We have always been told that Force to Load is what generates load containment, but recently, I have heard the term Total Applied Stretch. What is it, and what role does it play in load containment?
Hi Anne,
Thanks for sending us your question. Every day, there are new acronyms or industry buzzwords thrown around, but without true context, they are meaningless.
I will start by defining Total Applied Stretch, which is the total amount (percentage) that the stretch film has been stretched beginning from the point where it is unwound from the roll on the machine and finishing after it has been applied to the load. Yes, the answer is simple, but it will take a little explanation for you to understand the context, which is the important part. A force is required to stretch the film. As the percentage of stretch increases, the force needed to continue to stretch it will vary, until finally you reach a percentage of stretch where the film breaks. The maximum force, when the film breaks, is referred to as its Ultimate Strength. Most film manufacturers will use Ultimate Strength as a selling point. However, in practice, Ultimate Strength can rarely be achieved because the web will break on a sharp corner of the pallet or load as it is being wrapped. After all, as the film is stretched, it becomes less elastic or more brittle. Even the slightest puncture can propagate until the web breaks. Properties such as Ultimate Strength and puncture resistance vary with each grade of stretch film and are determined by the film’s resin blend.
We have tested films of virtually every grade from all the major manufacturers and have characterized their performance. Generally, films will reach maximum force at around 160% to 200% Total Applied Stretch. At around 225% their elasticity decreases to a point where the web will easily break. Some ultra-high-performance films may achieve up to 250%. With all stretch films, if you do not apply enough stretch to reduce elasticity in the film, the film will continue to stretch with little resistance during transportation when forces are applied to the load. As this happens, products will move, shift, and offset, leading to load failure. So, you can see that Total Applied Stretch is an integral part of load containment.
The dilemma has always been to reach a balance between stretching the film to the maximum for the best performance and not breaking the web. Unfortunately, that balance is typically a knife-edge, just a little one way or the other, and you lose. Process variation due to equipment wear can force you to move even closer to load containment underperformance.
We understand the material science of stretch film and therefore understand its limitations. By incorporating a little physics, we have solved the issue with film breaks at higher levels of stretch, in the range of 275% to 325% or more (enough to reach ultimate strength). Our Rapid Bander technology uses two rolls of stretch film, one full web and one split web. The combined thickness of two rolls of our Rapid Film is about the same as most single-web conventional stretch films. The bands pass through rollers, which mechanically roll the edges, forming filaments. Both the banded and full webs join before entering the pre-stretch carriage of the wrapping machine, where they are “laminated” together to form a single web with reinforcement filaments. The introduction of the filaments completely changes the dynamics of the film’s performance, allowing us to stretch it much further than conventional single-web films. Not only do we achieve maximum force to load, but we have also taken virtually all the elasticity or stretch out of the film, eliminating secondary stretch. If a sharp corner punctures the film, the resulting hole will expand to a filament and stop, preventing a web break. The reinforcement filaments give us exponentially greater performance than we could achieve with a conventional stretch film. And, because we can stretch the film further, you use up to 60% less film to wrap a pallet with the same load containment.
Thanks for asking!