FR2818577A1 - Three-dimensional objects such as plastic pipe sections for thermal welding has aluminum foil covering assembly regions of cross-linkable (co)polymers - Google Patents

Abstract

Three-dimensional objects for assembly by thermal welding and having at least one layer of a cross-linkable (co)polymer and assembly regions protected by metal foil have their assembly regions in two zones: the welding zones themselves and adjacent security zones which prevent or retard the cross-linking of polymers in the welding zones. Independent claims are also included for the following: (1) Method of protection of the three dimensional objects; (2) Installation for the protection of the three dimensional objects; (3) Method thermal welding; and (4) Use of the three dimensional objects.

Description

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 The present invention relates to three-dimensional objects and in particular protected tubes comprising crosslinkable polymers, as well as a protection process and installation making it possible to obtain them.

It also relates to a method and a thermal welding device for operating said objects. Finally, the invention also relates to the use of these objects, for example welded tubes, and the resulting long pipes for applications such as the distribution of gas, drinking water, etc.

 For applications of this type, the use of tubes made of thermoplastic resins, especially of high density polyethylene (HDPE), has become widespread because of their excellent characteristics, such as their flexibility, their elasticity and above all their aptitude for thermal welding. end to end.

 Other less favorable aspects of these tubes, such as a tendency to creep under pressure at long term and at high temperature and a certain mechanical sensitivity to abrasion and to notches, however, have enabled tubes made of crosslinked resins, for example in crosslinked polyethylene (PEX) to prevail in certain areas. In fact, these resins, which are in particular polyolefin resins onto which crosslinkable groups have been grafted, have in the crosslinked state better thermal stability and improved mechanical resistance resulting, among other things, in a considerable increase in the cracking resistance under stress and crack propagation.

 The resins used in practice comprise, for example, silane groups crosslinkable by moisture (obtained for example by the SIOPLASO or MONOSILTM processes), resulting in their gradual crosslinking. The storage of such objects, for example tubes, before welding is therefore greatly limited, not exceeding a few days or even less still under current storage conditions. Indeed, the problem with these resins is that once cured, they are not thermoplastic and can be welded end to end as thermoplastic resins. In reality, if you weld tubes even partially

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 cross-linked, the quality of the weld is poor and not very reproducible, both from the point of view of the shape (irregular bulges and too bulky), as from the point of view of the mechanical strength.

 A practical possibility for assembling tubes of this type is to use mechanical fittings, but these are expensive and less reliable since they will be subject to possible corrosion or at high temperatures (for example geothermal, collective heating , etc.). Indeed, the coefficients of thermal expansion of metals and plastics are very different generating very significant local stresses amplified by the tightening of the fittings.

 FR 2,606,487 proposes the use of welding sleeves electrofusion. However, this is not only expensive and reserved for small diameter applications, but above all requires the use of special tubes provided with an outer thermoplastic layer or fittings made of a weldable thermoplastic resin.

 Recently, the document WO 0034028 revealed the butt welding of crosslinked polyethylene (PEX) tubes by heating at very high temperature (420 to 450 ° C.) so as to break the crosslinks and using a specific heating element. A first disadvantage is the difference in properties between the weld and the rest of the tube due to the fact that the rupture of the crosslinks is, at least to a large extent, irreversible. The quality of the welds reaches the characteristics of non-crosslinked HDPE, for example in terms of pressure resistance, but without however approaching the level of PEX. As other disadvantages, one could also cite the relatively large size of the fittings limiting the useful diameter and the specificity of the equipment required due to the special heating element and the high welding temperatures.

 The objective of the present invention is therefore to provide three-dimensional objects comprising a crosslinkable polymer which can be stored under ambient conditions for sufficiently long periods while retaining, at least in certain areas, all the properties necessary for their implementation. work by thermoplastic welding.

