Patent Publication Number: US-2011056809-A1

Title: System for blowing plastic containers, specifically bottles

Description:
TECHNICAL FIELD 
     This invention relates to a plant for blow-moulding plastic containers, particularly bottles. 
     BACKGROUND ART 
     In the bottling industry, prior art plant of the type described, for example in patent applications EP-1445090-A1 and WO-0224435-A1, used for making plastic bottles, comprises: a blow-moulding wheel mounted in such a way as to rotate about a first longitudinal axis and equipped with a plurality of blow-moulding units, each of which is rotationally fed by the blow-moulding wheel about the first axis, comprises a mould for blow-moulding at least one bottle from a respective parison, and cooperates with at least one stretching rod designed to axially deform the parison. 
     Generally speaking, the stretching rods are moved along a line parallel to the first axis by a drive device comprising a first cam and, for each stretching rod, a respective first tappet roller engaged in the first cam itself. 
     The plant further comprises: an oven for thermally conditioning the parisons; a first feed device for advancing the parisons through the oven; a first transfer wheel mounted rotatably about a second longitudinal axis to transfer the parisons one after the other from the first feed device to the blow-moulding wheel; and a second transfer wheel mounted rotatably about a third longitudinal axis to transfer the bottles one after the other from the blow-moulding wheel to a second device for feeding the bottles to a bottle filling device or to another conveying device. 
     Usually, each transfer wheel comprises: a drum mounted to rotate about a respective second or third axis; a plurality of pick-up and transporting units, each of which is mounted on the drum to feed a respective parison or a respective bottle about the respective second or third axis, comprises a supporting arm rotatably coupled to rotate, relative to the drum, about a respective fourth axis, and is further equipped with a pick-up member rotatably coupled to the supporting arm to rotate, relative to the supporting arm, about a respective fifth axis; and an orienting device designed to orient the pick-up and transporting units about the respective fourth and fifth axes. 
     The orienting device comprises a second and a third cam and, for each pick-up and transporting unit, a second tappet roller mounted on the respective supporting arm and engaged in the second cam, and a third tappet roller mounted on the respective pick-up member and engaged in the third cam. 
     The orientation of the pick-up and transporting units about the respective fourth and fifth axes makes it possible to correctly transfer the parisons and the bottles, respectively, from the first feed device to the blow-moulding wheel and from the blow-moulding wheel to the second feed device according to the spacing of the parisons along the first feed device, the spacing of the moulding units and the spacing of the bottles along the second feed device. 
     Prior art bottle blow-moulding plants of the type described above are not, however, free of disadvantages due mainly to the fact that the passage from parisons and bottles of a first size to parisons and bottles of a second size, different from the first size, necessitates each time replacing the first, second and third cams, creating serious difficulties for personnel in charge and involving relatively long plant set-up times. 
     AIM OF THE INVENTION 
     This invention has for an aim to provide a blow-moulding plant for making plastic containers, particularly bottles, that is free of the above mentioned disadvantages and that is simple and inexpensive to implement. 
     Accordingly, this invention provides a plant for blow-moulding plastic containers, particularly bottles, as described in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings which illustrate a preferred, non-limiting embodiment of it and in which: 
         FIG. 1  is a schematic plan view, with, some parts cut away for clarity, of a preferred embodiment of the plant according to the invention; 
         FIG. 2  is a schematic plan view, with some parts cut away for clarity, of a first detail of the plant of  FIG. 1 ; 
         FIG. 3  is a schematic side view, with some parts cut away for clarity, of the detail of  FIG. 2 ; 
         FIG. 4   a  is a schematic plan view, with some parts cut away for clarity, of another embodiment of the detail of  FIGS. 2 and 3 , illustrated in a first operating position; 
         FIG. 4   b  is a schematic plan view, with some parts cut away for clarity, of another embodiment of the detail of  FIGS. 2 and 3 , illustrated in a second operating position; 
         FIG. 5   a  is a schematic side view, with some parts cut away for clarity, of a second detail of the plant of  FIG. 1 , illustrated in a first operating position; 
         FIG. 5   b  is a schematic side view, with some parts cut away for clarity, of the detail of  FIG. 5   a , illustrated in a second operating position; 
         FIG. 6  is a schematic side view, with some parts cut away for clarity, of another embodiment of the detail of  FIG. 5 ; 
         FIG. 7   a  is a schematic side view, with some parts cut away for clarity, of the detail of  FIG. 5   a  made according to a second embodiment; 
         FIG. 7   b  is a schematic side view, with some parts cut away for clarity, of the detail of  FIG. 5   b  made according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     With reference to  FIG. 1 , the numeral  1  denotes in its entirety a plant for blow-moulding plastic containers, in this particular case, plastic bottles  2  ( FIG. 3 ), from respective parisons  3  of known type ( FIG. 5 ), each of which comprises an elongated cup-shaped body  4  having an externally threaded open end  5 , and an annular neck  6  extending radially outwards from the outside surface of the body  4  itself. 
