Abstract:
A blow molding machine having a tool head that is quickly and efficiently interchanged to minimize the time required to switch between products being blow molded. The tool head is changed without the need for removing the heater bands and with minimal need for alignment during installation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention is directed to a die assembly for a blow molding machine and, more specifically, to a die assembly having a tool head that is quickly and efficiently interchanged to minimize the time required to switch between products being blow molded.  
         [0002]     Blow molding machines are generally used to make thermoplastic containers and parts, such as fuel tanks for vehicles. In operation, blow molding machines typically extrude an elongated parisan between an inner ring and an outer ring on the tool head. To form a container, such as a vehicle fuel tank, a large die is clamped around the parisan while the extruded parisan is still partially molten. The parisan is then injected with air or an inert gas causing the parisan to expand and conform to the shape of the die. The shape, configuration, size, and relative arrangement of the inner and outer rings set the wall thickness, diameter, and shape of the extruded parisan. The shape, wall thickness, and diameter of the parisan are important because the parisan must be capable of being blown into the final shape. For example, certain portions of the parisan expand a greater distance, such as the portions that expand to the comers of the container. Further, if any portion of the container requires additional reinforcements, the shape, size, and wall thickness of the parisan may also vary to provide extra material where the reinforcements are needed. Problems may occur if upon expansion into a container, the wall thickness of the container is too thin. Conversely, problems may also occur if the container&#39;s walls are too thick in addition to raising manufacturing costs through material wastage and slower extrusion times.  
         [0003]     One problem with most blow molding machines is that changing the tool head of the die assembly to provide different shaped parisans for forming different shaped containers is time consuming. For example, in some circumstances, changing the tool head to switch between fuel tanks made for different automobiles causes the manufacturing line to be shut down for long periods of time. Blow molding machines operate at high temperatures to form the molten parisan and head tooling must be changed at operating temperatures, to prevent the material in the head tooling from hardening. If the material hardens before or while changing, it is difficult to disassemble and change the head tooling. Existing blow molding machines generally include at least two heater bands  110  around the die assembly, as illustrated in  FIG. 1 . Before the head tooling may be completely removed, the heater bands  110  have to be removed, which may require skilled trade support to accomplish. The availability of the tradesman may be problematic depending on current work loads of the required tradesman. With the heater bands removed, the die assembly, including the tool head having an inner and outer ring  60 ,  90 , is removed and cleaned while hot. Generally, the components must be removed in a specified order until the exemplary portion illustrated in  FIG. 1  by line A-A is removed. The tool head when removed typically weighs 300 to 500 pounds, thereby requiring multiple people to loosen the individual components and special lifts to support the tool head as it is being removed. After the tool head is removed, the new tool head is assembled and attached to the molding machine by assembling the individual components and attaching the tool head to the die assembly using special lifts. Once the new tool head is attached, the inner die ring and the outer die ring must be centered and aligned relative to each other. Centering and aligning of the inner and outer rings is a lengthy, tedious and difficult process that is further complicated when one or both of the inner and outer rings  60 ,  90  include scallops, contours or other non-cylindrical shapes. More specifically, the inner and outer die rings must be aligned both rotationally about the axis of the blow molding machine as well as laterally and longitudinally. After the new tool head is installed with the inner and outer rings, the heater bands  110  are installed and connected to preheat the head tooling to operating temperature. Due to the mass of the die assembly and associated components of the blow molding machine, a significant amount of time is generally required to reach operational temperature. Due to variances related to temperature and the extrusion process, the final alignment is performed by qualified personnel while material is being extruded through the head tooling. A significant problem with the above process is that any alignment problems of the inner ring  60  or outer ring  90  may not be evident until the machine produces products that do not meet required specifications.  
         [0004]     The process for changing tool heads is complicated, lengthy and to avoid down time due to head tool changes, some manufacturers purchase extra blow molding machines and create additional assembly lines to avoid a loss of production while tool heads are being changed. Other manufacturers, to avoid the significant capital expenditure of additional machines, design multi-use tool heads that are capable of forming a variety of acceptable containers or products therefore typically the machine adversely affects the machine runtime. The problem with multi-use tool heads that they produce differing containers or product and generally prevent maximum performance of the tool head in forming any one container or one product. For example, in a container formed from a tool head capable of forming multiple containers, the formed container generally has heavier walls than needed in certain areas, thereby, adding to the weight of the container and wasting material used to form the container.  
