WO2011089471A2

WO2011089471A2 - Composite insulator

Info

Publication number: WO2011089471A2
Application number: PCT/IB2010/003442
Authority: WO
Inventors: Michael R. Maroney
Original assignee: Maclean Power, Llc
Priority date: 2009-12-01
Filing date: 2010-12-01
Publication date: 2011-07-28
Also published as: WO2011089471A3

Abstract

Disclosed herein is a composite insulator and methods of making a composite insulator for use on an electric power line wherein the insulator comprises a composite body coupled to a conductor and further including at least two connectors and a housing which substantially encloses the composite body.

Description

Composite Insulator

FIELD

[0001] Embodiments disclosed herein relate to composite insulators for electric power distribution and transmission systems.

BACKGROUND

[0002] Insulators have been made with various materials. For example, insulators have been made of a ceramic or porcelain material. The ceramic and porcelain insulators, however, are heavy and bulky; they require specialized assembly fixtures or processes and are awkward and difficult to handle and ship. The ceramic insulators are britde and easily chipped or broken.

[0003] As noted in Application No.10/173,386, filed on June 16, 2002, entitled "Composite Insulator for Fuse Cutout," the disclosure of which is incorporated herein by reference, problems have arisen with electrical insulators. One such problem occurs when electricity flashes directly from a conducting surface to a grounded surface. This phenomenon is referred to as "flashover." The electricity travel gap between the conducting surface and the grounded surface is called the "strike distance."

[0004] Another problem occurs when the electrical current travels or "creeps" along the surface of the insulator. "Creep" results when the insulator has an inadequate surface distance. This may occur when water, dirt, debris, salts, air-borne material, and air pollution is trapped at the insulator surface and provide an easier path for the electrical current. This surface distance may also be referred to as the "leakage," "tracking," or "creep" distance.

[0005] Because of these problems, insulators must be made of many different sizes so as to provide different strike and creep distances, as determined by operating voltages and environmental conditions. The strike distance in air is known, thus insulators must be made of various sizes in order to increase this distance and match the appropriate size insulator to a particular voltage. Creep distance must also be increased as voltage across the conductor increases so that flashover can be prevented.

[0006] Plastic or polymeric insulators have been designed to overcome some of the problems with conventional insulators. However, none of the prior plastic insulators have solved some or all of the problems simultaneously. For example, polymeric insulators have been made with "fins" or "sheds" which require time and labor for assembly. U.S. Pat. No. 4,833,278 to Lambeth, entitled "Insulator Housing Made From Polymeric Materials and Having Spirally Arranged Inner Sheds and Water Sheds," the disclosure of which is hereby incorporated herein by reference, discloses a resin bonded fiber tube made through filament winding (Col 5, 11. 15-17) with spiral ribs of fiberglass and resin to support a series of circular "sheds" (Col. 5, 11. 28-31; see also Fig. 1).

[0007] Other insulators require a complicated assembly of metal end fittings. For example, an electrical insulator is disclosed in U.S. Pat. No. 4,440,975 to Kaczerginski, entitled "Electrical Insulator Including a Molded One-Piece Cover Having Plate -like Fins with Accurately Displaced Mold Line Segments," the disclosure of which is incorporated herein by reference. However, the insulator of Kaczerginski involves a more complicated assembly of two end pieces and an insulating rod of an undisclosed material. Col. 1, 11. 66-68.

Similarly, in U.S. Pat. No. 4,246,696 to Bauer et al., the disclosure of which is incorporated herein by reference, an insulator having a prefabricated glass fiber rod manufactured through a pultrusion process is disclosed. Col. 3, 11. 47-49. Yet, the insulator of Bauer et al. requires a complicated attachment of metallic suspension fittings by fanning out the fiber reinforced stalk or by forcing the fittings on by pressure. Col. 3, line 67 to Col. 4, line 2.

[0008] Therefore, there exists a need for simple design that facilitates ease in the manufacture of the many different-sized cutouts and insulators the electrical power industry requires. There also exists a need for a lighter insulator that allows for greater ease in handling and shipping. Further, there exists a need for an insulator, which will not trap water, dirt, debris, salts, and air-borne material and thereby reduce the effective creep distance. Finally, there exists a need for a stronger insulator, which will not chip or break during shipping and handling.

