Leak-tightness test with carrier gas in foil chamber

Abstract

A method for performing a leak-tightness test on a test object (16) in a foil chamber (10) which has at least one flexible wall region (12, 14), having the steps: using a gas or gas constituent contained in the test object as test gas for the leak-tightness test, introducing the test object into the foil chamber, evacuating the foil chamber to a pressure lower than the test gas pressure within the test object and than atmospheric pressure, introducing a carrier gas into the foil chamber into the region outside the test object, and measuring the test gas concentration of the gas mixture that forms in the foil chamber in the region outside the test object.

Claims

1. A method for performing a leak-tightness test on a test object in a foil chamber which has at least one flexible wall region, wherein the test object comprises a test gas contained within the test object, the method comprising the following steps: introducing the test object into the foil chamber; evacuating the foil chamber to a pressure lower than the pressure of the test gas within the test object and lower than atmospheric pressure; continuously introducing a carrier gas into the foil chamber by natural permeation through the foil chamber wall from outside the foil chamber, thereby forming a carrier gas flow from gas components gassing out from an inner surface of the foil chamber wall facing the test object due to the vacuum in the foil chamber without actively supplying any external carrier gas from outside of the foil chamber using a conveyor means, the carrier gas passes through the foil chamber through a region outside the test object; and measuring a test gas concentration of a gas mixture that forms in the foil chamber in the region outside the test object, wherein the concentration of the test gas decreases after introducing the carrier gas.

2. The method of claim 1, wherein the foil chamber is evacuated to a pressure of at most circa 700 mbar before measuring the test gas concentration.

3. The method of claim 1, wherein nitrogen, oxygen or carbon dioxide is used as the test gas.

4. The method of claim 1, wherein aromatic substances from a product packaged in the test object are used as the test gas.

5. The method of claim 1, wherein a gas is used as the test gas, which gas is produced by a product packaged in the test object.

6. The method of claim 1, wherein the test object is filled with a test gas before being placed into the test chamber.

Description

(1) Embodiments of the invention are explained in more detail hereunder with reference to the Figures. In the Figures:

(2) FIG. 1 shows an embodiment with a continuous carrier gas supply by means of a conveyor means,

(3) FIG. 2 shows an embodiment in which components gassed out from the foil are used as a continuous carrier gas flow, and

(4) FIG. 3 shows an embodiment for a one-time supply of a predetermined quantity of carrier gas.

(5) In each embodiment the foil chamber 10 is formed by two foil layers 12, 14. The foils 12, 14 may be flexible foils sealingly laid one upon the other in their outer edge regions. The test object 16 is contained in the foil chamber 10. The foil chamber volume 18 in the region outside the test object 16 is connected in a gas-carrying manner to a vacuum pump 20 for the evacuation of the foil chamber. The gas quantity evacuated by the vacuum pump 20 is supplied to a gas sensor 22 for determining the concentration of test gas in the evacuated gas mixture. The gas sensor 22 may e.g. be a mass spectrometer.

(6) In the first embodiment illustrated in FIG. 1, the foil chamber volume 18 is additionally connected in a gas-carrying manner to a conveyor pump 24 and a carrier gas source 26. The conveyor pump 24 and the carrier gas sources 26 form a carrier gas conveying means 25 for supplying a continuous flow of carrier gas to the foil chamber. The conveyor pump 24 conveys the carrier gas contained in the carrier gas source 26 into the foil chamber 10. As an alternative, a throttle may be used instead of a conveyor pump 24.

(7) The embodiment shown in FIG. 2 differs from the first embodiment in that no carrier gas conveying means is provided. After the evacuation of the foil chamber 10, the gas components which gas out from the inner surfaces of the foil chamber walls 12, 14 due to natural permeation, are used as the carrier gas. The permeation of these gas components occurs in a constant manner.

(8) The third embodiment illustrated in FIG. 3 differs from the first embodiment in that the foil chamber volume 18 is not connected to a carrier gas conveying means, but is connected to a carrier gas source 28 instead which has a constant carrier gas volume (e.g. atmospheric pressure). After the evacuation of the foil chamber 10 by means of the vacuum pump 20, the valve 30 in the gas-carrying connection between the carrier gas source 28 and the foil chamber 10 is opened, whereby the carrier gas volume abruptly flows into the foil chamber 10.

(9) For the three embodiments, the method is performed as follows:

(10) In the first embodiment the foil chamber volume 18 is reduced by evacuating the foil chamber 10 using the vacuum pump 20. Then, a reduced carrier gas flow is continuously supplied to the foil chamber 10 using the carrier gas conveying means 25, while the gas flow drawn from the foil chamber 10 by means of the vacuum pump 20 is analyzed by the sensor 22. The sensor 22 determines the concentration of test gas in the measured gas flow. In case of a leak, the measured gas flow contains a mixture of the carrier gas and the test gas. The concentration c of test gas in the carrier gas flow is:

(11) $c=\frac{Q_{\mathrm{Leak}}}{Q_{\mathrm{Fl}}}+\left(c_0-c_0\frac{Q_{\mathrm{Leak}}}{Q_{\mathrm{Fl}}}\right)$

(12) Here, the first term stands for the concentration of test gas through the leak and the second term stands for the substitution of the initially existing concentration of test gas with test gas from the leak. One may also write:

(13) $c=\frac{Q_{\mathrm{Leak}}}{Q_{\mathrm{Fl}}}(1-c_{0)}+c_0$
where: c total concentration of test gas c.sub.0 initial concentration of test gas in the carrier gas flow Q.sub.Leck test gas leakage rate from the leak Q.sub.FI carrier gas flow

(14) In the second embodiment, the foil chamber volume 18 is reduced by evacuation of the foil chamber 10 using the vacuum pump 20. In each embodiment the test object 16 has been filled with a test gas before. Using the vacuum pump 20 an approximately continuous gas flow is supplied to the sensor 22. Here, the gas escaping inward by permeation from the foils 12, 14 is used as the carrier gas. The proportion of the test gas in this gas flow is determined using the sensor 22.

(15) In the third embodiment, the valve 30 is opened after the evacuation of the foil chamber 10. The carrier gas volume contained in the carrier gas source 28 then flows into the foil chamber 10. After a predetermined accumulation time has lapsed, in which test gas can escape into the foil chamber volume 18 through a possible leak in the test object 16, the sensor 22 determines the concentration of test gas. The carrier gas volume from the carrier gas source 28 can be supplied to the foil chamber volume 18 before, during or after the lapse of the accumulation time.