All About Shore D Hardness Scale

To fully understand how a product will function and hold up over time, you need to understand the specific physical characteristics of its materials—including its hardness. Finding this value comes down to using several interesting measuring techniques, depending on the material at hand, and when it comes to rubber and hard plastics, look no further than the Shore D Hardness scale.

With the help of this scale and its measuring device, manufacturers get more insight into how a material responds to pressure and can select the best material for their products. Below, you can learn about how it all works and how it’s used. 

What is the Shore D Hardness Scale?

The Shore D Hardness Scale is a method and reference system for measuring the hardness of materials such as rubber and plastic with a tool called a durometer. The exact measurement points to how much force a material can handle before an indent is created. 

This is done with the pointed tip of a durometer, which presses into the surface of your material and is controlled by a spring with a force that you or the operator will set. The depth of the indent that the pointed steel rod or needle creates translates into a certain rating on the scale. The scale runs from 0 to 100, and the higher the number the more difficult it is to indent the material (and therefore, the harder it is). The chart also gives users a good understanding of the best types of rubbers and plastics to use based on the durometer reading and the application for which it will be used.

Materials and Products Tested with the Shore D Scale

The Shore D scale can help manufacturers figure out what materials are best for applications like car doors, sports equipment, or contact lenses as it’s an ideal indicator of hardness. There are so many types of plastics and rubbers, but here’s a small sampling of how it’s an effective system for the following types of materials and applications:

1. Thermoplastic polyurethane (TPUs) are a type of bendable and elastic plastics that are part of everything from footwear to medical equipment that can be tested with a durometer.
2. ABS or acrylonitrile butadiene styrene is a popular material tested with the Shore D system, which helps manufacturers understand how it works for FDM printing, toys, car parts, or home appliances.
3. Polycarbonate or PC is found in everyday objects like corrective contact lenses or automotive parts and is another plastic with a hardness that can be measured through a durometer.
4. PET plastic—an acronym for polyethylene terephthalate—is another familiar material found in food and beverage containers and packaging that’s tested this way.

Example Shore D Hardness Values

To give you a better idea of the scale and where certain products and materials fall within the spectrum, we’ve listed out a few common objects below—some made of rubber and plastic and others not—and their values for reference:

• Hardback book cover: Shore D-40
• Golf ball: Shore D-50
• Swivel wheel: Shore D-60
• Wooden ruler: Shore D-70
• Computer casing: Shore D-80
• Bone: Shore D-90

Advantages and Disadvantages

There are a handful of benefits that come with using the Shore D scale, including:

• Precise results: It’s possible to get specific and precise readings with a durometer, making it a great option for finding the hardness of plastics and rubbers.
• Many materials: It’s possible to test a wide range of plastics and rubbers for different applications and it’s not just limited to a few industries. 
• Quick and efficient: Durometers are small and easy to transport, and their size and simplicity mean it’s a fast and easy way to get a material hardness reading.
• Non-destructive: A durometer doesn’t render a material useless or completely ruin it, so it can be used after testing.

Conversely, this scale also has a few limitations, such as:

• Compatibility issues: The Shore D Hardness Scale is only capable of testing different types of plastics and rubbers, so you’ll have to rely on another method for other materials.
• Material differences: The same material can show two different Shore D ratings depending on the surface finish it has, which can cause inconsistencies. 
• Temperature effects: Some materials will soften or harden in heat or cold, so you’ll want to work with the same temperature when testing them to avoid different readings.
• Room for error: Inconsistencies in a durometer’s precision or in how the operator takes measurements can lead to an incorrect reading.

Shore D vs. Shore A Hardness Scale

The Shore D and A scales actually measure the same thing and work on the same type of spectrum, but the former is reserved for harder plastics and rubbers, whereas the latter is better suited for softer plastics. The durometers used for each are built differently so they can best cater to the types of materials they’re pressing into. For the Shore D scale, the tip of the durometer indenter is sharper and pointed, whereas for the shore A scale, it’s rounded so that it doesn’t puncture or fully damage the softer materials. Examples of items you could test with the Shore A system include rubber bands, erasers, and even marshmallows.

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