SUMMARY

[0009] Disclosed herein are embodiments of an insulator for an electric power line. One embodiment comprises a composite body having at least two connectors and a housing. The composite body is coupled to a conductor. The composite body is located inside the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

[00010] Figure 1 is a frontal view of an embodiment of a composite insulator with an

F-neck and a tapped stud base as connectors; [00011] Figure 2 is an enlarged view of the outside of an embodiment of a composite insulator described herein;

[00012] Figure 3 depicts a cross-sectional view of a sheath;

[00013] Figure 4 depicts a method of forming an embodiment of a composite insulator described herein;

[00014] Figure 5 depicts a method of forming an embodiment of a composite insulator described herein;

[00015] Figure 6 depicts a method of forming an embodiment of a composite insulator described herein;

[00016] Figure 7 depicts an embodiment of a composite insulator with a "C" shaped connector and a bracket;

[00017] Figure 8 is a partial cross-sectional view of an embodiment of a body for a composite insulator with a shed, a "C" shaped connector and a bracket;

[00018] Figure 9 depicts a cross-sectional view of an embodiment of a composite insulator with "U" shaped connector;

[00019] Figure 10 is a perspective view of an end fitting for use with a composite insulator described herein; and

[00020] Figure 11 is a sectional view of an end fitting of Figure 10.

[00021] Figure 12 is a cross-sectional view of a body located within a housing with a hollow core and a fitting secured to the end;

[00022] Figure 13 is a cross-sectional view of a body located within a housing with an insulating material substantially filling the hollow core and a fitting secured to the end;

[00023] Figure 14 is a cross-sectional view of a body located within a housing with an insulating material substantially filling the hollow core, a barrier layer, and a fitting secured to the end;

[00024] Figure 15 is a cross-sectional view of a body located within a housing with a hollow core and a fitting secured to the end;

[00025] Figure 16 is a cross-sectional view of a body located within a housing with an insulating material substantially filling the hollow core with a barrier layer and a fitting secured to the end; [00026] Figure 17 is a cross-sectional view of a body located within a housing with an insulating material substantially filling the hollow core, a barrier layer, a fitting secured to the end, and a plate sealing the hollow core;

[00027] Figure 18 is a cross sectional view of a body located within a housing with an insulating material substantially filling the hollow core, a barrier layer, and closed-end fitting without a port secured to the end.

DETAILED DESCRIPTION

[00028] FIG. 1 depicts an embodiment of an insulator 10. The insulator 10 is provided with a body 30. In FIG. 1, the body 30 is located within a housing 50 located between end fittings 114, 116, and hence, is shown in dashed lines. In one embodiment, the housing 50 is made of a suitable polymer, such as silicone rubber. The body 30 is a cylinder of composite material and provided with a body axis 20. In one embodiment, the composite material is made from substances which provide electrically insulating properties, advantageously, a fiber impregnated with an epoxy resin. In one embodiment, a glass fiber impregnated with epoxy resin is used. In another embodiment, an aramid fiber impregnated with epoxy resin is used. In a further embodiment, a polyester fiber impregnated with epoxy resin is used.

[00029] In one embodiment, the body 30 is fabricated by a process referred to herein as filament winding. In fabricating the body 30 through filament winding, resin impregnated fibers are wound around an appropriately shaped mandrel, preferable a cylindrically shaped or frusto-conically shaped mandrel. In yet another alternative embodiment, the body 30 is fabricated by rolling a plurality of sheets of pre -impregnated unidirectional material around a mandrel. While fibers can be wound (or rolled as the case may be) around a mandrel, in an alternative embodiment, a braided or triaxial sock can be slipped over a mandrel, taped, and then cured in an oven. Alternatively, the epoxy resin can be cured by exposing the material to UV light. In still other embodiments, the body 30 is fabricated through other processes, such as extrusion.

[00030] In the case of a filament wound body 30, a hollow core 31 is created.

Advantageously, for some applications, the hollow core 31 of the body 30 is filled with a foam material, such as a closed-cell non-halogen polyurethane, as is used in the preferred embodiment. Closed cell polyethylene foams, closed cell crosslinked polyethylene foams, EVA forms, and closed cell polystyrene foams all may be used. In other alternative embodiments, a cellular polyisocyanurate is used. In still other embodiments, the foam material is a PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene-tetrafluoroethylene) and PVF (polivinylfluoride).

