The different types of packages
To better understand strapping and how it protects packages, you first need to know about the different types. Depending on how a package or load behaves, there are five package types:
Rigid/Self-Stacking - load dimensions remain constant before, during, and after strapping.
Expanding - dimensions become larger after the strapping material is applied.
Shrinking - dimensions become smaller after the strapping material is applied
Compressible - dimensions become smaller when under compression and rebound only slightly after pressure is removed.
- Combination - dimensions compress when packaging material is applied, rebound when compression is removed, compress again when other products are stacked on top, and rebound or expand once again after the products on top are removed.
For example, since the dimensions of rigid/self-stacking loads such as steel sheet remain constant before, during, and after being strapped, they require strapping that can be applied with high initial tension and that will retain high tension during storage, handling, and shipment.
Cotton bales are an example of an expanding load. These loads are first compressed in a baler, and then strapped. Since the load rebounds significantly when compression is removed, the strapping must have high strength to withstand the high pressure.
Shrinking loads need strapping that shrinks as the load gets smaller. A cube of bricks unitized together is an example of a shrinking load because the bricks become smaller as they rub against each other while being moved or transported. To compensate for the shrinkage, the strap must have excellent elongation and elongation recovery properties.
A newspaper bundle is an example of a compressible load. Its dimensions become smaller under compression; but, unlike the expanding load, rebounds only slightly after pressure is removed. Compressible loads require strapping that won’t expand.
Unitized, knocked down, corrugated containers are examples of a combination load. The load is compressed when strapped, expands when compression is removed, shrinks when other loads are stacked on top of it, and expands once again when the loads stacked on top are removed.
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