1、Designation: D 643 97 (Reapproved 2002)An American National StandardStandard Test Method forFolding Endurance of Paper by the Schopper Tester1This standard is issued under the fixed designation D 643; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the use of the Schopper typeof folding apparatus. It is suit
3、able for papers having a thicknessof 0.25 mm (0.010 in.) or less.1.2 The procedure for the M.I.T.-type apparatus is given inTest Method D 2176.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standar
4、d to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 585 Practice for Sampling and Accepting a Single Lot ofPaper, Paperboard, Fiberboard, and Related Product2D 685 Practice for Con
5、ditioning Paper and Paper Productsfor Testing2D 776 Test Method for Determination of Effect of Dry Heaton Properties of Paper and Board2D 1968 Terminology Relating to Paper and Paper Products2D 2176 Test Method for Folding Endurance of Paper by theMIT Tester2D 4714 Test Method for Determination of E
6、ffect of MoistHeat (50 % Relative Humidity and 90C) on Properties ofPaper and Board2E 122 Practice for Calculating Sample Size to Estimate,with a Specified Tolerable Error, the Average for a Char-acteristic of a Lot or Process32.2 ISO Standard:ISO 5626 Paper Determination of Folding Endurance43. Ter
7、minology3.1 DefinitionsDefinitions shall be in accordance withTerminology D 1968 and the Dictionary of Paper.54. Significance and Use4.1 Folding endurance is not a measure of the foldability ofpaper, but a measure of the strength of paper. In many cases, itis a better measure of strength than the co
8、nventional tests fortensile strength, bursting strength, and tearing resistance. Theuniqueness of the folding endurance tests leads to many specialuses for this test method.4.2 Folding endurance is determined by the number of timesthat the paper can be folded before it loses enough tensilestrength t
9、o break under the conditions of the test. It is the onlyone of the four strength tests that uses a repetitive mechanicaltreatment to weaken the sheet. Therefore, it is the only one ofthe strength tests that measures the durability of paper sub-jected to repeated or rough handling. It is an important
10、 test forpaper that will be subjected to continued folding and unfoldingduring use. Examples are maps and printed materials such asmusic, pamphlets, folded prints, and blueprints. It is also animportant test for any paper that will be handled repeatedly orwhich might be subjected to rough treatment
11、when it is beingused.4.3 The ratio between the machine direction and crossdirection folding endurance is a good measure of the fiberorientation in the sheet. For most papers, the machine directiontest will be higher than the cross direction test, and the morethe fibers are oriented in the machine di
12、rection, the greater thedifference will be. If the cross direction is higher than themachine direction, the paper has an unusually large number offibers oriented in the cross direction. This information may alsobe obtained from tests for tensile strength and tearing resis-tance but the folding endur
13、ance test is much more sensitive tothese differences than the other two tests.4.4 Folding endurance is more sensitive to the flexibility inthe paper than the other strength tests. Because flexibility islost with aging, folding endurance is commonly used as anindicator of strength loss in accelerated
14、 aging tests.1This test method is under the jurisdiction of ASTM Committee D06 on Paperand Paper Products and is the direct responsibility of Subcommittee D06.92 on TestMethods.Current edition approved Dec. 10, 1997. Published November 1998. Originallypublished as D 643 41 T. Last previous edition D
15、 643 95.2Annual Book of ASTM Standards, Vol 15.09.3Annual Book of ASTM Standards, Vol 14.02.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.5Available from the Technical Association of the Pulp and Paper Industry, P.O.Box 105113, Atlanta, GA
16、 30348.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.5 The folding endurance test is made on a very smallsection of the paper (15 mm by approximately 1 mm). The testis sensitive to very small changes in the paper, and as a result
17、there will be a significant variation in the tests made on thesame sheet using these very small test areas. The better theformation, the smaller this variation will be. Therefore, thevariation in individual fold numbers is an indirect indication ofthe uniformity of the formation.4.6 Variability of d
