Technology

Steel Wheel Technology

The goal of every Trackmobile unit is to ensure safety, reliability, ease of use, and low operational cost. None of this would be possible without the use of wheels that provide the most consistent application of tractive effort. Wheels play a huge role in how well the machine travels on railways and how much weight it can pull. Trackmobiles are equipped with steel wheels to provide the greatest and most consistent tractive effort.

Steel wheels have been the industry standard for railway transportation since the first steam locomotive was invented in 1814. Trackmobile subscribes to that standard still today for many of the same reasons and more. Durability and consistency in adhesion are the two main factors we consider when designing our machines.

Durability: How long do the wheels last?

Steel wheels have proven to be more durable and long lasting than either rubber or polyurethane. The friction created from operating on rails produces much less wear on steel wheels than with other materials. Steel wheels are also puncture-proof, while rubber tires must be either solid rubber or foam-filled to avoid puncture. These factors ensure that steel wheels need to be replaced far less frequently than rubber or polyurethane wheels, which saves you time and money associated with maintenance costs.

Adhesion: How well does the wheel grab the rail?

Any number of conditions can affect how well a wheel adheres to the rails: snow, ice, rain, or many different types of debris or environmental contaminants. The coefficient of friction for steel on steel remains more consistent throughout these conditions than the coefficient for rubber or polyurethane on steel. In other words, steel wheels are capable of adhering to the rail better, despite these conditions. There is also far less rolling resistance with steel wheels, as opposed to rubber or polyurethane. Similarly, steel wheels are unaffected by a range of railway obstructions, such as raised frogs, switch points, gaps between rails, and by material packed into grade crossings. The ability to perform consistently over both natural and constructed conditions is a key factor in our decision to use steel wheels.

Steel wheels are designed to maintain point contact with the rail. The width of the wheel is comparable to the width of the rail head which helps distribute the weight of the load evenly across each wheel. Rubber tires are much wider, so they deform over the width of the rail head. When a pneumatic rubber tire is placed on a railhead, one fourth of the vehicle weight plus some weight transferred from trailing loads is concentrated on only 2 inches of the tread width. Because of this, 75% of the tread width of a typical industrial tire is unsupported. The deformation imposes loads on tire sidewalls, cords and beads that are not experienced in normal tire applications.

Additionally, while rubber has good characteristics under compressive loads, it does not have good shear resistance. In a rail application, the tires are subjected to compression of the vehicle weight, and simultaneously to shear forces when torque is applied to rotate the tire. Under shear plus compression forces plus friction between the tire and the steel rail, the tread rubber heats rapidly to the point that the rubber breaks down.

The advantages in durability and adhesion are among the reasons that steel wheels have been the standard in serious railroading for so long, and why Trackmobile choses steel wheels as our main railwheels over rubber type tires.