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The bellows element is the most important component of an expansion joint. This thin-walled, corrugated membrane allows flexibility in a piping system while containing the pressure and media. When complete, each bellows has a unique working pressure, spring rate, and cycle life that are entirely dependent on its geometry and material.
EJS manufactures bellows using an expanding mandrel (punch forming) method followed by a finish rolling. This two part forming process first folds the metal into the convoluted shape preserving the metal thickness and avoiding extreme working of the metal. The rolling is a finishing process that completes the convolution shape without overworking the metal and maintains the metal thickness throughout the convolution. A rectangular sheet is sheared and rolled into a tube. The tube is welded using an auto flat-bed welder with no filler metal added. The longitudinal seam weld is then “plannished” back down to the parent material thickness. Any dye penetrant, x-ray, or air testing is performed at this time. When testing is complete, the convolutions are punched individually drawing material from the top and bottom of the tube. This drawing process eliminates any thinning in the bellows material.
At this point, the convolutions have more of a “V” shape than the final “U” shape that is required. This is easily solved with the final re-rolling of the bellows between a series of aluminum bronze rolls. After trimming the bellows attachment ends (skirts), the bellows is complete and ready to have attachment ends installed.
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Automatic Longitudinal Seamweld
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Plannishing the Seamweld
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Forming Convolutions
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Final Reroll Process
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