WO1996032769A1

WO1996032769A1 - A process for obtaining a rotor for an electric motor

Info

Publication number: WO1996032769A1
Application number: PCT/BR1996/000013
Authority: WO
Inventors: Egidio Berwanger
Original assignee: Empresa Brasileira De Compressores S/A. - Embraco
Priority date: 1995-04-11
Filing date: 1996-04-10
Publication date: 1996-10-17
Also published as: BR9501352A

Abstract

A process for obtaining a rotor for an electric motor, using a mold for forming the rotor cage, said mold being defined by: a package of annular blades (2) each one provided, adjacent to the respective outer border, with a plurality of slots (2a); a central shaft (1, 10) around which the blades are mounted in order that their slots (2a) define axial channels on the package of blades (2); an upper end cover and a lower end cover arranged around the shaft, concentrically with the blades and each one defining, with the adjacent end of the package of blades (2), an annular chamber open towards the axial channels of the package of blades (2), said process comprising the steps of: a) rotating the mold around the longitudinal axis; and b) depositing liquid metal through a central opening (12a) provided on the upper end cover (12), whereby to promote the ascendent filling of each axial channel, starting from the lower annular chamber, radially in direction to the central shaft (10) during the rotation of the mold.

Description

A PROCESS FOR OBTAINING A ROTOR FOR AN ELECTRIC MOTOR

Field of the Invention

The present invention refers to a process for obtaining a rotor in a cage for an electric motor of the type used in hermetic compressors for small size refrigeration systems.

Background of the Invention

One of the known processes for obtaining the rotor for electric motors of the above-mentioned type uses the injection, under pressure, of liquid metal, preferably aluminum, or copper and its alloys, into a mold to inject the cage of the rotor. Called rotor cage is a soft metal body including an assembly of bars and end metal rings shaped in a mold and retaining a plurality of rotor annular blades.

The bars are defined by the solidification of the metal injected into the mold through axial alignments of slots defined in each rotor blade, whereas the rings are obtained by the solidification of the metal injected at the end portions of the package of superposed blades.

For the molding of the rotor cage i t i s necessary that the blades be superposed and aligned according to a common central shaft and such that the slots of each rotor blade communicate with corresponding slots of the adjacent blades according to an axial alignment parallel or substantially parallel to the common central shaft, whereby to form with the latter a certain predetermined angle. The required alignment is obtained by means of a mold consisting of a common central shaft which orients the superposition of the rotor blades and a pair of end annular covers which enclose a plurality of blades in the desired layout and which will determine the conformation of the end rings of the rotor cage. The end annular covers present, at their internal faces, annular grooves open towards a plurality of axial alignments of slots of the package of blades, whereby to permit fluid communication therebetween when the liquid metal is injected. In the process of injection of liquid metal under pressure, after the disposition of the package of blades in the mold, aluminum under pressure is injected along the alignments of slots through the end cover which is provided with a certain number of orifices to be aligned with one or more slots from the package of blades. The alignment between each slot and a respective orifice of the end cover occurrs when the number of orifices and slots is equal. The metal injected through one of the annular covers reaches the opposite end cover there being deposited whereby to form, on the annular groove provided thereon, one of the end annular rings. In this process, the injection of liquid metal is effected under high pressure and at hiqh speed, which provokes a turbulence in the flow of the liquid metal being injected, favoring the appearance and the incorporation, to the process, of αases This problem is increased due to constructive unevennesses existent in the mold and blades. The incorporation of the gases produced generates bubbles, pores and aluminum oxides which produce electric properties exponentially detrimental to the application for which the rotor cage is intended, due to reducing the effective conductive section and increasing resistivity. The injection under high pressure apparently reduces the appearance of bubbles and pores but provokes a highly detrimental adherence of the aluminum to the package of blades. The high velocity component provokes hot metallizing along the interior of the axial alignments of slots, which means electric contact between cage and package of blades. Further to these shortcomings, when the rotor cage is submitted to a thermal treatment, the gases contained in the pores and in the bubbles expand, provoking deformations of the rings and increasing the contact between the cage and the package of blades .

