FAQ
Meule à rail
Rail grinding wheels are used to reshape worn rail heads, remove surface defects like corrugation and rolling contact fatigue (RCF), and restore the rail’s original profile. This maintenance extends the lifespan of the track by preventing cracks from developing into serious fractures and reduces noise and vibration for smoother train operation.
Selection depends on nine critical factors, including the hardness of the rail steel, the amount of material to be removed, and the type of grinding machine being used. Key technical specifications to consider are the abrasive type (e.g., aluminum oxide or ceramic), grit size (coarse for rapid removal vs. fine for finishing), and the bond type (often resinoid for high-speed cutting).
Preventive grinding: Performed regularly to remove microscopic defects and maintain an “optimal” profile before visible damage occurs.
Corrective grinding: A reactive process used to repair severe damage like deep fatigue cracks or heavy corrugation, which often requires deeper cuts and more machine passes.
The frequency is typically based on tonnage (traffic levels) or a set time interval. On heavily used mainlines, grinding may occur every 1–3 years, while lighter routes might only need treatment every 5+ years. Some advanced strategies use track radius to determine intervals, such as every 9 million gross tons (MGT) for sharp 300m curves.
Before mounting, operators should perform a “ring test”. By gently striking the wheel with a non-metallic object (like a wooden handle), a sound wheel will produce a clear, ringing tone. A dull, “dead” sound indicates internal cracks or damage, meaning the wheel must be discarded.
Grinding often takes place at night to avoid interfering with daytime train schedules, minimizing service disruptions for passengers and freight. Additionally, modern grinding trains use integrated water spray systems to manage the intense sparks and metal dust generated, which are more easily monitored and contained during nighttime maintenance windows.
Entretien ferroviaire
Regular maintenance is critical for safety, efficiency, and longevity. It prevents structural failures—such as broken rails or track buckling—that can lead to derailments. Furthermore, well-maintained tracks reduce friction, which lowers fuel consumption for locomotives and prevents premature wear on train wheels.
The industry generally categorizes work into three areas:
- Track Inspections: Using geometry cars and ultrasonic sensors to find hidden cracks.
- Surface Maintenance: Tasks like rail grinding and ballast tamping (realigning the stones under the track).
- Component Replacement: Swapping out worn wooden or concrete sleepers (ties), rusted spikes, or damaged sections of steel rail.
Ballast is the layer of crushed stone that supports the track. Over time, the weight of trains crushes the stone and shifts the rails out of alignment. Tamping involves a specialized machine that lifts the track and packs the stone underneath to ensure the rails are perfectly level and properly spaced.
Maintenance crews use Non-Destructive Testing (NDT), primarily ultrasonic and induction technology. Specialized “Geometry Cars” or handheld “Walking Sticks” send sound waves into the steel; if the waves bounce back prematurely, it indicates an internal flaw or “detail fracture” that needs immediate repair.
The lifespan of a rail depends heavily on the tonnage it carries. On a high-traffic freight line, rails might need replacement every 10 to 15 years. However, on lighter transit lines or with meticulous maintenance (like regular grinding), the steel can last 30 to 60 years.
Weather is a major factor. In extreme heat, steel expands, leading to “sun kinks” (buckling), while extreme cold causes the metal to contract and potentially snap. Maintenance teams must adjust “neutral rail temperatures” and perform seasonal inspections to mitigate these thermal stresses.
Rectifieuse pour rails
These machines use a series of high-speed abrasive grinding stones (units) mounted on motorized carousels. As the train moves slowly along the track, these stones are angled precisely to grind away a few millimeters of steel. Modern machines use computerized systems to adjust the angle of the stones in real-time to match the required rail profile.
There are three main categories based on the scale of the job:
- Production Grinders: Massive trains (sometimes over 100 stones) used for long stretches of mainline track.
- Switch/Turnout Grinders: Smaller, more nimble machines designed to navigate complex track geometry like switches and crossings.
- Handheld/Portable Grinders: Small, operator-guided machines used for localized repairs or welding finishing.
The number of “stones” or “heads” varies by the machine’s size. Small maintenance units may have only 10 to 20 stones, while heavy-duty production grinders (like those used by Loram or Harsco) can have 88 to 120 stones. More stones allow the train to achieve the desired profile in a single pass at higher speeds.
Unlike standard trains, rail grinding machines operate at a very slow, controlled pace. Most production grinders work at speeds between 3 to 15 mph (5 to 24 km/h). If the machine moves too fast, it won’t remove enough metal; if it moves too slowly, it risks overheating and damaging the steel rail.
Modern machines are equipped with optical laser measurement systems. Before the stones touch the rail, sensors “scan” the current shape. The onboard computer compares this to the “ideal profile” and automatically tilts the grinding motors to the exact angles needed to fix the deviations.
To prevent environmental hazards and fires, the machines use dust collection systems (large vacuums) to suck up metal filings. They also feature sophisticated fire suppression systems, including high-pressure water cannons and “shadow” vehicles that follow the grinder to extinguish any stray sparks in the vegetation.
Rail Welding
Traditional jointed tracks use fishplates (metal bars) and bolts to connect rail sections, leaving small gaps that cause the “clickety-clack” sound and increase wear. Continuous Welded Rail (CWR) fuses these sections into a single, seamless line, which significantly reduces maintenance costs, minimizes vibration, and allows for much higher train speeds.
Thermite welding is a chemical process that uses a mixture of aluminum powder and iron oxide. When ignited in a crucible, it triggers an exothermic reaction reaching temperatures over 2,500°C (4,500°F), producing molten steel. This liquid steel is poured into a mold around the rail ends, melting them slightly and fusing them into a solid, permanent joint as they cool.
Flash-butt welding uses heavy electrical currents to create an arc between two rail ends, heating them until they are plastic. The rails are then pressed together under extreme pressure to forge a bond. This method is primarily used in fixed production plants or specialized mobile “welding trains” because it produces the highest quality, most consistent welds for large-scale projects.
Thermite welding is the most common choice for field repairs and remote locations because the equipment is portable and does not require an external power source. While flash-butt welding is technically stronger, the massive machinery required makes it difficult to deploy for minor spot repairs or emergency fixes in hard-to-reach areas.
It is generally not recommended. Moisture in the mold or on the rail ends can cause steam explosions during the high-temperature thermite reaction or lead to “porosity” (tiny gas bubbles) in the finished weld, which weakens the joint. Most rail standards require shelters or specific dry conditions to ensure the weld’s integrity.
Weld failures often result from improper preparation, such as failing to remove rust or oil, or incorrect preheating temperatures. Other common causes include internal defects like “slag inclusions” and extreme temperature fluctuations that cause the steel to expand or contract, putting immense stress on the joint. To prevent this, railroads use ultrasonic testing (UT) to scan for hidden cracks inside the weld.
