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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 Rifeng PMI foam™ sheets. Forming processes should therefore be carried out only after heat treatment.
 
For processing (temperature up to 180°C), a heat treating process prior to processing Rifeng PMI foam is required, which can greatly improves its compression creep resistance.


First:  Drying for at minimum 4hrs at 135°C by using a heating cabinet with air circulation.
Second:  immediately after step 1, heat treating at 48hrs among 150°C to 180°C.


The net-shaped cores must be machined after the heat treating processing, because of the damages on core’s surface (temperature up to 190°C) and changes in dimension during drying.
 
Time Window For Further Processing 

Directly after heat treatment, the sheets must be protected from atmospheric moisture by diffusion-proof aluminum bags. 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.

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 of processed components cannot be repeated because it causes small changes in volume and surface area.


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