PAD FOR FORMING END BELLS IN PIPES MADE OF THERMOPLASTIC MATERIAL

Technical field

This invention relates to a pad for forming end bells in pipes made of thermoplastic material.

Background art

For the production of pipes by thermoplastic extrusion designed for making conduits for delivering and/or discharging fluids (used for example in the drainage networks and drinking water distribution networks of building works), belling machines are used for forming an end portion of the pipes into the characteristic “bell” shape. This wider shape is used to connect the pipes in succession with each other which form a conduit. In fact, un unshaped end of a pipe is normally inserted in the bell-shaped end of the adjacent pipe in the conduit. The bell may be cylindrical in shape, designed for simple snap-on couplings with or without gluing, or it may include a seat for an elastomer gasket designed for the hermetic seal of the joint.

The majority of belling machines make the bell with the hot forming process. They are equipped with one or more heating stations to heat the end of the pipe, changing the wall to be shaped into a plastically deformable softened state. Forming equipment then forms, by using a suitable mould, the heated end of the pipe into a bell shape and cools the bell shaped on the mould. The belling machines installed in the extrusion lines comprise an operating head equipped with at least one oven for heating the pipe and a forming device associated with a bench, provided with movement means, on which the pipes to be processed evolve in a continuous cycle. In all the types of belling machines the various pipe elements, consisting of rectilinear pieces, are processed one after another, after having been introduced on the bench of the machine along a direction coinciding with the longitudinal axis of the pipe. After arriving on the bench, they translate transversely to their direction of arrival, with intermittent step-like motion, remaining parallel to each other. During the stops between one step and the next the pipes undergo the individual processing which basically consists in the heating in the oven of the end to be shaped, followed by the forming of the bell. In addition to shaping the bell, cooling of the bell is simultaneous in the same forming station. Both the heating step and the forming step are performed by associating the oven and the device for forming the pipe by means of carriages which, suitably moved, move the oven and the forming device towards and away from the pipe according to the various operating steps.

The machines which make up the extrusion line are designed to process different sizes of pipe falling within a relatively large range of dimensions. Considering the belling machines, different elements must be replaced in the machine with variations in the dimensions of the diameter of the pipe. Amongst these interchangeable elements, the moulds designed to shape the end bell integrated in the pipe are of significant importance.

The process for forming the bell is strongly dependent on the material of the pipe; consequently, the shape of the moulds is also dependent on the material of the pipe. The most commonly used thermoplastic materials in pipe systems are unplasticised polyvinyl chloride (PVC-U), polypropylene (PP) and high-density polyethylene (HDPE). Amongst these, the PVC-U pipes are used in pipe systems for underground drains, in particular for sewer pipes.

Metal moulds shaped in the form of a cylindrical spindle are normally used in the PVC-U pipes for the internal shaping of the bell in the smooth cylindrical shape. These spindles are referred to as smooth pads since the outer surface of the pad reproduces the smooth cylindrical shape of the part of the bell to be coupled, as well as the part of the bell with a smooth conical shape which is joined to the pipe. The smooth pad is inserted in the end of the pipe, already softened by a prior heating and, by mechanical action, or by the simultaneous action of compressed air outside the bell or in a vacuum inside the bell, the end of the pipe adopts the shapes and dimensions of the smooth pad. When the bell is formed and cooled, the smooth pad is extracted from the bell.

It is also known, for the PVC-U pipes, to perform the internal shaping of a bell with gasket using two different techniques for forming the bell: the Rieber system and the mechanical pad system.

With the Rieber system the gasket is preloaded in the mould and, at the end of the belling process, the gasket is integrated in the wall of the bell; therefore irremovable and it can no longer be replaced in the finished bell. In the Rieber system the metal mould has a shape similar to the smooth pad, but it is equipped with a housing for the gasket. The gasket and the relative housing are shaped in such a way that, when the bell is formed and cooled, the pad is extracted from the bell and the gasket remains locked in the bell.

In the mechanical pad system the mould is a metal spindle, also called a mechanical pad, having an outer surface configured for forming the shape of the seat for the gasket in the wall of the bell. For this reason, the gasket will then be inserted in the finished bell and, in any case, the gasket in the bell is removable and replaceable. In short, in the mechanical pad belling system, the end of the pipe, already softened by a prior heating, is inserted in the pad, and by the action of compressed air outside the wall of the pipe, or vacuum inside the wall of the pipe, the end of the pipe adopts the shapes and dimensions of the pad. When the bell is formed and cooled, the pad is extracted from the bell. To allow the extraction of the pad from the bell, the part of the pad reproducing the seat of the gasket comprises expandable inserts which, by means of mechanisms and relative drives, withdraw completely inside the pad body allowing, in the condition of retracted inserts, the extraction of the pad from the bell.

The PVC-U pipes for sewers mainly uses pipes with bells including the gasket seat having a square shape. The bell has a high level of internal dimensional precision which can only be achieved with the mechanical pad technique.

The mechanical pads comprise a tubular body provided, along the lateral surface, with a circumferential opening facing a compartment inside the tubular body. The compartment houses a plurality of metallic sectors, also called inserts, curved externally according to the seat to be made on the pipe. By means of actuators and mechanisms inside the pad, the inserts are moved between two positions: expansion position, wherein the continuity of the metal outer surface of the mould which reproduces the internal shape of the cup is achieved, and contraction position, wherein they disappear completely inside the body of the pad. Amongst the numerous configurations of the mechanisms adopted for moving the inserts, significant ones are described in patent documents EP0052581 ; US4395218; IT1180547; DE2515461 and DE2758188. Currently, the most commonly used insert movement mechanisms are the rotary cam mechanism and the wedge-type mechanism which classify, respectively, the mechanical rotary cam pads and the mechanical wedge pads.

In the rotary cam pad, the movement of the inserts is achieved by several pairs of cams opposite each other and positioned in circular symmetry about the axis of the pad. Each pair of cams is attached to an insert. All the cams are connected, by keys, to a single shaft coaxial with the body of the pad, called the cam shaft. By means of an actuation, the shaft of the cams is rotated to determine two angular positions of the cams, which impose the expansion position and the contraction position of the inserts.

In the wedge-like pad, the “wedge” element is connected to the inserts and, by means of a jack drive and rods for rigid connection to the plunger of the jack, slides coaxially inside the body of the pad, in both directions, without the possibility of relative rotation. The wedge translates between two axial positions which impose, respectively, the expansion position and the contraction position of the inserts.

A common feature of cam pads and wedge pads is the presence of a first plurality of inserts, substantially triangular in cross-section and externally curved according to the seat to be made on the pipe, and a second plurality of inserts, substantially trapezoidal in cross-section, and externally curved like the first, alternated with the previous inserts. The particular shape of the inserts allows, both when expanding and retracting, a mutual sliding of the relative lateral walls which give rise to the so-called phenomenon of self-cleaning of the parts in contact with the inserts. The cam pads are characterised by a geometrical shape of the cams specific for the first plurality of inserts and a geometrical shape of the cams, different from the first, specific for the second plurality of inserts. In mechanical wedge-like pads, such as those described in patent documents EP0052581 , US4395218, IT1180547, the wedge is provided peripherally with a first and second series of equidistant guides which extend along the generatrices of the wedge alternating with each other. The first plurality of inserts is coupled with bilateral constraints to the guides of said first series. The second plurality of inserts is simply resting on the underlying respective guides of said second series.

