A bimetallic strip is used to convert temperature changes to mechanical displacement. This strip consists of two different metal strips that develop at different rates as they are heated, usually steel and copper, or in some cases steel and brass. Strips are combined together along its length with riveting, brazing or welding. A different expansion forces the flat strip to bend one way if heated, and in the opposite direction if cooled below its original temperature. Metals with higher heat expansion coefficients are on the outer side of the curve when the strip is heated and on the inner side when cooled.
The sideways move from the lane is much larger than the small elongation expansion in one of two metals. This effect is used in a variety of mechanical and electrical devices. In some applications, bimetal strips are used in flat form. On the other hand, it is wrapped into coils for compactness. The longer the rolled version provides increased sensitivity.
Video Bimetallic strip
History
The bimetallic first surviving strips were made by the eighteenth-century clockmaker John Harrison who is generally credited with his invention. He made it for his third marine chronometer (H3) in 1759 to compensate for changes caused by temperatures in spring balance. It should not be confused with the bimetallic mechanism to correct the thermal expansion in its gridiron pendulum. The earliest examples have two individual metal strips attached by rivets, but he also invented a technique which then directly melts the molten brass to the steel substrate. This type of dye is suitable for its last timer, H5. Harrison's discovery was recognized in a memorial to him in Westminster Abbey, England.
Maps Bimetallic strip
Apps
Clock
Mechanism clock mechanisms are sensitive to temperature changes that cause errors in keeping time. A bimetallic strip is used to compensate for this in several mechanisms. The most common method is to use a bimetallic construction for a circular wheel circumference. Since the spring that controls the balance becomes weaker with increasing temperature, the balance becomes smaller in diameter to keep the period of oscillation (and hence the punctuality) constant.
Thermostat
In heating and cooling settings, thermostats operating through various temperatures are used. In this case, one end of the bimetal strip is mechanically fixed and attached to the power source, while the other (moving) end carries electrical contact. In adjustable thermostats, other contacts are positioned with a knob or adjusting lever. The position set regulates the regulated temperature, called set point .
Some thermostats use a mercury switch connected to both electrical leads. The entire angle of the mechanism is adjusted to control the set point of the thermostat.
Depending on the application, higher temperatures may open contacts (such as in heating controls) or may close contacts (such as refrigerators or air conditioners).
Electrical contacts may control power directly (as in a household iron) or indirectly, divert electricity through relay or supply of natural gas or fuel oil through electrically operated valves. In some natural gas heaters, power can be provided with thermocouples heated by pilot light (small continuous flame). In a device without pilot lights for ignition (as in most modern gas-clothing dryers and some natural gas heaters and decorative fireplaces) the power for contact is provided by reduced household electrical power that operates the relay controlling the electronic ignitor, either resistance heaters or power generating devices electricity.
Thermometer
A direct call thermometer shows (such as a patio thermometer or meat thermometer) using a bimetallic strip wrapped into a coil. One end of the coil is attached to the housing of the device and the other moves the pointer. A bimetallic strip is also used in a recording thermometer. Breguet thermometer consists of a tri-metallic helix.
Hot engine
Simple toys have been built that show how the principle can be used to power the hot engine.
Electrical devices
Bimetal strips are used in miniature circuit breakers to protect circuits from overcurrent. The wire reels are used to heat the bimetal strips, which deflect and operate the connections that release spring-operated contacts. This interrupts the circuit and can be reset when the bimetal strip has cooled.
Bimetal strips are also used in time-delay relays, flash lights, and the beginning of fluorescent lights. In some devices the current that runs directly through the bimetal strip is sufficient to heat it and operate the contacts directly.
Calculation
Source of the article : Wikipedia
0 Comments