ABS (Acrylonitrile Butadiene Styrene) coils are widely used in automotive interiors, refrigeration liners, luggage shells, and general thermoforming applications due to their excellent impact resistance, thermal stability, and surface finish. Understanding the extrusion process for ABS coils is critical to achieving consistent thickness, flatness, and mechanical properties. Below is a detailed breakdown of the extrusion process for ABS coil production.
1. Raw Material Preparation
Material Drying: ABS resin is hygroscopic. Before extrusion, pellets must be dried using a dehumidifying dryer at 80–85°C for 2–4 hours to reduce moisture content below 0.05%. Excess moisture leads to surface splay marks, bubbles, and reduced mechanical strength.
Additives: Depending on application, UV stabilizers, flame retardants, or color masterbatches may be dry-blended or metered into the hopper.
2. Extruder System
Screw Design: A single-screw extruder with a three-stage screw (feeding, compression, metering) is commonly used. Length-to-diameter (L/D) ratio of 24:1 to 32:1 is preferred. Compression ratio typically ranges 2.5:1 to 3:1 to ensure uniform melting and shear.
Temperature Profile:
Feeding zone: 180–190°C
Compression zone: 200–210°C
Metering zone: 210–220°C
Adaptor and die head: 210–225°C
Overheating causes degradation (yellowish color and burnt odor); underheating leads to unmelted particles.
3. Die Assembly
T-Die (Flat Die): A coat-hanger or manifold T-die ensures uniform melt flow across the width. Die gap typically adjustable between 0.8–3.0 mm depending on final coil thickness (commonly 0.5–6 mm).
Die Lip Adjustment: Manual or automatic die lip bolts fine-tune thickness profile across the coil width.
4. Calibration & Cooling
Three-Roll Stack (Chill Roll Unit): The melt exits the die vertically downward or horizontally into a vertical or horizontal three-roll stack.
Top roll (polished chrome) – contacts the shiny side, determines surface gloss.
Middle roll (polished or matte) – main cooling and thickness control.
Bottom roll (rubber or steel) – provides contact pressure.
Roll Temperatures:
Roll 1: 70–85°C
Roll 2: 80–95°C
Roll 3: 70–80°C
Proper roll temperatures avoid warping, residual stress, and orange-peel surface defects.
Winding & Edge Trimming: After cooling, edges are trimmed by rotary slitters to remove uneven bead edges, then the continuous ABS coil is wound onto cores with controlled tension.
5. Process Parameters & Control
Melt Pressure: 100–250 bar, monitored by pressure transducers before the die. Sudden fluctuations indicate screen pack clogging or screw speed mismatch.
Line Speed: 1–8 m/min depending on thickness and cooling capacity. Thinner coils run faster.
Screw Speed: 30–80 rpm – must be synchronized with pull roll speed to avoid drawdown or buckling.
6. Quality Checks for ABS Coils
Thickness Tolerance: ±5% across width using online ultrasonic or beta gauge.
Width Shrinkage: ≤1% after 24 hours at 23°C (low residual stress).
Surface Defects: Pinholes, gels, black specs, and die lines are inspected online.
Mechanical Properties: Tensile strength ≥40 MPa, elongation ≥20%, impact strength (Izod) ≥25 kJ/m².
7. Common Defects & Solutions
| Defect | Cause | Solution |
|---|---|---|
| Thick center / thin edge | Die lip misalignment | Adjust die bolts laterally |
| Matte spots | Roll temperature too high or low | Optimize roll cooling profile |
| Gels / black specs | Degraded resin in stagnant zones | Clean die and screw; reduce melt temperature |
| Wavy edges | Uneven cooling or excessive tension | Adjust roll nip pressure & cooling |
8. Advantages of Extruded ABS Coils
Consistent mechanical properties due to controlled cooling and molecular orientation.
High surface quality – direct thermoforming or lamination ready.
Cost-effective for large-volume continuous production.