Seal Integrity Testing

This invention relates to apparatus and methods for testing seals and more particularly testing seals of food packages or containers.

According to one aspect of the present invention a container or package is received between means for compressing the package so that its internal pressure is increased to a predetermined level while the seal area is substantially free to permit flow of its internal atmosphere externally of the container or package, and means for determining or detecting external flow or the rate of decompression.

According to more particular aspects of the present invention the detecting means may comprise, singly or in combination, means for compressing selected boundary walls to increase the internal pressure of the package or container, means for monitoring the rate at which the compressing means is displaced during the course of compression, means for evaluating and displaying the rate of compression in order to classify the condition of the seal or means for sonically detecting the flow of gas across the seal of the package or container.

FIG. 1 shows a typical package being compressed between an upper stationary platen and a lower movable platen associated with a microphone for detecting flow of fluid across the package seal,

FIG. 2 also shows the package between compressing members associated with a microphone positioned to detect flow of internal package fluid across the sealed covering web,

FIG. 3 illustrates a system for evaluating the condition of a package seal by monitoring the rate of movement of one of the compressing platens, and

FIG. 4 shows typical graphs comparing changes in pressure and displacement for a selected time interval.

The seal integrity testing arrangement shown in FIG. 1, generally identified by the numeral 10, is shown associated with a container 12 formed with a deep bowl portion 14. The bottom wall of the bowl may be provided with one or more annular ridges similar to ridge 16 and the upper portion is formed with stepped flanges 18 and 20 with the upper flange 20 being turned to form a lip 22. Secured to the upper flange is a flexible covering web 24 which may be sealed to the flange 20 by heat and pressure and/or an adhesive.

The seal integrity testing device shown in FIG. 1 comprises a lower platen 26 formed with a cavity 28 conforming to the shape of the bowl 14. The container 12 is closed after being filled with a food product by the covering flexible web 24 which overlies flanges 20. An upper die or platen 30 formed with a web contacting convex surface 32 is carried by platen 34 fixed against movement and accordingly holding the upper die 30 stationary.

In accordance of one aspect of the present invention the condition of the seal formed in the area of the flange 20 is determined by providing means for detecting flow of the internal atmosphere of the package externally. One such means may comprise a microphone 36 (also used in the embodiment shown in FIG. 2) located adjacent the flange 20 so that movement of fluid across the seal may be sonically detected. It is to be understood that the microphone is part of an electronic system including an amplifier producing frequencies within the audible range.

With a package 12 inserted into the cavity 28 the lower platen 26 is moved toward the upper platen 34 a distance determined by calibrating the movement of platen 26 to the internal pressure generated by squeezing or displacing the covering web sufficient to impart shearing force to the circumferential seal of the web 24 to the flange 20. One exemplary limit of the squeezing action is represented by elastic deformation (shown in dotted line) of the flange 18 wherein the side walls of the container move upwardly relative to the flange 20 to define a deformation of the flange 18 such that it is inclined, indicated as 18a (FIG. 1), relative to its equilibrium position.

If as a result of package compression the microphone 36 fails to detect high velocity fluid streams, the package is classified as acceptable. It should be appreciated that several microphones, such as microphone 36, can be positioned adjacent the outer periphery of the flange 20 so that irrespective of where the circumferential seal may be impaired the fluid flow from the package will be detected.

The arrangement shown in FIG. 2 is substantially identical to FIG. 1 and accordingly similar parts are identified by the same numeral. The arrangement of FIG. 2 is provided with means 38 overlying the portion of the covering web 24 adjacent the flange 20 for applying pressure to the area of the seal for throttling and accordingly more likely rendering audible escape of the internal package atmosphere across the seal. The throttling means 38 comprises a ring 40 having rigidly mounted therein a circular flexible pad 42, which may be made of rubber or deformable substantially incompressible material. As in the case of the testing unit shown in FIG. 1, testing a container by providing a pad 42 would require calibrating the degree of displacement of the lower platen 26 so that undue bending of the flange 20 does not occur.