Another shortcoming of this process refers to the high consumption of metallizing material. To fill the devices, feeding channels and risers, approximately 50% of the aluminum are wasted. Disclosure of the Invention

Hence, it is an object of the present invention to introduce a process for obtaining a rotor for an electric motor that avoids the formation of bubbles of air within the metal bars of the rotor and the consequences of the existence of said bubbles, and further the adherence of the metal being injected, to the package of blades.

Another object of the present invention is to introduce a process that produces a rotor, such as obtained through the process of injection under pressure, however with a minimal consumption of metal material . These and further objects are attained through a process for obtaining a rotor for an electric motor, using a mold for injecting the rotor cage, said mold being defined by: a package of annular blades each one provided, adjacent to the respective outer border, with a plurality of slots; a central shaft around which the blades are mounted in order that their slots define axial channels on the packages of blades; an upper end cover and a lower end cover arranged around the shaft, concentrically with the blades and each one defining, with the adjacent end of the package of blades, an annular chamber open towards the axial channels of the package of blades, the process comprising the steps of: a- rotating the mold around the longitudinal axis; and b- depositing liquid metal through a central opening provided on the upper end cover, whereby to promote the ascendent filling of each axial channel, starting from the lower annular chamber, radially in direction to the central shaft during the rotation of the mold.

Through this process, the degassing of the liquid metal occurrs simultaneously with the formation of the rotor cage, whereas in the process of the state of the art an additional operation and also additional equipment are necessary. On account of the process of the present invention, it is not necessary to use risers or channels which consume about 50% of the metal material of the prior art. Furthermore, through the present solution a further segregation of the oxides generated during the process of injection of the metal into the mold occurrs. Description of the Drawings

The invention will be described hereunder in relation to the attached drawings, wherein: Figure 1 represents a schematic longitudinal sectional view of a package of annular rotor blades when subjected to a process of injection of the cage, according to the prior art;

Figure 2 illustrates a plan view of a rotor blade; Figures 3, 3a and 3b represent schematic longitudinal sectional views of a package of annular rotor blades when subjected to a process of injection of the cage according to the present invention, in three successive steps of this process; and Figure 4 represents a schematic longitudinal sectional view of a rotor.

Best Mode of Carrying Out the Invention

According to Figure 1, a rotor cage injection mold of the prior art which includes a central shaft 1 around which a plurality of annular blades 2 is mounted forming a package of blades closed at their ends by a first and a second annular end covers 4, 5, defining, respectively, an upper cover and a lower cover, said covers being mounted onto central shaft 1 against the package of rotor blades 2 is shown. In this embodiment, central shaft 1 extends outwards from annular end covers 4, 5.

The package of rotor blades 2 is formed by a plurality of annular disc shaped metal blades, each blade presenting a plurality of slots 2a provided adjacent to the outer border of said blades. The package of blades 2 is mounted onto central shaft 1 , whereby to produce a longitudinal alignment of the slots of each blade of the package, defining axial channels on the package of blades. In this solution, the end covers 4, 5 which close the mold are provided, at their respective internal faces facing the package of blades 2, with annular recesses 4a, 5a, defining respective annular grooves which, after the solidification of the metal injected into the mold, define the end rings of the rotor cage. In this construction, the insertion of eacl. end cover is just and without clearances.

According to the prior art and as indicated by the arrows in Figure 1, the liquid metal is introduced into through orifices provided on one from the first and second annular covers 4, 5, whereby to permit the pressurizing of liquid metal through each axial channel of the package of blades, until the complete filling of said channels . This process presents the forementioned shortcomings.

According to the present invention, illustrated in figures 3, 3a, 3b, the mold for obtaining the rotor cage comprises a central shaft 10 around which is mounted the plurality of rotor blades 2, as in the prior art. In this construction, central shaft 10 extends outwards from the package of blades 2 through only one of the ends of said package.

