Packs and Pallets and stillage are common methods for containing loads into manageable unitized
When a load consists of many small items or of oddly shaped items it is often best to contain these loads within a Pack, Pallet or Stillage (cages or crates). And then restrain the pallet etc. to the vehicle. These are sometimes referred to as unitised loads, because the act of stacking items on a pallet and covering them with wrap and/or straps, ‘unitises’ the pallet as a single item.
Packs and Pallets can be unitised using banding, strapping, gluing, stretch wrapping and shrink wrapping.
Or alternatively loads can be placed in stillage which is a term used for cages and crates used to contain loads.
When using unitised loads there are two important factors to consider in ensuring that you meet the performance standards. These are ensuring that the unitised loads are adequately restrained in or on the vehicle and ensuring that the unitised load maintains its own integrity.
When restraining the unitised load within the vehicle, in some cases, the vehicle may to have the capacity to directly restrain the unitised load.
But in other cases, the unitised loads may need to be tied down.
In many instances a combination of tie down and blocking movement of the load in the forward direction will be used.
If the load is being tied down it is important to consider the friction coefficient between the bottom of the pallet or stillage and the truck surface that it is in contact with.
There are a range of additional issues which need to be considered in relation to stillage which are outlined on pages 45-48 of the LRG
Once the restraint method has been chosen it is important to ensure the unitised load has sufficient strength to meet the performance standards.
Failure of Unitisation
Unitised load approaches to load restraint rely on the assumption that the restraint mechanism used to unitise the load can resist the forces specified in the performance standards.. If part of the load can leave the pallet or package the load restrain strategy as a whole is likely to fail.
This can be a problem for movement of items in packages subject to heavy braking forces, or sideways cornering forces. This is a particular problem where the friction between items in the package is low.
This can result in movements within the package such as spearing or other types of failure.
Ejection of single items from a pallet can be just as dangerous as movement or loss of the whole pallet.
In extreme cases this can cause the load to leave the vehicle potentially injuring other road users or for the vehicle to become unstable and roll over.
Ensuring the unitised load stays intact may require additional restraint on the pack to ensure that the pack can resist the braking, acceleration and cornering forces.
This might include additional wrapping and or strapping
Using Interlayer packaging or dunnage to stop movement between layers in a pack or pallet which have low friction.
Blocking the load using a headboard or barrier can also be a useful strategy to avoid these problems.
Page 251 of the load restraint guide has a section titled Design For Unitising which provides some simple tests which can be used to determine if the unitised pack is sufficient to withstand the forces required to meet the performance standards.
Deformation of packages Bundles- Bags Bales and Sacks
This section will talk about two issues:
When unitising loads it is important to ensure that their packaging is a ‘self supporting’ shape. When the loads are regularly shaped they can be packaged in shapes where the package will not shift within the strapping or other restraint. Good examples of this are triangular or hexagonal packs.
However, where the shapes within the pack do not interlock and are able to move within the pack failure of unitisation can occur. This is a particular problem when there are voids within the pack.
If these situations apply, it may be wise to consider other strategies such as containing the load.
|The other situation is packages such as bales, bags and sacks where the container for the load is in itself flexible or situations where the load is crushable and could deform if restrained with too much force.
In these situations, it may be wise to consider containment strategies using gates or other blocking mechanisms, or to unitise the loads into pallets.
With any load that may deform it is very important to regularly check the restraints and re-tension them as required.
It is also important to consider the centre of gravity of the load when restraining these materials and the impact that a shift in the load may have on the stability of the vehicle.
It is recommended that anyone carrying these types of loads read pages 75 to 80 and 130-132 of the load restraint guide