Brinell Hardness Testers And The Testing Method
One of the earliest invented methods of measuring the hardness of materials, the Brinell test, makes use of a special kind of tabletop hardness tester - the Brinell Hardness Tester. The Brinell Hardness Testers give the Brinell Hardness of a material by means of creating an indentation on the specimen material surface. For this, the Brinell Hardness Testers make use of either hard steel or tungsten carbide balls of specific diameters, which are driven into the test material under a specified load. The Brinell hardness number is arrived at by dividing the weight used (in kilograms) by the total surface area of the indentation (in square millimeters). (As long as the ball size and the test force correlation is the same, Brinell values are test force independent).
Brinell Test Method
During the test procedure, the indenter ball is pressed onto the surface of the test material by the application of controlled force, for no more than 10/15 seconds. This forced entry of the indenter ball creates a round indent in the sample material. The size of the indentation is determined by measuring the two diagonals of the round dent with the help of a portable microscope (to plus or minus 0.05mm). Thereafter, the area of the curved surface is derived by multiplying the square of the diameter by 3.14159 and then dividing it by 2.
The Brinell hardness can be calculated by dividing the force applied by the area of the grooved surface. A calibrated chart that allows you to match the corresponding hardness number with the diameter of the indentation is a simpler way to arrive at the Brinell hardness of the sampling.
The Brinell hardness number is usually represented in the following manner - '90 HB 10/500/15', meaning that a Brinell Hardness of 90 was obtained when a 10mm diameter hardened steel ball was pressed against the material using a 500 kilogram load for a period of 15 seconds.
Brinell hardness testers make use of tungsten carbide balls for extremely hard metals; otherwise, the steel ball is the common indenter used. The Brinell Hardness Testers apply loads of around 500 kilograms for soft metals and thin stock. Weights of about 1500 kilograms are used for aluminum castings and 3000 kilograms of weights are used for materials such as iron and steel.
Applications of the Brinell Hardness Test
Any metal can be tested using the Brinell test. All you need to do is change the test force and ball size. Brinell test is often used to determine the hardness of forgings and castings (these have a grain structure far too course for the Rockwell or Vickers Testers). The Brinell number, ranging between HB 50 and HB 750 for metals, increases with the growing hardness of the sample material.
The indenter balls of the Brinell Hardness Testers make deep and wide indentations. This allows for the calculation of hardness over a larger section of the material, giving near-perfect measures of material hardness.
Author: Robert Allen