Common Issues and Solutions for Polyurethane Foam Production-Part 2

14. Poor Rebound

A. Raw materials: high activity polyether polyols, low molecular weight, highly active silicone oil.

B. Process formulation: high silicone oil content, excessive tin, high water content with the same tin usage, high TDI index, large amount of white oil and powder.

15. Poor Tensile Strength

A. Raw materials: excessive low molecular weight polyether polyols, low functionality hydroxyl value.

B. Process formulation: insufficient tin, poor gelation reaction, high TDI index with the same tin usage, low water content, low crosslinking.

16. Smoke during Foaming

Excessive amine release a large amount of heat during water and TDI reaction, causing evaporation of low-boiling substances and smoke. If not core scorching, smoke mostly consists of TDI, low-boiling substances, and monomer cycloalkanes in polyether polyols.

17. Foam with White Streaks

Fast foaming and gelation reaction but slow transfer in continuous foaming, resulting in a dense layer due to localized compression, causing white streaks. Increase transfer speed or lower material temperature, reduce catalyst usage.

18. Brittle Foam

Excessive water in the formulation leads to excess biuret formation, which does not dissolve in silicone oil. Poor use of tin catalyst, insufficient cross-linking reaction, high content of low molecular weight polyether polyols, high reaction temperature causing ether bond breakage and decreased foam strength.

19. Foam Density Lower than Set Value

Foam index is too high due to inaccurate measurement, high temperature, low pressure.

20. Foaming with Skin, Edge Skin, and Bottom Air

Excessive tin, insufficient amine, slow foaming rate, fast gelation rate, low temperature during continuous foaming.

21. Elongation Rate Too High

A. Raw materials: high activity polyether polyols, low functionality.

B. Process formulation: low TDI index, insufficient cross-linking, high tin.

22. Uncontrolled Foam (Small bubbles rapidly moving beneath surface)

A. Low-pressure foaming machine: increase mixing head speed, decrease gas injection.

B. High-pressure foaming machine: increase mixing head pressure.

23.Milky Moving Lines

A. Increase conveyor speed

B. Adjust cushion plate inclination.

C. Reduce amine catalyst usage

24.Inserted Material Backflow

A. Increase conveyor speed.

B. Adjust cushion plate inclination.

C. Increase amine catalyst usage.

25.Moon Pits

A. Low-pressure foaming machine: reduce mixing head speed and gas injection.

B. High-pressure foaming machine: increase mixing head pressure.

C. Silicone oil quality issue.

D. Increase amine amount while reducing tin amount to ensure adequate cell opening.

26.Slow Curing,Sticky Surface

Polymer strength increases too slowly, resulting in soft, sticky foam that is difficult to cut.

Foam blocks appear unstable when exiting channels.

Increase catalyst usage, check polyol, water, and TDl measurement accuracy.