Foaming during winter often presents the following challenges:
1.Streak Marks: During foaming, visible streaks may appear on the surface. In severe cases, overlapping material at the pouring area may collapse, sometimes deeply.
2.Forward Surge of Raw Materials: When pouring, the material may surge forward excessively, creating a “subflow” where unreacted material rushes ahead and disrupts the foam. This can also affect the foam’s sidewalls.
3.Small Cracks on the Surface: Insufficient gelation due to low temperatures slows the reaction, leading to slower gel formation and small cracks.
4.Slow Skin Drying: This refers to delayed curing of the foam’s surface. Although it may seem inconsequential initially, it can affect cutting efficiency. Prolonged issues with skin drying may also cause fogging.
5.White Streaks Inside the Foam: These streaks result from material overlap. They easily tear with minimal force and are unacceptable. Severe cases show streaks throughout the foam or within about 10 cm from the base. Streak marks and raw material overlap are major contributors to white streaks.
6.Low Material Temperature: Experience indicates that foams with high powder content, methane, or black pigment are more sensitive to low material temperatures, significantly impacting the foaming process.
Key Adjustments for Winter Foaming:
1.Preheat Components: Warm amines, tin, silicon, and water components.
2.Preheat Core Materials: Raise the temperature of PPG, POP, TDI, and calcium carbonate powder.
3.Adjust TDI Levels: For some formulations, moderately increasing TDI may help. For example, when adding fillers like calcium carbonate, evaluate the need to adjust TDI based on foam stability. If stability is poor, consider adding more TDI.
4.Increase Amines: Adding amines is a common strategy to address raw material surging issues. Prioritize this adjustment when such issues arise.
5.Increase Water and Reduce MC: This is critical for adjusting reaction speed. When slow skin drying is significant, prioritize increasing water and reducing MC. This raises internal foam temperature, accelerating curing.
6.Install Heating Lamps in Molds: Preheat molds with lamps for at least 15 minutes before foaming.
7.Wrap the Machine Head with Heating Tape: This ensures uniform reaction speed. Without heating tape, the reaction accelerates unevenly within the first two minutes of foaming, leading to uneven foam height or inclined shapes. Preheating the machine head to about 27–28°C, matching raw material temperatures, stabilizes reaction speeds when production starts.
These adjustments help mitigate common winter foaming issues and improve sponge quality.