 A first aspect of the invention therefore proposes three-dimensional objects which can be assembled by thermal welding, comprising at least one layer of crosslinkable (co) polymer (s), provided with protective means comprising a metal sheet covering regions of assembly of said objects, these assembly regions comprising the zones to

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 weld themselves and adjacent security zones, so as to prevent or delay the crosslinking of or (co) polymer (s) cross-linkable (s) in areas to be welded.

 The indisputable advantage of the objects according to the invention is that they do not crosslink or are sufficiently weak in the protected regions and especially in the zones to be welded and that they thus retain all the qualities necessary to allow thermal welding, and this long after their protection.

Even by storing these objects protected under ambient conditions of temperature and humidity without any further precaution, their weldability is generally at least a few months or years.

 The three-dimensional objects provided with protection means (or protected) can be objects of any shape to be assembled by welding. Preferably, however, these are tubes to be assembled end to end by direct welding or by heat-sealable sleeves, which can themselves be objects according to the invention. By tubes and sleeves is meant, in the sense of the present invention, also short sections of variable shape, for example bent or comprising several branches, in T, X or Y, to produce networks comprising all kinds of connections or derivations.

 The crosslinkable (co) polymers which can be used in the context of the present invention are in particular polymers of olefins and copolymers of olefins with other monomers, (co) polymers which have been modified if necessary, for example by grafting or by copolymerization with suitable monomers, so that they can be crosslinked either by a treatment using specific chemical compounds, or, preferably, by crosslinking with liquid water or in gaseous form (for example air humidity ambient).

 Cross-linkable (co) polymers of the latter type (moisture-curable polymers) are known and widely used. They are, for example, (co) polymers of olefins, such as homopolymers of ethylene, of propylene, copolymers of ethylene and of propylene or copolymers of ethylene and / or of propylene with other monomers , such as (meth) acrylic monomers, vinyl monomers, halogenated monomers, etc., these (co) polymers being functionalized by hydrolysable groups either intrinsically by copolymerization with appropriate monomers, or by subsequent grafting. These hydrolyzable groups are preferably silane groups, such as vinyltrialkoxysilane groups.

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 In practice, objects made of crosslinkable (co) polymers will crosslink progressively during storage before welding by diffusion of moisture from the surface, with the exception of places provided with protective means, corresponding to the regions of assembly covering a larger area than the areas to be welded themselves by which the objects are fixed. In fact, the objects can even be completely crosslinked outside these regions, either deliberately by a crosslinking step, for example after the manufacture of the objects, or by spontaneous crosslinking during storage in the case of (co) polymers with hydrolysable groups.

 In reality, the maximum duration of storage is fixed by the maximum permissible crosslinking rate in the zones to be welded at the time of welding.

The crosslinking rate can be determined by ISO 10147 method and it should not be too high to ensure optimal welding. In practice, this maximum crosslinking rate of the crosslinkable polymer (s) must therefore generally remain less than 40% in the zones to be welded. Depending on the nature of the (co) polymers and the qualities required for the welded product, this maximum crosslinking rate can be or will preferably be lower, for example less than 35%, preferably less than 30% and particularly preferred less than 25%.

 The nature of the protection means is dictated by their capacity as a barrier to crosslinking agents, for example humidity in the case of polymers with hydrolysable groups. Research carried out within the framework of the present invention has shown that the application of a polymeric protective layer in liquid form in a solvent or in molten form, in particular by immersion, by coating or by sprinkling of the assembly regions, does not is not a sufficiently effective barrier to be used in practice. The protection means proposed by the present invention are therefore metal sheets which have excellent barrier qualities, even at very small thickness. In practice, we will preferably use aluminum sheets.

 These sheets can be applied for example by heat welding or gluing on the assembly regions. There are commercially available many products very suitable for this purpose.

 A variant of the invention provides for the thermal bonding of a web or sheet of aluminum pre-coated with polyethylene. These sheets exist under two

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 forms: peelable or not. The first option is generally preferred because it can remove more easily protection before the assembly of objects.

