Patent Publication Number: US-2012034327-A1

Title: Apparatus for compression moulding preforms

Description:
The invention relates to an apparatus for forming objects, in particular by compression-moulding plastics. The apparatus according to the invention is particularly suitable for forming preforms for containers, such as bottles, made, for example, of polyethyleneterephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), high-density polyethylene (HDPE) or polyethylene naphthalate (PEN). The preforms obtained by using the apparatus according to the invention can be subsequently transformed into containers, for example bottles, by a stretch-blow-moulding process. 
     The preforms for obtaining containers comprise a substantially cylindrical hollow body extending along a longitudinal axis having an end closed by a transverse wall that is generally dome-shaped. The hollow body further has an open end on which a mouth is obtained comprising a threaded zone that is suitable for engaging with a container closure. The open end of the preform is bounded by an edge zone that extends circumferentially around the longitudinal axis. 
     In manufacturing plants for producing the preforms, in order to offer the end customer containers that always have a different shape and less mass, manufacturing production batches of preforms in succession is becoming ever more frequent, each having a respective determined size. In other words, there is always greater need to offer an apparatus for the compression-moulding of preforms that is able to adapt to frequent requests for products that are different from one another (flexibility of demand). Manufacturing plants are known for forming preforms by compression-moulding of doses of plastics. Such plants comprise a plurality of moulds mounted in a peripheral region of a carousel that is rotatable around a vertical axis. 
     Each mould comprises a first half mould, a second half mould and two movable die elements. The first half mould comprises a punch, configured for shaping the substantially cylindrical internal surface of the hollow body of the preform; the second half mould comprises a die cavity, configured for shaping a substantially cylindrical portion of the external surface of the hollow body of the preform; the two movable die elements are provided with shaping surfaces configured for shaping the external threaded mouth zone of the preform. 
     It should be noted that the shape of the punch, of the die cavity and of the movable die elements determine the geometrical shape of the desired preform, i.e. the size thereof. In particular, the difference in diameter between the punch and the die cavity determines the final thickness of the preform whilst the longitudinal dimensions of the punch and of the die cavity determine the length of the preform. 
     In order to ensure that the plants for compression-moulding of preforms can pass rapidly from the production of a preform of one size to the production of a preform with a different size, there is therefore the need for the elements that determine of the size of the preform (punch and/or die cavity and/or movable die elements) to be replaced very rapidly. 
     The punch and the cavity are mutually movable towards and away from one another along a moulding direction that is typically vertical. Otherwise, the two movable die elements can move between a position spaced apart from the moulding direction in which the shaping surfaces associated with each die part are mutually distant and a contact position, in which the shaping elements are near one another. 
     The first half mould further comprises a cylindrical body that slidably houses internally in the moulding direction a hollow pressing sleeve that in turn slidably houses the punch, said pressing sleeve maintaining the movable die elements in contact together in the contact position at least in a final preform forming step and initial preform extracting step. The first half mould comprises at least a chamber obtained in the interior thereof that is supplied with pressurised fluid that acts on at least one wall of the pressing sleeve, so as to push the latter outside the cylindrical chamber in contact with the movable die elements. The chamber with the pressurised fluid provides a pneumatic system acting on this pressing sleeve. 
     During operation, the first half mould and the second half mould are spaced apart to receive inside the die cavity a dose of plastics to be shaped. Subsequently, when the two movable die elements are in reciprocal contact retained by the pressing sleeve of the upper half mould, the second half mould is brought near the punch by an actuating device and the plastics start to be distributed inside the die cavity. In this initial forming step, it is sufficient that the pneumatic system acting on the pressing sleeve exerts a relatively low initial force to maintain the two movable element in contact. During a final forming step, when the plastics reach the two movable elements, it is necessary for the pneumatic system to exert on the pressing sleeve a force that is significantly greater than the initially exerted force to contrast the action of the plastics that tend to move the two movable elements away from one another. 
     Each of WO 2007/017418 and WO 2007/144312 discloses the apparatus of the preamble of claim 1. 
     In order to ensure that the pneumatic system exerts on the pressing sleeve various forces at various forming steps, it is known from WO2007/017418 to provide the pneumatic system acting on the pressing sleeve by supplying the chamber inside the cylindrical body with a low-pressure first fluid in the initial step and by means of a second high-pressure fluid in the final step. Alternatively to the pneumatic system with a single chamber, WO2007/017418 discloses a pneumatic system having two chambers, obtained inside the cylindrical body and isolated from one another that are supplied respectively by a low-pressure fluid and by a high-pressure fluid that start operation in succession. In order to provide such chambers, the cylindrical body houses a cylindrical cup portion that is connected to the cylindrical body and arranged around the pressing sleeve and a further slidable intermediate sleeve that is interposed between said cylindrical cup portion and the external cylindrical body. One problem of the previously disclosed devices resides in the fact the pressurised chamber that provides the pneumatic system acting directly on the pressing sleeve faces and is bounded by a wall of the punch. As a result, dismantling the punch, for example replacing the punch in the event of production of preforms with a different size, can be performed only after interrupting the supply to the first and to the second circuit of pressurised fluid, and only after emptying the circuits. Further, as replacing the punch also implies dismantling and refitting the entire first half mould with complicated alignment operations between the various components with which the first half mould is provided, a size change over requires a long period of machine downtime for the compression-moulding apparatus. 
