From delicately packaged perishables to bulky bags of cement, many products spend at least part of their lifetime being stored and moved on pallets. Traversing warehouses, surviving transcontinental truck rides, and even crossing oceans these pallet loads are exposed to many environments and almost every step of the way there is the potential for damage.
There is no way to 100% safeguard a pallet load, but effective stretch wrapping gives loads a better chance of avoiding damage than almost anything else you can do. Even stretch wrapped pallet loads get damaged though, so it’s important to make sure every pallet load is stretch wrapped effectively to increase the likelihood of the pallet reaching its destination in as made condition.
Variables and choices complicate effective stretch wrapping
On its surface, effective stretch wrapping seems simple. After all, the basic stretch wrapping requirement is to ensure that each load has at least the required amount of containment force everywhere on it.
Containment force, as you know, is the key stretch wrapping metric. It’s the cumulative pressure of all the layers of stretch film on the load. It’s how hard the load is being squeezed and held together.
It’s OK to have more containment force than you need (as long as you don’t crush or twist the load) but not OK to have less. Meet your containment force obligation and you’re safe to ship.*
The caveat is that most customers are trying to get the necessary containment force with the least amount of film (lowest film cost) and this opens a huge can of worms. There are lots of choices they can make to do this.
The formula for containment force is film tension (as set on the stretch wrapper) times the number of film layers applied to the load or CF = FT x Number of FL. That shows we can get a specific amount of containment force on a load by adjusting the film tension and the amount of film layers.
More film tension and fewer film layers can produce the same containment force as less film tension and more film layers. Which is best? And how do you know?
Well, it depends. What are your comparative film costs per load? What affect will more film revolutions have on your cycle time and throughput requirements? The answer to these questions requires experimentation and testing.
Add to this the idea that stretch wrapper operators, particularly automatic stretch wrapper operators, have at least 12 significant choices to make that will affect the load’s containment force and complicate testing.
They are:
- Film width
- Film thickness
- Pre-stretch level
- Film tension
- Film revolutions at the top of the load
- Film revolutions at the bottom of the load
- Film band overlap amount up
- Film band amount overlap amount down
- Overwrap amount at the top of the load
- Film delivery speed up
- Film delivery speed down|
- Turntable or wrap arm speed
The relationships between these aren’t intuitive or easily visible. So, driving down to the lowest film cost to achieve your containment force can be quite a process. It’s hard and tedious work. And something we know about hard and tedious work that is that it often doesn’t get done – resulting in loads that are not optimally wrapped – even to the point of being unsafe to ship.
There’s abundant evidence that the great majority of loads being wrapped today have less than optimal wrap patterns, leading to billions of dollars of damage that could be avoided. Stretch wrapping technology is moving quickly to ensuring that all loads are indeed wrapped effectively.
Overcoming variable interactions
We have a lot of resources dedicated to helping you understand the variables that work together to create an effectively stretch wrapped load. Check out the Automatic Stretch Wrapper Buying Guide below for more insight into the types of stretch wrappers and technology available to help control the variables.
*Don’t forget, you can further enhance the effectiveness of your stretch wrapping by:
- Bonding or locking your load to its pallet with a film cable, and
- Ensuring there are no long or dragging film tails (longer than four inches).
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This post was published on November 1, 2016 and updated on November 27, 2018.
November 1, 2016