 You can also use an adhesive to apply the protective means. Different glues can be chosen, such as those used to assemble rigid PVC parts or even epoxy type glues.

The disadvantage of this variant lies in the fact that the bonding is not immediate (the glue must dry) and often requires the use of solvents, possibly flammable. For this reason, another favored variant of the present invention is a metal sheet pre-coated with a self-adhesive adhesive to be applied by simple bonding. Protection is easy to apply, immediate and inexpensive.

 The means of protection dimensions depend on the one hand of course the dimensions of the areas to be welded. However, the diffusion of the crosslinking agents taking place in all directions, therefore also from the inside from the unprotected regions, the invention provides for the protection of a greater surface area than the area to be welded proper, this enlarged area being designated assembly region. It comprises in addition to the zone to be welded a safety zone covering the adjacent parts not participating in the welding, but acting as a buffer zone.

 In the case of a tube, for example, protection is applied to the inner and outer faces of the ends of the tube, the safety zones exceeding the limits of the zones to be welded proper by at least 1 cm, preferably over approximately 1 to 10 cm.

 For heat-sealable sleeves, it is imperative to protect at least the inner face on which the welding is carried out. Given the generally reduced dimensions of these sleeves, it is possible to do without an external protection, if the sleeve is kept away from crosslinking agents, for example packaged in sealed bags or sachets, respectively provided with a diffusion barrier, in this case an aluminum layer.

 The size, and to a much lesser extent the thickness, of the protections will therefore be adapted to take into account factors as diverse as the nature and characteristics of the protection and of the objects, the expected time and conditions of storage, the rate of maximum crosslinking allowed, etc.

 The wall of these tubes or sleeves can comprise a single layer comprising at least one of the crosslinkable (co) polymers described above. he

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 these are, for example, crosslinkable polyethylene tubes of the PEX type with vinyltrialkoxysilane groups, for the manufacture of pipes for applications such as the distribution of fluids, such as drinking water, gas, or for geothermal and collective heating, or for industrial technical applications for the transport of hot, very cold (-30 C) and / or corrosive fluids.

 The invention also applies to objects or tubes comprising several layers, at least one layer of which comprises at least one of the above crosslinkable (co) polymers and at least one other layer of which comprises at least one thermoplastic (co) polymer . By thermoplastic (co) polymer means any homopolymer or copolymer which is known thermoplastic and is preferably compatible with at least one of (co) polymers crosslinkable. They are, for example, (co) polymers of olefins, such as homopolymers of ethylene, of propylene, copolymers of ethylene and of propylene or copolymers of ethylene and / or of propylene with other monomers , such as (meth) acrylic monomers, vinyl monomers, halogenated monomers, etc.

 In a particular embodiment, when the layer (co) polymer crosslinkable comprise PEX, the at least one thermoplastic (co) polymer is high density polyethylene. Such coextruded tubes ("robust pipes") made of HDPE and one or two outer layers of which are made of PEX-b (crosslinkable polyethylene with silane groups) are used in applications such as gas distribution or drinking water. In general, it will be preferable to crosslink the PEX-b part, with the exception of the protected regions, before the assembly of the network, for various reasons. In the case of gas transport, there will be no water in or near the tube to ensure crosslinking, while in the case of potable water transport, we will want to achieve complete crosslinking in order to be able to at the same time extracting the various reaction products (grafting, crosslinking) which would make the water unfit for consumption. In these two cases, butt welding will give results that are probably acceptable from the point of view of mechanical strength, but we will observe beads similar to those that can be seen in the case of a partially crosslinked PEX-b tube. These beads will have the same disadvantages as those mentioned above, in addition to constituting an area favoring deposits.

