Reasons for Avoiding Direct Water Cooling of Fluoroplastic (PTFE/FEP/PFA) Core Wires After Extrusion

Why can't the fluoroplastic core wire be directly water-cooled after being extruded? Fluoroplastic (such as PTFE, FEP, PFA, etc.) core wires cannot be directly water-cooled after extrusion, mainly due to the following technical reasons and solutions:

Core Cause Analysis

1. Quenching-Induced Crystalline Defects
Narrow crystallization range (e.g., PTFE: 310-320°C);
Direct water cooling (0-25°C) causes crystallization rate >100°C/s, forming microcracks (<0.5μm);
Test data: Rapid-cooled samples show 15% crystallinity reduction and 30% tensile strength loss.
2. Thermal Stress Cracking Risk
Mismatched CTE (Fluoroplastics: 12×10⁻⁵/°C vs. Copper: 1.7×10⁻⁵/°C);
Interfacial stress >8MPa (exceeds bonding strength) when temperature gradient >150°C/cm.
3. Dielectric Performance Degradation
Rapid cooling disrupts molecular chain orientation;
Dielectric constant fluctuation >10% (IPC standard requires <2%).

Standard Cooling Process

1. Gradient Cooling System
Stage 1: Hot-air slow cooling (250-200°C, 5-8°C/min);
Stage 2: IR-controlled cooling (200-150°C, 10°C/min);
Stage 3: Mist cooling (150-80°C, 15°C/min);
Stage 4: Water cooling (<80°C).
2. Critical Parameters
Crystallization zone (300-260°C) dwell time ≥3min;
Final cooling rate ≤20°C/min (per ASTM D3307).

Equipment Requirements

1. Dedicated Cooling Tower
Hot-air circulation (0.5-1m/s velocity);
IR temperature module (±2°C accuracy);
316 stainless steel nozzles (50-100μm droplet size).
2. Online Monitoring
IR thermography (30Hz scan rate);
Crystallinity analyzer (X-ray diffraction).

Quality Verification

1. Performance Tests
Crystallinity ≥75% (DSC method);
Dielectric strength ≥50kV/mm (IEC 60684-2);
Thermal shrinkage ≤2% (200°C×30min).
2. Microscopic Inspection
SEM: No microcracks (5000X magnification);
FTIR: Intact C-F bonds (1140cm⁻¹ peak);
Case Study: 0.5mm² FEP wire with gradient cooling:
Dielectric loss reduced from 0.0012 to 0.0008;
Lifespan at 200°C extended from 500h to 1500h.
Note: Direct water-cooled products show >50% insulation resistance drop within 72h in 85°C/85%RH testing.