Polyurethane wheels instead of a rail rebuild

Everyone was looking at the rails. That is where the wear was visible, that is where a rebuild project estimated at between $750,000 and $1.2 million was taking shape — a considerable sum in 1995 dollars. The solution that fixed the problem — and that served for eight years — came down to a component nobody was looking at: the wheel.

The context

In 1995, Soremag was called in to work with Stone Consolidated — a major Quebec paper maker at the time — on a serious wear problem affecting an overhead rail conveyor system.

At first glance, the problem looked simple: metal wheels ran on metal rails and, over the years, the rails had deteriorated. In reality, the situation was far more twisted than that.

The problem: a design that drove its own deterioration

The system relied on metal-to-metal contact — and the material combination chosen at the outset worked against it: the hardness of the rail metal was slightly lower than that of the wheels. Year after year, the repeated passing of the wheels therefore acted like a wear tool on the rail itself.

Normally, when a system has an easily replaceable component and a complex, expensive structure, you want the replaceable component to be the sacrificial element. Here it was the opposite: the rails — the hardest part to repair — were absorbing the wear.

And that wear was not uniform. Some sections stayed acceptable; others were severely deteriorated, especially in the curves and in the most heavily loaded areas. In places, the wear had created extremely irregular profiles and edges that had turned sharp. The problem went well beyond simply replacing the wheels.

First hypothesis: softer metal wheels

The logic was sound: use a steel softer than the rail so the wheel would deliberately become the sacrificial part. On a new installation, that could have worked.

But it was too late to simply reverse the hardness relationship. The trials with softer wheels performed very poorly: faced with the irregular profiles and the edges created by years of wear, those wheels underwent significant deformation and stresses that were too high. We could slow down the original wear mechanism — not erase the years of accumulated deterioration.

Second hypothesis: rebuild the rails in place

The other approach was massive: design a machine running on the rails themselves, able to prepare the damaged surfaces, build them back up by welding and grind them right in place — restoring the original profile, then moving to softer steel wheels, sacrificial again on refurbished rails.

Except that this machine did not exist. It had to be studied, engineered, drawn. The study, entrusted to a specialized firm, cost 50 000 $ — and that was only the design phase. The first budget estimates for the complete project were between $750,000 and $1.2 million — a lot of money at that time — for a repair whose long-term performance still could not be guaranteed.

On top of that cost came significant downtime — costly for a pulp and paper mill —, health and safety constraints that grew as the studies went on (weld build-up and grinding work on an overhead system), and a reality that took no break: the mill had to keep producing. As long as the equipment rolled on its metal wheels, the rails kept deteriorating.

The turning point: change the wheel instead of rebuilding the rail

That is the context in which Soremag was brought in more directly. The initial request: assess whether it would be possible to cover the surface of the rails with a polyurethane or another polymer to fill the worn areas.

We started evaluating that avenue. But during the site visits, watching how the system behaved, another idea took hold: rather than modifying an entire rail network, why not act on the smallest, most accessible and most easily replaced component? The wheel.

The challenge was real. The rail was no longer new: large variations in profile, heavily worn areas, aggressive edges, different conditions from one sector to another, high stresses in some curves. Applying a standard polyurethane to a wheel was not enough. The material had to be strong enough to take the loads and the abrasion, but tolerant enough to absorb the irregularities of the rail without the destructive deformation seen with soft metal wheels.

Some twenty models tested on the actual equipment

Rather than selecting a formulation on the basis of theoretical data, Soremag developed about 20 different models — two wheels of each, installed and evaluated directly on the equipment. Each formulation had its own color, which let the crews recognize the models during the trials and follow how they behaved in service.

The actual equipment became the validation environment: type and rate of wear, cuts, deformation, reaction in the curves, behavior under load, surface condition after use, ability to absorb the irregularities of the rail. The problem could not be solved by comparing data sheets — we had to see how each formulation reacted in real conditions.

Four models stood out. Their results were used to develop and refine new formulations, with additives chosen according to the wear data observed. Two final formulations were selected — in different colors, so they could still be tracked easily. It was no longer a matter of selecting a polyurethane hardness: the material was adjusted to the real problem, observed in the field.

The discovery that changed everything

The Cerathane wheels were still seen only as a temporary solution, while the rebuild studies went on. Then two results appeared.

The first: despite the very irregular condition of the rails, the wheels worked — without the deformation that had doomed the soft metal wheels. The material absorbed the variations in profile.

The second, more fundamental: the progression of the rail wear stopped. By removing the metal-to-metal contact, Soremag had eliminated the mechanism that had been deteriorating the rails for years. The solution did not only protect the new wheels — it protected the existing rails.

The “temporary solution” was starting to call into question the very need for the rebuild project.

The decision

The studies on the major project continued for about a year — the engineers and managers wanted to be sure the temporary solution was a credible alternative. In the meantime, the wheels simply kept working, and the data accumulated under real conditions became more and more convincing.

It was becoming hard to justify a project that expensive, requiring a major shutdown and carrying technical and safety risks, when a much simpler solution was already running on the equipment. Management went ahead with the Soremag wheels and postponed the rebuild. In the end, the project never needed to be carried out.

Beyond the amount avoided came the indirect consequences that were spared: production shutdowns, specialized work on an overhead system, mobilization of complex equipment, health and safety measures, additional engineering costs — and the uncertainty about the long-term performance of a rebuild. One approach wanted to rebuild a complete infrastructure; the other came down to understanding the wear mechanism and changing an easily replaceable component.

What followed: other mills, then the mines

Stone Consolidated's problem was not unique: metal wheels on rails existed elsewhere in the pulp and paper industry. Soremag went on to help several other mills facing comparable problems — each application analyzed according to the load, the wheel geometry, the condition of the rails, the speed, the type of equipment and the wear mechanisms observed.

The expertise then crossed industries: a first adaptation to the mining sector in 2004, then a second one in 2008. The principle stayed the same — understand the wear mechanism between the wheel, the rail and the environment, then develop a wheel and a formulation able to become a better interface between the components. But the formulation does not copy from one application to the next: the loads, the abrasion, the contamination and the geometry of a mining application have nothing to do with a paper mill. The solution adapts to the real conditions of each piece of equipment.

What this case shows

The part that wears is not necessarily the real cause of the problem. At Stone Consolidated, the visible problem was the wear of the rails; the logical reaction was to repair the rails. The most effective solution was to change the wheel — a relatively simple change that transformed the interaction between the components.

That is the philosophy Soremag still applies today. When a part wears out prematurely, we don't start by making a copy of it: we look to understand why it wears. The problem can come from the material, the hardness, the geometry, the load, the abrasion, a chemical attack, the temperature, the speed — or from contact between two incompatible materials, as here. And sometimes the best improvement is not making the part harder, but finding the right balance between its properties and the components it works with. That is the approach detailed in our roller and wheel diagnostics and our material selection guide.

The other lesson is the value of field trials : about 20 models made before the final formulations, compared under real conditions rather than on paper. Observe → understand → formulate → test → measure → improve. This methodology remains at the heart of our wheel coverings and of our reverse engineering — reproduce, but also improve. Three decades later, the knowledge gained on this project still feeds the way we analyze demanding applications, from pulp and paper to mines.