[00031] In one embodiment, the body 30 is cylindrical in shape and is provided with a body axis 20. Alternatively, the body 30 can be composed of a plurality of shapes. For instance, the body 30 can be composed of a plurality of cylindrical shapes having a plurality of radii. In another embodiment, the body 30 is composed of a frusto-conical shape. The body 30 can be composed of a plurality of frusto-conical shapes having a plurality of radii.

[00032] The body 30 has a first end 12 and a second end 14. The first end 12 and the second end 14 include terminal portions of the body 30.) In an embodiment comprising filament wound around a cylindrical mandrel, the body 30 includes an outer body surface 16 and an inner body surface 18, as shown in FIG. 2. The outer body surface 16 is provided with an outer body diameter 22 while the inner body surface 18 is provided with an inner body diameter 24. Adhered to the outer body surface 16 is a housing 50.

[00033] After the composite material comprising the body 30 is cured, the body 30 is filled with an insulating material 33. In the preferred embodiment, the insulating material 33 is a closed cell polyurethane foam 35 that is sprayed into the body 30. Alternatively, the closed cell polyurethane foam 35 is poured into the body 30 or injected into the body 30. In alternative embodiments, the body 30 is filled with a combination of polyurethane foam 35 and other insulating foam material. In yet another alternative embodiment, the body 30 is filled with an insulating gas, such as SF6. In still another alternative embodiment, the body 30 is filled with an insulating fluid, such as a silicone oil or a mineral oil.

[00034] After the insulating material 33 is inserted into the body 30, a barrier layer 37 of an elastomeric sealant (preferably a butyl rubber) is placed at both ends 12, 14.

Preferably, the barrier layer 37 is placed between any connector or end fitting and the insulating material 33. While the presently preferred embodiment utilizes a barrier layer of butyl rubber, alternative embodiments use other materials, such as a polyurethane, a silicone, a silicone rubber, a polyurethanesilicone, an acrylic latex, an epoxy, or a room temperature vulcanizing rubber (or "RTV"). By way of additional example (and not limitation), a barrier layer 37 within the scope of the present invention is in the form of a self-sealing membrane. [00035] In an alternative embodiment, the barrier layer 37 includes a blowing agent.

By way of example and not limitation, chemical blowing agents are used, such as dinitroso pentamethylene tetramine ("DPT"), cyclopentane, pentane, HFC-134A, and HFC245FA. Advantageously, the barrier layer 37 includes a temperature activating solvent as a blowing agent.

[00036] After the housing 50 is adhered to the outer surface 16 of the body and after the barrier layer 37 is sprayed within the body 30, the end fitting is secured to the body 30. It is within the scope of the present invention to use a number of different end fittings. By way of example and not limitation, an end fitting such as the end fitting 68 depicted in FIG. 10 or one of the end fittings 114, 116 depicted in FIG. 1 is used. FIG. 12 depicts an end fitting in the form of a closed-end flange 115 with a port 117. The port 117 functions as a fill port. As FIGS. 12, 13, and 14 illustrate, the body is filled with foam 35 as an insulating material and then the barrier layer 37 is injected through the port 117 to fill any void 370. Advantageously, the port 117 is threaded for a set screw (not shown) to seal the insulating material and the barrier layer 37 within the hollow core 31 of the body 30. After the foam 35 and the barrier layer 37 are sealed within the hollow core 31 of the body 30, the insulator 10 is heated. The heat activates the blowing agent within the barrier layer 37, causing the barrier layer 37 to expand and further remove any trapped air thereby improving the dielectric properties of the body. In the preferred embodiment, the heat is applied to vulcanize a housing 50 of silicone rubber and to activate the blowing agent within the barrier layer 37.

