Bellows Construction
Multilayer Expansion Joints
- Insulating layers
The function of the internal insulating layers is to dissipate the medium temperature out to the sealing films located further to the outside. Insulating layers consist of a glass fiber fabric or glass felt, ceramic fabrics or ceramic fiber mats, or of a combination of these materials.
- Sealing films
For almost all applications, these consist of PTFE film, and take over the actual sealing function of the expansion joint. The PTFE film may also be laminated onto glass fiber fabric on one or both sides, and ensures the necessary pressure tightness of the expansion joint for this material design as well. PTFE is chemically resistant to almost all media. In rare cases with extreme temperature requirements or high ambient temperatures in addition, stainless steel films are used. As opposed to PTFE film, which is welded to be gas-tight, stainless steel films are simply clinched tight and are only sufficient for low impermeability requirements.
- External layer
The external layer is usually a silicon-based glass fiber fabric or, in the event of harsh environmental conditions, a PTFE-coated glass fiber fabric. This layer is the pressure carrier and provides mechanical protection against external damage and weather effects. The choice of the external layer also depends on whether the expansion joint can be delivered in a closed state and thus already made „endless“ at the factory, or if it needs to be designed with an installation seam.