During wintertime, switch point heating systems are utilized for railway switch points. They are aiming to prevent snow and ice from accumulating between the moveable components of a switch point, and thus, maintain a faultless setting of the switch point. Electrical heating rods are a frequently used application of switch point heating systems. Clamps made of spring steel often realize the mounting of the heating rod to the rail. The clamps are set in a common distance of 30 cm along the rail. Considering a section reaching from the middle of one clamp along the rail to the middle of the consecutive clamp, previous investigations showed that significant higher temperatures occur at the heating rod in the middle of this section than at its ends. This suggests that the heat transfer between heating rod and rail is higher at the clamps than in between. Consequently, there is a correlation between the contact force of heating rod and rail, and the heat transfer.
Another assumption is that the presence of mechanical and thermal load can reduce the contact force provided by the clamps over time. In order to evaluate these correlations, new clamps were mechanically loaded by bending and additionally heated to 150 °C or 200 °C. The results show that considering a stress time up to 2000 h the thermal load for itself has no significant influence on the clamping force. The mechanical load, however, can decrease the clamping force by 7 % and the combination of mechanical and thermal load can decrease it by 13 %. This article explains the experimental setup for this investigation and the causes that lead to the reduction of the clamping force.

switch point heating; heating rod mounting; clamping force; thermal and mechnical load