Brinell Hardness Testing Machine
WilsonŽ Model "J"
J.A. Brinell proposed the first widely accepted and standardized
hardness test in 1900. A steel ball is pressed into the surface of the
specimen by a known load to plastically deform the material. The
fundamental concept is that the diameter of the indentation in a harder
material has a smaller diameter. The Brinell hardness number (BHN or
HB) is inversely proportional to the surface area of the indentation.
The WilsonŽ Model "J" Brinell Hardness tester is a hand
operated mechanical device. A dash pot system restricts the rate of
application of the load to avoid dynamic effects. A 10mm diameter
hardened steel ball is pressed into the specimen. The load is
adjustable. Applied loads from 500kg to 3,000kg are generated with different installed masses.
Smaller loads are used for soft materials and larger loads for harder materials.
For very hard materials a 10mm diameter tungsten-carbide ball is installed.
The specimen is placed on the anvil and raised to contact the
ball by rotating the handwheel at the bottom of the anvil column. The
handle on the right side is pushed backward to contact the rear stop.
The dashpot system restricts the rate of movement. The load is held
for 15 seconds to ensure that the plastic zone forms completely. The
handle is pulled back and the anvil is lowered.
The Brinell hardness number (HB) is the load divided by the
surface area of the indentation. The diameter of the impression is
measured with a microscope with a superimposed scale. The Brinell
Hardness Number HB is computed from the equation:
where
P is the applied load of 3,000, 1,500, or 500kg.
D is the diameter of the ball in mm. (10mm)
d is the mean diameter of the indentation in mm.
The units of HB are kg/mm^2. However, the results are usually reported with no units.
