andyTfoams
Registered
Hi everyone,
We’re experiencing issues with hardness variation (ILD Spread) across the height of the bun in some of our slabstock flexible polyurethane foam buns. Specifically, we’re seeing firmer hardness in the middle compared to the top and bottom, with overall spreads exceeding specification limits (20-50 N between the hardest and softest parts of the bun).
Context:
We’re experiencing issues with hardness variation (ILD Spread) across the height of the bun in some of our slabstock flexible polyurethane foam buns. Specifically, we’re seeing firmer hardness in the middle compared to the top and bottom, with overall spreads exceeding specification limits (20-50 N between the hardest and softest parts of the bun).
Context:
- Hennecke Slabstock line with fall plates and flat topping system,
- Hardness variation mostly observed in high density and/or high hardness liquid laydown pours
- No external blowing agent used for these liquid laydown pours
- Bun heights vary from 800 - ~1200 mm
- TDI-based foams
- Hardness spread variation also varies on a batch-to-batch basis, making it difficult to determine whether attempted fixes have had the intended effect (e.g. adjusting fall plates, adjusting flat top system)
- Ambient conditions during pour and curing are not controlled
- What have you found to be the most influential factors driving hardness spreads in high-density/hardness liquid laydown grades?
- Would the nature of a formulation itself contribute these spreads and how?
- Have you applied any specific strategies or best practices (e.g., pour pattern adjustments, fall plate settings, chemical handling, curing control) that significantly reduced hardness variation?
- Hennecke recommends allowing foam to fall 2/3 down and rise 1/3 up but that it's important to deviate from the optimal setting for low viscosity mixtures (refer to 'Tips & Tricks Slabstock - Hennecke'). How would you go about optimizing fall plate settings for liquid laydown type pours?
