Jiangsu Aokai New Materials, a professional manufacturer of PTFE high-temperature cloth, shares professional process guidance. Wrinkles generated on PTFE high-temperature cloth (fiberglass fabric coated with PTFE) during sintering are fundamentally caused by uneven thermal shrinkage and inconsistent stress of the substrate, coating and equipment under high temperature. Wrinkle prevention cannot only focus on the sintering furnace alone; systematic control covering the full workflow of raw material preparation, impregnation, drying, sintering and cooling is required.
The key control links and practical solutions are listed as follows:
I. Raw Material Substrate Control: Eliminate Internal Stress at Source
The quality of fiberglass substrate determines the difficulty of subsequent processing. Select fiberglass fabric with low twist and stable structure, featuring minimal skew and uniform edge tightness, which delivers consistent thermal shrinkage when heated.
1. Complete pre-dewaxing and heat setting: The substrate must undergo high-temperature dewaxing and thermal setting to fully eliminate weaving internal stress and stabilize its thermal shrinkage rate. Inadequate treatment in this stage will trigger uncontrollable severe shrinkage and wrinkles once the fabric enters the sintering furnace.
2. Incoming inspection: Inspect fabric flatness with straightedges or fabric inspectors. Cut off or return batches with loose edges, tight edges and bulges.
II. Impregnation & Drying Stage: Achieve Thin & Uniform Coating
Uneven coating thickness leads to inconsistent shrinkage of molten PTFE during sintering, inevitably forming wrinkles.
1. Multiple thin coating passes instead of single heavy coating: Adopt repeated impregnation and drying processes with small, even coating weight per pass to accumulate PTFE resin gradually. Avoid thick single-layer coating that causes inconsistent internal and external drying speeds.
2. Gentle temperature gradient in drying oven: Start with low-temperature zones to volatilize water and auxiliaries slowly, preventing rapid surface skin formation that traps internal stress from undried inner layers.
3. Synchronous active drive rollers in drying section: All guide rollers are motor-driven and synchronized with fabric line speed to avoid longitudinal stretching from passive dragging.
4. Direct inline transfer to sintering furnace after drying to eliminate winding indentations. If intermediate winding is mandatory, fully cool the fabric first and wind with low tension and large roll diameter to avoid permanent creases carried into sintering stage.
III. Sintering Furnace: Precise Matching of Temperature, Airflow and Tension
This is the core control segment for wrinkle suppression.
1. Tension Control: Reserve Adequate Space for Thermal Shrinkage
When PTFE melts above its melting point (~327°C), both substrate and coating produce thermal shrinkage. Excessive tension forcibly stretches the fabric, locking permanent deformation wrinkles after cooling; insufficient tension causes sagging and loose wrinkles.
· Install overfeed rollers at furnace inlet: Feed fabric into the furnace with 1%~3% overfeed to reserve allowance for thermal shrinkage.
· Closed-loop micro-tension control inside furnace: Real-time feedback via tension sensors adjusts motor speed of each section, maintaining only minimal tension required to keep fabric flat across the entire high-temperature zone, with the fabric kept slack without stacking.
2. Temperature Uniformity: Eliminate Transverse Shrinkage Discrepancy
Large transverse temperature deviation inside the furnace creates inconsistent shrinkage between fabric center and edges, the primary cause of longitudinal wavy edges and central bulges.
· Limit transverse temperature tolerance within ±5°C: Adopt multi-zone independent upper/lower temperature control and circulating hot air to form a uniform temperature field.
· Reasonable sintering curve: Adopt a gradient of preheating → high-temperature sintering → slow cooling to enable gradual melting and leveling of PTFE without instantaneous thermal shock.
· Prioritize air-flotation sintering furnaces: Fabric is suspended and conveyed by upward and downward cross-blowing clean hot air without contact rollers, fundamentally eliminating wrinkles induced by mechanical friction and adhesion, the optimal solution for premium high-temperature cloth production.
3. Airflow Control: Prevent Fabric Fluctuation & Stabilize Leveling
Circulating wind speed shall not be excessive, and airflow shall be rectified to avoid violent fabric sway from direct air impact. Alternately arranged upper and lower air nozzles deliver steady uniform airflow to guarantee heat exchange without disturbing fabric surface.
4. Anti-Wrinkle Roller Components for Physical Spreading
Install curved banana spreader rollers or crown spreader rollers at key positions inside the furnace and outlet. The camber of curved rollers applies lateral stretching force from center to edges to effectively eliminate fine longitudinal wrinkles. All carrier rollers shall be calibrated for horizontal and parallel accuracy regularly with error less than 0.1mm/m.
IV. Cooling & Setting Stage: Lock Flat Surface Permanently
Fabric remains thermoplastic upon exiting the sintering furnace; improper cooling will negate all prior processing efforts.
1. Gradual slow cooling: Avoid direct cold air quenching immediately after high-temperature zones. Pass through an insulated slow cooling section to lower the temperature of PTFE coating and substrate gently below melting point for full internal stress release.
2. Maintain spreading and overfeed during cooling: Fabric continues shrinking while cooling, so slight overfeed and spreader rollers are still required until fabric temperature drops below 100°C.
3. Full cooling before final winding: Ensure fabric temperature approaches room temperature without residual heat accumulation, then wind with consistent low tension for uniform flat rolls.
V. Online Monitoring & Timely Adjustment
Assign dedicated staff to inspect fabric surface with strong light at furnace outlet and cooling sections. Fine-tune tension, temperature or line speed immediately once micro-wrinkles are detected. Install non-contact infrared scanning systems to monitor real-time transverse temperature distribution with automatic alarms for out-of-tolerance conditions. Slight permanent wrinkles can be remedied online via hot calender rollers, yet prevention remains the core priority.
Most wrinkle defects can be eliminated by precise control of tension and temperature uniformity. Even air-flotation furnaces may generate wrinkles if process parameters mismatch substrate characteristics, which proves systematic full-process management outweighs single equipment optimization.
If you wish to obtain detailed specifications, application scenarios and customized solutions for our full product portfolio including PTFE high-temperature cloth, PTFE high-temperature adhesive tape, PTFE high-temperature mesh belt, seamless heat press belt, single-sided PTFE fabric, high-temperature resistant conveyor belt and heat-resistant fiberglass cloth, please contact us via the information below:
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