| 摘要 |
THE EXTERNAL SHAPE OF A PIPE WALL (1) IS FORMED OF SECTIONALLY RECTANGULAR WALL PORTIONS (2) AND SECTIONALLY CIRCULAR WALL PORTIONS (3) WHICH ARE DISPOSED ALTERNATELY IN AN AXIAL DIRECTION OF THE PIPE, AND THE INTERNAL SHAPE OF THE PIPE WALL (1) IS FORMED INTO A SUBSTANTIAL LINEAR CIRCULAR-CYLINDRICAL SURFACE (4). THE WHOLE OF THE PIPE WALL (1) IS FORMED OF A MATERIAL OF SYNTHETIC RESIN OR RUBBER. (FIGURE.1)
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