Current-insulated wheelset bearings
Wheelset bearings in trams must comply with the main-line track requirements. The axle load of trams is lower in comparison, while the curve radii are narrower and the lateral forces due to accelerations higher. The low floor of the vehicles also has a decisive influence on the choice of axlebox bearings. Trams therefore usually have an independent suspension similar to today’s automobiles. In order to meet the mentioned requirements, frequently paired tapered roller bearings can be found in these applications. They have the same axial load capacity, a smaller space than the usual in the mainline track cylindrical roller bearings. In order to avoid current feedback, the wheelset bearings are insulated against current passage unless other measures have been taken.
KRW has been supplying the above-mentioned, current-insulated tapered roller bearings for a long time. Due to the identical outer geometry, these can easily be exchanged for a non-insulated bearing. The axial internal clearance is adjusted with the help of intermediate rings, which have already been delivered finished from the factory. Despite this measure, the assembly in the workshops of the tram operators was often not without complications. In the case each three rings (two outer rings and the intermediate ring) had to be mounted separately. Tilting during thermal joining to damage to the insulation layer were the result. In close cooperation with the customer, KRW then further developed the bearing unit without affecting its interchangeability. With a continuous, insulated outer ring, the assembly is significantly less error-prone and manageable in a single operation.
Figure 1 shows the smaller-scale standard structure of the previous, commercially available solution.
Figure 2 shows the optimized structure of the new bearing.
Wheelset bearing – standard customary structure
Wheelset bearing – optimized design