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THE DEVELGPMENT OF A MHHC-D 0? TEST FOR SHOCK
ABSGRBWG iii-WEACTERES'H'CS 0F FOAM-ENePLACE
CUSHQGRENG MATEREALS

mesés for the Degree of M. S.
MECHiGAN STME UREVERSETY
EDWARD ALLEN CHURCH

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ABSTRACT

THE DEVELOPMENT OF A METHOD OF TEST FOR
SHOCK ABSORBING CHARACTERISTICS OF
FOAM-IN-PLACE CUSHIONING MATERIALS

BY

Edward Allen Church

The problem of this thesis was to establish a method for
determining the shock absorbing characteristics of foam—
in—place cushioning materials. This was done by evalua-
ting existing testing procedures used for determining
dynamic cushioning characteristics of other types of
cushioning materials. These materials consisted of
resilient sheet and loose fill materials. Drawing on
some of the adaptable segments of each procedure and dis“
carding the remainder, a new test method was specifically
developed for foam—in-place cushioning materials.

The developed method offers a choice of procedures
which utilize an actual package with a simulated product
held in place by the foam—in—place material. The package
is subjected to either free fall impact shocks or to con-
trolled shock inputs from a shock machine. The simulated
product using an accelerometer mounted within, monitors

the input shock to the simulated product. Thus the

Edward Allen Church

effectiveness of the foam-in-place cushioning material

can be evaluated.

THE DEVELOPMENT OF A METHOD OF TEST FOR
SHOCK ABSORBING CHARACTERISTICS OF

FOAM-IN-PLACE CUSHIONING MATERIALS

BY

Edward Allen Church

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

School of Packaging
1972

ACKNOWLEDGMENTS

For his outstanding direction and helpful guidance
I would like to give my sincere thanks to Mr. Stephen R.
Pierce, my major professor at Michigan State University.

My profound appreciation goes to INSTAPAK CORPORA-
TION for providing not only the equipment and material
but their knowledge and experience in the field of foam—
in-place.

I would also like to thank LANSMONT CORPORATION for
its understanding in allowing me time to conduct my thesis
research.'

I would like to dedicate this thesis to my wife,

Kay, and our son, David.

ii

TABLE OF CONTENTS

Page
ACKNOWLE DGMENTS O O O O O O C O O O O I O O i 1
LIST OF FIGURES O O O O O C O O O O O O O 0 iv
INTRODUCTION . . . . . . . . . . . . . . . 1
Chapter
I. APPLICATION OF EXISTING TEST METHODS . . . . 4
Part I--Platen Dr0p Test Method . . . . . 4
Part II—-Platform Drop Test Method . . . . ll
Part III--Shock Machine Method -
Step Velocity . . . . . . . . . . 19
II. PROPOSED TEST METHOD . . . . . . . . . 24
Proposed Method of Test for Shock Absorbing
Characteristics of Foam-in—Place
Cushioning Materials for Packaging
Applications . . . . . . . . . . 25
III. SUMMARY AND CONCLUSIONS . . . . . . . . 42
APPENDICES o o o o o o o o o o o o o o o 44

A. Foaming System and Safety Precautions . . 45

B. Monitoring System Used to RecOrd Peak
Acceleration and Impact Velocities . . . 49

BIBLIOGRAPHY . . . . . . . . . . . . . . . 51

iii

LIST OF FIGURES

Figure Page
1. Platen Drop Tester . . . . . . . . . . 6
2. Platen Drop Test Specimens . . . . . . . 9
3. Foaming Fixture for Platen Specimens . . . . lO
4. Comparison of Test Results of Three

Tes t Me thOdS O O I O O O O O O O O 12
5. Plywood Outer Box . . . . . . . . . . 15

6. Foaming Fixture for Drop Test and Shock
Machine Specimens . . . . . . . . . . l7

7. Platform DrOp Tester . . . . . . . . . 18
8. Test Results Comparing Plywood and Corrugated
Outer Containers . . . . . . . . . . 22
9. Shock Machine Set—Up . . . . . . . . . 23'
10. Test Block Diagram . . . . . . . . . . 31
ll. Foaming Fixture Diagram . . . . . . . . 34
12. Sample Test Specimen . . . . . . . . . 36
13. Velocity Change Calculation Method . . . . . 38

iv

INTRODUCTION

Polyurethane materials have been known for more
than a quarter of a century. Remarkable advances have
been made with this material in the past few years. One
of the advances in the packaging area is the polyurethane
foam-in-place system. In the past, polyurethane foam has
been used in packaging in sheet form (1.2 pounds per cubic
foot) and has been a good cushioning medium for rela-
tively light loadings (up to .5 p.s.i.). The polyurethane
foam manufactured by the foam-in—place system is a low
density (.5 pounds per cubic foot), semi—rigid material
that can be used over a wider static stress range and is
less costly.

The foam-in—place urethane recently developed has
been used as a dunnage and cushioning material for pack—
aging. With foam—in—place urethane being used as a
cushion material, the problem has arisen as to how to
design the package to protect the item for a specific
acceleration level. Present and potential users of this
material are requesting technical cushioning data from
the suppliers in the form of peak acceleration level

versus statis stress loading.