     A further problem of the devices disclosed above resides in the fact that the presence of two chambers supplied by respective pressurised fluids requires a mechanically complex structure and with many components for which high-precision production is required. 
     One object of the invention is to improve the apparatus for forming preforms by compression moulding. 
     Another object is to provide an apparatus that enables the punch of a first half mould to be replaced rapidly and easily without having to perform successive complex and laborious re-start and adjusting operations so as to minimise machine downtime. 
     A further object is to make an apparatus that enables pneumatic system acting for maintaining the movable elements pressed strongly against the second half mould in a final forming step, said apparatus being easy to make. 
     According to the invention, an apparatus is provided for compression-moulding preforms from a dose of plastics according to claim  1 . 
     Owing to the fact that the apparatus comprises a punch arrangement, a die arrangement provided with a cavity, at least two die elements that are mutually movable between a contact position and a detached position and that said punch arrangement is provided with a pressurised chamber that is entirely bounded by a pressing sleeve and by a jacket arrangement of said punch arrangement, a corresponding punch of the latter can be dismantled by the apparatus without emptying a circuit of pressurised fluid that is contained in said chamber and acts on the pressing sleeve. This enables the size change over operation to be accelerated, i.e. rapid replacement of the installed punch with a punch of a different size. 
     In one embodiment, the punch arrangement of the apparatus comprises a single chamber supplied in an initial forming step of said preforms with a first fluid at a first pressure and in a final forming step with a second fluid at a second pressure. 
     In a further embodiment, the punch arrangement of the apparatus comprises two chambers containing a first fluid at a first pressure and a second fluid at a second pressure that start to function in succession in an intermediate and final forming step of said preforms and stop functioning in succession in an initial and intermediate extracting step of said preforms. 
     Owing to this embodiment, the first chamber acts directly on the pressing sleeve and the second chamber acts directly on an intermediate sleeve that in turn acts on a forming sleeve mounted slidably on the punch. Said pressing sleeve and said forming sleeve cooperate, generating respective distinct forces acting on distinct portions of the movable elements to push simultaneously but independently said movable elements towards the die arrangement. 
     In one embodiment, the apparatus comprises a first fixing device and a second fixing device to lock the punch arrangement in respective seat elements of the compression-moulding apparatus. 
     According to this embodiment, when a scheduled maintenance operation is necessary for the punch arrangement, it is possible to dismount rapidly the punch arrangement and then replacing the punch arrangement without complicated centring and aligning operations of the mechanical components. 
     In one embodiment, the apparatus comprises a connecting device for removably connecting the punch to the punch arrangement when the latter is dismantled and extracted from the apparatus. 
    
    
     
       The invention can be understood and implemented better with reference to the attached drawings that illustrate some embodiments thereof by way of non-limiting example, in which: 
         FIG. 1  is a section of an apparatus for compression-moulding a dose of plastics for obtaining the preform in  FIG. 8 , showing a die arrangement, a punch arrangement and movable die elements in an open operating position; 
         FIG. 2  is an enlarged section of the apparatus in  FIG. 1 , showing the punch arrangement in an assembled configuration; 
         FIG. 3  is an enlarged section of the punch arrangement in  FIG. 1  in a first dismantled configuration, in which the punch is extracted from the first half mould; 
         FIG. 4  is a partially sectioned frontal view of the punch extracted from this punch arrangement; 
         FIG. 5  is a section of the punch arrangement in a second dismantled configuration in which they are partially dismantled and extracted from the respective seat elements of the apparatus; 
         FIG. 6  is an enlarged section of the apparatus in FIG.  2 , with some parts removed for the sake of clarity; 
         FIG. 7  is a section view along the line VII-VII in  FIG. 3 , in which the side pin is shown in an inserted position and is shown by a dashed line in the retracted position; 
         FIG. 8  is a schematic perspective view of preform compression-moulded by the apparatus of the invention and used to make a bottle. 
     
    
    
       FIG. 8  shows a preform  1  that is usable for obtaining a container, particularly a bottle, by a stretch-blow-moulding process. The preform  1  is made of plastics, for example polietilentereftalato (PET), polypropylene (PP), polyvinyl chloride (PVC), polyethylene naphthalate (PEN), high-density polyethylene (HDPE). The preform  1  comprises a hollow body  2  extending along a longitudinal axis Z and bounded by an external surface  3 . The hollow body  2  has a first end closed by a transverse wall  4 , shaped as a dome, bounded externally by a base surface  5 . At a second end of the preform  1 , opposite the first end, there is obtained a mouth  6 , also called “finish”, that is not subject to noteworthy variations in shape during the stretch-blow-moulding process. 
     The mouth  6  comprises a threaded portion  7 , that is suitable for engaging with a corresponding further threaded portion of a cap, a circular ridge  8  and generally a ring  9  arranged below the threaded portion  7 . The mouth  6  is bounded above by an annular edge zone  10 , substantially having the shape of a circular crown. 
       FIG. 1  shows a moulding apparatus  11  included in a moulding carousel to obtain preforms of the type shown in  FIG. 8 , by compression moulding of a dose D of plastics. 
     The moulding carousel, rotating around a rotation axis that can, for example, be vertical, may comprise a plurality of moulding apparatuses  11  mounted in a peripheral region of said carousel. 
