When we talk about injection molding parameters, the first thing to nail down is the relationship between material characteristics and mold design. For PE and PP, which are semi-crystalline plastics, the melt temperature typically ranges from 200–280°C for PE and 220–260°C for PP. Mold temperature should be kept at 30–60°C for PE and 40–80°C for PP to control shrinkage—PE can shrink 1.5–3.5%, PP around 1.0–2.5%. In mold design, this means adding proper cooling channels and sometimes adjusting gate size to avoid warpage. For PVC, which is amorphous and heat-sensitive, melt temperature must stay between 160–190°C; exceeding 200°C risks decomposition and corrosion of the screw and mold steel. We usually recommend chrome-plated or stainless steel cavities for PVC to extend mold life.

Pressure and speed settings are where shop-floor experience really pays off. For PC, a high-performance amorphous plastic, injection pressure often needs 80–120 MPa due to its high viscosity, and mold temperature should be 80–110°C to reduce internal stress. Slow injection speed is preferred for PC to avoid jetting and silver streaks. In contrast, PE and PP can handle faster fills, but excessive speed may cause surface defects like flow marks. A common troubleshooting tip: if you see short shots in PP, first check if the injection pressure is below 60–80 MPa or if the gate is too small. For PVC, low screw speed and minimal back pressure are critical to prevent overheating. Always use a decompression nozzle to avoid material drooling.

From a mold maintenance perspective, these parameters directly affect tool life. For example, running PC at low mold temperature increases cycle time but reduces stress cracking; running PE with high mold temperature improves surface finish but may cause sticking in deep ribs. We often adjust draft angles—at least 1–2° for PC, 0.5–1° for PE—based on shrinkage data. If you're sourcing molds for these materials, it helps to work with a supplier who understands these nuances. For more mold sourcing information and technical resources, visit MoldWorld at www.moldw.com.