Batelka, Joseph J.

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Institute of Paper Science and TechnologyAtlanta, GeorgiaIPST TECHNICAL PAPER SERIESNUMBER 391ITEM 222 AND RULE 41 EDGE CRUSH TEST COMPLIANCEJ.J. BATELKAAUGUST, 19911ITEM 222 AND RULE 41 EDGE CRUSH TEST COMPLIANCEJoseph J. BatelkaPrincipal Associate ScientistInstitute of Paper Science and TechnologyAtlanta, GeorgiaEXECUTIVE SUMMARYRecently approved changes in Item 222 and Rule 41 allow boxmakersto produce and certify corrugated paperboard packaging against EdgeCrust Test specifications. These changes will require boxmakers andbox users to understand the issues involved in achieving Item/Rulecompliance in a cost-efficient manner.Statistical equations are presented which allow the ECT complianceprobability to be calculated for a specific box lot from theaverage ECT and the ECT standard deviation. The relationships showthat the average ECT can be reduced by reducing the standarddeviation. At relatively low standard deviation levels, the ECTcompliance will be controlled by the 5/6 test and 20/24 retestcriterion. At relatively high standard deviation levels, ECTcompliance will be controlled by the criterion that no single testspecimen ECT shall be more than 10% below the specificationrequirement.The statistical equations will allow boxmakers and box users tocalculate the economic opportunity that may be available throughefforts aimed at minimizing the effect of converting operations onECT. The analysis shows that the effect of converting processes onboth the average ECT and the ECT variability need to be addressedin order to achieve the maximum economic opportunity.KEYWORDSItem 222, Rule 41, Edge Crush Test, Statistical Calculations,Converting Quality.ABSTRACTRecent changes to Item 222 and Rule 41 allow a box user to purchasepackaging certified to be in compliance with Edge Crush Test (ECT)specifications. Statistical relationships are presented that can beused by a boxmaker to determine the probability of achieving ECTcompliance with a given lot of boxes. The probability of complianceis dependent on the average ECT of the lot of boxes and on thevariability of individual ECT test values within the lot of boxes.At high variance levels, compliance will be controlled by the2specification that allows no ECT test value to be more than 10%below the minimum ECT for the grade. At lower variability levels,compliance will be controlled by the 5/6 test and 20/24 retestcriterion for the specification. Box plant quality control programsaimed at optimizing the ECT compliance capability of the plant needto address the effect of converting operations on both the averageECT and the variability of ECT within a box lot.INTRODUCTIONSignificant changes in Item 222 and Rule 41 were recently approvedafter a 15-year effort. One major change that was made allows acorrugated box user an option as to the specificationcharacteristic that must be met in order to conform with the Box-maker Certification stamp. A box may now be certified to be incompliance with the minimum combined weight of facings and minimumcombined board Mullen, which is unchanged from the requirementsadopted in the 1940s, or the box may now be certified to be incompliance with the minimum ECT. Both are equally acceptable bytruck and rail common carriers.This paper deals with mathematical calculations that can be used bya boxmaker to quantify the level of ECT performance that isrequired in order to achieve Item/Rule ECT compliance. It alsoaddresses the expected quantitative effect of quality controlprocedures aimed at minimizing the variability of ECT in the boxplant converting process. Such reductions in ECT variability andtherefore the average strength levels needed may offer economicopportunities in packaging costs.ITEM 222/RULE 41 ECT COMPLIANCE REQUIREMENTSThe test compliance protocol for Item/Rule ECT compliance has twomajor criteria that must be met. First, six test specimens aresampled from a given lot of boxes and tested for ECT. If no morethan one of the test specimen