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→5.4 Thermostatic Bimetals
The thickness ratios of the components can be selected according to the application requirements. The two outer layers usually have the same thickness.
==<!--5.4 -->Thermostatic Bimetals==
Thermostatic bimetals are composite materials consisting of two or three layers of materials with different coefficients of thermal expansion. They are usually bonded together by cladding. If such a material part is heated either directly through current flow or indirectly through heat conduction or radiation, the different expansion between the active (strong expansion) and passive (low expansion) layer causes bending of the component part.
*'''Stamped and formed parts''' for special designs and applications
The wide variety of thermostatic bimetal types is specified mostly through DIN 1715 and/or applicable ASTM standards <xr id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals"/> <!--(Table 5.23)-->. The different types have varying material compositions for the active and passive side of the materials. The mostly used alloys are iron-nickel and manganese-copper-nickel. Mainly used in circuit protection switches (i.e. circuit breakers) some thermo-bimetals include an intermediate layer of copper or nickel which allows to design parts with a closely controlled electrical resistance.
<figtable id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals">
<caption>'''<!--Table 5.23: -->Partial Selection from the Wide Range of Available Thermo-Bimetals'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
</figtable>
===<!--5.4.1 -->Design Formulas===
For the design and calculation of the most important thermostatic-bimetal parts formulas are given in <xr id="tab:Design Formulas for Thermostatic Bimetal Components"/> <!--Table 5.24-->. The necessary properties can be extracted for the most common materials from <xr id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals"/> <!--Table 5.23-->. The values given are valid only for a temperature range up to approximately 150°C. For higher temperatures data can be obtained from the materials manufacturer.
<figtable id="tab:Design Formulas for Thermostatic Bimetal Components">
<caption>'''<!--Table 5.24: -->Design Formulas for Thermostatic Bimetal Components'''</caption>
{| class="twocolortable" style="font-size:1em;"
|}
===<!--5.4.2 -->Stress Force Limitations===
For all calculations according to the formulas in <xr id="tab:Design Formulas for Thermostatic Bimetal Components"/> <!--Table 5.24 --> one should check if the thermally or mechanically induced stress forces stay below the allowed bending force limit. The following formulas are applicable for calculating the allowable load (Force P<sub>max</sub> or momentum M<sub>max</sub>):
