Abstract:
A multi-station rotary blow molding machine suitable for molding hollow articles from a thermoplastic parison is described. Plural, indexable dials present blow mold assemblies for parison insertion at a common, shared parison insertion station. The parisons can be extruded parisons or injection molded preforms.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to machines and sub-assemblies thereof for manufacturing hollow articles from thermoplastic materials by blow molding.  
         BACKGROUND OF INVENTION  
         [0002]    Blow molding is a fabrication method for hollow thermoplastic shapes.  
           [0003]    Two general classes of plastic products are made in this manner—packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and the like containers. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like.  
           [0004]    The blow molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a parison is lowered between mold halves from an extruder. The mold halves then close around the parison, and the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow molding process.  
           [0005]    In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment thereof is severed and positioned into a mold. The molds can be moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action. When the parison is extruded, the mold is moved under the extruder die head to receive the parison segment and then is moved to a blowing station.  
           [0006]    The positioning of the parison relative to the mold in a rotary system is relatively difficult, thus most of the current blow molding machines utilize the reciprocating mold concept according to which the molds are shuttled back and forth from station to station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate.  
           [0007]    In intermittent extrusion, the molds are mounted to a common platen and the parisons are extruded by either a reciprocating screw extruder or by a ram accumulator which holds in readiness a volume of molten plastic material needed to make the next part or parts.  
           [0008]    In injection blow molding the parison in first injection molded to a predetermined shape and then transferred to a blow mold to be blown into a finished product.  
           [0009]    In all cases, however, the parison has to be transported from station to station to complete the fabrication of a hollow plastic article.  
           [0010]    In view of the relatively large commercial demand for various types of plastic articles, it would be desirable to have a blow molding machine of relatively high capacity that can produce high quality articles at a relatively low cost. The present invention satisfies this desire.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention provides a blow molding machine capable of relatively high production rates at relatively low cost.  
           [0012]    The foregoing advantages are achieved by a multi-station blow molding machine in which a single parison insertion station is shared by more than one rotary mold array. In particular, the present multi-station blow molding machine is suitable for fabrication of hollow articles from parisons or tubular thermoplastic blanks and includes a base and a pair of rotatable, indexable dials each of which carries a pair of opposed blowing mold clamp assemblies that are indexable to a common parison insertion station but to separate blowing and take-out stations for each indexable dial. A drive is provided for each indexable dial, and the indexable dials can be driven independently or synchronously, as desired, as long as interference between the dials is avoided. The indexable dials are supported on a base for rotation about spaced, substantially parallel vertical axes.  
           [0013]    A blowing mandrel assembly mounted to a frame is provided at each blowing station for blow molding hollow thermoplastic articles. A blowing mandrel assembly particularly well suited for use with the present rotary multi-station blow molding machine has a housing that contains an array of reciprocatable blowing mandrels. The number of blowing mandrels provided in any given instance is dependent upon the number of cavities in each mold. A spring-actuated, apertured bushing plate is part of the housing and serves to guide the blowing mandrels from a rest position to a blowing position when a parison-bearing mold is presented at a blowing station.  
           [0014]    The housing is defined by the apertured bushing plate, a pair of upstanding guide bars with an end portion thereof affixed to the bushing plate, an apertured mounting plate which slidably receives the guide bars, and an apertured lift plate which is affixed to the guide bars at a mid-portion thereof and serves to lift the bushing plate together with the blowing mandrels as the blowing mandrels are elevated from a blowing position to a rest position. The lift plate is provided with at least one aperture sized to receive a blowing mandrel.  
           [0015]    Plural blowing mandrels are slidably mounted to the housing and extend into aligned apertures defined by the bushing plate and by the mounting plate. A biasing coil spring is situated around each guide bar and is positioned between the lift plate and the mounting plate. When the blowing mandrel assembly is in the rest position, the biasing coil spring is in a compressed state. When compression is released, the biasing coil spring exerts a downwardly driving force against the lift plate and urges the lift plate, together with the bushing plate, downwardly toward a mold assembly positioned thereunder. Distal end portions of the blowing mandrels extend through the bushing plate when in the blowing position. A spacer stop, which can be a rigid tubular sleeve or the like, is provided on at least one blowing mandrel that is slidably received in an aperture defined by the lift plate and serves to limit the travel of the lift plate in an upwardly direction when the blowing mandrels are raised to the rest position.  
