Metal founding – Means to shape metallic material – Including means to assemble mold parts
Patent
1997-01-17
1999-03-30
Ryan, Patrick
Metal founding
Means to shape metallic material
Including means to assemble mold parts
164341, 164312, 164314, 164319, 164320, 164333, 164334, B22D 3304, B22D 1704, B22D 1724
Patent
active
058876430
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuous application of International Patent Application No. PCT/JP 96/01326, filed May 20, 1996,
TECHNICAL FIELD
The present invention relates to a conductor casting apparatus for molding a conductor of a squirrel-cage rotor of an induction motor to be integrally with a rotor core, and more particularly, to a conductor casting apparatus provided with means for additionally pressurizing a molten metal that fills an end-connector ring cavity between a mold and a rotor core on the side remoter from the pouring gate of the mold, in order to eliminate blowholes formed in a molded conductor.
BACKGROUND ART
As shown in FIGS. 3A and 3B, a rotor core 12 of a squirrel-cage rotor used in an induction motor is formed of a laminate of magnetic sheets, such as silicon steel sheets, and comprises a plurality of conductor rods 46 arranged individually in a plurality of slots 44 that are formed in the axial direction along the substantially cylindrical outer peripheral edge, and a pair of end-connector rings 48 which are arranged individually at the axially opposite ends of the core 12 to short-circuit the conductor rods 46 one another.
These conductor rods 46 and the pair of end-connector rings 48 are integrally molded by casting, such as aluminum die casting. A cylindrical axial hole 50 in the center of the rotor core 12 which is integral with molded conductor portion is fixed on a shaft 52 by shrink fitting or the like, whereupon the well-known squirrel-cage rotor is formed.
This conductor molding method is excellent in productivity and facilitates molding of a conductor in a desired shape, so that it has an advantage of being able to improve the characteristics of the motor. Heretofore, it has been widely used for a small-sized induction motors, in particular.
Conductor molding by casting, however, may bring on a problem that shrinkage cavity or gas cavity is caused in a molded conductor. According to the die casing method in which a molten metal, such as aluminum, is loaded at high speed and under high pressure, in particular, the molten metal is liable to form a turbulent flow and trap gas as it is loaded, so that development of blowholes is unavoidable. In the squirrel-cage rotor, moreover, the radial sectional area of each conductor rod is much smaller than the radial sectional area of each end-connector ring. During the casting operation, therefore, the molten metal first solidifies in the slots (in which the conductor rods are arranged to form the squirrel-cage rotor) that axially penetrate the laminate of magnetic sheets, such as silicon steel sheets, so that a sufficient pressure cannot be transmitted to those end-connector ring portions which solidify after a delay (especially those end-connector ring portions which are located on the side remoter from the pouring gate), and blowholes tend to be easily formed. Since a conductor having blowholes is low in mechanical strength, it is difficult to apply a squirrel-cage rotor including such a conductor to a high-torque induction motor or high-speed induction motor with a speed of tens of thousands of rpm.
Already proposed is a casting method in which a molten metal filling an end-connector ring cavity between a mold and a rotor core is locally pressurized independently of the filling pressure, in order to prevent the formation of blowholes in the conductor (end-connector ring in particular). According to this method, the molten metal is loaded from one end-connector ring cavity, which communicates with a pouring gate, into the other end-connector ring cavity, on the side remoter from the pouring gate, through a plurality of slots, and first solidifies in the slots with a small sectional area, thereby cutting off applied pressure from the end-connector ring cavity on the side remoter from the pouring gate. As this is done, pressure is additionally applied to the molten metal in the end-connector ring cavity on the side remoter from the pouring gate before this molten metal solidifies. Thus, the e
REFERENCES:
patent: 1555285 (1925-09-01), Hoey
patent: 5067550 (1991-11-01), Maekawa et al.
patent: 5538067 (1996-07-01), Nakamura et al.
Kasama Minoru
Katsuzawa Yukio
Nakamura Kosei
Nakazawa Yasuyuki
Fanuc Ltd
Lin I.-H.
Ryan Patrick
LandOfFree
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