more difiicult to remove the sprues when such gates are employed.

Instead of the steel spacer blocks 140, it is possible in some cases to use a corresponding quantity of special laminations having slitted openings or ducts that extend from the rotor bore to the bottoms of slots 144, similar to an extension of projections in FIGURE 13d. Another variation that has been used on rotors having unusual slots which were difficult to vent, is to pour the metal downward through slots in prior art manner, but to have radial vents 142 that are small enough to prevent the flow of metal through them but which will yet permit air to escape radially inward from slots 144 to the bore at preselected points along the punching stack, in which case no aluminum is poured through the bore.

The arrangements in FIGURES 12 and 14 also permit the casting of internal end rings 148 to interconnect all the slots at preselected places along the punching stack, with such rings having a thickness equal to that of spacers 140, and a radial depth extending from the outer end of spacers 140 to the inner periphery of steel ring 146 or to the bore of special punching in FIGURE 1311.

In view of the above, it is evident that many modifications and variations are possible in light of the above teachings. It therefore is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of casting a winding in a rotor for a dynamoelectric machine comprising the steps of assembling a plurality of laminations having conductor slots therein to form a magnetic core, placing said core between a pair of iron molds and exerting an inward force thereon to compress the laminations by direct contact with the molds, said molds having cavities shaped to the configuration of fan blades and end rings and arranged for communication with said conductor slots, pouring molten aluminum into a central bore provided in said core and permitting the aluminum to flow outwardly into said cavities and the conductor slots formed in the laminations, venting air from said cavities and slots as pouring progresses, and removing said molds and excess aluminum from the rotor bore when all the cavities and conductor slots are filled with aluminum.

2. The method of casting a winding in a rotor for a dynamoelectric machine comprising the steps of assembling a plurality of laminations having conductor slots therein into a stack for forming a rotor core for said machine, placing said rotor core in a mold having upper and lower sections disposed on opposite sides thereof and being equipped with fan blade and end ring cavities, pouring molten aluminum in a bore provided in said rotor core and permitting it to flow outwardly from said bore into said fan blade and end ring cavities formed in the lower section of said mold prior to flowing upwardly in said conductor slots and thereafter filling the cavities in the upper section of the mold, venting said cavities through said bore and the upper section of said mold and sprue as the molten aluminum rises therein, feeding the molten aluminum from a sprue in the rotor core through gates into said cavity provided in the upper and lower molds to augment the aluminum therein and thereby prevent establishment of shrink holes in the winding, and removing the mold from said rotor core when the molten aluminum freezes and reaches a predetermined low temperature.

3. The method of casting a winding in a rotor core for a dynamoelectric machine comprising the steps of assembling a plurality of stacked laminations equipped with conductor slots into a mold having upper and lower sections wherein each of said sections is provided with indentations defining fan blade and end ring cavities, rotating said rotor on an axis passing through the center of said rotor core, pouring molten aluminum into the bore provided in said rotor core and causing said aluminum to be forced outwardly by centrifugal action through gates in the lower section and into the said cavities, causing it to rise upwardly in said conductor slots and the rotor bore feeding the molten aluminum into the upper fan blade and end ring cavities simultaneously from the slots and bore gates provided in the upper mold section, venting the air displaced by said aluminum in said conductor slots and cavities and thereby permitting complete filling with molten aluminum, continuing the pouring process until said bore is filled with aluminum, stopping rotation of said mold after freezing of the aluminum in said cavities and slots, removing said upper and lower mold sections from said core, and then removing the excess aluminum remaining in the rotor bore.

4. The method of casting a winding in a rotor core for a dynamoelectric machine comprising the steps of assembling a plurality of stacked laminations equipped with conductor slots into a mold having upper and lower sections wherein each of said sections is provided with indentations defining fan blade and end ring cavities, causing said rotor to rotate on an axis passing through the center of said rotor core, pouring molten aluminum into said bore for consecutively filling said cavities in the lower mold sections, conductor slots and cavities in said upper mold section, venting air from said cavities and conductor slots as it is displaced by the molten aluminum, providing a body of molten aluminum in the rotor bore which is in communication with said cavities and slots for feeding the latter casting and thereby accounting for shrinkage occurring during freezing of the aluminum initially poured in said cavities and slots, stopping rotation of said rotor core when said aluminum freezes and reaches a predetermined lower temperature, and removing the aluminum remaining in the bore after it has frozen in the slots and end cavities.

