WO2009087565A2

WO2009087565A2 - Coupling obtained by electrofusion welding, its production process and its management system

Info

Publication number: WO2009087565A2
Application number: PCT/IB2009/000025
Authority: WO
Inventors: Fabrizio Rivoli
Original assignee: Marotti, Alessandra
Priority date: 2008-01-10
Filing date: 2009-01-08
Publication date: 2009-07-16
Also published as: EP2238382A2; WO2009087565A3; ITTO20080017A1

Abstract

Electroflision joint, its production process and its management device, the production method of which is characterised by the following steps: production of the end of the socket pipe, installation of at least one electrical resistance, possible coating of said electrical resistance, protection of the entire spigot joint.

Description

Coupling obtained by electrofusion welding, its production process and its management system

DESCRIPTION The object of the present finding is a plumbing joint or a joint for other applications to be welded by electrofusion, its production process and its management device. Preliminarily, it should be specified that by plumbing joint we include the different components of which it can consist, typically a pipe and a spigot joint, but also pipes and pipe coupling, and the pipes can be straight pipes, fittings, curved pipes, elbows, tees and similar. In the state of the art, there are a limited number of examples of plumbing joints suitable for being used in the field of electrofusion welding. For example, patent application US20070145736 concerns an electrofusion joint that comprises a meltable element and a heating element fixedly connected to the pipe or to the fitting. The pipe or the fitting can be bevelled to make it easier to insert another pipe and form an electrowelded joint. Attachment devices are used to fixedly connect the heating element that extend beyond the fusion area. The power used melts the pipe near to the heating element.

Another example is reproduced in patent application WO99046532 that has as its object an electrofusion welding joint that joins plastic pipes. The joint houses the pipes inside it and the diameter of its ends is greater than that of the intermediate part so as to house the outer pipe at the end and the inner pipe in its intermediate part, in situations in which the coupling comprises two coaxial pipes with a space between them for controlling leakage. The joint comprises a resistance that makes the material of both pipes melt.

In any case, these and other examples do not contain a detailed description of the entire production process of the joint, which therefore is a product that is difficult if not impossible to make. The purpose of the finding object of the present invention is to provide a method for producing joints suitable for electrofusion welding that is industrially sustainable and of low cost. The finding object of the present invention solves the aforementioned technical problems since it concerns a plumbing joint or a joint for other applications to be welded by electrofusion, the production process of which is specified by claim 1. The product thus obtained is a spigot joint set up for joining with electrofusion like according to claim 21. These and other advantages shall become clear from the detailed description of the invention that shall refer specifically to the attached tables in which some preferred example embodiments of the present finding are represented, absolutely not for limiting purposes. In particular: • Fig. 1 shows the electrofusion spigot joint according to the invention; • Fig. 2 represents the product of the processing of a pipe of variable diameter;

• Fig. 3 is relative to one of the installation processes of the resistance; • Figs. 4-6 represent different methods of protection of a spigot joint according to the invention;

• Fig. 7 shows how a pre-seat is made from the installation of the electrical resistance;

• Fig. 8 shows some constructive details of the joint of Fig. 1 ; • Fig. 9 schematizes some alternative embodiments of the electrical resistance;

• Fig. 10 shows a variant connecter for the electrical resistance;

• Figs. 1 1 and 12 show two examples of electromagnetic wave receivers • Figs. 13- 17, lastly, depict some possible variants of the spigot joint.

With reference to the aforementioned figures, the process for producing a joint to be welded by electrofusion comprises four main steps: the production of the belled end, the installation of the electrical resistance, the possible coating of the same resistance and the protection of the entire spigot joint. The main steps shall be described hereafter in the different possible variants. Moreover, the process in object also includes some optional, but certainly advantageous, steps that shall also be described. The first step of the process in object concerns the production of the socket.

Five different methodologies are possible:

1. a. Using the thermoforming process, a pipe obtained by extrusion is inserted into a machine that is known as a belling machine. In the current state of the art, said belling machine uses three processing steps - heating, forming and cooling - and each step corresponds to one work station. In the process in object a further intermediate relaxation step has been foreseen, preferably using a fourth station. The pipe is subjected to heating, in the first station, at the point at which it needs to be widened. After having been heated, in a second step the pipe is left to sit in the second station, known as relaxation, at a controlled temperature and for a certain period of time, parameters that are a function of the magnitude of the diameter of the pipe and of the thickness of the pipe. In this way a relaxation of the piping is carried out, freeing it from the tensions accumulated during the extrusion process. Then it is inserted into the third station, in a form that causes it to gradually widen and, then, it is cooled in the fourth station and ejected. The internal calibration of the socket is carried out on a mechanical mandrel with expandable inserts. The heating of the end of the pipe takes place in distinct stations and steps. In the first step it occurs by means of a halogen short-wave infrared oven. In the second step and/or station the pipe is kept at a given temperature with a halogen short-wave infrared oven or with an electroventilated oven that produces very hot jets of air or, alternatively, it is left to sit without applying heat, for a certain period of time eliminating the tensions of the material.

