Plastic mold steel hardening, what, where, why and how.

Mold steel hardening is crucial for enhancing the performance and lifespan of molds used in manufacturing. Initially, mold steels typically have a hardness ranging from 20 to 30 HRC (Rockwell Hardness). After hardening, the target hardness usually reaches between 45 to 60 HRC, depending on the specific requirements and type of mold steel used.

Popular Processes to Harden Mold Steels

1. Heat Treatment
   • Process: Heat treatment involves heating the steel to a high temperature, typically between 800°C and 1100°C, followed by rapid cooling (quenching) and tempering.
   • Application: This method is versatile and applicable to most mold steels.
   • Hardness Achieved: 45 to 60 HRC.
2. Nitriding
   • Process: Nitriding introduces nitrogen into the surface of the steel at temperatures around 500°C to 550°C.
   • Application: Ideal for creating a hard, wear-resistant surface without significant distortion.
   • Hardness Achieved: Surface hardness can reach 60 to 70 HRC.
3. Cryogenic Treatment
   • Process: This involves cooling the steel to temperatures as low as -196°C to transform retained austenite into martensite.
   • Application: Enhances wear resistance and reduces residual stresses.
   • Hardness Achieved: Improves toughness without significantly increasing hardness.

Key Areas of a Mold That Must Be Hardened

Besides the core, cavity, and runners, several other areas of a mold benefit from hardening:

• Ejector Pins: These are responsible for pushing the final product out of the mold. Hardened ejector pins prevent bending and wear.
• Sprue Bushings: These guide the molten material from the injection nozzle into the runner system. Hardening prevents erosion and wear.
• Gate Inserts: These control the flow of material into the mold cavity. Hardened gate inserts ensure consistent flow and reduce wear.
• Guide Pins and Bushings: These components maintain the alignment of mold halves during the injection process. Hardening ensures they can withstand repeated stress without deforming.

Principles in Selecting Plastic Mold Steel Hardening Processes

The choice of hardening process depends on several factors:

1. Material Type: Different mold steels respond better to specific hardening methods. For example, some steels are better suited for nitriding, while others perform well with traditional heat treatment.
2. Desired Properties: If surface hardness and wear resistance are crucial, nitriding might be preferred. For overall toughness, heat treatment or cryogenic treatment could be more suitable.
3. Dimensional Stability: Processes like nitriding, which occur at lower temperatures, cause less distortion, making them ideal for precision components.
4. Cost and Complexity: Some processes, such as cryogenic treatment, can be more expensive and complex. The choice often balances performance benefits against cost and feasibility.
5. Application Requirements: The specific demands of the application, such as resistance to wear, impact, or thermal stresses, guide the selection of the hardening process.

By considering these factors, manufacturers can select the most appropriate plastic mold steel hardening method to ensure the mold’s performance and longevity meet the required standards.

VolksMolds is a leading plastic injection mold manufacturer known for its expertise, experience, and proven history. Moreover, the company excels in producing high-precision molds for various sectors, including packaging, store displays, and homewares. With a commitment to quality and innovation, VolksMolds consistently delivers reliable and efficient molds, thereby earning a strong reputation in the global market.