The problem explored in this thesis was the
development of a realistic testing procedure for evaluating
the dynamic cushioning characteristics of foam-in-place
polyurethane foam. The approach used was to evaluate
currently existing test procedures used to evaluate other
types of cushioning materials and to determine their
adaptability as a testing procedure for foam-in—place
polyurethane foam. Three existing test methods and varia-
tions of these methods were evaluated.

The test methods were evaluated on the basis of
correlation of data with the performance of the material
in the shipping environment, and repeatability of the test
results. If the test method is designed to reflect the
way the material is used then the data can be used as a
predictive measure for designing optimum cushioning. It
is also as important to be able to reproduce the test
results. When the data is reproducible and indictive of
the behavior of the material in usep'a cushioned package
can be designed with confidence.

Before proceeding with the test methods, the foam-
in-place method will be defined and briefly discussed.

The urethane foam is obtained by dispensing two liquids
through a dispensing device. The liquids are dispensed
into a container. Then the foam begins to expand and
within fifteen seconds expands one hundred times its
liquid volume to an approximate density of 0.5 pounds per

cubic foot. A plastic film is layed over the rising foam

and the product is then centered on the foam and covered
with another sheet of film. More foam is then injected
to fill the container and the container is closed.

The two liquids used to make the foam are crude
M.D.I. isocyanate or diphenyl methane di-isocyanate and
the resin or polyol part of the formulation. The resin
part is made up of many chemical components. Some of
these components are water, 11B type fluorocarbon "blow-
ing agent" and polyhydroxy compounds used in making the
urethane polymer, and minor concentrations of catalysts
and surfactants.

The fabricated foam is an Open fine cell material
from .48 to .55 pounds per cubic foot if it is allowed to
foam free, a compressive strength of normally 2 p.s.i.,
and a thermal conductivity (K—factor) of .26 Btu/hr.

(ftz) .

 

CHAPTER I

APPLICATION OF EXISTING TEST METHODS

The first chapter is a review of three existing
methods currently used for evaluating the dynamic cushion
characteristics of both resilient sheet and loose fill
cushioning materials.

These three test methods and their modifications,
the procedures used and the findings of the tests are each
discussed in the three parts that follow.

The foam—in-place material as well as the foaming
system were supplied by INSTAPAK CORPORATION. The poly“
urethane foam was used for evaluating all of the test
procedures and was not meant to be used to provide any
final data.

A brief discussion of the foaming system is
included in Appendix A. Because the monitoring system
used to record data was identical for all of the test

procedures, it is detailed in Appendix B.

Part I--Platen Drop Test Method
The first existing test method that was evaluated

was the platen test method. This method has been in use

for approximately ten years for the evaluation of resilient
sheet or slab cushioning materials. There are two speci-
fications that cover this method. One is MIL-C-26861B
(USAF) and the other is ASTM 1596-64. The two methods are
basically the same. The sections of the test methods that
were evaluated in relation to the testing of foam-in—place
urethane were the sections relating to the dynamic testing
of cushions to produce peak acceleration versus statis

stress data. Although this method has been found to have

 

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limitations for testing materials other than sheet mater-
ial, it was thought it was worthy of investigation because
of the ease of testing and the acceptance of the method.
This method uses a dynamic cushion tester like the
one shown in Figure l. The machine consists of a base or
anvil, a dropping head platen, guide rods, and an adjust—
able crosshead and release mechanism. The weight of the
dropping platen is adjustable by adding weights. The
anvil or base must weight at least fifty times the maximum
dropping platen weight. The platen is dropped vertically
and guided in a parallel manner to the base of the
machine. Because all machines have a certain amount of
friction present in the system, a certain impact velocity
is specified which is equivalent to.a free fall drop
height. This allows for standardization of impact veIOv
cities between different testing laboratories. The test
specimens are right square prisms with minimum dimensions

of 4" x 4" x 1" thick. Larger test specimens are

 

1.--P1aten Drop Tester.

Figure

recommended. The test specimen is positioned on the base
below the platen. The platen is then drOpped from a pre-
determined drop height onto the cushion. The platen is
dropped on the cushioning material five times with a
minimum of one minute between each drop. The acceleration
time data for each drOp is recorded. The acceleration data
for the final four drops is averaged and that average is
used as the peak acceleration at that static loading. The
static loading is determined by dividing the weight of the
dropping mass by the area of the cushion impaCt surface.
After five to seven static loadings have been
tested a dynamic cushion curve can be drawn. This curve
is graphed as peak acceleration versus static loading.
Once the curve has been drawn, the material can be
classified according to MIL—C~268GlB. According to this
specification, a material can be classified as to the
grade for each of their classes. There are six classes.
The classes are divisions of loading ranges. For example,
class one is the very light loading range (less than 0.08
p.s.i.) and class six is the extremely heavy loading range
(1.5—4.0 p.s.i.). The specification also grades a
cushion. The grades refer to the peak acceleration of
the material at the various loadings. For example, Grade
A is very low peak acceleration (less than 20 g‘s), Grade
D is high peak acceleration (less than 100 g's). The

cushion curve is the final result of the testing.

This method was used to test foam—in-place urethane
in three different ways. The first way was to test it as
a sheet material without "skins" on either side of the
material. The second method of testing was with "skin"
on both top and bottom of the foam. The last method was
to test the material with "skin" in a corrugated tray.
These three types of samples can be seen in Figure 2.