     The apparatus  11  comprises a punch arrangement  12  opposite a die arrangement  13 , the punch arrangement  12  facing the die arrangement  13  in order to interact together to form the preform  1 . In the example shown, the punch arrangement  12  is arranged above the die arrangement  13 , but it is possible for the punch arrangement  12  to be arranged below the die arrangement  13  or for the punch arrangement  12  and the die arrangement  13  to be positioned at the same level. 
     As shown in  FIGS. 2 and 6 , the punch arrangement  12  comprises a punch  14  extending along a moulding axis A and provided with an external forming surface  15  for internally shaping the preform  1 . The punch  14  is provided with a first shoulder  16  positioned above the external forming surface  15 . 
     Inside the punch  14  there is housed a pipe  17 , inside which there is defined an inlet conduit  18  that is arranged along the moulding axis A and can be traversed by a cooling fluid. The inlet conduit  18  communicates with a source of cooling fluid, not shown, through an inlet opening  19 . Between the pipe  17  and the punch  14  there is defined an outlet conduit  20 , in particular shaped as an annular gap that enables the cooling fluid to exit the moulding unit  11  through an outlet opening  21 . 
     As shown in  FIG. 1 , the apparatus  11  further comprises a pair of movable die elements  22 , that are suitable for shaping the mouth  6  of the preform  1 . The movable elements  22  can be moved by a driving device, not shown, between a contact position and a detached position. In the contact position, the movable elements  22  are in reciprocal contact and define a complex forming surface  23  that enables the threaded portion  7 , the circular ridge  8  and the ring  9  to be shaped. These zones of the preform  1  define undercut parts that can be removed from the moulding apparatus  11  by removing the movable elements  22  from one another, as occurs in the detached position, along a distance that is substantially orthogonal to the moulding axis A. 
     In an embodiment that is not shown, the moulding apparatus  11  may comprise more than two movable elements  22 . 
     Each movable element  22  is bounded transversely to the moulding axis A by a lower surface  24  and by an upper surface  25 . Inside each movable element  22  a step is obtained that is arranged above the complex forming surface  23 , the step is bounded by a transverse surface  26  that extends transversely to the moulding axis A and by a guiding surface  27  that is arranged substantially along the moulding axis A. On each movable element  22  it is possible to define a first coupling surface  28 , which is substantially frustoconical that laterally bounds the movable element  22  near the lower surface  24 . A second coupling surface  29 , which is also substantially frustoconical, is arranged outside each movable element  22  at a higher level than the first coupling surface  28 . The second coupling surface  29  is joined to the upper surface  25  by a cylindrical portion  30 . 
     As shown in  FIGS. 2 and 6 , the moulding apparatus  11  comprises a pressing sleeve  31  that interacts with the movable elements  22  to maintain the movable elements  22  in reciprocal contact in the contact position. The pressing sleeve  31  extends along the moulding axis A, around the punch  14 . In a lower portion of the pressing sleeve  31  and inside the latter a substantially frustoconical containing and retaining surface  32  is provided that in the contact position interacts with the second coupling surface  29  of the movable elements  22 . An internal cylindrical portion  33  obtained inside the pressing sleeve  31  above the retaining surface  32  is suitable for interacting with the cylindrical portion  30  of each movable element  22 . 
     With particular reference to  FIG. 6 , the punch arrangement  12  comprises a jacket arrangement  91  that includes a tubular external jacket  35  inside which the pressing sleeve  31  is slidably mounted so as to be movable linearly parallel to the moulding axis A. 
     The external jacket  35  comprises a side wall of substantially cylindrical shape provided with an internal side surface  38 , and a bottom wall that is substantially transverse to said side wall and provided with an annular bottom surface  138 . 
     In the illustrated embodiment, the jacket arrangement  91  comprises a cylindrical element  135  that is fixed to the external jacket  35  and makes an internal portion of said internal side surface  38  and of said annular bottom surface  138 . 
     The cylindrical element  135  can, however, also be made integrally with the external jacket  35 . 
     The pressing sleeve  31  has a cylindrical external surface  36  a portion of which located above the retaining surface  32  is suitable for interacting with a portion of said internal side surface  38  to guide the sliding of the pressing sleeve  31  inside the external jacket  35 . 
     A transverse annular wall  39  bounds the pressing sleeve  31  above from the cylindrical external surface  36  to the moulding axis A and from said transverse annular wall  39  a tubular protrusion  40  extends terminating with a respective end transverse wall  41 . An end portion of said tubular protrusion  40  is slidable inside the external jacket  35 . 
     A first pressurised fluid, for example compressed air at a first pressure, is contained in an annular lower first chamber  42  obtained above the transverse annular wall  39  and bounded by the latter, by the internal side surface  38  of the external jacket  35 , by a cylindrical surface portion  43  of the tubular protrusion  40  facing the external jacket  35  and by a lower annular edge of said cylindrical element  135 . 
     The first lower chamber  42  is thus entirely bounded by the pressing sleeve  31  and by said external jacket  35 . The first pressurised fluid enters the lower chamber  42  through a first supply conduit  44  obtained inside the external jacket  35  and supplied by an external source of pressurised fluid that is not illustrated. In particular, the first supply conduit  44  is obtained by a groove of the external jacket  35  that is open towards the exterior. 
