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 What is Seal Force?
One of the only ways to quantitatively and nondestructively test the sealing integrity of a filled, sealed parenteral vial is by measuring Residual Seal Force. RSF is the force that the rubber element is exerting on the underside of the crimped aluminum seal. It is measured by applying a known force to the top of the aluminum seal. When the force being exerted by the elastomeric element (normally a stopper) is overcome, the aluminum seal begins to move downward.
By looking at Residual Seal Force as a relationship of force and distance traveled, we have developed the Automated Residual Seal Force Tester. Force increases to a point where Residual Seal Force has been overcome and distance begins to be traveled. In an actual measurement, the curve is more difficult to determine visually. The force curve on a typical vial looks like the chart above. Changes in the force curve are calculated with the indicators shown. The intersection of the force curve and the second indicator is the residual seal force and in this case is approximately 11 pounds.
The Automated Residual Seal Force Tester takes multiple measurements of the same vial and, if those readings are within a predetermined range for similarity, it will average them and provide the result on the screen of the PLC. In addition to sealing forces, Residual Seal Force is influence by the specific rubber formulation and stopper configuration as well as the specific vial and aluminum seal being used. It is also influence by the stack of tolerances of these components. Therefore, data must be accumulated on each different vial, stopper and seal combination.
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