简单的说就是在螺栓加热棒内部放置一个双金属片，应为双金属片的两面用的是不同的材料，受热膨胀系数不同，利用这点就可以在达到你所设定的温度自动断开了，优势结构简单、低成本、操作可靠性相对较高。缺点是不管什么材料双金属，都有一个老化期，所以我建议大家在用2年就可以换一个了。

Simply put a double sheet metal bolt in the heating rod inside, should be on both sides of the double metal sheet with different materials, thermal expansion coefficient is different, the use of which can be reached in your set temperature automatically disconnected, the advantages of simple structure, low cost, operation reliability is relatively high. The disadvantage is that no matter what material bimetallic, there is an aging period, so I suggest that you can change one in 2 years.