[00037] Referring now to FIGS. 15, 16, and 17, one of the ends 12, 14 of the body 30 is shown with an end fitting 68 secured thereon. Insulating material in the form of foam 35 has been placed within the body 30 substantially filling the hollow core 31. In the event that the foam 35 leaves a void 370, as FIG. 15 illustrates, the barrier layer 37 is used, as FIG. 16 illustrates. In the embodiment shown in FIGS. 15, 16 and 17, the barrier layer 37 may be placed within the hollow core 31 before or after the end fitting is 68 is secured to the body 30. As FIG. 16 depicts, the barrier layer 37 is placed within the body 30 and skimmed so as to be level with the end of the body 30 and the end fitting 68. Then, after the barrier layer 37 fills the void 370, as FIG. 17 shows, a plate 118 is secured to the end fitting 68 and the hollow core 31 sealed via a seal 119 (which is in the form of an O-ring). [00038] Alternatively, a plate 118 and a seal 119 need not be used. Rather, as FIG. 18 shows, closed-end flange 115 without a port 117 is used. In such an arrangement, the barrier layer 37 is placed within the body 30 and skimmed so as to be level with the end of the body 30 and the end fitting 68. Then, after the barrier layer 37 fills the void 370, as FIG. 18 shows, the closed-end flange 115 is secured to the end of the body 30.

[00039] As noted above, after the foam 35 and the barrier layer 37 are sealed within the hollow core 31 of the body 30, the insulator 10 is heated. The heat activates the blowing agent within the barrier layer 37, causing the barrier layer 37 to expand and further remove any trapped air thereby improving the dielectric properties of the body. In the preferred embodiment, the heat is applied to vulcanize a housing 50 of silicone rubber and to activate the blowing agent within the barrier layer 37.

[00040] While the foregoing indicates that a housing of vulcanized silicone rubber is preferred, the scope of the present invention includes housings 50 of an organic material, such as a highly viscous material like an elastomer. In the preferred embodiment, the housing 50 is made of a silicone rubber; however, in another embodiment, the housing 50 is made of liquid silicone rubber ("LSR"). In an alternative embodiment, the housing 50 is made of an ethylene propylene rubber. In a further embodiment, the housing 50 is made of ethylene propylene diene monomer rubber. In an additional embodiment, the housing 50 is made of room temperature vulcanized rubber. In yet another embodiment, the housing 50 is made of an alloy of rubber and elastomer materials.

[00041] As shown in FIG. 1, the housing 50 includes a sheath 26 and a shed 28.

Referring now to FIG. 3, the sheath 26 is provided with an inner sheath surface 32, an outer sheath surface 34, a first edge 36, and a second edge 38. The inner sheath surface 32 contacts the outer body surface 18. In one embodiment, the edges 36, 38 are beveled. When viewed in longitudinal cross-section, the sheath 26 is shaped substantially like a parallelogram. As depicted in FIG. 3, the first edge 36 of the sheath 26 extends from the inner sheath surface 32 and terminates at the outer sheath surface 34 to form a first angle 40 with the outer sheath surface 34. As FIG. 3 also illustrates, the first angle 40 is an acute angle generally measuring about 45 degrees. The second edge 38 of the sheath 26 extends from the inner sheath surface 32 and terminates at the outer sheath surface 34 to form a second angle 48 which FIG. 3 illustrates as an obtuse angle generally measuring 135 degrees. [00042] In one embodiment, the sheath 28 is extruded onto the body 30. As depicted in FIG. 4, an extruder 56 is placed a distance from the body 30 and the sheath 26 is wrapped about the body 30. Advantageously, the sheath 26 is placed in tension so that the sheath 26 is tightly wound about the body 30 thereby closely adhering the sheath 26 to the body 30.

[00043] FIG. 4 depicts the sheath 26 being wrapped helically about the body 30 starting from the first end 12. As shown therein, an extruded sheath 42 extends from the extruder 56 with an applied sheath 58 being pressed into the outer body surface 16. As used herein, the term "extruded sheath" refers to a portion of the sheath 26 that is suspended between the body 30 and the extruder 56 as the sheath 26 is being wrapped around the body 30. The term "applied sheath" shall refer to a portion of the sheath 26 that has been applied to the body 30.

[00044] In one embodiment, the sheath 26 forms a helix about the body 30 and is wrapped so that the extruded sheath 42 is placed adjacent to the applied sheath 58. FIGS. 2 and 4 depict the sheath 26 being wrapped from the first end 12 of the body 30. As shown therein, the first edge 36 is located closer to the first end 12 than the second edge 38. ; While the sheath 26 is being helically wrapped about the body 30, the first edge 36 of the extruded sheath 42 is laid over the second edge 38 of the applied sheath 58to form a joint 62, preferably a joint free of voids.

