Hot-dip galvanized rod threads for sustainable construction are a unique feature of BESISTA® products.
Threads are the most sensitive part of a tension rod system. Fully conscious of its obligations in this respect, BESISTA® ensures top-class machining based on sound scientific principles. Since most tension rods are hot-dip galvanized, it is worth knowing the most important facts.
Our tension rods are made of S540N, an extra-high-quality, BESISTA®-modified S460N fine-grained structural steel, and have a guaranteed minimum yield strength of 540 N/mm² and minimum tensile strength of 720 N/mm². These values approach those of strength class 8.8. Hence, to avoid hydrogen embrittlement during the hot-dip galvanizing process, all threads at BESISTA® are cut with special tools and not rolled.
For us, the less expensive cold forming of threads by rolling is unacceptable due to the risk of the microstructure hardening such that hydrogen embrittlement cannot be ruled out, especially at the crack-prone thread base. Unlike small components such as bolts, long rods cannot be reliably treated after pickling.
At BESISTA®, all threads to be hot-dip galvanized are therefore cut back by the thickness of the zinc coat prior to galvanizing. After coating, the standard size is restored by recutting to gauge the thread, which is now flooded with zinc. This is the only way of ensuring that the necessary zinc coat remains on the rod threads and thus provides the internal threads of the rod anchors with cathodic protection against corrosion. The encapsulation of black threads or sealing of brushed or sprayed threads offers no alternative to this method of zinc coating. Moreover, performance may well be compromised should encapsulated or sealed threads require adjustment for the purposes of installation or coating, or where these are exposed to high temperature differences at outdoor locations. Such factors pose no problems for galvanized threads.
Re-threading is a time-consuming operation that can only be performed manually. Expert workmanship is required to trace the thread grooves for recutting once these are flooded with zinc. Even with the utmost care, such as that exercised by our craftsmen, the zinc coat may still work slightly loose at isolated points during the recutting operation, albeit with no significant impact on corrosion protection.
For reasons of quality, we absolutely refuse to supply low-price threads produced by the cheaper method of heating and brushing off excess zinc in the thread grooves. Nor do we accept solutions that involve simply spraying zinc paint onto uncoated threads cut into pre-galvanized rods. On the one hand, this may significantly reduce corrosion protection due to the absence of a zinc coat. On the other hand, there is a risk of stress accumulation due to the heat needed for brushing off the zinc and the “burning out” of the threads, with rolled threads being particularly at risk of further embrittlement.
If “hot-dip galvanized” is specified, the client is entitled to expect complete hot-dip galvanizing, including hot-dip galvanized rod threads. In recognition of the integral, good-practice galvanizing methods successfully applied to its rod systems, BESISTA® won the German Galvanizers’ Award as early as 1991 and 1995. For further details, see menu point “History”.
For additional safety with regard to the load-carrying capacity of the threads and sustainable performance, the internal threads of BESISTA rod anchors are about 40% longer than necessary. Millions of threads – successfully in use since 1987 – are a further testament to our quality philosophy.