CA1121474A - High voltage electric insulators made of resins-bonded glass-fibers and organic material, and process for manufacturing same - Google Patents
High voltage electric insulators made of resins-bonded glass-fibers and organic material, and process for manufacturing sameInfo
- Publication number
- CA1121474A CA1121474A CA000308135A CA308135A CA1121474A CA 1121474 A CA1121474 A CA 1121474A CA 000308135 A CA000308135 A CA 000308135A CA 308135 A CA308135 A CA 308135A CA 1121474 A CA1121474 A CA 1121474A
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- Prior art keywords
- curing
- central body
- insulator
- sleeve
- epr
- Prior art date
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B17/00—Insulators or insulating bodies characterised by their form
- H01B17/02—Suspension insulators; Strain insulators
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B17/00—Insulators or insulating bodies characterised by their form
- H01B17/32—Single insulators consisting of two or more dissimilar insulating bodies
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- Insulators (AREA)
- Laminated Bodies (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention is concerned with an electric insulator for average, high, and very high voltages, charac-terized in that the ribbed coating thoroughly coats a supporting central body and is made of an ethylene-propylene elastomer (EPR) having high elastic,anti-tracking, anti-erosion, ageing resistant, self-extinguishing, and water-repellency charac-teristics, said ribbed coating being shaped as ribs and supported by a sleeve-shaped tubular layer prepared from an ethylene-propylene elastomer (EPR) of qualities and charac-teristics identical with those of the EPR elastomer constituting said ribs. The coupling of said ribbed elastomeric coating with said central body, of said ribs with said sleeve, and of self-curing at room temperature,based on low-unsaturation olefinic polymers, analogous and compatible with the ethylene-propylene blend (EPR) of which the ribbed coating is made.The present invention is concerned also with the process to obtain the same. The electric insulator according to the invention shows a radical and definitive solution of the problem of achieving a perfect adherence between the r.b.g.f. body and the ribbed coating.
The present invention is concerned with an electric insulator for average, high, and very high voltages, charac-terized in that the ribbed coating thoroughly coats a supporting central body and is made of an ethylene-propylene elastomer (EPR) having high elastic,anti-tracking, anti-erosion, ageing resistant, self-extinguishing, and water-repellency charac-teristics, said ribbed coating being shaped as ribs and supported by a sleeve-shaped tubular layer prepared from an ethylene-propylene elastomer (EPR) of qualities and charac-teristics identical with those of the EPR elastomer constituting said ribs. The coupling of said ribbed elastomeric coating with said central body, of said ribs with said sleeve, and of self-curing at room temperature,based on low-unsaturation olefinic polymers, analogous and compatible with the ethylene-propylene blend (EPR) of which the ribbed coating is made.The present invention is concerned also with the process to obtain the same. The electric insulator according to the invention shows a radical and definitive solution of the problem of achieving a perfect adherence between the r.b.g.f. body and the ribbed coating.
Description
Z~ 4 This invention relates -to electric insula-tors for average, high and very high voltages, made of resin-bonded glass-fibers and equipped wi-th a ribbed coating made of an ethylene~
propylene elastomer having high physical properties and in partic-ular high dielectric properties, as ~well as to a process for manufacturing same.
Electric insulators composed of resin-bonded glass-fibers (r.b.g.f.) with a ribbed coating madle of organic materials are already well known and broadly utilized in the field of electric outdoor overhead average and high voltage lines and in the field of electric traction. The main advantage offered by the in-sulators made of resin-bonded glass-fibers and organic materials in respect of the conventional porcelain or glass insulators resides in the particularly low "weight/mechanical strength" ratio.
In fact, the conventional porcelain or glass insulators of the pin and cap type, when meant for outdoor overhead high and very high voltage mechanical loads due to the weight of the conducting wires, must be equipped with metal caps of large dimensions, as a result of which the weight of the whole insulator chain or assemblage is high and no longer negligible in respect of the weight of the conductor supported by said chain.
In the compound insulators made from resin-bonded glass-fibers and organic materials, the mechanical supporting function is left just to the r.b.g.f. rod-shaped article or central body, which is generally manufactured either continuously or discontinuously as a solid bar according to the "pulltrusion"
method, i.e., extrusion by pulling or traction -- in case of the use of glass fibers arranged in filaments parallel with one another and parallel with the direction of the mechanical stress which the suspension central body will be subjected to during operation, or in case . . ~
~2~ 7~
of the use of ferted glass fibers, i.e., glass fibers cu-t and arranged incoherently (chopped strand), or of woven glass fibers -- and which is manufactured in the form of a hollow cylindrical body according to the filament-winding m~thod in the case of continuous fibers, which in general are spirally arran-ged. For manufacturing the article (or body) in the form of a hollow cylinder also glass-fiber fabrics are utilized. In both cases (solid bar or hollow cylinder) the glass fibers are impregnated with a resin having the bes-t electrical properties (such as, for example, a cycloaliphatic epoxy resin). Such bodies exhibit a mechanical strength approximating that of steel, though having a specific gravity corresponding to only about one third that of steel.
In the case of electric railway and tramway traction field of use, the r.b.g.f. insulators offer also a considerable advantage in comparison with the conventional porcelain insulators, as in this field of use it is of the utmcst importance that the insulation shall sucessfully withstand the strong vi~rations it is subjected to during operation, what may be easily achieved merely by means of r.b.g~f. insulators, unlike those made of porcelain.
However, the manufacture of r.b.g.f. insulators that will prove to be fully satisfactory in every respect has met with a few serious obstacles: at first it was very difficult to find the proper materials (resistant to the combined action of ageing and of surface eIectric discharges, the latter involving undesired tracking and/or erosion phenomena) for preparing the generally ribbed coating of the insulator.
~ nce such essential condition of resistance to ageing and to surface discharges was attained thanks to the utilization of suitable materials (such as, e.g., cycloaliphatic epoxy resins, silicone elastomers, ethylene-propylene elastomers, fluorina-ted resins ~PTFE), and the like), there still remained to be overcome the difficulty of coupling the r.b.g.f. central body (solid bar or hollow cylindrical body) with the ribbed coating material.
In fact, the physical, and in particular the mechanical, properties of the r.b.gOf. body are such as not to allow a reliable coupling with materials reacting with non-elastic behavior to the deformations caused by mechanical stresses.
In consequence, and with a view to attempting to obviate these drawbacks, various methods of and cr~teria ~or coupling have been studied: e.g., by means of elastic resins or silicone greases, or rubber mastics, or even by the simple mechanical forcing of the ribbed coating material onto the r.b.g.f.
body. None of these, however, was capable of solving this problem satisfactorily: actually, every such method turned out to be or give rise to a weak point in the insulator from the electrical viewpoint.
It should be borne in mind, in fact that the~outside configuration of an average, high, and above all, very high voltage insulator, whose ribbings have considerable-widths and thicknesses, has been studied for the purpose of opposing to the electric discharge between the insulator's metal terminals (if any, or, in any case, between a live conductor and ground) a path as long as possible, i.e. a particularly high surface creeping line.
"Surface creeping line" means the path o~ an electric discharge over a surface (and therefore, following the insulator ribbing trend) bet:ween a live electrode and ground (i.e., in particular between a live conductor and any part of the ground-connected supporting structure, or, more generally, any part ofsuch structure having the same potential as the ground). In ~3 -LZ~ L 7L4~
general, a surface creeping li~e is deemed hiqh enough ~hen the ratio of said line to the straight line distance (or spacing), namely to the distance existing in straight llne between a live conductor and ground (as defined hereinabove), is at least equa~
to 2, or to 3, or even higher than 3, when taking intG consideration respectively insula-tors meant for norrnal use and insulators utilized under polluted or very polluted conditions.
It is therefore evident that a possible electric discharge generated in the gap or space between the r.b.g.f.
central body and the ribbed coating would be ruinous for the insulation, the effectiveness of which would decrease below the level for which it has been designed, and which would still further deteriorate within short time untill reaching even lower levels of effectiveness owing to the damage caused by the discharge.
