US20160208798A1

US20160208798A1 - Adjustable interference progressive cavity pump/motor for predictive wear

Info

Publication number: US20160208798A1
Application number: US14/913,416
Authority: US
Inventors: Wallace Gregory Sawyer; David B. Dooner
Original assignee: University of Florida Research Foundation Inc
Current assignee: University of Florida Research Foundation Inc
Priority date: 2013-08-23
Filing date: 2014-08-22
Publication date: 2016-07-21
Also published as: WO2015027169A1

Abstract

Various examples are provided for progressive cavity pumps and motors. In one example, among others, a progressive cavity pump (or motor) includes a stator having a hyperboloidal internal bore including a plurality of spiral lobes, and a rotor comprising a plurality of spiral lobes positioned within the hyperboloidal internal bore of the stator. A longitudinal axis of the rotor is non-planar, non-parallel, and non-intersecting with a longitudinal axis of the stator. The stator can include an elastomeric material coating the hyperboloidal internal bore of the stator, which can reduce the effect of friction and abrasion during operation. The elastomeric material can include fluoro-based elastomers, other elastomeric materials or combinations thereof. For example, a fluoromonomer such as tetrafluoroethylene (TFE) or a fluoropolymer such as polytetrafluoroethylene (PTFE) can be used. The rotor can be configured to allow for displacement to adjust an interference fit between the rotor and the stator.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, co-pending U.S. provisional application entitled “ADJUSTABLE INTERFERENCE PROGRESSIVE CAVITY PUMP/MOTOR FOR PREDICTIVE WEAR” having Ser. No. 61/869,438, filed Aug. 23, 2013, which is hereby incorporated by reference in its entirety.

BACKGROUND

Progressive cavity pumps and/or motors are frequently used in oil field applications for pumping fluids or driving downhole equipment in the wellbore. The progressive cavity mechanism includes a rotating gear member and a stationary gear member. When designed according to the basics of a gear mechanism of Moineau, and progressive cavity mechanism is generically known as a “Moineau” pump or motor. The progressive cavity mechanism can operate as a pump for pumping fluids or as a motor through which fluids flow to rotate the rotating gear member to produce torsional forces on an output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a cross-sectional view of an example of a progressive cavity pump and/or motor in accordance with various embodiments of the present disclosure.

FIG. 2 is a graphical representation of an example of a hyperboloidal configuration of a progressive cavity pump of FIG. 1 in accordance with various embodiments of the present disclosure.

FIG. 3 is a graphical representation of an example of a progressive cavity pump of FIG. 1 mounted in a wellbore in accordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

