Note: Descriptions are shown in the official language in which they were submitted.
CA 02494499 1994-10-05
- 1 -
METHOD OF LEAK TESTING
Field of the Invention
The present invention relates in general to a method for leak
testing of a container, to a test chamber therefor and to a
test machine for in-line testing of such containers. More
particularly, the present invention is directed to a method
for reducing test cycle time and for improving the measuring
accuracy of a leak testing process as well as of a test
chamber and to a test machine with reduced test cycle time and
improved measuring accuracy.
Background of the Invention
Methods for leak testing of containers are known in which a
pressure difference is applied between the interior and the
exterior of a container to be tested as an initial value for
latter measuring. Afterwards, a pressure value, which is
dependent on the pressure difference installed as the initial
value and on leakage conditions of the container to be tested,
is measured, as a leak indication.
From the article "Lecksuche mittels Differenzdruckmessungen"
by J.T. Furness, VFI 4/78, it is generally known to test a
container on leakage by monitoring its internal or its
external pressure. Thereby, it is described that, the smaller
that a volume is selected, wherein the time course of pressure
is monitored, the more accurate such a measuring will become.
There exists a clear need for shortening the time span
necessitated for a test cycle of a container and of improving
the accuracy of such tests to be able to detect smallest
leakages of such containers.
A method and test chamber for leak testing a container with a
substantially flexible wall portion disclosed in applicants'
CA 02494499 1994-10-05
- 2 -
earlier U.S. Patent No. 5 042 291 offer a solution to the
aforementioned need wherein the container is introduced into a
test cavity, so that the wall portion of the container is
spaced from an inner adjacent wall portion of the test cavity
with a gap being defined between the wall portion of the
cavity and the flexible wall portion of the container. A
pressure difference is installed as an initial value between
the interior of the container and the gap by applying a
pressure at least to the gap which is smaller than a pressure
inside the container. The flexible wall portion of the
container is supported from its exterior side within the test
cavity using a grid or a mesh structured inlay to prevent the
flexible wall portion from bending outwardly into contact with
the wall portion of the test cavity as a result of the
pressure difference. The time course of a pressure prevailing
within the gap is measured as a leak indicative signal. A
drawback of this technique is that provision of a mesh or a
grid necessitates a separate part which is critical with
respect to its form stability, necessitates separate cleaning
from time to time and may stick on the container and may be
removed therewith out of the test cavity.
Summary of the Invention
It is therefor desirable t.o overcome the above-identified
drawbacks. This is resolved by a method of leak testing a
container with a flexible wall portion, wherein the container
is introduced into a test cavity, so that said flexible wall
portion and an adjacent wall portion of said cavity form an
intermediate space, a pressure difference being applied from
the inside of said container into said space and a signal
depending from said pressure difference being determined as a
leak indicative signal and wherein bending outwards of said
flexible wall portion of said container is stabilized by at
least one abutment surface in said space, characterized by
CA 02494499 1994-10-05
- 3 -
the fact, that said abutment surface is formed by at least
one projection of said adjacent wall portion of said cavity.
Accordingly, the said object is resolved by a test chamber
for leak testing a container, the container comprising a
wall, wherein the wall comprises at least one flexible
portion and comprising a closable test cavity with an inner
wall wherein said container can be positioned, at least a
portion of said inner wall being located adjacent and spaced
from said flexible wall portion to form a space between said
flexible wall portion of said container and said inner wall
portion of said cavity, a pressurizing source to establish a
pressure difference between an inside of said container and
said space, and at least one abutment surface located in said
space, characterized by the fact that said abutment surface
is formed by at least one projection, projecting from said
inner wall portion of said cavity, and further comprising a
pressure sensor to sense a pressure dependant on the pressure
differences.
Remedising of the drawbacks mentioned above leads to a test
machine comprising a conveyor for carrying a stream of
containers and having at least two test chambers as described
above, which operates with significantly reduced service-
time-spans.
Thus, inventively the abutment surface is not anymore formed
by a separate part within the test cavity, but is formed by
at least one projection of the wall portion of the cavity as
an integral part of said cavity wall.
In a first embodiment, such abutment surfaces are formed by
projections as a distinct pattern, which is machined into the
wall of the cavity.
CA 02494499 1994-10-05
- 4 -
A preferred embodiment has a multitude of such abutment
projections, which is formed by the surface roughness of the
adjacent wall portion of the cavity. Thereby, it becomes
possible to support the flexible wall portion of the
container along a multitude of support surfaces, whereby,
between the multitude of projections forming the support
surfaces, surface roughness ensures the formation of an
intermediate space between which and the inside of the
container the pressure difference may be applied. Roughening
of the wall of the cavity may be performed by different well-
known methods such as blasting, edging and so on.
