Stator especially adapted for use in a helicoidal pump/motor and method of making same

Abstract

A method of making a stator for a helicoidal pump/motor formed by a network of fibers encapsulated in an elastomer. The core is formed by laying up elastomeric preforms into helical grooves formed in a mandrel and wrapping an elastomeric sheet around helical projections formed in the mandrel. Successive strips of calendered rubber/wire cloth are then laid up into the grooves so as to fill the grooves, which are then wrapped in another layer of calendered rubber/wire cloth. The assembly is then filament wound with reinforcing cords and compression cured so as to bond the elastomeric components into a unitary element. The assembly is then placed in the stator housing and additional elastomer injected into the annular passage between the stator housing and the assembly. The completed assembly is then further cured so that the injected and previously cured elastomers bond to form a unitary structure having good strength and heat transfer capabilities.

Description

FIELD OF THE INVENTION

[0002] The current invention is directed to a stator for a fluid handling device such as a fluid driven motor or a pump. More specifically, the current invention is directed to an improved stator for a helicoidal positive displacement pump/motor and a method for making such stator.

BACKGROUND OF THE INVENTION

[0003] Helicoidal positive displacement pumps, sometimes referred to as Moineau-type pumps, have a wide variety of applications, including the oil producing and food processing industry, where they are used to pump fluids containing solids. In addition, helicoidal motors, which are essentially helicoidal pumps operating in reverse, are used widely in the oil drilling industry. In this application, the drilling mud is used as the driving fluid for a helicoidal motor that serves to rotate the drill bit.

[0004] Typically, a helicoidal pump/motor is comprised of a stationary stator and a helical rotor that orbits eccentrically as it rotates within the stator. The rotor is typically metallic and has one or more helical lobes spiraling around its outside diameter. The stator has a number of helical lobes that form grooves in the stator inner surface that spiral along its length, with the number of helical lobes in the rotor being one less than the number of helical grooves in the stator.

[0005] The stator of a helicoidal pump/motor is typically formed by encasing an elastomeric material, which forms the helical grooves, within a cylindrical metal housing. An interference fit is provided between the stator elastomeric form and the rotor for sealing purposes. As a result of this interference fit, the elastomeric form undergoes deformation as the rotor lobes traverse the surfaces of the stator grooves. Thus, the stator must be strong enough to maintain the dimensional stability necessary to ensure a controlled interference fit and durable enough to withstand abrasion from particles in the fluid, yet be sufficiently flexible to deform under the action of the rotor. Consequently, the maximum capability of a helicoidal pump/motor, e.g., the maximum output torque in the case of a motor, is typically limited by the strength of the elastomer.

[0006] Unfortunately, the hysteresis associated the repeated cyclic stresses induced by the stator elastic deformation can generate substantial heat. Conventional helicoidal pump/motor stators cannot dissipate heat quickly. Consequently, overheating of the elastomer may result. Over time, such overheating causes deterioration and embrittlement of the elastomer. Such deterioration can lead to failure of the stator, for example, by a phenomenon known as “chunking,” in which large pieces of the elastomer are torn off under the action of the rotor.

[0007] One proposed solution to this problem, disclosed in U.S. application Ser. No. 08/950,993, filed Oct. 15, 1997, entitled “Improved Stator Especially Adapted for Use in a Helicoidal Pump/Motor,” now U.S. Pat. No. ______, hereby incorporated by reference in its entirety, involves the incorporation of a network of thermally conductive fibers into elastomer forming the core of the stator. Such a stator has improved strength and rigidity compared to conventional solid elastomer stator so as to ensure that an interference fit will be achieved and maintained between the stator and rotor, thereby providing good sealing. Nevertheless, such a stator core will be sufficiently flexible to undergo the required elastic deformation upon impact with the rotor lobes.

[0008] In addition, the fibers in such a stator form heat conduction paths that improve heat transfer within the stator. For example, the fiber network aids in the transfer of heat from the thick portions of the stator core between the grooves that are subject to the maximum heat generation to the thinner portions within the grooves, as well as the transfer of heat radially outward. Improving the heat transfer characteristics of the stator results in increased heat dissipation to the working fluid, thereby cooling the stator. Moreover, if the fibers are in contact with the housing, they permit the housing to act as a second heat sink in addition to the working fluid, thereby further improving the heat transfer. As can be readily appreciated, this improved heat transfer capability prevents overheating of the portions of the elastomer subject to the highest cyclic stresses. In any event, the fibers serve to strengthen and stiffen the elastomer so that it is better able to withstand a certain amount of degradation in properties without failure or chunking and can operate with less interference with the rotor without leakage.

