Alexei Volkov
Durometer, or Shore durometer, is a standardised way to measure the hardness of materials like rubber and plastics. It is a critical factor to consider when manufacturing with plastic, as hardness is a measure of how resistant a plastic is to deformation caused by mechanical indentation or abrasion. The Shore hardness scale is an internationally accepted standard that quantifies the hardness of a material, with 00 being the softest material and 100 being the hardest. When it comes to plastics, Shore A durometers are typically used for softer materials, ranging from flexible rubbers to semi-rigid plastics with minimal flexibility. On the other hand, Shore D durometers are used for harder materials, including hard rubbers, semi-rigid plastics, and hard plastics. While there is no direct relationship between IRHD readings and Shore durometer, the latter is generally preferred due to its widespread adoption and ease of measurement.
| Characteristics | Values |
|---|---|
| Durometer Definition | A standardized way to measure the hardness of materials like rubber (elastomers) and plastics |
| Durometer Measurement Scale | Ranges from 0 to 100 |
| Durometer Numbers | Represent a relative comparison of hardness between different but similar materials |
| Higher Durometer | Indicates harder plastics |
| Lower Durometer | Indicates softer plastics |
| Shore A Durometer | For softer materials, ranging from flexible rubbers to semi-rigid plastics with minimal flexibility |
| Shore D Durometer | For harder materials, including hard rubbers, semi-rigid plastics, and hard plastics |
| Shore OO Durometer | Measures extremely soft rubbers and gels |
| IRHD (International Rubber Hardness Degrees) | Another standard for measuring rubber hardness |
| Durometer Tester | An apparatus used by engineers to test the hardness of a material, resembling a round tire pressure gauge with a needle on a calibrated spring |
| Durometer Hardness Impact | Influences performance, longevity, and overall product quality in various applications |
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What You'll Learn
What is durometer?
Durometer, also known as Shore durometer, is a standardised way of measuring the hardness of materials like rubber (elastomers) and plastics. It is a critical factor in process control, especially in industries that utilise rubber and plastic materials. The durometer scale, developed by Albert Shore in the 1920s, quantifies hardness using various scales, including Shore A and Shore D. Shore A durometers are for softer materials, ranging from flexible rubbers to semi-rigid plastics with minimal flexibility. Shore D durometers, on the other hand, are for harder materials, including hard rubbers, semi-rigid plastics, and hard plastics.
Durometer measurements range from 0 to 100, but it is not a unit of measurement. Instead, it is a dimensionless measurement, indicating the relative hardness of a material compared to others measured using the same durometer scale. Lower durometer numbers represent softer materials, while higher numbers indicate harder ones. For example, 90A durometer polyurethane tubing is harder than 70A polyurethane tubing. The durometer measurement is obtained using a durometer tester, which resembles a round tyre pressure gauge with a needle on a calibrated spring. An engineer places the needle against the material and applies pressure, and the needle's penetration depth corresponds to the durometer hardness on the chosen scale.
The ASTM D2240 standard recognises twelve different Shore durometer scales for testing rubber hardness, including Shore OO, Shore A, and Shore D. Shore OO is used for extremely soft rubbers and gels, while Shore A measures flexible rubbers and Shore D measures hard materials. It is important to note that durometer hardness does not directly correlate with flexibility. Rather, it is an indirect measure of stiffness that provides a general sense of the material's feel. Additionally, hardness measurements should not be compared across different scales, as there is no direct relationship between hardness values on different durometer scales.
When selecting materials, engineers must balance desired hardness with other factors such as cost and ease of machining. Hardness is not the sole determinant of a material's properties, as it does not indicate strength or corrosion resistance. Other measurements, such as stiffness and compression modulus, may provide a more accurate assessment of a material's performance in specific applications. Nevertheless, understanding durometer hardness is crucial for ensuring materials meet the requirements of a project.
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How to measure durometer
Durometer refers to the hardness of a material, or its ability to resist deformation. It is a unitless value, meaning that a material's hardness is relative to the measured hardness of other materials when using the same durometer scale. Durometer is often used to measure the hardness of polymers and other nonmetals, especially plastics and rubbers.
To measure durometer, you need a durometer tool, which is a measuring device that uses specific, standardised techniques for measuring hardness. The tool is calibrated to meet the relevant technical standards. The ASTM D2240 is the standard measurement system used to measure the durometer of thermoplastic elastomers (TPEs), thermoset (vulcanized) rubbers, and elastomeric materials, among others. The most common Shore durometer scales used are Shore OO, Shore A and Shore D. Shore OO measures extremely soft materials like gels and rubbers. Shore A is for softer materials and ranges widely enough to cover flexible rubbers up to semi-rigid plastics with almost no flexibility. Shore D is for harder materials, including hard rubbers and plastics.
When using a durometer, the surface of the sample must be flat, clean and smooth. The durometer dial reads from 0 to 100 points. Readings less than 10 or above 90 should be avoided. If a reading is over 90 points on the A scale, use the D scale. If it is under 10 points on the D scale, use the A scale. Use other scales to obtain a reading closer to 50 points. If you are using a durometer that has been stored for a while, press the indentor on a surface about 20 times before using it. Measurements may tend to creep back if read at different times after testing, so it is recommended to keep this aspect consistent.