ECT values is below the minimumspecification value for the grade, the lot of boxes is incompliance with this Item/Rule ECT requirement. If two or more ofthe test values are below the minimum specification value required,a retest consisting of 24 new test specimens is allowed. No morethan four of the retest specimen values can be below the minimumspecification value in order for the lot of boxes to be incompliance. This test criterion is identical to that required todetermine compliance with the Mullen specification of theItem/Rule.The second criterion for ECT compliance requires that none of thespecimen test levels be more than 10% below the minimumspecification value. This requirement is specific to the ECTcertification and does not apply to the Mullen specification.3A box lot must meet both criteria to be in ECT compliance with theItem/Rule. If any one of the 24 valid retest values is more than10% below the table minimum ECT specification required by theItem/Rule, that box lot is not in compliance, and there is nofurther recourse allowed under the Item/Rule. These ECTspecification requirements for the Item/Rule are summarized bygrade in Table I.STATISTICAL METHODSBinomial probability statistics are an accepted method foranalyzing the compliance probability of this type of specificationprotocol (1), (2). The general binomial probability relationshipsare shown in Figure 1.Figure 2 shows the equations as they apply to the Item/Rule ECTcompliance calculations. The total probability of passing the 5/6test protocol is the sum of the probabilities of having all sixtest values at or above the minimum specification requirement plusthe probability of having five of the six at or above the minimumspecification. Similarly, the total compliance probability for theretest is the sum of the probabilities of having 24, 23, 22, 21,and 20 specimen test values at or above the minimum specification.It should be kept in mind that the population probability value,Po, must be the same in both the 5/6 and 20/24 equations for agiven box lot since it represents the distribution probability ofthe ECT strength in that lot of boxes. The probability equationsare shown in Figure 3 where the compliance probability is plottedagainst the population probability. The plot shows that the 5/6 and20/24 compliance definitions yield different probability curves.The two curves cross at a compliance probability of 0.85. Belowthis compliance probability, the 5/6 definition requires a lowerpopulation probability, and above this compliance probability, the20/24 protocol requires a lower population probability. Thepopulation probability for the combined test + retest criterionalways requires a population probability that is equal to or lessthan that of either compliance definition by itself.The second criterion of ECT compliance, which states that no testvalue shall be less than 10% below the specified table value, canalso be handled using the binomial statistics equations. Theappropriate equations for this second criterion are also shown inFigure 2. The calculations for both criteria one and two must beperformed to determine which criterion is controlling in terms ofcompliance. In general, criterion one will be controlling at lowerECT variability levels, and criterion two will be controlling athigher ECT variability levels.The corresponding population/compliance probability values for thevarious compliance criteria are given in Table II to serve as anease of use reference for the reader.4As shown by these equations, the compliance probability isdetermined by the box lot average ECT and the ECT standarddeviation once the compliance protocol (5/6 test, 20/24 retest, novalue more than 10% below) has been set. Therefore, for a definedcompliance probability, the box lot average ECT required decreasesas the ECT standard deviation decreases and increases as the ECTstandard deviation increases. This relationship between average andstandard deviation is the mechanism that can provide a box plantoperation with an economic opportunity through