Solving signalling problems on Insulated Block Joints

Metal particles, caused by train wheels grinding against the rails and at points, are a source of faults and delays on the railway. These particles adhere to the rails, which are magnetised by voltage spikes and return currents.

On tracks equipped with Insulated Block Joints, short circuits occur between the insulated rail sections because metal particles act as conductors. Passing trains have the same effect, so the safety system detects an occupied track section, resulting in incorrect red signals and delays.

Maintenance teams sometimes have to go out every week to remove metal particles. Apart of that expensive Rapid Response Teams have to act when a joint fails and trains are stopped. This is a particularly tiresome problem in conditions of low rainfall in the summer, in tunnels, at curves and close to crossings.

Solving the problem

In order to reduce the number of signalling failures, Prorail, VolkerRail and P&K did extensive research on cleaning of the Insulated Block Joints (IBJ’s). Different opportunities were investigated, for example manual or automated cleaning, greasing, magnetic removal of filings and new design of IBJ’s.

After comparison of different options, magnetic removal seemed to be the most efficient, robust, reliable and service friendly solution.

Designs were made and tested for active and passive magnets in different positions around the IBJ. The tests showed excellent reduction of faults after applying magnets.

Special attention was paid to magnetic fields influencing other magnetic, electrical or electronic (safety) systems. Calculations showed no impact on other systems, nor did extensive field tests.

Product engineering

Although the tests showed good results, the solution can only be successful when it is robust, easy to handle and maintain and costeffective. These were important starting points for the detailed product engineering.

The engineering process resulted in an engineered magnet on a mounting frame. Each magnet is configured in such a way that only the side facing away from the rail is magnetic. In this way, the captured metal particles are prevented from having short circuits at the electrical separation between the rails and the magnet bracket. The nonetheless indispensable maintenance teams have easy access to the magnets for cleaning them with extractors or non magnetic scrapers. The mounting frames are rail-profile specific and easy to (dis)mount.

Results

Since 2004, the magnets have been mounted in Holland, France, Sweden, Norway, Finland and the United Kingdom. Reports of the railoperators show significant reduction, up to 90%, in the number of faults attributable to the cause of electric bridging by metal particles. The permanent particle magnet makes a contribution to the objective of more punctual transport by rail that should not be underestimated.

Where the magnets do not require large investments or increase of maintenance costs the Payback Period is very short. Due to the robust construction it is a reliable solution that will last for a long time.

Versions available

Permanent particle magnets can be supplied for all rail profiles by using the mounting frame. We also designed magnets on frames that are bolted directly in holes in the rail-profile.