US 2125970 A
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Description (OCR text may contain errors)
Aug. 9, 1938. G. A. WATERS 2,125,970
METHOD OF MAKING SQUIRREL CAGE ROTORS FiledJan. s, 1956 FIG.8. 9 F162. 8
F l G INVENTOR.
l A.WAT'ERS 33 g:
Patented Aug. 9, 1938' PATENT OFFICE LIETHOD OF MAKING ROTOR SSQUIRREL CAGE Granville A. Waters, University City, Mo., as-
signor to Wagner Electric Corporation, St.
Louis, Mo., a
corporation of Delaware Application January 6, 1936, Serial No. 57,707
My invention relates to squirrel cage rotors for dynamo-electric machines. Such rotors are commonly made by casting the rotor bars and end rings into. and around the assembled laminae forming the core of the rotor. Rotors thus manufactured have certain disadvantages. The shrinkage of both the bars and rings subject the structure to undesirable strains. Further, blow-holes often occur in the bars and rings causing variations in their resistance with consequent variations in torque for different rotor positions with respect to the stator member, which irregular torque action results in what is known as ratchet action or saddle formation. Another serious difficulty experienced with cast rotors is that during the casting period the metal of the bars oozes from the inside of the slots to the periphery of the rotor between the laminae thus short circuiting the individual lamina and causing stray losses.
The object of the present invention is to overcome the difficulties above referred to by forming either the end rings alone or both the bars and end rings of powdered metal consolidated under pressure. This method of forming the rotorhas the further advantage that by suitable selection of material any desired ohmic resistance may be obtained in the rotor.
In the accompanying drawing, which illustrates a rotor made in accordance with my invention and the method of making the same, Figure 1 is a sectional view showing the method of assembling the laminae; Figure'2 is a sectional view showing the assembled laminae positioned in a mold; Figure 3 is an enlarged view of one end of the mold after compression of the powdered material; Figure 4 is a plan of one form of laminae; Figure 5 is a plan'view of a portion of another form of laminae; Figure 6 is a view showa modified form of bar; Figure 7 is a diagrammatic view of a skewed type rotor; Figure 8 is a side view of a completed rotor; and Figure 9 is a view on a greatly enlarged scale illustrative of the preferred form of metal powder employed.
The rotor laminae I are punched in the usual manner and provided with slots 2 adjacent to their peripheries and with central shaft openings 3. The laminae are assembled on a dummy shaft l with their slots 2 in alignment and firm 'l'y clamped between flanges 5 and 6 on the ends of the shaft. The flange 5 at one end of the shaft may be formed integral with or permanently secured to the shaft, but the other flange 6 is made removable to permit the insertion and removal of the laminae and is forced against the latter to tightly compress them by a nut 1 engaging the threaded end 8 of the shaft. Bars 9 are inserted in the slots with their ends projecting beyond the core. The assembly is positioned in a mold l having a cylindrical bore of the proper size to snugly fit the periphery of the core formed by the laminae I. Sliding between the flange and the mold at each end is an annular compressing member or plunger H. The spaces between the ends of the plungers and the core are filled with powdered metal l2 and the plungers are forced toward each other by suitable means to consolidate the powder into an end ring l2 having a volume of, approximately one-third of the volume of the powder. I find that a pressure of twentyfive tons per square inch, more, or less, will accomplish the result. After compression of the powder to form the end rings, the rotor is removed from the mold and heated in a reducing atmosphere to a temperature of about 700 C. and maintained at this temperature for several hours, after which it is allowed to cool to normal temperature. This baking and cooling process completes the solidification of powder forming the end rings into a mass of a consistency similar to virgin metal.
If it is desired to give the rotor the lowest resistance possible for given dimensions, the bars iii are formed of copper and the powder l2 for forming the end rings is also copper. If a higher resistance is required, either the bars or the rings or both may be made of brass. It is also possible to use a mixture of different metal powders to form the rings. For example, a mixture of nickel and copper may be employed to form end rings of relatively high resistance. A mixture of metal and non-metal powders may be used to obtain extremely high resistance. The form of powder which I prefer to employ in carrying out my invention is obtained by electrolytic means, and when highly magnified presents an appearance somewhat as shown in Figure 9, each particle of the powder showing finger like protuberances on its surface. These protuberances interlock with those on adjacent particles under the extremely high pressure applied to the powder during the process of consolidating it.
If it is desired to form a rotor in which the slots are of the semi-closed type, laminae I having slots I3 of the form shown in Figure are used. In this case it is desirable to provide means for preventing the powdered metal from entering the mouths M of the slots. This is most conveniently accomplished by placing at each end of the core one or more laminal having closed slots, as is shown in Figure 3.
' When the rotor is o! the skewed type, that is, when the bars are not parallel with the axis of the core but are spirally disposed around it, the projecting ends of the bars are preferably bent so as to position them perpendicular to the ends of the core, as diagrammatically shown in Figure '7. The pressure used to consolidate the powder is thus applied in a direction parallel with the projecting ends or the bars rather than in a direction more or less transverse to said ends.
Instead of forming a ring of powdered metal at each end the rotor only one such ring may be employed, the bars being connected at the opposite end in some other manner. One method of accomplishing this result is by the use of "hairpin bars 15 such as shown in Figure 6. These bars are all inserted in the rotor slots from the same end, the bars being connected at the opposite end by a metal powder ring as above described. One end oi. the resultant rotor will have the appearance of a standard D. C. armature.
' While in my preferred construction the end rings of powdered metal are applied to a rotor provided with bars formed of strips or rods oi. metal inserted in the slots of the core as shown,
both the bars and end rings may be formed from powdered metal. In this case it is advisable to' use a separate plunger for each core slot in order to secure sufficient pressure to form solid bars from the powder.
Having fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:
1. The method of forming a secondary member oil a dynamoelectric machine which comprises assembling slotted laminae to form a magnetic core, inserting metal bars in the core slots, said bars projecting from one end or the core, applying metal powder to said end of the core and around the projecting bars, and consolidating the powder under pressure to form an end 2. The method of forming a secondary member of a dynamoelectric machine which comprises assembling slotted laminae to form a magnetic core, inserting metal bars in the core slots, said bars projecting from one end oi. the core, applying metal powder to said end of the core and around the projecting bars, consolidating the powder under pressure to form an and ring, and subjecting the resultant secondary member to high temperature.
3. The method of forming a secondary mem' ber 01 a dynamoelectric machine which comprises assembling slotted laminae to form a magnetic core, inserting metal bars in the core slots, said bars projecting from one end of the core, applying to said end of the core and around the projecting bars a metal powder, the particles oi which have protuberances on their surfaces, and consolidating the powder under pressure to form an and ring.
4. The method of forming a secondary member of a dynamoelectric machine which comprises assembling slotted laminae to form a magnetic core, inserting metal bars in the core slots, said bars projecting from one end of the core, applying to said end of the core and around the projecting bars a metal powder, the particles of which have protuberances on their surfaces, consolidating the powder under pressure to form an end ring, and subjecting the resultant secondary member to high temperature.
5. The method of forming a secondary member of a dynamo-electric machine which comprises assembling slotted laminae to form a mag netic core, inserting metal bars in the core slots, said bars projecting from one end of the core, applying to said ends metal powder obtained by electrolytic means, whereby the particles or said powder are provided with surface protuberances adapted to interlock with each other, consolidating said powder under a pressure approximately twenty-five tons per square inch to compress it to approximately one-third of its original bulk, and sintering the compressed powder at a temperature or approximately 700 C.
GRANVHLE A. WATERS.