The test specimens for the first method of testing
were 9" x 9" x 4" thick blocks cut from the center of
larger blocks of foam by means of a band saw. The speci—
mens therefore had no "skin" and were not confined in any
way. The data generated using this test and method of
sample preparation indicates that this method is not a
realistic test for the evaluation of foam-innplace. The
cushioning material actually blew apart at .3 p.s.i. and
above. Where in actual use this material is used at much
higher loadings. The findings indicate that confinement
of the foam within a container is a significant factor
in its ability to effectively cushion.

The test specimens for the second method of testing
were 9" x 9" x 4" thick blocks of foam. These samples
were made using a fixture to control a flat surface area
and thickness. This fixture is shown in Figure 3. These
specimens had both skin and polyethylene top and bottom.
The specimens were cut on a band saw from a 10" x 10"
block and therefore had no side skin or confinement when

tested. The test results of this method confirm the

 

 

Figure 2.--P1aten Drop Test Specimens.

 

10

 

Figure 3.--Foaming Fixture for Platen Specimens.

ll

findings of the first method in that the cushion holds up
and performs over a wider loading because the specimens
were more confined by the skin and polyethylene. However,
the lack of cushion confinement on the sides of the cushion
makes this an unrealistic test and lead to an early break-
down of the material. FT;
The test specimens for the third method were
10" x 10" x 4" thick blocks of foam confined in a corru—

gated tray. These specimens were made by foaming directly

 

into a corrugated tray. The impact surface and thickness E!
were controlled by the same fixture as used in the previous
method. A piece of polyethylene film was placed over the
top of the foam as it was expanding. These specimens
therefore had skin and polyethylene on the impacting sur—
face. The results of the tests for this method further
confirms the necessity for confinement during tests. The
data from the three different test methods explored is
shown in Figure 4.

Methods one and two are graphed as only one point
because beyond that p.s.i. loading the test specimens were

destroyed upon impaCt before the completion of the tests.

Part II--Platform Drop Test Method
Drop test methods have been proposed by several
groups and individuals for establishing peak acceleration
versus static stress curves. All of these relate to the
evaluation of loose fill materials. The drop test method

is popular for two distinct reasons. The first reason is

12

 

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13

that it uses a simulated package and therefore tests the
materials as they are used. Secondly, the data from such
tests correlate more with the expected performance of the
materials in packaging applications. Both these points are
important to foam-in—place materials. Other preliminary
data generated by the Air Force and by the foam companies
themselves showed that conventional platen drop test data
did not correlate at all at high static stress loading
with the ability of polyurethane to provide adequate pro«
tection when actually used in packaging applications.
PIRA recently completed a procedure for the
"Determination of the Cushioning Properties of Loose Fill
Material." Their method is a modification of Technical
Report Number 19 of the School of Packaging, Michigan
State University under their Multi-Sponsor Research Pro—
gram. Both these methods essentially called for placing
an instrumented test block in an outer container. The
outer container had been partially filled to a predeter-
mined level. The test block was then placed in the outer
container and the rest of the container filled with
material. A preload would then be placed on the container
to settle the test block to a known depth. This resulted
in a known amount of cushioning material beneath the test
block. Using a vertical platform drop tester this system
can be drOpped from a pre-established height and by vary—
ing.the static stress loads an acceleration curve can be

generated for a given drop height. Their methods differed

14

to some degree primarily in the amount and application of
preload. This is not a problem to any great extent in

the case of foam—in-place, because the foam fills its own
void in the outer container. The pressure on the top will
be the same provided too much foam is not introduced.

The procedure used in this thesis was a combina-
tion of the platen drop test method and the free fall
drop test method. The appartus and dropping method were
taken from the latter while the method of taking the
average of the final four of five drops was taken from the
former.

Due to the difficulty in foaming samples in a
plywood box (it necessitated a polyethylene liner to keep
the foam from adhering to the wood) it was decided to see
if foaming in a corrugated box would produce the same or
near enough results.

The plywood exterior container was made of 3/4"
material. The corrugated box was made of 275 pound test
"C" flute board. The style of the container was that of’
an RSC (Regular Slotted Container).

The method used for foaming the samples for this
test was designed to closely simulate use conditions.

The method consists of using a plywood box with inside
dimensions of 8" x 8" x 18". This box is shown in Figure
5. A piece of polyethylene film is put into the bottom
of the box and the liquid foam is dispensed onto the film

and allowed to expand. A second piece of polyethylene

15

 

Figure 5.-—Plywood Outer Box.

16

film is placed on the expanding foam and a dummy load is
placed four inches from the bottom. This is accomplished
by using the fixture shown in Figure 6. The foam then
expands around the dummy load. A third piece of poly-
ethylene foam is then put over the dummy load and then
more liquid foam is dispensed into the box and allowed to
expand to a thickness of either four or five inches. The
top of the box was constructed such that a pistonelike
platform was suspended below the top. This enabled the
top cushion height to be variable so that the amount of
liquid dispensed for the top was not critical.‘ The dummy
load consisted of two boxes one whose outside dimensions
were 6" x 6" x 6" and the other 6" x 6" x 10". The boxes
were capable of being weighted so as to be able to test
different static loadings.

