What Is Secure Seal Testing? A Guide to Closure Leak Testing
Secure seal testing checks that a closure keeps a container tight under internal pressure. The container is pierced and pressurized from the inside with air while it is immersed in water: the pressure at which bubbles appear shows how well the cap, its liner and the bottle finish seal together. It is a standard test for carbonated drinks, whose closures must hold the pressure of the CO2 throughout the shelf life of the product.
How does a secure seal tester work?
A needle is inserted through the cap or through the bottle wall, and compressed air is applied inside the container. The closed package is observed under water: as long as the seal holds, no bubbles appear. Two types of test are common:
Leak pressure: the pressure is increased step by step until a continuous stream of bubbles appears at the closure. This pressure is recorded.
Pressure hold: the container is held at a set pressure for a set time, to check that it does not leak.
Piercing must not disturb the closure. The AT2E patent needle holds itself on the product by vacuum, which makes piercing quick and easy in any material. For plastic bottles, aluminum bottles and easy-open cans, the SSA-PLUS-P pierces through the neck, so that the test requires no operation on the cap.
Main applications
Carbonated drinks in PET or glass bottles: checking that the closure holds well above the carbonation pressure.
Cans: testing the seal of a can with a dedicated can test assembly.
Capped preforms: checking the seal of caps on preforms, up to 12 at a time.
Caps alone: with a cap holder and a cutting tool, the cap can be tested separately from the bottle.
Key concepts: leak pressure, cap release and torque
Leak pressure: the first continuous bubbles show at what pressure, and where, the seal fails: at the liner, at the top of the finish or through the threads.
Cap release: at higher pressures, a poorly applied cap can loosen or be pushed off the finish. The test therefore also checks that the cap stays in place.
Link with torque: the result depends on how tightly the cap was applied. Testing bottles capped at a known torque, and recording that torque, makes results comparable from one test to the next.
Accuracy depends on the instrument. The AT2E SSA-D measures 0 to 16.00 bar (0 to 232 psi) with a resolution of 0.01 bar and an accuracy of ±0.5 % F.S. The SSA-ECO has an analog display with a resolution of 0.5 bar and an accuracy of ±2.5 % F.S.
Why the test is done under water
The principle is the same as finding a puncture in a bicycle inner tube: inflate it, put it in water and look for bubbles. Water makes small gas leaks visible, and shows exactly where they come from. The pressure gauge adds the number that matters: the pressure at which the leak started.
Safety comes first. A pressurized plastic or glass bottle can burst during the test, so AT2E secure seal analyzers are built of stainless steel and designed to resist explosions.
Calibration of a secure seal tester
The pressure measurement is checked against a reference:
Compare the pressure reading of the tester with a certified reference indicator at several points of the range.
Check that the pressure holds when the test circuit is closed, so that a leak in the tester itself is not mistaken for a leak in the package.
Record the deviations, and adjust or recalibrate the instrument if they exceed the acceptable limit.
AT2E secure seal analyzers
AT2E secure seal analyzers range from a manual device to an automated multi-position system:
SSA-ECO: secure seal analyzer with analog display, 0 to 16.00 bar (0 to 232 psi), accuracy ±2.5 % F.S., AT2E patent needle.
SSA-D: touch screen model, 0 to 16.00 bar, accuracy ±0.5 % F.S., 2 stages of pressure and holding time.
SSA-PLUS: automated model with one-button start, automatic piercing and leak detection, and up to 12 stages of pressure, pressurizing rate and holding time; neck piercing (SSA-PLUS-P) or top piercing (SSA-PLUS-G).
SSA-PLC-12: secure seal analyzer for caps on preforms, with up to 12 positions.
Conclusion
A closure that leaks lets the CO2 out and air in, and the product can lose its quality before its best-before date. A secure seal test shows at what pressure a closure fails and where. Combined with a known application torque and a calibrated pressure measurement, it gives a clear picture of the sealing performance of a bottle and its cap.
Request a quote
AT2E is an ISO 9001 certified company (AFNOR Certification).
Request a quote: info@at2e.com
Comments