PEEK Injection Molding Problems: 10 Common Issues and How to Solve Them

Why PEEK Processing Is Uniquely Difficult

PEEK's processing window is only about 20°C wide — too cold and the part is amorphous with poor chemical resistance; too hot and the polymer degrades, losing mechanical properties and generating corrosive gases. This narrow window, combined with the 160-200°C mold temperature requirement (oil-heated, not water), makes PEEK the most challenging injection moldable polymer. Understanding the 10 most common failure modes saves weeks of trial-and-error.

Problem #1: Inconsistent Crystallinity (40% of PEEK issues)

The part is partially amorphous — some areas are crystalline (tan/opaque), others are amorphous (translucent brown). Root cause: mold temperature too low or uneven. PEEK requires 160-200°C mold temperature to crystallize. Below 160°C, the polymer quenches into an amorphous state. Fix: Verify actual mold surface temperature with a contact pyrometer, not the oil unit setpoint. Insulate the mold from the press platens (insulation boards reduce heat loss by 40-60%). Use cartridge heaters in addition to oil channels for thick sections.

Problem #2: Black Specks / Degradation (25%)

Root cause: residence time too long. PEEK degrades at 400°C+, and the degradation accelerates exponentially with time. Fix: Ensure shot size is 30-70% of barrel capacity. Purge with a thermally stable purge compound between material changes. Reduce barrel temperature by 5-10°C if cycle interruptions are frequent.

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• ISO. ISO 1043 — Plastics — Symbols and Abbreviated Terms. iso.org
• National Institute of Standards and Technology (NIST). Polymer Properties Database. nist.gov
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb — Material Property Data. matweb.com