CLOSURE COMPATIBILITY AND TORQUE PROBLEMS | INDUCTION SEALING PROBLEMS



CLOSURE COMPATIBILITY AND TORQUE PROBLEMS

1. Container Dimensions Compatibility with Closure Dimensions.

T & E dimension of the bottle and cap.

Too far apart will cause the closure thread to override the bottle thread and “strip off” the cap. Too close on dimensions will cause drag, which would give a false reading to automatic capping equipment, therefore not enough application torque.

Thread styles and threads per inch.

“L” style has a 30-degree thread contact surface and “M” style has a 10-degree thread contact surface. Thread per inch is the number of turns of the thread that would be found if the container neck were extended to a full inch. Matching thread styles and threads per inch insures a better fit.

H dimension of the bottle and cap.

H stands for height. If the H is too short on the bottle, the cap can bottom out on the bottle and not have enough thread turns for a good seal. It would create false reading for application torque to an automatic capping machine.

Mismatched S dimensions.

If S dimensions are mismatched, it can cause cocked caps or not enough turns of the thread for good retention of the application torque.

2. Proper Application Torque.

What is the proper amount of torque?

Various organizations have published suggested application torque charts. What is common among all of the recommendations are the values are grouped by closure size and are listed as a range of inch-pounds. A “rule of thumb” is to divide the closure by 2; i.e. 38mm is 19 in./lbs. See Reliable Caps suggested Torque Values.

Measuring application torque.

Unless the capping equipment records the measurements, which is not that common, application torque is recorded off line by measuring removal torque. Removal torque needs to be measured immediately after capping and before heat induction, if used. The reading should be 40% to 60% of the application torque.

Variables affecting torque:

• Cleanliness of the fill.
• Temperature of closure and container at time of fill.
• Lining materials and container materials.
• Dimensions (as discussed in 1).
• Capping equipment process control capability.
• Heat induction sealing.
• Quality of container finish: sealing land area.
• Storage conditions including temperature, relative humidity and static top load.

3. Common Problems Related to Application Torque.

Below standard application torque.

• Not enough stress to hold the closure in place. Becomes “loose in handling and transporting.
• Not enough pressure on sealing land area of bottle. Leaking. Non-bonding of heat induction liners.

Above standard application torque.

• Stress cracking of thermoplastic closures.
• Distortion of the closure creating uneven pressure on the land area which can cause leaking.
• Friction between the bottle land area and the liner in the closure can wrinkle the liner, which damages the seal. Even slight wrinkles in heatseal liners can create “pin holes” in the facing layer after heat induction.

Heat induction process.

The process of heat induction causes the bottle and cap to expand and shrink. Because these two items are usually made of different thermoplastics, and the timing and the rates of change are different, the torque is changed during the process. If a tightly closed bottle is required, it is recommended to re-torque the closure after heat induction.


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INDUCTION SEALING PROBLEMS

There are a few common problems sometimes encountered with induction heat sealing liners. The following list is designed to help you determine the problem(s) and the possible cause(s).