INFICON Product Engineer wins RUAG Innovation Award

INFICON uses tungsten springs as sensor elements for its vacuum sensors to measure the vacuum pressure. These springs are currently purchased from an external manufacturer. They consist of tungsten that is wound around a molybdenum core and then cut to the desired length. After that, the core is removed by etching with aqua regia. This dependency on an external supplier, as well as the dangerous and environmentally harmful etching process, are to be avoided. In addition, the aqua regia gradually attacks the tungsten, which impairs the quality of the springs. The use of aqua regia and the duration of the etching process also make automation difficult, both technically and economically.

The aim of this work is therefore to produce tungsten springs in an environmentally friendly way and in-house. For this purpose, a tungsten wire with a diameter of 10 µm was used to produce a spring with a diameter of 150 µm and a pitch of 50 µm and a length of 2 cm. To ensure the dimensional stability of the spring, it must be heated. First, a suitable core material was determined that would allow for easy separation of the spring from the core and at the same time be suitable for heating the spring. Various materials were tested in a trial setup, with a polymer-coated glass fibre proving to be the best solution. To stabilise the shape of the spring and prevent oxidation, a special box was constructed that is continuously flushed with argon. The spring is heated by an electric current applied to both ends. For the mechanical processing of the wire, it is essential that it is always under tension. With precise wire guidance and innovative clamping mechanisms, the wire can be processed and wound automatically. The structure showed that it is possible to produce a spring without the use of chemicals. Furthermore, the pitch and length of the spring can be adjusted as required.