Disclosed herein are various examples related to progressive cavity pumps and motors. Reference will now be made in detail to the description of the embodiments as illustrated in the drawings, wherein like reference numbers indicate like parts throughout the several views.
A progressive cavity pump transfers fluid through the pump in a sequence of small, fixed shape, discrete cavities that are defined by the rotor and stator of the pump. As the rotor is turned, the cavities move along the axial length of the pump. This produces a volumetric flow rate that is proportional to the rotational speed. With low levels of shearing being applied to the pumped fluid, progressive cavity pumps have applications in, e.g., metering and pumping of viscous materials. In general, no pulsing of the fluid is produced by the progressive cavity pump. Progressive cavity pumps may also function as motors when fluid is forced through the interior of the motor. As such, descriptions with respect to operation as a pump are equally applicable to operation as a motor.
Referring to FIG. 1, shown is a cross-sectional view illustrating an example of a portion of a progressive cavity pump (or motor) 100. The progressive cavity pump 100 includes a stator 103 surrounding a rotor 106. The stator 103 includes an outer portion and in inner portion formed of an elastomeric material 109. In some embodiments, the inner portion may be formed of a non-elastomeric material. The outer portion is generally fabricated using metal (e.g., steel or stainless steel), ceramic, or other composite materials, such as fiberglass, plastics, hydrocarbon-based materials and other structural materials, and may include strengthening members, such as fibers embedded in the material, and forms the shell of the stator 103. Homogeneous materials are typically utilized; however heterogeneous materials can also be used. The inner portion (or bore) of the stator 103 can include a coating of an elastomeric material 109 forming spiral lobes (or gear teeth) within the stator cavity. The elastomeric material 109 is flexible and resists abrasion. The elastomeric material 109 can include, e.g., rubber, Buna-N, nitrile-based elastomers, fluoro-based elastomers, Teflon™, silicone, plastics, other elastomeric materials or combinations thereof. The thickness of the coating of elastomeric material 109 can be in a range from about 1 mil to about 100 mil, or more. For example, the coating thickness can be in a range from about 1 mil to about 50 mil, from about 1 mil to about 25 mil, from about 1 mil to about 20 mil, from about 1 mil to about 15 mil, or from about 1 mil to about 10 mil. Other thicknesses of elastomeric material 109 may also be utilized.
In some cases, specially fabricated materials such as, e.g., fluoropolymers (e.g., from DuPont) may be used to improve operation of the progressive cavity pump 100. Fluoropolymers can be prepared from at least one unsaturated fluorinated monomer (fluoromonomer). A fluoromonomer suitable for use herein preferably contains about 35 wt % or more fluorine, and preferably about 50 wt % or more fluorine, and can be an olefinic monomer with at least one fluorine or fluoroalkyl group or fluoroalkoxy group attached to a doubly-bonded carbon. In one embodiment, a fluoromonomer suitable for use herein is tetrafluoroethylene (TFE).
An especially useful fluoropolymer is polytetrafluoroethylene (PTFE), which refers to (a) polymerized tetrafluoroethylene by itself without any significant comonomer present, i.e. a homopolymer of TFE, and (b) modified PTFE, which is a copolymer of TFE with such small concentrations of comonomer that the melting point of the resultant polymer is not substantially reduced below that of PTFE (reduced, for example, by about 8% or less, about 4% or less, about 2% or less, or about 1% or less). Modified PTFE contains a small amount of comonomer modifier that improves film forming capability during baking (fusing). Comonomers useful for such purpose typically are those that introduce bulky side groups into the molecule, and specific examples of such monomers are described below. The concentration of such comonomer is preferably less than 1 wt %, and more preferably less than 0.5 wt %, based on the total weight of the TFE and comonomer present in the PTFE. A minimum amount of at least about 0.05 wt % comonomer is preferably used to have a significant beneficial effect on processability. The presence of the comonomer is believed to cause a lowering of the average molecular weight.
The rotor 106 may be fabricated using metal (e.g., steel or stainless steel), ceramic, or other composite materials. Such materials are typically homogeneous; however heterogeneous materials including composites and/or new materials can also be used. The elastomeric material 109 comes in contact with spiral lobes (or gear teeth) of the rotor 106 at contact points 112. As can be understood, contact between the stator 103 and rotor 106 is a closed curve. In some embodiments, the outer portion of the rotor 106 can include a coating of the elastomeric material 109, which is flexible and resists abrasion. With the rotor coated, the inner portion (or bore) of the stator 103 may or may not include a coating of an elastomeric material 109. The thickness of the coating of elastomeric material 109 can be in a range from about 1 mil to about 100 mil, or more. For example, the coating thickness can be in a range from about 1 mil to about 50 mil, from about 1 mil to about 25 mil, from about 1 mil to about 20 mil, from about 1 mil to about 15 mil, or from about 1 mil to about 10 mil. Other thicknesses of elastomeric material 109 may also be utilized.
As FIG. 1 is a cross-sectional view, the contact points 112 are the intersection between the closed curve and an axial section. The number of spiral lobes on the rotor 106 is less than the number of spiral lobes on the bore of the stator 103. For example, the rotor 106 may include four spiral lobes and the stator 103 may include five spiral lobes. The contact between the stator 103 and rotor 106 defines the sealed cavities in which the fluid is transported through the progressive cavity pump 100. At the contact points 112, the surfaces are generally traveling transversely and axially. Areas or regions of sliding contact occur at contact points along the closed curve. These areas are lubricated by the pumped fluid, which may include abrasive components. The elastomeric material 109 may include specialized materials to reduce the effects of friction and abrasion in high temperature and/or high pressure applications such as, e.g., downhole mudpump operations in the petrochemical industry.
The longitudinal axis of the rotor 106 is offset from the longitudinal axis of the stator 103 and rotated by a defined angle to provide skew axes. The defined angle can be greater than zero degrees and less than 90 degrees. For example, the defined angle of rotation can be 0.5 degree, one degree, or other small amount of angular rotation. The defined angle of rotation can be in a range from about 0.001 degree to about 10 degrees, from about 0.005 degree to about 8.0 degrees, from about 0.01 degree to about 7.5 degrees, from about 0.05 degree to about 5.0 degrees, from about 0.1 degree to about 3.0 degrees, about 0.2 degree to about 2.0 degrees, from about 0.25 degree to about 1.5 degrees, from about 0.3 degree to about 1.2 degrees, or from about 0.5 degree to about 1.0 degree. In this way, the skew axes of the stator 103 and rotor 106 are non-planar, non-parallel, and non-intersecting.
As with the defined angle, the offset of the longitudinal axis of the rotor 106 from the longitudinal axis of the stator 103 can be a defined distance that covers a wide range of values (e.g., about 0.01 inch or more). For example, the defined distance can be in a range of about 0.01 inch to about 10 inches, about 0.02 inch to about 10 inches, about 0.05 inch to about 10 inches, about 0.05 inch to about 7.5 inches, about 0.05 inch to about 5 inches, about 0.1 inch to about 5 inches, about 0.1 inch to about 2.5 inches, about 0.25 inch to about 2.5 inches, or other ranges as can be understood. The offset can be based upon the diameter of the stator 103. For example, an offset of about 0.5 inch can be used for a 10 inch diameter. In other embodiments, more or less offset can be utilized.
