Metal wheels offer many benefits for a range of applications—from large-scale public transportation to private industrial and commercial operations. It makes sense that not all wheels are created the same. Here, we'll look at the difference between single versus double flanged wheels, and some of the more common applications for each.
The benefit of flanged rail wheels
Rail transportation is ideal when carrying loads between fixed locations on a regular basis. Loads can include anything from people to raw materials and products. Metal tracks offer low-friction movement, high-capacity loading and exceptional durability. They are also self-guiding, meaning they don't need to be steered by a driver.
Rail installations rely on a different type of precision and design than the wheels on your car or shopping cart. Rubber or plastic tires are made from softer materials to create traction with flat surfaces. Metal wheels used with rail, however, use precise geometry and engineering to keep them on track.
One might think the flange, that additional rim or lip that protrudes beyond the tread of the wheel, is what keeps a vehicle on track. But it isn't the case for most conventional rail applications.
What keeps a vehicle with flanged wheels on track? Wheels are manufactured with a tapered tread—making them slightly cone-shaped—and installed on a fixed axle. Because they are fixed, each wheel rotates at the same rate. Because they are cone-shaped, however, one wheel can spin with a faster tread speed than the other. When going around a bend, for example, the inside rail is shorter than the outside. To keep both wheels spinning at the same rate (and to keep the train on its tracks), the wheelset shifts to one side—so the wider portion of the wheel tread travels the greater outside distance and the smaller portion of the opposite wheel travels the shorter inside distance.
Single flanged wheels
If a flange isn't what keeps a wheel on track, why have it? Flanges are designed more as a safety feature. For a train or trolley travelling a curve too fast, or where rails may be bent or untrue, a flange helps ensure vehicles stay on track. In fact, the high-pitched squealing you hear when a train goes by is often caused by the flange rubbing against the rail. Wheels are meant to roll with as little friction as possible, and contact with wheel flanges introduces unnecessary metal-on-metal rubbing.
Because wheels are fixed to their axle in most rail applications, a single flange on each wheel is enough to prevent movement in either direction (as long as the flange is placed on opposing sides of opposite wheels, usually toward the center of a track).
Single flange wheels are common for most trains and trollies, as well as other commercial and industrial vehicles with fixed axles running on trued rails.
Doubled flange wheels
When do you need a second flange? Typically when operating conditions aren't as controlled, or where safety is of special concern.
Many material transfer vehicles don't have the benefit of operating in clean, controlled conditions. Lumber drying kilns are a prime example. Kiln operators typically transport lumber in and out of kilns using metal rail configurations. But due to the extreme weight requirements and high-impact loading, rail conditions are often less than ideal. It's not uncommon to see rails warped at varying angles from each other, making conventional track applications impossible.
Even when tracks are in poor condition, rail installations still offer high-capacity, low-friction transportation. For warped rails, wheels can be installed with bearings so that they rotate at their own speeds. They can also be designed to drift across a portion of an axle to accommodate bent rails. Because wheels move independent of each other, a flange on either side of the tread is needed to ensure they stay on track.
Double flanged wheels are also common for overhead cranes, where truck assemblies may span significant distances and safety is a key concern. Rather than rely on a fixed axle or crossbeam to align single flanged wheelsets, double flanges help ensure that each wheel tracks independently for more secure movement.
Most double flanged wheels feature a flat tread, as the tapered geometries typical of single flanged wheels don't offer any benefit—and, flanges are in fact what keep wheels on track.
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Material selection for metal wheels
Several factors determine what type of wheel is most suitable for a particular application. We've looked at how single and double flanged wheels benefit different applications. It's also important to consider material design characteristics. Double flanged wheels, for example, likely see frequent contact between the flange and the rail, meaning wear is an issue for the long term.
An important distinction to make is the difference between cast iron and steel wheels. Cast iron is typically cheaper to manufacture, but it is a much harder and more brittle material. Not only will it wear your track quicker, but it is more susceptible to fracture. Steel is a more robust metal, featuring the strength and ductility more suitable for industrial applications—especially where excessive contact with the flange is expected.
Other factors to consider include: load capacities, operating speeds and environmental conditions. The material, size and shape of a wheel will affect load capacity. It can be more economical to cast wheels because the process uses only as much material as is required to for a specific application. Environmental conditions, such as heat and exposure to chemicals, can also affect design. A range of steel alloys are available to suit different conditions to avoid unwanted corrosion and potential failure.
Know your wheels
Knowing what you need in a wheel is key to avoiding broken parts and work stoppages—essentially saving you money in the long run. Most importantly, the right wheels will help ensure the ongoing safety of your equipment and staff.