Abstract:
A method and apparatus for stabilizing a blow molded plastic preform and container in a blow mold during a demolding operation. The blow mold has a first mold section, a second mold section, and a mandrel. The mandrel cooperates with a pair of spring loaded jaws slidingly coupled to one or both of the mold sections. With the mold sections in their fully open position, the mandrel with an attached preform and/or container travels into the blow mold. During the final stage of closing the mold sections, the jaws contact the finish and restrain the container. As the mold sections begin to open, the jaws prevent any movement of the container relative to the mandrel.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention generally relates to blow molding methods and machines for producing heat set plastic containers. More specifically, this invention relates to a mechanism which stabilizes a blow molded plastic container in the blow mold cavity.  
         BACKGROUND OF THE INVENTION  
         [0002]    Stretch blow molding processes are performed in automatic machines which sequence preforms and containers through several stations to complete the bottle fabrication process. The blow molding operation is performed with a plastic preform which is inflated with a gas to form a container. If the container becomes unstable or hung up in the mold during demolding, the machine must be shut down and the operator must remove the obstructing container from the machine. This results in costly lost production time and an increase in the overall machine cycle time for each container. This is economically undesirable. The trend is to reduce the cycle time of each operation in the cycle. By increasing the speed of the operation, there is a greater possibility of losing control of a container during extraction from the mold because of the high acceleration rates of the various machine components.  
           [0003]    When the container is in the finish portion down orientation, there is a tendency for some types of containers to hang up or jam in the stretch blow molding station because of a loss of control of the container during the demolding process.  
           [0004]    Containers with a complex sidewall geometry or a high aspect ratio are particularly prone to adhering to one side of the mold as the mold is opened. The result is that the container can cock relative to the mandrel while the container is being removed from the mold. The mandrel is part of the core assembly which passes through the finish portion and into the container. When a container cocks on the mandrel, it can jam in the mold due to the loss of control of the orientation of the bottle. Another aspect of the problem relates to containers with dimensional variations in the inside diameter of the finish portion. If the inside diameter of the finish portion is too large, the container can fall off the mandrel as a result of being jostled by the mold opening which can result in the container being jammed in the mold.  
           [0005]    On many rotary type blow molding machines, a mechanism integral with the machine grips and stabilizes the container during demolding, preventing the problems described above. On linear type machines, a bottle stabilizer is not integral with the molding machine. Thus, there is a need for a container stabilizing device applicable to linear molding machines, with preforms in a threads or finish portion down orientation, which prevents the mold opening action from destabilizing the container relative to the mandrel thus preventing the container from getting hung up or jamming in the mold.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a blow molding device which is adapted for stabilizing a container formed from a preform. The container and preform each have a portion defining a finish. The device includes a mold having a first mold section, a second mold section and a cavity therebetween. The first mold section is movable toward and away from the second mold section. A mandrel is adjacent to the mold. The mandrel has one of the preform and the container disposed thereon. The first mold section and the second mold section is adapted to open and close about the mandrel in order to permit the mandrel to move into and out of the cavity in the mold. At least one jaw is adjacent to one of the first mold section and the second mold section. The at least one jaw conforms to the finish and moves transversely of the finish. The at least one jaw is biased by a resilient member to compress the finish of the preform and the bottle to the mandrel to stabilize the container when the first mold section and the second mold section move away from one another.  
           [0007]    No complex controls or actuators are required for the operation of the present invention. When the mold is fully opened, the at least one jaw disengages from the finish of the container and allows for the passage of the incoming mandrel and clamping device, the preform, the outgoing mandrel and clamping device, and finally the molded container. As the mold closes, each jaw comes into contact with the preform finish. Upon further closing of the mold, the jaws travel on guides to compress springs and grip the preform finish. After mold closure and the blow molding process, the spring loaded jaws continue to grip the container finish and retain the container&#39;s position relative to the mandrel as the mold initially opens. As the mold further opens, the jaws continue to contact the container finish by the bias of the springs until the jaws reach the end of their travel on the guide rods, and move with each of the mold sections during the remainder of the mold opening travel. Thus, the operation of the present invention is mechanically sequenced with the normal mold opening and closing procedure.  
