Metal Bellows FAQs

What is a bellows?

A metal bellows is a flexible, lightweight, spring-like component with ribbed or corrugated tubing which gives it an accordion-like quality. Metal bellows are precision components designed to perform a variety of functions in various machine components and assemblies.

What is a bellows function?

Metal bellows convert pressure, mechanical, vacuum, and temperature changes into linear or rotational motion. They can also be used in flexible electronic contact applications. Bellows provide a specifically defined dynamic response as part of a larger machine component or assembly often providing a more precise, more reliable, or less costly alternative to an existing engineering solution.

How are bellows made?

Our metal bellows are produced one of three ways; electrodepositing, hydroforming, or edge-welding technology. More information on each of these three processes and a breakdown of specifics between these three processes, including which process is preferred for which application, can be found in our Metal Bellows Comparison Guide.

What materials are recommended for metal bellows?

Nickel, Copper, Silver, and Gold. Materials used are generally the types of metals that can be formed through electroplating.

How long do bellows last?

Bellows can be designed to have an infinite cycle life. Our design engineers will design custom metal bellows to meet your application specification and will work with you to optimize performance.

What is a bellows maximum pressure allowance?

This depends on the process used. Electroformed bellows can accommodate up to 3000 PSI. Other methods (hydroforming and edge-welding will have different results). The specific application requirements will help us calculate the actual maximum pressure. More information on each process including maximum pressure can be found in our Metal Bellows Comparison Guide.

What are recommended joining methods for bellows assemblies?

Besides soldering, our bellows can be welded and various adhesives including epoxies onto mating components.

What end types are required for welding bellows to a hub?

The preferred method of welding bellows is with an electron beam welder. Since this method does not use filler material, it is important that there is no gap between the bellows and hub at the weld joint. Ends such as Type A, D, or I will result in bad, incomplete, porous welds since it is difficult to eliminate gaps between the bellows and hub and there is limited material available for fusion. An end such as Type E will provide a good weld joint because the flange can be pressed against the hub, eliminating any gap, and the beam can be focused perpendicular to the axis of the bellows ensuring that there is plenty of material from the bellows and hub that can be fused together.

What can be done to protect metal bellows from corrosion or make it biocompatible?

Depending on the application and media the bellows or electroform will be exposed to, it can be plated with a thin layer of gold or coated with parylene. Gold adds protection against corrosion in all types of climates and environments and is also an excellent conductor of electricity. Parylene is a polymer coating that provides moisture, chemical, and dielectric barrier properties, as well as dry-film lubricity. Both gold and parylene are biocompatible.

What is reverse bending?

From the free length, the bellows may be operated in compression and anywhere therein to max compression and up back to the free length, OR, from the free length, the bellows may be operated in extension and anywhere therein up to max extension and back to the free length. Reverse bending is when the bellows is operated in compression and is moved through the free length into the extension and vice versa. Reverse bending will reduce the cycle life of the bellows.

What metals can be used to make edge-welded bellows?

Any metal that can be easily formed, blanked, and welded. The common materials used at MW are:

• Stainless Metals: 304L, 316L, 321, 347, AM350
• Nickel Metals: Inconel 600, Inconel 625, Inconel 718, Inconel X750, Hastelloy C276, Haynes 242
• Titanium Grade 5

How many cycles can an edge-welded bellows endure?

This all depends on the customer’s design criteria. Axial stroke, lateral and angular offsets, pressures, media, temperature, cycle rate, and environment are just some of the variables that affect cycle life, so it is important to know all of these variables before predicting cycle life.

A bellows made from 304L, 316L, 321, 347, or titanium, with vacuum on the inside of the bellows, will typically be designed for cycle life less than 1,000,000.

A bellows made from AM350, Inconel 600, Inconel 625, Inconel 718, Inconel X750, Hastelloy C276, or Haynes 242, with vacuum on the inside of the bellows, will typically be designed for greater than 1,000,000 cycles.

How can I get the bellows force for a given deflection to be lower?

Here are three ways to reduce force. First, the easiest way is to reduce the bellows material thickness but depending on bellows performance requirements it may reduce the cycle life. The second, is to make the bellows longer by adding convolutions. The more convolutions a bellows has the lower the force will be if axial stroke length is unchanged. Third, is by changing the bellows material. The stainless steel we use all have a similar force but Titanium bellows will have about half the force of an AM350 or 316L stainless steel bellows.