In the third step, during widening, the heating comes from an internal contact and external radiation oven with metallic shell heated by band resistance equipped with ceramic insulation. The forming of the socket takes place with high- pressure compressed air action (up to 20 or more bars). The cooling of the socket takes place with pressurised nebulised water. l .b.Like the previous one apart from the cycle in the third station. According to this method, an apparatus brought to a high pressure and made up of mandrel mould and flange is exploited. Once heating is complete, the pipe is placed in the forming station and closed between the moulds, then the mandrel equipped with gasket penetrates and forms a seal inside the pipe; the fundamental moment of the process occurs when the flange moves forwards and, with the help of the high pressure air that comes out from the mandrel, pushes the pipe against the outer mould; once the socket is formed on the outer mould, it is compressed and calibrated on the inner mandrel. With this second method, the advantages are that the two widening and recalibration steps stabilise the size of the socket over time.

I .e. The third method starts from the production of the normal polyethylene pipe. For this, an extruder is normally used equipped with a head in which a die plate, which determines a given diameter of the pipe of plastified material, and on the inside, a matrix that determines the air gap with the die plate and consequently the thickness of the pipe, are mounted. The pipe is inserted into a fixed calibrator that is housed in a vacuum tank with nebulised water, where it is formed to the final size and, then, cooled. Finally, at the end of the line, there is a haul-off equipped with rubber tracks that hauls the pipe. In order to change the diameter of the pipe, according to the prior art, it is necessary to mount the die plate and the matrices of adequate size and to change the fixed calibrator, the containment flanges of the tanks and the adjustment of the haul-off at the end of the line. For some time, however, on the market there have been automatic lines able to change the size of the diameter of the pipe automatically without it being necessary to stop them. The line uses an extruder equipped with a head with die plate and on the inside there is a matrix that adjusts the cone or truncated cone-shaped air gap. According to the movement of the matrix forwards or backwards, it is possible to automatically modify the size of the air gap. The die plate is connected to a vacuum tank known as intake chamber, in which by changing suitable inserts, without stopping the line, the size of the pipe is determined. As an alternative to changing the inserts, it is possible to vary the diameter of the pipe by enlarging it or shrinking it, in the last case by means of vacuum pump or suction fans.

Inside the calibration tank there is a basket calibrator automatically adjustable within a certain range of diameters that widens or narrows according to the diameter to be produced. The haul-off at the end of the line also adjusts automatically. To produce the socket, during the production of the pipe at a certain length the automatic calibrator gradually widens and at the same time the matrix inside the die plate moves increasing the thickness proportionally, to compensate the widening of the diameter and thus maintain the wall thicknesses of the pipe. Automatic adjustment is also foreseen, also synchronised with the different opening times, in the intake chamber that acts as a die plate, because it may be the case that by itself the gauge does not manage to widen the diameter starting from a fixed size. As represented in Fig. 2, the product of the work are two sockets 2 and a length of pipe 7, to be separated along the cutting lines 6, wherein said length of pipe is used to produce one or more electrical couplings. l .d.The fourth method foresees the production of the socket through the injection process. Once extruded, the pipe is picked up from the line and, when positioning has occurred, the pipe advances inside the injection moulds that clamp it creating, together with a suitable inner plug, the injection chamber of the material. After the mould is closed the injection of the plastic material and at the same time the cooling of the injected socket through circulation of water inside the mould and the central plug takes place.

I .e. The last method foresees the separate production of the socket and, therefore, the connection to the pipe by welding. Once extruded, the pipe, with or without resistance, is positioned on a welding station, where the socket produced earlier is welded, for example by moulding. The socket can be welded on line or off line.

The second step of the process in object consists of the installation of the electrical resistance. Also in this case different methods are possible.

2. a. Injection moulding. With reference to Fig. 3, inside the socket, obtained with one of the methods outlined previously, a preformed piece 8 is inserted, equipped in advance with a groove 9, having an internal diameter corresponding to the nominal diameter of the pipe to be inserted. The preformed piece comprises an electric coil 3 already wound in the definitive position, whereas on the outer part of the socket it is foreseen for it to be possible to use moulds in combination with an injection press. The chuck equipped with holes for the insertion of molten material is connected 10 to an extruder and, with the preformed piece in the correct position, it is inserted into the socket. Then the same material of which the pipe is made is injected through the main channel 1 1 , until the spaces between the electric coils are filled covering them and the inner wall of the socket, said material, once cooled, becoming a single body with the socket.

2.b.The pipe equipped with belled end is positioned on an idler set. A first hole is made to house a first connecter for welding that will be connected to the electric coil. Inside the pipe an endless chuck is inserted equipped with a tool positioned with or without a certain inclination and of suitable shape (hot or

- otherwise). As the pipe rotates and advances, the tool cuts the inner wall of the pipe that can be smooth or with bumps, creating the housing of the resistance at a certain depth and, at the same time, the resistance will be positioned, which may or may not be heated to a certain temperature to be able to fix in the plastic material. Thereafter, the second hole is made where the second connecter for welding is installed. The same methodology can be applied, by foreseeing that it is the chuck that rotates and advances.