The method used fOr foaming in the corrugated test
containers was the same as that for the wooden container
with the following exceptions. The polyethylene film was
eliminated on the bottom and the top thickness of the foam
was restricted to four inches.

An L.A.B. Corporation Model 5D-100 Drop Tester was
used and can be seen in Figure 7. It is a one hundred pound
capacity spring loaded arm type package drop tester. The
test container with the test block in place was dropped five
times from a height of twenty-four (24) inches.

The findings of this testing program brings out the

following observations.

 

l7

 

Figure 6.--Foaming Fixture for Drop Test and Shock Machine
Specimens.

 

18

 

Figure 7.--Platform Drop Tester.

19

As concluded in the previously mentioned Technical
Report Number 19 of the Michigan State University School of
Packaging there is no discernible difference in data
generated using either a wooden or corrugated outer con-
tainer. There was no difference in results obtained from
the two different test blocks used. The overall results
indicate repeatable data providing great care is taken to
insure flat drOps.

Part III--Shock Machine Method -
Step VelociEy

Another method for the generation of dynamic
cushion curves that has been receiving a vast amount of
attention is a procedure that utilizes a shock machine.
The shock machine is a device used to yield an equivalent
free fall impact shock. This method simulates the effects
of a free fall drop in a highly accurate and repeatable
manner. The package is fastened rigidly to the table of
a shock test machine which is then subjected to short
duration programmed shock pulses. The package response
to these short pulses is the same as to the nearly instan-
taneous velocity change which the container experiences
during an actual free drop onto a hard surface. The cor-
relation of data from two technical papers bears these
statements out. In an unpublished paper by Mr. Stephen
Pierce of Michigan State University's School of Packaging
staff, the data offers the following conclusions: for all

types of cushioning materials cushioning acceleration points

20

are very close when averaged over the last four drops. Thus
the method of dropping the testing systems (free fall versus
shock machine) does not effect the resultant data.

A second paper concerning the application of a
controlled shock test machine to simulate free fall drops

is Technical Report Number 19 of the Multi-Sponsor Research

nearly

Program at the School of Packaging at Michigan State
University. In this report a method for evaluating dynamic
cushioning characteristics of loose fill cushioning materials
has been proposed. e“

The method utilizes an exterior plywood container
that is filled with the material to be tested. The material
surrounds a test block of variable weight which has acceler-
ometers mounted in it. This assembly is then mounted rigidly
on a shock machine and dropped from a predetermined drop
height that generates shocks equivalent to a twenty-four inch
free fall impact. The testing consists of five drops. The
peak acceleration readings of the second through fifth drop
are averaged. A peak acceleration versus static stress
curve is then drawn from the data. Again because of the
difficulty in foaming in the plywood box the alternative
of using a corrugated exterior container was investigated.
The method of foaming was identical to that used previously .
in the drop test method.

The foam polyurethane was then tested on a

shock test machine. The boxes with the foam and dummy

21

load were fixtured to the shock table. The shock table
was then dropped from a height of 9 1/4 inches. The

9 1/4 inches of machine drop height was equivalent to a
free fall drop height of twenty-four inches. An accelero—
meter was mounted on the dummy block to monitor the
response acceleration time pulses of the block. An
accelerometer was also mounted on the shock machine table
to measure the impact to the package.

The shock machine used was an IMPAC 2424 MARK II
with MRL 5958 plastic programmers manufactured by Monterey
Research Laboratory, Inc. The shock machine test equip-
ment is shown in Figure 9.

Figure 8 represents the findings for the shock
machine test method. The graph and data shows that
results from the two types of containers correlate within

10 percent.

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CHAPTER II

PROPOSED TEST METHOD

Chapter II is a proposed testing procedure for r}
evaluating the shock absorbing characteristics of foam—
in-place cushioning materials.

The proposal is written in American Society for

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Testing and Materials (ASTM) format. This not only is

a familiar format for the packaging engineer, it facili-
tates the adoption of such a proposed method in time to
come.

The method is a fabrication of various procedures
prevously developed and researched in the first chapter
of this thesis. Because this method utilizes actual
packages and the testing is conducted in a realistic
simulation of the in—use environment, the data generated
by them can be used to design protective packages.

The method offers two alternative prOcedures so
that data can be obtained by different testing facilities.
This is done because many engineers wish to generate
information within their own laboratories. However, they

may not have available to them a SOphisticated shock

24

25

machine. Therefore, a second procedure was included using
the free fall drOp test method. It should be pointed out
that by using these testing procedures the results from
different testing facilities and from tests conducted at
different times should be relatively identical. However,
differences .may occur when comparing results obtained
from the two different procedures. The benefits of having
these two alternatives outweighs the slight possible dife
ferences in data. Care should be taken to remember that
the drop test method has more chances for error and the
inputs are not as dependable as that of the shock machine.
Therefore, when discrepancies between the methods occur
the shock machine procedure will generate more reliable
and repeatable data.

Proposed Method of Test for Shock Absorbing

Characteristics of Foam-in-Place

Cushioning Materials for
Packaging_Applications

 

Scope

1. (a) This method of test determines the shock absorbing
' characteristics of foam-in-place package cushion-
ing materials. Two test procedures are presented:
1. Procedure A utilizes a shock test machine
to accurately and repeatably produce the
input acceleration pulses.

