On-Site Assessment and Control of Slow-Rebound Foam Production

No matter how good the formulation is, it only reveals its inherent value through production, yielding high-quality products. Therefore, achieving the formulation's intended goals necessitates accurate judgment and confident control of any issues arising during the production process.

In most cases, production conditions differ significantly from small-scale trials. Many formulations face no issues during trials but encounter numerous problems once scaled up for production.

Common issues during the production of slow-rebound foam include closed cells, cracking, collapsing, sinking, coarse cells, pressure lines, and localized core defects. At these times, rigidly adhering to the original formulation is not advisable; instead, immediate assessment and adjustments are necessary to identify and rectify the underlying causes.

A. Detection of Closed Cells

Closed cells can be easily identified in manual foam production. After removing the mold, squeeze the corners of the foam by hand. If the foam has closed cells, it will either feel very rigid or excessively inflated. This often results from insufficient cell-opening agents or an excess of tin in the formulation. If the foam's surface dries quickly, reduce the tin content by 3%-5% in subsequent production. If the surface dries slowly, increase the cell-opening agent by 3%-10% in the next batch. For continuous line production, closed cells can only be checked after the foam exits the oven. The treatment method is the same as above.

B. Cracking

Cracking can be either transverse (horizontal) or longitudinal (vertical). Transverse cracking usually indicates insufficient tin content, visible through the foam's excellent cell opening; adding about 5% more tin should solve the issue. Longitudinal cracking is often due to inadequate mixing intensity or insufficient mixing time and can be resolved with appropriate adjustments. Additionally, insufficient TDI can also cause cracking, which needs attention.

C. Collapsing Foam

Foam collapse has two primary causes: either forgetting to add silicone oil or adding an insufficient amount of it, and either forgetting to add tin or adding too little.

D. Sinking Foam

Sinking generally results from using poor quality silicone oil or the amount used being at a critical point where it barely prevents collapse but fails to maintain initial stability.

E. Post-Cutting Issues

Once the foam is cut, issues such as coarse cells, pressure lines, and core defects can be identified:

1. Coarse Cells: These can result from the quality and amount of cell-opening agents, insufficient TDI, excessively high material temperatures, or improper mixing speeds (either too low or too high).

2. Pressure Lines: In slow-rebound foam, pressure lines are mostly due to inadequate mixing and too fast of a cream time.

3. Core Defects: Internal core defects, especially if the core remains sticky for a long time, are caused by uneven mixing.

F. Closed Cell Shrinkage

If slow-rebound foam exhibits closed cell shrinkage, it becomes evident within 30-40 minutes after demolding, necessitating post-treatment. Common methods include manual trampling, wooden board striking, peeling for venting, and high-pressure air injection. The simplest and most effective method is manual trampling, which minimizes damage to the foam and can be adjusted based on the situation. In cold weather, repeat the process several times, alternating between trampling and sun exposure. As long as the cell-opening agent is of good quality, full recovery is achievable.