Patent Application
20120102738
Progressing cavity pumping systems, including progressing cavity motors and progressing cavity pumps, are used in a wide variety of applications. For example, progressing cavity pumping systems are employed in downhole, well applications to pump oil, water, or other types of fluids. A typical progressing cavity pumping system comprises a helical rotor which rotates within a helical stator. As the helical rotor rotates, progressing cavities are formed between the rotor and the stator in a manner which forces fluid from an inlet end to an outlet end of the system.
The efficiency with which fluid is moved through the progressing cavity pumping system depends at least in part on having a properly formed exterior of the helical rotor to form the desired progressing cavities. However, existing methods of forming the pumping system rotor present difficulties in obtaining and maintaining the desired external shape of the rotor. If the rotor is not constructed with the desired shape or if the desired shape is detrimentally changed during pumping, the overall pumping system will have a reduced pumping efficiency.
In general, a method is provided for making a progressing cavity pumping system rotor having a desired shape to facilitate pumping. The method comprises placing a resilient layer over a rotor core to create a composite progressing cavity pump system rotor. Generally, the rotor core is formed from a relatively harder material, such as a metallic material, including, but not limited to metals, composites, and powdered metals. Additionally, the composite rotor is placed in a mold which is designed to enhance the desired exterior surface shape of the resilient layer and to help secure the resilient layer to the rotor core.
Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
The embodiments described herein generally relate to a method for making an improved progressing cavity pumping system, such as a progressing cavity motor or a progressing cavity pump. A progressing cavity rotor is constructed in a manner which facilitates formation of a long-lasting rotor which has an outer layer with improved material properties and a more precisely defined surface contour to enhance the pumping action of the overall progressing cavity pumping system. The method provides better control over formation of the outer material layer to facilitate the maximization of desired material properties and to enhance the pumping efficiency which results from achieving a more optimal and longer-lasting surface contour of the rotor.
According to one embodiment, a method of manufacturing a thin resilient layer rotor for progressing cavity pumping systems is provided. The method may be applied to either uniform or nonuniform resilient layers affixed over a rotor core. In this particular embodiment, the rotor is subject to a compression molding technique in which a rotor core is covered by the resilient layer and introduced to a multi-segmented mold. The mold is constructed to enable pressure buildup within the mold to promote optimal properties of the resilient layer and an improved bonding to the rotor core.
In one example, the mold is constructed to expand less than the rotor core, and this differential in thermal expansion causes the desired increase in pressure within the mold during heating. By way of example, the relatively reduced expansion of the mold can be achieved when the mold is closed over the composite rotor and secured with bolts having a low coefficient of thermal expansion relative to the material used to form the rotor core. In this manner, the interior surface of the mold is held to a reduced expansion as the rotor core expands during a heating process, thereby increasing internal pressure.
Referring generally to
In
Referring generally to
The composite, progressing cavity pump rotor 44 comprises a rotor core 54 to which a surrounding, resilient layer 56 is affixed. The composite rotor 44 may have a variety of forms and configurations depending on the design and the capacity of the overall progressing cavity pumping system 24 and on the environment in which the pumping system 24 is operated. For example, both the rotor core 54 and the resilient layer 56 may have a variety of surface contours 58, 60, respectively, as further illustrated in
In the specific example illustrated, composite rotor 44 is formed as a helical rotor. Depending on the desired pumping capacity and pumping characteristics of pumping system 24, the helical, composite rotor 44 may be formed as a multi-lobe rotor having a plurality of rotor lobes 62 (see
To enhance a long-lasting affixation of resilient layer 56 to rotor core 54, an adhesive 66, e.g. an adhesive layer, may be applied between rotor core 54 and resilient layer 56. For example, an adhesive layer may be applied to the external, contoured surface 58 of rotor core 54. Additionally, or in the alternative, adhesive may be applied to an interior of the resilient layer 56 prior to placing the resilient layer 56 around rotor core 54. In some embodiments, the resilient layer 56 is positioned over rotor core 54 in tubular form or by wrapping a sheet of the resilient material over the rotor core. For example, the resilient layer 56 may be formed as a rubber sleeve and positioned over the rotor core 54 prior to the molding process. The adhesive 66 can be applied prior to locating the resilient layer material over the rotor core and prior to the molding process. Furthermore, the adhesive 66 may be cured during the molding process or the adhesive may be allowed to set independently of the molding process, depending on the specific type of adhesive desired and on the types of materials used to form the rotor core 54 and the surrounding resilient layer 56.
