Abstract:
Platen-mounted, post-mold cooling apparatus and method includes structure and/or steps for handling molded parts in an injection molding machine having a fixed platen, a moving platen, a core half, and a cavity half. A take off device coupled to the fixed platen is configured to remove molded parts from either the core half or the cavity half. A cooling device coupled to the moving platen is configured to cool the molded parts carried by the take off device. Preferably, the take off device extracts the just molded parts from the mold&#39;s core half and then moves linearly outboard of the mold halves. The subsequent movement of the moving platen to close the mold in the next molding cycle causes the cooling device&#39;s pins to engage the molded parts in the take off device part carriers. When the moving platen opens again, the molded parts are extracted from the part carriers by external gripping devices. When the moving platen is fully open, the cooling device is rotated to eject the cooled parts from the machine.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a method and apparatus for removing molded plastic articles from a take out plate after the molding operation is finished. In particular, the present invention relates to method and apparatus for an injection molding machine equipped with a post mold device mounted on a moving platen that cooperates with a multi-position robot take out plate to selectively unload some of the molded part carriers on the multi-position take out plate using grippers that grasp an external surface of the articles. The method and apparatus are particularly well suited for molded thermoplastic polyester polymer materials, such as polyethylene terephthalate (“PET”) preforms.  
       BACKGROUND OF THE INVENTION  
       [0002]     A variety of post mold preform transfer methods are currently employed on injection molding machines to optimize the cycle time of the molding machine. Some parts (for example plastic preforms) are typically injection-molded using PET resin, and can have a wall thickness varying from about 2.00 mm to greater than 4.00 mm, and require extended cooling periods to solidify into substantially defect-free parts. Heavy walled parts (such as those made from a material that has a high resistance to thermal heat transfer, like plastic resin) can exhibit “reheating” phenomena that can produce defective parts after they have been ejected from the mold.  
         [0003]     Several techniques are employed to perform a post mold cooling function, wherein partially cooled preforms are ejected from the injection mold after an initially cooled surface skin has formed to allow the part to be ejected without deformation. The partially cooled preforms are then handed off to a downstream device that continues to hold the preform while removing the remaining heat so that the preform can subsequently be handled without damage. Typically, the preform surface temperature needs to be lowered to about 70° C. to ensure safe handling.  
         [0004]     The early ejection of partially cooled preforms releases the injection molding equipment earlier in the molding cycle, thereby significantly improving the production efficiency of the equipment. The apparatus for removing the hot molded part from the take-off plate must handle the hot preform without damaging it.  
         [0005]     U.S. Pat. No. Re. 33,237 discloses a robotically-controlled multi-position take out plate for removing partially cooled injection molded parts from the core side of an injection mold. The parts are ejected from the mold directly into cooled carriers, as disclosed in U.S. Pat. No. 4,729,732, and transported by the robot to an outboard position where some of the parts are ejected onto a conveyor. The plate has multiple sets of carriers, each set being sufficient in number to hold one part from each of the cores of the multi-cavity mold. There are multiple sets of carriers on the plate so that multiple sets of molded parts can be held and cooled, the set that is ejected being the set that has been cooling the longest in the tubes of the plate. The disclosed method of ejecting the parts relies on the termination of a vacuum that is holding the parts in the carriers, thereby allowing gravity to cause the parts to fall out when the take out plate has been rotated 90 degrees to a discharge position. Without a positive ejection force, parts can stick in the tubes and cause jamming of the machine.  
         [0006]     U.S. Pat. No. 5,447,426 teaches unlocking performs by using ejector bars.  
         [0007]     U.S. Pat. No. 6,171,541 discloses inserting a cooling pin into the interior of a partially cooled part to discharge a cooling fluid therein to assist cooling. Also disclosed is a procedure to apply a vacuum through the same cooling pin to cause the part to remain attached to the pin when it is moved away from the carrier holding the part, thereby removing the part from the carrier. The pins, mounted to a frame, are then rotated 90 degrees to a discharge position and the vacuum terminated to allow the parts to fall off the pins. There is no disclosure of grippers for grasping an external surface of the parts to hold and transport a part.  
