Daniel Pyke
Member
Dear All,
I've been slowly writing a series of articles describing how rail is made. I'm publishing these on LinkedIn (as it will hopefully reach some of my potential customers), however I think they may well be of interest to the general rail user/enthusiast too.
I'll come back and add articles as I complete them
Making Tracks - Pt 1 - Steel
Making Tracks - Pt 2 - Casting
Making Tracks - Pt 3 - Rail Rolling
Making Tracks - Pt 4 - Rail inspection
Making Tracks - Pt 5 - Rail Finishing
I hope you find them interesting.
(Pictures and links are available via the links above - sorry they don't cut and paste easily!)
Part 2 below
Part 3 below
Part 4 below
I've been slowly writing a series of articles describing how rail is made. I'm publishing these on LinkedIn (as it will hopefully reach some of my potential customers), however I think they may well be of interest to the general rail user/enthusiast too.
I'll come back and add articles as I complete them
Making Tracks - Pt 1 - Steel
Making Tracks - Pt 2 - Casting
Making Tracks - Pt 3 - Rail Rolling
Making Tracks - Pt 4 - Rail inspection
Making Tracks - Pt 5 - Rail Finishing
I hope you find them interesting.
(Pictures and links are available via the links above - sorry they don't cut and paste easily!)
--- old post above --- --- new post below ---Making Tracks - Pt 1 - Steel
Welcome to the first in a brief series of articles giving a brief insight into how rails are made. This subject is close to my heart as I've spent some years at the end of this process route.
These ribbons of steel snake through our scenery conveying countless commuters and hauling freight to their desired destinations.
In the UK, where I'm based, passenger ridership has more than doubled in the last 10 years to 62.9 billion kilometres in 2014-15, with the volume of freight moved being the second highest on record at 22.2 billion net tonne kilometres.
Most people don't give the rails a second thought, as thankfully they rarely hit the headlines, and fewer still realise they are one of, if not the, most technically demanding rolled steel products produced.
In order to make good quality rails you need high quality steel. It's true what they say, "You cannot make a silk purse from a sow's ear." Or putting it in a slightly different way, any chef will tell you that the quality of ingredients is crucial to creating a great meal. Many high quality ingredients are needed to produce superior quality rails and I'll try and explain a few below.
Making Steel
Steel can be made via a few different process routes. The common ways are to refine iron ore dug from the ground via a blast furnace to create liquid iron which is refined into steel via the BOS (Basic Oxygen Steelmaking) process. The other main method is to use electricity to re-melt steel which has previously been manufactured (usually via the BOS process), via an electric arc furnace (EAF). The steel for Tata Steel rails is made via the blast furnace route.
Composition
Steel is a blend of mostly iron, with carbon and many other additions that tailor the metal's properties to its intended use. There are in excess of 20 different common steel specifications for rail. The blend of alloy elements is carefully controlled to provide the optimum properties desired to very high levels (parts per million in some cases). This provides some interesting challenges in preparing each 300 tonne ladle of steel which has been refined from materials dug out of the ground together with recycled scrap steel.
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Stirring of the steel to ensure uniform composition
Alloy additions are made to get the steel to the desired composition however, one of the key elements for rail steels, Hydrogen, requires a different approach to control its levels. If high levels of hydrogen are present in rail steels they may crack which is obviously unacceptable. To reduce the level of hydrogen a vacuum degassing unit is used to essentially suck the hydrogen out of the steel.
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The snorkels of a vacuum degasser, which are lowered into the ladle to remove hydrogen
Cleanness
One of the most critical and most challenging requirements for rail steel is its cleanness. By cleanness, I mean how free from undesired impurities the finished rail is. This requirement is challenging yet vital for safe durable rails. Tiny impurities (called inclusions), if present in the finished rail, can cause cracks to form within the rail under the repeated loading from traffic passing over it. If left unchecked, these cracks can grow and cause the rail to fracture.
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A small inclusion caused a fatigue crack to grow resulting in a rail failure
Modern steelmaking and continuous casting practices, together with modern non-destructive testing techniques have transformed this aspect of rail manufacture, so that this type of rail defect is now extremely rare. The European rail standard specifies two direct types of assessment of rail cleanness. The first is an oxide cleanness measurement which samples the rolled rail and looks at it under a microscope to assess the number and size of inclusions present. The second is a non destructive ultrasonic test of the entire length of every finished rail. The ultrasonic equipment must be capable of finding defects/inclusions of 2mm or greater in size in the head, web or foot of the rail.