For the assembly of the package of blades 2 onto central shaft 10, hereon is mounted, initially, a lower annular end cover 11 which receives and seats, on its internal face facing the package of blades, said package of blades 2. An upper end cover 12 is mounted at the opposite end of the package of blades 2. In this construction, the internal face of each end cover defines with the adjacent end blade of the package of blades 2, an annular chamber which will mold a corresponding metal ring of the rotor. According to the illustration, at the lower end cover 11 the annular chamber is defined by an annular groove lib open towards the axial channels of the package of blades 2 and provided with radial channels lie communicating said annular groove lib with the internal border of the lower end cover 11. The surface of the internal wall of the lower cover is provided with axial channels lid communicating with radial channels lie, whereby to permit the exit of gases produced during the process of injecting the metal onto the package of blades 2. Upper end cover 12 presents, as from its external border, a circular flap 12a which, through the assembly of upper end cover 12, sits on the external border of the adjacent end blade of the package of blades 2, externally to the slots thereof, spacing the inner surface of said upper end cover 12 from said adjacent blade of the package of blades 2, where, during the molding of part, one of the metal rings of the cage will be defined. The thickness, the height and the profile of circular flap 12a is a function of the desired profile for the ring being molded. In this case, the annular chamber for the molding of the respective metal ring is defined by the distance between the internal face of upper end cover 12 and the adjacent end blade of the package of blades 2.

Said upper end cover 12 presents a central opening 12b for the introduction of liquid metal during the process of deposition of the latter.

For the introduction of the liquid metal, the rotor cage mold is subjected to a rotation around its axis, while the liquid metal is poured through central opening 12b of upper end annular cover 12. Due to centrifugal force, the liquid metal is radially directed towards the axial channels of the package of blades 2, ascendently filling them as from the filling of annular groove lib of lower end cover 11, radially inwards from the outer surface of each said axial channel. This filling orientation direction permits that the gases segregated and present in the axial channels of the package of blades during the injection of liquid metal therein can be directed to axial channels lie of lower end cover 11 and eliminated, preventing that the cage be submitted to any additional treatment for the removal of said gases. The action of the centrifugal force produces an inclined profile of the internal face of the metal ring formed between the package of blades 2 and upper end cover 12. The gases produced during the filling of the region between the blades and upper end cover 12, which defines one of the rings of the rotor cage, are eliminated through central opening 12b of said upper end cover 12. In centrifugal injection, since the flow of injected liquid metal presents low relative velocity, it is lamellar and void of high pressure, the cage formed in the above-mentioned radial direction does not incorporate gases from the medium, furthermore promoting the elimination of those existent or eventually formed through the action of the centrifugal force, through openings centrally defined in the mold. The relative metal-blade insulation is obtained through the retraction of the injected material, due to the decrease of temperature of this material .

Claims

LAIMS

1 - A process for obtaining a rotor for an electric motor, using a mold for injecting the motor cage, said mold being defined by: a package of annular blades (2) each one provided, adjacent to the respective outer border, with a plurality of slots (2a); a central shaft (1, 10) around which the blades are mounted in order that their slots (2a) define axial channels on the package of blades (2); an upper end cover and a lower end cover arranged around the shaft, concentrically with the blades and each one defining, with the adjacent end of the package of blades (2), an annular chamber open towards the axial channels of the package of blades (2), characterized in comprising the steps of: a- rotating the mold around the longitudinal axis; and b- depositing liquid metal through a central opening (12a) provided on the upper end cover (12), whereby to promote the ascendent filling of each axial channel, starting from the lower annular chamber, radially in direction to the central shaft (10) during the rotation of the mold.

2 - The process, according to claim 1, characterized in comprising the step of eliminating gases present during the injection of liquid metal into the mold through channels (lie, lid) produced on the internal face of at least one from the upper and lower end covers (11, 12), turned towards the package of blades (2).

3 - The process, according to claim 2, characterized in that the lower chamber is defined by an annular groove

(lib).