[0009] Consequently, it would be desirable to provide an improved stator for a helicoidal type pump/motor and a method for efficiently making such a stator.

SUMMARY OF THE INVENTION

[0010] It is an object of the current invention to provide a method of making an improved stator for a helicoidal type pump/motor. This and other objects is accomplished in a method of making a stator for a helicoidal fluid handling device suitable for use as a positive displacement pump or motor, in which the stator comprises an elastomeric form having an inner surface, first portions of the elastomeric form form a number of grooves in the inner surface extending helically along the length of the stator, second portions of the elastomeric form form a projection on the inner surface between each of the grooves, the projections extending helically along the length of the stator, the method comprising the steps of (i) providing a mandrel having a helical groove for each of the stator projections, each of the helical grooves having a contour substantially matching that of its respective projection, (ii) forming a plurality of layers of fiber networks each of which is encapsulated by an elastomer, (iii) laying up successive adjacent layers of elastomeric elements into the mandrel grooves so as to at least partially fill the grooves, at least a portion of the layers comprising layers of elastomeric encapsulated fiber networks, (iv) curing the layers under compression so that the elastomer in each of the layers bonds to the elastomer in adjacent layers.

[0011] The invention also-encompasses an improved stator for a helicoidal fluid handling device suitable for use as a positive displacement pump or motor, the stator comprising an elastomeric form having an inner surface, the inner surface forming a number of grooves extending helically along the length of the stator, the elastomeric form comprising a network of fibers encapsulated in an elastomeric material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is longitudinal cross-section through a helicoidal pump/motor according to the current invention.

[0013] FIG. 2 is a cross-section through the helicoidal pump/motor shown in FIG. 1 taken along line II-II.

[0014] FIG. 3 is a longitudinal cross-section through a stator helicoidal pump/motor made according to the current invention.

[0015] FIG. 4 is is a cross-section taken along line IV-IV shown in FIG. 3.

[0016] FIG. 5 is a view of a mandrel for using in making the stator shown in FIGS. 3 and 4.

[0017] FIG. 6 is is a cross-section through the mandrel shown in FIG. 5 taken along line VI-VI.

[0018] FIG. 7 is a plane view of a sheet of woven wire cloth.

[0019] FIG. 8 is a cross-section through the woven wire cloth shown in FIG. 7 after being calendered with rubber.

[0020] FIG. 9 is a molded rubber insert.

[0021] FIG. 10 is a view of the mandrel shown in FIG. 5 after lay up of the rubber insert shown in FIG. 9.

[0022] FIG. 11 is a transverse cross-section through the mandrel shown in FIG. 10 after application of strips of rubber.

[0023] FIG. 12 is a detailed view in one of the grooves of the mandrel shown in FIG. 11 after lay up of the first strip of calendered rubber/wire cloth.

[0024] FIG. 13 is a view similar to FIG. 12 after lay up of successive layers of calendered rubber/wire cloth and filament winding.

[0025] FIG. 14 is a view of the partially formed stator core after filament winding.

[0026] FIG. 15 is a view similar to FIG. 13 after wrapping of the peel ply fabric, rubber sheet and constraining layer.

[0027] FIG. 16 is a view of partially formed stator core, on the mandrel, after curing and removal of the peel ply fabric, rubber sheet and constraining layer.

[0028] FIG. 17 is a longitudinal cross-section showing the partially formed stator core, on the mandrel, inserted into the stator cylinder and after attachment of the injection equipment.

[0029] FIG. 18 is a transverse cross-section taken along lines XVIII-XVIII shown in FIG. 17.

[0030] FIG. 19 is a cross-section through the stator after injection molding and final curing.

[0031] FIG. 20 is a view of a portion of the completed stator.