quality controltechniques to minimize the ECT variability. This opportunity is inaddition to the opportunity available by reducing the loss inaverage ECT in the box plant converting operation. The sensitivityof this relationship is discussed quantitatively in the followingsection.APPLICATION EXAMPLEThe 32 lb/in. ECT singlewall grade from Table I is used as anexample for applying the statistical analysis methods and fordemonstrating the sensitivity of the average ECT to the ECTstandard deviation. The compliance criterion one for this grade is32.0 lb/in. ECT, and the compliance criterion two, 10% below, is28.8 lb/in. ECT. Based on the probabilities given in Table II, apopulation probability of 0.950 is required to achieve a 1.000compliance probability for the test + retest criterion. A normaldistribution table from any statistical reference shows that a0.950 probability is equal to the lot average ECT plus 1.645 timesthe ECT standard deviation. Similarly, a population probability of0.997 is required to achieve a compliance probability of 0.999based on the second compliance criterion (no more than 10% belowthe table ECT value). A 0.997 population probability is equal tothe population ECT average plus 2.75 times the ECT standarddeviation.The box lot average ECT required to achieve the 1.000 and 0.999probabilities defined above will depend on the ECT standarddeviation. The relationship is shown in Figure 4. The lot averageECT required increases as the standard deviation increases, and thelowest ECT test value expected decreases as the standard deviationincreases. The ECT specification values which appear in theItem/Rule were generated using test data from 1989 corrugatedpackaging. The reported average industry ECT standard deviationfrom this study was 2.63 and is shown in Figure 4. The minimum testvalue line crosses the Item/Rule absolute minimum ECT of 28.8 atslightly above the 2.63 standard deviation. This indicates that theItem/Rule specification for this grade was set with an equalbalance between the two compliance criteria based on the averageindustry performance. For this grade, criterion two will become the5controlling specification if a box plant has an ECT variationhigher than the industry average, and criterion one will be thecontrolling specification for a box plant with an ECT standarddeviation equal to or lower than the industry average.The lot average ECT required is shown plotted against the ECTstandard deviation in Figure 5. The break point in the linerepresents the point at which the average ECT required for thedefined compliance probability changes from being governed by the5/6 + 20/24 criterion to being governed by the no more than 10%below criterion. The lowest lot average ECT to achieve the 100%compliance probability is 36.6 lb/in. at a standard deviation of2.63. A one-third reduction in the standard deviation reduces thelot average ECT required to 34.9 lb/in. A one-third increase in thestandard deviation increases the lot average ECT required to 41.6lb/in. Such differences in the average ECT level required may haveimportant economic implications.BOX PLANT QUALITY CONTROL IMPLICATIONSA great deal of attention is being given to box plant qualityissues that can impact on the ability of a converter to comply withthe ECT specification of the Item/Rule in the most cost-efficientmanner. Many of the efforts have concentrated on the effect ofconverting operations on the average ECT levels achieved. While theECT average is an important factor, the statistical analysisreported here strongly suggests that these quality improvementefforts should also address the effect of converting operations onthe variability of ECT. Quality issues such as crushing and poorbonding may occur in very localized areas of the package. Theiraffect on the average ECT may be relatively minor, but their affecton the ECT variability can be relatively major.This concept of the importance of ECT variability on achieving theItem/Rule ECT compliance also applies to the sample preparation andtesting