Tram and Commuter Train Track Maintenance

1)

Why do tracks in cities and populated areas have to be serviced and maintained?

a)

Reduction of noise emissions: Rail wear, damaged crossings, potholes, kicking, corrugation of the railhead surface etc. result in a substantial increase in noise emissions to the environment. Residents have become sensitized and want quieter rail vehicles.

b)

Economy: Tracks in cities are installed principally in streets. The costs for replacing track complexes when they have become worn exceed the costs for replacing railway tracks of Vignole rails that have their own separate roadbed many times over. Repairing the wear and damages of such complexes by welding is therefore a more cost-effective option, and the installation life of the track complex is lengthened.

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2)

What are the most frequent occurrences of wear or damages, and how can they be repaired?

2.1)

Inside running edge wear in curves

The most frequent work on tracks is the buildup welding of the worn inside running edge of curve rails. As a result of the high lateral acceleration, which is due to the fact that tram rails usually have no camber, strong wear will occur. The wear can occur not only to the inside running edge, as well on the guide rail. An inside running edge wear of from 12 to 15 mm is normally admissible. Once the wear exceeds this value, the rail has to be rebuilt by welding. In the case of long track sections the use of an automatic welding machine is the most effective way to perform the welding work.

2.2)

Reduction of vertical wear by means of railhead surfacing

With this 2-groove welding technology 2 grooves are ground into the railhead, filled out with a hard electrode (450 HB, approx. 1,600 N/mm2) and surface-ground. The same weld can also be made with a somewhat wider groove at the middle of the railhead.

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The purposes of both welds are: a)

To reduce the higher wear on the railhead in particular over acceleration and deceleration sections, at stops or before signals.

b)

To significantly retard corrugation.

These welding procedures are carried out with a welding machine using the open-arc method.

2.3)

Reduction of inside running edge wear by running edge groove welding

This weld is made on new rails prior to installation and bending. As shown in the figure above a groove is ground into the running edge, built up with a special welding wire containing manganese and surface-ground.

Autech AG CH-5102 Rupperswil

2.4)

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Tape welding

Narrow track bends that have a tendency to screech can be clad-welded with a chrome tape electrode. The chrome band itself serves as the electrode and is welded to the rail with the submerged-arc method. As demonstrated by the experience in the city of Zurich the curve screeching can be reduced by 80%.

2.5)

General remarks relating to the weldability of rails:

Normally, the welding work has to be performed while the line is in service or at night during the “no traffic” periods. Pre-heating is scarcely possible because the rails are embedded in the pavement. Rails with a tensile strength of 700 N/mm2 (approx. 210 HB) can be welded unproblematically. It is also possible to welded them numerous times and without preheating. The welding of rails with a strength of 900 N/mm2 (approx. 250 HB) is problematic due to the high carbon content. The rail has to be preheated, and there is a great risk of stress cracking.

Autech AG CH-5102 Rupperswil

3)

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Removal of short-pitch corrugations and small waves on the rail head by grinding:

Today, the formation of corrugations is experienced by all rail vehicle operators. Since there are various theories on the occurrence mechanism, no further deliberations on this subject will be made here. In any case, corrugations cause strongly audible vehicle traveling noises and strongly perceivable vibrations, which cause damage to the roadbed and to the vehicles.

The only sensible way to remove corrugations is by grinding the rail surface. It is even extremely effective to prevent the corrugations from exceeding a size of max. 0.2 – 0.3 mm by periodic grinding. The AT 1002 corrugation grinding machine and the AT VM 8000 2-way rail grinding machines are excellently suited for such grinding work.

Autech AG CH-5102 Rupperswil

4)

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General welding and grinding work:

As before, all the following maintenance work is done by the electrical manual welding method. In addition to the standard manual grinding machines, for the pre-welding grinding, the surface grinding and the reprofiling the highly versatile AT 2095 mechanical grinding machine is used.

4.1)

Welding and reworking of crossings

This picture shows a worn crossing prior to welding.

This picture shows how the wing rail and the crossing itself are welded.

Autech AG CH-5102 Rupperswil

4.2)

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Welding and grinding of groove floors of flat groove crossings

If the crossing angle of two rails exceeds a certain value, the wheel has to be forcefully lifted off the rail and must run over the crossing point on the wheel flange.

These flat grooves have to be surfaced regularly and, in particular when the wear has become excessive, the grooves have to be built up again by welding and ground plane.

Autech AG CH-5102 Rupperswil

4.3)

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Welding of potholes, kicking

Unevennesses on the rail caused by spinning or braking spots produce a much more audible impact.

Repair of a pothole by grinding out and buildup welding.

Autech AG CH-5102 Rupperswil

4.4)

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A few frequently used repair-welding methods are shown in the following pictures:

Welding of rail breakages

Scalloped rail welding

Welding of switch tongues

Welding of tongue tips

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Welding of a tongue guard

5)

Machines and equipment

Autech AG is able to supply individual machines or complete vehicles with all the necessary machines, which are capable of performing the maintenance work.

5.1)

Automatic welding equipment truck

A truck with a total weight of min. 12 tones equipped with a lifting platform serves as the base vehicle. The equipment consists mainly of the following parts: • • • • • • • • •

70 kVA power generator AT 4006 SE welding machine with inverter AT1002 K60 corrugation grinding machine AT 4019 mechanical grinding machine 1 electrical manual welder (Kempi, Lincoln...) Electrical cable roll for welding cable Compressor All cables and lighting equipment Small tools, angle grinders, flexible hand grinding shaft...

Autech AG CH-5102 Rupperswil

5.2)

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Manual welding equipment truck

A truck with a total weight of min. 3 – 5 tones serves as the base vehicle. The equipment consists mainly of the following parts: • • • • • •

5.2)

45 kVA power generator AT 4019 mechanical grinding machine (possibly on trailer) 2 electrical manual welders (Kempi, Lincoln...) 2 welding screens All cables and lighting equipment Small tools, angle grinders, flexible hand grinding shaft...

Various corrugation grinding machines • • •

AT 1002 K60 electrical corrugation grinding machine (cf. picture on page 5) AT VM 7000 BS 2-way rail grinding vehicle (cf. picture on page 5) Grinding units for CEMAFER/GEISMAR rail carrier vehicles

Autech AG reserves the right to alter specifications without notice. Edition: November 10 P:\PROSPEKT\Allgemein\Schienenunterhalt\Trackmaintenance.DOC