US2991518A - Apparatus for and method of casting - Google Patents

Description

July 11, 1961 E. J. SCHAEFER APPARATUS FOR AND METHOD OF CASTING Filed Sept. 3, 1957 J m a m I I I Unittid States Patent Filed Sept. 3, 1957, Ser. No. 681,595 20 Claims. (Cl. 22-73) The invention relates generally to metal casting and more particularly to casting apparatus and a method of casting utilizing vacuum.

The general object of the invention is to provide a novel apparatus for and method of casting metal, which prevent the entrapment of air in the cast metal.

Another object is to provide a novel apparatus for and method of casting metal, which lend themselves to automatic operation.

A further object is to provide a novel apparatus for and method of casting, in which the molten metal is confined to just the space where it is desired without excess flash on the casting, such space, however, being completely filled with metal and free of any air pockets.

It is also an object to provide a novel apparatus for and method of casting an article having a preformed insert, where it is desired to prevent any of the cast metal from lodging on the exterior of the insert.

In a specific aspect of the invention, it is an object to provide novel apparatus for and a method of casting an aluminum squirrel cage winding in a stack of laminations to form a squirrel cage induction motor rotor, in which the aluminum completely fills all the spaces desired and is prevented from forming a flash on the exterior of the stack of laminations.

Other objects will become apparent from the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a vertical sectional view of a casting apparatus for use in a method of casting, embodying the features of the invention;

FIG. 2 is an enlarged fragmentary horizontal sectional view taken on the line 2-2 of FIG. 1; and

FIG. 3 is a fragmentary sectional view similar to the lower end of the apparatus shown in FIG. 1 but illustrating a modified form.

While casting methods have heretofore been tried, which employed vacuum to withdraw air from the mold cavity to facilitate entry of molten metal into all parts of the cavity, such methods have not been entirely successful in that some air may become entrapped in the molten metal by permitting the metal to enter the mold before suiiicient vacuum is attained therein or by entrapment of air from the exterior by the molten metal in entering the mold. Former methods frequently involved the step of pouring the molten metal, which does not lend itself readily to an automatic process.

The present apparatus and method avoids the abovementioned difficulties and permits an automatic operation in which castings may be rapidly made. Generally, the apparatus comprises a mold support on which a mold is mounted. The mold comprises a sealed enclosure, access to which is provided for through a snout, which in this instance extends downwardly. Preliminary to the casting, the snout is sealed by a removable seal and vacuum is applied to the interior of the mold. While such vacuum is maintained within the mold, or While the vacuum is being drawn, the latter is moved over a pot of molten metal and is lowered sufliciently to immerse the snout in the molten metal to a depth such that no air from the surface of the metal will be drawn into the snout when the seal is removed and the metal enters.

The metal without any entrapped air is thus drawn into the mold by the vacuum and completely fills the mold vICC.

cavity. The mold may then be raised and moved away from the pot for removal of the mold from the casting.

Cooperating with the foregoing features, the'presentapparatus and method involves the use of a form of mold having novel means for sealing the mold so that vacuum may be readily applied thereto. Such mold is adapted particularly for use in making a casting having an insert, where the cast metal enters spaces within the insert but is preferably prevented from flowing ex teriorly of the insert. One example of such a casting is a cast squirrel cage winding in a stack of laminations for the rotor of a squirrel cage induction motor, in which it is highly desirable to prevent any of the metal from forming a flash on the exterior of the stack. If such flash were permitted on the exterior of the rotor, the efficiency of the motor would be adversely affected by eddy currents generated in the flash.

Heretofore such castings have .been made in metal molds which required at least slight clearance relative to the stack of laminations in order to permit such molds to be placed over the stack. Because of such clearance, together with the fact the diameter of stacks varies slight ly because of Wear in the punching dies, molten metal entered such clearance to form a flash. To get rid of it, a subsequent machining operation was required.

