WO2001051268A1

WO2001051268A1 - Method for placing an elastomer envelope around an elongated body

Info

Publication number: WO2001051268A1
Application number: PCT/FR2001/000052
Authority: WO
Inventors: Yves Garmy; Ghislain Fournier
Original assignee: Gouillardon Gaudry Sa
Priority date: 2000-01-11
Filing date: 2001-01-09
Publication date: 2001-07-19
Also published as: BR0107481A; AU2001231858A1; CN1416385A; CN1238173C; FR2803558B1; FR2803558A1; TNSN01004A1

Abstract

The compression moulding method consists in the following: two blanks are produced, whereby the shape thereof corresponds to the distribution of the material used for the envelope around the body; one of said blanks is positioned in the impression (14) of a lower moulding unit (11), said impression corresponding to the shape which is to be conferred upon the envelope; a plate or intermediate grid (19) defining the volume of the outer shaped of the body or part thereof on two main surfaces is positioned above the lower moulding unit which is provided with a blank; the second blank is placed on the upper surface of the grid in the voluminous area or the projection; the mould is closed, the upper unit thereof being also provided with an impression (16), during a sufficient length of time in order to produce two half shells which make up the final outer envelope for said body; the mould is opened and the plate or intermediate grid is removed; the body is placed at lower impression level, said lower impression being provided with the lower half shell, acting as a centering member for the body; the mould is closed for a sufficient period of time to allow cross-linking or vulcanization of the envelope and, consequently, at the junction of the half shells produced during the previous closing of the mould in order to create a continuous envelope: the mould is opened at the end of the cross-linking or vulcanization process, whereupon the body is removed and provided either fully or in part with the outer envelope (5).

Description

PROCESS FOR THE PLACEMENT OF AN ELASTOMERIC ENVELOPE AROUND AN ELONGATED BODY

The invention relates to a method for producing and placing an elastomeric envelope around a solid or hollow body, of elongated shape, with symmetry of revolution or not, using the technology known as by compression molding. .

It relates more specifically to the placement of such an envelope around a composite insulator.

Such an insulator is intended to be installed in particular at the level of the pylons supporting the power lines. Depending on the voltage of the current carried by these lines, these insulators have different dimensional, mechanical and insulating characteristics, which is easy to imagine.

These insulators fulfill a double function, that is to say both an electrical insulator function, between the actual power line and the pylon, and on the other hand, a mechanical support function, intended to support the weight of the power line, independently of the phenomena of dangling, or even of additional masses inherent in snow, frost, ice, etc.

Among the insulators available today, there are composite insulators typically comprising three components, namely two fittings located at the two

25 ends of said insulators, and acting as mechanical attachment, respectively to the cable and to the pylon, a connection between these two fittings, constituted by a core, made of an insulating material, in particular of thermosetting material reinforced with fibers, and preferably of glass fibers embedded in an epoxy resin or polyester, and finally a rubber coating or outer shell, having large

30 dielectric characteristics, as well as very good resistance to aging, ozone and ultraviolet.

This envelope is in particular made of EPDM rubber (ethylene-propylene-diene terpolymer), silicone rubber, or even an ethylene-propylene copolymer (EPR), and generally any vulcanizable or crosslinkable elastomer.

Traditionally, this outer envelope has radial annular fins, thus intended to define lines of leakage capable of preventing any formation of an electric arc between the two fittings. Furthermore, this outer casing is made in such a way that it adheres to the rod or core, as well as to the respective bases of the two fittings.

Different methods have been proposed for producing such insulators, and in particular for carrying out the installation of the external envelope.

Among these is injection. To do this, the bare insulator, that is to say made up of the only fittings connected together by the central rod of revolution, is placed in a mold and we proceed, in a completely traditional way, to the injection of the required rubbery material, constituting the envelope.

If on the technical level, this method of production is satisfactory, on the other hand it results in a prohibitive increase in the price of insulators, taking into account the machines to be used and the production of molds. Indeed, such a method requires the use of an expensive automatic centering or a ring for centering the rod or the core inside the mold, said ring being made of thermoplastic material, locally weakening said core.

It was then proposed to implement these external envelopes by compression. For example, a device has been described in document FR-N-2 732 155, aimed at producing the external envelope by compression. This device comprises a pair of molding units, respectively upper and lower, each defining a cavity for the formation of the envelope of the composite insulator. One of the molding units, in particular the upper unit, is provided with separation pads, located near the cavity, and intended to come to bear on the upper face of the second molding unit. The implementation of such a plate or pad is intended to minimize the outflow of the material of the envelope from the mold, during compression molding, so as to thereby reduce the formation of burrs inherent in this process of molding and in addition, to allow filling in a uniform and sufficient manner the cavity produced within the molds, and in particular fins of relatively large diameter.

