The rail industry is increasingly being challenged to improve the management and extend the life of one of its basic and most expensive assets, the rails themselves.
This challenge is being met by a better understanding of rail metallurgy, lubrication, profiles and direct intervention through material removal. Of these, the latter has seen the development of the rail grinding machine from the earliest days of converted trams to modern, purpose-built trains.
The benefits of rail management through rail grinding have long been recognised in the world-wide rail industry. In the UK, as economics, regulatory and safety issues have come more to the forefront over recent years, the technology has seen a steady increase in application.
Grinding, though, has its limitations, risks and environmental issues. It cannot be used in some tunnels or high fire risk areas, it has trouble dealing effectively with heavy rail damage, and much of its waste product remains on the track. So, after some 100 years of rail grinding, it is time to find a new tool in the toolbox.
The rail miller offers a more environmentally-effective method of rail management with an ability to do in one pass something that a rail grinder cannot do in many, if at all.
Most importantly, for many modern signalling and traction systems, milling does not leave its waste product behind on the track. Instead, it is recovered back inside the machine so it can be disposed of safely
An accepted technology
Rail milling has been covered in the rail engineer before, most recently in issue 69 (July 2010). The technology has become accepted in Europe and the Far-East, with investment in machines both by rail operators and contractors.
STRABAG Rail is at the forefront of this new technology and has invested heavily in it. A major service supplier to rail organisations around Europe, the company has a wide ranging fleet of rail maintenance machines to which it is now adding four rail milling machines, two rail-road and two track-based units, for a total investment of more than €100 million.
It has even had one of the rail-road machines specially converted for use on the British loading gauge. STRABAG Rail brought that unit over during 2010 and, having passed the requirements for operation on the Docklands Light Railway, it undertook some trial work which saw it complete some 9600 metres during six shifts of trouble-free track milling, producing 4100 metres of finished track allowing for areas of severe damage which required two or three passes.
Various representatives of Network Rail and London Underground saw the rail miller in operation, and were keen to try it on their own networks as soon as was practical. A return visit has been arranged for late in 2011.
One key advantage of the rail miller is that the finished rail profile is built into the cutting head. This is manufactured with renewable cutter teeth so that there is no possibility of inconsistency in the profile finish.
While the milling leaves small facets, around the size of a thumbnail, on the rail head these are easily removed by a tangential grinding wheel positioned just behind the milling head which leaves a finished roughness of 3-4µmm.
This is perfect for visual, ultrasonic or measurement inspection to ensure that defects have been removed, and that the desired profile has been achieved.
The design of the milling head unit and the patented grinding finish system ensures that both the swarf generated in milling and dust from the grinding are 99% recovered by a process that a conventional rail grinder cannot match.
So there is little or no residual waste left on the track to contaminate rolling stock and the track bed, especially significant for points equipment and track circuits. Recovered swarf can be recycled whilst the dust may be disposed of in a controlled manner.
The milling process, with a single final grinding pass, is also significantly quieter than a conventional rail grinder while, to the casual observer, it does not look like a mobile firework display, which can be a bit startling!
The lack of ‘fireworks’ also means that there is a very low fire risk arising from the milling process due to the enclosed nature of the grinding head and its spark containment. London Underground has been particularly interested in this aspect of rail milling.
STRABAG Rail’s rail-road milling machine is impressive in its appearance and design and offers the flexibility of being available to a range of operators as it can easily transfer from location to location.
It can be set up from road to rail mode in under an hour, transit to the required site at up to 45km/hour on track, and be working within 15 minutes of arrival at site.
It carries up to three sets of heads and each set, dependant on the duty required, can machine 1500 to 2000 metres of rail. Heads can be changed in around 20 minutes and so up to 3500 metres of finished track can be achieved in one shift.
Between shifts the tips on the heads are either rotated or replaced in a purpose built workshop trailer that accompanies the road-rail vehicle, and within 12 hours the machine can be working again with the same, but refurbished, heads.
During this break period the machine can be refuelled and emptied of swarf and dust. With more sets of heads the process can become almost continuous and with a well-organised logistics team this is quite practical.
The rail profile is built into the milling heads, so there is little chance of deviation from the desired dimensions. However, a number of tools can be used to check that the required standard, BS EN 13231-3 as a minimum, has been achieved.
For transverse rail profiles STRABAG Rail utilises either a DQM unit or a Mini-Prof for more exacting analysis, whilst a hand pushed trolley measures the longitudinal profile to check for corrugation. All such measurements are available immediately to check for compliance and quality control.
Following its successful trials on the DLR, the STRABAG Rail miller is coming back to the UK for further trials at 6 sites around the UK this November/December 2011.
Written by René Feuler for the rail engineer