How to Choose the Right Hardness Tester?

II. Types of Hardness Tester

① Rockwell Hardness Tester

A Rockwell Hardness Tester (HR) is used to measure the hardness of a material by measuring the depth of indentation left by the diamond penetrating cone. This depth is measured in inches or millimeters, depending on the model. This instrument can be used to evaluate hardened metals and other hard metals. It is not recommended for metals with under 785 N/mm² hardness.

Importance and Advantages:

• It does not use the optical method making it faster and automatic.
• This method is suitable for materials with a lapped or polished surface.
• The method is versatile and can be used to measure various shapes of samples such as spheres, cones, and cylinders.
• The measuring cycle in this method is short, making it fast.

Disadvantages:

• Limited test load ranges.
• The method is insufficient to test some materials, such as untreated steel; hence must be accompanied by Brinell indenter and use higher test loads.
• The degree of contact between the indenter and the sample surface affects the measurement’s accuracy. If the supporting surface has impurities, deformation may happen when the test load is applied, and the measurement may be inaccurate.

② Brinell Hardness Tester

The Brinell Hardness Tester is a mechanical apparatus used to measure the hardness of a material by measuring the force required to indent a metal plate at a given depth. This instrument measures the hardness of materials with a surface roughness of 1 micrometer or greater. It is primarily used in metal testing, but it can also be used on non-metals with an adequate hardness test load.

Importance and Advantages:

• This method is preferred for testing hardness on rough materials, which are difficult to measure using other methods.
• The Brinell Test method has higher loads of up to 3000 kg.
• The method can be used for various testing ranges because there are many different indenter sizes and loads. 
• The method can be used to test all types of metals
• Brinell test is more accurate compared to the Rockwell method because of even pressure distribution by the spherical indenter. 

Disadvantages:

• Since the impressions made are measured using an optical instrument, measuring errors are possible.
• The test sample surface must be prepared well and cleaned for accuracy and reliability to avoid surface imperfections.
• The Brinell method is not suitable for routine testing because the tests are usually long. (up to 60 seconds)
• This method cannot be used to measure cylindrical surfaces because it is only ideal for flat surfaces. 
• The method is more expensive because it uses optical equipment.

③ Vickers Hardness Tester

The Vickers method is a testing method similar to Brinell and is microhardness. It uses a penetrating diamond cone to test the hardness of a material by measuring the depth of indentation left by the cone at a given depth. This method is suitable for measuring metals with hardness ranging from 10 gf to 100 kgf.

Importance and Advantages:

• This method has a very wide measuring range
• Calculations do not depend on the diamond cone size.
• You can measure materials of different hardness levels with the same indenter.
• It is easy to perform the method and it’s preferred for laboratory tests.

Disadvantages:

• The dents on the surface are measured using an optical method such as a microscope which makes this method time-consuming and can result in errors.
• As with the Brinell method, the sample test must be well prepared before testing. 
• The impression of measurement can be less legible in some materials because of irregular load distribution by the diamond cone. 

④ Leeb Hardness Tester

The Leeb Hardness Tester is an alternative hardness testing method that uses a spring load and a series of steel balls to measure the hardness of a material by measuring the force required to drive one ball into the material.

This instrument measures most materials with a surface roughness of 1 micrometer or greater.

Importance and Advantages:

• This method is versatile for different applications, and it is less expensive.
• It is faster because it does not use an optical method.
• The method is faster and the results are legible.

Disadvantages:

• This method has a shorter measuring range than that of the Brinell instrument, making it slower in testing time. 
• This method requires a large amount of test sample material which could be costly if this method must be repeated time after time. 
• This method has the same disadvantages as the Brinell method.

⑤ Ultrasonic Hardness Tester

The Ultrasonic Hardness Tester is a non-destructive ultrasonic testing method used to measure materials’ hardness. The principle of this instrument requires a tool (gauge). The tool will be applied to the sample on which a probe will be fixed and then this probe will send out ultrasounds which will determine the hardness of the sample. The instrument uses a probe that carries an ultrasonic transducer, which generates waves in the audible range. 

Ultrasonic testing can be performed by immersion or contact.

Importance and Advantages:

• The ultrasonic method is non-destructive and it does not leave any marks during the test.
• This very sensitive method can be used for a wide range of materials.
• It can measure the hardness of the material accurately.
• The instrument operates automatically, making it time-saving.

Disadvantages:

• The method can only measure the surface hardness of the material and not the hardness at a depth.
• Ultrasonic testing requires high-frequency crystals which can be affected by aging and temperature changes.
• The method is affected by surface roughness, cracks, rough surfaces, inclusions, and pores. This may affect hardness measurements because these results will vary when compared to other methods.