Patent Publication Number: US-11655815-B2

Title: Semi-rigid stator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119, based on U.S. Provisional Patent Application No. 62/947,612, filed on Dec. 13, 2019 and titled “Semi-Rigid Stator,” the disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to progressing cavity devices, and more particularly to stators of progressing cavity devices that can pass fluids containing solids. 
     Progressing cavity pumps are frequently used in applications to handle highly viscous fluids and fluids containing solids. Depending on the size and shape of the solids, the solids can get jammed between the rotor and stator and cause the pump to lock up. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a longitudinal cross-section view of a portion of a semi-rigid stator; 
         FIG.  2    is a longitudinal cross-section view of the portion of the semi-rigid stator of  FIG.  1    with a pump rotor disposed therein; 
         FIG.  3    is a cross-sectional end view of the semi-rigid stator and rotor of  FIG.  2   ; 
         FIG.  4 A  is a perspective end view of an exemplary stator ring, according to an implementation described herein; 
         FIGS.  4 B- 4 D  are end, side, and side cross-section views of the stator ring of  FIG.  4 A ; 
         FIGS.  5 A and  5 B  are an enlarged views of a portion of the stator of  FIG.  1    showing relative movement between the stator rings; 
         FIG.  6    is a front perspective view of a portion of the helical passageway of  FIG.  1   ; 
         FIG.  7    is a longitudinal cross-section view of the portion of the semi-rigid stator of  FIG.  1    with a retention disk installed; 
         FIG.  8 A  is an end view of the retention disk of  FIG.  7   ; 
         FIG.  8 B  is an end view of the stator section of  FIG.  7    with the retention disk installed; 
         FIGS.  9 A- 9 C  are end, side, and side cross-section views of another exemplary stator ring, according to an implementation described herein; and 
         FIGS.  10 A and  10 B  are end views of other exemplary stator rings, according to implementations described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. 
     There are two common types of progressive cavity pump stators. One type is a deformable, elastomer-lined stator. The other type is a ridged, non-deformable stator. 
     Elastomer-lined stators can be damaged if sharp solids (such as rocks and debris) pass through the pump, if the pump is run dry, where there are extreme temperatures or corrosive chemicals, etc. Thus, rigid stators may be preferred for applications with highly viscous fluids and fluids containing solids. 
     Depending on the size and shape of the solids, the solids can get jammed between the rotor and the rigid stator and cause the pump to lock up. This can cause significant damage to the pump depending on the hardness and size of the solid. Furthermore, even small solids can cause rapid abrasive wear to the stator, rotor, or both. 
     Rigid stators are currently expensive to manufacture with extensive processing time and wasted material. The geometry as well as manufacturing processes limit the materials that the stator can be made from. This limitation prohibits use of materials and coatings that would aid in abrasion resistance. 
     According to an implementation described herein, a semi-rigid stator is provided. The stator includes rigid rings, a non-rigid layer, and a rigid tube. The rigid rings are stacked along a helix. The combination of the ring profile and the helix form the inner profile of the stator. The ring stack is bonded to an outer tube by a non-rigid (e.g., flexible, deformable) layer. By suspending the rigid rings in the non-rigid layer the rings are allowed to move relative each other and the rigid tube. 
     The flexibility of the non-rigid layer enhances the performance of the stator. More particularly, as a large solid passes through the pump, the rigid rings are able to move radially, preventing the pump from locking up. After the solid passes, the rigid rings are pulled back into place by the non-rigid layer. The ring movement prevents the high stress concentrations seen in a conventional rigid stator. 
     Furthermore, abrasion resistance is improved using the semi-rigid stator. In the case of small particles through a conventional rigid stator, a particle is typically forced between the rigid rotor and the rigid stator, which creates forced abrasion in the stator. Implementations described herein allow for a dynamic change in radial spacing between the stator and the rotor, which limits forced abrasion. The dynamic radial spacing also allows for new materials to be used in the stator that are not possible in a conventional stator. Such new materials can greatly increase abrasion resistance. 
       FIG.  1    depicts a partial, longitudinal cross-sectional view of an exemplary semi-rigid stator section  100 . In  FIG.  2   , a pump section  10  is shown with an elongated helically lobed rotor  12  extended through stator  100 .  FIG.  3    is a cross-sectional end view of pump section  10 . In one implementation, stator section  100  and rotor  12  may correspond to a progressive cavity pump section. Stator section  100  is a helically lobed structure preferably having at least one more lobe than the rotor  12 . In the configuration of  FIGS.  2  and  3   , for example, pump section  10  is part of a helical gear pump including an internal gear (stator section  100 ) with a double lobe and an external gear (rotor  12 ) with a single lobe (e.g., a circular transverse cross-section). The meshing of stator section  100  and rotor  12  forms a cavity  18 , which progresses along the axis (e.g., centerline CL) of stator section  100  as rotor  12  is rotated. 
