Metal bellows are essential many industrial processes, and making metal bellows is one of the most important manufacturing skills that we have acquired in modern times. The precise parameters of performance for any metal bellows depends on the process of making metal bellows, including how they are formed and how they are welded, as well as what materials they are made from.
Important Considerations in Design
Forming metal bellows correctly requires a number of initial parameters to be defined and considerations to be met.
Understanding Metal Bellows
Metal bellows can be thought of as a combination of both the piston and the spring. When pressure is exerted on metal bellows they respond much like a spring, with a reactive force. Like the pistons in a car engine, this reactive force can be turned into applied force. Force is one of the biggest considerations to be designed for when making metal fellows. What kind of pressures will the bellows be under and from what directions?
Other Things to Bear in Mind
Other important considerations include the environment around the bellows to which they will be regularly exposed. It’s also important to consider stroke rate and the necessary lifecycle for any metal bellows. Metal bellows are typically designed with a specific spring rate in mind, as well as a mean effective area.
Spring Rate And Mean Effective Area
The spring rate is determined by the thickness of the walls, the materials the bellows are made from, and ID of the convolutions. The mean effective area is found by calculating initial and final force with pressure values. Getting these right is key to making metal bellows that will be useful in a particular application.
Types of Bellows And The Bellow Forming Machine
One of the most popular forms of metal bellows are seamless, hydro-formed bellows. This particular type of bellows offers excellent and consistent performance, a tight spring rate tolerance, and readily definable responses to applied pressure. Seamless bellows also make it possible to avoid leak paths and to better calculate internal stresses.
Seam welded bellows are made from metal stock sheets and are the best way to efficiently and economically produce bellows that must have a large diameter. They can also be made longer. This type of bellows is important for processes that require large and inexpensive bellows, but are not good for applications that demand precise spring rates. This type of bellows also restricts material choices, so that brass and bronze are not acceptable materials for making metal bellows of this type.
Edge-welded bellows are first stamped into a ring shape. The diaphragms of these ring shapes are welded along the inside and the outside. This is one of the more expensive methods, but is excellent for producing small bellows with a good lifecycle under strict stroke requirements.
Electroformed bellows are made when nickel is deposited onto aluminum and offers the ability to tightly control wall thickness and build bellows with complicated shapes and unusual diameters. This type of manufacturing process allows for strict control of spring rates and mean effective area.
Materials for Making Bellows
The materials that any bellows are made out of will greatly affect the lifespan of the bellows as well as determine what applications they are suitable for. Here are some of the most common materials for making metal bellows:
This is perhaps the most popular choice because it is easy to solder and cheap. Brass bellows are capable of withstanding operating temperatures as high as 300°F.
Monell is a type of nickel alloy and offers excellent resistance to corrosion. It is particularly useful in situations where the bellows will be exposed to corrosive substances like saltwater.
Stainless steel bellows are strong and make for maximum stroke with minimum package size. Depending on the alloy used, stainless steel bellows can be resistant to corrosion and can operate at high temperatures.
Bronzes only slightly more expensive to use than brass but is more resistant to corrosion and conducts electricity better. With brazing, it can be used for applications in high-temperature environments.
Getting metal bellows right from the design stage to final manufacturing keeps our industries running smoothly.