Abstract:
A two-step blow molding machine ( 10 ) having flexible cavitation which includes a plurality of stations, a preform loading station ( 12 ), a thermal conditioning station ( 14 ) where preforms are heated and thermally conditioned prior to blow molding, a blow molding station ( 16 ) having a plurality of molds, the number of which defines the cavitation of the blow molding station, and an article unloader station ( 18 ). The machine includes a plurality of carriers ( 22 ) adapted to receive the preforms thereon at said preform loading station. The carriers are transported about the machine in an unrestrained manner where spacing of the carriers does not correspond with cavitation of the machine. First and second conveyors and associated drives convey the carriers at different rates. The first and second conveyors and their associated drivers are independently controllable from one another such that the first and second rates are independently variable which allows changeable cavitation.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a two-step blow molding machine and, more particularly, to such a machine having readily changeable or flexible cavitation.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    A two-step blow molding machine is an apparatus designed to produce plastic blow molded articles from a previously formed plastic preform. In the two-step machine, the previously formed preform is received by the machine and reheated to a temperature suitable for blow molding and, more specifically, stretch blow molding. Reheating of the preform is conducted in such a manner that the preform is conditioned to the proper temperature prior to being transferred to the blow molding station of the machine. In the blow molding station, a high pressure fluid medium is introduced into the interior of the preform and this, in conjunction with an axially extendable stretch rod, causes the preform to conform to the desired configuration as defined by the cavity surfaces of the molds themselves.  
           [0003]    A two-step blow molding machine differs from a one-step blow molding machine in that a one-step machine, in addition to blow molding the preform into the resultant article, also forms the preform, typically by injection molding.  
           [0004]    Two-step blow molding machines are typically of two styles, rotary and inline. In a rotary machine, preforms are received into the machine at one station, transferred to a second station by a rotary table or wheel where they are thermally conditioned. Next the table rotates to transfer the reheated preforms to the blow molding station.  
           [0005]    As one skilled in the art will readily appreciate, the cavitation of such machines is fixed, meaning that the number of blow mold cavities cannot be changed without rebuilding or drastically changing the configuration or other stations in the machine. In rotary machines, the number of neck splits  9  which hold the preforms) correspond both in number and spacing with the cavitation of the machine. Additionally, the number of heating pots used at the thermal conditioning station likewise corresponds in number and spacing. If the cavitation of the machine is to be changed, not only must the mounting of the neck splits to the indexing table be changed, but also the number of and spacing of the conditioning pots, the transfer mechanism for loading preforms into the machine and the transfer mechanism for discharging the resultant articles from the machine.  
           [0006]    Thus, when a blow molder desires to mold a larger diameter article, thereby necessitating a cavitation change, the blow molder must undertake a time consuming and expensive reconfiguration of the existing blow molding machine. Obviously, the expense and time does not lend itself to utilizing one machine for frequently switching between different cavitation requirements. As a result, blow molders typically buy a second or additional machine for each of their cavitation and article requirements.  
           [0007]    Inline two-step blow molding machines typically use one of three constructions. In one approach, the preform is mounted on a preform holder which is itself secured to a chain conveyor at fixed intervals. As the chain conveyor rotates, the preforms are cycled through a thermal conditioning station and then into a blow molding station. The fixed spacing of the holders on the chain conveyor is determined by and corresponds with the cavitation of the blow molding station. Additional constructions of inline blow molding machines similarly fix the relative position of the preforms to one another, with the spacing corresponding to the spacing of the mold cavities.  
           [0008]    The limitations recited above in connection with rotary machines similarly applies to inline blow molding machines. In changing over such machines, not only do the molds have to be changed themselves, but also numerous aspects with the respect to the holders of the preforms, the drive systems for moving the holders, and the conditions under which thermal conditioning occurs. For example, by changing cavitation it may cause an increase or decrease in the amount of time spent at the thermal conditioning station. Accordingly, the preform may be over or under heated resulting in an unacceptable article being molded at the blow molding station.  
           [0009]    One attempt to modularize a blow molding machine is found in U.S. Pat. No. 4,151,876. This machine utilizes component dye sets having modular elements so that containers of different sizes can be molded without requiring complete dye sets of each individual container size. While this design offers some flexibility regarding the size of the containers the machine is capable of manufacturing, it is still limited to a fixed number of mold cavities located at fixed mold centerlines. The cavitation is actually fixed.  