The methods of and criteria for coupling the r.b.g.f.
body with the ribbed coating practiced so far according to the prior art, and mentioned above, exhibit the above-described un-desirable drawbacks, as they are not capable of preventing electric discharges in the gap or spacing between the body and the coating.
For instance, silicone greases are subject to a pumping effect due to the elongation, under the action of the mechanical tensile stress, of the r.b.g.f. rod-shaped central body and to the consequent compression exerted by the ribbed coating on such body. In this way it might happen that the silicone grease would be expelled from the gap or space between the bar or rod and the coating and would not be sucked back again when, in case of reduction or elimination of the tensile stress, also the compression exerted by the coating decreases. Thin cavities or voids are then created which easily attract moisture l:~LZ~
and undesired electric dischar~es along the body (in the form of a bar of a hollow cylinder) and inside the ribbed coating.
Conversely, some -types of coupling resins are subjec-ted -- as they couple two materials different from each other ~i.e., the r.b.g.f. body and the ribbed coating which, for example, may be made of PTFE) and from the resins themselves --- to a shearing stress along the body, that too causes cavities or voids attracting pollutants and electric discharges.
The formation of small cavities or voids in the gap between the body and the coating permits the diffusion of mois-ture as well as the generation of partially localized electric dis-charges. These drawbacks, in their turn, involve as a consequence the striking of a direct, continuous and total discharge between the metal terminals of the insulator (or at least between the live conductor and ground) inside said insulator along the body ( a bar or a cylindrical pipe), which thus is irreparably jeopardized and, in consequence, puts the insulator out of service immediately or within a short time.
Neither the flame resistance characteristics nor the self-extinguishing power is to be neglected, such characteristics or self-extinguishing power being required to be as high as pos-sible, while with the organic materials used so far according to the prior art these properties were relatively low or poor, so that the resistance to flame propagation, if any, is of-very little effect.
It is an object of the present invention to eliminate the drawbacks described above, through a radical and definitive solution of the problem of achieving a perfect adherence between the r.b.g.f. body and the ribbed coating.
Another object of this invention is to provide an electFic insulator lor avera~o~ high an~ very high v~lta~es, of -~Z~74 the compound type, consisting of a r.b.g.f. body (rod-shaped central body) and of a ribbed coating made from a suitable elastic organic material, in which insula-tor the generation o~ creeping stresses between said central supporting body and the ribbed coating are prevented by virtue of the high elasticity of the ribbed coating.
A further object of ~his invention is to provide an insulator of the type cited above that permits one to avoid any other drawback depending on the low consistency or compatibility existing -- as noticed in the prior art -- between the r.b.g.f.
body and the ribbed coating.
Still another object of this invention i9 to provide an insulator of the type mentioned above, having a ribbed coating made of a material selected from the class of ethylene-propylene elastomers having good anti-tracking and anti-erosion properties, and high characteristics of elasticity, ageing resistance and op-position or resistance to flame propagation (self-extinguishing power), as well as a high impermeability and water repellency.
It is also a primary object of this invention to provide a process for manufacturing electric insulators according to the present lnvention, which will enable one to achieve all of the foregoing objects.
These and still other objects that will become more clearly apparent to those skilled in the art from the detailed description given hereinafter, are advantageously achieved by an electric insulator for average, high and very high voltages, consisting essentially of a resin-bonded glass-fiber ~r.bOg.~.) suppor-ting ccntral body in tl~ form of a rod, equipped with a ribbed coating prepared from an organic material, characterized in that said ribbed coating thoroughly coats said supporting central body and is made o~ an ethylene-propylene elastomer (EP~) ~ .
having high elastic, antl-tracking, anti-erosion, agei.ng resistant, self-extinguishing, and water-repellency charac-teristics, said ribbed coating being shaped as ribs and supported by a sleeve-shaped tubular layer prepared from an ethylene-propylene elastomer (EPR) of qualities and charac-teristics identical with -those of the EPR elastomer constitu-ting said ribs, the coupling of said ribbed elastomeric coating with said central body, of said ribs with said sleeve, and of said ribs with one another, being obtained by employ-ing a blend, self-curing at room temperature, based on low-unsaturation olefinic polymers, analogous and compatible with the ethylene-propylene blend (EPR) of which the ribbed coating is made.
The electric-insulator of the present invention is advantageously manufactured according to a process com-prising: preparing a mold for molding the whole elastomeric ribbed coating associated with a rod-shaped suspension central body made from resin-bonded glass fibers; treating the surface of said central body-- in the form of a solid bar or of a hollow cylinder depending on the intended use of the insulator -- according to a conventional technique selected from the following: sandblasting, rasping or rubbing with glass paper, spreading or smearing with a suitable adhesion-promoting mastic (the so-called primer>?; placing said body into said mold as prearranged, said body being supported in the mold at its ends; then molding and curing in said mold the entire ribbed coating on the rod-shaped central body according to one of the known prior art methods selected from the transfer method and the injection method, . 30 by employing,as molding material, an ethylene-propylene elas-tomer having particularly high characteristics: drawing out, finally,the whole so-molded insulator from said mold.
~lZ~
The described process con-templates also the alternative possibility of obtaining the ribbed coating separately and of assembling it successively, in such case the rubberizing of the suspension central body with an ethylene-propylene elas-tomer and the separate molding of the ribs wi-th the qame ethylene-propylene elastomer are carried out first, and the assembling of the insulator successively.
The electric insulator for average, high and very high voltages, made from resin-bonded glass-fibers and ethylene-propylene elastomer, and the re~levant manufacturing process that are the objects of this invention will now be described in still greater detail with reference to the enclosed drawings, this - further description being given merely for illustrative purposes, wherein:
. Figure 1 is a partially cutaway view of an electric insulator according to the present invention, having a supporting central body in the form of a solid bar, provided with a sleeve-shaped rubbery layer previously applied onto said bar, and with ribs successively added onto said sleeve;
Figure 1 bis i.s a partial and cutaway view of another form of electric insulator according to this invention, having a suspension central body in the form of a solid bar, the entire rib-bed coating being molded.in one piece directly on said bari Figure 2 is a partially cutaway view of still another form of electric insulator according to the present invention, having a suspension central body in the form of a hollow cylinder, provided with an inside and outside sleeve-shaped rubbery layer previously applied onto said hollow cylinder, and with ribs sub-sequently added onto the outside sleeve, Figure 2 bis is a partial and cutaway view of a fourth form of the electric insulator according to this invention, having ~ILZ1~7~
a supporting central body in the form of a hollow cylinder, the entire ribbed coating being molded in one piece directly on said hollow cylinder, and the sleeve-shaped inside rubbery layer being subsequen-tly added inside such hollow cylinder.
With reference to these figures, the high voltage electric insulator of this invention made from resin-bonded glass-fibers and ethylene-propylene elastomers, consists or consists essentially of an r.b.g.f. manufactured article or rod-shaped suspension central body -- either of the solid bar type 1 (Figures 1 and 1 bis) or of the hollow cylinder type 2 tFigures
propylene elastomer having high physical properties and in partic-ular high dielectric properties, as ~well as to a process for manufacturing same.
Electric insulators composed of resin-bonded glass-fibers (r.b.g.f.) with a ribbed coating madle of organic materials are already well known and broadly utilized in the field of electric outdoor overhead average and high voltage lines and in the field of electric traction. The main advantage offered by the in-sulators made of resin-bonded glass-fibers and organic materials in respect of the conventional porcelain or glass insulators resides in the particularly low "weight/mechanical strength" ratio.
In fact, the conventional porcelain or glass insulators of the pin and cap type, when meant for outdoor overhead high and very high voltage mechanical loads due to the weight of the conducting wires, must be equipped with metal caps of large dimensions, as a result of which the weight of the whole insulator chain or assemblage is high and no longer negligible in respect of the weight of the conductor supported by said chain.
