PAPER CHEMISTRY, APPLETON, WISCONSIN IPC TECHNICAL PAPER SERIES NUMBER 163 W. J. WHITSITT OCTOBER, 1985

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1 163 THE INSTITUTE OF PAPER CHEMISTRY, APPLETON, WISCONSIN O E G? o IPC TECHNICAL PAPER SERIES NUMBER 163 O4 o= o COMPRESSIVE STRENGTH RELATIONSHIPS AND FACTORS, C) t C= c. Md Qy W. J. WHITSITT OCTOBER, 1985

2 COMPRESSIVE STRENGTH RELATIONSHIPS AND FACTORS 1 W. J. Whitsitt 2 ABSTRACT Reltionships between compressive strength tests nd the elstic properties of continerbord nd combined bord re discussed. It is shown tht the elstic stiffnesses of continerbord correlte well with short spn compressive strength tests. They lso correlte well with combined bord edgewise compression. In other work results show tht ring crush nd short spn compressive strength tests re generlly well relted; however, such reltionships will not hold under ll ppermking conditions. In one exmple where wet pressing ws vried, the short spn compressive strength results on medium properly predicted increses in combined bord compressive strength; however, the ring crush results exhibited mximum t intermedite densities nd hence, filed to properly predict the observed increses in combined bord ECT. New developments in combined bord edgewise compression testing include specil cutters for specimen preprtion nd test fixtures. They offer promise of reducing test time nd test vribility. INTRODUCTION During their service life corrugted continers re often subjected to high compressive lods. Therefore, compressive strength is n importnt end-use requirement for corrugted boxes. McKee, et l. (1963) showed tht the top lod compressive strength of box is primrily dependent on two properties of the combined bord. They re edgewise compressive strength (ECT) nd flexurl stiffness. Their work revels tht ECT is the more importnt property. 1Extended bstrct of pper presented t the Compression Symposium [Forest Products Lbortory, Mdison, Wis., October 1-3, 1985]. 2 Willim J. Whitsitt is Assistnt Professor, Continer Group Leder t The Institute of Pper Chemistry, Appleton, WI. ECT is dependent on the compressive properties of the components nd on the conversion nd finishing opertions. Thus both continerbord nd mnufcturing qulity re fctors in chieving dequte ECT. Becuse of the emphsis on compressive strength new compressive test methods for evluting combined bord nd continerbord hve been nd re being, developed. Simpler ECT test methods for routine control purposes re being considered. Short spn compressive tests such s tht developed by the Swedish Forest Products Lbortory (STFI compression tests) re coming into wider use to test linerbord nd medium (Cvlin nd Fellers, 1975). Recently, we hve shown tht the compressive strength of pperbord is relted to the elstic stiffnesses becuse the fibrous elements within the sheet become unstble nd buckle (Hbeger nd Whitsitt, 1983). These stiffnesses cn be conveniently mesured using nondestructive ultrsonic techniques (Mnn, et l., 198). Becuse of their nondestructive nture, ultrsonic techniques cn be used on the pper mchine for mesurement nd control purposes (Bum nd Hbeger, 198). The purpose of this pper is to briefly review progress in these res. The results discussed were obtined t the Institute in reserch sponsored by the Fourdrinier Krft Bord Group of the Americn Pper Institute. Their support is grtefully cknowledged. RING CRUSH AND STFI COMPRESSION TESTS Ring crush is common wy to mesure the compressive strength of continerbord. However, the STFI short spn compression test is coming into wider use. The STFI compression test is simple, ccurte nd ppers to hve mny dvntges. Ring crush is more complex test thn the short spn type test becuse of its cylindricl 1

