Abstract:
Pre-heating apparatus for pre-heating a selected portion of each of a series of preforms to achieve a persistent thermal gradient prior to re-heating and blow-molding the preform. The pre-heating apparatus is adjustably mounted to a gravitational slide that transports the series of preforms downward under the influence of gravity through the preheating apparatus toward a reheat blow molding machine. The pre-heating apparatus includes a housing coupled to the slide so that the selected portion of each of the series of preforms is shielded from the general environment, and heating elements fixed within the housing so that heat from the heating elements is directed toward the selected portion of each of the series of preforms as the preforms descend down the gravitational slide.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention is directed to blow molding systems that employ previously formed parisons or preforms that are reheated in a reheating stage, typically from an ambient temperature to a molding temperature, prior to blow molding. More particularly, the present invention is directed to an additional preheater for such a blow molding system for preconditioning the preforms prior to the reheating stage so that a temperature differential is achieved in each preform that allows for a preferential distribution of the resin forming the preform during blow molding.  
           [0002]    In a blow molding operation employing previously formed parisons, the temperature of each preform as it is being blown is one of the most critical process variables. Ideally, the temperature should be as consistent as possible from one preform to the next in order to achieve product uniformity of the blow molded product. The rate at which a preform can be heated from ambient temperature to a temperature suitable for blow molding is controlled in part by the thermal conductivity of the resin forming the preform. Other factors include the thickness of the material of the preform, the distance between the preform and the source of heat, the energy density or power of the heat source, and the need to not waste heat. Some prior art processes have adopted reheating profiles that are intended to achieve the desired reheating in a particularly expeditious manner such as that disclosed in U.S. Pat. No. 5,066,222.  
           [0003]    Most reheating processes include some cooling or at least reduced heating periods to allow for equilibration of the temperature through the wall thickness of the preform. The time typically required to reheat a preform from ambient temperature to blow molding temperature far exceeds the time required to perform the blow molding and cooling steps. Thus, the time required to achieve the desired temperature characteristics for the preform, within the limits of the prior art reheating and equilibrating steps, when coupled with the physical geometry of the reheating apparatus, places a practical limit on the maximum line speed for the blow molding operation for each given apparatus. Any increases in line speed must be compensated by correspondingly lengthening the reheating apparatus so that the residence time of any preform in the reheating process is sufficient to achieve the necessary temperature profile prior to blow molding.  
           [0004]    On occasion, it is desirable to achieve some temperature variation within each preform so that some desirable physical property can be obtained in the blow molded product. Such temperature variations have been achieved in the reheating process. Examples of the creation of temperature variations in preforms can be found in U.S. Pat. Nos. 3,775,524; 3,950,459; 4,079,104; 4,117,050; 4,423,312; 5,292,243; 5,681,521; 5,853,775 and 6,146,134. Generally, the temperature variation required to achieve any significant property difference during a blow molding process or in the product obtained from such a process is at least about 3° C. It has been recognized in U.S. Pat. No. 5,607,706 and some of the prior art discussed therein, that variations in temperature that are present in preforms prior to a reheating process can affect the final temperature of the preform and can affect the subsequent blow molding process. However, it has not previously been recognized that a purposeful introduction of temperature variations into preforms prior to a normal reheating process can be used advantageously to create desirable temperature variations affecting the blow molding process.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with the present invention, a selected portion of each preform is preheated to generate a temperature gradient between the selected portion and the remainder of the preform. The preheated preform is then introduced into a normal reheating process while the temperature gradient is still present in the preform. At the end of the reheating process, the fully reheated preform still exhibits a residual temperature gradient between the selected potion and the remainder of the preform. The fully reheated preform is then subjected to a blow molding operation while the residual temperature gradient is still present. The residual temperature gradient can be employed to improve resin flow in selected regions of the blow mold so that the final article produced by the process exhibits desirable properties that are difficult or impossible to achieve in the absence of the residual temperature gradient.  
