Description of the expansion process

When used for packaging it is desirable to obtain a final dunnage product with a very low density. It saves raw material costs and gives a very competitive product.

SPAN PACK® is a highly expandable product and with it you will obtain the low density required.

Some loose-fill raw materials needs 4 expansion passes to obtain a low density. SPAN PACK®  can  reach the lowest density in 3 expansion passes. It means that the material needs to be expanded 3 times.

Here is the layout and steps to follow:



1- Expand raw material SPAN PACK® sending it to silo nr.1 (1st pass)

2- Keep it in silo nr.1 maturing for a minimum of 24 hours

3- Do a second expansion  (moving the already expanded material from silo nr.1 to silo nr.2 passing through the expander)

4- Send the material to silo nr.2

5- Keep it in a silo nr.2 maturing for a minimum of 24 hours

6- Do a third expansion  (passing the already expanded material from silo nr.2 to silo nr.3 through the expander)

7- Leave it in silo nr.3 absorbing air about 24 hours (the material will continue to expand in the silo).

8- Now the material is finished and ready to be sold (in bulk or usually in 1/2 cubic meter bags)


 When SPAN-PACK® is heated with steam at about 90ºC / 194ºF to 99ºC / 210ºF it becomes a foam with small closed cells. When cooling the expanding agent and steam condenses inside the cells creating a vacuum. Then the foam tends to absorb air to equalize with atmospheric pressure by air diffusing through the cell walls. This stage is called the maturing period or intermediate aging and can last 24 to 48 hours depending on the density. This process takes place in well  ventilated silos. The condensed expanding agent gives extra power for a further expansion. After maturing, the mechanical stability of the foam increases.

During this process the bulk density of the material drops from about 500 / 550 kg /m3 (31 / 34 pcf) to about 3 / 4 kg /m3 (0.19 / 0.25 pcf) in a cycle foaming or multi-stage foaming process comprising up to three expansion passes.  Finished expanded particles do exhibit a superior resiliency depending on the temperature and residence time. . The process provide a plurality of expanded cellular styrene polymer particles, each of the particles having a plurality of cells, the cells having walls, the walls having a plurality of folds therein. Folds and struts appear as a result of shrinkage and partial copllapse of the foam  Such folds are often referred to as "accordion folds"
Low density resilient particles are suitable for use as free flow dunnage material particularly for delicate articles, such as instruments, glass fabricated articles and the like.