Function and Safety of the Turnout Spring Setting Device in Finland

In the turnouts, the present-day point machines are very complex and also expensive technical solutions. Therefore, a need has arisen to look for more cost-effective solutions with which at least part of the point machines of a single switch could be replaced. In this article, one such solution which is discussed, is a fully mechanical spring-actuated setting device. These kinds of setting devices have been used in the Finnish rail network since 1991 and, nowadays, there are over 1500 devices on track. The device is simple and effective, yet, at the same time, it has been suspected to contain properties that increase vibration, which can result in the opening of switch blades and derailment. To investigate this issue, this article presents the basic operating principle of the spring setting device currently used in Finland, and the mathematical and experimental force curve generated by the device. In addition to the force curve, this article also presents the dynamic vibration properties of the device which, if correctly adjusted, do not add to the vibration elsewhere in the turnout structure, thus allowing the switch blades to be held securely in place. In the inspections of the devices, however, it has been noted that there are a lot of spring setting devices with misalignments in the Finnish rail network. This has a drastic impact on the forces holding the switch blades in place. This article also presents a spring setting device piloted in Finland which is more versatile, when it comes to its adjustment properties, than the device that is currently in use.