The present apparatus avoids the formation of any such flash on the exterior of the insert and hence avoids the necessity of the machining operation. To this end, the mold .is made of a flexible material, sufliciently heatresistant, and is caused to hug the insert tightly by applying vacuum to the interior of the mold. Flow of molten metal onto the exterior of the insert is thus prevented; The flexible character of the mold also has another advantage in that it can be stretched by applying vacuum to the exterior of the mold. When so stretched, it can easily be slid over the insert, and when the vacuum on the exterior is released and vacuum applied to the in terior, the tight fit of the mold on the insert is accomplished. If desired, to insure such tight fit, air under pressure may be applied to the exterior of the mold to assist the vacuum therein. I

While the winding of a rotor for a squirrel cage induction motor has been referred to hereinbefore and will be described hereinafter as one example of the type of casting contemplated, it is of course obvious that an apparatus and method embodying the invention is useful for casting other items. The apparatus and method embodying the invention may also be used in casting other metals than aluminum, such as lead, zinc, copper and others.

The embodiment of the invention illustrated in the drawing is adapted to cast an aluminum squirrel cage winding in a stack of laminations to form the rotor of a squirrel cage induction motor. The stack of laminations is indicated at 10, and each lamination is provided with an annular series of slots 11, each slot having a narrow opening 12 extending to the periphery of the lamination as shown in FIG. 2. Each lamination is circular in form, so that the stack is cylindrical, and is provided with a center hole to receive the shaft of the motor. The laminations are angularly displaced a small amount relative to each other, so that the narrow openings 12 form elongated helices as illustrated in FIG. 1. The aluminum winding is formed by filling the slots 11 and the openings 12 with molten aluminum and at the same time forming cast annular portions 13 at both ends of the stack, the aluminum of course immediately hardenmg.

The casting apparatus herein shown comprises a base plate 20 on which a lower mold plate 21 is placed. The lower mold plate 21 is provided with a cavity 22 to form one of the annular portions 13 of the rotor and supports the stack of laminations. The cavity 22 thus communicates with the slots 11 in the laminations. On top of the stack 10 of laminations is an upper mold plate 23, similar to the lower mold plate 21 and having a cavity 24 therein to form the other annular portion 13 of the rotor, the cavity 24 also communicating with the slots 11.

The stack 10 is adapted to be clamped between the upper and lower mold plates 23 and 21 and to this end, a rod 25 is threaded at its lower end into the lower mold plate 21 and extends upwardly through the stack 10 and the upper mold plate 23. A C-shape clamp 26 is provided, which has an inwardly turned flange slidably received in notches 27 formed in the rod 25, the clamp 26 hearing against the upper mold plate 23 and thus rigid ly clamping the stack 10 between the two mold plates.

Molten metal may be admitted into the cavities 22 and 24 and the slots 11 through means located at any convenient point. In the present instance, a ring 30 is placed around the lower mold plate 21. The lower mold plate 21 is provided with a gate 31 registering with an angularly shaped passage 32' formed in the ring 30. The passage 32 also registers with a passage 33 extending downwardly through the base plate and a downwardly extending snout 34 formed thereon, the function of the latter being hereinafter described.

The mold, as hereinbefore mentioned, comprises a flexible member in the form of a sleeve 35. The latter is made of a heat-resistant flexible material and in the present instance is made of silicone rubber. This material has sufficient resistance to heat to withstand contact with molten aluminum for a short period of time without deteriorating. In the present instance, molten aluminum contacts the sleeve 35 only in flowing outwardly in the narrow openings 12 and the aluminum is rapidly cooled therein and solidified. The sleeve 35 preferably has a normal diameter slightly less than the diameter of the stack 10 so that it tends to hug tightly against the stack and the two mold plates which are the same diameter as the stack. The sleeve 35 is closed at its upper end by an end wall 36. The sleeve is shown as being longer than the present stack 10 and the two mold plates to accommodate longer rotors, in which case, either a longer rod is utilized or additional notches 27 may be provided in the rod to receive the clamp 26.

At its lower end, the sleeve 35 is enlarged, as at 37, to fit over the ring and extends downwardly, as at 40, at the outer periphery of the ring, where it is provided with an outwardly extending flange 41 lying flat against the base plate 20. The flange 41 forms a seal against the base plate so that a vacuum may be attained within the sleeve, and to render the flange 41 sufliciently flexible for this purpose, a downwardly opening groove 42 may be formed in the lower face thereof to reduce the thickness of the flange for part of its radial width.

