| 摘要 |
The present invention relates to a process for producing a sound absorbing hollow body such as an air duct in a conventional twin-sheet vacuum-thermoforming process. To improve the sound absorption characteristics of a hollow body a layer of a sound absorbing material is placed between the two sheets forming the outer shell of the hollow body while being in contact with at least one of the two outer sheets. Surprisingly, even though the inner layer is allowed to be in contact with upper or lower sheet, in the twin-sheet thermoforming process of the present invention only the two outer layers are vacuum-formed while the inner layer remains essentially flat and is sandwiched and welded between the two outer layers only along the perimeter where the moulds have pressed the sheets. |
