How Are Cast Polyurethane Rollers Manufactured?
The manufacturing of cast polyurethane rollers involves several precise steps, including prepolymer preparation, casting, curing, and surface processing. Each stage plays a vital role in ensuring the performance and durability of the final product.
1. Prepolymer Preparation Example
Polyester Dehydration: A polyester with a molecular weight of 2000 (hydroxyl value 53–59 mgKOH/g, melting point 40–50°C) is heated and melted in a stainless steel or enamel reactor. Dehydration should occur at 100–140°C under 5 mmHg vacuum for 30–60 minutes until moisture is below 0.05 percent.
Prepolymer Synthesis: The choice of raw materials, ratios, and conditions directly affects product performance. Materials should be selected based on temperature, stress, media contact, and service life requirements. The mixture should be synthesized under dry nitrogen to prevent unwanted reactions and maintained at 80±5°C for 1–2 hours to balance isocyanate content.
Prepolymer Degassing: Degas at 85±5°C and 5 mmHg for 30–60 minutes to remove air bubbles.
2. Casting Process
Casting Equipment: A casting machine is essential for cast polyurethane production. It must ensure accurate mixing ratios, consistent material flow, and bubble-free uniform mixing.
Casting Procedure: The A and B components are preheated in separate tanks. Once they reach the target temperature, they are mixed at high speed and poured into preheated, pretreated molds.
3. Curing and Post-Treatment
Mold Curing: The roller is cured in the mold at 100–120°C for 60–120 minutes.
Post-Curing: After demolding, the roller undergoes post-curing at 90–110°C for 3–10 hours to improve final properties.
Surface Processing: The roller surface may be machined or polished based on end-use requirements.
4. Key Considerations
Mold Design: Molds must be structurally sound and properly sealed to prevent leakage or air entry.
Temperature Consistency: Mold, core, and material temperatures must be balanced to avoid surface defects.
Adhesion Cleanliness: The bonding surface of the core should not be contaminated by mold residue.
Curing Strength: Rollers should not be moved until fully cured to avoid cracking.
5. Mold and Core Heating Systems
Mold and core heating systems should maintain a consistent temperature of 90±10°C. This can be achieved using infrared electric heaters with temperature control features.