Bimetals and clad alloys consist of two or more different alloy layers that are integrally bonded together; usually into a metal plate, strip, sheet, or other stock shape.

Bimetals

Bimetals consist of two metal layers with different coefficients of thermal expansion (CTE). They are different from alloys in that they are not a mixture of two metals but are separate layers joined together. They bend or deflect due to the CTE differences between the layers.

Defining Selection Properties

The major difference between bimetals lies in the internal resistance of each given type. Under an electrical load, each type of bimetal will exhibit a different internal resistance; a bimetal’s resistivity. The higher the resistivity, the more heat will be generated by the effects of the current passing through. The more heat generated, the quicker the bimetal will deflect or bend.

The amount of deflection or bending a bimetal exhibits is its flexivity. This is another property dependent on the materials used that is important for determining how the bimetal responds to the self-heating process.

Clad Alloys

Clad alloys and metals are metals that use a thinly bonded layer or layers of dissimilar metals over top of less expensive or less durable base metals to create a stronger, more attractive or otherwise more durable and desirable surface.

In many cases, clad metals are a better option than electroplated or galvanized metals, because the capability exists to clad more types of metals than can be electroplated or galvanized. Further, the cladding process used to create clad metal is more durable and lasting than a plating or galvanizing process.

Types of Cladding Processes

The two most prominent cladding processes are inlay cladding and overlay cladding.

  • Inlay cladding is a highly complex and useful cladding process that bonds dissimilar metals together only where they need to be joined. It allows for the placement and use of a precious metal’s properties exactly where you need them.
  • Overlay cladding is used to bond materials together using no adhesives, filler materials, or welds. It is attained through the application of extreme pressure and, in some cases, heat. The process can produce what are normally called single clad (two layers), double clad (three layers), and in some particular instances as many as seven layers. Overlay clads can be custom made to meet specific industrial requirements.

 

Using Bimetals and Clad Alloys

Most bimetals are used in temperature indicating, thermostat, and thermal actuator applications. Many circuit breakers are equipped with bimetal actuators that detect heating from overload conditions and mechanically trip the circuit-protection device. Cladding has a wide range of industrial applications, including use in creating bearing and seal surfaces, pump components, drive train parts, turbine blades, extruders, forging dies, rolls, and tanks.

References

YouTube Video – Heat Bimetallic Bi Metallic Strip

Lusk Metals – Basic Metallurgical Concepts