PA (polyamide) materials, including PA6, PA66, glass-filled PA, and flame-retardant PA, have high shrinkage, certain abrasiveness, and may produce corrosive gases during processing.Therefore, mold steel selection must focus on wear resistance, corrosion resistance, polishability, dimensional stability, and thermal conductivity.Reasonable mold steel selection can effectively extend mold life, ensure product appearance and dimensional stability, and improve production efficiency.
Key Characteristics of PA Materials Affecting Mold Steel
PA materials have a shrinkage rate of about 0.8%–2.0%, and the shrinkage is more obvious after glass fiber addition.Glass-filled PA has strong abrasiveness, which will accelerate the wear of mold cavity and core.Some flame-retardant or modified PA will release corrosive substances during processing, which may corrode the mold surface.PA materials also require good mold exhaust and stable temperature control to avoid defects such as shrinkage cavity, warpage, and poor appearance.
Basic Requirements of Mold Steel for PA Products
Excellent wear resistance, especially for glass-filled PA materials.High hardness and stability to ensure dimensional accuracy in long-term production.Good corrosion resistance for flame-retardant and corrosive modified PA.Good machinability and polishing performance to ensure smooth surface and demolding.Suitable thermal conductivity to ensure consistent cooling and shorten molding cycle.
Common Mold Steel Selection Comparison Table for PA Products
| Material Type | Typical Mold Steels | Hardness Range | Main Advantages | Suitable Scenarios |
|---|
| Unfilled PA6, PA66 | P20, 718H, NAK80 | HRC 28–35 | Good toughness, easy machining, good polishability | Low to medium production, general appearance requirements |
| Glass-filled PA | H13, SKD61, S136 | HRC 48–54 | High wear resistance, good heat stability | High production, strong abrasiveness, long mold life required |
| Flame-retardant / Corrosive PA | S136, STAVAX, 420SS | HRC 50–54 | Excellent corrosion resistance, high polishability | Corrosive additives, high-gloss appearance, long service life |
| High-gloss PA parts | NAK80, S136 | HRC 30–54 | Mirror polishing, no rust, stable surface | Transparent / high-gloss appearance, no demolding marks |
Mold Steel Introduction for Different PA Materials
For conventional unfilled PA6 and PA66 products with low to medium production volume, pre-hardened plastic mold steels such as P20 and 718H are the most cost-effective choices.
They have good processing performance and can meet basic service life and appearance requirements.
NAK80 can be used for products with high surface requirements, which can achieve better polishing effect without quenching and tempering.
For glass-filled PA products, the abrasiveness is greatly increased, so it is necessary to choose mold steels with high wear resistance.
H13 and SKD61 have good high-temperature strength and wear resistance after heat treatment, and are suitable for long-term mass production.
S136 stainless steel has both high wear resistance and corrosion resistance, and is suitable for high-demand working conditions.
For flame-retardant PA and chemically modified PA, corrosive gas will be produced during processing, so stainless mold steels such as S136 must be used.
It can effectively prevent mold surface corrosion and rust, and ensure product surface quality and mold life.
Surface Treatment and Hardness SuggestionsAppropriate surface treatment can further improve the service life of the mold.
Nitriding treatment can form a high-hardness and wear-resistant surface layer, which is suitable for most glass-filled PA molds.
Coating treatments such as TiN and DLC can reduce friction and improve demolding performance.
The hardness of pre-hardened steel is generally controlled at HRC 28–35, and the hardness of quenched and tempered steel is controlled at HRC 48–54.
SummaryUnfilled PA can choose conventional pre-hardened mold steels.
Glass-filled PA needs to choose wear-resistant tool steels.
Flame-retardant and corrosive PA must use corrosion-resistant stainless steels.
Combined with production volume, appearance requirements and service life, the mold steel can be reasonably selected to ensure the stability and economy of PA injection molding production.
