WO2000064028A1

WO2000064028A1 - High efficiency submersible electric motor and components

Info

Publication number: WO2000064028A1
Application number: PCT/US2000/010493
Authority: WO
Inventors: Christopher L. Demler; Dale K. Carlock
Original assignee: Thermo Black Clawson Inc.
Priority date: 1999-04-20
Filing date: 2000-04-19
Publication date: 2000-10-26

Abstract

The magnetic members of the motor and/or a related magnetic bearing has poles (52) formed by laminations of a magnetic sheet material and slots (60) are formed between poles and are filled with material such as epoxy (65) to form a smooth circumferential surface and bridges the gaps between the laminations in a continuous manner. The coating has a thickness that does not substantially increase the magnetic pole gap and comprises a wear resistant, nonconductive and nonmagnetic solid fiber that seals the exposed surfaces of magnetic components permitting operation in direct contact with corrosive process fluids.

Description

HIGH EFFICIENCY SUBMERSIBLE ELECTRIC MOTOR AND COMPONENTS

BACKGROUND OF THE INVENTION In many instances it is desirable that a motor and related components be designed to operate with its major electrical components submerged in liquid material being processed. This may require the motor and/or stator magnetic components to come into direct contact with such process liquid.

The immersion of motors within a liquid being processed has generally been limited to systems in which such liquids are not, themselves, highly corrosive to the exposed motor components. Thus, submersible motors, in which the motor magnetic components operate in a wet condition, i.e.. wetted by the liquid being processed, have been successfully used in petroleum pumps, refrigeration systems, and other systems in which destructive or corrosive liquids, such as water or water based products, are absent, and in which the process liquid is a constant and is relatively benign with respect to the magnetic components. On the other hand, submersible electric motors as used, for example, in down-hole installations such as wells, sump pumps, and the like, are submersible in the context that the package is located within the fluid mass while the motor itself is encapsulated or canned such that the motor stator, and usually also the motor rotor, are dry, and the shaft extends externally of the encapsulating member to drive a processing element, such as a pump, employing shaft seals to maintain the dry integrity of the motor. Further, in instances where both the stator and the rotor are separately encapsulated, the encapsulating material necessarily extends through the magnetic gap separating the poles of the stator and the rotor, frequently increasing the separation gap with a resultant loss in efficiency and, frequently, interposing a material in the gap which itself induces a losses. Such further loss in efficiency is not only caused by the increase in the gap dimensions but also in eddy current loss, to the extent that such material is conductive, and magnetic loss to the extent that the material has magnetic properties. For example, stainless steel encapsulation can insert a loss as high as about 10% due to eddy current losses.

Current packing and sealing systems and practices are believed to be a major source of failure of electric motor driven systems, including bearing failures, unscheduled maintenance requirements, and safety concerns. The conventional packing systems and mechanical seals are deemed to be far from ideal due either to maintenance, initial cost, or their lubrication requirements. In systems for processing potentially corrosive fluids, a particularly acute problem is that of protecting the rotor and/or stator laminations. The laminations, in order to have excellent electrical and magnetic properties, are formed of a relative "soft" iron product that can be formed or stamped, and stacked. Therefore, such materials with good magnetic and conductive properties are inherently prone to damage due to the corrosive effect of liquid being processed. Such liquid may be as innocuous appearing as water that has been "softened'^" by the replacement of the calcium ions with sodium ions, as well as the more obvious condition when a water based liquid has either an unusually high or low pH or contains abrasive particles or both.

The chemical and severe process industries use submersible motor driven pumps in process machinery to minimize environmental and safety risks of through-shaft machinery. To protect the motor laminations and other components from the process, typically a stainless steel can or film, or an engineered plastic, has been used to isolate the motor components. Stainless steel cans can be welded, shrink-fitted, or otherwise attached to the motor rotor and stator. As previously noted, this material is sufficiently conducted so that a .005 thick stainless steel layer can result in a 6-8% efficiency loss. Often, such a thin can itself is not practical for many manufacturing operations and a thicker can is required, bringing the losses up to about 30%. Such losses result in heat that further complicates or compromises the motor insulation and its cooling design.

