The Shore test is one of the static mechanical tests that can be used to measure the hardness of plastic and rubber materials.
Tires, shoe insoles and gaskets are just a few examples, although it can actually be used in all polymer, elastomer, rubber and gel-like materials.
In specific, the measurement is made using a Shore hardness tester. However, this instrument comes with many variants, normally classified according to two characteristics:
Before listing the many scales available, keep in mind that two main differences should be considered when choosing your Shore hardness tester: the shape of the indenter and the force of the spring.
These two parameters are assessed based on the specific elastic and viscoelastic properties of the material being measured.
Here are some of the most commonly used Shore hardness testers:
It is, however, important to keep in mind that for the Shore hardness measurement according to one of the reference standards – ASTM D2240 -, there are other types of scales: B, C, DO, E, M, O, OOO, OOO-S, and R.
When added to those previously listed, we therefore have a total of 12 scales.
The value calculated varies from 0 (in which the indenter generates a particularly deep indentation, indicating minimum hardness) to 100 (in which the indenter generates an almost zero indentation, indicating maximum hardness).
Therefore, the closer the generated value is to “0”, the softer the tested material is. Conversely, the closer the value is to “100”, the harder the tested material is.
In this case, we talk about analogue Shore and electronic Shore hardness tester.
We recommend that you identify the procedure better suited to your needs by referring to the following standards: ASTM D2240, ISO 48-4, ISO 868 and JIS Z 2246.
Shore testing is mainly carried out using practical hand-held Shore hardness testers designed to meet your requirements. It is normally possible to install them on a special bench top stand, therefore minimizing human interference when carrying out the hardness test.
First of all, keep in mind that Shore hardness measures the depth of the indentation generated by the indenter, not its surface area. Clearly, the softer the material tested, the greater the depth of the generated indentation.
But what happens in practice? The test cycle varies depending on the Shore instrument selected. A portable hardness tester or a hardness tester installed on a bench top stand should be selected based on specific needs:
Start by placing the sample to be measured on a flat, solid and horizontal surface. Hold the Shore hardness tester in an upright position. Bring the tip sticking out from the body of the instrument closer to the sample being measured. Apply the pressure required by the standard on the hardness tester in the direction of the test sample. Please note that depending on the Shore hardness scale chosen:
Apply a localized pressure for several seconds (depending on the Shore scale chosen) and then lift the instrument. Repeat this procedure five times at different locations on the specimen (at least 6mm apart). The final Shore hardness value is given by the arithmetic mean of the five values.
It is not the hardness tester that is brought to the specimen (as with the portable tester) but the other way around.
The Shore instrument is therefore integrated into a stand, also known as a bench top stand, and becomes a true bench top hardness tester.
Other factors affecting hardness measurements – such as the application of force and the perpendicularity of the measuring probe to the sample tested -, can be controlled and standardized.
Using the bench top stand undoubtedly provides greater reliability and repeatability in Shore hardness testing than using a portable Shore hardness.
The hardness of plastics and rubbers can also be measured using the IRHD (International Rubber Hardness Degrees) method. Here are the main advantages and disadvantages of Shore testing compared with IRHD.