ITMI20101343A1 - PLANT AND METHOD FOR THE MANUFACTURE OF TUBES - Google Patents

Description

PLANT AND METHOD FOR MANUFACTURING PIPES

The present invention relates to a plant and a method for manufacturing pipes and in particular for manufacturing flexible pipes provided on their external surface with a plurality of spiral corrugations.

In the field of pipes, so-called "spiral" flexible pipes are widespread, ie pipes which have on their external surface a plurality of corrugations which extend around it in the longitudinal direction forming a spiral. These pipes, made for example of PVC, PU, ÈVA, LDPE, HDPE, PP and PE, are generally used for conveying water, oil and air, as well as sheaths for electrical cables and are a valid alternative to traditional flexible pipes in eraser. Their characteristics of lightness, flexibility, strength and economy are in fact well known.

Spiral tubes are generally made by coextrusion processes in special plants comprising an extrusion head and a winding mandrel. Inside the extrusion head, the flows of plastic material produced by two extruders are conveyed so as to form a single profile through a special matrix. A first portion of the profile, having a substantially rectangular cross section, is intended to form the cylindrical wall of the pipe and a second portion, having a semicircular or polygonal cross section, is intended to form the corrugations. The profile thus obtained is directed, still in the plastic state, towards the spindle, which is connected to a motor through a suitable reducer, and is wound on it according to a spiral, progressively forming the tube. The tube is then made to advance towards a cooling station suitable to allow its consolidation and dimensional stabilization and proceeds by rotating towards a cutting unit.

The plastic materials used in the extrusion process generally have different mechanical characteristics. In particular, the material intended to form the first portion will have a lower elastic modulus than the material intended to form the second portion, thus allowing to confer characteristics of flexibility to the cylindrical wall of the pipe and an adequate rigidity to the corrugations which, in fact, they operate as real ribs in the uses foreseen for this type of pipes. For example, it is possible to use LDPE for the cylindrical wall of the pipe and HDPE for the corrugations. The combination of plasticized PVC for the cylindrical wall with rigid PVC for the corrugations is also very popular.

In order to allow the spiral winding of the extruded profile around the mandrel, two alternative solutions are generally known. In a first embodiment, the profile proceeds towards the mandrel in a manner substantially perpendicular to its longitudinal axis and the perimeter structure of the mandrel consists of a plurality of flexible rods inclined at a predefined angle with respect to said longitudinal axis. The rods are supported by means of a plurality of plates constrained to the same support bar which extends in the direction of the axis of the mandrel. The rods are constrained to the plates in a rotatable way around their own axis and can be rotated by the motor, thus allowing the profile to be wound around the spindle. The inclination of the rods with respect to the longitudinal axis of the mandrel combined with their rotation generates a thrust on the profile during the winding phase, which therefore advances in the longitudinal direction.

In a second solution, the profile proceeds towards the mandrel maintaining a predetermined angle of inclination with respect to the direction perpendicular to the longitudinal axis. Similarly to the first solution, the inclination of the feed direction of the profile combined with the rotation of the mandrel generates a thrust in the longitudinal direction on the profile during the winding phase, thus allowing, as explained above, the formation of the tube.

In both cases, the pitch of the corrugations is less than the width of the profile, therefore, during winding, the coils of the profile, which are still in the plastic state, compact and weld one to the other, generating the spiral tube. .

Examples of manufacturing spiral tubes are described, for example, in Japanese publications JP 02-134484 and JP 11-286058.

As mentioned above, spiral tubes are well known for their characteristics of flexibility and sturdiness and therefore constitute a valid alternative to rubber tubes generally used for the transport of liquids.

In a traditional rubber tube, the sealed connection to a power source, a remote device or another tube is carried out with suitable connection elements of substantially tubular shape. A free end of the tube is fitted onto the tubular element and subsequently "choked" on it, or compressed circumferentially, by means of clamps or ring nut elements mounted coaxially around the tubular element. Compression in the circumferential direction achieves the desired sealing effect.

It will be understood that in a spiral tube the presence of corrugations on the cylindrical wall constitutes an obstacle to the realization of a sealed connection, both due to the presence of elements in relief on the surface and to the fact that these elements intentionally have a higher rigidity than that of the cylindrical wall and therefore oppose the compression action and an effective adaptation to the fitting.

