How does a bimetal work?
Solid bodies expand when heated - who doesn't know photos of bent railroad tracks and crashed wagons. This effect is cleverly exploited with a bimetal.
Two metals in close connection - the bimetal
- In fact, the name says it all with the bimetal: It is created by joining (screwing, soldering, gluing, etc.) two metals such as iron and brass. Most bimetals are elongated strips.
- If you heat such a strip, the two metals expand. But: The linear expansion when the temperature rises is not the same. For example, brass expands more than iron. Physically speaking, brass has a higher coefficient of linear expansion.
- So it happens that the bimetal strip bends, because the brass simply needs more space than the iron part.
Gimmick or a phenomenon suitable for everyday use?
- At first glance, one could actually mistake such a crooked stripe for some kind of academic gimmick - just a nice demonstration. Nevertheless, the small strip has found countless applications in everyday life.
- The more crooked, the warmer: bimetal strips, provided with a suitable display and calibrated scale, are suitable as thermometers. If the thermometer is transparent, you can see the strip as a winding in the middle.
- No iron without a thermostat: Once the desired temperature has been reached, the curved bimetal strip in the thermostat switches off the heating (read: the power supply). The strip serves as a switch here.
- On the safe side with bimetals: Many other safety aspects that depend on the temperature can also be easily dealt with with a bimetallic strip. These include valves, fuse boxes or coffee machines, toasters or Kettles that switch off automatically after reaching a certain temperature.
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