2,c.The pipe equipped with belled end is positioned on an idler set. A first hole is made to house a first connecter for welding that shall be connected to the electric coil. Then, a robot ' inserts a head with a certain inclination to mount the resistance in the form of a helical coil. The head is equipped with a suitably shaped tool (heated or otherwise) that as the pipe rotates and advances, cuts the inner wall of the pipe creating the housing of the resistance at a certain depth and, at the same time, the resistance shall be positioned, which may or may not be heated to a certain temperature so as to be able to fix into the plastic material. Thereafter, the second hole is made where the second connecter for welding is installed. The same methodology can be applied, by foreseeing that it is the head that rotates and advances.

2. d. Insertion of the resistance through an expanding chuck. The resistance is heated and pressure-inserted into the wall of the socket. The consequent pre-tensioning of the coil is compensated with possible dandy roll when the chuck expands. With this insertion method, a resistance is better installed that is shaped like a T, although a triangle or any other shape can be used. For example, Fig. 9 represents some examples of resistances shaped like a "T" without (3') and with anti-slip fins (3") and shaped like an "L" without (3'") and with anti-slip fins (3"") .

The third step of the process consists of coating the electrical resistance. Different methodologies are possible. 3. a. Once the resistance has been installed complete with connecters, a chuck is inserted that acts as an inner mould and the same type of plastified material is entered, which after having cooled becomes a single body with the socket coating the resistance.

3. b. After the installation of the resistance complete with connecters, an articulated arm is inserted with a nozzle at the top that can be of different shapes, connected to an extruder, and the plastified material is applied just on the groove of the resistance, coating it. At the same time, a small roller, by pressing on the applied material shall take care of making the material penetrate into the groove and shall align the coating flush with the wall removing the excess material.

3. c. This method is carried out in parallel to the installation step of the resistance. A tool is used equipped with two ends, the first makes a thin and wide cut lifting a film of a certain thickness, the second end shall make the incision on the wall where the resistance will be housed. Once the resistance has been inserted, a roller or other suitable tool, heated or otherwise, through pressing contact, shall take care of coating the resistance with the lifted film.

The fourth step is to give adequate protection to the socket and to allow it to be stored in a warehouse, even in open air. Different methodologies are possible.

4. a. With reference to Fig. 4, a shaped plug 12 that reproduces the inner part of the socket is inserted into the socket, with a pressing action. The same plug has one or more through holes where stoppers will be inserted, equipped on the head of a plug 13, preferably threaded and with a gasket, suitable for protecting the connections of the welder and at the same time avoiding the plug itself slipping out.

4. b. With reference to Fig. 5, inside the socket a layer of heat- shrinking film 14 is applied that sticks to the inner walls of the socket with a fold on the entire circumference of the pipe and, a closing plug 12 is applied on top. Plugs 13 for coupling with a gasket are inserted onto the connectors of the welder, and then some extendable film 15 is wound. 4. c. With respect to variant 4. a and with reference to Fig. 6, the plugs for the connections 13 are fixedly connected to the main plug 12, i.e. they are produced and moulded together and two anti-slip toothed bands 16, like those used in the field of electrics, are also foreseen. 4. d. Finally, with reference to Fig. 5, this last approach, compared to the methods described previously, foresees that the inner plastic film 14 is fixed with a strip of adhesive or glue.

As we have seen, the process comprises a specific step for the installation of the electrical resistance. During such a step, a seat is created for the resistance and, simultaneously, it is installed. Of course, it is also possible to create a raised seat or at least a raised pre-seat for the electrical resistance in advance (Fig. 7).

5. a. During the thermoforming process an expanding and heating chuck is used with the ridges already cut on it. In this way, the socket, once produced, shall be equipped on the inside with the seat 17, in which the resistance will be inserted. 5. b. During the moulding process, a mould is used with the final shape of the socket that comprises a shaping suitable for producing the seat of the resistance. Of course, the method can be used both on sockets obtained in one piece with the pipe and on sockets overmoulded on the pipe. 5. c. After the formation of the socket, a chuck with a tool takes care of creating the ridges and the grooves ready for the insertion of the resistance.

The product thus obtained is therefore a spigot joint prepared for joining with electrofusion comprising a pipe portion 1 equipped with belled end 2, inside of which an electrical resistance 3 is housed, equipped with electric terminals 4 passing through holes 5 formed in the belled end. Along the belled end there are also suitable holes 20 to inspect the welds and 21 to house possible microchips (Fig. 1 ).