Depending on how much outwards bending of the containers
flexible wall portion shall be admitted, the at least one
projection forming the support surface, is spaced from the
flexible wall portion of the container once the container is
introduced into the cavity and before the pressure difference
is applied or, the said projection with the support surface
contacts the flexible wall portion of the container before
the pressure difference is applied.
In a further improved embodiment, the container is
mechanically stressed during testing in that a biasing member
is pushed from the cavity on a further flexible wall portion
of the container. Thereby, the mechanical biasing may be
formed, from a flexible wall portion of the container, which
is different from the flexible wall portion inventively
supported for preventing outwards bending. Alternatively,
mechanical biasing may be performed at the same flexible wall
portion, which is also supported by the inventive projection.
In a most simple way, mechanical biasing is installed by
closing the cavity with the container therein.
CA 02494499 1994-10-05
- 4a -
Especially, when the container has at least two flexible wall
portions which are linked along a distinct link-area, by the
said biasing technique it becomes possible to specifically
stress that link-area as a container portion which is
critical with respect to leakage.
Preferably, more than one of said projections are provided
forming a distinct projection-pattern in said space.
Alternatively, a multitude of said projections is formed by
surface roughness of said wall portion of said cavity.
In another preferred embodiment at least one projection is so
formed, so that said container once introduced contacts said
abutment surface before said source being enabled.
Alternatively, the at least one projection is so formed, that
said container does not contact said abutment surface before
said source is enabled.
In a further preferred embodiment, the test chamber comprises
a biasing member along the wall of said cavity, which biasing
member biasing a further flexible wall portion of said
container inwardly, once said container is introduced into
said cavity and said cavity is closed. More preferably, the
biasing member is distinct from said at least one portion of
said wall.
The biasing member can be formed by at least one portion of
said cavity wall, preferably located at a cover for said
cavity and/or at the bottom of said cavity.
The inventive technique is especially suited for testing
flexible prefilled containers as yoghurt-containers, powder
CA 02494499 1994-10-05
- 4b -
containers or so Called blisters, so for instance for coffee-
powder, tea, medicament-powder and so on.
Provision of a prior art mesh for preventing outwards bending
of flexible wall portions of the container and, additionally,
provision of mechanical biasing of a separate wall
portion of the container to mechanically stress an
area of the container disposed between the first and
the second flexible wall portions is considered
inventive. By such combination, on the one hand, in
spite of mechanical biasing, it is preventing, that a
CA 02494499 1994-10-05
- 5 -
flexible wall portion bends outwards under test conditions,
and, on the other hand, a specific area of the container is
mechanically loaded in a way, which would, without prevention
of outwards bending, expand the container so that its wall
would be pressed against the cavity wall.
Brief Description of the Drawings
The invention will be more specifically understood when the
following detailed description is considered in conjunction
with the accompanying drawings in which:
Fig. 1 is a cross-sectional representation of a prior art
embodiment of a test chamber for leak testing cup-shaped
containers such as yoghurt cups;
Fig. 2 is a cross-sectional view of a first embodiment of a
test chamber according to the present invention;
Fig. 3 is a cross-sectional view of the test chamber of Fig. 2
taken along the line VIII-VIIT, the container of Fig. 2 not
being shown, so that a distinct pattern of longitudinally
extending, intersecting horizontal and vertical channels can
be seen;
Fig. 4 is an enlarged view of a portion of the test chamber
wall in a second inventive embodiment depicting a roughened
surface; and
Fig. 5 is a cross-sectional representation of another
embodiment of an inventive test chamber for leak testing of
cup-shaped containers such as yoghurt cups, which makes use of
prior art supporting mesh according to Fig. 1.
CA 02494499 1994-10-05
- 6 -
In Fig. 1. there is schematically shown a prior art test
chamber. As an example, it is constructed for testing closed
containers 3 of substantial truncated cone form; as for
testing yoghurt cups. With respect to leakage. A container 3
to be tested and with a covering lid 7 is shown in dashed
lines. The inventive test chamber comprises a receptacle 39
which is formed according to the outside form of the con-
tainer 3. The cross-sectional area of the receptacle 39, F39
diminishes in direction of the central axis A substantially
conelike departing from a receptacle opening 41, towards the
bottom 43 of the receptacle 39 and defines a cavity which is
substantially similar in the sense of geometric similarity
with the container 3, so that, when the container 3 to be
tested is introduced, there are defined between its wall and
the inside wall of the receptacle 39 substantially constant
distances.
