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Difference Between Brinell and Rockwell Hardness: Complete Details

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Difference Between Brinell and Rockwell Hardness

The main difference between Brinell and Rockwell Hardness is mostly in their testing methodologies and the type of impact they make. Brinell hardness testing involves pressing a hardened steel or carbide ball into the material surface with a constant load, measuring the diameter of the resulting impression. Rockwell hardness testing uses two types of loads one is minor and the other is major, using different types of intender shapes such as a diamond cone or steel ball. 

Rockwell can be used to test materials of different sizes and levels of hardness, while Brinell is better for testing materials with rough surfaces or coarse gain structures. Read on to learn more about tests and the difference between Brinell and Rockwell hardness.

What is Absolute Brinell Hardness?

Brinell hardness is a way to figure out how hard a material is and how easily it can be permanently dented by a normal load. It tells you how well an object can handle being pushed and shaped. To do the Brinell hardness test, you press a hard steel or carbide ball into the test material’s surface and measure the diameter of the indentation left behind.

Here’s a breakdown of the key points of Brinell’s hardness.

  • Testing method: A hard ball indenter (typically made of steel or carbide) is pressed into the material under a specific load.
  • Measurement: The diameter of the indentation is measured after the load is removed.
  • Units: Brinell hardness is expressed as a Brinell Hardness Number (HB), which is calculated by dividing the applied load (in kilograms) by the surface area of the indentation (in square millimetres).

Brinell hardness is particularly useful for testing softer metals, castings, and other materials where a larger indentation is preferred. It provides a good overall indication of a material’s hardness throughout its thickness.

What is Relative Rockwell Hardness?

Rockwell Hardness is different from Brineell hardness because Rockwell hardness tests how deeply a certain load makes a depth in a material. Brinell measures the size of the depth is made, while Rockwell measures how well the material can stop being penetrated.

Here’s a closer look at Rockwell’s hardness.

  • Testing method: Similar to Brinell, it uses a standardized load, but Rockwell employs either a diamond cone-shaped indenter or a hardened steel ball indenter depending on the chosen scale. 
  • The test involves applying a two-stage loading process: a minor load followed by a major load. 
  • Measurement: The Rockwell hardness value is defined by a combination of a capital letter (indicating the specific scale used) and a number. Unlike Brinell’s units, Rockwell hardness is a dimensionless number.
  • Applications: Rockwell hardness is favoured for its versatility and speed, making it suitable for a wide range of metals, including harder materials that might be unsuitable for Brinell testing. 
  • It’s also considered a non-destructive testing method, allowing for multiple measurements on a single sample.

Both Brinell and Rockwell hardness are valuable tools in material science, but their ideal applications differ based on factors like material type, desired measurement approach, and the level of indentation acceptable.

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What is the Difference Between Brinell and Rockwell Hardness?

Here is the table summarizing the main differences between Brinell and Rockwell hardness.

ParticularsBrinell Hardness Testing
Rockwell Hardness Testing
IndenterSpherical (usually made of hardened steel or carbide)
Conical (for HRA and HRD scales) or Spherical (for HRC scale)
Indenter
Material
Typically hardened steel or carbideTypically hardened steel or diamond
Indentation
Size
Larger diameter indentation (typically 1-10 mm)
Smaller diameter indentation (typically less than 1 mm)
Force ApplicationThe applied force is constantApplied force varies depending on the hardness scale
MeasurementThe diameter of indentation
is measured
Depth of indentation is measured
Hardness
Scales
Typically ranges from 100 to 700 HBVarious scales (e.g., HRA, HRB, HRC) covering different ranges
Surface PreparationRequires a flat surface for testingLess stringent surface preparation required
Material SuitabilitySuitable for softer materials, rough surfaces, and large grain sizes
Suitable for a wide range of materials, including very hard materials

Difference Between Brinell and Rockwell Hardness Formulas

There isn’t a single formula directly used for either Brinell or Rockwell hardness measurements. They both rely on specific test procedures and calculations based on the resulting measurements. Here’s a breakdown for each:

Brinell Hardness (HB)

The Brinell Hardness Number (HB) is calculated using the following:

HB = (F) / (D^2 x π/2)

Where:

  • HB = Brinell Hardness Number
  • F = Applied load (in kilograms)
  • D = Diameter of the indentation (in millimetres)
  • π (pi) = Constant value (approximately 3.14159)

Rockwell Hardness

  • Rockwell hardness doesn’t have a single formula as it uses a different measurement approach.
  • The test involves a two-stage loading process, and the hardness value depends on the difference in depth of indentation between the minor and major loads.
  • Rockwell hardness is reported as a combination of a capital letter (indicating the scale used) and a number. The specific conversion of depth readings to hardness values is done through reference tables or built-in calculations in Rockwell testing machines.

Where are Brinell and Rockwell Hardness Tests Used?

Brinell and Rockwell hardness tests find applications in a wide range of industries due to their effectiveness in determining a material’s resistance to wear and deformation.

  • Throughout the manufacturing process of metals like steel, aluminium, and alloys, Brinell and Rockwell hardness testing plays an important role in ensuring material quality control.
  • From engine components like pistons and crankshafts to car frames and suspension parts, Brinell and Rockwell hardness tests are essential for selecting materials that can withstand the stresses and strains of automotive operation.
  • It ensures the materials used in aircraft, spacecraft, and jet engine parts possess the necessary strength and wear resistance for flight.
  • The selection of materials for building components like beams, fasteners, and tools often relies on Brinell and Rockwell hardness testing.
  • It might be used on tools, hardware, and sporting goods to confirm they have the appropriate hardness for their intended function.

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FAQ’s

What is the difference between BHN and HRC?

Britnell hardness (HB) is usually used for soft materials like steel before or after heating or heat-treating non-ferrous metals. When talking about hard materials, like those that have been heated or something, Rockwell hardness (HRC) is usually used.

Which is better Rockwell or Brinell?

Because it uses a circular indenter that spreads pressure evenly, the Brinell method gives more exact and reliable results than the Rockwell method.

Why is Brinell better than Rockwell?

Brinell testing is more exact than Rockwell testing because the load is spread out evenly on the material’s surface by the circular indenter.

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