This article first appeared in the Railway-News magazine Issue 5 2021.
What do rolling stock or infrastructure maintenance engineers have in common with vehicle developers and derailing analysists? They all put a lot of weight on the parameter of equivalent conicity. Because this parameter is so relevant to safety, calculating equivalent conicity is quite complex. A powerful tool enters the game with the CALIPRI measurement module for equivalent conicity.
As unpleasant as the thought of a derailed train is, this potential thread is the driving force behind the calculation of equivalent conicity. To understand the parameter and interpret its value, there needs to be a basic understanding of how a train moves.
The train moves in a sinusoidal motion due to two characteristics of the wheel-rail interaction. First of all, the geometry of the wheel is a conical shape, although it is much more complex. As soon as the train is set in motion, this conical-like shape induces a sinusoidal motion pattern as shown in the drawing below.
This motion pattern requires a track gauge that is slightly broader than the back-to-back distance of the wheelsets – otherwise there would be no space for the wheelsets to move left and right. The importance of this way of moving forward becomes significant when thinking about taking a curve. Naturally one wheel – the outer wheel – will have to drive a longer distance, thus having to drive faster than the inner wheel with the shorter distance.
This effect, by the way, also occurs with cars. While a car makes use of the differential to balance the rotational speed of the wheels in a curve, a train makes use of the conical shaped wheels.
So, what exactly does the equivalent conicity (EC) parameter tell us? The name itself derives from the geometry of the wheel: the equivalent conicity defines to what extend the motion behaviour of a rail wheel equals a conical shape. In other words, the equivalent conicity tells us how fast the wheels are oscillating with a sinusoidal motion to the side.
Railway-News Magazine issue 3 2021: Nextsense – How China’s Metros Are Benefitting from Faster, More Reliable Profile Measurements
The rail plays a central role in the wheel-rail-system. In order to reliably fulfill its functions, regular maintenance is crucial.
Nextsense, measurement expert for the rail industry, has developed the CALIPRI Track Geometry Gauge – an add-on to their well-known systems.
mgw Service uses contactless, laser-based CALIPRI wheel profile measurement gauge for preventive maintenance.
Use the form opposite to get in touch with NEXTSENSE GmbH directly to discuss any requirements you might have.