         [0005]     In view of the above problems and limitations, there is a need in the art for a quick change blow molding die assembly and tool head which allows easy and efficient changes of the tool head to accommodate various containers without significant down time.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a die assembly for a blow molding machine and, more specifically, to a die assembly having a tool head that is quickly and efficiently interchanged to minimize the time required to switch between products being blow molded. More specifically, in a first embodiment, the present invention is directed to a tool head for a blow molding machine having a die ring, an outer ring and a retaining ring. The die ring has a lower die edge, an outer die surface, and an inner die surface. The outer ring has an outer profiled surface and a lower ring surface, wherein the outer profiled surface engages the inner die surface and the retaining ring engages the lower die edge and the lower ring surface. A heater coil is coupled to the die ring so that the retaining ring and the outer ring are removable from said die ring without removing the heater coil.  
         [0007]     In a second embodiment, the present invention is directed to a tool head having a die ring, an outer ring and at least one heater coil coupled to said die ring. The die ring is substantially located between the heater coil and the outer ring. More specifically, the outer ring may be removed from said die ring without removing said heater coil. The retaining ring couples the outer ring to the die ring, with the retaining ring engaging a lower die surface of the die ring and a lower ring surface on the outer ring.  
         [0008]     In a third embodiment, the tool head includes a die ring, an outer ring coupled to the die ring, and an outer key assembly for rotationally aligning the outer ring with the die ring. The tool head further includes a die pin and an inner ring coupled to the die pin. The die pin and the inner ring include an inner key assembly for rotationally aligning the inner ring relative to the outer ring, with the inner ring and the outer ring defining an extrusion gap therebetween.  
         [0009]     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which:  
         [0011]      FIG. 1  is a prior art sectional view of a tool head for a blow molding machine;  
         [0012]      FIG. 2  is a sectional view of a tool head;  
         [0013]      FIG. 3  is a sectional view of an alternative embodiment;  
         [0014]      FIG. 4  is an exploded view of the tool head;  
         [0015]      FIG. 5  is a bottom plan view of the tool head; and  
         [0016]      FIG. 6  is a bottom plan view of an alternative embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     A die assembly  10  for a blow molding machine (not shown) constructed in accordance with the present invention is illustrated in  FIG. 2 . In general, the die assembly  10  includes a removable tool head  20  having an inner assembly  50  and an outer assembly  80  aligned along an axis  11  and defining a gap  79  therebetween. Heater coils  110  surround the die assembly  10  to heat the die assembly  10  to operational temperature so that the material in the die assembly  10  is heated until it is molten and forms a parisan that is extruded from the gap  79  between the inner and outer assemblies  50 ,  80 . A support assembly  120  (partially illustrated in  FIGS. 1 and 2 ) secures the die assembly  10  including the head tooling  20  to a blow molding machine (not shown).  
