| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent deformation or to keep restorability at column parts and panel walls without deteriorating bulge-preventing functions brought about by self-weight and minute pressure at filling and decompression absorptivity after filling by a method wherein depressed reinforcing beads are formed entirely in the vertical direction respectively at the center of each of the panel walls formed at the barrel part. SOLUTION: Panel walls 7, being eight in number, each in a tracklike shape at its circumference and in a section depressed at its center in the diametral direction, are formed at equal intervals at the periphery of the lower barrel part 4B, and a depressed reinforcing bead 8 is formed entirely in the vertical direction at the center of each of the panel walls 7 while column parts 9 are formed respectively between each of the panel walls 7. The depressed reinforcing beads 8 prevent, when break, buckling or the like is produced at the column parts 9, entirely breaks from being produced at the depressed panel walls 7. Furthermore, annular indented grooves 10 and 11 are formed for reinforcing the lower barrel part 4B. Since the panel walls 7 and the depressed reinforcing beads 8 are respectively in inwardly depressed form, they are excellent in respect of absorption of decompression. The depth of the depressed reinforcing bead 8 is desirable to be 1-3 mm.</p> |
