Manufacturing Technology

By Pasquale Cozzolino, tier 1 manager EU GMF – region Europe/India GMF, Atotech

A shift is taking place in the building construction industry towards sustainable resources, ‘end of life’ recyclability, longevity and durability. As timber is a renewable resource, wood construction is on the rise – creating a 20% to 40% smaller carbon footprint than steel and concrete – and it caters to current trends for natural, rustic design.

Cost-effective timber is therefore being used instead of steel to construct modern, creative multistorey office and residential buildings. In part, this is also due to the resilience of timber in a wide range of environments and its ability to resist horizontal and lateral forces from wind and earthquakes.

Timber: A challenge for any fastener

Timber is not only deployed as plywood or in light frame constructions, but also in heavy, mass timber and prefabricated panel constructions. It is generally joined with mechanical fasteners, which must meet a host of specific requirements, including compatibility with wood preservatives, impregnated timber, sealings and fire retardants. In addition to user-friendliness in automated and handcraft applications, fasteners must have a high performance in corrosion resistance, appearance, friction, hardness and scratch resistance.

When we look into the requirements that a woodscrew must fulfil, we encounter a range of corrosion performance tests and standards – demanding various levels of corrosion resistance, depending on the environment in which the fastener will be applied. For woodscrews, tests like NSST, Kesternich, NordTest (NT MAT 003-2002), the outdoor exposure test, and ASTM G198, determine the required corrosion protection. Additionally, woodscrews must possess a high hardness level without deforming or embrittling effects. 

Innovative fastening systems for wood construction need to fulfil high technical performance requirements, such as application efficiency, which is defined by drilling time, less energy used by the tools, user-friendliness, and good performance in automatic applications – such as prefabricated timber constructions. In addition, fasteners for wood construction must be flexibly applicable to combined materials – e.g wood and concrete.

The growing demand for alternative fastener substrates

Standards in the construction industry vary by country, region, and often by manufacturer and application. The environment in which a house is built determines the required fastener properties and quality level. For this reason, a wide range of different performance level specifications and requirements have emerged over the past few decades, posing challenges to fastener manufacturers and job coaters.

Increasingly stringent demands on construction fasteners and continuing import problems call for more investment in fastener production and expansion across Europe and North America. In recent years, stainless steel shortages and skyrocketing prices have also impacted the fastener industry, sparking a shift towards alternative substrates, such as steel, carbon steel and bi-metallic combinations.

The need to find substitutes for stainless steel in fastener manufacturing subsequently calls for alternatives in corrosion protection, bringing systems into focus that combine electrolytic and zinc flake coatings and can withstand extreme corrosion conditions. Shielding and protecting fastener substrates from their corrosive environment within timber structures requires a coating with maximum corrosion resistant properties. In addition, this coating must have a high-level of scratch resistance and is responsible for the friction behaviour of the screw. The coating also must not constrict the drilling capability of a woodscrew and needs to withstand the tooling. 

Atotech’s coating toolbox meets diverse requirement levels 

With our broad portfolio of electrolytic zinc, zinc alloy, and zinc flake coatings, we are a ‘one stop solution’ provider for specialised coatings and combined coating systems that are fit for the construction fastener market – fulfilling the requirements of state of the art woodscrews used in timber construction.

Atotech is proud to have decades of experience in developing specialised fastener coatings for the automotive and heavy machinery industries. In these industries, specific requirements for friction, high corrosion protection, scratch resistance, appearance, and colour stability, play a vital role. They are based on fixed standards within tight variation windows.

In our range of products dedicated to timber construction fasteners, Atotech offers a colour spectrum ranging from blue or iridescent to silver and black. Moreover, we provide a selection of passivates that act as adhesion promoters for subsequent coating processes, such as powder coatings, as well as eCoats for fasteners requiring specific colours.

Our range of coating systems encompasses solutions for very high corrosion protection and dedicated systems for different requirement combinations, including friction behaviour, local and international standards, and corrosion performance requirements. Our coating systems also meet diverse requirements for economic efficiency, as demonstrated by their corrosion performance in various corrosion tests, such as NSST, cyclic corrosion test, and the Kesternich test. Our comprehensive portfolio of standalone lubricants, top coats, and sealers with integrated lubrication, fulfil the requirements for appropriate friction behaviour in construction.

