Patent Application
20090062020
The present invention is directed to shaft couplings and, in particular, to couplings for use in magnetic-drive pumps. Magnetic-drive pumps comprise a dry portion, which is connected to a power supply, and a wet portion, which is connected with a source of working matter. The wet portion is separately encased within a sealed shell that isolates the wet portion from the dry portion such that the need for sealing the dry portion is avoided and the wet portion can be placed in direct contact with the working matter. The dry portion typically comprises and electric drive motor that rotates a magnetic outer drive, while the wet portion typically comprises a centrifugal impeller that is connected to a magnetic inner drive. The inner drive is concentrically disposed within the outer drive such that the inner drive is magnetically coupled to the outer drive through the sealed shell of the wet portion. Thus, as the outer drive is driven by the electric motor, the inner drive rotates to turn the impeller to pump the working matter. Thus, the wet portion, including the inner drive, is directly exposed to the working matter. Furthermore, the working matter is used as a lubrication to facilitate rotation of the impeller on a non-rotating shaft in conjunction with a sleeve-type bushing. In order to reduce the need for sealing the wet portion and to permit the use of the pump with corrosive materials, the operative components of the wet portion, including the impeller, the non-rotating shaft and the sleeve-type bushing, are encased in or comprised of corrosion resistant materials such as polymers or resins.
In typical inner drive assemblies, the shaft is rigidly mounted to a wet portion housing such that it does not rotate, and the bushing is fitted over the shaft such that it is permitted to rotate. The bushing is then rigidly connected to the inner drive and the impeller such that as the inner drive is rotated by the outer drive, the impeller is driven to pump the working fluid. Typically, the bushing is connected to the inner drive through a force fit or a keyed connection. However, keyed connections require that the bushing and the inner drive be properly aligned in the axial and radial directions before assembly. Furthermore, keyed connections require tight tolerances to reduce the potential for slippage and failure of the keyed connection. Force fit connections also require tight tolerances in order to transmit the required torque from the inner drive to the bushing, which also makes the force fit difficult to disassemble. Inner drive assemblies including keyed connections or force fit connections incur increased manufacturing costs in order to produce the tight tolerances required for the connections. Furthermore, keyed connections and force fit connections require that each bearing and each inner drive be individually matched for each specific pump, which inhibits interchangeability of standardized components. Additionally, the assembly and disassembly concerns associated with keyed connections and force fit connections increase the burden of performing maintenance of the pump. For example, it is sometimes necessary to change out the inner drive if the magnets become demagnetized. There is, therefore, a need for a coupling that facilitates ease of manufacture, repeatability and interchangeability, while also maintaining compatibility with corrosive working matter and the sealless pump design.
The present invention is directed to a keyless coupling assembly for connecting concentric shafting components. In one embodiment, the keyless coupling assembly comprises a first shafting member, a second shafting member and a plurality of torque strips. The first shafting member comprises an annular body and an inner surface disposed within the annular body. The second shafting member comprises a cylindrical body and an outer surface. The cylindrical body is disposed within the inner surface of the first shafting member. The outer surface encircles the cylindrical body and faces the inner surface. The torque strips are positioned between the outer surface and the inner surface to form anti-rotation grooves to prevent relative rotation between the first and second shafting members.
