How it was mention the packing must be able to protect the product against shock, pressure and other external influence.
It exist very much foam, but you can not use all, for example when the material properties are not good ore when it is uneconomical.
As a rule the packing materials are calculate with help from the upholstery - diagram. This diagram shows the connection between the needed upholstery thickness, the allowed tension and the touchiness of the packing product, in the case of the real shock. This diagram are make according to DIN 55 471 and always refers to the foam. The producer determines the needed parameter when he carries out experiments so he makes the diagram.
Picture II.21: The upholstery diagram of the Styrofoam EPS20 [4]
If a packing product fall down so it is a complete elastic shock. Now the sentence of the conservation of energy is valid. This says that energy one and energy two are the same. Here is energy one the potential energy from the body in the near of earth and the energy two is the energy of the impact. That is:
In which
After the sentence of the conservation of energy also energy 1 = energy 2 you get
The shock factor, which you can read them from the diagram, is
The fall height is not a fixed parameter. Nevertheless the different logistic - firms have regulations how deep a packing product can fall.
Picture II.22: regulations from the Deutsche Bahn and the Post AG of the fall height
Further more the packing have to be sack up , that means that the first packing have to carry the weight of the packing which lie over. The result compressive stress have to be smaller then the allowed compressive stress.
If a cooler is needed then this weight has to be calculated.
An important indication of the upholstery is the compression hardness. This is dependent on the nominal density. If the nominal density is higher then the compression hardness is higher too. This quantity says how much force you need when you press the foam for a percentage share.
Picture II.23: compression hardness dependence on the nominal density of the LD 15 - LD70 products of the ZOTOFOAMS
Of course this materials characteristic is dependent on the product. So the LD 60 of the firm ZOTOFOAMS have a compressive hardness of 1.15N/mm² and the foam RG of the W.Dimer GmbH has the same nominal density but a compressive hardness of 0.07 N/mm², that’s more soft.
Styrofoam has compression hardness by a nominal density of 20 and 30 kg/m³ from 2 N/mm² respectively from 3,5N/mm². That is why you can say, that the packing materials have to show a compressive hardness between 2 and 4 N/mm². Then the materials protect the product optimal.
Picture II.24: More packing foams