The materials of rotor core 54 and resilient layer 56 may be selected according to a variety of parameters related to the progressing cavity pumping system 24 and/or the environment in which the pumping system is employed. For example, many applications are amenable to employing a metallic rotor core 54, although other materials, e.g. ceramic materials, may be suitable in some applications. By way of example, the metallic rotor core 54 may be constructed from materials such as steel, stainless steel, aluminum, titanium, and other suitable metals. As used herein, metallic rotor core includes rotor cores (e.g., 54) formed from composite materials and powder metal cores. According to one embodiment, rotor core 54 is formed as a composite rotor core by combining materials, such as metallic and non-metallic materials; dissimilar metallic materials; or dissimilar non-metallic materials.
Similarly, the resilient layer 56 may be formed of several types of suitable materials, including polymer materials, rubber materials, and other resilient materials. The materials are selected based, at least in part, on their suitability for long-term use in the working conditions of the composite rotor 44. For example, if the progressing cavity pumping system 24 is employed in a downhole, wellbore environment, the resilient material 56 must be able to function properly in the high temperature, high-pressure, and deleterious chemical environment often found downhole. Resilient layers 56 formed of rubber may be selected from the families of rubbers acceptable for downhole use, including fluoroelastomers (Viton or similar rubbers), per-fluoroelastomers, carboxylated hydrogenated nitrile-butadiene rubber (XHNBR), hydrogenated nitrile-butadiene rubber (HNBR), nitrile-butadiene rubber (NBR), and various nitrile rubbers. The rubber material forming resilient layer 56 also may be fully or only partially cured depending on the application. In some environments and applications, high temperature resistant polymers also may be employed. Examples of such polymers include polymers which become rubbery above their glass transition temperature (Tg), such as polyetheretherketone (PEEK). These latter types of materials are non-resilient at room temperatures, but they become resilient when heated above their known or predetermined glass transition temperatures (Tg). Depending on the materials selected for the rotor core 54 and the resilient layer 56, adhesive 66 may be applied between the rotor core 54 and the resilient layer 56 to improve the bonding therebetween.
In an alternate embodiment, the external surface of the rotor core 54 and/or the internal surface of resilient layer 56 may be prepared in a manner also designed to enhance bonding between the rotor core 54 and resilient layer 56. For example, a surface treatment such as a plasma treatment can be applied to one or more of the bonding surfaces. The surface treatment may be used alone or in combination with adhesive 66 to improve the bonding between materials.
Regardless of whether adhesive 66 is applied between the rotor core 54 and resilient layer 56, the resilient layer 56 is securely bonded to the rotor core 54 by a molding process. The rotor core 54, e.g. metallic rotor core, and the surrounding layer of resilient material 56 are placed within a mold 68, as illustrated in
The mold 68 may be constructed with different numbers of molded pieces 70 having different configurations, but regardless of the number and configuration, the mold pieces cooperate to provide an interior mold surface 76 which has an appropriate profile to form the desired surface contour/profile 60 of resilient layer 56. By way of example, mold surface 76 may be formed in a helical shape with an opposite profile of the finished composite rotor 44 to ensure the mold shell provides resilient layer 56 with the precise and desired final profile to enable efficient pumping when operated in the corresponding stator 46.
Mold 68 is designed to facilitate affixation of the resilient layer 56 to the rotor core 54 and to provide a specific, long-lasting surface contour 60 for the resilient layer 56. In other words, the multipiece mold 68 is designed to enhance an exterior surface shape of the resilient layer 56 by enabling application of one or more desired mold processes to the composite rotor 44. According to one embodiment, the materials and configuration of mold 68 are selected such that during application of heat to mold 68 and rotor core 54, the rotor core expands greater than the corresponding mold pieces 70 to cause pressure buildup inside the mold as the temperature rises. The mold 68 (or portions of the mold 68) may be constructed from materials having a lower thermal coefficient of expansion than that of the material used to construct rotor core 54. Depending on the materials used to construct composite rotor 44, components of mold 68 may be formed from a variety of materials, including steel, stainless steel, aluminum, titanium and other suitable materials.
In the specific example illustrated, bolts 74 may be constructed from material having a lower coefficient of thermal expansion compared to the rotor core 54. Consequently, heating of the rotor core 54 and/or mold pieces 70 causes greater expansion of the rotor core and thus increased pressure within a mold cavity 78 defined by mold surface 76. The increased pressure causes improved formation of the surface contour 60 and better adhesion between resilient layer 56 and rotor core 54. In some applications, vacuum passages 80 also may be formed in rotor core 54 for cooperation with the contoured rotor core surface 58. The vacuum passages 80 allow application of a vacuum to an interior of resilient layer 56 during the molding process to further enhance adherence of the resilient layer 56 to the rotor core 54 while creating a precisely defined external surface contour 60.