           [0008]    Further features and advantages of the invention will become apparent from the following discussion and accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a sectional side view of a preform in a mold cavity used to form a blow molded container in accordance with the present invention;  
         [0010]    [0010]FIG. 1 a  is a side view of a blow molded container formed in the mold cavity shown in FIG. 1;  
         [0011]    [0011]FIG. 1 b  is a side view of the preform shown in FIG. 1;  
         [0012]    [0012]FIG. 2 is a simplified plan view in the direction of arrows  2 - 2  labeled in FIG. 1 showing the container finish and the container stabilizer device of the present invention with the mold sections in a fully open position;  
         [0013]    [0013]FIG. 3 is the same view as FIG. 2 with the mold sections in a partially closed position; and  
         [0014]    [0014]FIG. 4 is the same view as FIG. 2 with the mold sections in a fully closed position.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    The container stabilizer device according to the invention is shown in FIGS. 1 through 4 and is designated by the numeral  100 . The container stabilizer device  100  includes a blow mold  12 , a mandrel  34  and an integral clamping device  36 . The container stabilizer device  100  is adapted to work in conjunction with a plastic preform  5  and a container  10 .  
         [0016]    As illustrated in FIGS. 1 and 1 b,  the preform  5  having a finish  18  and threads  22  is provided. The preform  5  is inflated with gas or fluid to form the container  10  as shown in FIG. 1 a.    
         [0017]    In FIG. 1, the preform  5  is oriented in a mold cavity  11  of the blow mold  12  in a threads down orientation. A thread down orientation is defined as a condition wherein the preform  5  is positioned in the mold cavity  11  of the blow mold  12  with the threads  22  below the plastic body of the preform  5 . In FIG. 1 b,  the preform  5  is shown in a threads up orientation.  
         [0018]    With continued reference to FIGS. 1, 1 a  and  1   b,  the blow mold  12  includes a first mold section  14 , a second mold section  16  and the mold cavity  11  therebetween. The container  10 , is processed from the preform  5  which includes a finish  18  having a bore  17  and threads  22  adapted to receive a screw on cap (not shown). A flat region known as an A band  24  is located on the finish  18 . The A band  24  is located on the finish  18  between a tamper ring  26  and a support ring  28 . Other container  10  features include a sidewall  30  and a base  32  to enclose the bottom of the container  10 . The mandrel  34  is adapted to pass through an inner diameter  19  of the finish  18  of the container  10 .  
         [0019]    The mandrel  34  includes a top portion  31  and an inner projecting portion  35 . The mandrel  34  has a passage  33  extending through both the top portion  31  and the inner projecting portion  35 . The inner projecting portion  35  has an outer diameter  37  which is less than the inner diameter  19  of the finish  18 . Thus, the inner projection portion  35  of the mandrel  34  is capable of being disposed within the finish  18  of the preform  5 . The passage  33  provides a flow path for the introduction of gas or fluid into the bore  17  of the preform  5  as is conventional. The mandrel  34  is axially related to the top of the blow mold  12 .  
         [0020]    The inner projecting portion  35  of the mandrel  34  has a top flange  39 , a smaller flange  41  adjacent to the top flange  39  and an undercut  43  between the top flange  39  and the smaller flange  41 . The top flange  39  of the inner projecting portion  35  has ball detents on its outer periphery to assist in its retention in a cavity extending through the top portion  31  of the mandrel  34 .  
         [0021]    The top portion  31  of the mandrel  34  also has an outer peripheral portion  45  and an undercut  47  on its inner diameter. The inner projecting portion  35  of the mandrel  34  is connected to the top portion  31  of the mandrel  34  by means of a conventional retainer such as a snap ring  49  which fits into the undercut  47  of the top portion  31  and the undercut  43  of the inner projecting portion  35  to lock the two portions together, as is conventional.  