To solve this problem, special connection devices have been developed for spiral tubes in which the tubular element has a seat, formed circumferentially in its thickness, suitable for receiving a free end of the tube. The sealing connection is carried out under pressure, as in rubber pipes, in correspondence with the inner wall of the pipe, engaging and radially compressing the corrugations in the circumferential seat and possibly using glue. Connection devices for spiral tubes provided with ring nut locking elements are also known. An example in this sense is described in the Italian patent 1364532, in which the ring nut is associated with a special internal gasket which is modeled in accordance with the corrugations obtained on the cylindrical wall of the tube, favoring the sealing connection and performing at the same time a retention action. in the longitudinal direction.

The aforementioned connection devices are rather complex and expensive and moreover require particular attention in the assembly of the tube to avoid sealing problems in correspondence with the corrugations of the spiral profile.

There is therefore a need to find further solutions for the sealing connection of the spiral tubes, which are simpler, more reliable and less expensive than those known to date, which constitutes the main object of the present invention.

The inventor has understood that for the realization of efficient and reliable sealing connections for spiral tubes it is not strictly necessary to create connection devices able to adapt to the conformation of the external surface of the tube, but that it is also possible and much more effective to modify locally this conformation to allow the assembly of traditional type connection devices.

A solution idea underlying the invention is, therefore, to modify the conformation of the external surface, and therefore the cross section, of the pipe by predetermined lengths in the longitudinal direction directly during the manufacturing phase, by acting on the cross section of the plastic profile coming out of the extrusion head. For this purpose, in the plant according to the invention the extruder which produces the flow of plastic material which forms the corrugations is provided with an interception valve able to block or divert to lose the flow for a predetermined time. The temporary blocking of the flow, or its deviation to lose, which forms the corrugations determines the formation of completely cylindrical portions on the pipe, i.e. without spiral corrugations, which will constitute, after the pipe has been cut, the portions suitable for allowing the assembly of traditional connection devices.

In addition or alternatively, the extrusion head can comprise a further selectively operable extruder adapted to feed a flow of an additional plastic material which joins the extruded profile downstream of the extrusion die. Depending on the type of connection devices provided, the cross section of the flow of injected plastic material can have a height greater, less than or equal to that of the second portion of the profile, or of the corrugations, and a width less than or equal to that of the first portion of the profile, whereby the finished pipe will have sections with spiral corrugations alternating with one or more cylindrical sections having a diameter greater than, less than or equal to that of the spiral pipe suitable for allowing the tight assembly of clamp connection devices, with traditional ring nut or pressure.

The main advantage offered by the invention is that the possibility of selectively controlling the extruder of the flow that forms the corrugations and / or the presence of a further extruder able to feed a flow of an additional plastic material allows to choose with maximum freedom the position, extension and composition of the cylindrical portions suitable for allowing the sealing assembly of the connection devices. For example, it is possible to completely coat a section of pipe comprising a certain number of corrugations, thus creating a cylindrical portion in which the spiral corrugations are embedded in a matrix of additional material. Alternatively, it is possible to make cylindrical portions between contiguous coils, which makes it possible not to excessively stiffen the connecting portions of the pipe.

According to another aspect of the invention, the mandrel comprises at least a radially expandable portion, so that it is possible to make portions of pipe, in particular the connecting portions, having a diameter different from the nominal one, for example greater, allowing to maintain the dimensions foreseen according to the use of the pipe while adapting its ends to connection devices of standard dimensions.

Furthermore, the mandrel can be configured in such a way as to allow variations in the pitch of the spiral corrugations in predetermined sections. This aspect of the invention allows to modify in an extremely simple and precise way the stiffness characteristics of the pipe in the portions covered by the additional material, which, due to the overlapping of several materials, have a higher stiffness not always suitable for the foreseen applications.

Further advantages and characteristics of the plant and of the manufacturing method for pipes according to the present invention will become evident to those skilled in the art from the following detailed and non-limiting description of some of its embodiments with reference to the attached drawings in which:

Figure 1 schematically shows a plant according to the invention;

Figure 2 is a cross-sectional view taken along the line Π-Π of Figure 1; Figure 3 schematically shows the extrusion head of the plant of Figure 1; Figures 4 and 5 are cross-sectional views similar to that of Figure 2, showing two examples of the profile obtainable with the extrusion head;

figure 6 shows a longitudinal portion of a tube made with the implant according to the invention;

Figure 7 is a cross section, taken along the line VII-VII of Figure 1, which shows the structure of the mandrel on which the extruded profile is wound; and Figure 8 is a cross section, similar to that of Figure 7, showing a portion of the mandrel in an expanded condition.