Similarly, plastic encapsulating cans are typically cast iη an engineering plastic material that has been chosen so as not to react with the processed liquid. Again, depending on pressures and temperatures, fiber reinforcements have been used to create a structurally sound product, resulting in thicknesses that cause the motor "air'^* gap to be widened well beyond ideal. Therefore, efforts in plastic can encapsulation have resulted in reduced motor efficiency in exchange for motor protection.

Many technologies could benefit from a fully submerged motor, free of drive shaft seals, free of through shafts, and providing a smaller footprint, but cannot justify the manufacturing and/or operating cost disadvantages of current technology. A need accordingly exists for a motor design that permits efficiencies in packaging, safety, and low maintenance with no decrease in efficiency, and at a competitive cost.

SUMMARY OF THE INVENTION This invention relates to electric motors and other similar electrical components, such as magnetic bearings, in which the otherwise exposed poles are sealed with a thin water impervious and non-magnetic solid film layer that permits full and continuous immersion of the motor into the process liquid. The motor design is particularly adapted for use in the integrated paper pulp and process machinery', such as the wholly enclosed paper pulp refiner shown in Applicant^'s published International application WO 99/52197. incorporated herein by reference. In that application a switched reluctance motor is integrated into a twin-disc paper pulp refiner, in which a processing rotor is suspended on magnetic bearings, and processing refiner discs are formed or carried at each end of the rotor. The abutting faces of the supporting magnetic bearings as well as the driving rotor and stator are wetted by the processing liquid, and the entire rotation assembly is enclosed within the refiner housing with no external shaft or other moving components. The invention is directed to an immersible motor or related electrical component, such as a magnetic bearing, and a process, in which a laminated stack forming a magnetic pole is continuously sealed over the face of the pole and between adjacent poles with a thin solid film layer such that the pole is isolated from process liquid, the working gap is not increased, and the magnetic efficiency is not compromised. In the realization of the invention, the electrical component, at least at the pole faces, is covered with a polymer layer having a thickness that preferably does not substantially exceed 0.008 inches, extends between adjacent laminations without gaps or cracking, is bonded to the metal of the poles, and has low porosity, conductivity, and minimal magnetic properties. The laminated components of the rotor and stator, including corresponding components of the magnetic bearings, are characterized by one or more of the following: 1 ) The relative surfaces following treatment are smooth to minimize drag loads and have low friction surface characteristics.

2) The sealing layer has a surface bond with the laminations and with other components to which it may be bonded, the material provides a seal with a thickness, at the magnetic gap, preferably not substantially exceeding about 0.008 inches, except as may be acceptable for large rotating components.

3) The surface preparation does not damage the laminations or interrupt the existing lamination-to-lamination insulation, and bridges the gaps between laminations. 4) The sealing layer is a solid film material after curing, does not crack with flexing and resists wear.

5) The coefficients of expansion and contraction are in harmony with those of the steel laminations and other parts, such as end plates and the like with which the coating layer come into contact. 6) The sealing solid film material has extremely low porosity to fluids and has minimal water absorption, and withstands the process temperature range and pH range, and the motor operating temperature up to the temperature rating of the motor insulation, commonly about 250 °F.

7) The sealing solid film material withstands the rotational turbulence and the abrasion of solid materials carried within the process liquid.

8) The sealing solid film material requires little if any maintenance and if damaged, is field repairable.

9) The sealing solid film material has good dielectric properties, that is extremely low electric conductivity, and have little or no magnetic properties. In addition to protecting the stator and/or rotor magnetic poles from corrosion, it is also desirable to protect the pole surfaces from wear. In applications such as described in the above-identified International published application, cellulose fibers and paper pulp are generally abrasive and can erode susceptible surfaces with which they come in contact by reason of the process. The motor components of this invention have the otherwise exposed surfaces sealed and encapsulated by a solid film coating that also preferably has lubrication qualities and is highly resistant to erosion by reason of impact and contact with such solids in the process medium.

Suitable compositions for this purpose include urethanes that have small molecular size and therefore low porosity, such as fluorinated polyurethanes sold under the trade name ELIXIR and sold by 21^s' Century Coatings. 12074-86^,h Avenue, Surrey. British Columbia, V3W 3H7 Canada.