     Stator section  100  may include multiple like-shaped rigid rings  102  (referred to herein as “rigid rings  102 ” or “stator rings  102 ”) secured to a tubular housing  130  by a non-rigid material  110  (also referred to herein as a “deformable layer”). As can best be seen in  FIGS.  4 A- 4 D , each rigid ring  102  includes a central opening  104  with an exemplary ring  102  having two symmetrical lobes  103  radially extending toward centerline CL. As shown, for example in  FIG.  4 B , opening  104  may thus be in the form of a rectangle with a semi-circle added at opposite ends, where the size of the rectangular separation between the semicircles is proportional to the offset (or eccentricity) of rotor  12 . In one implementation, all of rigid rings  102  have substantially identical construction and dimension. 
     As shown in  FIG.  1   , rigid rings  102  may be stacked together to form a helically convoluted chamber or passageway  120  for stator section  100 . In the stacked configuration, each of rigid rings  102  may be aligned along a common centerline (CL) with each ring being rotated slightly from the rings on either side (e.g., creating a small angular difference between the rings such that the adjacent openings  104  form a helical winding inside tubular housing  130 . 
     Rigid rings  102  may be formed into the helical passageway  120  of stator section  100 , for example, by stacking rigid rings  102  onto an alignment assembly, including an alignment mandrel/core with a profile that matches lobes  103  of rigid rings  102  with its profile cut in a helical pattern in the alignment core. Rigid rings  102  may also be aligned with an alignment assembly including a jig which interacts with ring features other than the inner profile or through features built into rigid rings  102  (e.g., grooves on an exterior surface or apertures through a ring surface) that rotate each ring slightly relative to neighboring rigid rings  102 . 
     As shown, for example, in  FIGS.  4 A- 4 D , each of rigid rings  102  may include a front side surface  107   a  and a rear side surface  107   b  (referred to collectively as “sides  107 ” or generically as “side  107 ”) extending along a perimeter of opening  104 . In one implementation, front side surface  107   a  and rear side surface  107   b  may define parallel planes, with an interior surface  106  and an exterior surface  108  of ring  102  being perpendicular to each of front side surface  107   a  and rear side surface  107   b  along the entire perimeter. According to another implementation, interior surface  106  and sides  107  may connect at rounded edges  105 , as shown in the example of  FIG.  4 D . Rounded edges  105  may help solids to more easily pass between rotor  12  and interior surface  106 , as described further herein. 
     Each of rigid rings  102  may have an axial thickness, T A , which also defines a depth of the opening  104  through each rigid ring  102 . Interior surface  106  along opening  104  extends in the convoluted shape for the thickness T A  when measured in a direction parallel to the common centerline. The thickness of the rigid rings determines the size of the step between sides  107  as they are aligned into the desired helical formation of passageway  120 . Thicker rings may provide larger steps. 
     Each of rigid rings  102  may also have a radial thickness, T R , which defines a distance between interior surface  106  and exterior surface  108  on each rigid ring  102 . While radial thickness T R  is shown as generally uniform in the illustrated examples, in other implementations, radial thickness T R  may vary along a rigid ring. For example, exterior surface  108  may form a circular, rectangular, or irregular shaped perimeter of ring  102  that would provide non-uniform radial thicknesses at different parts of ring  102 .  FIGS.  10 A and  10 B  provide end view illustrations of rigid rings  102  with non-uniform radial thicknesses. 
     Each of thicknesses T A  and T R  may be sized to resist deformation (bending) of rigid rings  102 . Each of thicknesses T A  and T R  may be sized based on a type of material used, accounting for strength of material, material hardness, etc. According to an implementation, thickness T A  may be in the range of about 0.05 inches to 0.50 inches (1.27 mm to 12.7 mm) or more. In one example, thickness T A  may be about 0.10 inches (2.54 mm). Thickness T R  may be in the range of about 0.05 inches to 1 inch (1.27 mm to 25.4 mm) or more. In one example, thickness T R  may be at least about 0.06 inches (1.5 mm). In some implementations, rigid rings  102  with optimized thicknesses T A  and T R  for a particular application may use less rigid material and provide cost savings over stacked disk-shaped structures. 
