WO2000006899A1

WO2000006899A1 - Magnetically coupled pump

Info

Publication number: WO2000006899A1
Application number: PCT/US1999/016498
Authority: WO
Inventors: John Zavisa; David Michael Terry
Original assignee: Standex International Corporation
Priority date: 1998-07-31
Filing date: 1999-07-21
Publication date: 2000-02-10

Abstract

A magnetic drive assembly for a fluid pump comprises an inner magnet assembly (44) secured to the end of the drive shaft. The drive shaft and inner magnet project from the pump housing at a point encompassed by a canister alignment boss (26). The alignment boss includes an outside cylindrical seal surface surrounded by an annular seal surface (28) that extends normally from said cylindrical seal surface. A closed end seal canister (51) of non-magnetic material having an outwardly turned flange at an open end and a closed opposite end covers the inner magnet and sockets over the alignment boss with a fluid sealed interface with the cylindrical seal surface. A pump-to-motor adapter (60) includes a pump attachment flange turned inwardly to a circular aperture that receives the seal canister body but overlies the canister flange.

Description

MAGNETICALLY COUPLED PUMP

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic drive coupling for a pump. More particularly, the invention comprises a highly effective but inexpensively fabricated seal assembly for a sliding vane pump having a magnetic drive coupling.

Rotation of a pump impeller requires penetration of the pump housing or casement by an axially rotating drive shaft. Confinement of the pressurized fluid within the housing according to traditional designs necessarily requires a dynamic seal between the stationary housing wall and the rotating shaft surface. Although substantially complete dynamic sealing may be achieved for a while, corrosion abrasion or chemical deterioration will eventually compromise the seal. In some applications, such as with highly corrosive or toxic chemicals, fluid leakage from a pump is intolerable. In other applications the leakage may be merely unsanitary, unsafe or disruptive but nevertheless, highly undesirable.

Responsive to such needs, magnet drive couplings have been developed to eliminate dynamic fluid seals around the pump drive shaft. Generally, magnetic couplings include a pair of concentrically aligned annular magnets. An inner magnet is secured to the end of the pump drive shaft. An outer magnet is secured to the motor shaft and aligned to concentrically overlie the inner magnet. Drive torque is transferred from the outer magnet to the inner magnet by the flux field between the magnets. The fluid environments around the two magnets are isolated by an enclosure around the inner magnet and pump drive shaft that is fabricated of magnetic field transparent material. This inner magnet enclosure is statically secured to and sealed against the pump housing. Consequently, there are no dynamic seals that separate the pumped fluid from the surrounding atmosphere.

It is, accordingly, an objective of the present invention to provide a magnetic pump drive having an inexpensive fabrication and assembly cost. Another objective of the invention is a magnetic pump drive having a highly effective fluid seal. Also an object of the invention is a magnetic drive coupling having a minimum number of manufacturing and assembly steps.

SUMMARY OF THE INVENTION

The body or housing of the present invention pump is fabricated with an alignment boss for receiving and securing a non-magnetic material sealing canister about the inner drive magnet. This alignment boss includes a cylindrical outer surface that is aligned coaxially with the pump drive shaft axis and grooved with an O-ring seating channel. Length of the boss cylindrical surface is referenced from an annular sealing face on the pump body that radiates normally from the boss cylindrical surface.

The pump drive shaft usually is an integral extension of the pump rotor and journals. The journals laterally flank the rotor. Bearing plates having outer rim perimeters that interface with the pump rotor cavity secure the location of the rotor/drive shaft axis within the pump housing. Relative to the bearing plate rims, the axes of journal bearing sockets are positioned to seat and confine the respective rotor journals.

The end of the drive stub shaft is tapered to secure a magnet mounting hub by axial friction load imposed compressively by an end screw. A ceramic type inner magnet having an annular configuration is bounded to the magnet hub. A cylindrical canister that is closed at one axial end and open at the other axial end is provided with an inside diameter that is greater than the outside diameter of the inner magnet. The inside diameter of this sealing canister at the open end has a close slip-fit to the outside diameter of the housing alignment boss. The open end of the canister also includes a narrow, outwardly turned flange. Typically, the sealing canister has a non-magnetic stainless steel material composition. An O-ring fluid seal is seated around the outer cylindrical surface of the alignment boss to be compressed by engagement with the sealing canister. The canister open end flange fits contiguously to the annular seal face on the pump housing around the alignment boss.

The sealing canister is secured in place by the inwardly turned flange of a pump-to-motor adapter. This inwardly turned adapter flange overlies the outwardly turned flange of the sealing canister. A plurality of machine screws inserted through the inwardly turned adapter flange and twisted into threaded sockets in the pump housing secures the assembly and clamps the sealing canister flange against the annular seal face of the pump housing.