[0032] FIG. 21 is an alternate embodiment of the invention using compression curing in an external mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] A helicoidal pump/motor according to the current invention is shown in FIGS. 1 and 2. As is conventional, the pump/motor is comprised of a stator 2 and an elongate rotor 4. The rotor 4 is preferably formed from a metal and features three radially outward projecting lobes 20′, 20″, 20′″, each of which has two opposing convex sides, equally spaced about its periphery. As shown best in FIG. 1, the lobes extend helically around the rotor 4 along its length. The stator 2 has a core 8 encased within a cylindrical housing 6. The stator core 8 is an elastomeric form having an inner surface 12. The inner surface 12 has an undulating profile that forms four helical radially inward extending grooves 16-19 separated by four helical projections 42-45. The grooves 1619 and projections 42-45 are oriented at an angle, the helix angle, to the stator axis so as to wind helically around the stator 8 core along its entire length.

[0034] For purposes of illustration, FIGS. 1 and 2 show the rotor as having three lobes 20′, 20″, and 20′″ and the stator as having four grooves 16-19. However, as those skilled in the art will readily appreciate, the invention could be practiced in helicoidal pump/motors with greater or lesser numbers of rotor lobes and stator grooves. However, in order to function as a helicoidal pump or motor, the rotor must have at least one lobe and the number of grooves in the stator should equal the number of rotor lobes plus one. Consequently, the pitch of the stator grooves is equal to the pitch of the rotor lobes multiplied by the ratio of the number of stator grooves to the number of rotor lobes.

[0035] When the rotor 4 is encased by the stator 2, a series of sealed helical cavities 14, each of which extends one pitch length, are formed between them, as shown in FIGS. 1 and 2. As the rotor 4 rotates, its center line orbits around the centerline of the stator 2. This rotation of the rotor 4 causes the seal cavities 14 to “move” helically along the length of the rotor. If the apparatus is a pump, rotation of the rotor 4 causes the sealed cavities 14 to transport the fluid being pumped. If the apparatus is a motor, the transport of the fluid through the cavities 14 imparts a torque that drives the rotation of the rotor 2. Although in conventional helicoidal pump/motors, the stator 2 is a stationary member and the rotor 4 is a rotating member, it is only necessary that one of the members rotate relative to the other member. For example, a helicoidal pump/motor could also be operated by rotating the stator about a rotor that is held stationary. Consequently, as used herein the term stator refers to the outer member, whether stationary or rotating, and the term rotor refers to the inner member, whether stationary or rotating, than is encircled by the stator.

[0036] A preferred embodiment of a stator 102 for a helicoidal pump/motor is shown in FIGS. 3 and 4. The stator 102 is comprised of a stator core 108 and a cylindrical housing 106. In this embodiment, the undulating inner surface 112 of the stator 102 forms five helically extending grooves 116-120 separated by five helically extending projections 142-146, all of which are oriented at helix angle “A” to the axial centerline of the stator. Such a stator would be suitable for use in a helicoidal pump/motor in which the rotor had six lobes.

[0037] A preferred method of making the stator 102 will now be discussed in detail. FIGS. 5 and 6 show a mandrel 200, which is preferably made of steel, for use in the manufacture of the stator 102. The mandrel 200 has five helical projections 116′-120′ having contours that match those of the stator grooves 116-120 except that they are inverted—that is, they extend radially outward rather than inward. Similarly, the mandrel 200 has five helical grooves 142′-146′ having contours that match those of the stator projections 142-146 except that they are also inverted in that they extend radially inward rather than outward. The mandrel 200 has threaded portions 202 and 204 at each of its ends.

[0038] Manufacture begins with the preparation of a network of fibers, such as a woven wire cloth 150, shown in FIG. 7. Preferably, the woven wire cloth 150 is formed from fibers made from a material that is strong and has a high coefficient of thermal conductivity, such as a metal and most preferably copper. However, other materials, such as Kevlar™ or graphite could also be used. In general, any material, whether organic or inorganic, that is capable of increasing the strength or heat transfer characteristics of the stator can be advantageously used. The wire cloth 150 is comprised of a first group of fibers 152 extending in one direction that are interwoven with a second group of fibers 154 extending in a second direction, which is preferably perpendicular to the first direction.

