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Measuring of hardness or hardness testing

What is hardness?

Hardness is a quantity for material that describes how big force that is needed to deform a material. Hardness is not the same as density. Density is a measure of a materials closeness, this means what mass the material has per volume quantity.

Hardness test is an important part of material testing. One distinguishes between two main groups for hardness testing:
•    Plastic measuring, where the testing deforms the sample and causes a remaining mark in the material.
•    Elastic measuring, where the sample regain its original shape after the testing is finished.

Hardness measuring/hardness testing is performed by either measuring the depth of the impact from the indenter or by measuring the size of the impact from the indenter.
One common used definition of hardness in a material is: “the resistance a material exercise against a permanent deformation through penetration of another harder material”.Hardness measuring instruments is often called Durometers, they have their origins in instruments that were used for measuring metal. The world Durometer derives from the Latin word Duro meaning “Hard/Tough”.

Different ways in measuring hardness

There are different ways in measuring hardness. Rockwell, Brinell and Vickers are all different types of instrument measuring the depth of the penetration of a ball or a diamond pyramid pressed into the surface under a known load. These methods are shown to be clumsy when measuring softer materials.

The technique used today for hardness measuring on i.e. rubber and other softer materials is a development from another hardness measuring method for metals, this method was from start called Shore Scleroscope. The new methods instrument became to be called for Durometers, several companies from several parts of the world have contributed to the development of the Durometer to the refined instrument it is today.

It’s important to remember that values from hardness testing are always arbitrary since hardness is not a fundamental material feature. Therefore it’s important to relate a result from hardness testing to how it was performed.

Hardness measuring of a variety of products

Hardness measuring can be done in a variety of products and different industries. There are also a variety of different international standards that describes how it should be performed.

Some examples of products/materials that can be tested for hardness:
•    Rubber
•    Plastic
•    Metal
•    Wood
•    Fruit and vegetables
•    Pharmaceutical products (i.e. gelatin capsules)
•    Cardboard/paper
•    Asphalt
•    Foam material
And many more.

How are the test executed?

The hardness is determined by penetration of the indenter into the sample. This is done with a standardized load and measuring time. Also the ambient temperature is standardized to get as comparable results as possible. 

Different measuring scales

There are several different measuring scales which are used for different types of material, here are some examples:
Plastic and rubber material: Shore, Asker, IRHD, VLRH and Pusey & Jones.
Metals: Barcol, Vickers and Rockwell.
Wood: Brinell.
Glass: Moh.

The Shore scale

Shore that is most common for hardness test on rubber materials have several different scales, and each scale are divided in grades from 0 to 100 ° Shore. Where 0 is the softest and 100 the hardest value on each scale. In general it’s suitable to think of changing the measuring scale when you get values in the outer limits, between 0 – 30° to a softer scale and between 90 – 100° to a harder scale.

The most common Shore scales from softer to harder scales are: Shore OOO, Shore OO, Shore O, Shore AO, Shore A, Shore B, Shore C, Shore DO, Shore D. Each of these scales has their own standardized loads, indenters and sizes of measuring foots as well as which measuring time that should be used. This information is presented in the international standards.

If you can’t find suitable equipment for your testing needs on our website, please contact us. We can help you with other equipment/instruments than we have presented on this website.

(Note: see under each supplier presentation for which countries we can sell the equipment too.)

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