     Rigid rings  102  may be manufactured in a variety of ways, with preferred methods including machining via laser, water jet, electrical discharge machining (EDM), milling etc. or a stamping/punching process. They may also be made to shape originally by casting, powder metallurgy or any similar process. In one implementation, rigid rings  102  may be formed from metal, such as a hardened tool steel from one of the American Iron and Steel Institute (AISI) grades of tool steel. In other implementations, a different material, such as ceramic, may be used to form rigid rings  102 . A primary factor behind the method of ring manufacture is the ring material and the cost of manufacture for that material. For example, stamping is cost effective for some rings made of metals but unfeasible for rings made of ceramics. 
       FIGS.  5 A and  5 B  are enlarged views of a portion “B” of  FIG.  2   .  FIG.  6    is a front perspective view of a portion of helical passageway  120 . As shown in  FIGS.  5 A and  5 B , rings  102  are secured to tubular housing  130  by non-rigid material  110 . Non-rigid material  110  may hold rigid rings  102  in the structure of helical passageway  120  in stator section  100 . Non-rigid material  110  may bond to both rigid rings  102  and tubular housing  130 . More particularly, non-rigid material  110  may adhere to an inner surface  132  of tubular housing  130  and exterior surface  108  of each rigid ring  102 . Non-rigid material  110  may also adhere to portions  109  (see, e.g.,  FIG.  6   ) of sides  107  that are exposed outside of helical passageway  120  when rigid rings  102  are assembled in the structure of helical passageway  120 . 
     Non-rigid material  110  may include, for example, any suitable deformable elastomeric material (e.g., rubber, plastic, etc.). In some implementation, non-rigid material may include butyl rubber polyamide, polyester, olefin, silicone, styrenics, urethane, and a composite of a thermoplastic and cured rubber. More specific non-limiting examples of non-rigid material  110  include room temperature vulcanization silicone, an uncured ethylene-propylene-diene-monomer (EPDM) blended with polypropylene, a styrene-butadiene-styrene block polymer, a styrene-ethylene-butylene-styrene block polymer, a cured ethylene-propylene-diene copolymer/polypropylene blend, a cured isobutylene isoprene rubber/polypropylene blend, and a cured nitrile butadiene rubber/polyvinylchloride blend. The non-rigid material  110  both bonds rigid rings  102  together as helical passageway  120  and permits radial movement of rigid rings  102  relative to each other and relative to tubular housing  130 . 
       FIG.  5 A  shows a default position, when rigid rings  102  are assembled in helical passageway  120 . For any given longitudinal cross section, exterior surface  108  of a rigid ring  102  is positioned at a radial distance, x, from inner surface  132  of tubular housing  130  and a radial distance, y, from exterior surface  108  of an adjacent rigid ring  102 . For example, as shown in  FIG.  5 A , rigid ring  102 - 2  is located at a distance, x1, between exterior surface  108 - 2  and inner surface  132  and a distance, y1, between exterior surface  108 - 2  and adjacent exterior surface  108 - 1 . When rotor  12  rotates within stator section  100  and solid-free fluids pass through pump section  10 , the above x and y distances may generally remain constant. 
       FIG.  5 B  shows a solid  20  passing between rings  102  and rotor  12 . As rotor  12  pushes the solid  20  against the rigid rings  102 , non-rigid material  110  may deform and allow rings  102  to move radially relative to inner surface  132  and relative to each other. For example, as shown in  FIG.  5 B , rigid rings  102 - 2  and  102 - 3  may be temporarily displaced from a default position. Referring specifically to rigid ring  102 - 2 , rigid ring  102 - 2  may move to a distance, x2, between exterior surface  108 - 2  and inner surface  132  and a distance, y2, between exterior surface  108 - 2  and adjacent surface  108 - 1 . Rigid ring  102 - 3  may be similarly displaced when contacting solid  20 . 
     Radial displacement of rigid rings  102  may allow solid  20  to pass between rotor  12  and rigid rings  102  with less abrasive force than would occur in a rigid stator. In some embodiments, non-rigid material  110  may permit radial displacement of rings  102  relative to tubular housing  130  (e.g., the change from x1 to x2) of at least 0.1 inches (2.54 mm) or more. According to an implementation, the diameter of tubular housing  130 , the material properties of non-rigid material  110 , and the radial thickness T R  of rigid rings  102  may be configured to prevent y2 from exceeding T R . According to another implementation, a force exerted (e.g. by solid  20 ) on one rigid ring  102  may cause one or more adjacent rigid rings  102  to also move relative to tubular housing  130 . For example, compression of non-rigid material  110  by one rigid ring  102  may cause non-rigid material  110  to radially displace adjacent rings  102  (e.g., applying force at exterior surfaces  108 ), although to a lesser degree than the ring(s)  102  that is contacting the solid. As shown in  FIG.  5 B , for example, displacement of ring  102 - 3  by solid  20  may also cause non-rigid material  110  to draw ring  102 - 4  away from rotor  12 . 