With reference to Fig. 8, an important auxiliary step consists of the installation of the connecter. As we have seen, once the socket has been produced, the holes for housing the connecter are made. The hole has a first part that is wider to allow the insertion of the connecter of the welder, whereas the second part of the hole is smaller. A male connecter with the finned tail (straight or helical) is inserted in the latter hole, so that, once inserted, the connecter shall be removably clamped, by a moulded piece. The connecter has a through hole where the wire of the resistance is inserted and it is clamped at the tip with a weld. The connecter can also be circular in shape (female) by mounting adapters to the connecters of the welder, and the outer part can be smooth or with threadings and equipped with a through hole. Moreover, the connecter can have the end worked part that is inserted in the socket equipped with knurling (5' in Fig. 10) so that the resistance can be clamped by winding. Finally, it is possible to equip the socket with an outer coating, which can prevent or limit deformations, to be installed in the production step of the socket or in the welding step of the electrical resistance. This is carried out, for example, by applying a coil 18 that may be of steel or plastic material onto the outer part of the socket. The coil is three-quarters inserted into an indentation made by a suitable tool, and becomes fixedly connected to the socket itself.

The coil is also essential to carry out good welding: since the thickness of the wall of the socket is equal to that of the wall of the pipe, during heating they expand in the same way, not creating the necessary pressure sufficient for good quality welding to take place. The coil indeed allows the necessary pressure between socket and pipe to be ensured. Finally, in the case of deformation of the socket due to incorrect transportation or storage, it is possible to connect the welder to the two ends of the outer coil that will thus act as a resistance. By giving a predetermined voltage, the socket (or the electric pipe coupling) rounds off again and goes back, to its original shape given by the thermoforming process.

Alternatively, a band of plastic material containing glass fibres of substantial length, aligned in the direction of extrusion, can be applied hot onto the outer part of the socket so as to give the maximum longitudinal resistance.

Advantageously, the male pipe 19 to be coupled with the spigot joint can have a differentiated thickness in particular with greater thickness in the coupling area with the spigot joint. This is for various reasons. Firstly, in order to standardise the design of the resistances. Indeed, the resistance designed for a pipe of greater thickness, for example of class pn 16 or pn 25, could not be used for a pipe of smaller thickness, for example a pn 10, since it would cause the pipe to thermally collapse, due to the amount of heat used during the welding step. Secondly, in the case of use of the pipe with socket with anti-slip ring: when the pipe tends to slip out due to pressure on the ring it forces the pipe inside throttling it. This could, over a long period, cause problems for the lifetime of the pipe.

With regard to the electrical resistance, a problem to be solved is that linked to its resistivity. Indeed, the resistance goes outside tolerance when the temperature of the pipe coupling exceeds 45°C. This occurs because with the type of resistance used (copper, aluminium or similar) according to the temperature, the resistivity changes. The barcode attached to jointing systems displays the resistivity at 20⁰C with the due tolerances and it is interpreted as safety index: with the resistivity outside tolerance the welding process does not obtain approval to be able to begin. There are two solutions: either the material of the resistances are optimised or resistivity correctors are used. With regard to the material, a possibility is to use a constantan alloy. Constantan is a binary alloy made up of copper (60%) and nickel (40%) that, at room temperature, has a resistivity of about 5 x 10-7 Ωm. One of its properties is that of keeping its resistivity unchanged as the temperature varies, which increases through the Joule effect as current passes.

Another possibility is to use shape memory alloys. They are alloys that contain the intermetallic binary compound NiTi, one of which is known as "NlTINOL" (abbreviation of Nickel Titanium Naval Ordinance Laboratory) and possesses excellent properties both in terms of shape memory and of superelasticity. It also has good electrical and mechanical properties, resistance to fatigue and to corrosion. Such a compound also possesses the characteristics such as to be able to be electrically activated by the Joule effect: i.e. when an electric current passes through it, sufficient heat is generated to cause phase transformation.

Further alloys that can be used are Nickel-chrome, Fecral (iron- chrome-aluminium) or Manganin (86% CU,2%NI, 12%Mg) alloys. On the other hand, resistivity correctors are additional connecters that are arranged between the connecters of the welder and the connecters of the joint. They can be of a different material according to the resistivity range to be recovered. The resistivity of these correctors can be fixed according to the material used and the temperature of use or variable, using electrical or magnetic energy. They can be autonomous, running on battery, or else connected to an energy generator. By operating this way it is possible to use normal welders and conventional low-cost resistances made from copper and aluminium.

The spigot joint according to the invention or the male pipe to be coupled with the joint can also be equipped with one or more microchips and/or MEMS, with radio wave RFID technology or another suitable technology. The microchips can be active with microbattery, semi-passive with battery that only activates when it receives radio waves and, consequently, lasts longer or passive since it is activated by the waves emanating from the receiving device. The microchip can be combined with sensors, which can be position (GPS SIS), temperature, acidity or pressure sensors or sensors that read the variations in the conditions that determine the water pollution, or sensors of other types according to needs. The reading of data can take place through a suitable programmable reader, manually or automatically, at different frequencies according to the operating conditions (laying depth, type of ground, presence of disturbances from other apparatuses, etc.). The data can be amplified by means of signal amplifiers made from conductive material to be applied to the pipe systems with or without the help of the liquid that passes in the pipe systems that is a conductor that can also be used by itself, the same liquid can be used to activate all of the microchips present on the entire piping system, activating them, with a single simple operation. The microchip can be installed in the inner part, the outer part or in the thickness of the pipe, by means of an adhesive label containing the microchip itself, or else, with prior incision or perforation, inserted in the thickness of the wall of the pipe. It can be left uncovered or coated with material, which will be the same as the different pipe. In this case the material can be conductive so as to amplify the signal, thus compensating for the low conductivity of the plastic materials. It is possible to use microchips already encapsulated in the plastic material to be applied through welding or by means of glues both in the inner and outer part or in the thickness of the pipe systems, and the microchips can be inserted in the processing step of the pipe systems (extrusion), inserted in the mixture of the raw material necessary for the formation of the pipe. Alternatively, in multilayer pipe systems the microchip can be inserted in the mixture by extrusion to produce the inner layer of the pipe or in that to produce the outer layer of the pipe or in both; moreover, it can be inserted during the extrusion at predetermined distances, through auxiliary apparatuses connected with the head of the extruder, which shall be suitably modified to foresee the insertion of the microchips without making them pass through the screw and cylinder of the unit where it could suffer damage and thus not work.