[0039] Preferably, the fibers 152 and 154 are interlaced so that they contact each other. Contact between the fibers aids in the conduction of heat throughout the fiber network and, therefore, through the elastomer forming the stator core 108. Interlacing can be achieved by weaving together multiple fibers, for example, into a layer of flexible fabric as discussed above. The fibers may also be interlaced by knitting them together, thereby interlocking the fibers with respect to each other. Such interlocking has the advantage of restraining relative motion between the fibers as the stator core 108 undergoes deflection, thereby increasing the stiffness of the core 108 and reducing the heat generation. In addition, interlocking assures good contact between fibers from different groups, thereby facilitating the transfer of heat along the network of fibers. Alternatively, or in addition to knitting, all or a portion of the fibers can be interlocked by brazing or epoxying the fibers together where they cross so as to restrain relative motion and ensure good contact between the fibers.

[0040] In a preferred embodiment of the invention, the fiber network is formed by a copper woven wire cloth that is 36 inches wide and has a mesh size of 16×16×0.011 inch. The cloth is preferably abrasively cleaned using 170 to 325 grit glass beads and then coated with a bonding agent, such as CilBond 10™, available from Compounding Ingredients Ltd., 217 Summit Road, Walten Summit Center, Bamber Bridge, Preston, PR58AQ, Lancashire, England 01772-311844. Next, a sheet of uncured elastomer, preferably 0.032 inch thick nitrile rubber, is calendered onto the woven wire cloth 150 so as to encapsulate the fiber network and form a rubber/wire cloth 156, shown in FIG. 8.

[0041] Although as illustrated, the fiber network in the cloth 156 consists of only one layer of fibers, the cloth could be formed by laying successive layers of fiber networks and elastomer sheets on top of each other and calendering the entire sandwich so as to form a multilayer network of elastomeric encapsulated fibers. In addition, although as illustrated only two groups of fibers are utilized, additional groups of fibers, including fibers extending in a third direction, such as the radial direction, could be incorporated into the fiber network.

[0042] In addition to forming the cloth, five strips of uncured elastomer, such as nitrile rubber, are extruded or formed in a mold so as to form preforms 158 having a shape that conforms to the innermost portion of the profile of the grooves 142′-146′ of the mandrel—that is, the outermost portion of the profile of the projections 142-146 of the stator core 108, as shown in FIG. 9. Each preform 158 is then laid up in one of the mandrel grooves 142′-146′ by wrapping it helically around the mandrel so as to follow the grooves, as shown in FIG. 10. In addition, five sheets 160 of uncured elastomer, preferably nitrile rubber 0.032 inch thick, are laid up on the projections 116′-120′ of the mandrel 22 by wrapping them helically around the mandrel so as to follow the projections, as shown in FIG. 11. The rubber sheets 160 ensure that the inner surface 112 of the stator core 108 will be formed by rubber, leaving the fibers unexposed, thereby protecting the rotor from wear. In addition, the rubber sheets 160 protect the mandrel 200 from damage by contact with the fibers.

[0043] Strips 162 are then cut from the calendered rubber/wire cloth 156. Preferably, but not necessarily, each strip 162 is sufficiently long to extend the entire length of the stator 102 when wrapped helically around it. Each strip 162 is then laid up in one of the mandrel grooves 142′- 146′, on top of a preform 158, by wrapping it helically around the mandrel so as to follow the grooves, as shown in FIG. 12. Preferably, the strips 162 are laid up so as to facilitate the transfer of heat from the hotter portions of the stator core to the cooler portions. In a preferred embodiment, each strip 162 is cut so that its second group of fibers 154 follows the mandrel groove so as to extend parallel to the helix angle, while its first group of fibers 152 extends perpendicular to the helix angle so that, in the finished stator, the first group of fibers traverse from the portion of the stator core forming one of the projections 142-146 to the portions forming the grooves 116-120, thereby aiding in the transfer of heat from the projections to the grooves. Alternatively, the strips 162 can also be cut from the cloth 156 at an angle so that both the first and second groups of fibers extend at an angle to the helix angle, such as axially or circumferentially, so that neither group of fibers follows the helix but, rather, both groups traverse across it, extending from the projections to the grooves of the stator core. Using the methods discussed above, additional strips 163-170 are then cut from the calendered rubber/wire cloth 156 and successively laid up into each of the mandrel grooves on top of the previous, adjacent layer so as to completely fill the groove, as shown in FIG. 13. In the finished product, the strips 162-170, together with the preforms 158 will form the stator projections 142-146. At this point, the assembly has an approximately cylindrical outer surface.

