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Key Vacuum Casting Process Parameters to Improve Part Density & Mechanical Properties

Created on 05.21

Meta Description: Optimize core vacuum casting process parameters including vacuum degree, resin mixing ratio, mold temperature, and curing time to boost PU part density, tensile strength, and impact resistance for functional low-volume production. #vacuum casting process parameters #PU resin mechanical properties #vacuum casting density control #low volume PU casting

Mechanical performance (tensile strength, impact resistance, Shore hardness, bulk density) is the core evaluation indicator for functional vacuum-cast parts, rather than only surface appearance quality. Many customers encounter problems including soft texture, easy breakage, low density, and unstable batch performance due to unreasonable parameter setting and non-standardized workflows. Combined with industrial-grade PU resin characteristics and silicone mold casting principles, we summarize five controllable core parameters to significantly improve part density and mechanical properties.

1. Vacuum Degree & Degassing Time (Core Factor Determining Density)

• Standard Parameter: Vacuum chamber pressure −0.09 ~ −0.095 MPa, degassing time 3–5 min

• Low vacuum (<−0.08 MPa): Severe internal bubbles, reduced tensile strength by over 30%, low bulk density

• Over-long degassing: Partial premature curing of PU resin, poor fluidity, incomplete mold filling

• Optimization Rule: Extend degassing time to 4–5 min for thick-wall parts (wall thickness ≥4 mm)

2. PU A/B Resin Mixing Ratio & Precision Control

• Strictly follow factory-specified weight-based mixing ratio (common industrial ratios: 1:1 or 2:1; volume ratio is prohibited)

• Mixing ratio deviation >3% causes incomplete curing, reduced hardness, and unstable mechanical performance

• Mixing speed: 200–400 rpm low-speed stirring to avoid air entrapment and ensure uniform component mixing

• Mixed resin temperature: Maintained at 25–30 °C to keep stable chemical reactivity

3. Silicone Mold Preheating Temperature

• Optimal Preheating Temperature: 40–50 °C

• Too low temperature: Rapid surface solidification of resin, incomplete internal curing, low bulk density

• Too high temperature (>60 °C): Accelerates silicone aging and shortens mold service life

• Consistent mold temperature ensures uniform resin curing and batch-to-batch stable mechanical properties

4. Gradient Control of Curing Temperature & Time

• Standard Curing Curve: 40 °C pre-curing for 1 h → 50–60 °C full curing for 2–4 h

• Rapid high-temperature curing triggers internal residual stress, shrinkage cracks, and reduced impact resistance

• Thick-wall parts require extended low-temperature curing time to ensure complete cross-linking chemical reactions

5. Pouring Speed & Filling Direction Control

• Slow, continuous wall-following pouring (speed 5–10 cm/s) is mandatory

• High-speed turbulent pouring is prohibited to avoid air bubble entrapment

• Single-direction filling is preferred to reduce weld lines and local performance weakening

By strictly locking the above five core process parameters, we improve PU part bulk density by 8–15% and tensile strength by 20–40%, enabling vacuum-cast parts to approach injection-molded part performance for low-volume production scenarios. Our engineering team provides parameter customization for different PU grades and complex part structures.