Durometer is important when choosing the right materials for a project. For example, in heat seal packaging applications, harder durometer rubbers provide better heat transfer properties than softer durometers.
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Shore hardness scales
The Shore A hardness scale ranges from 0 to 100, with higher numbers indicating a harder material. For example, a soft rubber band may have a Shore A hardness of around 40, while a hard rubber tire may have a Shore A hardness of 80.
The Shore D hardness scale also ranges from 0 to 100, but is used for harder materials. For instance, a soft plastic bottle may have a Shore D hardness of around 50, while a hard plastic polycarbonate may have a Shore D hardness of 85.
It's important to note that the Shore hardness scales are relative measures and that the hardness of a material can vary depending on factors such as temperature and the applied force. Therefore, Shore hardness values are typically measured at a standard temperature and using a specific type of durometer, which is a device used to measure hardness.
In the context of your query, "70 durometer plastics" refers to plastics that have a hardness of 70 on the Shore hardness scale. This hardness value is measured using a durometer with a specific spring force and a specified indentation diameter. The "tpi" in your query might refer to "threads per inch," but without additional context, I cannot provide a direct relationship between the Shore hardness of 70 and the number of threads per inch.
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Durometer and IRHD
Durometer is a standardised way to measure the hardness of materials like rubber (elastomers) and plastics. It is also known as Shore durometer, named after its inventor Albert Ferdinand Shore, who developed it in the 1920s. The durometer scale quantifies hardness using various scales, including Shore A and Shore D. Shore A durometers are for softer materials and range from flexible rubbers to semi-rigid plastics with almost no flexibility. Shore D durometers are for harder materials and compare hard rubbers, semi-rigid plastics and hard plastics. Shore OO is another scale, which measures extremely soft rubbers and gels.
Durometer measurements range from 0 to 100 but there is no durometer unit of measurement. Instead, durometer numbers represent a relative comparison of hardness between different but similar materials that have been measured using the same durometer scale, device and measurement standard. A higher durometer number indicates a harder material. For example, 90A durometer polyurethane tubing is harder than 70A polyurethane tubing.
The Shore durometer is the name of the measurement device. Over time, the name of this tool and its shortened form, durometer, have become a way of referring to a material’s hardness number. The Shore durometer is a widely adopted, fast and easy way to measure the hardness of rubber and plastic.
The International Rubber Hardness Degrees (IRHD) is another standard for measuring rubber hardness. The IRHD instrument has a spherical indentor that indents the sample under a minor and major load. The test is zeroed at this indentation position, and then the test force is applied. The distance between the two applied forces is measured and converted to an IRHD hardness value. There is no direct relationship between IRHD readings and Shore durometer, although Briscoe and Sebastian analysed the durometer indentation, providing an approximate relationship between IRHD and Shore A of (IRH º HA + 4).
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Durometer in relation to product application
Durometer is a standardised way to measure the hardness of materials like rubber (elastomers) and plastics. It is a critical factor in process control, especially in industries that utilise rubber and plastic materials. For instance, in heat seal packaging applications, harder durometer heat seal silicone rubbers provide better heat transfer properties than softer durometers.
The durometer scale, developed by Albert Shore in the 1920s, quantifies hardness using various scales, including Shore A and Shore D. Shore A durometers are for softer materials, ranging from flexible rubbers to semi-rigid plastics with almost no flexibility. Shore D durometers are for harder materials, comparing hard rubbers, semi-rigid plastics, and hard plastics.
When selecting materials for a project, engineers and product teams must consider the durometer in relation to the product's end-use application and project requirements. For example, in heat seal tooling, a harder durometer is recommended for the heated side, typically in the 70 to 90 Shore A durometer range, while 60 durometer or lower is suitable for the unheated side.
Additionally, durometer numbers are relative to the materials on their specific scale, and there is no direct relationship between hardness on different durometer scales. For instance, a material with a durometer hardness of 80 on the Shore 00 scale is about as hard as a pencil eraser, but the same measurement on the Shore D scale corresponds to the hardness of a hard hat. Therefore, it is crucial to compare materials' hardness only within the same scale.
Overall, durometer plays a significant role in product applications by helping engineers and product teams select suitable materials that meet the specific hardness or softness requirements of their projects.
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Frequently asked questions
Durometer, or Shore durometer, is a standardised way to measure the hardness of materials like rubber and plastics. It was developed by Albert Shore in the 1920s.
The durometer scale ranges from 0 to 100, with 00 being the softest material and 100 being the hardest. There are three main Shore hardness scales: Shore 00, Shore A, and Shore D. Shore A durometers are for softer materials, ranging from flexible rubbers to semi-rigid plastics with minimal flexibility. Shore D durometers are for harder materials, including hard rubbers, semi-rigid plastics, and hard plastics.
Durometer measurement is crucial when selecting materials for projects. For instance, a higher durometer elastomer provides better heat transfer properties, making it suitable for heat seal tooling applications. Additionally, when creating a mould for parts with delicate features, a lower durometer elastomer like Shore 30A silicone rubber is preferred as it allows for easy removal without damaging the part.
