Method for leak testing and leak testing apparatus

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 vapour 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.

1 . A method for producing a closed and filled container comprising the steps of:
 filling a container with a material comprising at least one liquid component;   sealingly closing said container; and   leak testing said container by:
 applying a pressure difference across at least a part of the wall of the container which part is to be tested by evacuating the surrounding of said container by means of a pumping arrangement; 
 exploiting loading of said pumping arrangement by evaporation of liquid as an indicia for a leak in said container. 
   
   
   
       2 . The method of  claim 1 , wherein said evacuating lowers the pressure in said surrounding toward a pressure valve which is lower than a vapor pressure of the at least one liquid component by a factor of at least two decades (10 2 ). 
   
   
       3 . The method of  claim 2 , wherein said container is filled with more than one liquid component, and said vapor pressure is the higher vapor pressure of the vapor pressures of said at least two components. 
   
   
       4 . The method of  claim 1 , wherein said testing is performed at room temperature. 
   
   
       5 . The method of  claim 1 , wherein said exploiting is performed after the surrounding has been evacuated to a pressure value at least according to vapor pressure of said at least one liquid component. 
   
   
       6 . The method of  claim 1 , wherein the exploiting includes monitoring the pressure in the surrounding at first and second points in time and utilizing a difference in the results of the monitoring as said indicia for a leak in said container. 
   
   
       7 . The method of  claim 6 , wherein said monitoring the pressure at said first point in time results in a first pressure measuring signal which is stored at least up to said second point in time. 
   
   
       8 . The method of  claim 6 , including 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 when utilizing said difference in the results of said monitoring as said indicia for a leak in said container. 
   
   
       9 . The method of  claim 6 , including 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  claim 6 , including storing a first measuring signal which results from said monitoring the pressure at said first point in time by means of an analog-to-digital converter, which is enabled for conversion at said first point in time. 
   
   
       11 . The method of  claim 10 , including reconverting the digital output signal of said analog-to-digital converter into an analog signal. 
   
   
       12 . The method of  claim 1 , including simultaneously leak testing a batch of filled and closed containers as one container. 
   
   
       13 . The method of  claim 1 , further comprising performing an impedance measurement at or at least adjacent to said part of said wall in said surrounding wherein said impedance measurement is 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 , including providing a test cavity with a test chamber snugly fitting the outer shape of said 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 , further comprising providing a test cavity for said container, said test cavity defining a test chamber significantly larger than the volume of said container. 
   
   
       16 . The method of  claim 1 , including providing a test cavity for said container and cleaning at least said test cavity after a container therein has been detected as leaking. 
   
   
       17 . The method of  claim 1 , including in-line testing a series of said containers in a set of test cavities and further comprising 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 container by mechanically biasing at least a part of its wall inwardly. 
   
   
       19 . The method of  claim 1 , wherein said liquid component is water, and including evacuating said surrounding to less than 20 mbar. 
   
   
       20 . The method according to  claim 1 , wherein said pressure in said surrounding is lowered towards a pressure value which is lower than said vapor pressure by a factor of at least three decades (10 3 ).