           [0010]    From the above, it is clearly seen that there exists a need for a blow molding machine having the ability to quickly and easily change the mold cavity spacing utilized in the machine.  
           [0011]    In view of the above limitations and drawbacks of the prior art, it is the object of the present invention to provide a blow molding machine having flexible cavitation.  
           [0012]    Another object of the present invention is to provide a blow molding machine in which preforms are carried in a manner that allows the cavitation of the machine to be changed without changing the manner and mechanism by which the preforms are carried about the machine.  
         SUMMARY OF THE INVENTION  
         [0013]    In overcoming the limitations of the prior art and achieving the above and other objects, the present invention provides a two-step blow molding machine having a novel construction which allows for the cavitation of the machine to be flexible. As used herein, references to a machine having flexible cavitation is intended to mean that the cavitation at the blow molding station of the machine can be changed, molds positioned on different mold centerlines, without requiring significant changes in the main other stations of the machine. With the present invention, changes to the other stations principally includes changing programmable control of those stations and in particular controlling the rate at which preforms are transferred through the various stations.  
           [0014]    In accomplishing the above, the present invention provides a two-step blow molding machine having a plurality of stations including a preform loading station where preforms are loaded into the machine, a thermal conditioning station where preforms are heated to enable blow molding of the preforms, a blow molding station where the preforms are blow molded into articles, and an article unloading station where the articles are removed from the machine. In addition to the above, the machine includes a plurality of preform carriers which receive preforms at the preform loading station and are utilized to transport the preforms through each of the various stations of the machine. The machine further includes a first conveyor which transports the carriers and preforms through the thermal conditioning station at a first rate. A driver is associated with the first conveyor for controlling the rate of the first conveyor. A second conveyor and associated driver conveys the carriers and preforms from the thermal conditioning station to the blow molding station. The first and second conveyors with their associated drivers are independently controllable such that the conveyance rate of each conveyor can be independently varied with respect to the conveyance rate of the other.  
           [0015]    By enabling this variance in conveyance rate of the carriers, and resultingly the preforms, through the conditioning station and to the blow molding station, the present invention enables the blow molding machine of the present invention to exhibit flexible cavitation as defined above.  
           [0016]    In another aspect, the present invention provides a two-step blow molding machine in which the soak time, the time from exiting the thermal conditioning station until the time of blow molding, is variable. As such, the present invention in this aspect is a blow molding machine having a plurality of stations including a preform loading station for loading preforms into the machine, a thermal conditioning station where the preforms are thermally conditioned for blow molding, a blow molding station where the preforms are blow molded into articles, and an article unloading station where the articles are removed from the machine. The present invention in this aspect also includes a plurality of preform carriers which receive and carry the preforms at the preform loading station to transport the preforms through the blow molding machine. In this aspect, the present invention further includes a conveyor and associated driver which conveys the carriers with the preforms engaged thereon, from the thermal conditioning station to the blow molding station. The rate at which the conveyor and its associated driver conveyed the carriers from the thermal conditioning station to the blow molding station is variable such that the time from which the preforms emerge from the thermal conditioning station until they are taken into the blow molding station can be increased or decreased. The time is thus variable and this length of time is referred to as the soak time. The term soak time relates to the amount of time available for the temperature of the interior surface of the preform wall to equalize with the temperature of the exterior surface of the preform wall, as a result of the preform being heated through its exterior wall in the thermal conditioning station.  
           [0017]    The above and other objects of the present invention will become apparent to one skilled in the art upon a reading of this specification, including the claims and with reference to the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a schematic illustration of a two-step blow molding machine according to the principles of the present invention.  
         [0019]    [0019]FIG. 1A is a top plan view of a machine according to the present invention.  
         [0020]    [0020]FIG. 2 is an isolated view of the conveyor and associated driver which transports the carriers from the preform loader to the thermal conditioning station and from the thermal conditioning station to the blow molding station.  
         [0021]    [0021]FIG. 3 is a cross sectional view through one oven of the thermal conditioning station illustrating the heating elements of the oven as well as the various conveyor and rotational mechanisms utilized therein.  
         [0022]    [0022]FIG. 4 is a top plan view of the thermal conditioning station with the housing and heating elements removed to illustrate the conveying mechanisms, as well as the positioning of the carriers and preforms relative to one before during and after entering the thermal conditioning station.  