Magnetic coupling assembly 16 includes coupling housing 28, which connects wet housing 18 with drive motor 26. Within magnetic coupling assembly 16, an outer drive connected to a drive shaft of motor 26 is magnetically coupled to an inner drive that rotates about a stationary shaft within wet housing 18. The inner drive is connected to the impeller such that torque from motor 26 is transmitter to the impeller. The outer drive is separated from the inner drive by a barrier within wet housing 18 such that the process fluid flowing through housing 18 is isolated from dry portion 14. As such, pump 10 is also referred to as a sealless pump due to the lack of the need for sealing off the dry portion from the process fluid. Thus, pump 10 is frequently used in conjunction with harmful or hazardous process fluids, such as acids, or food products since the impeller can be placed in direct contact with the process fluid in a safe and sanitary manner. In order to further facilitate the corrosion-resistant and sanitary properties of pump 10, and to reduce interference with the magnetic coupling, wet parts (i.e. parts coming in to contact with the process fluid) are made from corrosion resistant, non-metallic materials. In particular, the inner drive is enclosed within a polymeric material to isolate magnets within the inner drive from the process fluid. The inner drive is mounted to the stationary shaft through a bushing that is sheathed in a polymeric material, as better shown in
Drive motor 26, which, in one embodiment, comprises a magneto-electric motor, is connected to an electric power source and converts electrical power input into a mechanical shaft power output at drive shaft 34. Coupling housing 28 connects drive motor 26 to wet housing 18 of wet portion 12. Coupling housing 28 is connected to drive motor 26 and wet housing 18 with, for example, threaded fasteners 52. Coupling housing 28 comprises a cylindrical shell that not only provides a structural frame for pump 10, but also provides a sealed enclosure in which magnetic coupling assembly 16 is disposed, thus isolating outer drive 42 and the operative side of drive motor 26 from potentially harsh operating environments. In one embodiment, wet housing 18 and coupling housing 28 are comprised of cast iron, stainless steel, alloys or other metals. Outer drive 42 is connected with motor shaft 40 through, for example, a keyed connection at joint 51 (key not shown). Outer drive 42 comprises an annular cylinder into which outer magnets 44 are mounted. Accordingly, outer magnet assembly 44 is rotated about pump centerline A as drive motor 26 drives output shaft 40. Outer drive 42 is also sized to receive inner drive assembly 30. Inner drive 50 of inner drive assembly 30 includes an annular ring of magnets that form a magnetic coupling with outer magnet assembly 44 of outer drive 42. Thus, as drive motor 26 rotates outer magnet assembly 44 about inner drive assembly 30, inner drive 50 rotates impeller 34 about centerline A within wet housing 18.
Wet housing 18 comprises an annular body in which inner drive assembly 50 is disposed to interact with outer drive 42, and impeller 34 is disposed to receive working matter W at inlet 22. Inner drive assembly 50 is disposed about centerline A on shaft 46 within wet housing 18 such that inner drive 30 is able to rotate impeller 34 about shaft 46. Impeller 34 comprises an annular disk that includes a plurality of helical blades that react with incoming working matter W. Impeller 34 includes a large axial opening for receiving working matter W from inlet 22, and an elongate annular opening for dispersing working matter W to outlet 24. As outer drive 42 rotates inner drive 30, impeller 34 sucks working matter W into the axial opening, such as through a pipe connected to flange 56 of wet housing 18. Working matter W continues through impeller 34 and is expelled from pump 10 at outlet 24 into, for example, a pipe connected to flange 58 of wet housing 18.
Shaft 46 is anchored within pump 10 by shell 32 and thrust ring 36. For example, shaft 46 is press fit into bores within shell 32 and thrust ring 36. The outer periphery of shell 32 is clamped between wet housing 18 and coupling housing 28. Thrust ring 36 is disposed within inlet 22 and comprises an annular disk through which working matter W is permitted to enter pump 10. Thrust ring 36 assists in supporting thrust bearing 38 within housing 18. Thrust bearing 38 provides an axial running surface upon which impeller 34 is permitted to rotate. Shell 32, thrust ring 36 and shaft 46 are thus maintained stationary by wet housing 18 during operation of pump 10 such that impeller 34, inner drive 50 and bushing 48 rotate around shaft 46. Shell 32 also comprises a dome-like annular body into which inner drive assembly 30 is situated to provide a barrier between outer drive 42 and inner drive assembly 30. Likewise, the interior of wet housing 18 is lined with lining 54 such that inner drive assembly 30 and impeller 34 are encapsulated in a sealed, sanitary and corrosion-resistant chamber. In one embodiment, shell 32, lining 54 and thrust ring 36 are comprised of a non-conductive plastic resin such as ethylene-tetra-fluoro-ethylene (ETFE) with a carbon fiber filler for strength. Likewise, the other wet parts of pump 10 are themselves comprised of or encapsulated in corrosion-resistant materials. Shaft 46 is comprised of a high-strength, corrosion-resistant, durable material such as ceramic, silicon carbide, tungsten carbide, alumina, bauxite, zirconia, stainless steel, forged aluminum or the like. Impeller 34 is comprised of a fiber reinforced plastic such as a mixture of polyacrylonitrile (PAN) carbon fiber and ETFE. Thus, working matter W is provided with a sealed flow path that can be directly integrated into a pipeline with reduced risk of foreign matter entering the flow of working matter W. Working matter W is also circulated through impeller 34 to lubricate and facilitate rotation of bushing 48 about shaft 46. For example, working matter W is permitted to enter the inner diameter of bushing 48 along axial groove 59 positioned on shaft 46.
Impeller 34 is connected to both bushing 48 and inner drive assembly 50 such that the three components rotate in unison about shaft 46. Bushing 48 comprises a bearing having wear surfaces that facilitate rotation of bushing 48 about shaft 46. Inner drive 50 comprises magnets and other means for transmitting torque to bushing 48 and impeller 34. Inner drive 50 is connected to bushing 48 through the keyless coupling of the present invention.
