Hardness is a commonly specified property for rubber components, but the various measurement scales and their applications can be confusing. In this blog, we’ll explore the Shore hardness scales and how they impact the performance of elastomeric components.
What is Shore Hardness?
Shore hardness measures the resistance of rubber to indentation. Named after Albert Ferdinand Shore, who developed the measurement method in the 1920s, it provides a quick, non-destructive way to evaluate rubber firmness. The measurement is taken with a durometer, which presses a specific type of indenter into the material under controlled conditions.
Shore A vs. Shore D: Which Scale to Use?
The two most common scales for elastomers are:
- Shore A: Used for measuring softer materials (5A-95A)
- Shore D: Used for harder materials (30D-90D)
There’s overlap between these scales, with Shore 95A approximately equivalent to Shore 45D. For ultra-soft materials, other scales like Shore OO may be used.
How Hardness Impacts Performance
Hardness influences several key performance characteristics:
- Compression force: Harder materials require more force to compress
- Sealing ability: Softer materials conform better to irregular surfaces for low sealing pressure. Higher pressure needs a higher hardness to prevent blowout.
- Abrasion resistance: Generally increases with hardness
- Rebound: Typically decreases as hardness increases
Common Hardness Ranges for Applications
- Dynamic seals: 70-80A for optimal balance of sealability and wear resistance
- Static seals: 60-70A for better conformability to mating surfaces
- Vibration isolation: 40-60A for greater dampening capability
- Structural components: 80A-60D for load-bearing applications
Beyond the Number
While hardness is important, it shouldn’t be the only consideration when specifying rubber materials. Tensile strength, elongation, compression set, and chemical resistance also play crucial roles in component performance.
Understanding Shore hardness scales helps engineers select the right rubber compound for their specific application requirements, balancing the trade-offs between softness for conformability and hardness for durability and structural integrity.
Looking for more information about Shore hardness scales in rubber components? Contact the helpful engineers at Apple Rubber!