The application of the microchip has many uses. It is used to allow a quick inventory, good tracking both before, conserving all of the item production and identification data, and after laying, to indicate at a later date the exact position of the type of item and the depth - information that is very useful in the case in which other excavations are being carried out. Otherwise it is used, after exceptional occurrences like floods or earthquakes, to check, through the use of sensors already foreseen before, the actual depth of the piping, or else whether or not it has moved. In this way it is known in advance, before there are leaks or infiltrations in the piping system with subsequent pollution, whether a maintenance intervention is needed. The same check can also be carried out without the help of sensors: using the return times of the radio waves the reader calculates the depth and compares it with that memorised in the microchip. Another very important use is the possibility, for the authorised user, to write on the microchip, to record anything that is needed, like the date of checking of the pipe systems or else maintenance carried out or whatever he feels fit without limitations. The data will be sent to the apparatus that carries out the welding adjusting its parameters in combination with the barcode or individually. It is also used for water quality control in its main parameters (acidity or else amount of chlorine dioxide, used to disinfect drinking water from aqueducts). Moreover, it is useful for recording welding parameters, which is very important information when carrying out an assessment of the welds, or in the case of unexpected maintenance it is possible to immediately check in loco all of the parameters used. Finally, the end user can load data of interest to him onto the microchip, like data on installation, laying depth and similar.

As an alternative to the microchip, it is possible during the production/extrusion process, by means of a co-extruder, to add a layer or a strip of material containing ferromagnetic or metallic tracers onto the surface of the pipe. In this way, any type of pipe or family of pipe shall be identified according to the type of tracer, the detection will be carried out through metal detectors or similar machines with radio frequency emissions or electromagnetic waves. The electrofusion joint according to the invention, in its plumbing application in plastic pipes, is suitable for all machines that carry out welding, both manual and automatic, with barcode reading and with the possibility of memorising numerous pieces of data, for example the number of welds made, the name of the operator of the welding process. In particular, it is suitable for welders equipped with gps-sis module and connect card module, integrated or connected to them for data transmission via gsm, umts, and in any case wirelessly. The use of such welders allows a series of further advantages to be obtained: providing the data for any database, checking the progress of work, receiving gps data and checking them with the original project, integrating the data of the welder with the data of the microchip present on the pipe with a suitable programme that has stored the drawings of the items previously loaded, drawing the updated design in real time, mapping out the entire piping system in real time.

A preferred but not limiting welding method is electromagnetic induction welding. The welding system is made up of an induction coil that has the purpose of generating an electromagnetic field at a certain frequency, this electromagnetic field induces in the conductive materials a heating effect by the Joule effect due to the currents that are generated. The main advantage is the modularity of the voltage with consequent accurate and repeatable heating and with a very fast execution speed compared to conventional methods. In the case under consideration there are different solutions according to whether one decides to eliminate the conventional resistance or keep it. In the first case, welding without resistances, a compound made up of the same raw materials and of ferro-magnetic, metallic and non-metallic fillers, which will act as susceptors (then become resistances), is added into the mixture of material that is used to produce the piping. In practice, the heating effect of the susceptors will occur through the magnetic field applied. The application of the compound can also take place in different ways, for example on inner or outer layers of the piping, by injection or by co-extrusion, or else by applying inserts, perhaps annular shaped ones in suitable throats of the socket. In the case in which a conventional electrical resistance has been installed it is always possible to use the method of induction welding. It will be sufficient to apply to the connecters some electromagnetic wave receivers that, being electrically connected with the resistances, at the passage of current heat up melting the material. The receivers can be of any shape and preferably are square or rectangular (20 and 20' respectively in Fig. 1 1 and Fig. 12). The receivers can be equipped with microchips fitted with temperature sensors (they read the temperature of the resistance and guide the welding process sending input to the welder). The welding can also take place by connecting directly to the connecters of the electrofusion system and electromagnetic waves can be emitted through a suitable welder instead of electric current. The connecters shall also be equipped with temperature sensors that read the temperature and send the data to the welder. In the welding process one of the most difficult problems during the step of joining the pipes, regardless of the type of joint used, is the roundness discrepancy of the pipe, i.e. its oval shape. It often occurs that the tolerances and therefore the roundness of the pipe do not coincide with those of the joint, causing leaks or unsuitable welds. By using the joint in object it is possible to propose some solutions to this type of problem:

• At the end of the extrusion step, in a predetermined point, preferably on the top part that is visible, a line is made on the entire length of the pipe through a marking or alignment notches are made so that the pipes that will form part of the same production batch and that have a roundness that is the same or different but in the same tolerance class, can be aligned correctly having an unequivocal reference point. The marking or the notches can, for example, be made with rotary markers, with heated stamps, using tapes, adhesives and similar;

• At the end of the line, a station is added that finishes the roundness of the pipe. The station can be single or combined with the various formation systems of the socket, like belling machine, for example, wherein the pipe, once extruded, thus still not completely cooled, is inserted into two metallic shells and a male chuck is inserted inside. The shells and the chuck can be heated to a suitable temperature and for suitable times, as a function of the size of the diameter and the thickness of the pipe;

• Fractioning the welding process into a first step, in which the resistances are taken to a certain temperature for a certain period of time, according to the size of the diameter and the thickness, and a second step in which the material is made to melt. With this system it is possible to use different production batches or pipes produced by other firms, even with different oval shapes: by heating the belled joint and male pipe system without melting, the walls through the effect of the heat move closer together, adapting, and the pipes tend to round. Another advantage is the elimination of detergent residues, used to clean the surfaces through the effect of the heating heat. Preferably, the welding process is carried out using voltage ramps in the welders and thus consequently heat ramps given to the joining system. These ramps are very flexible in terms of the voltage values and times. This system is very useful at the design stage of the resistances and of the entire joint because it allows the welding times to be optimised, possibly be varied in the case of certain conditions and statistically it allows the best welding condition to always be obtained according to the various situations that occur from one time to the next.

Finally, again in the field of the present finding, it is possible to define methodologies to determine with certainty the depth of insertion of the pipe and the thickness of outer surface of the pipe to be peeled to eliminate the oxidised material. In order to insert the pipe a marking is made, through a rotary marker that can be integrated as a function in the marker for the alignment of the oval shapes or else be independent from it, on the entire circumference of the pipe defining the depth of insertion. The marking can be hot with coloured tapes, with inkjet, laser and similar.

A marking with triangular or other shaped incisions or with alphanumerics is made on the peeling surface, through rotary markers, suitably modified to ensure the depth of incision in the oval-shaped points, which can be integrated as a function in the marker for the alignment of the oval shapes and of the depth of insertion or else be independent, so as to cover most of the surface of the depth of the peeling, to be carried out according to the standards, so that when the peeling itself is carried out and the incisions can no longer be seen it is guaranteed that the depth necessary to carry out a welding up to standard has been reached. Returning to , the spigot joint, Figs. 13 to 17 represent some possible variants of the shape of the socket, to stiffen it, to improve assembly and to comply with welding standards. In Fig. 13 it is possible to see a reinforcement 21 to give rigidity to the socket; Figs. 14 and 15 show two examples of drafts 22, 22' to improve the introduction of the pipe; Fig. 16 depicts a reinforcement 23 that avoids bangs to the connecters. Finally, Fig. 17 shows the portion C that widening out follows the application standard of the electroweldable joint: indeed, whereas the two walls that weld together are considered as if they were one, all of the parts that are not welded must respect the SDR of the joint, i.e. the ratio of pipe outer diameter divided by pipe thickness. This number unequivocally defines the pressure class of the pipe and of the joint according to the type of material used. At the moment when the outer diameter widens to make the socket, excluding the two walls that are welded, it is necessary to widen the portion C of the socket and the most cost-effective way is to do so proportionally 24 as the diameter widens (reference 24 in Fig. 17). In any case the thickness of the portion C will always be greater than that of the pipe. In sizing it is important for the angle Rl to be within the range 0.09-0.35 degrees per mm of the outer diameter of the pipe.

Claims

1 ) Process for producing a joint, for plumbing applications or for other applications, to be welded by electro fusion, comprising a pipe and a spigot joint, or else a pair of pipes and a pipe coupling, the pipes being straight pipes or else, fittings, curved pipes, elbows, "TEEs" and similar, characterised by the following steps: production of the end of the socket pipe, installation of at least one electrical resistance, possible coating of said electrical resistance, protection of the entire spigot joint.

2) Process according to claim 1 , wherein said step of producing the end of the socket pipe is obtained by thermoforming of a pipe extruded in a belling machine according to the steps of oven-heating, forming in a form that causes it to gradually widen out into a socket and, thereafter, cooling and expulsion.

3) Process according to claim 2, characterised by the use of a further intermediate relaxation step, by means of an additional work station, where said end of the pipe tempered by the heating station is left to sit at a certain controlled temperature and/or for a certain period of time.