However, we observe with this type of device significant stresses exerted on the insert, insofar as the latter must ensure the creep of the rubber. Furthermore, given the shape of the cavity, relatively high intensity stresses can develop locally. Finally, because of the technique used for the preparation of the blanks, this device cannot be envisaged mainly for the only parts with symmetry of revolution. EP-N-0 624 446 has also proposed a method for producing the external envelope of a composite insulator by compression molding, which consists of:

• first of all, to first form a rubber layer around the core; • then to position the core provided with this rubber layer between the two parts of the mold;

• forming a compression molding by compression of said rubber layer into a predetermined shape inside a cavity defined by said mold parts; • to polymerize the compressed molding to form said envelope.

According to this document, said rubber layer is produced by extrusion molding, and furthermore, said parts of the mold are equipped with a positioning element of the core in order to achieve the desired position of the latter within the cavity, and therefore to ensure correct centering of the core with respect to the envelope to be produced. This device proves to be used at a relatively high cost, mainly due to the complexity of the tooling, and the step of producing the blank directly at the core. In addition, the corresponding process is difficult to automate.

The object of the invention is to provide a method for producing and installing the external envelope made of elastomer at the level of a body, of elongated shape, and in particular of a composite insulator, combining all reliability, efficiency, and reduction of implementation costs.

This process for producing and installing an outer elastomer envelope at the periphery of a body of elongated shape by compression molding consists of:

• first of all to produce for the body or part of said body, two blanks from the material of which the envelope is desired, and typically made of EPDM rubber, the shape of which corresponds to the distribution of material of the envelope around the body or part thereof;

• positioning one of said blanks within the female imprint of a lower molding unit, said imprint corresponding to the shape to be given to the envelope; • to position above said lower unit of the mold thus provided with the blank, an intermediate plate or grid, defining in volume the external shape of the body or part thereof, at its two main faces, respectively upper and lower; • to position on the upper face of the grid at the volume level or protrudes the second of said blanks;

• closing the mold, said upper unit thereof also being provided with a female imprint, and this for a sufficient time to induce the plasticization of the blanks, the distribution of material which constitutes them, their shaping at the level of said impressions, so as to produce two half-shells or preforms, intended to ultimately constitute the external envelope of the body or part thereof;

• open the mold and remove the plate or intermediate grid;

• to position the body or part of it at the lower cavity of the lower unit of the mold, said lower cavity being provided with the half-shell or lower preform, then acting as a body centering member ;

To close the mold, for the time necessary for the crosslinking or vulcanization of the material constituting the envelope and as a corollary, at the junction of the two half-shells or preforms produced during the previous closing of the mold, in order to lead to a envelope continues.

In other words, the invention basically consists in providing within a compression molding unit, the implementation of an intermediate plate or grid, the projecting volume of which corresponds substantially to the volume that the body would occupy. or the part of said body to be coated with said external envelope, so as to limit and standardize the stresses generated by the compression of the constituent material of the envelope during the shaping of the blanks at the level of said body or said part of it. It also makes it possible to avoid a step of extruding the blanks directly onto the body or part of it, as for example described in the aforementioned prior art. Finally, it overcomes the implementation of any centering member or equivalent device, insofar as the centering is ensured, in the process according to the invention, directly by the lower preform.

Advantageously, a degassing phase is provided when the mold is closed for the first time. Likewise, a second degassing phase takes place during the second closing of the mold. These degassing phases aim, in a known manner, to ensure the elimination of air bubbles, in particular for the production of envelopes of relatively complex structure or shape. These degassing phases can also comprise several degassing operations proper.

According to another advantageous characteristic of the invention, the mold cavities as well as the intermediate plate or grid receive a non-stick agent or undergo a non-stick treatment. This agent is typically constituted by PTFE (polytetrafluoroethylene). Furthermore and advantageously, when the material used is made of EPDM rubber, the duration of the first mold closing phase is between 20 and 40 seconds, while the duration of the second mold closing phase, aimed at achieving the crosslinking or, in this case, the vulcanization of the rubbers, is between 6 and 10 minutes, these values being indicated for a mold temperature close to 170 ° C.

