Pattern Molding

Pattern Molding

The pre-expanded EPS beads are injected into the pre-heated tool cavity and the tool is steam-heated and water cooled to expand, soften, fuse, and cool the polystyrene to form a finished pattern.

Proper design and control of the steam-cool cycle is critical for strong, smooth- finish, and dimensionally-accurate patterns.

A cold tool surface or a short steam step produces "underfusion."
- Underfusion fails to fully expand and bond the beads, producing a rough "beady" surface and low strength sections in the pattern.
Extended steam exposure or inadequate cooling produces "overfusion."
- Overfusion collapses the beads on the surface producing surface waviness.
Inadequate cooling in the tool can produce "post expansion."
- In post expansion, the soft, warm beads can locally expand after removal from the tool, producing dimensional variations.

After ejection from the tool, the foam pattern is aged to release residual pentane & water and to stabilize the pattern to the final dimensions.