7
4.3 Supporting a Test Sample
When using optional impact devices DC or D+15 (Impact energy=9ft/lbs), please refer
to the following support requirements:
•
For test samples weighing over 11 lbs. (5 kg), no support is required.
•
Samples having a cantilever or thin shell shape and weighing between 4.4 to 11
lbs. (2 to 5 kg) must be firmly coupled to bearing supports weighing over 11 lbs.
(5 kg) in order to prevent bending, deformation or displacement due to the
impact force.
•
Test samples weighing less than 4.4 lbs. (2 kg) should be firmly coupled to a
support weighing over 11 lbs. (5 kg).
•
The coupling surface between the sample and the support should be smooth.
•
A moderate, non-excessive amount of coupling paste should be applied between
the coupling surfaces when testing thin cross section pieces with larger massed
support plates.
•
The direction of impact should be perpendicular to the coupled surface.
•
Minimum weight of a test sample should be 0.2 lbs. (100 g).
•
Minimum thickness of a test sample should be 0.2 in (5 mm).
•
Minimum depth of hardened layer should be 0.03 in (0.8 mm).
•
The testing surface of the sample should be perpendicular to the impact
direction.
Note:
The above restrictions referring to the rigidity of test samples can be decreased
when Type
C
(2ft/lbs) impact device is used as should be increased when Type G (72
ft/lbs.) is used.
4.4 Large Test Samples
When the test sample is a large plate, long bar or bent work piece, the impact force
can cause a deformation or instability when the impact device is released. This may
bring about an error in measurement, even if the weight or thickness of the test sample
seems applicable. In this case, a reinforcement should be attached to the back of the
sample surface opposite to the impact force.
4.5 Test Sample Properties
Requirements for a sample’s weight thickness and roughness differ for each impact
device, as shown in Table 8.
Table 8: Sample Requirements for Hardness Testers
Sample
Sample Weight(kg)
Min. Thickness
(mm)
Max. Roughness
(or Min. Fineness)
Impact
Device
Needs
Support
Needs to
be
stabilized
No
strength-
eing
needed
Sample
Hardened
layer
ISO Ra Rz
D, DC
D+15
0.05-2 2.5 >5
3 0.8 N
7
2
µ
10
µ
∇
6
G
0.5-5 5-15 >15 10
N
9
7
µ
30
µ
∇
4
C
0.02-
0.05
0.5-
1.5
>1.5 1 0.2 N
5
0.4
µ
2.5
µ
∇
8