The invention, as already specified, more specifically relates to the production and installation by compression molding of an external envelope made of elastomer around an insulator. This method consists: • first of all, for each insert, that is to say for each insulator provided only with hooking fittings and the core connecting them, two blanks from the material of which the envelope is to be made, and typically made of EPDM rubber, the shape of which corresponds to the distribution of material of the envelope around said insert;

• positioning one of said blanks within the female imprint of a lower molding unit, said imprint corresponding to the shape to be given to the envelope;

• to position above said lower unit of the mold thus provided with the blank, an intermediate plate or grid, defining in volume the external shape of the body or part thereof, at its two main faces, respectively upper and lower;

• to position on the upper face of the grid at the volume level or protrudes the second of said blanks;

• closing the mold, said upper unit thereof also being provided with a female imprint, and this for a sufficient time to induce the plasticization of the blanks, the distribution of material which constitutes them, their shaping at the level of said cavities, so as to produce two half-shells or preforms, intended to ultimately constitute the outer envelope of the insulator;

• open the mold and remove the plate or intermediate grid;

• positioning the insert at the lower imprint of the lower unit of the mold, said lower imprint being provided with the half-shell or lower preform, then acting as a centering member for the insert;

To close the mold, for the time necessary for the crosslinking or vulcanization of the material constituting the envelope and as a corollary, at the junction of the two half-shells or preforms produced during the previous closing of the mold, in order to lead to a envelope continues. The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the example of embodiment which follows, given by way of non-limiting example, in support of the appended figures.

Figure 1 is a schematic representation in longitudinal section of an insulator obtained according to the method according to the invention.

Figure 2 is a schematic representation of the mold implementing the method according to the invention in the open position, of which Figure 3 is a representation in the closed position. Figure 4 is a schematic representation seen from above of the lower or upper unit of the mold.

Figure 5 is a schematic top view of the plate or intermediate grid, Figure 6 is a cross-sectional view.

Figure 7 is a schematic representation of a blank for the production of the envelope according to the invention.

The following description is more particularly directed towards the production and installation of an external envelope around an insulator. It should however be emphasized that this description cannot in this limit the effective scope of the invention, the latter applying to the production and installation of such an envelope around any type of body , elongated, hollow or solid, of symmetry of revolution or not, and in particular to the tubes.

The composite insulator (1), whose method according to the invention is intended to produce an external envelope, has been shown diagrammatically in FIG. 1, in longitudinal section.

It basically consists of two metal fittings (3) and (4), typically made of aluminum, steel or galvanized cast iron, and each pierced with through holes to allow attachment to a pylon and an electrical cable respectively.

These two fittings (3) and (4) are interconnected by a rod or core (2), produced as already said in insulating material, and in particular in plastic material reinforced with glass fibers. This rod (2) is received at the base, respectively (7) and (9) of the fittings (3) and 4), and fixed at this level by constriction (8, 10).

Finally, the insulator receives an outer casing (5), also dielectric, typically made of EPDM rubber, and adhering respectively to the rod and at the bases (7) and (9) of the fittings (3) and (4). This external envelope (5) has fins (6), the function of which for optimizing the electrical insulation has already been mentioned previously.

According to the invention, the production and the establishment of the external envelope (5) at the level of the insulator is carried out by compression molding.

There is shown very schematically in Figures 2 and 3 the installation of compression molding as proposed by the invention. This basically comprises a mold consisting of two molding units, respectively lower (11) and upper (12), capable of being driven in an upward or downward movement, guided by guide columns (18).

In the example described, the lower molding unit (11) is capable of being driven in an upward or downward movement, by means of a press, the piston of which has been shown diagrammatically by the reference (13).

Of course, this mold is brought to the appropriate temperature, the latter being adjustable according to the materials used, on the one hand, to result, as will be described later, in the plasticization of the material constituting the envelope. , but also to its crosslinking or vulcanization, and on the other hand, in order to take account of the maximum temperatures likely to be accepted by the material constituting the rod or core (2) of the insulator.

Each of the molding units, lower (11) and upper (12) is provided with a cavity or imprint (14), respectively (16), as it appears in more detail in FIG. 4. This imprint , of generally semi-cylindrical shape, also presents the form which the external envelope (5) will have to adopt. One can in particular observe the recesses intended to allow the realization of the fins (6).

According to a fundamental characteristic of the invention, the installation further comprises an intermediate plate or grid (19), intended to be positioned between the lower unit and the upper molding unit (11) and (12), and more specifically come to bear against the upper face (15) of the lower molding unit (11), and against the lower face (17) of the upper molding unit (12). It is also pierced with through holes (20), intended to cooperate with the guide columns (18). This plate (19) projecting, respectively at its upper and lower face, a volume substantially less than the volume of the bare insert, that is to say of the insulator free from the external envelope (5).