Rotation of the rotor 106 produces a circular movement about the longitudinal axis of the stator 103. As the rotor 106 is rotated, the outer surface moves within the bore of the stator 103, which is hyperboloidal (e.g., generally shaped like a single surface hyperboloid) as illustrated in FIG. 2. The hyperboloidal internal bore of the stator 103 exhibits a hyperboloidal shape for at least a portion of the axial length of the stator 103. In the example of FIG. 1, the rotor 106 axially tapers from a larger end to a smaller end. In other embodiments, the taper of the rotor 106 may also be hyperboloidal.
The spiral lobes of the stator 103 may be defined by a major diameter corresponding to the diameter at the bases of the spiral lobes and a minor diameter corresponding to the diameter at the peaks of the spiral lobes. In contrast, the spiral lobes of the rotor 106 may be defined by a major diameter corresponding to the diameter at the peaks of the spiral lobes and a minor diameter corresponding to the diameter at the bases of the spiral lobes. Referring to FIG. 2, shown is a graphical representation of an example of the hyperboloidal configuration. In some implementations, the applicable section 203 of the hyperboloid may be below the throat of neck 206 of the single sheet hyperboloid 200. The rotor axis 212 and the tangent line between the rotor and stator surfaces 215 are non-planar, non-parallel, and non-intersecting skew lines. As can be understood, the dimensions of the spiral lobes vary along the axial length of the progressive cavity pump 100. The dimensions of the spiral lobes on the stator 103 can vary along the axial length of the stator 103 as illustrated by the hyperboloidal surfaces as illustrated by the hyperpoloidal stator pitch surface segment 209. The dimensions of the spiral lobes on the rotor 106 can vary based on the taper of the rotor 106. In some implementations, the spiral lobes on the rotor 106 may vary along the axial length of the rotor 106 based upon the hyperboloidal taper.
Placement of the rotor 106 in the stator 103 creates a plurality of cavities (e.g., 2 through 12 or more) along the axial length of the progressive cavity pump 100. The cavities progress along the axial length of the progressive cavity pump 100 as the rotor 104 rotates within the stator 103. Contact of the rotor 106 with the elastomeric material 109 of the stator 103 creates an interference fit that can vary depending on the operations conditions. The design of the stator 103 and rotor 106 is independent of thermal effects. The combination of a tapered rotor 106 and a stator 103 with a hyperboloidal bore provides the ability to adjust the sealing between cavities and account for thermal expansion. A difference in fit between the rotor 106 and stator 103 allows axial displaced to adjust for these effects. The rotor 106 may be configured to allow for movement in the direction of the longitudinal axis of the rotor 106, thereby allowing the relative position of the rotor 106 to be changed with respect to the stator 103.
The adjustment between the rotor 106 and stator 103 fit can be made manually or automatically and can account for variations in operating conditions. For example, the fit between the rotor 106 and the elastomeric material 109 could be increased to achieve increased pumping efficiency, if the elastomeric material 109 has worn. In other implementations, if an operation temporarily swells the elastomeric material 109, such as an increase in the fluid temperature, the rotor 106 can be adjusted for a looser fit to allow for the swelling and then readjusted to a desired fit after the swelling subsides. In addition, it may be desirable to adjust the interference fit to allow for the passage of various fluids, such as fluids containing particulate matter. In some cases, the interference fit may be adjusted to prevent the operating pressures from becoming excessive. By knowing the characteristics of the rotor and stator (e.g., wear rate of materials), the wear can be predicted and used to position the rotor 106 to extend the operational life of the progressive cavity pump 100. In some cases, the position of the rotor 106 with respect to the stator 103 may be automatically carried out the extend life of the progressive cavity pump 100.
Referring next to FIG. 3, shown is a graphical representation of an example of a progressive cavity pump 100 mounted downhole in a wellbore. A wellbore 303 can be formed in the ground for a variety of applications. Generally, the wellbore 303 includes a casing 306 to stabilize the hole in the ground. The progressive cavity pump 100 is positioned within the wellbore 303 and coupled with a drive motor 309 through, e.g., a gearbox 312 and a drive shaft 315. In some embodiments, the drive motor 309 may be directly coupled to the drive shaft 315. The drive shaft 315 may be flexibly coupled to the rotor 106 (FIG. 1) of the progressive cavity pump 100 to allow for the skew of the rotor 106. For example, the drive shaft 315 may be coupled to the rotor 106 of the progressive cavity pump 100 through one or more universal joints. The drive shaft 315 may also allow for axial adjustment of the rotor 106 within the stator 103 (FIG. 1) of the progressive cavity pump 100.
If the progressive cavity pump 100 is used as a pump, generally the wellbore 303 contains some amount of fluid 318. In many cases, the progressive cavity pump 100 can be configured to operate as a submersible pump. Openings at one end of the progressive cavity pump 100 allow fluid to enter the suction side 115 (FIG. 1) of the pump 100. Rotation of the rotor 106 with respect to the non-rotating stator 103 produces relative motion, which pumps the fluid 318 from the low pressure suction side 115 to a higher pressure discharge side 118 (FIG. 1) of the progressive cavity pump 100. A discharge casing (or pipe) 321 is inserted down the wellbore 303 to direct fluids discharged from the progressive cavity pump 100 out of the wellbore 303. The discharge casing 321 includes an outlet port 324 through which the fluid is directed out of the discharge casing 321.
Fluid 318 can be pumped up the wellbore 303 through the progressive cavities formed between the stator 103 and the rotor 106 and then through the discharge casing 321 and out the outlet port 324. Alternatively, fluid may be pumped downhole by entering the outlet port 324, moving the fluid down the discharge casing 321 and through the progressive cavity pump 100. If the progressive cavity pump 100 is used as a downhole motor, the discharge casing 321 may be used to flow fluid downward through the progressive cavity pump 100. The rotor 106 would be coupled to a drive shaft (not shown) for operating downhole equipment such as, e.g., mills and drill bits.
As mentioned above, the elastomeric material 109 can include fluoro-based elastomers such as, e.g., fluoromonomers and/or fluoropolymers (e.g., from DuPont) that may be used to improve operation of the progressive cavity pump 100. Embodiments of various types of fluoropolymer are described herein. In particular, embodiments of the present disclosure can have a low coefficient of friction (e.g., about 0.2 to about 0.4) and very low wear rate (e.g., about 1×10⁻⁷mm³/Nm to about 1×10⁻⁸mm³/Nm, or less). In addition, embodiments of the present disclosure provide for elastomeric material 109 that is resistant to chemicals, have a high strength, are biocompatible, are water resistant, and/or have high thermal resistance (e.g., withstand extreme temperatures).
In an exemplary embodiment, the elastomeric material 109 can include a lubricant and one or more filler components (e.g., a filler and other materials that may be present in the filler component). In an embodiment, the lubricant can be about 5 to 95 weight % or about 75 to 95 weight % of the mixture. In an embodiment, the filler component can be about 5 to 95 weight % or about 5 to 25 weight % of the mixture. In an embodiment, the filler component can be about 5 to 25 weight % of the mixture and the lubricant is about 75 to 95 weight % of the mixture.