In both cams and wedge pads the body of the pad is supported by a central load-bearing shaft. The body of the pad is configured in two parts, front and rear, rigidly joined to the load-bearing shaft and separated by the insert compartment. The outer surface of the rear part of the body of the pad shapes the end edge of the bell and the outer surface of the front part shapes the cylindrical part of the bell and the conical part which is joined to the pipe. In the cam pads the load-bearing shaft performs the function of constraining and guiding the inserts and in its longitudinal extension it has a cavity which encloses inside it the rotary movable shaft of the cams, which is coaxial with the load-bearing shaft. In the wedge-like pads the load-bearing shaft performs the function of constraining and guiding the wedge in its translation movement.

In the belling of PVC-U pipes, the formation of the bell at the end of the pipe in the hot state occurs with a thermal state of the end of the pipe inserted in the pad at optimum temperatures of 105°C - 140°C, therefore higher than the vitreous transition temperature of the PVC-U (approximately 80°C), so that the wall of the pipe is plastically deformable. After the inner end of the pipe has adopted the shape of the pad, the bell becomes rigid and dimensionally stable when the temperature of the PVC- U reaches values less than the vitreous transition temperature. In the belling processes, the wall temperature of the bell at the end of cooling is less than 55°C, normally falling within the range of 40°C - 50°C.

The inner geometrical and dimensional precision of the bell necessary for the functionality of the joint is very high; for this reason it is important to limit the spontaneous dimensional contraction of the bell when it is extracted from the pad resulting from the reduction in the specific volume of the material with the lowering of the temperature. In the belling of the PVC-U, the pad is usually sized considering a spontaneous shrinkage of the bell extracted from the pad of 0.35% - 0.45% with respect to the optimum internal dimensions of the bell defined at an ambient temperature of 23°±2°C. The shrinkage corresponds precisely to the volumetric contraction which is determined in the PVC-U with the passage of thermal equilibrium from 45°C - 55°C to 23°C.

Moreover, the diametric contraction of the bell is not uniform in the circumference of the bell, because the thickness of the wall of the pipe produced in extrusion is not uniform. For example, a pipe with nominal external diameter of 110 mm with a nominal minimum wall thickness of 3.2 mm is considered to be compliant and usable when the wall thickness varies in the range of 3.2 mm - 3.7 mm. The variability of the wall thickness causes, during the cooling of the bell extracted from the pad, an ovalisation of the finished bell, which will be greater the greater the thermal jump which the bell extracted from the pad must make in order to reach the ambient temperature. The effect of ovalisation is accentuated if the cooling of the bell being formed on the pad in the belling process is not uniform around the circular extension of the bell. Similarly, if the cooling during belling is not uniform in the longitudinal direction of the bell, the bell extracted from the pad will be deformed conically.

The efficiency of the step of cooling the belling process is a decisive factor for the economic yield of the belling machine since, for the marketing of the belled pipe, certain precisions of the bell are necessary, in terms of shape and dimensions established for the functionality of the bell joint. Moreover, the economic yield potential of the belling machine will be greater the greater is the speed of production of the machine.

As described above, it is important to make the process of cooling the bell being formed uniform in the circular and axial extension of the bell and quick to make the bell compliant with the operating requirements.

The belling systems for forming smooth and Rieber bells use smooth pad moulds without internal mechanisms; it is therefore simple, as well as advantageous, to configure the body of the pad with inner cavities symmetrical relative to the axis of the pad and to circulate cooling liquid in the cavities. Conveniently, the cooling liquid is water mixed with glycol distributed by an autonomous cooling machine connected to the belling machine in a closed circuit, or the hydraulic circuit of the belling machine is connected to a centralised cooling system which is able to serve several machines of the factory for the production of plastic pipes. The symmetrical configuration of the inner chamber of the pad, in which the cooling liquid flows, facilitates a uniform cooling in the circular extension of the bell, which is therefore optimum for minimising the ovalisation of the bell.

In the belling machines, in order to make the cooling step faster, simultaneously with the cooling by conduction by direct contact of the wall of the bell with the cold metal wall of the pad, convective cooling systems are activated, acting on the outer wall of the bell being formed, by means of air and/or water. The air may be ventilated or pre-cooled compressed. In most belling machines with the highest performance levels the external cooling systems by convection have sprinkler-type water distribution or nebulised water with compressed air.

The pads cooled with cooling liquid are suitable for multi-belling machine configurations. During multi-belling, the belling machine picks up the pipes one at a time coming from the extrusion line, and accumulates them in groups of two or more pipes. Groups of several pipes which are transferred and processed in the various stations for heating and formingcooling the belling machine with obvious advantages in terms of quantity of pipes processed over time.

The multi-belling configuration, however, is not favourable for uniform external convective cooling in the circular extension of the bell or equal for all the pipes of the multi-belling group. In effect, in a single cooling chamber which encloses all the pipes of the multi-belling unit, the inner pipes in the multi-belling unit are exposed to convective cooling fluids in a different way to the lateral pipes of the unit. Even with multiple cooling chambers, that is to say, single for each pipe of the multi-belling unit, it is technically difficult to divide the convective flow in the various chambers equally, in particular if the convective flow is totally or partly gaseous.

The cooling of the bell achieved by conduction by the smooth pads set up with circulation of inner cooling water is not affected by the above- mentioned drawback. In effect, in order to limit the effects of ovalisation of the bell and maintain high production capacity values it is sufficient to make the cooling contribution made inside the bell by conduction prevalent with respect to the contribution outside the bell made by convection.

In the mechanical pad belling systems, however, the method for cooling the pad with internal circulation of cooling liquid is prevented by the configuration in expandable sectors as well as by the mechanisms for movement of the inserts which occupy the inner body of the pad. The mode of internal cooling of the mechanical pad occurs by means of compressed air and/or ventilated which enters from the rear part of the pad and then escapes from the front end of the pad. The cooling air is normally preheated in radiators or heat exchangers. The air cooling capacity is considerably less than that of the water, consequently, so as not to penalise the performance of the belling machines, even at the cost of increasing the consumption of compressed air and/or electricity, sophisticated cooling systems have been introduced over time which combine the convective process of cooling the outside of the bell with the internal cooling of the pad by air. These systems, such as those described in patent documents EP0516595; EP0684124 and EP2189268, have proved particularly effective and are widely used in mechanical pad belling machines.

Over time, the technology of heating the end of the pipe has also evolved in terms of speed of the heating step in the belling process, to the point that in the mechanical pad belling systems the limit to the minimum time necessary to perform the belling cycle is determined by the minimum time for cooling the bell being formed on the pad. Shorter times would highlight a progressive overheating of the mechanical pad until exceeding the maximum acceptable temperature for making a bell according to the operating requirements.

This technical limit is particularly critical in the production of PVC-U pipes for sewers characterised by bells with a seat for gaskets with a square shape made with the mechanical pad technique. In effect, in the sector of PVC-U sewer pipes, the pipes with smaller diameters, such as those with outer diameters of 110 mm, 125 mm, 160 mm and 200 mm, are applied and therefore required by the market especially in relatively short lengths, that is to say, the pipes with nominal commercial lengths of 1000 mm and 500 mm plus the bell. For this reason, for the same extrusion speed, the more the pipes are of short length the greater will be, over time, the number of pipes which the belling machine must receive and process. The forming of the bell with mechanical pad guarantees a very high quality of the bell but, with the modern extrusion systems, a single belling machine is not able to support production programs involving small diameter and short pipes.

When compatible with the market demand, less onerous production plans are prepared for the belling where the production of short pipes occurs simultaneously with the production of longer pipes. If even this condition is not sufficient to be dealt with by a single belling machine, two or more belling machines are installed which are independent of each other or two or more belling machines integrated in a single machine where the operating stations of the two or more belling machines are positioned in parallel, but served by a single bench for moving the pipes. Mechanical pad belling machines which are able to work in multi-belling mode would be advantageous, but for the reasons mentioned above, and in particular due to the absence of a system for cooling the inside of the pad with cooling liquid such as to make the inner cooling of the bell more effective than the outer convective cooling of the bell, this possibility of development is excluded according to the current prior art.

