There are various accidents and problems encountered in the actual foam production, and the production of each accident is caused by many factors.
In the accident analysis 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 some frequently encountered accidents and their causes.
1. Coke (the temperature of the reaction center exceeds the anti-oxidation temperature of the raw material)
(1) There is a problem with the quality of polyether polyols: during the production, storage and transportation process, the water content in the product exceeds the standard, the content of peroxides and low-boiling impurities is too high, the concentration of metal ions is too high, and the type and concentration of antioxidants are inappropriate;
(2) Formula: In the low-density formula, the TDI index is too high, the proportion of water and physical foaming agent in the foaming agent is improper, the physical foaming agent is too small, and the water is too much;
(3) Climate influence: high temperature in summer, slow heat dissipation, high material temperature, high air humidity, and the temperature of the reaction center exceeds the anti-oxidation temperature;
(4) Improper storage: When the TDI index increases, the accumulated heat energy increases during post-curing, resulting in an increase in the internal temperature and anxiety.
2. Large compression deformation
(1) Polyether polyols: the functionality is less than 2.5, the proportion of ethylene oxide is greater than 8%, there are many small molecular components, and the degree of unsaturation is greater than 0.05mol/kg;
(2) Process conditions: the temperature of the reaction center is too low or too high, the post-curing is not good, the reaction is not complete or there is partial coke;
(3) Technological formula: too low TDI index, excessive stannous octoate of silicone oil, low foam ventilation and high closed cell rate.
3. The foam is too soft (the hardness decreases under the same density)
(1) Polyether polyol: low functionality, low hydroxyl value, and large relative molecular mass;
(2) Technological formula: the amount of stannous octoate is small, the gel reaction speed is slow, and the amount of tin is the same, the amount of water is small, the amount of physical foaming agent is large, the activity of silicone oil is high, the amount is large, and the TDI index is low.
4. Large pores
(1) The mixing is not good; the mixing is uneven, and the milky white period is short;
(2) Process formula: the amount of silicone oil is lower than the lower limit, the amount of stannous octoate is small and the activity is poor, and the gelation speed is slow.
5. Higher than the set density
(1) Polyether polyol: low activity and high relative molecular mass;
(2) Process formula: the amount of silicone oil is lower than the lower limit, the TDI index is low, and the foaming index is low;
(3) Climate conditions: low temperature and high air pressure.
6. Collapsing foam holes (gassing speed is greater than gel speed)
(1) Polyether polyol: The acid value is seriously exceeding the standard, there are many impurities, the activity is low, and the relative molecular weight is large;
(2) Process formula: the amount of amine is more, the amount of tin is less, and the TDI index is low. When the amount of tin is the same, the TDI index is too high, the gas generation speed is greater than the gel speed, the skeleton strength is small, and the foam collapses or local holes appear.
1. High closed cell rate
(1) Polyether polyol: high proportion of ethylene oxide and high activity, which mostly occurs in the replacement of polyether polyols with different activities;
(2) Technological formula: the amount of stannous octoate is high, the isocyanate activity is high, the cross-linking degree is large, and the cross-linking speed is fast. If it is too large, it will also lead to a high closed cell rate.
2. Shrinkage (gel speed is greater than foaming speed)
(1) The closed cell rate is high and shrinks when cooling;
(2) Process conditions: low temperature and low material temperature;
(3) Process formula: excessive silicone oil, excessive physical foaming agent, and low TDI index.
3. Internal fissure
(1) Process conditions: the temperature is low, and the temperature of the reaction center is high;
(2) Process formula: low TDI index, more tin, and high early foaming strength;
(3) Silicone oil has high activity and low dosage.
4. Capping (unbalanced aerogel speed)
(1) Process conditions: low temperature and low material temperature;
(2) Process formula: the amount of catalyst is insufficient, the amount of amine is small, and the quality of silicone oil is not good.
5. Bottom corner cracks (the amount of amine is too much, the foaming speed is too fast)
Large pores on the surface: The amount of physical foaming is too large, and the quality of silicone oil and catalyst is poor.
6. Poor low temperature performance of foam
The inherent quality of polyether polyol is poor, with the same hydroxyl value, low functionality, high degree of unsaturation, and the same amount of tin, the TDI index is low.
7. Poor ventilation
(1) Climate conditions: low temperature
(2) Raw materials: high polyether polyol, high activity of silicone oil;
(3) Process formula: more tin, or less water and amine content when the amount of tin is the same, and high TDI index.
8. Poor resilience
(1) Raw materials: polyether polyol has high activity, small relative molecular mass, and high activity of silicone oil;
(2) Process formula: the amount of silicone oil is large, the amount of tin is large, and the amount of water is large at the same amount of tin, and the TDI index is high.
1. Poor tensile strength
(1) Raw materials: too many low molecular polyether polyols and low functionality with the same hydroxyl value;
(2) Process formula: less tin gel reaction is not good, at the same amount of tin, the TDI index is high, and the degree of crosslinking is low with less water.
2. Smoke when foaming
Excess amine promotes the reaction of water and TDI to release a lot of heat, and the low-boiling substances evaporate and emit smoke. If it is not coke, the smoke is mostly composed of TDI, low-boiling substances and monomer naphthenes in polyether polyols.
3. Foam with white ribs
The foaming and gel reaction speed is fast, the transfer speed is slow in the continuous foaming, and the local extrusion produces a dense layer, resulting in the phenomenon of white streaks. The transfer speed should be increased in time, or the material temperature should be lowered, and the catalyst dosage should be reduced.
4. Crispy foam
There is a lot of water in the formula, the biuret formed is mostly undissolved in silicone oil, the tin catalyst is poorly used, the cross-linking reaction is insufficient, the content of polyether polyol with small relative molecular weight is high, the reaction temperature is too high, and the breakage of ether bonds reduces the foam strength. .
5. 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.
6. The foam has bottom skin, edge skin, bottom step cavitation
Less tin polyamine, slow foaming speed, fast gel speed, and low temperature in continuous foaming.
7. Large elongation
(1) Raw materials: polyether polyol has high activity and small functionality;
(2) Process formula: low TDI index, insufficient cross-linking, more tin, and more silicone oil;
(3) The temperature is high.
