Application Torque

To determine whether your threaded closure was applied successfully you can measure its applied torque. There are two main problems that can occur with application torque: Excessive torque and Insufficient torque. Below is a list of some of the problems you may encounter with application torque.

Excessive Torque

• Damage of cap aesthetics.
• Lid-fault: raising of the lid causing a visible gap between the lid and neck.
• Fracturing of closure at the neck
• Scoring of closure body (fluted or smooth wall).
• Damage or breakage of hinge.
• Shearing of lid from body.
• Ineffective seal between bottle and closure.
• Orientation in excess of maximum limits.
• Stressing closure neck (bulging) that may result in future failure during distribution.
• Thread "jumping", or stripping of bottle.

Insufficient Torque

• "O" Torque retention.
• Closures "rattling" and falling off during transit.
• Product leakage.
• Failure of liner (induction) seal to bottle.

The application torque of closures must be controlled in order for the closures to perform properly in the field. Closures must be applied tight enough to maintain a seal and to resist closure back off, but must not be applied so tightly that the end user cannot remove the closure.

A general guide is that the application torque should equal the inch pounds of approximately ½ the closure millimeter size.

Closures - Torque

Proper application torques are critical to provide a seal in shipment, and on the shelf.

Too much torque may:

• Crush the liner, which destroys the compression tension that holds the cap in place, thus causing "back-off".
• On plastic bottles, cause distortion of the threads. Over a period of time, the plastic will flow and the closure will "back off".
• With metal closures, the threads may strip or become enlarged.

Too little torque may cause the closure to loosen and "back off" because of vibration in the shipment.

With the use of servo motors on bottle capping machines, application torque can be measured accurately. Since each package will have its own relationship of application to removal torque, the packager should determine this relationship for each of his packages. By applying caps by hand with a torque meter and immediately measuring the removal torque, a correlation between application and removal torque can be determined. This correlation can then be used as an indicator of the actual application torque generated by the capper. By checking removal torque regularly after capping, one can determine if there is a need for adjustment.