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 pinching, slow foaming in the initial reaction, slow initiation and other quality problems. All possible situations are recorded as follows. Due to the length of the article, it is divided into three parts. This is the third one:
The following material A represents polyurethane white material-blend polyether polyols, material B represents polyurethane black material-polymerized MDI (polyisocyanate).
7. Rigid polyurethane foam cracks or heartburn: ① High material temperature; ② Excessive amount of catalyst in material A; ③ Too much pouring at one time, and the foam is too thick; ④ Too much water is added when used as a foaming agent; ⑤ There are metal salt impurities in the material.
8. Rigid polyurethane foam falls off: ① The humidity of the spraying working surface is high, which makes the reaction incomplete and the bottom foam is crispy, brittle and powdery; ② The sprayed working surface is unclean, with oil stains and too much dust;
9. Rigid polyurethane foam emits smoke: ① The amount of catalyst in material A is too high; ② The polyether hydroxyl value in material A is too high; ③ The material temperature is too high, etc.
From the analysis of the above problems, it is known that in addition to objective factors, the components of material A involve many factors. In actual production, adjusting viscosity, milky time, foaming time, curing time, etc. is mainly to adjust material A.
Blend polyether polyols rigid polyurethane foam is not just a mixture of materials A and B. It is necessary to understand the principle of generating polyurethane rigid foam and the interaction between the components, comprehensively analyze various factors, and judge the existence of problems. It is not difficult to produce high-quality polyurethane rigid foam products.