           [0016]    Each blowing mandrel is provided with an actuator that reciprocates the blowing mandrel between a relatively lower blowing position and a relatively higher rest position. The actuator is connected to a proximal end portion of the blowing mandrel through the mounting plate and is affixed to the mounting plate of the housing. The actuator can be a hydraulic cylinder, a pneumatic cylinder, a solenoid device, or the like, as desired. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    In the drawings,  
         [0018]    [0018]FIG. 1 is a partial plan view of a blow molding machine that embodies the present invention. Shown in bold single digit numerals in FIG. 1 are the several work stations for paired indexing dials that carry blow mold assemblies. Station  1  is shared by the paired indexing dials.  
         [0019]    [0019]FIG. 2 is a partial side elevation of an indexing dial with mold assemblies at Stations  1  and  3 B, and illustrating parison insertion at shared Station  1 .  
         [0020]    [0020]FIG. 3 is a partial side elevation of an indexing dial with mold assemblies at Stations  2 A and  4 A, and illustrating dial position during a blowing operation at Station  2 A and a finished article takeout at Station  4 A.  
         [0021]    [0021]FIG. 4 is a partial side elevation, rolled out to show guide bar details and partly in section, illustrating a preferred blowing mandrel assembly for use with the present blow molding machine.  
         [0022]    [0022]FIG. 5 is a plan view, partly in section, taken along plane  5 - 5  in FIG. 4.  
         [0023]    [0023]FIG. 6 is a plan view, partly in section, taken along plane  6 - 6  in FIG. 4. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    The invention disclosed herein is, of course, susceptible to embodiment in many different forms. Shown in the drawings and described in detail hereinbelow are certain preferred embodiments of the present invention. The present disclosure, however, is an exemplification of the principles and features of the invention, but does not limit the invention to the illustrated embodiments.  
         [0025]    For ease of description, the rotary multi-station blow molding machine and the blowing mandrel array of this invention will be described as they exist in a normal operating position, and terms such as upper, lower, top, bottom, vertical, horizontal, etc. will be used with reference to that position.  
         [0026]    Referring to FIG. 1, rotary multi-station blowing machine  10  includes paired indexable dials  12  and  14  that are supported on base  15  and mounted for rotation about spaced, substantially parallel vertical axes. Dials  12  and  14  are provided with respective drives  16  and  18 . As shown in FIG. 1, drive  16  indexes dial  12  clockwise, and drive  18  indexes dial  14  counterclockwise, both sequentially through respective work stations  1 ,  2 A,  3 A and  4 A for dial  12  and work stations  1 ,  2 B,  3 B and  4 B for dial  14 . Work station  1 , the parison insertion station, is shared by both dials. Drives  16  and  18  preferably are synchronously driven so as to minimize the likelihood of interference between dials  12  and  14 , but can be driven in any convenient manner.  
         [0027]    The parison to be molded is supplied by continuous extruder  20 , also mounted to base  15 . Instead of continuous extrusion, the parison to be molded can also be supplied to the parison insertion station as a preform which can then be inserted into the mold at Station  1  in any convenient manner.  
         [0028]    Dial  12  is provided with diametrically opposed mold assemblies  22  and  26 . Mold assembly  22  includes complementary mold halves  23  and  24 , as well as mold clamp assembly  25 . Likewise, mold assembly  26  includes complementary mold halves  27  and  28  as well as mold clamp assembly  29 . Dial  14  is provided with diametrically opposed mold assemblies  32  and  36 . Mold assembly  32  includes complementary mold halves  33  and  34 , as well as mold clamp assembly  35 . In the same manner, mold assembly  36  includes complementary mold halves  37  and  38 , as well as mold clamp assembly  39 . The molds, and thus the respective mold halves on each of the dials, can be the same or different, depending upon production requirements.  
         [0029]    Mold halves  34  and  35  on dial  14  at Station  1  are shown in an open position, ready to receive an extruded parison, whereas mold halves  37  and  38  at Station  3 B are shown in closed position. On dial  12 , mold halves  23  and  24  at Station  2 A, the blowing station, are in a closed position, and mold halves  27  and  28  at Station  4 A, the take-out station, are shown in an open position.  
         [0030]    The present rotary multi-station design provides substantial manufacturing flexibility. For example, post-blow cooling for the molded article can be effected while the article is still in the mold by providing a shot of cold fluid (liquid or gas) at Stations  3 A and  3 B, or even at Stations  4 A and  4 B just prior to take-out without materially affecting the overall rate of production.  
