Tool with multiple operative phases, to form stable bell mouths in terminal junction sections of pipes made of thermoplastic material

Abstract: Tool comprises a composite madrel (1) with multiple operating phases, to form stable bell mouths (21) on the terminal junction sections (2) of pipes (20) made of thermoplastic material, comprising: a first portion (11) movable from a first retracted position, wherein it presents diameter (D11) smaller than the inner diameter of the pipe (20), to a second expended extreme position, with diameter (D12) greater than the nominal and final inner diameter (DN) of the definitive bell mouth (21); a second portion (12), geometrically fixed and consecutive to the first, with diameter equal to that, nominal and final (DN) of the definitive bell mouth (21), said mandrel (1) acting first to pre-form a bell mouth (21') with diameter (D12) greater than the nominal one (DN), then to calibrate it on the second portion (12) at the nominal diameter, during its spontaneous retraction.

Description: The present invention relates to a tool with multiple operative phases, to form stable bell mouths on the terminal junction section of pipes made of thermoplastic material, of the type operating inside the terminal junction section previously heated to the plastic state, according to the precharacterising part of claim 1. In this technological sector there are difficulties to be overcome, linked to the necessary precision that the bell mouths must have at least internally, in order to obtain an effective junction between multiple lengths of pipe, as well as to the problem of the shrinkage of the thermoplastic material, after the definitive formation of the bell mouth. It is well known that the molecules of the thermoplastic materials that are subjected to a dimensional change, "remember" the previous physical state and tend to return to the original state. Hence, when the bell mouths, which increase the diameter of the pipe, extruded when hot, are formed, the pipe would tend to return to the previous state, i.e. with a smaller diameter than the one formed with the bell mouth. Moreover, the aforesaid shrinkage varies according to the thermoplastic material in use (PVC, polyethylene, polypropylene, polyolefins in general). To solve the problem of the precision of the internal dimensions of the bell mouth, techniques have for instance been adopted to shape the bell mouth with mechanical mandrels shaped according to the bell mouth to be obtained and able to be forcibly introduced inside the terminal section of tube to be formed as a bell mouth, previously heated to the plastic deformation temperature. In case of bell mouths comprising ring-shaped inner gaskets, for better sealing, radially expandable and subsequently retractable mechanical sectors have been provided, to allow to form, upon heating, the seat for the gasket in the bell mouth. In regard to the aforesaid technique, reference is made to patent EP N.052.581, of 14 October 1981, in the name of the same Applicant, wherein the wedge shaped activating means (with inclined plane to fasten each mechanical sector) are described, along with the conformation of the mechanical sectors themselves, shaped in such a way as to constitute, when expanded, a homogeneous surface to stop and shape, from within, the ring seat for the bell mouth gasket. Techniques have also been studied whereby pressure is imparted from the outside inwards, on the pre-heated terminal section of the pipe, with the countering action of an internal mandrel, but such techniques are not applicable to the case at hand, which aims to obtain a precise bell mouth without material shrinkage, even for corrugated pipes or presenting outer lugs or shapes, which obviously cannot be heat treated by external pressure of fluid or mechanical means To solve instead the problem of thermoplastic material shrinkage, as far back as 1983 the Applicant perfected an apparatus comprising a shaping chamber defined internally by a mandrel that presents the nominal shape and dimensions of the bell mouth to be obtained, and externally by dies whereon the terminal section of pipe to be treated is preliminarily made to adhere by means of pressurised air coming from inside the mandrel. The terminal section is thus expanded beyond its required nominal size, maintaining it for a certain time in contact against the aforesaid outer dies, then allowing the bell mouth thus formed to shrink spontaneously and to calibrate itself with precision on the underlying mandrel, whereon are provided exhaust conduits for the pressurised air. It has been observed that in such cases the shrinkage of the thermoplastic material was absent or markedly reduced after the complete formation of the bell mouth and an adequate precision was obtained, an inner calibration of the bell mouth itself being always present Unfortunately, this technique too cannot be applied to pipes made of thermoplastic material that are corrugated or in any case externally provided with lugs and/or shapes. Document US-A-3677684, discloses an expanding mandrel, which is adjustable from a fully contracted position, wherein it fits freely within the terminal section of a pipe, to a fully expanded position, which dilates the terminal section which encompasses it, to form a bell mouth having an inner diameter which is equal to its final, nominal one. This prior art is considered the base for the preamble of claim 1. In document FR-A-2184857, a plastic pipe is positioned inside a closed mould, so shaped to form a bell mouth at one end thereof. A hot fluid is used to heat the pipe to a plastic deformation temperature and then pressurized to expand the pipe against the inner walls of the mould, so as to form a bell mouth having a diameter greater than the required nominal one. The pipe, while maintained against the walls of the mould to avoid any uncontrolled, spontaneous shrinkage, is cooled using the same pressurized fluid to obtain a rigid product. The pressure is then released and the pipe (now rigid and, therefore, stable) is extracted and brought to a separate, distant part of the apparatus, where the bell mouth portion is freely inserted on a calibration mandrel (having the exact nominal shape of the bell mouth to be formed), heated again (by any suitable heating means belonging to this part of the apparatus), allowed to shrink spontaneously onto the calibration mandrel to get its final, nominal shape and then cooled again. In document FR-A-2 022 958, a mandrel, for forming a bell mouth at one end of a pipe, has a fixed diameter and is rotated around its longitudinal axis during the forced insertion in a pipe having circular or helicoidal external shapes, to reduce stresses and to limit the risk of making the pipe bend around or collapse along its