Technical field The present invention relates generally to the sector of gardening, leisure activities and civil and industrial plant engineering and in particular concerns a method for sealingly coupling unions to pipes made of plastic so as to produce hydraulically sealed pipe/union assemblies.

A further aspect of the invention relates to a pipe/union assembly which is sealingly coupled using the abovementioned method.

Background art In the abovementioned technological sectors very frequently there exists the need to connect a pump, a valve, a tap or a manifold to other utilities such as an irrigator, a nozzle, a distributor or similar accessories provided with an inlet and an outlet.

In order to perform this connection the user must have an assembly essentially consisting of a pipe provided with one or more end unions made of relatively rigid material. The pipe may be of the rigid, semi-rigid or flexible type. In this latter case it may be uniform, reinforced with a spiral of semi-rigid plastic material and optionally have a smooth external surface.

The unions are normally provided with internal or external threads or, alternatively, may also have other coupling devices, for example of the expansion or snap- engagement type, for connection to corresponding devices.

Some methods for performing the connections between pipes and unions are

widely known. One of these methods envisages the use of an ordinary metal pipe- clamping band which may be tightened by means of a screw or other similar device. Although this solution has the advantage that it is simple and can be easily disassembled, it is unreliable, not cost-effective and aesthetically unsatisfactory since it projects visibly from the profile of the pipe and the union and may therefore easily come loose or be dangerous for the user.

In place of the band it is possible to use other clamping devices such as, for example, rings, bevel gear pairs, annular arrangements, etc. , as for example illustrated in US-A-5, 580,100, US-A-5, 028,078, US-A-3, 751,075, EP-A-1103752, EP-A-940620, EP-A-410843, WO-A-97/42442.

Another method envisages forming of the union of plastic material directly on the pipe by means of a press or a special mould. Examples of these methods and assemblies are illustrated in US-A-5,775, 740, US-A-3,977, 708, EP-A-599316 and EP-A-440566.

This method has the disadvantage that it requires a special mould for each type and diameter of the pipe and unions and is therefore somewhat costly and inflexible.

Yet another method envisages bonding together the pipe and the union on the outside or the inside thereof by means of special adhesives, as described in DE-A- 19906015, DE-A-19927431, DE-A-4339479andWO01/21996.

This method has the disadvantage that it requires unions with relatively small machining tolerances in order to ensure optimum adhesion of the components to be bonded, with negative effects from a purely economic point of view.

Disclosure of the invention A primary object of the present invention is that of overcoming the

abovementioned drawbacks by providing a method for coupling a pipe and a union made of plastic materials, which has the characteristics of high efficiency, reliability, ease of manufacture, low cost and aesthetic appeal.

A particular object is that of developing a coupling method which can be performed using standard equipment and materials which can be easily found commercially, without requiring complex and specific machines.

Another particular object is that of designing a pipe/union assembly made of plastic materials with the characteristics of an optimum hydraulic seal, reliability and aesthetic appeal.

These objects together with others, which will appear more clearly below, are achieved by a method for coupling a pipe and a union made of thermoplastic material, comprising, in accordance with Claim 1, the steps of formation of a first element consisting of a pipe end section made of plastic material with a predetermined external diameter, formation of a second element consisting of a union made of substantially tubular plastic material with a substantially cylindrical or slightly conical internal wall having an internal diameter smaller than the external diameter of the pipe, alignment of said first and second elements along a longitudinal axis, relative rotation about said axis and axial mutual compression of said elements so as to generate heat as a result of friction and cause melting of the zone of mutual contact, and stoppage of relative rotation of said first and said second element in order to cool the melting zone, causing solidification of the plastic material, so as to produce a hydraulically sealed joint between of the two elements.

According to a further aspect of the invention, the latter envisages a pipe/union assembly which is made of plastic material and which, in accordance with Claim 15, comprises a pipe section made of plastic material and having a constant diameter and end sections and a union which is also made of plastic material and coupled to at least one of said end sections, characterized in that said union has a

tubular portion having an internal surface which is substantially cylindrical or has a slight conicity, with a mean diameter which is smaller than the external diameter of the corresponding end section, said end section being inserted inside said tubular portion of the union and being uniformly coupled to its internal surface by means of frictional melting following relative rotation in the zone of mutual contact, so as to produce a hydraulically sealed joint in this zone.

