ROHACELL sheets with an integral structure are produced in a press which can be cooled and heated. A cold suitably over sized ROHACELL sheet is placed between heated platens at 320-356of (160 - 180oc) and then the press closed immediately.

The specific molding pressure should be about 30% less than the compressive strength of the particular ROHACELL grade at 68of (20oc) As the heat penetrates into the ROHACELL sheet, the outer cells correspondingly give way and are squeezed flat.

The procedure gives a higher density in this layer. The molding time depends on the desired degree of compression until the thickness stop is reached. The sheet must now be cooled to about 176of (80oc) before it can be taken out of the press. This prevents the flattened cells from recovering their original shape (fig 34). The method also serves for partial compression ol molded articles (fig. 35).

In practice, this procedure is also utilized for sandwich parts with thin skins in order to increase the bending stiffness of the sandwich. Another important fact is that the indentation resistance is considerably improved through the higher density of the edge zones. During hot curing of the adhesives or resins, the outer surface is compressed until the desired thickness stop is reached.

Molding with complex exterior contours

After heating the ROHACELL part to be molded to the forming temperature (338 - 374of (170 - 190oc) depending on material grade). it is placed in a heated mold and brought to the required geometrical form by compression. The molding must be cooled down to about 176of (80oc) before it can be taken out of the mold.

The described method is far more cost-effective than other techniques, because there is no machining to a precise exterior contour.