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Pic. 2:
Schematic tribological system
with variables
Examples in the literature show the importance of
accurate knowledge on the tribological system. In the
area of abrasion wear, the upper shelf-lower shelf
characteristics of material is known. Already small
increases in the hardness of the abrasive material can
massively increase loss of material, Picture 3. The change
in the wear mechanism, in relation to the strain angle α in
erosive wear shows that small changes already have big
effects on wear behaviour of material, Picture 3. Different
materials show their maximum in various strain angles.
While highly hard materials undergo a massive material
loss in wear by impingement (90° impact angle), softer
material like Polyurethan (PUR) often show a minimum.
The reason is the change in the damage mechanism,
since in wear by impingement, ductile materials elastically
absorb the impact energy, so that an elastic blow to the
individual grains occurs. Highly hard material that is less
ductile has a different reaction, so that the kinetic energy
of the abrasive goods is converted in the material and thus
leads to breaking out of material from the surface. In small
strain angles a grove forming strain is predominant. Due to
the almost parallel direction of movement of the abrasive
Issue 04 | 2010
TRANSFER OF TECHNOLOGY
good to the material surface, the application of energy is
significantly lower. While in this case highly hard materials
offer a good wear resistance, ductile materials can hardly
resist this cutting strike.
These two cases from the literature already show the
importance of a wear test that is compatible to tribological
systems, with regard to optimized endurance of machines
and plants.
The wear-testing of materials in combined strains, like
for example in hammer mills and rock crushers, proves
particularly difficult. For these tests the Institute of Welding
and Machining of the Clausthal University of Technology
uses special setups, Picture 4.
The combined strain from abrasion and hitting component
leads to a changed wear pattern, Picture 5. The demolition
of the hard phase portions can clearly be seen. With sole
abrasion a washing out of the softer matrix material can
be seen.
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