A further and preferred coating material is a metal filled and proprietary epoxy-based resin sold under the trade name EVERLUBE 10026 by E/M Corporation of 14830 Twenty-Three Mile Road. Shebly Township, Michigan 48006. Another suitable product for the hard film coating is sheet polyetheretherketone (PEEK) sold under the trade name of ARLON available from Greene Tweed. 2374 North Perm Road. Hatfield. Pennsylvania 19440. The thin PEEK films may be applied by an epoxy or using thin 3M double side adhesive tape No. 9731.

In the manufacture of the motor components of this invention the outside diameter of the rotor and the inside diameter of the stator, in the spaces between the poles, are filled with a suitable filling epoxy and formed into smooth cylindrical shape using forms that conform closely to the inner or outer diameter, as the case may be. and the interstices or pole gaps are filled such as with an epoxy, and cured with the forms in place so that a smooth O.D. or I.D. is formed and in which the pole laminations, forming part of the circumference, are exposed. The rotor or stator pole slots between poles may be partially filled with a "stick." that is, an axially extending strip of phenolic or pultruded fiber glass or other suitable rigid or semi-rigid filler material. This may be more relevant for the rotor slots than for the stator slots in view of the fact that the stator slots taper toward each other and therefore form a self-locking shape. The filling epoxy must be hard when cured so that it does not flex and crack the solid film coating to be applied on the exposed cylindrical surface. Non-magnetic fill members as disclosed in U.S. Patent 5,053,666 may alternatively be used to fill the rotor slots provided that the material used meets the conditions as previously stated for the epoxy fill material. When suitably filled, rotor and stator surfaces are formed in which the physical gaps between poles are eliminated to form cylindrical smooth surfaces. The epoxy surfaces may be roughened slightly by sanding or beadblasting to provide a better surface for adhesion of the solid film coating. Also, the filling materials used should have consistent coefficients of thermal expansion with the rotor shaft and laminations, and in the case of the stator, with the stator body. Similarly, the rotor end plates where used should be consistent with this requirement or designed so that they do not create coating cracking where the components may have a different expansion or contraction rate with temperature.

Where magnetic bearings are used, such as the bearings 24 as described in the above-reference International application, the exposed pole surfaces are treated in accordance with this invention and the remaining electromagnetic structure is encapsulated to permit emersion of the bearing magnets.

In the bearings as used in a preferred embodiment of the above International application, the rotor of the active magnetic bearing system does not have poles so that the O.D. surface is smooth and does not require any forms or molds. Therefore, the solid film coating and lubricating film may be applied directly to such surface. In some instances, it may be desirable to apply the protective wear resistant solid film coating around the immediate pole edges as well as the pole faces, in the case of magnetic bearing stator components. Then, the entire assembly can be capsulated in a suitable polymer such as polyurethane or silicone so as to protect and seal the winding, as magnetic gap and space requirements are not a concern in areas remote from the poles.

It is accordingly an important object of this invention to provide motor components and magnetic bearing components that may be totally or fully immersed in corrosive process liquid, in which the pole faces are coated with a thin solid film coating of wear resistant nonconductive and nonmagnetic material providing a continuous seal on and between the pole laminations of such components.

Another object of the invention is the provision of a method for protecting otherwise exposed magnetic laminations of a motor/stator or of a shaft supporting magnetic bearing that is, in use, immersed in a corrosive process liquid in which a solid, low friction hard film-type coating is applied to the exposed lamination surfaces and bridging the gaps between laminations to provide a seal with high integrity, and having a thickness at the lamination surfaces sufficiently small so as to operate within the optimum magnetic gap distance without having to increase the magnetic gap because of the film or films.

