US2784333A

US2784333A - Cast rotor and method

Info

Publication number: US2784333A
Application number: US372123A
Authority: US
Inventors: Wayne H Gunselman
Original assignee: Reliance Electric and Engineering Co
Current assignee: Reliance Electric and Engineering Co
Priority date: 1953-08-03
Filing date: 1953-08-03
Publication date: 1957-03-05
Anticipated expiration: 1974-03-05

Description

March 1957 w. H. GUNSELMAN 2,784,333

CAST ROTOR AND METHOD Filed Aug. 5, 1953 IN VEN TOR. WAYNE H. GUN SE LMAN March 5, 1957 w. H. GUNSELMAN 2,784,333 CAST ROTOR AND METHOD Filed Aug. 3, 1953 2 Sheets-Sheet 2 INVENTOR. WAYNE H. GUNSELMAN BY United States Pater-i 2,784,333 iatented Mar. 5, 1957 CAST ROTOR AND METHOD- Wayne H. Gunselman, Cleveland, Ohio, assignor to Reliance Electric and Engineering Company Application August 3, 1953, SerialNo. 372,123 6 Claims. (Cl. 310-211) The invention relates in general to casting methods and moreparticularly to a means for permanent mold casting the end. rings for a squirrel cage induction motor rotor for use in high slip, high torque, and excessive mechanical abuse. applications.

Pressure-die casting has been used for many years to 2 form the conductor system for a squirrel cage induction motor rotor. The metals generally used in such die casting operations were alloys, principally aluminum and magnesium alloys. Such alloys require a temperature of one thousand to one thousand two hundred degrees Fahrenheit to be sufliciently molten to be pressure die cast. The melting temperature might be about nine hundred degrees, and this temperature was sufiiciently low that if the motor was heavily abused, such as high frequency of starts and stops, the electrical losses in the rotor would become so great as to melt the squirrel cage conductor system. In a typical prior art system of pressure die casting the molten metal was placed in a die casting pot which was lined with asbestos and mica, and these two materials were also used in the dies as a seal. For a typical large sized rotor approximately five hundred pounds of aluminum alloy would be melted and in the die casting pot. Approximately one hundred fifty pounds of the alloy would be shot under pressure to form the conductor bars and end rings of the squirrel cage conductor system. This meant that three hundred fifty pounds of the alloy was wasted because it was mixed with particles of asbestos and mica so that it was not reclaimable.

An object of the invention is to cast the short circuit ing endrings on a squirrel cage rotor and to effect a satisfactory electrical and mechanical bond with separately permanently molded conductor bars in the slots of the rotor.

Another object of the invention is to provide a rotor of high mechanical strength and rigidity.

Another object of the invention is to provide a squirrel cage rotor having a conductor system made of high meltingpoint alloy which will withstand the internal heat created by excessive starting and stopping of the motor underload.

Another object of the invention is to provide a squirrel cage rotor conductor system permanently molded from an alloy which cannot successfully be die cast because of excessive temperatures which would damage the rotor laminations. {)0

Another object of the invention is to provide a method of making squirrel cage conductor systems wherein the molten metal not actually used in forming the conductor bars and end rings may readily be reclaimed.

Another object of the invention is to provide a squirrel cage conductor system on an induction motor rotor wherein the rotor does not have any appreciable residual stresses resulting from improper directional solidification and/ or non-uniform shrinkage.

Another object of the invention is to provide a squirrel 7 cage rotor which is more tightly compressed at the periphery than near the center thereof.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

Figure 1 shows a three-dimensional view of a separately cast conductor bar;

Figure 2 shows a perspective view of a combined press and mold for making a-squirrel cage rotor;

Figure 3 is a view of the rotor laminations;

Figure 4'isathree-dimensional view of the rotor after the end rings are cast and with one pair of gates and risers trimmed off;

Figure 5 is a partial longitudinal sectional view through the completed rotor; and

Figure 6 is an enlarged partial sectional view of a modification.

