Is Your Product’s Cap Tight Enough?
Whenever you need to screw a CT cap onto a bottle, a torque test is a key part of the process. Proper measurement of torque control is essential to ensure that the threaded closure is properly engaged. Many people believe that the tighter the closure is applied, the chances of a leak occurring are lower. But, in fact, the opposite is true. If your bottle capping equipment has excessively high torque, the cap can actually shear away from the bottle’s body, strip or jump the thread, or possibly even crack the closure. The result will be leakage and damage. Of course, it stands to reason that under tightening the bottle cap should also be avoided since the result can be product leakage and a rattling closure. Therefore, having proper torque control is essential.
How Is Application Torque Measured?
The term “application torque” refers to the rotational force used to apply a cap to the bottle and it is measured in pounds per inch. The right measurement for application torque should be half the closure’s diameter. For example, if you were using a closure that measured 43 millimeters in diameter, its correct application torque should be 21 to 22 pounds per inch. While this sounds very simple, unfortunately, this isn’t the end of the story.
Measuring Removal Torque
Despite the many impressive features of capping machines today, such as precision clutches or a magnetic brake, there is still, unfortunately, no way of measuring application torque directly. This means that measuring the removal torque is really the only possible way you can be sure the cap has been properly applied.
The term “removal torque” refers to the maximum amount of force necessary to remove a closure. In general, it should measure between 40 and 60 percent of its application torque. Testing, however, should only be carried out 24 hours after the closure’s application. This is because, over that period of time, the closure may “back off” the application torque. So, if we take the same example of the 43-millimeter-in-diameter closure and then work out 40 percent to 60 percent of its application torque, we get a removal torque of 8 to 13 pounds per inch.
Torque Testing Techniques
These measurements may seem straightforward, but they aren’t as simple as they sound. Since application torque can’t be measured directly, requiring a measurement of removal torque to validate it, and backing off closures reduces their removal torque as time goes on, several steps need to be taken to test the torque definitively. Usually, fillers choose a 30-package batch for measurement, apply their closures using a variety of application torques, and then choose several samples from the batch to be measured for their removal torque once five minutes has passed. The remainder is then measured once 24 hours have passed. Once the application torque has been correlated, the best option is selected before the best five-minute correlation for torque removal is pinpointed and used. Because measuring torque must be as precise as possible, there are now both automated and manual measuring machines in use to assist in the process. Manual torque testers are used in hand-tightening applications with automated testers being used for higher speed applications on fill lines in order to eliminate the possibility of manual variances.
Precision Tork specializes in the manufacture of aftermarket bottle capping equipment. Producing optimal solutions for a wealth of torque limiting and tensioning applications, we supply every high-quality capping machine part you could possibly need, from a magnetic clutch to a capping chuck. We keep your capping operation running thanks to our long-lasting, corrosion-resistant, and custom-engineered products.