Steve Broekema, Product Manager, Wheels
Two key factors influence the “toughness” of overhead crane wheels: The hardness of the raw material used to make the wheels—such as alloys, low-carbon steel or medium-carbon steel and the heat treating techniques used to enhance the metal’s hardness.
For most crane wheels, medium-carbon steel is the most commonly employed material, due to its wide availability and lower cost.
As a general rule, the greater the carbon content of steel, the greater the hardness potential. Thanks to advances in heat treating technology, the hardness of crane wheels made with medium-carbon steel has been increasing. This toughness counts most where the crane wheel meets the rail: the crane wheel tread. A hardened crane wheel tread reduces wear and extends the life of crane wheels.
On the other hand, crane wheel flanges should not be hardened. Flanges require ductility so that they can bend, and not break, when subjected to lateral forces, such as a misaligned rail. You don’t want broken wheel flange pieces endangering your employees.
While many manufacturers can heat treat and harden crane wheels and other steel crane parts, results vary from one vendor to another. When purchasing crane wheels, you want to make certain that you acquire them from a company with the expertise to provide consistent deep hardening of the crane wheel tread.
Determining the surface hardness of crane wheel tread is a critical aspect of wheel hardness and relatively simple to measure. More difficult to measure, however, is the depth of hardness of the wheel. Because this measurement can be difficult to determine, it’s often neglected, leading to potential problems. When hardening doesn’t go deep into the wheel tread, the crane wheel is subject to spalling—that is, metal fragments breaking off the surface and shortening the life of the wheel.
But the lifespan of a wheel depends on more than hardness alone. The wheels, the only parts of the crane that make direct contact with the runway, can be the weakest link of the crane. Commonly, they are the first crane parts to show the effects of crane problems, such as misaligned rails.
Periodic inspection of cranes, including the wheels, can detect premature wheel wear and provide clues to correct issues before they can cause substantial damage.
It is recommended to measure and document the thickness of wheel flanges so you can keep track of the rate of wear between inspections. If wheels take 10 years to wear a quarter of an inch, you may have little cause for concern. But that type of wear in just two weeks can indicate a serious problem.