5. The process of casting a winding in a rotor core for a dynamoelectric machine comprising the steps of placing a rotor core equipped with conductor slots in a mold apparatus comprising upper and lower sections, each of said sections being provided with cavities shaped to the configuration of fan blades and end rings and having communication with a bore of the rotor through gates provided in said sections, inserting a disposable cylindrical ring in the rotor bore, rotating said mold apparatus, pouring molten aluminum into the bore provided in said rotor core and causing it to be forced outwardly by centrifugal action through gates into said cavities provided in the lower section, permitting it to rise upwardly through and completely filling said conductor slots prior to entering said cavities provided in the upper section of said apparatus, venting air displaced by said molten aluminum from the mold apparatus, filling said rotor bore with molten aluminum and thus permitting aluminum to be fed through said gates in the upper and lower sections to the fan blade and end ring cavities therein, and providing a sprue available to continue supplying molten aluminum to said conductor slots and cavities during the time when said aluminum is freezing, stopping rotation of said mold apparatus and removing the mold sections from the rotor core prior to driving the remains of said sprue from the rotor core.

6. The process of casting a winding in a rotor core for a dynamo-electric machine comprising the steps of placing a rotor core equipped with conductor slots in a mold apparatus comprising upper and lower sections,

each of said sections being provided with cavities shaped to the configuration of fan *blades and end rings and having communication with a bore of the rotor through gates provided in said sections, inserting a cylindrical ring in the rotor bore, rotating said mold apparatus, pouring molten aluminum into said rotor bore and causing it to be forced outwardly by centrifugal action through the gates in said lower section into said fan blade and end ring cavities, causing the aluminum to rise in said conductor slots and venting displaced air inwardly through the gates in the upper section and upwardly through the upper mold bore, continuing the pouring operation until molten aluminum fiows outwardly through said gates in the upper section to finish filling the upper fan blade and end ring cavities, venting remaining air from said upper section through additional vents provided therein, filling said rotor bore above the gates in the upper section to provide a molten sprue available to furnish aluminum simultaneously through the upper and lower gates to said conductor slots and fan blade and end ring cavities as the aluminum initially poured therein shrinks during freezing, stopping rotation of said mold apparatus and removing the sections from said rotor core, and finally driving the remains of said sprue from said rotor bore.

7. The process of casting a winding in a rotor core for a dynamo-electric machine comprising the steps of placing a rotor core equipped with conductor slots in a mold apparatus comprising upper and lower sections, each of said sections being provided with cavities shaped to the configuration of fan blades and end rings and having communication with a bore of the rotor through gates provided in said sections, inserting a cylindrical ring in the rotor bore, rotating said mold apparatus, pouring molten aluminum into the rotor bore through a funnel positioned in but spaced from the sides of said bore and having its bottom end terminating below the gates connecting said bore with the upper fan blade and end ring cavities, causing said molten aluminum to flow outwardly through the lower gates as a result of centrifugal action to first fill the lower fan blade and end ring cavities, permitting said molten aluminum to rise thereafter in said conductor slots to fill them and also subsequently to partially fill the upper fan blade and end ring cavities while simultaneously venting air displaced by said aluminum through the large upper gates and past the funnel to the atmosphere, thereby permitting a rapid pour, and finally completing the filling of said upper fan blade and end ring cavities including cavities provided for balancing lugs by feeding aluminum through said upper and lower gates, venting the small remaining portion of air from said upper cavities through vents provided therein, filling said bore prior to removing said funnel so as to provide a sprue of molten aluminum, and simultaneously feeding said aluminum therefrom through said upper and lower gates into said slots, fan blade and end ring cavities to augment the aluminum initially poured and thereby account for shrinkage therein, freezing the aluminum and removing the rotor core from the mold apparatus upon reaching a predetermined temperature, and finally driving said sprue from the rotor core.

8. The method according to claim 7 defining the consecutive use of the upper gates first as large air vents and subsequently as gates for molten aluminum, the additional step of permitting molten aluminum to flow radially outward from the bore into openings provided through the rotor core at intervals along the length of said rotor bore and into said conductor slots for preventing the aluminum in the latter from freezing prior to reaching the upper fan blade and end ring cavities, and also to permit the venting of air radially inward from conductor slots to the bore at selected locations along the rotor length, with the funnel extending down into the bore below the lowermost opening in the rotor bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,190,054 Wiard July 4, 1916 2,351,720 Stoody et a1. June 20, 1944 2,370,953 Greenberg Mar. 6, 1945 2,381,616 Pfieger Aug. 7, 1945 2,386,028 Young Oct. 2, 1945