PRINCIPLE OF THE BRINELL HARDNESS TEST

Calibration

Determination of the values of the significant parameters by comparison with values indicated by a reference instrument or by a set of reference standards.

Indenters

Indenters for the Brinell hardness test shall be tungsten carbide balls of four allowed diameters (1, 2.5, 5 and 10 mm). Dust, dirt, or other foreign materials shall not be allowed to accumulate on the indenter, as this will affect the test results.

Portable Brinell hardness testing machine

A Brinell hardness testing machine that is designed to be transported, carried, set up, and operated by the users, and that measures Brinell hardness by the Brinell indentation hardness test principle.

Brinell hardness machine

Equipment for Brinell hard- ness testing usually consists of a testing machine, which supports the test specimen and applies an indenting force to a ball in contact with the specimen, and a system for measuring the mean diameter of the indentation in accordance with the Brinell hardness test principle. The design of the testing machine shall be such that no rocking or lateral movement of the indenter or specimen occurs while the force is being applied. The design of the testing machine shall ensure that the force to the indenter is applied smoothly and without impact forces.

Specimen Support

A specimen support or “anvil” shall be used that is suitable for supporting the specimen to be tested. The seating and supporting surfaces of all anvils shall be clean and smooth and shall be free from pits, deep scratches, and foreign material. If the anvil is damaged from any cause, it shall be repaired or replaced. Common specimen support anvils should have a minimum hardness of 58 HRC.
Flat pieces should be tested on a flat anvil that has a smooth, flat bearing surface whose plane is perpendicular to the axis of the indenter.
Small diameter cylindrical pieces shall be tested with a hard V-grooved anvil with the axis of the V-groove directly under the indenter, or on hard, parallel, twin cylinders properly positioned and clamped in their base.
Special anvils or fixtures, including clamping fixtures, may be required for testing pieces or parts that cannot be supported by standard anvils.

Standardization

To bring in conformance to a known standard through verification or calibration.

Test Piece

For best results, both the test surface and the bottom surface of the test piece should be smooth, even and free from oxide scale, foreign matter, and lubricants. An exception is made for certain materials such as reactive metals that may adhere to the indenter. In such situations, a suitable lubricant such as kerosene may be used. The use of a lubricant shall be defined on the test report.
Preparation shall be carried out in such a way that any alteration of the surface hardness of the test surface (for example, due to heat or cold-working) is minimized.

The error E

The error in the performance of a Brinell hardness machine at each hardness level, under the particular verification conditions, is estimated by the percent error of the average of n indentation measurements made on a standardized test block as part of a performance verification relative to the certified average hardness value of the standardized test block.
Indenters – Indenters for the Brinell hardness test shall be tungsten carbide balls of four allowed diameters (1, 2.5, 5 and 10 mm). Dust, dirt, or other foreign materials shall not be allowed to accumulate on the indenter, as this will affect the test results.

The repeatability R

The repeatability R in the performance of a Brinell hardness machine at each hardness level, under the particular verification conditions, is estimated by the percent range of diameter values of n indentations made on a standardized test block as part of a performance verification, relative to the average of the n measured diameter values.

Verification

Checking or testing to assure conformance with the specification. Brinell testing machines shall be verified periodically using test blocks.