The aluminum and magnesium alloys previously used in many die cast rotors would melt at about nine hundred degrees, and this was sufiiciently low that several squirrel cage conductor systems melted under operating conditions which were such as to cause heavy electrical losses in the motor. A higher melting point alloy thus became necessary. An aluminum bronze alloy containing about ninety percent copper, nine percent aluminum, five-tenths percent nickel, and a small quantity of iron is found to have a high melting point of about one thousand nine hundred ten to one thousand nine hundred sixty degrees Fahrenheit, and yet have the same resistance required for this high slip motor of ten percent or more slip. This alloy had the required high melting point for such abusive operating conditions but was found to be impossible to die cast. The laminations of the rotor have thereon an insulating film to prevent eddy current losses, and this insulating film would withstand a temperature of only about three hundred fifty degrees. To die cast aluminum bronze at the high temperature required in the order of two thousand two hundred degrees Fahrenheit would require that the rotor be preheated so that the molten metal even under pressure could be forced completely through the slots before it solidified. Such preheating of the rotor would have to be at temperatures of about one thousand degrees, and this was impractical because not only would the lamination insulation be burned off but the laminations themselves would be damaged. Further, the insulation around the openings of the dies would not withstand the temperature and pressure.

The present invention relates to a method of separately casting the conductor bars, placing them through the slots of the rotor, and then casting by a permanent mold process end rings in electrical and mechanical contact with the ends of the conductor bars.

The Figure 1 shows a conductor bar 11 separately cast by a permanent mold process. Permanent molding is differentiated from die casting in that the metal to be cast is poured by gravity flow into a mold rather than being forced thereinto by pressure. The conductor bars 11 have exposed ends 12 each of which has mechanical locking grooves 13 and a plurality of serrations 14. The serrations 14 are preferably sharp to establish a fusible surface. The bars 11 may have slightly

curved surfaces

15 and 16 in order to facilitate their removal from the mold in which cast.

The Figure 3 shows a plan view of a rotor lamination 19 having a plurality of slots 20. These slots may be either open or closed in accordance with usual practices. A keyway 21 may be incorporated in each of the laminations 19.

The Figure 5 shows the completed squirrel cage rotor 22 and shows that a plurality of laminations 19 are stacked on a spider 2 3. The spider is a heavily constructed weldment including a tubular center 24 and arms 25 welded thereto. This construction is better shown in Figure 4. The laminations 19 are placed on the spider 23 in groups 26, there being four such groups in the particular rotor shown. Ventilating air spaces 27 are provided between the groups 26. Spacer fingers 28 in the air spaces 27, which may be disposed generally radially, maintain the groups 26 separated. One of the spider arms may contain a keyway 29 with a key 30 placed therein and engaging the keyway 21 on the laminations Y 19. Such keyway 2? may be skewed if desired in accordance with conventional practices. The groups of laminations 26 and spacer fingers 28 are assembled on the spider 23 with this assembly then placed in a press mold 31, shown in Figure 2. This press mold 31 is a horizontal press having an end frame 32 at the right end and'a similar end frame at the left end, not shown. Strain rods 33 hold together the end frames. A movable head 34 slides on the strain rods 33 and is actuated by a pres sure source such as a fiuid motor, not shown, at least before molding the last to be molded of the two end rings. A three-part mold, comprising

mold parts

35, 36, and 37, is provided near the end frame 32. A similar three-part mold, including the mold part 38 and two other parts not shown, is provided on the movable head 34. Each three-part mold together with a rotor in place defines an end ring cavity, shown principally at 39, for casting the end rings 46, shown in Figure 5. The

mold parts

35 and 36 are mounted on a pivot 41 and are shown in an open position.

Pneumatic motors

42 and 43 open and close the

mold parts

35 and 36. The outer edge 44 of the end faces of the stack of rotor laminations engages the annular edge 45 of the mold part 37. The mold part 37 also includes an annular ring 46 which closely encompasses the spider 23 and abuts the major portion 47 of the end laminationson the rotor. Tongues 48 on the mold part 37 establish a plurality of gates 49 through which the molten metal may flow to the end ring cavity 39. A riser cavity 50 is provided in the mold part 37, and this riser cavity has a top opening 51. A blind riser .52 and air vent 54 are also provided in the mold part 37. A conical centering member 53 is also fixed relative to the mold part 37 and engages and centers the end of the tubular center 24 of the spider 23.

Before permanent molding of the end rings 49 annular spacer strips, not shown, may be temporarily placed in the ventilating air spaces 27 and tack welded in place to aid the spacer fingers 28 in maintaining parallelism of the laminations 19. The press mold 31 includes gas lines 56 leading to burners, not shown, on the outside of the mold, for preheating the mold parts 35 to 38 to approximately seven hundred to nine hundred degrees Fahrenheit. This heat will also preheat the rotor when placed in the mold to about three hundred degrees Fahrenheit.

