Steel Selection for PFA Injection Molds

PFA (perfluoroalkoxy alkane) resin is a high-performance fluoroplastic widely used in chemical, medical, semiconductor, and fluid handling applications due to its excellent heat resistance, corrosion resistance, and non-stick properties. However, PFA requires extremely high molding conditions: processing temperatures reach 330–380°C, mold temperatures 180–220°C, and it releases trace corrosive gases such as hydrogen fluoride (HF) at high temperatures. Ordinary mold steels quickly corrode, rust, pit, or deform under such conditions. Therefore, PFA mold steels must meet four core requirements: high corrosion resistance, thermal stability, wear resistance, and high polishability.

1. Core Requirements for PFA Mold Steels

First, corrosion resistance to withstand HF vapor. Second, thermal stability to resist softening or cracking under long-term high temperatures. Third, wear resistance to endure high-viscosity melt flow. Fourth, superior polishability to prevent sticking and ensure smooth demolding.

2. Preferred Mold Steels

S136 (1.2083) Stainless Steel

S136 is the most widely used steel for precision, medical, and high-gloss PFA parts. With high chromium content, it offers excellent corrosion resistance and can be hardened to 48–52 HRC. It polishes to a mirror finish (Ra ≤ 0.1 μm), effectively preventing sticking and ensuring stable long-term production.

H13 (1.2344 / SKD61) Hot Work Tool Steel

H13 is preferred for high-volume, thick-walled PFA parts. It provides exceptional thermal fatigue resistance and high-temperature strength, maintaining hardness under prolonged high heat. After proper heat treatment, it achieves 48–52 HRC and excellent wear resistance. Chromium plating or nitriding is recommended to enhance corrosion resistance.

Cronidur 30 High-Nitrogen Stainless Steel

This premium grade offers superior corrosion and wear resistance for high-end semiconductor and medical PFA applications. It supports ultra-high polishing and extended mold life but is costly and difficult to machine.

3. Economic Alternative Steels

NAK80 pre-hardened steel is suitable for small-batch or trial production. It offers moderate corrosion resistance and good polishability without additional quenching. 316L stainless steel provides exceptional corrosion resistance for medical and food-grade applications but has low hardness and requires surface hardening.

4. Unacceptable Steels

P20, 718, 45# steel, and general Cr12MoV are not corrosion-resistant or heat-stable enough for PFA and will rapidly corrode or fail.

Table: PFA Mold Steel Selection Guide

5. Key Processing Recommendations

Conclusion