What is Shore Hardness Scale? | The Complete Guide

Hello people, today I will share an integrating guide on shore hardness scales – the most reliable measurement method to determine plastic’s hardness. So without further ado, let’s get started.

What is Shore D Hardness Scale?

The Shore D hardness test, aka the durometer test, came into existence so people could have a common reference when discussing materials. There are several scales made for discussing different materials. The test is mainly utilized when the materials are too soft for the Rockwell test. Materials with a very soft texture like rubber and TPE should be tested with Shore D.

There are three most popular Shore hardness scales:

Shore 00 – Used for measuring gels and rubbers that are very soft in nature.

Shore A is used to measure the hardness of flexible mold rubbers that range from very soft and flexible to somewhat medium flexible to hard with no flexibility whatsoever. Often, semi-rigid plastics are also measured on the high end of the Shore A Scale.

Shore D – Utilized to measure the hardness of semi-rigid plastics, hard rubbers, and hard plastics.

How Does the Shore Hardness Test Work?

Durometer, Source - omnexus.specialchem.com

A spring-loaded needle is kept under the plastic in Shore hardness, and pressure is registered. Once the needle is pierced as far as possible, the depth of indentation of the needle is measured, proportional to the plastic’s hardness. ASTM D2240 and ISO 868 are the test methods used for measuring Shore D hardness

Shore hardness measures are dimensionless, which comes between 0 to 100. Higher the number harder the material.

The resulting penetration is dependent on the following factors:

• Material hardness
• The shape of the indenter
• Its viscoelasticity
• Duration of the test

Fascinating Read – What is Processing and Drying Temperatures of Plastics

Below is a table with typical Shore D hardness values:

Shore Hardness Chart – 

Interesting Read – Mold Temperature in Plastics | A Complete Analysis

What does Shore hardness Mean for a Manufacturer?

Durometer scale hardness or Shore D hardness, which mold rubber should be used to mold a specific component or part.

Now, the question is, how seamlessly will you be able to remove the original model from the mold once it is cured?

As a manufacturer, one needs to understand that material with specific hardness for your application. For example, you wouldn’t choose rubber or a material with a durometer of 70A to make a product that is supposed to be flexible. A 70A materials are hard and stiff and wouldn’t provide enough flexibility to remove the part without breaking it.

A wiser choice would be a Shore 30A material that will offer enough flexibility to remove the part easily.

FAQs – 

1. What is hardness measured in?

Ans. The SI unit of hardness is N/mm². The unit pascal is also often used for hardness. However, hardness should never be confused with pressure. Different hardness has different scales of measurement. Therefore, the units are not suitable for direct comparison.

2. What is a Durometer?

Ans. Durometer or Shore Durometer is a standard way to measure the hardness of materials like plastics and rubbers. Durometer measurement scales range from 0 to 100, but there is no such thing as a durometer unit of measurement. In laymen’s terms, a durometer is a dimensions measurement.

3. What is the difference between Shore A and Shore D?

Ans. The major difference between Shore A hardness scale and Shore D is that the former measures softer rubbers (including thermoplastic rubber). The latter is used for measuring harder, more rigid materials.

4. What is the difference between Shore and Rockwell hardness testing methods?

Ans. As mentioned earlier, Shore A and Shore D testing methods measure hardness in flexible and semi-flexible materials. In contrast, the Rockwell hardness method is generally chosen for ‘tougher’ plastics such as polycarbonate polystyrene, nylon, and acetal.

5. Which is the strongest plastic in the world?

Ans. Going by the terms of the durometer scale, Polycarbonate is the strongest plastic globally in terms of strength, durability, and impact resistance. It is 200 times stronger than glass and is warranted against cracks and breakage.

Suggested Read – 

• What is the Density of Plastics? | The Complete Guide
• 7 Types of Plastics | An Helpful Illustrated Guide
• What is Rotational Molding | Rotational Molding Process | Advantages & Disadvantages | Best Material for Rotational Molding
• 6 Best Plastic Molding Techniques | A Complete Analysis
• What is a Plastic Pallet? | The Definitive Guide
• Food Grade Plastic: The Best Plastics for Food Applications
• What is Condensation Polymerization? | The Definitive Guide
• What is Anionic Polymerization? An In-Depth Analysis
• Types of Gates for Injection Molding – A Detailed Guide

The Takeaway – 

That was my take on the Shore hardness scale and all its attributes. Choose wisely and strategically with durometer hardness, making your material selection process much easier.

Kindly share your thoughts and questions in the comment box.

Have a terrific day.