     The plant  1  comprises a blow-moulding machine  7  in turn comprising a blow-moulding wheel  8  mounted in such a way as to rotate continuously about its longitudinal axis  9 , which is substantially vertical and at right angles to the drawing plane of  FIG. 1 , and a plurality of moulding units  10  which are mounted round the edge of the wheel  8 , are uniformly distributed around the axis  9  according to a predetermined spacing, and are advanced by the wheel  8  around the axis  9 . 
     Each unit  10  comprises a mould  11  in turn comprising two half-moulds of known type, not illustrated, that move between an open position where the half-moulds (not illustrated) are positioned at a predetermined distance from each other to receive a parison  3  or release a bottle  2 , and a closed position, where the half-moulds (not illustrated) form inside them at least one moulding cavity  12  having the shape of a bottle  2  and being open to the outside at a hole  13  at the top of it smaller in diameter than a neck  6 , and acting in conjunction with a pneumatic device of known type, not illustrated, designed to blow compressed air into the parison  3  inside the cavity  12 . 
     As illustrated in  FIG. 5 , each cavity  12  acts in conjunction with a respective stretching rod  14  which extends along a vertical line  15  parallel to the axis  9 , is mounted at a position coaxial with the cavity  12  and is mobile along the line  15  between a raised position ( FIG. 5   a ), where the rod  14  is located substantially outside the respective parison  3 , and a lowered position ( FIG. 5   b ), where the rod  14  engages the respective parison  3  in such a way as to stretch it axially along the line  15 . 
     The stretching rods  14  are moved along the line  15  by a drive device  16  comprising, for each stretching rod  14 , a respective drive motor  17  fixed to a mounting bracket  18  of the unit  10 , and having an output shaft  19  that is mounted to rotate about a longitudinal axis  20  parallel to the line  15 , is coupled by a lead nut and screw mechanism to a plate  21  on which the stretching rod  14  itself is mounted and is rotationally driven by the motor  17  so as to move the stretching rod  14  in a straight line between its raised and lowered positions. 
     More specifically, each drive motor  17  comprises an electric motor  17   a  (in this particular case, a brushless electric motor) and a control encoder  17   b  connected, together with the encoders  17   b  of the other electric motors  17   a,  to an electronic control unit  22  designed to control the operation of the motors  17  and, hence, the movement of the stretching rods  14  along the line  15  according to the size of the parisons  3 , that is to say, according to the dimensions and/or shape of the parisons  3 . 
     In other embodiments which are not illustrated, the lead nut and screw coupling is eliminated and, instead, there is, for example, a transmission belt system and each drive motor  17  comprises a linear motor. 
     In the embodiment illustrated in  FIGS. 7   a  and  7   b , the stretching rod  14  is connected directly to a linear electric motor  100  which moves it vertically. 
     The motor  100  might also be of the non-linear type. 
     The use of the linear electric motor  100  allows the stretching rods  14  to be driven at very high speeds. 
     More in detail, the stretching rod  14  moves vertically at an average speed of up to more than 1.5 metres per second. 
     In a first configuration of the plant, the stretching rod  14  moves vertically at an average speed of between 1.5 and 3 metres per second. 
     In a second configuration of the plant, the stretching rod  14  moves vertically at an average speed of between 3 and 6 metres per second. 
     This is an extremely advantageous aspect: in fact, it has been observed that stretching the parisons  3  at high speed has a strain hardening effect on the plastic the bottles  2  are made of and improves the mechanical properties of the material. 
     In this way, the quantity of plastic used to make a bottle  2  can be further reduced, allowing significant savings in terms of bottle  2  production cost and lessening the environmental impact of the plant. 
     Increasing the stretching speed of the rods  14  also means that the pressure of the fluid used for blow-moulding the parisons  3  can be less than 30 bar. 
     In particular, the fluid can be applied at a pressure of between 7 and 25 bar. 
     This is made possible by the high stretching speed imparted to the rods  14 . 
     The embodiment illustrated in  FIG. 6  differs from the one illustrated in  FIG. 5  only in that, for moving the respective rod  14  from the raised to the lowered position, each motor  17  acts in conjunction with a respective pushing device  23  comprising, in this particular case, a pneumatic compensation cylinder  24  having an output rod  25  fixed at a free end of it to the respective plate  21 . 
     With reference to  FIG. 1 , the plant  1  further comprises an oven  26  of known type for thermally conditioning the plastic material of the parisons  3  to a temperature greater than its glass transition temperature; a feed wheel  27  of known type for feeding the parisons  3  to the oven  26 ; a first transfer wheel  29  for transferring each parison  3  from the oven  26  to a respective moulding unit  10 ; and a second transfer wheel  30  for transferring each bottle  2  from the respective moulding unit  10  to a customary feed line, not illustrated, of a customary plant, not illustrated, for filling the bottles  2 , or to a bottle  2  outfeed line (not illustrated). 
     Each wheel  29 ,  30  comprises a drum  31  mounted to turn continuously about its substantially vertical longitudinal axis  32  parallel to the line  15 , and a plurality of pick-up and transporting units  33  (in this particular embodiment six pick-up and transporting units  33 ) that are mounted along a peripheral edge of the drum  31 , protrude radially outwards from the drum  31 , and are advanced by the drum  31  itself around the axis  32 . 