 Another aspect of the present invention is a method that allows for the protection of three-dimensional objects to be welded

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 thermal, comprising at least one layer of crosslinkable (co) polymer (s), characterized in that the protection consists in applying protective means comprising a metal foil to regions of assembly of said objects, these regions of assembly comprising the zones to be welded proper and adjacent security zones, so as to prevent or delay the crosslinking of the crosslinkable (co) polymer (s) in the zones to be welded. As indicated, the objective will be to maintain a crosslinking rate of less than 40%, advantageously less than 35%, preferably less than 30% and particularly preferably less than 25%, of the at least one crosslinkable (co) polymer in the areas to be welded.

 An additional objective of the present invention is an installation making it possible to carry out the method for protecting three-dimensional objects described above, preferably by integrating it into the installation or unit for producing these objects or by using it directly downstream. of it.

 The advantage of this conformation is not only to minimize crosslinking of the connecting regions before the application of means of protection, but also full or partial automation of production / protection system.

une étape de mise à nu des zones à souder une étape de chauffage des zones à souder et une étape d'assemblage forcé desdits objets. Another important aspect is a method of thermally welding two or more three-dimensional objects comprising at least one crosslinkable (co) polymer, in which three-dimensional objects comprising applied protection means are welded to each other by zones to be welded. on assembly regions, these assembly regions comprising the zones to be welded proper and adjacent safety zones, so as to prevent or delay the crosslinking of the crosslinkable (co) polymer (s) in the areas to be welded, the process comprising

a step of exposing the areas to be welded a step of heating the areas to be welded and a forced step of assembling said objects.

 Such a welding method is economical, rapid and reliable and makes it possible to solve the problems associated with welding objects comprising a crosslinkable material. In fact, by using objects comprising protective means in the zones to be welded and thereby largely preserving the thermoplastic character therein in order to be able to weld them by thermal welding, it is possible to obtain welds of excellent quality. both in terms of size and appearance of the beads, and in terms of mechanical strength. In

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 Furthermore the welding zones retain their ability to cross-linking, so that after full crosslinking objects, features welds are identical to those of the other zones of the welded objects. The actual welding step of the present process can be carried out under completely conventional conditions for thermoplastic materials.

 The step of exposing the areas to be welded can be limited to the outright removal of the protection means, particularly in the case of peelable protections. Elimination can be envisaged by any chemical or physical process or even by a combination of physical and chemical processes, such as pickling, abrasion, peeling, cutting, turning, etc. Depending on the shape of the three-dimensional objects, as in the case of tubes, it may be advantageous to cut, for example by means of a circular saw, before or after the removal of the metal sheet, a ring of a certain width , for example 1 cm, to obtain a fresh wafer, that is to say sufficiently little crosslinked.

 The actual welding, that is to say the heating and assembly step, can be carried out by means of equipment suitable for the welding of thermoplastic materials, in this case a welding apparatus with mirror.

The operating conditions are therefore preferably those used for the welding of thermoplastic materials, for example by heating the assembly regions so as to melt the material therein, at a temperature between 180 and 250 C, preferably between 200 oC and 240 oC and by subsequent assembly of the objects to be welded, preferably by joining the objects by their molten edges at the heating stage by applying an assembly pressure, preferably maintained until the cooling zone is substantially cooled. welding.

 In a particularly preferred embodiment of the present invention, the crosslinking of the welded objects is then substantially completed, preferably at least up to a crosslinking rate of 60%, more preferably up to a crosslinking rate of at least 65%.

 Indeed, in the case of polymers with hydrolysable groups, the objects retain their ability to crosslink in the assembly regions to then crosslink slowly thanks to the humidity of the ambient air. In some cases, it may however prove necessary, desirable or advantageous to complete or accelerate the crosslinking once the welding has been carried out in order to directly confer the final characteristics on the object.

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 These objects can be crosslinked for example by exposing them to water, either in liquid form or vapor form, preferably at a temperature above ambient temperature and especially above 50 OC.