4) Process according to claim 2 or 3, wherein said forming step exploits an apparatus brought to a high pressure and made up of mould, mandrel and flange; said pipe is placed in the forming station and closed between the moulds, then the mandrel equipped with gasket penetrates and forms a seal inside the pipe; then the flange moves forwards and, with the help of the air under high pressure that comes out from the mandrel, pushes the pipe against the outer mould; once the socket is formed on the outer mould, it is compressed and calibrated on the inner mandrel.

5) Process according to claim 1 , wherein said step of producing the end of the socket pipe is obtained using an automatic line comprising an extruder equipped with a head with die plate and, on the inside, a matrix that regulates the cone or truncated cone-shaped air gap; since said die plate is connected to an intake chamber, which can be automatically adjustable and synchronised, in which by changing suitable inserts, i.e. the diameter of the pipe, without stopping the line, the size of the pipe is determined.

6) Process according to claim 5, wherein the product of the work are two sockets (2) and a length of pipe (7), to be separated along the cutting lines (6), and wherein said length of pipe is used to product one or more electrical couplings.

7) Process according to claim 1 , wherein said step of producing the end of the socket pipe is obtained using an injection process according to which the pipe moves forwards inside the injection moulds that clamp it creating, together with a suitable inner plug, the material injection chamber and, after the mould is closed, the injection of the plastic material takes place and at the same time the cooling through circulation of water in the injected socket.

8) Process according to claim 1 , wherein said step of producing the end of the socket pipe is obtained through separate production of the socket, for example by moulding, and subsequent welding thereof to the pipe.

9) Process according to one of the previous claims, wherein said step of installing at least one electrical resistance is obtained with injection moulding, by firstly inserting into the belled end a preformed piece (8), equipped in advance with a groove (9), having an internal diameter corresponding to the nominal diameter of the pipe to be inserted and comprising an electrical coil already wound in the definitive position; then, by connecting (10) a chuck, equipped with holes for the insertion of molten material, to an extruder and, with the preformed piece in the correct position, inserting it into the socket and finally injecting the same material that makes up the pipe from the main channel ( 1 1), until the spaces between the electrical coils and the inner wall of the socket are filled.

10) Process according to one of claims 1 to 8, wherein said step of installing at least one electrical resistance is obtained by positioning the pipe equipped with belled ends on a set of rolls making a first hole to house a first connecter for welding and inserting inside the pipe a chuck equipped with a shaping tool and positioned with a certain inclination; then, through advancing and rotation of the pipe or, alternatively, of the chuck, the inner wall of the pipe is cut with said tool, creating the housing of the resistance and, at the same time, the resistance itself is positioned; finally, the second hole is made for the installation of the second connecter for welding.

1 1 ) Process according to one of claims 1 to 8, wherein said step of installing at least one electrical resistance is obtained by positioning the pipe equipped with belled end on an idler set, making a first hole to house a first connecter for welding and inserting inside the pipe, through a robot, a head with a certain inclination equipped with a suitably shaped tool and positioned with a certain inclination; then, through advancing and rotation of the pipe or, alternatively, of the head, the inner wall of the pipe is cut with said tool, creating the housing of the resistance and, at the same time, the resistance itself is positioned; finally, the second hole is made for the installation of the second connecter for welding.

12) Process according to one of claims 1 to 8, wherein said step of installing at least one electrical resistance is obtained through an expanding chuck, with heated resistance and pressure-inserted into the wall of the socket. 13) Process according to one of the previous claims, wherein said step of coating the electrical resistance is carried out by inserting a chuck that acts as an inner mould and injecting the same type of plastic material as the socket, which after having cooled becomes a single body with the socket itself, coating the resistance.

14) Process according to one of claims 1 to 12, wherein said step of coating the electrical resistance is obtained by inserting an articulated arm with a nozzle at the tip, connected to an extruder, and applying the plastic material onto the groove of the resistance, coating it; at the same time, a small roller, by pressing on the material applied, shall make the material penetrate into the groove and shall align the coating flush with the wall removing the excess material.

15) Process according to one of claims 1 to 12, wherein said step of coating the electrical resistance is obtained using a tool equipped with two ends, the first of which make a thin and broad cut lifting a film of a certain thickness, whereas the second makes the incision on the wall where the resistance will be housed; then, once the resistance has been inserted, a roller or other suitable tool, by applying the appropriate pressure, takes care of covering the resistance with the lifted film. 16) Process according to one of the previous claims, wherein for said step of protecting the entire spigot joint a shaped plug

(12) is pressed into place that reproduces the inner part of the socket and has one or more through holes where plugs

(13) for the connections shall be inserted. 17) Process according to one of claims 1 to 15, wherein for said step of protecting the entire spigot joint a layer of heat- shrinking film (14) is applied that sticks to the inner walls of the socket with a rim on the entire circumference of the pipe and a closing plug is applied on top; then, plugs for coupling with a gasket are connected onto the connectors of the welder, and then some extendable film ( 15) is wound. 18) Process according to claim 16, wherein said plugs for the connections are fixedly connected to the main plug, and one or more toothed bands ( 16) are also foreseen. 19) Process according to claim 17, wherein said film is fixed with a strip of adhesive or glue.