[00045] As FIG. 4 depicts, a roller 64 is positioned so that pressure is placed upon the sheath 26, and the sheath 26 is pressed into the outer body surface 16. In one embodiment, the roller 64 is positioned so that it is located axially to be about one turn away from the extruder 56. The roller 64 is dimensioned to extend over both the joint 62 and the applied sheath 58. In one embodiment, the roller 60 is positioned so that the inner sheath surface 32 is pressed into the outer body surface 16, the first edge 36 of the extruded sheath 42 and the second edge 38 of the applied sheath 58 are pressed together, and the joint 62 is rolled into the outer surfacel 6 of the body 30.

[00046] Advantageously, the housing 50 is provided with different sheath layers.

One layer provides weather resistance; another layer prevents damage caused by pollutants in the air, while yet another layer is hydrophobic (and thereby prevents water adhesion). The roller 64 removes air from between the sheaths (as well as between the body 20 and the sheath 26) and thus forms a homogeneous sheath layer on the body 20, free of air or pockets within the sheath 26 or between the sheath 26 and the body 20.

[00047] After the sheath 26 is pressed into the body 30 (and after any additional sheath layers are rolled thereon), but before the applied sheath 58 is cured or, if rubber is used, before the applied sheath 58 is cross-linked, a shed 28 is placed onto the sheath 26. In one embodiment, the shed 28 is formed of a non-tracking material that is flexible for shipping and handling, such as high viscosity silicone or EPDM. Because the shed 28 is placed onto the applied sheath 58, the shed 28 may be fabricated of a material different from the material of the sheath applied sheath 58. For instance, in one embodiment, the shed 28 may contain less aluminum oxide than the applied sheath 58 to provide a housing 50 that is less cosdy than other housings 50. In another embodiment, the material of the sheath 26 is an electrically insulating material to improve dielectric properties of the housing 50; in yet another embodiment, the material of the shed 28 is flexible material to improve shipping and handling. In still yet another embodiment, the material of the shed 28 is hydrophobic.

[00048] In the presently preferred embodiment, the shed 28 is extruded onto the sheath 26. In extruding the shed 28 onto the sheath 26, an extruding head 66 is positioned to be tangent to the outer sheath surface 34, as is depicted in FIG. 5 and FIG. 6. In the preferred extrusion process, the extruding head 66 is positioned relative to the outer sheath surface 34 so that the extruding head 66 contacts the outer sheath surface 34. The extrusion process blends the rubber into a homogeneous joint. It is also preferred that the shed and the sheath are free of voids and anomalies that create dielectric weakness and are knitted together to form a unitary molded joint.

[00049] However, in an alternative process, the extruding head 66 can vary its distance from the outer sheath surface 34 so that a shed with a varying diameter is created. In such an arrangement, the extruding head 66 extrudes around the body 20 a plurality of sheds, each of which extends 540° (or three turns) before the diameter of each shed is reduced to zero. The housing 50 is thus provided with a series of 540° sheds (which break up the water flow path along the outer surface of the housing 50).

[00050] In the preferred embodiment, the extruding head 66 is positioned at an angle

67 relative to the axis 20 of the body 30. The angle 67 of the extruding head 66 is varied to provide differentiy spaced sheds and a plurality of helices, with each helix including a different degree of steepness. By way of example and not limitation, the helices located at the ends 12, 14 are shaped to increase creepage distance (and are more shallow) while helices located between the ends 12, 14 are shaped to prevent buildup of pollutants and other air borne particulate matter (and are more steeply shaped). In an alternative embodiment, the sheds are oriented to form a helix that breaks up water flow.

[000511 Additionally, the body 30 may be rotated about its axis 20 while

simultaneously moved axially with respect to the extruding head 66. By altering the speed of rotation and axial movement, differing shed profiles are possible. For example, faster movement axially produces a helix with a steeper incline. In the same vein, faster rotation produces a helix with a more shallow incline. Thus, the mechanism by which the sheds are extruded onto the body 20 can be controlled to produce different helices.