           [0006]    This process can be achieved by providing a preheating apparatus according to the present invention that is situated adjacent to a preform input of a reheat-blow molding machine. The apparatus includes a housing that envelops the preforms as they are carried by a conveyor into the reheat-blow molding machine input. Heating elements are provided within the housing that are directed toward a selected portion of the preforms traveling along the conveyor to define a temperature gradient in the preforms prior to their introduction into the reheating section of the reheat-blow molding machine.  
           [0007]    In a preferred embodiment, the preheating apparatus is coupled to a gravitational slide forming an input to a reheating portion of a reheat-blow molding machine. The preheating apparatus preheats a selected portion of each preform as the preform travels down the slide. The pre-heating apparatus includes a housing having a first longitudinal wall fixed to a first side of the gravitational slide. A second longitudinal wall of the housing is hinged to the first longitudinal wall and is releasably coupled to a second side of the gravitational slide. Heating elements are coupled to the longitudinal walls so that the heating elements will preheat a selected portion of each preform gravitationally traveling down the slide. The heating elements are preferably in the form of infrared emitters but can include other heating emissions that will suitably interact with the resin forming the preforms. The preheating generates a defined temperature gradient in each preform prior to introduction of the preforms into the reheating section of the reheat-blow molding machine that is particularly useful in the formation of footed containers as disclosed in U.S. Pat. Nos. 5,603,423; 6.085,924; and 6,276,546.  
           [0008]    In a preferred embodiment, a plenum is coupled to an outside surface of the first longitudinal wall over a plurality of openings between the outside surface and the inside surface of the first longitudinal wall. A fan is coupled to an opening in the plenum to exhaust air from the plenum. This causes an air flow outward through the openings in the first longitudinal wall, which in turn causes an inward flow of air downward between the performs as they travel down the slide, to ensure adequate cooling of portions of the preforms. The air flow also cools the rails of the slide, the heating elements and related hardware. Shielding elements are located adjacent to the heating elements to inhibit the heating of portions of each of the preforms that are not intended to be preheated. The shielding elements can comprise reflecting elements that reflect the infrared and other heating emission of the heating elements. Focusing elements are also coupled adjacent to the heating elements to focus the infrared and other heating emission from the heating elements toward the selected portions of the preforms intended to be preheated. End baffles can also be coupled to the ends of the longitudinal walls of the housing to help control the heat emission from the preheater.  
           [0009]    One feature of the present invention is the capacity of the apparatus to be added to any linear entry feed of preforms into a reheat-blow molding machine so long as the region of the preform sought to be pre-heated is not shielded by the entry feed mechanism. This feature has the advantage of allowing the present invention to be adapted to a variety of reheat-blow molding machines without requiring any modification to the reheat-blow molding machine itself.  
           [0010]    Another feature of the present invention is the capacity of the apparatus to thermally preprogram preforms to have a thermal gradient in a given region without having to modify the reheating schedule of the reheating portion of the reheat-blow molding machine. This feature has the advantage of adding a significant control feature to the process of manufacture carried out by the reheat-blow molding machine without requiring any modification to the reheat-blow molding machine itself.  
           [0011]    Additional features and advantages will become apparent to those skilled in the art upon consideration of the following description of a preferred embodiment that is illustrated in the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a side elevation view of a preheating apparatus of the present invention coupled to an input of a reheat-blow molding machine.  
         [0013]    [0013]FIG. 2 is a perspective view from the opposite side of the pre-heating apparatus of FIG. 1, with the nearest sidewall lowered to allow access to the interior of the preheating apparatus.  
         [0014]    [0014]FIG. 3 is an exploded perspective view of the pre-heating apparatus of the present invention in relation to a preform input slide.  
         [0015]    [0015]FIG. 4 is an exploded perspective view of a heater and shield assembly for a pre-heating apparatus of the present invention, and the supporting hardware therefore.  