Aim of the invention

In this context, the need has been felt of providing a pad for forming end bells made of pipes made of thermoplastic material, in particular PVC-U, which resolves the above-mentioned drawbacks.

An aim of the invention is to provide a pad for forming end bells made of pipes made of thermoplastic material, in particular PVC-U, which reduces the time for cooling the bell being formed compared with conventional mechanical pads, thus increasing the production capacity.

A further aim of the invention is to provide a pad for forming end bells made of pipes made of thermoplastic material, in particular PVC-U, which cools the bell being formed uniformly in the circular extension of the bell, performing mechanical pad-like belling processes in multi-belling mode. Brief description of the drawings

The technical characteristics of the invention are clearly described in the claims below and its advantages are apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate a preferred embodiment of the invention provided merely by way of example without restricting the scope of the inventive concept, and in which:

- Figure 1 illustrates a pipe processed by belling by means of a pad for forming end bells in of pipes made of thermoplastic material according to the invention and a belling machine;

- Figures 2A and 2B illustrate a schematic front and side cross section view, respectively, of a forming pad according to the invention;

- Figure 3 is a schematic cross-section view of the forming pad in Figure 2B, highlighting some details;

- Figures 4A and 4B are cross sections illustrating a schematic representation of a detail of a belling machine and of a PVC-U thermoplastic pipe respectively in a disengaged and engaged condition;

- Figure 5 is a cross-section view of a schematic representation of a belling machine operating on a thermoplastic pipe made of PVC-U;

- Figure 6A is a perspective view of a first embodiment of a forming pad according to the invention;

- Figures 6B and 6C are perspective cross sections showing the embodiment of a forming pad according to the invention illustrated in Figure 6A;

- Figure 6D is a perspective cross-section view of certain details of the forming pad illustrated in Figure 6A;

- Figures 6E and 6F are cross sections showing certain details of the forming pad illustrated in Figure 6A in different operating positions;

- Figure 7A is a perspective view of a second embodiment of a forming pad according to the invention; - Figures 7B and 7C are cross sections showing the embodiment of a forming pad illustrated in Figure 7A;

- Figures 7D and 7E are cross sections showing certain details of the forming pad of Figure 7A in different operating positions;

- Figure 7F shows a detail of the forming pad of Figure 7A;

- Figure 7G shows two cross sections of the detail of the forming pad of Figure 7F;

- Figure 8A is a perspective view of an embodiment of a belling machine;

- Figure 8B is a perspective cross section view of the belling machine illustrated in Figure 8A;

- Figure 9 is a cross section of an embodiment of a belling machine;

- Figure 10 is a cross section of an embodiment of the belling machine;

- Figure 11 is a schematic block diagram of the belling machine.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes a pad for forming end bells in pipes 100 made of thermoplastic material, in particular PVC-U (hereinafter also referred to simply as forming pad 1 or pad 1 ).

Each pipe 100 has a first end 110 intended to be shaped like a bell 101 .

As shown in Figure 1 , the first end 110 of the pipe 100 shaped with a bell 101 has a conical portion 102 connecting the bell 101 and the pipe 100, a portion 103 cylindrical in shape adjacent to the conical portion 102, a further portion 104 cylindrical in shape at the end of the bell 101 and a portion 105 interposed between the cylindrical portions 103 and 104 and configured for housing a gasket.

In other words, as shown in Figure 1 , the portion 105 of the bell 101 is a portion cylindrical in shape with a radius greater than that of the cylindrical portions 103 and 104 in such a way as to define a seat for a gasket. The seat may be, for example, but without limiting the scope of the invention, a seat with a square shape. According to the invention, the mechanical pad 1 comprises a main body 10, which is substantially cylindrical, having a main axis of longitudinal extension X, configured for fitting at least partly the first end 110 of the pipe 100.

The main body 10 has a compartment 4 designed to house a plurality of inserts 3 and means 5 for moving the inserts 3.

In other words, the compartment 4 for containing the inserts 3 is formed in the main body 10 of the pad 1 .

The movement means 5 are configured for moving the inserts 3 between a retracted position P1 , wherein they are positioned at least partly inside the compartment 4, and an expanded position P2, wherein at least a portion of the inserts 3 is positioned outside the compartment 4.

According to an aspect of the invention, the inserts 3 are divided into first inserts 3A and second inserts 3B, alternated with each other and both curved externally.

The main body 10 comprises a front portion 8 and a rear portion 7.

According to the invention, the inserts 3 are interposed between the front portion 8 and the rear portion 7 of the main body 10.

The main body 10 comprises a load-bearing shaft 6 supporting the main body 10 and at least means 5 for moving the inserts 3 which extend parallel to the main axis of longitudinal extension X.

In the accompanying drawings, for a faster understanding, a second axis Y and a third axis Z are further defined perpendicular to each other and perpendicular to the main axis of longitudinal extension X.

According to an aspect of the invention, the rear portion 7 and the front portion 8 of the body of the pad 10 are two separate tubular pieces assembled coaxially to each other through the load-bearing shaft 6 and known locking means 29.

The load-bearing shaft 6 has the contact surfaces 9 configured for mutually fixing the front portion 8 and the rear portion 7. The front portion 8 and the rear portion 7 are assembled so as to form the compartment 4 for containing the inserts 3.

In other words, the front portion 8 and the rear portion 7 have respective surfaces 11 , perpendicular to the main axis of longitudinal extension X and facing each other and the mutual arrangement of said portions 8, 7 defines between the surfaces 11 a circumferential opening having a width suitable for housing the inserts 3, that is to say, the compartment 4. The surfaces

11 are also configured to allow the sliding of the inserts 3 between the retracted position P1 and the expanded position P2.

The front portion 8 of the main body 10 has at least one end element 12 intended to form the conical portion 102 of the first end 110 of the pipe 100.

According to a preferred embodiment, the end element 12 is removably connected to the front portion 8 of the main body 10.

The end element 12 comprises a portion of conical outer surface 13 configured, in use, for determining the conical portion 102 of the first end 110 of the pipe 100.

In other words, the portion of conical outer surface 13 of the end element

12 corresponds to the conical portion 102 of the bell 101 which is connected to the pipe 100.

The end element 12 comprises a conical end nose-piece portion 12A configured to be inserted inside the pipe 100.

It should be noted that the conical nose-piece portion 12A of the end element 12 has a diameter less than the internal diameter of the pipe 100. Advantageously, the end element 12 inserts into the pipe 100 without interference.

Advantageously, the end element 12 is removable relative to the main body 10 since the pipes 100, for the same external diameter and bell, may have different dimensional classes of thickness and consequently different values of internal diameter. For this reason, with changes to the thickness of the pipe 100 being processed, in order to make the bell 101 in the pipe 100 it is not necessary to replace the entire mechanical pad 1 , but it is sufficient to replace the end element 12.

By way of example, in the PVC-U sewer pipes 100 with nominal external diameter of 110 mm there are pipes 100 with nominal minimum thickness of 3.2 mm and 4.0 mm both to be made with a bell 101 equal in shape and internal dimensions. The pad 1 will have two end elements 12: one suitable for forming the pipe 100 with a thickness of 3.2 mm and one suitable for forming the pipe 100 with a thickness of 4.0 mm.

According to the invention, the pad 1 comprises a system 23 for cooling the main body 10.