Since the sleeve has a normal diameter slightly less than the diameter of the stack 10 and mold plates 21 and 23, it must be stretched to place it over the stack and mold plates. Such stretching may be readily affected by applying vacuum to the exterior of the sleeve. To this end, a cylindrical housing 43 encloses the sleeve 35 in spaced relation thereto. The housing 43 is closed at its upper end by an end wall 44, and is flared outwardly at its lower end, as indicated at 45, and is provided with an outwardly extending flange 46 adapted to seat against the flange 41 of the sleeve.

To apply vacuum to the space between the housing 43 and the sleeve 35 to stretch the latter, the end wall 44 of the housing may be provided with an angularly bent tube 47 leading to a valve 50, the latter being connected to a suitable vacuum pump (not shown). Thus, when the valve is adjusted to connect the tube 47 with the vacuum pump, vacuum will be applied to the space between the housing and the sleeve and the latter will thereby be stretched sufficiently to permit it to 4 easily slid over the mold plates and the stack of laminations. This vacuum will also hold the flange 41 in tight sealing engagement with the flange 46 of the housing so that the vacuum may be maintained in the space.

When the sleeve has been lowered over the stack of laminations and the mold plates, and the flange 41 of the sleeve is seated on the base plate 20, the valve 50 may be adjusted to connect the tube 47 to the outside atmosphere, thus relieving the vacuum in the space between the housing and the sleeve so that the latter may contract into engagement with the stack and the mold plates. The valve 50 is also connected with the interior of the sleeve by a tube 51, and when air at atmospheric pressure is applied to the exterior of the sleeve by adjustment of the valve 50, such adjustment may also serve to connect the tube 51 to the vacuum pump. Vacuum is thus applied to the interior of the sleeve, drawing the latter into tight engagement with the stack and mold plates. If such engagement is found, in any instance, to be insufficient to prevent the molten metal from flowing onto the exterior of the stack, the valve 50 may also be connected to a source of air under pressure so that, by proper adjustment of the valve, air from said source may be introduced into the space between the housing and the sleeve. In such case, the flange 46 of the housing is adapted to be secured to the base plate 20 as by clamps 52 to clamp the flange 41 of the sleeve therebetween. To support the portion of the sleeve above the upper mold plate 23, a rigid cup-shaped support 48 may be placed above the upper mold plate. The length of the support 48 will be varied for different lengths of rotors. When vacuum is applied to the interior of the sleeve, additional pressure will thus be applied to clamp the upper mold plate downwardly on the stack of laminations.

When vacuum is applied to the interior of the sleeve, the passage 33 in the snout 34 must be sealed. The passage 33 is utilized to introduce molten metal into the mold, the vacuum therein being adapted to draw the molten metal in. However, one of the important features of the invention is the prevention of entrapping air in the molten metal as it enters through the passage 33. The passage 33 is therefore kept sealed until the desired vacuum is attained within the sleeve. In one specific instance, the vacuum attained is 5 mm. of mercury. With the passage 33 kept sealed until the desired vacuum is attained, the inrushing molten metal cannot mix with air in the mold during withdrawal of the air. Air pockets in the casting are thereby prevented.

The snout 34 is adapted to be immersed in molten metal contained in a suitable pot, and when immersed, the seal for the passage 33 is removed to admit the molten metal. The seal must be of a character which maintains the sealed condition until the snout 34 has been immersed in the molten metal a suflicient depth to prevent air from being drawn downwardly along the side of the snout from the surface of the metal and entering the lower end of the passage 33. The entrance of the lower end of the snout tends to momentarily depress the surface of the molten metal around the snout, so that the lower end of the snout must be well below the depressed surface of the metal.