3 r geometry. There re lso differences in mode of filure. In ring crush tests on lightweight mterils filure occurs by buckling; on hevy weight mterils filure occurs t the loded edges which re wekened by cutting s the specimens re prepred. 4C 33 STFI *.234 RC..148 r,.98 If we keep these fctors in mind, ring crush nd short spn STFI compression test results cn then be correlted, prticulrly over rnge of bord weights. Figures 1 nd 2 illustrte such reltionships for lightweight (26- nd 33-lb linerbords) nd hevyweight (42- nd 69-lb linerbords), respectively. The reltionship for medium is similr to tht for the lightweight linerbords s would be expected. For mny purposes such reltionships cn be useful. However, becuse of the differences between the tests such reltionships will not hold under ll ppermking conditions. For exmple, when medium is wet pressed to vrying degrees, figure 3 shows tht CD ring crush exhibits mximum, wheres the STFI compression test results increse stedily over the density rnge. The ECT results chieved with these mediums incresed in the sme wy s the STFI compressive test results (fig. 4). Thus the short spn STFI results were more indictive of the fluted performnce of the medium thn ring crush. Seth (1984) hs lso noted tht ring crush results on lighter weight sheets pss through mximum s density increses..i II 3 2C mo / / 4:2b imr I ~/ 69 o _ Io CD RING CRUSH, lb/6;n Figure 2.--CD STFI vs. CD ring crush weight liners. 35i 31 z b MEOIUM 2 for hevier RIG CRUSHTF STFI.ISORC u Is 1.'^_----^ G CRUSH 2 I MEDIUM DENSITY, kg/ms.e ; 16 _ /' / / ;/o Figure 3.--CD STFI nd ring crush show different trends with incresing medium density. 7i 421b Liners 41b Medium 1 * flb Itoe * $32lb o CD RING CRUSH, lb/6i 1 V6 c6o Figure 1.--CD STFI vs. CD ring crush for lightweight liners. 9- u we Ring crush nd short spn STFI compression test results exhibit significntly different MD/CD rtios. This indictes the tests re ffected differently by such ppermking fctors s fiber orienttion nd wet strin. These differences re believed to be due to the circulr configurtion nd buckling modes of filure ssocited with the ring test. S5< MEDIUM DENSITY, kg/m Figure 4.--Wet pressing medium to higher densities increses the ECT of combined bord. 2

4 For present purposes we hve relted ECT to short spn compressive strength tests on the liner nd medium. Figure 6 shows tht ECT results re well correlted to the STFI strengths of the components for bords mde with wide rnge of component bsis weights. The overll correltion coefficient is high s would be expected from the bsis weight rnge; however, the within grde correltions were lso sttisticlly significnt nd reltively fvorble. In generl, it ppers tht short spn STFI compression test results re quite well relted to ECT. Similr results hve been reported by Seth (1985). As we mentioned erlier compressive strength is dependent on the elstic stiffnesses of linerbord nd medium. Figure 7 shows tht ECT is lso well relted to the elstic stiffnesses of the components. Thus, nondestructive techniques for mesuring the elstic properties cn be used to chrcterize the compressive strength nd other physicl properties of pperbord. LITERATURE CITED Cvlin, S. nd C. Fellers Svensk Ppperstidn 9:329. Bum, G. A. nd Hbeger, C. C Tppi 63(7): 63. Johnson, M. W., Jr., T. J. Urbnik nd W. C. Denniston USDA Forest Service Reserch Pper, FPL 348. Forest Products Lb, Mdison, WI. Koning, J. W., Jr Tppi 58(12):15. Mnn, R. W., G. A. Bum, nd C. C. Hbeger Tppi 63(2):163. McKee, R. C., J. W. Gnder, nd J. W. Wchut Pperbord Pckging 48, no. 8:149. Seth, R. S Tppi 67(2):114. Seth, R. S Tppi 68(3):98. O 61 / oo o Sprgue, C. H. nd W. J. Whitsitt Tppi 65(12):14. Urbnik, T. J USDA Forest Service Reserch Pper, FPL 41, Forest Products Lbortory, Mdison, WI. 4E o o 39-2 UU y STFI, (2L * DM), lb/in 1 Figure 6.--Reltion between STFI nd combintions. ECT for liner LIRl WITH 211t MEDIU / o/ 57 U A8 o O o //,, O.t 39 /o I W. E. 1/ 7 2 i4 6 ir '1 U FNS. OU INU I STIFFNESS. 2L OM. kn/i Figure 7.--Reltion between ECT nd elstic stiffnesses for liner combintions. 4 I

5 IPC TECH. Pper Series #163 Compressive Strength Reltionships nd Fctors IPC TECH, Pper Series.#163 Compressive Strength Reltiondhspsfnd Fctor s. -n GEORGIA-PACIFIC CORPORATION ATLANTA, GEORGIA -_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~