         [0022]    The outer diameter  37  of the inner projecting portion  35  is smaller than the inner diameter  19  of the finish  18  of the preform  5  so as to accommodate for dimensional fluctuations in the inner diameter  19 . An annular seal member  7  is disposed in a counterbore in the mandrel  34 . The seal member  7  abuts the end of the finish  18 . Alternatively, the seal member  7  is disposed about the outer periphery of the finish  18 . The seal member  7  prevents the blow molding fluid from leaking out of the bore  17  of the plastic preform  5  when the container  10  is being formed. The mandrel  34  extends into the inner diameter  19  of the finish  18  and between a pair of jaws  38 , and is fastened thereto by conventional means.  
         [0023]    [0023]FIGS. 2 through 4 show the integral clamping device  36 , the finish  18  of the container  10  and the container stabilizer device  100  with the mold sections  14  and  16  of the present invention. Mandrel  34  has been removed for clarity. The integral clamping device  36  is disposed in a cavity  15  formed on top of and between the mold sections  14  and  16 , and is fastened, in any commonly known manner, on each mold section  14  and  16 , respectively. The clamping device  36  has a pair of jaws  38 . Each jaw  38  is mounted on a pair of spaced apart guide bars  40 . Each jaw  38  is preferably semicircular in shape having a contact surface  51  in the plan view which conform to the curved surface of the A band  24  of the preform  5  and the container  10 . The guide bars  40  pass through and glide in bores  42  in the mold sections  14  and  16 , respectively. Each guide bar  40  captures and preloads a biasing member  44  between the jaw  38  and the mold  12 . Each guide bar  40  is threaded on an end opposite the jaw  38 . Nuts  46  are used to attach and compress biasing members  44 . Each bore  42  is counterbored to provide appropriate seats for the biasing members  44 , nuts  46  and any appropriate washers or shims, as is conventional. The free position of each of the jaws  38  and the preload of the biasing members  44  can be adjusted by rotating each nut  46  and appropriate washers and shims as is well known in the art. The biasing members  44  may be helical springs, or any other resilient member that is within the teachings and scope of the present invention.  
         [0024]    In the initial open position of the blow mold  12 , as shown in FIG. 2, a clearance is provided between the mold sections  14  and  16 , respectively, to permit the mandrel  34  with an attached preform  5  to be positioned between the mold sections  14  and  16 . The mold  12  is then moved to a partially closed position, as shown in FIG. 3, at which point each of the jaws  38  contact the A band  24  of the preform  5 . As the mold  12  proceeds to a fully closed position, as shown in FIG. 4, each of the opposed jaws  38  continue to contact and press against the A band  24 . The biasing members  44  are compressed as each of the jaws  38  translate into the cavity  15  as the mold sections  14  and  16  are closed. When the mold sections  14  and  16  are in the closed position, the biasing members  44  are fully compressed, and each jaw  38  grips and applies pressure to the finish  18  of the preform  5 .  
         [0025]    Once the mold  12  is fully closed, the preform  5  is stretch blow molded as is conventional to form the container  10 . Once the container  10  is formed, the mold  12  is partially opened. During this time, the opposing pair of jaws  38  continue to apply pressure to each side of the A band  24  and, in turn, the mandrel  34  because of the compressed biasing members  44 . The pressure of the jaws  38  captures the container  10  around the circumference of the A band  24  in the horizontal direction, and between the tamper ring  26  and the support ring  28  in the vertical direction. This stabilizes the container  10  and prevents any movement of the container  10  relative to the mandrel  34  as the mold  12  is initially opened.  
         [0026]    As the mold sections  14  and  16  continue to open, the jaws  38  continue to apply pressure against the A band  24 , thus maintaining the container  10  in the desired stabilized position until the mold sections  14  and  16  are approximately half open (see FIG. 3). At this point, the jaws  38  begin to disengage from the A band  24  since the travel of each jaw  38  is limited by the length of the guide bars  40 . Thereafter, each jaw  38  moves with each respective mold section  14  and  16  to the position shown in FIG. 2. This position allows the mandrel  34  to be retracted out of the mold  12  and permits the removal of the completed container  10  from the mold  12 . Thereafter, another cycle of the molding process can be repeated.  
         [0027]    The foregoing discussion discloses and describes a preferred embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the true spirit and fair scope of the invention as defined in the drawings and in the following claims.