Common Issues and Solutions for Polyurethane Foam Production-Part 1

1. Core Scorching (Center temperature exceeding material's oxidation temperature)

A. Poor quality polyether polyols: excessive moisture, high peroxide content, high boiling point impurities, elevated metal ion concentration, improper use of antioxidants.

B. Formulation issues: high TDI index in low-density formulas, improper ratio of water to physical blowing agents, insufficient physical blowing agent, excessive water.

C. Climate impact: high summer temperatures, slow heat dissipation, high material temperatures, high humidity leading to center temperature surpassing oxidation temperature.

D. Improper storage: Increased TDI index leading to accumulation of heat during post-curing, resulting in elevated internal temperature and core scorching.

2. Large Compression Deformation

A. Polyether Polyol: Functionality less than 2.5, propylene oxide ratio greater than 8%, high proportion of low molecular weight components, unsaturation greater than 0.05 mol/kg.

B. Process Conditions: The reaction center temperature is too low or too high, poor post-curing, incomplete reaction, or partial scorching.

C. Process Formula: TDI index too low (controlled within 105-108), excess silicone oil stannous octoate and silicone oil, low foam air content, high closed-cell content.

3. Soft Foam (Decreased hardness at same density)

A. Polyether polyols: low functionality, low hydroxyl value, high molecular weight.

B. Process formulation: insufficient T9 octoate, slow gelation reaction, lower water content with the same amount of tin catalyst, higher amount of physical blowing agents, high dosage of highly active silicone oil, low TDI index.

4. Large Cell Size

A. Poor mixing: uneven mixing, short cream time; increase mixing head speed, reduce mixing head pressure, increase gas injection.

B. Process formulation: silicone oil below lower limit, insufficient or poor quality octoate tin, slow gelation speed.

5. Density Higher than Set Value

A. Polyether polyols: low activity, high molecular weight.

B. Process formulation: silicone oil below lower limit, low TDI index, low foam index.

C. Climate conditions: low temperature, high pressure. A 30% increase in atmospheric pressure increases density by 10-15%.

6. Collapsed Cells and Hollows (Gas evolution rate greater than gelation rate)

A. Polyether polyols: excessive acid value (affects reaction rate), high impurities, low activity, high molecular weight.

B. Process formulation: excess amine, low tin catalyst (rapid foaming and slow gelation), low TDI index, insufficient or ineffective silicone oil.

C. Low-pressure foaming machine: reduce gas injection and mixing head speed.

7. High Closed-Cell Ratio

A. Polyether polyols: high epoxy ethane ratio, high activity, often occurs when switching to polyether polyols with different activity levels.

B. Process formulation: excessive octoate tin, high isocyanate activity, high crosslinking degree, high crosslinking speed, excessive amine and physical blowing agents leading to low foam pressure, high foam elasticity resulting in poor cell opening, excessively high TDI index leading to high closed-cell ratio.

8. Shrinkage (Gelation rate greater than foaming rate)

A. High closed-cell ratio, shrinkage during cooling.

B. Process conditions: low air and material temperature.

C. Process formulation: excessive silicone oil, less amine, more tin, low TDI index.

D. Low-pressure foaming machine: increase mixing head speed, increase gas injection.

9. Cracking

A. "八" shaped cracks indicate excess amine, single line cracks indicate excess water.

B. Mid and bottom cracks: Excessive amine, fast foaming rate (excessive physical blowing agent, poor silicone oil and catalyst quality).

C. Top cracks: Unbalanced gas-evolution gelation rate (low temperature, low material temperature, insufficient catalyst, less amine, poor silicone oil quality).

D. Internal cracks: Low air temperature, high center temperature, low TDI index, excessive tin, high early foaming strength, highly active silicone oil in small quantities.

E. Side middle cracks: Increase tin dosage.

F. Cracking throughout the process may be due to discrepancies in dropping plate and foaming reaction, or premature foaming, or incorrect plates. Apart from formulation, it also relates to the smoothness of the base paper; if the base paper is wrinkled, it can divide the liquid into several parts, causing cracks.

10. Blurred Cell Structure

A. Excessive stirring speed.

B. High air injection volume.

C. Inaccurate metering pump flow.

D. Clogged material pipelines and filters.

11. Bottom Edge Cracks (Excessive amine, fast foaming rate)

Surface large pores: excessive physical blowing agent, poor silicone oil and catalyst quality.

12. Poor Low-Temperature Performance

Poor inherent quality of polyether polyols: low hydroxyl value, low functionality, high unsaturation, low TDI index with the same tin usage.

13. Poor Ventilation

A. Climate conditions: low temperature.

B. Raw materials: high polyether polyol content, highly active silicone oil.

C. Process formulation: excess tin, or low tin and amine content with the same tin usage, high TDI index.