The safety seatbelt has been a mandatory feature in new vehicles in Germany since January 1976, consistently saving lives every day. The metal components used in seatbelts must meet strict standards for mechanical strength and long-term durability. These requirements are typically achieved through galvanically separated protective coatings made from nickel and chrome. However, the conventional chrome(VI) compounds used in chrome plating have come under scrutiny due to the REACH regulation.
To adopt more environmentally friendly materials, ZF LIFETEC modernized its in-house galvanizing facility in 2023, transitioning to an advanced chrome(III)-based system. This upgrade was carried out in close collaboration with Dr.-Ing. Max Schlötter GmbH & Co. KG, which also designed and executed the necessary conversion work.
Most passenger cars are equipped with three-point seatbelts. “For safety systems like these, the metal components must not only be highly resilient but also maintain long-term stability under varying climatic conditions. At the same time, their decorative appearance is also an important factor,” explains Thomas Haberfellner, COO at Dr.-Ing. Max Schlötter GmbH & Co. KG.
The components are coated with an electroplated nickel and chrome layer and must also be selectively overmoulded with plastic. During use, the functional nickel and chrome surface is subjected to high levels of corrosion and friction.
In response to upcoming European chemical regulations, Alfdorf-based ZF LIFETEC has adopted a chrome(III)-based system, proactively supporting the automotive industry in meeting future compliance requirements. The company leverages the expertise of Dr.-Ing. Max Schlötter GmbH & Co. KG, which has been researching and developing chrome(III)-based electrolyte systems for many years. For applications like these, their advanced electrolytes provide a fully viable alternative to conventional chrome(IV) systems.
From raw material to premium coating
Before coating, the metal parts are produced in precise manufacturing steps during which they are punched, deburred, hardened and pre-finished by vibratory grinding. The advanced vibratory finishing process at ZF LIFETEC, not only reduces processing times in parts production, but also prepares the surfaces for optimal galvanic coating. In the fully automated galvanising lines, the parts are degreased, nickel-plated and finally chrome-plated so they can fulfil demanding requirements for corrosion resistance and aesthetic appearance.
Full leverage of the advantages of the chrome(III) process
In advance of the changeover, comprehensive testing and adjustments to the technical equipment had to be carried out before the properties of the established coatings were attained. With the Chrombad SLOTOCHROM BC 4130 brand name, Schlötter is offering the latest development stage of chrome(III) systems.
“Changeover to the chrome(III) system was an important step in making our production fit for the future,” reports Harald Häfele, Head of the Surfaces Department at ZF LIFETEC.
Technical challenges and solutions
A few adjustments to the technical plant equipment were needed to facilitate the introduction of the new chrome(III) system. Changes to ensure stable operation included installation of a selective ion exchanger for bath maintenance as well as automatic dosing of bath components.
Additionally, electrolytic post-treatment creates the necessary passivity of the layers and in doing so ensures the required level of corrosion resistance.
Future-oriented production and environmental responsibility
Since September 2023, ZF LIFETEC has been using the SLOTOCHROM BC 4130 chrome bath and the SLOTOCHROM DR 2340 post-treatment in regular operation for finishing metal parts. As well as very successfully fulfilling functional and aesthetic requirements, this technology also fits seamlessly into the existing infrastructure and so facilitates efficient upgrading. “The fantastic collaboration with Schlötter was decisive for the success of this project,” emphasised Häfele. With this new approach, ZF LIFETEC is supporting its customers’ environmental protection efforts and also its own sustainability goals.
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