Film chamber having double film

Abstract

The invention relates to a film chamber 10 which has a film chamber wall for testing the sealing tightness of a gas-filled test specimen 38, which film chamber wall defines a chamber volume 32 for holding the test specimen 38 and has a first vacuum connection 28 for evacuating the chamber volume 32 by means of a first vacuum pump 30 connected to the first vacuum connection 28, wherein at least a portion of the film chamber wall has a flexible film 12, 14, characterized in that the film 12, 14 has two layers 20, 22 arranged adjacent to each other which surround an evacuable film interspace 26.

Claims

1. A film chamber comprising a film chamber wall provided for a tightness test on a gas-filled test specimen, said film chamber wall defining a chamber volume for accommodating said test specimen and being provided with a first vacuum connection for evacuating said chamber volume by means of a first vacuum pump connected to said first vacuum connection, wherein at least a portion of the film chamber wall comprises a flexible film and wherein said film comprises two layers arranged adjacent to each other and surrounding an evacuable film interspace, wherein a second vacuum connection is provided to which a second vacuum pump is connected for evacuating the film interspace, wherein the film chamber comprises two adjacent films between which the chamber volume is defined and which are respectively made up of two adjacent layers having respective film interspaces arranged between said two layers.

2. The film chamber according to claim 1, wherein in the film interspace a gas-permeable material separating the two layers from each other is arranged.

3. The film chamber according to claim 2, wherein the gas-permeable material is a nonwoven fabric.

4. The film chamber according to claim 1, wherein the outer edge area of each film is provided with a frame holding said film and being sealingly connected with said film, wherein said two frames constitute or comprise the first and/or the second vacuum connection.

5. A method for leakage detection on a test specimen using a film chamber according to claim 1, comprising the steps of: introducing said test specimen into the chamber volume, closing said chamber volume, evacuating said chamber volume down to a predetermined vacuum pressure below atmospheric pressure, measuring over time the pressure inside said film chamber in the area outside said test specimen, detecting an increase of the measured pressure, and evacuating at least one, and preferable each film interspace during the leakage detection, wherein the film interspace is permanently kept below a limit vacuum pressure during the pressure measurement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Hereunder an exemplary embodiment of the invention is explained in detail with reference to the accompanying drawing in which:

(2) FIG. 1 shows a sectional view of the film chamber in an empty condition, and

(3) FIG. 2 shows the sectional view of FIG. 1 with the test specimen accommodated in the film chamber.

DETAILED DESCRIPTION OF THE INVENTION

(4) The film chamber 10 is made up of two flexible films 12, 14 whose edge areas are respectively mounted in a gastight manner in a frame 16, 18. The two films 12, 14 are each circular, and each frame 16, 18 is configured as a circular ring. Other shapes are conceivable.

(5) Each of the two films 12, 14 is made up of two layers 20, 22 between which a layer of a gastight material 24 in the form of a nonwoven fabric is arranged. The upper layer 20, the gastight material 24 and the lower layer 22 of each film 12, 14 are arranged in parallel to each other and close to each other. Between the upper film layer 20 and the lower film layer 22 of each film 12, 14 an evacuable film interspace 26 is defined where the gas-permeable nonwoven material 24 is arranged.

(6) The two layers 20, 22 of each film 12, 14 are fixedly mounted in the same frame 16 and 18, respectively.

(7) Between the two frames 16, 18 a first vacuum connection 28 for connecting a first vacuum pump 30 evacuating the chamber volume 32 defined between the adjacent films 12, 14 is provided.

(8) In addition, each frame 16, 18 comprises a second vacuum connection 34 for connecting a second vacuum pump 36 which evacuates the film interspace 26 of the respective film 12, 14.

(9) In FIG. 2 a test specimen 38 in the form of a gas-filled food package is placed into the chamber volume 32. The film chamber 10 is closed in a gastight manner. Between the two frames 16, 18 a sealing ring 40 prevents gas from entering the evacuated film chamber 10. With the aid of the first vacuum pump 30 the film chamber 10 is evacuated in the area outside the test specimen via the first vacuum connection 28 down to a predetermined vacuum pressure. The two films 12, 14 flexibly cling to the outer shape of the test specimen thus reducing the chamber volume 32. A valve 44 disposed in a gas line 42 connecting the first vacuum pump 30 and the first vacuum connection 28 is closed. The chamber volume 32 is hermetically sealed towards the atmosphere 46 surrounding the film chamber from the outside.

(10) By means of a pressure sensor not illustrated in the Figures, the pressure inside the chamber volume 32 is measured and recorded over time. An increase of this pressure may serve as an indication of a leak in the test specimen 38 when an appropriate limit value for the pressure increase has been exceeded. This limit value may be set smaller than that of the conventional film chambers in that during the pressure measurement the pressure in the two film interspaces 26 is kept below an appropriate limit value of the vacuum pressure. This is realized by permanently evacuating the two film interspaces 26 via the two second vacuum connection 34 with the aid of the second vacuum pump 36. Gas escaping from the film layers 20, 22 and in particular from the two inner film layers 22—either in the form of gas desorbing from the film layers or gas diffusing through the film layers—is sucked into the film interspaces 26 due to the vacuum pressure in the film interspaces 26 and evacuated by means of the second vacuum pump 36. Preferably, at least during the pressure measurement the vacuum pressure in the two film interspaces 26 is lower than the pressure inside the chamber volume 32 such that desorbing or diffusing gas fractions are not fed into the chamber volume 32 but into the film interspaces 26.