Brief description of the drawings Further characteristic features and advantages of the invention will be more clearly understood from to the following description of certain preferred, but not exclusive embodiments of a method for coupling a pipe and a union in a hydraulically sealed manner and pipe/union assembly made using the abovementioned method, which are illustrated by way of a non-limiting example with the aid of the accompanying drawings in which: FIG. 1 shows a perspective view of a general embodiment of a pipe/union assembly according to the invention before assembly thereof; FIG. 2 shows a perspective view of the assembly according to Fig. 1, completely assembled; FIG. 3 shows a partially sectioned view of a first embodiment of the assembly according to Fig. 1; FIG. 4 shows the assembly according to Fig. 3, completely assembled ; FIG. 5 shows a partially sectioned view of a second embodiment of the assembly according to Fig. 1; FIG. 6 shows the assembly according to Fig. 5, completely assembled.

Detailed description of the preferred embodiments) In the said figures the same reference numbers will be used to identify identical or corresponding structural elements of the different embodiments.

With specific reference to Figs. 1 and 2, these show a sealed assembly according

to the invention, denoted in its entirety by the reference number 1 and essentially consisting of a pipe section T made of plastic materials with end unions 4,5 also made of plastic materials.

The coupling method according to the invention is described below with reference to both ends of the pipe T, although it is obvious that it may be applied to only one of these ends.

The method envisages a step a) involving formation, in the pipe section T made of plastic material, for example PVC, of a first element consisting of at least one of the end sections 2,3 cut at a right angle.

Then, it is envisaged forming a second element consisting of at least one of the end unions 4,5, also made of material which is plastic, but relatively more rigid, for example rigid PVC.

In particular, the union 4 is formed with a substantially tubular portion 6 having an internal surface 7 which is substantially cylindrical with a constant diameter DR which is smaller, by a few tenths, for example 0 to 0.3 mm, than the external diameter DT of the pipe T.

The union 4 also has an externally threaded end portion 8 for connection to a pump, a valve, a tap or any other accessory.

Similarly, the other union 5 will also be formed so as to have a tubular portion 9 with a substantially cylindrical internal surface 10 having a constant diameter DR<DT and an externally threaded end portion 11 coupled, by means of a ring nut 12, to an internally threaded connecting ring 13.

Obviously, apart from the tubular portions, the unions 4,5 may also have other forms without thereby departing from the scope of the invention.

Preferably, both the tubular portions 6,9 of the unions 4,5 are provided with end chamfers 14,15 in order to favour the insertion of the end sections 2,3.

According to the invention, a step c) involving alignment of each end section/union pair 2,4 and 3,5 along a longitudinal axis L is envisaged.

At this point, a step d) involving relative rotation about the axis L and simultaneous axial mutual compression of each end section/union pair 2,4 and 3,5 with a force F of predetermined value is envisaged.

As a result of the friction produced between the pairs of elements 2,4 and 3,5, a large amount of heat is generated, resulting in melting of the surface layers of the unions in the zone Z of mutual contact. During this step, as a result of the mutual compression, the melted surface layers of the unions 2,3 and the end sections 4, 5 will interpenetrate and may emerge from the edge of the union 4,5 in the form of a small bead of plastic material.

Finally, it is envisaged stopping e) relative rotation of the end section/union pairs 2, 4 and 3,5 in order to cool the melting zone Z, causing solidification of the plastic material, so as to produce sealed coupling together thereof.

In order to perform the relative rotation, it is possible to rotate and axially lock only one of the elements of each pair and rotationally lock and compress the other element.

In particular, it was preferred to rotationally lock and compress each end section 2, 3 and cause rotation, axially locking each union 4,5 by means of suitable apparatus.

