Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
  • G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
  • G01M3/3281—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators removably mounted in a test cell

Definitions

• the invention relates to a film chamber for leak detection of a gas-filled test specimen, such as a food packaging.
• Such film chambers have a chamber volume bounded by a film chamber wall into which the test object is introduced for leak detection.
• the foil chamber is provided with a first vacuum port to which a vacuum pump for evacuating the chamber volume is connected.
• At least one region of the film chamber wall is designed as a flexible film in order to be able to conform to the outer shape of the test object during evacuation.
• Such a film chamber is used for example in the leak detection device INFICON ® Contura ® S400.
• the pressure increase method is used to measure a leakage rate of a sample such as a packaging bag.
• the film chamber is evacuated via the first vacuum connection, so that gas contained in the test object flows through a possible leak into the chamber volume.
• the pressure within the chamber volume in the area outside the test specimen increases over time.
• This pressure increase is measured and serves as an indication of a possible leak.
• the accuracy or the detection limit of the pressure rise method depends on the net chamber volume, that is to say on the chamber volume in the region outside the test object (chamber volume minus the test sample volume). The smaller this chamber volume, the greater the pressure increase over time at a given leak rate.
• the film chamber of the INFICON ® Contura ® S400 leak detection device clings to the DUT during evacuation, so that the net chamber volume is particularly low.
• Another function of the film is to apply atmospheric pressure to the device under test from outside the film chamber so that the chamber volume (that is, the space between the films and the device under test) can be evacuated without bursting the device under test.
• the chamber volume that is, the space between the films and the device under test
• Increasing the difference between the pressure within the specimen and the pressure within the film chamber in the area outside the specimen increases the gas leakage rate at given leakages, which improves the leak detection.
• the smallest detectable leak rate of a test object is at a film chamber, such as that of the Contura ® S400, typically limited by the effect of a pressure rise within the film chamber, which is measured in thick test specimen and even with empty film chamber. This increase in pressure is caused by gases that desorb from the film of the film chamber or diffuse through the film. These are gases that are in the film are dissolved and dissolved out of the film under vacuum or permeate through the film.
• the choice of useful film materials for a film chamber is limited by this effect.
• a sufficient thickness of the film must be selected in order to create a sufficient diffusion barrier. Due to its thickness, the film should sufficiently prevent gases from diffusing through the film, thus leading to an increase in pressure within the evacuated film chamber.
• the film material used must have a low solubility for gas components of the air in order to limit the outgassing. Therefore, the film of a film chamber can not be designed as flexible as possible in order to enclose the specimen gently and as closely as possible. The quality of the flexibility of the film decreases with increasing thickness.
• Highly elastic materials, such as silicone films which are particularly good and closely conform to a test specimen, have a high permeability and solubility of gases and significantly reduce the detection limit for a leak. In conventional film chambers, such films are therefore not used.
• the invention has for its object to provide an improved film chamber with improved detection limit, especially in the pressure rise method.
• the film chamber according to the invention is defined by the features of claim 1.
• a film of the film chamber wall has at least two layers arranged adjacent to one another, which delimit between them an evacuable film gap.
• evacuating the film gap are dissolved by desorption from the film or dissolved by diffusion through the film passing gas fractions in the Foil gap sucked and do not get into the chamber volume. These gas fractions thus do not affect the pressure increase in the chamber volume.
• the two superimposed film layers are sealed to the edge and provided with a vacuum port for evacuating the film gap.
• the thin film gap formed between the film layers is permanently evacuated during operation of the film chamber for leakage detection of a test object.
• a vacuum pump is connected to the gas connection (vacuum connection) connected to the film gap.