         [0016]    [0016]FIG. 5 is a detail schematic view of the preheating operation using a preheating apparatus of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    A conventional re-heat blow molding system  10 , such as a Sidel model SBO-16/24, is shown in FIGS. 1 and 2 to include a gravitation input  12  for receiving a series of previously formed parisons or preforms  14 . The preforms  14  are individually loaded from the input  12  onto carriers  16 , schematically shown in FIG. 1, that carry each preform  14  through a reheating stage  18  where the preforms are heated from ambient temperature to a temperature suitable for blow molding. The carriers  16  then transport each reheated preform  14  into a blow molding stage  20  where the preform is subjected to a molding operation to transform the preform  14  into another object  22  such as a bottle or other container. The molded objects  22  are then disgorged from the molding system  10  for subsequent processing and use.  
         [0018]    The preforms  14  are transported to the input  12  on a pair of spaced rails  24  that are typically inclined as shown in FIG. 1 to form a gravitational slide  26 . That is, the inclination of the rails  24  is set so that the preforms  14  slide down the rails  24  into the input  12  substantially solely due to the influence of gravity. Some small amount of vibration of the rails  24  due to the normal operation of the molding system  10  can also contribute to reducing the friction between the rails  24  of the slide  26  and the preforms  14 . The rails  24  are shown in greater detail in FIG. 3 to be formed of segments of square or rectangular tubing  21 . Opposed, inwardly directed flanges  23  are fixed to the top surfaces  19  of the square tubing segments  21  so that they are spaced from each other by a distance greater than the diameter of the preforms  14  and less than the diameter of the preform support rings  11 , shown in FIG. 5. Short bridging pieces  15  couple the ends of adjacent flanges  23  together to form one continuous surface for supporting the preforms  14  by their support rings  11 .  
         [0019]    A preheating apparatus  30  of the present invention is shown in FIGS. 1 and 2 to be coupled to the gravitational slide  26  adjacent to the input  12  to the reheating portion  18  of the reheat-blow molding machine  10 . The preheating apparatus  30  can preheat any selected portion of each preform  14  as the preform travels down the slide  26 , so long as the selected portion extends below the lower surfaces  17  of the tubing segments  21 . As shown generally in FIGS. 1 and 2, the pre-heating apparatus  30  includes a housing  32  having a first longitudinal wall  34  fixed to a first side  25  of the gravitational slide  26 . A second longitudinal wall  36  of the housing  32  is hinged to the first longitudinal wall  34  and is releasably coupled to a second side  27  of the gravitational slide  26 . A plurality of heating assemblies  38  are coupled to the longitudinal walls  34  and  36  so that the heating assemblies  38  will preheat a selected portion of each preform  14  as the preform gravitationally travels down the slide  26 . A plenum  40  is coupled to an outside surface  42  of the first longitudinal wall  34  over a plurality of openings  44  between the outside surface  42  and the inside surface  46 .  
         [0020]    As shown in greater detail in FIG. 3, the first longitudinal wall  34  of housing  32  includes a horizontal portion  31  and a vertical portion  33 . The vertical portion  33  of the first longitudinal wall  34  includes a plurality of vertical slots  35  that allow for vertical adjustment of the first wall  34 . A set of fasteners  48  secures the first wall  34  to the first side  25  of the gravitational slide  26  at a desired vertical position. An inner margin  29  of the horizontal portion  31  of the first wall  34  includes a hinge  50 . An inner margin  37  of the second longitudinal wall  36  of the housing  32  includes a second portion of hinge  50  and is hinged to the first longitudinal wall  34 . The second wall  36  includes a similar set if vertical slots  35  that allow for vertical adjustment of housing  32  with respect to the second side  27  of the gravitational slide  26 .  
         [0021]    The plurality of heating assemblies  38  that are coupled to the longitudinal walls  34  and  36  are shown in greater detail in FIG. 4. Each of the heating assemblies  38  includes a base support member  52  that is coupled to one of the walls  34  or  36  by a plurality of stand-offs  54 . A plurality of bases  56  are fixed to the base support member  52 . Each of the bases  56  includes grooves  58  that receive electrical coupling elements  60  that are coupled to the ends of the heating elements  62  and support focusing elements  86 . The coupling elements  60  are connected to wires  64  leading to a suitable source of power, such as 220 VAC, through an appropriate control unit that can be operated in conjunction with the operation of the molding machine  10 . The bases  56  also include slots  66  that receive ends  68  of reflective shielding elements  70  that are located above and below the heating elements  62 . Keepers  72  are employed to hold the coupling elements  60  and the shielding element ends  68  in place in the bases  56 .  
