Description

Bimetallic Strip

A bimetallic strip is a clever and simple device that utilizes the principle of thermal expansion for various purposes. Here’s a breakdown of its construction, function, and applications:

Construction:

• Made of two thin strips of different metals bonded together along their entire length, typically by welding, riveting, or brazing.
• Common metal pairings include:
  • Steel and brass
  • Steel and copper
  • Invar (low expansion alloy) and steel

Function:

• Each metal in the bimetallic strip has a different coefficient of thermal expansion. This means that when heated, one metal expands at a greater rate than the other.
• As a result, the bimetallic strip bends in the direction of the metal with the lower coefficient of thermal expansion.
• The greater the temperature change, the more pronounced the bend will be.

Applications:

The simple yet effective design of the bimetallic strip makes it a valuable component in various applications:

• Thermostats: A classic application. As the temperature rises, the bimetallic strip bends, triggering an electrical switch that controls heating or cooling systems.
• Circuit Breakers: Bimetallic strips can be used to interrupt excessive electrical current. Heat generated by the current causes the strip to bend, tripping the breaker and protecting the circuit.
• Temperature Gauges: The bending of the bimetallic strip can be linked to a pointer or dial, providing a visual indication of temperature changes.
• Safety Valves: In some devices, bimetallic strips can trigger the release of pressure or gas if temperatures exceed safe limits.
• Flashers: In older turn signal systems, a heated bimetallic strip caused a blinking effect for turn signals.