WO2002078145A1

WO2002078145A1 - Industrial production method for cold-shrink joints and terminations with multiple elastic walls

Info

Publication number: WO2002078145A1
Application number: PCT/IT2002/000184
Authority: WO
Inventors: Amelio Incollingo
Original assignee: Elcon S.R.L.
Priority date: 2001-03-28
Filing date: 2002-03-22
Publication date: 2002-10-03
Also published as: ITAV20010004A0; ITAV20010004A1; EP1285482A1

Abstract

Purpose of the present invention is the production of elastic tubes for electrical joints and terminations by cold shrink component, formed by walls having multiple layers, each layer having different electrical and mechanical characteristics, not by using co-moulding and/or coextrusion process, but extruding and/or moulding and/or otherwise producing one by one the single tube layer and then expanding one layer tube on the previous one according to the need. By the said method the single layer tubes may be produced with the characteristic more suitable for the application, without being subject to a compromise between the wanted characteristics and the production process. Other feature of the method to reduce the mechanical stress, by which the cold shrink tubes are stressed during the expanding process on tubular rigid support and hence to reduce drastically the diameter sizes needed for a certain range of application.

Description

-TITLE

Industrial production method for cold-shrink joints and terminations with multiple elastic walls.

-TECHICAL FIELD This method finds the main application for the cables accessories in the power production and distribution installations.

-BACKGROUND ART

A termination and/or joint and/or other component, to be called cold-shrink, has to be made out of elastic materials as natural rubber and/or synthetic rubber and/or other material with similar characteristics, because it has to be expanded, firstly, to a diameter slightly larger than that one on which it will be larger installed and then, thanks to its intrinsic elastic memory, to shrink strongly up to insure the wanted pressure on the cables, without using external force or power.

The expanding process takes place normally in the factory and it is one of the production cycle phase. In practice the elastic tube is expanded and parked on a rigid support, having generally cylindric shape and an internal diameter larger than that one on wich the elastic tube has to be applied.

The expanded preassembied tube will be stored up to the selling or, better, to the final application.

It is very important that, during the wharehouse shelf life, the tube is not loosing too much elastic memory or force; namely it has to keep the property of shrinking almost to the primary diameter and shape it has before being expanded and, overall, it has to keep sufficient elastic force.

All types of cold-shrink joints and terminations presently produced and marketed are realized by moulding or extruding at same time the various rubbery materials, which are needed to get the various electrical and mechanical features (see fig. 1), by very critical and expensive process.

Looking to the fig. 1 , it can be seen that the final elastic tube is formed by one or more layers of rubber, each layer having a different performance. Generally, the internal layer will make the electrical stress control relief and will be made out of filled rubbery compound. The external layer will make the mechanical sealing of the joint or termination and the needed electrical insulation grade and then it will be made out of different rubbery compound The eventual intermediate layers can make, time by time, the various functions, both electrical and mechanical, contributing in increasing the final features of the product. The different characteristics of the rubbery compound used for producing each layer, in addition to give those electrical properties tipical of the function, produce also some mechanical properties which not always are desirable and/or which reduce the range of applications and/or make difficult the assembling in the factory and/or reduce the warehouse shelf life. Several researchs of different laboratories have shown that the rubber items, of various type and composition, pre-expanded and stocked, loose about 15% of their elastic memory after only two years. The filled rubbers, which generally are used for the internal layer of the product, have low elastic memory and lose up to 50% of it within 2 years storage. In the production process of comolding and/or coextrusion the compounds to be used have to reach a compromise between the best ones suitable for the applications and those ones compatible with the process for industrial production. Furthermore, another important limitation of production process by co-molding and coexstrusion is that the sizes of the single layers at moment of the production have to be complementary and then it is not possible to increase the elastic force of the external layer, that one not filled, to compensate the elastic memory loss of the internal layer, that one filled.

-DISCLOSURE OF INVENTION AND BRD2F DESCRIPTION OF DRAWINGS In order to better describe the invention it is sufficient to imagine of taking to pieces the item of fig.l into the different layers, so obtaining a series of single tubes made out of elastic rubbery compound formulated in various way.

