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FUNCTION OF FABRIC EXPANSION JOINT COMPONENT

A. Gas Seal Membrane: The gas seal membrane is intended to withstand system pressure and be resistant to chemical attack from the interior and the exterior. The gas seal must also have the flexibility to absorb thermal movements. Depending on system temperature, it may require additional thermal protection.

B. Insulating Layers: The insulating layers provide a thermal barrier to ensure that the inside surface temperature of the gas seal membrane does not exceed its maximum service temperature. The insulating layer can also reduce condensation caused by the gas stream coming in contact with the “cool” surface of an insulated gas seal membrane.

C. Insulating Retainer Layer: This layer is provided to keep the insulating layers in place in order to maintain thermal integrity. The retaining layer must be capable of withstanding gas stream temperatures and must be chemically compatible with system media.

D. Back up bars: Back up bars, positioned at the flange attachment, use clamping pressure to create the fabric-to-duct seal and restrain the fabric when it is subjected to the system pressure. The thickness and width of the back up bars should be sufficient to perform this function with the bolt spacing being used. The edges of the back up bars should have a radius to preclude cutting of the fabric.

E. Metal Liner or Baffle: A liner is designed to protect the gas seal membrane and insulating layers of the flexible element from abrasive particles which may be present in the gas stream. A liner is also used to reduce flutter of the fabric element caused by turbulence, to help control the accumulation of dust or ash in the expansion joint cavity, and to reduce the temperature of the flexible element.s

F. Accumulation Bag: An accumulation bag is intended to deter flash from building up in the expansion joint cavity, It is typically used, in conjunction with a liner, in duct runs from boilers to air clean-up equipment such as precipitators, scrubbers and bag houses, or whenever high amounts of duct or ash are present in the gas. A flash barrier must be capable of retaining its strength and flexibility while being exposed to maximum system temperatures and media.

G. Fabric Attachment Flanges: Fabric attachment flanges are required to connect the flexible element to the ductwork. Properly designed, they can be attached directly to the duct work and thus eliminate the necessity for an adjoining duct flange. Flanges can be designed with a “landing bar” duct attachment which allows some installation misalignment without affecting the flexible element. the edges of the flanges in contact with the gas seal membrane should also have a radius to prevent damage.

H. Gasket: Fabric belts with insulating layers require a thermal insulating gasket to protect fabric components from hot attachment flanges and backup bars. Low temperature, single ply designs require flexible, chemically insert gasket.

STRUCTURE OF FABRIC BELLOWS (BELLOWS LAYERS)

Multi-layer expansion joints

By combining different materials and taking into account their thermal, chemical and mechanical resistance as well as their fatigue properties, we ensure the optimum solution both in technical and economical respect. Basically, the design of multi-layer expansion joints comprises four groups of materials.

Outer cover materialProtects the expansion joint from pressure and temperature and guarantees from stability. In most cases the material is coated and may also function as gas sealing barrier. Stainless steel wire mesh and steel bands are further used for special designs to give added mechanical protection and dimensional stability.
Gas sealing foilThe gas sealing foil is the actual sealing element, usually imbedded between fabric layers. Impermeable and chemically resistant
Temperature-resistant fabricsVery strong and Temperature resistant fabrics are used to protect the gas sealing foil and/or the insulation materials.
Insulating materialsProtect both the gas sealing foil and other expansion joint materials from high temperatures of the medium.

STRUCTURE OF FABRIC BELLOWS (INSULATION LAYERS)

Variables to consider

The following considerations will influence the design and the choice of the right expansion joint type.

MediumThe choice of expansion joint type is determined, among other things, by possible chemical influences. Abrasion from solid atter is largely prevented by using a sleeve/baffle construction.
TemperatureA specific number of insulating materials are required for reducing the temperature. Our Technical Department determines the insulating effect by calculating and measuring the temperatures in a compute expansion joint. The exact temperature flow is found by means of temperature probes and recorders. Temperature range: -60...+ 1,200℃ (-76...+2,192℉) (dependant on design)
PressureWill the expansion joint be used in a positive pressure or negative pressure area? This will ,have influence on both type and design of the expansion joint. The main application area covers the pressure range of 400 amber ( 40 kPa). (fabric expansion joints will resist pressures of up to approx 0.3 bars), dependant on other operating parameters.
Tightness (sealing)The requirements for tightness have influence on the design and especially the configuration of the flange area. If the sealing rate must be documented (Nekal tightness or specific leakage rates), the expansion joints are built with special flange designs. We are able to determine leakage rates for various materials and complete expansion joint structures on our test rigs.