The cooling system 23 comprises a plurality of conduits 230 for conveying a liquid 80 which extend at least partly in the rear portion 7 of the main body 10, in the front portion 8 of the main body 10 and in the load-bearing shaft 6.

Preferably, the conveying conduits 230 are connected to each other by couplings comprising prior art hermetic sealing elements.

The liquid 80 is, for example, in a non-limiting manner, water or a cooling liquid.

According to a preferred, non-limiting embodiment, the liquid 80 is a solution of water and glycol pressurised at 3 bar - 4 bar thermo-controlled at 8°C - 12°C by a cooling machine outside the pad 1 .

Advantageously, the extension of the conduits 230 for conveying the liquid 80 into the rear portion 7, into the front portion 8 of the body and into the load-bearing shaft 6 allows the liquid 80 to reach various portions of the pad 1 , even with a single circulation through said conveying conduits 230.

According to the invention, the conduits 230 for conveying the liquid 80 comprise at least a first annular chamber 15, made in the rear portion 7 of the main body 10, and a second annular chamber 16, made in the front portion 8 of the main body 10. The first annular chamber 15 and the second annular chamber 16 extend at least partly about the main axis of longitudinal extension X of the main body 10.

According to an aspect of the invention, the main body 10 comprises a lateral wall 14 both in the front portion 8 and in the rear portion 7.

The lateral wall 14 of the main body 10 is configured for delimiting the first annular chamber 15 in the rear portion 7 and the second annular chamber 16 in the front portion 8.

It should be noted that the first chamber 15 and the second annular chamber 16 are positioned on opposite sides of the main body 10 relative to the compartment 4.

The annular chambers 15 and 16 extend in size to enable the movement means 5 of the inserts 3 to be actuated without interference.

According to the invention, the conduits 230 for conveying the liquid 80 comprise at least a delivery conduit 32 and at least a return conduit 35 inside the load-bearing shaft 6 and having a main direction of extension parallel to the main axis of longitudinal extension X of the main body 10.

The delivery conduit 32 is in fluid communication with the first annular chamber 15 and with the second annular chamber 16.

The delivery conduit 35 is in fluid communication with the second annular chamber 16.

Advantageously, the delivery 32 and return 35 conduits extending in the load-bearing shaft 6 allow the fluid communication between at least a part of the conduits 230 positioned in the rear portion 8 and at least a part of the conduits 230 positioned in the front portion 7.

Advantageously, the arrangement of the delivery conduit 32 and of the return conduit 35 inside the load-bearing shaft 6 allows the communication of fluid between the conduits 230 positioned in the rear portion 7 and in the front portion 8 to occur passing beyond, without interference, the compartment 4 for containing the inserts 3 and the movement means 5 of the inserts 3. Preferably, the delivery conduit 32 and the return conduit 35 are parallel to the main axis of longitudinal extension X.

According to an embodiment, the delivery conduit 32 and the return conduit 35 are longitudinal holes made directly in the body of the loadbearing shaft 6, passing through and closed at the ends by a plurality of caps 17.

Advantageously, the delivery conduit 32 and the return conduit 35 made as longitudinal through holes facilitate the cleaning and maintenance of the load-bearing shaft 6 and of the pad 1 .

According to an alternative embodiment, in the case of a hollow loadbearing shaft 6, the delivery conduit 32 and the return conduit 35 can be flexible or rigid conduits inserted inside the cavity of the load-bearing shaft 6.

According to a preferred aspect of the invention, the conduits 230 for conveying the liquid 80 comprise an inlet opening 21 for the liquid 80 in fluid communication with the first annular chamber 15 and an outlet opening 22 for the liquid 80 in fluid communication with the second annular chamber 16.

Preferably, the inlet opening 21 and the outlet opening 22 of the liquid 80 are positioned in the rear portion 7 of the main body 10.

Described below, with reference in particular to Figure 3, is a preferred, non-limiting embodiment of the cooling system 23 and, more specifically, the path followed by the liquid 80 inside the pad 1 by means of a plurality of conduits 230 is defined for conveying the liquid 80 (hereinafter also referred to simply as conduits 230).

The conduits 230 comprise:

- a first channel 30 extending from the inlet opening 21 of the liquid 80 to the first annular chamber 15;

- a second channel 31 extending from the first annular chamber 15 to the delivery conduit 32; - a third channel 33 extending from the delivery conduit 32 to the second annular chamber 16;

- a fourth channel 34 extending from the second annular chamber 16 to the return conduit 35;

- a fifth channel 36 extending from the return conduit 35 to the outlet opening 22 of the liquid 80.

More specifically, the expression “a channel extends from one conduit to another conduit” means that the channel places one conduit in fluid communication with the other conduit.

In other words, this embodiment defines a path for loading and unloading the liquid 80 relative to the first and second annular chambers 15, 16.

With reference in particular to Figure 3, the continuous line of arrows indicates the path for loading the liquid 80 in the annular chambers 15, 16 and the dashed line of arrows indicate the path for discharging the liquid 80 from the annular chambers 15, 16.

The conduits 230 comprise the following small channels inside the loadbearing shaft 6 and transversal to it:

- first transversal channels 37 configured to place the second channel 31 in fluid communication with the delivery conduit 32;

- second transversal channels 38 configured to place the delivery conduit 32 in fluid communication with the third channel 33;

- third transversal channels 39 configured for putting in fluid communication the fourth channel 34 with the return conduit 35;

- fourth transversal channels 40 designed for putting in fluid communication the return conduit 35 with the fifth channel 36.

The first annular chamber 15 has a first hole 41 configured to place the first annular chamber 15 in fluid communication with the second channel 31.

The second annular chamber 16 has a second hole 42 configured for putting in fluid communication the second annular chamber 16 with the fourth channel 34. More specifically, the path of the liquid 80 inside the pad 1 is illustrated by the conduits 230 in the embodiment described.

The liquid 80 supplies the first annular chamber 15 through the first channel 30, in fluid communication with the inlet opening 21 and preferably positioned, in use, at a height lower than the axis X. The liquid 80 fills the first annular chamber 15 up to the level determined by the first hole 41 . Preferably, the first hole 41 is positioned, in use, at the largest possible height above the axis X. In effect, the position in height of the first hole 41 establishes the limit of filling the first annular chamber 15 and for maximising the effectiveness of cooling the pad 1 it is convenient to achieve the maximum filling of the chamber 15. The first hole 41 , through the second channel 31 and the first transversal channels 37 made in the load-bearing shaft 6, transfers the liquid to the delivery conduit 32 intended to convey the liquid 80 to the second annular chamber 16. Consequently, the liquid 80, coming from the first annular chamber 15 flows through the delivery conduit 32 towards the second transversal channels 38, which are connected to the third channel 33. The third channel 33 allows the liquid 80 to flow to the second annular chamber 16 by a connection positioned preferably, in use, at a height lower than the axis X. The second annular chamber 16 has the second outlet hole 42 for the liquid 80 positioned, in use, at the greatest possible height above the axis X, in such a way as to guarantee the maximum filling of the second annular chamber 16. The liquid 80 flowing out of the second annular chamber 16 through the fourth channel 34 and the third transversal channels 39 reaches the return conduit 35. Through the fourth transversal channels 40, the liquid 80 reaches the fifth channel 36, which is connected to the outlet opening 22.