In fact, this projection comprises at each of the faces, respectively upper and lower of the plate (9), a first half-cylinder (21), corresponding substantially to the volume of a longitudinal half of the rod or core (2) of the insulator, and a second half-cylinder (22), corresponding to the external surface of the bases (7) and (9) of the respective fittings (3) and (4).

The plate (19) has also been shown in cross section, thus making it possible to appreciate these different volumes.

As already said, this plate is intended to be positioned between the lower (11) and upper (12) units, and, when the mold is closed, said plate is in contact with the two units, as can be observe in figure 3.

The mode of operation of this installation will now be described in more detail, in accordance with the invention.

The mold being in the open position, a first blank, of the type shown in FIG. 7, made from the material of the envelope, is positioned at the level of the cavity (14) of the lower unit. Typically, this material is made of EPDM rubber.

This blank is in the form of a dumbbell, taking care to distribute the amount of material according to the volumes that are needed at each of the places of the insulator.

Of course, and in a known manner, the quantity of material present at the level of the blanks is greater than the volume which is actually needed for the total production of the envelope.

Once this blank is in place, the grid (19) is positioned which is advantageously received for this purpose at the level of guide rails. A second blank of identical shape to the first is placed on the grid, and in particular on the volumes (21) and (22), then the mold is closed, so that the said second blank will position itself at the level of the impression (16) of the second molding unit (12).

After closing the mold, for example by actuation of the piston (13), a first degassing is carried out and heating is carried out for approximately 30 seconds, the time necessary to soften the material constituting the blanks and to make it penetrate, in particular at the level of the female imprints (14) and (16), so as to give already, the shape in particular of the fins (6) that has the final envelope.

Two half-shells or preforms are thus obtained, the assembly of which in the next step will result in the production of the complete envelope (5).

In addition, the lower preform will act as a centering member or cradle, thus capable of receiving the insert according to an adequate positioning.

The grid is then removed and the insert is positioned, that is to say the bare insulator, consisting of the only reinforcements and of the rod which joins them, in said lower preform, itself received at the lower footprint of the molding unit (11).

The mold is then closed again. A first degassing phase is carried out allowing the air to be evacuated by the expansion of the rubber, then the mold being already brought to the desired temperature, typically 170 ° C. taking into account the choice of the material constituting the envelope (EPDM). , it is kept closed for a period varying between 6 and 10 minutes, in order to result in the crosslinking or vulcanization of said material, and on the other hand, in the welding and the junction at the two lateral edges of the two half-shells made during the previous step of closing the mold, in order to result in a continuous envelope (5).

In certain applications, it is desirable for the envelope to adhere to the rod (2) and to the bases (7) and (9) of the fittings (3) and (4). In this configuration, the insert receives, prior to its installation, a layer of suitable bonding agent.

The method according to the invention makes it possible to effectively protect the core or rod (2), taking into account the uniform nature of the pressure distribution of the material constituting the envelope. Indeed, as the two half-shells constituting the envelope are produced during a prior step, in which the insert has been replaced by the grid provided with a protruding volume, the core itself of the insert does not not undergo the pressure of the material, both during the step of shaping said half-shells, and during the crosslinking or vulcanization step. It therefore becomes possible with the method according to the invention, to produce large insulators, typically reaching 5 6 meters, which are used for very high voltages (220,000 to 400,000 volts), which the we did not know how to economically to date.

It should also be emphasized that the process can be automated, insofar as it is possible first of all to work in masked time, in particular when making the blanks, and on the other hand, to proceed when the grid is removed and as the mold enters its second heating cycle, when the blanks are placed on the grid for the production of the following envelopes. Simultaneously, it is possible to deburr the insulators then obtained during the previous cycle during this heating step.

It is therefore easy to understand the advantage of such a process, which makes it possible, in addition to producing an envelope for large insulators, to also significantly reduce the costs of installing this envelope.

Furthermore, the method according to the invention makes it possible to produce overmoldings of various shapes, and in particular complex, on relatively fragile inserts, in particular hollow or solid tubes.

Finally, by implementing this process, the insert is self-centering during the actual overmolding step, thus making it possible to dispense with any centering member, of which the difficulty of implementation, in addition to the cost of finished products.

