FAQ durometer

What is a durometer?

The durometer is a measuring device for the technical hardness testing of rubber and plastic articles as well as of non-metallic materials.

What is hardship?

Hardness is understood to mean the resistance to the penetration of an indenter with a certain geometric shape and a defined force into the sample.

The penetration path is measured and displayed in analog or digital form.

What is Shore?

The Shore hardness is a material parameter for elastomers. The Shore Instrument Co. dealt with the hardness testing of elastomers. Shore Instrument Co pioneered the Shore hardness scales.

Which parts can be measured with Shore?

From soft silicones to elastomers and plastics. The material thickness and width are also decisive.

For which areas of application are the variants used?

• Durometer A: Soft rubber, elastomers, natural rubber ...
• Durometer D: Hard rubber, rigid thermoplastics ...
• Durometer AO: Foams, steering wheels, interior panels, motor vehicles ...
• Durometer B: Hard elastomers where the hardness is between Shore A and Shore D.
• Durometer C: Medium-hard elastomers ...
• Durometer DO Dense-grained materials, textile fabrics ...
• Durometer O: Soft elastomers, textile fabrics ...
• Durometer OO: Foam, foam and cellular rubber ...

How big is the penetration path?

Depending on the variant and in the unloaded state (display 0 Shore), the indenter protrudes 2.5 mm * over the pressure plate. If the hardness tester is pressed on a ground steel plate, the display shows 100 Shore (no penetration into the elastomer).

* Except Asker C = 2.54 mm

What is the geometry of the indenter?

• Durometer A and C: ø0.79 mm / 35 ° / ø1.25
• Durometer D and B: R0.1 / 30 ° / ø1.25
• Durometer AO: ø5 mm
• Asker C durometer: ø5.08 mm
• Durometer DO, O and OO: ø2.38 mm

What is the max. Spring force (at 100 Shore)?

• Durometer OO: 1.11 N
• Durometers A, AO, B and O: 8.05 N
• Asker C durometer: 8.39 N
• Durometer D, C and DO: 44.5 N

Every Shore hardness tester has a spring. This spring produces the required force

(Hooke's law - after Sir Robert Hooke). Ie each penetration path has an assigned force.

In which measuring range should the durometers be used?

The measuring range is from 0 to 100 Shore. The values from 0 to 10 and from 90 to 100 should not be used. If values in these ranges occur, a different Shore hardness scale is used.

What material thickness is required?

≥6 mm or layers 2 mm + 2 mm + 2 mm = 6 mm

If the test object is 1.5 mm, for example, the Shore method cannot be used.

The indenter stands 2.5 mm away from the pressure plate in the unloaded state, in this case the surface would influence the measurement.

What do I have to consider with the measurement time?

The measuring time begins after the pressure plate has been placed. There are different measurement times depending on the standard. This means that the measured values of different standards can only be compared to a limited extent.

Example:

ASTM D 2240 standard (Durometer A) measuring time: 1 second

ISO 7619-1, Shore A measuring time: 3 seconds

ASTM D 2240 hardness values are higher compared to ISO 7619-1 hardness values. With ISO 7619-1, the indenter has more time to penetrate the material. If the measured values are to be comparable, the same time must always be used.

What is a split second?

The regular pointer always shows the current hardness value. If the knurled screw in the middle of the display is turned counterclockwise, the drag pointer is set to the value 0. During a hardness measurement, the regular pointer takes the drag pointer with it up to the maximum hardness value. The drag pointer then remains in this position (eg 62 Shore A). The regular pointer can show a lower value (e.g. 59 Shore A) because the material is flowing (depending on the material and measuring time).

Why should a test stand be used for the Shore hardness test?

Testing by hand:

The pressing force of the durometer on the sample is produced by hand (mass hardness tester + hand force).

Subjective measurement errors, caused by incorrect pressure or non-vertical measurements, are possible. This means that the measured values vary more - larger deviations (range is larger).

Test stand:

When using a test stand, the hardness tester is lowered smoothly with a constant test force - with the help of a rocker arm. The hardness tester + holder + shaft + weight represents the mass. For Shore D an additional weight of 4000 g is required.

How often should a calibration be performed?

The calibration of Shore is described in the ISO 18898 standard (also ASTM D 2240 for hardness testers who are not described in ISO 18898). The minimum requirements of the measuring equipment are also described (in ISO 18898). During calibration, the geometry of the indenter and pressure plate, the measuring force (spring) and the measuring path are checked.

We recommend an annual calibration.

How do I store the durometer?

The durometer should be stored in a clean, dry place out of direct sunlight. Ideally in the case provided.

How can I avoid mistakes when measuring?

• Before measuring, it must be checked whether the durometer is suitable for the material of the workpiece to be tested. The reading should be between 10 and 90.
• The ambient temperature, the temperature of the workpiece and the temperature of the durometer are ideally 23 ° C.
• The specified material thickness must not be undercut.
• The surface of the test item must be clean and flat and have two parallel surfaces.
• The direction of measurement is vertical from top to bottom. It must be ensured that the contact surface of the durometer is parallel to the surface of the test object at all times.

• The touchdown and measuring speed should be around 2.5 mm / s (max. 3.2 mm / s according to the standard).
• The measuring time must be observed.
• If several measurements are carried out on a test item, each measuring position may only be used once, ie after each measurement the workpiece or the durometer is moved.
• If the durometer has been used improperly, it must be checked or recalibrated.