Temperature and Time
Steel is continuously cast and I'll describe this in the next article, but one of the key things is timing. Steel needs to be ready at the right time and the right temperature as well as having the correct cleanness and composition to allow casting to take place efficiently. When you consider that a dozen ladles of steel may be cast consecutively, each arriving at the casting machine at exactly the right time and temperature to continue the casting process without ever stopping, you can see this task is complex. When you add in the fact that there may be several different casting machines operating at the same time, you can see that conducting this orchestra of processes and movements requires a mastery of logistics and timing.
For those who want to 'play' with a virtual steel plant to make steel then I can recommend the online simulations found here at steeluniversity.org.
I hope you enjoyed this brief article and I hope you'll continue to follow me for more in this series and other rail content. If you have any comments, questions or even a request for a future article then please let me know either below or via a message.
Part 2 below
--- old post above --- --- new post below ---Making Tracks - Pt 2 - Casting
Welcome to the second in a brief series of articles giving a brief insight into how rails are made. If you missed the first part on steel then have a look here.
Today we look at turning a 300 tonne bucket of refined molten steel from my previous article into a product which can be rolled into a high-quality rail.
In days gone by molten steel was poured into metal moulds to solidify into blocks of steel (ingots), much like freezing ice cubes in a tray in your freezer at home. However this process has its issues controlling cleanness and segregation – and as a result, the rail industry moved to mandate the use of continuously cast steel to provide greatly improved product quality.
Continuous casting is the process of pouring molten steel into a mould and withdrawing the semi-solidified product from the base of the mould at the same time. In theory, this means molten steel can be continuously poured into the top and product removed from the bottom in an 'endless' cycle. This cycle produces a “strand” of steel, as shown above, that is cut up into shorter lengths usually called “blooms”. Blooms are typically rectangular with dimensions of approximately 250-350mm. The length is dependant on the length of product to be rolled but could be in the region of eight metres and weigh seven tonnes. Typically, casting machines have multiple strands to maximise productivity. The casting machine for rail at Scunthorpe has six strands. The steel is transferred from the ladle to the strand by a large bath of steel called a tundish. This provides a reservoir (like a header tank) to allow more than one ladle to be cast without stopping the casting process. Using this method a caster can run for up to 18 hours continuously.
The 90 second video from Tata Steel here illustrates and explains it well
Another good interactive overview of a casting machine in action can be found here
The resulting blooms are uniquely identified to ensure traceability and can then move onto the next process - rail rolling which I'll cover in my next article.
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I hope you enjoyed this brief article and I hope you'll continue to follow me for more in this series and other rail content. As usual if you have any comments or questions then let me know either below or via message.
Part 3 below
--- old post above --- --- new post below ---Making Tracks - Pt 3 - Rail Rolling
In this article I’ll describe how we turn the 7+ metre lump of cast steel bloom from a previous article into the rail which we recognise.
Each year we make around 10,000km of rail. That’s easily enough to build a railway between New York and San Francisco. By weight, that’s equivalent to 50 Eiffel Towers or 20 Statues of Liberty. We roll over 100 different profiles of rail for use in networks worldwide. We generally use two rail production mills, one based in Scunthorpe, UK, and the other in Hayange, France to produce the 100+ different profiles of rails that global networks require. These mills differ in layout, but the essential processes of rail production remain common to both mills.
This post is a little longer than most so far as there is a lot to cram in, so for those that prefer to watch a video than read then Network Rail have a great video of the process at Scunthorpe rail mill (plus other useful stuff) here (57 seconds on for the production bit)
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Video from Network Rail showing where rails come from
Reheating
The blooms following casting are reheated in a furnace to over 1200°C (that’s over 2200°F), in order to make them soft enough to roll into the desired rail profile. The reheating process takes several hours to complete so blooms are continuously walked through the furnace to ensure the rolling process continues 24 hours a day.
Descaling
Prior to rolling, the blooms pass through a high pressure water jets, covering all faces of the bloom. The removal of scale reduces the possibility of surface defects on the finished rolled product leading to improved surface quality. Descaling is also carried out at various points along the rolling process to provide excellent levels of surface quality.
Rolling
The hot steel is then squeezed between carefully designed sets of steel rolls to alter its shape and extend its length. The rolling process itself takes less than 10 minutes, but in this time the bloom is transformed from 7+metres to over 120metres in length. The profile dimensions are critical and the tolerances are exceptionally stringent. For example most rails rolled have a tolerance of just 0.5mm on the rail height.
The Scunthorpe plant uses a state-of-the-art continuous 7 stand finishing train, which means that the rail passes through 7 sets of shaping rolls all at once. The rail coming out is travelling more than twice the speed of the hot steel going in!
