Definition
"Active" and "passive" bimetallic strips are both types of bimetallic components-metal elements formed by bonding, rolling, or stamping together two metal sheets with different coefficients of thermal expansion. Their primary differences lie in their structure and application.
Structure
An active bimetallic strip typically consists of a thin sheet and a thicker sheet; the thin sheet has a higher coefficient of thermal expansion and actively bends, while the thicker sheet has a lower coefficient and primarily provides structural support. A passive bimetallic strip consists of two sheets of equal thickness, with one having a higher coefficient of thermal expansion than the other; upon temperature change, the strip undergoes bending deformation to achieve the desired effect.
Materials
Material selection differs for active and passive bimetallic strips. Generally, the active strip requires a material with a high coefficient of thermal expansion, such as aluminum, copper, or nickel; the passive strip requires a material with a low coefficient of thermal expansion, such as stainless steel, iron, or chromium alloys.
Working Principle
During temperature fluctuations, the thin sheet of the active bimetallic strip bends due to its higher coefficient of thermal expansion. Similarly, the passive bimetallic strip undergoes bending deformation due to the difference in thermal expansion coefficients between its two layers. This bending deformation is utilized in various applications-such as thermometers, temperature compensators, and thermocouples-for measurement, control, and compensation purposes.
Applications
Active and passive bimetallic strips are widely used in industry. Active strips are typically found in electronic components like temperature sensors, constant current sources, and thermistors, where they detect temperature changes and output corresponding electrical signals. Passive strips are commonly used in industrial automation systems-such as temperature controllers, expansion joints, and temperature compensators-leveraging their spontaneous curvature changes to regulate and control engineering parameters.
In summary, active and passive bimetallic strips differ in terms of structure, materials, working principles, and applications. Understanding these differences allows for the selection of the appropriate bimetallic component for a specific scenario, thereby maximizing performance and meeting requirements for processing, control, and measurement.