2. Procedure B utilizes package drop apparatus.

133‘ A». f. vAtJ

 

'm '
II..- -.I--

Summary

(b)

26

Test levels and tolerances given in this method
represent the correlation of the best information
currently available from research investigation
and experience. If more applicable or accurate
data is or becomes available, it should be

substituted.

of Method

The method consists of using the material to be
tested to cushion a weighted test block inside

a package. The complete container is then sub!
jected to controlled shocks or drops and acceler—
ations transmitted to the test block are measured.
From these data, performance properties of the

cushioning material may be obtained.

Significance

3.

(a)

(b)

(C)

The dynamic data obtained by this method may be
used to determine the cushioning characteristics
of foam-in-place packaging materials so as to
provide adequate and economical protection for
goods during shipment.

This test method closely simulates the configura-
tion of the actual packaged product and interior
packaging material and therefore provides data
which accurately describes performance.

This general test method may also be applied to
other forms of cushioning material; i.e., sheet,

molded, loose fill, etc.

 

Ra "

27

Definitions

 

4.

(a)

(b)

(C)

(d)

(e)

(f)

Foam-in-place Cushioning Materia1—-A semi-rigid,
open cell foam cushioning which, when sprayed
into a shipping container, expands and conforms
to the shape of both the packaged product and
the outer container. 4

Velocity--The rate of change of position of a

_._J- um‘..‘x WI F
r

body in a specified direction with respect to

time, measured in feet per second (meters per

 

second).

Acceleration—-The rate of change of velocity of

a body with respect to time, measured in feet per
second per second (meters per second per second).
g—-Symbol for the acceleration due to the effects
of the earth's gravitational pull. While sOme—
what variable, it is usually considered a constant
value of 386 inches per second per second (980.4
centimeters per second per second) or 32.2 feet
per second per second (9.8 meters per secOnd per
second).

G--Symbol for the dimensionless ratio between an
acceleration in length per time squared units

and the acceleration of gravity in the same units.
Drop Height-—The height of free fall required for
the falling body to attain a measured or given

impact velocity.

n AV!“ .3 link;

  

 

 

28

(g) Velocity Change-~The sum of the impact velocity

and any rebound velocity.

Apparatus

 

5. (a) Test Machine

1.

Procedure A--Shock Test Machine

(i) The machine shall consist of a flat
horizontal test surface (carriage) of
sufficient strength and rigidity to remain
essentially flat and horizontal under the
stresses developed during the tests. The
test surface shall be guided to move only
vertically, without rotation or translation
in other directions.

(ii) The machine shall be configured and
equipped to produce acceleration versus

time shock pulses at the carriage surface

as specified in paragraph 8. (b) (1) (ii).
Shock pulse repreduceability shall be within
1 5%.

(iii) Means shall be provided to arrest the
motion of the carriage after impact to prevent
secondary shock.

Procedure B-—Package Drop Machine

(i) The machine shall consist of a release
mechanism which holds and releases the con—
tainer in such a way as to insure flat—face

impacts.

 

29

(ii) The machine shall permit accurate
control of the drop from specified heights.
(iii) The impact surface shall be rigid and-
level and shall be integral with a mass which
shall be at least fifty times the weight of
the dropping container. Neither the depth F51
nor width of the mass shall be less than A
half the length. The dropping surface,

firmly anchored to the mass, shall be a steel

 

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plate not less than 1/2 inch (1.27 cm) thick.
(b) Instrumentation. Accelerometers, signal condi-
tioners, and data storage apparatus are required
to monitor the acceleration versus time histories
at various points on the test machine and test
specimen. The instrumentation systems shall have
the following properties.
1. Frequency response to be from 0.5 Hz or less
to 2000 Hz or greater.
2. Accuracy of reading to be within i 5% of
the actual value.
3. Cross axis sensitivity less than 5% of full
scale.
(c) Test Block--The test block shall be a rigid
rectangular of not less than six inches (15.2
cm) on a side. It shall include provisions for
firmly mounting ballast weights inside to adjust'

its total weight to the desired value. An.

(d)

(e)

30

accelerometer mounting attachment shall be
provided near the center of gravity of the block.
The block shall be designed and constructed

to be as rigid as possible and to minimize rela—
tive motion of the various components. A sug-
gested configuration is shown in Figure 10. {I
Outer Container—~The outer container shall be a
RSC (Regular Slotted Container) corrugated box

fabricated out of 200 pound test "C" flute.

 

board . L
Conditioning Apparatus—~In those cases where

special atmospheric conditions may be required,

adequate facilities shall be provided for con—

ditioning the test material at prOper humidity

and temperature prior to test.

Sampling

6.

Because the user foams his own cushioning material
it is very important that foaming equipment manua
facturers directions be followed exactly. Great
care should be taken that samples are of good
quality. Such things as correct component tempera-
tures affect the quality of foam produced. Samples
of foam should be run and checked before actual

specimen foaming occurs.

31

Accelerometer

Cable 55’

Ballast
Weights

   

Wood Spacer Accelerometer

Figure 10.--Test Block Diagram.

32

Conditioning

 

7. The test material shall be conditioned by exposure
to standard or other fixed conditions of air temp-
erature, humidity, or other anticipated service
conditions for not less than 24 hours prior to
conduct of the test.* The tests shall be per-
formed in the conditioned environment or immedi-

ately upon removal from that environment.