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7 close-coupled rolling stands are utilised for finish rolling at the Scunthorpe rail mill
Identification
There are two forms of identification for rails. The first is known as the brand. This is rolled into each rail along its length and depending on the rail ordered, contains various information, such as the manufacturer, profile and steel grade.
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Example: Tata Steel, Scunthorpe, R260 grade, 2016, 60E1 profile
The second form of identification is a unique number stamped into the web of each rail along its length. This number means that each rail is uniquely identified and can be traced back to the liquid steel from which is was made even many years after it was manufactured.
Inspection
Now that we have turned our 7t block of steel into a 120m red hot rail, the process of inspection commences.
A high-tech profile gauge measures the profile of the rail along its entire length to verify and control the dimensions of the finished rails. A separate system of lights and cameras provides feedback on the surface quality of the rail and finally physical samples are also taken when required to perform mechanical tests.
Cooling
We now have to cool our 120m rail down so we can further process it. The cooling of the rails is not as simple as it sounds. The rails are actually pre-curved when they are placed onto the walking cooling banks. This is done to counteract the shape change that occurs during cooling. Because the rail is not symmetrical in all planes and different areas of the rail cool at different rates, the rail changes shape as it cools. As the rail cools it becomes straight again! The temperature change also affects the rail length as well as shape with the rail shrinking by around 1 metre as it cools.
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Long rails cooling on the cooling bank. Note the shape change from left to right
Straightening
Once cooled the rail is passed through our roller straightening machines. These work in both the vertical and horizontal planes to deliver high levels of both straightness and flatness required for high speed traffic use, where for example limits in vertical flatness deviations of less than 0.3mm over a 3m span are specified.
Once we have a straight rail, then the rail moves to the finishing and inspection facilities which will be detailed in my next article in the series.
I hope you have found this interesting. Please follow me for more rail related content. As usual all comments on content are gratefully received.
Part 4 below
Making Tracks - Pt 4 - Rail inspection
Firstly, sorry to any avid readers for the delay in releasing this instalment of my ‘Making Tracks’ series; it just didn’t seem right to me to talk about our excellent railmaking processes, when so many of my Tata Steel Strip, Tube and Speciality colleagues were coming to terms with an uncertain future and all the press interest and speculation. I certainly wish them the best of luck in securing their futures, as we have done in the Long products area.
If you’ve been following this series of articles, you’ll have seen in my previous article how we produce rails. People may be forgiven for thinking the process is now complete, now we have a rail that is up to 120m long. But the process of rail production is far from complete. Those that have watched the video link completely in my last post will have had a sneak peak at this part of the process (from 2:35 up to 3:01)
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Due to the fact that the rails form one of the most critical parts of railway infrastructure, they must undergo extremely stringent testing. Unlike the vast majority of hot rolled steel products, where only a sample of the produced material is tested, 100% of rails are subject to a battery of tests to assess the quality both inside and out.
Profile
The dimensional tolerances for rail are extremely stringent. For example rail height must be within +/- 0.5mm along the entire length of the 100+ metre rail. The dimensions on our rail are verified along the entire length by a high-tech laser profile gauge which uses an array of lasers and cameras to provide extremely accurate measurements. The measurements are taken many times per metre to give a complete picture of the rail profile rather than the reliance on the ‘old fashioned’ way of using templates to measure the dimensions at just each end of the rail.
Flatness
Flatness is critical for high speed traffic. Undulations in rail surface of just tiny amounts can produce significant issues for trains travelling over them at extreme speed. Vertical flatness specifications can be just 0.3mm deviation over a 3m length required for high speed track. The verification is done using a system of lasers and cameras to measure both the vertical and horizontal flatness of every rail.
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Lasers and camera systems are used to verify high levels of rail flatness
Surface quality
The surface quality of the head and foot of the rail is critical as these are the most highly stressed regions of the rail in service. Automated inspection of these areas is carried out using various techniques including image analysis and eddy current inspection to ensure the rail surface is defect free. The eddy current inspection machine I think is an engineering work of art with arrays of static probes, looking for transverse issues, and also rotating probes looking for longitudinal defects. Once again very high specifications exist with just a 0.3mm tolerance in critical areas; that is the same as the thickness of your fingernail.
