15 Problems and Reasons Frequently Encountered in The Production of Flexible PU Foam

15 problems and reasons frequently encountered in the production of flexible polyurethane foam
The accidents and problems encountered in the actual foam production of flexible polyurethane foam are diverse, and each production accident is caused by many factors. In the analysis of accidents caused by complex factors, it is generally difficult to list all the influencing factors and the main factors that really work. Below is a summary of 15 frequently encountered problems and causes, let’s take a look.
1. High closed cell rate
Polyether polyol: high ethylene oxide ratio and high activity, which usually occurs when replacing polyether polyols with different activities.
Process formula: large amount of stannous octoate, high isocyanate activity, high degree of cross-linking, fast cross-linking speed, too much amine and physical blowing agent cause low foam internal pressure, foam cannot be opened when its elasticity is large, and TDI index is too large It will also lead to a high closed cell rate.
2. Shrink [gel speed is greater than foaming speed]
The closed cell rate is high and shrinks when cooled.
Process conditions: low temperature, low material temperature.
Process formula: excessive silicone oil, excessive physical foaming agent, TDI index is too low.
3. Internal fissure
Process conditions: low temperature, high reaction center temperature.
Process formula: low TDI index, more tin, high early foaming strength.
Silicone oil has high activity and low dosage.
4. Capping [imbalance of foaming gel speed]
Process conditions: low temperature, low material temperature.
Process formula: insufficient amount of catalyst, little amount of amine, and poor quality of silicone oil.
5. Bottom corner crack [Too much amine dosage, too fast foaming speed]
Large pores on the surface: The physical blowing dose is too large, and the quality of silicone oil and catalyst is poor.
6. Poor low temperature performance of foam
Polyether polyols have poor inherent quality, with the same hydroxyl value, low functionality, and large unsaturation. When the same amount of tin is used, the TDI index is low.
7. Poor ventilation
Climate conditions: low temperature.
Raw material: high polyether polyol and high activity of silicone oil.
Process formula: When there is more tin or the same amount of tin, the content of water and amine is small, and the TDI index is high.
8. Poor rebound
Raw material: Polyether polyol has high activity, low relative molecular mass, and high activity of silicone oil.
Process formula: large amount of silicone oil, large amount of tin, more water at the same amount of tin, high TDI index.
9. Poor tensile strength
Raw material: Too much low-molecular-weight polyether polyol, with low functionality of the same hydroxyl value.
Technological formula: less tin is not good for gel reaction, at the same amount of tin, the TDI index is high, and the degree of crosslinking is low with less water.
10. Smoke when foaming
Excessive amine promotes the reaction of water and TDI to release a lot of heat, and low-boiling substances evaporate and smoke.
If it is not the coke core, the flue gas is mostly composed of TDI, low-boiling substances and monomeric cycloalkanes in polyether polyols.
11. Foam with white ribs
The foaming and gel reaction speed is fast, the transfer speed is slow in continuous foaming, and the dense layer is formed by local squeezing, resulting in the phenomenon of white ribs. The transfer rate should be increased in time, or the material temperature should be reduced, and the amount of catalyst should be reduced.
12.Foam and crispy
There is a lot of water in the formula, most of the biuret produced is not dissolved in silicone oil, the tin catalyst is poor, the crosslinking reaction is insufficient, the content of low molecular weight polyether polyol is high, the reaction temperature is too high, and the break of the ether bond reduces the foam strength .
13. The foam density is lower than the set value
The foaming index is too large due to inaccurate measurement, the temperature is high, and the air pressure is low.
14. The foam has bottom skin, side skin, and bottom cavitation
Tin polyamine is less, the foaming speed is slow, the gel speed is fast, and the temperature is too low during continuous foaming.
15. Large elongation
Material: Polyether polyol has high activity and low functionality.

Process formula: low TDI index, insufficient cross-linking, more tin, and more silicone oil.