         [0023]    [0023]FIG. 5 is an enlarged view of the thermal conditioning station where carriers and preforms are staged prior to entry into the blow molding station.  
         [0024]    [0024]FIG. 6 is a side elevational view of the station seen in FIG. 5.  
         [0025]    [0025]FIG. 7 is a partial perspective view of the clamp assembly found in the blow molding station.  
         [0026]    [0026]FIG. 8 is a partial perspective view of the stretch rod and blow assembly used in the blow molding station.  
         [0027]    [0027]FIG. 9 is a top plane view of the mechanisms used to transfer carriers, preforms and/or articles between the blow molding station, the article unloading station and the preform loading station.  
         [0028]    [0028]FIG. 10 is a partial side elevational view of the article unloading station and the preform loading station.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring now the drawings, seen diagrammatically in FIG. 1 is a two-step blow molding machine  10  according to the principles of the present invention. The machine is provided with a number of stations including a preform loading station  12 , a thermal conditioning station  14 , a blow molding station  16  and an article unloading station  18 . In addition to the above stations, the machine  10  utilizes a transport conveyor  20  and carriers  22  to move the preforms  24  (seen in FIG. 3) from the preform loading station  12  to the blow molding station  16 . The carriers  24  are additionally utilized in transfer of the preforms  24  into the blow molding station  16  and subsequently to the article unloading station  18 . All of these features are further described below.  
         [0030]    Preforms  24 , are received in bulk at a preform feeder  26 . The preform feeder  26  orients the preforms  24  in a consistent manner and delivers the preforms  24  via a guide rail  28  to the preform loading station  12 . The preform feeder  26  may be one of numerous known constructions utilized in the blow molding industry and therefore its full construction is not described in greater detail herein.  
         [0031]    From the guide rail  28 , the preforms  24  are received by a preform staging mechanism  30  which spaces the preforms  24  such that they may be manipulated by a preform loader  31  and loaded on to carriers  22 . The preform staging mechanism  30  utilized in the present invention incorporates a screw drive which engages and intermittently advances a series of preforms  24 , six as seen in FIG. 1A. During advancement of the preforms  24  by the screw (not shown) the preforms  24  are appropriately spaced out as required by the preform loading station  12 . Various constructions exist for preform staging as will be appreciated by those skilled in the art. It should be understood that the preform staging mechanism  30  illustrated in the blow molding machine  10  could incorporate any of those numerous alternate constructions. Accordingly, the preform staging mechanism  30  need not and is not discussed in further detail.  
         [0032]    The preform loading station  12  includes a series of fingers  32  which are advanced by a mechanical cam driven actuator  34  such that the fingers  32  engage the preforms  24  adjacent to the preforms neck finish. The fingers  32  are pivotally connected at their inboard-most end to a frame member  36  of the preform loading station  12 , which is mounted for rotation about its longitudinal axis. To enable the fingers  32  to retainingly engage the preforms  24 , each set of fingers  32  is biased by a spring  38  into a closed position. On advancement of the fingers  32  by the actuator  34 , the fingers  32  contact the preforms  24  and are forced outward against the bias of the spring  38  until they snap around the neck finish  52  of the preform  24 . The spring  38  accordingly retains the fingers  32  in a clamping action around the neck finish  52  of the preform  24 .  
         [0033]    A servo motor  40  then rotates the frame  36  180 degrees about its longitudinal axis, thereby removing the preforms  24  from the preform staging mechanism  30 . On the opposing side of the preform loading station  12 , as the frame  36  rotates the preforms  24  are brought down by the fingers  32  and mounted upon a series of preform carriers  22 . The carriers  22  are themselves held in position as the preforms  24  are engaged therewith at the preform loading station  12  by a preform end  42  of a transfer rake  44  (further discussed below). Once the preforms  24  have been mounted to the carriers  22 , the rake  44  is retracted laterally away from the preform loading station  12 , releasing the carriers  22 , with the preforms  24  mounted thereto, onto the transport conveyor  20 . Lateral movement of the rake  44  is accomplished through utilization of an actuator  46 , coupled to the rake  44 , which may be a pneumatic or other know type of actuator.  
         [0034]    While not illustrated in connection with the preform loading station  12 , a carrier  22  having a preform  24  mounted thereto is illustrated in FIG. 3 in connection with the thermal conditioning station  14 .  
