ASTM D643-97 pdf free.Standard Test Method for Folding Endurance of Paper by the Schopper Tester.
The folding endurance test is made on a very smallsection of the paper (15 mm by approximately 1 mm). The test is sensitive to very small changesn tnethaptersts made on the same sheet using these very small test areas.The better the formation,the smaller this variation will be.Therefore,thevariation in individual fold numbers is an indirect indication ofthe uniformity of the formation.
Variability of data from tests made on the same sheet ofpaper has sometimes raised concerns regarding the value of thefolding test. This variability comes in part from the sensitivityof the test to changes in the papermaking process, and in partfrom the very wide range of values that will be encountered forapparently similar papers. For example,low fold endurancepapers may have values as low as two or three folds，whilestrong papers will withstand 5000 or more folds.Other strengthtests might typically vary by an order of magnitude for strongand weak papers, but would not approach the 1000-folddifferences sometimes seen for fold.A process or furnishchange causing a 10 % change in fold might not be detected byanother strength test such as tensile or tear. Folding enduranceis a reliable measure of paper strength,particularly for thegrades mentioned in 4.2; however, differences in the range of10 % in fold numbers may not have practical significance.The fact that a small difference between two foldnumbers is not significant creates a problem as to what shouldbe considered a significant difference. A difference of 30between averages of 20 and 50 would be very significant,buta difference of 30 when the averages are 600 and 630 would bemeaningless. To solve this problem，folding endurance isreported as the average of the logarithms of the individual foldnumbers. For example, the fold numbers of 20 and 50 becomefolding endurances of 1.301 and 1.699 or a difference of 0.398,which would be a significant difference.The fold numbers of600 and 630 would become folding endurances of 2.778 and2.799,or a difference of only 0.021which would not be asignificant difference.ASTM D643 pdf download.