     The first pressurised fluid acts on the transverse annular wall  39  of the pressing sleeve  31 , pushing the pressing sleeve  31  towards the outside of the external jacket  35 , i.e. to the movable die elements  22 . In other words, the first pressurised fluid exerts on the pressing sleeve  31  a pressure force that is parallel to the moulding axis A, directed towards the die arrangement  13 , thus providing a first pneumatic system acting on said pressing sleeve. 
     The lower chamber  42 , along the moulding axis A, is shaped and has a first portion  42   a,  the annular cross section thereof being substantially constant and a second portion  42   b,  made owing to a corresponding recess obtained in the pressing sleeve  31 , the annular cross section of which on the other hand increases towards the die arrangement  13  and ends with the transverse wall  39 , with the greatest cross section. In this manner it is possible to obtain a lower chamber  42  that has substantially small overall dimensions whilst obtaining an extended surface of interaction between pressurised fluid and pressing sleeve  31 . 
     On a lower portion of the external jacket  35  a stopping ring nut  47  is mounted that is arranged for preventing the exit of the pressing sleeve  31  pushed by the pressurised fluid of the lower chamber  42  towards the die arrangement. 
     The stopping ring nut  47  is arranged in particular for abutting on an external shoulder  48  obtained on the external surface  36  of the pressing sleeve  31 . 
     The stopping ring nut  47  constitutes the limit stop of the pressing sleeve  31  in an operating position of maximum extent of the latter. In particular, between the external shoulder  48  of the pressing sleeve  31  and the stopping ring nut  47 , there is interposed a replaceable element  46 , substantially a cylindrical annular spacer, that enables the limit stop position of the pressing sleeve  31  to be modified with respect to the external jacket  35 . 
     The jacket arrangement  91  further comprises a tubular inner jacket  49 , fixed to the external jacket  35  and provided with a through housing  59  which is arranged for receiving the punch  12  and for supporting the punch together with the external jacket  35 . 
     The inner jacket  49  has a first portion  50 , contained inside the external jacket  35  and having a substantially cylindrical external surface  51 , and a second portion  52 , opposite the first portion  50  that extends outside the external jacket  35 . 
     The punch arrangement  12  comprises an intermediate sleeve  53  slidably mounted and interposed between the external jacket  35  and the first portion  50  of the inner jacket  49 . In order to guide the sliding of the intermediate sleeve  53  between the external jacket  35  and the inner jacket  49 , a cylindrical external surface  54  of the intermediate sleeve interacts with a portion of the internal side surface  38  of the external jacket  35 ; a cylindrical internal surface  55  of the intermediate sleeve  53  interacts with a portion of the external cylindrical surface  51  of the inner jacket  49 . The intermediate sleeve  53  is bounded above by a substantially transverse wall  56 . 
     A second pressurised fluid, for example compressed air at a second pressure, is contained in an annular upper second chamber  57 , which is made above the transverse annular wall  56  and is bounded by the latter, by the internal side surface  38 , by the bottom surface  138  of the external jacket  35  and by the external surface  51  of the first portion  50  of the inner jacket  49 . The second pressurised fluid of the upper chamber  57  is at a second pressure, the second pressure being greater than the first pressure of the pressurised fluid of the lower chamber  42 . 
     The second fluid at said second pressure enters the upper chamber  57  through a plurality of respective supply conduits  58  (or also, in an alternative embodiment that is not shown, by a single second supply conduit  58 ) obtained inside the external jacket  35  and supplied by a second external source of pressurised fluid that is not illustrated. The pressurised fluid acts on the transverse annular wall  56  of the intermediate sleeve  53 , pushing the intermediate sleeve  53  outside the external jacket  35 , i.e. to the movable die elements  22 . In other words, the pressurised fluid exerts on the intermediate sleeve  53  a pressure force that is parallel to the moulding axis A and is directed to the die arrangement  13 . 
     The inner jacket  49  comprises a first annular ridge  60  an upper wall of which constitutes a shoulder that is suitable for abutting on a corresponding shoulder  61  of the intermediate sleeve when the latter is pushed to the die arrangement  13  by the pressurised fluid of the upper chamber  57  and is in an operating position of maximum extent. The first annular ridge  60  of the inner jacket  49  thus constitutes the limit stop of the intermediate sleeve  53  in an operating position of maximum extent. 
     The inner jacket  49  further comprises a tubular protrusion  62 , connected to the ridge  60  on a side opposite the second chamber  57 , extending towards the die arrangement and provided with a respective end transverse wall  63 . 
     The intermediate sleeve  53  comprises a transverse lower annular wall  64  that extends from the cylindrical external surface  54  on an opposite side to the upper transverse wall  56 . Adjacent to said wall  64 , a tubular protrusion  65  extends that terminates with a transverse end wall  66 . Between said intermediate sleeve  53  and said external jacket  35 , in particular between said tubular protrusion  65  and the internal side surface  38  of the external jacket  35  there is defined an annular seat  67  that is suitable for slidably receiving the tubular protrusion  40  of the pressing sleeve  31 . In particular, the transverse end wall  41  of the tubular protrusion  40  of the pressing sleeve  31  is suitable for approaching without ever abutting on, the transverse lower annular wall  64  of the intermediate sleeve  53 , when the pressing sleeve  31  is in a retracted operating position. In this operating position of the pressing sleeve  31 , as will be explained better below, the pressurised fluid in the second chamber  57  acts directly on the intermediate sleeve  53  whilst the pressing sleeve  31  is pushed towards the die arrangement  13  by the thrust generated directly thereupon by the pressurised chamber  42 . 
