Measuring and modeling the effect of time and temperature on removal torque and sealing force of a continuous thread closure

A new technique for measuring the sealing force of a container-closure system was developed by employing a strain gage based transducer. The sealing force is considered a direct indicator for monitoring the mechanical seal integrity of the container-closure systems. A sealing force measuring device and a torque meter were used to investigate the effect of environmental conditions on the relaxation behavior of a 28--400 closure system. The responses from both devices during storage over time were transformed to the percent (%) force retention (FRT) and percent (%) torque retention (TRT) and used to analyze the effect. The high temperature and relative humidity of tropical conditions showed significant effect on the relaxation of the systems studied. It was found that the % TRT over time data were less consistent than the % FRT due to the nature of torque measurement and effect of environmental conditions. The % TRT data were higher than the % FRT indicating less relaxation of torque than of force. Therefore, using the removal torque or % TRT may be misleading in the interpretation of the seal integrity of the container-closure systems. The apparent seal integrity is less when measured by force retention. Mathematical modeling of the relaxation behavior of the systems revealed that the theoretical models derived from spring and dashpot are not applicable. Empirical models using the curve fitting techniques were then applied and excellent agreement with the experimental data was found. The mathematical models developed were extended to long-term prediction for 3 years; the predicted values of the % FRT and % TRT were in the acceptable range for agreement among the models.