Durometer / Shore Durometer

The prefix Duro comes from Latin and is usually used when it goes about “hard”. A durometer is therefore a measuring device with which the hardness of materials can be determined. In general, however, only those devices for measuring hardness are called durometers that press a specially shaped indenter onto the test surface with a controlled amount of force. In many standards for hardness testing of plastics and elastomers, the term durometer is used almost universally for the hardness testing devices.

Test methods for determining hardness
The hardness of a material generally indicates its resistance to penetration by a harder body. In contrast to hardness, strength describes resistance to deformation and separation. While some materials, such as glass, are hard but break easily, for the others, e.g. certain structural steels, the hardness can be used to infer the strength. The harder a material is, the more force is required to deform it. Since the resistance to penetration and the response time of different materials differ greatly due to their structure, various hardness test methods have been developed. For some of the test methods, a durometer is sufficient for hardness measurement, for the other methods several devices are needed. For example, in the case of the methods in which, after the test specimen has been pressed in, the surface of the resulting imprint is determined by measurement under the microscope. One of these methods is the Brinell hardness test, which is described in the EN ISO 6506-1 and ASTM E10-08 standards and was developed especially for metals and metal alloys.

In addition to the tests with high-precision testing devices under the laboratory conditions, test procedures have also become established with which important characteristic values can be tested quickly and easily, even on permanently installed or very large parts, in product development, incoming goods, production and during repeat tests. Many methods differ primarily in the size and shape of the indenter, the amount of force applied and how the effect of the applied force is measured. In order to be able to classify the hardness data correctly, they are marked with the abbreviation of the test method and, if necessary, further information on the test conditions:

Measuring the penetration depth
HS Shore hardness, differentiated into A, A0 or E, AM or M, B, C, D, D0 and 0
HR Rockwell hardness, differentiated into A, B, C, D, E, F, G , H, K, L, M, P, R, S, V, N. T, W, X, Y
HBa Barcol
HM Martens hardness, continuous measurement of force, depth and time during the test
HW Hardness according to Webster, for thin and soft materials

Measuring the area of the imprint left by the indenter
HV Hardness according to Vickers
HB Brinell hardness
HK Knoop hardness

Measuring the rebound height
HL Hardness according to Leeb, differentiated into D, S, E, DL, D+15, C and G Schmidthammer for testing building materials such as concrete, gives the value of the compressive strength, which is important for building materials.

Comparability of hardness data from different test methods
As there are so many methods for testing hardness, it is important to ensure that the method used to determine the value is correctly stated when giving the hardness data. For some materials, the measured values of certain frequently used methods can also be given as hardness values according to other methods or as tensile strength due to sufficiently available comparative measurements. For this purpose, the values are read from the material-specific tables or, in the case of the digital durometer, can be output directly via the stored comparative values.

EN ISO 18265 contains conversion tables between Vickers hardness, Brinell hardness. Rockwell hardness and tensile strength for six different metallic materials:
Annex A unalloyed and low-alloy steels and cast steels.
Annex B Quenched and tempered steels
Annex C Cold work steels
Annex D High speed steels
Annex E Hard metals
Annex F Non-ferrous metals and alloys

There is also a correlation between the measured values of the frequently used test methods Shore A and Shore D, so that under certain conditions they can also be given as the value of the other quantity.

Selection criteria for the durometer
Many durometers enable fast and uncomplicated measurements of hardness. However, the basic prerequisite is that the model chosen is suitable for the materials and components to be tested. In order to obtain usable data, however, the requirements for the materials to be tested must be met, as well as the specifications for the procedure of the respective measurement and the handling of the device.

Durometer for mobile or stationary use
Mobile durometers are particularly suitable for testing large or already installed parts. Random samples and parts with suitable dimensions can also be tested with stationary devices or with the durometer fixed on a tripod or test stand. Stationary testing simplifies above all the maintenance of the set-up angle and the spacing of the test points.

Advantages of digital durometers
Analogue durometers are easy to operate and do not require batteries. They are particularly suitable for measurements where no values need to be stored. The models with drag pointer allow easy reading of the maximum value after the measurement. Digital durometers generally show the maximum value of the measurement. However, many types of durometers also allow the maximum, minimum and average values of the measurement series to be retrieved. Models with memory and data interface also facilitate the documentation and further processing on the computer. The more samples need to be tested and documented, the greater the advantages of easy storage and data transfer are. Also the possibility of displaying the measured values as hardness values according to other methods also makes the evaluation of the measurement results much easier. However, it is essential to ensure that the appropriate hardness scales for the material being tested are stored in the durometer.

Selection according to the test method
Basically, it is important to pay attention to the test method when selecting the durometer. VDI/VDE Guideline 2616 provides information on the areas of application and the advantages and disadvantages of the most common methods of hardness testing. The durometers, where the measured value is displayed directly after the measurement, differ mainly in terms of the energy used and the design of the indenter. The harder the material is, the more it can be stressed during the test. Many digital durometers can indicate the hardness as a value according to different methods, but they test only according to one. For the values that are not directly measured, it is important to check whether they may be used for the material being tested. However, some models with an external impact device that work according to the Leeb method can perform different Leeb tests, e.g. according to Leeb C, Leeb D and Leeb G, by using several impact devices.