Preparation of Apparatus

 

PJ‘- '1.. lb.“ '1: m-~-.

 

8. (a) Test Block, Outer Container, and Test Material
1. Add or remove ballast weights from the test

block to achieve the desired cushion material
static stress value. Static stress equals
the block's weight divided by the area of its
bottom surface and is expressed in pounds per
square inch (kilograms per square centimeter).
When weighing test block do not forget to add
in the weight of the accelerometer. Attach
the accelerometer and after step 8.(a)4.
attach accelerometer cable and route so that
it will not be damaged during the test.
Insure that all components of the test block

are rigidly mounted.

 

*The preconditioning of the material can be critiv
cxil due to hysteresis and therefore this effect should be
investigated.

 

33

Spray a layer of the cushioning material in
the bottom of the outer container that will
foam to a depth equal to the thickness to be
tested. Great care should be used to insure
the correct thickness and position of the
test block. The excess foam is allowed to
expand up and around the test block. Figure
11 shows a simple device that can be used to
accurately form thickness desired.

Nestle the test block or an equivalent size
block into the cushioning material as it is
expanding, leaving a material thickness under
the block of the final desired test thickness.
The actual amount of foam necessary must be
determined by experiment. The relative
dimensions of test block and outer container?
shall be such that the clearance on all sides
between the vertical surfaces of the block
and the interior walls of the container is
the same as that of the bottom being tested.
Using the test block without the accelerometer
cable attached, place it in position in the
foamed bottom of the outer container. Place
a piece of polyethylene over the test block.
Foam a second quantity of foam on top of the
test block. As it expands fold over the

excess polyethylene and close the flaps of

 

34

 

 

-—-——-————--r-o

 

7mm/

 

 

4

 

 

 

//77/M4/M/A////V

 

 

 

/V///////ZA////V

 

 

b’r--‘--------

 

 

 

 

 

 

 

 

 

Figure ll.--Foaming Fixture Diagram.

35

the container and hold shut until foam has
completed its expansion. If an excess amount
of foam causes pressure that starts to bulge
the sides of the box release the top and
allow excess foam to emerge out of the box.
This cushion shall be discarded and the step f
repeated. The layer of material above the
block should be equal to the layer beneath

the block. ’ .

 

The top cushion from the container and the E
test block should be removed. Attach the
accelerometer cable and place thetest block
in the outer container. The top cushion is
added and the box securely closed. Again,
taking care not to damage the accelerometer
cable.

If any of the requirements of paragraph 8

are not met, the container and cushioning
material shall be discarded, and the loading
procedure repeated with new material. Adjust—
ments should be made in the test block's
initial position so as to achieve the correct
final position. Figure 12 shows a typical

test specimen assembled and ready for test.

36

 

 

\\\\\\\\\\\\\

Accelerometer
Cable ___ST>

Foam-in-Place
Top Cushion

   

 

 

Test Block

 

 

 

 

Foam-in-Place
Bottom Cushion

<
TZL-—Corrugated Box

 

 
 
  

 

  

7////////////

 

 

 

.V////7/Z////F]/Z//7///f/

K\\\\\\\\\\\.\\

 

 

Figure 12.--Sample Test Specimen.

 

37

(b) Test Machine
1. Procedure A--Shock Test Machine

(i) Calculate the required carriage velocity
change from V = /§§H— where V = required
velocity change in inches per second (centi-
meters per second). G = the acceleration F
of gravity in inches per second per second
(centimeters per second per second).'

h = the desired simulated free-fall drop

 

height. E
(ii) Following the shock machine manufac—
turer's recommendations, adjust the machine
to produce a shock pulse of not greater than
2 milliseconds total duration and having a
velocity change equal to that calculated in
paragraph 8.(b)1.(i) above.* The carriage
acceleration versus time histories shall be
measured by an accelerometer rigidly mounted
on the carriage as close as possible to the
outer container mounting position.

(ii) Take care to insure that the machine
holds and releases the test specimen in such

a way as to produce a flataface impact of the

 

*Velocity change equals the area under the accelera—
ticul versus time pulse. This area may be obtained directly
frxnn an accurate graph or trace of the pulse by use of a
planimeter or equivalent technique. In those cases where
the pulse shape may be described mathematically (i.e. half
Silug, triangle, etc.), the area may be calculated. If it
is required to "fair" or smooth the actual acceleration

 

38

test specimen with the dropping surface.
This shall be verified either before each
test series by monitoring the outputs of

4 accelerometers, one each mounted in the
bottom 4 corners of a wooden container equal
in size to the corrugated outer container. [K
An adequate flat-face drop shall be defined g
as one which produces outputs from the four

accelerometers such that the maximum time

 

lapse between the initial onset of any 2 Le
outputs is less than 10 percent of the average

total pulse durations. If this verification

is performed prior to each test series but

not for each actual test, enough trials must

 

versus time history to obtain the correct mathematical
shape prior to calculation, take care to insure that the
area of the faired pulse is the same as the area of the
actual pulse.

Example: Figure 13 shows a velocity change calculation
method which may be used if the shock pulse
closely approximates a half sine shape.

