With launch of our new Norton Quantum3 Rail cutting disc specifically designed for railway tracks, we thought it was fitting to give a brief overview of how a section of railway is cut and replaced. So wonder no longer, here’s how it’s done….
The Norton Rail range is a complete portfolio of cutting discs that provide precision, speed and power on any rail type (subway, tram, train) and any rail cutting machine with a clamping device (electrical and petrol). Both the Norton Rail ZA24Q and Norton Quantum3 Rail cutting discs (pictured right) are highly versatile and ideal for this kind of application.
We are going to be talking about Continuous Welded Rail (CWR) using Thermite welding in this article as most modern railway tracks are constructed using this approach.
Initially, the high strength bolts that anchor the portion of the track to be removed are unscrewed by a rail-specific wrenching unit and the newly loosened section is then heat-treated. The rail is pre-stressed or laid when the track is said to be "stress neutral,” this is an ambient temperature dependant on the local climate; the point between the lowest winter and warmest summer temperatures is selected.
Next, a rail saw is equipped with a specialised cutting disc (such as the Norton Quantum3 Rail) and is then fixed to the section of the track to be removed. Cutting rail track is a challenging process that requires a high level of skill and precision. The difficulties posed are almost all derived from the significant vibration that the operator experiences whilst cutting, which hampers the ability to make a clean straight cut. An inaccurate cut makes welding more problematic and can increase the time taken to complete any given job. As one would expect, vibration induced White Finger (VWF or HAVS) is also a common complaint amongst rail-side workers, so any product or tool that reduces operational vibrations is a must in this case.
Once the old section of the track is cut, the new track is brought up to the correct location and moved precisely into place, ensuring a 25mm expansion gap is left between the two sections and they are in alignment with each other.
Welding using Thermite
A weld mould is constructed around the expansion gap between the track sections and packed tightly with sand; ensuring that every gap is filled in order to retain heat. Now, pre-heating takes place by using a propane powered blowtorch; angled into the mould gap. As the two sections of track increase in temperature, so the metal becomes softer and the expansion gap begins to close.
It is these aspects that make the cutting disc is perfect for the railway night-shift as their operational time is often extremely tight and in many cases, they work in difficult conditions. This disc cuts quicker, is more comfortable to use and lasts longer than any other cutting wheel in the rail market today – making it the obvious choice.
A graphite cauldron is filled with Thermite and positioned close to the pre-heating mould. When the time comes, the Thermite is ignited and quickly placed into position so that the molten iron run-off wells-up inside the mould; directly infiltrating down between the two sections of track.
It takes less than 5 minutes for the liquid iron to solidify enough for the mould to be removed. With great care, the operator hammers the waste material away from the area, leaving just the white-hot weld. The newly formed metal is now pinched in place, during “melt squeezing” to further stabilise the joint.
What is Thermite?
Thermite is an extremely reactive mixture of aluminium and iron oxide in powder form. Upon igniting Thermite, the mixture produces an extremely exothermic reaction, which has been measured at around 2500 degrees Celsius (or about half as hot as the surface of the sun). The molten iron produced as a by-product makes Thermite an ideal for welding rail tracks together and has been used in this application for over 100 years now.
Grinding and Finishing
Finally, the newly welded track needs to be ground and finished. Norton offers a varied range of cutting discs, grinding wheels, cups and plugs for all rail track repair and maintenance operations - performance solutions for both portable hand-held and track mounted machines.
Our range spans everything from organic grinding wheels to grind the lateral edge of the track, to wheels that feature the specialised profiles required for grinding the connection chambers and web of the track. Download our rail brochure for all Norton track grinding solutions.
For more information about selecting the right grinding wheel for your process, take a look at one of our previous expertise articles. If you have any general grinding questions, you might find your answer amongst our handy grinding FAQ videos. For anything else, our Norton experts are always glad to help, contact us today.