In the compound insulators made from resin-bonded glass-fibers and organic materials, the mechanical supporting function is left just to the r.b.g.f. rod-shaped article or central body, which is generally manufactured either continuously or discontinuously as a solid bar according to the "pulltrusion"
method, i.e., extrusion by pulling or traction -- in case of the use of glass fibers arranged in filaments parallel with one another and parallel with the direction of the mechanical stress which the suspension central body will be subjected to during operation, or in case . . ~
~2~ 7~
of the use of ferted glass fibers, i.e., glass fibers cu-t and arranged incoherently (chopped strand), or of woven glass fibers -- and which is manufactured in the form of a hollow cylindrical body according to the filament-winding m~thod in the case of continuous fibers, which in general are spirally arran-ged. For manufacturing the article (or body) in the form of a hollow cylinder also glass-fiber fabrics are utilized. In both cases (solid bar or hollow cylinder) the glass fibers are impregnated with a resin having the bes-t electrical properties (such as, for example, a cycloaliphatic epoxy resin). Such bodies exhibit a mechanical strength approximating that of steel, though having a specific gravity corresponding to only about one third that of steel.
In the case of electric railway and tramway traction field of use, the r.b.g.f. insulators offer also a considerable advantage in comparison with the conventional porcelain insulators, as in this field of use it is of the utmcst importance that the insulation shall sucessfully withstand the strong vi~rations it is subjected to during operation, what may be easily achieved merely by means of r.b.g~f. insulators, unlike those made of porcelain.
However, the manufacture of r.b.g.f. insulators that will prove to be fully satisfactory in every respect has met with a few serious obstacles: at first it was very difficult to find the proper materials (resistant to the combined action of ageing and of surface eIectric discharges, the latter involving undesired tracking and/or erosion phenomena) for preparing the generally ribbed coating of the insulator.
~ nce such essential condition of resistance to ageing and to surface discharges was attained thanks to the utilization of suitable materials (such as, e.g., cycloaliphatic epoxy resins, silicone elastomers, ethylene-propylene elastomers, fluorina-ted resins ~PTFE), and the like), there still remained to be overcome the difficulty of coupling the r.b.g.f. central body (solid bar or hollow cylindrical body) with the ribbed coating material.
In fact, the physical, and in particular the mechanical, properties of the r.b.gOf. body are such as not to allow a reliable coupling with materials reacting with non-elastic behavior to the deformations caused by mechanical stresses.
In consequence, and with a view to attempting to obviate these drawbacks, various methods of and cr~teria ~or coupling have been studied: e.g., by means of elastic resins or silicone greases, or rubber mastics, or even by the simple mechanical forcing of the ribbed coating material onto the r.b.g.f.
body. None of these, however, was capable of solving this problem satisfactorily: actually, every such method turned out to be or give rise to a weak point in the insulator from the electrical viewpoint.
It should be borne in mind, in fact that the~outside configuration of an average, high, and above all, very high voltage insulator, whose ribbings have considerable-widths and thicknesses, has been studied for the purpose of opposing to the electric discharge between the insulator's metal terminals (if any, or, in any case, between a live conductor and ground) a path as long as possible, i.e. a particularly high surface creeping line.
"Surface creeping line" means the path o~ an electric discharge over a surface (and therefore, following the insulator ribbing trend) bet:ween a live electrode and ground (i.e., in particular between a live conductor and any part of the ground-connected supporting structure, or, more generally, any part ofsuch structure having the same potential as the ground). In ~3 -LZ~ L 7L4~
general, a surface creeping li~e is deemed hiqh enough ~hen the ratio of said line to the straight line distance (or spacing), namely to the distance existing in straight llne between a live conductor and ground (as defined hereinabove), is at least equa~
to 2, or to 3, or even higher than 3, when taking intG consideration respectively insula-tors meant for norrnal use and insulators utilized under polluted or very polluted conditions.
It is therefore evident that a possible electric discharge generated in the gap or space between the r.b.g.f.
central body and the ribbed coating would be ruinous for the insulation, the effectiveness of which would decrease below the level for which it has been designed, and which would still further deteriorate within short time untill reaching even lower levels of effectiveness owing to the damage caused by the discharge.
The methods of and criteria for coupling the r.b.g.f.
body with the ribbed coating practiced so far according to the prior art, and mentioned above, exhibit the above-described un-desirable drawbacks, as they are not capable of preventing electric discharges in the gap or spacing between the body and the coating.
For instance, silicone greases are subject to a pumping effect due to the elongation, under the action of the mechanical tensile stress, of the r.b.g.f. rod-shaped central body and to the consequent compression exerted by the ribbed coating on such body. In this way it might happen that the silicone grease would be expelled from the gap or space between the bar or rod and the coating and would not be sucked back again when, in case of reduction or elimination of the tensile stress, also the compression exerted by the coating decreases. Thin cavities or voids are then created which easily attract moisture l:~LZ~
and undesired electric dischar~es along the body (in the form of a bar of a hollow cylinder) and inside the ribbed coating.
Conversely, some -types of coupling resins are subjec-ted -- as they couple two materials different from each other ~i.e., the r.b.g.f. body and the ribbed coating which, for example, may be made of PTFE) and from the resins themselves --- to a shearing stress along the body, that too causes cavities or voids attracting pollutants and electric discharges.
The formation of small cavities or voids in the gap between the body and the coating permits the diffusion of mois-ture as well as the generation of partially localized electric dis-charges. These drawbacks, in their turn, involve as a consequence the striking of a direct, continuous and total discharge between the metal terminals of the insulator (or at least between the live conductor and ground) inside said insulator along the body ( a bar or a cylindrical pipe), which thus is irreparably jeopardized and, in consequence, puts the insulator out of service immediately or within a short time.
Neither the flame resistance characteristics nor the self-extinguishing power is to be neglected, such characteristics or self-extinguishing power being required to be as high as pos-sible, while with the organic materials used so far according to the prior art these properties were relatively low or poor, so that the resistance to flame propagation, if any, is of-very little effect.
It is an object of the present invention to eliminate the drawbacks described above, through a radical and definitive solution of the problem of achieving a perfect adherence between the r.b.g.f. body and the ribbed coating.
Another object of this invention is to provide an electFic insulator lor avera~o~ high an~ very high v~lta~es, of -~Z~74 the compound type, consisting of a r.b.g.f. body (rod-shaped central body) and of a ribbed coating made from a suitable elastic organic material, in which insula-tor the generation o~ creeping stresses between said central supporting body and the ribbed coating are prevented by virtue of the high elasticity of the ribbed coating.
A further object of ~his invention is to provide an insulator of the type cited above that permits one to avoid any other drawback depending on the low consistency or compatibility existing -- as noticed in the prior art -- between the r.b.g.f.
body and the ribbed coating.
Still another object of this invention i9 to provide an insulator of the type mentioned above, having a ribbed coating made of a material selected from the class of ethylene-propylene elastomers having good anti-tracking and anti-erosion properties, and high characteristics of elasticity, ageing resistance and op-position or resistance to flame propagation (self-extinguishing power), as well as a high impermeability and water repellency.
It is also a primary object of this invention to provide a process for manufacturing electric insulators according to the present lnvention, which will enable one to achieve all of the foregoing objects.
These and still other objects that will become more clearly apparent to those skilled in the art from the detailed description given hereinafter, are advantageously achieved by an electric insulator for average, high and very high voltages, consisting essentially of a resin-bonded glass-fiber ~r.bOg.~.) suppor-ting ccntral body in tl~ form of a rod, equipped with a ribbed coating prepared from an organic material, characterized in that said ribbed coating thoroughly coats said supporting central body and is made o~ an ethylene-propylene elastomer (EP~) ~ .
having high elastic, antl-tracking, anti-erosion, agei.ng resistant, self-extinguishing, and water-repellency charac-teristics, said ribbed coating being shaped as ribs and supported by a sleeve-shaped tubular layer prepared from an ethylene-propylene elastomer (EPR) of qualities and charac-teristics identical with -those of the EPR elastomer constitu-ting said ribs, the coupling of said ribbed elastomeric coating with said central body, of said ribs with said sleeve, and of said ribs with one another, being obtained by employ-ing a blend, self-curing at room temperature, based on low-unsaturation olefinic polymers, analogous and compatible with the ethylene-propylene blend (EPR) of which the ribbed coating is made.
