Tech Tips: Abrasion – the Grit Hits the Fan
By Jim Wywrot, P.Eng.
There are three main areas that affect the wear on equipment such as fans, pumps, conveyor belting, etc., that come in contact with abrasive materials. They are: the speed at which the particles hit t...
There are three main areas that affect the wear on equipment such as fans, pumps, conveyor belting, etc., that come in contact with abrasive materials. They are: the speed at which the particles hit the surface, the hardness of the particles relative to the hardness of the surface, and the geometry, or angle of attack.
Material-moving equipment such as bucket elevators or road graders that are subject to wear are usually provided with wear plates. However, there is no perfect material for the wear plates that suits every application. 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 this case, wear plates, such as checker plates of mild steel, can be used. The plates are bolted on to protect the wheel and housing steel from abrasive attack.
As the attacks from abrasion increase, you need to consider harder wear protection. But harder materials are generally more brittle. A good everyday example is ceramic tile for flooring. It’s very tough to drill through but it can be cracked easily with a hammer.
Toughness pertaining to metals refers to how susceptible they are to brittle fractures. A material with high toughness would not be brittle. Plain mild steel falls into this category. As abrasion levels increase, you need to trade off toughness characteristics for increased hardness characteristics.
An example of this progression would be to move from using mild steel checker plate to chrome carbide, to tungsten carbide, to ceramic. There are more possibilities in between. Ceramic plates are a high-wearing material with a high hardness surface. They are engineered to withstand the impact of the abrasive particles by varying the thickness of the plate material. Every installation has to be evaluated individually so suitably engineered plates can be provided.
The energy of the particle impact increases with speed, so keeping the fan speed lower usually reduces the rate of wear. In the evaluation of the selection of the fan and the wear protection, the speed of the fan wheel and the cost of the equipment should be considered.
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 others that are unique to Europe. Through travel and telecommunications, you now have easier access to this kind of information.
With any change, though, 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.
Jim Wywrot is one of the creators of the Fan Guys. The illustrations are drawn by Richard Comely, and the column is produced by Mark Bugdale. For more information, visit www.fanguys.com.