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  Semiconductive coating and application process for shielded elastomeric electrical cable accessoriesUSPTO Application #: 20070074886Title: Semiconductive coating and application process for shielded elastomeric electrical cable accessories Abstract: A method is provided for manufacturing a semiconductive insulating shield for an electrical cable accessory. The method includes providing a substrate having a desired contour in relation to the electrical cable accessory. The substrate is then coated with an elastomeric semiconductive material to form a coated substrate. An elastomeric insulating dielectric material is then molded around the coated substrate, and the elastomeric semiconductive material and elastomeric insulating dielectric material are cured by applying heat and pressure sufficient to transfer the elastomeric semiconductive material to the elastomeric insulating dielectric material by chemical bonding. (end of abstract)
Agent: Hoffman & Baron, LLP - Syosset, NY, US Inventor: John Paul Bolcar USPTO Applicaton #: 20070074886 - Class: 174036000 (USPTO) Related Patent Categories: Electricity: Conductors And Insulators, Anti-inductive Structures, Conductor Transposition, Conductor Only The Patent Description & Claims data below is from USPTO Patent Application 20070074886. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to application Ser. No. 10/339,054, filed Jan. 9, 2003 which is hereby incorporated by reference. FIELD OF THE INVENTION [0002] The present invention relates to shielded electrical cable accessories. More particularly, the present invention relates to a method for manufacturing a semiconductive shield useful for providing geometric electrical stress control and shielding to medium and high voltage electrical cable accessories. BACKGROUND OF THE INVENTION [0003] Termination or connection of high or medium voltage electrical cables in the field requires electrical shielding or stress control. Geometric electrical stress control and/or shielding of elastomeric cable accessories may be generally accomplished by one of the two following methods. [0004] In one method, an elastomeric semiconductive geometric stress control insert is pre-molded in one manufacturing operation. The insert is subsequently bonded to an elastomeric insulating dielectric in a second molding operation. This method has certain disadvantages. The pre-molded semiconductive components are nominally 0.020 inches thick or thicker. The component, therefore, must be trimmed of flash and cleaned. Also, the components must be specially stored to accommodate the secondary molding and bonding process. The thicker pre-molded semiconductive components may impart undesirable physical characteristics to the final product. These characteristics include a higher modulus, resulting in a stiffer final product. This is especially significant in the wide range of cable accessory designs where the product is radially expanded significantly and the modulus must be controlled. [0005] Another method includes molding the elastomeric insulating dielectric by one process and applying a semiconductive coating in a second process. This semiconductive coating may be applied by conventional techniques such as brushing, dipping, or spraying. This technique also has certain disadvantages. The application of the secondary coating to irregular interior surfaces is very difficult to achieve effectively and is costly to apply. Chemical cross-linking (chemical bonding) between an elastomeric semiconductive coating and an elastomeric insulating dielectric cannot be satisfactorily achieved unless the coating is subsequently cured or vulcanized by using heat and/or pressure during a secondary operation. The shelf life of these components is limited in that the coatings are reactive systems containing catalysts. [0006] It is therefore desirable to provide a coating and application process for an elastomeric electrical cable accessory which is more reliable and cost-effective to achieve. SUMMARY OF THE INVENTION [0007] The present invention provides methods for manufacturing a semiconductive shield useful for providing electrical stress control and shielding to medium and high voltage electrical cable accessories. [0008] In a first aspect of the invention, a method is provided for manufacturing a semiconductive shield for an electrical cable accessory. The method includes providing a substrate having a desired contour in relation to the electrical cable accessory. The substrate is then coated with an uncured elastomeric semiconductive material to form a coated substrate. The substrate should be a material to which the elastomeric semiconductive material will not bond during curing. Examples of substrate materials include steel, stainless steel, aluminum, and polytetrafluoroethylene. The constituents of the elastomeric semiconductive material can be suspended in suspension solvents, in which case it is preferable to permit the elastomeric semiconductive coating to dry before proceeding. An uncured elastomeric insulating dielectric material is then applied around the coated substrate, and the elastomeric semiconductive material and elastomeric insulating dielectric material are concurrently cured by applying heat and pressure sufficient to transfer the elastomeric semiconductive material to the elastomeric insulating dielectric material by chemical bonding. [0009] In a preferred embodiment, the method further includes the step of applying an outermost semiconductive jacket. More preferably, the method includes applying a pre-molded semiconductive jacket over the coated substrate leaving a space between the coated substrate and outer jacket, positioning a mold over the outer jacket; and applying the uncured insulating dielectric material around the coated substrate by injecting the uncured insulating dielectric material into the space between the outer jacket and the coated substrate. [0010] In another embodiment, the outer jacket is applied by coating the inner surface of a mold with semiconductive jacket material. The mold is then positioned over the coated substrate leaving a space between the coated inner surface of the mold and the coated substrate. Uncured elastomeric insulating dielectric material is applied around the coated substrate by injecting the uncured insulating dielectric material into the space between the semiconductive jacket material and the coated substrate. The semiconductive jacket material, elastomeric insulating dielectric material, and elastomeric semiconductive material are then concurrently cured. [0011] In another preferred embodiment, the elastomeric semiconductive material does not contain a catalyst. Rather, the uncured insulating dielectric material can include a catalyst, such as peroxide, which can enter the elastomeric semiconductive material during the curing step. [0012] In another aspect of the invention, an article of manufacture is provided. The article of manufacture includes an elastomeric semiconductive material transferred to and chemically bonded with an elastomeric insulating dielectric material by applying an uncured elastomeric insulating dielectric material around an uncured elastomeric semiconductive material and concurrently curing the elastomeric insulating dielectric material and elastomeric semiconductive material. [0013] In another aspect of the invention, a shield cable accessory is provided. The shield cable accessory includes a coating-formed elastomeric semiconductive material portion and an elastomeric insulating dielectric material portion molded about the elastomeric semiconductive material portion. The elastomeric semiconductive material portion and the insulating dielectric material portion are concurrently cured to effect transfer of the elastomeric semiconductive material portion to the elastomeric insulating dielectric material portion by chemical bonding. [0014] The present invention will allow coating thickness as low as 0.0005 inches and requires only one molding operation. In addition, due to the method of applying the coating, there is no need for secondary operations of trimming flash or cleaning. The present invention also results in significant reduction of raw material usage without any adverse effects on the physical characteristics, especially the modulus or stiffness of the final product. The invention allows the transfer of coating from an intermediate exterior surface to any interior surface, regardless of the geometry or surface irregularity. The invention results in the transfer and subsequent cross-linking of the semiconductive coating simultaneously with the cure of the elastomeric insulating dielectric. Furthermore, it is contemplated that the formulated semiconductive coating may be made without a catalyst, thereby rendering the shelf life of the final product indefinite. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a plan view of a steel mandrel with an applied semiconductive coating. [0016] FIG. 2 is a plan view of a steel mandrel with an applied semiconductive coating, insulative dielectric material, and outer semiconductive jacket. [0017] FIG. 3 is a plan view as set forth in FIG. 2, including a mold used to apply the insulative dielectric material over the semiconductive coating and under the outer semiconductive jacket, according to a preferred embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION [0018] The present invention provides a method for manufacturing a semiconductive shield capable of providing geometric electrical stress control and/or shielding to medium to high voltage electrical cable accessories. The process of the present invention includes the transfer of a conventionally applied elastomeric semiconductive coating from an intermediate substrate to an elastomeric insulating dielectric during cure of the coating and insulating dielectric. Continue reading... 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