According to an aspect, by means of known elements (pipes and connectors), outside the pad 1 , the inlet opening 21 and the outlet opening 22 are connected to a cooling machine also outside the pad 1 . Advantageously, the liquid 80 circulating in the first and second annular chambers 15, 16 facilitates the transfer of heat by conduction from the walls of the bell 101 to the chambers 15, 16. The transfer of heat, and hence the cooling of the bell 101 , is particularly effective in the cylindrical portions 103 and 104 adjacent to the portion 105 of the bell 101. In effect, the cylindrical portions 103 and 104, being processed for forming the pipe 100, are in contact with the walls of the main body 10 delimiting the annular chambers 15, 16 cooled by the liquid 80 in continuous circulation. According to an aspect of the invention, the cooling system 23 comprises one or more inlet branches 45 for a gaseous fluid 82, extending in the rear portion 7 of the main body 10 starting from inlet openings 451 towards one or more outlet openings 452 leading into the compartment 4, and one or more outlet branches 46 for the gaseous fluid 82, extending in the front portion 8 of the main body 10 starting from inlet openings 461 in communication with the compartment 4 towards one or more outlet openings 28 leading to the outside environment.

In other words, the inlet branches 45 convey the gaseous fluid 82, through the inlet openings 451 of the inlet branches 45, to the compartment 4, through the outlet openings 452 of the inlet branches 45.

Similarly, the outlet branches 46 convey the gaseous fluid 82 from the compartment 4, through the inlet openings 461 of the outlet branches 46, to the outside environment, through the outlet openings 28.

Advantageously, the gaseous fluid 82, conveyed by the inlet and outlet branches 45, 46, allows the areas of the pad 1 in which it circulates to be cooled.

According to an aspect of the invention, the outlet openings 452 of the inlet branches 45 of the gaseous fluid 82 are configured for dispensing the gaseous fluid 82 on a portion of surface 47 of the first annular chamber 15 which faces the compartment 4.

The inlet branches 45 have openings 18 configured for conveying the gaseous fluid 82 towards the surface portion 47 of the first annular chamber 15.

Advantageously, by means of the outlet openings 452, the gaseous fluid 82 cools the compartment 4 and the inserts 3 which it houses.

Advantageously, dispensing the gaseous fluid 82 on a portion of surface 47 of the first annular chamber 15 allows the gaseous fluid 82 to touch the first annular chamber 15. For this reason, the gaseous fluid 82 is cooled by the contact with the surface 47 of the first annular chamber 15, inside of which flows the liquid 80.

According to an aspect of the invention, the inlet openings 461 of the outlet branches 46 of the gaseous fluid 82 are configured for conveying the gaseous fluid 82 onto a portion of surface 48 of the second annular chamber 16 which faces the compartment 4.

The outlet branches 46 have openings 19 configured for conveying the gaseous fluid 82 towards the portion of surface 48 of the second annular chamber 16.

Advantageously, conveying the gaseous fluid 82 on a portion of surface 48 of the second annular chamber 16 allows the gaseous fluid 82 to touch the second annular chamber 16. For this reason, the gaseous fluid 82 is cooled by contact with the surface 48 of the second annular chamber 16, inside of which the liquid 80 flows.

According to an aspect, the inlet and outlet branches 45, 46 comprise elements 84 for conveying the gaseous fluid 82 configured for favouring the contact between the gaseous fluid 82 and, respectively, the portions of surfaces 47, 48 of the first and second annular chambers 15, 16.

The branches 46 for the gaseous fluid 82 have a gap 490 configured for conveying the gaseous fluid 82 on an inner surface 49 of a portion of the end element 12 designed to form the conical portion 102 of the first end 110 of the pipe 100.

In other words, the outlet branches 46, through the gap 490, are configured so that the gaseous fluid 82 touches the inner surface 49 of the end element 12. Advantageously, the gaseous fluid 82 which touches the inner surface 49 of the end element 12 allows its cooling.

The outlet openings 28 of the outlet branches 46 for the gaseous fluid 82 are positioned on an end wall 120 of the end element 12 perpendicular to the main axis of longitudinal extension X of the main body 10.

Advantageously, the outlet openings 28 located on an end wall 120 of the end element 12 allow the gaseous fluid 82 to touch as much as possible the surface 49 of the end element 12 and therefore maximise the cooling of the end element 12.

It should be noted that, advantageously, the embodiment of the pad 1 comprising the presence of both the plurality of conduits 230 for conveying the liquid 80, in particular the annular chambers 15, 16, and the inlet and outlet branches 45, 46 which convey the gaseous fluid 82 to touch the annular chambers 15, 16, allows an optimisation of the cooling of the pad 1 , substantially in all the portions which make up the pad 1 .

Basically, as described, the cooling system 23 is configured to circulate the gaseous fluid 82 inside the pad 1 in such a way that it touches: the surface portion 47 of the first annular chamber 15, the surfaces of the inserts 3 inside the compartment 4, the surface portion 48 of the second annular chamber 16 and the inside surface 49 of a portion of the end element 12. For this reason, the gaseous fluid 82 cools the inserts 3 and the end element 12 previously touching the first and second annular chambers 15, 16, respectively. The pad 1 comprises inside it a heat exchanger system so as to cool the gaseous fluid 82 before the gaseous fluid 82 cools down elements of the pad 1 , in particular the inserts 3 and the end element 12.

Advantageously, the cooling system 23 of the pad 1 makes it possible to optimise, render uniform and speed up the cooling of the pad 1 .

A uniform cooling of the pad 1 , optimised and speeded up, results in improved productivity. The invention also defines a belling machine 200 for pipes 100 made of thermoplastic material, in particular PVC-U, each of which has the first end 110 intended to be shaped in the form of a bell 101 .

The belling machine 200 comprises a belling station 202 comprising the pad 1 .

According to an embodiment, the belling machine 200 comprises a bell forming unit 20 configured to achieve the fluid pressure action on the outer wall of the pipe 100, towards a lateral surface 2 of the main body 10 of the pad 1 , and forming it into the shape of a bell 101 , as illustrated in Figure 4B.

More specifically, the forming unit 20 forms a hermetic container of pressurised air having the function of shaping the heated and softened end of the pipe 100 against the lateral surface 2 of the pad 1 to form the bell 101.

The bell forming unit 20 comprises a forming chamber 43, a plurality of clamps 58 for locking the pipe 100, half-flanges 59 applied to the locking clamps 58 and a flange 67 movable relative to the pad 1 and connected telescopically to the forming chamber 43 by means of compression springs.

The forming chamber 43 comprises an elastomer gasket 57 which adheres to the outer wall of the pipe 100 and, in the front, to the flat surfaces of the half-flanges 59.

According to the invention, the belling machine 200 comprises a cooling chamber 203 configured for cooling the first end 110 of the pipe 100 and for housing inside it, at least partly, the forming pad 1 .

The belling machine 200 comprises means 25 for dispensing a fluid 81 comprising a gaseous part 82 and a liquid part 83 in the cooling chamber 203 configured for dispensing the fluid 81 on the first end 110 of the pipe 100 at least partly fitted by the forming pad 1 .

More specifically, the dispensing means 25 dispense a convective cooling flow outside the bell 101 of the pipe 100. According to a preferred embodiment, the dispensing means 25 comprise a plurality of nozzles configured for diffusing the fluid 81 , comprising the gaseous part 82 and the liquid part 83, on the first end 110 of the pipe 100 shaped like a bell 101 for optimising the convective cooling of the bell. Preferably, the dispensing means 25 are fixed to the flange 67.

With reference to Figure 5, in the most advanced prior art configuration, as indicated in document EP2189268, the convective flow for cooling the outside of the bell is achieved with a fluid 81 of compressed air 82 and finely nebulised water 83.

The belling machine 200 comprises a channel 24 for introducing into the cooling chamber 203 of the fluid 81 pre-cooled by known external means.