Advantageously, the speed of relative rotation co and the compressive mutual force F of the unions 4,5 and the end sections 2,3 is such that melting of the zone of mutual contact Z occurs in a predetermined time period tf.

For technical and production-related reasons, it was ascertained that the optimum time tf is between for example 2 and 10 seconds and is preferably close to 5 seconds. In this way, the plastic material of the two elements is allowed to interpenetrate and to bond together so as to ensure a perfect seal.

Good results have been achieved with a speed of rotation eo of between 50 and 1500 revolutions per minute and preferably close to 300 revolutions per minute.

The compressive force F applied during rotation is substantially constant and between 30N and 500N, and is preferably close to 100N.

Advantageously, an annular projection, indicated respectively by 16,17, with an internal diameter dR, less than the external diameter DT of each end section 2,3, is formed on the internal surface 7,10 of each union 4,5. This contact element determines the end of travel of axial displacement of the end sections 2,3 during the rotation of the unions 4,5.

The embodiment illustrated in Figs. 3 and 4 differs from that of the preceding figures essentially in that the internal surface of the tubular portion 6,10 of the unions 4,5 is slightly conical with an angle of conicity a of between 1° and 5° and preferably close to 2°.

Moreover, the pipe T is of the"spiralled"type, namely made of relatively flexible plastic material with a reinforcement made of relatively rigid plastic in the form of a continuous spiral.

By way of a non-limiting example, the plastic materials chosen for each of said elements may be PVC, PUR, EVA, PE, PP, PBT or PET, natural or synthetic rubbers or combinations thereof.

The materials forming the unions and the pipe may be identical or similar so as to

be able to be easily heat-weldable.

Experimentally the apparatus for implementing the method consisted of a simple lathe in which the chuck of the rotating head causes rotation of the unions 4,5 without the possibility of axial displacement and the tailstock locks rotation and allows translation of the end sections 2,3 of the pipe T. The force F on the end sections 2,3 may be exerted manually or by a hydraulic piston which is suitably controlled.

A pipe/union assembly made of plastic material and obtained by means of the method described above comprises a pipe section T made of plastic material with a constant diameter and having end sections 2,3 and one or more unions 4,5 also made of plastic material and coupled to the respective end sections.

Each union 4,5 has a tubular portion 6,9 with an internal surface 7,10 which is substantially cylindrical or has a slight conicity, with a mean diameter DR smaller than the external diameter DT of the corresponding end section 2,3.

Each end section 2,3 is inserted inside the tubular portion 6,9 of the respective union 4,5 and is uniformly coupled to the internal surface 7,10 by means of frictional melting following relative rotation in the zone of mutual contact Z so as to produce in this zone a hydraulically sealed joint.

Preferably, the assembly comprises both the end sections 2,3 coupled to the end unions 4,5.

The pipe T may be of the type comprising a uniform relatively rigid wall or of the "spiralled"type namely a wall which is relatively flexible with a reinforcement in the form of continuous cylindrical spiral.

Advantageously, the tubular portion 6,9 of each union 4,5 may have on its internal surface 7,10 an annular projection 16,17 with an internal diameter dR less

than the external diameter DT of each end section 2,3. Each end section 2,3 is inserted inside the respective tubular portion 6,9 with the longitudinal end of the end section at the end of its travel path against the corresponding annular projection 16,17.

From the above description it is obvious that the method and the assembly according to the invention achieve the predefined objects and particular attention is drawn to the simplicity, reliability, cost-effectiveness and aesthetic appeal of the coupling obtained.

In particular, as a result of the coupling method according to the invention, it is possible to couple pipes T having an external diameter of up to 30 mm with a tolerance of up to 0.3 mm and an external diameter of up to 100 with tolerances of up to 0. 6 mm.

This allows the operations to be simplified and the production costs of the pipes and thus the finished pipe/union assemblies to be reduced.

The instant application is based upon and claims priority of patent application no. VI2001 A000181, filed on 31.08. 2001 in Italy, the disclosure of which is hereby expressly incorporated here in reference thereto.