| 摘要 |
A helically wound tube made of at least two sheets of preperforated flat roll paper material. Each sheet is helically wound in edge abutting relation such that one longitudinal edge of the sheet abuts the other longitudinal edge of the sheet to form a ridgeless seam. Some of the perforations of the subsequently wound sheets overlap some of the perforations of the previously wound sheets to form a reinforced cylindrical tube having perforations that permit radial flow through the cylindrical tube.
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