Rapidly pass through the crystallization-sensitive zone The melting point of PTFE is 327°C, and the standard sintering temperature ranges from 380°C to 400°C. During temperature reduction, the core requirement is to quickly cross the temperature zone around 310~315°C where the crystallization rate peaks sharply.
Recommended operation methods Immediately after exiting the sintering furnace, implement forced air cooling, compressed air blast cooling, or utilize cooling rollers / water cooling systems to rapidly drop the fabric temperature below 250°C.
Reference cooling rate indicators Subject to product thickness, the general cooling rate shall be no less than 30~50°C/min. For thin-gauge high-temperature cloth (0.08mm~0.25mm), air cooling can achieve a cooling rate above 100~200°C/min, enabling instantaneous passage through the critical crystallization zone.
II. Process Mechanism: How Cooling Rate Impacts Product Performance
Crystallinity determines core product properties Cooling modes directly govern the crystallinity of PTFE, which further dictates key coating characteristics including flexibility, adhesion and non-stick performance.
Performance Comparison Between Fast and Slow Cooling
Cooling Mode
Crystallinity
Coating Performance Behavior
Rapid Cooling (Quenching)
Low (approx. 45~50%)
Soft, excellent toughness, smooth surface, strong adhesion, superior non-stick property, resistant to delamination and cracking
Slow Cooling (Furnace Cooling)
High (over 60~70%)
Relatively rigid, high brittleness, prone to shrinkage and peeling, microcrack generation, shortened service life of non-stick effect
Microstructural Explanation Rapid cooling restrains the growth of large-size spherulites and forms a fine microcrystalline structure. This renders the PTFE film denser and more ductile, while minimizing residual stress between the coating and fiberglass substrate.
III. Key Control Points in Mass Production
Guarantee uniform cooling Cooling air flow or cooling rollers must maintain consistent temperature across the fabric width. Uneven local crystallinity will result in mottled surfaces or wrinkling defects.
Avoid excessive thermal shock For thick high-temperature cloth (0.5mm and above), direct water spraying or immediate contact with ultra-cold rollers may trigger severe deformation caused by mismatched thermal shrinkage between substrate and coating. A preferable workflow is intensive air cooling down to below 250°C before further cooling.
Cooling management for multi-pass sintering For multi-impregnation & multi-sintering processes, moderate fast cooling is acceptable for intermediate sintering cycles. However, the final surface sintering step must adopt rapid cooling to secure optimal surface functional performance.
IV. Core Summary
1. Rapid cooling is mandatory post PTFE cloth sintering to enable molten PTFE to skip the high-temperature crystallization zone quickly.
2. Rapid cooling generates a low-crystallinity microcrystalline structure, which is the key to outstanding flexibility, fold resistance and long-lasting non-stick performance.
3. Strictly regulate cooling uniformity, prevent thermal shock, and standardize cooling schedules for multi-stage sintering to stabilize consistent product quality.
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