What is Durometer? Material Selection Guide

While manufacturing any plastic product, the manufacturers consider the mechanical, chemical, and physical properties of the product. They use different methods to evaluate the material hardness for manufacturing accurate wall thickness.

Do you know durometer measurements are often used to ensure that materials are safe and effective for their intended use?

You know why?

Durometer measurement is the most effective way to ensure the material does not compress or deform. Testing the hardness of manufactured plastic bottles and rubber products is essential to ensure they work flawlessly in different environments and meet specific quality standards. So, how do engineers measure the hardness of the material before manufacturing?

In this article, we will find out everything about a durometer. By the end of this article, you will be able to understand the durometer measurements and factors you must consider for material selection according to your application demand.

Please keep reading!

What is a Durometer?

Durometer is a type of instrument used to measure a material’s hardness and resistance. According to the general durometer definition, the construction of the device consists of a durometer gauge and an indenter that is usually pressed into the material to test hardness.

Albert F. Shore invented major scales for identifying the accurate hardness of the material in compliance with IRHD (International Rubber Hardness Degree).

The indenter consists of a spring-loaded mechanism that gives hardness in two main scales known as shore A and shore D. In addition to these two scales; there is another scale called shore OO.

Different Durometer Shores and Their Functions:

It is crucial to understand the useability of varying shore scales to determine the hardness and resistance of the material. You must think about how you would know which scale you must consider using and why? Well, that’s simply very easy. Let’s discuss what these three scales mean and how they function;

Shore A:

It is the most widely used shore for determining soft to medium-hard material’s rigidity and indentation hardness. With the shore A scale, you can identify the hardness of flexible to medium complex or semi-rigid products.

The scale has a wide range starting from 0 to 100, which is ideal for measuring range of materials. The indenter used for this scale is of the truncated cone shape.

If you are wondering what is material durometer? Here are a few examples of materials having a shore A hardness level;

Table 1.1: Different material with shore A hardness

Shore D:

This scale level is used for measuring medium-hard to extreme hard products. It allows you to identify the indentation hardness of thick, rigid, and high-resistance plastic products.

It consists of a 90-degree cone indenter which pierces the material with greater force than scale A to test its hardness. The hardness range of this scale starts from 0-100.

Here are a few examples of materials with shore D hardness levels:

Table 1.2: Different materials with shore D hardness

Shore OO:

This scale is specified for measuring very soft elastomers and rubbers. It typically consists of a conical indenter. It ranges from 0 to 100 (incredibly soft to medium hard material). You can check the hardness of very soft materials such as gummies and slimy materials.

Here are a few examples of materials with shore OO hardness levels;

Table 1.3: Different materials with shore OO hardness

Other duro scales are available such as scales B, OOO, C, DO, and M, for testing the thickness and hardness of the materials. However, they are not commonly used in the manufacturing industries for measurement.

What Actually is Hardness?

Hardness is the degree of resistance a material posse to withstand operational, mechanical, and environmental stress. Different plastic and rubber products have different hardness levels depending on their application. It is a measure of understanding how difficult it is to deform the product’s structure.

It is one of the most crucial properties you must consider while selecting a material to ensure that it fulfils your application demands. In durometer measuring, hardness is identified by pressing the specific indenter in the material. When you press the measuring object with an indenter tip, it forces the surface of the material.

A study suggested that shore hardness can comprehensively cover all properties of the filled rubber in the tire tread and provide proven results.

For example, hard elastomers or plastic materials used in manufacturing motors or engines provide high-degree protection from constant pressure and temperature. However, the rubber used in tires and shock absorbers has a low hardness to provide precise gripping.

Now, you can analyze and measure the depth of indentation to find out the hardness of the material. More rigid material usually gets less impacted with less indentation, while softer material gets high impact with deeper indentation.

In addition to other factors such as compression, thickness, impact resistance and force deflection, durometer hardness is vital to evaluating which material is ideal for your specific requirements.

Why Does a Durometer Matter for Flexible Plastic Tubing?

As we all know, flexible plastic tubing is widely employed in industries such as automotive, medical, pharmaceutical, food and beverages. Since all sectors have specific flexibility, resistance, and durability requirements, durometer hardness is the most crucial aspect to consider if you plan to buy flexible plastic tubing for your application.

Durometer hardness is a standardized factor to identify the hardness or softness of flexible tubing. It directly affects the impact resistance, reliability, and longevity of the product. Shore A is a typical scale used to determine how hard or soft is the plastic tubing.

For example, due to material hardness, 70A plastic tubing is relatively harder than 40A. Medical grade plastic tubing has a hardness range between 40-70A, while flexible tubing used in beverage industries exhibits a 60-90A hardness level.

What if I select the wrong plastic tubing hardness?

If you select too soft plastic tubing, it may deform or fail to work correctly under high pressure or temperature. On the contrary, if the chosen material has a high hardness level, it will resist chemical and mechanical stress to ensure error-free functioning.

To ensure the flexibility and reliability of the plastic tubing, selecting the material that compliments your application demand is important.

Here is a simple checklist that you can follow to choose appropriate flexible plastic tubing for your application:

• Analyze the intended use of the plastic tubing material before selection.
• Identify the optimum pressure and temperature involved in the application.
• Find out the fluid viscosity and thickness that is being transported.
• If used for medical purposes, check the material composition and safety standards beforehand.
• Lastly, find out the chemical resistance of the material before finalizing it.