A still further object of the invention is to provide an improved electric motor and/or a magnetic bearing as outlined above, in which both the rotor and stator may be immersed in corrosive processed liquid, with minimal losses in efficiency and in total magnetic gap spacing.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRA WINGS

Fig. 1 is a partial section through a rotor treated in accordance with this invention:

Fig. 2 is an enlarged partial transverse sectional view of the rotor of Fig. 1 taken along lines 2 - - 2 of Fig. 1 ; Fig. 3 is an enlarged partial sectional view through a motor stator and rotor treated in accordance with this invention;

Fig. 4 is a perspective view of the stator of a typical conical magnetic bearing; and

Fig. 5 is an enlarged view of one of the magnet segments of the bearing of Fig. 4 that has been treated and sealed in accordance with this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, Figs. 1 and 2, as well as the central portion of Fig. 3, represent a switched reluctance rotor 10 mounted and keyed onto a support shaft 12. For the purpose of this invention, the shaft 12 may be likened to the shaft 15 of the above-referenced International patent application in that the ends 13 and 14 may be supported or mounted on suitable bearings, such as magnetic bearings, and positioned wholly within the housing of the motor, with the opposite ends of the shaft being connected for driving a rotating refiner disc or other suitable processing apparatus, while the rotor 10 and its related shaft 12 are wholly submerged within the processing fluid, such as a slurry of water and ground wood fibers. The rotor 10 includes the usual poles 15 formed by stacked or laminated individual magnetic plates 16, and the poles are separated by slots 17 (Fig. 2).

The ends of the poles 15 are commonly exposed at the periphery or circumference of the rotors 10, and in many applications, where the rotor is operated dry, the slots 17 may be permitted to be open and unfilled. However, for the purposes of this invention, the slots 17 are filled and extend axially between nonmagnetic rotor end plates 18 and 19, as shown in partial section in Fig. 1. The major volume of the slot 17 are preferably filled by a reinforcing rod 20 that extends between recesses 21 formed in the respective end plates, and through a center opening formed in a central support plate 24 (not required for shirter motors or low speed motors). The rods 20 are likewise formed of non-magnetic material such as phenolic or pultruded fiberglass.

The length of the slots 17 are then filled with an epoxy 25 while the rotor 10 is held in a form, not shown, so that the epoxy. at its radial outer portion, conforms accurately to the circumference defined by the exposed surfaces 27 of the poles 15 and fully fill in the space surrounding the rods 20. After such forming and curing, the form is removed and the poles surfaces 27 are exposed as well as the associated continuing surface of the fill epoxy 25. In this manner, the slots are filled and do not interact with the process fluid to cause drag. The epoxy materials 25 may be locked in place by forming the laminations 16, near the pole ends or surfaces 27, by an undercut or notch 28 thereby defining a circumferentially inwardly formed boss 30 that tends to lock the epoxy 25 in place within the rotor.

Alternatively, in lieu of the epoxy 25, top "sticks" may be used to fill the rotor slots and define the arcuate continuation surface between the stator ends or poles 15 such as in the manner described in U.S. Patent 4,147,946 issued April 3, 1979, provided that the insert or "stick" is made to conform to and define a surface arcuately continued from the poles across the slots.

It will be understood that the pole ends 27 define a slightly irregular surface consisting of the terminal curved ends of the individual rotor lamination 16, therefore, a surface not entirely smooth but defined by slight undulations interrupted by the co-joining side walls of the individual laminates. It will be understood that the laminations themselves commonly have oxidized or treated side walls that isolate and insulate the laminations from each other to break up the flow of eddy currents, and in doing so, leave the ends of the laminations exposed and invite intrusion of liquid between adjacent laminations. This surface as well as the intervening outer arcuate surfaces 30 of the filled slots 17 and the coaxially joined outer surfaces of the end plates 18 and 19, and center plate 24, are coated or covered with an unbroken extremely thin solid film layer 40. shown with exaggerated thickness in Figs. 1 and 2. The layer 40 preferably has a thickness between about 0.002 to 0.008 inches, is bonded similarly to the exposed surfaces of the poles 15 and the exposed surfaces of the fill 25 and the end rings and center rings as necessary, and bridges the eddy gaps between laminations while following the contour of the undulations, to provide a seal and moisture barrier having high integrity. As previously noted, it is preferred to use one of the above-defined materials, with EVERLUBE 10026 being a preferred material as it can be applied as a liquid and cured in place. The solid film coating 40 also acts as a solid film lubricant and therefore decreases the friction loss of the rotation of the rotor and. in the case where the rotor is suspended on magnetic bearings, reduces the likelihood of wear at rotor start up or during unintended rotor excursion into contact with the stator.