Accessories for durometers
Often, the scope of delivery already includes suitable calibration plates so that the user can check the measuring accuracy of the durometer himself. Instrument versions with memory are often supplied with a data cable or storage medium. Some models also come with free PC software for evaluating the measurement data. Optional accessories include tripods, test stands or various adapters for mounting on convex or concave surfaces. These facilitate centring and alignment and thus help to avoid measurement errors.

Calibration and adjustment of the durometer
Calibration is the process of checking the accuracy of a measuring instrument. Depending on the measurand, there are different procedures for this. The durometer can be calibrated with the test specimens of the known hardness. With suitable test blocks, the user can thus check the accuracy of his instrument at any time. In some companies there is a requirement for external calibration. Many calibration laboratories offer calibrations according to ISO or DAkkS for durometers and issue calibration certificates for them. When requesting calibration, be sure to specify the method, e.g. Leeb, Rockwell, Barcol, and the numerical values at which your instrument is to be calibrated. If the test values are outside the device-specific accuracy, most durometers can be adjusted, i.e. set back to the specified accuracy.

A durometer is a device for measuring the hardness of materials, especially elastic or rubber-like materials. The calibration of a durometer is important to ensure that it provides accurate and reliable measurements. Here is some information about the calibration of a durometer:

Calibration standard: To calibrate a durometer, you need a calibration standard. This is a material with a known hardness that is used to check the accuracy of the durometer. The calibration standard should ideally have a hardness that is close to the typical materials you want to measure with the durometer.

Selection of the calibration standard: The selection of the correct calibration standard depends on the scale of the durometer you want to calibrate. There are different scales such as Shore A, Shore D, Shore OO, etc. Each scale has a different hardness range. Make sure that the calibration standard is suitable for the selected scale.

Checking the durometer scale: Make sure that the durometer is set to the correct scale. Check the display or the adjustment knob to make sure that the durometer is calibrated to the appropriate scale you want to use.

Measurement of the calibration standard: Place the calibration standard on a stable base and bring the durometer into contact with the material. Press the durometer firmly on the calibration standard to get an accurate measurement. Read the value on the ad.

Comparison with the known value: Compare the measured value with the known value of the calibration standard. Make sure that the deviation is acceptable. Ideally, the measured value should be close to the known value.

Adjustment and calibration: If the durometer does not provide the expected value, adjustments may need to be made. Check the operating instructions of the durometer for instructions on adjustment. In some cases, professional calibration may be required. Contact the manufacturer or a specialized calibration device.

Repetition of calibration: The calibration of a durometer should be repeated regularly to ensure that it continues to provide accurate measurements. The frequency of calibration depends on the frequency of use and the requirements of your specific area of application.

Please note that this is general information on the calibration of a durometer. The exact steps and requirements may vary depending on the manufacturer and model. It is advisable to consult the manufacturer's specific instructions for your durometer.

Calibration is the control of measurement magnitudes correction for a measuring instrument without intervention in the measurement system, or the determination of the systematic display deviation in relation to the real value of the measuring magnitude.

A calibration certificate is a document that confirms that the technical properties of test instruments comply with a recognized standard of measurement.

The introduction of International Standards Organization (ISO) 9000 brought about new requirements for quality control. As a result, many companies and laboratories must obtain ISO calibration certificates for their measuring instruments. An ISO calibration certificate is a controlled document that confirms that the specific test instruments meet the minimum requirements of the appropriate ISO standard. An ISO calibration certificate can be acquired for any shore durometer offered by PCE Instruments.

A durometer calibrator or calibration device must conform to national and international standards such as DIN ISO 7619, ISO 868, ISO 7619 and ASTM D2240. According to these standards, shore durometer readings must be within +/-1 of the point indicated on the scale. To perform correct measurements, a durometer must be calibrated regularly. The period of time between calibrations is called a calibration interval. It is the responsibility of each shore durometer user to determine and check the interval between calibrations. To determine the calibration interval for your durometer, consider the following factors:

- Measuring magnitude and allowed margin of tolerance
- Performance of the measuring instrument
- Frequency of use
- Operating conditions
- Stability of previous calibrations
- Required measuring accuracy
- Quality control requirements for your company or laboratory

PCE Instruments’ friendly and knowledgeable technical experts are available to answer any questions related to the process of establishing a calibration interval. However, as a guideline for best practice, PCE Instruments recommends a calibration interval between 1 and 3 years.

PCE Instruments is a trusted manufacturer and supplier of accurate, reliable shore durometer products. Each test instrument is calibrated and adjusted according to the highest possible quality standards by PCE Instruments itself, or by a first-class calibration laboratory partner.

The picture at left shows a sample ISO calibration certificate for a shore durometer