Spatial Prediction of a Pre-curved Bimetallic Strip Under Combined Loading

Abstract

This work establishes a way of calculating the free end point position, of a pre-curved bimetallic strip, that is subjected to uniform heating. The prediction of the endpoint of a bimetallic strip is required during the design phase of an electronic control circuit sensor switch that uses a sensing/activating unit containing a bimetallic strip. Bimetallic sensors are normally flat at ambient temperature and at the required sensing temperature the strip bends into a radius of curvature, this then displaces the contact on the end of the strip to make or break an electrical circuit. Although the normal, flat type of bimetallic sensor exists, this work concentrates on a pre-curved bimetallic sensor at ambient temperature. A curved bimetallic strip sensor provides a much larger sensing range and displacement at the free end of the strip, per degree of temperature change, than for a straight bimetallic strip. The greater sensing range is due to the arc length of the bimetallic strip being longer which affords a greater flexibility at the activation point when compared to the chord length of an equivalent straight bimetallic strip. Pre-curved bimetallic test samples were subjected to heating whilst the motion of the free end point of the strip was recorded on a metal plate. As the heat applied to the samples was increased, many temperature points were recorded to generate approximate loci of points. The loci of test points compared well to theoretical curve generated by the derived formulae. Therefore the advantages of this work offers a less critical sensing range, it also benefits from a mechanism which can be designed to be much smaller and take less space in the product compared to a comparable flat bimetallic strips sensor.