         [0035]    The carrier  22  is provided with a one piece construction and is accordingly machined from a single piece of suitable material, such as aluminum. The carrier  22  includes a protruding nipple  48  formed in its upper most surface  50 . The outer diameter of the nipple  48  substantially corresponds to the inner diameter of the neck finish  52  of the preform  54 . During downward rotation of the preform at the preform loading station  12 , by the fingers  32 , the neck finish  52  of the preform  24  is brought into engagement over the nipple  48  of the carrier  22 . Immediately surrounding the nipple  48  is a recess  54  into which the neck finish  52  descends. An o-ring  56  or other means may be provided in this recess  54  to aid in sealing the carrier  22  and preform  24  during blow molding at the blow molding station  16  (as discussed below). In the illustrated embodiment, the outer diameter of the nipple  48  and the inner diameter of the neck finish  52  are such that the preform  24  is retainingly engaged on the carrier  22 . In alternative embodiments of the carrier  22 , positive retention means or provisions to assist in retention may be provided. Additional features of the carrier  22  are further described below in connection with the thermal conditioning station  14 .  
         [0036]    The transport conveyor  20 , seen in FIGS. 1 and 2, is illustrated in isolation in FIG. 2. As seen therein, the transport conveyor  20  is an endless conveyor having a sectional belt  58  driven by a driver  60 , such as a servo motor. Preferably the belt  58  is constructed of a hard plastic or other material and is sectioned enabling the belt  58  to readily navigate corners  62  as required by the present invention. The belt  58  is retained in its desired configuration by a frame  64  constructed of aluminum or other material and provided on both sides of the belt  58 . At its ends  66 , the belt  58  is trained back upon itself. In this manner, the return path of the belt  58  is directly beneath the upper surface of the belt  58  and similarly guided by the frame  64 . Individual sections of the belt are coupled to adjacent sections in a finger jointed and pivotal manner which allows the belt  58  to readily navigate corners  62  without binding. Such belts are well known in the manufacturing industries and need not be further discussed herein as the full construction will be appreciated by those skilled in the art.  
         [0037]    The transport conveyor  20  mentioned above delivers the carriers  22 , and the preforms  24  mounted thereon, to the thermal conditioning station  14 . The thermal conditioning station  14  includes a plurality of ovens  15  (five in the schematic illustration of FIG. 1 and six in the illustration of FIG. 1A). While illustrated with five and six ovens, the construction of the thermal conditioning station  14  may include a greater or lesser number of ovens  15  depending on the specific design criteria. Additionally, the station  14  may be modular in design allowing ovens  15  to be taken off-line or added on-line, depending on the then current operating conditions of the blow molding machine  10  and the specific design of the machine.  
         [0038]    As seen in FIG. 3, each oven  15  includes a housing  68  through which the carriers  22  and preforms  24  are transported at the thermal conditioning station  14 . Interiorly of the housing  68 , each oven  15  is provided with a plurality of heat lamps  70  which typically extend the length of each oven  15 . The heat lamps  70  are mounted within each oven  15  such that their transverse positioning (designated by arrow  71 ) within the oven  15  relative to the preform  24  maybe adjusted as required by the specific shape of the preform&#39;s body  72 . As seen in FIG. 3, the transverse positioning of the lamp  70  may be adjusted to conform to the profile of the body  72  of the preform  24 . The mounting of such lamps  70  for lateral displacement is common in the industry and, accordingly, is not described in great detail, but typically includes a retainer plate or similar structure  73 . The ovens  15  are provided with a reflective surface  74  on a surface opposite the lamps  70 . In this manner, the side of the preform  24  opposite the lamps  70 , is reflectively heated without the need for additional lamps  70 .  
         [0039]    Once entering into the thermal conditioning station  14 , the rate of conveyance through the station  14  is no longer governed by the transport conveyor  20  and the rate of the belt  58 . Within the thermal conditioning station  14 , the carriers  22  are contacted on one side by a plurality of rollers  76  coupled together in a chain conveyor assembly  78  by rigid lengths  80 . Opposite the chain conveyor assembly  78 , the carrier  22  is engaged by a belt  82  which is part of a rotational conveyor assembly  84 . These features and their engagement with the carrier  22  are best seen in FIGS. 3 and 4.  
