package design guide

8/10/2019 Package Design Guide

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Package Design Guide Steps

1. Determine Product Fragility2. Determine Conditions3. Calculate Cushion Requirements4. Recognizing Design Constraints5. Design Prototypes and Test6. Consider Vibration Effects7. Monitor Performance

Package Design GuideThis guide has been p repared to a ssist packaging designers in the selectionand utilization of ETHAFOAM* brand polyethylene foam and otherPerformance Foams products for protective packaging applications. Itcontains recommended considerations and procedures for the design anddevelopment of highly protective and cost-efficient packaging.

This information is offered to facilitate the process of designing anddeveloping packing that provides the de sired level of protection at the mostreasona ble cost. It is recommended that, once a p ackage des ign has bee ndetermined, a prototype product-package combination sho uld be developedand tested for performance prior to final inspection.

Preliminary Design Considerations

The first step in designing a protective p ackaging sol ution is the selection of a cushioning material that is appropriatefor the application.

As a general rule, ETHAFOAM* polyethylene foams are best suited to protect products w hich can be described asrelatively high in value and moderately fragile. Keeping damage rates for products of this nature to a minimumrequires a strong, resilient cushioning material that reliably protects against multiple impacts. In other words, caremust be taken to select a cushioning material that is not damaged by initial impacts and recovers to maintain itscushioning protection against repea ted sho cks.

ETHAFOAM products are resilient in nature, giving them outstanding recovery characteristics that provide outstandingcushioning protection against rep ea ted impact s. A n d ETHA FOAM products are available in a variety of strengths,making them suitable for prote cting product s rangi ng from just a few pounds up to hundreds o f pounds in weight.

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Package Design Guide

STEP ONE: Determine Product Fragility

The first step toward determining the a mount of cushioning a productrequires is to determine the amount of mechanical shock the product cansurvive on its ow n. There are s evera l common terms for this, with "fragility"and "g-factor" being the most common.

Fragility is normally expres sed in units of "gs" and indicate s the maximumdeceleration the product can withstand without being da maged. The morefragile a produ ct is, the low er its g-factor. The ta ble be low he lps to illustratethis concept.

Approximate Fragility of Ty pical Packaged Articles

Extremely Fragile Aircraft a lt imeters , gyroscopes , items with de lica te me cha nica l a lignme nts 15-25 gsVe ry De lica te Me dica l d ia gno stic ap pa ra tus , X -ray equipmen t 25-40 gsDelicate Display terminals , printers , tes t ins truments, hard disk drives 40-60 gsModerate ly Delicate Stereos and te levision receivers, floppy disk drives 60-85 gsModerate ly Rugged Major appliances, furniture 85-115 gsRugged Table saw s, sew ing machines, machine tools 115 gs and up

Idea lly, the fragility of a product is de termined by sub jecting it to a series o f gradua lly more severe sho cks(decelerations) in order to find the lowest severity impact that will damage the product. The highest deceleration,which did not cause da mage, is the n known to be t he pro ducts g-factor.

It may be necess ary to dete rmine fr ag ility le vels for a pro duct in various orientations , as it is not uncommon for aproduct to exhibit grea ter streng th in one direction than anoth er. Even very similar models sho uld be tes tedindividually as its se ldom that fragility for one mode l may be sa fely assumed from another.

There is no substitute for fragility test data. Educated guesses as to a products fragility are often counterproductiveto the d esign process. If the g-factor is e stimated too high, and the product is unable to s urvive as much shock asanticipated , the pa ckaging will be und erde signed a nd significant shipp ing damage is likely to occur. On the other hand,if the g-factor is estimated too low, and the product can actually withstand more shock than a nticipated, thepackaging will be overdesigned a nd unnecess arily expensive.





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STEP TWO: Determine Conditions the Product Will Encounter

Once product fragility is determined, the packaging designer should nextconsider the ha ndling a nd transpo rtation e nvironment the product w ill face.

To es tablish the a mount of shock the product may encounte r, it is necess aryto dete rmine the height from which the product may be dropped . Dropheights are generally established by the products we ight, which usua llyreflect how the product w ill be ha ndled.

