Ethan Clarke
Plastic model kits are a popular hobby, with a range of complexities to suit all skill levels. From aircraft to automobiles, tanks to trains, these kits offer an engaging way to build and paint intricate models. A key factor in the manufacturing of these kits is the durometer or shore durometer, which measures the hardness of the plastic used. This is particularly important when creating injection-moulded parts, as the durometer will determine how resistant the plastic is to deformation and how easily the final product can be extracted from the mould. With a scale from 0 to 100, durometer is a standardised way to measure hardness, ensuring product teams can select the appropriate materials for their designs.
| Characteristics | Values |
|---|---|
| Definition | Durometer or Shore durometer is a standardised way to measure the hardness of materials like rubber (elastomers) and plastics. |
| Scale | Durometer is measured on a scale of 0 to 100, with lower numbers indicating softer plastics and higher numbers indicating harder plastics. |
| Measurement | Durometer is a dimensionless measurement, meaning the numbers represent how hard or soft a material is relative to other materials measured using the same durometer scale. |
| Testing | Durometer hardness is tested using a durometer tester, which looks like a round tyre pressure gauge with a needle on a calibrated spring. The needle is pressed against the material with a precise amount of force, and the depth of the indentation is measured to determine hardness. |
| Shore Scales | There are multiple Shore hardness scales, with the three most common being Shore 00, Shore A, and Shore D. Shore 00 measures extremely soft materials, Shore A measures flexible materials ranging from very soft to hard, and Shore D measures hard materials. |
| Applications | Durometer is critical for injection moulding and additive manufacturing, as it affects the final performance of parts and processing considerations. It is also important when choosing mould rubber to ensure the original model can be easily extracted. |
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What You'll Learn
What is durometer?
Durometer is a standardised way of measuring the hardness of materials like rubber or plastic. It is a critical factor to consider when manufacturing with plastic, especially for injection moulding and additive manufacturing. It also affects the final performance of a part, such as a plastic gear, and processing considerations like machine tools and deburring methods.
Durometer is measured on a scale of zero to 100, but it does not have units of measurement. Instead, it is a dimensionless measurement that compares the hardness of a material relative to others tested using the same durometer scale. Lower numbers indicate softer plastics, while higher numbers indicate harder plastics. For instance, 90A polyurethane tubing is harder than 70A polyurethane tubing.
Durometer hardness is typically measured using a durometer tester, which resembles a round tyre pressure gauge with a needle on a calibrated spring extending from one end. To test for durometer hardness, an engineer places the needle against the elastomer or plastic and applies pressure. The needle penetrates the material, and the measurement needle indicates the corresponding durometer hardness on the appropriate scale.
There are various durometer scales, including Shore 00, Shore A, and Shore D, as different materials require different scales. Shore 00 is used for extremely soft rubbers and gels, Shore A measures flexible rubbers ranging from very soft to hard, and Shore D is for hard rubbers and plastics. It is important to note that durometer hardness does not directly correlate with the flexibility of the material.
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How is it measured?
Durometer is a standardised way of measuring the hardness of materials like rubber or plastic. It is a dimensionless measurement, meaning durometer numbers indicate how hard or soft a material is relative to other materials that have been measured using the same durometer scale. Lower numbers indicate softer plastics, while higher numbers indicate harder plastics. For example, 90A polyurethane tubing is harder than 70A polyurethane tubing.
Durometer is measured using a durometer tester, which looks like a round tyre pressure gauge and has a needle on a calibrated spring extending from one end. To test for durometer hardness, an engineer places the needle against the elastomer or plastic and applies pressure. Once the needle has penetrated the material as much as it can, the measurement needle indicates the corresponding durometer hardness on the appropriate scale. The basic test requires applying force in a consistent manner, without shock, and measuring the hardness or depth of the indentation. If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6mm (0.25 inches) thick.
The three most common shore hardness scales are shore 00, shore A, and shore D. Shore 00 is used to measure the hardness of extremely soft rubbers and gels, shore A measures flexible rubbers that can range from very soft to hard, and shore D is used to measure hard rubbers and plastics. The ASTM D2240 standard recognises twelve different durometer scales using combinations of specific spring forces and indentor configurations. These scales are referred to as durometer types, meaning that the scale does not exist separately from the durometer. The two most common scales are the ASTM D2240 type A and type D scales. The A scale is for softer materials, while the D scale is for harder materials.
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Why is it important?
Durometer is a critical factor in manufacturing with plastic, as it helps determine the hardness of a material. It is a standardised way of measuring how resistant a material is to deformation caused by mechanical indentation or abrasion. This is particularly important when selecting materials for specific applications, such as flexible plastic tubing or heat seal tooling, where the wrong hardness could lead to issues like leaks or inadequate heat recovery.
