Shore A What is hardness?
Silicone hardness commonly used Shore A Indicates that the larger the value, the "harder" it is. Hardness has a direct effect:
- Sealing and Laminating Capability
- Extrusion resistance
- Assembly feel and assembly risk
- Compression set and lifetime performance (in conjunction with formulation/process)
4 Questions to Ask Before Choosing Hardness
- Is it a static or dynamic seal?
- Is the gap large? Is the pressure high?(Decision to crowd out risk)
- What is the assembly method?(hand fitted/automatic assembly/with or without chamfering)
- Does it need to feel and look good?(buttons, grips, mom and pop, etc.)
How to use common hardness intervals (experience oriented)
- 30-40A: Softer and better fitting for products with imperfect fitting surfaces or those that require a soft touch; but more prone to extrusion or scratching.
- 50-60A: The most widely used, taking into account the fit and structural support, commonly used in gaskets, silicone rings, overmolded parts.
- 70A and above: More resistant to extrusion and supportive for larger gaps or higher pressure scenarios; more sensitive to assembly chamfers and surface quality.
If you don't have definitive data, many projects can start with 50-60A as a starting point for proofing and fine tuning.
Hardness is not the only indicator: it also depends on the "recipe and process".
Again, 60A, different formulas can vary a lot in these areas:
- tear resistance
- rebound (of stock market etc)
- Odor and precipitation
- aging resistance
- Permanent deformation in compression
When do I need to "lower my hardness"?
- Assembly surface is not flat, needs better fit
- High sealing requirements but limited compression
- Desire to reduce assembly force
When do I need to "harden up"?
- Large gaps, risk of extrusion
- Need for stronger structural support
- Product has relative motion, worry about biting edges
Suggested validation methods (more Google-compliant and implementable)
- Do it once with a sampleAssembly verification: Assembly force, scratch condition
- do it onceSeal verification: Spray/water immersion/airtight (to your standards)
- If sealed for a long time: doThermal aging + compression setcomparison
You can submit requirements like this
"For XX structural seals, compression approx. XX, operating temperature XX, medium XX, assembly method XX, hardness range recommendation and sample verification desired."