         [0018]     The support assembly generally includes a die assembly retaining ring  122  and a die rod  124 . The die assembly retaining ring  122  supports the outer assembly  80  ( FIG. 2 ) to the blow molding machine. The die rod  124  supports the inner assembly  50  ( FIG. 2 ). The die assembly retaining ring  122  may be formed in a variety of shapes and configurations, but in the illustrated embodiment is a ring with an “L-shaped” sectional view in which a lower support surface  123  supports a die ring support surface  78 . The die assembly retaining ring  122  may also be made with key slots (not shown) for easy removal for cleaning of the blow molding machine. However, during changing of the head tooling  10 , the die assembly ring  122  remains coupled to the blow molding machine, thereby keeping the die ring  82  coupled to the blow molding machine. An adjustment mechanism  127  may be included on the die assembly ring  122 , however, this generally does not need to be adjusted during changes of the head tooling. By not changing the die ring  82  with the tooling head  10 , the die ring  82  does not need to be adjusted relative to the blow molding machine  10 . As shown in  FIGS. 2-3 , the die rod  124  is coupled to a die pin  32  which is in turn coupled directly or indirectly to the inner assembly  50 . In the illustrated embodiment, the die pin  32  is bolted to the die rod  124  with a die rod bolt  126 . The die pin  32  is secured from movement relative to the die rod  124 . The die pin  32  includes an upper pin outer surface  36 , a lower pin outer surface  38 , and an inner pin surface  40 . The lower pin outer surface  38  is configured to receive and locate the inner assembly  50 . The size, shape, and configuration of the lower outer surface  38  may vary depending on the desired configuration of the inner assembly  50  and the overall die assembly  10 . The inner assembly  50  may be aligned relative to the die pin  32  through a die pin key assembly  46 , as illustrated in  FIG. 4 . The key assembly  46  may include a removable key. The inner pin surface  40  is configured to receive the die rod  124  and couple the die pin  32  to the die rod  124 . Portions of the die rod  124  are generally configured to mate with the inner pin surface  40 . The die pin  32  supports the inner assembly  50  and couples the inner assembly  50  to the die rod  124 . The size, shape, and configuration of the die pin  32  and the inner pin surface  40  may vary depending on the application. A lower pin fastener assembly  42  may couple the inner assembly  50  to the die pin  32 .  
         [0019]     The die assembly  10  further includes a receiver  52  for partially defining a flow path for the material and defining a cavity  53  for receiving the die pin  32  and die rod  124 . The receiver  52  is generally fastened to the blow molding machine with an upper pin fastening assembly (not shown). The upper pin fastener assembly locates the position of the receiver  52  and secures the receiver  52  from movement relative to the blow molding machine and the die ring  82 . The upper pin fastener assembly passes through holes  51  defined by the receiver  52 . In the illustrated embodiment, the receiver  52  is generally not changed as part of the change in tool heads  20  and therefore once the receiver  52  is set and aligned, changing of the tool head  20  will not require changing of the receiver  52  or alignment of the tool head  20 . As illustrated in  FIG. 2 , the receiver  52  is formed in somewhat of a frustoconical shape with a hollow center that forms the cavity  53 . The receiver  52  includes an inner receiver surface  54  configured to receive the die pin  32  and, more specifically, receive the upper pin outer surface  36 . The die pin  32  is coupled to the die rod  124  and is operationally movable within the cavity  53  to vary the gap  79  for profiling differential thicknesses of the parisan. During extrusion of the parisan, and to vary the gap  79 , the die pin  32  moves relative to the receiver  52  with the inner receiver surface  54  sliding along the outer surface  36 . The receiver  52  further includes a tapered outer receiver surface  56  that defines a portion of a pathway  24  along which the material flows in a molten state to the gap  79  where it is extruded to form the parisan. The gap  79  acts as the terminus of the pathway  24 .  
         [0020]     The inner assembly  50  includes an inner ring  60  and a cap  74 . In the illustrated embodiment, the inner ring  60  is coupled to the die pin  32  with the cap  74 . A lower pin fastener assembly  42  releasably couples the cap  74  to the die pin  32 . The inner ring  60  generally includes, as illustrated in  FIGS. 2-4 , an inside surface  62  configured to receive the die pin  32  and align the inner ring  60  relative to the die pin  32  and a shaped surface  63 . The shaped surface  63  further includes a top inner edge  64  and an extrusion edge  66 . The inner ring  60  may be formed in a variety of sizes, shapes, and configurations, depending on the desired size, shape, diameter, and wall thickness of the extruded parisan. As illustrated in  FIGS. 2 and 3 , the inner ring  60 , specifically the extrusion edge  66 , may have