Choosing the Right Hardness Tester

A hardness tester is a measuring instrument used to assess the stiffness or strength of a material.

Hardness testers are used to determine the resistance of a material to deformation by means of a harder tool, most often a diamond cone or steel ball, which penetrates the surface of the material being tested. The hardness tester then measures the penetration depth of the tool and the impression left by the tool on the surface of the sample.

Different test methods exist. This guide will present different hardness testers with their advantages and disadvantages.

View hardness testers

  • How to choose a hardness tester?

    Here are the main elements to consider before choosing a hardness tester:

    The test load: this is determined by the hardness of the material. Metals such as steel or alloys, for example, require test loads of up to 3,000 kgf, while soft metals require only 500 kgf. The higher the load, the higher the accuracy. It is important to note that the impression should not exceed 1/10 of the thickness of the sample.

    The hardness range: determines the material of the indenter. Over 650 HB/30 hardness, you should favor a diamond indenter. Below this value, steel or hard metal indenters are suitable.

    The accuracy level: depends on the surface to be measured (cleanliness, flat surface, static or dynamic system, etc.).

    The adaptibility of the device: its importance varies according to the shape and size of the samples to be tested.

    Selection criteria:

    • Test load
    • Hardness range
    • Level of accuracy
    • Flexibility of the device
  • What are the different types of hardness testers?

    Hardness testers are classified according to the test method they use:

    • the Brinell method
    • the Rockwell method
    • the Vickers method
    • the Knoop method
    • use of ultrasound
  • Why choose a Brinell hardness tester?

    INNOVATEST Brinell hardness tester

    The Brinell method is the most commonly used hardness measurement technique in industry. To mark the surface of the sample, this test method uses a steel ball indenter with a diameter that varies according to the sample to be measured. A microscope or measuring magnifier complete the device. 

    This method has many advantages:

    • First of all, it is the preferred method for measuring the hardness of rough samples, which are more difficult to handle with other methods.
    • The test loads applied are high (3,000 Kg).
    • There are many indenter sizes and loads possible, which means the measuring range is very wide.
    • A Brinell hardness tester can test all types of metals.
    • The results of the Brinell method are more accurate and reliable than those obtained by the Rockwell method because the use of a spherical indenter distributes pressure evenly.

    This method has some disadvantages as well however:

    • Measuring errors are possible since the impression made on the sample surface is measured with an optical instrument.
    • Even if the test load is higher than with other test methods, the surface of the sample must be well prepared, clean and flat as imperfections can interfere with the accuracy and reliablity of measurements.
    • This means tests using this method are quite long (up to 60 seconds, not counting the sample preparation time). This method is therefore not ideal for routine testing.
    • You cannot use this method to test cylindrical surfaces because it is only accurate and reliable on flat surfaces.
    • Lastly, due to the presence of optical equipment, this method is also more expensive.
  • Why choose a Rockwell hardness tester?

    Tinius Olsen Rockwell hardness tester

    The Rockwell method is the most universal because it uses both a penetrating diamond cone and a penetrating steel ball to measure the hardness of a material.

    • The diamond cone can only be used on hardened steel and hard metals. It is not recommended below 785 N/mm² hardness.
    • The steel ball is used with softer materials. But be careful, the softer the material, the larger the diameter of the ball must be and the lower the total load.
    • Ball indenters with a large diameter are used to test plastic materials.

    The Rockwell method also has other advantages:

    • It is the only method that offers measurements without optical equipment, which means this solution can be made automatic and faster.
    • This method is less sensitive to imperfections in the sample.
    • It can be used to measure cylindrical, spherical or conical samples.
    • It is fast because the measurement cycle is short.

    However, it also has disadvantages:

    • The test load ranges are limited.
    • For some materials, such as untreated steel, this method alone is not sufficient and must be accompanied by a Brinell indenter using higher test loads.
    • The accuracy of the measurement depends on the contact between the indenter and the sample surface. If there are impurities on the supporting surface, deformation may occur when the test load is applied and the measurement may be erroneous.
    • This method is less accurate for hard materials.
  • Why choose a Vickers hardness tester?

    MITUTOYO Vickers hardness tester

    The Vickers method is a microhardness testing technique. It is similar to the Brinell method. It is suitable for all solid and metallic materials and for all hardness ranges from 10 gf to 100 kgf.

    The difference between the Vickers method and the Brinell method is that the latter uses a diamond penetrating pyramid with a square base and a fixed load. An optical instrument measures the impression. This technique allows light test loads as well as macro loads up to 30 kg.

    The advantages to this technique are:

    • The measuring range is very wide. This method can be used to test all types of materials, whether they are particularly soft or hard.
    • The test is easy to perform.
    • The calculations are independent from the size of the diamond pyramid.
    • The same indenter can be used to measure materials of a different hardness.
    • This technique is perfect for laboratory tests.

    However, it also has disadvantages:

    • This is a time-consuming process because the imprint on the surface is measured optically, with a microscope for example, which can also be a source of error.
    • As with the Brinell method, the surface of the sample must be well prepared.
    • On some materials, the measurement of the impression is less legible due to the irregular distribution of the test load by the pyramid (the load is higher on the edges than on the sides).
  • Why choose a Knoop hardness tester?

    AFFRI Knoop/Vickers hardness tester

    The Knoop method is another microhardness testing technique, an alternative to the Vickers technique, that uses a narrow diamond shaped indenter. This technique allows for light test loads of just a few grams.

    It is mainly used to assess the risk of cracking in brittle materials such as ceramic and to test the hardness of thin layers of a sample, including coatings.

    It is often combined with the Vickers method.

  • Why choose an ultrasounic hardness tester?

    INNOVATEST ultrasonic hardness tester

    The ultrasonic hardness tester is used for non-destructive hardness testing of materials. This inspection technique uses sound waves to evaluate the quality of solid materials (metals, concrete, bricks), determine their thickness and detect the presence of internal defects.

    Ultrasonic testing can be carried out either by contact or by immersion. The equipment, consisting of a probe, is portable.

    • Testing by contact allows for the inspection of bulky parts that are impossible to transport.
    • Immersion testing involves immersing the material in a liquid in order to obtain better movement of the sound waves. This method enables better detection of small defects.
  • Should I choose a benchtop or portable hardness tester?

    • Benchtop hardness testersare the traditional hardness testers using the Brinell, Rockwell or Vickers methods. These are heavy and bulky pieces of equipment that require installation on the ground or on a test bench. Their main advantage lies in the fact that they allow hardness measurement with conventional methods.
    • Portable hardness testers are much smaller, lighter and more compact. Their main advantage is that the user does not need to take a sample of the material to perform the test. They are therefore more practical in most cases.
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1 comment
  • PCTE says:

    This is a very detailed blog post about choosing the right hardness tester. It would help people who are looking to buy hardness

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