[0044] The width of the strips can be varied so to efficiently fill each groove. In addition, at least a portion of the strips 162-170 should be laid up so that the fibers in at least one of the groups of fibers are displaced from the stator axis by a distance that varies along as the fibers extend along their paths, thereby aiding in the radial transfer of heat. This is dramatically illustrated in the finished product shown in FIG. 20, in which the first strip 162, for example, was laid up so that the fibers in the first group of fibers 152 in that strip extend along a path that approximately follows the undulations of the inner surface 112 of the stator-core 102.

[0045] Although as illustrated, each groove 142′-146′ is filled using a plurality of strips 162-170, each grooves could also be filled by a single strip comprising multiple layers of fiber networks encapsulated by elastomer, for example, by cutting a strip from a thick cloth formed by calendering a sandwich of multiple layers of fibers networks and elastomeric sheets, as previously discussed.

[0046] After the mandrel grooves 142′-146′ have been filled by the strips 162-170, a layer 171 of the calendered rubber/wire cloth 156 is wrapped around the entire assembly. Unlike the prior layers, it is not necessary that the layer 171 extend along the helix angle—that is, it can be wrapped at angle greater than the helix angle so as to extend almost directly circumferentially. The layer 171, however, should be sufficiently wide and wrapped in such a manner so that it encloses the entire approximately cylindrical surface of the assembly.

[0047] The entire assembly is next strengthened by filament winding reinforcing cords 172-174 around the assembly, as shown in FIGS. 13 and 14. Preferably, this is accomplished by filament winding 0.20 SHT hose reinforcing wire, available from Bekaert, Rome, Georgia. Although the reinforcing cord is preferably made from steel, however, other materials having sufficient strength could also be utilized. Although only three layers of reinforcing cord 172-174 are shown in FIG. 13, preferably, a total of 15 layers of cord are wound around the assembly.

[0048] As shown in FIG. 14, collars 206 and 208 having winding lugs 210 are threaded onto the ends 202 and 203 of the mandrel 200. The winding lugs allow the direction of winding to be reversed with each successive pass of the reinforcing cord. As the cord approaches a mandrel end, it is looped around between two lugs 210, wrapped around 120° to 180°, and its direction is reversed. Preferably, the six innermost layers of cord are wound at a helix angle of that alternates between approximately +65° and −65°, followed by nine layers of cord that are wound at a helix angle of that alternates between approximately +33° and −33°. There should be sufficient gaps between the reinforcing cord 172-174 to permit the passage of elastomer during injection, discussed further below. The winding pressure should be sufficiently snug to keep the assembly tight but not cut into the rubber.

[0049] As shown in FIG. 15, a protective fabric 180, such as a nylon peel ply fabric, available from Northern Fiberglass Sales in Hampton, NH, is then wrapped about the filament reinforced assembly. The protective fabric 180, which is preferably applied in two layers, protects the elastomeric surface of the assembly and keeps it free of contaminants prior to curing. A layer 182 of material having a relatively high coefficient of thermal expansion, such as ⅛ inch thick silicon rubber of 40 to 50 durometer, is then wrapped around the protective fabric 180. Finally, a constraining layer 184 of a material that is strong and has a relatively low coefficient of thermal expansion is then wrapped around the layer 182 of high thermal expansion material. Preferably, the constraining layer 184 is formed by filament winding two layers of Kevlar™ tows of 28/40 Denier Kevlar™ 49 around the entire outer surface so as to completely cover the layer 182.

[0050] Aluminum end caps (not shown) are then threaded on the mandrel ends 202 and 203. The end caps prevent movement of rubber axially out of the assembly while the constraining layer 184 prevents movement of the rubber radially outward.

[0051] The entire assembly is then compressively cured. The compressive curing process will depend on the type of elastomer used but, for nitrile rubber, curing should preferably be at about 265° F. for 2 hours. Alternatively, the assembly could be only partially cured at this time, for example, by subjecting it to 165° for 4 hours and fully cured following injection, discussed below. During curing, the layer 182 of high thermal expansion material, such as silicon rubber, will expand more than the layer 184 of low thermal expansion material, such as Kevlar™, and, therefore, be constrained from expanding radially outward by the layer 184. This will result in the generation of large radially inward pressures, as much as several hundred to several thousand pounds per square inch, causing the layers of nitrile rubber to bond and to flow into any gaps within the assembly. Following curing, the layers 182 and 184 can be removed.

