Linear bearings for track and tunnel cleaning

ZWEIWEG International GmbH & Co. KG develops and manufactures special vehicles that can travel on the road and on rails. Mostly based on lorries and equipped with rail undercarriages, they are used for cleaning, overhead line and track construction or tunnel rescue, for example.
For the commissioning of a third metro line in Riyadh in Saudi Arabia, such a cleaning vehicle was needed for both the track bed and the tunnels. The challenge: the tracks of the metro in Riyadh are not laid in ballast, but slightly elevated in a concrete trough and require a particularly flexible cleaning solution with movable cleaning arms.
For example, a large high-pressure unit with rotating nozzles for cleaning the tunnels is installed behind the driver's cab, which can be extended and moved. A suction arm at the rear of the vehicle must also be movable so that it can be immersed deep into the concrete trough of the track bed. Finally, a construction of a total of eight arms arranged in a star shape, each with five nozzle tips for tunnel cleaning, had to be flexibly movable.
For all these movable components, the manufacturer was looking for components that were absolutely lubricant- and maintenance-free, as compact as possible and still allow a long reach when extended. In particular, the high counter-pressure during cleaning with water required bearings with a high degree of rigidity that would not give way. And even high levels of dust and dirt in outdoor use should not cause any problems for the solution.

The suction arm at the rear, which is to be immersed in the concrete trough of the track bed, moves on a combination of housing bearing and supported aluminium shaft from the drylin® R series from our linear technology range. Although ZWEIWEG has a high level of vertical integration, our catalogue products were used here, which were convincing in terms of price and freedom from lubrication and maintenance. The linear drive receives the control commands from sensors that scan the track bed and cause the suction arm to be raised when obstacles are detected.
For each of the eight star-shaped arms for tunnel cleaning, the designers opted for two double-shaft profiles from the drylin® W series, which are connected back to back and driven by the on-board pneumatics. The system is very compact when not in use and has a long reach when extended. It also has the necessary rigidity to withstand the back pressure during high-pressure cleaning - and it is resistant to water. In addition, the bearings easily compensate for tolerances in the vehicle and are insensitive to dust and dirt. 
The conclusion was correspondingly positive: With this project, the engineers have realised a two-way cleaning vehicle that enables 360o cleaning of track beds, tunnels and railway stations under special conditions.