Abstract:
Ovens for preforms in plastic material, applicable in particular but not exclusively to blowing machines and stretch blowing machines, are provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and benefit of Italian Patent Application No. MI2011A001762 filed Sep. 30, 2011, the contents of which are incorporated by reference in their entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to ovens for preforms in plastic material, applicable in particular, but not exclusively, to blowing or stretch-blowing machines. 
       BACKGROUND OF THE INVENTION 
       [0003]    Obtaining containers by blowing special preforms appropriately heated inside a mould of the desired shape is a method widely used in the packaging sector, in particular for making bottles for drinks. 
         [0004]    Two basic methods exist which include on the one hand simple blowing and on the other, stretch-blowing, both of which provide for pneumatic blowing and mechanical stretching of the preforms in a mould. In both cases the preforms must reach the blowing or stretch-blowing machine in a thermal condition corresponding to the softening point of the material, so as to be plastically deformable inside the moulds. 
         [0005]    Softening of preforms is performed in special ovens which include a series of heating modules positioned in series along a circuit of preforms. 
         [0006]    To maximize both the heat efficiency of the oven and its dimensions, it is advisable for preforms to be inserted and slid inside the oven at as close a pitch as possible. (It is understood in this context that the term “pitch” refers to the spacing between one preform and an adjacent one.) This requirement is however contrary to the need for heated preforms to be sufficiently distanced for their insertion in the moulds of the blowing or stretch-blowing machine, the pitch of which, for obvious reasons of size, cannot be reduced beyond a certain limit. 
         [0007]    In conventional machines, this distancing operation of the preforms to the pitch of the moulds is implemented by means of drive means, in particular distribution stars, which comprise a plurality of gripping means of preforms which are positioned at the same pitch as the moulds in the blowing machine or at an intermediate pitch between the latter and that of the preforms coming out of the oven. As a result, the distribution stars are placed in rotation at a higher speed than the supply speed of the heated preforms and lower or equal speed to the rotation speed of the blowing machine. 
         [0008]    This change of speed imparts a considerable acceleration to the preforms. If one considers that preforms coming out of the oven are not rigid but softened, such acceleration may cause a deformation of the preforms, with a consequent formation of imperfections in the bottle obtained after blowing or stretch-blowing. In fact, deformed preform may contact the surface of the mould before the beginning of blowing, causing an abrupt cooling of the preform in the point of contact which is thus no longer able to undergo expansion. 
       SUMMARY OF THE INVENTION 
       [0009]    The problem addressed by the present invention is to make available ovens and preforms which overcome the drawbacks described above. 
         [0010]    Such problem is resolved by an oven for preforms as delineated in the appended claims which forms an integral part of this description. 
         [0011]    Further characteristics and advantages of the present invention will be more clearly comprehensible from the description given below of some of its embodiments, made by way of a non-limiting example, with reference to the following drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]      FIG. 1  shows a schematic plain view of an oven-blowing machine assembly according to embodiments of the invention. 
           [0013]      FIG. 2  shows a partial perspective view of an oven for preforms according to embodiments of the invention. 
           [0014]      FIG. 3  shows a detailed perspective view of a mandrel of the oven of  FIG. 2 . 
           [0015]      FIG. 4  shows another detailed perspective view of the mandrel of  FIG. 3  in a different operating position. 
           [0016]      FIG. 5  is a side view in the direction A in  FIG. 4 . 
           [0017]      FIG. 6  is a side view in the direction B in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    With reference to the figures, reference numeral  1  globally denotes ovens for preforms according to the invention, which may be operatively connected to drive units  2 ,  3  of the preforms, respectively entering and leaving the oven  1 . Such drive units  2 , 3  may include, but are not limited to distribution stars which may include a series of gripping members  4 , such as notches or indentations, adapted for engaging the preforms, for example at the neck. 
         [0019]    The drive units  3  for preforms coming out of the oven  1  in turn may be operatively connected to a blowing machine  5  (the term “blowing machine” used in the present description refers to any type of blowing or stretch-blowing machine) which includes, for example, a plurality of moulds  6  in which heated preforms, are inserted and from which they come out in the form of a blown (or stretch-blown) bottle. 
         [0020]    The blowing machine  5  in turn may be operatively connected to distribution unit  7 , typically including a distribution star, suitable for picking up the blown bottles coming out of the blowing machine and transferring them, by a suitable transport mechanism, to a subsequent operating unit. The distribution star  7  may include for to such purpose a plurality of notches  4 ′ suitable for engaging the neck of the blown bottles. 
