1. What is the correct torque for tightening railway bolts and nuts?
The correct torque for railway bolts and nuts depends on the bolt's size, material, and application-there is no one-size-fits-all value. For example, a 20mm diameter Grade 8.8 carbon steel bolt used on wooden sleepers might require 150-200 N·m of torque, while a larger 24mm alloy steel bolt for concrete sleepers could need 250-300 N·m. Railways follow standards (e.g., UIC or AREMA) that specify torque values for each bolt type. Torque is measured with a torque wrench to ensure it's neither too low (which causes loose connections) nor too high (which can stretch or break the bolt). Proper torque ensures the bolt applies enough clamping force to hold track components together without damaging the fastener.
2. Can railway bolts, nuts, and washers be reused after removal?
Whether railway fasteners can be reused depends on their condition after removal. If bolts are not bent, cracked, or heavily rusted, and their threads are still intact, they can be reused-though they should be cleaned and inspected for wear. Nuts can be reused only if their threads are not stripped and they still apply sufficient clamping force; lock nuts with nylon inserts are often not reused, as the insert loses grip after first use. Washers can be reused if they are flat (not warped) and free of rust or damage. However, in critical sections (e.g., high-speed rails or rail joints), new fasteners are preferred to avoid safety risks. Reused fasteners are typically limited to low-stress areas like branch lines.
3. What happens if railway bolts are over-tightened?
Over-tightening railway bolts causes several problems: first, it can stretch the bolt beyond its elastic limit, leading to permanent deformation or even breakage-if a bolt breaks while a train passes, the rail could shift and cause a derailment. Second, over-tightening crushes washers and damages the surface of rails or sleepers; for example, it might crack concrete sleepers or split wooden ones. Third, it distorts the bolt's threads, making it hard to remove the nut later (even for maintenance). Finally, over-tightened bolts create excessive stress in the track component, which can lead to premature wear. To avoid this, workers use torque wrenches to ensure bolts are tightened to the exact specified value.
4. What types of washers are used with railway bolts, and what are their specific roles?
Three common types of washers are used with railway bolts: flat washers, lock washers, and spring washers. Flat washers are the most basic-they have a smooth, flat surface to distribute nut pressure and protect track components from scratches. Lock washers (e.g., split washers or toothed washers) have a flexible design that creates tension between the nut and washer, preventing the nut from loosening due to vibration. Spring washers are made of a slightly curved, elastic metal; when tightened, they flatten and exert a continuous spring force on the nut, maintaining clamping force even as the bolt expands or contracts with temperature changes. Each type is chosen based on the track's vibration level and load requirements-flat washers for low stress, lock or spring washers for high vibration.
5. How do railway bolts adapt to thermal expansion of rails?
Railway bolts are designed to allow slight rail movement from thermal expansion while keeping components secure. They are not fully rigid-instead, they use a combination of proper torque and washer flexibility to accommodate expansion. For example, when rails heat up and expand, they push against the bolted fishplates; the bolt's clamping force holds the fishplate in place, but the washer (especially spring washers) compresses slightly to absorb the extra pressure. Additionally, bolts are spaced to leave small gaps between rail ends (expansion joints), giving rails room to expand without pulling or bending the bolts. This balance ensures rails stay aligned and bolts don't break from thermal stress.