The reference guide below contains industry standard application torque specifications. It is important to not over-torque or under-torque the cap in order to achieve a properly sealed container. Many people believe the tighter the cap, the better the seal; this is not the case. Over tightening a cap will cause an uneven seal on the container and is a common cause of leakage. Of course, under tightening a cap will also cause leakage.
Verifying application torque is required for companies to understand if their closures have been properly applied.
The amount of torque a capping machine applies to a cap cannot be measured directly. For this reason the packaging industry standard is to measure the removal torque of caps applied by capping machines. The Removal Torque Method works because there exists a relationship, or correlation, between the amount of torque applied to a cap and its corresponding removal torque.
|APPLICATION TORQUE GUIDE
* Torque is measured in units of inch lbs.
|Cap Size (MM)
|Onto a Plastic Container
|Onto a Glass Container
Torque Verification and Measurement - The Removal Torque Method
A bottle cap torque tester is required to perform the Removal Torque Method. A bottle cap torque tester serves four main purposes:
- It allows you to determine the correlation between the application torque specification and removal torque specification for your cap.
- It allows you to measure the removal torque of the caps applied by your capping machine.
- It guides you in calibrating your capping machine to apply the proper amount of torque to your caps.
- It validates that your capping machine is applying the proper amount of torque to your caps.
Calibrating a Capping Machine Using the Removal Torque Method
To get started you will need the application torque specification for your particular cap and bottle. Let us say that you have a 28mm cap the application torque specification for this cap is 13.0 - 17.0 inch lbs. Within this torque range, the cap will be properly seated onto the container and provide a high quality seal.
Now that you have the application torque specification, you will have to determine the correlating removal torque specification. This is done with the aid of the bottle cap torque tester. You will start at the low end of the specified torque range, 13.0 inch lbs. Clamp the bottle into the bottle cap torque tester. By hand, apply the cap to the bottle slowly and evenly.
It is important to understand that bottle cap torque testers use slow speed transducers to measure torque. With this in mind, when you are applying or removing a cap from a bottle that is clamped into a bottle cap torque tester you must do so slowly and at an even rate. Be consistent with your approach on every trial. Try not to be slow and steady on one trial and then noticeably faster on the next. Applying or removing caps quickly or erratically will produce inaccurate results.
Be sure to always use new caps and bottles when performing your tests. Reusing caps and bottles will produce inaccurate results.
Set the torque meter to "Close" and zero out the display.
As you tighten the cap you will notice the torque tester is displaying the amount of torque you are applying to the cap. Continue to tighten the cap until the torque tester indicates that you have applied 13.0 inch lbs. of torque.
There are two time intervals used to measure removal torque: instant (approximately 5 minutes) and 24 hours intervals. Through the experimentation process you can establish correlations between application torque and removal torque.
Change the torque tester mode to "Open", reset the torque tester to indicate zero, and then unscrew the cap from the bottle slowly and steadily. Continue to unscrew the cap until you feel it break free, or release. When the cap breaks free, the torque tester will provide you with the removal torque value. Let’s say for example that the instant removal torque reading was 10.0 inch lbs. You now know that when applying 13.0 inch lbs. of torque onto the cap, the corresponding instant removal torque is 10.0 inch lbs. Applying the same methodology and testing 24 hours later you may expect a removal torque of 50% of the original application torque, 6-7 inch lbs.
You will then perform the same procedure for the high end of the application torque specification, 17.0 inch lbs. For our example, let us say that after testing, an application torque of 17.0 inch lbs resulted in an instant removal torque value of 12.0 inch lbs.
You now have your correlation; an application torque range of 13.0 - 17.0 inch lbs correlates to an instant removal torque range of 8.0 - 12.0 inch lbs., and a 24 hour removal torque range of 6-8 lbs.
Now that you have your removal torque range, you can begin applying caps with the capping machine. Tighten a cap as you would normally with the capping machine. After the cap has been tightened, promptly clamp the capped bottle into the torque tester. Unscrew the cap from the bottle to determine the removal torque.
Let's say you received a removal torque reading of 6.5 inch lbs on your first trial. You know that the cap is not tight enough because the instant removal torque of the cap did not fall within the range of 8.0 - 12.0 inch lbs. You must increase the torque output of the capping machine. Continue to adjust the torque output of the capping machine until you consistently receive removal torque values within the acceptable range of 8.0 - 12.0 inch lbs. Your capping machine is now properly calibrated.
It is important to test calibrated packages 24 hours later to determine that the package is properly retaining the application torque and that the closures are remaining tight.