         [0008]     U.S. Pat. No. 4,836,767 discloses a rotatable table mounted on the moving platen on which is mounted two core sets for the mold. While one core set is in the closed mold position for injection molding parts, the other is positioned outboard for ejecting the parts into cooled carriers that are mounted on an indexable, four-sided carousel that is mounted to the stationary platen of the machine. Four sets of molded parts can be carried on the carousel allowing an extended cooling time to be performed. The parts remain on the cores for one additional cycle time sequence that provides a small extension of cooling time of the interior of the parts before they are transferred to the carousel.  
         [0009]     U.S. Pat. No. 3,804,568 discloses a robot mounted to the moving platen of an injection molding machine, wherein the robot drives a take out plate into and out of the open mold area to remove ejected parts. A second transfer plate then unloads the take out plate while it is in the outboard position. The motion of the moving platen is used, via cams and linkages, to actuate the take out plate vertical motion and to synchronize it mechanically so that there is no risk of collision with the mold during its operation.  
         [0010]     U.S. Pat. No. 5,354,194 discloses a molded part removal unit mounted to the side of the fixed platen.  
         [0011]     An earlier Husky preform molding system used a robot with a single position take out plate with carriers to unload PET preforms. The robot was mounted on the stationary platen and moved the take out plate vertically. In the outboard position, above the mold, a vacuum tube carrier of a transfer plate was aligned with the carriers and removed the molded parts therefrom by application of vacuum to their interiors. The transfer plate moved to a second outboard position at the non-operator side of the machine and rotated to allow the parts to drop from the tubes when the vacuum was terminated.  
         [0012]     Copending Husky U.S. published application 2004/0185136 published Sep. 23, 2004 describes a molded part handling apparatus for an injection molding machine having a fixed platen and a moving platen. A take off device is coupled to the fixed platen and configured to remove molded parts from between the fixed platen and the moving platen. A cooling device is coupled to the moving platen and configured to cool the molded parts carried by the take off device.  
       SUMMARY OF THE INVENTION  
       [0013]     According to a first aspect of the present invention, structure and/or steps are provided for a molded part handling apparatus for an injection molding machine having a fixed platen, a moving platen, a core half, and a cavity half. A take off device is coupled to the fixed platen and is configured to remove molded parts from one of the core half and the cavity half. A cooling device is coupled to the moving platen and is configured to cool the molded parts carried by the take off device and remove the parts from the take-off device by grasping an external surface of the molded part.  
         [0014]     According to another aspect of the present invention, structure and/or steps are provided for a molded part transfer apparatus for an injection molding machine having a core half and a cavity half. A take off device is configured to remove molded parts from one of the core half and the cavity half. A cooling device is configured to cool the molded parts carried by the take off device. Movement control structure is configured to cause: (i) simultaneous relative movement of the core half toward the cavity half, and the cooling device toward the take off device; and (ii) simultaneous relative movement of the core half away from the cavity half, and the cooling device away from the take off device and removal of some of the parts from the take-off device by grippers grasping external surfaces of some of the parts in the take off device.  
         [0015]     The invention also provides apparatus for transferring a molded part from a mold take-out plate to a cooling plate. The apparatus comprises a gripping device for gripping an external surface of the part and a device for preventing the gripping device from gripping the part.  
         [0016]     The invention further provides a gripping device for gripping a molded preform. The gripping device has a plurality of flexible fingers. The flexible fingers have an internal surface conforming at least in part to a portion of an external surface of the preform. The fingers are flexed into an open position for receiving the preform and released to collapse into gripping engagement with the preform at the surfaces when the preform is received within the fingers.  
         [0017]     The invention further provides a gripping device for gripping molded performs that includes a pair of solid tubes. Each tube has a cutout portion at each preform gripping position. An inflatable bladder extends along the interior of each tube. Each bladder is expandable outside the tube at each gripping position when inflated to grasp an outer surface of each preform in each gripping position.  
         [0018]     Thus, the present invention advantageously provides post-mold cooling method and apparatus for efficiently cooling and transferring molded plastic pieces. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings in which:  
         [0020]      FIG. 1  is a plan view of an embodiment of the present invention showing a multi-position take out plate at an outboard position with a multiple cooling device with part grippers.  
         [0021]      FIGS. 2   a ,  2   b , and  2   c  comprise plan views of the  FIG. 1  embodiment showing the multi-position take out plate at the first of the three outboard positions with the multiple cooling device shown in three positions: prior to engagement  2   a ; engaged  2   b ; disengaged with selected parts removed  2   c.    
