Drying and Heat Treatment Improves Creep Behavior

The processing method used in the manufacture of a sandwich component determines whether drying or heat treatment should be chosen. In addition to the process pressure (in the autoclave or press), the process temperature is critical for curing of the skins. Drying is recommended for process temperatures above 100°C, depending on the process pressure. Special heat treatment is usually required for process temperatures up to 190°C.

Drying and heat treatment are best carried out in circulating-air flow ovens. The duration of heating depends also on the thickness of the sheets; further information is available at Drying and Heat Treatment. Heat treatment can change the volume and surface area of ROHACELL^® sheets. Forming processes should therefore be carried out only after heat treatment.

Time window for further processing

Directly after heat treatment, the sheets must be protected from atmospheric moisture by diffusion-proof aluminum bags (as specified for example in MIL-PRF-131J). After removal of the sheets from these bags, the time available for processing (out-time) is limited. However, this time window is accumulative provided that the material is returned to the bags when not in use.

Storage condition: 23°C (73.4°F), 50% r.h.
Test condition: 180°C (356°F), 2 hours, 0.7 MPa (100 psi)
Drying: 130°C (266°F), 2 hours
Heat treatment: 190°C (374°F), 48 hours

If the allowed processing time of the sheets is exceeded, drying can be repeated. For processed (milled) components, however, this is possible only to a limited extent because of dimensional changes.

Heat treatment (HT) of processed components cannot be repeated because it causes small changes in volume and surface area.