A seal for the passage 33, that has been found particularly suitable, comprises a plug in the form of ball 53 adapted to seat in the countersunk lower end of the passage 33. The ball 53 is preferably made of silicone rubber which has been found to be capable of resisting the heat of the molten metal for a short period of time without deterioration. To remove the ball 53 from sealing relation with the passage 33, the ball is connected to a chain 54 or the like attached at its upper, for example, to the base plate 20. To prevent the chain 54 from becoming coated with the metal, it may be enclosed in a protective cover 58 preferably made of silicone rubber. Thus, when the snout 34 has been immersed in the molten metal to the required depth, the chain 54 may be pulled to move the ball 53 from the end of the passage 33. The molten metal may then rush in through the passage 33 in a full stream, drawn in by the vacuum, and the cavities 22 and 24 in the two mold plates and the slots 11 and narrow openings 12 in the stack of laminations will be filled. The metal as it flows outwardly in the narrow openings 12 meets the sleeve 35 and, due to the tight engagement of the sleeve with the stack of laminations, the metal is prevented from flowing onto the external surface of the stack. The metal in the mold plates and laminations quickly solidifies so that the snout may be removed from the molten metal and any molten metal remaining in the snout will run back into the pot as the snout is removed.

The foregoing apparatus and the method involved lend themselves readily to automatic operation. Thus, the base plate may be carried on a conveyor through a series of stations. At one point, the ring 30 and the stack of laminations clamped between the mold plates 21 and 23 may be placed on the base plate. The housing 43 with the sleeve 35, after the latter is stretched by applying vacuum to its exterior, may then be lowered over the foregoing parts. If air under pressure is later to be introduced into the space between the housing and the sleeve, the flange 46 of the housing is secured to the base plate by the clamps 52. However, if only air at atmospheric pressure is to be introduced into such space, the clamps 52 are unnecessary.

When the housing and sleeve are in place, the ball 53 is placed in the opening of the passage 33 and, by manipulation of the valve 50, vacuum is applied to the interior of the sleeve.

Such vacuum holds the ball 53 in place in sealing relation with the passage 33. When the desired vacuum has been attained within the sleeve, the apparatus may be moved to a position over the pot of molten metal and then lowered to immerse the snout 34- in the molten metal. When the snout has been immersed to the required depth, the ball 53 is removed to permit the molten metal to be drawn upwardly into mold to fill the cavities therein. This occurs quickly so that the apparatus can be raised very soon to remove the snout from the molten metal. The apparatus may then be shifted away from the pot, and the housing and sleeve removed.

In FIG. 3, another form of readily removable seal for the lower end of the passage 33 in the snout 34 is shown. The seal in this instance comprises a disc, indicated generally at 55, adapted to seat against the end of the snout. The disc 55 has a peripheral portion 56 shaped to fit the end surface of the snout. The central portion 57 of the disc is preferably crowned downwardly and is adapted to fuse from the heat of the molten metal when immersed therein. The central portion 57 also has suflicient mass to require time of fusing such that the snout 34 may be immersed to the required depth before the fusing occurs. It is dmired to permit a full stream of molten metal to enter the passage 33 when the disc fuses, and it has been found that, by forming the central portion 57 with a slight crown, the entire central portion appears to fuse at the same time, so that a full stream of molten metal enters the passage. The disc is preferably made of the same metal as the molten metal so as not to contaminate it with another metal or material and so that it will readily fuse at the temperature of the molten metal. The disc thus provides a removable seal which provides suflicient time for the snout to be fully immersed before the disc fuses.

I claim:

1. Apparatus for making a casting, comprising means forming a mold cavity comprising at least two cooperating members, means including a flexible sleeve enclosing said first-mentioned means, a housing outside of said sleeve, means cooperating with said first-mentioned means and providing an opening for introducing molten metal into said cavity, means for sealing said opening, and means for applying a vacuum to the interior of said sleeve and thereby draw the sleeve into tight engagement with said cooperating members, whereby, when said sealing means is removed, molten metal is drawn into said cavity.

2. Apparatus for making a casting having an insert, comprising a flexible sleeve adapted to be slid over the insert, means cooperating with said sleeve and providing an opening for introducing molten metal into said sleeve, means for sealing said opening, and means for drawing air from the interior of said sleeve to provide a vacuum therein and thereby draw the sleeve into tight engagement with said insert whereby, when said sealing means is removed, molten metal is drawn into the sleeve but is prevented from flowing exteriorly of said insert between the insert and the sleeve.