The exposed ends 12 of the conductor bars are preferably tinned with silver solder and then coated with flux and inserted through the slots of the stacked rotor laminations. The spider 23 with the groups 26 of rotor laminations with the conductor bars 11 in place may then be placed in the press mold 31. The movable head 34 may then be moved forward on the strain rods 33 by the motor of the press mold. The annular ring 46, and a similar ring on the head 34 will therefore contact the end laminations of the rotor to greatly compress the rotor laminations. The

mold parts

35 and 36 and the similar mold parts on the other end ring may then be closed to form the end ring cavities. The aluminum bronze alloy is then ready to be poured into the top openings 51. The aluminum bronze alloy is heated to a temperature of about two thousand two hundred fifty degrees and the pouring crucibles are preheated to prevent chilling of the metal in the pouring crucibles. The pouringtempera- 'ture is approximately two thousand one hundredto two thousand two hundred degrees Fahrenheit and iskept generally at a low temperature relative to the melting temperature of the alloy so as not to cause burning out or thirds the depth of the end rings.

oxidation of the alloy elements such as aluminum and nickel during the pouring operation. The riser cavities 50 and gates 49 are made of ample capacity so that the entire pouring operation may be rapidly completed and the end rings 46 completely cast before solidification. In the present case rotors actually cast are thirty inches diameter and the force of the press is one hundred twenty tons, with about two hundred seventy-five pounds of aluminum bronze alloy being melted for each rotor with the end rings weighing approximately one hundred seventy-five pounds and the remaining one hundred pounds being in the gates and risers which is immediately reusable and reclaimable since it contains no contaminants.

The temperature of the metal as cast, under the conditions outlined above, and the cross-sectional area of the end rings 40 is sufiicient to cause a satisfactory electrical bond with the exposed ends 12 of the conductor bars 11, especially at the sharp edges of the serrations 14. The molten metal of the end rings flows around the exposed ends 12 and forms good mechanical interlocking engagement with the mechanical locking grooves 13. Thus, a good mechanical bond is achieved at the locking grooves 13 and a good electrical bond is achieved at the serrations 14. V

A fusion between the conductor bars and the end rings is not absolutely necessary, as evidenced by the usual bus bar construction andthe type of contact made in electrical switches. What is desired is a satisfactory electrical bond or connection between the end of the conductor bars and the end ring. To determine if there is a satisfactory electrical bond, the motor is repeatedly tested under full load locked rotor conditions, creating repeated heating and cooling cycles. Such satisfactory electrical bond is demonstrated by the fact the the amount of slip of the motor before and after such testing cycles is essentially the same. This shows that the electrical bond is tight enough so that repeated heating and cooling, with consequent expansion and contraction, will not create oxidation at the joint which will change the resistance of this joint. The exposed ends of the conductor bars 12 have been shown as and are preferably about two- The conductor bars as previously permanently molded have cross-sectional dimensions approximately .010 inch less than the crosssectional dimensions of the slot apertures. This assures that the bars will be able to slide through the slot apertures.

After solidification of the end rings the mold may be opened and the press pressure released and the rotor removed. Upon releasing the pressure of the press mold 31, the conductor bars 11 will be placed under tension, in this case approximately six to seven thousand pounds per square inch on each conductor bar. The aluminum bronze alloy has a tensile strength many times this figure; hence, it will retain the outer periphery of the stack laminations in a tightly compressed condition. The annular spacer rings in the ventilating air spaces 27.may then be removed since they have served their purpose of assuring parallelism of the laminations 19, and in practice the annular spacer rings may conveniently be removed during the machining operation which makes the outer diameter of the rotor cylindrical. Thus these spacer rings do not appear in the completed rotor view of Figure 5. The gates and risers may next be trimmed off and are immediately reusable. The Figure 4 shows one end ring 46 after being trimmed and with the far end ring still retaining the gates 57 and risers 58. To complete the rotor, annular end plates 59 are pressed up against the end faces of the rotorand welded thereto as shown at 60. This last-mentioned compressional force is preferably not nearly as great as the pressure originally used to longitudinally compress the rotor. 'It may be only a force sufficient to make sure that the end plates 59 are in intimate contact with the end faces of the rotor before welding thereto. This will establish thatuthe outer periphery of the rotor is compressed more than the portion of the rotor next to the spider 23. Next, these end plates and the end group of laminations may be drilled and tapped, and cap screws 61 screwed therein with the cap screws welded at 62 to the end plates 59. This makes a mechanically rigid structure which will stand extreme abuse, both mechanical and electrical.

The annular spacer rings temporarily used at the periphery of the air spaces 27, plus the fact that the conductor bars 11 are previously cast and in a solid state at the time of casting the end rings on a rotor tightly compressed, establishes a completed rotor wherein the laminations do not have any waviness since there is no non-uniform shrinkage of the conductor bars as in die cast rotors.