         [0021]    A path is thus defined for the preforms, shown in  FIG. 1  by the direction of the arrows, from their being fed to the oven  1  to their entrance in the moulds  6  of the bowing machine  5 . 
         [0022]    The oven  1  may include a transport mechanism  8 , adapted for moving the preforms along a path inside said oven, and heating units  9 . 
         [0023]    The heating units  9  may include of a plurality of heating modules  10  aligned along the preform path, typically outside the transport mechanism  8 . Such heating modules  10  may include, for example, one or more infrared lamps and suitable reflective surfaces to optimise the output of the lamps. 
         [0024]    The transport mechanism  8  may include a track  11  on which a plurality of mandrels  12  slide, each adapted for engaging a preform. The track  11  may include two rectilinear sections  13 ,  13 ′ substantially parallel and two curved sections  14 ,  14 ′ which connect the rectilinear sections  13 ,  13 ′ at their ends according to a circular arc route. At the point of said curved sections  14 ,  14 ′ respective conductor wheels  15 ,  15 ′ may be placed, as will be described further below. 
         [0025]    The track  11  may include a pair of rails  16   a,    16   b  placed vertically, each in turn divided into rectilinear sections and curved sections at the rectilinear sections and curved sections  13 ,  13 ′,  14 ,  14 ′ of the track  11 . 
         [0026]    The rails  16   a,    16   b  may include an L-shaped cross-section profile, comprising a rack bar  17   a,    17   b  which forms one side of the L and a guide bar  18   a,    18   b  which forms the other side of the L. In the track  11 , the rack bars  17   a,    17   b  of the rails  16   a,    16   b  may be facing, while the relative guide bars  18   a,    18   b  extend in opposite directions on the same vertical plane. 
         [0027]    The rack bars  17   a,    17   b  may include, on the rectilinear sections  13 ,  13 ′ of the track  11 , a double rack profile  19  separated by a furrow  20 , while on the curved sections  14 ,  14 ′ a single rack may be present. Such single rack may be made of an elastically deformable material, such as polyurethane. 
         [0028]    The guide bar  18   a,    18   b  may have a wedge-shaped profile  21  at the apex. 
         [0029]    A first conductor wheel  15  may be placed in a distal position in relation to the feed point of the preforms into the oven  1 , while the second conductor wheel  15 ′ may be placed in correspondence with a release point of the heated preforms from the oven and in a proximal position to the feed point of the preforms into the oven  1 . 
         [0030]    The conductor wheels  15 ,  15 ′ each may include two pairs of discs. 
         [0031]    The first conductor wheel  15  may include a pair of lower discs  22   a  and a pair of upper discs  22   b,  respectively positioned below and above the rails  16   a,    16   b  and inside the curved section  14  of the track  11 . The two pairs of lower and upper discs  22   a,    22   b  may be associated with the same vertical shaft  23  which is fitted idle to an adequate support (not shown) so that the shaft may rotate freely on the support on which it is hinged (i.e. it is not driven). 
         [0032]    The pair of lower discs  22   a  may include a first and a second disc  24 ,  24 ′, the second disc  24 ′ being distanced above the first disc  24 , by means of suitable spacers  25 , and having a lesser diameter than that of the first disc  24 . 
         [0033]    Both the first and the second disc  24 ,  24 ′ of the pair of lower discs  22   a  may include along their periphery a plurality of semi-circular indentations  26  positioned in sequence, in such a way that the indentations  26  of the first disc  24  may be radially aligned with the indentations  26  of the second disc  24 ′. 
         [0034]    The pair of upper discs  22   b  may include a first and a second disc  24 ″,  24 ′″, the second disc  24 ′″ being distanced above the first disc  24 ″, by means of suitable spacers  25 , and having a greater diameter than that of the first disc  24 ″. In particular the second disc  24 ′″ of the pair of upper discs  22   b  may have the same diameter as the first disc  24  of the pair of lower discs  22   a,  while the first disc  24 ″ of the pair of upper discs  22   b  may have the same diameter as the second disc  24 ′ of the pair of lower discs  22   a.    
         [0035]    Both the first and the second disc  24 ″,  24 ′″ of the pair of upper discs  22   b  may include along their periphery a plurality of semi-circular indentations  26  positioned in sequence, in such a way that the indentations  26  of the first disc  24 ″ are radially aligned with the indentations  26  of the second disc  24 ′″ and with the indentations  26  both of the first and the second disc  24 ,  24 ′ of the pair of lower discs  22   a.    
