Ask Steve
December 23, 2024
Question from Chris: We have major issues in our distribution center wrapping pallets. Our stores constantly complain about spilled loads. We have made several changes, but none have solved our problem. What can be done to minimize load failures?
Hi Chris,
Thanks for sending in your question. We are quite familiar with the challenges distribution centers face when wrapping what we call “C” loads like yours. As a matter of fact, there is a distribution center at the north pole that I believe is quite busy this time of year. Each of their loads contains a wide variety of items like: boxes of Legos, doll houses, hobby horses (do they still have those?), and well, you get the idea. In a “C” load, every imaginable configuration of packaged items is piled on a pallet with the expectation it can all be wrapped with the same amount of load containment as a pallet full of square boxes. However, common sense tells us that just isn’t so. The only way to solve “C” load containment failures is with a little science.
Let’s start with some fundamentals. When you stretch wrap a load, the film is stretched around the load as it is applied, and because the film has a memory, it retracts by a percentage of its initial stretch, just like a rubber band does. When the film retracts (we refer to that as snap-back) it pulls the individual items in the load tightly together, unitizing them. If a load is fully unitized, then forces that are applied to it during transportation are evenly distributed throughout the load, providing the highest level of load containment. The unitizing force that the film applies around the load is called Force-to-Load and it can be measured using one of several methods. Theoretically, the more force-to-load you have, the better your load containment. However, “C” loads present a real challenge to that theory. You have a combination of heavy and light weight items stacked on the pallet, and most often, not so neatly stacked. If you apply too much tension as the load is being wrapped, it will literally pull the lighter items right off the pallet and scatter them on the floor. When that happens, the load must be restacked and rewrapped. After several of these “spills” most operators will find their own solutions, like turning the tension on the wrapper down. That may keep the load intact while wrapping, but it greatly reduces load containment and load failures can occur.
If you have had people, with some technical knowledge of stretch wrap, optimize your process, it is likely they increased the stretch wrap machine’s pre-stretch (film stretch in the machine’s carriage, before it is applied to the load) and used moderate to low applied tension. The lower tension prevents items from being pulled off the load as it is wrapped. Let’s explore why that can be effective. As the film is stretched, it becomes stiffer. The stiffer it is, less unitizing force is necessary to contain the load, because stiffer film will not continue to stretch under force (we call this secondary stretch). Sounds simple, problem solved – case closed, right? The unfortunate truth is that there is still a limiting factor, while you may have solved the issue with the lighter items being pulled off the load, it has been replaced by an equally disruptive issue, web breaks! By increasing the pre-stretch, we stiffened the film, but the byproduct is that the film also becomes more brittle and prone to breaking. When the film reaches any sharp corner or protruding surface during the wrap cycle, it immediately breaks. So, our innovative operators find a solution to this, and believe it or not, it is the same thing they did to keep the light items from pulling off the load, they turn the tension down until the web no longer breaks. And you can imagine what happens to load containment, right back to load failure city.
There is some light at the end of the tunnel, and now to answer your question, yes, there is something that will address the specific challenges that “C” loads present, and I as promised, it involves a little science.
We begin with a high-performance film that maximizes its stiffness at a very specific percentage of stretch. We target a certain Total Applied Stretch which is the sum of the pre-stretch in the machine’s carriage and the applied tension between the carriage and the load. To reach the maximum Total Applied Stretch needed for performance, we can adjust the ratio of those two components based on the load we are wrapping. You are probably wondering why that would make a difference since you may have tried it already and traded one problem for another as we discussed above. The reason we can make this work and take full advantage of the stretch film’s performance properties is that we incorporate a series of reinforcement filaments from a second web on the machine, which allows us to achieve the high level of total stretch necessary for your application without the web breaking. We can use a much greater percentage of pre-stretch and lower levels of applied tension, so those light items will remain on the load as it is being wrapped. You will also apply substantially less film and fewer wraps.
How we developed this patented solution is very simple, it was the result of our study of load containment. The stretch film suppliers study film, the equipment suppliers study equipment. To fully understand load containment, you must consider material science (the film), the methods of applying it (equipment) and the physics of dynamic applied forces during transportation and how different types of loads react to them. We began with theory, applied that theory in our load containment test lab, and validated its effectiveness in the field. No magic, no smoke or mirrors.
I hope this sheds some light on why no matter what you have tried, it just didn’t seem to help. We will be happy to evaluate your needs and develop a solution that will make your operators, your stores, and you very happy.
Thanks for asking.
