Understanding rubber hardness is essential when selecting materials for specific applications, particularly for rubber seals and gaskets. Shore A and IRHD are two standard hardness scales that help determine the strength and durability of rubber. But how do they differ, and why is it important for your rubber product choices?
The key difference between Shore A and IRHD lies in the method of measurement and their applications. Shore A is commonly used for softer materials like rubber seals, while IRHD is suited for harder elastomers.
Rubber hardness determines how well a material will perform under pressure, stress, or compression. Both Shore A and IRHD measure this, but each scale is tailored for different material types and testing conditions. In this post, we will dive into the differences, and how to choose the right scale for your application.
What is the meaning of IRHD hardness?
To understand the differences between Shore A and IRHD, we first need to define IRHD hardness and what it means in rubber testing.
IRHD1 (International Rubber Hardness Degree) measures the resistance of harder rubber compounds to indentation, often used for industrial rubber products.
IRHD hardness1 is a global standard for measuring the hardness of harder rubber materials, particularly those used in engineering and heavy-duty applications. This scale uses a special indenter to measure how much a sample resists indentation under a defined force. Unlike Shore A, which is designed for softer materials, IRHD is intended for tougher elastomers, such as those used in automotive seals, industrial wheels, and heavy machinery parts. Understanding IRHD helps in selecting materials that need to withstand high pressure and heavy-duty use.
What is the difference between Shore A and IRHD?
Now that we understand what IRHD measures, let's explore the key differences between Shore A and IRHD.
| Feature | Shore A | IRHD |
|---|---|---|
| Indenter Type | Truncated cone | Spherical |
| Measurement Method | Spring-loaded indentation | Load-based indentation |
| Time Required | 1-3 seconds | 35 seconds |
| Sample Thickness | Typically 6 mm | Typically 2 mm for micro tests |
| Destructive Testing | Yes (leaves an indentation) | No (non-destructive) |
| Applications | General rubber products | Soft rubber materials, O-rings |
Shore A2 measures the hardness of softer rubber, while IRHD is used for harder rubbers. Both scales serve specific purposes based on the material's flexibility and use.
Shore A and IRHD differ mainly in the way they measure hardness and the types of rubber they are used for. Shore A measures softer elastomers like gaskets and seals, typically ranging from 20A to 100A. IRHD, on the other hand, measures harder materials such as engineering rubbers and elastomers, with higher ranges that reflect a more rigid structure.
Shore A uses a durometer with a blunt needle to measure resistance to indentation. The scale is primarily used for materials that require flexibility and compression, such as rubber seals and hoses. For example, a soft rubber hose used in HVAC systems may have a Shore A hardness of 50-70.
IRHD, however, uses a smaller indenter with a greater force to assess harder elastomers. This scale is ideal for materials like rubber wheels or industrial seals, which need to maintain rigidity and durability under heavy use.
What is the Shore scale for hardness?
What exactly is the Shore scale? Let’s break down how it works to measure hardness for rubber materials.
The Shore scale3 is a standard used to measure the hardness of rubber materials, primarily focusing on the degree of resistance to indentation.
The Shore scale ranges from 0 to 100, with higher numbers indicating harder materials. Shore A specifically measures softer elastomers, while other scales (Shore D, Shore OO) measure different hardness levels suited for harder or more flexible materials.
How to calculate Shore hardness?
Calculating Shore hardness is relatively straightforward, but it requires careful measurements using specific tools and conditions.
Shore hardness4 is measured using a durometer, which applies a specific amount of pressure to the material and measures how much it resists indentation.
To calculate Shore hardness, a durometer is pressed into the surface of the material, and the depth of indentation is measured. This depth is then converted into a numerical value based on the Shore scale. The higher the Shore value, the less the material compresses under pressure, indicating greater hardness.
What is IRHD hardness measurement?
Similar to Shore hardness, IRHD also measures the resistance of rubber to indentation, but with a specific focus on harder elastomers.
IRHD hardness measurement5 involves an indenter that measures how much resistance a harder rubber sample offers when pressure is applied.
The IRHD measurement is performed using a specially designed indenter and a constant force, ensuring accurate readings for harder rubbers. The result is recorded on a scale that ranges typically from 40 to 100 IRHD, depending on the material's hardness. This measurement method is essential for products that require higher strength, such as automotive components or heavy-duty seals.
Shore A vs. IRHD: How to Converse?
So, how do you convert between Shore A and IRHD if necessary? Understanding the conversion process helps when you work with different scales.
To convert hardness test results between Shore A and IRHD, it is essential to understand the relationship between these two scales. The conversion is not direct but can be approximated using established formulas based on empirical data.
Approximate Conversion Formula
The commonly referenced equation for converting Shore A hardness to IRHD is:
IRHD≈Shore A+4IRHD≈Shore A+4
This means that if you have a Shore A reading, you can estimate the corresponding IRHD value by adding 4. For example, a Shore A hardness of 60 would approximately equal an IRHD of 64.
Conclusion
Understanding the difference between Shore A and IRHD is crucial for selecting the right rubber material for your application. Each scale serves a distinct purpose, ensuring your products meet the necessary performance standards for hardness and durability.
I'Kelly, at Julong Rubber, is committed to offering high-quality rubber products tailored to your specific needs, whether for softer seals or harder industrial components.
For further assistance in selecting the right testing method or optimizing your quality control processes, feel free to reach out for expert guidance tailored to your specific requirements.
Footnotes:
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IRHD is a global standard for harder elastomers, essential for testing industrial rubber products. ↩ ↩
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Shore A measures softer rubber materials and is essential for selecting materials that need flexibility and compression. ↩
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Shore scale defines the resistance of rubber to indentation, which is key in determining the hardness of rubber products. ↩
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Shore hardness is measured using a durometer and is a fundamental process in selecting materials for specific applications. ↩
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IRHD hardness measurement is crucial for accurate testing of harder elastomers, especially for heavy-duty components. ↩