         [0022]    Returning to FIG. 3, the heating assemblies  38  are fixed to both of the longitudinal walls  34  and  36  at a fixed location. Any vertical adjustment in position of the heating assemblies  38  with respect to the preforms  14  is achieved by adjusting the vertical position of the walls  34  and  36  with respect to the slide  26  so that the heating assemblies  38  will preheat a selected portion of each preform  14  as the preform gravitationally travels down the slide  26 . One preferred position for the heating assemblies is illustrated schematically in FIG. 5. The preform  14  is seen to include a generally hemispherical bottom portion  80  that is unitarily formed at the lower end of a right cylindrical sidewall portion  82 . A transition or heel area  84 , which has the form of a curved ring located between the sidewall portion  82  and the gate area  83 , is of principal interest as this heel area  84  is employed to form the foot portions of a footed container. The present invention can be of significant benefit to improve the plastic flow of resin in this area of the preform during the blow-molding of such footed containers. The shielding elements  70  are located adjacent to the heating elements  62  to inhibit the heating of unwanted portions of the performs  14 . In particular the upper shielding elements  71  shield the sidewall portion  82  of each of the preforms  14  so that a temperature gradient of at least about 3° C., and more preferably about 17° C. is developed, between the heel portion  84  and the sidewall portion  82  of each preform  14 , the gradient being measured at the end of the preheating apparatus  30  adjacent to the input  12  to the reheating portion  18  of the reheat-blow molding machine  10 . The shielding elements  70  can comprise reflecting elements that reflect infrared emissions of the heating elements  62 . Focusing elements  86  are also coupled adjacent to the heating elements  62  to focus infrared emissions from the heating elements  62  toward the selected portions of the preforms  14 . In the illustrated embodiment, the lower shielding elements  73  act to shield the gate area  83  of the preform  14  so that a temperature gradient of at least about 3° C., and more typically about 6° C., is developed between the heel portion  84  and the gate area  83  of each preform  14 , the gradient again being measured at the end of the preheating apparatus  30  adjacent to the input  12  to the reheat-blow molding machine  10 .  
         [0023]    Returning again to FIG. 3, the plenum  40  is coupled to the outside surface  42  of the first longitudinal wall  34  over a plurality of openings  44  that permit an outward flow of air into the plenum  40  from the preheating apparatus  30 . The flow of air is achieved by a plurality of fans  74  that are coupled to exhaust openings on a lower surface  76  of the plenum  40 . To achieve the desired cooling of the non-preheated portions of the performs  14 , the slide  26 , and the equipment forming the preheating apparatus  30 , the fans  74  are preferably powered continuously. It will be appreciated that some temperature control can be achieved by varying the number of fans  74  operating or varying the speed of operation of the fans  74 . A bottom cover  90  is provided that contains the power connections for the wires  64 . End baffles  88  can also be coupled to the ends of the longitudinal walls  34  and/or  36  of the housing  32  to help control the heat emission from the preheating apparatus  30  and the air flow patterns caused by the fans  74 . The outward flow of air through the openings  44  in the first longitudinal wall  34  inhibits overheating of those portions of the preforms  14  being directly heated by the heating elements  38 .  
         [0024]    In operation, the preheating apparatus  30  provides a thermal bias in the form of a temperature gradient between a first selected portion of each preform  14 , such as the heel portion  84 , and a second selected portion of each preform  14 , such as the sidewall portion  82 . This thermal bias or thermal gradient persists at least to some extent during the reheating stage  18  so that when the preforms  14  enter the blow molding stage  20 , the selected portion  84  remains at a temperature that permits an enhanced plastic flow so that the article formed by the molding process, such as a bottle or container, can be formed more quickly and with higher quality characteristics that are possible in the absence of the preheating apparatus  30 .  
         [0025]    It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts and details of operation.