Turntables have existed since the 1830s, but nowadays they must adapt to brand-new requirements, which we will address in this article. We will also try to answer the question of how to transform them without generating exorbitant costs, while minimizing shutdown times?
A railway turntable (or wheelhouse) is a system allowing rotation of railway equipment, generally locomotives, that are limited to rectilinear motion. Turntables are mainly found in a depot or a terminal.
When a railway module is reoriented to the desired entrance of the building, it can then proceed smoothly to its destination to receive mechanical maintenance. A turntable is also used to pivot a railway module 180° so that it can then leave in the opposite direction.
Facilities operating on a budget or with reduced space often take advantage of this equipment, which avoids the need to build a turning star. Although most of the diesel locomotives can operate in both directions, they are treated as “front ends” and “rear ends” and still need to be turned.
Moreover, turntables are very useful to pivot the observation cars of “tourist” trains, so that their glazed lounge faces the rear of the train to offer a better view.
Operation
A turntable typically includes a circular pit in which a steel deck turns. The deck generally is supported and balanced by a central pivot. A steel rail often is installed around the floor of the pit and supports the ends of the deck when a locomotive enters and leaves it. The turntables have a locking mechanism that aligns the deck rails with the exit track. The deck can be rotated manually (“Armstrong” platen [1] [2]), or by an external power source, or by the locomotive’s braking system.
The challenge: a new era of equipment to support
The new generations of locomotives are increasingly heavy, which requires turntables that are capable of supporting their substantial weight. Serious work to adapt non-modernized equipment is necessary.
Faced with this challenge, when replacing an existing turntable, the organizations, in principle, must dig deeper foundations to comply with the table height standards based on the loads imposed by the locomotive, which represents 40% to 60% of the total cost of the replacement work. In addition to the transformation/adaptation expenses, you must add the costs associated with the operational shutdown period, which necessitates the use of a crane for handling the locomotives in the interim. These costs may be high. Regardless of whether the fleet belongs to a railway service company or another type of organization, such as a mining company, these additional costs generally are quite unwelcome.
Any turntable must meet the standard of the AREMA Manual for Railway Engineering [3]. This standard specifies the requirements for loading cases, strength limits, design and manufacturing requirements, quality criteria and more.
An innovative solution
During replacement of a deck built several years ago, the height of the beams must be raised, in principle, so that it can meet the new loads imposed by recent locomotives. The height of the deck beams is fixed according to the load of the heaviest locomotive.
To avoid digging into the existing foundation to allow installation of a bridge with higher beams, which is costly and takes a long time, asset integrity and reliability management (AIRM) specialists propose a new approach.
These specialists are accustomed to modifying different kinds of existing equipment to adapt it to new requirements, in contexts that may even have an impact on public safety. To do this, they first use stronger materials, either by better chemical composition or that have received special treatments. For example, high-performance steel with superior shock resistance and steel with an increased elastic limit both weld and bend as easily as the usual materials.
Moreover, the AIRM experts resort to specialized global structural analysis software to define beams that vary in their web and geometry, instead of using standard rolled steel products. This is also innovative.
They also use local analysis software to determine the stress concentrations in the assemblies and eliminate incipient fatigue cracks.
They recommend production of a lattice beam made with bent and rounded plates, instead of a standard rolled steel beam, to install it at the ends of the turntable, as in the case of bridge cranes used for industrial lifting.
Finally, they also suggest installing the wheels outside the lattice, contrary to the usual practice of integrating wheels into the beams.
Remember that the purpose of all of the above-mentioned improvements is to retain the height of the existing cross beams and avoid digging deeper foundations, while allowing the passage of heavier new locomotives. This method also has the advantage of reducing the work time and allowing a resumption of operations after only a week. The facilities then are modernized for the next 50 years.
Conclusion
It is sometimes useful to take a step back to rethink the ways things are done, relying on a team composed of diversified expertise, capable of proposing better innovative solutions. Organizations are increasingly aware of the significant gains of refurbishing existing facilities (“brown is the new green™”) by recovering certain parts instead of starting over from scratch. Many engineers increasingly specialize in designs with the constraints of the existing environment, because this is also part of a corporate social responsibility (CSR) movement.
References :
- MMcGuirk, Marty (2002). Model Railroader’s Guide to Locomotive Servicing Terminals (1st ed.). Waukesha, WI: Kalmbach Books. p. 41. ISBN 0-89024-414-6– via Google Books. A lever was installed at the two ends of the deck and the table was deposited by hand, a method commonly known as the “Armstrong” method.
- “Turntable platen” American-Rails.com. Recovered January 31, 2021.
- AREMA, Manual for Railway Engineering, Volume 2, Chapter 15, Part 8 – Miscellaneous.
- https://en.wikipedia.org/wiki/Railway_turntable
Patrice Pagé holds a university degree in mechanical engineering, a DEC in civil engineering technology and has completed a series of university studies in structure. He possesses extensive practical experience in the manufacturing, industrial and equipment sectors. He has also taught at the college level in the metallurgy department.
With Norda Stelo, he is involved in the integration and life extension of equipment: process, mechanical, lifting, as well as building and equipment structures.