 

’

jleration actual pulse
cce / ----- faired pulse

IL} time A AV 252 where

AV velocity change
i, ’ A peak acceleration
\ of the faired pulse
time duration of

|<%____ T 9 the faired pulse

If A is measured in G and T in milliseconds, AV = 0.245AT
in./sec., or AV = 0.624AT cm/sec.

 

 

 

'9
II

Procedure

 

9.

(a)

39

be conducted to indicate that the machine
can reliably reproduce the above-defined

flat-drop.

Procedure A--Shock Machine Test

1.

Securely fasten the properly prepared test ET
specimen to the carriage of the shock test I
machine. Attach the input-pulse-monitoring
accelerometer to the carriage as close as

L_

 

possible to the outer container. Properly
connect and make ready the block accelera—
tion and input acceleration measuring channels.
Operate the machine in accordance with the
manufacturer's instructions to produce the
acceleration versus time pulse determined in
paragraph 9. (b)l.(ii). Examine the carriage
acceleration versus time history to verify
that the proper pulse is being obtained.
Record the following data:

(i) Input pulse parameters or an actual trace
or plot of the acceleration versus time curve.
(ii) Peak acceleration recorded by the block
accelerometer.

Repeat paragraphs 9.(a)2. and 9.(a)3. for a
total of 5 trials at the specified test

condition.

(b) Procedure B--Package Drop Machine Fe

1.

40

The maximum number of tests to be conducted
with one sample of the cushioning material

is 5. If more tests are to be run (i.e. at
different drop heights or static loadings),

new material must be used.

Place the properly prepared test specimen on

the machine such that it will be released to

"AB—‘Z‘WTWM ~1' -‘ ‘A

produce a flat-face impact with the dropping

n‘ 137$]-

 

surface. Properly connect and make ready the t-
block acceleration and outer container accel-
eration (if used) measuring channels.

Operate the machine in accordance with the
manufacturer's instructions to produce the
desired free—fall drop. Insure that an
adequate flat-face impact is produced.

Record the following data:

(i) Height of free-fall drOp

(ii) Peak acceleration recorded by the

block accelerometer.

Repeat paragraphs 9.(b)2. and 9.(b)3. for a
total of five trials at the specified test
condition.

The maximum number of tests to be conducted
with one sample of the cushion material is
five. If more tests are to be run (i.e. at
different drop heights or static loadings),

new material must be used.

41

 

Calculations
10. For each series of five trials, make the following
calculations:

(a) The static stress value. Static stress is defined
as the weight of the test block divided by the area
of its bottom surface. r-

(b) The equivalent free-fall drop height (Procedure A).

Report

11. The report shall include the following information:

 

(a) The number of specimens tested, conditioning
parameters, description of material, and date
tested.

(b) The original thickness of the cushion material
layer, immediately prior to start of the test
series.

(c) The static stress value and the dimensions of
the test block's bottom surface.

(d) The equivalent or actual free-fall drop height.

(e) If this test method is used to generate complete
curves of peak transmitted acceleration versus
static stress for a given drop height and cushion
material thickness, the average of the last four
(4) shall be plotted.

(f) Detailed description of any deviations from the

procedure as specified herein.

 

CHAPTER III

SUMMARY AND CONCLUSIONS

wan-11":J

This chapter offers a short summary of the problem

and conclusions.

The problem was one of evolving a workable and

 

applicable method for evaluating the dynamic shock absorbv é,
ing characteristics of foam-in—place cushioning materials.

A proposed method of test is presented in Chapter II that

allows evaluation of the dynamic cushioning characteristics

of foam—in-place materials as they are being used for

product protection in packaging. The method is written

in a format that could be used as an industry standard.

The proposed test method is a combination of
Parts II and III of Chapter I of this thesis. They ful—
filled the objectives of being realistic and repeatable.
PartI, Platen Drop Test, was omitted because it caused
Inaterial failure at very low static stress loadings which
is; contrary to the actual ability of the material to perv
.form1in.the real use environment.

Peak acceleration versus static stress loading

currves can be drawn from this procedure. They will permit

42

 

43

the packaging engineer to scientifically predict the
amount of protection he can expect from an optimal amount
of foam-in-place material.

The method of testing in an actual package with a
monitored test block is adaptable to evaluate all other
presently used cushioning materials. This is yet another F“
step toward the final development of a single testing pro-

cedure for all cushioning materials.

 

APPENDICES

44

 

APPENDIX A

FOAMING SYSTEM AND SAFETY PRECAUTIONS

45

 

FOAMING SYSTEMS AND SAFETY PRECAUTIONS

The system used for foaming samples to be tested
was an INSTAPAK Model 501 supplied by INSTAPAK CORPORATION F:‘
of Danbury, Connecticut. It consisted of the following
pieces:

Temperature control system (base heater
for two canisters)

 

Applicator gun

Gun cables

Two filled chemical canisters

They also supplied a nitrogen regulator and two
nitrogen bottles. The system is assembled by attaching
the applicator gun to the cable or air lines and the
other end to the two canisters. The nitrogen regulator ‘
is attached to a bottle and the pressure line is attached
to the applicator gun. A pressure of 100 p.s.i. is
applied to the system. Then both canisters are placed
on the base heater and raised to a temperature of 1309F.
The applicator gun is then filled with "INSTAPAK gun
solvent" and then the system is ready for operation.

