We are independent & ad-supported. We may earn a commission for purchases made through our links.

Advertiser Disclosure

Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.

How We Make Money

We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently from our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Bimetallic Strip?

By Paul Scott
Updated May 17, 2024
Our promise to you
AboutMechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At AboutMechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A bimetallic strip is a simple device which converts thermal energy into mechanical motion. It is used as a thermally activated switch or heat indicator and works on the principle of differential expansion of heated dissimilar metals. The bimetallic strip is made up of two different metals which are bonded together to form a straight, flat strip or a concentric coil. When the strip is heated, one of the metals heats up and expands faster than the other, causing the strip to bend. This mechanical deflection is then harnessed in various ways to switch electrical circuits or move a dial to a give heat value indication.

When any solid, fluid, or gas is heated, its molecules start to move away from each other leading to expansion. As long as a heated material is not contained at some point, it will expand in a balanced fashion. If, for some reason, the material is contained or prevented from expanding along one of its surfaces, the unrestrained expansion in the rest of the material will cause it to deflect or bend. Obviously some materials will heat up quicker or expand more than others depending on their molecular structure. If two such dissimilar materials bond together, the one that heats slower will restrict expansion along one face of the other and cause this deflection phenomenon to occur.

This principle of thermal deflection of dissimilar materials is utilized to supply heat-related mechanical motion in a wide range of electrical and measurement equipment. Bimetallic strips are generally constructed of two dissimilar metals with brass and steel and copper and steel being typical combinations. The two materials are typically welded, brazed, or riveted together to produce an even, secure union between the two contact faces. Bimetallic strips may be formed as straight or concentric coil spring type elements. Their physical deflection when heated is then harnessed in a variety of ways to achieve different functions.

One of the most common methods of utilizing the deflection of a bimetallic strip is employing the strip as an electrical contact to make or break circuits. Heater thermostats are a good example of this type of application and use the straight, unheated strip to maintain contact with a switch point and keep the heater circuit active. When the temperature rises to a predetermined point, the strip heats and bends, thereby breaking the circuit and switching the heater off. When the strip cools down again, it straightens and reactivates the heater circuit. This allows a constant temperature range to be maintained.

The coil type bimetallic strip tends to unwind as it heats and turns the needle of a dial type thermometer to indicate a temperature value. Bimetallic strips are also used as thermal overload devices to cut the power supply to electrical equipment when they draw excessive current or physically overheat. The known expansion characteristics of the different metals in the bimetallic strip allows for very accurate tailoring of these devices to operate at exact temperatures. This makes the strips a reliable and affordable method of using heat as a control or measurement input.

AboutMechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.

Discussion Comments

AboutMechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

AboutMechanics, in your inbox

Our latest articles, guides, and more, delivered daily.