What are the most frequent occurrences of wear or damages, and how can they be repaired?
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, but on the guide rail as well.
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.
Reduction of vertical wear by means of rail head surfacingWith this 2-groove welding technology 2 grooves are ground into the rail head, 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 rail head.
The purpose of both welds are:To reduce the higher wear on the rail head in particular over acceleration and deceleration sections, at stops or before signals.
To significantly retard corrugation.
These welding procedures are carried out with a welding machine using the open-arc method.
Tape welding
Narrow track bends that have a tendency to screech can be clad-welded with a chrome band 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%.
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 vacation 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.
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 RQ 1002 corrugation grinding machine and the RQ VM 7000 2-way rail grinding machine are excellently suited for such grinding work.
