Picking the right shot blasting and peening equipment pays big dividends when it comes to railway applications. Yves Dufour, Senior Vice President at Wheelabrator - Global Air, explores the current state of the art in surface finishing for this sector.
Rail remains a global opportunity for the metal finishing industry. Shot blasting and peening are central to railway manufacturing and refurbishing alike, with everything from wheels to whole carriages requiring expert surface finishing.
Employing just under a million people in the EU alone, rail has seen a renaissance over the last few years and, despite Covid applying the emergency brakes, the market outlook remains positive. According to the most recent EU figures, rail traffic increased annually by 2.5% for passengers and by 4.1% for freight between 2015 and 2018. The total length of track designated as congested more than doubled during that period as well.
More intense usage of tracks and rolling stock means extra maintenance, and, as rail traffic starts to pick up post-Covid, service providers will need enough capacity to handle it. That turns the spotlight onto airblast and wheelblast processes – and the enormous productivity advantages they offer over manual processes with hand-held power tools.
A green light for efficient blasting
The two main blast applications involved in rail are first, cleaning and preparing surfaces to the correct roughness before painting and coating
or prior to inspections like Non-Destructive Testing (NDT) and second, peening to increase component fatigue strength. Parts vary widely in size, configuration, complexity and quantity, from a few small castings through to a fleet of hundreds of complete coaches with their bogies and wheelsets.
Like any surface finishing application, selecting the proper equipment, designing the process and choosing the correct media are vital precursors to a successful outcome. Airblast has a concentrated blast area that needs careful direction, while wheelblast machines deliver a huge quantity of high energy media towards the part being cleaned, which makes it perfect (and very cost-efficient) for processing larger rail components – especially when combined with automated part handling.
Blasting lots of complex parts is a challenge that Wheelabrator is well used to helping operators like SNCF meet. Whether you're cleaning new railway lines or peening springs, processing lots of small components or just a few large ones, there is a solution to fit. Here’s a round-up of typical applications and the state-of-the-art technologies available to handle them.
Don’t get derailed
Railway tracks must provide a dependable surface for trains to roll on and, to achieve that, surface finish is critical. Shot blasting is the most efficient way to descale new rails as they leave the factory and to clean up used rails prior to other operations like profile regrinding or milling.
Roller conveyor wheelblast machines are ideal for this application, able to rapidly clean rails in a continuous feed-through process either as a standalone unit or integrated into a larger production line. Wheelabrator offers a variety of roller conveyors for different applications and work speeds, with the Type G a popular choice for rail.
Used by large operators like Deutsche Bahn, the Type G can handle through-feed widths from 600mm to 3m, with its blasting wheels positioned above and perpendicular to the flow direction of the roller conveyor. The largest models have up to eight blast wheels, ensuring full coverage of every part of the rail profile. Descaling would typically employ coarse abrasive media, for example, steel balls with a shot size of S390 and over.
Working with wheelsets
Wheelsets – the wheels and axles that the train rides on – define safety-critical components; they simply cannot fail in use without risking a serious accident. Regular inspection and periodic refurbishment are vital.
Shotblasting provides a fresh, clean metal surface for ultrasonic or magnetographic crack detection on axles and wheels, as well as the correct surface roughness for grip on the rail. Blasting is also good preparation for any lathe re-turning required to remove larger surface defects and restore the desired wheel profile.
Installed at one Paris-based rail and metro operator, Ventus 350 PR cabinets offer up to three manual airblast stations that can clean an axle in around 30 minutes. A range of specialised tooling is available to support the axles (minus wheels), with a carriage to move components in and out.
Automation that handles whole fleets
Where there are many axles to blast, companies including a large Swiss national rail operator pick equipment like the new Ventus 350 PR AXT. This semi-automatic, 2-axis machine features one or two airblast nozzles and processes one axle in 25-30 minutes. As well as greater throughput, automation offers more consistent surface quality – perfect for these vital components.
Cleaning lots of complete wheelsets requires more room and more muscle, and the MC 2200 A provides that in spades for operators like SNCF and SNCB. Fully automated, with a much larger blast cabinet and 2- or 3-axis options, the base version uses two high-flow airblast nozzles to clean 30 standard wheelsets in an 8-hour shift to a quality level of SA 2-3. Media like angular steel shot or steel grit (LG 80, 55-60 HRC) typically produce a roughness of 0.6 to 4μm.