The Figure 6 shows a modified form of construction forachieving a mechanical and electrical bond. In this Figure 6 a conductor bar 65 has a modified form of exposed end 66. In this form there is only one mechanical locking groove 13 which is positioned on the side closest to the axis of the rotor. The side 67 of the exposed end 66 remote from the axis of the rotor is left generally straight. The serrations 14 may be retained. In this modification the exposed ends 66 do not need to be tinned and fiuxed. The bars 65 are inserted through the slots in the rotor so that the exposed ends 66 are symmetrical on each end of the rotor. The rotor with the bars in place is then placed in the press mold 31 as before, and the end rings 69 cast in place. After the rotor is removed fromthe press mold, a peripheral groove 68 is machined in the outer periphery of the end ring 69. This groove 68 is made deep enough to cut into each of the sides 67 of the bars 65. i The rotor is then placed in a welding machine, such as an inert gas welder, and the grooves 68 filled up with weld metal 70 which is preferably of the same composition as the aluminum bronze used in the bars 65 andend rings 69. The weld metal 70 therefore assures a complete electrical bond between the bars 65. and the end rings 69. It also, in combination with the locking groove 13 and serrations 14, will provide mechanical locking engagement therebetween. The complete squirrel cage rotor 22 may be completed by the welding on of the end plate 59 and cap screws 61 as before.

With either of the constructions. shown in Figures 5m 6 an advantage of the present invention is that the entire rotor need not be scrapped when there is an imperfect casting as was the case in the pressure die casting of the squirrel cage structure. In this invention the rotor laminations may be salvaged since in the event of an imperfect end ring casting, such end rings may be cut off, the conductor bars slid out of the slots, and thus the rotor laminations may be salvaged for reuse.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement or parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. The method of making a squirrel cage conductor structure for a laminated member having longitudinal slots, said method comprising, forming separate conductor bars for said slots having a length longer than said rotor, inserting a bar in each of said slots substantially longitudinally symmetrically to establish exposed portions at each end thereof, molding by a permanent molding process first and second end rings on the end faces of said rotor and with said bar end portions embedded in said end rings, cutting a peripheral groove in said end rings to a depth sufificient to cut into said bar exposed portions, and filling said groove with weld metal to establish electrical and mechanical interconnection of said bars and end rings.

2. A squirrel cage conductor structure for an alternating current induction motor laminated member having longitudinal slots around the periphery thereof, comprising separately cast conductor bars having cross-sectional dimensionsapproximately .010 of an inch undersize of the slots in said member, said bars having a length greater than that of the member to establish two exposed ends outboard of the faces of the member, a mechanical locking groove on each exposed end of said bars, sharp fusible protrusions on each exposed end of said bars, and first and second annular end rings in contact with the longitudinal ends of said member joining opposite exposed ends of said bars, said end rings and bars being formed of aluminum bronze consisting of approximately ninety percent copper, nine percent aluminum, five-tenths percent nickel, and a small quantity of iron, said end rings being cast at a temperature and with a cross-sectional area sufiicient to transfer a quantity of heat to the end portions of the bars to cause a satisfactory electrical bond between said end rings and bars especially at said protrusions and with mechanical interlocking engagement between said locking grooves and said end rings, said laminated member having the greatest compression at said periphery, peripheral grooves cut into said end rings to a depth sufficient to cut into said bar exposed ends, and weld metal filling said peripheral grooves and establishing electrical and mechanical interconnection of said bars and end rings.

3..A squirrel cage conductor rotor structure for an alternating current induction motor laminated rotor having longitudinal slots around the periphery thereof, comprising separately cast rotor bars having cross-sectional dimensions approximately .010 of an inch undersize of the slots in said rotor, said bars in cross-section having at least two generally opposite sides at least slightly curved,said bars having a length greater than that of the rotor to establish two exposed ends outboard of the faces of the rotor, first and second generally opposite deep locking grooves on each exposed end of said bars, each exposed end of said bars having sharp serrations thereon, said exposed ends being tinned with silver solder and coated with flux, and first and second annular end rings in contact with said rotor faces joining opposite exposed ends of said bars, said end rings and bars being formed of aluminum bronze consisting of approximately ninety percent copper, nine percent aluminum, five-tenths percent nickel, and a small quantity of iron, said end rings being cast at a temperature of approximately two thou sand one hundred degrees Fahrenheit by a permanent mold process with the cross-sectional area of the end rings being sufiicient to transfer a quantity of heat to the end portions of the bars to cause a satisfactory electrical bond between said end rings and bars especially at said serrations with the exposed ends of the bars embedded in the end rings approximately two-thirds of the depth of the end rings and in mechanical interlocking engagement with said deep grooves, said permanent mold casting being accomplished during longitudinal compression of said rotor to thus place the rotor bars in the com pleted rotor under a tensile force of approximately seven thousand pounds per square inch to thus accomplish greater longitudinal compression near the periphery of the rotor than near the center of the rotor.

