9
10
Divide the difference between the mean hardness value of the 5
points measured and determined according to the above mentioned
method and the hardness value of the standardized block by the
hardness value of the standardized block, this is the shown value
error of the hardness tester. The allowable tolerance is ±2%.
Divide the maximum value and the minimum value of the hardness
values of the 5 points by the mean hardness value, this is the
changeable value of the hardness tester. The allowable tolerance is
2.5%.
The shown value precision of the hardness tester has been adjusted
before leaving the factory. In case error produced due to vibration in
the course of transportation, the testing personnel shall make
suitable adjustment on the basis of understanding its structural
principles. Take away the upper cover, if the shown value measured
is greater than the marked value of the hardness block, when it is
required to lower the hardness reading, then you may use a screw-
driver to turn clockwise one degree of the slotted countersunk head
screw 2 which is on the spring leaf, meantime tighten one degree of
the slotted countersunk head screw 1 by turning it counter clockwise
of the optical lever (Fig. 2). Note the rotated degree should be
basically conformed. Test the shown value again, until it is adjusted
within the specified range of error.
If the shown value measured is less than the standardized block,
than the revolving direction of the screw shall be reversed.
Fig
.
2
Switch on the power supply, based upon the test method, open
the switch.
The surface of the sample to be tested shall be level, bright and
clean, it shall not present any outstanding machining traces such
as pollutants, oxidized flakes, cracks and pockets etc.
The supporting surface of the sample and the test platform shall
also keep clean, so as to ensure better closely engaged, the
relationship between the minimum thickness of the sample and
the hardness may refer to table 2, table 3 and table 4.
The preparing work before test:
Table 2: The relationship between the minimum thickness and
hardness HB
Operation
1
