Shore durometer

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Two inline skating bikes with Shore hardness levels 85A and 83A.
Digital Shore hardness tester

The Shore durometer is a test device for measuring material hardness . Typically, polymers, elastomers and natural rubber are examined.

Higher measured values ​​mean greater resistance to indentations and thus harder materials.

The term is also used to describe the hardness of a material.

history

The scale was defined by Albert Ferdinand Shore , who defined a device for measuring hardness in the 1920s . The Shore durometer hardness tester was neither the first nor the first who durometer ( duro - and -meter was called). Nevertheless, nowadays a durometer usually refers to the Shore hardness. Other devices measure in Rockwell , for example .

Durometer scales

There are several durometer scales that are used for materials with different properties. The two most common scales that use slightly different measuring systems are designated as Type A and Type D in the ASTM D2240 standard . The A scale is for softer materials and the D scale for harder materials.

The ASTM D2240-00 test standard defines twelve different scales for different uses: Types A, B, C, D, DO, E, M, O, OO, OOO, -S and R. Each scale has values ​​between 0 and 100. Where 100 describes the hardest materials.

There are other standards such as DIN EN ISO 868 and DIN ISO 7619-1 . DIN EN ISO 868 knows type A and D. DIN ISO 7619-1 knows type A, D, AO and AM.

Measurement method

Drawing of the indenter for type A and D.

Durometer, like many other hardness tests, measures the depth of a depression in the material that is created by a given force on a standardized indenter. This depth depends on the hardness of the material, its viscoelastic properties, the shape of the indenter and the duration of the test. ASTM D2240 durometers allow the measurement of the initial hardness or the indentation hardness after a certain time. The basic test requires a uniform and shock-free application of force and measurement of the hardness (penetration depth). The force is applied for the required time and then read. The material to be tested should be at least 6.4 mm (0.25 inch) thick.

Test setup for type A & D
Durometer type Indenter Mass (kg) Resulting force (N)
Type a Hardened steel rod with a diameter of 1.1 mm - 1.4 mm with a truncated cone with a 35 ° cone, 0.79 mm diameter 0.822 8.064
Type D Hardened steel rod with a diameter of 1.1 mm - 1.4 mm with a 30 ° cone and a tip of 0.1 mm 4,550 44.64

The ASTM D2240 standard knows twelve different durometer scales using different spring forces and indenters. The different scales are called Shore Durometers ... The following table contains all types with the exception of type R.

Durometer type construction diameter Penetration depth Spring force in N Recommended contact pressure in kg
A. 35 ° truncated cone ( truncated pyramid ) 1.4 mm (0.06 in) 2.54 mm (0.1 in) 8.05 1
C. 44.45 5
D. 30 ° cone
B. 8.05 1
M. 0.79 mm (0.03 in) 1.25 mm (0.05 in) 0.765 0
E. 2.5 mm (0.1 in) ball 4.50 mm (0.18 in) 2.54 mm (0.1 in) 8.05 1
O 1.2 mm (0.05 in) ball 2.40 mm (0.09 in) 1
OO 1.111 0.4
DO 44.45 5
OOO 6.35 mm (0.25 in) ball 10.7 mm (0.42 in) - 11.6 mm (0.46 in) 1.111 0.4
OOO-S 10.7 mm (0.42 in) plate radius 11.9 mm (0.47 in) 5.0 mm (0.2 in) 1,932 0.4

Type R is not a separate type, but the name for the measurement with a special indenter. The R stands for radius, as this indenter has a diameter of 18 ± 0.5 mm (0.71 ± 0.02 in). Spring forces and indenter shape remain the same. The measurement according to type R is possible with every D2240 type except M. The R is added in the form of type xR.

The following requirements must be met according to DIN ISO 7619-1:

  • When measuring Shore A, the foot penetrates the material, while with Shore D the foot penetrates the material surface.
  • The material to be tested must be stored in the laboratory for at least one hour before the test.
  • The measuring time is 15 s.
  • The force is 1 kg +0.1 kg for Shore A and 5 kg +0.5 kg for Shore D.
  • Five measurements must be made.
  • The durometer is calibrated once a week with elastomer blocks of different hardness.

The final value of the hardness depends on the penetration depth, which is reached after 15 seconds. For types A and D, a penetration of 2.54 mm (0.100 inch) and more is a hardness of 0 and, if it does not penetrate at all, a hardness of 100. There are different scales to represent different hardnesses. Hardnesses of <10 ° Sh or> 90 ° Sh are generally not regarded as trustworthy. The measurement is then repeated with the neighboring type.

Durometer is a dimensionless quantity and there is no direct relationship between the Shore values ​​of different scales.

Degree of hardness of different materials
material Shore value scale
Gel insert of a bicycle saddle 15-30 OO
chewing gum 20th OO
Sorbothane 30-70 OO
Elastic band 25th A.
Door seal 55 A.
Automobile tires 70 A.
Soft rolls of roller skates and skateboards 78 A.
O-ring for use in hydraulics 70-90 A.
Hard rollers from roller skates and skateboards 98 A.
ebonite 100 A.
Truck tires 50 D.
Hard hat (typically polyethylene ) 75 D.
Polyurethane (solid material, no foam) 80 D.

Patents

  • US patent 1770045 , AF Shore, "Apparatus for Measuring the Hardness of Materials", issued July 8, 1930
  • US patent 2421449 , JG Zuber, "Hardness Measuring Instrument", issued June 3, 1947

See also

Individual evidence

  1. ↑ Shore (Durometer) Hardness Testing of Plastics . Retrieved July 22, 2006.
  2. ^ Material hardness . CALCE and the University of Maryland, College Park . Archived from the original on July 7, 2007. Retrieved July 22, 2006.
  3. ^ Rubber hardness . National Physical Laboratory, UK . Retrieved July 22, 2006.
  4. ↑ DuroMatters! Basic Durometer Testing Information . CCSi, Inc .. Retrieved May 29, 2011.
  5. ↑ ASTM (Ed.): Standard Test Method for Rubber Property — Durometer Hardness1 . D2240 - 15'1, November 2017, p. 5 , doi : 10.1520 / D2240-15E01 .
  6. ↑ ASTM (Ed.): Standard Test Method for Rubber Property — Durometer Hardness1 . D2240 - 15'1, November 2017, p. 10 , doi : 10.1520 / D2240-15E01 .
  7. ↑ Shoreprovning . In: Wikipedia . February 22, 2015.

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