Top performing combined corrosion protection systems 

Atotech’s high-end corrosion protection coating systems, which are based on the combination of electroplated zinc or zinc nickel layers, together with zinc flake coatings, meet the most stringent demands for corrosion protection, optical performance and tribological properties. Both electrolytic layers, being sacrificial coatings, provide good cathodic corrosion resistance, while zinc nickel layers also provide high hardness and excellent wear resistance. The subsequently cured top coat layers exhibit strong chemical resistance and, by containing pigments and lubricants, provide both the desired optics and the required friction behaviour.

Techdip^® Silver SL is one example of a top coat that was developed for combined corrosion protection systems and zinc flake coating systems in construction applications. The organic, silver coloured, solvent-based top coat, with integrated lubricant, exhibits excellent adhesion on these surfaces. The top coat provides a corrosion resistance of more than 1,000 hours in NSST, and 15 cycles in the Kesternich test 2.0. The Techdip^® Silver SL top coat layer does not show flake-off after drilling into wood and provides excellent chemical resistance, as well as a high UV stability.

Sustainable, economic processes for enhanced productivity

Atotech has made an uncompromising commitment to developing more sustainable and durable coating systems and to eliminating harmful substances from its product range. We offer Cr(VI)-free and cobalt-free passivates for zinc and zinc alloy plating, as well as boric acid-free acid zinc and acid zinc nickel processes. Our processes for zinc plating pretreatment are free of chrome VI and our alkaline zinc plating processes do not contain cyanides. Furthermore, all our zinc flake systems are free of chrome VI, cobalt, nickel, cadmium and other toxic heavy metals. Our products also contribute to reducing wastewater, energy and chemical consumption.

With our ever increasing focus on helping our customers to reduce their CO₂ footprints, Atotech is continuously developing products that lower chemical and energy usage – while also enhancing productivity. One example is our Zintek^® ONE HP, a base coat that has been designed for corrosion protection performance of up to 720 hours NSST with just a single application layer. With the base coat’s optimised flow characteristics, customers can achieve uniform coating thickness distribution, minimise touch marks, and make the layer thickness distribution more homogenous, which in turn leads to more reliable and reproducible corrosion protection capabilities. The one layer system can be applied as a one layer base coat, plus one layer top coat, exhibiting the same performance as older systems requiring two base coats and one top coat. With this more economical approach of reducing one base coat layer, the capacity of the coating equipment can be increased up to 50%. Zintek^® ONE HP, therefore, can be an attractive alternative to multi-layer zinc flake coatings, hot dip galvanising and plating finishes.

Current efficiency is key when comparing the energy consumption of coating processes. With that in mind, Atotech has developed Zinni^® 220, a zinc nickel electrolyte with a current efficiency of up to 90% and an excellent initiation covering power for woodscrews. Zinni^® 220 is well suited to barrel production of hardened fasteners and fasteners with complex shapes. It can reduce plating time by up to 50%, outperforming state of the art alkaline zinc nickel electrolytes in terms of productivity. Several factors, including less intensive cooling requirements and higher current efficiency, result in a reduced number of plating tanks; increased barrel loads or shorter plating times; and lower energy consumption. 

Summary

Wood is increasingly being favoured as a construction material because it can help to reduce emissions, waste, pollution and costs. This has sparked a major shift in woodscrew manufacture, encompassing professional truss fasteners and fasteners for DIY wood construction, as well as a wide range of fastener types for professional wood construction. 

In the fastener industry, attempts to substitute stainless steel, the prevalent substrate for fasteners, with other substrates, such as steel and carbon steel, call for more sophisticated alternatives in corrosion protection, as technical and performance requirements for fasteners are continuously becoming more stringent. Atotech offers a range of electrolytic depositions, zinc flake coatings, and combined coating systems, which provide outstanding solutions for corrosion protection. They also fulfil additional combined property requirements, which comprise of friction behaviour, appearance, cutting force and self-tapping properties. Atotech’s portfolio complies with both international and local standards. Our environmentally sound, durable coating processes do not only contribute to reducing wastewater, energy and chemistry consumption; they also improve manufacturers’ productivity by simultaneously reducing operating costs.

With a rise in construction supply chain issues, and the transition to new fastener substrates presenting new challenges on the market, we offer excellent surface technology solutions that meet stringent new technical requirements in timber construction and its advanced automated execution. As the preferred global partner for corrosion resistant coatings, we provide our customers with the best local service and guarantee the consistent high-quality of our solutions all over the world.