     As illustrated in  FIG. 4  and in  FIG. 6 , between the pressing sleeve  31  and the punch  14  a forming sleeve  68  is interposed that has a tubular shape that is slidably mounted on said punch  14  and is substantially coaxial thereto. A portion of the punch  14  bounded by the external forming surface  15  exits from the forming sleeve  68  and faces the die arrangement  13 . 
     The forming sleeve  68  is bounded below by an end  69  in which an annular forming surface  70  is obtained, arranged towards the punch  15  and suitable for shaping the annular edge  10  of the preform  1 , and a first transverse interaction surface  71  is obtained, arranged externally and facing the transverse surface  26  of each movable element  22 . 
     Parallel to the moulding axis A and near the lower end  69  thereof, the forming sleeve  68  is bounded externally by an external guiding surface  72  that can engage with the guiding surface  27  of each movable element  22 . Inside, the forming sleeve  68  is on the other hand bounded by an internal guiding surface  73  that can slide along the punch  14 . 
     Above the external guiding surface  72 , the forming sleeve  68  has a zone of greater diameter and is bounded below, transversely to the moulding axis A, by a second interaction surface  74  that can interact with the upper surface  25  of each movable part  20 . 
     A ring nut element  75  is fixed to an upper end of the forming sleeve  68 , for example by a threaded connection, and said ring nut element  75  has an internal edge  76  that is suitable for engaging with a second shoulder  77  obtained on the punch  14 . 
     The second shoulder  77  constitutes the limit stop of the forming sleeve  68  in a respective operating position of maximum extent and in fact prevents the forming sleeve  68  from detaching from the punch  14  and limits the movement thereof during the forming process. 
     Inside the forming sleeve  68  an internal shoulder  78  is obtained that can abut on the first shoulder  16  obtained on the punch  14 . 
     The forming sleeve  68  further comprises an annular ridge  79  provided at the upper surface of said forming sleeve  68  and arranged for abutting on the transverse end wall  66  of the intermediate sleeve  53  when the latter is in the respective operating position of maximum extent. In this operating position, the second pressurised fluid in the second chamber  57  acts directly on the intermediate sleeve  53  and indirectly on the forming sleeve  68 , which is pushed towards the die arrangement  13  by the transverse end wall  66  of the intermediate sleeve  53 . The second pressurised fluid thus provides a second pneumatic system acting on said intermediate sleeve  53 . 
     With reference to  FIGS. 3 ,  4  and  5 , the forming sleeve  68  and the punch  14  are connected and are dismantleable by the punch arrangement  12 , without the need to empty the first pressurised fluid in the first lower chamber  42  and the second pressurised fluid in the second upper chamber  57 . In fact, as shown in  FIG. 3  in which the punch  14  is dismantled, both the first and the second chamber are entirely bounded by the walls of the inner jacket  49  and/or of the external jacket  35 , and by walls that are part of the intermediate sleeve or of the pressing sleeve  31  and accordingly both the first and the second chamber are completely isolated from the punch  14 , which can be possibly replaced by another one of another type. 
     It should further be noted that the apparatus  11  comprises a manifold  95  for distributing both the cooling liquid and the first pressurised fluid and the second pressurised fluid. In particular, the manifold comprises a hollow ring-shaped element located above the punch arrangement  12  to which the first pressurised fluid, the second pressurised fluid and the cooling liquid flow in distinct angular positions, which is able to isolating the circulating liquid inside the punch  14  from the rest of the liquid circulating in the distribution circuit. 
     When dismantling the punch  14 , it is not therefore necessary to empty entirely the circuit of the cooling fluid and only the fluid inside the punch  14  will be lost. 
     The apparatus  11  further comprises seat elements  80  ( FIGS. 3 and 5 ) arranged for receiving the punch arrangement  12 . In particular, the seat elements  80  comprises a first seat  81  arranged for housing the jacket arrangement  91 , i.e. the external jacket  35 , the possible cylindrical element  135  fixed to the external jacket  35  and the inner jacket  49 , and a second seat  82  arranged for housing an end portion  83  of the punch  14 , opposite the external forming surface  15 . 
     Inside the second seat  82 , the apparatus  11  comprises a first fixing device  84  for removably locking said punch  14  in said second seat  82 . The first fixing device  84  comprises, for example, a female screw  85  that is rotatably inserted into the second seat  82  and has an internally threaded end portion that is suitable for receiving the threaded end portion  83  of the punch  14 . 
     It should be noted that the punch  14  has an abutting portion  86 , that is an abutting edge, which abuts on the transverse end wall  63  of the tubular protrusion  62  of the inner jacket  49 , when the punch  14  is inserted inside the inner jacket  49 . The abutting edge  86  thus enable the jacket arrangement  91  to be locked inside the first seat  81  with a force parallel to the moulding axis A and directed to the first fixing device  84 , when the punch  14  is locked by the first fixing device  84  in the second seat  82 . 
     The apparatus  11  comprises a second fixing device  87  that enables the jacket arrangement  91  to be locked removably in said first seat  81  when the punch  14  is dismantled. 