         [0031]    A hydraulic cylinder arrangement is utilized to open and close the mold halves carried in the respective mold clamp assemblies  25  and  29  on dial  12  and mold clamp assemblies  35  and  39  for dial  14 . Hydraulic cylinder  43  (FIG. 2) mounted to base  15  at station  1  is used to clamp mold assembly  32  closed and hydraulic cylinder  49  (FIG. 3) mounted to base  15  at station  4 A is used to unclamp mold assembly  26 .  
         [0032]    The linkages associated with each mold clamp assembly include a toggle which is secured to each mold clamp assembly and has a central pivot which is attached to the mold clamp frame. A pivotable arm is located between each mold clamp and its associated toggle. The toggle is pivotally positionable about its central pivot in one of two orientations, a first orientation at which a pivot connecting the toggle to the arm is raised and the mold clamps are opened away from one another, and a second orientation in which another pivot is raised and the mold clamps are closed against one another. The pivot orientations are over-the-center orientations such that the center of the pivot connecting the arm and the toggle is passed through a line between the center of the pivot of the arm and the central pivot of the toggle as the toggle is pivoted between the open and closed orientations to provide an over-the-center latching mechanism for each of the mold clamp assemblies. Preferably the over-the-center latching mechanism is cylinder actuatable, i.e., actuatable by a hydraulic cylinder or a pneumatic cylinder. If desired, an electromechanical actuator such as a solenoid can be utilized to actuate the latching mechanism.  
         [0033]    [0033]FIG. 2 shows mold assembly  32  on dial  14  at common Station  1  where parison  21  extruded from continuous extruder  20  is positioned between complementary mold halves  33  and  34 . Mold cavity defined by mold halves  33  and  34  is shown in phantom. At the same time mold  36 , also on dial  14 , is indexed to Station  3 B, which can be an idle work station or a work station at which any desired secondary operation, e.g., cooling of a blow molded article, can be performed.  
         [0034]    Toggle  42  for mold clamp assembly  35  is shown in the mold-open position, while toggle  44  for mold clamp assembly  39  is shown in the mold-closed position. Hydraulic cylinder  43  actuates toggle  42  from a mold-open to a mold-closed position when mold assembly  32  with parison  21  on dial  14  is at Station  2 B.  
         [0035]    [0035]FIG. 3 shows mold assembly  22  on dial  12  at Station  2 A where a parison enveloped by mold halves  23  and  24  is being blow molded by a molding gas introduced via blowing mandrel  50 . At the same time, opposite mold assembly  26  on dial  12  is at Station  4 A, the take-out station, and in an open position so that molded container  30  can be removed therefrom.  
         [0036]    Toggle  46  for mold clamp assembly  22  is shown in the mold-closed position, while toggle  48  for mold clamp assembly  26  is in the mold-open position. Hydraulic cylinder  49  actuates toggle  48  from a mold-closed position to a mold-open position when mold assembly  22  arrives at Station  4 A. Mold assembly  26 , shown at Station  4 A, remains open as it is indexed to the shared Station  1  to receive another parison for molding.  
         [0037]    A blowing mandrel assembly eminently well suited for use with the hereinabove described rotary multi-station blow molding machine is depicted in FIG. 4. Blowing mandrel assembly  52  is constituted by an array of blowing mandrels  54 ,  56 ,  58  and  60  mounted to a common housing  62  which, in turn is supported by a frame  17  attached to base  15  (FIG. 1).  
         [0038]    Housing  62  includes apertured bushing plate  66 , guide bars  68  and  70 , apertured lift plate  72 , and apertured mounting plate  74 . Tapping plate  76  is attached to apertured mounting plate  74  for added rigidity, and also forms part of a frame that supports blowing mandrel assembly  52  in place at a blowing station, such as Stations  2 A and  2 B shown in FIG. 1. Guide bars  68  and  70  are shown in FIG. 4 in a rolled out position from their location in housing  62  so as to depict more detail.  
         [0039]    Lower end portions of guide bars  68  and  70  are fixed into bushing plate  66 , and optionally are provided with register pins, such as pins  73  and  75 , that project outwardly and downwardly beyond bushing plate  66  for engagement with complementary sockets  83  and  85  of a blow mold assembly positioned at Stations  2 A or  2 B during a blowing cycle. Register pins  73  and  75  coact with corresponding sockets  83  and  85  to facilitate proper alignment of the individual blowing mandrels in the blowing mandrel assembly with corresponding mold cavities in the mold assembly that is presented by an index dial at a blowing station.  
