Ask Steve
November 25, 2024
Question from Dave: What causes our boxes to collapse after stretch wrapping? The pallets look good when we ship, but then we receive complaints from customers after the product arrives.
Hi Dave,
That is a great question and something that we have researched in depth, but it requires some explanation.
In some cases, we have found that the packaging itself (box, folding carting, bottle, etc.) has been changed. It is becoming more common with industry wide pressure to downgauge materials. As I have discussed in previous Ask Steve articles, even with minor changes, there can be unintended consequences to downgauging. If the force that the film exerts around the load after wrapping exceeds the resistance of the box corners, they will collapse. Restoring the boxes to their original strength (or thickness) may not be an option. In that case, you need to increase the pre-stretch of the wrapping machine and reduce the applied tension as the load is being wrapped. This will still achieve the total film stretch needed for it to perform but will apply less direct force to the boxes themselves. However, that may not be possible as we will learn.
What if there were no changes to the packaging. Now it gets a little trickier. As you said, the pallets look great when they leave your plant, what could possibly be happening? To understand the answer will require the application of a little physics. Fortunately, we have done the research and testing, so I will just give you a highlighted version.
When stretch wrapping with conventional film, you can only stretch it so far before it breaks. The maximum stretch that can be achieved with conventional film is well below the level necessary to remove all of its stretch. In other words, the film is still stretching at the level you are wrapping. Since the film is still in an elastic state, it will naturally retract by some percentage. The amount that the film retracts is proportional to the stretch left in it. Now that we understand the general concept, let’s take the next step. The film has a tacky surface which allows each layer to stick to the previous wrap (and to a certain extent, to the contents of the load). The objective of this feature is to help unitize the load, preventing movement during transportation. Remember, I mentioned unintended consequences? Here is another example. The retraction force is multiplied with each layer of film. The more film you apply to the load, the greater the force exerted on the load as the film retracks, but it is important to remember that it may take some time to fully retract. Since it does not happen immediately, the product looks good leaving your plant, but by the time the customer receives the shipment, the boxes are crushed.
Now that we know the cause, the solution can be a little more challenging. If you increase the machine’s pre-stretch and reduce the applied tension as I mentioned earlier, you will have constant web breaks as the pallets are being wrapped leading to frustrated employees, loss of plant throughput, and an increase in load failures during transportation. Doesn’t sound like a very viable solution. Or you can leave things as they are and deal with customer complaints. That doesn’t sound like a consideration either.
Again, with the application of a little science, we can help you eliminate the issue without sacrifice. We developed our Rapid Technologies solutions to achieve maximum performance from the film, by stretching it enough that there is little, if any, stretch left in the film. We can achieve the high level of stretch necessary through increased pre-stretch while applying minimal application force. This means that we provide the same amount of unitizing force around the load without crushing the boxes and can do that without the web breaking when the pallet is being wrapped. And as forces are applied during shipment, the film will not stretch further, so its dynamic load containment performance is far greater than can be achieved with conventional stretch film. We will also apply less film and fewer wraps adding to the benefit. This is a patented process that incorporates reinforcement filaments into the web that prevent web breaks as the film is stretched to achieve maximum performance. The reinforcement filaments also help tie the layers of the load together preventing layer-to-layer shifting.
How do we know it works? We have proven it not only on paper but in our lab and in the field. We wrapped a pallet of lightweight folding cartons with conventional film using the same film and wrapping convention our customer used (who was having the same issue you are). We also wrapped another pallet using our Rapid Bander. We achieved the same force to load as the conventionally wrapped load. We used far less film, fewer wraps and tested both by applying normal transportation and high impact forces. In both cases, the Rapid Bander wrapped pallet achieved superior load containment performance. We wrapped another set of pallets using the same protocol, measured the unitizing force and left them in the lab for a week. After the week, we again measured the force to load. The conventional wrapped pallet had a significant increase in force and the corners of the cartons were deformed, just like yours are. The Rapid Bander wrapped pallet had no change to force and no deformation. At week 2 the cartons on the conventionally wrapped pallet were crushed, however, no change on the Rapid Bander pallet. In fact, we continued to measure for a year with no change in force on the Rapid Bander pallet (we still have the pallet in our lab after three years, and it looks just the same as the day it was wrapped).
I have always believed that you tackle a problem by fully understanding what causes it before you can fix it. Others may offer you a solution by adding additional materials like corner boards and strapping. At the end of the day, they sell more, and you pay more, even when it isn’t necessary.
Thanks for asking.