     The second fixing device  87  comprises a bush  88  housed inside the first seat  81  and fixed, for example by a threaded connection, to the free end  52  of the inner jacket  49 . The second fixing device  87  further comprises a removable transverse pivot  89  that fixes the bush  88  to a wall of the first seat  81 . 
     The punch arrangement  12  of the invention comprises substantially an external cartridge  90 , to which the jacket arrangement  91 —i.e. the external jacket  35  and the inner jacket  49 —the pressing sleeve  31  and the intermediate sleeve  53  belong, and inside which cartridge the first chamber  42  and the second chamber  57  are entirely bounded. The external cartridge  90  remains fixed in the first seat  81 , by virtue of the second fixing device  87 , with the pressurised chambers, even when the punch  14  is extracted. 
     Between the bush  88  and the first fixing device  84 , the apparatus  11  comprises a removable connecting device  92  comprising for example an extractable safety spring that secures the punch  14  to the external jacket  35  and to the inner jacket  49 , regardless of the first fixing device  84  and of the second fixing device  87 . In this manner the punch arrangement  12  can be extracted completely from the seat elements  80 , for maintenance operations. 
     During operation, the moulding apparatus  11  is located initially in an open position shown in  FIG. 1 , in which the die arrangement  13  is spaced apart from the punch arrangement  12  to receive a dose D of plastics in melted/pasty state in the die cavity from a transferring arrangement that is not shown. 
     The movable elements  22  are maintained in the contact position by the pressing sleeve  31  in the respective operating position of maximum extent, inasmuch as the pressing sleeve  31  is pushed initially to the die arrangement  13  by the first fluid at a first pressure of the first lower chamber  42 . Also the intermediate sleeve  53  is in the respective operating position of maximum extent, being pushed by the second fluid at a second pressure of the second chamber  57 . Similarly, as already previously illustrated, also the forming sleeve  68  is in the operating position of maximum extent inasmuch as it is pushed by the intermediate sleeve  53 . 
     Subsequently, in an initial forming step, an actuator moves the die arrangement  13  to the punch arrangement  12 . The upper end of the dose D comes into contact with the lower end of the punch  14 . 
     Whilst the actuator continues to move the die arrangement  13  towards the punch arrangement  12 , the punch  14  starts to squeeze the dose D, deforming the dose and redistributing the dose inside the die cavity. In particular, the plastics, pressed by the punch  14  expands and entirely occupies the part of the die cavity arranged below the punch  14  and starts to take the shape of the internal forming surface of the die cavity that will constitute the external surface  3  of the preform  1 . 
     Subsequently, the die arrangement  13  comes into contact with the lower surface  24  of the movable elements  22 . In particular, the frustoconical surface  28  of the movable elements  22  is engaged in a shapingly coupled manner with the upper portion of the die arrangement  13 , which has a complementary shape. 
     The plastics contained inside the die cavity, pressed by the punch  14  start to rise to the movable elements  22 , whilst maintaining themselves below the lower surface  24  of the latter. In this forming step, even if the plastics flow to a higher level already in this step, they could not penetrate the gap between the upper surface of the die cavity and the movable elements  22  because the latter are maintained pressed against the die arrangement  13  by the pressing sleeve  31 , on which the fluid at a first pressure of the first chamber  42  acts. 
     Subsequently, the actuator continues to move the die arrangement  13  upwards and consequently, the die arrangement  13  being in contact with the movable elements  22 , the actuator also moves the movable elements  22  and the pressing sleeve  31 , which move integrally with the die arrangement  13 . 
     In this step, the forming sleeve  68  is still stationary, kept in the operating position of maximum extent inasmuch as pushed by the intermediate sleeve  53 , whilst the guiding surface  27  of the movable elements  22  flows along the external guiding surface  72  of the forming sleeve  68  and the external surface  36  of the pressing sleeve  31  slides on the internal side surface  38  of the external jacket  35 . The tubular protrusion  40  of the pressing sleeve  31  slides inside the seat  67  defined between the tubular protrusion  65  of the intermediate sleeve  53  and the external jacket  35 . The first fluid at a first pressure contained in the first lower chamber  42  contrasts the pressing sleeve  31  strongly, which maintains the movable elements  22  pressed towards the die arrangement  13 . 
     In an intermediate forming step, the transverse surfaces  26  of the movable elements  22 , pushed by the actuator, are positioned near the first interaction surface  71  of the forming sleeve  68 , such that they position themselves ad a distance from the interaction surface  71  that is so small as to prevent the plastics from flowing between the transverse surfaces  26 , whilst enabling the air inside the die cavity to exit. Simultaneously, the upper surfaces  25  of the movable elements  22  are positioned in contact with the second interaction surface  74  of the forming sleeve  68  and the upper wall of the annular ridge  79  of the latter continues to abut on the transverse end wall  66  of the intermediate sleeve  53 . The first transverse end wall  41  of the tubular protrusion  40  of the pressing sleeve  31  slides retracting inside the seat defined between the tubular protrusion  65  of the intermediate sleeve  53  and the external jacket  35 . 
     Between the punch arrangement  12  and the die arrangement  13 , there is thus defined a first closed forming chamber, not yet having a shape corresponding to the definitive shape of the preform  1 , inasmuch as the punch  14  and the die cavity have not yet reached the corresponding final configuration. The annular forming surface  70  of the forming sleeve  68  closes the first forming chamber whilst the plastics start to fill the first forming chamber completely. 