 This step is obviously necessary in the case of crosslinkable (co) polymers requiring specific treatment by means of appropriate chemical compounds and / or radiation or whose crosslinking under ambient conditions is too slow.

 Another objective of the present invention is to provide an installation making it possible to carry out the welding process described above, preferably incorporating all the steps necessary for thermal welding of objects.

 This installation for welding three-dimensional objects which comprise at least one crosslinkable (co) polymer and which comprise protective means applied to assembly regions, these assembly regions comprising the zones to be welded proper and safety zones adjacent, so as to maintain a maximum crosslinking rate of the at least one crosslinkable (co) polymer in the areas to be welded of less than 40%, comprises - devices for exposing the areas to be welded, that is to say elimination of the means of protecting objects in the regions intended to be welded, - thermal welding devices proper integrating means for heating the zones to be welded and means for forced assembly of the objects in said regions, and - optionally , crosslinking completion devices used to increase the crosslinking rate of the objects assembled by thermal welding to a value greater than 60%, preferably greater than 65%.

 The advantage of such a facility is not only incorporate all the necessary steps in order to benefit from the advantages mentioned above, such an installation also allows partial or full automation of the welding process described above. The incorporation of the devices necessary for the crosslinking of welded objects also makes it possible to immediately dispose of objects with all their desired characteristics and aimed at leaving the installation according to the invention.

 Such an installation is particularly suitable for carrying out the direct thermal butt welding of tubes, such as those described above.

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 The other characteristics and preferences of the elements mentioned in the context of the process or of the installation, such as for example the nature of the crosslinkable (and possibly thermoplastic) (co) polymers of which the objects to be welded are made up, have been presented in the paragraphs below. above.

 The invention also contemplates, in another of its aspects, the use of tubes in the sense of the invention for the manufacture of very long pipes or networks of pipes, such as for the realization of pipes used for distribution fluids, such as drinking water, gas, hot water for geothermal or collective heating, etc.

 The invention further relates to very long pipes or networks of pipes obtained by thermal welding, either directly end to end, or by heat-sealable sleeves, of tubes protected in the direction detailed above by a welding process according to the invention and / or by means of a welding installation in accordance with the present invention.

Examples
The test examples below are carried out on polyethylene plates crosslinkable type PEX-b obtained by the method SIOPLASO.

sont chauffés à 170 C. Lorsque la matière est fondue, on prélève le crêpe et on le place dans un moule en forme de parallélépipède d'une épaisseur de 5,5 mm et on presse le tout à l'aide d'une presse à plateaux (COLOMBES 30 1965) afin d'obtenir une plaque de 5,5 mm d'épaisseur. La mesure du taux de gel selon la norme ISO 10147 indiquait que le taux de réticulation atteignait 6, 5 %. These plates were made from a mixture of 135 g, consisting of 95 parts of the grafted compound (ELTEXE TUXIOO) and 5 parts of the master catalyst mixture (ELTEXE CATI00) which is brought to fusion using a mixer. rollers (Schwabenthan POLYMIX 110) whose cylinders

are heated to 170 C. When the material is melted, the pancake is removed and placed in a mold in the shape of a parallelepiped with a thickness of 5.5 mm and the whole is pressed using a press. trays (30 COLOMBES 1965) to obtain a plate of 5.5 mm thick. The measurement of the gel content according to the ISO 10147 standard indicated that the crosslinking rate was 6, 5%.

Example 1 (comparative example)
We take half of this plate and immersed in a water bath at 90 OC for a period of 24 h, to make the crosslink. After this treatment, the measurement of the gel content according to the ISO 10147 standard indicated that the degree of crosslinking was 63%.