According to the invention, the belling station 202 comprises a conduit 26 for discharging the fluid 81 comprising a gaseous part 82 and a liquid part 83 flowing out from the cooling chamber 203.

In other words, the flow of the liquid 81 , after having impacted and cooled the bell 101 , escapes from the cooling chamber 203 through the discharge channel 26.

According to the invention, the belling station 202 comprises a separator 205 configured for separating from the fluid 81 flowing out from the cooling chamber 203 the gaseous part 82 from the liquid part 83.

The discharge conduit 26 is configured for conveying the fluid 81 comprising a gaseous part 82 and a liquid part 83 towards the separator 205.

The separated liquid part 83 is discharged outside the belling station 202 by known means.

It should be noted that it is known that the gaseous part 82, also after the action of the separator 205, remains moist.

According to the invention, the belling station 202 comprises a source 204 of gaseous fluid 82 under pressure in fluid communication with the inlet openings 451 of the inlet branches 45 for the gaseous fluid 82 of the forming pad 1 . According to an aspect of the invention, the separator 205 is in fluid communication with the source 204 of pressurised gaseous fluid 82 and is configured for supplying the gaseous part 82 of the fluid 81 to the source 204 of pressurised gaseous fluid 82.

According to an aspect of the invention, the belling machine 200 comprises an inlet conduit 27 extending between the source 204 of pressurised gaseous fluid 82 and the inlet branch 45 of the gaseous fluid 82 in the pad 1 .

Preferably, the inlet conduit 27 extends adjacent to the surface of the first annular chamber 15.

More specifically, the belling machine 200 is configured for conveying the gaseous fluid 82, still moist and cold, inside the pad 1 through the inlet conduit 27. According to the embodiment of the pad 1 described above, the moist gaseous fluid 82 passes through the inside of the pad 1 and leads into the outside environment through the outlet openings 28 positioned on the end wall 120 of the end element 12.

Advantageously, the belling machine 200 can recover at least part of the convective cooling flow which has performed the outer cooling of the bell 101 , that is to say, it can recover at least part of the fluid 81 .

It should be noted that, as described, this embodiment is not exclusive and the source 204 may introduce gaseous fluid 82 into the pad 1 , through the inlet openings 451 , even without the gaseous fluid 82 being recovered, partly or totally, starting from the fluid 81 for cooling the outside of the bell 101.

According to a preferred embodiment, the belling station 202 comprises a pair of forming pads 1 for simultaneously belling two pipes 100 at a time, thereby defining a double belling operating mode.

This embodiment can be configured in a first configuration and in a second configuration.

The first configuration comprises a single cooling 203 and/or forming 43 chamber which houses at least partly the two forming pads 1 . The second configuration comprises two cooling 203 and/or forming 43 chambers, each of which houses at least partly a forming pad 1 .

In both configurations the padsl are positioned parallel to each other in such a way as to define a centre-to-centre distance D between the two pads 1. It is convenient to set a centre-to-centre value D as small as possible. In effect, the greater the centre-to-centre distance D the greater will be the transversal dimensions of the belling machine 200 and the dimensions of the belling apparatuses with consequent penalties in terms of longer time necessary for moving the pipes 100 from one work station to another and longer time necessary for moving the belling apparatuses.

In the first configuration, with a single cooling chamber 203, the minimum value of D is conditioned by the evident need to avoid contact between the two bells 101 and/or by the dimensions of the mechanical pad 1 , but also by the need not to adversely affect the cooling uniformity. In effect, the convective cooling flow coming from the dispensing means 25 of the cooling chamber 203 is different and less intense than that which occurs in the opposite lateral zones of the two bells 101 being formed opposite each other. In other words, the two bells 101 , relative to the convective flow distributed by the dispensing means 25, are shielded from each other. This negative effect of non-uniformity of the cooling is progressively less the greater the value of D. With the increase in the value of D the size of the cooling chamber 203 also increases with penalisation in terms of increase in the time necessary for its pressurising and depressurising, as well as increasing the consumption of pressurised air. The pad 1 for the particular cooling system 23 inside the pad 1 with liquid 80 attenuates the above- mentioned negative effect.

In the second configuration, with two cooling chambers 203, the phenomenon of non-uniformity of cooling of the bells 101 due to the mutual screening of the two bells 101 to the convective flow does not exist, since each pad 1 is housed in its own cooling chamber 203. In this configuration the phenomenon of non-uniformity of cooling of the bell 101 is in any case present, since it is technically difficult to divide in an equal fashion the convective flow of fluid 81 in the two cooling chambers 203. The pad 1 for the particular cooling system 23 inside the pad 1 with liquid 80 attenuates the above-mentioned negative effect. On the other hand, in the second configuration the minimum value D which can be achieved is equal to the transversal dimensions of the forming 43 and/or cooling 203 chamber and mechanical pad 1 assembly which can be obtained with an arrangement of the cooling chambers 203 adjacent to each other as well as parallel, as illustrated in Figure 10.

Experimentally, in order to obtain the advantages of economic yield for a higher productivity which can be achieved by processing in double belling compared with the single belling, it has been evaluated that in the production of PVC-U sewer pipes 100 with bell 101 having a sealing seat, defined as “de” the value in mm of the external diameter of the pipe being processed and “s” the value in mm the wall thickness of the pipe, the value in mm of centre-to-centre distance D must comply with the condition D < DI, where

DI = [2 + f]de with f = [2.125-0.0416(de/s)].

This means that the value in mm of centre-to-centre distance D must comply with the condition

D < [4.125-0.416 (de/s)]de.

Due to the features of the mechanical pad 1 according to the invention, in especially of the particular internal cooling system 23 of the pad 1 and the transversal size of the pad 1 , which is always equal to or not greater than that of the prior art mechanical pads, both in the first configuration and in the second configuration, the condition D < DI is generally satisfied. In particular, in the second configuration it is convenient to adopt as a value of D the value of the transversal dimensions of the assembly composed of the forming 43 and/or cooling 203 chamber and the mechanical pad 1 , as illustrated in Figure 10. With reference to the production capacity of the belling machine 200, the consumption of pressurised air for the forming and the consumption of liquid 80 for cooling the outside of the bell 110, the second configuration is more advantageous than the first configuration, since it allows a sizing of the cooling chamber 203 such that the sum of the inner volumes of the two cooling chambers 203 of the second configuration is less than that of the single cooling chamber 203 according to the first configuration.

In short, this embodiment of the belling machine 200 allows two pads 1 to be cooled simultaneously as if they were single and therefore speed up the process for making the bells 101 .

The simultaneous cooling of the two pads 1 allows the productivity to be increased as it potentially allows twice the number of pipes 100 to be processed in the same period of time.

These advantages are more evident in cases of short pipes 100. In effect, the extrusion of the pipe 100 made from thermoplastic material occurs at predetermined extrusion speed and therefore cutting short pipes 100 requires the processing of a greater number of pieces compared with any longer pipes 100 cut from an extruded pipe 100 at the same speed. Speeding up the cooling implies the possibility of not reducing the extrusion speed and, consequently, of keeping the productivity at an optimum level.

According to an embodiment, the source 204 of gaseous fluid 82 under pressure is in fluid communication with the inlet openings 451 of the inlet branch 45 of the gaseous fluid 82 of the respective forming pads 1 .

In other words, the source 204 of gaseous fluid 82 under pressure is the same for both the pads 1 .

According to an embodiment, the discharge conduits 26 of the respective cooling chambers 203 are configured for conveying the fluid 81 comprising a gaseous part 82 and a liquid part 83 towards the same separator 205. In other words, the separator 205 is the same for both the pads 1 .