     Subsequently, the actuator continues to move the die arrangement  13  upwards and consequently, the die arrangement being in contact with the movable elements  22 , the actuator moves integrally upwards the movable elements  22 , the pressing sleeve  31  (the retaining surface  32  of the pressing sleeve is in contact with the second coupling surface  29  of the movable elements  22 ), the forming sleeve  68  (the upper surfaces  25  of the movable elements  22  are in contact with the second interaction surface  74  of the forming sleeve  68 ) and the intermediate sleeve  53 , the latter being in contact with the forming sleeve  68  and being moved by the latter. 
     In this final forming step, the volume of the forming chamber is reduced progressively until the punch arrangement  12  and the die arrangement  13  reach the final operating configuration in which a second forming chamber is defined having a geometry corresponding substantially to that of the final preform  1 . The second fluid at a second pressure of the second upper chamber  57  acts as a gas spring and exerts a contrasting action on the intermediate sleeve  53 , which is pushed strongly towards the die arrangement. In this manner the forming sleeve  68 , pushed by the intermediate sleeve  53 , pushes the movable elements  22  to the die arrangement  13  pressing the movable elements  22  towards the latter. In particular, the annular forming surface  70  of the forming sleeve  68  effectively forms the edge zone  10  of the preform, contrasting the rise of the plastics, whilst the second interaction surface  74  of the forming sleeve  68  strongly pushes the movable elements  22  towards the die arrangement  13 . 
     Simultaneously, the pressing sleeve  31 , pushed by the fluid of the first chamber  42  with a pressure force that is due to the first fluid at a first pressure, continues to maintain the movable elements  22  in contact, pressing the movable element  22  strongly towards the die arrangement  13 , contrasting the action of the plastics in the forming chamber at the movable elements  22 . 
     The first transverse end wall  41  of the tubular protrusion  40  of the pressing sleeve  31 , in the retracted operating position, comes to being near to contact with the lower transverse wall  64  of the intermediate sleeve  53 , but without abutting the lower transverse wall  64 , whilst the first fluid at a first pressure of the first lower chamber  42  continues to push the pressing sleeve towards the die arrangement  13 . In the final forming step, the second chamber  57  thus acts on the forming sleeve  68 , inasmuch as the intermediate sleeve  53  abuts on said forming sleeve  68  pushing the forming sleeve  68  towards the movable die elements  22 , whilst the first chamber  42  continues to act on the pressing sleeve  31 . It should thus be noted that the first chamber  42  and the second chamber  57 , although starting to operate in succession, the first chamber  42  by starting to operate before the second chamber  57 , cooperate in the intermediate and final forming step, generating respective distinct pressure forces directed to the die arrangement  13  to push simultaneously but independently the movable elements  22  to the die arrangement  13 . 
     In particular, the first chamber  42  and the second chamber  57  act on distinct portions of said movable elements  22 , inasmuch as the first chamber  42  acts on the frustoconical coupling surface  29  of the movable elements  22  whilst the second chamber  57  acts on the upper surface  25  thereof. 
     When the preform  1  has been cooled and stabilised to a temperature at which it can be handled without risks of damage, the moulding apparatus  11  is opened to enable the preform  1  that has just been formed to be removed. It should be noted that as the preform  1  cools it shrinks, remaining firmly clamped around the punch  14 . 
     In an initial extracting step, the actuator remove the die arrangement  13  from the punch arrangement  12 , by moving the die cavity downwards. 
     As a result the second chamber  57 , by acting on the intermediate sleeve  53  that abuts on the forming sleeve  68 , slides the forming sleeve  68  downwards. In turn, the second interaction surface  74  of said forming sleeve  68  abuts on the upper surface  25  of the movable die elements  22  and pushes the latter downwards or towards the die arrangement  13 . Simultaneously, the first chamber  42  pushes the pressing sleeve  31  downwards and thus also the pressing sleeve  31 , as the retaining surface  32  of said pressing sleeve  31  abuts on the frustoconical coupling surface  29  of said movable elements  22 , pushes the movable elements  22  downwards. It should therefore be noted that the first chamber  42  and the second chamber  57  cooperate in the initial extracting step, generating respective distinct forces directed towards the die arrangement  13  to push simultaneously the movable elements  22  downwards. 
     In this initial extracting step, the preform  1  is associated with the movable elements  22  because the threaded portion  5 , the circular ridge  6  and the ring  7  are clamped by the complex forming surface  23 . Moving towards the die arrangement  13 , the movable elements  22  thus detach the preform  1  from the punch  14 , overcoming the friction between the preform  1  and the punch  14 . 
     It is important to remark that the preform  1  is removed from the punch  14 , guided by the forming sleeve  68  as far as the operating position of maximum extent of the forming sleeve  68  is achieved, inasmuch as the forming sleeve  68  slides downwards, the annular forming surface  70  of the forming sleeve  68  pushing on the edge zone  10  of the preform  1  and preventing possible deformations thereof. 
     The pressing sleeve  31 , which cooperates as disclosed above with the forming sleeve  68 , contributes to removing the preform  1  from the punch  14  and in particular stabilises the threaded portion  5  of the preform  1 , preventing possible radial deformation thereof. 