     As illustrated in  FIGS. 2 and 3 , each unit  33  comprises a supporting arm  34  that extends transversally of the axis  32 , is hinged to the drum  31  to rotate, relative to the drum  31  itself, about a pivot axis  35  substantially parallel to the line  15 , and mounts a pick-up member  36  which extends transversally of the axis  32  and which comprises a crank lever  36   a  hinged to the arm  34  to rotate, relative to the arm  34  itself, about a pivot axis  37  substantially parallel to the line  15 . 
     The member  36  also comprises a pick-up element  36   b  having the shape of a fork and in turn comprising two arms  38  which are mounted to oscillate about respective pivot axes  39  parallel to the line  15  between a position of releasing (not illustrated) and a position of clamping ( FIG. 2 ) a respective bottle  2  or a respective parison  3 , and which a spring  40  interposed between the arms normally holds in the clamping position where the arms  38  grip it. 
     The units  33  are oriented about the respective axes  35  and  37  by an actuating device  41  comprising, for each unit  33 , a respective first drive motor  42  that is mounted on the drum  31  and has an output shaft  43  which is parallel to the line  15  and which the respective arm  34  is keyed to, and a respective second drive motor  44  that is fixed to the respective arm  34  and has an output shaft  45  which is parallel to the line  15  and which the respective crank lever  36   a  is keyed to. 
     In use, rotation of the wheels  29 ,  30  about the respective axes  32  and simultaneous orientation of the supporting arms  34  about the axes  35  and of the pick-up members  36  about the axes  37  enables the wheel  29  to receive the parisons  3  according to the spacing of the oven  26  and to release them to the blow-moulding machine  7  according to the spacing of the moulding units  10 , and enables the wheel  30  to receive the bottles  2  according to the spacing of the moulding units  10  and to release them to the above mentioned filling plant (not illustrated) according to the spacing of the above mentioned feed line (not illustrated) or to the above mentioned outfeed line (not illustrated) according to the spacing of the outfeed line itself (not illustrated). 
     More specifically, each drive motor  42 ,  44  comprises an electric motor  42   a,    44   a  (in this particular case, a brushless electric motor) and a control encoder  42   b,    44   b  connected, together with the encoders  42   b,    44   b  of the other electric motors  42   a,    44   a,  to the electronic control unit  22  designed to control the operation of the motors  42 ,  44  and, hence, the orientation of the pick-up and transporting units  33  about the respective axes  35 ,  37  according to the size of the bottles  2  and of the parisons  3 . 
     The embodiment illustrated in  FIG. 4  differs from the one illustrated in  FIGS. 2 and 3  only in that the pick-up members  36  are eliminated and each substituted by a respective pick-up unit  46  which comprises a rocker arm  47  hinged to the respective arm  34  to rotate about the axis  37  and which in turn comprises a first and a second arm  48 ,  49  opposite each other, the arm  48  being equipped with a pick-up element  50   a,  similar to the elements  36   b,  and the arm  49  being equipped with two pick-up elements  50   b  that are similar to the elements  36   b,  are parallel to each other and to the element  50   a  and have concavities opposite the concavity of the element  50   a  itself. 
     In use, the drive motors  44  allow the pick-up units  46  to be selectively oriented about the respective axes  37  according to the size of the bottles  2  to be blow-moulded and/or the number of moulding cavities  12  in each mould  11 . In particular, the pick-up elements  50   a  are moved towards the outside of the respective wheel  29 ,  30  to an operating position and the pick-up elements  50   b  are moved towards the inside of the respective wheel  29 ,  30  to a rest position ( FIG. 4   a ) when each mould  11  has a single moulding cavity  12  for blow-moulding a single bottle  2 , while the pick-up elements  50   a  are moved towards the inside of the respective wheel  29 ,  30  to a rest position and the pick-up elements  50   b  are moved towards the outside of the respective wheel  29 ,  30  to an operating position ( FIG. 4   b ) when each mould  11  has two moulding cavities  12  for blow-moulding two bottles  2 . 
     In another embodiment that is not illustrated, each supporting arm  34  is slidably coupled to the respective drum  31  and each pick-up member  36  or pick-up unit  46  is slidably coupled to the respective supporting arm  34 . Alternatively, one of the elements of each pick-up and transporting unit  33  is slidable while the other element of each pick-up and transporting unit  33  is rotatable. 
     In a further possible embodiment that is not illustrated, the orienting device  41  comprises a pick-up and transporting unit  33 , a first drive motor  42  for moving the coupling element  34 , while the pick-up member  36 ;  46  is driven by kinematic couplings such as cams or sliders. 
     Alternatively, in a yet further possible embodiment that is not illustrated, the orienting device  41  comprises, for each pick-up and transporting unit  33 , a first drive motor  42  for moving the pick-up member  36 ;  46 , while the coupling element  34  is driven by kinematic couplings such as cams or sliders.