TAPPI T 409 sp-09


Machine Direction of Paper and PaperboardTechnical Association of the Pulp and Paper Industry / 01-Jan-2009 / 4 pages

1.1 This Standard Practice describes several procedures for determining the machine direction of most gradesof paper and paperboard. Most of the procedures embody the principle that fibers tend to be aligned in the machinedirection of the sheet, and this alignment produces observable effects. However, the extent of restraint used in drying canbe very important in determining machine direction.
1.2 Application of the procedures in this Standard Practice to certain grades of paper, such as sheetslaminated to film, creped papers, extensible papers (where it is not unusual for the machine direction tensile to berelatively low and the stretch to be relatively high), and papers reinforced with textile materials, usually result inunreliable determinations. Tearing resistance and folding endurance may be used to determine machine direction forpaper known to have been made on a cylinder machine. Tearing resistance should not be used for paper made on afourdrinier machine, and folding endurance should be used only as specified in Section 7.7.
1.3 During manufacture of paper, cross flows coming from the headbox and the forming section may causepreferential alignment of fibers at an angle to the machine direction. Since the procedures in Section 7.11 are affected byfiber orientation, differences as great as 15° may be expected for sheets of uncertain orientation.

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