Common problems and solutions in soft foam production
The accidents and problems encountered in actual foaming production are various, and the production of each accident is caused by various factors. In the accident analysis of complex factors, it is generally difficult to list all the influencing factors and the main factors that actually play a role. The following is a summary of frequent accidents and causes. NO. 1
1. Coke core (the temperature of the reaction center exceeds the antioxidant temperature of the raw material)
(1) quality problems of polyether polyols: excessive water content in products, excessive content of peroxide and low boiling point impurities, excessive concentration of metal ions, inappropriate type and concentration of antioxidant agents;
(2) formula: in the low-density formula, TDI index is too high, the proportion of water in the foaming agent is improper, the amount of physical foaming agent is low, and the amount of water is excessive;
(3) climate impact: high temperature in summer, slow heat dissipation, high material temperature, high air humidity, and temperature of reaction center exceeding antioxidant temperature;
(4) improper storage: when TDI index is raised, the accumulated heat energy during post-curing increases, resulting in the increase of internal temperature and the coke heart.
2. Large compression deformation
(1) polyether polyols: the functional degree is less than 2.5, the proportion of ethylene oxide is more than 8%, the number of small molecular components is more than 0.05mol/kg;
(2) process conditions: the temperature of the reaction center is too low or too high, and after curing is not good, and the reaction is not complete or partial coke center is not available; (3) process formula: too low TDI index, too much stannous silicate, low foam ventilation and high closed porosity.
3. Foam oversoft (hardness decreases at the same density)
(1) polyether polyol: low function, low hydroxyl value, high relative molecular weight;
(2) technological formula: less stannous sinate, slow gel reaction speed, less water, more physical foaming agent, high activity of silicone oil, low TDI index under the same amount of tin.
4. Thick bubble
(1) bad mixing; The mixture was not uniform and the milk white period was short.
(2) technological formula: the amount of silicon oil is lower than the lower limit, the amount of stannous octanate is lower and the activity is poor, and the gel speed is slow.
5. Higher than the set density
(1) polyether polyol: low activity, high relative molecular weight;
(2) technological formula: silicon oil consumption is lower than the lower limit value, TDI index is low, and foaming index is low;
(3) climatic conditions: low temperature and high pressure.
6. Foaming holes (gas velocity is greater than gel velocity)
(1) polyether polyols: the acid value is seriously excessive, the impurities are many, the activity is low, and the relative molecular weight is large;
(2) process formula: the amount of amine is large and the amount of tin is small, the TDI index is low, the TDI index is too high when the same amount of tin is high, the gas generating speed is greater than the gel speed, the skeleton strength is small and foams or local holes appear.
1. High obturation rate
(1) polyether polyols: ethylene oxide has high proportion, high activity and mostly occurs in the replacement of polyether polyols with different activity; (2) technological formula: the amount of stannous octanate is large, the activity of isocyanate is high, the crosslinking degree is large, the crosslinking speed is fast, too much amine and physical foaming agent causes the pressure inside the foam, the foam cannot open the hole when the elasticity is large, and the closed hole rate is high when the TDI index is too large.
2. Shrinkage (gel speed is faster than foaming speed)
(1) high obturation rate and shrinkage during cooling;
(2) process conditions: low temperature and material temperature;
(3) technological formula: excessive silicon oil, excessive physical foaming agent, and low TDI index.
3, internal crack
(1) process conditions: low temperature and high temperature of reaction center;
(2) process formula: low TDI index, more tin, high early foaming strength;
(3) high activity and low dosage of silicon oil.
4. Cracking (imbalance of aerogels velocity)
(1) process conditions: low temperature and material temperature;
(2) technological formula: insufficient amount of catalyst, low amount of amine and poor quality of silicon oil.
5. Floor Angle crack (too much amine and too fast foaming speed)
Big hole on the surface: large amount of physical foam, poor quality of silicon oil and catalyst.
6. Low temperature foam performance is poor
The intrinsic quality of polyether polyols is poor, and the TDI index is low at the same hydroxyl value, low functional degree, high unsaturation degree, and the same tin dosage.
(1) climatic conditions: low temperature
(2) raw material: high polyether polyol, high activity of silicon oil;
(3) technological formula: more tin, or less water and amine content at the same time of tin dosage, with high TDI index.
(1) raw materials: polyether polyol has high activity, low molecular weight and high activity of silicon oil;
(2) technological formula: large amount of silicon oil, more amount of tin, more water in the same amount of tin, high TDI index
1. Tensile strength difference n5 2q-6h
(1) raw material: too many polyether polyols with low function of the same hydroxyl value;
(2) technological formula: the reaction of tin oligogel is not good,TDI index is high and water crosslinking degree is low when the same amount of tin is used.
2. Smoke when foaming
Excessive amine can cause the reaction of water and TDI to release a lot of heat, and the low-boiling material will evaporate and smoke.
Low boiling point materials and monomers in polyether polyols are composed of cycloalkanes.
3. The foaming and gel reaction speed of foam belt is fast, the transmission speed is slow in continuous foaming, and the dense layer is formed by local extrusion, thus the phenomenon of white rib is generated
Improve the transfer speed in time, or reduce the feed temperature, reduce the amount of catalyst.
4. Crispy foam
In the formula, there is much water, the polyethylene urea is mostly undissolved in silicone oil, the tin catalyst is used poorly, the crosslinking reaction is not sufficient, the content of polyether polyol with small relative molecular weight is much, the reaction temperature is too high, and the break of ether bond reduces the foam strength.
5. The foam density is lower than the set value
Foaming index is too high due to improper measurement, high temperature and low pressure.
6. Foam with base, edge and bottom step cavitation tin is less polyamine, slow foaming speed, fast gel speed, and low temperature in continuous foaming.
7. High elongation
(1) raw material: polyether polyol has high activity and low function;
(2) technological formula: low TDI index, insufficient cross-linking, more tin, more silicon oil;
(3) high temperature