## Brinell test procedure

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In the Brinell hardness test, an optical method, the size of indentation left by the indenter is measured. In contrast to the likewise optical Vickers method,which involves a pyramid-shaped indenter being pressed into a specimen, the Brinell method uses a spherical indenter.

The larger the indent left in the surface of a workpiece (specimen) by the Brinell indenter with a defined ball diameter and a defined test force, the softer the tested material.

In order to determine the Brinell hardness (HBW) according to ISO 6506, the spherical, hard metal (tungsten carbide) indenter is pressed into a specimen (workpiece) with a defined test load (between 1 kgf and 3000 kgf).

The Brinell hardness (HBW) results from the quotient of the applied test force (F in newtons (N)) and the surface area of the residual indent on the specimen (the projection of the indent) after withdrawing the test force (see formula below). To calculate the surface area of the residual spherical indentation, the arithmetic mean (d) of the two perpendicular diagonals (d1 and d2 in mm) is used, because the base area of Brinell indents is frequently not exactly round.

In practice, the formula is not calculated for every single test in order to determine the hardness value. Alternatively, the hardness value can be read from tables or specially programmed test software, which indicate the hardness value for all standardised ball diameters and test loads as a function of the average indent diameter (d) (see poster "Hardness comparison table").

The test force must be selected such that the average indent diameter (d) is between 0.24 D and 0.6 D.

In order to adhere to these limits, the test force must be coordinated with the ball diameter. This results in different force-diameter indexes (also referred to as loading levels or load factors) within the Brinell method, whereby the quotient of test force and square of the ball diameter is kept constant: B = 0.102*F/D2. The five common force-diameter indexes are 1, 2.5, 5, 10 and 30. Testing of a material with different ball diameters and test forces must be conducted within the same force-diameter index in order to achieve comparable test results (see overview table "Brinell methods and applications").

The ball diameter must be selected in such a way that the indent covers the largest possible workpiece area – representative for the specimen.

According to the standard (ISO 6506), the test load should be increased to its final value within a minimum of two to a maximum of eight seconds Generally, the dwell time for the test load is ten to 15 seconds (s). If the dwell time is any longer, the duration in seconds must also be specified in the hardness value, e.g.: 210 HBW 5/250/30 (dwell time of 30 s).