Abstract:
A plug for providing a predetermined flow rate of leakage gas from a sealed package for purposes of calibration of gas measurement instruments, the plug having an axial passage therethrough with a threaded interior wall; and a bolt for threading into the plug axial passage, the bolt having an axial passage therethrough, and an insert for insertion into the bolt axial passage, the insert having a predetermined size opening for permitting only a predictable flow of leakage gas through the plug.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to devices for measuring gas leakage from sealed packages of various types, usually made from plastic film or molded plastic. More particularly, the invention relates to a device for providing a “calibrated leak” to a package, which means that the invention, when applied to a package, allows a predetermined and precise amount of leakage from the package. The usefulness of the invention lies in the fact that it enables leak measurement equipment to receive a predetermined and known precise amount of leakage gas, thereby to permit calibration of the leakage measurement equipment to the known leakage. Once the leakage measurement equipment has been calibrated using the invention, subsequent packages can be measured to provide an accurate measure of the leakage from each subsequent package. 
     The invention relates particularly to the type of packaging described in copending U.S. application Ser. No. 09/845,914, entitled “Multi-port Gas Leakage Measurement Fixture,” filed Apr. 30, 2001, owned by the assignee of the present invention, and packages similarly constructed of plastics for the purpose of holding articles in a confined and relatively sterile, isolated environment. 
     It is a principle object of the present invention to provide a calibration tool for the measurement equipment which provides a measure of leakage from packages and the like. 
     It is another object of the present invention to provide a calibration tool which can be used by a variety of gas leakage equipment to provide a standard basis for calibrating all such equipment, thereby to provide measurement data which is valid for a number of different types of measurement equipment. 
     An advantage of the present invention is that it provides a quick and consistent calibration technique for many different measurement devices which might be in use at the same time, and thereby ensures that all such devices are providing data of the same or very similar accuracy. 
     Other and further objects and advantages of the invention will become apparent from the following specification and claims and with reference to the appended drawings. 
     SUMMARY OF THE INVENTION 
     A device for attachment to a package, including a deformable plug for insertion through a hole in the package, a bolt threadable into the plug, to cause deformity and sealing of the plug against the package wall as the bolt is tightened; the bolt has an axial passage which joins to a side passage through the head of the bolt, and an insert having a predetermined-size leak opening is press-fit into the axial passage. The insert has alternative forms: one form comprises a jewel such as sapphire having a precise hole drilled through it; a second form comprises a capillary tube having a precise internal diameter and a predetermined length. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a typical plastic container of the type which is tested by the invention; 
     FIG. 2 shows a side view in cross section of the container of FIG. 1; 
     FIG. 3 shows an expanded portion of FIG. 2; 
     FIG. 4 shows an alternative form of the invention in cross section; and 
     FIG. 5 shows an end view of the device of FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing figures, In the figures, like reference characters refer to the same or functionally similar parts of the respective components illustrated in each of the figures. FIG. 1 shows an isometric view of a typical plastic tray  10  for holding a sterilized product, with a deformable plug  20  inserted through a hole made in the tray&#39;s side wall. The tray  10  would normally have a sealed cover (not shown) over the top open area, and a product of a particular type (not shown) inside the tray volume. The deformable plug  20  is used merely for calibrating the test equipment which is used to measure the amount of gas leakage which emanates from the package and the package seals. The test equipment and the process for testing is disclosed in co-pending patent application, Ser. No. 09/845,914, filed on Apr. 30, 2001, and entitled “Multi-port Gas Leakage Measurement Fixture.” 
     FIG. 2 shows a side elevation view in cross-section, along a line bisecting the length dimension of the package. FIG. 3 shows an exploded portion of the view of FIG. 2, showing the plug  20  in cross-section view. Plug  20  has an outer deformable body  21  which is sized to be press-fit through an opening  12  made through a side wall of package  10 . When it is inserted as shown in FIG. 3, the outer body forms a leak-tight seal against the package  10  side wall. 
     Plug  20  has an interior threaded bore  22 , which may preferably be formed by an internally-threaded, press-fit metal sleeve insert  24 , which is pressed, through a central passage in housing  21  and is fixedly held in position inside housing  21 . The central passage in housing  24  has an enlarged diameter portion  23  through its top end, and a flange  25  which is sealably positioned against the package  10  side wall. 
     A threaded bolt  30  is inserted into the threaded bore  22 , and bolt  30  may be tightened against the flange  25  to provide a leak-tight fit. Tightening of the bolt  30  causes the plug  20  to deform and bulge outwardly as shown by the dotted outline  21   a , thereby creating a tight seal against the wall of tray  10 . The bolt  30  has an axial central passage  31  which opens through the bottom end of bolt  30 , and has a radial passage  32  which joins the passage  31  and opens through an outer edge of bolt  30 . The bottom portion  31   a  of passage  31  is of enlarged diameter. An insert  40  is sized for press-fit insertion into the passage  31   a . Alternatively,passage  31   a  may have an internal threaded portion which is engageable against a similarly threaded portion of insert  40 , as shown in FIG.  3 . An O-ring  42  is compressed between the bottom end of insert  40  and the shoulder formed at the junction of passage  31   a  with the smaller diameter passage  31 . Insert  40  has an axial bore sized to receive a capillary tube  50 , which is sealed against leakage by the compressed O-ring  42 . 
     In operation, the assembly of deformable housing  21  is pressed into opening  12 , the insert  40  is tightly engaged into the passage  31   a  in the bolt  30 , and the bolt  30  is tightly threaded into housing  21  so as to create only a single leakage path; namely, a leakage path through the capillary tube  50  internal opening. Capillary tube  50  is typically chosen to have a length of about ¼ inch to about ½ inch and a bore of about 5 mils (0.012 cm). It is possible to mathematically predict the volume flow rate of a gas through the capillary tube by using Poiseuille&#39;s Law, which is 
     
       
         V=πpr 4 /8Lη 
       
     
     where v=volume flow rate; 
     P=pressure differential across the tube ends; 
     r=radius of tube 
     L=length of tube 
     π=3.14159 
     η=coefficient of viscosity 
     For a given set of test conditions, all of the foregoing can be measured or determined from reference materials, and therefore the volume flow rate can be predicted. If a plug construct having the defined test parameters is used with the test equipment and test procedures described in the aforementioned co-pending patent application, the test equipment can be calibrated to display the predicted volume flow rate. Thereafter, the equipment and test procedure can be used to accurately measure the volume flow rate of leaks in other packages having similar designs. 
     An alternative embodiment of the invention is illustrated in FIG.  4  and FIG.  5 . In this alternative, the volume flow rate of a pinhole leak can be simulated, as contrasted with the volume flow rate of a capillary tube which has been described previously. Referring to FIG. 4, which is a cross-section view taken along the lines  4 — 4  as shown in FIG. 5, the insert  40  is used to clamp a jewel  60  having a predefined orifice size at the bottom of passage  31   a , so that leakage can occur only through the orifice in the jewel  60 . FIG. 5 is an end view of the invention, with the passages  31  and  32  shown in dotted outline. In this embodiment, the volume flow rate can be predicted for any size orifice, using Poiseuille&#39;s Law, as described above. Because the length of the orifice passage is shorter than that of a capillary tube, the volume flow rate through the orifice will be somewhat higher for the same size orifice as is used for the capillary tube diameter. 
     The present invention may be embodied in other forms without departing from the spirit or essential attributes thereof; and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.