Abstract:
The present invention relates to an oven for preforms in plastic material, and particularly to a heating module to be used in said oven. Particularly, the present invention relates to a heating module ( 10 ) for ovens ( 1 ) for heating preforms (P).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Italian Patent Application No. MI2012A001855, filed Oct. 31, 2012, which is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an oven for preforms and particularly to a heating system to be used in said oven, which comprises one or more infrared heating modules. 
       BACKGROUND 
       [0003]    Obtaining containers by blowing of special preforms of plastic material suitably heated within a mould having a desired shape is a widely used technique in the packaging field, in particular for manufacturing bottles for beverages. 
         [0004]    There are substantially two different techniques, simple blowing and stretch-blowing, providing for the pneumatic blowing and the concomitant mechanical stretching of the preform in the mould. In both cases, the preforms have to reach the blowing or stretch-blowing machine in a thermal condition corresponding to the softening point of the material, so as to be able to be plastically deformed within the moulds. 
         [0005]    Softening of preforms is carried out in special ovens, which comprise a series of heating modules arranged in series along the path of the preforms. 
         [0006]    In order to maximize both the thermal efficiency and the dimensions of the oven, it is desired that the preforms are introduced and made to slide within the oven at the closest pitch as possible. 
         [0007]    In fact, the problem of the loss of the heat generated by the heating modules is a particularly felt issue, since it dictates the energy consumption, which, for such oven, is always extremely high. 
       SUMMARY 
       [0008]    The object of the present invention is to provide a heating system of preforms in an oven dedicated thereto, specifically an infrared oven, allowing maximizing the thermal efficiency, hence obtaining considerable energy savings. 
         [0009]    A further object of the invention is to provide a heating system of preforms allowing obtaining an optimal energy distribution. 
         [0010]    Such and other objects are achieved by a heating system for preforms as set forth in the appended claims, the definitions of which are an integral part of the present description. 
         [0011]    Further characteristics and advantages of the present invention will be more clearly apparent from the description of some implementation examples, given herein below by way of indicative, non-limiting example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the drawings, like reference numbers and designations in the various drawings indicate like elements. 
           [0013]      FIG. 1  represents a plan schematic view of an oven-blowing machine assembly; 
           [0014]      FIG. 2  represents a simplified schematic view in cross-section of a heating module according to the invention; 
           [0015]      FIG. 3A  represents a perspective view of a heating module according to the invention; 
           [0016]      FIG. 3B  represents a cross-sectional view of the heating module of  FIG. 3A ; 
           [0017]      FIG. 4A  represents a perspective view of a detail of the heating module of the invention according to the direction A of  FIG. 3B ; 
           [0018]      FIG. 4B  represents a perspective view of the detail of  FIG. 4A  according to the direction B of  FIG. 3B ; 
           [0019]      FIG. 5A  represents a perspective view of a different detail of the heating module of the invention according to the direction A of  FIG. 3B ; 
           [0020]      FIG. 5B  represents a perspective view of the detail of  FIG. 5A  according to the direction B of  FIG. 3B . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    With reference to the Figures, an oven for preforms is indicated with the number  1 , which oven is operatively connected with handling means  2 ,  3  of the preforms, entering and exiting the oven  1 , respectively. 
         [0022]    Such handling means  2 ,  3  are typically composed of distribution stars comprising a series of gripping means  4 , for example, notches, recesses, or pliers, adapted to engage the preforms, for example, at the neck. 
         [0023]    The handling means  3  for the preforms exiting the oven  1  are in turn operatively connected with a blowing machine  5  (the term “blowing machine” as used in the present description means any type of blowing or stretch-blowing machine) that comprises a plurality of moulds  6  in which the heated preform is inserted and from which it comes out in the shape of a blow molded (or stretch-blow molded) bottle. 
         [0024]    The blowing machine  5  is in turn operatively connected with distribution means  7 , typically a distribution star, adapted to draw the blow moulded bottles exiting the blowing machine and to transfer them, by a suitable transport system, to the next operative unit. To this aim, the distribution star  7  comprises a plurality of notches  4 ′ adapted to engage the neck of the blow moulded bottles. 
         [0025]    A path of the preforms is thus defined, which is indicated in  FIG. 1  by the directions of the arrows, from their supply to the oven  1  to the entering thereof into the moulds  6  of the blowing machine  5 . 
         [0026]    The oven  1  comprises transport means  8 , adapted to handle the preforms P along a path inside the same oven, and to make them to rotate about the vertical axis thereof, and heating means  9 . 
         [0027]    The heating means  9  are composed of a plurality of heating modules  10  aligned along the preform path. 
         [0028]    The transport means  8  comprise a plurality of mandrels  12  each being adapted to engage a preform. The preform path typically comprises two rectilinear lengths and two curvilinear lengths, connecting at the two ends the rectilinear lengths according to an arc-of-circle-shaped path. Corresponding driving wheels  15 ,  15 ′ are arranged at said curvilinear lengths. 
