Polyurethane foaming is affected by the conditions, equipment, process and ambient temperature during the construction process. Various abnormal phenomena will occur during the polyurethane reaction process, such as foam shrinkage, brittleness, too soft, heartburn, cracking, smoking, shedding, bubble collapse, coarse foam pores, fine powder after being pinched, slow foaming in the initial stage of the reaction, slow initiation, and a series of quality problems. All possible situations are recorded as follows. Due to the length of the article, it is divided into three articles. This is the first one:
The following material A represents polyurethane white material-blend polyether polyols, material B represents polyurethane black material-polymerized MDI (polyisocyanate).
1. A and B materials do not foam after mixing: ① Low material temperature; ② Inaccurate distribution ratio of the two groups; ③ Catalyst is not added to A material; ④ Material B is of poor quality; ⑤ Foaming agent is not added to A material.
2. Shrinkage of polyurethane rigid foam: ① Too many components in material A, which causes the strength of polyurethane rigid foam to decrease and cause shrinkage: ② The material and liquid in the spray gun are not mixed evenly, the spray air is too small, or the material viscosity is too high; ③ Curing is too fast, forming more closed cells; ④ Gas thermal expansion and contraction deformation.
3. Brittle polyurethane rigid foam: ① Too many components in material A; ② Too much water; ③ Too low working surface temperature; ④ The acid value of material B is large and contains many impurities; ③ Too much flame retardant added to material A.