Embodiments of the filler can be a filler particle such as: mullite (two stoichiometric forms 3Al₂O₃2SiO₂or 2Al₂O₃SiO₂), pyrophyllite (Al₂Si₄O₁₀(OH)₂), kyanite (Al₂O₃.SiO₂), dolomite (CaMg(CO₃)₂), or a combination thereof. In an embodiment, the filler particle can have one or more dimensions (e.g., diameter, length, width, height) on the nanometer scale (e.g., about 1 to 500 nm) to the micrometer scale (e.g., about 500 nm to 500 micrometers. In an embodiment, the filler particles can have a mixture of sizes, where, for example, some of the particles are about 1 to 500 nm along the longest dimension and other particles are about 1 micrometer to about 500 micrometers along the longest dimension.
In an embodiment, the filler component can include other materials such as minerals, clays, silicates, sepiolite, kaolinite, halloysite, clinochlore, vermiculiate, chamosite, astrophylilite, clinochlore, glauconite, muscovite, talc, bauxite, quartz, mica, cristobalite, tremolite, and a combination thereof. In an embodiment, the other material(s) present can be or sum up to, if more than one is present, about 0.01 to 60 weight % of the filler component. In an embodiment, the other material can be removed so that the filler(s) is at a higher percentage of the mixture. In an embodiment, the other material can have a dimension (e.g., diameter) on the nanometer scale to the micrometer scale, or include a mixture of sizes of particles.
In an embodiment, the filler can be pyrophyllite, which can be purchased from R. T. Vanderbilt Company, Inc. (i.e., composition: <40 wt % pyrophyllite with impurities of quartz (50-60 wt %), mica (18-25 wt %) and kaolin clay (5-10 wt %), where quartz, mica and kaolin clay can be the other materials).
In an embodiment of the elastomeric material 109, where the filler component is pyrophyllite and the lubricant is PTFE, elastomeric material 109 can have a coefficient of friction of about 0.22 to 0.26 and can have a wear rate of about 5×10⁻⁷mm³/Nm or less. The filler component can be about 5 wt % of the mixture and the lubricant can be about 95 wt % of the mixture.
In an embodiment, the filler can be mullite, which can be purchased from Kyanite Mining Corporation (i.e., composition: 75-85 wt % mullite with impurities of amorphous silica (glass) (5-10 wt %) quartz (1-5 wt %), kyanite (1-5 wt %) and cristobalite (1-5 wt %), wherein quartz, kyanite, and cristobalite can be the other materials).
In an embodiment of elastomeric material 109, where the filler is mullite and the lubricant is PTFE, elastomeric material 109 can have a coefficient of friction of about 0.25 to 0.29 and can have a wear rate of about 4×10⁻⁷mm³/Nm or less. The filler component can be about 5 wt % of the mixture and the lubricant can be about 95 wt % of the mixture.
In an embodiment, the filler can be dolomite, which can be purchased from Specialty Minerals Inc. (i.e., composition: 60-100 wt % dolomite with <1% quartz and <1 wt % tremolite, wherein quartz and tremolie can be the other materials).
In an embodiment of the elastomeric material 109, where the filler is dolomite and the lubricant is PTFE, the elastomeric material 109 can have a coefficient of friction of about 0.29 to 0.33 and can have a wear rate of about 9.3×10⁻⁸mm³/Nm or less. The filler component can be about 10 wt % of the mixture and the lubricant can be about 90 wt % of the mixture.
In an embodiment, the filler can be kyanite, which can be purchased from Kyanite Mining Corporation (i.e., composition: 85-95 wt % kyanite with impurities of quartz (5-10 wt %), titanium dioxide (1-5 wt %), and cristobalite (<0.1%), where quartz, titanium dioxide, and cristobalite, can be the other materials).
In an embodiment of the elastomeric material 109, where the filler is kyanite and the lubricant is PTFE, the elastomeric material 109 can have a coefficient of friction of about 0.3 to 0.34 and can have a wear rate of about 4×10⁻⁷mm³/Nm or less. The filler component can be about 5 wt % of the mixture and the lubricant can be about 95 wt % of the mixture.
As mentioned above, the elastomeric material 109 can include a lubricant such as a fluoropolymer. Embodiments of various types of fluoropolymer are described herein.
In an embodiment, an individual fluoropolymer can be used alone; mixtures or blends of two or more different kinds of fluoropolymers can be used as well. Fluoropolymers useful in the practice of this disclosure are prepared from at least one unsaturated fluorinated monomer (fluoromonomer). A fluoromonomer suitable for use herein preferably contains about 35 wt % or more fluorine, and preferably about 50 wt % or more fluorine, and can be an olefinic monomer with at least one fluorine or fluoroalkyl group or fluoroalkoxy group attached to a doubly-bonded carbon. In one embodiment, a fluoromonomer suitable for use herein is tetrafluoroethylene (TFE).
In one embodiment, the fluoropolymer can be polytetrafluoroethylene (PTFE), which refers to (a) polymerized tetrafluoroethylene by itself without any significant comonomer present, i.e. a homopolymer of TFE, and (b) modified PTFE, which is a copolymer of TFE with such small concentrations of comonomer that the melting point of the resultant polymer is not substantially reduced below that of PTFE (reduced, for example, by about 8% or less, about 4% or less, about 2% or less, or about 1% or less). Modified PTFE contains a small amount of comonomer modifier that improves film forming capability during baking (fusing). Comonomers useful for such purpose typically are those that introduce bulky side groups into the molecule, and specific examples of such monomers are described below. The concentration of such comonomer is preferably less than 1 wt %, and more preferably less than 0.5 wt %, based on the total weight of the TFE and comonomer present in the PTFE. A minimum amount of at least about 0.05 wt % comonomer is preferably used to have a significant beneficial effect on processability. The presence of the comonomer is believed to cause a lowering of the average molecular weight.
PTFE (e.g., and modified PTFE) typically have a melt creep viscosity of at least about 1×10⁶Pa·s and preferably at least about 1×10⁸Pa·s. With such high melt viscosity, the polymer does not flow in the molten state and therefore is not a melt-processible polymer. The measurement of melt creep viscosity is disclosed in col. 4 of U.S. Pat. No. 7,763,680, which is incorporated herein by reference. The high melt viscosity of PTFE arises from its extremely high molecular weight (Mn), e.g. at least about 10⁶. Additional indicia of this high molecular weight include the high melting temperature of PTFE, which is at least 330° C., usually at least 331° C. and most often at least 332° C. (all measured on first heat). The non-melt flowability of the PTFE, arising from its extremely high melt viscosity, manifests itself as a melt flow rate (MFR) of 0 when measured in accordance with ASTM D 1238-10 at 372° C. and using a 5 kg weight. This high melt viscosity also leads to a much lower heat of fusion obtained for the second heat (e.g. up to 55 J/g) as compared to the first heat (e.g. at least 75 J/g) to melt the PTFE, representing a difference of at least 20 J/g. The high melt viscosity of the PTFE reduces the ability of the molten PTFE to recrystallize upon cooling from the first heating. The high melt viscosity of PTFE enables its standard specific gravity (SSG) to be measured, which measurement procedure (ASTM D 4894-07, also described in U.S. Pat. No. 4,036,802, which is incorporated herein by reference) includes sintering the SSG sample free standing (without containment) above its melting temperature without change in dimension of the SSG sample. The SSG sample does not flow during the sintering.
Low molecular weight PTFE is commonly known as PTFE micropowder, which distinguishes it from the PTFE described above. The molecular weight of PTFE micropowder is low relative to PTFE, i.e. the molecular weight (Mn) is generally in the range of 10⁴to 10⁵. The result of this lower molecular weight of PTFE micropowder is that it has fluidity in the molten state, in contrast to PTFE which is not melt flowable. The melt flowability of PTFE micropowder can be characterized by a melt flow rate (MFR) of at least about 0.01 g/10 min, preferably at least about 0.1 g/10 min, more preferably at least about 5 g/10 min, and still more preferably at least about 10 g/10 min., as measured in accordance with ASTM D 1238-10, at 372° C. using a 5 kg weight on the molten polymer.