         [0022]      FIGS. 3   a ,  3   b , and  3   c  comprise plan views of the  FIG. 1  embodiment showing the multi-position take out plate at the second of the three outboard positions with the multiple cooling device shown in three positions: prior to engagement  3   a ; engaged  3   b ; disengaged with selected parts removed  3   c.    
         [0023]      FIGS. 4   a ,  4   b , and  4   c  comprise plan views of the  FIG. 1  embodiment showing the multi-position take out plate at the third of the three outboard positions with the multiple transfer device shown in three positions: prior to engagement  4   a ; engaged  4   b ; disengaged with selected parts removed  4   c.    
         [0024]      FIG. 5A  is a plan view of a partially assembled multiple transfer device.  
         [0025]      FIG. 5B  is a sectional view of the device of  FIG. 5A  along the sectional line B-B.  
         [0026]      FIG. 6A  is a side sectional view of a preferred embodiment of a preform gripper mechanism gripping a part.  
         [0027]      FIG. 6B  is a side sectional view of the preferred embodiment of  FIG. 6A  with the gripper mechanism in a releasing or open position.  
         [0028]      FIG. 7  is an isometric view of the partially assembled device of  FIG. 5A  showing the mechanism for shifting the gripping device shown in  FIGS. 6A and 6B  between the open and closed positions.  
         [0029]      FIG. 8  is an isometric view of the gripping device of  FIGS. 6A and 6B  when holding a preform and when empty of a preform.  
         [0030]      FIGS. 9A and 9B  are sectional views of an alternative embodiment of a preform gripper mechanism in the closed and open positions.  
         [0031]      FIG. 10  is a side elevation view in partial section of a third embodiment of a preform gripper mechanism.  
         [0032]      FIG. 11  is a plan view of the third embodiment of gripper mechanism.  
         [0033]      FIG. 12  is side elevation view in partial section of a modification of the third embodiment of gripper mechanism.  
         [0034]      FIG. 13  is a plan view of the embodiment shown in  FIG. 12 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     The present invention will now be described with respect to several embodiments in which a plastic injection molding machine has a cooling device fixed to the movable platen, and a take off device fixed to the fixed platen. In a preferred embodiment, the cooling device has a plurality of cooling tubes and a lesser number of external grippers, and the take off device has a plurality of preform carriers. After the movable platen is moved to open the mold, the take off device moves linearly in between the mold halves to extract the freshly molded preforms from the mold cores onto the preform carriers. The take off device is then moved linearly to a position outboard of the mold halves. Then, when the movable platen moves toward the fixed platen to close the mold and mold a new set of preforms, the cooling device moves simultaneously to engage the take off device carriers with the cooling pins and transfer grippers. When the moving platen again moves to open the mold, a group of preforms from the carriers are extracted by a gripper means onto the cooling device. By the time the moving platen has reached its fully open position, the cooling device has rotated about a horizontal axis to drop the molded and cooled parts onto a conveyor.  
         [0036]     Preferably, the cooling device includes cooling pins that are inserted into each preform on the take out device each time the cooling device approaches the take out device. The cooling air is injected to the interior tip of the preform and flows down the inside surface of the preform to the outside.  
         [0037]     With reference to  FIG. 1 , a top plan view of an injection molding machine  10  is shown comprising, an injection unit  11 , a clamp unit  12 , a robot unit  13 , and a transfer device  14 . Also included is an injection mold comprising two halves: (i) the cavity half  35 , containing mold cavities (not shown), attached to the stationary platen  16  of the machine  10 ; and (ii) the core half  17  which is attached to the moving platen  41  of the machine  10 .  
         [0038]     The robot unit  13  is mounted on the stationary platen  16  and includes a horizontal “Z” beam  20  that projects to the non-operator side of the machine and upon which rides a carriage  21 , moved along the beam by (typically) a servo-electric driven belt drive (not shown). Multi-position plate  107  is attached to the carriage  21 . Multiple sets of carriers  108  are mounted on plate  107  and may be cooled for transporting multiple molded shots of parts ejected from the mold from an inboard (loading) position (not shown).  