     In an intermediate extracting step, the forming sleeve  68  stops in an advanced operating position, inasmuch as the internal edge  76  of the ring nut element  75  engages with the second shoulder  77  obtained on the punch  14 . In the meantime, the tubular protrusion  40  of the pressing sleeve  31 , which continues to be pushed by the first fluid of the first chamber  42 , slides inside the seat  67 , defined between the tubular protrusion  65  of the intermediate sleeve  53  and the external jacket  35 , towards the die arrangement  13 . 
     It should therefore be noted that first chamber  42  and the second chamber  57 , although ceasing to operate in succession, the second chamber ceasing to operate before the first chamber  42 , cooperate both in the initial and in the intermediate extracting step, generating respective distinct forces directed to the die arrangement  13  to push simultaneously, but independently, the movable elements  22  towards the die arrangement  13 . 
     In a final extracting step, the first pressurised fluid contained in the first lower chamber  42  further pushes the pressing sleeve  31  towards the die arrangement  13  and moves away from the forming sleeve  68 , maintained stationary by the second shoulder  77  of the punch  14 . The movable elements  22 , maintained in reciprocal contact by the pressing sleeve  31 , moves downwards together the latter and continue to remove the preform  1  from the punch  14 . It should be known that in this step the preform  1 , which is already detached from the external forming surface  15 , can be removed from the punch  14  with a relatively low extracting force, which is performable only by the first pressurised fluid contained in the first lower chamber  42 . 
     During an operation of maintenance of the compression-moulding apparatus, in which, for example, cleaning and/or testing of the punch arrangement  12  installed in the apparatus  11  is necessary, it is above all necessary to proceed by emptying the supply conduit  44  of the compressed air to the first chamber  42  and the supply conduit  58  of the compressed air to the second chamber  57 , that is the circuit of the compressed air of the apparatus  11 . Further, the distribution of the circulating cooling liquid in the apparatus must be isolated from the cooling liquid circulating inside the punch arrangement  14 . 
     It is possible to dismantle the punch arrangement  12  completely from the apparatus  11 , extracting the punch arrangement  12  from the seat elements  80 , by acting on the female screw  85  on which the punch  14  is screwed and by extracting laterally the transverse pivot  89  that fixes the bush  88  on the seat elements  80 . The removable connecting device  92  will anyway maintain the punch  14  connected to the corresponding cartridge  90 , ensuring safe dismantling of the punch arrangement from the apparatus  11 . 
     It should be known that, after the maintenance operation, the punch arrangement  12  is mounted without the need to perform long adjusting and aligning operations of the components, inasmuch as the seat elements constitute per se the centring device of the punch arrangement during the mounting step. 
     During a size change over operation, or when there is the need to make preforms  1  of a different weight and/or of a different shape, by isolating the distribution of the circulating cooling liquid in the apparatus from the circulating cooling liquid inside the punch  14  it is possible to replace in a short time the punch  14  with a punch of different size by acting on the female screw  85  on which the punch  14  is screwed. When the punch has been dismantled, both the first chamber  42  and the second chamber  57  inside the cartridge  90  continue to remain pressurised, and therefore, after screwing the new punch  14  having different size inside the inner jacket  49  and after re-establishing the cooling liquid inside the latter, the apparatus  11  is already ready for being operational. The punch  14  does not in fact need any type of alignment inside the inner jacket  49 , sliding inside the latter during mounting and being locked thereupon by the abutting edge  86 . 
     The apparatus  11  disclosed above thus has the advantage of ensuring optimum pressure force acting on the movable elements  22  by means of the pressing sleeve  31  and by means of the forming sleeve  68 —in particular a reduced pressure force in an intermediate forming step, a much greater pressure step in the final forming step—whilst enabling great flexibility during operation. In particular, making the chambers  42 ,  57  entirely defined by walls of the pressing sleeve  31  and of the jacket arrangement  91  enables the aforesaid chambers  42 ,  57  to be isolated from the punch  14  in order to permit rapid dismantling and mounting of the punch  14  for a size change over. 
     Further, the structure of the apparatus  11  is particularly simplified as the first pneumatic system made by the first chamber  42  and the second pneumatic system made by the second chamber  57  generate pressure forces that are parallel to one another and of a different value, that push distinct portions of said movable elements  22  towards the die arrangement  13 . This is also particularly advantageous, inasmuch as it enables a respective optimum pressure force to be applied to each portion of said movable elements  22 , said force being able to form and subsequently extract the mouth zone  6  of the preform  1  from the punch  14  without deformation, in an intermediate and final forming step and in an initial and intermediate extracting steps. 
     In one embodiment that is not illustrated, the first chamber  42  and the second chamber  57  cooperate exclusively in the final forming step and initial extracting step, when there is a need for maximum pressure force to push simultaneously but independently the movable elements  22  to the die arrangement  13 . 
     In an alternative embodiment that is not shown in the figures, the apparatus  11  has a single chamber, for example the upper chamber  57  supplied with a pressurised fluid that in an intermediate forming step has less pressure and in a final forming step has greater value. The pressing sleeve  31  and the intermediate sleeve  68  collaborate integrally together to make a single slidable pressing sleeve  31  acting on the movable elements  22 . It should be known that also in this alternative embodiment, the punch  14  can be extracted from the punch arrangement  12  without the need to empty the circuit of the pressurised fluid.