Further in accordance with the present invention testing of seal integrity can be achieved by measuring the rate at which tha package or container is elastically deformed or the rate at which pressure in a double acting linear actuator 44 (FIGS. 1-3) varies with respect to a selected time increment. A system adaptable to detect the rate of displacement or the rate at which the pressure in the actuator changes under compression is illustrated in Figure with the piston rod of the actuator 44 being illustrated as being connected to the lower platen 26 in FIGS. 1 and 2 and being connected to the upper platen 30 in the FIG. 3 embodiment. The upper platen 30 is directly connected to a double acting linear actuator 44 which is powered from a source of compressed air which sequentially passes through a filter 46, a pressure regulator 48, an oiler 50 and a valve 52 which may be a manual value operated by a hand lever 54 or a solenoid value to selectively direct pressure air to the head end or rod end of the actuator 44. If it is desired to evaluate the container by observing or recording the rate of change in pressure within a selected time, either a transducer or increment a pressure gage 56 or a transducer may be connectd to the line 58 supplying the head end of the actuator 44 with pressure air.

The rod 60 of the actuator 44 mounts the upper platen 30 (FIG. 3) and a laterally extending rod 62 fixed to a collar 64 which is in turn secured to the rod 60. The laterally extending rod 62 makes contact with an input plunger 66 of a linear displacement transducer 68 having its output through line 70 connected to a data acquisition system 72 which in turn is connected by line 74 to a computer 76. Also, a line 71 is connected between the transducer 56 and the data acquisition system 72.

If it is chosen to operate the seal integrity testing system by measuring the rate of linear displacement, measurement is commenced after the platen 30 makes intimate forceable contact with the covering web 24 initially raising the internal pressure of the container 12. At this point the plunger 66 is actuated by the rod 62 and further movement and the rate thereof of rod 60 is transmitted by the transducer 68 to the data acquisition system 72. The rate of movement data input to 72 is read by the computer 76 which is provided with a program for analyzing the displacement data. A suitable display, such as a CRT, may be incorporated to visually display the computer output. In addition, a suitable diverting system (not shown), such as a gate or a reject conveyor can be coupled to respond in those instances where the computer has determined a package or container has an unacceptable seal.

If it is desired to monitor pressure change a pressure transducer may replace the gauge 56, and the transducer may be connected to detect pressure in the line 58 connecting the head end of the actuator 44 with the source of pressure air. The pressure transducer may be connected to the data acquisition system 72 through line 71 then to the computer 76 through line 74.

FIG. 4 is a composite graph comparing displacement rate and pressure changes over an increment of time delta T although it should be understood that the graphs shown in this figure are merely representative of experimental activity as opposed to use in a commercial installation. The graph plotting pressure against time shows a solid line trace and a dash line trace associated with the legend good container and bad container, respectively. A representative pressure difference for a good container is represented by the vertical line 80 extending between pressures P.sub.1 and P.sub.2 in legend, good delta P whereas a bad container represented by the vertical line 82 and associated with the legend bad delta P extends between pressures P.sub.3 and P.sub.4 which are readings between the time increments T.sub.1 and T.sub.2.

If it is desired to use a linear displacement transducer the representative curves plotting displacement versus time is also shown in FIG. 4. The trace of a chain dotted line indicates a bad container and is legended "CONTAINER WITH LARGE HOLE OR LOW FILL". The trace indicated by the dash line is legended "CONTAINER WITH SMALL HOLE" and the solid line trace is legended "GOOD CONTAINER". Displacement of the rod 60 where the solid line curve (good container) intersects T.sub.1 and T.sub.2 is the distance between S.sub.1 and S.sub.2 yielding a change in displacement indicated as GOOD delta S representative of a good container; whereas the dash line curve, intersecting T.sub.1 and T.sub.2 indicating a displacement between S.sub.3 and S.sub.4 classifies a container as a bad container delta S unacceptable due to the displacement change between the indicated time limits. A container tracing a curve by the chain dotted line would be a container with a large hold or low fill yielding results of displacement versus time clearly indicating a bad container.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.