         [0039]     The transfer device  14  includes a cooling plate  100  upon which are mounted multiple cooling pins  112 . A hollow structure  45  attaches the plate  100  to the hollow cylinder  40 , and allows services to be carried from the machine through the structure  45  to the plate  100 . By virtue of this lightweight construction and the fact that the transfer device carries only one molded shot of parts at any one time, the plate  100  can be rotated very quickly through a 90-degree arc by any suitable means. For example, the rotation of the plate  100  can be effected by an electric drive (not shown) mounted to the hollow structure  45 .  
         [0040]     In operation, one shot of molded parts is transferred into the carriers  108  when the mold is open and the multi-position take off plate  107  is positioned such that empty carriers are aligned with parts on the mold cavities. In the example shown in  FIG. 1 , a 32-cavity mold is transferring 32 parts into 32 carriers on a 3 position take off plate  107 . The multi-position take off plate  107  is then moved to its outboard position by the robot  13 , as shown in  FIG. 1 . The mold is then closed and clamped for the next molding cycle. Meanwhile, as the mold closes, the transfer device  14  moves the plate  100  and its grippers  111  so as to grasp one third or 32 of the parts  109  held in the carriers  108 . At the same time, a cooling pin  112  enters each of the 96 parts  109  held by the carriers  108 .  
         [0041]     When the molding cycle ends and the mold opens, the grippers extract one third or, in this case, 32 of the parts  109  from the carriers  108  on the plate  107 . The plate  100  is then rotated 90 degrees and the parts held by the grippers  111  are dropped onto a conveyor beneath (not shown). The remaining parts continue to be held in their carriers  108  by vacuum.  
         [0042]     The multi-position take off plate  107  preferably has multiple sets of carriers  108  mounted to it which hold the molded parts by vacuum. Preferably, there are 3 sets of carriers (numbering 32 in each set in this example) so that three molding shots of parts (96 in total) from the 32-cavity mold can be carried at any one time on the multi-position take off plate  107 .  
         [0043]     The transfer device  14  is mounted on the hollow cylinder  40  on the side of the movable platen  41 . The transfer device  14  can rotate about a (preferably only a single axis) horizontal axis through 90 degrees. The plate  107  is made of lightweight aluminum, or similar material, and carries cooling pins sufficient in number to exceed the number of carriers  108  on the multi-position carrier plate  107  by a number equivalent to two rows of carriers  108 .  
         [0044]      FIG. 1  shows a conditioning plate  100  on which an additional two rows of cooling pins  112  have been mounted. Rows of gripping devices  111  are provided with every third row of cooling pins  112 . This example of tube layout is suitable for operation with a three position multi-position take out plate  107 .  
         [0045]      FIGS. 2   a , 2   b , 2   c ;  3   a , 3   b , 3   c ; and  4   a , 4   b , 4   c ; in combination, show a complete sequence of operations of the multi-position take out plate to cool and remove the parts  109  in the carriers  108 .  FIG. 2   a  shows the multi-position take out plate  107  in the first of its three outboard positions in which a molded part  109  is aligned with grippers  111  on the plate  100 . Every third position has a gripper  111  to grip and remove parts  109  from the take out plate  107 . Each cooling tube  112  on the plate  100  is, preferably, continually discharging cooling fluid even when the tubes  112  are not inside the parts as shown in  FIGS. 2   b ,  3   b  and  4   b . Each of the molded parts  109  is aligned with a corresponding cooling tube  112 .  FIG. 2   b  shows the plate  100  engaged with the parts  109  allowing cooling to take place.  FIG. 2   c  shows the plate  100  disengaged from the take out plate  107  with grippers  111 , to be more fully described hereinafter, removing selected parts  109  from carriers  108 . The parts being removed comprise the molding set that has been in the carriers the longest. The grippers  111  subsequently release these parts. The grippers  111  grasp an external surface of the part  109  and the tubes  112  continue to cool the parts  109  while held in the grippers  111 .  
         [0046]      FIG. 3   a  shows the second outboard position of the multi-position take out plate  107  in which the set of molded parts that has been on carriers  108  the longest is aligned with the same grippers  111 .  FIGS. 3   b  and  3   c  show the remaining steps in the portion of the complete sequence in which all the parts are cooled and transferred.  