Why Does a Durometer Matter for High-temperature Silicone Rubber?

Starting from the medical to the aerospace industry, high-temperature silicon rubbers have a diverse range of applications in different commercial sectors. The silicon material has incredible insulation and chemical resistance features that can tolerate high temperatures.

So, if you are finding high-temperature silicon rubber that fits your application, consider durometer hardness.

Like all other elastomers and soft plastics, you can measure silicon rubbers using a durometer. Generally, silicon rubbers fall between 25-65 shore A hardness.

However, high-temperature silicon rubbers differ from typical elastomers due to high temperatures. Rubber material gradually deteriorates when exposed to excessive heat, UV radiation, and ozone.

Therefore, it is crucial to determine the durometer hardness of the high-temperature silicon rubber because chemical properties, tensile strength, and physical structure change at high temperatures.

Let’s take a simple example for the explanation;

The silicon rubber used in the aerospace and automotive industry has high hardness, ranging from 50-70A and can withstand temperatures up to 305 °C. But the hardness range of soft silicon used in the medical industry falls between 20-60A hardness range.

Silicon rubber that is already hard will become brittle or deform at high temperatures; however, soft silicon will become resistant to temperature and can withstand pressure at high temperatures.

Thus, it is highly crucial to determine the hardness of silicon rubber at high temperatures to ensure optimal performance and safety. However, silicon is not a high-strength material and does not provide standard tear resistance.

Therefore, you must ensure the chosen silicon material is compatible with high-temperature applications and works flawlessly without deforming.

How Durometer Hardness Factor Into Material Selection?

If you choose the wrong elastomer or soft plastic material, the entire performance deteriorates. It also increases mechanical and financial stress.

But how do we identify the hardness level of the material?

Different rubber and plastic materials have different durometer hardness levels. While finalizing the material, keep hardness, flexibility, stability, and resistivity to ensure that the material works appropriately. So, align your intended application, temperature and pressure requirements before choosing a material for machining.

Let’s elaborate on the importance of durometer hardness of material with common application examples:

Medical Industry:

In the medical industry, durometer hardness plays a significant role when selecting materials for tubing, catheters, and other medical devices.

A certain level of durometer hardness is attained to ensure the flexibility and pressure resistance of the device. Choosing the suitable hardness allows the final product’s error-free functioning and durable performance.

Automotive Industry:

The automotive industry demands highly sturdy and resistant material to protect the engine and other parts from wear and tear. Therefore, if you are finding rubber material for automotive applications, hard to super-hard plastic is ideal because it can withstand the high pressure and temperature required for the intended application.

Food and Beverage Industry:

Rubber and plastic materials play a significant role in the food and beverage industry’s seals, gaskets, and conveyor belts. These rubber materials should be FDA-approved and safe for food contact. Moreover, its hardness must comply with safety standards.

Durometer Considerations for Injection Molds

Manufacturers consider different factors for injection mold manufacturing and parts production. It is essential to find out the appropriate hardness of the material to ensure smooth molding operation. Typically, shore A and D scales evaluate durometer hardness for injection molds.

Here are the few durometers hardness key considerations you must keep in mind for manufacturing injection molded parts:

• Consideration #1: While designing molds, it is important to consider the hardness of the mold because the rigidity of the material will make it difficult to extract the mold once the material solidifies. Thus, always choose flexible and material less hard than 70A for injection molding purposes.
• Consideration #2: Select the material compatible with the final molded product. For example, more rigid material is used for manufacturing automotive parts. Similarly, the softer rubber material is appropriate for medical and household molded parts.
• Consideration #3: Material selection can impact the surface finishes, edges sharpness, and parting lines. Therefore, you must keep the mold released and prevention from defects before you select material for injection molding.

Durometer Considerations for Additive Manufacturing

Durometer hardness is a key factor for additive manufacturing, such as 3D printing. It can significantly improve the final product’s performance, flexibility, and durability if considered. All three standard scales, A, D, and OO, are used for measuring the hardness of material for additive manufacturing.

Table 2.1: Scales for Durometer Hardness for Different Applications

Different Additive Manufacturing Processes:

Material selection for additive manufacturing also depends on the selected manufacturing process. For instance, material extrusion 3D printing, such as (FDM), requires high-strength durometer materials to achieve high durability and strength.

However, in contrast, DLP and SLA processes demand flexibility and usage accessibility; therefore, low durometer ranges material typically from scale A or OO is used for such operations.

Get Started With Kemal– Manufacture Your Custom Plastic Parts

For high-quality custom plastic parts, choose Kemal. We utilize state-of-art technology and proven expertise to provide on-demand services. Our experienced engineers closely understand your application requirements and analyze the material with the appropriate durometer for hardness testing.  

It also ensures the desired flexibility and stability of the product are achieved. You can take a step closer to premium-quality, precisely defined, and exclusive manufacturing with Kemal. Whether you want plastic injection molds or additive manufacturing, we have got you covered.

Before You Go!

Before you go, we would like you to check out our services, including mold manufacturing, injection molding and CNC machining services. We provide expertise, experience and commitment to carry out your project seamlessly.

If you want to discuss your project details and specific requirements with our team, feel free to contact us. We will get back to you with an accurate quote and cost details.