When unitising/palletising cases of products for transport it is import that the hazards anticipated in the supply chain are understood, so that the packaging is designed to provide sufficient protection to the product. One particular hazard unique to unitised/palletised products is that of load stability.
This is an expression of the stack’s ability to remain upright and stable when subjected to the forces that are experienced during dynamic events, such as accelerating, braking and cornering when in the back of a truck or on the tines of a forklift.
Picture jelly on a plate. When the plate is moved back and forth the jelly wobbles. A pallet of cases moves in much the same way during accelerating, braking and cornering events as the load is typically only secured to the pallet by stretch wrap, shrink wrap, strapping or a combination thereof.
Below are Smithers Pira’s top 5 areas to consider when designing packaging to address pallet stability;
This means designing your packaging to use as much of the pallet footprint as possible (without overhanging the pallet of course). Any underhang of the load on the pallet means more space for that load to move about.
Commonly more and more products are shipped in easy open shelf ready cases, with perforations along the vertical faces. Such perforations can introduce weakness to the case strength and allow cases to yield, especially when perforations cut through the vertical edges of a case.
Stretch wrap material and stretch wrapping parameters have a significant impact on a load's stability performance. Too much stretch wrap can cause damage to the case and thus the product, whilst too little can mean load instability and collapse.
Whilst a columnar stacking pattern gives the best overall compressive strength, an interlocked stacking pattern (when cases are turned in different orientations between 1 layer and the next) can mean greater lateral strength and stability. The pallet pattern is inherently linked to the pallet utilisation.
The taller the stack of cases, the greater opportunity for that load to move during dynamic events and the greater the risk of instability, as the centre of mass is further away from the floor, making the load top heavy. This is especially true for narrow rectangular pallet sizes (e.g. Euro pallets).
There are numerous other factors that also need to be considered that can have an impact on the pallet stability performance e.g. the use of other tertiary packaging components (i.e. anti-slip sheets, vertical corner posts etc.). Smithers Pira’s Distribution Testing laboratory is capable of testing full palletised loads to assess pallet stability, either as a standalone performance investigation or as part of a wider study assessing all the hazards of the palletised supply chain.
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