Hardness tests are used to check the hardness of a material. Hardness test is done with the help of a machine called the hardness tester. Many types of hardness testers are available. It is done by penetrating the material being tested with a material that is harder than the sampling material. Hardness tests help to decide the resistance of a material to deformations. Brinell and Rockwell hardness tests are the most common hardness tests used.
Brinell vs Rockwell Hardness
The main difference between Brinell and Rockwell hardness is that Brinell hardness uses only one type of indenters but, Rockwell hardness uses two types of indenters. The duration of indenting also differ in Brinell hardness it is 30-60 second while in Rockwell hardness, it is 10-15 seconds. Rockwell hardness is comparably easier than Brinell hardness.
Brinell hardness is one of the scales by which the level of hardness of a material is measured. The instrument used in this test is called a Brinell indenter. This scale is used to make indentations on the sample and then the measured indentation is converted into a value using the Brinell hardness scale.
Rockwell hardness is also a scale to measure the hardness of material just like Brinell hardness. It also has a specific Rockwell indenter. This indenter is of a specific size and a specific amount of force is applied to the sample to form an indentation. The measurements are then converted into Rockwell hardness values.
Comparison Table Between Brinell and Rockwell Hardness
|Parameters of Comparison||Brinell Hardness||Rockwell Hardness|
|Accuracy||Less accurate||Very accurate|
|Indenter||Spherical Steel ball||Diamond cone and Spherical Steel ball|
|Size of Indenter||10mm||<4mm|
|Duration||30-60 sec||10-15 sec|
|Sensitivity||Sensitive to small imperfections on the surface of the sample||Not very sensitive to imperfections|
|Drawback||Very hard samples cannot be measured||The cone of indenter may be subjected to breakage|
What is Brinell Hardness?
The Brinell hardness machine has an indenter that is 10mm in diameter. The indenter should be a hardened steel ball or a carbamide ball. This spherical ball can be used to exert a load of about 3000kg in the case of a harder material.
However, this load can be decreased when the material tested is softer to avoid extra indentation. Brinell hardness is usually used to determine the hardness of materials with heterogeneous structures. The surface of the sample must be prepared before indentation. It should be flat and perfect. Any imperfections can lead to error.
The Brinell hardness tester is easy to handle and portable. The diameter of the incision made with the tester is measured with a help of a simple low-powered microscope. The Brinell hardness value is obtained by dividing the load applied by the surface area of the indentation. There must be no vibration while measuring because it can influence the value and lead to error.
Brinell hardness tester can be applied for all types of material. The load applied is high compared to other hardness testers. The size of the indenter and load can be adjusted accordingly. Since Brinell testers use a spherical indenter that exerts pressure evenly there is only a little chance for the occurrence of error.
What is Rockwell Hardness?
Rockwell hardness method is the universal method for hardness testing. This method has no optical equipment like a microscope to measure the indentation. There are two types of indenters used in this method. One is a diamond cone and the other one is a steel ball. The diamond cone is used on very hard samples which must be above 785 N/mm² hardness.
The steel ball is used for other softer samples. The diameter of the ball must increase and the load must decrease with the decrease in hardness of the material. Plastic materials are tested with ball indenters of larger diameters. This method ignores the errors as it is not very sensitive to the imperfections on the sample. Spherical, cylindrical, or conical-shaped samples can be also measured. It takes less time and the value is generated automatically.
It has a low test loading capacity. Aluminum, Soft steel, and Copper alloys are normally tested using this method. However, for untreated steel material in addition to this method Brinell method must also be used.
There are three types of Rockwell hardness methods. They are Rockwell C, Rockwell 15N, and Rockwell B. Rockwell C method uses the diamond indenter. It is used to test the hardness of nuts, bolts, seat belt buckles, etc. Rockwell B uses the spherical steel indenter. Rockwell 15N method exerts a low pressure on the sample.
Main Differences Between Brinell and Rockwell Hardness
- The size of the indenter used in the Brinell test is 10mm. It is a steel ball. Whereas, the indenter used in Rockwell hardness is either a diamond cone or a spherical steel ball of less than 4mm diameter.
- In the Brinell hardness the surface area of the indentation is measured but, Rockwell hardness measures the depth of the indentation made.
- Brinell hardness is used to measure hard materials while the Rockwell test does not apply to very hard materials.
- Brinell test has high loading capacity compared to Rockwell hardness test which has relatively low loading capacity.
- Rockwell hardness is cheap and easy to use than the Brinell test which is costly as it includes optical instruments like a microscope.
- Value can be readily obtained in Rockwell hardness, it is also very accurate than Brinell hardness. But, Brinell’s hardness can be subjected to errors.
Hardness tests are very helpful in determining the hardness of a material. Only by knowing the hardness of a material, it can be made into different things. Hardness tests should be chosen depending on the material to be tested. Rockwell and Brinell methods can be used accordingly to measure the hardness of materials considering several properties of the sample.
These tests are very helpful for engineering metallic parts and for producing plastic materials. However, these methods also have several drawbacks like errors due to improperly flattened sample surfaces, vibrations, etc. The ductility and wear resistance of the material can be determined with the help of hardness tests. Since, resistance to friction, erosion, and water will be higher for harder substances. This hardness property help to determine if the particular material is suitable for the desired work or not.