         [0047]      FIG. 4   a  shows the third outboard position of the multi-position take out plate  107  in which the next, third molding shot of molded parts are again aligned with the same grippers  111 .  FIGS. 4   b  and  4   c  show the remaining steps in which the parts that have been in the carriers for the previous two segments of the sequence receive a further cooling prior to being removed from their tubes  108  as shown in  FIG. 4   c . Thus, in the complete sequence, the parts  109  are cooled three times before being removed from their carriers  108  by grippers  111 .  
         [0048]     Obviously, several multi-position take out plate configurations can be provided having greater or lesser numbers of carriers corresponding to the number of parts produced by a variety of multiples of molding shots, and correspondingly the multiple cooling and gripping device can be configured to match such variations so as to optimize the cooling and removal processes provided to the parts.  
         [0049]     A first preferred embodiment of the gripping device will now be described with reference to  FIGS. 5A, 5B ,  6 A,  6 B,  7  and  8 . As shown in  FIG. 5A , the plate  100  includes a plurality of columns and rows for receiving and cooling molded parts. In this configuration, every third column includes a gripping device  96  (only one shown). Every column would include a cooling tube  98  (only two shown) but only those columns with gripping devices  96  would actually grasp and hold parts. As indicated previously, the cooling tubes  98  are carrying cooling fluid at all times, however, they only effectively cool the molded parts when the mold is closed and the transfer device  14  with plate  100  positions the cooling tubes  98  inside the molded parts  109  held in the carriers  108  or when the gripping device  96  is gripping a molded part  109 . When the mold opens, the grippers  96  grasp the parts  109  in those columns aligned with the grippers  96  as more fully described hereinbefore with reference to  FIGS. 2   a  to  4   c . As shown in  FIG. 5A , the cooling and picking plate  100  consists of 14 columns and 8 rows. This enables the plate  100  to cool 96 parts  109  on the multi-position plate  107  while the four rows of grippers  96  align with and grip  32  of the molded parts for subsequent removal from the carriers  108  on the multi-position plate  107 . The parts grasped by the grippers  96  continue to be cooled by cooling tubes  98  associated with the grippers  96  as the cooling air flows continuously through the tubes  98  independently of the position of the plate  100 .  
         [0050]     As shown in  FIGS. 6A and 6B , a detent member  50  is associated with each gripper  96  and is operable to open and close the grippers  96  in response to movement of the bar  52 . Bar  52  may be operated by a pneumatic cylinder  54  or other suitable mechanism.  
         [0051]     In  FIG. 6A , the grippers  96  are shown in the closed position. Movement of the bar  52  causes the detent member  50  to slide in a sliding bearing  54  in gripper  96 . When the detent member  50  moves upwards as shown in  FIG. 6A , the shoulder  58  on the detent member  50  fully engages the inner surface  60  on the gripper  96  to permit the spring  62  and the natural resiliency of the gripper fingers  64  to close the fingers  64  and grasp the part  109 . Retracting the detent member  50  moves the shoulder  58  into contact with a raised portion of the inner surface  60  and forces the resilient fingers  64  into an open or part releasing position as shown in  FIG. 6B .  
         [0052]     The spring  62  ensures that the fingers  64  of the gripper cannot overextend into an adjacent region and interfere with the transfer or cooling of an adjacent part.  
         [0053]     The sliding bearings  54  in the plate  100  permit the detent  50  to slide back and forth. Each detent  50  is firmly attached to the bar  52 . As shown in  FIG. 7 , pistons  56  connected to air cylinders  58  drive each bar  52 .  FIG. 7  shows the bar  52  in the raised position to cause the detents  50  to close the grippers  96  around a part  109 .  
         [0054]     In the event that the grippers  96  should fail to open when the plate  100  moves into position with the multi-position plate  107 , the tapered surface  74  would engage the lip of the part  109  and thereby force the fingers  64  to open. When the plate fully engages with the plate  107 , the fingers  64  will return to the closed position gripping the part  109  as shown in  FIG. 6A . Of course, if the detent member  50  cannot open the gripper  96 , the part  109  would have to be removed manually from the gripper  96  before the gripper could be used to grip another part. However, the failure would not interfere with the operation of the mold and cannot cause any catastrophic failure of the molding operation.  
