A bellow or expansion joint is an assembly designed to safely absorb the heat-induced expansion and contraction of construction materials, to absorb vibration, to hold parts together, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.

Building faces, concrete slabs, and pipelines expand and contract due to warming and cooling from seasonal variation, or due to other heat sources. Before expansion joint gaps were built into these structures, they would crack under the stress induced.

Control joints (often confused with bellows) are cut into the concrete or asphalt, and are different from bellows. Control joints are cut into the pavement at regular intervals to allow cracking to occur in a controlled fashion. Road control joints may be sealed with hot tar, cold sealant (such as silicone), or compression sealant (such as rubber).

Wrapping Fabric Reinforced Rubber Sheets

Rubber bellows are mainly manufactured by manual wrapping of rubber sheets and fabric reinforced rubber sheets around a bellows-shaped product mandrel. Besides rubber and fabric, reinforced rubber and or steel wires or metal rings are added for additional reinforcement. After the entire product is built up on the mandrel, it is covered with a winding of nylon peel ply to pressurize all layers together.

Moulded Rubber Bellows

Some types of rubber bellows are made with a moulding process. Typical bellows that are moulded are medium-sized bellows with bead rings, which are produced in large quantities. These rubber bellows are manufactured on a cylindrical mandrel, which is wrapped with bias cut fabric ply. At the end the bead rings are positioned and the end sections are folded inwards over the bead rings. This part is finally placed in a mould and moulded into shape and vulcanized. This is a highly automated solution for large quantities of the same type of bellow.

Automated Winding of Rubber Bellows

New technology has been developed to wind rubber and reinforcement layers on the bellow-shaped mandrel automatically using industrial robots instead of manual wrapping. This is fast and accurate and provides repeatable high quality. Another aspect of using industrial robots for the production of rubber expansion joints is the possibility to apply an individual reinforcement layer instead of using pre-woven fabric. The fabric reinforcement is pre-woven and cut at the preferred bias angle. With individual reinforcement it is possible to add more or less fibre material at different sections of the product by changing the fibre angles over the length of the product