Durometer or shore durometer is a way for industry professionals to measure how hard such things as plastic, rubber, and non-metallic materials genuinely are.
Its focus is to measure on a Shore A or Shore D scale, looking at how robust material is when examining its resistance to surface penetration.
You will often find that those that are identified as hard materials are more resistant to wear, yet less flexible in their movement. Hence, choosing the right o ring durometer for your application is essential to ensure the overall product’s wear and lifespan.
Ashore durometer is the actual measuring device.
Measured on a scale from 0 – 100, the durometer is a dimensionless measurement as its numbers simply represent a comparison between different, yet very similar materials.
The higher the durometer measurement, the harder the elastomer.
A durometer scale can run from:
Very soft urethanes – suitable when applying coatings, and typically found in the range of 10A-50A.
Soft urethanes – suitable for particle impingement applications, with ranges between 50A and 85A.
We then move on to the mid-range, where urethanes here provide medium resilience and offer longevity to a material. Typical ranges on the durometer scale include 80A to 95A.
Hard urethanes are great for impact and various abrasion applications, with ranges varying from 90A to 95A.
The last on the scale is the very hard urethanes, suitable for bearing and brushing applications, with scales running from 60D to 75D.
The shore durometer standards provide a universal, consistent, and easy reference to allow anyone to compare material hardness effectively and efficiently.
Two different types of Shore
Most rubber materials will be presented as either Shore A or Shore D, and these are two different durometer scales.
Shore A is a scale suitable for softer materials, covering flexible rubbers and semi-rigid plastics.
Shore D, therefore, you might have guessed it, is for harder materials, those hard rubbers, and plastics.
There is a third Shore, Shore OO, which measures extremely soft rubbers and gels. However, this type of durometer testing is not always suitable for flow control components.
Choice of materials
When we talk about hardness, we refer to a material’s ability to resist penetration or permanent indentation.
Therefore, it’s essential to know how hard a material is before choosing it for your given application.
Ideally, you’re looking for the best material to create the best seal hence reducing the chances of a leak occurring.
Another example of why durometer choice is vital is when processing heat seal packaging applications.
Here harder durometer heat seal silicone rubbers will provide much better heat transfer properties than those with softer durometers.
One of the best features of using the shore hardness scale is that it uses equipment and testing procedures suitable for selecting materials that you will be using.
When it comes to o rings however, other measurements must be considered when identifying overall sealing performance.
These include testing its strength, resistance to scratching, overall wear and tear, etc.
For example, a rubber’s compression modulus measurements and stiffness can often be much more accurate than an o-ring durometer for indicating sealing performance; however, this is still a vital element and one which is used across various sectors.
O ring suppliers, UK
Tested o rings are available from numerous suppliers throughout the UK, all with different durometer measurements.
The most common are those o rings that sit with a durometer measurement of between 70 and 90.
Back up rings will typically be 90.
To put it into perspective, o rings measuring with a durometer of 70 tend to be the same hardness of a shoe heel. This range is also the one that offers the best combination of properties suitable for most o ring applications.
Of course, those with a softer compound are easy to stretch and seal, which often works better on rougher surfaces.
Those harder compounds are more abrasion and extrusion resistant, which is ideal when high pressure is used. These harder compounds are also greater for more dynamic applications.
O ring suppliers, Leeds
Specialist Sealing Products are the leading supplier of o rings and seals throughout Leeds, Yorkshire, and beyond.
We offer a range of o-rings and sealing products suitable for various applications operating across different industry sectors.
To find out more about o ring durometer and how we can help you, call 01535 274 776
Reference video: BJBEnterprises