Hot-dip galvanized rod threads for sustainable construction are a unique feature of BESISTA® products.
The threads of a tension rod system are highly critical components. Understanding the significance of this aspect, BESISTA® places great emphasis on delivering top-quality machining that adheres to sound scientific principles. Given that the majority of tension rods undergo hot-dip galvanization, it is essential to be aware of the key facts surrounding this process.
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.
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 has the right to expect a comprehensive hot-dip galvanizing process, which includes hot-dip galvanized rod threads. Over the years, BESISTA® has demonstrated its commitment to employing effective galvanizing methods for their rod systems, in line with industry best practices. This recognition is based on the successful application of such methods since 1990.
|Threads flooded with zinc that were cut back by the thickness of the zinc coat prior to galvanizing||Optimum corrosion protection, BESISTA®-style: zinc coat remaining on the threads after the zinc-flooded grooves are recut to the standard size||Not BESISTA®: inadequate corrosion protection for threads following the removal of zinc by heating and brushing off to make them fit the nut threads||Not BESISTA®: inadequate corrosion protection by spraying zinc paint onto black threads cut into pre-galvanized rods|