How to Select Mold Steel for TPR Products

TPR is a thermoplastic elastomer with medium fluidity and low corrosion. Mold steel selection depends on hardness, transparency, output, and appearance requirements.

Key Requirements for TPR Molds

Wear resistance: Critical for filled/reinforced TPR or high-recycled-content materials.Corrosion resistance: Necessary for TPR grades that release acidic additives at high temperatures.Polishability: Essential for high-gloss, textured, or transparent TPR surfaces.Toughness: Required for high-speed injection or thin-wall products to prevent mold chipping.

Material Selection by Production Volume & Appearance

Low volume / Prototype / Standard appearance (＜100,000 shots): 

45# steel / P20 / 718H (low cost, easy machining).

Medium volume / Matte finish / Regular TPR (100,000–500,000 shots): 

718H / NAK80 (uniform hardness, rust-resistant, cost-effective).

High volume / High-gloss / Durability (＞500,000 shots): 

NAK80 / S136 (pre-hardened, wear-resistant, stable polishing).

Transparent TPR / High-gloss finish: 

S136 / S136H (high purity, mirror polishable, corrosion-resistant).

Highly filled TPR / Extreme wear: 

H13 (quenched) / SKD61 / wear-resistant stainless steel (high hardness, erosion-resistant).

Practical Selection Rules

Standard soft TPR (0–50A) / Non-transparent: 718H / NAK80 is sufficient.

Medium-high hardness TPR (60A–90A) 

Mass production: NAK80 / S136H.Transparent/semi-transparent TPR 

High-gloss: S136 / S136H.Filled TPR / High wear 

High recycled content: SKD61 / H13 / wear-resistant stainless steel.Export molds

High durability / Stability: S136 or imported NAK80.

Selection Pitfalls to Avoid

Do not use low-grade steel to save cost: 45# steel causes flash, wear, and rust in long-term production.

Use mirror stainless steel for transparent TPR: P20/718 leads to water marks, flow lines, or yellowing.

Choose high-wear steel for filled TPR: Otherwise, cavity erosion and dimension deviation occur quickly.