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2 MEASUREMENT
2.1 MEASUREMENT
PRINCIPLE
The Digital Hammer measures the rebound number of a paper and film rolls. The
rebound number is related with the harness, stiffness and strength of the material.
There are several factors that must be taken into account when analyzing the
rebound number of rolls.
2.1.1 Impact
direction
The impact direction of the system has an effect that must be taken into
account at the time to correlate the rebound data taken from different
directions, this factor it is not relevant for the paper industry. It has to
consider this point when testing paper rolls in different directions and the
results want to be compared. The system allows the user to choose the
angle of impact, which could be -90 degrees when testing in floors or
slabs type of structures or against any horizontal surface, 0 degrees when
testing against walls or vertical concrete members and f90 degrees
when testing in an overhead position such as against ceilings. The
reason why this is a needed parameter is because the gravity force affects
the results and this effect must be taken into account, in Fig 1. this effect
is shown in the correlation curves.
2.1.2 Surface
texture
The surface texture has an important effect on the accuracy of the test
results. It is recommended to test rolls with smooth surfaces. When
testing rough textured surfaces, much of the hammer impact energy
causes excessive crashing on the surface and a reduced rebound number
is expected.
2.1.3 Moisture
effect
The presence of surface moisture and the degree of saturation of the
surface may have an effect on the rebound number. It is expected to
obtain lower rebound numbers when testing wet materials.
