Applying the pallets to the stretch hooder
When a pallet of goods is completed, it is moved to the stretch hood installation. This can be done either by roller conveyors or the pallet can be put directly on to the stretch hooder with a fork lift. Note that the pallet is put on a kind of piedestal. Thanks to this piedestal the machine will be able to cover the pallet with stretch hood foil until under the pallet which makes the pallet completely hermetic from the outside world !
The measuring of the pallet
Once positionned on the machine an electronic eye is measuring the height of the pallet. Some more sofisticated stretch hood lines are also looking at the dimensions of the pallet. In function of this information the machine will choose which stretch hood foil to use (in that case two foil formats are mounted on the line). Note that with one size of stretch hood foil you can pack several formats of pallets, but when they differ to much you need to use different foil sizes (e.g. for 60*80 CM and 110*130 MM pallets you should better use two formats of tubular stretch hood foil).
Placing the stretch hood on the stretching arms of the machine
With all these dimensional informations the machine will roll of the needed length of the correct stretch hood foil. Once the length reached, the foil is sealed together and cut of the roll.
The foil is then rolled of on four mechanical stretching arms. This process is very important because it influences a lot the end result of the packed pallet. When badly positioned on the arms, the stretch hood will show up wrinkles or it will not be put equally over the four sides of the pallet.
The horizontal stretch
Now it is time to stretch the hood. With Plastic Union's TOPFlex stretch hood filml you can stretch out the foil up to more than 100%. This gives you a lot of flexibity when a same stretch hood is used for several pallet formats ! Once the foil is stretched the circumference of the foil is bigger than the one of the pallet and now the next step is ready to take place.
The vertical stretch
The stretched hood are now placed on the pallet. As soon the stretch hood film leaves the mecanical arms of the machine, the memory of the film is acting and the film is searching after its original size. By doing this the stretch hood is placed nicely over the pallet and helding the pallet load together !
The smaller the original stretch hood size was, the higher the tension will be on to the pallet. For some applications a maximal tension is desired (eg stone bricks) but for other applications this has to be avoided (eg too much tension on a tetra pak milk pallet could deform the boxes).
On some stretch hood machines it's also possible to regulate the vertical tension of the film. In that case the film is mecanically unrolled from the arms during the downwards movement of the arms. If we only unroll 0.8 meter stretch hood film for a vertical movement of 1 meter, in that case we realise a vertical stretch of 25%. This vertical stretch, that can be modulated, increases the pallet stability.
The output of the goods
The job is done, the arms are going up again and the pallet can be taken of the stretch hood line, ready to be piled up in the warehouse and to be shipped safely all over the world !