         [0040]    If desired, bushing plate  66  can be provided with plural rest buttons, such as rest buttons  89 ,  91 ,  93  and  95  shown in FIG. 6. At least three, preferably four, such rest buttons are provided on a bushing plate.  
         [0041]    Guide bars  68  and  70  also pass through lift plate apertures  78  and  80  (FIG. 5). Guide bar  68  is situated behind blowing mandrel  54 , and guide bar  70  is situated in front of blowing mandrel  60 . Lift plate  72  is secured to guide bars  68  and  70  at a midportion thereof by upper retaining ring  131  and lower retaining ring  132  for guide bar  68 , and by upper retaining ring  141  and lower retaining ring  142  for guide bar  70 . End portions of guide bars  68  and  70  extend into apertures  82  and  84  in mounting plate  74 . Washers  86  and  88 , together with respective screws  90  and  92 , retain mounting plate  74  on guide bars  68  and  70 .  
         [0042]    Actuators  94 ,  96 ,  98  and  100  are mounted atop of apertured mounting plate  74 , and are connected to respective blowing mandrels  54 ,  56 ,  58  and  60  by connecting rods  104 ,  106 ,  108  and  110  that extend through apertures  114 ,  116 ,  118  and  120  in mounting plate  74 . These actuators can be hydraulic cylinders, pneumatic cylinders, solenoid devices, or the like. Hydraulic cylinders are the preferred actuators, however.  
         [0043]    Connecting rods  106  and  108  of respective blowing mandrels  56  and  58  also extend through lift plate apertures  79  and  81 , and are provided with spacer stops, such as rigid sleeves  112  and  113 , in the region between lift plate  72  and mounting plate  74 . Body portions  196  and  198  of blowing mandrels  56  and  58  are larger in diameter than lift plate apertures  79  and  81 , and are configured to abut lift plate  72  as they are raised to their respective rest positions.  
         [0044]    Biasing coil springs  122  and  123  are provided around guide bars  68  and  70 , respectively, and are situated between lift plate  72  and mounting plate  74 . When in compression, biasing coil springs  122  and  123  abut both lift plate  72  as well as mounting plate  74 .  
         [0045]    Bushing plate  66  (FIG. 6) is provided with individual apertures  124 ,  126 ,  128  and  130 , respectively, for blowing mandrels  54 ,  56 ,  58  and  60 , lined with replaceable bushings  134 ,  136 ,  138  and  140  that are held in place with retaining screws  144 ,  146 ,  148  and  150 .  
         [0046]    Returning to FIG. 4, stop collars  154 ,  156 ,  158  and  160  of respective blowing mandrels  54 ,  56 ,  58  and  60  are slidably received in bushings  124 ,  126 ,  128  and  130 , and serve to limit the penetration depth of the distal end of the blowing mandrels into the mold assembly during the blowing operation.  
         [0047]    Blowing gas ports  164 ,  166 ,  168  and  170  are provided in the respective body portions of blowing mandrels  54 ,  56 ,  58  and  60 , as well as cooling medium inlet ports  174 ,  176 ,  178  and  180 , and cooling medium outlet ports  184 ,  186 ,  188  and  190 .  
         [0048]    The blowing mandrels of blowing mandrel assembly  52  are shown in the extended, blowing position. Upon completion of the blowing operation, actuators  94 ,  96 ,  98  and  100  are energized and first retract the distal end portions of mandrels  54 ,  56 ,  58  and  60  to clear a mold assembly situated at a molding station below. As retraction of these mandrels is continued to a rest position, body portions  196  and  198  of the respective mandrels abut lift plate  72  and elevate it together with bushing plate  66 , while coil springs  122  and  123  are compressed until rigid sleeves  112  and  113  abut the lower surface of mounting plate  74  and then held in a compressed state. When another mold assembly is positioned below blowing mandrel assembly  52  by action of an index dial, or like expedient, actuators  94 ,  96 ,  98  and  100  release, and coil springs  122  and  123  urge lift plate  72  downwardly until register pins  73  and  75  are seated in their respective sockets  83  and  85  and rest buttons  89 ,  91 ,  93  and  95  abut a pre-selected reference surface on the mold assembly. Thereafter, the actuators extend the distal end portion of each blowing mandrel into the corresponding mold cavity to a blowing position to commence the blowing cycle.  
         [0049]    The foregoing description and the drawings are illustrative of the present invention and are not to be taken as limiting. Still other variants and rearrangements of parts within the spirit and scope of the present invention are possible and will readily present themselves to those skilled in the art.