Removal torque effects of vibration and fatigue on discontinuous-thread closures

This research investigated the effects of random vibration and warehousing on the removal torque of linerless discontinuous thread polymer closures. An application torque level of 12 in-lb was applied to cross linked high-density polyethylene (CL HDPE) and polypropylene (PP) type closures of the same design. Following vibration and warehousing, torque values were measured, and percent torque reduction was calculated and analyzed by t-test at 95% confidence level.PP closures showed approximately 11.3% greater torque reduction compared to CL HDPE closures. Warehousing duration had a significant effect on removal torque. The average difference in torque loss between the 30 and 90 day warehousing was about 6.9%. Pre and post-warehousing vibration had no significant impact on torque loss. The data confirm that torque reduction is influenced by warehousing and polymer type and that CL HDPE linerless discontinuous thread closure is the better cap material selection on CL HDPE bottles used in the study.