Bushing 48 comprises two journal or sleeve-type bearings that utilize working matter W as a lubricant. In one embodiment, bushing 48 utilizes a partial hydrodynamic film lubrication, in which a thin film of working matter W is provided between shaft 46 and bearing 48 to lubricate the surfaces of bushing 48. Radial bearings 60 and spacer 62 are typically comprised of inert materials such that they can contact working matter W without reaction. In one embodiment, radial bearings 60 comprise silicon carbide and spacer 62 comprises Teflon. Radial bearings 60 provide a wear-resistant surface which rotate on stationary shaft 46. However, spacer 62 has a slightly larger inner diameter than radial bearings 60 such that a pocket is formed between radial bearings 60 when bushing 48 is fitted over shaft 46. Working matter W is trapped within this pocket between spacer 62 and shaft 46 such that a thin-film bearing is formed to provide partial support to bushing 48. Spacer 62 provides a low-resistance surface upon which working matter W circulates. Typically, bushing 48 is fitted over shaft 46 such that an approximately 0.003 inch (˜0.00762 cm) clearance is provided between shaft 46 and the inner diameter surfaces of radial bearings 60. The outer diameter of radial bearings 60 and spacer 62 are encased within sleeve 64. Sleeve 64 also comprises an inert material such that it is able to contact working matter W without reacting. However, sleeve 64 must also be comprised of a material suitable for receiving torque transmitted from inner drive 50.
Inner drive 50 transmits torque imparted by outer drive 42 to impeller 34 and bushing 48, and includes yoke 66, drive ring 68, magnets 70, spacer 72 and outer shell 74. Yoke 66 provides a structural reinforcing member for inner drive 50. Yoke 66 typically comprises a magnetic metal such as a cast iron or steel. Along with drive ring 68, yoke 66 also provides a flange that is inserted into a notch in impeller 34 at joint 78. The bottom of yoke 66 is ridged to provide an intermeshed connection with outer shell 74. Yoke 66 provides a platform on which to mount magnets 70 and spacer 72. Magnets 70 comprise an annular array of magnets sized to fit within outer drive 42 (
Outer surface 90 includes anti-rotation grips 80, which comprise protrusions extending radially from surface 90. Upon full insertion of bushing 48 into inner bore 86 of inner drive 50, outer surface 90 adjoins inner surface 88 such that anti-rotation grips 80 are disposed between outer surface 90 and inner surface 88. The outer diameter of outer sleeve 64 is sized such that a clearance fit is produced between sleeve 64 and inner surface 88. In other embodiments, the outer diameter of outer sleeve is slightly larger than the diameter of inner bore 86 such that a loose force-fit is produced upon insertion of bushing 64 into bore 86. The height of anti-rotation grips 80 are sized such that a tighter force-fit connection is formed when bushing 48 is pushed far enough into bore 86 such that anti-rotation grips 80 engage inner surface 88. Anti-rotation grips 80 do not extend to the end surfaces of sleeve 64 so that bushing 46 is more easily inserted into inner bore 86 at either end of bushing 46 before anti-rotation grips 80 begin. For example, in one embodiment, anti-rotation grips extend across approximately sixty percent of sleeve 64. Additionally, outer surface 90 and inner surface 88 are circular in shape such that bushing 46 fits into inner bore 86 in any radial orientation. This facilitates easy assembly by eliminating the need to radially align bushing 48 with inner drive 50. Furthermore, bushing 48 can be repeatedly removed from bore 88 such that maintenance or repair of inner drive assembly 30 is easily performed.
In various embodiments, the geometry and number of anti-rotation grips 94 is configured to permit slippage between first body 98 and second body 102 in the event of an over speed situation. For example, in the case of pump 10 (
Anti-rotation grips 94 thus provide a convenient, low cost and effective means for joining and limiting relative rotation of concentric shafting members. Anti-rotation grips 94 are easily manufactured into a mating surface of a shafting member without the need for machining a key slot with tight tolerances, which increases manufacturing costs. As such, greater interchangeability of bushing 46 and inner drive 50 is achieved. Anti-rotation grips 94 also facilitate easy initial insertion of one shafting member into another without the need for aligning or clocking the two members. Anti-rotation grips 94 provide a tight, rigid connection capable of transferring torque loads commonly associated with centrifugal pumps and other shafting applications. Anti-rotation grips 94 also permit rapid and easy disassembly of shafting components in a manner that permits reassembly.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