[00052] The preferred embodiment of the insulator 10 is provided with at least one connector. In an embodiment shown in FIGS. 5 and 6, the connector is an end fitting 68 that attaches the body 30 to a breaker unit (not shown for clarity). In an embodiment shown in FIGS. 7 and 8, the connector is a support connector 70 that supports the body 30 when it is mounted on a utility structure, such as a utility pole or a cross arm. In a further embodiment, the connector is one of a plurality of end connectors that couple the body 30 to a conductor.

[00053] In some embodiments, the body 30 can be coupled to a conductor via a number of end connector configurations. FIG. 7 and 8 depict connector 44 configured in the shape of a "C." FIG. 9 depicts connector 45 with a configuration known in the art as a "U" shaped connector.

[00054] In some embodiments, the connectors are formed of metal. In some embodiments, the connectors are made of a metal, such as aluminum and the like, a metal alloy and other suitable materials.

[00055] FIG. 10 shows one embodiment of an end fitting 68. The end fitting 68 is an aluminum casting formed in a mold. The end fitting 68 shown in FIG. 10 includes a flange 72 with a fitting axis 74 and a plurality of reinforcing ribs 76, 78, 80, 82, 84, 86, 88. The end fitting 68 is provided with a body-accepting end 90 and an attaching end 92 as well as an inner fitting surface 94 and an outer fitting surface 96. As FIG. 11 illustrates, the end fitting 68 is provided with an outer fitting diameter 98 and, as shown in FIG. 10, an inner fitting diameter 100. The inner fitting diameter 100 is machined to fit with the outer body diameter 22. In one embodiment, the inner fitting surface 94 decreases in diameter as the inner fitting surface 94 extends from the body-accepting end 90 of the end fitting 68 toward the flange 72. In one embodiment, the inner fitting surface 94 includes a plurality of grooves 102, 104, 106, 108 each of which are dimensioned to retain adhesive. As is also shown in FIG. 11 , the inner fitting surface 94 has been machined to provide a stop 111.

[00056] The body- accepting end 90 is dimensioned to accept and retain the body 30.

Extending from the body-accepting end 90 is a substantially smooth outer surface 110. In one embodiment, the substantially smooth outer surface 110 extends radially outwardly as the smooth outer surface 110 extends from the body- acce ting end 90 of the end fitting 68 towards the attaching end 92 of the fitting 68. The substantially smooth outer surface 110 is machined so that the sheath 26 can be pressed into the outer fitting surface 96 without voids being created between the substantially smooth outer surface 110 and the housing 50. Because the outer fitting diameter 98 and the outer body diameter 22 are different, the substantially smooth outer surface 11 Oismachined to provide a transition 112 between the outer fitting surface 96and the outer body surface 18. As FIG. 2 depicts, the transition 112 is frusto-conically shaped. In one embodiment, the outer fitting diameter 98 is larger than the outer body diameter 22, and accordingly, the transition 112 slopes from outer fitting diameter 98 to the outer body diameter 22.

[00057] Referring back to FIG. 1, the body 30 is provided with a first end fitting 114 and a second end fitting 116. In one embodiment, a gas-tight joint is provided between the end fittings 114, 116 and the body 30. In one embodiment, this assembly is accomplished via a heat-shrink process whereby the end fittings 114, 116 are heated and assembled onto the body 30 to which adhesive has been applied. The adhesive may be applied to the body 30 directly, or the adhesive may be applied to the grooves 102, 104, 106, 108 located on the inner surface 94 of each end fitting 114, 116. Appropriate combinations of these methods are possible as well.

[00058] Referring to FIG. 1, the body 30 is tubular in shape and is provided with the first end 12 and the second end 14. In an embodiment where end fittings 1 14, 116 are attached at each end 12, 14, at least one groove 52 is machined into the outer body surface 16. Any desired number of grooves 52 may be provided. The groove 52 is formed or machined so as to define a reduced outer diameter band or region on the external circumference of the body 30. In this manner, a relatively reduced outer diameter band or region formed by grooves 50 alternates with a relatively increased outer diameter portion body 30.