With reference to Figure 1, regret 1 for the manufacture of pipes with spiral corrugations according to the invention comprises an extrusion head 2 to which a plurality of extruders are connected, in particular two extruders 3 and 4 in the example shown in the figure, respectively adapted to feed flows of plastic materials 30, 40 into the extrusion head 2 along suitable channels 2a, 2b. As can be seen, the channels 2a, 2b flow into each other conveying the flows 30, 40 to form, through a suitable matrix 20, a profile 5 whose cross section is shown in Figure 2.

With reference to Figure 2, it can be seen that a first portion 5a of the profile 5 has a substantially rectangular cross section intended to form the cylindrical wall of the tube. The profile 5 also comprises a second portion 5b having a semicircular cross section intended to form the corrugations on the outer surface of the tube. The cross section of the second portion 5b of the profile 5 can also have different geometries, for example square, rectangular or polygonal.

The plant 1 also comprises a spindle 6 driven by a motor 7 connected to a reducer 8. The spindle 6 comprises, in a known way, a plurality of flexible rods 9 inclined at a predefined angle a with respect to its longitudinal axis. The rods 9 are supported by means of a plurality of plates 10 constrained to a support shaft 11 which extends along the axis of the mandrel 6. The rods 9 are constrained to the plates 10 so that they can rotate around their own axis and can be rotated from the motor 7 through the reducer 8 to allow the winding of the profile 5 around the spindle 6.

As is known, the profile 5 proceeds towards the mandrel 6 in a direction substantially perpendicular to its longitudinal axis and the inclination of the rods 9 according to the angle a combined with their rotation generates a thrust on the profile 5 in the longitudinal direction during the winding phase. which allows the spiral winding of the profile 5 on the spindle 6.

The pitch P of the corrugations defined by the inclined rods 9 is deliberately less than the width W of the profile 5, therefore the spindle 6 generates a compacting action in the longitudinal direction on the coils of the wrapped profile, which allows it to be in close contact and welding, thus continuously forming a tube 12.

The tube 12 thus made advances by rotating around the axis of the mandrel 6 towards a cooling station 13 suitable for allowing its consolidation and dimensional stabilization, possibly by means of rollers not shown, and then proceeds towards a cutting unit (not shown).

As better shown in Figure 3, the extruder 3 which produces the flow 30 of plastic material which forms the corrugations is provided with an on-off valve 3 a adapted to block the flow 30 or to divert it to lose. The blocking, or the non-returnable deviation, of the flow 30 which forms the corrugations for a predetermined time interval determines the formation of completely cylindrical portions on the tube 12, which allow, after the tube 12 has been cut, the assembly of connecting devices of traditional type.

In addition or alternatively, the plant 1 also comprises a further extruder 14, associated with the extrusion head 2, able to feed a flow 140 of an additional plastic material, compatible with those that form the tube, on the profile 5, for example Plasticized LDPE or PCV.

The extruder 14 is connected to the extrusion head 2 in correspondence with a channel 2c adapted to receive the flow 140 of additional material and which flows downstream of the matrix 20 into a channel 2d through which the profile 5 passes.

In other words, the addition of the plastic material fed by the extruder 14 occurs following the formation of the profile 5 by the extrusion matrix 20, for example immediately downstream of this, when this is still in the plastic state and before the its winding on the mandrel 6. Similarly to the extruder 3 of the flow 30 of material which forms the corrugations, also the extruder 14 is provided with an interception valve 14a adapted to block the flow 140.

Again with reference to Figure 3, the extruder 14 is preferably associated with an injector 15 connected to the extrusion head 2 in correspondence with the channel 2c. During the operation of the plant 1, the extruder 14 produces a flow of plastic material which fills a cylinder 15a of the injector 15. The on-off valve 14a is then opened and a piston 15b of the injector 15 is activated, which injects the flow 140 of additional material in the channel 2c of the head 2. Once the cylinder 15a has been emptied, the on-off valve 14a is closed again allowing the extruder 14 to refill the cylinder 15a.

It is clear that the volume of the cylinder 15a defines the maximum quantity of additional injectable material at each cycle, but by acting on the shut-off valve 14a and / or on the stroke of the piston 15b it is possible to inject smaller quantities of additional material, thus being able to coat portions of length variable of profile 5 and therefore of tube 12.