3. Apparatus for making a casting having an insert, comprising a pair of mold end plates adapted to clamp the insert therebetween, a flexible sleeve having an internal size slightly smaller than said insert, a housing enclosing said sleeve in spaced relation thereto, means for drawing a vacuum in the space between said housing and said sleeve to stretch the sleeve and thereby increase its internal size so that it may readily be slid over the insert, said vacuum being released when the sleeve is over the insert, means cooperating with said sleeve and providing an opening for introducing molten metal into said sleeve, means for sealing said opening, and means for drawing air from the interior of said sleeve to provide a vacuum therein and thereby draw the sleeve into tight engagement with said insert, whereby, when said sealing means is removed, molten metal is drawn into the sleeve but is prevented from flowing between the insert and the sleeve.

4. Apparatus according to claim 3, including means for introducing fluid under pressure into the space between said housing and said sleeve when the vacuum is released therefrom to assist the vacuum in the interior of the sleeve in holding the sleeve in tight engagement with the insert.

.5. Apparatus for making a casting having an insert, comprising a rigid housing, a flexible sleeve mounted within said housing in spaced relation thereto, said sleeve having an internal size slightly smaller than said insert, a pair of mold end plates adapted to clamp the insert therebetween, means cooperating with said sleeve and said housing and providing an opening for introducing molten metal into said sleeve, means for sealing said opening, and means for drawing a vacuum in the space between said housing and said sleeve and in the interior of said sleeve, including valve means for first drawing a vacuum in said space to stretch said sleeve so that it may readily slide over said insert and said plates, and then for introducing air into said space and for drawing a vacuum in the interior of said sleeve and thereby draw the sleeve into tight engagement with said insert whereby, when said sealing means is removed, molten metal is drawn into said sleeve but is prevented from flowing between the insert and the sleeve.

6. Apparatus for making a casting having an insert, comprising a base plate, means for supporting the insert on the base plate, a flexible sleeve adapted to fit over the insert and to seat at its lower end on said base plate, a rigid housing enclosing said sleeve in spaced relation thereto and having means for holding the lower end of said sleeve seated on said base plate, said base plate being provided with an opening for introducing molten metal into said sleeve, means for sealing said opening, means for drawing a vacuum in the space between said housing and said sleeve to stretch the sleeve so that it may be readily slid over the insert on the base plate and for introducing air into said space when the sleeve is over the insert, and means for drawing a vacuum in the interior of said sleeve and thereby hold said sleeve in tight engagement with said insert, whereby when said sealing means is removed, molten metal is drawn into said sleeve 7 but is prevented from flowing between said sleeve and said insert.

7. Apparatus for making a casting having an insert, comprising a base plate, a lower mold plate resting on said base plate for forming the lower end of the casting and for supporting said insert thereover, an upper mold plate for forming the upper end of the casting, means for clamping the insert between said mold plates, a flexible sleeve adapted to fit over said mold plates and insert, means for applying vacuum externally to said sleeve to enable it to be readily slid over said mold plates and insert and for releasing said vacuum when the sleeve is thereover, said base plate having means providing an opening for the introduction of molten metal into said mold plates and insert, means for sealing said opening, and means for applying a vacuum to the interior of said sleeve and thereby hold said sleeve in tight engagement with said insert and mold plates, whereby, when said opening is immersed in molten metal and said sealing means is removed from said opening, molten metal is drawn into said mold plates and insert but is prevented from flowing between said sleeve and said insert.

8. Apparatus according to claim 7, in which said clamping means comprises a rod secured at its lower end to said lower mold plate and extending upwardly through said insert and said upper mold plate, and a clamping member detachably engageable with said rod and bearing against said upper mold plate.

9. Apparatus according to claim 7, in which said sleeve is longer than said mold plates and insert to accommodate mold plates and inserts of greater length, and a rigid support is located within the interior of the upper portion of said sleeve for supporting the same.

10. Apparatus according to claim 7, in which a ring is fitted about said lower mold plate and has a passage providing communication between the interior of said lower mold plate and said opening.

11. Apparatus according to claim 9, in which said rigid support assists in clamping said insert between said mold plates when vacuum is applied to the interior of said sleeve.

12. Apparatus according to claim 10, in which said sleeve has an enlarged portion at its lower end adapted to fit over said ring and a flange extending outwardly from said enlarged portion and adapted to lie flat against said base plate and to be held in sealing relation therewith when vacuum is applied to the interior of said sleeve.

