“I want to measure the torque that was applied by a separate torqueing device but it seems to apply the torque that I input on the set up screen and not the peak prior to the cap slipping, in the CW direction. We are unable to have any CCW rotation as it is a sterile operation. What can I do?”
In the past, we have successfully used one of the following methods for “non-destructive” torque testing:
- Run a release test using the “torque/fallback” method for validation.
Set the Release torque limit to the minimum torque requirement.
Set the low error and low warning limits to the minimum torque requirement.
Set the high error and high warning limits to 80 (or the maximum permissible torque).
Then, run the tests. The machine will increase the torque output to the release torque limit value. If the threads break below the limit, the test fails. Then, a low torque value is displayed. Please note this is only a pass/fail test – it does not provide you with any indication of the actual thread break torque, so it is possible that a bottle/cap passes the test, but your customers would struggle opening the closures due to the caps being too tight.
2a. Run a release/reapply test using the “rotation” method and set the rotation for <20 degrees. (The required degrees of rotation must be carefully evaluated using leak testing.)
2b. Run a release/reapply test using the “torque/fallback” method and set the fallback to 0.5lbfin.
Typically, the thread break torque of a closure can be measured before the seal breaks. Once the thread break peak is measured, the machine can automatically reapply the closure to a torque or rotation setpoint without affecting the product integrity/potency.
We tested two bottles, one bottle at 10lbfin of application torque and 15 degrees of non-destructive removal, and the other at 50lbfin application torque. At 10lbfin the cap remained sealed. At 50lbfin, it was possible to rotate the cap 45+ degrees before loss of internal pressurization, but resulted in inferior seal quality.
Seal quality was analyzed using a crude setup of a 5PSI pressure source, a digital pressor sensor and bubble submersion leak testing. To achieve a seal, 50lbfin seems like an awful lot of pressure. It made us wonder if there was some minor imperfection at the opening of the bottle, or if the system would behave differently in the presence of negative pressure inside the bottle.
Visual inspection of a bottle can reveal defects that may result in loss of pressurization or poor cap seals. The following are possible defects causing the leak at the sub-50lbfin application torque (5PSI internal pressurization):
We tried different closures on this same bottle and they all had similar leak characteristics.
At 50lbfin application torque finally we were able to achieve acceptable seal integrity (no leak).
After <5min dwell time, we measured the removal torque and found that the thread break peak can only be determined with rotation-based release torque validation. We tried releasing the cap to different angles, first 30 degrees then 15 degrees, both of which resulted in loss of seal integrity. At 8 degrees, the machine was able to detect the thread break peak and there was no leak.
So, our recommended test settings are:
Test Mode: Release then Re-apply Mode
Head u/d: Enabled
No. of Cycles: 1
Release Torque Limit: 50lbfin
Start Torque: 10%
Max Rrotation: 8deg
Start Torque 10%
Max Rotation: 360° (assuming cap is pre-tightened to ~2lbfin)
If you need any assistance with your non-destructive torque test, please contact our Mesa experts.
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