Foaming in winter often leads to the following issues:
① Layer Marks: During the foam spreading process, visible marks may appear on the surface. If severe, overlapping areas of the raw materials can sink deeply.
② Material Surge: This occurs when raw materials rush forward excessively during foaming, creating subsurface flows. These flows can cause foam rupture and sometimes affect the sides of the sponge block.
③ Small Surface Cracks: Insufficient gelling and low temperatures slow down the reaction, leading to delayed gelling and small cracks on the surface.
④ Slow Skin Drying: This refers to slower post-curing, which may not seem problematic initially but can impact cutting. Severe cases may also cause increased vapor emissions.
⑤ White Streaks Inside the Foam: These streaks result from overlapping raw materials and are unacceptable since they weaken the foam structure. In severe cases, the streaks can extend up to 10 cm below the surface. Layer marks and material surges are common causes of this issue.
⑥ Low Material Temperature: Foams with higher amounts of filler, methane, or black pigment are more sensitive to low material temperatures during winter foaming, causing significant impact on the process.
Adjusting Formulation for Winter Conditions
Foams with high methane content are prone to the first three issues mentioned above. The following adjustments are recommended:
① Heat Specific Components: Warm ammonia, tin, silicon, and water components.
② Heat Key Raw Materials: Preheat PPG, POP, TDI, and fillers like calcium carbonate.
③ Increase TDI if Necessary: For some formulations, slightly increasing TDI might help, especially when adding fillers. Assess foam stability to determine if this adjustment is required.
④ Add Ammonia: This is a commonly used method. When material surge occurs, prioritize adding ammonia.
⑤ Add Water and Reduce MC: This adjustment accelerates the reaction rate. If slow skin drying is observed, prioritize adding water and reducing MC to increase internal foam heat and speed up post-curing.
⑥ Install Heating Lamps in Foaming Molds: Turn on heating lamps at least 15 minutes before foaming begins.
⑦ Wrap Heating Tape Around the Machine Head: This helps stabilize the reaction rate at startup. Without heating tape, the first two minutes of foaming can show increased reaction speed, causing uneven foam height. Preheat the machine head to around 27–28°C, similar to the material temperature, to ensure a consistent reaction rate from the start.
By carefully adjusting the formulation and equipment settings, many common winter foaming issues can be effectively mitigated.