13. Apparatus for casting an aluminum squirrel cage winding in a stack of laminations to form a rotor for a squirrel cage induction motor, the stack of laminations being provided with longitudinal slots having narrow openings at the periphery of the stack, comprising a flexible sleeve having an internal diameter slightly smaller than said stack, a rigid housing enclosing said sleeve in spaced relation thereto, means for drawing a vacuum in the space between said sleeve and said housing to expand the sleeve so that it may readily he slid over said stack and for releasing said vacuum when said sleeve is thereover, means cooperating with said sleeve and providing an opening for introducing molten metal into said slots, means for sealing said opening, and means for applying a vacuum to the interior of said sleeve and thereby draw said sleeve into tight engagement with said stack, whereby, when said sealing means is removed, molten metal is drawn into said slots and said narrow openings but is prevented from flowing between said stack and said sleeve.

14. Apparatus according to claim 13, in which upper and lower mold plates are positioned at the upper and lower ends of said stack and clamp the stack therebetween, said mold plates having cavities connecting said slots at, their respective ends and being of substantially the same diameter of said stack, said sleeve being drawn into tight engagement with said mold plates as well as with said stack when vacuum is applied to the interior of said sleeve, said lower mold plate having a passage connecting the cavity therein with said means providing an opening.

15. Apparatus for making a casting having an insert, comprising a flexible sleeve having an internal size slightly smaller than said insert, a housing enclosing said sleeve in spaced relation thereto, means for drawing a vacuum in the space between said housing and said sleeve to stretch said sleeve and thereby increase its internal size so that it may readily he slid over the insert, said Vacuum being released when the sleeve is over the insert to permit the sleeve to tightly grip the insert, and means cooperating with said sleeve and providing an opening for introducing molten metal into said sleeve, the tight gripping engagement of the insert by the sleeve preventing the molten metal from flowing between the insert and the sleeve.

16. The method of casting an aluminum squirrel cage winding in a stack of laminations provided with longitudinal slots having narrow openings at the periphery of the stack to form a rotor for a squirrel cage induction motor free of cast metal on the peripheral surface of the stack, said method comprising applying vacuum to the exterior of a flexible sleeve having an internal diameter slightly smaller than said stack to expand the sleeve, placing said sleeve over said stack, releasing said vacuum when the sleeve is over said stack, said sleeve having cooperating means providing an opening for introducing molten metal therein, sealing said opening, applying a vacuum to the interior of said sleeve to draw said sleeve into tight engagement with said stack, and immersing said opening in molten metal and removing said seal, whereby molten metal is drawn into said slots and said narrow openings but is prevented from flowing around the periphery of said stack.

17. The method according to claim 16, including clamping said stack between a pair of mold plates, and placing said sleeve over said mold plates as well as over said stack.

18. The method of making a casting employing a mold provided with a cavity and closely spaced portions forming a slot opening outwardly from the mold cavity, said method comprising sliding a flexible sleeve over said mold; hermetically sealing said sleeve; applying a vacuum to the interior of said sleeve to draw said sleeve into tight engagement with said spaced portions of said mold to close said slot; and establishing communication between the evacuated interior of said sleeve and a body of molten metal whereby said molten metal is drawn into and fills said cavity with the tight engagement of said sleeve with said mold preventing metal from flowing outwardly through said slot.

19. The method according to claim 18, in which vacuum is first applied to the exterior of said sleeve to stretch said sleeve so that it may readily be slid over said insert and thereafter is released when the sleeve is over the insert.

20. The method according to claim 19, in which, when said vacuum applied to the exterior of said sleeve is released, fluid under pressure is applied to the exterior of said sleeve to assist in holding the sleeve in tight engagement with said insert.

References Cited in the file of this patent UNITED STATES PATENTS 1,793,110 Mantei a- Feb. 17, 1931 2,515,654 Kalina July 18, 1950 2,517,902 Luebkeman Aug. 8, 1950 2,781,565 Atchison Feb. 19, 1957 2,807,844 Hemphill Oct. 1, 1957 FOREIGN PATENTS 455,258 Canada Mar. 22, 1949

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