The following safety precautions and health hazards
are reproduced from INSTAPAK CORPORATION's technical data

sheet 72-002 and should be followed.

46

47

INSTAPAK CORPORATION
Technical Data Sheet

Safety Precautions and Health Hazards of Instapak Packaging
System

Introduction

 

As in any mechanicalvchemical industrial system,
all personnel packaging with and servicing the Instapak
Packaging System should be thoroughly trained and know—
ledgeable of the Instapak System. A supervised training
course and reading of the Instapak Instruction Manual
should be minimum requirements.

Nitrogen Supply

The customer is responsible for the supply of
nitrogen which is used as a propellent of the chemicals.
Instapak will supply the nitrogen regulator which attaches
to the nitrogen tank and to which the Instapak air hose
attaches. Nitrogen supplied should be H.P. (high purity)
dry nitrogen. (Do not use water primed nitrogen.) The
nitrogen fitting should be a female, right hand fitting
to properly accept the regulator supplied by Instapak.

 

Instapak supplies a pressure relief valve to pre-
vent excess pressure being allowed to flow into the
chemical tanks. The pressure relief valve should
never be removed from the regulator. Nitrogen size "T"
tanks are normally used and these tanks should be secured
properly to the wall or steel support.

A dangerous situation exists if filled nitrogen
tanks are handled carelessly. If the tank is dropped and
the fitting is jarred loose, the 2000+ lbs. of nitrogen
pressure will act as a dangerous propellent. Extreme
caution should be employed when handling filled nitrogen
tanks.

Handling of Chemicals

 

The Instapak System has been designed to reduce to
an absolute minimum the exposure of the chemicals to the
atmosphere. The Instapak chemicals are completely closed
to the atmosphere during normal operation of the system,
and there is never a situation where raw Component A or
Component B should be exposed to the atmosphere for more
than 60 seconds.

 

 

 

48

Care should be taken at all times to bleed off the
100 p.s.i. nitrogen before removing a manifold from one of
the tanks or removing a foam gun.

If there is a machine malfunction, immediately
bleed and shut off the nitrogen supply. This will stop
the flow of chemicals to the gun.

While changing guns or chemical tanks, it is
advisable to wear rubber gloves.

Handling Component A (Red Container)

 

Direct contact of Component A, isocyanate, with the
skin or eyes should be avoided. If Component A comes in
contact with the skin, it should be rinsed immediately .
with Instapak Gun Solvent and then with soap and water. f
It is possible that isocyanate can irritate the skin and g
it will cause temporary discoloration of the skin.

 

It is strongly advised that rubber or P.C.V. gloves
be worn when changing chemical tanks or foam guns.

The vapors of Instapak Component A do not present
a health hazard. (Refer to "Precautions and Health Hazards
Involved in Operation").

Handling Component B (Blue Container)
Component B is light and sticky and can be washed

away with soap and hot water. Component B should not
irritate the skin.

APPENDIX B

MONITORING SYSTEM USED TO RECORD PEAK

ACCELERATION AND IMPACT VELOCITIES

49

 

MONITORING SYSTEM USED TO RECORD PEAK

ACCELERATION AND IMPACT VELOCITIES

The acceleration measuring equipment consisted of
a Kistler model 818 piezoelectric accelerometer and
coupler. The accelerometer was mounted directly on the
dropping head during the platen drop. Also for the
platen drop the impact velocity of the platen was measured
and calibrated to provide an equivalent 24 inch drop
height. This was accomplished by using a Sanborn linear
velocity transducer. For both the free fall and shock
machine methods the accelerometer was attached to the
base of the test blocks and was protected from the weights
by means of wooden spacers.

In the case of the platen and free fall drOp tests
a Krohn—Hite band-pass filter was used to filter out high
frequency noise. This does not affect the peak accelera—
tion signal because the filter was set with the upper
limit at 1000 cycles per second. This will filter out the
noise of the bearings as the platen free falls.

The peak accelerations were recorded on a Tektronix
model 564B storage oscilloscope triggered by either a
microswitch arm (platen drop and shock machine) or with a

light beam device (free fall drop test).

50

BIBLIOGRAPHY

51

 

BIBLIOGRAPHY

Sperry, C. R. Personal Communication, Instapak Corpora—
tion, July 25, 1972.

. "Military Specification Cushion Material,
Resilient Type, General." MIL—C-26861B United
States Air Force, December 29, 1970.

 

. 1972 Annual Book of ASTM Standards. "Shock
Absorbing Characteristics of Package Cushioning
Materials." ASTM 1596-64, Part 15, Easton,
Maryland, American Society for Testing and
Materials, 1972.

 

 

. "Determination of the Cushioning Properties

of Loose Fill Materials." Testing Procedure

used by PIRA (The Research Association for the
Paper and Board, Printing and Packaging Industries).
Leatherhead, England, 1972.

 

Pierce, S. R. "Drop Test--Step Velocity Comparison."
Unpublished manuscript, Michigan State University
School of Packaging, 1969.

. "Safety Precautions and Health Hazards of
Instapak Packaging System." Instapak Corporation
Technical Data Sheet, No. 72-002, 1972.

 

52

 

   

"‘MATT“