Adjacent to the opening 41 of the receptacle 39 there is
preferably provided a positioning groove for a collar, which
is usually provided at such containers to which collar the
covering foil-like lid of the container is welded.
The test chamber further comprises a cover 45 which is
movingly driven, as shown by reference P . and is moved to-
wards or from the receptacle 39, so as to either sealingly
close it with the help of the seals 43 or to open it.
At the bottom of the receptacle 39 there is provided an
axially movable and controllably driven piston 47 which is
retracted, when a container 3 to be tested is introduced in
the test chamber and during the testing of the container, and
which, after opening the cover 45, is driven into the test
chamber, so as to eject the tested container 3. The piston 47
comprises an enlarged piston head.
CA 02494499 1994-10-05
-
At the bottom of the receptacle 39, adjacent to the piston
head, a drain sleeve 49 enters into the test chamber, which is
sealingly closed by means of the head of the piston 4? by
means of seals 51, once the piston 4? is retracted. Thus,
after testing a container 3 which Was leaking, so that mate-
rial contained in the container 3 could possibly penetrate
into the test chamber, the test chamber may be rinsed after
the piston 4? has been driven into the test chamber 31 to
eject the leaking container 3. Thus, the test chamber 31 is
rinsed and the rinsing liquid will be drained out of the open
drain sleeve 49. For further improving rinsing of the test
chamber, there may be provided, as at the cover 45, a rinsing
liquid feed line, possibly with a nozzle arrangement, to eject
rinsing liquid into the test chamber (not shown).
The test chamber, according to Fig. 1, comprises, as again
schematically shown, pressure feed and pressure monitoring
means to install a pressure difference from the inside of the
container into the space 4 between the wall of container 3 and
the wall of the test chamber.
Further and as known and therefore not shown in Fig. 1,
monitoring means are provided to monitor the pressure in the
space 4 which results from the initial pressure difference
value installed across the wall of the container 3 as a
function of its tightness or leakness.
For leak testing of containers, as for yoghurt-, cream-, tea-
coffee-, medicament- etc. cups, blisters, etc. continuously in
line with filling and closing operations for such containers,
by which leak testing e. g. every container of the production
shall be tested, a multitude of test chambers. one of which
having been described with the help of Fig. 1, are normally
combined to form a test machine. In such a machine the
CA 02494499 1994-10-05
_
multitude of test chambers according to Fig. 1 are preferably
arranged on a turnably driven carousel table (not shown), so
that, in line with filling and closing of the containers, all
of them are pressure leak tested before these containers are
stored ready for package.
For testing of such containers with a flexible wall or at
least wall portion by means of applying under-pressure in
space 4, portions of the container walls may be pressed on the
inner wall of the test chamber. To prevent this it is known to
provide a mesh inlay along and slightly distant from the wall
of the test chamber, so e.g. in the form of a cone-shaped mesh
inlay which is open at its bottom end and in which the
container 3 to be tested is introduced. Such a mesh inlay
mechanically stabilizes the wall of the container 3 with
respect to outwards bending. Thus, with the help of such a
mesh inlay it is prevented that the flexible container wall is
bent, so as to tightly reside on the inner wall of the test
chamber, when under-pressure is applied in the space 4.
Possibly pressure equalizing connections are provided between
the lower part oft the receptacle 39 and the upper part
adjacent to the cover 41 to ensure pressure equalization all,
around a container 3 to be tested, if a cover of the container
tends to sealingly separate the lower part volume of the test
chamber from the said upper part volume.
Such connections between lower and upper parts of the test
chamber to provide for equalization of the pressure may be
provided by appropriate grooves at the cover region of the
test chamber, linking the lower part of the space 4 with an
upper part 4a thereof.
CA 02494499 1994-10-05
- 9 -
By the inventive technique, illustrated in Fig. 2, it becomes
possible to avoid the prior art mesh or grid, which is applied
to test containers according to Fig. 1 (not shown).
