What distinguishes thermite welding from flash-butt welding?

Thermite welding and flash-butt welding are distinguished by their heat source, equipment requirements, and application suitability. Thermite welding uses a chemical reaction to generate intense heat to melt and fuse the rail ends together, while flash-butt welding uses electrical resistance to generate heat and pressure to forge the rail ends together. Thermite welding is a portable process that uses a mixture of iron oxide and aluminum, which reacts to produce molten steel and aluminum oxide. The molten steel flows into a mold surrounding the rail ends, fusing them together. Thermite welding requires relatively simple equipment, making it suitable for field repairs and remote locations. Flash-butt welding is a stationary process that uses a welding machine to clamp the rail ends together and pass a high electrical current through the joint. The resistance to the current generates intense heat, melting the rail ends. The machine then forces the rail ends together, forging them into a solid weld. Flash-butt welding requires specialized equipment and a power source, making it more suitable for shop welding and new rail installations. Thermite welding is often used for repairs because of its portability, while flash-butt welding is often used for new rail installation because it creates a higher quality weld. Flash-butt welding generally results in a stronger, more consistent weld with better metallurgical properties than thermite welding, but it is less practical for field repairs.