Definition of Shore hardness testing
The hardness of rubber and elastomers according to Shore is determined using test procedures standardized in compliance with ISO 48-4 or ASTM D2240.
In the Shore hardness test, the indentation depth is measured using a spring-loaded indenter made of hardened steel to indent the material/specimen. The indentation depth is a measurement for Shore hardness, that is determined on a scale of 0 Shore (2.5 millimeter indentation depth) to 100 Shore (0 millimeter indentation depth). A range of different Shore scales have been established based on a variation in indenter forms and spring characteristics. The most well-known scales are Shore A and D. Other scales, such a Shore B, C, 0, 00, 000, and D0 apply to specific applications.
Shore scales and application examples:
- Shore A: Soft rubber, elastomers and natural rubber
- Shore D: Harder elastomers, plastics and rigid thermoplastics
- Shore 0: Soft elastomers and textile fabrics
- Shore 00: Expanded rubber, sponge rubber and cellular rubber
- Shore B: Harder elastomers than Shore A
- Shore C: Medium hard elastomers
VLRH (IRHD supersoft)
Shore 00
Shore A/B
Shore A/B
Shore D/C/D0
Micro Shore
Shore hardness test classification to ISO 48-4 and ASTM D2240
The Shore hardness test is a static test method and has the following characteristics:
- It is one of the standardized methods (ISO 48-4 and ASTM D2240).
- The method is used to determine hardness in the macro range with a test force of 3.924-50 N.
- It is a depth measurement method. This means that in order to determine the hardness value of a test piece, the true indentation depth and not the permanent indentation created by the indenter is measured.
- Indenter shape and material: hardened steel pin with different pin and steel ball versions, depending on the method.
| Standard | ISO 48-4 | ASTM D2240 |
| Specimen thickness | 6 mm | 6 mm |
| Layers | Yes (3 layers) | Yes |
| Measurements | 5 | 5 |
| Measuring distance | 6 mm | 6 mm |
| Test time | 3 s for vulcanized rubber 15 s TPE | Less than 1 s |
| Load | 1 kg Shore A 5 kg Shore D | 1 kg |
| Hardness specification | 54 Shore A 3 s 54 Shore A 15 s | A / 54 / 1 A / 54 / 15 |
Shore hardness test procedure
For the Shore hardness test method to ISO 48-4, the following parameters must be considered in advance:
- To determine the hardness of the material, the standard states that five measurements must be taken from which the median value is then calculated.
- The test time is 15 s; if other test times are used, this must be indicated in the hardness value.
- The material to be tested should be stored at room temperature of +23 °C ± 2°C for at least one hour.
In the first step of the test, the indenter is pressed into the specimen with a spring force of 1.11-44.5 N. Then the indenter is pressed onto the specimen with a contact force of 3.92-50 N for 15 seconds. The indentation depth in the specimen is between 0-2.5 mm. This penetration depth is measured with the hardness tester and the hardness value is derived from it. The indenter should act on the specimen with the full contact force and a duration of 15 seconds. If the duration of the applied force is exceeded or is not met, this must be indicated in the hardness value. The longer the duration, the lower the Shore hardness value will be.
The minimum distance of the test points must be maintained according to the standard. The center distance between the indentations should be ≥ 5mm and ≥ 12mm to the specimen edge.
Shore hardness testing methods
The individual methods are differentiated by:
- The shape of the indenter (see image)
- The magnitude of the spring force F
- The magnitude of the contact force FA
The different resulting test methods use seven different indenters and four different levels of contact force. More specific information on the differences between the individual methods can be found in the table below.
Method | Spring force F [N] | Contact force FA [N] | Indenters | Measurement travel t [mm] | Specimen thickness [mm] | Measurement range |
Shore A | 8.050 N | 9.81 N | Truncated cone, 35° cone angle | 2.5 | ≥6 | 10 … 90 <20 Shore D |
Shore A0 or Shore E | 8.050 N | 9.81 N | Ball, Ø 2.5 mm | 2.5 | ≥6 | <20 Shore A |
Shore AM or Shore M | 0.764 N | 9.81 N | Cone with 30° angle | 1.25 | ≥1.25 | 10 … 90 |
Shore B | 8.065 N | 9.81 N | Cone with 30° angle | 2.5 | ≥6 | 10 … 90 |
Shore C | 44.5 N | 49.0 N | Truncated cone, 35° cone angle, truncated cone dia. 0.79 mm | 2.5 | ≥6 | 10 … 90 |
Shore D | 44.5 N | 49.0 N | Cone with 30° angle | 2.5 | ≥6 | 30 … 90 >90 Shore A |
Shore D0 | 44.5 N | 49.0 N | Ball, Ø 3/32“ | 2.5 | ≥6 | 10 … 90 |
Shore 0 | 8.05 N | 9.81 N | Ball, Ø 3/32“ | 2.5 | ≥6 | 10 … 90 |
How is the hardness value read and represented?
The Shore test hardness value consists of three main components:
- 1. A numerical hardness value;
- 2. The word Shore, to indicate Shore hardness
- 3. The designation of the Shore method that defines the indenter and the associated parameters
If the dwell time deviates from the standard, a time is indicated as a suffixed fourth component.
Example of how to represent and read a hardness value:
| 75 Shore A 10 | |
|---|---|
| 75 | ... Hardness value |
| Shore | ... According to shore |
| A | ... Shore method truncated cone with cone angle 35°, spring force 8.065 N and contact force 12.5 N |
| 10 | ... Dwell time of the contact force outside the recommended duration, in this case 10 seconds |