The durometer scale typically ranges from 0 to 100, with lower numbers indicating softer materials and higher numbers indicating harder ones. This scale is relative, meaning it compares the hardness of materials within the same group, such as elastomers and plastics. Durometer is not a unit of measurement but a dimensionless measurement, providing a general idea of a material's hardness.
Engineers use a durometer tester, which resembles a tyre pressure gauge, to test a material's hardness. They place the tester's needle against the material and apply pressure. The needle then indicates the corresponding durometer hardness on the appropriate scale. This standardised testing method ensures objective and repeatable measurements, allowing engineers to make informed decisions about the suitability of materials for specific applications.
Additionally, durometer considerations are essential when selecting mould rubber. The shore hardness of the rubber will impact the ease of extracting the original model and castings from the mould. For instance, a delicate part with thin segments at different angles would require a more flexible rubber with a lower durometer value.
Finally, while durometer is a critical characteristic, it does not predict other material properties like strength or scratch resistance. Other measurements, such as stiffness and compression modulus, may be more indicative of certain performance aspects. Nevertheless, durometer remains a vital aspect of material selection, especially when specific hardness requirements are necessary for a product's functionality and performance.
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Shore hardness scales
Durometer, or Shore durometer, is a standardised way to measure the hardness of materials like rubber (elastomers) and plastics. It is a dimensionless measurement, meaning that durometer numbers measure how hard or soft a material is relative to other materials that have been measured using the same durometer scale. Lower numbers indicate softer plastics, while higher numbers indicate harder plastics. For example, 90A polyurethane tubing is harder than 70A polyurethane tubing.
The three most common shore hardness scales are shore 00, shore A, and shore D. Shore 00 is used to measure the hardness of extremely soft rubbers and gels, shore A measures flexible rubbers that can range from very soft to hard, and shore D is used to measure hard rubbers and plastics.
Shore hardness is an important consideration when choosing materials for a project. For example, in mould-making, the shore hardness of the rubber will determine how easily the original model and castings can be extracted from the mould once it has cured. A harder material may seem ideal for operations involving heavy loads and impacts, but it can also be more brittle, making it difficult to remove from the mould after curing.
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Durometer tester
When manufacturing with plastic, one of the most important factors to consider is the durometer, which indicates the hardness of a material. Engineers can test a material's hardness using a durometer tester, which looks like a round tyre pressure gauge with a needle on a calibrated spring extending from one end. To test for durometer hardness, an engineer places the needle against the elastomer or plastic and applies pressure. The needle will penetrate the material, and once it has reached its maximum depth, the measurement needle will indicate the corresponding durometer hardness on the appropriate scale.
Durometer is a standardised way of measuring the hardness of materials like rubber or plastic. Hardness is a measure of how resistant a plastic is to deformation caused by mechanical indentation or abrasion. Although durometer can be measured on a scale of zero to 100, it does not have units of measurement. Instead, it is a dimensionless measurement, meaning durometer numbers measure how hard or soft a material is relative to other materials that have been measured using the same durometer scale. Lower numbers indicate softer plastics, while higher numbers indicate harder plastics. For example, 90A polyurethane tubing is harder than 70A polyurethane tubing.
There are several types of durometer testers available, including analog and digital testers, and handheld or test stand designs. Some common brands that manufacture durometer testers include Checkline.com, ELECTROMATIC Equipment Co., Inc., and Akozon. Checkline.com offers a range of testers that meet or exceed ASTM D-2240, DIN, ISO, and JIS standards, including Asker durometers, Shore A durometers, and Shore D durometers. They also offer multi-scale Shore durometers and slim probes for working in tight spaces. ELECTROMATIC Equipment Co., Inc. offers PC lab software to log measurements and chart data from some of their digital durometer testers. The Akozon durometer tester is a Shore Type A/O/D hardness meter tester with a large LCD display.
Different shore hardness scales were invented so that engineers could discuss the hardness of materials using a consistent, universal, and reproducible reference. The three most common shore hardness scales are shore 00, shore A, and shore D. Shore 00 is used to measure the hardness of extremely soft rubbers and gels, shore A measures flexible rubbers that can range from very soft to hard, and shore D is used to measure hard rubbers and plastics. It is important to note that durometer hardness does not directly correlate to the flexibility of the material.
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Frequently asked questions
Durometer is a standardised way of measuring the hardness of materials like rubber or plastic.
Durometer is measured on a scale of zero to 100, with lower numbers indicating softer plastics and higher numbers indicating harder plastics.
Engineers test a material's hardness using a durometer tester, which looks like a round tyre pressure gauge with a needle on a calibrated spring extending from one end. The needle is pressed against the material and the corresponding durometer hardness is indicated on the scale.
Shore hardness is a collection of internationally recognised measurement standards based on Shore durometers. Shore A measures flexible rubbers and softer plastics, while Shore D measures hard rubbers and plastics.
Durometer is critical for injection moulding and additive manufacturing, as it affects the final performance of a part as well as processing considerations such as machine tools and deburring methods.
