Choosing the right Shore hardness: Explained from 0A to 90A
Shore hardness is one of the most important material properties when selecting silicones. It determines whether a component will be soft and flexible or rigid and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for developing functional prototypes and series production products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured according to DIN ISO 7619-1 . The measuring principle is based on the penetration depth of a standardized test specimen into the material surface under a defined force. The deeper the test specimen penetrates, the softer the material and the lower the Shore value.
There are different Shore scales for different hardness ranges:
Shore 00: For very soft, gel-like materials (0-100). The indenter is a ball with low spring force. Typical for soft gels and foams.
Shore A: The most common scale for elastomers (0-100). The indenter is a truncated cone. It covers the range from very soft to medium-hard rubber materials and is the standard scale for RTV silicones.
Shore D: For hard elastomers and soft plastics (0-100). The indenter is a pointed cone. This scale is used for very hard rubber compounds and thermosets.
For silicones, Shore A and Shore D are relevant, with Shore A covering the majority of the range. The scales partially overlap: a material with Shore A 90-95 corresponds approximately to Shore D 40-45. RTV silicones typically range between Shore A 0 and Shore A 70.
Shore hardness table
| Shore A | hardness level | Everyday comparison | Typical application |
|---|---|---|---|
| 0-10 | Very soft, gel-like | Jell-O, chewing gum | Softest impressions, skin imitations, special cushions |
| 10-20 | Very soft, pliable | Soft bath sponge | Soft seals, medical cushions, flexible potting compounds |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molded rubbers, soft O-rings |
| 30-40 | Medium soft | Car tire tread | Universal molding silicones, standard gaskets |
| 40-50 | Medium-firm | Solid eraser, door seal | Mold making standard, technical seals |
| 50-60 | Firmly | Golf practice ball, shoe sole | Precision molds, durable seals |
| 60-70 | Hard | Shopping cart brake | Heavy-duty molds, industrial seals |
| 70-80 | Very hard | heel of a leather shoe | Special shapes with high stability |
| 80-90 | Extremely hard | Hard plastic transition | quasi-rigid technical components |
In practical terms, this means:
- Shore A 15-25: Maximum flexibility, low mechanical strength
- Shore A 30-40: Optimal compromise for detailed impressions
- Shore A 40-50: Standard in professional mold making
- Shore A 60-70: When mechanical stability is more important than flexibility
Shore hardness of silicones in practice
Silicone-based elastomers are generally divided into RTV-1 (one-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 silicones typically have a Shore A hardness of 15-50. They are supplied pre-mixed and cure through exposure to atmospheric moisture.
RTV-2 silicones offer significantly more flexibility. They cover the entire range from Shore A 0 (ultra-soft gels) to Shore A 70 (very hard molding compounds).
Relationship between Shore hardness and mechanical properties:
- Tensile strength: Typically increases with Shore hardness.
- Elongation at break: Behaves in the opposite direction. Softer silicones achieve higher elongations.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness is suitable for which application?
Mold making and molding
Shore A 20-30 (soft): Ideal for models with strong undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototype construction and small-series mold making. Example: SILISIL RTV MF Dura 30 with Shore A 30.
Shore A 50-60 (hard): For precise, dimensionally stable molds with a long service life.
Seals and O-rings
Shore A 40-50: Standard range for static seals.
Shore A 60-70: For dynamic seals in pneumatics and hydraulics.
Shore A 70-80: Special applications with high mechanical loads.
Technical components
Shore A 30-40: Vibration dampers, rubber feet, flexible couplings.
Shore A 50-60: Roller coatings, conveyor belt elements, protective padding.
Shore A 60-80: Technical rollers, gears, buffers with high load capacity.
Common mistakes when choosing Shore hardness
1. Mold too soft for large castings:
A Shore A 20 mold can sag under large, heavy castings. Solution: Use at least Shore A 30-40 or provide the mold with a support sleeve.
2. Mold too hard for complex undercuts:
A Shore A 60 mold is difficult to demold. Solution: Choose Shore A 30-40 or construct the mold in multiple parts.
3. Shore hardness without considering processing temperature:
Silicones soften at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion between Shore A and Shore D:
Shore D 40 is significantly harder than Shore A 40. Solution: Always pay attention to the correct scale.
5. No long-term stability testing:
Soft silicones can harden over months due to plasticizer migration. Solution: Conduct aging tests.
FAQ
Conclusion
Choosing the correct Shore hardness is crucial for the success or failure of a silicone application. For mold making and mold construction, the Shore A 30-50 range is optimal. For seals, the mechanical load determines the hardness: Shore A 40-50 for static applications, Shore A 60-70 for dynamic applications.
Are you unsure which Shore hardness is optimal for your application?
Our application engineering team at SILITECH will be happy to advise you personally. Contact us for a free initial consultation and sample delivery.
Choosing the right Shore hardness: Explained from 0A to 90A
Shore hardness is one of the most important material properties when selecting silicones. It determines whether a component will be soft and flexible or rigid and dimensionally stable. For engineers, mold makers, and product developers, understanding the Shore scale is crucial for developing functional prototypes and series production products.