         [0036]    The second conductor wheel  15 ′ similarly may include a pair of lower discs  27   a  and a pair of upper discs  27   b,  respectively positioned below and above the rails  16   a,    16   b  and inside the curved section  14 ′ of the track  11 . The second conductor wheel  15 ′ may be the same as the first conductor wheel  15 , except that the semicircular indentations  26  are positioned at an angular distance from one another which corresponds to the pitch of the notches  4  of the distribution star  3  for the heated preforms. 
         [0037]    Each of the mandrels  12  may include a housing  28  integral with a sliding support  29 . 
         [0038]    The sliding support  29  may include a forked bar  30  with a C-shaped profile which may be placed astride the track  11 . Said forked bar  30  may include a vertical plate  30   a,  from the two ends of which two arms  30   b,    30   c  extend. Two cogged teeth  31 ,  31 ′ may be joined to the vertical plate  30   a  so as to rotate, positioned along a vertical axis between the rack bars  17   a,    17   b  of the rails  16   a,    16   b  in such a way as to engage with each other and with the rack  19  of the respective bars. Each of the cogged teeth  31 ,  31 ′ may include of two coaxial cogged pinions, positioned so as to engage with each other and with the double racks  19  present on the rectilinear sections of the rails. Vice versa, at the curved sections, only the outermost cogged pinion engages with the single rack in such embodiments (see  FIG. 3 ). 
         [0039]    In addition, two cylindrical bearings  32   a,    32   b  may include fitted so as to rotate on the vertical plate  30   a,  near the arms  30   b,    30   c.  Said bearings  32   a,    32   b  may include a groove  33  positioned along the cylindrical surface, suitable for engaging in rotation with the respective guide bar  18   a,    18   b.    
         [0040]    The arms  30   b,    30   c  may include guides associated with the mandrel  12  adapted for engaging with the indentations  26  of the discs  24 ,  24 ′,  24 ″,  24 ′″ of the conductor wheels  15 ,  15 ′. 
         [0041]    Such guides may include a first pair of guide castors  34  fitted so as to rotate next to the distal end of the arms  30   b,    30   c  and positioned in such a way as to face one another. This first pair of guide castors  34  may interfere with the indentations  26  of the second disc  24 ′ of the pair of lower discs  22   a,    27   a  and with the first disc  24 ″ of the pair of upper discs  22   b,    27   b  of the conductor wheels  15 ,  15 ′. 
         [0042]    The guides may further include a second pair of guide castors  35  fitted so as to rotate on opposite sides of the arms  30   b,    30   c,  next to the connection point between the arms  30   b,    30   c  and the vertical plate  30   a.  The second pair of guide castors  35  may be destined to interfere with the indentations  26  of the first disc  24  of the pair of lower discs  22   a,    27   a  and with the second disc  24 ′″ of the pair of upper discs  22   b,    27   b  of the conductor wheels  15 ,  15 ′. 
         [0043]    Coaxially to the guide castor  35  positioned on the upper arm  30   b,  a thrust wheel  36  may be fitted so as to rotate. The function of said thrust wheel  36  will be evident from description below. 
         [0044]    The housing  28  of the mandrel  12  may include a gripping finger  37  for a preform P (shown in  FIG. 3 ). The gripping finger  37  may have a diameter slightly smaller than the inner diameter of the preform P and may include on the distal portion of its outer surface an engagement portion  37 ′ comprising in turn one or more annular prominences  38  which favour the engagement with the inner neck of the preform. For example such prominences  38  may be made of elastic material such as an elastomer, or may be composed of elastic sectors which may radially retract or expand in relation to the cylindrical surface of the gripping finger  37 , exerting a retention pressure on the inner surface of the preform. 
         [0045]    The gripping finger  37  may further include a stem  39  which may be inserted in the housing  28  and may be vertically mobile. A driven body  40  may be joined to the stem  39  which may project externally from the housing  28  through a slit  41  positioned vertically on the housing body  28 . Such driven body  40  may include a wheel adapted for interacting with a cam profile (not shown) which permits the raising or lowering of the gripping finger  37 . 
         [0046]    A spiral spring  42  may be positioned on the stem  39  and may push on a shoulder  43  next to the engagement portion  37 ′ of the gripping finger  37 . Such spring  42  may allow the elastic return downwards of the gripping finger  37 . 
         [0047]    The transport mechanism  8  of the oven  1  may further include drive and distancing units of the mandrels  12 . Such drive units may include a first screw  44   a  positioned at the feed point of the preform into the oven, between the conductor wheel  15 ′ and a first rectilinear section  13  of the track  11 ; and a second screw  44   b  positioned at a junction point between the second rectilinear section  13 ′ of the track  11  and said conductor wheel  15 ′. 