         [0029]    The preforms P conventionally comprise a hollow body B—which will be blow moulded to form the container—, a neck portion C on which a thread or a joint geometry is typically obtained, and a flange F separating the hollow body B from the neck portion C. 
         [0030]    The heating system of preforms according to the present invention comprises at least one heating module  10  as shown in  FIGS. 3A and 3B  and, in a simplified schematic form, in  FIG. 2 . 
         [0031]    The heating module  10  comprises a base plate  19  on which a body  20  with a fork-shaped structure, i.e., having a U-shaped cross-section, is mounted. The fork-shaped body  20  comprises a first side panel  25  and a second side panel  26 , said panels  25 ,  26  mutually facing so as to create a gap  24  having such a shape and dimensions as to let the preform P moving along the transport means  8  passing therebetween. 
         [0032]    The second panel  26  comprises a plurality of vertically arranged infrared lamps  23 . Lamps of a conventional type and having a tubular shape are used. Typically, 5 lamps, so as to cover the whole height of the preform P, are used. 
         [0033]    The panels  25 ,  26  comprise reflecting surfaces  21 ,  22  that are opposite and oriented so as to convey the thermal radiations on the preform surface. 
         [0034]    First reflecting surfaces  21  are arranged on the panel  25  and facing the lamps  23 , so as to reflect the thermal radiation within the gap  24 , hence against the preform P which is passing. 
         [0035]    In some embodiments, with reference to the  FIGS. 5A and 5B , the first reflecting surfaces  21  comprise first  21   a  and second  21   b  mirror elements arranged on planes incident along a vertical corner  27 , so as to create an open V with a concavity facing the gap  24 . In this manner, a convergence effect of the thermal radiations inwards of the cavity  24  is obtained. 
         [0036]    The second reflecting surfaces  22  are arranged on the second panel  26  and comprise a plurality of vertically arranged recesses  28 , each of which housing an infrared lamp  23 . 
         [0037]    As shown in  FIGS. 2 ,  3 B, and  4 B, the recesses  28  extend parallel along the entire length of the lamps  23 , hence for most of the cavity  24  length. 
         [0038]    Each recess  28  houses a cavity  31  and comprises inner portions  22   a ,  22   b , and upper and lower side boards  22   c ,  22   d  forming a plurality of parallel tabs  29 . The inner portions  22   a ,  22   b  are arranged on planes incident along a horizontal corner  30 , so as to create a V with a concavity facing inwards of the cavity  31 . This configuration of the reflecting surfaces  22  allows each of the recesses  28  focusing the thermal radiations toward a portion of the preform P surface with a low incidence angle, thereby ensuring an optimal exploitation of the emitted thermal energy. By the term “low incidence angle” is meant an incidence angle that is less than 20°, as calculated relative to the perpendicular of the generator of the hollow body B of the preform P. 
         [0039]    In some embodiments, with reference to the  FIGS. 2 ,  3 B, and  5 A, the first reflecting surfaces  21  comprise a third mirror element  21   c  arranged in the upper portion of the first side panel  25 , above the first and second mirror elements  21   a ,  21   b  to form a longitudinal cavity  32  in which an infrared a lamp  23 ′ is housed. 
         [0040]    The mirror element  21   c  has a concavity oriented towards the portion of the preform P arranged immediately under the flange F. In fact, such portion typically has the need of a thermal profile that is different with respect to the remaining part of the hollow body C, thus it requires dedicating and focusing an energy amount that is not equal to the rest of the hollow body for a proper softening. 
         [0041]    The lamp  23 ′ arranged within such longitudinal cavity  32  has a surface portion  33 , i.e., the one facing the gap  24 , which is screened. In this manner, the preform P does not receive direct thermal radiations, but only the radiations reflected by the mirror element  21   c.    
         [0042]    In some embodiments, with reference to the  FIGS. 2 ,  3 A, and  5 A, a mobile mirror element  34  protruding within the gap  24  and located under the space taken by the preform P is associated to the first reflecting surfaces  21 . 
         [0043]    The mobile mirror element  34  comprises a mirror bar  35 , inclined with respect to the longitudinal vertical plane intersecting the gap  24 , and two side boards  36  arranged at the ends of the minor bar  35 . The side boards  36  flank the sides of the panel  25  and have a vertical loop  37 . Stop means  38 , for example, a stop screw, are associated to said vertical loops  37  and to the sides of the panel  25 . In this manner, it is possible to height adjust the mobile mirror element  34  according to the height of the preform P that undergoes a heating and to secure it at the desired point. In fact, the function of the mobile mirror element  34  is to reflect part of the thermal radiations emitted by the lamps  23  towards the preform bottom, with otherwise would remain partially screened. 
         [0044]    In some embodiments, the minor bar  35  inclination ranges between 20° and 30° to a vertical plane. 
         [0045]    In some embodiments, the reflecting surfaces  21 ,  22  are gold-plated, so as to impart them the highest reflectance as possible. 
