No matter how good a formulation is, its true value can only be demonstrated by producing high-quality products. Therefore, achieving precise problem identification and effective control during production is essential to realizing the intended goals of the formulation design.
In most cases, production conditions differ significantly from small-scale trials. Many formulations perform well in trials but encounter numerous issues in mass production.
Common problems in the preparation of slow-rebound foam include closed cells, cracking, collapse, sinking, coarse pores, compression bands, and localized internal defects. At such times, rigidly adhering to the formulation is impractical. Instead, timely judgment, root cause identification, and adjustments are required.
Key Issues and Solutions
A. Closed Cells
Closed cells can be easily detected in manual foaming. After removing the mold, press the foam corners. If closed cells are present, you will notice stiffness or a bloated feel. This usually occurs due to insufficient foaming agent or excess tin catalyst in the formulation.
-If the foam surface dries quickly, reduce the tin catalyst by 3%-5% for subsequent production.
-If the drying process is slow, increase the foaming agent by 3%-10%.
For production lines, closed cells are identified after the foam exits the curing oven. The corrective actions remain the same.
B. Cracking
Cracks appear as either horizontal surface cracks or vertical linear cracks:
-Horizontal Cracks: Typically caused by insufficient tin catalyst, which also results in excellent foam porosity. Adding about 5% more tin usually resolves this issue.
-Vertical Cracks: Often due to inadequate mixing intensity or duration. Adjusting the mixing process can resolve this. Sometimes, insufficient TDI content may also lead to cracking and should not be overlooked.
C. Collapse
Collapse can occur due to:
-Forgetting to add silicone oil or using insufficient amounts.
-Forgetting to add tin catalyst or using inadequate amounts.
D. Sinking
Sinking typically arises from poor-quality silicone oil or using it at a critical threshold—just enough to prevent collapse but insufficient to maintain initial system stability.
E. Issues Detected After Cutting
After foam cutting, the following problems may become apparent:
1.Coarse Pores:
-Linked to the quality and amount of the foaming agent.
-Insufficient TDI.
-Excessively high material temperature.
-Improper mixing speed (either too low or too high).
2.Compression Bands:
Often caused by inadequate mixing or excessively rapid cream time.
3.Internal Defects (Sticky Cores):
Result from uneven mixing. Sticky cores that remain tacky for extended periods indicate this issue.
F. Post-Treatment for Closed-Cell Shrinkage
If closed-cell shrinkage occurs, it can be detected within 30-40 minutes after demolding. Immediate post-treatment is necessary. Common methods include:
-Manual stomping.
-Striking with wooden boards.
-Peeling the foam to release trapped air.
-Injecting high-pressure air.
Among these, manual stomping is the simplest and least damaging to the foam. The method can be adapted to specific circumstances. In cold weather, additional cycles of drying and stomping may be required. If the foaming agent is of good quality, full recovery is achievable.