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Why can the thermal expansion rates of different metals drive mechanical devices?
In many daily applications, we have witnessed the practical application of the thermal expansion phenomenon. From clocks to temperature control devices, the thermal expansion rates of different metals can drive a variety of mechanical devices, which makes people wonder, what is the principle behind this? This article will explore the history, characteristics and principles of bimetallic strips, as well as their role in various applications.
Basic knowledge of bimetal strips
A bimetal strip is a device composed of two different metal strips that have different coefficients of thermal expansion. When a bimetal strip is heated, the two metals expand at different rates, and this difference causes the strip to bend.
The most common metal combinations for bimetal strips are steel and copper, or steel and brass. The different properties of these various metals cause them to bend to varying degrees when heated, and for mechanical devices, this bending is converted into force or displacement. The most famous inventor of the bimetallic bar was John Harrison, an eighteenth-century clockmaker. His invention allowed clocks to run more accurately, compensating for the effects of temperature changes on the pendulum.
How bimetal strips work
When one end is fixed and the other moves with temperature changes, the difference in expansion of the two metals can cause mechanical displacement. For example, if one end of a bimetallic strip is heated, the expanding metal will push the strip to bend to one side, and in the opposite direction as it cools. These effects are particularly important when designing thermostats and other mechanical devices.
Application scope of bimetallic strips
Clock
The operation of a mechanical clock is very sensitive to temperature changes because the tolerances of each component are very small, causing errors in time calculations. Many clocks use bimetallic bars to compensate for this phenomenon, especially in the rounded edges of the balance wheel. This design can adjust the inertia as the temperature changes and keep the swing period unchanged.
Thermostat
The operation of the thermostat relies on the deformation of a bimetallic strip. The fixed end of the device is connected to the power supply, while the other end has electrical contacts. When the temperature exceeds the set range, the bimetal strip will bend and trigger the switch to regulate the heating and cooling of the system. This is used in homes to control heating or air conditioning systems, effectively maintaining a comfortable living environment.
Thermometer
A common design used in direct-reading thermometers for home use is a bimetallic strip made into a ring. As the temperature changes, the expansion of the bar causes the pointer to rotate, accurately indicating the current temperature. This design is not only accurate, but also easy to use, and is widely used in various types of temperature measurements.
Other applications
In addition to clocks and thermostats, bimetal strips are also used in miniature circuit breakers to protect circuits from overcurrent. When the current is too large, the bimetal strip will bend due to overheating, cutting off the power supply. In addition, the application of bimetal strips in time delay relays and gas furnace safety valves makes the equipment more reliable.
Conclusion
The working principle of bimetal strips is based on the thermal expansion properties of different metals, allowing them to effectively convert temperature changes into mechanical displacement. This technique has been widely used since the 18th century and still has a place in modern technology. As new materials and designs develop, will we be able to discover more innovative application scenarios to enhance this technology?