Example 2 (according to the invention)
Take the second half of the plate and glue on each side a sheet of aluminum pre-coated with polyethylene (TOTAL PAC Cde 10551/01 Blue, thickness 50 um, width 43 mm) by proceeding as follows: two strips on each side of the plate and placed all surrounded

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de deux feuilles de MYLAR dans la presse à plateau préchauffée à 170 C. On referme la presse et on maintient une pression hydraulique de 30 kg pendant dix secondes, après quoi l'ensemble est retiré. On plonge alors la plaque dans un bain d'eau à 90 oC pendant une durée de 24 h, afin de la faire réticuler. Après ce traitement, la mesure du taux de gel de la partie couverte par l'aluminium selon la norme ISO 10147 indiquait que le taux de réticulation atteignait 11,5 %.

of two sheets of MYLAR in the plate press preheated to 170 C. The press is closed and a hydraulic pressure of 30 kg is maintained for ten seconds, after which the assembly is removed. It then dips the plate in a water bath at 90 ° C for a period of 24 h, to make the crosslink. After this treatment, the measurement of the gel rate of the part covered by aluminum according to ISO 10147 standard indicated that the crosslinking rate reached 11.5%.

 The protection according to the invention effectively makes it possible to postpone crosslinking and therefore to preserve assembly regions (ends), which therefore offers the possibility of assembling the objects by a thermal welding process even after an extended storage period.

Claims (30)

1-Three-dimensional objects to be assembled by thermal welding, comprising at least one layer of crosslinkable (co) polymer (s), provided with protective means comprising a metal sheet covering regions of assembly of said objects, these regions of assembly comprising the zones to be welded proper and adjacent security zones, so as to prevent or delay the crosslinking of the crosslinkable (co) polymer (s) in the zones to be welded.  2-three-dimensional objects according to claim 1, characterized in that the maximum crosslinking rate of the crosslinkable (co) polymer (s) in the areas to be welded is less than 40%.  3-three-dimensional objects according to claim 1, characterized in that the maximum crosslinking rate of the crosslinkable (co) polymer (s) in the areas to be welded is less than 35%, preferably less than 30% and particularly preferably less than 25%.  4-three-dimensional objects according to any one of the preceding claims, characterized in that the metal sheet is an aluminum sheet.  5-three-dimensional objects according to claim 4, characterized in that the aluminum sheet is an aluminum sheet pre-coated with polyethylene applied by thermal welding.  6-dimensional objects according to claim 4, characterized in that the aluminum foil is an aluminum sheet pre-coated with a pressure sensitive adhesive applied by adhesive bonding.  7-three-dimensional objects according to any one of claims 1 to 6, which are tubes to be welded end to end for the manufacture of pipes of great length.  8-three-dimensional objects according to claim 7, characterized in that the protective means cover the inner and outer faces of <Desc / Clms Page number 13>  ends of the tubes, the safety zones exceeding the limits of the zones to be welded proper, preferably 1 to 10 cm.  9-three-dimensional objects according to any one of claims 1 to 6, which are heat-sealable sleeves used to assemble tubes for the manufacture of pipes of great length.  10-three-dimensional objects according to claim 9, characterized in that the protective means cover at least the inner face of the heat-sealable sleeves.  11-dimensional objects according to any one of claims 1 to 10, characterized in that the wall of the objects comprises a single layer comprising at least one (co) polymer cross-linkable.  12-three-dimensional objects according to any one of claims 1 to 10, characterized in that the wall of the objects comprises two or more integral layers, at least one layer of which comprises at least one (co) crosslinkable polymer and of which at least one another layer comprises at least one thermoplastic (co) polymer.  13-Three-dimensional objects according to claim 12, characterized in that the at least one (co) thermoplastic polymer is high density polyethylene.  14-Three-dimensional objects according to any one of claims 1 to 13, characterized in that at least one of the (co) crosslinkable polymers is a (co) polymer of ethylene functionalized by hydrolysable groups.  15-dimensional objects according to claim 14, characterized in that the (co) polymer functionalized ethylene is polyethylene functionalized with groups vinyltrialkoxysilanes.  16-A method of protecting three-dimensional objects to be assembled by thermal welding, comprising at least one layer of crosslinkable (co) polymer (s), characterized in that the protection consists in applying protective means comprising a metal sheet on assembly regions of said objects, these assembly regions comprising the zones to be welded proper and adjacent security zones, so as to prevent or prevent <Desc / Clms Page number 14>  delay crosslinking of the crosslinkable polymer (s) in the areas to be welded.  17-A protection method according to claim 16, characterized in that the metal foil is an aluminum foil applied by thermal welding in the form of aluminum foil precoated polyethylene.  18-A protection method according to claim 16, characterized in that the metal foil is an aluminum foil applied by adhesive bonding in the form of aluminum foil precoated with a pressure sensitive adhesive.  19-A protection method according to any one of claims 16 to 18, characterized in that the three-dimensional objects to be assembled by thermal welding are tubes to be welded end to end for the manufacture of long pipes and that the means of protection are applied to the inner and outer faces of the ends of the tubes, the safety zones exceeding the limits of the zones to be welded proper, preferably from 1 to 10 cm.  20-Installation for protecting three-dimensional objects to be assembled by thermal welding, comprising at least one layer of crosslinkable (co) polymer (s), comprising - at least one holding device serving to hold said objects in place and - at least one application device used to apply protection means to the assembly regions of said objects by means of a method according to any one of claims 16 to 19.  21-A method of thermal welding of two or more three-dimensional objects comprising at least one crosslinkable (co) polymer according to any one of claims 1 to 15, in which three-dimensional objects are welded to each other by zones to be welded comprising protective means applied to assembly regions, these assembly regions comprising the zones to be welded proper and adjacent security zones, so as to prevent or delay the crosslinking of the (co) polymer (s) ) crosslinkable in the areas to be welded, the method comprising - a step of exposing the areas to be welded - a step of heating the areas to be welded and - a step of forced assembly of said objects. <Desc / CRUD Page number 15>