[00059] During assembly of one embodiment, adhesive may be applied over the groove 52. The inner fitting diameter 100 of the end fittings 114, 116 is dimensioned at normal temperatures to be a predetermined dimension less than the outer diameter 22 of the tubular body 30 at the groove 52, e.g. a decrease of about .010 of an inch for body 30 provided with an outer body diameter 22 of approximately 5 inches. Thus, an interference fit is formed between the portions of the body 30 and the end fittings 114, 116. The end fittings 114, 116 (fabricated from aluminum) are heated to afford clearance between the outer body surface 6 (body 30 is fabricated of fiberglass) and inner fitting surface 94, i.e. heating to a temperature substantially within the range of 150 to 200 degrees Celsius for end fittings 1 4, 1 6. An appropriate interference fit, e.g. a joint that is gas-tight over a temperature range of -40°C to +85°C with a gas pressure of 75 psi, results when these items are cooled. In one embodiment, the grooves 52 are approximately 0.005 inches deep and the region defined by the grooves 52 are approximately 0.250 inches wide. These dimensions have been found to provide a suitable gas-tight joint using an epoxy adhesive in the grooves 52, i.e. the grooves 52 retain sufficient adhesive during and after assembly.

[00060] During assembly, the end fittings 114, 116 are heated and telescoped over the body 30. The stop 11 1 on the end fittings 114, 116 ensure that the end fittings 114, 116 are not telescoped too far over the body 30 while, at the same time, ensuring that each of the ends 12,14 of the body 30 are sufficiently inserted into each of the end fittings 114, 116.

[00061] The relative dimensions including the depth of the groove 52 are chosen to ensure that a desirable and appropriate amount of adhesive is retained therein during the heat-shrink assembly process and even if some wiping action occurs. These dimensions have also been found suitable to avoid excessive adhesive that might result from a groove 52 of excessive depth that might result in any significant degradation of the joint between the end fittings 114, 116 and the tubular body 30 during thermal extremes. Thus, the groove 52 maintains the appropriate amount of adhesive to ensure a gas-tight joint, the gas-tight interference joint is maintained at 85C and no damage is done to the body 30 as a result of the added compressive forces at— 40C. Additionally, the gas-tight joint is maintained when the body 30 is loaded with a resultant moment at the joint of 20-30,000 in-lb. [00062] While this invention has been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMED IS:

A method of manufacturing an insulator comprising the steps of: a) providing a composite body that is generally cylindrical in shape, including a hollow core, a first end, and a second end;

b) placing the composite body within a housing;

c) placing an insulating material within the hollow core;

d) placing a barrier layer within the hollow core; and

e) providing at least one of the ends with a connector.

Claim 2 A method of manufacturing an insulator according to Claim 1 wherein the step of placing insulating material within the hollow core further includes: a) providing a closed-cell non-halogen polyurethane; and

b) spraying the closed-cell non-halogen polyurethane into the hollow core.

Claim 3 A method of manufacturing an insulator according to Claim 1 wherein the step of placing insulating material within the hollow core further includes: a) providing a closed cell polyethylene foam; and

b) spraying the closed cell polyethylene foam into the hollow core.

Claim 4 A method of manufacturing an insulator according to Claim 1 wherein the step of placing the barrier layer within the hollow core includes:

a) providing an elastomeric sealant; and

b) spraying the elastomeric sealant within the hollow core of the body.

Claim 5 A method of manufacturing an insulator according to Claim 1 wherein the step of placing the barrier layer within the hollow core includes:

a) providing a butyl rubber; and

b) placing the butyl rubber between at least one of the connectors and the insulating material.

Claim 6 A method of manufacturing an insulator according to Claim 1 wherein the step of placing the barrier layer within the hollow core includes: a) providing a silicone; and

b) placing the silicone between at least one of the connectors and the insulating material.

Claim 7 A method of manufacturing an insulator according to Claim 1 further comprising the steps of:

a) providing a blowing agent;

b) placing the blowing agent within the barrier layer.

Claim 8 A method of manufacturing an insulator comprising the steps of:

a) providing a mandrel;

b) providing a fiber impregnated with an epoxy resin;

c) filament winding the fiber about the mandrel to form a body;

d) removing the body from the mandrel so that the body is provided with an outer body surface, an inner body surface, a body axis, a first end, and a second end;

e) providing a silicone rubber;

f) adhering the silicone rubber to the outer body surface so that the body is provided with a sheath and at least one shed;

g) placing an insulating material within the body; and

h) placing a barrier layer axially within the body so that the barrier layer is

located between the insulating material and at least one of the ends of the body.

