Investigations on the Heat Transfer between an Electrical Heating Rod and a Rail for Heated Railway Switch Points

Electrical heating rods are a commonly used application for switch point heating in order to keep switch points free from ice and snow. Clamps made of spring steel usually attach the heating rod to the rail. They are localized at certain positions at a distance from each other. Thermal images showed significant temperature differences on the surface of the heating rod depending on the longitudinal position. That might be an indicator of a varying heat transfer due to a changing joint force applied by the clamps. In order to investigate the correlation between the joint force and the heat transfer between the heating rod and rail, the clamping force of newly manufactured heating rod clamps was measured initially. Therefore, a modified tensile test was used. Applied thermal and mechanical loads over a period of 4000 h could reduce the clamping force by 13%. Finally, the correlation between the heat transfer resistance, the joint force and the surface condition was experimentally determined with a heating test setup. Considering only the clamp area, the specific thermal contact resistance will not change due to a change in the joint force. However, surface preconditioning, such as milling or an application of a thermal-conducting paste, is capable of significantly reducing the thermal contact resistance.