Choosing the right metal alloy
Metal bellows are available in a variety of materials—with brass, bronze, beryllium copper, Monel and stainless steels. Each has its own advantages depending on the application.
Here is an overview of which material to use and when:
A traditional and popular bellows material with a low manufacturing cost, brass solders easily even with today’s lead free solders. Suitable for operating temperatures up up to 300ºF (150ºC), brass bellows applications typically involve an air medium. Examples include mechanical altimeters and thermostatic assemblies.
With a slightly higher tensile strength, better corrosion resistance and better electrical conductivity than brass, bronze also offers a low manufacturing cost. Bronze solders as easily as brass, but it can also be brazed for use in high temperature applications. Bronze bellows are often used in high-volume applications, such as appliances and HVAC equipment.
Beryllium copper (BeCu) has a superior tensile strength and electrical conductivity when compared to the other bellows materials. It can be soldered or brazed. Age hardened beryllium copper is often incorporated into a bellows assembly, which can then be heat treated for maximum dimensional stability. Beryllium copper bellows are often favored in applications requiring a small package size and demanding lifecycle requirements. Among these applications are aerospace systems and instrumentation.
A nickel alloy, Monel offers better corrosion resistance than brass, bronze or beryllium copper. Monel is routinely welded, though it can be brazed as well. With similar mechancial performance to bronze, Monel is often used in corrosive environments, such as those containing steam or salt water.
Bellows can be manufactured from a variety of stainless steels, with 300 Series steels the most common. Stainless steel has excellent tensile strength, making it easier to maximize stroke and minimize package size. Stainless steel also have excellent corrosion resistance in multiple environments and media. Typically brazed or welded, stainless steel bellows withstand high operating temperatures. Stainless steel bellows applications include electrical interrupters, power transmission systems and industrial controls.
Nickel is a hard material with excellent corrosion resistance. Electrodeposited bellows are made from nickel, but the material is also useful as a corrosion resistant plating for other types of bellows. Nickel is very widely used in aerospace applications.