Extrusion Molding Process for Straight-through TWC Substrates
A brief introduction to the extrusion process for TWC straight-through substrates.
Extrusion Molding Process for Straight-through TWC Substrates
The TWC flow-through substrate is manufactured via an extrusion process, comprising four key stages: formulation, extrusion, drying, and sintering.
Raw Material Formulation
Cordierite serves as the primary material; the raw material ratio is as follows:
Component | Function | Proportion |
Kaolin | Provides SiO₂ and Al₂O₃ | 40%-50% |
Talc | Provides MgO | 30%-40% |
Alumina | Adjusts Al₂O₃ content | 10%-20% |
Binder | Improves plasticity | 3%-8% |
Pore-forming agent | Adjusts porosity | 5%-10% |
Mixing and Pugging
Powder + Water + Binder → Kneading (15–30 min) → Vacuum Pugging (-0.09 MPa, 2–4 passes) → Homogeneous, plastic clay body. Removing air bubbles during pugging is crucial for preventing extrusion defects.
Extrusion Molding
The clay body is extruded through a die to form a honeycomb green body with uniform channels:
Die: Core precision determines channel dimensions (tolerance ±0.05 mm)
Extrusion speed: 0.5–2 m/min
Channel specifications: 400–600 cpsi; wall thickness 2–4 mil (0.05–0.10 mm)
Shape: Primarily cylindrical; diameter 76–144 mm
Drying
Moisture content of green body: 15%–20% → Dried to 1%–2%
Method | Temperature | Time |
Microwave drying | Microwave heating | 5–20 minutes |
Hot-air drying | 80–120°C | 4–12 hours |
A combined microwave and hot-air process is commonly used in industry: rapid dehydration via microwave followed by gradual drying using hot air.
Sintering
The dried green body undergoes high-temperature sintering in a tunnel kiln:
Heating rate: Room temperature to 600°C (1–3°C/min, for binder burnout); 600–1200°C (3–5°C/min)
Maximum temperature: 1350–1420°C, with a holding time of 1–3 hours
Key specifications: Cordierite phase content ≥95%; coefficient of thermal expansion ≤1.5 × 10⁻⁶/°C
Post-processing
End-face grinding → High-pressure air purging → Inspection of cell density, wall thickness, compressive strength, and coefficient of thermal expansion
Summary
The extrusion process for TWC substrates can be summarized as follows: cordierite formulation → mixing and kneading → mold extrusion → microwave/hot-air drying → sintering at 1350–1420°C → post-processing. Mold precision determines channel dimensions, while sintering determines the cordierite phase content and the low coefficient of thermal expansion. This is a mature process suitable for continuous production and serves as the mainstream manufacturing route for TWC substrates.