While PTFE micropowder is characterized by melt flowability because of its low molecular weight, the PTFE micropowder by itself is not melt fabricable, i.e. an article molded from the melt of PTFE micropowder has extreme brittleness, and an extruded filament of PTFE micropowder, for example, is so brittle that it breaks upon flexing. Because of its low molecular weight (relative to non-melt-flowable PTFE), PTFE micropowder has no strength, and compression molded plaques for tensile or flex testing generally cannot be made from PTFE micropowder because the plaques crack or crumble when removed from the compression mold, which prevents testing for either the tensile property or the MIT Flex Life. Accordingly, the micropowder is assigned zero tensile strength and an MIT Flex Life of zero cycles. In contrast, PTFE is flexible, rather than brittle, as indicated for example by an MIT flex life [ASTM D-2176-97a(2007)], using an 8 mil (0.21 mm) thick compression molded film] of at least 1000 cycles, preferably at least 2000 cycles. As a result, PTFE micropowder finds use as a blend component with other polymers such as PTFE itself and/or copolymers of TFE with other monomers such as those described below.
In other embodiments, a fluoromonomer suitable for use herein, by itself to prepare a homopolymer or in copolymerization with other comonomers such as TFE, can be represented by the structure of the following Formula I:
where R¹and R²are each independently selected from H, F and Cl; R³is H, F, or a C₁˜C₁₂, or C₁˜C₈, or C₁˜C₆, or C₁˜C₄straight-chain or branched, or a C₃˜C₁₂, or C₃˜C₈, or C₃˜C₆cyclic, substituted or unsubstituted, alkyl radical; R⁴is a C₁˜C₁₂, or C₁˜C₈, or C₁˜C₆, or C₁˜C₄straight-chain or branched, or a C₃˜C₁₂, or C₃˜C₈, or C₃˜C₆cyclic, substituted or unsubstituted, alkylene radical; A is H, F or a functional group; a is 0 or 1; and j and k are each independently 0 to 10; provided that, when a, j and k are all 0, at least one of R¹, R², R³and A is not F.
An unsubstituted alkyl or alkylene radical as described above contains no atoms other than carbon and hydrogen. In a substituted hydrocarbyl radical, one or more halogens selected from Cl and F can be optionally substituted for one or more hydrogens; and/or one or more heteroatoms selected from O, N, S and P can optionally be substituted for any one or more of the in-chain (i.e. non-terminal) or in-ring carbon atoms, provided that each heteroatom is separated from the next closest heteroatom by at least one and preferably two carbon atoms, and that no carbon atom is bonded to more than one heteroatom. In other embodiments, at least 20%, or at least 40%, or at least 60%, or at least 80% of the replaceable hydrogen atoms are replaced by fluorine atoms. Preferably a Formula I fluoromonomer is perfluorinated, i.e. all replaceable hydrogen atoms are replaced by fluorine atoms.
In a Formula I compound, a linear R³radical can, for example, be a C_bradical where b is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and the radical can contain from 1 up to 2b+1 fluorine atoms. For example, a C₄radical can contain from 1 to 9 fluorine atoms. A linear R³radical is perfluorinated with 2b+1 fluorine atoms, but a branched or cyclic radical will be perfluorinated with fewer than 2b+1 fluorine atoms. In a Formula I compound, a linear R⁴radical can, for example, be a C_cradical where c is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and the radical can contain from 1 to 2c fluorine atoms. For example, a C₆radical can contain from 1 to 12 fluorine atoms. A linear R⁴radical is perfluorinated with 2c fluorine atoms, but a branched or cyclic radical will be perfluorinated with fewer than 2c fluorine atoms.
Examples of a C₁˜C₁₂straight-chain or branched, substituted or unsubstituted, alkyl or alkylene radical suitable for use herein can include or be derived from a methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, trimethylpentyl, allyl and propargyl radical. Examples of a C₃˜C₁₂cyclic aliphatic, substituted or unsubstituted, alkyl or alkylene radical suitable for use herein can include or be derived from an alicyclic functional group containing in its structure, as a skeleton, cyclohexane, cyclooctane, norbornane, norbornene, perhydro-anthracene, adamantane, or tricyclo-[5.2.1.0^2.6]-decane groups.
Functional groups suitable for use herein as the A substituent in Formula I include ester, alcohol, acid (including carbon-, sulfur-, and phosphorus-based acid) groups, and the salts and halides of such groups; and cyanate, carbamate, and nitrile groups. Specific functional groups that can be used include —SO₂F, —CN, —COOH, and —CH₂—Z wherein —Z is —OH, —OCN, —O—(CO)—NH₂, or —OP(O)(OH)₂.
Formula I fluoromonomers that can be homopolymerized include vinyl fluoride (VF), to prepare polyvinyl fluoride (PVF), and vinylidene fluoride (VF₂) to prepare polyvinylidene fluoride (PVDF), and chlorotrifluoroethylene to prepare polychlorotrifluoroethylene. Examples of Formula I fluoromonomers suitable for copolymerization include those in a group such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, vinyl fluoride (VF), vinylidene fluoride (VF₂), and perfluoroolefins such as hexafluoropropylene (HFP), and perfluoroalkyl ethylenes such as perfluoro(butyl) ethylene (PFBE). A preferred monomer for copolymerization with any of the above named comonomers is tetrafluoroethylene (TFE).
In yet other embodiments, a fluoromonomer suitable for use herein, by itself to prepare a homopolymer or in copolymerization with TFE and/or any of the other comonomers described above, can be represented by the structure of the following Formula II:
wherein R¹through R³and A are each as set forth above with respect to Formula I; d and e are each independently 0 to 10; f, g and h are each independently 0 or 1; and R⁵through R⁷can each be selected from the same radicals as described above with respect to R⁴in Formula I except that when d and e are both non-zero and g is zero, R⁵and R⁶are different R⁴radicals.
Formula II compounds introduce ether functionality into fluoropolymers suitable for use herein, and include fluorovinyl ethers such as those represented by the following formula: CF₂═CF—(O—CF₂CFR¹¹)_h—O—CF₂CFR¹²SO₂F, where R¹¹and R¹²are each independently selected from F, Cl, or a perfluorinated alkyl group having 1 to 10 carbon atoms, and h=0, 1 or 2. Examples of polymers of this type that are disclosed in U.S. Pat. No. 3,282,875 include CF₂═CF—O—CF₂CF(CF₃)—O—CF₂CF₂SO₂F and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), and examples that are disclosed in U.S. Pat. Nos. 4,358,545 and 4,940,525 include CF₂═CF—O—CF₂CF₂SO₂F. Another example of a Formula II compound is CF₂═CF—O—CF₂—CF(CF₃)—O—CF₂CF₂CO₂CH₃, the methyl ester of perfluoro(4,7-dioxa-5-methyl-8-nonenecarboxylic acid), as disclosed in U.S. Pat. No. 4,552,631. Similar fluorovinyl ethers with functionality of nitrile, cyanate, carbamate, and phosphonic acid are disclosed in U.S. Pat. Nos. 5,637,748, 6,300,445 and 6,177,196. Methods for making fluoroethers suitable for use herein are set forth in the U.S. patents listed above in this paragraph, and each of the U.S. patents listed above in this paragraph is by this reference incorporated in its entirety as a part hereof for all purposes.
Particular Formula II compounds suitable for use herein as a comonomer include fluorovinyl ethers such as perfluoro(allyl vinyl ether) and perfluoro(butenyl vinyl ether). Preferred fluorovinyl ethers include perfluoro(alkyl vinyl ethers) (PAVE), where the alkyl group contains 1 to 5 carbon atoms, with perfluoro(ethyl vinyl ether) (PEVE) and perfluoro(propyl vinyl ether) (PPVE), and perfluoro(methyl vinyl ether) (PMVE) being preferred.
In yet other embodiments, a fluoromonomer suitable for use herein, by itself to prepare a homopolymer or in copolymerization with TFE and/or any of the other comonomers described above, can be represented by the structure of the following Formula III:
where each R³is independently as described above in relation to Formula I. Suitable Formula III monomers include perfluoro-2,2-dimethyl-1,3-dioxole (PDD).