18、ata 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 forapparent
19、ly 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 so
20、metimes 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 fo
21、ld numbers may not have practical significance.4.7 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 w
22、hen 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 s
23、ignificant difference. The fold numbers of600 and 630 would become folding endurances of 2.778 and2.799, or a difference of only 0.021, which would not be asignificant difference.NOTE 1To determine the difference that must be exceeded in order toconsider the difference to be significant, follow the
24、same procedure thatwould be used to calculate the precision of any other strength test.However, for other strength tests, the absolute value will usually increaseas the average test value increases and as a result, the repeatability isexpressed as a percentage. Because the folding endurance is expre
25、ssed asthe logarithm of the fold number, the absolute repeatability value mayrepresent all levels of folding endurance. The value will vary dependingupon the variability of the paper being tested, but it should not varybecause of the magnitude of the folding endurance. The repeatabilityshould be abo
26、ut the same for a fold number of 600 as it is for a foldnumber of 60.5. Apparatus5.1 Folding Tester, consisting of the following:5.1.1 Clamping Jaws, two horizontally opposed and mov-able, which hold a specimen 100 mm (4 in.) long undervariable tension during the folding cycle, while a slottedfoldin
27、g blade, sliding back and forth between four creasingrollers, folds the paper at 105 to 125 double folds/min. Theclamps are supported from below on rollers, and while inmotion, are freely suspended between tension springs. Thefolding blade is 0.50 6 0.0125 mm (0.020 6 0.0005 in.) thick,with a vertic
28、al folding slot 0.50 6 0.0125 mm (0.020 6 0.0005in.) wide, the slot extending somewhat above and below thenormal position of the test specimen. The vertical edges of theslot are cylindrical, with radius equal to half the thickness ofthe blade. The four creasing rollers, each 6 mm (approximately0.25
29、in.) in diameter and 18 mm (approximately 0.75 in.) long,are arranged symmetrically about the midposition of thefolding slot, and provided with antifriction or jeweled bearings.5.1.2 Counter, to register the number of double folds and tostop the instrument when the specimen breaks.5.1.3 MotorA means
30、 of imparting approximate harmonicmotion to the reciprocating blade at 115 6 10 double folds/min.5.2 Cutter, to provide test strips, 15.0 6 0.1 mm (0.590 60.004 in.) wide, with clean edges.5.3 Calibration Equipment:5.3.1 A device for applying a tension of 7.60 N (780 gf) onthe spring loaded jaw as s
31、pecified in the calibration instruc-tions.5.3.2 A device for measuring a variable tension on thespring loaded jaw ranging from 9.3 to 10.3 N (950 to 1050 gf)as specified in the calibration instructions.6. Sampling6.1 If the paper is being tested to determine the acceptanceof a lot, obtain a sample i
32、n accordance with Practice D 585.6.2 Where testing is for purposes other than acceptance,Practice E 122 may be used as an alternative for samplingpurposes.7. Test Specimens7.1 From each conditioned sample, cut ten specimens ineach principal direction of the paper, with each specimenhaving a width of
33、 15.0 6 0.1 mm (0.590 6 0.004 in.) and alength of 100 mm (4 in.). Select specimens that are free fromwrinkles or blemishes not inherent in the paper and be sure thatthe area where the folding is to take place does not contain anyportion of a watermark and appears to be of average opacity.7.2 Handle
34、each specimen by an end and do not touch itwith hands in the region in which it is to be folded.8. Adjustment and Calibration8.1 Test the clamps as follows:8.1.1 Insert a specimen in place and alternately apply andrelease the tension a number of times. Then, with tensionreleased, note whether the sp
35、ecimen remains smooth andstraight as originally inserted. Buckling or waviness indicates afaulty clamp which has allowed the specimen to slip.8.1.2 Inspect and correct the supporting rollers for wornsurfaces and for bearing friction. Adjust the rollers so that theydo not bind against the clamps in a
