Method for leak testing and leak testing apparatus

• US 20010006003A1
• Filed: 02/20/2001
• Published: 07/05/2001
• Est. Priority Date: 05/27/1997
• Status: Active Grant

• Current Assignee: Wilco AG
• Original Assignee: Martin Lehmann
• Inventors: Lehmann, Martin
• Granted Patent: US 6,305,215 B2
• Time in Patent Office: Days
• US Class Current: 73/49.3
• CPC Class Codes: B65B 3/04 Methods of, or means for, filling the material into the containers or receptacles
• CPC Class Codes: G01M 3/04 by detecting the presence of fluid at the leakage point
• CPC Class Codes: G01M 3/22 for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
• CPC Class Codes: G01M 3/226 for containers, e.g. radiators
• CPC Class Codes: G01M 3/3263 using a differential pressure detector G01M3/3245, G01M3/3272 take precedence
• CPC Class Codes: G01M 3/3281 removably mounted in a test cell
• CPC Class Codes: G01M 3/329 for verifying the internal pressure of closed containers
• CPC Class Codes: G08B 21/20 responsive to moisture
• CPC Class Codes: Y10T 29/49771 Quantitative measuring or gauging
• CPC Class Codes: Y10T 29/53022 with means to test work or product

Abstract

For leak testing closed containers (9) which are filled with a filling product containing at least one liquid component the container is introduced in a test cavity (1) which is evacuated at least down to vapor pressure of that liquid component. The pressure in the surrounding of the container (9) and thus within test cavity (1) is monitored. Monitoring is performed by a vacuum pressure sensor (7), whereas lowering pressure surrounding the container (9) is performed by a vacuum pump (5). Leakage is detected by monitoring a pressure change in the surrounding of the container which is due to evaporation of liquid emerging from a leak and being evaporated in the low pressure surrounding.

Claims

1. A method for leak testing at least one closed and filled container, whereby the content of said 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 tested, said pressure difference being directed towards the surrounding of said container and wherein the pressure in said surrounding is monitored as a leak indicative signal, characterised by the fact that said pressure difference is established by lowering said pressure in said surrounding at least to a value according to vapour pressure of said at least one liquid component.

2. The method of

claim 1

, characterised by the fact that said pressure in said surrounding is lowered towards a pressure value which is lower than said vapour pressure by at least two, preferably by at least three decades.

3. The method of

claim 1

, wherein more than one liquid component is present, characterised by the fact that said vapour pressure is the higher vapour pressure of the vapour pressures of said at least two components.

4. The method of

claim 1

, characterised by the fact that said test is performed at room temperature.

5. The method of

claim 1

, characterised by the fact that said pressure monitored as said leak indicative signal is monitored after reaching said vapour pressure.

6. The method of

claim 1

, characterised by the fact that said pressure monitored is sampled at a first point in time, resulting in a first pressure measuring signal and is sampled at a second, subsequent point in time, resulting in a second pressure measuring signal and that a pressure difference formed by said two pressure measuring signals is evaluated as leak indicative signal.

7. The method of

claim 6

, characterised by the step of generating said first and second measuring signals as electrical signals, and storing said first signal at least up to said second point in time.

8. The method of

claim 6

, characterised by the step of providing a pressure measuring sensor in said surrounding and operationally connecting said sensor to both inputs of a difference forming unit at said first point in time, generating a zero offset signal dependent from the output signal of said difference forming unit, storing said zero offset signal and compensating zero-offset at said signal difference of said two measuring signals by said stored zero offset signal.

9. The method of

claim 6

, characterised by the step of providing a pressure measuring sensor in said surrounding and comparing the output signal of said sensor with one or more than one predetermined signal values.

10. The method of claims 6, characterised by the step of storing said first measuring signal by means of an analogue to digital converter, enable for conversion at said first point in time.

11. The method of

claim 10

, characterised by the step of reconverting the digital output signal of said analogue to digital converter into an analogue signal.

12. The method of

claim 1

, further comprising the step of simultaneously testing a batch of said containers as one container.

13. The method of

claim 1

, further comprising the step of performing an impedance measurement at or at least adjacent to said part of said wall in said surrounding, preferably a resistance measurement with DC and enabling or disabling further lowering of said pressure in said surrounding by the result of said impedance measurement.

14. The method of

claim 1

, characterised by the step of providing a test cavity with a test chamber snugly fitting the outer shape of said at least one container, thereby maintaining at least at said part a residual volume to be lowered in pressure and between said part and the wall of said test cavity.

15. The method of

claim 1

, characterised by the step of providing a test cavity for said at least one container, said test cavity defining for a test chamber significantly larger than the volume of said container.

16. The method of

claim 1

, characterised by the step of providing a test cavity for said container and cleaning at least said test cavity after a container therein has been detected as leaking, said cleaning being performed by evacuating said cavity and/or by flushing with a gas, preferably by nitrogen and/or by heating.

17. The method of

claim 1

, characterised by the step of inline testing a series of said containers in a set of test cavities and further comprising the step of disabling testing in a test cavity for at least one testing cycle if the container previously tested therein has turned out to be leaky.