In case of the co-moulding and/or coextrusion process, the single layers, after hipotetic separation, would show the following characteristic lengths LI, Lin, L2, LS and with complementary diameters, that is the external diameter of the internal tube will be equal to the internal diameter of the first intermediate tube and so on, up to get the external diameter of the last intermediate tube equal to the internal diameter of the external tube, that is: Del= DiIn, DeIn= Di2 The rigid tubular support has its own length LS and its own diameter DiS and DeS In fig. 2 a typical application is shown only as a example to better describe the invention, hence it doesn't constitute a limitation for the developments which may result from the various applications which maybe realized time by time; developments and/or additions which are understood to be included in the claims of the present invention.

Based on the production process described in the present patent application, each rubbery tubular layer forming the item is produced separately by the processing technique more suitable to give it those properties mechanical and/or electrical and/or superficial or others which are desired (see fig. 3, fig. 4, fig. 5 and fig. 6) .

The lengths of each component will be those ones more or less corresponding to the application to be made, while the diameters and walls thickness will be fixed with particular care to prevent the fore-said phoenomena of elastic memory loss, to simplify the preassembling in the factory and to reduce the size range to be stocked.

If, by example, the internal tube (fig. 3) has to be made out of a particular filled compound, which reduces the elastic memory of the same, the primary diameter of the tube, will be not far away from the diameter of the support on which it has to be positioned, in order to reduce the risk of damage during the expansion phase. This choice involves that this layer alone will be not suitable for the various application diameters to which is destined.

The various intermediate layers (fig. 4) will be realized based on the same principle, giving to each one, time by time, the characteristic considered more important.

The external layer (fig. 5) will be realized having as target to insure the suitable memory and elastic force to the whole item, besides to other features capable to tighten, by the due force, the internal layers on the final application diameter.

Only as example and not as a limitation, if the plastic rigid support (fig. 6) has the outside diameter DeS, the first (internal) rubber tube (fig. 3) may be produced with a diameter Dil not for away from DeS; the intermediate rubber tubes (fig. 4) may have primary diameters conforming to the desired characteristics for the application; the last (external) rubber tube (fig. 5) may have primary internal diameter Di2<DeS or Di2«DeS, namely even smaller than the diameter of the rigid support. In this example the elastic force and memory may be assigned only to the external tubes (fig. 5) , which generally may be produced by rubbery compound having excellent elastic characteristics and excellent compression set (elastic memory). In order to get the final preassembled item, the different rubber tubes, forming the various layers, will be expanded and positioned on the support one on the previous one, beginning from the "internal tube", as shown in fig. 2.

Claims

-CLAIMS

1- Industrial production method with multiple technical walls or layers for cold shrink joints and terminations, without using co-moulding or coextrusion process and with excellent elastic force and memory.

2- Industrial production method, as in claim 1, characterized in that for producing the single layers/tubes separately.

3- Industrial production method, as in claim 1, characterized in that for producing the single layers/tubes by the most suitable technical process for each one of them.

4- Industrial production method, as in claim 1, characterized in that for producing the single layers/tubes by the most suitable raw material for each one of them.

5- Industrial production method, as in claim 1 characterized in that for producing the single layers/tubes by the most suitable dimensions/diameter sizes for each one of them.

6- Industrial production method, as in claim 1, characterized in that for preassembling the single layers/tubes on the rigid tubular support positioning on it the various layers/tubes one on the previous one, beginning from the internal tube.

7- Industrial production method, as in claim 1, characterized in that for preassembling the single layers/tubes positioning each one on rigid tubular support and hence utilizing only those layers/tubes required by the particular application.

8- Industrial production method, as in claim 1, characterized in that for not requiring particular machines/tools for moulding or extruding contemporary two or more different rubber compounds.

9- Industrial production method, as in claim 1, characterized in that for not limiting the variety of the production diameters of the single layers/tubes, but allowing the realization of the external layers/tubes with primary diameters smaller than those ones of the internal layers/tubes and/or viceversa.

10- Industrial production method, as in claim 1, characterized in that for getting the final preassembled item or the final product formed by an undetermined number of layers/tubes, each one with its own characteristics and dimensions.

11- Industrial production method, as in claim 1, characterized in that for reducing the diameter's range of the internal and/or external layers/tubes, transferring the cold-shrink capability, and hence the adaptability to various application diameters, to the layers/tubes more external/internal. - Industrial production method, as in claim 1, characterized in that for producing the single layers/tubes in different time and place - Industrial production method, as in claim 1, characterized in that for assembling the single layers/tubes also directly on the final application (joints/terminations) positioning consecutively the needed layers/tubes. - Industrial production method as in all the previous claims, in the description paper and attached drawings.