36、ny position. With a feelergage, check the four creasing rollers for parallelism andclearance. Also, make sure that the two edges of the foldingslot are parallel with each other and with the creasing rollers.The distance between the folding blade and the two creasingrollers on each side is required t
37、o be 0.38 6 0.05 mm (0.015 60.002 in.), and the width between the rollers of the spaceoccupied by the unbent specimen should be approximately 0.5D 643 97 (2002)2mm (0.02 in.). As a final test of alignment, fold a specimensomewhat short of failure, and inspect it for uniformity of wearalong the creas
38、e. If the specimen seems weaker at one end ofthe crease than at the other, and the ends of the strip aresatisfactorily clamped, this indicates faulty alignment of therollers or the folding slot and will lead to low folding results.8.1.3 Using a dead-weight load of 780 g, adjust the tensionon the spr
39、ings attached to the clamps so that the tension on thespecimen during a test is 7.60 6 0.1 N (780 6 10 gf) when theclamps are farthest apart (when the specimen is straight andfree). Instructions for making these adjustments are given inX1.3. These adjustments are preferably made in situ, with theaid
40、 of a calibrating device that automatically ensures that thetwo clamps are extended the proper distance. A device formaking this measurement is described in X1.1 and X1.2. Ifsuch a device is not used, the operator should make sure thatthe clamps are extended the same distance and that this is thedis
41、tance that they will be extended when a test specimen is inplace ready for the test to begin.8.1.4 After the minimum tension is properly set, tighten thesmall Allen setscrew on the barrel to lock the 7.60 N setting inplace. For routine calibrations, the maximum tension does notneed to be checked and
42、 the calibration is completed. When newsprings are installed and occasionally during routine calibra-tions, check the maximum tension to determine whether bothjaws are the same.8.1.5 Instructions for measuring the maximum tension aregiven in X1.3.2. If the maximum tension of the two jaws differsby m
43、ore than 0.5 N (50 gf), a new set of matched springsshould be installed. If the variable weight specified in X1.3.2 isnot available, a rough check may be made using the 1000 gweight to check the maximum tension. If both jaws check at1000 gf, there is no need to make further measurements.However, if
44、the maximum tension is not 1000 gf, do not adjustthe minimum tension spring settings previously established.See Note 2.NOTE 2The minimum tension is the most important value and shouldbe set as accurately as possible at 7.60 N (780 gf). The specimen alwaysbreaks at minimum tension because the change
45、in the direction of the foldgives the specimen a shock that breaks it. The specimen never breaks atthe maximum tension because there is no shock at that point, and thegradual increase in tension will not cause it to break. Therefore, the valueof the maximum tension is not important, but the differen
46、ce between themaximum tension of the two jaws is important because a difference inmaximum tension is a definite indication that the springs are not matched.8.1.6 Adjust and calibrate the instrument at least once amonth if it is in continual use, or immediately before a test ifnot used on a regular b
47、asis.9. Conditioning9.1 Prior to cutting test specimens, condition the paper in anatmosphere in accordance with Practice D 685.9.2 As folding endurance is very sensitive to the moisturecontent of the specimen, it is important to strictly observe therequirements for preconditioning from the dry side,
48、 for bothconditioning and conditions during testing.10. Procedure10.1 Lock the vertical slot of the reciprocating blade in itscentral position. Without touching the center of the specimen,place it in the slot and fasten the ends firmly and squarely in thejaws with the surface of the specimens lying
49、wholly within oneplane.10.2 Apply the specified tension and fold the specimen at auniform rate of approximately 115 double folds/min until itbreaks.10.3 Record the number of double folds made beforefracture.11. Report11.1 Reporting Terminology:11.1.1 fold numberthe number of double folds required tocause failure of the test specimen.11.1.2 folding endurancethe logarithm to the base 10 ofthe fold number.11.1.3 Specimens with their length in the machine directionare measuring the strength of the paper in the machinedirection and are reported as machine direction fold numbersand
