Signal set to go

The words 'signal failure' can make the blood of many travellers boil as they know their journey to work or home is going to be a lot longer than anticipated.

One common cause of this commuter nightmare is faulty track joints that short out signals and falsely indicate the presence of a train in the rail section.

While we in the UK have grown accustomed to complaints about our train service, one Canadian rail-fastening company thinks it might have come up with the solution to relieving rail woes, though it is yet to be taken up in the UK.

NorFast has developed a breed of insulated joints made of tougher, modular components which promise to cut down on rail line maintenance and delay times. The joints are made of a combination of thermoplastic polyester and an elastomer that can be installed without in-track welding. The product, called NIJ-6 Hercules, would replace steel joints, which are bolted and glued into the middle of the rails with epoxy resin.

Insulated joints play an important role in current railway circuit-based signal systems, but the epoxy resin traditionally used to affix them can introduce weak points in the rail that can lead to signal failure or potential derailment.

Insulated joints divide track into electrically isolated, two to five-mile segments that detect train presence and activate trackside signals. When an epoxy de-bonds it can cause the bars or bolts in the joint to make contact with the rails and short out the signal in each block, which then falsely indicates the presence of a train in the rail section.

These type of undependable joints, nicknamed 'glue joints,' were popular and effective when they first came out in the 1960s, says Paul Tucker, NorFast vice-president for operations.

'When glue joints came on the scene they were absolutely wonderful, but if you go back and look at what was happening on the freight railroads in the 1960s, probably one of the heaviest lines that you had would be 20-25 million gross tonnes (MGTs),' he said. 'As time went on, into the mid to late-1980s, tonnages, axle loads and frequency of trains increased, and the railroad line that ran 20MGT in the 1960s was all of a sudden running 100MGT, whereas the life of a glue joint runs somewhere from 175MGTs to 300MGTs.'

In the 1960s, he said it would have taken 10 to 12 years to get wear and tear equal to 300MGT on a component. 'By the early 1990s, you were talking two to four years to get that kind of traffic accumulation on the tracks,' he said. 'The result was that these track components were disintegrating on the lines. First the glue would disintegrate, and once it started that process the whole joint would deteriorate rapidly.'

NorFast called on its sister design company, ARRT, to come up with an enhanced model with better materials. Jude Igwemezie, ARRT president and the lead designer of the new joints, said he chose to use a DuPont thermoplastic polyester elastomer, called Hytrel, for four essential parts of the joint because of its reported flexibility and high resistance to strain, impact and fatigue. The joint uses the material as an insulation between the two adjacent rails, a liner between the joint and the rails and a strengthening thimble for the six fixing bolts. The material was also used as an insulating pad between the rail and a specially integrated saddle for the joint. The saddle was designed to provide extra strength and structural redundancy in event of bar failure.

Along with its redundant design, the joints have increased strength because they do not need to be welded to the track. 'Field welds are very expensive and they are a weak link in the chain,' said Tucker. 'They have a limit on their life.'

After testing the joints on a rig at NorFast, Igwemezie found the joints had a greater stiffness than the rail itself. Igwemezie also ran the joints under 27,000kg vertical loads for three million cycles and found no wear or damage to the parts. The end results concluded the insulation parts of the joint showed 56 per cent less stress compared with standard joints. The thimbles for the bolts showed reduced stress by about 75 per cent.

'We guarantee it for 300MGTs. which is at least three years in the heaviest lines,' said Tucker, adding that quick installation of the joints are also a feature. 'We can install one of these things, in the track, in less than 30 minutes.'