Figures 4 and 5 show two examples of the cross section of the profile 5 obtainable with this process. In Figure 4, the cross section of the flow 140 of the additional material has a width W substantially corresponding to the width W of the first portion 5a of the profile 5, and overlaps it forming a portion 5c which completely covers the second portion 5b. In Figure 5, on the other hand, the cross section of the flow 140 has a width W smaller than the width W of the first portion 5a and overlaps it forming a portion 5d arranged above it alongside the second portion 5b.

In both embodiments, the height H 'of the portion 5c, 5d made with the additional material is greater than the height H of the second portion 5b of the profile 5, but, depending on the dimensions of the standard connection device provided, it could also be inferior.

More generally, the cross section of the flow 140 of additional material can have a height greater, less than or equal to that of the second portion 5b of the profile 5 and a width less than or equal to that of the first portion 5a, allowing to obtain on the pipe 12 one or more sleeve cladding portions which substantially completely cover the corrugations. In this way it is possible to guarantee an easy and correct sealing assembly of a connection device of the traditional type, because it is avoided that it comes into contact with the spiral corrugations and interferes with them.

Figure 6 shows an example of a sleeve coating obtained starting from the profile 5 shown in figure 4. The sleeve coating, indicated by the number 16, covers a continuous section of the pipe 12, thus modifying locally the conformation of the external surface and the section transversal. In this section, the tube 12 has the same surface characteristics as a conventional type of flexible tube, on which standard connection devices can be mounted. The sleeve covering 16 is intended to be cut, thus constituting the end of the tube 12 suitable for mounting a connection device. In figure 6, the cutting plane is schematically indicated by the line C.

If the tube 12 is made with the profile 5 shown in Figure 5, a plurality of sleeve coatings will be obtained instead, interspersed with the corrugations.

The operation of the on-off valves 3a, 14a and of the injector 15 can be suitably managed by means of an automatic and programmable control system (not shown).

The absence of corrugations and / or the presence of sleeve coatings for predetermined lengths determine a discontinuity in the flexural rigidity characteristics of the pipes produced with the plant according to the invention, with potential difficulties in the use and / or assembly of the devices connection.

Thanks to the presence of the shut-off valves 3 a, 14a of the extruders 3 and 14 it is possible to create numerous configurations of the portions of the pipe intended for the assembly of the connection devices, designed in such a way as to keep the rigidity characteristics of the pipe substantially constant or to define a suitable stiffness according to the type of connection envisaged.

For the same reason, the mandrel 6 can be configured to determine one or more variations of the pitch P of the spiral corrugations. For example, it is possible to decrease the pitch P in the portion of pipe that is coated by the additional material, thus obtaining, for example, a sleeve coating that covers a smaller number of corrugations so that the corresponding pipe section will have a lower flexural stiffness than that which would have kept the pitch P unchanged. Similarly, it is possible to increase the pitch P in the portion of the pipe that is coated by the additional material, obtaining a sleeve coating that covers a greater number of corrugations and therefore characterized by greater flexural rigidity.

In order to be able to vary the pitch of the spiral profile of the tube, as shown in figure 7, at least one of the plates 10 which support the flexible rods 9 of the mandrel 6 is mounted in a rotatable manner with respect to the shaft 11 and can be operated in rotation with respect to it. , for example by means of a hydraulic or pneumatic control. A rotation of the plate 10 by an angle β around the axis of the shaft 11 will cause a local variation of the angle a of inclination of the flexible rods 9 and therefore a local variation of the pitch P of the corrugations.

It will be understood that, according to the manufacturing requirements, this last feature of the invention can be combined with the temporary block or the disposable deviation of the feed of the flows 30, 140 of the extruders 3, 14, helping to define, through the system control system 1, a plurality of tube configurations.

According to a further aspect of the invention, at least a longitudinal portion of the mandrel 6 is radially expandable to allow one or more local variations in the diameter of the pipe 12. It is thus possible to realize portions of the pipe, in particular those intended for the assembly of the connecting devices, having a diameter different from the nominal one, for example greater, allowing to keep the dimensions of the tube 12 unaltered according to its use, adapting however the coated portions to the dimensions of the connection devices of the standard type.

With reference to Figure 8, one or more of the plates 10 fastened to the shaft 11 comprise a plurality of elements 17 movable radially outwards to which the portions of the plate 10 which support the flexible rods 9 are constrained. By operating the elements 17, the rods 9 are then stressed radially towards the outside, thus determining a local increase in the diameter of the tube 12.