What is Shore hardness?
Shore hardness is a measure of the indentation hardness of elastomeric materials and is measured according to DIN ISO 7619-1 . The measuring principle is based on the penetration depth of a standardized test specimen into the material surface under a defined force. The deeper the test specimen penetrates, the softer the material and the lower the Shore value.
There are different Shore scales for different hardness ranges:
Shore 00: For very soft, gel-like materials (0-100). The indenter is a ball with low spring force. Typical for soft gels and foams.
Shore A: The most common scale for elastomers (0-100). The indenter is a truncated cone. It covers the range from very soft to medium-hard rubber materials and is the standard scale for RTV silicones.
Shore D: For hard elastomers and soft plastics (0-100). The indenter is a pointed cone. This scale is used for very hard rubber compounds and thermosets.
For silicones, Shore A and Shore D are relevant, with Shore A covering the majority of the range. The scales partially overlap: a material with Shore A 90-95 corresponds approximately to Shore D 40-45. RTV silicones typically range between Shore A 0 and Shore A 70.
Shore hardness table
| Shore A | hardness level | Everyday comparison | Typical application |
|---|---|---|---|
| 0-10 | Very soft, gel-like | Jell-O, chewing gum | Softest impressions, skin imitations, special cushions |
| 10-20 | Very soft, pliable | Soft bath sponge | Soft seals, medical cushions, flexible potting compounds |
| 20-30 | Soft, flexible | Eraser, soft shoe sole | Flexible molded rubbers, soft O-rings |
| 30-40 | Medium soft | Car tire tread | Universal molding silicones, standard gaskets |
| 40-50 | Medium-firm | Solid eraser, door seal | Mold making standard, technical seals |
| 50-60 | Firmly | Golf practice ball, shoe sole | Precision molds, durable seals |
| 60-70 | Hard | Shopping cart brake | Heavy-duty molds, industrial seals |
| 70-80 | Very hard | heel of a leather shoe | Special shapes with high stability |
| 80-90 | Extremely hard | Hard plastic transition | quasi-rigid technical components |
In practical terms, this means:
- Shore A 15-25: Maximum flexibility, low mechanical strength
- Shore A 30-40: Optimal compromise for detailed impressions
- Shore A 40-50: Standard in professional mold making
- Shore A 60-70: When mechanical stability is more important than flexibility
Shore hardness of silicones in practice
Silicone-based elastomers are generally divided into RTV-1 (one-component, moisture-curing) and RTV-2 (two-component, addition-curing or condensation-curing) systems.
RTV-1 silicones typically have a Shore A hardness of 15-50. They are supplied pre-mixed and cure through exposure to atmospheric moisture.
RTV-2 silicones offer significantly more flexibility. They cover the entire range from Shore A 0 (ultra-soft gels) to Shore A 70 (very hard molding compounds).
Relationship between Shore hardness and mechanical properties:
- Tensile strength: Typically increases with Shore hardness.
- Elongation at break: Behaves in the opposite direction. Softer silicones achieve higher elongations.
- Compression set: Tends to improve with increasing hardness.
- Abrasion resistance: Increases with hardness.
Which Shore hardness is suitable for which application?
Mold making and molding
Shore A 20-30 (soft): Ideal for models with strong undercuts and complex geometry.
Shore A 30-40 (medium): The standard in prototype construction and small-series mold making. Example: SILISIL RTV MF Dura 30 with Shore A 30.
Shore A 50-60 (hard): For precise, dimensionally stable molds with a long service life.
Seals and O-rings
Shore A 40-50: Standard range for static seals.
Shore A 60-70: For dynamic seals in pneumatics and hydraulics.
Shore A 70-80: Special applications with high mechanical loads.
Technical components
Shore A 30-40: Vibration dampers, rubber feet, flexible couplings.
Shore A 50-60: Roller coatings, conveyor belt elements, protective padding.
Shore A 60-80: Technical rollers, gears, buffers with high load capacity.
Common mistakes when choosing Shore hardness
1. Mold too soft for large castings:
A Shore A 20 mold can sag under large, heavy castings. Solution: Use at least Shore A 30-40 or provide the mold with a support sleeve.
2. Mold too hard for complex undercuts:
A Shore A 60 mold is difficult to demold. Solution: Choose Shore A 30-40 or construct the mold in multiple parts.
3. Shore hardness without considering processing temperature:
Silicones soften at elevated temperatures. Solution: Choose a harder formulation or use HTV silicones.
4. Confusion between Shore A and Shore D:
Shore D 40 is significantly harder than Shore A 40. Solution: Always pay attention to the correct scale.
5. No long-term stability testing:
Soft silicones can harden over months due to plasticizer migration. Solution: Conduct aging tests.
FAQ
Conclusion
Choosing the correct Shore hardness is crucial for the success or failure of a silicone application. For mold making and mold construction, the Shore A 30-50 range is optimal. For seals, the mechanical load determines the hardness: Shore A 40-50 for static applications, Shore A 60-70 for dynamic applications.
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