Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2001-09-04
2002-08-27
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S052000
Reexamination Certificate
active
06439033
ABSTRACT:
FIELD OF INVENTION
The present invention is generically directed on a technique for leak testing closed and filled containers, whereby the filling material comprises at least one liquid component.
BACKGROUND
Leak testing techniques according to which closed containers are introduced in a test cavity which, after having sealingly been closed, is lowered in pressure by a suctioning pump are known. If the container is not leaking, then once a predetermined pressure has been reached in the test cavity and thus in the surrounding of a container to be tested; this pressure will be kept substantially constant. If a leak is provided in an area of the container, wherein air is entrapped, a flow of air out of the container will lead to a rise of the surrounding pressure. If a leak is present in the area of the container where filling good is entrapped, the question whether such leak will lead to a significant rise of the surrounding pressure is largely dependent on the kind of filling good as of its viscosity, whether solid particles are present in the filling good and, obviously, on the largeness of the leak.
Different approaches have become known to accurately detect leaks at such product-filled containers, irrespective whether the leak is present in an air entrapping container area or in a container area covered with filling good. One such approach which is the topic of the co-pending European patent application EP-A-0 791 814 and the U.S. patent application Ser. No. 08/862,993 proposes to provide an impedance measurement, specifically a resistance measurement, just adjacent to the outer wall of the container by means of an electrode arrangement: As soon as liquid emerges from a leak it will contact a respective pair of impedance measuring electrodes and lead to a significant change of impedance measured between such electrodes.
Nevertheless, such an approach necessitates considerable additional expenditure with respect to provision of the impedance measuring arrangement in each test cavity, especially of a multi-cavity in-line inspection machine and does not enable detection of very small leaks far below of one micron and largely independent from container shape and kind of filling good.
OBJECT OF THE INVENTION
It is a primary object of the present invention to provide a leakage test method and apparatus, which may be applied to a very large scale of different containers and of different filling goods, provided at least one component thereof being liquid.
It is a further object of the present invention to provide such method and apparatus which are rather inexpensive with respect to electronic and further equipment, and which thus allow for very economic testing.
It is still further an object of the present invention to provide such method and apparatus which have a short measuring cycle and nevertheless a very high measuring accuracy.
SUMMARY OF THE INVENTION
These objects are realised by the testing method for leak testing at least one closed and filled container, whereby the content of the container comprises at least one liquid component and wherein a pressure difference is applied across at least a part of the wall of the container which part is to be leak tested and wherein the applied pressure difference is directed towards the surrounding of the container and wherein further the pressure in the surrounding of the container is monitored as a leak indicative signal which is characterised by the fact that the pressure difference is established by lowering the pressure in the surrounding of the container at least to a value which accords to the vapour pressure of the at least one liquid component of the filling product of the container to be tested.
The present invention departs from the recognition that if a container is leaking and liquid is drawn by the lower surrounding pressure to its outside this will—at a constant volume of the surrounding—lead to evaporation of the liquid as soon as the surrounding pressure reaches its vapour pressure. This leads to a significant change in surrounding pressure compared with the surrounding pressure which would establish at the same measuring conditions but with an unleaking container.
Monitoring the pressure in a test cavity containing the container, once vapour pressure of the possibly leaking liquid is reached reveals as being a very accurate technique for leak testing. It has been noted that by such a technique leak detection of containers with a very large spectrum of filling products may accurately be performed and that leaks at present moment down to 0.02 &mgr;m are accurately detectable.
Further, it has been noted that the volume of the test cavity is uncritical, so that by the inventive technique it becomes possible to simultaneously test batches of containers, thereby accurately detecting if one container of such a container batch is leaking.
As soon as the pressure surrounding a leaking container is lowered with respect to its interior pressure, some of the liquid is suctioned out of the container and as soon as the surrounding pressure reaches vapour pressure it starts to evaporate. As at a constant volume of the surrounding area of the container evaporation of the liquid leads to increase of pressure and the pump lowering the surrounding pressure must now remove vapour of the liquid too, significant measurements may be done especially after the surrounding pressure of the container becomes lower than the said vapour pressure. Nevertheless, it is preferred to provide pumping abilities which may evacuate the surrounding of the container to be tested to a significantly lower value than said vapour pressure, namely by at least two, preferably even by at least three decades.
As a leak-significant pressure change may be detected as soon as one of possibly several liquid components of the filling good starts to evaporate—in the case the content of the container contains more than one liquid component—it is recommended to select the vapour pressure of that component of the several liquid components which is the higher and to lower the pressure of the surrounding of the container at least to that vapour pressure value.
Although and as well known vapour pressure is a function of temperature and thus it might be advantageous in some cases e.g. to heat the surrounding of the container to a predetermined temperature so as to settle the relevant vapour pressure for a predetermined liquid, the inventive method and apparatus becomes significantly less complex if the test is performed at room temperature, and thus the vapour pressure to be at least reached is considered at room temperature, i.e. around 20° C.
Further, a very accurate leak detection becomes possible if the surrounding pressure of the container is measured at two subsequent points in time, whereby we understand under “point” that interval of time necessary for accurately measuring the prevailing pressure. Although it is absolutely possible to realise leak detection by applying the pumping action of the evacuating pump to the surrounding of the container and then by measuring the resulting surrounding absolute pressure after a predetermined time span, the said measuring of the surrounding pressure at two specific points in time allows to use the first value is measured as a reference value and then to form the difference of the second value measured with respect to the reference value. There is thereby realised a pressure difference measurement instead of an absolute pressure measurement. More specifically, the first pressure signal which is measured at the first point in time is stored as an electric signal, then, after having measured the second pressure value, a difference is formed between the first value (still stored) and the second value.
The PCT patent application No. WO94/05991 with its U.S. counter-part No. U.S. Pat. No. 5,239,859, assigned to the same applicant as the present invention, describes a method and apparatus for very accurately offset-compensated pressure difference measurement. In a preferred mode of operating the method according to the present invention
Antonelli Terry Stout & Kraus LLP
Wiggins David J.
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