22-Welding method according to claim 21, characterized in that the three-dimensional objects to be assembled by thermal welding are tubes to be welded end to end and optionally heat-sealable sleeves for the manufacture of long pipes.  23-A welding method according to claim 22, characterized in that the bare step includes the removal of the protective means, preceded or followed if necessary by cutting a wafer or a ring.  24-Welding method according to any one of claims 21 to 23, characterized in that the areas to be welded are heated to a temperature between 180 and 250 C.  25-A welding method according to any one of claims 21 to 24, further comprising a subsequent step of substantial completion of the crosslinking up to a crosslinking rate greater than 60%, preferably greater than 65%.  26-Installation for welding three-dimensional objects which comprise at least one crosslinkable (co) polymer and which comprise protective means applied to assembly regions according to any one of claims 1 to 15, these assembly regions comprising the zones to be welded proper and adjacent security zones, so as to maintain a maximum crosslinking rate of the at least one crosslinkable (co) polymer in the zones to be welded less than 40%, the installation comprising - setting devices bare the areas to be welded, - thermal welding devices proper integrating means for heating the areas to be welded and means for forced assembly of the objects in said areas, and - optionally, devices for completing the crosslinking serving to increase the rate of crosslinking of objects assembled by welding

 thermal at a value greater than 60%, preferably greater than 65%.  27-Installation of welding according to claim 26, characterized in that the exposure of devices allowing the withdrawal protection means, preceded or followed where appropriate by the cutting of a slice or a ring. <Desc / Clms Page number 16>  28-Welding installation according to claim 27, characterized in that the stripping devices comprise a lathe and / or a circular saw.  29-Use of three-dimensional objects according to one or more of claims 7 to 15 which are tubes and optionally heat-sealable sleeves for the manufacture of long pipes or networks of pipes, such as for the production of pipes for distribution fluids.  30-pipes of great length pipes or networks obtained by the thermal butt-welding or heat-sealable sleeve tubes protected by a protection method according to any one of claims 16 to 19.