The electric-insulator of the present invention is advantageously manufactured according to a process com-prising: preparing a mold for molding the whole elastomeric ribbed coating associated with a rod-shaped suspension central body made from resin-bonded glass fibers; treating the surface of said central body-- in the form of a solid bar or of a hollow cylinder depending on the intended use of the insulator -- according to a conventional technique selected from the following: sandblasting, rasping or rubbing with glass paper, spreading or smearing with a suitable adhesion-promoting mastic (the so-called primer>?; placing said body into said mold as prearranged, said body being supported in the mold at its ends; then molding and curing in said mold the entire ribbed coating on the rod-shaped central body according to one of the known prior art methods selected from the transfer method and the injection method, . 30 by employing,as molding material, an ethylene-propylene elas-tomer having particularly high characteristics: drawing out, finally,the whole so-molded insulator from said mold.
~lZ~
The described process con-templates also the alternative possibility of obtaining the ribbed coating separately and of assembling it successively, in such case the rubberizing of the suspension central body with an ethylene-propylene elas-tomer and the separate molding of the ribs wi-th the qame ethylene-propylene elastomer are carried out first, and the assembling of the insulator successively.
The electric insulator for average, high and very high voltages, made from resin-bonded glass-fibers and ethylene-propylene elastomer, and the re~levant manufacturing process that are the objects of this invention will now be described in still greater detail with reference to the enclosed drawings, this - further description being given merely for illustrative purposes, wherein:
. Figure 1 is a partially cutaway view of an electric insulator according to the present invention, having a supporting central body in the form of a solid bar, provided with a sleeve-shaped rubbery layer previously applied onto said bar, and with ribs successively added onto said sleeve;
Figure 1 bis i.s a partial and cutaway view of another form of electric insulator according to this invention, having a suspension central body in the form of a solid bar, the entire rib-bed coating being molded.in one piece directly on said bari Figure 2 is a partially cutaway view of still another form of electric insulator according to the present invention, having a suspension central body in the form of a hollow cylinder, provided with an inside and outside sleeve-shaped rubbery layer previously applied onto said hollow cylinder, and with ribs sub-sequently added onto the outside sleeve, Figure 2 bis is a partial and cutaway view of a fourth form of the electric insulator according to this invention, having ~ILZ1~7~
a supporting central body in the form of a hollow cylinder, the entire ribbed coating being molded in one piece directly on said hollow cylinder, and the sleeve-shaped inside rubbery layer being subsequen-tly added inside such hollow cylinder.
With reference to these figures, the high voltage electric insulator of this invention made from resin-bonded glass-fibers and ethylene-propylene elastomers, consists or consists essentially of an r.b.g.f. manufactured article or rod-shaped suspension central body -- either of the solid bar type 1 (Figures 1 and 1 bis) or of the hollow cylinder type 2 tFigures
2 and 2 bis) -- to which the ribbed coating is applied. This coating may be in one piece, like 7 in Fig. 1 bis or 8 in Fig. 2 bis, or it may consist of a separate sleeve-shaped rubbery layer, such as 3 in Fig. 1 and 4 in Fig. 2, and or ribs, ~ and 6 respec-tively applied onto said sleeve-shaped rubbery layer 3 or 4.
Furthermore, in the rod-shaped suspension central body made of re3in-bonded glass-fibers consists or consists essentially of a hollow cylinder 2, as shown in Figs. 2 and 2 bis (this modification being usually adopted wh,en the insulator is meant for utilization as a bushing insulator), then a sleeve-shaped rubbery layer 10 in the~inside of hollow cylinder 2 is'provided, this inside rubbery layer 10 at the end zone 14, i.e., at the cylinder end, being connected in an integral manner with the external sleeve-shaped rubbery layer 4, in order to ensure a complete coating, and consequently providing full protection for the r.b.g.f. body 2.
It will be understood that a similar integral construction is employed at the upper end of the hollow cylindrical body 2, although not actually illustrated in ~ig. 2 for the sake of simplicity.
Generally, two metal terminals 9 at the end of suspension central body complete the insulator. The terminals 9 _g_ 1~121~74 are fixed to the central body by one of the well known clamping methods of the prior art (e.g., conic ends, inserted wedge, outside notch, compression clamping, application of outside and`
inside cones, threading, etc.). ~Iowever, in case the ribbed coating is molded in one piece, a di~terent type of cIamping may be adopted, as in this case it is possible to prepare r.b.g.f.
bodies with enlarged ends, as described more in detaiI below.
The process for manufacturing the insulator according to the variants illustrated above compriseC the following steps:
One starts from an r.b.g.f. rod- shaped central body ~previously manufactured according to conventional methods) either of the solid bar type 1, or of the hollow cylinder type 2, the selection of course depending on the final type of insulator desired.
In both cases, and prior to any other operation, -the central body is treated thus: more particularly, it is sand-blasted orrasped or rubbed with glass paper according to the usual prior art methods for the purpose of increasing the contact surface and of obtaining good adhesion of the coating blend. As an alternative to the sandblasting or rasping, one may smear or ; spread, over the surface of the body ( a bar or a hollow cylinder), an adhesion promoter, a so-called "primer". After this treatment,-one may then proceed to the application of the organic elastomeric material: more precisely, the central body may be now provided with the ribbed coating prepared from an ethylene-propylene elastomer (EPR), such coating (as explained above) being either in one piece 7 or 8, or consisting separately of a sleeve-shaped rùbbery layer 3 or 4, with ribs 5 or 6 successively added thereonto.
In case of the one-piece coating (Figs. 1 bis and 2 bis), a mold is prepared for molding the entire ribbed .,: .
-10-- , " .
' .
~Lz~
coating 7 or 8 associated with the rod-shaped central body 1 or 2. The cen-tral body is put into the mold while being supported at both ends. The entire elastomeric ribbed coating is then molded and cured on the rod-shaped central body and in said mold according to the transfer method or the in~ection method.
Finally, the whole insulator thus molded is withdrawn from the mold.
For an insulator whose central body is of the solid bar type, the manufacturing process is concluded at this stage.
Conversely, for an insulator whose central body is of the hollow cylinder type, the sleeve-shaped rubberizing of the inside surface must then be carried out according to the procedure described below, when dealing with the coating preparation in consecutive steps. The inside rubberizing, however, may also be carried out, if desired, before molding -the whole ribbed coating.
Conversely, in the case of a separately prepared coating, the rod-shaped central body is at first coated with a tubular layer of EPR elastomer (sleeve), this operation being hereinafter called rubberizing for the sake of brevity.
When the central body consists of a solid bar, the sleeve-shaped rubberizing may be carried out according to one of the following methods:
(a) molding and curing by compression;
(b) molding and curing by transfer, (c) molding and curing by injection, or (d) extrusion from a T-head extruder and successive steam-curing in an autoclave or in a liquid bath.
for example in a liquid bath of molten salts.
Convërsely, when the central body consists in a hollow cylinder, the elastomeric tubular layer (rubberizing) may be pFepared according to any of the processes listed below, ]n a ~LlZi~4 manner quite analogous to -the corresponding processes employed for the solid bar:
(b) molding and curing by transfer; or (c) molding and curing by injection.
By op~rating according -to either process, both the inside and the outside surfaces of the hollow cylinder are simultaneously rubberized.
