In the search for a hypophosphite-free passivation the collaboration between REISSER-Schraubentechnik and Dörken has once again proved fruitful.

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Sustainability, environmental protection and climate change are no longer niche issues, but instead find great resonance within our society. One area of this is the issue of (industrial) wastewater and transfer to waterways. In the scope of environmental legislation threshold values are therefore defined and prescribed for chemical components in wastewater. These also include hypophosphite. Fundamentally, phosphorous is a trace element that is vital for people, animals and plants. However, the excessive presence of phosphate (compounds) in wastewater can lead to problems such as the over-fertilisation of water ways. I.e., plants in water ways can be stimulated to excessive growth, leading to a subsequent lack of oxygen or even the death of fish. In the scope of electroplating processes, a further problem is that water-soluble complexes are formed with toxic metal ions, which can then no longer be removed from the wastewater via precipitation.


Reaching objectives together
To counter this problem, REISSER-Schraubentechnik GmbH and Dörken have joined forces to develop a new passivation without the additive hypophosphite. One key issue here was that this new passivation offers a high level of corrosion protection, temperature stability and compatibility with existing top coats and sealing products. REISSER-Schraubentechnik GmbH of Ingelfingen is one of the leading manufacturers of stainless-steel screws and bolts in Europe and a licensee of DELTA-PROZINC® and zinc flake systems from Dörken. Together with the Herdecke-based company and the plant engineering firms A.S.T. and Forplan Surface Technology, last year they developed a state-of-the-art electroplating drum unit that is regarded as one of the most modern worldwide in the field of alloy-free zinc technology. The high level of trust amongst all participants was already evident with this project.

Challenge overcome
And this project could also be completed successfully! After several months of co-operation DELTA®-PASSIVATION SHINY 30 was developed and produced, meeting all of the requirements in full. The passivation is chromium VI-free, can be applied to acidic and alkaline zinc and used as thick film and blue passivation.

Further advantages: the recipe avoids using hypophosphite, bath life could be significantly extended and concentration reduced. The results are impressive: in the case of acidic galvanisation in the drum the system comprising the passivation DELTA®-PASSIVATION SHINY 30 + topcoat can achieve corrosion protection of up to 1,000 hours without red rust for components.

“With REISSER-Schraubentechnik we have a partner that has tackled the problem in an agile and collaborative manner,” reports Matthias Basler, Application Engineer at Dörken. “Together with our Research and Development department we have developed a product that not only lies below the required threshold values but also displays excellent corrosion results after temperature stressing.”