| 摘要 |
PURPOSE:To eliminate breakage at corners which generates in the stage of rolling up a filter medium having corrugated sectional shape by providing notched line on at least sloped surface of the inside peripheral side of the filter medium from its external peripheral side toward the internal peripheral side. CONSTITUTION:Bending lines 12 are applied along a sector of a sectorial filter medium 10 by hot-pressing a line cutting knife held at high temp. to a filter medium 10, etc. then the filter medium 10 is bent by a bending device to give the filter medium corrugated sectional shape. Further, crest parts (a)-(e) are formed on the filter medium 10, and plural numbers of notched lines 14 directing from the top of the crest toward the valley are formed at regular intervals on the inside sloped surface of the crest parts (a)-(e). As the result, the rolling of the filter medium 10 can be executed exactly along the notched lines 14, so the rolling is done to obtain polygonal shape exactly similar to the desired shape.
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