Larger again, the top specification MC 2200 A employs two groups of 3-axis manipulators and four blast nozzles to drive down cycle times to below 15 minutes. Both MC machines feature sophisticated pass-through processing, with axles on carriages entering and leaving the cabinet through automatic doors. The machines automatically recognise each part and select the relevant treatment programme, further enhancing throughput.
De-stress your wheels with peening
Supporting hundreds of tons and rotating many millions of time annually, train wheels are at serious risk of fatigue failure – hence the need for crack testing. By adding compressive stresses to the wheel surface, peening helps prevent cracks forming in the first place.
Rail specialists like MG-Valdunes have long employed Wheelabrator's fully-automated, high-capacity, in-line machines to efficiently peen highly stressed components. Shot blasting equipment like the Railway Wheel Peener (RWP) offers fine process control, able to monitor and control variables such as blast velocity, blast media size and media flow rate.
While two blast wheels fire shot at the wheel or axle from both sides, wheels roll in and out of the RWP’s blast cabinet assisted by automated work handling tooling, while a roller arrangement spins individual wheels in the blast stream to assure an even finish.
For the springiest springs
The cyclical stress endured by leaf and coil springs makes them vulnerable to fatigue failure; shot peening helps prevent it. As well as increasing fatigue strength and lifespan, peening springs also raises their maximum working load and prevents sagging.
In-line shot peening machines like the Wheelabrator RDS are the most productive solution, conveying coil springs on parallel rotating rollers with pusher fingers that transport them through the blast zone. Multiple blast wheels target the springs from different angles, peening them completely as they spin through the cabinet.
Parameters like throughput speed, blasting time, discharge speed, shot size and distribution can be controlled with absolute precision, letting the user deliver exactly the right intensity to reach their desired Almen value and coverage.
Bogies are the rolling stock assemblies that incorporate the train wheels, suspension, brakes and, in powered units, the traction motors. Once stripped of their component parts, with wheelsets and other items processed separately, shotblasting the bare chassis readies it for inspection, NDT and painting or coating, followed by reassembly.
A blasting booth with one or more operators controlling open-circuit airblast nozzles is the typical way to process small numbers of bogies but, where larger volumes are involved, a robotised solution offers the highest capacity.
Within an air-tight cabin, a robot arm directs an airblast nozzle that fires media like steel or corundum to blast away accumulated rust, dirt and old paint. Bogies are carried on trolleys which can simply be pushed through the loading door into position, while a 2m-deep pit collects used media that is automatically recycled for re-use.
Blast a fishplate or a whole carriage
Some rail components don’t fit neatly into a certain blasting category. Smaller cast parts are best processed using fixed airblast cabinets while others may require blasting in situ outside the usual facility.
The latter case requires mobile blasting, with portable pressure-fed, closed-circuit airblast kits offering extreme flexibility plus much higher productivity over conventional power tools. Powerful, easy to use, compact and manoeuvrable, these machines’ recovery systems continuously reclaim dust and debris while recycling reusable abrasive back to the gun, removing dust or disposal problems.
At the other end of the scale, closed-circuit machines are also perfect for refurbishing very large assemblies like carriages either off-site or within a custom-built booth where multiple operators stand on access platforms and operate the blast nozzles manually.
Wheelabrator also builds large pass-through wheelblast machines for whole carriages. These airblast rooms can be made to any size, feature honeycomb floors for abrasive recycling, and cut cycle times by half or more compared to manually directed airblast.
Get ready for rail business
As well as providing an alternative to congested roads, low-emission railways are essential to meet global sustainability objectives. Train passengers will soon return in their millions as Covid recedes.
With more railway miles and with wear and maintenance on the way, rail’s need for surface finishing is set to grow. If you intend to serve this market or improve your offering to clients, highly automated, efficient blasting is the best route to profit.
Wheelabrator Group SAS (Charleville)
24 Rue Camille Didier, 08000, France
Tel. +33.3.24 33 63 00
Fax +33.3.24 33 63 27