different diameters which affect the diameter of the extruded parisan. As illustrated in  FIGS. 2 and 3 , depending upon the diameter of the extrusion edge  66 , the shaped surface  63  may vary in shape and configuration because the diameter size and shape of the top inner edge  64  generally is consistent. More specifically, during changing of a tool head  20 , the inner assembly  50 , including the inner ring  60 , are removed with the die pin  32  and receiver  52  remaining on the die assembly  10 . Therefore, the top inner edge  64  which engages the receiver  52  or die pin  32  remains constant between different inner rings  60 , as shown in  FIGS. 2 and 3 , while the shaped surface  63  and extrusion edge  66  may vary to form different extrusion shapes. More specifically, the top inner edge  64  remains constant because it mates with a portion of the die assembly that is not removed and therefore mates to form a smooth extrusion pathway. The top inner edge  64  is illustrated in  FIGS. 2 and 3  as being aligned with the upper pin outer surface  36 , although in some embodiments, the top inner edge  64  may be aligned with the tapered outer receiver surface  56 , or configured to be extended within the cavity  53  of the receiver  52  (not illustrated), with the receiver  52  fitting partially over the inner ring  60 , wherein the tapered surface  56  terminates approximately against the shaped surface  63 . As illustrated in  FIGS. 2 and 3 , the top inner edge  64  is generally configured to provide a smooth transition between the receiver  52  and the inner ring  60 . A smooth transition between the receiver  52  and inner ring  60  facilitates a smooth extrusion pathway  24 . A smooth extrusion pathway  24  with minimal obstructions or obstacles helps the material flow through the pathway  24  to the gap  79  with minimal applied force. The inner shaped surface  63  and the inner extrusion edge  66  may have a variety of configurations of which exemplary embodiments are shown in  FIGS. 5 and 6 . The inner shaped surface  63  is generally dependent upon the relative shapes and sizes of the inner extrusion edge  66  and the top inner edge  64 . The size and shape of the inner ring  60 , specifically the inner extrusion edge  66 , is generally set by the desired size, shape, and wall thickness of the extruded parisan. The inner extrusion edge  66  may further include scallops  68  as shown in  FIG. 5 , which may increase or decrease wall thicknesses in specified spots. As shown in the alternative embodiment in  FIG. 6 , the inner extrusion edge  66  may be formed in a non-cylindrical shape such as an elliptical or oblong shape.  
         [0021]     The inner surface  62  of the inner ring  60  is configured to be installed and retained on the die pin  32  with minimal effort and alignment. The inside surface  62  is formed to engage the lower pin outer surface  38  to longitudinally and laterally align the inner ring  60  relative to the die pin  32 . The inner ring  60  may also be rotationally aligned about the axis  11  using an inner key assembly  70 . The inner key assembly  70  may be a slot on one of the inner ring  60  or die pin  32  into which a projection on the other of the inner ring  60  or die pin  32  slips into, as illustrated in  FIG. 2 .  
         [0022]     In the illustrated embodiment, the inner ring  60  and the cap  74  are configured to allow easy installation and accurate alignment with minimal effort. As shown in  FIG. 4 , the cap  74  releasably attaches the inner ring  60  to the die pin  32  with the lower pin fastener assembly  42 . The cap  74 , as illustrated in  FIGS. 5 and 6 , includes a variety of fastener holes  76  which may be keyed, such as, the holes  76  in the cap  74  having a non-symmetrical orientation about the cap  74 . In some embodiments, the cap fastener holes  76  may include key slots (not shown) which allow loosening of the bolts and removal of the cap  74  by twisting, without the need to fully remove the fastener assembly  42 . Thereby, the inner ring  60  may be removed without complete removal of the lower pin fastener assembly  42 . Using key slots allows for easier installation by allowing insertion of the inner ring and then securing the inner ring  60  with the cap  74  in an intermediate position without tightening the bolts of the lower pin fastener assembly  42 . After the cap  74  is in the intermediate position, the lower pin fastener assembly  42  may be tightened.  
         [0023]     The die assembly  10  further includes the die ring  82 . The die ring  82  is attached to the blow molding machine by the die assembly retaining ring  122 . The die ring  82  generally includes an inner surface  84  having an angled portion  86 , a recessed portion  85 , and a lower die ring edge  88 . The die ring  82  further includes a die ring outer surface  83  for supporting and receiving heater coils  110  as described below. The die ring inner surface  84 , specifically the recessed portion  85 , is configured to receive, retain and align the outer assembly  80  relative to the die ring  82 . The angled portion  86  defines a portion of the pathway  24  opposing the tapered outer receiver surface  56 . The angled portion also includes a lower angled edge  87 .  