20) Process according to claim 2 and one of claims 9 to 19, wherein during the thermoforming process an expanding and heating chuck equipped with ready cut ridges (17) is used to make a seat for the insertion of the resistance.

21) Process according to claim 7 and one of claims 9 to 19, wherein during the moulding process, a mould is used with the final shape of the socket that comprises a shaping suitable for producing the seat of the resistance, said method being able to be used both on sockets obtained in one piece with respect to the pipe and on sockets overmoulded on the pipe.

22) Process according to one of claims 1 to 19, wherein a chuck with tool takes care of creating the ridges and the grooves for the insertion of the resistance.

23) Spigot joint provided for jointing with electrofusion comprising a pipe portion (1 ) equipped with belled end (2), inside which an electrical resistance (3) is housed, said electrical resistance being equipped with electric terminals (5) passing through holes (4) formed in said belled end, obtained from pipe in a single body with the process according to at least one of the previous claims.

24) Spigot joint according to claim 23, wherein said electrical resistance is a constantan alloy, or else a shape memory alloy.

25) Spigot joint according to claim 23, comprising at least one additional connecter with the function of a resistivity corrector, arranged between the connectors of the welder and the connecters of the joint (5). 26) Spigot joint according to claim 24 or 25, wherein said holes for the passage of the electrical connections of the resistance comprise a first wider part to allow the insertion of the connecter of the welder, and a second smaller part in which a male connecter equipped with a finned tail or, alternatively, a circular female connector is inserted. 27) Joint according to claim 26, wherein said connecter has a through hole where the wire of the resistance is inserted and it is clamped at the top with a weld.

28) Joint according to one of claims 23 to 27, wherein said socket is equipped with an outer coating to prevent or limit deformations.

29) Joint according to claim 28, wherein said coating is a coil inserted into an indentation and fixedly connected to the socket itself. 30) Joint according to claim 28, wherein said coating is a band of plastic material containing glass fibres of substantial length, aligned in the direction of extrusion.

31 ) Joint according to one of claims 23 to 30, characterised by the application and by the use of at least one microchip and/or an MEMS, either in rolls or in rods.

32) Joint according to one of claims 23 to 31 , wherein the thickness of the fitting portion C between the pipe and the socket is greater than the thickness of the pipe.

33) Joint according to one of claims 23 to 32, wherein the angle Rl is within the range of 0.09-0.35 degrees per mm of the outer diameter of the pipe.

34) Pipe (19) to be coupled with the spigot joint according to one of claims 23 to 33, characterised by a differentiated thickness, in particular with a greater thickness in the coupling area with the spigot joint. 35) Pipe according to claim 34, characterised by the application and by the use of a microchip, either in rolls or in rods.

36) Device for the management and the welding by electrofusion of a spigot joint according to one of claims 23 to 33 with a pipe according to claim 34 to 35, comprising a welding machine and equipped with a gps-sis module and connect card module, integrated or connected to it for data transmissions in gsm, umts, and in any case wireless mode and with the possibility of receiving data from microchips. 37) Electromagnetic induction welding process, able to be used with or without a conventional resistance.

38) Welding process according to claim 37, wherein, without a conventional resistance at the joint, a compound made up of the raw materials of the joint and of ferro-magnetic fillers is added according to any method.

39) Welding process according to claim 37, wherein in the case in which a conventional electrical resistance has been installed, electromagnetic wave receivers, possibly equipped with microchips fitted with temperature sensors, are applied to the connecters.

40) Spigot joint according to one of claims 23 to 33 and pipe according to claim 34 or 35, characterised in that it is visibly marked for identification of the roundness tolerance class, through a suitable marker. 41 ) Process for recording the roundness of a spigot joint according to one of claims 23 to 31 and/or of a pipe according to claim 34 or 35 through station for recording roundness.

42) Process according to claim 41 , wherein said station for recording roundness is combined with the various socket formation systems.

43) Welding process of a spigot joint according to one of claims 23 to 33 and/or of a pipe according to claim 34 or 35 characterised in that it is fractioned into a first step, in which the resistances are taken to a certain temperature for a certain period of time, according to the size of the diameter and of the thickness, and in a second step in which the material is made to melt.

44) Welding process according to claim 40, wherein during the process voltage ramps are used that are very flexible in terms of the voltage values and time.

45) Process for the insertion of a spigot joint according to one of claims 23 to 33 and/or of a pipe according to claim 34 or 35 to a defined depth, characterised by a marking over the entire circumference of the pipe that defines the insertion depth, carried out through a rotary marker that can be integrated as a function in the marker for alignment of the oval shapes according to claim 31 or else be independent from it. 46) Process for the peeling of the surfaces to be welded of a spigot joint according to one of claims 23 to 33 and/or of a pipe according to claim 34 or 35 characterised by a marking with triangular or other shaped incisions, or with alphanumerics so as to cover most of the surface of the 5 depth of the peeling, carried out through rotary markers, suitably modified to ensure the incision depth in the oval- shaped points, which can be integrated as a function in the marker for alignment of the oval shapes and of the insertion depth or else it can be independent.

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