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Hei-Cast 8400 Series Vacuum Casting Material
The Hei-Cast 8400 Series is a versatile family of polyurethane elastomers designed to simulate the properties of commercial rubber and silicone. Unlike rigid plastics, these resins offer excellent flexibility, tear strength, and resilience. What makes this series unique is its adjustable hardness range—from soft Shore 40A to semi-rigid Shore 90A. At JUCHENG, we utilize the 8400 series to prototype functional seals, gaskets, and soft-touch buttons. It is also our primary material for overmolding applications, where a soft rubber layer is cast over a rigid substrate to create ergonomic grips.
Hei-Cast 8400

Basic Characteristics & Composition

The 8400 series consists of multiple grades (e.g., 8440, 8450, 8460, etc.) that can be mixed to achieve precise hardness targets.
  • Rubber Simulation: It effectively mimics the look, feel, and performance of TPE, TPU, and vulcanized rubber.
  • Variable Hardness: JUCHENG can dial in the specific durometer required for your project, ensuring the prototype feels exactly like the final product.
  • High Tear Strength: It resists tearing even when stretched or twisted, suitable for functional testing.
  • Good Rebound: Offers excellent elastic recovery (memory) after deformation.
Hei-Cast 8400 rubber grip

Color Options

  • Standard: Milky White / Translucent (depending on grade) or Black.
  • Pigmentation: Elastomers accept color pigments very well. We can produce parts in Black, Red, Blue, or custom colors.
  • Painting: Painting rubber is difficult due to flexibility. We recommend integral coloring (adding pigment to the liquid resin) for the most durable finish that won't crack when bent.

Key Technical Parameters

1. (We cover the full spectrum of hardness options):
Grade Hardness (Shore A) Tensile Strength (MPa) Elongation (%) Tear Strength (kN/m) Ideal Application
8440 40 A (Soft) 3 - 5 500 - 600 20 - 25 Soft gaskets, bellows, flexible masks.
8460 60 A (Medium) 10 - 15 350 - 450 35 - 40 Door seals, buttons, shoe soles.
8470 70 A (Standard) 15 - 20 300 - 400 45 - 50 Automotive tires (RC models), hoses.
8490 90 A (Hard) 20 - 25 200 - 300 60 - 70 Hard rubber feet, industrial rollers, semi-rigid clips.
  • Linear Shrinkage: 0.5% - 1.0% (Higher than rigid resins, compensated in mold design).
2. PROCESSING 
  • Vacuum Casting: Essential to remove bubbles which would ruin the tear strength of rubber parts.
  • Pot Life: Varies by grade, typically 10-15 minutes.
  • Demolding: Elastomers take longer to cure than rigid plastics. Demold time is usually 60-90 minutes at 70°C.
  • Post-Cure: Extended post-curing is critical to achieve the final rated hardness and rebound properties.
 

Application Scenarios & Fields

  • Sealing: O-rings, flat gaskets, waterproof seals for electronic enclosures.
  • Human Interface: Soft-touch keypads, rubberized grips, ergonomic handles.
  • Automotive: Vibration dampeners, hoses, interior knobs, grommets.
  • Overmolding: "Soft-over-Hard" prototypes (e.g., a power tool handle with a soft grip). We cast the 8400 resin directly onto a pre-made rigid plastic or metal core.

Vacuum Casting Process Compatibility

  • Silicone Tooling: Elastomers are very easy to demold from silicone tooling, even with deep undercuts, due to their flexibility.
  • Adhesion: Excellent adhesion to primed metal or rigid urethane inserts for overmolding projects.
  • Surface Finish: We recommend a VDI (Textured) finish on the mold. High-gloss rubber can feel "tacky" or sticky; a texture provides a better tactile experience.

Advantages vs. Limitations

Advantages Limitations
Custom Hardness: Tailored to specific shore requirements. Surface Tack: Very soft grades (<40A) can feel sticky and attract dust.
Durability: Excellent resistance to abrasion and tearing. Machining: Cannot be machined or sanded effectively (it just bends). Must be cast to net shape.
Overmolding: Bonds well to other materials. Shrinkage: Higher shrinkage rate than rigid parts makes tight tolerances harder to hold.
Elasticity: Great elongation and recovery. Paint: Surface painting is not recommended; pigmentation is preferred.

Manufacturers & Alternatives

  • Manufacturer: Hei-Cast (H&K Ltd., Japan).
  • Alternatives at JUCHENG:
For a European Alternative (High Performance): We recommend Axson UP 7495.
For rigid parts: Use Hei-Cast 8150.
Learn more about ABS type materials
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