a bimetallic strip is made of two metals that have difference cofficients of wt
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A bimetallic strip is made of two metals that have difference cofficients of linear expansivity.
A bi-metallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper. The strips are joined together throughout their length by rivets, by brazing or by welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its normal temperature. The metal with the higher expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.
The sideways displacement of the strip is much larger than the small lengthways expansion in either of the two metals. This effect is used in a range of mechanical and electrical devices. In some applications the bi-metal strip is used in the flat form. In others, it is wrapped into a coil for compactness. The greater length of the coiled version gives improved sensitivity.
The bimetallic strip was probably invented by the eighteenth century clockmaker John Harrison for his third marine timekeeper (H3) to compensate for temperature-induced changes in the balance spring. It should not be confused with his bimetallic mechanism for correcting for thermal expansion in the gridiron pendulum. His earliest examples had two individual metal strips joined by rivets but he also invented the later technique of directly fusing molten brass onto a steel substrate. A strip of this type was fitted to his last timekeeper, H5. His invention is recognized in the memorial to him in Westminster Abbey, England. Other sources trace the bi-metallic strip back to invention by British engineer Eric Taylor in the 1940s. It was implemented as a method to control Royal Air Force pilot's flying suits and act as a switch to regulate temperature. Later Taylor diversified its use and created the company Otter Controls, dealing in bi-metallic technology.
- Heat engines
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