High-per­for­mance pro­tec­tion for fas­ten­ers in the con­struc­tion sec­tor

Whilst in the construction of actual façades the fasteners of the cladding are subject to very strict specifications, such as the mounting guidelines of the IFB (international lightweight metal construction association), there are also many applications in external construction fields such as solar panels or photovoltaic units that are not covered by these stringent requirements. Specifically, this means that steel fasteners can be used in these areas, and these are not required to be manufactured from austenitic stainless steels as is the case with façade construction fasteners. Despite this, contractors and fitters are faced with numerous challenges. For example, there is the problem of contact corrosion when fastening two different materials together. If steel bolts with an unsuitable “protective film” are screwed to an aluminium profile, for example, this often results in premature corrosion and therefore to safety defects and expensive repairs. In view of this, the effective protection of screws and bolts against corrosive attack is urgently required, especially for safety-relevant components.

In practice, fasteners made from carbon steel or stainless steel are typically used today. To create corrosion protection, the screws made from carbon steel are either electroplated and passivated or alternatively coated via hot-dip galvanisation. However, these coatings often come up against their limitations, particularly where the corrosion protection requirements are very high and further functional requirements also need to be fulfilled. The protective performance achievable with a galvanic coating is comparatively low and unsuitable for use with fasteners under tough environmental conditions. In many cases, the problem with hot-dip galvanisation is that the high annealing temperatures during application place great stress on the parts. In addition, the thickness of the coating is relatively high – which can result in difficulties in assembly for screwed fasteners with internal drive in particular. In recent years, stainless steel screws and bolts have established themselves as a common solution for projects with high corrosion protection requirements. These do not require additional surface protection, but are comparatively very expensive.

The zinc flake coating is advisable for use with carbon steel fasteners wherever very high requirements of corrosion protection need to be met and where functional characteristics such as enhanced barrier effect against moisture are required. From an economic viewpoint also, these represent an advantageous alternative to stainless steel fasteners.