The chart below show s typical drop heights for products of various w eights,and may be use d if you lack spe cific information abou t the ha ndling likely to be en countere d in your productsparticular distribution chain.

Typical Drop Heights

Weight RangeGross Weight in lbs. Type of Handling

Drop Heightin inches

0-10 1 person throw ing 4210-20 1 person carrying 3620-50 1 person carrying 30

50-100 2 person carrying 24100-250 Light equipment 18

250+ He avy equipment handling 12 NOTE: Palletized products may receive drops o f up to six i nches.





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Typical dynamic cushioning curve

Determining Cushion Thickness24" drop height, 2-5 drop aver age


STEP THREE: Calculate Fundamental Cushion Requirements

Wh en pro duct fragility (g-factor) and hand ling en vironment (drop height)have be en de termined, the procedure that follows can b e use d to de terminethe amount of functional cushioning material which will provide adequateprotection for the packaged item.

By functional cushioning material, we mean that portion of the design whichdirectly supports the load and functions to a bsorb s hock during impacts.There may be a dditional material used in the des ign as w ell to connectfunctiona l cushioning pa rts tog ethe r, facilitate p ack as sembly, etc. Thisprocedure doe s not take into account such factors as the effect of the outer container or other effects that may takeplace inside the container.

Generally such effects are beneficial so that this proc edure can c onfidently be used as a starting point to developpackaging that provides an assured level of protectio n and optimum cost-efficiency. To calculate functional cushioningneeds it will be necess ary to understand a nd use dynamic cushioning curves.

Using Dynamic Cushioning Curves: An Overview

A cushioning curve show s how a p articular packaging material of agiven thickness behaves at different impact conditions. Curves aregenerated by dropping a series of k nown w eights onto a cus hionsample from a specified height and measuri n g the amo unt of shockexperienced by the w eights as they impact the foa m. In s impleterms, this testing represents a pro duct dro pping o n a cus hionfrom a height likely to be en counter ed d urin g ship m ent.

An idealized cushioning curve is show n be low. It represents thecushioning performance of a cushi oning ma terial f or a givencombination of thickness and drop height. The horizontal axisrepresents a range of static loadings (in pounds per s quare inch)that packaged items might apply to the cushioning material. Thevertical axis repres ents the shock experienced as the cushion isimpacted. Curves a re often p resented for both first impact andmultiple impact (average of drops 2-5) data. It is common toinclude data for several cushion thicknesses from a constant dropheight on a single set of axes.

Cushioning curves for ETHAFOAM* products may be obtained bycontacting your local Dow -authorized fabricator, your local Dowrepresentative, or Dows Research and Development facility.

Using Dynamic Cushioning Curves:

An ExampleAn object to be pa ckaged is a 10-inch cube w eighing 60 poundswith a frag ility of 50 gs. Since a product typically faces rep ea tedimpacts d uring shipment, you will probably wish to use multiple-impact data. The typical drop height for a product of this weightmay be estimated from the chart below a s 24 inches, howeverspecific knowledge of shipping conditions or corporate sta ndardsmay dictate a different choice for drop height.

First, obtain the cushioning curves for the cushioning material youwish to use. Locate curves that represent multiple impact datafrom a drop he ight of 24 inches. One such se t of curves is show nhere.

Determining Thickness

Using the chart be low a s a reference, locate our products fragilitylevel (50 gs) on the ve rtical axis of the figure, and dra w a nimaginary horizontal line across the chart at this level.

This se parates the chart into tw o se ctions:

our fragility line a nd low er, where the pa ckaged item w ill beable to survive the anticipated shock level, andthe section above our line w here the shock levels are high enough to damage the p roduct

Note tha t in this example, a 1-inch thicknes s of this cushioning material will not protect the item dow n to 50 gs

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Determining Static Loading Range24" drop height, 2-5 drop average

because the entire 1-inch curve is located abo ve the 50 g line, in the " damage" zone. All of the o ther curves,representing cushions 2 inches thick and greater, have portions down in the "no damage " zone , and thus can beused. In most case s, shipping and ha ndling considerations provide a s trong cost incentive to de sign as small apackage size as p ossible, so the thinnest cushion thickness w hich will do the job is most often selected. In this case,we will choose a thickness of 2 inches.