Claims

1. Method for producing and installing an outer envelope (5) of elastomer at the periphery of an elongated body by compression molding, characterized in that it consists:

First of all to produce for the body or part of said elongated body, two blanks (23) from the material of which the envelope is to be produced, the shape of which corresponds to the distribution of material of the envelope around the body or part of it; • positioning one of said blanks within the female imprint (14) of a lower molding unit (11), said imprint corresponding to the shape to be given to the envelope;

• to position above said lower unit of the mold thus provided with the blank, an intermediate plate or grid (19), defining in volume the external shape of the body or part thereof, at its two main faces , respectively upper and lower;

• to position the second of said blanks (23) on the upper face of the grid at the level of the volume or protrusion;

• to close the mold, said upper unit thereof also being provided with a female imprint (16), and this for a sufficient time to induce the plasticization of the blanks, the distribution of material which constitutes them, their shaping at the level of said imprints, so as to produce two half-shells or preforms, intended to ultimately constitute the external envelope of the body or part thereof; • open the mold and remove the plate or intermediate grid;

• to position the elongated body or part of it at the lower cavity of the lower unit of the mold, said lower cavity being provided with the lower half-shell or preform, then acting as a centering member for the body ; To close the mold, for the time necessary for the crosslinking or vulcanization of the material constituting the envelope and as a corollary, at the junction of the two half-shells or preforms produced during the previous closing of the mold, in order to lead to a continuous envelope;

• to open the mold at the end of crosslinking or vulcanization, then to remove the elongated body then fully or partially provided with the external envelope (5).

2. Method according to claim 1, characterized in that the external envelope (5) is made of a material chosen from the group comprising vulcanizable or crosslinkable rubbers, and in particular EPDM rubber, silicone rubber, ethylene-propylene copolymers .

3. Method according to one of claims 1 and 2, characterized in that a degassing phase is implemented prior to the first closing of the mold.

4. Method according to one of claims 1 to 3, characterized in that a second degassing phase is implemented during the second closing of the mold.

5. Method according to one of claims 1 to 4, characterized in that the intermediate plate or grid undergoes, prior to its installation in the mold, a non-stick treatment, and in particular receives a PTFE coating.

6. Method according to one of claims 1 to 5, characterized in that the body coated with the outer casing (5) is a hollow or full tube.

7. Method for producing and installing the outer insulating envelope (5) at a composite insulator (1) by compression molding, said insulator comprising an insulating ring or core (2), made in a composite material, and connecting two attachment fittings (3, 4), and an outer envelope (5) also insulating, characterized in that it consists:

• first of all to be produced for each insert, that is to say for each insulator provided with only the hooking fittings (3, 4) and the core (2) connecting them, two blanks (23) from the material of which it is desired to produce the envelope, the shape of which corresponds to the distribution of material of the envelope around the insert;

• positioning one of said blanks (23) within the female imprint (14) of a lower molding unit (11) of a compression molding installation, said imprint corresponding to the shape to be given to the 'envelope (5);

• to be positioned above said lower unit (11) thus provided with the blank, an intermediate plate or grid (19), defining in volume (21, 22) the external shape of the insert at its two main faces , respectively upper and lower;

• to be positioned on the upper face of the plate or intermediate grid (19) at the volume or projection (21, 22) the second of said blanks; • closing the mold, said upper unit (12) thereof also being provided with a female imprint (17), and this for a sufficient time to induce the plasticization of the blanks, the distribution of material which constitutes them, their shaping at the level of said imprints, so as to produce two half-shells, intended to ultimately constitute the outer envelope of the insulator;

• open the mold and remove the intermediate plate or grid (19);

• positioning said insert at the level of the lower cavity of the lower unit of the mold, provided with the half-shell or lower preform then serving as a member for centering the insert; To close the mold for the time necessary for crosslinking or vulcanization of the material constituting the envelope and as a corollary, at the junction of the two half-shells produced during the previous closing of the mold, in order to result in an envelope keep on going ;

• to open the mold at the end of polymerization, then to remove the insulator then provided with the external envelope (5).

8. Method according to claim 7, characterized in that the external envelope (5) is made of a material chosen from the group comprising EPDM rubber, silicone rubber, ethylene-propylene copolymers.

9. Method according to one of claims 7 and 8, characterized in that one or more degassing phases occur during the various closings of the mold.

10. Method according to one of claims 7 to 9, characterized in that the intermediate plate or grid (19) undergoes, prior to its installation in the mold, a non-stick treatment, and in particular receives a coating of PTFE .