Q: Our foaming machine produces foam with uneven cells and density that falls out of specification. What are the possible causes and how can we fix them?
A: Uneven cells and density problems usually come from the following causes. Check them one by one.
Raw Material Ratio Error
An imbalance between polyol and isocyanate (TDI/MDI), or inaccurate metering of the blowing agent (e.g. 141b or water). Calibrate the metering pumps, verify batch stability of raw materials, and keep the ratio error within ±1%.
Mixing Head Fault
Internal wear or incomplete cleaning of the mixing head leads to uneven mixing. Check the stirring speed regularly (normally ≥3000 rpm), clean out residues, and replace worn components when necessary.
Abnormal Temperature Control
Fluctuating raw material temperature (ideal 20–25°C) or uneven mould temperature affects the reaction. Check the thermal-oil circulation and temperature sensors, and keep the temperature difference within ±1°C.
Line Speed Mismatch
A conveyor running too fast shortens the foaming time. Adjust it to match the foaming rate (typically 5–10 m/min in the low-speed section).
Recommended Measures
- Run a no-load trial before startup every day to verify metering accuracy.
- Monitor mixing-head pressure in real time with a high-precision sensor (normal 6–10 bar).
- Record production data and build a process-parameter archive for traceability and optimisation.