~ ne sleeve-type rubberizing of the central body in the form of a hollow cylinder may also be carried out in two steps :
-- rubberizing of the outside surface, obtainable according to any of the methods listed above under - (a) to (d) for the case of a solid-bar body, -- rubberizing of the inside surface, obtainable according to the following method:
a sufficiently thick pipe, previously prepared from a crude blend and extruded, is introduced into the cylinder cavity, whereupon said pipe is made to adhere to the inside surface of the r.b.g.f. cylinder by means of an inflatable air tube of suitable shape, that is introduced into the crude blend pipe and is inflated during curing occuring in a furnace or in a liquid bath at a suitable temperature, or if desired, in a stream autoclave. The pressure required inside the blend pipe for causing it to adhere to the inside surface of the r.b.g.f. cylinder may be obtained by means of a proper substance (e~g., sodium bicarbonate ) that, at the curing temperature, evolves gases, and as a consequence, causes the pressure to rise.
The rubberizing blend, causing the formation of the elastomeric tubular layer that coats the solid bar, as well as the L47~
blend utilized for obtaining the two elastomeric tubular layers that coat the insi~e and ou-tside surfaces of the hollow cylinder, have the same composition as the blend used for molding the ribs, such molding being described below.
The molking of the ribs may be effected according to two differen-t criteria: as a separate molding of single ribs or as a molding of groups of more units forming a whole with one another. Figs. 1 and 2 show only single ribs 5 and 6, as in seen from the separa-tion lines between one rib and the successive rib at 11 and 12 respectively.
When manufactured as single ribs, molding can occur according to any of the following processes:
(a) molding and curing by compression' (b)`molding and curing by transfer, or (c) molding and curing by injection.
In any case, for processing economy, the molds have multiple impressions, i.e., in every mold there is more than one impression of a single rib.
Conversely, when the ribs are manufactured as groups of more-than one unit in regular succession forming a whole with one another, either process cited below may be followed for the molding, quite analogously with what is done for the single ribs:
(b) molding and curing by transfer, or (c) molding and curing by injection.
At the conclusion of curing, the ribs(if manufactured individually), or the groups of ribs in one piece, are withdrawn from their respective molds.
Different criteria may be followed for the insulator~
assembling:
-- According to a first assembling criterion, the pre-molded ribs, either single ribs or in multiple groups, are slipped ~2~4t~4 or driven, preferably by forced assembling or mounting, onto the r.b.g.f. suspension central body previously treated (i.e., sand-blasted, or rasped, or smeared or spread with a primer, as already described) and then smeared or spread with a blend which is self-curing at room temperature, based on low-unsaturation olefinic polymers, similar to or compatible with the ethylene-propylene blend (EPR) employ~d for rubberizing the body and for molding the ribs. This room temperature self-curing blend must be applied also on the surfaces (having a very limited area and generally the shape of a circular ring) through which the ribs -- either individual ribs or in multiple groups -- are in contact with one another , surfaces whose intersection lines with the drawing plane are indicated by reference numerals 11 and 12, respectively, in Figs. 1 and 2. More particularly, the room temperature self-curing blend employed includes: a low-unsaturation amorphous olefinic terpolymer consisting of ethylene, an alpha-olefin, a cyclic or acyclic polyene having non-conjugated double bonds, a reinforcing filler; preferably anti-oxidants, pigments and other additives and, as a curing agent, an organic hydroperoxide. Such a blend may be prepared according~to Italian Patent ~o. 780,429 owned by Montedison, S.p.A.
-- According to another assembling criterion, the pre-- molded ribs, either single ribs or in multiple groups, are slipped or driven as mentloned before, preferably by forced assembling, onto the r.b.g.f. suspension central body but, unlike the previously described criterion, the suspension central body used in this case is already rubberized, i.e., already covered with an elastomeric tubular coat; and it is just such tubular coat or sleeve that is spread or smeared with the room temperature self-curing blend securing the desired adhesion between the ribs(singleribs or group of ribs) and said tubular coat, in the same way as ~2~L~74 (when the first criterion is Eollowed) the same blend secures a direct adhesion between -the ribs and the treated, but not rubber-ized, suspension central body.
-- Finally, according to a third assembling criterion, use is made of pre-molded ribs, either single or in multiple groups, cured only partially, more precisely: cured to the extent of 50 %, which are slipped or driven, preferably by forced mounting, onto the r.b.g.f. central body (a bar or a hollow cylin-der) provided with a rubber coating, it -too being cured only partially, to the extent of 50 % rme unit, so assembled, is then placed into a proper molding-press to complete the curing, which is attained by radial compression and by heating in said mold at a temperature ranging from 160 to 210C, and preferably from 160 to 180C.
By employing the technique according -to this third assembling criterion it is possible to achieve excellent results as regards the adhesion among the various assembled parts, even without using self-curing adhesives as is contemplated conversely, by the two previously described assembling criteria.
As concerns the curing times, it is to be borne in mind that, in any process step, the employed ethylene-propylene elastomer (EPR) blend takes from 5 to 4 minutes, and more particularly from 10 to 40 minutes, for thorough curing. Conse-quently, a curing conducted, in a first step, up to about 50 %
(as illustrated in the third assembling criterion mentioned above) requires from 3 to 22 minutes, and more particularly from 5 to 20 minutes. As many minutes are required for the second step in which the curing of the entire assembled insulator is brought from about 50 % to 100 %.
As for the curing temperatures to which the blend is to be subjected during the above-specified time periods, these '~
~LlZ~
are the same as indicated above in connection wi-th the already-described third insulator assembling criterion, i.e., from 160 to 210~C, and preferably from 160 to 180C.
The adhesive blend is self-curing, and therefore it cures at room temperature. The widest curing temperature range is from 5 to 6~C. As to the times required to complete -the curing process, these vary from 20 to 48 hours or at the most from 20 to 96 hours.
As pointed out in the course of the present descrip~
tion of the insulator manufactured according to this invention, the metal terminals are fastened to the supporting central body according to any of the well kncwn conventional clamping methods, but when the ribbed coating is molded in one piece, it is possible to prepare, as from the beginning, the supporting central body with both its ends shaped as a head oversized in respect of the supporting rod and with undercuts properly arranged for an anchor-age safe from any risk of the slipping-off of the insulator's suspension metal connections 9.
In fact, by molding the ribbed coating in one piece directly on the supporting central body it is no longer necessary - to slip-or drive the ribs onto said central body. Thus it is possible to use a previously manufactured central body with over-sized heads, and this represents a further advantage of the process for molding the ribbed coating ln one piece.
Of course, structurally and operatively equivalent modifications and variants may be incorporated as a part of the present invention, as described and illustrated hereinbefore and claimed hereinafter, without either departing from the spirit of the invention or falling outside the scope of the claims. For instance, the process for molding the ribbed coating may be pract-iced,according to a further variant, by coating the rod-shaped _, - .
supporting centr~l body with a tubular elastomeric layer (sleeve), i.e., by effecting the rubberizing, as in the case of the separ-ately prepared ribbed coa-ting, but keeping the curing at a rather low degree, then by placing the already rubberized manufactured article or central body into a suitably prearranged mold and by molding therein all the ribs in one piece, directly on the pre-viously rubberized article or central body, as in the case of the entire ribbed coating considered as a whole.
Furthermore, in the rod-shaped suspension central body made of re3in-bonded glass-fibers consists or consists essentially of a hollow cylinder 2, as shown in Figs. 2 and 2 bis (this modification being usually adopted wh,en the insulator is meant for utilization as a bushing insulator), then a sleeve-shaped rubbery layer 10 in the~inside of hollow cylinder 2 is'provided, this inside rubbery layer 10 at the end zone 14, i.e., at the cylinder end, being connected in an integral manner with the external sleeve-shaped rubbery layer 4, in order to ensure a complete coating, and consequently providing full protection for the r.b.g.f. body 2.
It will be understood that a similar integral construction is employed at the upper end of the hollow cylindrical body 2, although not actually illustrated in ~ig. 2 for the sake of simplicity.
Generally, two metal terminals 9 at the end of suspension central body complete the insulator. The terminals 9 _g_ 1~121~74 are fixed to the central body by one of the well known clamping methods of the prior art (e.g., conic ends, inserted wedge, outside notch, compression clamping, application of outside and`
inside cones, threading, etc.). ~Iowever, in case the ribbed coating is molded in one piece, a di~terent type of cIamping may be adopted, as in this case it is possible to prepare r.b.g.f.
bodies with enlarged ends, as described more in detaiI below.