         [0024]     The outer assembly  80  generally is coupled to the die ring  82  and includes an outer ring  90  and a retaining ring  104  for securing the outer ring  90  to the die ring  82 . The outer ring  90  generally includes an outer profiled surface  92  and an outer ring inner surface  96  having a top outer edge  98  and an outer extrusion edge  100 . In the illustrated embodiment, the outer profiled surface  92  is profiled to mate with the lower die inner surface  84 . The outer profiled surface  92  is configured to engage the die ring  82 , specifically the lower die inner surface  84 , and align the outer ring longitudinally along the axis  11 . The outer ring  90  and die ring  82  further include an outer key assembly  94  to rotationally align the outer ring  90  about the axis  11  and relevant to the die ring  82  and the inner ring  60 , as illustrated in  FIG. 2 . By aligning both the inner and outer rings  60 ,  90  about the axis with the inner and outer key assemblies  70 ,  94  the inner and outer rings  60 ,  90  may be easily aligned without the need for extensive adjustment. As with the inner ring  60 , the outer ring  90  may be formed in a variety of sizes, shapes, and configurations to form the desired extruded parisan. More specifically, as shown in  FIGS. 2 and 3 , as the inner ring  60  increases in diameter, the outer ring  90  generally decreases. Further, the outer ring inner surface  96  depends on the relative diameter of the outer extrusion edge  100  and the shaped surface  63  of the inner ring  60  to provide a sufficient pathway  24 .  
         [0025]     In the illustrated embodiment, the outer ring  90  further includes a retention recess  93  for engaging the retaining ring  104 . The retaining ring  104  holds the outer ring  90  to the die ring  82 . The retaining ring  104  generally includes a plurality of key slots  108  and is attached to the die ring  82  through the retainer fastener assembly  106 . The key slots  108  allow for easy removal of the retainer ring  104  and thereby the outer ring  90  by loosening the fastener assembly  106  and then rotating the retaining ring  104  relative to the die ring  82 .  
         [0026]     The heater coils or heater bands  110  are located on the die ring  82  surrounding the outer surface  83  so that the retaining ring  104  may be removed without removal of the heater bands  110 . The heater bands  110  not engaging any of the removable tool head allows efficient changes of the tool head  20  without the need to remove the heater bands  110  and eliminating the need for a qualified tradesman in tool head  20  changes. As illustrated in  FIGS. 2 and 3 , the heater bands  110  do not engage any portions of the tool head  20  or any parts of the die assembly  10  that must be removed.  
         [0027]     The above tool head  20 , including the outer and inner assemblies  80 ,  50  uses minimal parts thereby minimizing the number of parts that need to be removed and reinstalled. In the illustrated embodiment, the tool head  20  includes only four parts, the inner ring  60 , the outer ring  90 , the cap  74  and the retaining ring  104 , that are removed to change a tool head  20 . The number of parts is reduced in formation of the die assembly  10  by eliminating a variety of pieces between the inner and outer rings, such as requiring the die ring  82  to include a recessed portion  85  into which the outer ring  90  fits without any intermediate parts. This elimination of parts minimizes the cost of the die assembly as well as the cost of individual tool heads. Further, the elimination of parts also minimizes assembly time by requiring fewer parts to be disassembled and reassembled in changing the tool head  20 . The assembly time is further minimized by designing the die ring  82  and die pin  32  to engage the inner and outer rings  60 ,  90  in a specified lateral, longitudinal and rotational position that eliminates time consuming adjustments and any mechanisms required for adjusting and aligning the rings  60 ,  90  relative to each other. The retaining rings  104  and caps  74  are also designed for easy installation and removal. The elimination of parts, as well as minimizing the number of removable parts by designing the die assembly  10  and removable tool head  20  for easy removal also creates a relatively light weight tool head easily handled by one to two people without special lifts. Further, the inner and outer rings  60 ,  90  may be designed so that only one needs to be changed to switch between containers while maximizing performance.  
         [0028]     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.