At its axially opposite end, the pump-to-motor adaptor also includes an outwardly turned flange for attachment interface with an electric motor. Machine screws through the flange and into the motor housing secures the adapter position.

The outer or driving magnet of the assembly is bonded to the inside wall of a cylindrical magnet housing. One axial end of the magnet housing is provided with a motor shaft socket. The other axial end of the magnet housing is open. The inside diameter of the outer magnet is sized to receive the sealing canister therein.

BRIEF DESCRIPTION OF DRAWINGS The preferred embodiments of the invention are described in detail with reference to the drawings wherein: FIG. 1 is an axial cross-section of the invention assembly;

FIG. 2 is a side view of the pump housing; FIG. 3 is an end view of the pump housing; FIG. 4 is an end view of the seal canister;

FIG. 5 is an axial cross-section of the seal canister along the cutting plane 5-5 of

FIG. 4.

FIG. 6 is an end view of the adapter motor flange;

FIG. 7 is an axial cross-section of the adapter along the cutting plane 7-7 of FIG. 6; FIG. 8 is an end view of the adapter pump flange; and,

FIG. 9 is an axial cross-section of the adapter along the cutting plane 9-9 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Relative to the drawings wherein like reference characters designate like or similar elements throughout the several figures of the drawings, FIG. 1 illustrates an assembly of the invention wherein the dominant components comprise the motor 10, the pump 12 and the pump motor adapter 14. The motor housing usually includes an alignment element such as ring 71 that provides a structural circumference about the axis 16 of the motor drive shaft 70. The motor shaft 70 is received within a shaft receptacle 73 in the outer magnet hub 72. A socket screw 73 secures the assembly. The outer magnet cylinder 76 has a rigid structural relationship, preferably integral, with the outer magnet hub 72. An outer magnet body 78 is secured to the inner perimeter of the outer cylinder 76. This outer magnet body is preferably a cylindrically configured annulus formed of a ceramic material such as that described by U.S. Patent No. 5,090,944, for example. The inside diameter of the outer magnet is sized for a close clearance fit over the outer surface elements of the sealing canister 50.

The preferable pump 12 type for the invention is generally characterized as a rotary vane pump. The structural body of the pump includes a housing 20 having an internal rotor cavity 21 and fluid supply/discharge connector bosses 22 and 24.

The rotating elements of a vane pump 12 include a rotor body 30 flanked laterally by journals 34 and 36 and an integral stub shaft 32. The rotor body functions as a guide for a plurality of radially sliding vanes which are the impeller elements for vane type pumps. The journals 34 and 36 are rotatively confined within bearing sockets respective to each of the bearing plates 35 and 37. The outer perimeters of the bearing plates are formed to a sliding axial fit within the rotor cavity 21 and secure the lateral position of the rotor axis 33 relative to the pump housing 20. The rotor assembly is secured in the axial direction at the assembly end of the rotor cavity 21 by a perimeter sealed end plate 38 held in place by an internal snap ring 39. The rotor assembly stub shaft 32 is preferably formed with a tapered outer surface to conform with an inside socket taper in an inner magnet hub 40. A machine screw 42 compresses the internal surface of the hub taper against the external surface of the shaft taper to secure the two elements against relative rotation about the common axis 33. The ceramic material inner magnet 44 is bonded to the outer perimeter of the hub 40. The seal canister element 50 of the assembly illustrated by FIGS. 4 and 5 comprises an axially elongated cylindrical wall 51 and an end closure wall 53. The material substance of the seal canister 50 includes non-magnetic properties such as a stainless steel. Other materials such as non-ferrous metals and high density polymers may also be used to fabricate the seal canister 50. Axially opposite from the end closure wall 53, the canister end is open and surrounded by an outwardly turned flange 52. An alignment boss projection 25 from the pump housing 20 includes an outer cylindrical surface having an O-ring seating groove 28. Circumscribing the boss cylindrical surface is an annular seal face 27. The outside cylinder surface of the alignment boss 26 is given a diameter that corresponds with a close sliding fit within the canister open end. Canister positionment compresses the O-ring 29 for a fluid-tight seal between the internal canister wall and the external wall of the alignment boss. The close radial fit between the canister and alignment boss 26 secures the canister alignment about the rotor axis 33 whereas a securely clamped face of canister flange 52 against the annular seal face 27 of the pump secures the angular alignment of the canister axis with the rotor axis 33.