The process for manufacturing the insulator according to the variants illustrated above compriseC the following steps:
One starts from an r.b.g.f. rod- shaped central body ~previously manufactured according to conventional methods) either of the solid bar type 1, or of the hollow cylinder type 2, the selection of course depending on the final type of insulator desired.
In both cases, and prior to any other operation, -the central body is treated thus: more particularly, it is sand-blasted orrasped or rubbed with glass paper according to the usual prior art methods for the purpose of increasing the contact surface and of obtaining good adhesion of the coating blend. As an alternative to the sandblasting or rasping, one may smear or ; spread, over the surface of the body ( a bar or a hollow cylinder), an adhesion promoter, a so-called "primer". After this treatment,-one may then proceed to the application of the organic elastomeric material: more precisely, the central body may be now provided with the ribbed coating prepared from an ethylene-propylene elastomer (EPR), such coating (as explained above) being either in one piece 7 or 8, or consisting separately of a sleeve-shaped rùbbery layer 3 or 4, with ribs 5 or 6 successively added thereonto.
In case of the one-piece coating (Figs. 1 bis and 2 bis), a mold is prepared for molding the entire ribbed .,: .
-10-- , " .
' .
~Lz~
coating 7 or 8 associated with the rod-shaped central body 1 or 2. The cen-tral body is put into the mold while being supported at both ends. The entire elastomeric ribbed coating is then molded and cured on the rod-shaped central body and in said mold according to the transfer method or the in~ection method.
Finally, the whole insulator thus molded is withdrawn from the mold.
For an insulator whose central body is of the solid bar type, the manufacturing process is concluded at this stage.
Conversely, for an insulator whose central body is of the hollow cylinder type, the sleeve-shaped rubberizing of the inside surface must then be carried out according to the procedure described below, when dealing with the coating preparation in consecutive steps. The inside rubberizing, however, may also be carried out, if desired, before molding -the whole ribbed coating.
Conversely, in the case of a separately prepared coating, the rod-shaped central body is at first coated with a tubular layer of EPR elastomer (sleeve), this operation being hereinafter called rubberizing for the sake of brevity.
When the central body consists of a solid bar, the sleeve-shaped rubberizing may be carried out according to one of the following methods:
(a) molding and curing by compression;
(b) molding and curing by transfer, (c) molding and curing by injection, or (d) extrusion from a T-head extruder and successive steam-curing in an autoclave or in a liquid bath.
for example in a liquid bath of molten salts.
Convërsely, when the central body consists in a hollow cylinder, the elastomeric tubular layer (rubberizing) may be pFepared according to any of the processes listed below, ]n a ~LlZi~4 manner quite analogous to -the corresponding processes employed for the solid bar:
(b) molding and curing by transfer; or (c) molding and curing by injection.
By op~rating according -to either process, both the inside and the outside surfaces of the hollow cylinder are simultaneously rubberized.
~ ne sleeve-type rubberizing of the central body in the form of a hollow cylinder may also be carried out in two steps :
-- rubberizing of the outside surface, obtainable according to any of the methods listed above under - (a) to (d) for the case of a solid-bar body, -- rubberizing of the inside surface, obtainable according to the following method:
a sufficiently thick pipe, previously prepared from a crude blend and extruded, is introduced into the cylinder cavity, whereupon said pipe is made to adhere to the inside surface of the r.b.g.f. cylinder by means of an inflatable air tube of suitable shape, that is introduced into the crude blend pipe and is inflated during curing occuring in a furnace or in a liquid bath at a suitable temperature, or if desired, in a stream autoclave. The pressure required inside the blend pipe for causing it to adhere to the inside surface of the r.b.g.f. cylinder may be obtained by means of a proper substance (e~g., sodium bicarbonate ) that, at the curing temperature, evolves gases, and as a consequence, causes the pressure to rise.
The rubberizing blend, causing the formation of the elastomeric tubular layer that coats the solid bar, as well as the L47~
blend utilized for obtaining the two elastomeric tubular layers that coat the insi~e and ou-tside surfaces of the hollow cylinder, have the same composition as the blend used for molding the ribs, such molding being described below.
The molking of the ribs may be effected according to two differen-t criteria: as a separate molding of single ribs or as a molding of groups of more units forming a whole with one another. Figs. 1 and 2 show only single ribs 5 and 6, as in seen from the separa-tion lines between one rib and the successive rib at 11 and 12 respectively.
When manufactured as single ribs, molding can occur according to any of the following processes:
(a) molding and curing by compression' (b)`molding and curing by transfer, or (c) molding and curing by injection.
In any case, for processing economy, the molds have multiple impressions, i.e., in every mold there is more than one impression of a single rib.
Conversely, when the ribs are manufactured as groups of more-than one unit in regular succession forming a whole with one another, either process cited below may be followed for the molding, quite analogously with what is done for the single ribs:
(b) molding and curing by transfer, or (c) molding and curing by injection.
At the conclusion of curing, the ribs(if manufactured individually), or the groups of ribs in one piece, are withdrawn from their respective molds.
Different criteria may be followed for the insulator~
assembling:
-- According to a first assembling criterion, the pre-molded ribs, either single ribs or in multiple groups, are slipped ~2~4t~4 or driven, preferably by forced assembling or mounting, onto the r.b.g.f. suspension central body previously treated (i.e., sand-blasted, or rasped, or smeared or spread with a primer, as already described) and then smeared or spread with a blend which is self-curing at room temperature, based on low-unsaturation olefinic polymers, similar to or compatible with the ethylene-propylene blend (EPR) employ~d for rubberizing the body and for molding the ribs. This room temperature self-curing blend must be applied also on the surfaces (having a very limited area and generally the shape of a circular ring) through which the ribs -- either individual ribs or in multiple groups -- are in contact with one another , surfaces whose intersection lines with the drawing plane are indicated by reference numerals 11 and 12, respectively, in Figs. 1 and 2. More particularly, the room temperature self-curing blend employed includes: a low-unsaturation amorphous olefinic terpolymer consisting of ethylene, an alpha-olefin, a cyclic or acyclic polyene having non-conjugated double bonds, a reinforcing filler; preferably anti-oxidants, pigments and other additives and, as a curing agent, an organic hydroperoxide. Such a blend may be prepared according~to Italian Patent ~o. 780,429 owned by Montedison, S.p.A.
-- According to another assembling criterion, the pre-- molded ribs, either single ribs or in multiple groups, are slipped or driven as mentloned before, preferably by forced assembling, onto the r.b.g.f. suspension central body but, unlike the previously described criterion, the suspension central body used in this case is already rubberized, i.e., already covered with an elastomeric tubular coat; and it is just such tubular coat or sleeve that is spread or smeared with the room temperature self-curing blend securing the desired adhesion between the ribs(singleribs or group of ribs) and said tubular coat, in the same way as ~2~L~74 (when the first criterion is Eollowed) the same blend secures a direct adhesion between -the ribs and the treated, but not rubber-ized, suspension central body.
-- Finally, according to a third assembling criterion, use is made of pre-molded ribs, either single or in multiple groups, cured only partially, more precisely: cured to the extent of 50 %, which are slipped or driven, preferably by forced mounting, onto the r.b.g.f. central body (a bar or a hollow cylin-der) provided with a rubber coating, it -too being cured only partially, to the extent of 50 % rme unit, so assembled, is then placed into a proper molding-press to complete the curing, which is attained by radial compression and by heating in said mold at a temperature ranging from 160 to 210C, and preferably from 160 to 180C.
By employing the technique according -to this third assembling criterion it is possible to achieve excellent results as regards the adhesion among the various assembled parts, even without using self-curing adhesives as is contemplated conversely, by the two previously described assembling criteria.
