How To: Design Packaging with Ethafoam's Shock Data

photo of ethafoam packaging designed for a large electronic device

Intro

To protect and stabilise items, thoughtful calculations, design/shaping and material/density selections all need to be considered to achieve the ideal balance of packaging cost and amount of protection it will provide. Packaging or cushioning foams act as shock absorbers for the items that are packaged. The longevity and sustainability of returnable dunnage packaging should also be considered.

Step One: Determine the item’s fragility

What is Electrolysis and galvanic corrosion?

Galvanic Corrosion is the corrosion that occurs when two dissimilar metals are used together in a structure and exposed to an electrolyte (salt water, chemical, petrol) and the less noble of the 2 metals will corrode. For example; aluminum sheet with steel fasteners on a boat. Some pairings of metals are more at risk of . Check a galvanic series or chart.

Electrolysis is the acceleration of the galvanic corrosion when electricity is introduced to the metals in question. Connected by an , the less metal experiences accelerated galvanic corrosion.

while both processes involve metals and electrolytes, their dependence on an external voltage source distinguishes them.

The fragility of an item can be determined by finding the amount of G-force or deceleration (shock) in which the packaged items can reach at the point of damage to the item (see table 1).

This is measured at the point of impact when the item is dropped from its standardised typical drop height (see table 2). The item must be damaged to determine its exact limitations, to avoid this, packaging designers can be guided by the already established ranges for categories of common items (see table 1).

For reference, an object being dropped from only 30cm onto a concrete floor reaches about 50G’s. When items are “loose loaded” (items that are totally unsecured) in transport it’s expected the item can easily experience shocks over 50 G’s during handling. So anything more fragile than an item rated 'delicate' is almost certain to break in transport without protective packaging.

Table 1 - Fragility Ratings

Extremely Fragile 15-25 G’s

Special military equipment, precision aligned test instruments, altimeters, hard drives, missile guidance systems, precision aligned test equipment, gyroscopes, inertial guidance systems

Very Delicate 25-40 G’s

Mechanical instruments, electronic equipment, altimeters, digital electronics equipment (hard drives), medical diagnostic apparatus, x-ray equipment, mechanically shock mounted instruments

Delicate 40-60 G’s

Computer display terminals and printers, electric typewriters, amplifiers, aircraft accessories; typical Paintings - 50 Gs; Glass Bottle - 60 Gs (Art in Transit)

Moderately Delicate 60-85 G’s

Video equipment, video monitor, stereos and television receivers, floppy disc drives, aircraft accessories.

Moderately Rugged 85-115 G’s

Major appliances and furniture, electromechanical equipment, equipment with minimal electronic controls.

Rugged 115+ G’s

Table saws, sewing machines, machine tools, aircraft structural parts such as landing gear, control surfaces, hydraulic equipment.

Table 2 - Typical Drop Heights

Gross Weight

Type of Handling

Drop Height in Inches

0-10lbs (4.5kg)

1 person throwing

42 inches (106cm)

10-20lbs (4.5 - 9kg)

1 person carrying

36 inches (91cm)

20-50lbs (9 - 22.5kg)

1 person carrying

30 inches (76cm)

50-100lbs (22.5 - 45kg)

2 people carrying

24 inches (61cm)

100-250lbs (45 - 113kg)

Light equipment handling

18 inches (46cm)

250+lbs (113+kg)

Heavy equipment handling

12+ inches (30cm)

*Palletized products may receive drops of six inches

Step Two: Determining Static Loading

Take both the fragility rating and typical drop height for your item(s) from the tables above. With this info check the cushion curves to determine best protection and most economic choice of foam.

To find the load bearing required for the item, first find the cushion curve graph that matches the type of foam material and the drop height.

Now knowing the fragility rating and drop height determine the static loading range for your item(s) using the shock data (cushion curve) graphs.

In the example graph below the following is used:
1. Fragility rating - Deceleration of 40-60 G’s
2. Typical drop height - drop height of 30”
3. Foam material - Ethafoam 220 50mm Thick

To create a packaging design that is most economical (least amount of foam) and of the smallest size possible (most affordable shipping costs), the highest static loading within the safe area should be chosen. This ensures adequate cushioning and protection with the least amount of foam.

Step Three: Calculating Load Bearing Area

To calculate the bearing area in square inches, divide the weight of the item by the static loading chosen. The result will be the amount of square inches of foam required to bear the weight of the item.

