Question from Stacy:
There are different tools for measuring Force to Load. Do they all measure it the same way and will the results be the same?
Hi Stacy! On the surface, seems like your question is a slow pitch right over home plate. But like most things in life, it’s a little more complicated than a short yes or no.
First, let’s visualize what we are measuring. Place your hand around a cup and squeeze. Your hand is the stretch film, the cup is the load and the pressure against the cup is the force to load. There are many different tools that measure Force to Load. In theory, they should all measure the pressure the stretch film is applying to the load surface accurately; and in theory, the results should all be the same – but they are not, not by a long shot.
Next, let’s look at how the tools work. The principal is common to most tools: insert a device so that it is positioned between the film and the load, pull it away from the load by a specific distance, then read the force on a scale.
Several factors influence results: how the tool is designed, surface area of the tool, how much the film is compromised by inserting the tool, location of the measurement (more or less mechanical advantage introduced based on the distance between the measuring point and the corner of the load), how much the primary packaging collapses when the measurement is taken, and let’s not forget about the operator (each person using the tool may have a slightly different technique - and as a result, get very different measurements).
Three of the more common tools are the Wing Tool, 6” Pull Plate, and the Lantech CFT6. When comparing readings from these tools based on the manufacturer’s recommendations, the Wing Tool will yield the highest Force to Load numbers, next the 6” Pull Plate (about 20% less than the Wing Tool), and finally the CFT6 tool (about 50% of the Wing Tool). There are a couple of reasons for the difference. One is the greater surface area of the wing tool and 6” pull plate, the second is the recommended location of the measurement. The Wing Tool measurements are taken 10” from the corner of the load while the 6” Pull Plate is at 18” and finally, the CFT6 tool is taken at 22”. I mentioned mechanical advantage earlier; think of a lever, the longer the lever (the distance between the measuring point and the corner of the load), the less the force needed to do the ”work” (pull or twist the tool). You can test this principal easily by placing a pencil on your desk, let most of it overhang the edge and press it to the desk with one thumb. With the other thumb press down on the pencil, just past the edge of the desk, then press the pencil all the way to the free end. Notice a big different in the force required to bend or deflect the pencil? That is the reason placement of the tool when taking FTL measurements is an important consideration!
Although we at Allied have all these tools in our containment lab, we prefer the CFT6. The incision into the film is smaller; and compared to the other tools, it is much quicker and easier to insert; there is an indicator that lets you know exactly when the reading should be taken; and a digital scale that records the maximum force.
Regardless of the tool you use, remember the most important thing is consistency. If you have a containment standard that includes FTL measurements, and you have achieved that standard using a specific tool, continue using it because you want to ensure sure you are wrapping within spec by taking periodic measurements (it’s the old apples-to-apples).
Finally, Force to Load is just one aspect of a proper load containment standard. The other is Total Applied Stretch which is an indication of how much force will be required to stretch the film anymore once it has been applied to the load. Both are critical to load containment. Only measuring one may give you a false sense of security. If you don’t have a containment standard, we will be happy to help you develop one, and it will be based on science, not gut feel…
Thanks for asking,