Products

Metal Bellows

What is a Metal Bellows?
Metal Bellows design
Types of Metal Bellows
Manufacturing methods of Metal Bellows
Custom made Metal Bellows

What is a Metal Bellows?

A metal bellows is a flexible element consisting of one or more corrugations and the end
tangents. It is the key element of an expansion joint and gives the flexibility the Expansion Joint
needs to function properly and absorb the movements for which it was designed.

A corrugation (convolution) is the flexible unit of a bellows and end tangents are the straight uncorrugated
portions at the ends of a bellows.

The flexibility of the metal bellows is derived from the inherent flexibility of the corrugation given
its shape and its own design.

In the design and construction of metallic bellows, in addition to considering that they must be
flexible and such flexibility must be controlled, other operating parameters such as pressure,
temperature and chemical resistance to fluid passing through them must be considered.

MACOGA is a world-renowned manufacturer of metal bellows offering solutions for all industrial
applications.

Main features of MACOGA Metal Bellows

From 15 mm up to 10 meters diameter
Single ply or Multiply construction
Reinforced and unreinforced
Available in austenitic stainless steel, duplex, nickel alloys, low alloyed steels, titanium,
carbon steel, etc.

Main parts of metal bellows

Corrugation or convolution

Flexible unit of a bellows with a leakproof wall consisting of one or more plies. Ply element of the bellows’ wall usually made from sheet or strip material.

End tangent

Straight un-corrugated portion at the ends of a bellows.

Assisting and reinforcing collar

Ring placed around the end tangents for reinforcement and to facilitate welding.

Metal Bellows design

In the design of metal bellows, consideration must be given to:

Grade of flexibility (spring rate) and service life required
Corrosion and fluid resistance
Temperature resistance
Pressure resistance

Pressure resistance, flexibility and service life is guaranteed by proper bellows design
combining elements such as material used, shape, number and type of waves, etc. and can be
verified mathematically.

By selecting the right material, we can guarantee resistance to temperature corrosion.

MACOGA metal bellows are designed in accordance with:

E.J.M.A. (Expansion Joint Manufacturers Association, Inc.)
ASME VIII, Div. I, App. 26
EN 14917, European Standard. Metal bellows expansion joints for pressure
applications.

MACOGA is a leading and active member of EJMA (The Expansion Joint Manufacturers
Association, Inc.) with representation on the technical and management committees.

EJMA is the worldwide association of leading expansion joint manufacturers and its mission is
to maintain the highest quality design and manufacturing standards.

Types of Metal Bellows

Metallic bellows can be classified according to different criteria or parameters such as the shape
of the convolution, the number of plies used in their construction, the manufacturing method,
etc.

In a simplified way, they can be classified as follows:

By the shape of the duct

Round
Rectangular
Oval

By the thickness of the plies

Thin wall bellows
Thick wall bellows: Lens type and Flanged and Flued type

By the shape of the convolution in cross-section

Omega shape
U-shaped
V-shaped
Toroidal

By the method used in their manufacture

Hydroformed Bellows
Expanded mandrel or punch formed
Rolled

By number of plies

Single-ply
Multiply

Whether or not they incorporate reinforcing rings

Reinforced: with reinforcing rings
Unreinforced: without reinforcing rings

Manufacturing methods of Metal Bellows

Each manufacturer uses their own methods to manufacture metal bellows although in all cases the bellows are manufactured using seamless tubes or metal cylinders welded along their length.

Depending upon a range of different contributing factors (e.g. diameters, the number of sheets used, the materials used, etc.), the following are the most commonly used bellows forming methods:

Expansion (Expanding Mandrel) Forming

Individual convolutions are formed in a tube by an expanding internal mandrel. Flat spots are minimized by expanding the mandrel partially, and rotating the tube slightly. This process is repeated until an intermediate convolution height is achieved. Each convolution is subsequently sized by means of specially contoured inner and outer rollers.

Hydraulic Forming

A tube is placed in a hydraulic press or bellows forming machine. Circular external die rings of suitable contour are placed outside the tube at longitudinal intervals approximately equal to the developed length of the completed convolutions. The tube is filled with a medium such as water and pressurized until circumferential yielding occurs. This forming operation continues with a simultaneous circumferential yielding and controlled longitudinal shortening of the tube until the proper configuration is obtained. Individual or multiple convolutions may be formed by this method. Depending on the bellows configuration, several partial-forming steps with intermediate heat treatment may be required. Reinforced bellows may be formed by utilizing external reinforcing rings that act as part of the forming dies. After completion, when the dies are removed, the rings remain as an integral part of the bellows.

Elastomeric Forming

A longitudinal welded tube is inserted over a mandrel containing a rubber torus. Axial force on the mandrel expands the torus, forming a bulge in the tube. The torus is then relaxed and the bulge is axially compressed into a convolution by external dies. Convolutions are formed one at a time. The tube is free to shorten as the convolution is formed.

Roll Forming

A tube is placed in a forming machine and individual or multiple convolutions are formed by means of pressure exerted by forming wheels. Generally, the wheels are on both the inside and outside of the tube. Controlled longitudinal shortening of the bellows tube occurs during the forming operation. The tube may rotate about fixed-shaft forming wheels, or the tube may be fixed and the wheels rotated about the tube's circumference.

Press-Brake Forming

A flat sheet is convoluted using a press-brake die to form the individual convolutions. This method is used primarily in the manufacture of bellows for rectangular Expansion Joints. The most common styles are the "U" profile and "V" profiles.

Custom made Metal Bellows

MACOGA provides solutions for your unique challenges whether it's a specific design for a
particular application, a special shape or an exotic material, we can manufacture a custom
metal bellows to meet your needs.

We have the possibilities in our workshop to produce expansion joints in any shape:

Circular
Oval
Inverted convolutions
Conical
Rectangular
Etc.