Referring to the fragmentary sectional view of Fig. 3, a stator 50 defines poles 52 by individual stacked stator laminations, defining an inside diameter at exposed pole faces 55. Stator coils 58 are formed in coil slots 60, the open ends of which are closed by an epoxy material 65 which the slots are closed by a form. The material may be the same as the epoxy 25 of the rotor. Epoxy 65, at the inner pole slots, is locked and held in by depressions 67 and protuberances 68 at the open ends of the slots, but the converging side walls of the slots also helps to hold the epoxy in place. The epoxy fills the slots and defines an inner diameter surface that is an arcuate continuation of the stator pole faces 55. The magnetic pole faces 55 and the intervening continuous slot spaces are similarly coated with a coating 70 and cured, preferably identical to the coating 40 described above.

Fig. 4 represents an array of individual magnet members 80 defining the conical inside surfaces 82 of the stator part 85 of a magnetic bearing. It will be understood that a conical stator rotor, tapered to conform to the surfaces 82, would be mounted on a shaft within the magnetic stator 85 and would have a smooth outer conical surface that may also be protected with a coating identical to coating 40 in accordance with this invention. A single magnet 85a is shown in Fig. 5 in which the major portion of the magnet body, remote from the exposed magnetic surface 82, is encapsulated by being molded in an enclosing layer of high temperature urethane or silicone 90. The encapsulating layer 90 extends to but does not include the magnetic face 82. These faces including the surrounding magnet edges, are encased in a thin solid film coating of a nonconductive and nonmagnetic wear resistant material 92 identical to the materials described in connection with film layer 40.

It is accordingly seen that the invention provides rotating electrical magnetic components including rotors, stators. and magnetic bearing components, that have magnetic pole pieces encapsulated and protected by thin polymeric solid film coatings of wear resistant nonconductive and nonmagnetic material. Preferably, the thickness of the solid film layer 40 and the corresponding solid films layers 70 and the layers, not numbered, protecting the exposed components of the magnetic bearings, should have a thickness that does not exceed 0.008 inches, although this thickness could be greater for large horsepower and/or large diameter components that customarily operate with a substantially wider magnetic gap. Good results have been obtained with coating thicknesses on the order of 0.005 inches, without having to increase the magnetic gaps which may be in the order of 0.016 inches for a 1 HP motor, leaving a running gap of 0.010 inches. Again, the optimized magnetic gap increases with motor size.

While the method and product herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and product, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims. What is claimed is:

Claims

-CLAIMS-

1. A submersible electric motor having magnetic poles with pole faces subject to corrosive process fluid, characterized by a solid, low friction, hard film type nonmagnetic, nonconductive and water impervious coating fully enclosing said pole faces.

2. The submersible electric motor of claim 1 in which said poles form pole faces comprising stacked magnetic laminations further characterized by said coating covering said laminations, bridging the spaces between adjacent laminations, and having a thickness between about 0.002 inches and 0.008 inches.

3. The submersible electric motor of claim 1 in which said poles are part of the motor rotor or a motor stator and in which adjacent poles are separated by slots in which said slots are filled with an epoxy material and define surfaces as a continuation of such pole faces further characterized by the fact that said coating is applied uniformly to said pole faces and to said surfaces.

4. The submersible electric motor of claim 1 in which said poles are components of a magnetic bearing portion of the motor.

5. The submersible electric motor of claim 1 further characterized by said coating having flexibility so that it does not crack with flexing of a substrate on which it is coated and having coefficients of expansion and contraction in harmony with such substrate.

6. A process of protecting the magnetic components of a submersible electric motor including motor magnetic poles having slots between the poles characterized by the steps of filling such slots that they form a continuous annular surface with said poles and then coating said surface and said poles with a continuous coating material, said material having a solid low friction surface and being formed of non-conductive, non-magnetic and water impervious material fully enclosing said poles and having a thickness that does not substantially exceed 0.008 inches.