• a gas-permeable material for example a fleece, is arranged between the two film layers, separating the two layers from one another.
• the gas-permeable material allows for improved evacuation of the film gap even in closely spaced layers of film.
• all films of the film chamber walls in each case two layers, between each of which an evacuated film gap is formed.
• the two film layers are held by a frame and connected to this gas-tight.
• the frame (s) may comprise or form the first and / or the second vacuum port.
• a corresponding method for leakage detection on a specimen contained in a foil chamber of the type described above is also claimed.
• the chamber volume is evacuated in the area outside the test specimen via the first vacuum connection.
• the film gap is preferably evacuated via the second vacuum port.
• the leakage detection is done by means of the pressure increase method, wherein the pressure within the film chamber in the area outside the test object is measured over time. An increase in pressure then serves as an indication of a leak.
• the chamber volume is brought to a vacuum pressure and then the film chamber is not further evacuated upon reaching this vacuum pressure. After reaching the predetermined vacuum pressure, the pressure increase over time is measured. During the measurement of the pressure rise, it is preferable to permanently and continuously evacuate the film gap of each film formed from two layers.
• Fig. 1 shows a section through the film chamber in the empty state
• Fig. 2 shows the section of FIG. 1 with the sample contained in the film chamber.
• the film chamber 10 is formed from two flexible films 12, 14, which are clamped gas-tight in the edge region in each case in a frame 16, 18.
• the two films 12, 14 are each circular and each frame 16, 18 formed as a circular ring. Other forms are conceivable.
• Each of the two films 12, 14 consists of two layers 20, 22, between each of which a layer of a gas-permeable material 24 is arranged in the form of a non-woven.
• the top layer 20, the gas permeable material 24 and the bottom layer 22 of each film 12, 14 are arranged parallel to each other and closely adjacent to each other.
• an evacuatable film gap 26 is formed, in which the gas-permeable nonwoven material 24 is arranged.
• Both layers 20, 22 of each film 12, 14 are firmly clamped in the same frame 16 and 18 respectively.
• a first vacuum port 28 for connecting a chamber volume 32 between the adjacent sheets 12, 14 evacuated first vacuum pump 30 is formed.
• Each frame 16, 18 also has a second vacuum port 34 for connecting a second vacuum pump 36, which evacuates the film gap 26 of the respective film 12, 14.
• a test specimen 38 in the form of a gas-filled food packaging is introduced into the chamber volume 32.
• the foil chamber 10 is closed in a gastight manner.
• a sealing ring 40 prevents gas from penetrating into the evacuated film chamber 10.
• the film chamber 10 is evacuated via the first vacuum connection 28 in the area outside the test piece to a predetermined vacuum pressure.
• the two sheets 12, 14 nestle flexibly against the outer shape of the test piece and thus reduce the chamber volume 32.
• a valve 44 which contains the gas line path 42 connecting the first vacuum pump 30 and the first vacuum connection 28 is closed.
• Chamber volume 32 is hermetically separated from atmosphere 46 surrounding the film chamber.
• the pressure within the chamber volume 32 is measured over time and recorded. An increase in this pressure may serve as an indication of a leak in the device under test 38 if a suitably selected pressure rise limit is exceeded.
• This limit can be set lower than in the conventional film chambers, that during pressure measurement, the pressure in both film spaces 26 below a suitably chosen Vacuum pressure limit is maintained. This is done by permanently evacuating the two film interspaces 26 via the two second vacuum ports 34 by means of the second vacuum pump 36.
• the vacuum pressure in both film interstices 26, at least during the pressure measurement, is less than the pressure within the chamber volume 32, so that desorbing or diffusing gas fractions do not enter the chamber volume 32, but into the film interspaces 26.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Examining Or Testing Airtightness (AREA)

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• 2017
  • 2017-01-23 DE DE102017201004.5A patent/DE102017201004A1/de not_active Withdrawn
• 2018
  • 2018-01-17 JP JP2019539832A patent/JP6944527B2/ja active Active
  • 2018-01-17 US US16/476,820 patent/US11143571B2/en active Active
  • 2018-01-17 CN CN201880005707.8A patent/CN110312920B/zh active Active
  • 2018-01-17 AU AU2018209168A patent/AU2018209168B2/en active Active
  • 2018-01-17 WO PCT/EP2018/051116 patent/WO2018134258A1/de not_active Ceased
  • 2018-01-17 EP EP18700679.6A patent/EP3571486B1/de active Active

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