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What you need to know about the importance of shore hardness for 3D design and 3D printing
With us you will find the possibility of printing resin (in PolyJet printing) as well as TPU (SLS process) in various shore hardnesses. For this reason, we would like to explain a little more about shore hardening and its importance in additive manufacturing.
Named after the American inventor Albert Ferdinand Shore (1876-1936), Shore hardness is a key figure for the hardness of materials. This is directly related to the penetration depth, which in turn is tested according to a standardized procedure. The certification of materials according to Shore hardness is used in particular for elastomers (= elastically deformable plastics) and rubber-elastic polymers and is therefore of central importance for industrial 3D printing users.
Definition and measurement method
Specifically, the Shore hardness is measured by inserting a spring-loaded pin made of hardened steel of a standardized thickness (as an intender) into the material to be tested, which must be done at an angle that is also defined. A distinction was made until 2012 (according to the then valid DIN 53505) between Shore hardnesses A, C and D.
Shore A hardness is used for soft rubber (including resin and TPU), while Shore C and D hardness is used for elastomers and soft thermoplastics.
To determine the Shore hardnesses A and C, according to DIN 53505, a truncated steel cone with an end face of 0.79±0.01 mm in diameter and an opening angle of 35±0.25° is used as the indenter for the Shore hardness D with a radius of 0.1 ± 0.01 mm and an included angle of 30 ± 1° was used. An additional device to increase the precision is in the Shore hardness test method used in connection with a measuring stand. This now presses the test specimen to be measured with a contact force of 12.5 ± 0.5 N for Shore A or 50 ± 0.5 N for Shore D without impact onto the support of the measuring table. A temperature interval of 23 °C ± 2 K is also specified.
The Shore hardness values are determined on a scale according to which a penetration depth of 2.5 mm corresponds to 0 Shore and 0 mm to 100 Shore. The higher the Shore value, the greater the resistance of the material to penetration, and consequently the harder the material.
The 2012 rewrite
The previously valid DIN 53505 was replaced in 2012 by the ISO 7619-1 replaced, the standardized Shore hardness test expanded. The Shore AO (for low hardness values) and AM (for thin elastomer test specimens) methods were newly introduced, and the intender geometry for Shore hardness D was corrected from 30 ± 1° to 30 ± 0.25°.
At the same time, the contact pressure for Shore hardness A was corrected from 12.5 ± 0.5 N to 1 + 0.1 kg, for Shore hardness D from 50 ± 0.5 N to 5 + 0.5 kg. In addition, the measurement time was reduced from 3 to 15 seconds, while the storage of the test specimens in the standard climate was reduced from 16 to 1 hour.