A Complex Process
Steam, the propellant for the locomotive engine, is produced in a container (boiler) through which flue gas tubes have been inserted. Hot gases from burning coal passing through the tubes, the heat is transferred to the water in the boiler, converting it to steam. This steam is then superheated by recirculation across a further set of boiler tubes and the resulting steam is fed into engine cylinders to operate pistons. Slide bars, connecting the engine pistons to the wheel connection rods, convert the reciprocating (linear) thrust of the pistons to the rotary motion of the train's driving wheels.
The complexity of the locomotive requires a wide variety of scientific factorsmaterial, structural, and operationalto be taken into account.
Early locomotives contained wood used for wheel parts and framing and iron (both cast and wrought) for the boiler, chimney, drive connectors, and wheel rims. Flue tubes were made from copper using that metal's superior heat transfer capability. Other materials, such as brass, were tried but failed the durability test. Old Ironsides was the appropriate name of Baldwin's first locomotive. After the invention of the Bessemer process in the mid-1850s, steel replaced the iron and wood.