axis during belling. It is the object of the present invention to provide an improved tool for efficiently and quickly obtaining precise and stable bell-mouths on the terminal junction sections of pipes made of thermoplastic material, even for corrugated pipes or for pipes presenting outer lugs or shapes. This object is achieved according to the invention by the tool as defined in claim 1. Particular embodiments of the invention are the subject of the dependent claims. The invention presents the advantage of being applicable to any type of thermoplastic pipe on the market, including corrugated ones and/or those with external shaping, obtaining precise and stable bell mouths. Additionally, its construction is simple, as it preferably comprises a composite mandrel, set on a single axis coaxial to that of the pipe to be treated, operating with mechanical means and able easily to be adapted to any thermoplastic material used, since all that is required is to replace, depending on the cases, a single piece of the composite mandrel. Not the least advantage is also to provide for a remarkable speed of execution. Additional characteristics and advantages shall become more readily apparent from the detailed description that follows, made with reference to the enclosed drawings, which represent an embodiment provided purely by way of non limiting example, wherein: Figure 1 shows a preferred embodiment of the subject tool, comprising a composite mandrel, in a side view and in a first operative phase, with some parts shown in schematic form and others removed, the better to highlight other parts; Figure 2 shows the mandrel in Figure 1, in a second operative phase; Figure 3 shows the mandrel in Figures 1 and 2, in a third operative phase; Figure 4 shows the mandrel in the previous figures, during the final operative phase. With reference to the aforesaid figures, the subject tool preferably comprises a composite mandrel 1 with multiple operative phases. It essentially comprises, proceeding from the front end 10 to the rear end 19, a first portion 11 and a second portion 12. The first portion 11 is movable from a first retracted extreme position (see Figures 1, 3 and 4), wherein it presents a diameter D11 smaller than the inner diameter D of the pipe 20, thereby being able to be introduced freely and preliminarily inside the terminal section 2 of the pipe 20, which represents the first operative phase, to a second expanded extreme position (see Figure 2) which dilates the part of the terminal section 2 that surrounds it and which represents the second operative phase. Thus a bell mouth 21' is formed, whose provisional inner diameter D12, which corresponds to the outer diameter of the first portion 11 in position of extreme expansion, is greater than the final inner nominal diameter DN of the definitive bell mouth 21. The first portion 11 then returns to the first retracted extreme position (see Figure 3). The second portion 12, which instead is geometrically fixed and placed consecutively to the first 11, presents an outer diameter equal to the nominal and final inner diameter DN of the definitive bell mouth 21. The second portion can be introduced inside the pre-formed bell mouth 21' (see Figure 3), after the complete intervention thereon by the first portion 11 which, in retracted position, allows the free subsequent introduction of the second portion 12 inside the pre-formed bell mouth 21' (this is the third operating phase). This second portion 12, having a diameter rigorously equal to the nominal one required, guarantees and has the function of exactly calibrating the inner diameter of the bell mouth 21, preliminarily widened to the provisional one 21' and which is subjected to spontaneous retraction, after the previous dilation, as a result of the natural characteristics of such materials (this represents the fourth and final phase, see Figure 4). Stability is thereby guaranteed to the bell mouth 21, even if provided with lugs or external shaping. Note that, in the aforesaid first operative phase, the second portion 12 acts as a stop on the front end 22 of the first portion 11 inside the terminal section. In order to co-ordinate the various movements synchronously according to the various phases and with minimum time expenditure, means 3 to provide relative motion between mandrel 1 and pipe 20, operating along the longitudinal axis 5 of the mandrel 1, are provided as well as means 4 driving the expansion and retraction of the first portion 11. In particular, the first portion 11 is of the type with radially movable mechanical sectors 6, whose length, measured along the longitudinal axis 5 of the mandrel 1, is equal to the length of the bell mouth 21,21'. In this case, as in the known case of Patent EP. n. 052.581, the driving means 4 are represented by a wedge with inclined planes, shown schematically because it is already known. For the proper operation of the means 4 the first portion 11 is to be interposed between the second portion 12 and an end head 7, also presenting a smaller diameter than the inner diameter D of the tube 20, so that the mechanical sectors 6 are bilaterally guided along perpendicular planes to the longitudinal axis 5 of the mandrel 1. It is important to stress that the first portion 11 is heated to a temperature greater than or equal to the one of the terminal section 2, so that the latter does not give off heat during its plastic dilation to form the pre-formed bell mouth 21'. The second portion 12 instead is cooled below the temperature of the terminal section 2, in order to bring the definitive bell mouth 21 to ambient temperature quickly, once it has spontaneously retracted from the diameter D12 to the definitive nominal diameter DN. In particular, the first portion 11 is heated by heating means 8 introduced therein, whereas the second portion 12 is cooled by cooling means 9, 99 both inside and outside the portion itself. Whilst the internal cooling means provide cooling in essentially continuous fashion, because they are effective only when in contact with the portion 2 of the bell mouth that has undergone its spontaneous shrinkage, the external cooling means 99 operate on the definitive bell mouth 21 preferably immediately after it has spontaneously retracted onto the second portion 12 that calibrates it internally, to quicken the spontaneous retraction of the bell mouth. It should lastly be observed that, advantageously, the diameter DN of the second portion 12 is computed according to the type of thermoplastic material used for the pipes 20 to be treated. Thus the second portion 12 is removably interchangeable. The invention thus conceived can be subject to numerous modifications and variations, without thereby departing from the scope of the inventive concept expressed below.

