Strapping Elongation Recovery and Retained Tension
There are two important characteristics of plastic strapping that determine how effective it will be, which are elongation recovery and retained tension. These two features of plastic strapping work together to provide durable protection and tight load holding capabilities.
You need both of these characteristics to be precise if you want to send and receive secure packages. When these elements of your strapping aren’t at the right level, products are at risk of damage and workers are in danger of injury. Let’s dive deeper into how elongation recovery and retained tension affect a load.
Elongation and Recovery
All plastic strapping has the ability to elongate under tension. This means plastic strapping will essentially stretch out and expand in length as tension is applied. Some elongation capability is important for loads that are subject to impacts during transit. This allows the strapping to expand on impact and absorb some of the shock without breaking. However, you don’t want to elongate the strapping too far because it will disrupt its ability to recover.
Elongation recovery is the strapping’s natural inclination to return to its original state, or the length it was before being stretched. This of it like a rubber band effect. As a rubber band is stretched, it extends to be quite large in order to fit over an object. Once the pressure is removed from the rubber band, it will shrink back to the original size it was before it was stretched. Plastic strapping behaves in a similar way.
Elongation recovery is especially important for packages that may shrink or settle as they travel. If there enough elongation recovery available, the strapping should settle along with the load and contract to provide a tight hold. If the amount of elongation recovery isn’t enough, the plastic strapping remains loose on the load as products settle down into a smaller size. Loose strapping leaves the load open to damage, and any workers who deal with the load may be at risk of injury.
Plastic strapping materials can vary drastically in their ability to elongate and recover. Polyester strapping has good elongation recovery and high retained tension over long periods of time. This makes it ideal for heavy-duty loads that will experience some shifting and impacts as they travel.
Polypropylene strapping has excellent elongation and recovery, but it offers low retained tension over time. As polypropylene strapping is stretched for extended periods of time, it will lose about 50 percent of its tension. This makes it ideal for short-term storage or shipping of products that need high elongation and low recovery. For example, compressible lightweight loads work well with polypropylene strapping, so the products have plenty of room to expand after being compressed.
All plastic strapping is applied under tension to create a durable and strong hold. However, the strapping will lose tension over time under the constant pressure of the load and the shipping environment. The amount of tension left in the strapping after a given period of time is referred to as retained tension. The level of retained tension determines how secure your load will be after a certain amount of time.
All packages require some level of retained tension if you want the straps to stay tight on the load. When retained tension is not at the correct level, the load is subject to shifting. This could lead to a complete containment failure where products fall apart and get damaged. Even if product damage doesn’t occur, a load failure will cause delays as loads have to be rebuilt and re-strapped.
The amount of retained tension will vary between different strapping materials, so you need to choose which is right for your application carefully. Polyester strapping exhibits excellent levels of retained tension, which allows it to hold a load effectively for longer periods of time. This makes it ideal for medium to heavy-duty loads that will travel for a long time. Polypropylene offers less retained tension over time, making it better suited for lightweight loads that will be stored or transported for shorter periods of time.
Now that you have a stronger understanding of elongation recovery and retained tension, you can begin selecting different strapping materials and testing them for your specific application. Measuring these two strapping characteristics carefully will allow you to protect your loads and ship unitized products with confidence.