         [0040]    The chain conveyor assembly  78  includes a toothed gear drive  81  and is driven by a servo motor  86 . As seen in FIG. 4, a pair of rollers  76  of the chain conveyor assembly  78  engage each carrier on opposing sides of a centerline of the carriers  22 . As such, the carrier  22  becomes trapped between the rollers  76  and the belt  82  of the rotational conveyor assembly  84 . Movement of the carrier  22  along belt  58  of the transport conveyor  20  is thereafter restricted because of the trapping engagement of the rollers  76  with the carrier  22 . Accordingly, when the carriers  22  and preforms  24  are within the thermal conditioning station  14  the chain conveyor assembly  78  determines the rate of conveyance of the carriers  22  through the station  14 . This is further permitted because the carriers  22  are not positively or retainingly engaged with the belt  58  and, instead, merely rest on the top surface of the belt  58 . When engaged by the chain assembly  78 , the belt  58  and the carriers  22  move relative to one another with the belt  58  sliding underneath and ahead of the carriers  22  when the rate of the chain conveyor assembly  78  is less than the rate of the belt  58 .  
         [0041]    While the carriers  22  are transferred through the ovens  15  at a rate determined by the movement of the rollers  76  in the chain conveyor assembly  78 , the rotational conveyor assembly  84  causes the carrier  22  and the preform  24  to additionally rotate about the vertical axis  86  of the carrier  22 . The belt  82  of the rotational conveyor assembly  84  extends about a pair of end pulleys  88  and through the entire length of the rotational conveyor assembly  84 . A series of tension pulleys  90  are located between the end pulleys  88  and are spring or otherwise biased by biasing mechanisms  91  into contact with the belt  82  thereby forcing the belt  82  into engagement with the carriers  22 . For clarity purposes, only a representative number of the tension pulleys  90  are labeled as such in FIG. 4.  
         [0042]    The belt  82  is additionally entrained around a drive pulley  92  which is in turn caused to rotate by a servo motor  94 . Being provided with its own servo motor  94 , the belt  82  of the rotational conveyor assembly  84  is capable of being rotated at a rate and in a direction differing from the rate at which the chain conveyor assembly  78  moves the carriers  22  through the thermal conditioning station  14 . As a result, and in conjunction with the rollers  76 , the belt  82  causes the carriers  22  and the preform  24  positioned thereon to rotate about their axes  86  as they are transported through the thermal conditioning station  14 . As those skilled in the art will appreciate, by rotating the preforms  24  as they pass through the ovens  15 , uniform heating of the material forming the body  72  of the preform  24  can be achieved.  
         [0043]    Upon exiting the thermal conditioning station  14 , the carriers  22  are released by the chain assembly  78  and the rotational conveyor assembly  84  onto the transport conveyor  20 . Once again their rate of movement is dictated by the transport conveyor  20  as they freely rest upon the surface of that belt  58 .  
         [0044]    From the thermal conditioning station  14 , the carriers  22  and heated preforms  24  are next transported to the blow molding station  16 . The time from which the carriers  22  and preforms  24  exit the thermal conditioning station  14  until they are blow molded in the blow molding station  16  is known as the soak time. Soak time refers to the time available for the temperature of the interior surfaces  96  of the preforms  24  to equalize with the temperature of the exterior surfaces  98  of the preform  24 . Depending upon the thickness of the body  72  of the preform  24  and upon the specific material of the preform  24 , greater or lesser soak times may be warranted or desired. Additionally, it may be desirable to limit the amount of thermal equalization between the internal and external surface temperatures for reasons related to the article being manufactured.  
         [0045]    The machine  10  of the present invention, in addition to allowing for flexible cavitation at the blow molding station  16 , allows for a variable soak time. This variability of the soak time is achieved by controlling the servo motor  60  governing the rate of movement of the belt  58 . By increasing the speed of the belt  58 , soak time can be decreased. Conversely, by decreasing the speed of the belt  58 , the soak time may be increased.  
         [0046]    As seen in FIG. 4, the rate at which the carriers  22  are transported through the thermal conditioning station  14  is such that the carriers  22  and preforms  24  are located in side by side or immediate adjacent positioning as they progress therethrough. Accordingly, the carriers  22  and preforms  24  exhibit a first preform density as they pass through this thermal conditioning station  14 . As the carriers  22  and preforms  24  are released from the chain assembly  78  of the thermal conditioning station  14 , movement of the carriers  22  and preforms  24  is again determined by the rate at which the belt  58  is moving. By moving the belt  58  at a rate greater than the rate at which the chain assembly  78  is moving, the carriers  22  and preforms  24  are accelerated out of the thermal conditioning station  14  and are thereafter spaced apart from one another. Accordingly, a second preform density is exhibited as the carriers  22  move with the belt  58 .  