Claims: Tool with multiple operative phases, to form stable bell mouths on the terminal junction section of pipes made of thermoplastic material, of the type operating inside the terminal junction section (2) previously heated to the plastic state and comprising a first portion (11), movable from a first retracted extreme position wherein it presents a diameter (D11) smaller than the inner diameter (D) of the pipe (20), thereby being able to be introduced freely and preliminarily into the terminal section (2) of the pipe (20), to a second expanded extreme position which dilates the entire part of the terminal section (2) which encompasses it, thereby preforming a bell mouth (21'), characterized in that: the inner provisional diameter (D12) of the bell mouth (21'), corresponding to the outer diameter of the first portion (11) in position of extreme expansion, is greater than the final inner nominal diameter (DN) of the definitive bell mouth (21), said first portion (11) then returning to the first retracted extreme position; the tool further comprises a second portion (12), geometrically fixed, presenting an outer diameter equal to the nominal and final inner diameter (DM) of the definitive bell mouth (21), said second portion (12) being able to be introduced inside the pre-formed bell mouth (21'), after the complete intervention of said first portion (11) which, in retracted position, allows the free subsequent introduction of said second portion (12) inside the pre-formed bell mouth (21'), said second portion being able exactly to calibrate the inner diameter of the bell mouth (21), subject to spontaneous retraction after the previous dilation; said first and second portions (11) and (12) being in mutual combination to form a single composite mandrel (1), set on a single axis coaxial to the pipe (20) to be treated, wherein the second portion (12) is positioned consecutively to the first. Tool according to claim 1, characterised in that the first portion (11) is of the type with radially movable mechanical sectors (6), whose length, measured along the longitudinal axis (5) of the mandrel (1), is equal to the length of the bell mouth (21,21') and in that said first portion (11) is interposed between the second portion (12) and an end head (7), which also presents a smaller diameter than the inner diameter (D) of the pipe (20), so that the mechanical sectors (6) are bilaterally guided along planes perpendicular to the longitudinal axis (5) of the mandrel (1). Tool according to claim 1 or 2, characterised in that it comprises, inside the first portion (11), means (8) for heating the first portion (11) to a temperature higher than or equal to that of the terminal section (2), so that the latter does not give off heat during its plastic dilation to form the pre-formed bell mouth (21') and means (9,99) for cooling the portion (12), both internally and externally, the external cooling means (99) operating on the definitive bell mouth (21) immediately after it has spontaneously retracted onto the second portion (12) which calibrates it internally, in such a way as to bring the definitive bell mouth (21) to ambient temperature quickly, once it has spontaneously retracted to the nominal definitive diameter (DN). Tool according to any one of the previous claims, characterised in that the diameter (DN) of the second portion (12) is computed according to the thermoplastic material. Tool according to any one of the previous claims, characterised in that means (3) for imparting relative motion between mandrel (1) and pipe (20) are provided, said means (3) operating in combination and synchrony with means (4) for driving the expansion and retraction of the first portion (11). Tool according to claim 5, characterised in that the second portion (12) realises a stop on the front end (22) of the terminal section (2), during the preliminary introduction of the first portion (11) inside the terminal section (2). Tool according to claim 5 or 6, characterised in that at least the second portion (12) is removably interchangeable.

Inventors: SAVIOLI LEOPOLDO, SAVIOLI, LEOPOLDO
Applicants: SICA SPA, SICA S.P.A.
Application year: 1998
Main classification: B29C57
IPC codes: B29C57, B29C61