Wiper arms for train applications have tended to follow the same specification as that used on truck and bus applications, where they are attached to the output shaft by engagement with a tapered spline. This tapered spline is covered by a DIN standard where the specifications used related to both the 12 DIN and 16 DIN shaft sizes.
Arduous applications
The security of this method of attachment is extremely good for road vehicles
but can lead to certain problems in the more arduous and heavier duty applications
in railway environments. These can include such things as 'bird strikes',
impact by 'flying ballast', 'shock waves' caused by trains passing in opposite
directions or entering into a tunnel, and turbulence caused when two cabs
are coupled nose to tail. These conditions can cause the arm to overstress
the interface of the spline joint, resulting in slippage of the wiper arm
relative to the shaft, which causes the arm to wipe outside of the designated
area with the potential of further damaging effects.
There has been a tendency in these cases to rectify the situation by re-positioning the wiper arm and re-tightening its retaining nut on the shaft. However, this does not always resolve the problem because the shaft splines have now reamed the bore of the wiper arm head, filling the valleys with swarf and reducing the integrity of the joint. The tendency here is to over-tighten the nut, which often leads to torsional failure of the threaded stud at the end of the shaft - so the problem gets worse rather than better.
Changed shaft design
In recent years, the above problems have been partially overcome by Matador
changing the shaft design such that it no longer has a threaded stud at the
end. This feature has been replaced by a high-tensile bolt, which is screwed
into the tapped end of the shaft. Hence, if the bolt shears, it s invariably
possible to remove the shank of the bolt without removing the shaft from the
installation.
Matador reports that it has now moved further forward with design innovation by introducing a new range of wiper arms that are fitted to a square-ended shaft instead of a tapered spline. This ensures not only that the wiper arm is fitted in the correct park position "right first time", it is also retained on the shaft by a pinch bolt that engages in a groove around the square, thus providing a secondary locking mechanism to prevent axial disengagement. An additional feature that has been incorporated into the new square drive wiper arms is an anti-lock back device to prevent arm and blade lift-off under turbulent and high-speed operating conditions.
ELECTRIC WINDSHIELD WIPER AND WASHER SYSTEMS
SPECIFICALLY DESIGNED FOR RAILWAY APPLICATIONS.