         [0047]    Referring now to FIGS. 5 and 6, prior to moving into the blow molding station  16 , the carriers  22  and preforms  24  are transported by the transport conveyor  20  to a preform spreading station  100 . At the preform spreading station  100 , a pneumatic or other type of actuator  102  advances a finger  104  to interfere with movement of the carriers  22  and preforms  24  by the transport conveyor  20 . This may cause a stacking up of the carriers  22  as illustrated in FIG. 5. When the station  100  is clear of already admitted carriers  22 , the finger  104  is retracted by the actuator  102  and an appropriate number of carriers, corresponding to the cavitation of the blow molding station  16 , are permitted to enter the station  100 . These carriers  22  and associated preforms  24  are transported into the station  100  by the transport conveyor  20 , which thereafter begins its return path. Within the station  100 , the carriers  22  progress along the transport conveyor  20  until contacting a stop surface  106  which limits further travel of the carriers  22 . With the appropriate number of carriers  22  admitted into the station  100 , the actuator  102  again advances the finger  104  stopping the movement of any additional carriers  22  into the station  100 .  
         [0048]    With the appropriate number of carriers  22  within the station  100 , a push blade  108  is brought into contact with the series of carriers  22  in a direction generally transverse to movement of the transport conveyor  20 . As a result of contact with the push blade  108 , the carriers  22  and associated preforms  24  are pushed off of the transport conveyor  20  and on to a spreader plate  110 . As best seen in FIG. 6, the push blade  108  is supported by a frame  112  coupled to guide rods  114  located above the spreader plate  110 . A pneumatic or other type of actuator  116  is additionally coupled to the frame  112  and retraction of the actuator  116  will cause the push blade  108  to be drawn across the transport conveyor  20  pushing the carriers  22  onto the spreader plate  110 . In FIG. 6, the frame  112  and push plate  108  are illustrated in both the advanced and retracted positions.  
         [0049]    As the carriers  22  are drawn across the spreader plate  110 , the carriers  22  engage diverter bars  118  positioned on top of the spreader plate  110 . The bars  118 , beginning at the mid-point of the series of carriers  22  engage tapered ends  120  of the bars  118  and act to spread out and equidistantly position the carriers  22  relative to one another. This spacing coincides with the cavitation of the blow molding station  16 . Stray lateral movement of the carriers  22  is prevented by lateral guides  122  also mounted to the top of the spreader plate  110 .  
         [0050]    Continued advancement of the push plate  108  moves the carriers  22  into engagement with a transfer rake  124 . The transfer rake  124  includes a series of teeth  126  defining recesses  128  therebetween and into which the carriers  22  are received. The centerline spacing of the recesses  128  corresponds with the centerline spacing and cavitation of the blow molding station  16 . Once the carriers  22  are fully seated within the transfer rake  124 , the actuator  116  moves the frame  112  and the push plate  108  back to its initial position and a new series of the carriers  22  and preforms  24  are admitted into the station  100  for the next cycle.  
         [0051]    In an alternative embodiment, the push blade  108  may be of limited stroke so as to move the carriers  22  and preforms  24  off of the conveyor  20  the distance of approximately one carrier width. When subsequent carriers  22  are advanced by the push blade  108 , the previously advanced carriers  22  will be in turn moved additionally toward, and eventually into, the transfer rake  124 . In doing so, additional soak time can be added to the machine  10 .  
         [0052]    With the carriers  22  fully seated within the recesses  128  of the rake  124 , a linear servo motor  130  is actuated causing the rake  124  to move in a direction transverse to that in which it received the carriers  22 . At this point the carriers  22  are slid along a stationary or dead plate  132  located substantially parallel to the guide rail  134  along which the servo motor  130  moves for its linear motion. The stationary plate  132  may include a lip or gib  136  to prevent the carriers  22  from inadvertently moving out of the rake  124  and off of the dead plate  132 .  