Determining Static Loading and Bearing Area

Only a portion of the 2-inch cushion curve can be used to protectour product to 50 gs. As seen be low, the useable pa rt of thecurve is bound ed by a static loading of 0.3 psi at the low end, and1.4 psi at the h igh end. This tells us that, w ith a 2-inch cushion,we can app ly a static loading anyw here w ithin this "cushioningrange " and s till protect to 50 gs or low er.

We now must choose a static loading to use w ithin this range anddesign our cushions. The highest static loading value within thecushioning range will result in the most economical designbecause it will use less cushioning material to provide a dequa teprotection, thus low ering design costs. C ontinuing w ith ourexample will illustrate how.

Once we have se lected a static loading, we can calculate howmany square inches of foam in our chosen thickness we ll need tosupport and protect any side of the packaged product. In mostcases it will be necess ary to design a cushion to protect each of the faces of the product.

The cushion bearing area is easily calculated as the productweight divided by our chosen static loading. In this example, wehave an allowa ble static loading range of 0.3 to 1.4 psi. If we w ere to choose to design w ith a static loading at thelower end of our range, 0.3 psi, we would divide our 60 pound product weight by 0.3 psi and find that we w ould needto support our product w ith 200 square inches of foam to produce a des ign which loads the foam to 0.3 psi.

If we w ere to choose the higher loading value of 1.4 psi instead, we would divide 60 p ounds b y 1.4 psi and find thatonly 43 square inches of foam are necess ary to suppo rt the product at this higher loading. This is a 78.5% reduction incushioning material compared to designing at 0.3 psi. You can imagine the cost savings that can result.

The use of higher loading values to optimize des igns cannot be overemphasized. As a general rule, if you can doubleor triple the loading value and still not exceed your product fragility level, you can reduce your cushion usage by one-half to two -thirds. As a re sult, total material costs will be minimized .

Note that it may be p ossible to use even a smaller volume of foam by increasing thickness somewha t and takingadvantage of the higher loading (and smaller bea ring area ) this a llows . The resulting increase in shipping andhandling costs d ue to pa ckage size increas e is often greater than the sa ving in cushion material costs, so de signing tothe minimum thickness is the ge neral practice.

By repeating this procedure with several materials, you can quickly generate comparisons, which will allow you tostrike an e conomical balance betwe en material cost and package size.





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Buckling Coefficients for ETHAFOAM 220 at Various Static Loadings


STEP FOUR: Recognizing Design Constraints

In most cases , the design approach w e use d in step three, i.e. using thehighest possible static loading, will produce economical designs whichadeq uately protect your packaged product. There a re three constraints thatmust be checked how ever, to be sure this loading w ill not create otherproblems: compressive creep, cushion buckling, and extreme temperatureeffects.

Consider Compressive Creep

Compressive creep is the g radual loss of thickness a material may experience if placed unde r a constant load for anextend ed p eriod of time. Significant compressive cree p w ill result in the pa ckaged product loosening in the cushion andbecoming vulnerable to excessive movement inside t he package d urin g s hipment.

As a ge neral rule, creep of 10% is recognized as a pr actical upper li mit. In some cases creep losses of over 10% inthickness ha ve bee n show n to res ult in a significant loss o f cushion pe rformance.

Should it be found tha t creep in excess of 10% is anticipated, d esigners s hould recalculate the functional foamrequirement using a lower static-loading figure. Spreading the loading over a larger area will reduce compressivecreep.

The recommended loading limits to avoid excessive creep for various ETHAFOAM* polyethylene foam products areshown in below. Published dynamic cushioning data on ETHAFOAM cuts cushioning curves off at these limits to preventyou from inadvertently exceeding th em.

These limits are believed to be a de quate for temperature s encountered in a normal shipping environment. If exposureto excessive temperatures above 120 F are anticipated, lower loadings may be desirable. Consult product datasheets for compressive creep data on individual products.

