bimetallelement

A bimetal element is a structural component made from two different metals bonded together, each with a distinct coefficient of thermal expansion. When the temperature changes, the metals expand by different amounts, causing the element to bend, curl, or snap. The bending direction and degree depend on which metal has the higher expansion and on the thickness and geometry of the composite. Bimetal elements are commonly formed as strips or discs and are often designed so that bending occurs within a specified temperature range.

Materials typically used include pairs such as steel with brass, steel with copper, or nickel-based alloys. The steel layer usually provides mechanical strength and a lower expansion, while the other metal provides a higher expansion. The bond between the layers is achieved through lamination, soldering or brazing, diffusion bonding, or adhesive bonding, producing a single, continuous piece.

Performance characteristics of bimetal elements include a relatively simple, robust response, low cost, and no need for external power. However, their response is nonlinear and may exhibit hysteresis and aging due to metal creep and changes at the bonded interface. Designers optimize thickness, geometry, and surface area to tailor the operating temperature range, response time, and mechanical load capacity.

Applications are widespread in passive thermal devices such as thermostats, thermal switches, and over-temperature protection elements in household appliances, automotive components, and industrial equipment. In these uses, the bending action provides contact actuation or direct mechanical switching without electronics or external power.