According to a preferred embodiment, the belling machine 200 comprises one or more heating stations 201 , positioned upstream of the single belling station 202 according to a feed direction V for processing the pipes 100, as illustrated in Figure 11 .

Each heating station 201 comprises a single oven 206 configured for heating the ends 110 of a pair of pipes 100.

In other words, the belling machine 200 has in the heating stations a single oven 206 for the two ends 110 of two pipes 100.

Example embodiments for the forming pad 1 are described below. The examples refer to pads 1 intended to form end bells with gasket seat in PVC-U sewer pipes with external diameter of 110 mm and nominal wall thickness of 3.2 mm.

Preferably, the pad 1 is a mechanical pad.

According to an embodiment, illustrated in Figures 6A to 6F, the means 5 for moving the inserts 3 comprise a wedge-like mechanism 50.

Figures 8A and 8B illustrate the pad 1 with wedge 50 positioned inside the forming chamber 43 dimensionally optimised and specific for the size of the pipe 100 to be belled.

In the pad 1 with wedge 50, the load-bearing shaft 6 has the shape of a cylindrical bar and is configured to support the main body 10, the wedge 50 and the inserts 3. The load-bearing shaft 6 is also a guide for the sliding of the wedge 50.

The wedge 50 comprises a pair of sliding bushings 51 which engage in the load-bearing shaft 6.

In short, the means 5 for moving the inserts 3 in the pad 1 shaped like a wedge 50 consist of the wedge elements 50 and bushings 51 .

The pad 1 comprises a jack 60 screwed to the rear portion 7 of the main body 10, a plunger 62 of the jack 60 and a pair of rods 61 , passing through the rear portion 7 of the main body 10 which rigidly connects the wedge 50 to the plunger 62. The jack 60 is a linear actuator which controls the translation movement of the wedge 50 which moves the inserts 3 between the retracted position P1 and the expanded position P2.

The stroke of the jack 60, which corresponds to the operating stroke of the wedge 50, is labelled C in Figure 6C.

The two rods 61 are configured to prevent rotation of the wedge 50 about the load-bearing shaft 6 and therefore rotation of the wedge 50 and inserts 3 about the axis X.

According to an example embodiment of the pad 1 shaped like a wedge 50, the load-bearing shaft 6 is solid and has an external diameter dimension of 20 mm. The delivery conduits 32 and the return conduits 35 which allow communication, during the circulation of the liquid 80, between the rear portion 7 and the front portion 8 of the main body 10 are made as through holes, parallel, symmetrical relative to the axis X and with a diameter of 5 mm. The holes are closed at the ends with caps 17 fitted with rubber sealing elements.

The delivery conduit 32 is intercepted by the first and second transversal channels 37, 38.

The return conduit 35 is intercepted by the third and fourth transversal channels 39, 40.

The delivery conduit 32 and the return conduit 35 form a passage section sufficient to maintain a minimum flow rate of the liquid 80 circulating in the pad 1 in the order of 6 - 8 lit/min. This flow rate is sustainable by conventional industrial chillers and sufficient to achieve an effect for reducing the time of the step for cooling the bell 101 which, compared with conventional air-cooled mechanical pads, allows an increase in productivity of the belling machine 200, relative to the PVC-U sewer pipe with outside diameter of 110 mm and nominal wall thickness of 3.2 mm, of greater than 15%.

The first annular chamber 15 is extended beyond the position that the larger base of the wedge 50 reaches in the conditions of inserts 3 in the retracted position P1 and the longitudinal length value of the rear chamber Lc is greater than the operating stroke C of the wedge 50. This configuration increases the heat exchange surface and therefore increases the intensity of the cooling of the bell 101 .

The belling machine 200, comprising the pad 1 with wedge 50, comprises an electromechanical device configured for signalling to an electrical control unit of the belling machine 200 the position of the sectors 3. The device is located directly in the jack 60 for actuating the wedge 50 by means of sensors applied to the jacket of the jack 60. These sensors can be activated by a magnetic ring integrated in the plunger 62.

In the example illustrated in the accompanying drawings, the device is applied outside the cradle of the jack 60 by means of a metal pin 52 with a mushroom-shaped head the axis of which, preferably, coincides with the axis X of the pad 1 . The pin 52 is slidable in an axial direction and held in the rest position by axial contact achieved by a compression spring 53. At the end opposite the head of the mushroom, the pin 52 is connected to a metal element 63 outside the jack 60. In the rest position, the head of the mushroom-shaped pin 52 is located inside the chamber 64 of the jack 60. With the plunger 62 in the rear end of stroke position, an axial movement of the pin 52 is made such that the metal element 63 activates a proximity sensor 54 outside the jack 60. The proximity sensor 54 signals to the electrical command and control unit of the belling machine 200 the retracted position P1 of the inserts 3. With the plunger 62 in the forward end of stroke position, the pin 52, by means of the compression spring 53, returns to the rest position and the proximity sensor 54, deactivated, signals the condition of inserts 3 in the expanded position P2.

According to an embodiment, illustrated in Figures 7A to 7G, the means 5 for moving the inserts 3 comprise a cam mechanism 55.

Figure 9 shows the pad 1 with cams 55 integrated with a flange 68 fixed to the pad. The pad 1 is positioned inside the forming chamber 69. The forming chamber 69 is intended to operate with pads of different sizes, that is to say, pads intended to bell pipes of different sizes and larger than those with an outer diameter of 110 mm.

The load-bearing shaft 6 is hollow in the pad 1 with cam 55. In this cavity, the shaft of the cams 70 is coaxial with the load-bearing shaft 6.

The pad 1 comprises two annular elements, a rear element 71 and a front element 72, opposite each other relative to the compartment 4, and keys 56 configured for connecting the shaft of the cams 70 to the annular elements 71 and 72.

The annular elements 71 and 72 are substantially flanges specular relative to the inserts 3.

The elements 71 and 72 have the same longitudinal dimension B and the cams 55 are made in these elements. For this reason, the rotation of the shaft of the cams 70, by means of the keys 56, performs the rotation movement of the annular elements 71 and 72 and consequently the radial translation movement of the inserts 3.

The pairs of cams 55 made in the annular elements 71 and 72 have the same shape and size, but are opposite each other.

In short, the means 5 for moving the inserts 3 in the pad 1 with a cam 55 comprise the annular elements 71 and 72 of the cams 55 and the keys 56. The pad 1 comprises an actuator 65, preferably installed and already integrated in the belling machine 200, configured for controlling the rotation of the shaft of the cams 70.

The actuator 65 comprises a coupling 66 by which it is connected to the shaft of the cams 70.

More specifically, unlike the pad 1 with wedge 50, the pads 1 with cam 55 engage with a shared actuator 65 for moving the inserts 3 already present in the belling machine 200.

According to an example embodiment of the pad 1 with pad 55, pad 1 again intended to form end bells 101 with gasket seat in PVC-U sewer pipes with outside diameter of 110 mm and nominal wall thickness of 3.2 mm, the outside diameter of the load-bearing shaft 6 is 42 mm. The diameter of the cavity is 19 mm. The delivery conduits 32 and return conduits 35 which allow the communication between the rear portion 7 and the front portion 8 of the main body 10 are made in the most peripheral zone of the load-bearing shaft 6 and are made as through holes, parallel, symmetrical to the axis X and with a diameter of 5 mm. These holes are closed at the ends with threaded caps 17 with a hermetic seal.

The delivery conduit 32 is intercepted by the first and second transversal channels 37, 38.

The return conduit 35 is intercepted by the third and fourth transversal channels 39, 40.

