When it comes to conducting a hardness test, it is important to understand the different methods available and their respective advantages and disadvantages. The most commonly used methods include Rockwell, Vickers, Brinell, Knoop, and Leeb.
Rockwell Hardness Test & Formula
Rockwell hardness testing is the most widely used method in industry. It is a simple and quick method that involves applying a known load to the material being tested and then measuring the depth of penetration of an indenter, typically a diamond or carbide ball, into the material. The depth of penetration is then converted into a hardness number using a standard chart.
- The formula for Rockwell testing is HR = (100-A/B)+(C-100) where A is the depth of the indentation before applying the load, B is the depth of the indentation after applying the load, C is the scale and HR is the Rockwell hardness number.
Vickers Hardness Test & Formula
Vickers hardness testing is similar to Rockwell, but it uses a diamond pyramid indenter instead of a diamond-tipped or carbide ball. The advantage of Vickers testing is that it can be used to test small areas with high accuracy. However, the disadvantage is that it requires a microscope for measurement, which can be time-consuming.
- The formula for vickers is HV = 2F/D^2, where HV is the Vickers hardness, F is the applied force, and D is the diagonal length of the indentation.
Brinell Hardness Test & Formula
Brinell hardness testing is similar to Vickers, but instead of a diamond-tipped indenter, a hardened steel ball is used. The advantage of Brinell testing is that it can be used on larger areas than Vickers testing. However, the disadvantage is that it leaves a permanent indentation on the surface of the metal.
- The formula for brinell is HB = (F/D^2)*2, where F is the applied force, D is the diameter of the indentation and HB is the brinell hardness number.
Knoop Hardness Test & Formula
Knoop hardness testing is also similar to vickers testing, but it uses a diamond pyramid indenter with a longer diagonal than vickers. The advantage of Knoop testing is that it can be used to test small and thin materials.
The formula for knoop is HK = F/L^2 where F is the applied force, L is the long diagonal of the indentation and HK is the Knoop hardness number.
Leeb Hardness Test
Leeb hardness testing is a dynamic test, it uses a impact device to generate a force on the material. A sensor on the material measures the rebound velocity and the hardness value is calculated based on the velocity and the impact device properties. The advantage of Leeb testing is that it can be used to test hard materials and it’s portable.
How to Conduct Hardness Testing
When conducting a hardness test, it is important to take into consideration the specific properties of the material being tested. For example, some materials may have a very thin surface layer that is harder than the underlying material, and it is important to use a test method that can accurately measure the hardness of this surface layer. Additionally, some materials may be brittle and may crack or break under high loads, so it is important to choose a test method that applies a lower load to the material.
Another important factor to consider when conducting a hardness test is the size and shape of the test specimen. The size and shape of the test specimen can affect the accuracy of the test results, and it is important to ensure that the test specimen is large enough and has the correct shape to provide accurate results.
It is also important to ensure that the test equipment is properly calibrated and that the test is performed by a trained and experienced operator. This will help ensure that the test results are accurate and that any errors in the test results can be traced back to specific sources.
Conclusion
In summary, hardness testing is an important aspect of ensuring the quality of metals and mechanical parts. By choosing the appropriate test method, considering the specific properties of the material being tested, and ensuring that the test equipment is properly calibrated and the test is performed by a trained and experienced operator, businesses can ensure that their products meet the required standards and avoid costly defects. It is also important to include hardness testing as part of a regular quality inspection checklist to ensure that the products continue to meet the required standards over time.
