Pipe expansion joints
Pipe expansion joints are necessary in systems that convey high temperature substances such as steam or exhaust gases, or to absorb movement and vibration. A typical joint is a bellows of metal (most commonly stainless steel), plastic (such as PTFE), fabric (such as glass fibre) or an elastomer such as rubber. A bellows is made up of a series of convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept axial, lateral, and angular deflections. Expansion joints are also designed for other criteria, such as noise absorption, anti-vibration, earthquake movement, and building settlement. Metal expansion joints have to be designed according to rules laid out by EJMA, for fabric expansion joints there are guidelines and a state-of-the-art description by the Quality Association for Fabric Expansion Joints.
Pipe expansion joints are also known as compensators, as they ‘compensate’ for the thermal movement.
Pressure balanced expansion joints
Expansion joints are often included in industrial piping systems to accommodate movement due to thermal and mechanical changes in the system. When the process requires large changes in temperature, metal components change size. Expansion joints with metal bellows are designed to accommodate certain movements while minimizing the transfer of forces to sensitive components in the system.
Pressure created by pumps or gravity is used to move fluids through the piping system. Fluids under pressure occupy the volume of their container. The unique concept of pressure balanced expansion joints is they are designed to maintain a constant volume by having balancing bellows compensate for volume changes in the bellows (line bellows) which is moved by the pipe. An early name for these devices was “pressure-volumetric compensator
Rubber expansion Joint
Wrapping fabric reinforced rubber sheets
Rubber expansion joints are mainly manufactured by manual wrapping of rubber sheets and fabric reinforced rubber sheets around a bellow-shaped product mandrel. Besides rubber and fabric, reinforced rubber and/or also steel wires or metal rings are added for additional reinforcement. After the entire product is build up on the mandrel, it is covered with a winding of (nylon) peel ply to pressurize all layers together before pressurization. Because of the labor-intensive production process, a large part of the production has moved to eastern Europe and Asian countries.
Molded rubber expansion joints
Some types of rubber expansion joints are made with a molding process. Typical joints that are molded are medium sized expansion joints with bead rings, which are produced in large quantities. These rubber expansion joints 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 mold and molded into shape and vulcanized. This is a highly automated solution for large quantities of the same type of joint.
Automated winding of rubber expansion joints
New technology has been developed to wind rubber and reinforcement layers on the (cylindrical or 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 fiber material at different sections of the product by changing the fiber angles over the length of the product