Instead of employing a mesh inlay for mechanically stabili-
zing the flexible wall portion of the container with respect
to outward bending as a result of a pressure difference bet-
ween the inside of the container and the remaining volume of
the test cavity as was described, according to the inventive
test chamber and method as depicted in Figs. 2 to 4 gene-
rally, at least portions of the wall of the test chamber
itself are structured to, on the one hand, support the
flexible side wall of the container with respect to the
outward bending as a result of a reduced pressure within the
cavity with respect to pressure within the container, and on
the other hand, maintain a spacing between the flexible side
wall of the container and at least first, relatively recessed
portions of the adjacent wall of the test cavity with 'a gap .
being defined between at least the first, relatively recessed
portions of the inner wall of the test cavity and the flexible
side wall such that a pressure difference can be installed
between the interior of the container and at least the gap by
applying a pressure at least to the gap, which is smaller than
the pressure inside the container. This structure of at least
portions of the wall of the test chamber itself may be
realized by mechanically machining of channels, bores and so
on into the test chamber wall by milling, drilling, eroding,
etc. A second and prefered possibility is to increase
roughness of the surface of at least preselected areas of the
test cavity wall. This may be done by, for example, sand
blasting or blasting with glass bullets. The two techniques of
mechanically machining and of surface structure roughening may
be used individually or may be combined selectively for
CA 02494499 1994-10-05
-
predetermined test chamber surface areas as in the embodiment
of Figs. 2 to 4.
More particularly, in the embodiment of Figs. 2 to 4, there is
disclosed a test chamber of the invention which could be used
as the test chamber of Fig. 1 or 5. The test chamber of Figs.
2 to 4 comprises a receptacle 130, wherein at least portions
of the wall 131 of the receptacle are distinctly structured by
machining a plurality of channels 132 therein which extend
vertically and horizontally. The channels intersect with one
another as seen in Fig. 3. A pressurizing feed line 17 extends
from the bottom of one of the channels 132 as shown in Fig. 2.
Because the channels intersect with one another, the pressure
installed in the test cavity about the container therein is
communicated about the container by way of the interconnected
channels 132, even though, a flexible side wall of the
container may expand outwardly into contact and be supported
by relatively raised portions 133 of the wall located between
the channels.
The surface of thewrelatively raised portions 133 or, gene-
rally, at least a portion of the cavity or test chamber wall
can be roughened as shown in Fig. 4, as by sand blasting or
blasting the inner wall of the test cavity with glass bullets
to provide relatively raised portions 134 and recessed
portions 135 as shown in Fig. 4. With such a roughened surface
per se or additionally to a distinct pattern of raised and
recessed portions, as shown in Figs. 2 and 3, the flexible
side wall of the container can be supported on the high
points, that is the relatively raised portions 134, while
permitting a pressure difference installed to communicate
along relatively recessed roughness-portions 135. The
roughening procedure of the test cavity inside wall can be
accomplished over the entire wall prior to machining of the
CA 02494499 1994-10-05
- 11 -
channels 132 if such channels are provided. In such a case,
relatively recessed portions 136 of the wall 131 formed by the
channels 132, e.g. the bottom of the channel 132, need not be
roughened as the flexible side wall of the container will be
supported outwardly therefrom on raised portions 133 to
mechanically stabilize the flexible side wall with respect to
further outward bending as a result of an installed pressure
difference.
A test chamber and method for leak testing a container
according to a still further embodiment of the invention
involves reducing the inside volume of the container during
testing by mechanically biasing at least a flexible portion of
the the container from the outside to the inside, thereby
increasing the pressure within the container and applying
additional stress to selected areas of the container. In a
disclosed form of this embodiment, as illustrated in Fig. 5,
the test chamber is like that shown in Fig. 1, except that the
cover 45~ of the test chamber is formed with a projection 140
in the form of a rounded protrusion which biases the flexible
r
lid of the container 3 inwardly, when the cover 45 sealingly
closes the test cavity. Thereby, the inside of the container 3
is additionally pressurized and a critical part of the overall
container, namely the lid at its bonded seam, is extremely
loaded, so that such area may be tested under a selectively
increased stress during the installation of a pressure
difference as described above with respect to the other
embodiments.
Although not shown -in Fig. 5 a supporting mesh or grid is
provided as was described, so as to prevent the wall of
container 3 to be pressed against the cavity wall, due to the
pressure difference installed and, additionally, mechanical
biasing by cover 45~. Thereby, an area of the container
CA 02494499 1994-10-05
- 12 -
between a first flexible wall portion being mechanically
biased, and a second flexible wall portion being prevented to
bend outwards is especially stressed as for instance and
especially a link-area of said two container wall portions,
which is an especially critical part with respect to leaking.
In prefered embodiments, the supporting surfaces are realized,
as was described in connection with the Figs. 2 to 4, i.e. by
a determined pattern of projecting and recessed portions in
the cavity wall and/or by roughness of at least portions of
the cavity wall.
While I have shown and described only several embodiments in
accordance with the present invention, it is understood that
the same is not limited thereto, but is susceptible to nume-
rous changes and modifications as known to those skillled in
the art.
Therefore, I do not wish to be limited to details shown and
described herein, but intend to cover all such changes and
modifications as are encompassed by the scope of the appended
claims.