         [0055]     As shown in  FIG. 8 , the preferred construction of the gripper  96  has 6 flexible fingers  64  that are formed by creating long slits  66  along the length of the gripper  96 . Forming openings  68  at the base of each finger  64  further increases the flexibility of the fingers  64 .  
         [0056]     A suitable material for the gripper  96  has been found to be a synthetic resinous plastic material sold by Du Pont de Nemours under the trade mark Delrin. This material has the strength to withstand many flexing operations and retain its flexibility so that the gripper operates satisfactorily for long periods.  
         [0057]     It should be noted that with this design of the gripper  96 , if a failure does occur, the gripper will retain the part and not release it inappropriately because the gripper  96  fails safe in the closed rather than the open position.  
         [0058]      FIGS. 9A and 9B  illustrate a further embodiment of a gripper. In this embodiment the gripper  96  is unchanged from the gripper described with reference to FIGS.  6  to  8 . However, the actual operation of the gripper  96  is modified. In this embodiment, a bladder  70  is inflated to open the gripper  96 . When deflated, the bladder  70  permits the gripper  96  to be in the part grasping position to grasp a part  109  along the support ledge  114 . A cup  72  surrounds the base of the gripper  96 . The cup  72  prevents the gripper  96  from extending outside its part-capturing zone and into an adjacent part zone if the bladder  70  should over inflate as a consequence of a failure in the air supply lines to the bladders  70 .  
         [0059]     The bladder  70  is held in place against the cooling tube  98  by sleeves  102  and  104 . An air channel  106  (shown in dotted lines) along the cooling tube  98  receives air from the supporting plate as shown by the arrows  110 . When air is supplied to the channels  106 , the bladder  70  inflates and when the air pressure is removed, the natural resiliency of the fingers  64  of the gripper  96  deflates the bladder  70 . If the fingers  64  should become less flexible, the spring  62  can assist in the deflation of the bladder  70 .  
         [0060]     The cup  72  also ensures that the fingers open symmetrically even when the bladder  70  may inflate unevenly because the cup  72  restrains expansion of the bladder so that it cannot extend beyond the inner surface of the cup  72 .  
         [0061]     The sloped surface  74  provided at the top of the gripper  96  enables the gripper  94  to grasp a part  109  from a carrier  108  in the event that the bladder  70  bursts and fails to open the gripper  96  when the plate  100  approaches the take off plate  107 .  
         [0062]      FIGS. 10 and 11  show an alternative embodiment for grasping the external surface of parts and removing them from a take-out device. In this embodiment, an aluminum tube  116  extends along both sides of a row of parts  109 . The tubes  116  are supported in locating brackets  122  that are bolted to the plate  100 . The portions of the tubes  116  within the confines of the blocks  122  are flattened to mate with the flat surfaces in the slots  124  and prevent rotation of the tubes  116 . An inflatable tube  118  extends along the interior of the tube  116 . At pick off or grasping positions along the tube  116 , portions  120  are removed. To grasp a part  109 , air is injected into the inflatable tube  118  and causes the tube  118  to inflate at the cut out portions  120  to grasp the associated part  109 . The part  109  can then be carried out of the take out device and transported to a receiving station where it is released by deflating the tube  118 .  
         [0063]     This embodiment has the advantage that it can be used with parts  109  of different dimensions. To accommodate a wider part the blocks  122  simply have to be positioned farther apart. Thus, new parts are not required to pick new and different parts as the blocks  122  and tubes  116  will be standard for all parts.  
         [0064]     In the embodiment shown in  FIGS. 10 and 11 , the tube  118  engages the ledge  114  of the part  109 . To ensure that the tube  118  engages the part reliably the tube  118  is positioned slightly upward of the ledge  114  so that it has a tendency to move the part  109  toward the plate  100  rather than away from it thus avoiding the possibility of ejecting the part prematurely. To prevent the perform  109  from misaligning and possibly contacting the cooling tube  98 , soft flexible pads  126  are provided. These pads  126  provide a soft support for the performs  109  and stabilize the so that they remain erect when gripped by the inflatable tube  118 .  
         [0065]     The embodiment shown in  FIGS. 12 and 13  is essentially the same as the one shown in  FIGS. 10 and 11 . In this embodiment the tube  118  grasps the threads  150  on the part  109  rather than the ledge  114 .  
         [0066]     While the present invention has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.