Recommended Loading Limits for ETHAFOAM Brand Products

Material Static Loading Limit

ETHAFOAM Nova 1.5 psiETHAFOAM Select 2.0 psi

ETHAFOAM 220, 4101, M1 2.5 psiETHAFOAM HS-45, M3 5.0 psi

ETHAFOAM HS-600, M4 10.0 psiETHAFOAM HS-900, M5 20.0 psi

Consider Cushion Buckling

Buckling is the non-uniform compress ion of a cushion. Wh en bu ckling occurs,the ene rgy of the impact is not transferred evenly throughout the cushionand more shock is transferred to the package contents. Buckling usuallyoccurs w hen the cushions be come too ta ll and thin.

Buckling is actually les s of a pro blem with ETHAFOAM* products tha n w ithmany other cushioning mate rials. Yet it is one more factor you ha ve toconsider when designing a p ackage. By using the charts and formulaspresented below, youll be ab le to account for buckling in your designs a ndprevent any p otential problems.

The tables help determine w hen the sha pe of the cushions can cause non-uniform compress ion, or buckling. They provide w idth-to-thicknesscoefficients for different static loading values and enable the de signer tocheck for buckling p otential.

To use the charts, determine the static loading (in psi) your product placeson the cushion (divide product weight by surface area). Next, find the staticloading value on the horizontal axis of the chart and read up to w here thecurve crosse s it to find the b uckling coe fficient.

Next, multiply this coefficient b y the thickness of the cush ion to de terminehow wide the cushion must be to resist buckling. The e xample be low w illhelp illustrate how the chart and formula are us ed.

In cases whe re you must increas e be aring area to avoid buckling, thisresults in decreased static loading. Check to se e if this brings you into an

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Buckling Coefficients for ETHAFOAM Select at Various Static Loadings

Buckling Coefficients for ETHAFOAM Novaat Various Static Loadings

Typical values, not product pecification limits.

Note: for higher strenght, higher densityETH AFO AM products, the use of a constantbuckling coefficient (W/T) of 0.75 isrecommended.

appropriate loading range for the next lower s trength grade of ETHAFOAMpolyethylene foam, as it may be pos sible to redes ign into a lower strengthmaterial more econo mically.

Lets assume you plan to use a 3-inch thick pad of ETHAFOAM 220 to cushiona side of your product, which presents a static load of 10 psi. Youd refer toBuckling Coe fficients for ETHAFOAM 220 a t Various Static Load ings, find 1.0psi along th e bo ttom and follow the vertical line straight up until it interse ctsthe plot line. From this po int, follow the ho rizontal line to the left whe re youllfind the W /T coefficient. In this ca se, the coefficient is 0.7. Using the formulaT x W/T = W, you can now find th e minimum width: 3"x 0.7 = 2.1". Yourcushion must be at least 2.1 inches wide o r long to resist buckling.

Note: For higher strength, higher density ETHAFOA M products, the use of a 0.75 buckling coefficient is recommended.

Consider Extreme Temperature Effects

One o f the advantag es of ETHAFOAM* polyethylene foams is that they retaintheir properties and characteristics w ith minimal change over a wide range of tempera tures. How ever, as w ith all thermoplas tic foams, whe n they areexposed to extremely high or low temperatures over a considerable lengthof time, they may be a ffected. The materials become s tiffer at lowtemperatures a nd increasingly softer a t higher temperatures. In extremecases, it may become necessa ry to compensa te for these effects in yourdesign. Cons ult the individual product da ta s heets for ETHAFOAM availabledata on cushioning performance at extreme temperatures.





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STEP FIVE: Design Prototypes and Test

Certa inly no spe cific re com mend a tion s can be m ade ab out how to fabricateand p osition the foam on or around a pa rticular product. Each packagingdesign must be developed s eparately, given the large number of variablesinvolved.

The functional foam determinations made in conjunction w ith dynamiccushioning curves of ETHAFOAM* products, does not account for anyprotective contribution made by an ou ter container. It also do es no t accountfor effects such as s hea r and friction w ithin the container, all of which mayenhance the performance of the design to low er shock levels than those indicated by dynamic cushioning curves.