In other embodiments, alternate or additional techniques may be employed to build up pressure within mold 68. The increased pressure enhances bonding of the resilient layer 56 to rotor core 54 and also improves the external profile 60 of the resilient layer 56. Examples of alternate techniques to increase the mold pressure acting on the resilient layer 56 of composite rotor 44 include application of mechanical or hydraulic clamping pressure against the mold pieces 70 to increase the internal pressure between the internal surface 76 of the mold and the composite rotor 44 located therein. The mechanical or hydraulic clamping pressure may be applied alone or in combination with heating, as described above. Additionally, shrinkable wraps including shrinkable nylon wrapping can be placed around the mold pieces 70 to increase the pressure. When the shrinkable wrapping passes a certain temperature, the material begins to shrink and applies a clamping force to the mold to increase internal pressure. Independent of the method used for building internal pressure, the composite rotor 44 may be molded as a single, long unit in a single molding run. Alternatively, the composite rotor 44 may be molded in sections in which shorter sections of the composite rotor 44 are separately subjected to the molding process. For example, short adjacent sections of the composite rotor may be molded sequentially. Other methods of mold filling also may be employed, including transfer molding and injection molding. For example, the resilient layer 56 can be injection molded around the rotor core 54.
Referring generally to
As illustrated in
If adhesive 66 is employed, the adhesive 66 may be applied between the tube or sheet of resilient material 56 and the rotor core 54 to securely adhere the resilient layer 56 to the rotor core 54, as represented by block 86. By way of example, the adhesive 66 may be applied onto a metal material of the rotor core 54 and/or to an internal surface of the resilient material used to form resilient layer 56. In many applications, the adhesive 66 is applied before the resilient material is positioned around the rotor core. Additionally, several techniques may be employed for applying the adhesive 66, including spraying, brushing, and other suitable application techniques.
The rotor core 54 and the resilient layer 56 are then located in the multipiece mold 68, as represented by block 88. By way of example, the combined rotor core 54 and resilient layer 56 may be positioned generally in the middle of the open mold 68 and can be centralized by an appropriate fixture, such as end caps fitted at longitudinal ends of the mold 68. The internal mold surface 76 may be prepared with an appropriate release agent to facilitate release of the composite rotor 44 after completion of the molding process. Subsequently, the mold 68 is closed over the combined rotor core 54 and resilient layer 56. Depending on the design of mold 68 and mold pieces 70, the technique for closure of the mold may vary. However, in the example illustrated in
Once mold 68 is closed, a desired molding process is conducted to create desired properties of the composite rotor 44, as represented by block 90. For example, the molding process may be designed to ensure affixation of the resilient layer 56 to rotor core 54, to obtain desired properties in the resilient layer, and/or to enhance the outer surface contour of resilient layer 56. Additionally, the shell design of mold 68 and the material selection for both mold 68 and rotor core 54 may further facilitate the molding process.
As described above, the materials of mold 68 and rotor core 54 may be strategically selected to cause a buildup in pressure during heating. For example, heat may be applied to the mold 68 and/or the internal composite rotor 44 during curing of resilient layer 56. The heat causes the rotor core 54 and the mold 68 to expand. However, if the materials are selected properly the rotor core 54 expands more than the surrounding mold components 70 to create the increased pressure. One method for limiting the expansion of mold 68 is to use bolts 74 with low thermal expansion in a multipiece mold design, such as that illustrated in
The profile of composite rotor 44 is controlled by making the appropriate design/material choices for both the rotor core 54 and the mold shell 68, e.g. selecting materials with dissimilar coefficients of thermal expansion. However, other components and materials also may be selected to affect the resultant, composite rotor 44. For example, the resilient layer 56 may be inserted into mold 68 with rotor core 54 as a partially cured rubber. When the mold is closed and temperature is applied, the elastomer/rubber is fully cured. The heating and curing also is beneficial in assisting bonding of a variety of resilient materials to the rotor core 54 which may be formed from a metallic material. Thus, the molding process may be used to improve the component stability of the composite rotor 44 and extend the life of the progressing cavity pumping system 24. The curing and/or application of heat and pressure further ensures that the outer rotor profile accurately matches the designed profile selected for use with a given stator 46. Following the heating/curing process, mold 68 is opened and the composite rotor 44 is removed for use in a corresponding stator 46.
The progressing cavity pumping system 24 may be designed for use in many types of applications in downhole locations or other locations. Additionally, the materials employed are selected according to the application and environmental factors to which the pumping system is subjected. The contour of the rotor core and the consequent contour of the resilient layer also may be selected according to the parameters of a given application and/or environment. For example, the resilient layer may be of a constant thickness or variable thickness. Additionally, the number, pitch, and configuration of the rotor lobes may be selected according to the specific parameters of a given application. Similarly, the number, design, and materials of the mold may vary according to the size, configuration, materials, and desired end characteristics of the composite rotor.
Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.
