| 摘要 |
<p>PROBLEM TO BE SOLVED: To judge the presence of a cavity in the heat insulating layer of a plastic conduit while dispensing with the work by a skilled person, allowing the continuous carrying of an intermediate product, and preventing the deterioration of the manufacturing efficiency of the plastic conduit. SOLUTION: The outer surface of the intermediate product of the plastic conduit is automatically hammered, the sound pressure of the generated sound is detected, and the sound pressure data are frequency-analyzed, thereby, it is judged whether a cavity is present in the intermediate product or not. The carrying speed of the intermediate product is detected, the time when a prescribed part of the intermediate product reaches a printing position is calculated, and a prescribed mark is printed on the outer surface of the intermediate product when the presence of the cavity in the intermediate product is judged.</p> |