         [0046]    Both the first and the second side panels  25 ,  26  comprise cooling means  39 ,  39 ′ of the reflecting surfaces  21 ,  22 . 
         [0047]    In the embodiment shown in the Figures, such cooling means  39 ,  39 ′ consist in a cooling system with a coolant fluid, typically water, glycol, or mixtures thereof, which is circulated in the panel  25 ,  26 , behind the reflecting surfaces  21 ,  22 , through an inlet connector  40   a  and an outlet connector  40   b . In fact, an excessive overheating of the reflecting surfaces  21 ,  22  would alter over time the thermal profile which the preforms P have to be subjected to. 
         [0048]    The side panels  25 ,  26  further comprise respective screening profiles  41 ,  42  for the flange F of the preform P. The screening profiles comprise a hollow bar  43  having an elongating tongue  44  extending almost up to contact the flange F of the preform. The hollow bar  43  comprises cooling means, consisting in a cooling system with coolant fluid, typically water, glycol, or mixtures thereof, which is circulated in the hollow bar  43  through inlet  45 ,  45 ′ and outlet  46 ,  46 ′ connectors. The cooling means of the screening profiles  41 ,  42  have the function of maintaining at a low temperature the optical screening structure of the flange F, hence the neck portion C of the preform P, which would be damaged at high temperatures. In fact, this portion has not to undergo alterations during the blowing process of the container. 
         [0049]    The screening profiles  41 ,  42  may be height and width adjustable, so as to adapt the module  10  to the different types of preforms P. 
         [0050]    In some embodiments, with reference to the Figures, the second side panel  26 , housing the plurality of infrared lamps  23 , is removable, so as to allow maintaining the same panel  26  and accessing the side panel  25  facing it. To this aim, the panel  26  is mounted on slide means  47  that are slidable on a track  48  integral to the base plate  19 . Grasping means  49  are arranged to promote the panel  26  withdrawal. 
         [0051]    In other embodiments, the first side panel  25  could be removable, while the other panel  26  could be fixed, or both could be removable. 
         [0052]    The heating module  10  further comprises means for the circulation of air within the gap  24 . Such air circulation means promote a homogeneous distributing of heat about the preform P, avoiding undesired thermal build-ups in certain areas of the gap  24 . 
         [0053]    The air circulation means comprise ventilation means  50  and suction means  51 . 
         [0054]    The ventilation means  50  are arranged on the first side panel  25  and comprise a fan  52  housed in a case  53 . The case  53  comprises a baffle  54  ending in a lamellar opening  55  arranged above the reflecting surfaces  21 , so as to send a flow of coolant fluid tangential to the reflecting surfaces  21 . 
         [0055]    The suction means  51  are arranged below the base plate  19  and communicate with the gap  24  through special openings that are present in said base plate  19 . 
         [0056]    The suction means  51  comprise a suction hood  56  that is flared downwards, below which a suction device  57  is arranged, typically a blade suction device. The suction device  57  is contained in a case  58  that may comprise a base flange  59  for securing the module  10  to the oven floor or structure. 
         [0057]    In some embodiments, the suction flow rate is higher than the output flow rate of the ventilation means  50 . 
         [0058]    The advantages of this solution are several. 
         [0059]    As stated before, the arrangement of the reflecting surfaces  21 ,  22  according to the invention ensured an efficient collimation of the thermal radiations towards the preform P. In fact, the thermal radiations, following the various reflections which they are subjected to, reach the portion of preform surfaces in a condition of substantial parallelism. Therefore, the typical cone-shaped diffusion of the thermal radiations is avoided, according to which part of the radiations hits the preform surface with low incidence angles, thereby decreasing the efficiency thereof. In fact, in the conventional ovens this problem is solved by arranging a number of lamps such as to obtain a partial overlapping of the radiation cones. Of course, this results in an increase of the operating costs for the oven. 
         [0060]    Furthermore, the fact that the thermal radiations reaching the preform surface are substantially parallel avoids that the distance of the lamps from the preform has to be adjusted according to the diameter thereof. This fact is solved by a constructive simplification of the module  10 . 
         [0061]    The arrangement of the mirror element  21   c  and the corresponding lamp  23 ′, as well as the mobile mirror  34 , allows focusing part of the thermal radiation to the critical areas of the preform P, thus ensuring a complete control of the heating functions thereof. 
         [0062]    To this aim, the cooling air circulation system is also configured to ensure a homogeneous distribution of the heat. 
         [0063]    By the heating module  10  according to the invention, it is possible to decrease the number of lamps compared to the conventional modules, reducing it to half of the lamps to be used. Furthermore, lamps will be able to be used with a power that is less than those typically employed (for example, 1500 W instead of 2500 W), thereby the energy consumption is substantially reduced. 
         [0064]    It shall be apparent that only some particular embodiments of the present invention have been described, to which those skilled in the art will be able to make all those modifications that are necessary for the adaption thereof to particular applications, without for this departing from the protection scope of the present invention.