         [0053]    Advancement of the rake  124  as discussed above, moves the carriers  22  and the preforms  24  into the blow molding station  16 . Once the carriers  22  and preforms  24  are properly located within the blow molding station  16 , a pneumatic or other type of actuator  136  retracts the rake  124  away from the dead plate  132  and the servo motor  130  returns the rake  124  back into the preform spreader station  100 . With the rake  124  located back within the preform spreader station  100 , the actuator  136  advances the rake  124  back into position where it may receive the next series of carriers  22  as they are spread out or spaced within the station  100 .  
         [0054]    Two major components of the blow molding station  16  are illustrated in FIGS. 7 and 8. More specifically, FIG. 7 illustrates the clamp assembly  138  while FIG. 8 illustrates the stretch rod and blow air assembly  140 .  
         [0055]    The clamp assembly  138  includes a pair of platens  142  which support the molds (not shown) of the blow molding station  16 . Servo driven mechanical linkage  144 , coupled to the platens  142 , causes the platens  142  to be opened or closed as desired. Obviously, the platens  142  and the molds attached thereto are opened as carriers  22  and preforms  24  are advanced into the blow molding station  16  and as blow molded articles are transported out of the blow molding station  16  on the carriers  22 . Many varieties of clamp assemblies are well know in the blow molding art and for this reason those skilled in the art will readily appreciate the features and operation of the present clamp assembly  138 . Accordingly, the clamp assembly  138  is not discussed in greater detail herein.  
         [0056]    One feature of the clamp assembly  138 , which has not been previously seen, allows for movement of the clamp assembly  138  in a manner which more readily facilitates the changing of the molds and therefore the cavitation of the machine  10 . Specifically, the clamp assembly  138  includes a stationary frame  146  and a rotatable plate  148 .  
         [0057]    The platens  142 , linkage  144  and all componentry associated with the opening and closing of the molds are carried by the rotational plate  148  which is supported and guided by rollers (not shown) on the stationary frame  146 . During operation of the blow molding machine  10 , the illustrated linkage  144  is oriented toward the exterior of the machine  10  as seen in FIG. 1A. This orientation of the clamp assembly  138  does not lend itself to easy changing of the molds because the interior faces of the platens  142  are not readily accessible from the exterior of the machine  10  and must be accessed from the side. To alleviate this problem, the clamp assembly  138  of the machine  10  allows for access to the platens  142 , linkage  144  and associated componentry through rotation of the rotation plate  148  and these components. By rotating this plate  148  90°, direct and easy access can be gained to the platens  142  from the exterior of the machine  10  since the platens  142  are then oriented such that the opening between them is also open in a direction exteriorly of the machine  10 .  
         [0058]    Rotation of the plate  148  and the componentry of the clamp assembly  138  mounted thereon can be achieved in various ways including engagement of a tooth drive wheel  150  with a correspondingly tooth portion of the rotational plate  148  and rotation of the drive wheel  150  by an electric motor  152  or other driver. In an alternative embodiment, a belt may be engaged with the rotational plate  148 , extending therearound, and driven by a drive pulley and an electric motor (analogous to the drive wheel  150  and motor  152  discussed above). To insure that the rotational plate  148  is fixedly positioned relative to the rigid frame  146  during actual blow molding, a pneumatic or other type of actuator  153  may advance pins (not shown), of a locking assembly  154  rigidly mounted to the frame  146 , into engagement with corresponding portions  156  formed in or mounted to the rotational plate  148 .  
         [0059]    In an alternative embodiment, the clamp assembly  138  may be constructed to slide outward of the machine  10  proper in order to provide access to the platens  142  and molds mounted thereto.  
         [0060]    The stretch rod and blow air assembly  140 , seen in FIG. 8, includes numerous features which are well know within the industry. For this reason, a construction and working of the stretch rod and blow air assembly  140  need not be discussed in great detail herein. It is noted, however, that all of the stretch rods  162  are simultaneously and commonly advanced during the blow molding of the preforms  24  into articles by advancement of a rack  158  coupled to a moveable belt  160  driven by a motor (not shown) or other driver. During actual blow molding, the frame  164  is raised by pneumatic or other type of actuators  166  bringing blow seals  168  into general engagement with a central bore  169  defined through the carriers  22 . The blow seals  168  themselves are pneumatically actuated to sealingly engage the carriers  22 . To permit the stretch rods to enter into the bores through the carriers  22 , the dead plate  132  is provided with a central slot  171  in a position above the stretch rod and blow air assembly  140 . As seen in FIG. 8, the blow seals  168  are individually carried on blow manifolds  170  that can be readily repositioned in the frame  164 , depending upon the cavitation of the blow molding station  16 . Removable pins  172  are illustrated for this purpose. While it is anticipated that each manifold  170  will be individually supplied with blow air, a common supply could similarly be used.  
