Improving Creep Behavior for High-Temperature Processing
Heat treatment is a critical preparatory process for ROHACELL® PMI foam cores when manufacturing sandwich components at elevated temperatures. This specialized conditioning significantly improves the foam’s compressive creep resistance, enabling reliable performance during demanding autoclave and press-molding operations.
When Is Heat Treatment Required?
While basic drying is sufficient for moderate process temperatures above 100°C, special heat treatment is required for process temperatures up to 190°C. The exceptional compressive creep behavior of ROHACELL®—one of its defining characteristics—can be further enhanced through proper heat treatment, allowing processing at temperatures up to 180°C and pressures up to 0.7 MPa.
Heat Treatment Procedure
Heat treatment is best carried out in circulating-air flow ovens and follows a two-step process.
The first step involves drying the foam for a minimum of 4 hours at 135°C using a heating cabinet with air circulation. This removes atmospheric moisture from the material.
Immediately following the drying step, the second phase begins: heat treatment at temperatures between 150°C and 180°C for 48 hours. This extended thermal conditioning fundamentally improves the foam’s resistance to compressive creep under processing conditions.
Important Considerations
Heat treatment can cause small changes in volume and surface area of ROHACELL® sheets. For this reason, net-shaped cores must be machined after the heat treatment process, not before. Any forming processes should also be carried out only after heat treatment is complete.
It is important to note that heat treatment of already-processed components cannot be repeated, as this causes dimensional changes that may affect tolerances. Plan your manufacturing sequence accordingly.
Post-Treatment Handling and Out-Time
Directly after heat treatment, sheets must be protected from atmospheric moisture by storing them in diffusion-proof aluminum bags. After removal from these bags, the time available for processing (out-time) is limited but cumulative—material can be returned to protective storage when not in use.
If the allowed processing time is exceeded, drying can be repeated for unprocessed sheets. However, for milled components, this is only possible to a limited extent due to potential dimensional changes.
Technical Expertise from CHEM-CRAFT
Understanding the correct heat treatment parameters for your specific ROHACELL® grade and application is essential for achieving optimal results. CHEM-CRAFT’s team of composite specialists provides expert guidance on thermal conditioning for all our ROHACELL® grades, including IG-F, HF, RIMA, WF, SL, and XT variants.
Contact us for detailed heat treatment specifications tailored to your processing requirements.