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Eddy current testing is used to verify surface quality
Ultrasonic (Internal) inspection
Now that we have assessed the rail has the right dimensions, is as flat as possible and is free from surface defects, the time now comes to assess the internal soundness of the rail. Historically when rails were made from ingots (rather than the modern continuously cast steel), internal defects were a common reason for rail failure. Internal defects could be an area of porosity, a large inclusion in the steel or even residual “pipe” when ingots were used. However modern steelmaking and continuous casting processes have transformed the internal soundness of rails and today’s internal quality assessment is usually focussed on finding any large inclusion or collection of inclusions in the steel. An array of up to 18 ultrasonic probes is used to assess the internal quality of the rail, looking for anything that shouldn’t be inside. The probes are calibrated to detect defects smaller than 2mm typically along the entire length of every running rail. I guess the nearest comparison I can give is looking for things narrower than a grain of rice along the entire length of every 100m+ long rail. It is a bit like looking for a needle in a haystack.
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Ultrasonic inspection uses up to 18 probes continuously along every rail
The reason that the internal quality specifications are so stringent is because under the repeated loading that a rail experiences in track, small internal defects can initiate fatigue cracks which can then grow and cause the rail to fail. This is why we spend so much time, money and effort making sure the steelmaking practices are optimal to stop potential defects being introduced, as well as having high tech equipment to prove that none have been introduced into the finished rail.
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From small internal defects (centre) can grow large problems! Modern steelmaking and inspection technologies help avoid this issue
In the next article I’ll look at some of finishing operations that can be applied to the inspected and verified rail including cold bolt expansion and flashbutt welding to ready-it for track service. Please follow me for the rest in the series and as always I welcome any comments or suggestions for future content.
Making Tracks - Pt 5 - Rail Finishing
In my previous articles I've detailed how we at Tata Steel's Long Products business (soon to be renamed!) make a rail and prove it is fit for use. However, the story doesn't quite end there. The finishing operations provide added value for customers making rails easier to use and often improving their life too.
Length
It may seem obvious that a rail needs to be the right length for its intended destination. What aren't so obvious are the tight tolerances that are often needed in a myriad of different sizes for constructing or refurbishing switches and crossings for example. Here a tolerance of just 5mm can be applied on a 30m rail which equates to a permissible variation of less than 0.02%. This variation can be halved to 0.01% if drilled rail is supplied to bolt directly into service.
Drilling and cold expansion
Rails have historically been bolted in track via fishplates. Despite the almost universal popularity of continuously welded rail (CWR) for new installations, there are still routes out there which utilise traditional jointed track and other applications where bolted connections are still used. To supply rail into these applications, holes can be pre-drilled into the rail to accept the fishplates. Common fishplates use two or three holes drilled into each rail end. To improve the fatigue performance of the joint and avoid crack formation around the bolt holes, further processing by cold expanding can be carried out. This process essentially modifies the residual stress of the rail to put the surface of the drilled hole into compression. If the surface of the hole is in compression it is far less likely to generate a crack in service and so cracking around the boltholes is greatly reduced.
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Cracking from boltholes can result in rail failure
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Video from Hird Rail showing the cold expansion process (we use a similar process)
Welding
At our Scunthorpe plant, we have our own dedicated flash butt welding facility to join long length rails into even longer welded rails for dispatch by dedicated rail delivery trains direct to the worksite. The typical length of welded rails at Scunthorpe is 216m, and usually one weld is used to join two 108m rails together. Flash butt welding is generally regarded as the highest quality rail welding available, giving long reliable service. The welding process uses large electrical currents (70,000 amps) and large forces to effectively melt and forge the rail ends together. There is no 'filler' metal added to the weld meaning the weld is 100% parent material. The welding process is carefully controlled to minimise the hardness variation across the weld to ensure the weld doesn't wear differentially in service (sometimes known as cupping), which is often an issue with the wider aluminothermic welds.
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Flash butt welding in action
Delivery
The delivery and logistics for a long product such as rail can be very challenging. We have decades of experience in getting rails to the right place at the right time all across the globe. Transporting rail by both rail and road virtually every day and with local ports experienced in shipping rail, our logistics team ensures rails arrive at the right destination, at the right time, in the right condition.
One of the questions I'm often asked is:
"How do we get the long rails around corners"
My usual perhaps flippant answer of "Carefully" is often met with a wry smile, however my practical demo on plant tours moving around tens of metres of rail with just one hand on a rail inspection bench explains things far better. It usually causes a widening of the eyes and you can almost see the lightbulbs coming on, as people realise steel is more flexible than they had previously thought. Rail is designed to be very stiff in the vertical direction to carry traffic, but it is far less rigid side-to-side. The result is that rail is relatively flexible in long lengths when it is required to negotiate curves during rail transport. That doesn't mean it is easy to transport, so my answer is quite true, with much time and technology going into ensuring that rails are delivered both safely and without damage, but getting it around the curves is certainly not impossible as can be seen in the video clip below.
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Long welded rails being dispatched from Scunthorpe
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