As concerns the curing times, it is to be borne in mind that, in any process step, the employed ethylene-propylene elastomer (EPR) blend takes from 5 to 4 minutes, and more particularly from 10 to 40 minutes, for thorough curing. Conse-quently, a curing conducted, in a first step, up to about 50 %
(as illustrated in the third assembling criterion mentioned above) requires from 3 to 22 minutes, and more particularly from 5 to 20 minutes. As many minutes are required for the second step in which the curing of the entire assembled insulator is brought from about 50 % to 100 %.
As for the curing temperatures to which the blend is to be subjected during the above-specified time periods, these '~
~LlZ~
are the same as indicated above in connection wi-th the already-described third insulator assembling criterion, i.e., from 160 to 210~C, and preferably from 160 to 180C.
The adhesive blend is self-curing, and therefore it cures at room temperature. The widest curing temperature range is from 5 to 6~C. As to the times required to complete -the curing process, these vary from 20 to 48 hours or at the most from 20 to 96 hours.
As pointed out in the course of the present descrip~
tion of the insulator manufactured according to this invention, the metal terminals are fastened to the supporting central body according to any of the well kncwn conventional clamping methods, but when the ribbed coating is molded in one piece, it is possible to prepare, as from the beginning, the supporting central body with both its ends shaped as a head oversized in respect of the supporting rod and with undercuts properly arranged for an anchor-age safe from any risk of the slipping-off of the insulator's suspension metal connections 9.
In fact, by molding the ribbed coating in one piece directly on the supporting central body it is no longer necessary - to slip-or drive the ribs onto said central body. Thus it is possible to use a previously manufactured central body with over-sized heads, and this represents a further advantage of the process for molding the ribbed coating ln one piece.
Of course, structurally and operatively equivalent modifications and variants may be incorporated as a part of the present invention, as described and illustrated hereinbefore and claimed hereinafter, without either departing from the spirit of the invention or falling outside the scope of the claims. For instance, the process for molding the ribbed coating may be pract-iced,according to a further variant, by coating the rod-shaped _, - .
supporting centr~l body with a tubular elastomeric layer (sleeve), i.e., by effecting the rubberizing, as in the case of the separ-ately prepared ribbed coa-ting, but keeping the curing at a rather low degree, then by placing the already rubberized manufactured article or central body into a suitably prearranged mold and by molding therein all the ribs in one piece, directly on the pre-viously rubberized article or central body, as in the case of the entire ribbed coating considered as a whole.
Claims (26)
1. An electric insulator for average, high and very high voltages, consisting essentially of a resin-bonded glass-fiber (r.b.g.f.) supporting central body in the form of a rod, equipped with a ribbed coating prepared from an organic material characterized in that said ribbed coating thoroughly coats said supporting central body and is made of an ethylene-propylene elastomer (EPR) having high elastic, anti-tracking, anti-erosion, ageing resistant, self-extinguishing, and water-repellency characteristics, said ribbed coating being shaped as ribs and supported by a sleeve-shaped tubular layer prepared from an ethylene-propylene elastomer (EPR) of qualities and characteristics identical with those of the EPR elastomer constituting said ribs,the coupling of said ribbed elastomeric coating with said central body, of said ribs with said sleeve, and of said ribs with one another, being obtained by employing a blend, self-curing at room temperature, based on low-unsaturation olefinic polymers, analogous and compatible with the ethylene-propylene blend (EPR) of which the ribbed coating is made.
2. An electric insulator according to claim 1, charac-terized in that said supporting central body is an r.b.g.f.
solid bar.
solid bar.
3. An electric insulator according to claim 1, charac-terized in that said supporting central body is an r.b.g.f.
hollow cylinder.
hollow cylinder.
4. An electric cylinder according to claim 1, 2 or 3, characterized in that the ribbed coating is made unitary together with the sleeve-shaped tubular layer.
5. An electric insulator according to claim 1, 2 or 3, characterized in that the ribbed coating consists essentially of at least a sleeve-shaped tubular layer intimately coupled with said central body and supporting the ribs.
6. An electric insulator according to claim 3, characterized in that said hollow cylinder is internally lined with another tubular sleeve made of an ethylene-propylene elastomer, and integrally connected at each of the hollow cylinder ends with an outer tubular sleeve, the EPR elastomer of the inner sleeve exhibiting qualities and properties identical with those of the EPR elastomer of which the outer sleeve is made.
7. An electric insulator according to claim 1, characterized in that said self-curing blend includes a low-unsaturation amorphous olefinic terpolymer consisting essen-tially of ethylene, an alpha-olefin, a cyclic or acyclic polyene having non-conjugated double bonds; a reinforcing filler; and , as a curing agent, an organic hydroperoxide.
8. An electric insulator according to claim 7, characterized in that self-curing blend includes an anti-oxidant, pigments and other additives.
9. An electric insulator according to claim 7, characterized in that the organic hydroperoxide is the benzoyl peroxide.
10. A process for producing a high voltage electric insulator, of the type consisting essentially of an r.b.g.f.
supporting central body in the form of a rod, equipped with an elastomeric ribbed coating, said process comprising the steps of: prearranging a mold fox molding the entire elastomeric ribbed coating integral with the supporting central body;
treating the surface of said supporting central body according to a technique selected from amongst the following: sandblasting, rasping, spreading with an adhesion-promoting mastic; placing said supporting central body into said mold, said supporting central body being supported in said mold at its ends; then molding and curing, on the supporting central body and in the same mold, the whole ribbed coating according to a method selected from the transfer method and the injection method, utilizing, as molding material, an ethylene-propylene elas-tomer (EPR); and finally withdrawing the entire insulator so molded from said mold.
supporting central body in the form of a rod, equipped with an elastomeric ribbed coating, said process comprising the steps of: prearranging a mold fox molding the entire elastomeric ribbed coating integral with the supporting central body;
treating the surface of said supporting central body according to a technique selected from amongst the following: sandblasting, rasping, spreading with an adhesion-promoting mastic; placing said supporting central body into said mold, said supporting central body being supported in said mold at its ends; then molding and curing, on the supporting central body and in the same mold, the whole ribbed coating according to a method selected from the transfer method and the injection method, utilizing, as molding material, an ethylene-propylene elas-tomer (EPR); and finally withdrawing the entire insulator so molded from said mold.
11. A process for producing an insulator according to claim 10, characterized in that the ribbed coating is molded separately and assembled successively.
12. A process for manufacturing an insulator according to claim 10, characterized in that, when a supporting central body consisting of a hollow cylinder is employed, a further process step is employed consisting in rubberizing the inside surface of said cylinder by means of an EPR elastomer having qualities and characteristics identical with those of the EPR elastomer forming the outside coating, said rubberizing being carried out optionnally as the initial or the final step of the process, by introducing into the hollow cylinder a tubular sleeve made of a crude EPR blend, of suitable dimensions; in successively applying the sleeve to said inside surface through by either (1) inflating, during curing, an air tube placed inside the sleeve; or (2) creating the necessary pressure inside said tubular sleeve by means of a substance, which gasifies at: the curing temperature;
and finally curing the inside tubular EPR sleeve.
and finally curing the inside tubular EPR sleeve.
13. A process for manufacturing an insulator according to claim 12, characterized in that said substance creating the necessary pressure inside the tubular sleeve is a sodium bicarbonate.
14. A process for manufacturing an insulator according to claim 12, characterized in that the inside tubular EPR sleeve is cured by heating in a furnace.
15. A process for manufacturing an insulator according to claim 12, characterized in that the inside tubular EPR sleeve is cured by heating in a liquid bath.
16. A process for manufacturing an insulator according to claim 12, characterized in that the inside tubular EPR sleeve is cured by heating in a steam autoclave.
17. A process for manufacturing an insulator according to claim 11, characterized in that the assembling of the insulator consists essentially in slipping the ribs, by forced assembling, directly onto the supporting central body, previously treated and spread with a blend, self-curing at room temperature, based on low-unsaturation olefinic polymers;
said blend being furthermore applied also onto the surfaces of the ribs, which have to remain in intimate contact with one another.
said blend being furthermore applied also onto the surfaces of the ribs, which have to remain in intimate contact with one another.