18. The method of

claim 1

, further comprising the step of increasing internal pressure of said at least one container by mechanically biasing at least a part of its wall inwardly.

19. The method of

claim 1

, for at least one container, wherein said one component is water, characterised by the step of evacuating said surrounding to less than 20 mbar, preferably to approx. 10⁻

2 mbar.

20. The method of

claim 1

, further comprising the steps of

initiating lowering said pressure with a predetermined suctioning power;

identifying for a large leak if said pressure monitored does not reach a first predetermined pressure value in a predetermined time;

disabling further lowering of said pressure;

monitoring a change of said pressure monitored during a further predetermined time and identifying a small leak or no leak dependent on the extent of said change.

21. The method of

claim 1

, further comprising the step of lowering said pressure during a predetermined time and at a predetermined suctioning power.

22. The method of

claim 1

, further comprising the step of establishing a maximum threshold value for said pressure monitored to be reached after a predetermined time of lowering and disabling a pumping arrangement from lowering said pressure of said surrounding if said pressure monitored does not reach said maximum threshold value at said predetermined time.

23. The method of

claim 22

, said disabling comprising disconnecting said pumping arrangement from said surrounding.

24. The method of

claim 23

, further comprising the step of switching said surrounding to a further pumping arrangement for performing a subsequent leak testing cycle.

25. The method of

claim 1

, further comprising the steps of providing said surrounding within a test cavity for said at least one container and disabling said test cavity for at least one further testing cycle if a leaky container is detected in said test cavity.

26. The method of

claim 25

, further comprising the step of reconditioning said test cavity during said at least one testing cycle.

27. The method of

claim 26

, further comprising the step of performing said reconditioning by at least one of heating, gas purging and liquid purging.

28. The method of

claim 26

, further comprising the step of checking whether said test cavity is properly reconditioned by performing said leak testing at said test cavity empty from a container to be tested.

29. The method of

claim 1

, further comprising the steps of comparing a signal derived from said pressure monitored with at least one threshold value to identify leakage condition of said container and deriving said at least one threshold value from said pressure monitored at a test cavity defining for said surrounding and void of such container.

30. The method of claims 1, further comprising the step of monitoring said pressure at at least one predetermined moment after starting said lowering, comparing a signal derived from said pressure monitored at said predetermined moment with a threshold value for identifying leak-condition of said container, enabling a further signal derived from said pressure monitored to be averaged with such further signals for containers previously tested if said identifying reveals an unleaky container and deriving said threshold value from the result of said averaging.

31. The method of

claim 30

, wherein said signal derived from said pressure monitored at said predetermined moment is a difference signal to a signal derived from said pressure monitored at a further predetermined moment.

32. The method of

claim 1

, further comprising the step of providing at least one test cavity for said container and calibrating said pressure monitored by performing said leak testing at said test cavity void of container and connected to a reference leak arrangement.

33. The method of

claim 32

, further comprising the step of providing said reference leak arrangement by a needle valve to a reservoir containing a liquid and being controllably pressurisable.

34. The method of

claim 33

, said reservoir containing distilled water.

35. The method of

claim 33

, further comprising the step of controlling said reference leak and pressure to prevent liquid to leak therefrom and to enable vapour of said liquid to transit therethrough.

36. The method of

claim 1

, further comprising the step of providing said surrounding in a test cavity and subsequently performing said leak testing with said test cavity on different of said containers, thereby disabling said test cavity from further testing if a leaky container was identified therein for a predetermined number of subsequent tests.

37. The method of

claim 1

, further comprising the step of heating said surrounding during said testing to a predetermined temperature.

38. The method of

claim 1

, further comprising the step of performing a testing operation for identifying larger leaks of said at least one container, previously to performing said method for leak testing.

39. The method of

claim 1

, further comprising the step of inline testing a series of said containers in a set of test cavities, thereby converting said pressure monitored in each of said test cavities in an electrical signal and generating at least one reference electrical signal by lowering said pressure in said test cavities void of containers.

40. The method of

claim 1

, comprising the steps of providing a set of test cavities each defining for one of said surroundings and monitoring said pressure in said surroundings at at least one predetermined moment after starting lowering said pressure in said respective surroundings,

comparing, respectively, a signal derived from said pressure monitored at said respective predetermined moment with a common threshold value for identifying leak condition of containers in said test cavities,

enabling a further signal derived from said pressure respectively monitored to be averaged with such further signals generated previously if said identifying reveals an unlaky container and deriving said common threshold value from the result of said averaging.

41. The method of

claim 40

, wherein said signal respectively derived from said pressure monitored at said predetermined moment is a difference signal with respect to a signal derived respectively from said pressure monitored at a further predetermined moment.

42. The method of one of claims 17, 25, 36 further comprising the step of reconditioning said test cavity disabled from testing and re-enabling said test cavity for testing after reconditioning.

