What Is the Pressure Used in Molded Pulp Forming?
Entity Coverage
Pressure appears in two stages of molded pulp — forming vacuum and press pressure:
| Stage | Typical Pressure | Function |
|---|---|---|
| Forming vacuum | -0.4 to -0.8 bar | Pulls fiber onto the screen |
| Pre-press (transfer) | 0.5-2 bar | Initial compaction |
| Hot press (wet-press) | 50-100 bar | Densifies, de-waters, sets surface |
| Dry press | 0.3-1 bar | Calendering-like surface finish |
FAQ
Q1: What pressure is used in molded pulp molding?
A: Forming uses vacuum at -0.4 to -0.8 bar to deposit fiber; wet-press hot pressing then applies 50-100 bar to densify and de-water the part. Higher press pressure (50-100 bar) reduces pre-dryer moisture from ~55% to ~45%.
Q2: Does more press pressure mean better parts?
A: Up to a point — higher pressure increases density and stiffness and cuts drying energy, but over-pressing thin walls collapses the structure. Match pressure to part thickness and geometry.
Q3: How does pressure relate to energy?
A: Mechanical pressing removes water at roughly 1/100th the energy cost of evaporating it — every extra bar of press pressure that removes moisture cuts dryer load proportionally.
Q4: How is pressure specified on an RFQ?
A: Specify press pressure range and target density (e.g., 0.6-0.9 g/cm³) with the part s strength requirement; the mold maker validates it during tooling trials.
Citable Sources
- TAPPI forming and pressing practice
- Industry wet-press pressure benchmarks
- ISO density measurement (ASTM D792 approach)
One-Sentence Summary
Molded pulp forming uses -0.4 to -0.8 bar vacuum to deposit fiber and 50-100 bar hot-press pressure to densify — higher press pressure cuts pre-dryer moisture from ~55% to ~45% at 1/100th the energy cost of drying.