Claim 9 A method of manufacturing an insulator according to Claim 8 further comprising the steps of:

a) machining at least one end of the body;

b) providing at least one connector in the form of an end fitting that includes an aluminum and that has been cast in a mold to include a flange, an inner fitting surface that has been machined, an outer fitting surface, a body- accepting end, an attaching end, and a fitting axis;

c) heating the connector so that the inner fitting surface expands; and d) securing the connector at the machined end of the body so that the fitting axis and the axis of the body are generally coaxial.

Claim 10 A method of manufacturing an insulator according to Claim 8 wherein the step of placing the barrier layer within the body includes:

a) providing a butyl rubber; and

b) placing the butyl rubber between the connector and the insulating material.

Claim 11 A method of manufacturing an insulator according to Claim 8 wherein the step of placing the barrier layer within the body includes:

a) providing a polyurethanesilicone; and

b) placing the polyurethanesilicone within the barrier layer.

Claim 12 A method of manufacturing an insulator according to Claim 8 wherein the step of placing the barrier layer within the body includes:

a) providing an acrylic latex; and

b) placing the acrylic latex between the connector and the insulating material.

Claim 13 A method of manufacturing an insulator according to Claim 8 wherein the step of placing the barrier layer within the body includes:

a) providing an epoxy; and

b) placing the epoxy between the connector and the insulating material.

Claim 14 A method of manufacturing an insulator according to Claim 8 further comprising the steps of:

a) providing a blowing agent;

b) placing the blowing agent within the barrier layer.

Claim 15 A method of manufacturing an insulator comprising the steps of:

a) providing a plurality of fibers and an epoxy resin;

b) orienting the fibers so as to provide a body that includes a body axis, an outer body surface, a first end, and a second end; c) providing an end fitting with an inner fitting diameter and a fitting axis; d) heating the end fitting so that the inner fitting diameter expands; e) after heating the end fitting, placing the end fitting onto at least one of the ends of the body so that the body axis and the fitting axis are generally coaxial;

f) after placing the end fitting onto at least one of the ends, allowing the end fitting cool;

g) adhering a sheath onto the outer body surface; and

h) forming a shed onto the sheath;

Claim 16 A method of manufacturing an insulator according to Claim 1 wherein the step of adhering the sheath onto the outer body surface further includes: a) providing a silicone rubber;

b) extruding the silicone rubber to form the sheath; and

c) exerting pressure upon the sheath to adhere the sheath to the outer body surface.

Claim 17 A method of manufacturing an insulator according to Claim 1 wherein the step of forming the shed onto the sheath further includes:

a) providing a silicone rubber;

b) extruding the silicone rubber to form the shed on the sheath so that the shed and the sheath to form a generally unitary structure; and c) vulcanizing the silicone rubber.

Claim 18 A method of manufacturing an insulator according to Claim 1 further

comprising the steps of:

a) providing a first silicone rubber;

b) extruding the first silicone rubber to form the sheath;

d) providing a second silicone rubber; e) extruding the second silicone rubber to form the shed;

f) knitting the shed and the sheath to form a generally unitary molded joint; and

g) vulcanizing the silicone rubber within the shed and the sheath.

Claim 19 A method of manufacturing an insulator comprising the steps of:

a) providing a mandrel;

b) providing a fiber impregnated with an epoxy resin;

c) filament winding the fiber about the mandrel to form a body;

e) extruding a sheath so as to adhere the sheath to the outer body surface; and f) extruding a shed onto the sheath so that the shed and the sheath form a generally unitary structure.

Claim 20 A method of manufacturing an insulator according to Claim 5 wherein the sheath includes a silicone rubber.

Claim 21 A method of manufacturing an insulator according to Claim 5 wherein the shed includes a silicone rubber.

Claim 22 A method of manufacturing an insulator according to Claim 5, further

comprising the steps of:

a) machining at least one end of the body;

b) providing at least one connector in the form of an end fitting that includes an aluminum and that has been cast in a mold to include a flange, an inner fitting surface that has been machined to provide an inner fitting diameter, an outer fitting surface, a body-accepting end, an attaching end, and a fitting axis;

c) heating the connector so that the inner fitting diameter expands; d) after heating the connector, securing the connector at the machined end of the body so that the fitting axis and the axis of the body are generally coaxial;

e) after securing the connector at the machined end of the body, allowing the connector to cool.