Polyketone (POK) is increasingly used in high-performance engineering applications due to its excellent wear resistance and chemical stability. However, many processing issues arise when engineers apply PA66 or POM molding conditions without adjustment. This often leads to surface defects, dimensional instability, or thermal degradation.
To achieve stable production, POK requires a controlled processing window that accounts for its semi-crystalline structure and shear sensitivity. The following guide summarizes key parameters and troubleshooting practices for industrial injection molding.
If you are transitioning to polyketone from polyamide (PA66) or acetal (POM), it is essential to understand how POK’s unique molecular configuration impacts its physical behavior under heat and shear.
Review POK Material Properties & Competitor Benchmarks →Material Drying and Moisture Control
Although POK has relatively low moisture absorption (around 0.5% at equilibrium), residual water can still significantly affect processing stability. At melt temperatures, even small amounts of moisture may trigger hydrolytic chain scission, leading to reduced impact strength and surface defects.
Recommended Drying
- 80–85°C for 3–4 hours
- Dew point < -40°C
- Avoid >100°C
Injection Molding Processing Parameters
Feed Zone
210–220°C
Compression Zone
225–235°C
Metering Zone
235–245°C
Melt Temp
230–245°C
Mold Temperature
60–80°C
Injection Pressure
50–120 MPa
Nozzle Temperature
235–240°C
Mold Design Considerations
Because this material exhibits semi-crystalline behavior and relatively high shrinkage (approximately 1.5–2.0%), mold design plays a crucial role in dimensional accuracy and surface quality.
- 1 Large, balanced gates (edge or pin-point) to reduce shear stress
- 2 Vent depth: 0.02–0.03 mm
- 3 Uniform wall thickness to minimize warpage
Common Defects and Troubleshooting
Sink marks
Often caused by insufficient packing pressure or uneven cooling.
Warpage
Typically results from uneven crystallization or inconsistent wall thickness.
Splay or silver streaks
Usually linked to residual moisture or overheating in localized barrel zones.
Purging and Shutdown Practice
During short interruptions, reducing barrel temperature to around 200°C helps maintain material stability. For longer shutdowns or material changeovers, complete purging is strongly recommended.
Recommended Purging Materials:
High-viscosity PP, HDPE, or dedicated purging compounds
"Leaving POK in a heated barrel for extended periods should be avoided, as thermal degradation may lead to carbonization and equipment contamination."
Conclusion
Successful POK injection molding depends on three core principles: strict moisture control, balanced thermal processing, and well-designed mold geometry. When these conditions are properly managed, the material can deliver stable mechanical performance, high surface quality, and reliable long-term processing consistency.
For engineers transitioning from PA66, POM, or HDPE systems, adopting these optimized parameters helps reduce trial-and-error cycles and improves overall production efficiency in demanding industrial applications.
