Rail milling is a spark- and dust-free rotational cutting process that is popular in Europe. In this article, we look at the key item that makes it work.
Each rail milling cutter head consists of 140 to 220 carbide inserts, depending on the diameter (400mm or 600mm) of the cutting head. Depending on the type of machine, rail milling can remove as little as 0.1mm (0.004 in.) or as much as 5mm (0.2 in.) per pass at speeds up to 1.3 mph.Heat from the milling process is transferred from the rail to the milling tool and the metal chips, which are collected on board the milling machine for recycling afterwards. The low heat generated by the milling process prevents bluing or the generation of martensite, an unwanted by product of heat-related material transformation at the surface of the rail.
The carbide inserts can be turned up to 7 times before they’re recycled. Depending on rail conditions and metal-removal depth, the carbide inserts can stand up to 2 km of cutting rail before they must be turned or exchanged. If cutting inserts are worn or damaged, cutting heads are changed on track to best utilize the available track time.
The shape of the high-precision cutting head determines the resulting shape of the rail profile. Any pre-defined rail profile can be produced by the milling process. Multiple profiles can also be produced by changing cutting heads, which can be done on the fly or within a few minutes, depending on the number of milling units on the milling train.
The milling trains incorporate a polishing unit that includes a completely enclosed circumferential grinding wheel with a small off-set angle in order to produce a finished surface roughness of Ra < 5µm and a smooth longitudinal profile that meets the most stringent noise standards.
Check out this article for more on rail milling and its recent arrival in North America.