[0052] In the embodiment discussed above, compressive curing is performed without the use of an external mold. Alternatively, compressive curing can be accomplished by installing the assembly, wrapped in the protective layer 180, in a heated compression mold 300, shown in FIG. 21. Pressure is then applied to the molding sections 301-305 so that they compress the assembly together, eliminating any air gaps. Heat is transferred from the mold sections 301-305 to the assembly, thereby causing curing to occur. In this embodiment, the layers 182 and 184 are not necessary.

[0053] Regardless of the technique utilized, after compressive curing, the rubber preform 157, rubber layer 160, and the layers 162-171 of calendered rubber/wire cloth will preferably have formed a seamless, unitary elastomeric element 186, as shown in FIG. 16. Note that in FIG. 16 both groups of fibers 152 and 154 in the network of fibers are shown.

[0054] Following compressive curing, the peel ply layer 180 is removed and the assembly is placed within the stator housing 106, which is preferably made from steel, as shown in FIGS. 17 and 18. It is important that outside diameter of the assembly not be touched after the peel ply is removed. Preferably, the inner surface of the stator housing 106 is coated with a bonding agent. As shown in FIG. 17, a flow guide 214 is threaded onto the winding lug collar 208 at one end 202 of the mandrel 200. An injection head 212 is also threaded onto the end 202 of the mandrel 200. An end cap (not shown) is threaded onto the other end 203 of the mandrel 200 to prevent movement of elastomer axially out of the assembly. A plurality of injection ports 214 are circumferentially spaced around the injection head 212. The flow guide 214 directs the flow of elastomer from the ports 214 to the annular passage 220 formed between the outer surface of the stator core assembly and the inner surface of the stator housing 106. Preferably, the inside diameter of the stator housing 106 is enlarged in the vicinity 108 of the flow guide 214 to facilitate the flow of elastomer into the passage 220.

[0055] Preferably, the assembly is heated to 165° for 12 hours prior to injection. Using techniques well known in the art, uncured elastomer, such as nitrile rubber, is injected into the passage 220 of the heated assembly. A low injection flow rate should be used to reduce stress on the previously cured rubber. Following injection, the assembly is cured at 265° F. for two hours. The curing causes the injected rubber 190 and the previously cured rubber 158, or previously partially cured rubber, to bond into a preferably seamless, unitary elastomeric element that forms the stator core 108, thereby bonding the stator core to the stator housing 106, as shown in FIG. 19.

[0056] As shown in FIG. 20, the finished stator 102 is comprised of a stator core 108 formed by an elastomeric element bonded to the stator housing 106 and having a network of fibers 152 and 154 that strengthen the core and transfer heat from the hotter to the cooler portions, as well as reinforcing cord 172-174 that further strengthen the assembly.

[0057] Although the current invention has been illustrated in connection with a helicoidal type pump/motor, the invention is also applicable to other fluid handling devices in which an elastomeric stator is used. Accordingly, the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

1. A method of making a stator for a helicoidal fluid handling device suitable for use as a positive displacement pump or motor, said stator comprising an elastomeric form having an inner surface, first portions of said elastomeric form forming a number of grooves in said inner surface extending helically along the length of said stator, second portions of said elastomeric form forming a projection on said inner surface between each of said grooves, said projections extending helically along the length of said stator, comprising the steps of: a) providing a mandrel having a helical groove for each of said stator projections, each of said helical grooves having a contour substantially matching that of its respective projection; b) forming a plurality of layers of fiber networks each of which is encapsulated by an elastomer; c) laying up successive adjacent layers of elastomeric elements into said mandrel grooves so as to at least partially fill said grooves, at least a portion of said layers comprising said said layers of elastomeric encapsulated fiber networks; d) curing said layers under compression so that said elastomer in each of said layers bonds to said elastomer in adjacent layers.

2. The method according to claim 1, further comprising the steps of: e) enclosing said cured layers, while maintained on said mandrel, in a stator housing so as to form an annular passage therebetween; f) injecting additional elastomer into said annular passage; g) curing said injected elastomer so as to bond said injected elastomer to said previously cured layers.

3. A stator for a helicoidal fluid handling device suitable for use as a positive displacement pump or motor, said stator comprising an elastomeric form having an inner surface, said inner surface forming a number of grooves extending helically along the length of said stator, said elastomeric form comprising a network of fibers encapsulated in an elastomeric material.