43. The method of

claim 42

, further comprising the step of performing said reconditioning by at least one of heating, gas flushing, liquid flushing.

44. The method of

claim 42

, further comprising the step of checking whether said test cavity is properly reconditioned by performing said leak testing at said test cavity void of said at least one container.

64. The use of the method according to one of

claims 1

to

44

or of the apparatus according to at least one of

claims 45

to

63

for leak testing blisters, vials, medical application containers, foodstuff or beverage containers, tanks.

65. The use of the method according to one of

claims 1

to

44

or of the apparatus according to one of

claims 45

to

63

for permanently testing tank plants for leakage.

45. A leak testing apparatus for leak testing at least one closed and filled container, whereby the content of the container comprises at least one liquid component and comprising:

at least one sealingly closable test cavity

at least one evacuation pump operationally connected to said test cavity

at least one pressure sensor operationally connected to said test cavity

characterised by the facts that

said evacuation pump is selected so as to pump said test cavity down to at least vapour pressure of said component approx. at room temperature

said pressure sensor is a vacuum pressure sensor.

46. The apparatus of

claim 45

, characterised by the fact that said evacuation pump is at least one of a drag vacuum pump, a piston valve vacuum pump, a diffusion pump, a turbo vacuum pump.

47. The apparatus according to

claim 45

, wherein said sensor comprises a Pirani sensor.

48. The apparatus of

claim 45

, characterised by comprising a timing unit operationally connecting the output of said sensor to an output of said apparatus generating a leak indicative signal, once pressure within said test cavity has reached at least said vapour pressure value.

49. The apparatus according to

claim 45

, said evacuation pump being selected so as to be able to pump said test cavity down to a pressure at least smaller than said vapour pressure by one, preferably by two decades or even more preferred by three decades.

50. The apparatus of

claim 45

, characterised by comprising a storage unit operationally connected to the output of said sensor and a difference forming unit, one input thereof being operationally connected to the output of said storage unit, the second input thereof being operationally connected to the output of said sensor, a timing unit operationally connecting the output of said sensor at a first point in time to the input of said storage unit and operationally connecting at a second point in time the output of said storage unit to said one input of said difference forming unit and the output of said sensor to said other input of said difference forming unit.

51. The apparatus of

claim 50

, characterised by said timing unit enabling said operational connection of said output of said sensor to said storage unit after said sensor has detected a pressure within said test cavity reaching said vapour pressure.

52. The apparatus of

claim 50

, characterised by said storage unit comprising an analogue to digital converter, said timing unit being operationally connected to the conversion control input of said analogue to digital converter.

53. The apparatus of

claim 45

, characterised by said timing unit operationally connecting at said first point in time the output of said sensor to both inputs of said difference forming unit and further by comprising a further storage unit operationally connected to the output of said difference forming unit and being enabled at said first point in time, the output of said further storage unit being operationally connected with the output of said difference forming unit at said second point in time.

54. The apparatus of

claim 52

, characterised by a digital to analogue converter operationally connected to the output of said analogue to digital converter, the output of said digital to analogue converter being operationally connected to said difference forming unit.

55. The apparatus of

claim 45

, wherein said test cavity has a shape snugly fitting said at least one container and comprising sustaining means at its inner wall to maintain a free space between the wall of said container and the wall of said test cavity once the volume therebetween is lowered.

56. The apparatus of

claim 55

, characterised by at least one pair of impedance measuring electrodes within said cavity, connected to an impedance measuring unit, preferably to a resistance measuring unit, the output thereof switchingly enabling and disabling further evacuation of said test cavity by means of said evacuation pump.

57. The apparatus of

claim 45

, characterised by said test cavity being large enough to receive at least two, preferably a multi-container batch of said containers.

58. The apparatus of

claim 45

, characterised by said test cavity being significantly larger than said container and thus being apt to flexibly receive differently shaped and different volume containers.

59. The apparatus of

claim 45

, characterised by said cavity comprising a removable cover and at least a pair of seals around the opening opened by said cover, the space between said two seals being pumped.

60. The apparatus of

claim 45

for in-line testing a multitude of containers, characterised by a set of said test cavities to which a respective number of containers is fed for testing, further comprising control means to prevent a test cavity being filled with at least one container to be tested once the container previously tested in said one test cavity has been detected as leaking.

61. The apparatus of

claim 45

, further comprising at least one cleaning gas line abutting into said cavity and being connected to a cleaning gas tank, preferably containing nitrogen.

62. The apparatus according to

claim 45

, comprising a multitude of test cavities, arranged on a carrousel for in-line leak testing containers.

63. The apparatus of

claim 45

, comprising

an evaluation unit with at least one pressure signal input, said evaluation unit comprising

at least one comparator unit, one input thereof being operationally connected to said at least one pressure signal input, a second input thereof being operationally connected to a controllable threshold value unit;

an averaging unit controllably operationally connected to said input;

said evaluation unit generating a leak-identifying signal;

said leak-identifying signal controlling said operational connection of said input and said averaging unit;

the output of said averaging unit controlling said controllable threshold unit.