Simply stated, edge welded bellows are manufactured by welding stamped, metal diaphragms into a long, flexible assembly. Strips of metal in sheet form are hydraulically stamped into the shape of the diaphragm. The pressure, stroke length, spring rate and temperature help to determine the thickness and material required to meet the applications’ demands.
The shape of the ripples and inside and outside edges of the diaphragm are crucial to the performance of the bellows assembly. The ripples need consistency between diaphragms to survive high cycles and create accurate spring rates. The inside and outside diameters will be welded later in the process; with properly stamped edges and concentric diaphragms, welds are leak-tight.
Once stamped, diaphragms are inspected for quality and cleaned. The cleaning preparation varies between manufacturers, but the main focus is to ensure that the material is free of any grease or dirt to ensure the welds are strong and leak-tight. The diaphragms need special handling after the process as well to ensure that the natural oils of skin do not come into contact with the diaphragms.
For nested ripple edge welded bellows, the diaphragms are positioned back-to-back (male to female) to pair the inside diameter holes. Once the inside diameters come into contact with each other, they are welded together. The weld shape and penetration are key factors to edge welded bellows design. As shown above, BellowsTech edge welded bellows have deep penetration as well as a match-tip shape to ensure a leak-tight joint that can withstand high cycle applications. Cantilever edge welded bellows are paired opposite to nested ripple bellows, creating a shape similar to a hydroformed bellows. Cantilever bellows cannot compress onto itself with an internal vacuum or external pressure.
Depending on the manufacturer and material, welding can be accomplished through plasma, laser, arc, or electron beam welding equipment. Vision systems can aid the accuracy and consistency of welds. This process is continued in order to make the proper number of convolutions. The convolutions give the bellows assembly the flexibility and performance characteristics.
Once the inside diameter welds are completed, the convolutions can be prepared for outside diameter welding. Depending on the welding equipment, copper rings can be inserted between the convolutions in order to ensure that the heat from the welds does not distort or change material properties in the adjacent material.
End plates or flanges can be welded to the end of each side of the bellows assembly per customer requirements. Depending on the application, heat treatment can be applied to the bellows to strengthen the material. Once completely assembled, edge welded bellows are helium leak tested to ensure the assembly is completely sealed. The industry standard leak rate is 1×10-9 for stainless steel material, but lower leak rates are required for certain applications.
Why Choose BellowsTech?
While the principle manufacturing processes above are followed by BellowsTech to manufacture edge welded bellows, proprietary stamping, cleaning and welding techniques make the difference in performance. Additionally, BellowsTech engineers and sales support staff understand the principles of vacuum and positive pressure movement, the differences between internal and external pressures, and how these variables can change the diameter, length, and stroke parameters.
While a common question for bellows is, “what pressure can the bellows hold,” it is typically answered with a question or series of questions. The differential pressure between the inside (P1) and outside (P2) of the bellows is critical as well as if P1 or P2 is greater. The details regarding how the bellows is used in the application also help to design the it to ensure proper function and cycle life. Axial and lateral offsets can also change the pressure capabilities of the bellows assembly. BellowsTech engineers can use various bellows design techniques to satisfy customer demands from ultra high vacuum to high pressure applications.
Temperature is easier to define. Once the ambient and environmental temperatures are understood, the correct material is selected.
Edge welded bellows are flexible in design to accommodate round, oval and rectangular shapes. BellowsTech offers over eighty standard sizes; for customer requirements, design, machining and tooling are completed at BellowsTech to ensure quality and competitive pricing.
For a list of products available by type and material, visit our Metal Bellows Product Page.
To purchase products directly, visit: buy.bellowstech.com
Do you have a edge welded bellows custom design requirement? Use the Edge Welded Bellows Design Form to begin the process.
