Bursting Strength

5/19/2018 Bursting Strength

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BURSTING STRENGTH

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Thickness GSM of the paper gives the strength for the box.

You will notice that paper weight from 100 to 150 GSM has a bursting factor of 14. Paper weighf 180

GSM will have bursting strength of 16 and paper with a weight of 230 GSM will have a bursting factor

of 22.

Introduction

The bursting strength of paper or paperboard is a composite strength

property that is aected by various other properties of the sheet, principally

tensile strength and stretch. Generally, bursting strength depends upon the

kind, proportion, and amount of bers present in the sheet, their method of

preparation, their degree of beating and rening, upon sheet formation, and

the use of additives.

Bursting strength is measured by means of a Mullen tester. The test

specimen, held between annular clamps, is subected to an increasing

pressure by a rubber diaphragm, which is e!panded by hydraulic pressure at

a controlled rate, until the test specimen ruptures. The pressure reading at

the instant of rupture is recorded as the bursting strength. The units of

e!pression are pounds per s"uare inch or #points#. The measurement is

variously termed the #Mullen#, #pop test#, or simply the #burst#. The burst

test for paperboard diers from that of lighter papers in that a heavier

Mullen tester is used with a larger diaphragm opening.

Signifcance

Bursting strength is used widely as a measure of strength in many

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kinds of papers, primarily as an indication of the suitability of certain bers

and the e!tent of beating and rening. $ts main reason for e!istence is that

it is one of the oldest of the strength tests, it is easy to run, it appears to

correlate with some use re"uirements, and everyone has the e"uipment.

%hile interpretation is empirical, the bursting strength serves as a "uick

check on the utility of some papers which do not have an absolute tensile

re"uirement. The bursting strength test also is used for combined

containerboards, both corrugated and solid berboard as a re"uirement of

the &niform 'reight (lassication, )ule *+, for shipping containers. The

bursting strength of the containers is generally controlled by the strength of

the linerboard so this test is critical as a paper mill control test. Burst test

results on a doubleface or doublewall corrugated board are highly

variable and correlate poorly, if at all, with most of the performance values

of the nished containers.

Burst Factor and Burst Index

$n addition to bursting strength, one fre"uently reports the burst factor

and-or the burst inde!. The burst factor is calculated according to

The burst inde! is calculated according to

ote that + k/a 0 + k-m1, where k/a stands for kilopascal and k for

kilonewton. Grammage is the basis weight in units ofgf-m1.

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The Mullen Burst Testers

Two "uite dierent Mullen testers are available commercially and are

both used in the /aper Testing 2aboratory3

4 The Model ( Mullen tester5 this is a comparatively light instrument for

the testing of paper.

4 The Model 6 Mullen tester5 this is a much heavier instrument for the

testing of paperboard.

The light Model ( instrument for testing paper has two gages, one

ranging from 7 to 87 psi, the other from 7 to +17 psi. Never exceed the

range o a gage, because serious damage to the gage may result.

9bviously, this instrument is intended for testing papers of bursting strength

less than +17 psi. The circular specimen area tested has diameter 87.:7 ;

7.7: mm.

The heavy Model 6 tester for paperboard also has two gages, with

ranges 7 177 psi and 7


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diaphragm which is e!panded by hydraulic pressure. 6 ma!imum reading

gauge is included in the hydraulic system. The bursting test value is the

ma!imum gauge pressure re"uired to produce rupture of the specimen. The

observed gauge value includes the hydraulic pressure re"uired to distend

the rubber diaphragm in addition to that re"uired to rupture the specimen.

Tests

Make ten acceptable tests for each sample, ve tests on each side.

Make no tests on areas containing water marks, creases, imperfections, or

visible damage.

!erating Instructions

Model " Mullen Tester or #a!er$oard

4 /lace the handle with the red knob, which operates the clamp, in the

central or vertical position.

4 Turn on the motor switch, which is located at the bottom of the front

side.

4 /lace the sample to be tested over the diaphragm plate.

4 2ower the clamping plate by turning the the handle with the red knob

clockwise to #(29=>#.

4 The rst test on a new sample should always be done with the gauge

of greater range ?7 to , and the valve to the other gauge ?7 to 177 psi@ is (29=>A.

4 Make sure the red ma!imum hand on the gauge you want to use is at

ero5 otherwise, return it gently to ero by manually turning the

knurled metal knob in the center of the gauge counterclockwise.

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4 To burst the sample, proceed as follows. 'ind the operating lever with

the black knob, located at the far right of the instrument. Move the

operating lever to the 2>'T and hold it there, all the while keeping

your eyes on the gauge. $f either the sample bursts or the pressure

indicator needle comes too close to the ma!imum pressure of the

gauge, it is extre%el& i%!ortant that &ou 'uic(l& %ove the

o!erating lever to the RIGHT as ar as it )ill go and release it

i%%ediatel&* ailure to %ove the o!erating lever to the right

i%%ediatel& the sa%!le $ursts %a& result in a ru!tured

dia!hrag%. The instrument will automatically return to the starting

position.

4 )ecord the bursting pressure indicated by the red ma!imum hand of

the gauge used in the test.

4 )eturn the ma!imum hand of the gauge gently to ero by manually

turning the knurled metal knob in the center of the gauge

counterclockwise.

4 9pen the clamp by turning the handle with the red knob

counterclockwise to the #9/># position.

4 )emove the old sample. The instrument is now ready for the ne!t

test. The motor is kept running continuously5 do not turn it o

between tests.

Model + Mullen Tester or #a!er

4 Make sure that the valve to the pressuried air supply line is 9/>.

This valve is located to the left and above the nearest 2orenten C

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%ettre tensile tester.

4 Turn on the motor switch.

4 /ush the brass ring located at the top of the clamp assembly upward

to raise the clamping plate.

4 /lace the sample to be tested over the diaphragm plate.

4 2ower the clamping plate by pushing the brass ring downward.

4 The rst test on a new sample should always be done with the gauge

of greater range ?7 to +17 psi@. Make sure that the valve to this gauge

is 9/>, and the valve to the other gauge ?7 to 87 psi@ is (29=>A.

4 Make sure the red ma!imum hand on the gauge you want to use is at

ero5 otherwise, return it gently to ero by manually turning the

knurled metal knob in the center of the gauge counterclockwise.

4 To burst the sample, proceed as follows. 'ind the operating lever with

the black knob, located at the far right of the instrument. Move the

operating lever to the 2>'T and hold it there, all the while keeping

your eyes on the gauge. $f either the sample bursts or the pressure

indicator needle comes too close to the ma!imum pressure of the

gauge, it is extre%el& i%!ortant that &ou 'uic(l& %ove the

o!erating lever to the RIGHT as ar as it )ill go and release it

i%%ediatel&* ailure to %ove the o!erating lever to the right

i%%ediatel& the sa%!le $ursts %a& result in a ru!tured

dia!hrag%. The instrument will automatically return to the starting

position.

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4 )ecord the bursting pressure indicated by the red ma!imum hand of

the gauge used in the test.

4 /ush the brass r ing upward and remove the old sample. The

instrument is ready for the ne!t test. The motor is kept running

continuously5 do not turn it o between tests.

Re!ort

)eport the mean bursting strength in points ?lb-in1@ as the arithmetical

mean of all ten tests on a sample, the burst factor, and the burst inde!. 6lso

report D:E condence intervals.

Reerences

6=TM A FF*

T6//$ T *78, #Bursting =trength of /aper#

T6//$ T


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,Mechanical #ro!erties

Bursting Strength

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