In an ideal situation, the setpoint should be based on consumer group and package testing results. The following steps will guide you through the process:
- Determine application versus release torque quotients. In batches of 50, apply torque to 50%, 75%, 100%, 125% and 150% of the cap diameter (in mm) divided by 2. For example: apply 50 caps to 5lbfin, 50 caps to 7.5lbfin, 50 caps to 10 lbfin, 50 caps to 12.5lbfin and 50 caps to 15lbfin. Measure the removal torque of 10 samples 5 minutes after application. Do this for each group to understand the torque retention of the closure system. You may want to do this at given time intervals also to understand the effect of dwell time, aging and transportation.
- Take 10 samples of each torque batch and determine the low ideal and high acceptable release/application torque values, so you meet the target consumer/user expectations. Call these “T Low – Consumer” and “T High – Consumer.”
- Take 10 samples of each group to determine the lowest application torque that provides a sufficient seal, to maintain potency and avoid contamination. Leak testing is required to test the integrity of the seal. Call this the “T Low – Leak” value.
- (Induction sealed liners: Take 10 samples of each group, run them through the induction sealing process and verify that the foils are sealed properly. Wrinkles indicate an application torque that is too high, a foil that is not attached indicates insufficient torque. Call these “T High – Seal” and “T low – seal”).
- Using a separate group of samples, determine the strip torque (the application torque at which the threads break). This is an important parameter for production purposes. Call this “T High – Strip.”
Determine the process range based on the following guideline:
Low Limit: The higher value of “T Low – Leak”, “T Low – Consumer.”. “T low – seal”
High Limit: The lower value of “T High – Strip” and “T High – Consumer.”, “T high – seal”
Setpoint: The mid-range value.
If the High limit and low limit variables are within 0-2 lbfin, consider a different package design. A tight process range will cause production headaches later on.
Please Note: Removal torque and application torque values are not the same. Typically, removal is 50-90% of application, depending on cap/bottle/liner composition.
If working with previously established process ranges, always compare the manual torque tester results and the automated torque tester results. Due to the automated cap/ bottle gripping and programmable angular speed, the automated torque tester can produce values that are different from the manual process.