In yet other embodiments, a fluoromonomer suitable for use herein, by itself to prepare a homopolymer or in copolymerization with TFE and/or any of the other comonomers described above, can be represented by the structure of the following Formula IV:
where each R³is independently as described above in relation to Formula I. Suitable Formula IV monomers include perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD).
In various embodiments, fluoropolymer copolymers suitable for use herein can be prepared from any two, three, four or five of these monomers: TFE and a Formula I, II, III and IV monomer. The following are thus representative combinations that are available: TFE/Formula I; TFE/Formula II; TFE/Formula III; TFE/Formula IV; TFE/Formula I/Formula II; TFE/Formula I/Formula III; TFE/Formula I/Formula IV; Formula I/Formula II; Formula I/Formula III; and Formula I/Formula IV. Provided that at least two of the five kinds of monomers are used, a unit derived from each monomer can be present in the final copolymer in an amount of about 1 wt % or more, or about 5 wt % or more, or about 10 wt % or more, or about 15 wt % or more, or about 20 wt % or more, and yet no more than about 99 wt %, or about 95 wt % or less, or about 90 wt % or less, or about 85 wt % or less, or about 80 wt % or less (based on the weight of the final copolymer); with the balance being made up of one, two, three or all of the other five kinds of monomers.
A fluoropolymer as used herein can also be a mixture of two or more of the homo- and/or copolymers described above, which is usually achieved by dry blending. A fluoropolymer as used herein can also, however, be a polymer alloy prepared from two or more of the homo- and/or copolymers described above, which can be achieved by melt kneading the polymer together such that there is mutual dissolution of the polymer, chemical bonding between the polymers, or dispersion of domains of one of the polymers in a matrix of the other.
Tetrafluoroethylene polymers suitable for use herein can be produced by aqueous polymerization (as described in U.S. Pat. No. 3,635,926) or polymerization in a perhalogenated solvent (U.S. Pat. No. 3,642,742) or hybrid processes involving both aqueous and perhalogenated phases (U.S. Pat. No. 4,499,249). Free radical polymerization initiators and chain transfer agents are used in these polymerizations and have been widely discussed in the literature. For example, persulfate initiators and alkane chain transfer agents are described for aqueous polymerization of TFE/PAVE copolymers. Fluorinated peroxide initiators and alcohols, halogenated alkanes, and fluorinated alcohols are described for nonaqueous or aqueous/nonaqueous hybrid polymerizations.
Various fluoropolymers suitable for use herein include those that are thermoplastic, which are fluoropolymers that, at room temperature, are below their glass transition temperature (if amorphous), or below their melting point (if semi-crystalline), and that become soft when heated and become rigid again when cooled without the occurrence of any appreciable chemical change. A semi-crystalline thermoplastic fluoropolymer can have a heat of fusion of about 1 J/g or more, or about 4 J/g or more, or about 8 J/g or more, when measured by Differential Scanning calorimetry (DSC) at a heating rate of 10° C./min (according to ASTM D 3418-08).
Various fluoropolymers suitable for use herein can additionally or alternatively be characterized as melt-processible, and melt-processible fluoropolymers can also be melt-fabricable. A melt-processible fluoropolymer can be processed in the molten state, i.e. fabricated from the melt using conventional processing equipment such as extruders and injection molding machines, into shaped articles such as films, fibers and tubes. A melt-fabricable fluoropolymer can be used to produce fabricated articles that exhibit sufficient strength and toughness to be useful for their intended purpose despite having been processed in the molten state. This useful strength is often indicated by a lack of brittleness in the fabricated article, and/or an MIT Flex Life of at least about 1000 cycles, or at least about 2000 cycles (measured as described above), for the fluoropolymer itself.
Examples of thermoplastic, melt-processible and/or melt-fabricable fluoropolymers include copolymers of tetrafluoroethylene (TFE) and at least one fluorinated copolymerizable monomer (comonomer) present in the polymer in sufficient amount to reduce the melting point of the copolymer below that of PTFE, e.g. to a melting temperature no greater than 315° C. Such a TFE copolymer typically incorporates an amount of comonomer into the copolymer in order to provide a copolymer which has a melt flow rate (MFR) of at least about 1, or at least about 5, or at least about 10, or at least about 20, or at least about 30, and yet no more than about 100, or no more than about 90, or no more than about 80, or no more than about 70, or no more than about 60, as measured according to ASTM D-1238-10 using a weight on the molten polymer and melt temperature which is standard for the specific copolymer. Preferably, the melt viscosity is at least about 10²Pa·s, more preferably, will range from about 10²Pa·s to about 10⁶Pa·s, most preferably about 10³to about 10⁵Pa·s. Melt viscosity in Pa·s is 531,700/MFR in g/10 min.
In general, thermoplastic, melt-processible and/or melt-fabricable fluoropolymers as used herein include copolymers that contain at least about 40 mol %, or at least about 45 mol %, or at least about 50 mol %, or at least about 55 mol %, or at least about 60 mol %, and yet no more than about 99 mol %, or no more than about 90 mol %, or no more than about 85 mol %, or no more than about 80 mol %, or no more than about 75 mol % TFE; and at least about 1 mol %, or at least about 5 mol %, or at least about 10 mol %, or at least about 15 mol %, or at least about 20 mol %, and yet no more than about 60 mol %, or no more than about 55 mol %, or no more than about 50 mol %, or no more than about 45 mol %, or no more than about 40 mol % of at least one other monomer. Suitable comonomers to polymerize with TFE to form melt-processible fluoropolymers include a Formula I, II, III and/or IV compound; and, in particular, a perfluoroolefin having 3 to 8 carbon atoms [such as hexafluoropropylene (HFP)], and/or perfluoro(alkyl vinyl ethers) (PAVE) in which the linear or branched alkyl group contains 1 to 5 carbon atoms.
Preferred PAVE monomers are those in which the alkyl group contains 1, 2, 3 or 4 carbon atoms, and the copolymer can be made using several PAVE monomers. Preferred TFE copolymers include FEP (TFE/HFP copolymer), PFA (TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE, MFA (TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least two carbon atoms) and THV (TFE/HFP/VF₂). Additional melt-processible fluoropolymers are the copolymers of ethylene (E) or propylene (P) with TFE or chlorinated TFE (CTFE), notably ETFE, ECTFE and PCTFE. Also useful in the same manner are film-forming polymers of polyvinylidene fluoride (PVDF) and copolymers of vinylidene fluoride as well as polyvinyl fluoride (PVF) and copolymers of vinyl fluoride.
Fluoropolymers that are thermoplastic, melt-processible and/or melt-fabricable are in general characterized by a melt flow rate as described above, and can be distinguished from fluoroelastomers, which typically have a glass transition temperature below about 25° C., exhibit little or no crystallinity at room temperature, and/or have a combination of low flex modulus, high elongation, and rapid recovery from deformation. Fluoroelastomers can also be characterized, in various applications, by the definition in ASTM Special Technical Bulletin No. 184 under which they can be stretched (at room temperature) to twice their intrinsic length, and, once released after being held under tension for 5 minutes, return to within 10% of their initial length in the same time.