4. A squirrel cage conductor rotor structure for an alternating current induction motor laminated rotor having longitudinal slots around the periphery thereof, comprising separateiy cast rotor bars having cross-sectional dimensions slightly undersize of the slots in said rotor, said bars having a length greater than that of the rotor to establish two exposed ends outboard of the faces of the rotor, a deep locking groove on each exposed and of said bars, each exposed end of said bars having sharp serrations thereon, and first and second annular end rings in contact with said rotor faces joining opposite exposed ends of said bars, said end rings and bars being 5 formed of aluminum bronze consisting of approximately rings being cast at a temperature of approximately two 7 thousand one hundred degrees Fahrenheit with the crosssectional area of the end rings being sufiicient to transfer a quantity of heat to the end portions of the bars to cause a satisfactory electrical bond between said end rings and bars especially at said serrations with the exposed ends of the bars embedded in the end rings and in mechanical interlocking engagement with said deep groove, said casting being accomplished during longitudinal compression of said rotor to thus place the rotor bars in the completed rotor under a tensile force of approximately seven thousand pounds per square inch to thus accomplish greater longitudinal compression near the periphery of the rotor than near the center of the rotor, peripheral grooves cut into said end rings to a depth suflicient to cut into said bar exposed ends, and weld metal filling said peripheral grooves and establishing electrical and mechanical interconnection of said bars and end rings.

5. A squirrel cage conductor rotor structure for an alternating current induction motor laminated rotor hav-- ing longitudinal slots around the periphery thereof, comprising separately cast rotor bars having cross-sectional dimensions approximately .010 of an inch undersize of the slots in said rotor, said bars in cross-section having at least two generally opposite sides at least slightly curved, said bars having a length greater than that of the rotor to establish two exposed ends outboard of the faces of the rotor, a deep locking groove on each exposed end of said bars, each exposed end of said bars having sharp serrations thereon, and first and second annular end rings in contact with said rotor faces joining opposite exposed ends of said bars, said end rings and bars being formed of aluminum bronze consisting of approximately ninety percent copper, nine percent aluminum, five-tenths percent nickel, and a small quantity of iron, said end rings' being cast at a temperature of approximately two thousand one hundred degrees Fahrenheit by a permanent mold process with the cross-sectional area of the end rings being sutficient to transfer a quantity of heat to the end portions of the bars to cause a satisfactory electrical bond between said end rings and bars especially at said serrations with the exposed ends of the bars embedded jin the end rings approximately two-thirds of the depth of the end rings and in mechanical interlocking engagemerit With said deep groove, said permanent mold casting being accomplished during longitudinal compression of said rotor to thus place the rotor bars in the completed rotor under a tensile force of approximately seven thousand pounds per square inch to thus accomplish greater longitudinal compression near the periphery of the rotor than near the center of the rotor.

6. A squirrel cage conductor structure for a laminated member having longitudinal slots, said conductor structure comprising a plurality of separate conductor bars in said slots each having a length longer than said rotor and substantially longitudinally symmetrically placed in said slots to establish exposed portions at each end of said bars, first and second end rings cast on the end faces of the rotor and with said bar end portions embedded in said end rings, a peripheral groove cut into said end rings to a depth suflicient to cut into said bar exposed 7 end portions, and weld metal filling said groove and establishing electrical and mechanical interconnection of said bars and end rings.

References Cited in the file of this patent UNITED STATES PATENTS 558,271 Falk Apr. 14, 1896 1,603,544 Johnson Oct. 19, 1926 1,695,799 Daun Dec. 18, 1926 1,719,829 7 Bunker July 9, 1929 1,755,283 Adams Apr. 22, 1930 1,777,320 McCollum Oct. 7, 1930 1,807,689 Deputy June 2, 1931 1,925,052 Larsh Aug. 29, 1933 2,265,243 McCullough et al Dec. 9, 1941 2,285,811 Gay June 9, 1942 2,326,418 Van Amerongen Aug. 10, 1943 2,328,788 Deputy Sept. 7, 1943 2,544,671 Grange et al. Mar. 13, 1951 FOREIGN PATENTS 47,857 Switzerland June 10, 1909