Closure Torque

Application Torque - The rotational force required to properly attach a closure to a container. Application torque affects the seal integrity and the tightness between the bottle and closure. Proper application torque will provide integrity of the seal under expected conditions or temperatures, humidity and shock.

Back-Off – Closure “Back-Off” is the actual physical movement of the closure backwards off of the bottle finish. Back Off is a visible manifestation of this movement.

Low Removal Torque – This is a weakening of the marriage of a closure and bottle, such that the amount of force required to remove the closure from the bottle, is lower than the manufacturer/industry recommended values.

Stripping Torque - The application torque which is sufficient to cause the closure and/or bottle finish to distort and override the matching closure/bottle threads, resulting in loose caps, no seal, or package component deformation.

Removal Torque -The rotational force required to remove a closure from a container. It is usually expressed in Pounds inches (lb-in) or Kilogram centimeter (kg cm). The removal torque range should be appropriate for its intended use and the consideration of any requirements for child resistant or tamper evident closure needs.

Torque Values - Torque is defined in inch-pounds or Newton-meters and is measured by various types of torque meters. Specific methods for performing torque tests are defined in Technical Bulletin PBI No. 7. The optimum relationship between applied and removal torques and good sealing characteristics under various physical and environmental conditions must be established for each individual package. Application torque requirements also vary according to the closure size being used.

• UN rated packaging will likely require higher than industry standard application torques. In these cases, the consumer should always follow the recommended closing instructions provided with the UN performance Package. Third Party testing is always recommended to insure that the closure system can hold up to the elevated torque requirements for these packages.
• The plastics industry has a known standard for torque removal. Removal torques should register between 40% and 60% of the recommended application torque. For example if a closure has a recommended application torque of 16 in-lbs, then the corresponding removal torque should be 7 to 9 in-lbs.
• Application torque for high speed capping machines can be inferred based upon known removal torques.
• Plastic bottles produced using Extrusion Blow Molding (EBM) processes have different torque back-off failure modes than bottles produced using an Injection Blow Molding (IBM) process.

• The package contents (fill) are incompatible with the liner system
• The package contents (fill) are incompatible with the bottle
• There is an incompatibility or lack of interference, between the bottle dimensions and closure dimensions
• The capping machine did not apply the correct application torque during the capping process
• Back-off is exacerbated by temperature or pressure changes within the package or the environment around the package
• Back-off is more likely when there is a mismatch of thread profiles between the bottle and the closure
• Fill substance on Threads during application torque.
• Industrial capping machines commonly used in the market cannot definitively dial in application torque. Their standard dial in is usually Rotations per Minute or Line Speed per minute. For testing purposes, a digital torque meter can be used to hand apply closures, to insure the correct application torque is being used each time
• Inconsistent power to the capping machine, causing capper to not have enough energy for a short period of time. (Power fluctuations to the capper machine)
• Excessive application torque. If a bottle is over-torqued, a “whip back” affect may occur. The package will try to stabilize itself and the two parts will back away from each other. Breakage of the closure can also occur in this case
• No Re-Torque of the Closure after Induction Sealing of the liner to the bottles. Closures with induction seal liners will back-off sufficiently enough to cause the closure to fall off. It is essential to re-torque closures onto bottles after the Induction Sealing Process