Face alignment between the canister flange 52 and the pump housing face 27 is secured by an inwardly turned flange 64 of the pump motor adapter 14 as illustrated by

FIGS. 6 through 9. The internal aperture of the flange 64 is greater than the external diameter of the canister wall 51. However, the internal diameter of the flange 64 is less than the outer perimeter diameter of canister flange 52. Consequently, when the machine screws 66 are inserted through the apertures 67 in the flange 64 and turned tightly into threaded sockets in the pump housing, the adapter flange 64 clamps the canister flange 52 in place.

Preferably, a shallow depth ring rabbet 65 is formed around the adapter flange inner perimeter for an additional measure of mutual alignment and to permit a face-to-face seal between the contiguous adapter flange surface and the surface of the pump annular face 27.

Many materials are suitable for fabrication of the adapter 14 but a polypropylene composite with about 30 % (weight) glass fiber provides a strong, dimensionally stable, corrosion impervious and accurately castable component.

The internal diameter of the adapter body 60 is sufficiently greater than the external diameter of the outer magnet cylinder 76 for convenient assembly. At the motor end of the adapter 14, a ring rabbet 63 meshes with the motor alignment ring 71 for concentric radial alignment of the motor flange 62 about the motor axis 16. Machine screws not shown are positioned through the motor screw apertures 69 and twisted tightly into threaded sockets in the housing of motor 10. Gland channels 68 in the motor flange 62 body provide additional environmental isolation of the adapter interior.

It is to be noted from the foregoing description of the invention that no fluid sealing is attempted between pump impeller elements and the rotating elements of the inner magnet. The inner magnet rotates in the wet presence of the pumped fluid, whether gas or liquid. However, to escape canister 50 enclosure, the fluid must defeat the cylindrical O-ring seal 29, the seal between the annular face 27 and the canister flange 52 and the seal between the annular face 27 and the adapter flange 64. Since all of these seals are static, the seal integrity is not compromised by abrasive particles carried by relatively sliding elements.

Note also the fact that the tool heads of the pump mounting screws 66 are inside of the adapter enclosure for an aesthetically clean appearance.

Having fully described our invention, those of ordinary skill will understand the corresponding equivalents. As our invention therefore,

Claims

WE CLAIM

1. The combination comprising a pump having fluid impeller means confined for rotation within pump housing means, said impeller means being driven about an axis of rotation by drive shaft means having an end projecting from said impeller means along said axis of rotation, said axis of rotation being laterally confined within said housing means, said housing means having a canister alignment boss substantially circumscribing the projecting end of said drive shaft means, said alignment boss also having a substantially cylindrical surface concentric about and parallel with said axis of rotation and an annular seal surface substantially circumscribing said cylindrical surface and normal thereto, the projecting end of said drive shaft means having inner magnet means secured thereto; a substantially cylindrical seal canister having an open axial end, a closed axial end and a substantially cylindrical wall therebetween about an internal canister volume, said open axial end being substantially circumscribed by an external flange and an internal perimeter, the external flange having a greater outside diameter than an outer surface of said cylindrical wall, said internal perimeter having a sliding seal fit relationship over the cylindrical surface of said alignment boss, the internal canister volume substantially enclosing the projecting end of said drive shaft means and the magnet means secured thereto, said seal canister being formed of non-magnetic material; and, pump adapter means having a pump flange at one end, a motor flange at an opposite end and an internal adapter volume therebetween, said pump flange circumscribing a substantially circular aperture having an inside diameter less than an outside diameter of said external flange of said seal canister but greater than an outside diameter of the cylindrical wall, said pump flange having an assembly face about said aperture substantially corresponding with the annular seal surface of said housing means whereby compressive fasteners through said pump flange compress said canister flange against said annular seal surface.

2. The combination described by claim 1 wherein the fit of said seal canister over the cylindrical surface of said alignment boss is sealed by an O-ring.

3. The combination described by claim 2 wherein an O-ring seating groove is formed about the cylindrical surface of said alignment boss.

4. The combination described by claim 1 wherein the assembly face of said adapter means pump flange comprises a rabbet channel about said aperture corresponding with the outside diameter of the seal canister flange.

5. The combination described by claim 1 wherein said fluid impeller means comprises sliding vane elements confined within a rotating hub.

6. The combination described by claim 5 wherein said impeller means axis of rotation is laterally confined within said housing means by bearing plates whereby said rotating hub is disposed between said bearing plates.

7. The combination described by claim 1 further comprising a motor having a rotating power shaft, said power shaft having outer magnet means secured thereto for rotation with said power shaft, said outer magnet means having an interior open space for receiving said seal canister therewithin.