Linear bearings for track and tunnel cleaning

• What was needed: undefined undefined
• Requirements: lubrication- and maintenance-free components that are compact and yet provide a high reach for thorough cleaning of tracks and tunnels. They also have to be highly rigid and resistant to dust and dirt.
• Industry: railway technology
• Success for the customer: The lubrication- and maintenance-free linear technology is compact when retracted and yet allows for a long extension length that does not yield too much under the high water pressure. As it is lubrication-free, dirt and dust do not affect its functionality.

ZWEIWEG International GmbH & Co. KG develops and manufactures special vehicles that can travel on roads and rails. They are usually based on lorries and equipped with rail undercarriages, and are used, for example, for cleaning, overhead line and track construction or tunnel rescue.
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 in gravel 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 cabin and can be extended and moved. Furthermore, a suction arm at the rear of the vehicle must also be movable so that in can plunge deep into the concrete trough of the track bed. Finally, a construction of altogether eight arms arranged in the shape of a star, each equipped with five nozzle tips, had to be flexibly movable for tunnel cleaning.
For all these movable components, the manufacturer was looking for components that operate absolutely without lubrication maintenance, are as compact as possible and still allow a long reach when pushed out. In particular, the high back-pressure during cleaning with water required bearings that are extremely rigid and do therefore not yield. Even large amounts 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, travels on a combination of undefined from our linear technology program (Picture 2). Although ZWEIWEG has a high level of vertical integration, our catalogue products were used here, which were convincing in terms of price and because they don't require lubrication or maintenance. The linear drive receives the control commands from sensors that scan the track bed and cause the suction arm to move up when they detect obstacles.
For the eight arms for tunnel cleaning, which are arranged in the shape of a star, the designers decided on two undefined each connected back to back and driven by the on-board pneumatics (Picture 3). The system is very compact at rest and has a long range when pushed out. It also provides the necessary rigidity to withstand the back pressure of 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 realised a two-way cleaning vehicle that enables a 360o cleaning of track beds, tunnels and stations under special conditions.

Picture 2: The movable sensor-controlled suction arm takes over the cleaning of the track bed. The sliding suction arm is guided in a drylin R linear system. The bearing easily compensates for tolerances in vehicle construction.

Picture 3: The rotary nozzles for tunnel cleaning can be extended. Two drylin W linear systems arranged "back-to-back" provide the linear motion. Good to see: the combination of aluminium guide and pillow block with plastic sliding element.