For this reason, it is highly recommended that you bu ild and tes t a pr ototype of your cushion design to determine itsactual pe rformance. In many case s you w ill find that i ts performa nce exceeds your needs and, base d on prototypetesting, you can cut back on the amount of ETHAFOA M in the pack e ven further for an even more economical packdesign. Any such modified des igns should a lso then be tested to verify their performance.

Performance tes ting of prototype p ackages d esigned with ETHAFOAM polyethylene foam products is one of theservices a vailable from our rese arch cente r. For more information, contact ou r technical staff at (800) 441-4369, oryour local Dow-autho rized fab ricator.

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STEP SIX: Consider Vibration Effects

For most products, a p ackage that provides protection a gainst mechanicalshock during shipment is all that is required. There are some products,howe ver, which are known to be susceptible to damage from vibration theymight experience during transportation.

Every mode o f transport subjects the packages being shipped to someamount of vibration at various frequencies. In order to provide productswhich are prone to vibration damage with protection ag ainst such effects, itis ess ential to determine the na tural frequency of any component which isprone to vibration damage, and compare it against the vibration characteristics o f your package design.

Every cushioning system has a range of vibrational fr equencies in whi ch it amplifies vibration and passes on a moresevere vibration to the pa ckaged product than it rece ives from th e transp ort environment. At frequencies lower thanthe amplification range, the cushion will pass the vibr ation on to the pa ckaged product ess entially unchanged. In s uchcases, the packaged product is said to be directly coupled to the external container.

At frequencies higher than the amplification range, the cushion will attenuate the vibration, that is, it will absorb someof the vibration w ithin the cushion and reduce the severity of the vibration it passes on to the packaged product.

For most vibration-sensitive products, making sure that the package design does not amplify vibration in the productsnatural frequency is enough to prevent vibrational damage from occurring during shipment. For severely vibration-sensitive p roducts, however, it may be necessa ry for the pa ckage des ign to actually attenuate the frequencies of concern.

As w ith shock, there is no substitut e for actu ally testing t he vibration chara cteristics of your de sign. Howe ver, in somecases, vibration performance may be estimated from some knowledge of the vibrational characteristics of theETHAFOAM* product used.

Typical Forcing Frequencies of Carriers

Carrier Frequency Range Conditions

Railroad 2 - 7 Hz (suspension)50 - 70 Hz (structural)

Moving freight car

Truck 2 - 7 Hz (suspension)15 - 20 Hz (tires)50 - 70 Hz (structural)

Normal highway travel

Aircra ft 2 - 1 0 Hz (p ro pe lle r)100 200 Hz (jet)

On a ircraft floor during flight

Ships 11 Hz (on deck)100 Hz (bulkheads)

Vibrations caused by interference to the flow of w ater by the ship, and fromimbalance and misalignment of the propeller shaft system.

Material response is often given in diagrams similar to those below, w hich represe nt performance for a given thicknessof material. Note that for any frequency, one can estimate whether the package will perform in direct coupling,amplification, or attenuation mode as a function of the static loading applied to the cushion.

Check the product data shee ts for any vibrational response data which may be available for the individual ETHAFOAMpolyethylene foam products.

Vibrational performance testing of prototype p ackages designed with ETHAFOAM polyethylene foam products is o ne o f the s ervices available from our rese arch center. Some size a nd w eight limits apply. For more information, contact ourtechnical staff at (800) 441-4369, or your local Dow-au thorized fabricator.

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STEP SEVEN: Monitor Performance

If it works, question it

There are many assumptions that we nt into your design development,among them that the drop height likely to be encountered is rea listic, andthat the fragility value used is representative of the product actually beingpackaged. Even w hen you a re lucky enough to be working with a fragilityvalue that was obtained by actual testing, in many case s w hat wa s testedwa s a prototype, and the production units may be more or less rugge d thanindicated.

For these reasons , it is a good practice to monitor th e performance of your des ign in actual use. This will help you todete rmine if your design is pro viding more rea l-wo rld performance tha n is actually required, or not enough. It can alsoallow you to determine when internal changes in the design of t he p ackaged product might alter the requirements forpackage performance.

Just as no s hipper can afford high damage rates, neither can he afford to overpackage.Monitoring of packaging performance on an o ngoing bas is can a lso help de termine if further economies can beachieved without sacrificing protection.

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