The delivery conduit 32 and the return conduit 35 form a passage section sufficient to maintain a minimum flow rate of the liquid 80 circulating in the pad 1 in the order of 6 - 8 lit/min. This flow rate is sustainable by conventional industrial chillers and sufficient to achieve an effect for reducing the time of the step for cooling the bell 101 which, compared with conventional air-cooled mechanical pads, allows an increase in productivity of the belling machine 200, relative to the PVC-U sewer pipe with diameter of 110 mm and nominal wall thickness of 3.2 mm, of greater than 15%.

The first annular chamber 15 is extended beyond the position of the element 71 and the longitudinal length value of the rear chamber Lc is greater than the longitudinal extension B of the element 71. This configuration increases the heat exchange surface and therefore increases the intensity of the cooling of the bell 101 .

It should be noted that the shape of the outer surface of the annular elements 71 and 72 is made to perform the function of conveyor 84 of the gaseous fluid 82 for touching the surfaces of the first and second annular chambers 15, 16.

The belling machine 200, comprising the pad 1 with pad 55, comprises an electromechanical device configured for signalling to an electrical command and control unit of the belling machine 200 the position of the sectors 3. So as not to condition the optimum inner embodiment of the pad 1 for the internal cooling of the pad 1 , this device is made outside the main body 10 of the pad 1 .

It should be noted that in the pad 1 according to the invention, as in the example embodiments, shape and dimensions of the outer surface 2 of the pad 1 (including the jack 60 in the case of pad 1 with wedge 50), are in the order of conventional mechanical pads, in particular the radial size is not greater than that of conventional mechanical pads. According to the example embodiments, the systems for fixing corresponding conventional pads to the belling machine 200 are maintained. These features, which can be obtained with the invention, are advantageous since they make the pads 1 according to the invention installable and usable in the majority of belling machines 200 present in the systems for the production of the PVC-U pipe 100, also in conventional belling machines already operating in existing extrusion lines.

In effect, normally, the specialised belling machines 200 for mechanical pad 1 processing of the PVC-U pipes 100 are equipped for also processing smooth pads 1. The smooth pads 1 comprise the cooling system 23 inside the pad 1 with liquid 80. Therefore, the belling machine 200, comprising the cooling system 23 of the smooth pads 1 , can be used, with the same system, for belling processes which use the mechanical pads 1 as per the invention.

The example embodiments of the invention relate to apparatuses intended to make the bell 101 in the PVC-U sewer pipes 100 in the smallest dimension of the diameter of the specific sewer pipes 100, that is to say, 110 mm. The embodiment according to the invention in apparatuses intended to make the bell 101 in the sewer pipes 100 with larger diameters is without doubt easier and more versatile, since, obviously, the greater the diameter of the pipe 100, the greater is also the space inside the pad 1 available to make the particular features according to the invention. In particular, the conduits 32 and 35 inside the load-bearing shaft 6 may be composed of more than two conduits or conduits with a larger passage cross-section. The construction shape of the conduits 32 and 35 may also be conveniently different from that of through holes made directly in the body of the load-bearing shaft 6, for example they may be rigid or flexible pipes, which can be enclosed in a removable fashion in cavities inside the load-bearing shaft 6.

Figure 10 illustrates the example embodiment of the belling machine 200 for multi-belling, specifically for double belling, in the configuration of two cooling 203 and/or forming chambers 43 each of which houses a forming pad 1. The pad 1 illustrated in Figure 10 is the wedge-shaped pad 50 already described as an example embodiment, as well as illustrated in Figures 8A and 8B inserted in the forming 43 and/or cooling 203 chamber. The belling station 202 comprises two cooling 203 and/or forming 43 chambers, one for each pad 1 with wedge 50 of the pair of forming pads 1 . The forming 43 and/or cooling 203 chambers are positioned adjacent as well as parallel to each other and define a centre-to-centre distance D between the two pads 1 the value of which is equal to the dimensions of the cooling 203 and/or forming 43 chamber.

More specifically, according to the embodiment illustrated in Figure 10, an application example should be considered wherein the Applicant has made a belling machine 200 intended for belling a PVC-U sewer pipes 100 with a diameter of 110 mm and a nominal wall thickness of 3.2 mm, with a centre-to-centre value D equal to 210 mm. Considering the formula for defining the value of DI, DI = [2 + [2.125-0.0416(de/s)]]de, there is “de”=110 mm and “s”=3.2 mm and therefore Dl=296 mm and, therefore, this value D meets condition D < DI.

Advantageously, the pad 1 cooled internally with liquid 80 allows a more uniform cooling in the circumference of the bell 101 compared with conventional mechanical pads. This advantage, together with the reduced radial size of the pad 1 , is favourable for the use of the pads 1 cooled with liquid 80 in the multi-belling processes both with a single cooling chamber 203 for all the pipes 100 of the group of multi-belling pipes 100 and with multiple cooling chambers 203, therefore individual for each pipe 100 of the group of multi-belling pipes 100.

Advantageously, the pad 1 is cooled from the inside by the circulation of the liquid 80.

Advantageously, the flow of gaseous fluid 82 intended for cooling the inserts 3 and the end element 12 is cooled by the liquid 80 by means of the metal surfaces cooled by the liquid 80 itself circulating in the main body 10 of the pad 1 .

Advantageously, the convective cooling of the inserts 3 and of the end element 12 using the gaseous fluid 82 is intense and uniform.

Advantageously, the cooling system 23 inside the pad 1 with liquid 80 allows the pad 1 to remain within the radial dimensional limits of the conventional mechanical pads.

Advantageously, the cooling system 23 inside the pad 1 with liquid 80 according to the invention allows the pad 1 to be made in accordance with the requirement of interchangeability with conventional mechanical pads and, therefore, applicability and possibility of installation in conventional belling machines.

Advantageously, the pad 1 according to the invention increases the productivity of belling machines in making bells 101 with the mechanical pad system.

Advantageously, the pad 1 according to the invention allows the production of belling machines with mechanical pad system in a multibelling configuration.

Advantageously, the pad 1 according to the invention and the belling machine 200 according to the invention improve the energy efficiency of the cooling in the mechanical pad belling, in particular reducing the consumption of compressed air intended for cooling the bell 101 .

These advantages can be quantified in the non-limiting example of the production plan described below. The PVC-U pipe 100 to be belled with a mechanical pad is the pipe 100 with external diameter 110 mm with a real wall thickness of 3.5 mm.

The time of the belling cycle tb is given by the sum of 3 contributions: tb = tm + tf +tr, where: tm = time of movement of the pipe and of the belling apparatuses tf = minimum time needed to shape the end of the pipe in the pad tr = cooling time of the bell being formed in the pad.

In general, the following conditions apply:

- tm is longer in the double belling since the movement strokes of the pipes 100 in the belling machine 200 are longer;

- tf is conditioned by the material, by the shape of the bell 101 and by the volume of the forming chamber 43, in particular by the volume to be pressurised; tr is shorter in the use of the pad 1 cooled with liquid 80.

For a conventional mechanical pad cooled internally by air and single belling: tb = tm + tf + tr = 6 + 3 + 6 = 15 secs (with production speed OS = 240 bells/hour and compressed air consumption per bell = 280 Nl).

For a mechanical pad cooled internally with liquid and single belling: tb = tm + tf + tr = 6 + 3 + 3 = 12 secs (with OS = 300 bells/hour and compressed air consumption per bell = 150 Nl per cycle).

For a mechanical pad cooled internally with liquid and double belling: tb =tm+tf+tr = 9 + 4 + 3 = 16 secs (with OS = 225 x 2 = 450 bells/hour and compressed air consumption per bell = 150 Nl per cycle).