7
8
The microscope shall be perpendicularly fixed on the clamping
chuck, and install the exterior lighting lampshade which is used
for testing the Brinell hardness.
Use a plug to switch on the power supply, the lamp spigot is
situated on the edge of the bakelite cover.
Based upon the test method, select and mount the objective,
generally, for the Brinell hardness test, use 2.5x objective, for
the Vickers hardness test, use 5x objective.
Press several indentations step by step on the standardized test
blocks, remove the upper sliding plate under the microscope to
look for the indentation. The sliding plate which makes use of
the axis hole of the lifting and lowering screw rod as its centre
makes circumferential rotation and carefully makes the upper
and lower adjustment, align to the focal distance until the
indentation appears in the centre of the visual field, then tighten
the nut, after completion of the preparation, it is ready for test.
Inspection the precision
After making adjustment for the hardness tester according to the above
mentioned methods, then make the shown value precision inspection
for the hardness block.
Rockwell hardness test:
Measure and determine six points on the different positions of the
working surface of the standardized Rockwell hardness block, the
central distance of two adjacent indentations and the distance from
the center of the indentation to the edge of the hardness block shall
not be less than 3 mm. give up the first point, then take the mean
value of the rest five points, the difference between the mean value
and the standardized hardness block is the shown value error of the
hardness tester. The error shall not exceed ±1 HR.
Within the five points, the difference between the maximum value
and the minimum value shall not exceed that specified in the
following:
Target rod A is 1.0 HR
1
Target rod B is 1.2 HR
Target rod C: HRC 35 - 67 is 1.0 HR
HRC 20 - 35 is 1.2 HR
2
Brinell hardness test:
Measure and determine five points which are evenly distributed on
the standardized Brinell hardness block, the central distance
between two adjacent indentations shall not be less than 4 times the
diameter of the indentation. The distance from the center of the
indentation to the edge of the hardness block shall not be less than
2.5 times the diameter of the indentation. The measurement for the
diameter of each indentation is carried out on two directions which
are mutually perpendicular, and take the mean value. The ratio
between the difference of the two mutually perpendicular diameter
and the shorter diameter shall not be greater than 1%.
Divide the difference between the mean hardness value of the five
points measured according to the above mentioned method and the
standardized hardness value by the hardness value of the
standardized block, this is the shown value error of the hardness
tester. When the test force is greater than 1839N, the tolerance
allowed is ±3%; when the test force is less than 1839N, the
tolerance allowed is ±4%.
Divide the difference between the maximum value and the minimum
value of the hardness values of the five points by the mean
hardness value of the 5 points, for the hardness block of 30D , 10D ,
it shall not exceed 3.5%; for the hardness block of 2.5D , it shall not
exceed 5.0%.
3
Vickers hardness test:
Measure and determine 5 points which are evenly distributed on the
standardized Vickers hardness block, the distance between the
center of the two adjacent indentations and the distance from the
centre of the indentation to the edge of the hardness block shall not
be less than 2.5 times the diagonal length of the indentation.
Measure the two diagonals for every indentation and take its mean
value.
The ratio between the difference of two diagonals to the shorter
diagonal shall not be greater than 2%.