         [0061]    In order to transfer carriers  22  and blow molded articles  24 ′ thereon out of the blow molding station  16 , a second transfer rake  44  is used. Transfer rake  44  is illustrated in FIGS. 9 and 10 in connection with the blow molding station  16 , the article unloading station  18  and the preform loading station  12 . These two views of the apparatus differ from those presented previously as in FIG. 5, in that the machine  10  is viewed from the opposing side.  
         [0062]    As with the transfer rake  124 , the transfer rake  44  is mounted and rides upon the guide rail  134  for a reciprocating movement between the blow molding station  16  and the article unloading station  18  and the preform loading station  12 . Also like the prior transfer rake  124 , the transfer rake  44  is moved along the guide rail  134  by a linear servo motor  176  appropriately coupled thereto. The transfer plate  44  is coupled to the servo motor  176  such that the transfer rake  44  can be retracted from and advanced toward the dead plate  132  and the transport conveyor  20 . In this regard, an actuator  46  similar to actuator  136  is provided and coupled to the transfer rake  44 .  
         [0063]    In its retracted position, the transfer rake  44  is moved by the servo motor  176  such that an article end  180  of the transfer rake  44  is located within the blow molding station  16  and a preform end  42  of the transfer rake  44  is located at the article unloading station  18 . Such a position would be located to the right of that illustrated in FIG. 9. Actuator  46  then advances the transfer rake  44  such that the respective teeth and recesses of the transfer rake engage carriers  22  in the blow molding station  16  and in the article unloading station  18 . Once the articles  24 ′ have been blow molded at the blow molding station  16  and the previously blow molded articles  24 ′ have been removed from the carriers  22  at the article unloading station  18 , the servo motor  176  shifts the transfer rake  40  such that the article end  180  is re-positioned at the article unloading station  18  and the preform end  42  is re-positioned at the preform loading station  12 . Once the articles  24 ′ have been removed from the carriers  22  at the article unloading station  18  and preforms  24  have been loaded onto the carriers  22  at the preform loading station  12 , the actuator  46  retracts the transfer rake  44  beginning a repeating of the cycle described above. At the article unloading station  18  and as seen in FIG. 10, the dead plate  132  is again formed with a slot  184 . Positioned within the slot  184  is a plate  186  coupled to a pneumatic or other type of actuator  188  which operates to raise the plate  186  into engagement with the bottom surfaces of the carriers  22  being held at the article unloading station  18  by the article end  180  of the transfer rake  44 . Preferably the actuator  188  is pneumatically actuated, but other methods of actuation may be utilized.  
         [0064]    It is preferred that linear servo motor  130  and linear servo motor  176  are independently operable and controllable from one another. In this way advancement of the carriers  22  and preform  24  toward the blow molding station  16  can begin before the molded articles  24 ′ and carriers  22  are removed therefrom. In this manner, cycle time of the machine  10  can be further optimized.  
         [0065]    The mechanism utilized at the article unloading station  18  may be substantially similar to the mechanism utilized at the preform loading station  12  except that the mechanism would generally be operated in reverse order and further a cam assembly would be utilized to force open the fingers of the mechanism as they are advanced while holding the articles  24 ′ This opens the fingers and releases the blow molded article  24 ′ onto an outfeed conveyor  190  (seen in FIG. 1A).  
         [0066]    Additional features of the preform unloading station  12  are also illustrated in FIGS. 9 and 10. One illustrated feature is the interplay of the dead plate  132  and the transport conveyor  20 . At the end of the transport conveyor  20  where the belt  58  has completed its return path, the belt  58  returns to its top surface position by returning up through a fork  192  in the end of the dead plate  132 . Additionally, in order to secure the carriers  22  during mounting of the preforms  24  thereon, a pair of rails  194  are located outboard of the belt  58  and over which the carriers  22  are held by the preform end  42  of the transfer rake  44 . The rails  194  are mounted to be raised by a pneumatic or other type of actuator  196  thereby retainingly holding the carriers  22  between the rails  194  and the preform end  42  of the transfer rake  44 .  
         [0067]    The foregoing discussion discloses and describes one preferred embodiment of the 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 following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.