Weathering the storm with climatic testing

Climatic testing provides manufacturers with valuable information on the performance of rail vehicles and critical components before they are subjected to the rigours of service operation. Gabriel Haller, technical director of Rail Tec Arsenal, Austria, explains how climatic wind tunnel testing helps to prepare new trains for even the most extreme operating conditions.

MODERN rail vehicles and components must meet stringent safety and quality standards even in the most extreme weather conditions. Functional tests can make a valuable contribution to increasing overall vehicle reliability by reducing the risk of failure of critical components. In a climatic wind tunnel, the temperature and precipitation conditions prevailing during regular service operation can be precisely replicated so vehicles can be tested realistically. This means any improvements made can be immediately verified, saving time and money.

Efficient and effective functional tests require detailed knowledge of how different climatic conditions affect individual components. These include:
• extreme temperatures and humidity levels, and their impact on the operation of mechanical, electrical, electronic and pneumatic components
• the effect of rain and wind on connecting corridors, doors, windows and windscreen wipers
• wet snow on doors, steps, couplings and roof equipment.
• dry snow on air intakes and gaskets, and
• ice on the pantograph, circuit breakers, doors, steps and couplings

To obtain meaningful results, the components must be installed in the vehicle and tested under realistic operating and climatic conditions. This is the only way to detect potential design shortcomings or unexpected interactions between components and systems in specific weather conditions. Rail Tec Arsenal has developed standardised test procedures to identify typical problems encountered by different subsystems during service operation.

Insufficient insulation and/or leaks in the vehicle body often have a negative impact on interior temperatures and may cause condensation in the passenger areas or driving cab. In turn, floor surface temperatures in the vestibules may fall below freezing point at low outside temperatures, leading to ice formation.

Leaks can be located on the basis of smoke and wind simulation, while insulation problems in the vehicle body, doors, windows or corridor connections can be identified using a thermographic camera.

Inadequately-functioning windscreen heater or air inlets in the driving cab can cause the windscreen or side windows to mist up. Snow and ice accumulation impairs visibility and may lead to complete failure of the windscreen wiper, rendering the train unsuitable for service.

These problems can usually be eliminated by adjusting the settings of the windscreen washer, wiper and heating systems, and the air-conditioning unit of the driving cab using the results of climatic wind tunnel tests.

Bogie components such as dampers, sanding, tilting and brake systems are safety critical components, which are usually very exposed and therefore prone to the accumulation of snow and ice. The possible consequences may range from partial malfunction to complete failure, such ice build-up on the sanding system.

All these environmental conditions acting on the underframe components can be realistically simulated on a dynamometer in a climatic wind tunnel. Measures designed to reduce these problems, such as heaters or housing for sanding equipment, can be subsequently tested for their effectiveness.

Extremities of temperature, combined with high humidity, typically lead to problems with electric and electronic components such as the main switch, transformer, converter, battery and on-board electronics. Ice build-up usually causes additional mechanical problems with the pantograph.

Climatic wind tunnel tests allow these problems to be identified and remedied in good time to ensure reliable functioning of the power supply system during regular service operation.

Accumulations of ice and snow in the door area obstruct or even prevent opening, closing or automatic reversal of doors and may cause retractable steps to become stuck.

Some targeted design modifications or improvements in the control system are often sufficient to eliminate these problems. In a climatic wind tunnel these measures can be investigated and tested efficiently under reproducible snow and ice conditions.

	Testing the effects of snow and ice accumulation on windscreen wipers.

A survey conducted by Rail Tec Arsenal revealed that door and step malfunctions are the most frequent problems reported by train operators. The test procedure for these two components are therefore described in more detail. These components are tested for proper opening, closing and obstacle detection under snow and ice conditions.

Ice tests are carried out at ambient temperatures of -20oC. The passenger areas are cold and the air-conditioning unit is switched off. The vehicle doors and the steps are covered with a layer of ice about 2mm thick using a manual sprinkler. Once the last water film has been applied, the ice is allowed to harden for 10 minutes. This procedure is designed to simulate freezing rain.

To simulate wet snow, the passenger area is set to regulated mode and a wet snow layer around 20mm deep is applied to the extended step at an ambient temperature of -10oC, using mobile snow nozzles. The snow is compacted by foot and the step is subsequently retracted. The vehicle is then switched to driving mode for approximately 15 minutes, causing the snow to cool down and turn to ice. This cycle is repeated at least three times.

This procedure is designed to simulate a normal drive cycle where the step is extended, stepped on by passengers and subsequently retracted. The snow brushed off from passengers’ shoes may cause ice build-up on the step and the step enclosure, resulting in potential malfunction. This effect can be further enhanced by alternating climate tests, where the vehicle is moved to another environment (+10oC) for the simulation of partial thawing during a station stop.

The criteria for successful operation are:
• step detects obstacles and peak force is below 300N on contact
• step does not move when the door is fully open
• light barrier detects an obstacle when closing and door reopens
• the maximum closing force is ≤150N for the first closing process and no more than 200N for subsequent closing processes
• the entrapment protection device detects the test piece and the door opens, or the test piece can be withdrawn with a force ≤150N, and
• the emergency unlocking system is fully functional.

The test described above is just one example of the comprehensive standardised test procedures developed by Rail Tec Arsenal for different components and systems. Each procedure includes a detailed description of the test conditions and the assessment methods to be used to verify whether the compliance criteria have been met.

The tests and functional requirements laid down in these procedures have been adapted to real-world conditions based on many years of experience in climatic wind tunnel testing and feedback from regular service operation. They ensure a high degree of comparability, providing a sound basis for the future standardisation of functional tests on rail vehicles at a European level.