     The other adjacent rings  102  in helical passageway  120  may prevent torsion or axial movement of radially displaced rigid rings  102 . After the solid  20  passes beyond rigid rings  102 - 2  and  102 - 3 , for example, these rigid rings may be forced back into the default position (e.g.,  FIG.  5 A ) by non-rigid material  110 . Thus, non-rigid material  110  allows for a dynamic change in radial spacing between the stator rings  102  and rotor  12  during operation of rotor  12 . 
       FIG.  7    depicts a partial, longitudinal cross-sectional view of an exemplary semi-rigid stator section  100 , with optional retention disks  150  installed.  FIG.  8 A  is an end view of retention disk  150 , and  FIG.  8 B  is an end view of stator section  100  with retention disks  150  installed. Retention disk  150  may have a substantially circular circumference with an opening or aperture  154  that is as large as or larger than opening  104  of rigid ring  102 . Retention disk  150  may be bonded to the inside surface  132  of tubular housing  130  by for example, welding, fusing, soldering, brazing, sintering, diffusion bonding, mechanical fastening, or via an adhesive bond. 
     Retention disk  150  may be positioned to generally prevent movement of rigid rings  102  in an axial direction. Retention disk  150  may also secure non-rigid material  110  within tubular housing  130 . Although a retention disk  150  is shown at both ends of tubular housing  130  in  FIG.  7   , in other implementations, a retention disk  150  may be used at only one end of tubular housing  130  or between sections of helical passageway  120 . 
     According to an implementation, retention disk  150  may include one or more access holes  152 . Access holes  152  may be used to inject uncured non-rigid material  110  during assembly of stator section  100 . Some access holes  152  may also be used as bleed holes to prevent air entrapment during assembly. 
     According to one implementation, the shape of aperture  154  may be different than the shape of opening  104 . For example, aperture  154  may be asymmetrical and/or include lobes that engage a portion of ring  102  (e.g., parts of side  107 ) to prevent axial movement while permitting radial movement. The shape of aperture  154  may permit solids (e.g. solid  20 , not shown in  FIG.  7  or  8   ) to pass through retention disk  150  when an adjacent rigid ring  102  (e.g., the last ring in helical passageway  120 ) is displaced. 
       FIGS.  9 A and  9 B  provide end and side views, respectively, of a rigid ring  182  according to another embodiment.  FIG.  9 C  is a side cross-section view of rigid ring  182  along section D-D of  FIG.  9 A . Each rigid ring  182  includes a convoluted opening  184  with an exemplary ring having a number of equally spaced symmetrical lobes  183  radially extending toward the centerline CL. While six lobes  183  are shown in the configuration of  FIGS.  9 A- 9 C  (e.g., to accommodate a five-lobe rotor, not shown), other lobe configurations may be used. In one implementation, all of rigid rings  182  have substantially identical construction and dimension. Rigid ring  182  may be implemented as described above in connection with rigid ring  102  to form helical passageway  120 . 
     According to another embodiment, stator section  100  may be formed adjacent to other types of stator sections in pump section  10 . For example, stator section  100  may be axially aligned with other stator sections that use an elastically deformable liner in contact with rotor  12  to form a hybrid stator section. The liner may include an elastically deformable elastomeric material, such as rubber, with an even or smooth profile. 
     In implementations described herein, a semi-rigid stator is provided for a helical gear device. The stator includes a stack of rigid rings, a deformable or non-rigid material, and a rigid housing. Each of the rigid rings includes a central opening and an exterior surface. The rigid rings are aligned along a common centerline and rotated slightly relative to each other such that the stack of rigid rings forms a helically convoluted chamber. The stack of rigid rings is secured within the rigid stator housing by the deformable material disposed between the exterior surface of each of the rigid rings and the rigid housing. The deformable material bonds the rigid rings together as the ring stack and permits movement of the rigid rings relative to each other and relative to the rigid housing. 
     The foregoing description of exemplary implementations provides illustration and description, but is not intended to be exhaustive or to limit the embodiments described herein to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the embodiments. 
     Although the invention has been described in detail above, it is expressly understood that it will be apparent to persons skilled in the relevant art that the invention may be modified without departing from the spirit of the invention. Various changes of form, design, or arrangement may be made to the invention without departing from the scope of the invention. Different combinations illustrated above may be combined in a single embodiment. Therefore, the above-mentioned description is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined in the following claims. 
     No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.