Pressure Difference (External Vacuum) Method

A. Introduction 

Non-destructiveTo detect microleaks in hermetically sealed packages by measuring electrical discharges between the food product and device electrodes.> 20 μm pinhole, > 50 μm micro-channelReal-time, on-line> $20,000

B. Operation 

In the vacuum method, a package is placed inside an enclosed chamber where a vacuum is drawn to create a pressure differential across the package wall. Gas or liquid will flow out of the package if there is a leak or a weak seal, because the pressure inside the package (at about 1 atmosphere) is higher than the pressure in the vacuum chamber. The increase of pressure inside the chamber, the movement of a package's upper wall, or the loss of force applied on the upper wall of a package is monitored using a pressure sensor, a LVDT (Linear Variable Differential Transformer) displacement sensor, or a load sensor, respectively. The vacuum method is suitable for packages having a well-defined headspace. It is suitable for detecting gross leaks (≥ 100 μm) and for testing the seal strength of packages under differential pressure conditions such as those which can occur during air transportation.

  • Package
  • A chamber equipped with a vacuum decay sensor, a LVDT displacement sensor, or a load sensor
  • Vacuum pump
  1. Put the package in to the enclosed chamber.
  2. Vacuum the chamber.
  3. Monitor the decay of vacuum inside a chamber, the movement of a package's upper wall, or the loss of force applied on the upper wall of a package.
  4. Record.

Positive

If the monitors detect any changes, the package leaks.

False Positive

If the monitors detect any changes when the package is good sealed, the change might be caused by the unsealed chamber.

Negative

If the monitors do not detect any changes, the package is good sealed.

False Negative

If the monitors do not detect any changes, the leaking channel may be plugged.

C. Application 

PACKAGE TYPES AND DEFECTS

 PACKAGE TYPE
DEFECTSFlexible PouchSemi-rigid and
Rigid plastic container
Plastic Can (Double-seam Metal End)Paperboard
Abrasion
Corner Dent   
Crushed  
Cut (Fracture)
Delamination 
Double Seam Defects*   
Flexcracks  
Foreign Matter Inclusion  
Gels  
Hotfold   
Label Foldover   
Leaker   
Leaker (Channel) 
Leaker (Corner)   
Leaker (Notch)   
Leaker (Perforation)   
Leaker (Pulltab)   
Leaker (Seal)   
Loose Flap or Ear   
Malformed  
Puncture (Pinhole)
Seal Defects (Blister)   
Seal Defects (Blocked)   
Seal Defects (Burnt)   
Seal Defects (Compressed)   
Seal Defects (Contaminated)  
Seal Defects (Convolution/Embossing)   
Seal Defects (Creep)   
Seal Defects (Crooked)   
Seal Defects (Incomplete)   
Seal Defects (Misaligned/Deformed)  
Seal Defects (Nonbonding/Weak)   
Seal Defects (Plastic Lumps)   
Seal Defects (Seal-width Variation)   
Seal Defects (Stringy)   
Seal Defects (Uneven Impression)   
Seal Defects (Uneven Juncture)   
Seal Defects (Wrinkle)  
Swell (Swollen Package)
Waffling   

D. Source 

  • TM Electronics, Inc. 45 Main Street , Boylston, MA, 01505. TEL (508)-869-6400 (http://www.tmelectronics.com/)Moncon. 7500 Mendelssohn Ave N., Minneapolis, MN 55428 USA. TEL (763)-493-6370 (http://www.mocon.com/index.php)Packaging Technologies and Inspection. 145 Main Street Tuckahoe, New York, 10707. TEL (800)-532-1501 (http://www.ptiusa.com/)ASTM F2338 - 09 Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method
  • ARNDT., G.W. JR. 1998. Chapter 22C Examination of Flexible and Semirigid Food Containers for Integrity. FDA Bacteriological Analytical Manual (8th Ed)
  • Blakistone and C. Harper. 1995. Pressure differential technique for package integrity inspection. In Plastics Package Integrity Testing, Assuring Seal Integrity. FPA, Washington, DC.
  • Tetra Pak Technical Bulletin 1991. Issue 1. Tetra Pak, Sweden.