procedures. As much care needs to be taken in preparing andtesting individual specimens as is taken in controlling the overallcalibration of the test instrument.LITERATURE CITED1. J. J. Batelka, Packaging Technology, "How Proposed Changes inRule 41/222 Will Effect Mulllen Strength," 40 (1980).2. J. J. Batelka, Paperboard Packaging, "A Critic's Birdseye Viewof the Classification Rules," 78 (1979).TABLE IItem 222 and Rule 41 ECT SpecificationsGradeSinglewallMinimum ECT,CriterionOne23262932404455lbs./inchCriterionTwo20.723.426.128.836.039.649.5DoublewallTriplewall42485161718237.843.245.954.963.673.867809011260.372.081.0100.8-Table IICompliance Probabilities for Item 222 and Rule 41 ECT ProtocolCRITERION ONE CRITERION TWOFOR FORFOR FOR TEST FOR FOR TESTFOR 5/6 20/24 PLUS 5/6 20/24 PLUSPOPULATION TEST RETEST RETEST TEST RETEST RETEST1.000 1.000 1.000 1.000 1.000 1.000 1.0000.990 0.999 1.000 1.000 0.941 0.786 0.9870.980 0.994 1.000 1.000 0.886 0.616 0.9560.970 0.988 0.999 1.000 0.833 0.481 0.9130.960 0.978 0.998 1.000 0.783 0.375 0.8640.950 0.967 0.994 1.000 0.735 0.292 0.8120.940 0.954 0.987 0.999 0.690 0.227 0.7600.930 0.939 0.977 0.999 0.647 0.175 0.7090.920 0.923 0.961 0.997 0.606 0.135 0.6590.910 0.905 0.941 0.994 0.568 0.104 0.6130.900 0.886 0.915 0.990 0.531 0.080 0.5690.880 0.844 0.847 0.976 0.464 0.047 0.4890.860 0.800 0.761 0.952 0.405 0.027 0.4210.840 0.753 0.663 0.917 0.351 0.015 0.3610.820 0.704 0.561 0.870 0.304 0.009 0.3100.800 0.655 0.460 0.814 0.262 0.005 0.2660.780 0.606 0.366 0.750 0.225 0.003 0.2270.760 0.558 0.283 0.683 0.193 0.001 0.1940.740 0.510 0.213 0.614 0.164 0.001 0.1650.720 0.464 0.156 0.548 0.139 0.000 0.1390.700 0.420 0.111 0.484 0.118 0.000 0.1880.680 0.378 0.077 0.426 0.099 0.000 0.0990.660 0.338 0.052 0.372 0.083 0.000 0.0830.640 0.301 0.034 0.325 0.069 0.000 0.0690.620 0.266 0.022 0.282 0.057 0.000 0.0570.600 0.233 0.013 0.243 0.047 0.000 0.0470.580 0.203 0.008 0.209 0.038 0.000 0.0380.560 0.176 0.005 0.180 0.031 0.000 0.0310.540 0.152 0.003 0.155 0.025 0.000 0.0250.520 0.129 0.001 0.130 0.020 0.000 0.0200.500 0.109 0.000 0.110 0.016 0.000 0.0160.460 0.076 0.000 0.076 0.009 0.000 0.0090.420 0.051 0.000 0.051 0.005 0.000 0.0050.380 0.032 0.000 0.032 0.003 0.000 0.0030.340 0.020 0.000 0.020 0.002 0.000 0.0020.300 0.011 0.000 0.011 0.001 0.000 0.0010.260 0.006 0.000 0.006 0.000 0.000 0.0000.220 0.003 0.000 0.003 0.000 0.000 0.0000.180 0.001 0.000 0.001 0.000 0.000 0.0000.140 0.000 0.000 0.000 0.000 0.000 0.000FIGURE 1BINOMIAL PROBABILITY EQUATIONSn)! (P 0 ) (0= ECTSPEC + Z(T)X.1 to xiWHERE:n = THE NUMBER OF INDIVIDUAL OBSERVATIONS IN ASINGLE TEST SET.xi = THE NUMBER OF TIMES THAT THE DESIRED RESULT ISOBSERVED IN A SINGLE TEST SET.P = THE PROBABILITY OF THE DESIRED RESULT IN THEACTUAL POPULATION REPRESENTED BY THE TESTSET SAMPLE.PT) THE TOTAL PROBABILITY OF OBSERVING THExi DESIRED RESULT xi TIMES IN A SINGLE TEST SET.ECTMN = THE MINIMUM POPULATION AVERAGE ECT NEEDEDTO ACHIEVE THE COMPLIANCE PROBABILITY P(T)ECTSPEC = THE SPECIFICATION MINIMUM ECT.Z =)  THE NUMBER OF STANDARD DEVIATIONX-1 to 1 UNITS CORRESPONDING TO P(T)x.1 toS.D = THE STANDARD DEVIATION OF ECT WITHIN THEACTUAL POPULATION.(T)xi xi! ( n - xi 1-PP(T)x=1 to iECTMIN=P + P +(T)X1 (T)2(n - xi))(S.D.)(~T) xFIGURE 2ITEM 222/RULE 41 ECT STATISTICAL EQUATIONSFOR CRITERIA ONE, 5/6 TEST.- 5( 6P =6(Po ) 5()5/6FOR CRITERIA ONE, 20/24 RETEST.P o24= 8855(Po) 2 4 36960(Po) 23 + 57960(Po J2- 40480(Po) 2 + 10626(Po)FOR CRITERIA TWO, 5/6 TESTp =p 65/6 0FOR CRITERIA TWO, 20/24 RETEST.P =P2420/24 0FOR COMBINED TEST + RETEST.P =P + ( 1 -P )(PT 5/6 5/6 20/24n o"I v0 0 LO) 0n co In ocCO CO3 C CM-JOF- <>wUc<OWJ wO-LOLOCOz0-J0w(5w0-iX0mZLLJO0z0LT~:DO0I <-01cMF-wC0LU-LorjWt-LOIn -CO0nco0LOI-i 0 _ -- ZLO 0 L)-i0Q WO- ZWWoUJWo -r-LD<)Lt)L)z0-jCo0z-JZzZ-J0L20H0-JC4MC\JcjIHLU jLoDh-zLoOCOI OO.CLCM WCr LLOLUrrCC0LL0LULO10LO)106r00CO

Item 222 and rule 41 Edge crush test compliance

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Item 222 and rule 41 Edge crush test compliance

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