Views: 0 Author: Site Editor Publish Time: 2025-06-18 Origin: Site
Types of Cold Runner Systems:
Two-Plate Mold: The simplest design, where runners and parts eject together.
Three-Plate Mold: Separates runner and part ejection, ideal for multi-cavity molds.
Runner Dimensions:
Main Runner Diameter: Typically 4–8mm (must match the injection nozzle).
Sub-Runner Cross-Section: Trapezoidal or circular (5–10mm diameter).
Flow Balance Analysis: Moldflow simulation ensures uniform filling across cavities.
Gate Types: Edge gate, pin gate, submarine gate, etc.
Gate Size: Usually 0.8–2mm (prevents shear heating or sink marks).
Runner Plate: Same as core/cavity steel (e.g., P20, H13, hardened to HRC 48–52).
Sprue Bushing: Wear-resistant alloys (e.g., SKD61).
Runner Channels:
Machined with ball-nose end mills (surface finish ≤ Ra 1.6μm).
Rounded transitions (R1–R3) reduce flow resistance.
Gates:
Pin gates require micro-drilling (0.5–1mm) or laser drilling.
Edge gates are wire-cut (EDM) for precision.
Runner Polishing: Mirror finish (Ra ≤ 0.8μm) prevents material sticking.
Critical Tolerances:
Sprue bushing-to-nozzle clearance (≤ 0.02mm).
Alignment with taper pins to prevent misalignment.
Mold Temperature: 40–80°C (lower than hot runners to solidify plastic).
Injection Pressure: 10–20% higher (compensates for pressure loss in runners).
Packing Time: Extended to counter shrinkage in runners.
| Issue | Cause | Solution |
|---|---|---|
| Short Shot | Unbalanced runners | Adjust gate size/runner balance |
| Runner Sticking | Poor polishing | Increase draft angle (5°–10°) |
| Stringing | Nozzle temp too high | Reduce temperature or use degating design |
Cleaning: Remove residual plastic (especially POM, PC) after shutdown.
Wear Inspection: Check sprue bushings every 50,000 cycles.
| Factor | Cold Runner | Hot Runner |
|---|---|---|
| Cost | Low (no heaters) | High (requires controllers) |
| Waste | High (runners discarded) | Low (no scrap) |
| Materials | All thermoplastics | Sensitive materials (e.g., PEEK) |
| Cycle Time | Longer (cooling needed) | Shorter (direct gating) |
✔ Low-volume production
✔ Cost-sensitive projects
✔ General-purpose plastics (PP, ABS, etc.)
❌ Avoid for:
Optical parts (visible runner marks)
Medical devices (risk of contamination from runners)
Cold runner systems remain a cost-effective and reliable choice for many injection molding applications. Proper design, machining, and maintenance ensure high-quality production with minimal defects.
