PTFE Compression Ratio Calculator

Scope and process

Engineering protocol for PTFE preform sizing: (1) Determine finished sintered part dimensions; (2) Apply sintering shrinkage factors (1.5% to 3.5% diametral and axial shrinkage depending on cooling rate and resin grade) to determine required green preform dimensions; (3) Calculate required powder fill depth: H_fill = H_green × (Density_green / Density_bulk); (4) Design mould cavity height with sufficient lead-in chamfer to accommodate the expanded loose powder volume; (5) Configure press PLC for controlled 5–10 mm/sec compaction speed with programmable 3–5 second dwell at 25 MPa to achieve complete air evacuation and uniform particle cohesion.

Materials we work with

PTFE granular resins behave unlike thermoplastic pellets: they do not melt or flow under pressure, but undergo cold plastic deformation where fibrous fibrils mechanically interlock. Different grades have varying bulk densities: Free-flow granular grades (~500–550 g/L, CR ≈ 3.2:1), non-free-flow fine-cut grades (~400–480 g/L, CR ≈ 3.6:1), and high-density filled compounds (carbon/bronze filled, CR ≈ 2.5:1 to 3.0:1). Tooling cavity depths must be sized to the specific resin grade.

Tooling support

Tooling design for high compression ratios requires precision guide lands on punches and controlled micro-bleed clearances (0.025–0.035 mm) around perimeter ejector pins. If clearances are too tight, air is trapped causing laminar cracks; if too loose, powder flashes, causing dimensional inconsistency.

Choosing the right option

When ordering custom PTFE compression moulds or preforming presses, provide your component sintered drawing, resin grade datasheet, and target cycle time. HEMSUN toolmakers calculate exact shrinkage and compression ratio geometry.

Quality checks and inspection

Preform density is verified by water displacement specific gravity testing (ASTM D792) and micrometer height measurement immediately after press ejection to confirm uniform compaction across the part volume.

Commissioning and handover

Trial pressings at Dahegam verify mould filling, de-airing behavior, and sintered dimensional accuracy before tooling and press dispatch.

Export packing and lead time

Compression ratio formulas, shrinkage allowance guidelines, and tooling operational sheets are provided in comprehensive technical documentation with all export dies.

Maintenance and spare parts

Keep mould cavity walls polished (Ra ≤ 0.15 µm). Avoid abrasive tools during cavity cleaning to preserve exact diametral clearance and prevent powder binding during deep fills.

Specifications