18. A process for producing an insulator according to claim 11, characterized in that the assembling of the insulator consists in slipping the ribs , by forced assembling, onto the supporting central body, previously treated,rubberized and spread with a blend self-curing at room temperature, said blend being furthermore applied also onto the surfaces of the ribs which have to remain in intimate contact with one another.
19. A process for producing an insulator according to claim 11, characterized in that it consists essentially in stopping the curing of both the rubberizing of the supporting central body and the separately molded ribs, when said curing has substantially reached a 50% extent; in assembling the insulator by slipping said ribs, by forced assembling, onto the supporting central body previously treated and rubberized;
in prearranging a suitable mold for containing the entire assembled insulator; in placing said insulator into said mold;
in completing the curing of the whole insulator by radial compression and by heating in said mold; and finally in withdrawing the entire assembled and cured insulator from said curing mold.
in prearranging a suitable mold for containing the entire assembled insulator; in placing said insulator into said mold;
in completing the curing of the whole insulator by radial compression and by heating in said mold; and finally in withdrawing the entire assembled and cured insulator from said curing mold.
20. A process for producing an insulator according to claim 10, 11 or 19, characterized in that curing is conducted at temperature between 160° and 210°.
21. A process for producing an insulator according to claims 10,11 or 19, characterized in that curing is conducted at temperatures between 160° and 180° C.
22. A process for producing an insulator according to claims 10 or 11, characterized in that curing is completed in a time ranging from 5 to 45 minutes.
23. A process for producing an insulator according to claims 10 or 11, characterized in that curing is completed in a time ranging from 10 to 40 minutes.
24. A process for producing an insulator according to claim 19, characterized in that curing is brought to an extent of 50% in times ranging from 3 to 22 minutes, and is then completed in times ranging from 3 to 22 minutes.
25. A process for producing an insulator according to claim 24, characterized in that curing is brought to an extent of 50% in time ranging from 5 to 20 minutes.
26. A process for producing an insulator according to claim 24, characterized in that curing is completed in time ranging from 5 to 20 minutes.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT26187/77A IT1114909B (en) | 1977-07-27 | 1977-07-27 | ELECTRIC INSULATOR IN FIBERGLASS AND ORGANIC MATERIAL FOR HIGH VOLTAGES AND RELATED MANUFACTURING PROCEDURE |
| IT26187A/77 | 1977-07-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121474A true CA1121474A (en) | 1982-04-06 |
Family
ID=11218874
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000308135A Expired CA1121474A (en) | 1977-07-27 | 1978-07-26 | High voltage electric insulators made of resins-bonded glass-fibers and organic material, and process for manufacturing same |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5425481A (en) |
| BR (1) | BR7804801A (en) |
| CA (1) | CA1121474A (en) |
| CH (1) | CH634683A5 (en) |
| DE (1) | DE2832543A1 (en) |
| ES (1) | ES472010A1 (en) |
| FR (1) | FR2399105A1 (en) |
| GB (1) | GB1601379A (en) |
| IT (1) | IT1114909B (en) |
| SE (1) | SE433545B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4505033A (en) * | 1979-03-12 | 1985-03-19 | Interpace Corporation | Methods of making high voltage resistant members |
| US4312123A (en) * | 1979-03-12 | 1982-01-26 | Interpace Corporation | Methods of making high voltage electrical insulators and oil-less bushings |
| FR2461343A1 (en) * | 1979-07-11 | 1981-01-30 | Ceraver | INSULATING ELEMENT WITH FINS OR MONOBLOCS OF VULCANIZED FINS ARRANGED END-TO-END |
| JPS5673821A (en) * | 1979-11-17 | 1981-06-18 | Ngk Insulators Ltd | Synthetic resin insulator |
| DE3003095A1 (en) * | 1980-01-29 | 1981-07-30 | Siemens AG, 1000 Berlin und 8000 München | METHOD FOR PRODUCING ELECTRICAL PLASTIC COMPOSITE INSULATORS |
| FR2511179A1 (en) * | 1981-08-05 | 1983-02-11 | Ceraver | HAUBAN ISOLATOR OF COMPOSITE TYPE |
| FR2511180A1 (en) * | 1981-08-05 | 1983-02-11 | Ceraver | ELECTRICALLY INSULATING ELEMENT COMPRISING A MONOBLOC FAN GROUP |
| FR2543356B1 (en) * | 1983-03-25 | 1986-01-10 | Ceraver | METHOD AND DEVICE FOR MOLDING THE INSULATING COATING OF A LARGE ORGANIC INSULATOR |
| FR2576655B1 (en) * | 1985-01-25 | 1990-02-23 | Alsthom Atlantique | INSULATING STAY |
| HU194293B (en) * | 1985-05-17 | 1988-01-28 | Villamos Ipari Kutato Intezet | Process and equipment for production of forms from materials based on siliconelastomer and resistant against harms made by birds |
| IT1185406B (en) * | 1985-10-10 | 1987-11-12 | Rebosio Ind Elettrotecnia Spa | INSULATOR FOR ELECTRIC LINES AND ITS MANUFACTURING PROCEDURE |
| US4749824A (en) * | 1987-01-30 | 1988-06-07 | Dow Corning Corporation | High voltage insulators |
| US5223190A (en) * | 1991-02-01 | 1993-06-29 | Pirelli Cavi S.P.A. | Apparatus and method to make composite insulators for electric overhead lines |
| CN107731427B (en) * | 2017-09-28 | 2020-03-06 | 句容市大唐电气有限公司 | Extensible insulator |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1569181B2 (en) * | 1964-04-24 | 1973-10-31 | Montecatini Edison S.P.A., Mailand (Italien) | Use of organic hydro peroxides for cold vulcanization of ethylene copolymers and a process for the production of molded bodies |
| DE1544896A1 (en) * | 1965-03-11 | 1969-01-30 | Bayer Ag | Corrosion-resistant composite materials |
| GB1292276A (en) * | 1968-09-04 | 1972-10-11 | Raychem Ltd | Improvements in and relating to insulators |
| GB1391249A (en) * | 1971-04-27 | 1975-04-16 | Trans Dev Ltd | Shedded electrical insulators |
| GB1434719A (en) * | 1972-09-01 | 1976-05-05 | Raychem Ltd | Heat recoverable products |
| DE2425076A1 (en) * | 1974-05-24 | 1975-11-27 | Rhein Westfael Isolatoren | Outdoor electrical insulators - made by vertically casting resin weather sheds round G.R.P stalk |
-
1977
- 1977-07-27 IT IT26187/77A patent/IT1114909B/en active
-
1978
- 1978-05-31 GB GB24931/78A patent/GB1601379A/en not_active Expired
- 1978-07-24 SE SE7808090A patent/SE433545B/en not_active IP Right Cessation
- 1978-07-25 DE DE19782832543 patent/DE2832543A1/en not_active Ceased
- 1978-07-25 BR BR7804801A patent/BR7804801A/en unknown
- 1978-07-26 CA CA000308135A patent/CA1121474A/en not_active Expired
- 1978-07-26 JP JP9056378A patent/JPS5425481A/en active Granted
- 1978-07-26 CH CH802878A patent/CH634683A5/en not_active IP Right Cessation
- 1978-07-26 ES ES472010A patent/ES472010A1/en not_active Expired
- 1978-07-27 FR FR7822227A patent/FR2399105A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2399105B1 (en) | 1980-07-04 |
| BR7804801A (en) | 1979-04-17 |
| JPS635845B2 (en) | 1988-02-05 |
| CH634683A5 (en) | 1983-02-15 |
| IT1114909B (en) | 1986-02-03 |
| SE7808090L (en) | 1979-01-28 |
| JPS5425481A (en) | 1979-02-26 |
| GB1601379A (en) | 1981-10-28 |
| SE433545B (en) | 1984-05-28 |
| ES472010A1 (en) | 1979-02-01 |
| DE2832543A1 (en) | 1979-02-15 |
| FR2399105A1 (en) | 1979-02-23 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |