by Jim Wywrot P.Eng.
Equipment that comes in contact with abrasive materials such as fans, pumps,
conveyor belting etc. has three main aspects that impact on wear. The speed
at which the particles hit the surface, the hardness of the particle
relative to the hardness of the surface and the geometry, or angle of
Material moving equipment such as bucket elevators or road graders subject
to wear can be provided with wear plates. There is no one perfect material
for the wear plates to be used for all applications. In many cases it may be
the same material as the main equipment, but bolted in place for easy
replacement. The wear plate is then called sacrificial.
The same applies to fans that experience abrasive wear. In these cases wear
plates, such as checker plates of mild steel can be used and are often
bolted on to protect the wheel and housing steel from abrasive attack.
As the attack from abrasion goes up one needs to consider harder wear
protection. Harder materials are generally more brittle. A good everyday
example is a floor ceramic tile. Very tough to drill through, but can be
easily cracked with a hammer.
Toughness pertaining to materials means how susceptible it is to brittle
fractures. A material with high toughness would not be brittle. Plain mild
steel falls into this category. As abrasion levels increase, we need to
trade off toughness characteristics for increased hardness characteristics.
An example of progression would be mild steel checker plate to chrome
carbide, to tungsten carbide, to ceramic. There are more possibilities in
between. In addition the means of fastening is important because a failure
of the fastening mechanism will expose the unprotected metal to attack.
Every installation has to be evaluated individually and suitable engineered
The energy of the particle impact increases with speed so keeping this speed
lower reduces wear. It is not necessarily the rpm of the fan but the speed
of the blade at the tip that counts.
If your equipment is wearing out sooner than you feel it should, trust your
instincts and explore new techniques or newer technologies. Research what is
being done in your industry and what your industry is doing in other
countries. There are techniques unique to North America and those unique to
Europe. Through travel and telecommunications we now have easier access to
With any change there is also risk. Lee Iaccoa was asked how one makes a
decision to ensure success. He made the following statement – “One can never
have enough information to make a completely safe decision. One must
research it well, think hard, but ultimately one must make a ‘leap of faith'”.
Summing up, research well, build a case and remember to always have faith in
your detailed decision.
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