High Speed Grinding (HSG) is a rail care concept developed by the company Stahlberg Roensch from Seevetal, Germany. It is based on the principle of rotational grinding and serves to grind rails at up to 100 km/h (62 mph).
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Since roughly the beginning of the 1990s, rail network operators have experienced increasing problems with rail surface defects. Head checks, squats, corrugation and slip waves all contribute to higher maintenance costs, intensified noise pollution, traffic obstructions, and ultimately a shortened rail lifespan. These increasingly common flaws are exacerbated by the growing density and speed of both freight and passenger traffic. The direct consequence of these problems is a growing need for rail maintenance.
The principle challenge for modern rail maintenance is the fact that less and less time is available for it due to the aforementioned higher traffic densities. Accordingly, conventional rail maintenance machines (e.g. rail milling, planing or grinding) working at speeds from 1 to 10 km/h (0.6 to 6 mph) can only work during possession time (track closure) which is in most cases only available at night.
HSG was developed in order to cope with these challenges. It allows for working speeds of up to 100 km/h (62 mph) and thus is deployable within regular traffic. As a normal train run HSG works between scheduled passenger and/or freight trains.
HSG is based on the principle of circumferential grinding. Cylindrical grinding stones are pulled over the rail at a certain angle, inducing rotation as well as an axial grinding motion. The grinding stones are mounted on grinding units hauled by a carrier vehicle.
Two things are achieved through the combination of pulling and rotating motion: First, the required material removal rate is obtained through the relative motion between grinding stone and rail. Second, by rotating the stones, overheating, glazing and lopsided wear of the grinding stones is prevented.
The usual grinding speed on Deutsche Bahn's rail network is 80 km/h (50 mph).
Today two machines using HSG technology exist. Both are operated by the company Stahlberg Roensch. The larger machine RC01 has four grinding units, each carrying 24 grinding stones. A smaller machine using just one grinding unit with 16 grinding stones is also in use. RC01 is used on main line and high speed tracks of DB Netz AG, while the smaller version is deployed mostly on commuter and metro rail networks.