Bearing Area Calculation: Weight (pounds) ÷ Static loading (psi) = Number Square inches

Example: High Performance Commercial Amplifier

An amplifier is to be packaged. This is in the fragility category of: Delicate 40-60 G’s.

The amplifier in this example weighs 40 pounds (18kg), checking the typical drop heights table; this is expected to be carried by 1 person with a drop risk of 30 inches (76cm).

The below calculator can be used to convert the measurement the static loading measurement grms/cm2 (used in Ethafoam's shock data graph) to PSI for calculating the bearing load area.

Unit Converter

Grams/cm² to PSI

Grams/cm²: PSI:

Kilograms to Pounds

Kilograms: Pounds:

Centimeters to Inches

Centimeters: Inches:

an example of stock data or cushion curves that are referenced when designing packaging with Ethafoam

Now checking the cushion curve for a 30” (76cm) drop that reads under the fragility rating of 40 G’s for 2-5 drops. There is a safe area from 42 to 140grms/cm2 using the 75mm thick line, which converts to a range of 0.6 to 2psi.

The highest static loading within the safe area is 2 psi. Any static loading within the safe area is appropriate, however higher static loading will require less foam and therefore more affordable packaging. Divide the weight by the chosen static loading.

Required Bearing Area: 40 (pounds)/2 (psi) = 20 square inches.

This equates to about a 5 inch x 4 inch surface, 20 square inches. 20 square inches of bearing area per side of the package that could be dropped onto the ground. Now the designer can begin to visualise how much of the high quality foam is required to protect and cushion against shocks, impacts and package mishandling.

an illustration showing how cushion curves and load bearing surfaces are required when designing packaging with Ethafoam

Here’s an example of how the design could look using the transmitted shock data graph (cushion curves). It recommends 20 square inches of 75mm thick Ethafoam 220. 5 square inches on each of the 4 corners, totalling 20 square inches for the item to sit on.

(image) Count the square and half square inches to a total of 5 square inches for each corner foam piece.

Load Bearing of the Other Sides

The dropping of the package onto any of its sides should also be considered. This would require the same bearing area, taken from the transmitted shock data cushion curves, but on the side bearing the load and the possible impact of a drop.

Here is an example of how an corner cap design can provide the bearing area required for:

front and back impact load bearing surface

(image) The front and back.
5 inches squared of load bearing surface, on each of the 4 corners totalling 20 square inches, just over the required 18.6 square inch.

side load bearing for protective packaging

(image) The sides.
5 inches squared of load bearing surface, on each of the 4 corners totalling 20 inches squared.

protective packaging of electronic device using ethafoam's shock data and cushion curves

(image) The top. Now, all sides are covered, if dropped onto the topside, left side, right side, front, back or bottom the load bearing area will be 20 square inches. This meets all of the impact and shock guidelines for this item to be safely protected.

(image) If a lower quality packaging foam is used, the designer can consider producing a more sophisticated design with larger load bearing surfaces to compensate for the lack of stability, cushioning and durability of the foam.

Step Four: Checking for Buckling

Buckling occurs when the foam bearing a load is too tall and thin to compress evenly, the foam will then bend and become unsupportive.

Calculating Buckling

Ethafoam is more resistant to buckling than other foams, however the designer can check that the minimum length or width of the foam bearing area is met to stop buckling. Using the buckling coefficients for Ethafoam 220 seen below, take the static loading (psi) used for the package to read the buckling coefficient, then make the following calculation to understand the minimum length or width required to prevent buckling.

Thickness (inches) x Buckling Coefficient (W/T) = Minimum Width (inches)

For Example the amplifier packaging used 2” thick Ethafoam 220 and 1.8psi of static loading with equals 0.8 buckling coefficient on the graph.

2 (inches) x 0.8 (Buckling Coefficient) = 1.6 inches.

example of measuring faces for buckling prevention

(image) The image shows that this design uses load bearing areas that are more than 1.6 inches in either length or width, as calculated as the minimum buckling requirement based on the thickness and static loading.

Step Five: Prototype and Test

It's the designers responsibility to explore available options to consider shipping dimensions and amount of packaging material to maintain efficient costs, while considering all possible transit or storage threats to the item(s). This should include creating prototypes and drop testing packages to ensure the safety of the item(s) and the suitability of the packaging foam.