| 摘要 |
The mold(3) has a number of ultrasonic vibrators(4) fitted at set intervals along at least one straight line in the axial direction of the mold to the outer surface of each of the side walls, to produce vibration waves of identical wavelengths in the axial direction. The waves of the axially adjacent vibrators are deviated by 180 deg. from each other, i.e. vibrators are positive (4a, 4c) or negative (4b, 4d). As a result longitudinal vibration waves in the axial direction have idientical wave forms, giving an amplified wave.
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