How do PTFE-lined flexible connections work?

Usually PTFE-lined flexible connections should have high corrosion resistance to a variety of corrosive media, good high-temperature strength and low-temperature toughness, this aspect of the processing technology and technical requirements are also increasingly high. Secondly, the size (wall thickness accuracy), shape accuracy requirements of PTFE-lined flexible connections also prompted online detection, automatic control technology continues to progress. The requirement for lower cost of PTFE-lined flexible connections makes its production process to a short process, near the end of the molding direction. The advantage of PTFE-lined flexible joints is that it can destroy the casting organization of the ingot, refining the grain of stainless PTFE-lined flexible joints and eliminating microstructural defects, thus making the metallographic organization of PTFE-lined flexible joints more dense and improving mechanical properties. This improvement is usually reflected mainly in the rolling direction, so that the Teflon lined material is no longer isotropic to a certain extent, and can also be welded under high temperature and pressure previously formed during the casting of bubbles, cracks and looseness.
After vulcanization, the non-metallic inclusions (usually sulfides and oxides, and silicates) inside the PTFE-lined material are pressed into thin sheets and delamination occurs. Delamination can greatly deteriorate the performance of the Teflon lined flexible joint in tension along the thickness direction, and there is a risk of interlayer tearing during weld shrinkage. The local strain induced by weld shrinkage can often be several times the yield point strain, which is much stronger than the load-induced strain. Uneven cooling during the vulcanization process will produce residual stress, the so-called residual stress is the internal self-balancing stress in the absence of external forces, the vulcanization of a variety of flexible connections have this residual stress, the larger the size of PTFE-lined flexible connections, the greater the residual stress.
 
Although the residual stress is self-balancing, but the performance of PTFE-lined flexible connections under the action of external forces will still have an impact. For example, it will be detrimental to the deformation of stainless steel, stability, fatigue resistance and other aspects. In the vulcanization is easy to twist, easy to bend and twist flexure when pressurized, poor torsional performance; In addition, the vulcanization molding steel wall thickness is small, there is no thickening at the corners of the plate articulation, resulting in PTFE-lined soft connections Bur to withstand the localized concentrated load is weak.