         [0048]    Both screws  44   a,    44   b  may include a spiral groove  45  of variable pitch to interfere with the thrust wheel  36  of each mandrel  12 . The screws  44   a,    44   b  may be fitted in an inverted position in the drive direction of the mandrels  12 , in such a way that the first screw  44   a  has its greatest pitch upstream in the drive direction, while the second screw  44   b  has its greatest pitch downstream. 
         [0049]    The screws  44   a,    44   b  may be moved independently but in synchrony by respective motors (not shown), or by a single motor equipped with mechanical transmission. 
         [0050]    Ovens for preforms according to the invention may function as follows: 
         [0051]    The preforms may be fed into the oven  1 , for example, by means of the distributions star  2  shown in  FIG. 1 . At the feed point or in an upstream position, the mandrels  12  which may be pushed by the first screw  44   a  and may be in procession along the track  11  in contact with one another may interfere, by means of their driven body  40 , with a suitable cam profile. This way, the gripping finger  37  may be raised from the cam and then lowered, thanks to the recall of the spring  42 , so as to insert itself in the neck of the preform P and engage with it. From this point on each mandrel  12  may bear a preform which is kept in suspension. 
         [0052]    The mandrels  12  with the preforms then may pass through the various heating modules  10  of the first rectilinear section  13  and, again, pushed by the first screw  44   a,  may be guided by the conductor wheel  15  passing to the second rectilinear section  13 ′ of the track  11 , where the preforms may be further heated by the other heating modules  10 , until reaching the correct softening temperature of the material. 
         [0053]    At this stage the mandrels  12  with the softened preforms, having reached the second screw  44   b,  may interfere with the respective groove  45  by means of the thrust wheel  36 . Given that the groove  45  may have an increasing variable pitch, the mandrels  12 , which come into contact with each other, are distanced at a greater pitch which corresponds to the pitch of the notches  4  of the distribution star  3 . The preforms then may be picked up by the distribution star  3 , but given that the pitch of the screw  44   b  may be the same as that of the star  3 , the transfer may take place in constant velocity conditions, that is to say, the preforms may not undergo acceleration during such transfer. 
         [0054]    The release of the preforms by the mandrels  12  may take place when the driven body  40  of the mandrels  12  interferes on a suitable cam profile, which may cause the raising of the gripping finger  37  in synchrony with the picking up of the preform by the distribution star  3 . 
         [0055]    The mandrels  12  deprived of the preforms and distanced at the greater pitch then may be guided by the conductor wheel  15 ′ as far as the first screw  44   a.  The latter, which may have a groove  45  with decreasing pitch in the drive direction of the mandrels  12 , may bring them back to the minimum pitch condition and may push them along the track  11  in contact with each other. 
         [0056]    The advantages of this solution are multiple. 
         [0057]    First, the system described herein makes it possible to maximise the efficiency of the oven in that the mandrels  12  may proceed in contact with each other, and thus at the minimum distance possible. 
         [0058]    In addition, in certain embodiments, the mandrels  12  are not directly connected to the transport mechanism  8  but are pushed by the two screws  44   a,    44   b.  This permits a significant simplification of the machine resulting in cost savings and reduced maintenance times. 
         [0059]    The guide system which may include the cogged wheels  31 ,  31 ′ which engage on the double rack bars  17   a,    17   b,  as well as the guide castors  34 ,  35  which may engage with the indentations  26  of the conductor wheels  15 ,  15 ′ permit an efficient control of the position of the mandrels  12 , throughout their path, in relation to the oscillations around longitudinal or transversal axes of said mandrel. 
         [0060]    The bearings  32   a,    32   b,  which may slide on the respective guide bars  18   a,    18   b  may help maintain the correct position of the mandrels  12 . 
         [0061]    In addition, the second screw  44   b  may hold the mandrels  12  at the same pitch as the distribution star  3  which picks up the heated preforms, determining a constant velocity transfer of the same. This results in an absence of acceleration on the preforms and thereby avoids their deformation which, as said previously, may have undesirable effects on the final result of the blowing operation. 
         [0062]    A person skilled in the art may make modifications based on the present disclosure to adapt it to specific applications. It is intended that such applications are within the scope of protection of the present invention. 
         [0063]    For example in one embodiment, the bearings  32   a,    32   b  and the respective guide bars  18   a,    18   b  may be eliminated, without thereby jeopardizing the stability of the mandrels  12 .