The selection of steel for the hot runner nozzle in an injection mold is a critical factor that directly determines the system's service life, part quality, and production stability. The nozzle is subjected to extreme conditions: continuous high temperatures, high-pressure melt flow, and repeated thermal cycling. Therefore, the material must exhibit excellent thermal conductivity, high temperature strength, wear resistance, corrosion resistance, and machinability. This list outlines the key steel grades, their core properties, application scenarios, and selection priorities for hot runner nozzles.
1. Core Performance Requirements for Hot Runner Nozzle Steels
The hot runner nozzle is the "heart" of the system, and its material must meet several non-negotiable criteria:
Thermal stability: To maintain consistent temperature distribution and resist thermal fatigue.
High temperature strength: To prevent deformation and failure under prolonged exposure to molten plastic (200–350°C).
Wear and corrosion resistance: To withstand the erosive and corrosive effects of filled and engineering plastics.
Thermal conductivity: To ensure efficient heat transfer and prevent cold slugs.
Machinability: To allow for the precise fabrication of complex internal flow channels.
2. Recommended Steel Grades and Their Applications
1. Primary Choice: H13 (1.2344 / SKD61) Hot Work Tool Steel
H13 is the industry standard and most recommended material for hot runner nozzles. Its exceptional combination of high temperature strength, toughness, and thermal fatigue resistance makes it ideal for the demanding environment of hot runner systems. When properly heat-treated to HRC 48–52, H13 nozzles offer excellent durability and resistance to deformation. It is suitable for a wide range of plastics, from general-purpose materials like PP and ABS to engineering plastics such as PA and PBT. For applications involving highly filled or corrosive materials, H13 can be further enhanced with surface treatments like nitriding or PVD coatings.
2. High-Corrosion Resistance: S136 (1.4313) Martensitic Stainless Steel
For applications involving corrosive plastics like PVC, PPS, or flame-retardant materials, S136 is the superior choice. This high-chromium stainless steel, when hardened to HRC 48–54, provides outstanding corrosion resistance, preventing the nozzle from rusting or degrading due to acidic decomposition products. Its excellent polishability also ensures smooth melt flow, reducing the risk of shear-induced degradation. S136 is the preferred material for high-precision, high-quality hot runner systems in the medical, electronic, and automotive industries.
3. High-Wear Performance: DC53 (Modified SKD11) Cold Work Tool Steel
When molding highly filled materials (e.g., >40% glass fiber), the wear on the nozzle becomes the primary concern. DC53, with its high hardness (HRC 58–62) and exceptional wear resistance, is designed for these extreme conditions. It can withstand the constant scouring of abrasive fillers, significantly extending the nozzle's service life. However, its lower toughness requires careful heat treatment and design to avoid cracking under thermal stress.
4. Cost-Effective Option: 420 Stainless Steel
For less demanding applications, such as molding unfilled plastics in moderate volumes, 420 stainless steel offers a cost-effective alternative. It provides good corrosion resistance and can be hardened to HRC 45–50, offering a reasonable balance of performance and cost. It is commonly used in standard hot runner systems for consumer goods and packaging.
Conclusion
The selection of steel for a hot runner nozzle is a strategic decision that balances performance, cost, and application requirements. H13 remains the versatile workhorse for most applications, while S136 and DC53 provide specialized solutions for corrosion and wear challenges, respectively. By carefully matching the steel grade to the specific molding conditions, manufacturers can ensure the reliability, longevity, and efficiency of their hot runner systems.
