There is no experience for clinched bushes in long-term tests. In contrast there is no loss known for weld couplings since 1960s because of crevice corrosion. All relevant producers weld their couplings on highly stressed positions!
To guarantee the highest possible safety for all application cases Flexseal welds all its sealing collars!
In the case of resistance spot welding, the parts that should be connected are pressed together at individual points by water-cooled copper electrodes. At this point, stream flows from one electrode to the opposite electrode. Because of the electrical resistance between the plates, the material is heated and melts. The result is a lens-shaped welding point. For resistance welding the parameters of welding duration, current flow and pressure to the materials and the dimensions of the welding points have to be adjusted.
Clinching is a patented process of Fa. Tox Pressotechnik, that was designed to connect low and medium thickness aluminum sheets economically – as an alternative to welding, screwing, riveting, gluing etc. For this method the plates that should be joined are pressed into a die by a plunger. Because of the force applied by the plunge the plates flow together into an undercut. This results in a press-button-like connection that holds both plates together. This process was carried out for the first time during the construction of the Audi A2 in mass production. The good flow behavior of ALUMINUM (not steel) favors this joining technique.
Asset and drawbacks:
The only detectable asset for clinching is the economic efficiency of the process – this is only valid for connecting aluminum. This depends on the endurance of the tools, the slightly lower demand for energy and the associated lower costs of operation.
The postulated steel for sealing collars is way more ductile and hard and therefore a higher pressure is needed. At the same time the endurance of the tools decreases significantly!
THE MENTIONED CORROSION PROBLEMS THAT ALLEGED APEAR WHILE SPOT WELDING CAN BE NEGLECTED FOR OUR PRODUCTS (COUPLINGS FOR SEWAGE WATER)! This corrosion only appears in areas with an increased chloride percentage. This is the case of contaminated grounds, seawater and in grounds with tidal flow. A verifiable structural change can only be detected when the influence of temperature lasts longer than one minute. For spot welding this is NOT the case. Even if the connection is used on acid soil and gets surface corrosive action this has NO relevant influence on the tensile strength!
Internal tests of clinched connections had shown that there is a low stability at certain tension tests!
Even our competitors weld their couplings on highly stressed spots (tension band: there the pressure is for the pipe to seal it). The connection only gets clinched on the less strained shear band connection!
Find further detailed information below:
“Korrosionshandbuch für rostfreie Stähle” (ISBN: 91-630-2122-6)
Work of reference: Nickel Institutes:”Umformen von Edelstählen für die Wasserwirtschaft”