Container leak testing

Details Container leak testing Container leak testing

1994-07-15

1996-04-23

Williams, Hezron E.

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

For fault location

73 40, G01M 340

Patent

active

055107184

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to leak testing of containers, and is particularly, but not exclusively, concerned with the leak testing of blow molded containers.
2. Description of the Related Art
It is an inherent feature of the blow molding process used for producing plastics bottles and the like that small holes are sometimes formed in the container walls due to the occurrence of flaws in the molding medium. It is therefore essential, in applications in which the container is required to be fluid tight, that each container is subjected to leak testing prior to use. Conventionally such leak testing is performed on a conveyor line by initially pressurising each container with air and subsequently detecting by means of a pressure transducer any decay of the pressure within the container which might indicate the occurrence of a leak. While this leak method operates satisfactorily in practice, it requires use of a pressure transducer which is both costly and delicate. Also, since the method requires monitoring of the pressure within the container over a period of a few seconds, the period of each testing cycle cannot be decreased below a certain value.


SUMMARY OF THE INVENTION

It is an object of the invention to provide generally improved apparatus and methods for leak testing such containers.
According to the present invention there is provided apparatus for leak testing a container comprising an electrically conductive probe for communicating with the interior of the container by way of an opening of the container, electrically conductive shield means for location externally of the container, electrical connection means for application of a high voltage between the probe and the shield means, and sensor means for detecting current flowing between the probe and the shield means indicating the presence of a hole or weakness in the intervening container wall, and characterised in that the electrical connection means is arranged to apply the high voltage to the probe, and that moving means is provided for effecting relative displacement of the container and the shield means so as to surround at least a major portion of the container with the shield means.
Such apparatus can be implemented at relatively low cost and is highly reliable in practice. It is capable of detecting not only very small holes in the container wall, but also weaknesses in the container wall provided that a sufficiently high voltage is used. Since the occurrence of current flow in the form of a spark is almost instantaneous in the event of a hole or weakness being detected, the apparatus may be incorporated in a conveyor line and mechanised in such a manner that each testing cycle takes place in a relatively short period of time. The spark corresponds to a breakdown of insulation between the two conductors such as to cause a current discharge between the conductors under the applied electric field.
The probe advantageously has a form which ensures that parts of the probe are located in close proximity to the inside wall of the container at a plurality of locations during testing. For example the probe may include an inflatable electrically conductive balloon, or a plurality of electrically conductive strands capable of spreading out under the influence of a static charge, or even a plurality of mechanically actuable electrically conductive vanes.
The shield means may comprise electrically conductive plates or electrically conductive foam pads or electrically conductive brushes for conforming to the external profile of the container. In a further alternative the shield means may comprise a plurality of parts which are electrically insulated from one another and connected to earth (ground) by respective discriminating means so as to enable the approximate location of the hole or weakness to be detected by the sensor means.
The moving means preferably comprises a plurality of mechanical actuators for moving associated parts of the shield means into close proximity with the outside wall of the

REFERENCES:
patent: 3252572 (1966-05-01), Erren
patent: 4677372 (1987-06-01), Meguro et al.

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