Aim :- To determine the indentation hardness of mild steel, cast iron , brass, aluminum etc using Brinell Hardness Testing Machine.
Apparatus Required:- Brinell Testing Machine, hard mild steel etc.
Theory:-
Brinell hardness test is
most commonly used to test materials that have a structure that is too rough or
too coarse to be tested using other test methods, e.g., castings and forgings.
In brinell testing machine the load is applied by a lever mounted on knife
edges and carrying a hanger for suspending the required load. The supporting
table for spacing the specimen can be raised or lowered by a steel screw by
operating a large hand wheel. When testing, the load is applied and removed by
hydraulic power controlled by a hand lever. The indenter used is a hardened
steel ball which will have a diameter of 10mm, 5mm or 2.5mm. The reading
microscopic has a 25-fold magnification. The gap between successive graduations
of the scale is 0.5mm and a micrometer is arranged sideways, the eye piece of the
reading microscope may be turned up by 90 degree so that the impressions of the
ball can be measured in two perpendicular directions.A well structured Brinell
hardness number reveals the test conditions, i.e., "70 HB 10/500/30" which
means that a Brinell Hardness of 70 was obtained using a 10mm diameter hardened
steel ball with a 500 kilogram load applied for a period of 30 seconds. Highly
hardened steel cannot be tested by a hardened steel ball because the ball will
get flattened and become permanently deformed. The appreciable error in BHN
occurs at indentation diameter less than 2.9mm and for softer materials inaccuracy
is at diameter greater than 6mm. On tests of extremely hard metals a tungsten
carbide ball is substituted for the steel ball (upto 444-627 HB) and a special
hardened and burnished steel ball called the “Hulked” ball may be used up to
500 HB.
Compared to the other
hardness test methods, the indenter used in brinell makes the deepest and
widest indentation, so that test averages the hardness over a wider amount of
materials which will accounts for multiple grain structures and any
irregularities in the uniformity of the material.
The Brinell hardness number
is defined as the ratio of test load to the surface area of indentation.
Where,
Constant = 0.102 = 1/(g ) = 1/9.81
g = acceleration due to gravity
F = Force in Newton
Procedure:-
1. Select the load P based
on the type of material selected.
2. The specimen is placed on the supporting table, then the hand wheel below
the table is
turned in clockwise direction until the gap between the surface of the specimen
and the
indentor is 5 mm.
3. The motor is switched on. The hand lever is pulled into load position. The
load is applied
for a period of 10 to 15 seconds.
4. The hand lever is pulled back into unload position. The diameter of the
impression is
measured through a microscope attached to the apparatus.
5. Repeat the experiment at other positions of the test piece.
6. Calculate the value of HB.
Observation:-
|
Trial |
Material |
Diameter of |
Load P (kg) |
Average |
HBW |
Average HBW |
|
1 |
||||||
|
2 |
Results:-