It is clear that the embodiments of the invention described and illustrated here are only examples susceptible of numerous variations. For example, the plant 1 can comprise one or more matching rollers (not shown) arranged parallel to the mandrel 6 and able to come into contact with the outer surface of the tube 12 to shape it and / or contribute to its dimensional stabilization.

Claims (10)

CLAIMS 1. Plant (1) for manufacturing pipes with spiral corrugations comprising an extrusion head (2) to which a plurality of extruders (3, 4) are connected, said extruders (3, 4) being respectively adapted to feed towards said extrusion head (2) flows (30, 40) of plastic materials, said flows (30, 40) being conveyed inside the head (2) through special channels (2a, 2b) towards an extrusion die (20) to form a profile (5), said profile (5) comprising a first portion (5 a) intended to form the cylindrical wall of a tube (12) and a second portion (5b) intended to form the corrugations on the external surface of said tube (12), said plant (1) further comprising a mandrel (6) adapted to receive said profile (5) and configured so as to allow its spiral winding in a longitudinal direction for forming the tube (12), characterized from the fact that the extruder (3) which produces the flow (30) of plastic material that forms the corrugations is provided with an interception valve (3a) able to block said flow (30) and by the fact that the plant (1) comprises, in addition or alternatively, a further extruder (14) provided with an interception valve (14a) is connected to the extrusion head (2) in correspondence with a channel (2c) which flows downstream of the extrusion die (20), said further extruder (14) being able to feed into the extrusion head (2) a flow (140) of an additional plastic material on the profile (5), the cross section of said flow (140) having a height (Η ') greater than, less than or equal to the height (H) of the second portion (5b) of the profile (5). Plant (1) according to the preceding claim, characterized in that the flow (140) of the additional material has a width (W) substantially corresponding to the width (W) of the first portion (5a) of the profile (5) and overlaps thereto forming a portion (5c) which substantially completely covers the second portion (5b). Plant (1) according to claim 1, characterized in that the flow (140) of the additional material has a width (W) smaller than the width (W) of the first portion (5a) of the profile (5) and overlaps with it forming a portion (5d) arranged alongside the second portion (5b). Plant (1) according to one of the preceding claims, characterized in that the mandrel (6) comprises a plurality of flexible rods (9) inclined by a predefined angle (a) with respect to its longitudinal axis, called flexible rods (9) ) being supported by a plurality of plates (10) constrained to a support shaft (11) which extends in the direction of the axis of the mandrel (6), and by the fact that the flexible rods (9) are constrained to said plates ( 10) in a rotatable way around its own axis and can be rotated by a motor (7) to allow the winding of the profile (5) around the mandrel (6). 5. Plant (1) according to the preceding claim, characterized in that at least one of the plates (10) supporting the flexible rods (9) of the mandrel (6) is mounted in a rotatable manner with respect to the shaft (11) and can be operated in rotation with respect to it according to a predetermined angle (β). Implant (1) according to one of the preceding claims, characterized in that at least a longitudinal portion of the mandrel (6) is radially expandable. 7. Plant (1) according to one of claims 4 to 6, characterized in that at least one of the plates (10) fastened to the shaft (11) comprises a plurality of elements (17) movable in a radial direction, said elements (17 ) being constrained to the portions of the plate (10) which support the flexible rods (9). Plant (1) according to one of the preceding claims, characterized in that it further comprises one or more compacting rollers arranged parallel to the mandrel (6) and able to press against the outer surface of the tube (12) to shape the tube (12) and / or contribute to its dimensional stabilization. 9. Method for manufacturing a tube with spiral corrugations comprising the steps of: i) feeding flows (30, 40) of plastic materials to an extrusion head (2) by means of respective extruders (3, 4); ii) forming, by means of an extrusion matrix (20), a profile (5) comprising a first portion (5a) intended to form the cylindrical wall of the tube and a second portion (5b) intended to form the spiral corrugations; rii) feeding said profile (5) towards a winding mandrel (6); and iv) winding the profile (5) around said mandrel (6) according to a spiral, characterized in that it also comprises a phase of temporary interruption of the flow (30) of plastic material that forms the corrugations and / or a phase of feeding of a flow (140) of an additional plastic material on the profile (5), the cross section of said flow (140) having a height (Η ') greater than, less than or equal to the height (H) of the second portion (5b) of the profile (5), said feeding step being performed after the step of forming the profile (5) when this is still in the plastic state and before the winding step. Method according to the preceding claim, characterized in that the flow (140) of the additional plastic material has a cross section having a width (W) less than or equal to the width (W) of the profile (5).