To properly ready the cushion curves or shock data charts, a few values need to be known.
1. Fragility - Determine the fragility of the item(s) using the fragility table.
2. Weight - Measure the weight of of item(s).
3. Drop Height - Find the typical drop height for the weight of the item, or total weight of all items to be packaged using the Typical Drop Heights table.
4. Drop Frequency - Is the package expected to be stored and only at risk of a single drop, or to be shipped which will be exposed to multiple drops or impacts?
5. Impact Shock - Explore which cushion curve graphs from the foam suppliers PDFs best suit the fragility, drop height and drop frequency for the item(s).
The curve should dip below the fragility/deceleration G’s required to break the item(s) as established in the fragility.
6. Find the Correct Static Loading - With all of the info and values above, now the cushion curve/ shock data chart can be read to finalise the static loading range it can be found on the cushion curve graph. (see safe area on cushion curve example graph).
7. Calculate The Required Load Bearing Area - Bearing areas can be established for each side of the item(s) to be packaged.
Designers can follow the required safe bearing area range and best foam type, density and thickness to produce a package that meets all the impact and shock guidelines for this item to be safely protected in transport.
To better understand how to read cushion curve graphs 3 examples are given below using Ethafoam, each one showing:
1. Varying Drop Heights
Understand the increase of deceleration forces when items are dropped from increased heights.
The curves generally dip down in the 1.0 - 1.7psi range. This suggests that items with too much or too little load bearing area for their weight will experience increases deceleration forces, making the items likely to break in transit.
Varying drop heights:
12” (30.5cm),
24” (61cm),
30” (76cm),
36” (91.5cm),
up to 42” (over 1 metre)
The Varying Drop Height graph shows that the deceleration experienced by the packaged item increases as the package is dropped from a greater height.
2. Varying Densities of Foam
Varying densities of foam:
1.8, 2.2, 4.0 lbs/ft3 (pounds/cubic foot)
OR
29, 35, 64 kg/m3 (kilograms/cubic metre)
The Varying Density graph shows the average of all the different drop height tests per the various foam densities, 180 (1.8lbs/cubic foot), 220 (2.2lbs/cubic foot), 400 (4.0lbs/cubic foot). The higher density foams perform better producing less G-force when the package has higher static loading (weight per surface area). The lower density foam performs better with the lighter static loading.
However, increases in density can incur significant cost increases over lower density foams.
3. Varying Thicknesses of Foam
The thickness of the cushioning foam has a big effect on the protection of the packaged items.
Foams can be stacked up to equal the same effects of thicker foams.
Varying thicknesses of Ethafoam:
50, 75, 100mm
The Varying Thicknesses graph shows that certain thicknesses will pass drop tests for very fragile items (40Gs) with over about 1.0 psi of static loading. It also shows that if using a thinner, 50mm foam the risk of item breakage is likely for items that have a fragility rating of 50, 40 or 30G’s. Always check drop height is suitable for your item.
