Shore durometer

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Durometer is one of several ways to indicate the hardness of a material, defined as the material's resistance to permanent indentation. It is named for instrument maker Albert F. Shore, who developed a measurement device called a durometer in the 1920s. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers.^[1]

1 Durometer Scales
2 Method of measurement
3 Durometer of various common materials
4 Patents
5 References
6 See also

[edit] Durometer Scales

There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the A and D scales. The A scale is for softer plastics, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in a value between 0 and 100, with higher values indicating a harder material.^[2]

[edit] Method of measurement

Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. Shore durometer allows for a measurement of the initial indentation, or the indentation after a given period of time. The basic test requires applying the force in a consistent manner, without shock, for 15 seconds, and measuring the depth of the indentation. If instantaneous depth is desired, force is applied for only 1 second. The material under test should be approximately 6.4 mm (.25 inch) thick.^[3]

**Testing equipment - Shore Durometer Type A and D^[3]**
Durometer	Indenting foot	Applied force (g)
Type A	Hardened steel rod 1.1 mm - 1.4 mm dia, with a truncated 35º cone, 0.79 mm dia.	822 grams
Type D	Hardened steel rod 1.1 mm - 1.4 mm dia, with a 30º conical point, 0.1 mm radius tip	4550 grams

The final value of the hardness depends on the depth of the indenter's penetration. If the indenter penetrates 2.5mm or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. Durometer is a dimensionless quantity, and there is no simple relationship between a material's durometer in one scale, and its durometer in any other scale, or by any other hardness test.^[1]

[edit] Durometer of various common materials

An automotive tire tread, one of the many rubber or polymer objects categorized by its durometer hardness. Tires typically range from 50A to 70A, depending on their application.

Material	Durometer	Scale
Hard Hat	75	D
Ebonite Rubber	100	A
Hard skateboard wheel	98	A
Solid truck tires	50	D
Soft skateboard wheel	75	A
Automotive tire tread	70	A
Door seal	55	A
Rubber band	25	A
Sorbothane	40	OO
Sorbothane	0	A
Chewing Gum	20	OO