Fluoropolymers suitable for use herein thus also include fluoroelastomers (fluorocarbon elastomers), which typically contain at least about 25 wt %, or at least about 35 wt %, or at least about 45 wt %, and yet no more than about 70 wt %, or no more than about 60 wt %, or no more than about 50 wt % (based on the total weight of the fluoroelastomer), of a first copolymerized fluorinated monomer such as vinylidene fluoride (VF₂) or TFE; with the remaining copolymerized units in the fluoroelastomer being selected from other, different fluoro-monomers such as a Formula I, II, III and/or IV compound; and, in particular, hydrocarbon olefins. Fluoroelastomers may also, optionally, comprise units of one or more cure site monomers. When present, copolymerized cure site monomers are typically at a level of 0.05 to 7 wt %, based on total weight of fluorocarbon elastomer. Examples of suitable cure site monomers include: (i) bromine-, iodine-, or chlorine-containing fluorinated olefins or fluorinated vinyl ethers; (ii) nitrile group-containing fluorinated olefins or fluorinated vinyl ethers; (iii) perfluoro(2-phenoxypropyl vinyl ether); and (iv) non-conjugated dienes.
Preferred TFE-based fluoroelastomer copolymers include TFE/PMVE, TFE/PMVE/E, TFE/P and TFE/P/VF₂. Preferred VF₂based fluorocarbon elastomer copolymers include VF₂/HFP, VF₂/HFP/TFE, and VF₂/PMVE/TFE. Any of these elastomer copolymers may further comprise units of cure site monomer.
Embodiments of the progressive cavity pump 100 including an elastomeric material 109 such as fluoropolymers (e.g., including the lubricant and a filler) can be made using any suitable processing technique that results in an elastomeric material 109 coating comprising the fluoropolymer matrix, which can include alumina and silica particles dispersed therein.
For example, embodiments based on fluoropolymers that are not melt processible can be made by a sintering or molding technique, in which the components are first mixed (e.g., by mechanical mixing, dispersion in a liquid, or other forms of mixing). The mixture is then transferred to a molding chamber where it is consolidated with pressure. In an implementation, the molding can be done at a pressure of about 20 to 200 MPa for about 10 seconds to 10 minutes and thereafter the fluoropolymer can be heated to above its melting point, held for a period of time (e.g., about 10 minutes to 10 hrs) to permit the fluoropolymer to sinter, and then cooled to ambient temperature. The sintering operation can be carried out under continued application of compression (denominated herein as “compression molding”) or as a free sintering, i.e., without continued application of a compressive force. One possible implementation of a free sintering manufacture is set forth in ASTM Standard No. 1238-10. In other implementations, the consolidation is carried out at a pressure of about 20 to 250 MPa for a time of about 10 sec to 10 min. The sintering may be accomplished by ramping the temperature at a rate of about 2° C. per minute to a preselected temperature of about 360° C. to 390° C. and held for a period of about 1 to 10 hrs) and then cooled (e.g., at about 2° C. per minute) down to room temperature. Optionally, the compressive pressure is maintained during the sintering.
Other methods of making the coating are also contemplated within the scope of the present disclosure. For example, alternative embodiments provide fluoropolymer composite bodies formed by melt processing the composite powder material. In some implementations, the melt processing comprises a multistage process, in which an intermediate is first produced in the form of powder, granules, pellets, or the like, and thereafter remelted and formed into an article of manufacture having a desired final shape. In an implementation, the intermediate is formed by a melt compounding or blending operation that comprises transformation of a thermoplastic resin from a solid pellet, granule or powder into a molten state by the application of thermal or mechanical energy. Requisite additive materials, such as composite powder material bearing fluoropolymers and particle additives (e.g., silica and alumina) prepared as described herein, may be introduced during the compounding or mixing process, before, during, or after the polymer matrix has been melted or softened. The compounding equipment then provides sufficient mechanical energy to provide sufficient stress to disperse the ingredients in the compositions, move the polymer, and distribute the additives to form a homogeneous mixture.
Melt blending can be accomplished with batch mixers (e.g., mixers available from Haake, Brabender, Banbury, DSM Research, and other manufacturers) or with continuous compounding systems, which may employ extruders or planetary gear mixers. Suitable continuous process equipment includes co-rotating twin screw extruders, counter-rotating twin screw extruders, multi-screw extruders, single screw extruders, co-kneaders (reciprocating single screw extruders), and other equipment designed to process viscous materials. Batch and continuous processing hardware suitable for carrying out steps of the present method may impart sufficient thermal and mechanical energy to melt specific components in a blend and generate sufficient shear and/or elongational flows and stresses to break solid particles or liquid droplets and then distribute them uniformly in the major (matrix) polymer melt phase. Ideally, such systems are capable of processing viscous materials at high temperatures and pumping them efficiently to downstream forming and shaping equipment. It is desirable that the equipment also be capable of handling high pressures, abrasive wear and corrosive environments. Compounding systems used in the present method typically pump a formulation melt through a die and pelletizing system.
The intermediate may be formed into an article of manufacture having a desired shape using techniques such as injection molding, blow molding, extruded film casting, blown film, fiber spinning, stock shape extrusion, pipe and tubing extrusion, thermoforming, compression molding, or the like, accomplished using suitable forming equipment. Such embodiments may require that the fluoropolymer powder particles used to form the slurry and composite powder material be composed of a melt-processible fluoropolymer.
In other implementations, material produced by the melt-blending or compounding step is immediately melt processed into a desired shape, without first being cooled or formed into powder, granules, or the like. For example, in-line compounding and injection molding systems combine twin-screw extrusion technology in an injection molding machine so that the matrix polymer and other ingredients experience only one melt history.
In other embodiments, materials produced by shaping operations, including melt processing and forming, compression molding or sintering, may be machined into final shapes or dimensions. In still other implementations, the surfaces of the parts may be finished by polishing or other operations.
In still other embodiments, the composite powder material can be used as a carrier material by which the particles (e.g., filler) are introduced into a matrix that may include an additional amount of the same fluoropolymer used in the composite powder material, one or more other fluoropolymers, or both. For example, the composite powder material may be formed using the present slurry technique with a first fluoropolymer powder material that is not melt-processible, with the intermediate thereafter blended with a second, melt-processible fluoropolymer powder. In an embodiment, the proportions of the two polymers are such that the overall blend is melt-processible. Other embodiments may entail more than two blended fluoropolymers.
Alternatively, the intermediate can be formed with a non-melt processible fluoropolymer and thereafter combined with more of the same fluoropolymer and processed by compression molding and sintering.
It should also be noted that the tribological properties of articles of the present disclosure can be designed for a particular application. Thus, embodiments of the present disclosure can provide articles that can satisfy many different requirements for different industries and for particular components.
It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt % to about 5 wt %, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include traditional rounding according to significant figures of numerical values. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Claims

Therefore, at least the following is claimed:

1. A progressive cavity pump, comprising:

a stator having a hyperboloidal internal bore including a plurality of spiral lobes; and

a rotor comprising a plurality of spiral lobes positioned within the hyperboloidal internal bore of the stator, where a longitudinal axis of the rotor is non-planar, non-parallel, and non-intersecting with a longitudinal axis of the stator.

2. The progressive cavity pump of claim 1, wherein the longitudinal axis of the rotor is offset from the longitudinal axis of the stator and rotated by a defined angle.

3. The progressive cavity pump of claim 2, wherein the defined angle is in a range from about 0.001 degree to about 10 degrees.

4. The progressive cavity pump of claim 2, wherein the longitudinal axis of the rotor is offset from the longitudinal axis of the stator by a defined distance.

5. The progressive cavity pump of claim 4, wherein the defined distance is in a range from about 0.01 inch to about 10 inches.

6. The progressive cavity pump of claim 2, wherein skew axes of the stator and rotor are non-planar, non-parallel, and non-intersecting.

7. The progressive cavity pump of claim 1, wherein the rotor is tapered from a larger end to a smaller end.

8. The progressive cavity pump of claim 7, wherein the taper of the rotor is hyperboloidal.

9. The progressive cavity pump of claim 1, wherein the stator comprises an elastomeric material coating the hyperboloidal internal bore of the stator.

10. The progressive cavity pump of claim 9, wherein the elastomeric material reduces the effect of friction and abrasion when operating under high temperature conditions.

11. The progressive cavity pump of claim 10, wherein the elastomeric material comprises a fluoropolymer.

12. The progressive cavity pump of claim 11, wherein the fluoropolymer is polytetrafluoroethylene (PTFE).

13. The progressive cavity pump of claim 10, wherein the elastomeric material further comprises a filler component.

14. The progressive cavity pump of claim 13, wherein the filler component comprises mullite, pyrophyllite, kyanite, dolomite, or a combination thereof.

15. The progressive cavity pump of claim 10, wherein the elastomeric material has a coefficient of friction in the range of about 0.2 to about 0.4 and a wear rate of about 1×10⁻⁷mm³/Nm or less.

16. The progressive cavity pump of claim 1, wherein the rotor is configured to allow for displacement to adjust an interference fit between the rotor and the stator.

17. The progressive cavity pump of claim 16, wherein the rotor can be displaced along the longitudinal axis of the rotor.