Conversion of electroplating to chromium(III) process

The in-house electroplating facility of an automotive supplier has been converted to an advanced chromium(III)-based system. Previously, chromium(VI) compounds were used for this, which have come under pressure due to the REACH regulation.

Seat belts have been mandatory in new vehicles in Germany since January 1976. It is a component whose reliability saves lives every day. The metal components used must meet high requirements in terms of mechanical strength and long-term stability. Traditionally, electroplated protective layers of nickel and chromium are used for this purpose. However, the chromium (VI) compounds used in the past for the deposition of chromium have come under pressure due to the REACH regulation. In an effort to use more environmentally friendly materials, ZF Lifetec has upgraded its in-house electroplating facility and switched to an advanced chromium(III)-based system. This innovation was implemented in 2023 in close cooperation with Dr.-Ing. Max Schlötter GmbH & Co. KG, with Schlötter also planning and carrying out the necessary conversion work. ZF AG is one of the world's largest suppliers to the automotive industry.

Three-point seat belts are usually used in passenger cars. "For such safety systems, the metal components must not only be resilient, but also permanently stable under variable climatic conditions. At the same time, high demands are placed on the decorative appearance," explains Thomas Haberfellner, COO at Dr.-Ing. The components are coated with an electroplated nickel-chromium layer and also selectively overmolded with plastic. The functional nickel-chromium surface is exposed to high corrosion and friction loads during operation.

With the introduction of chromium(III)-based systems, ZF Lifetec from Alfdorf responded to the upcoming requirements of European chemicals legislation and thus also supported the automotive industry in advance. The company relies on the expertise of Dr.-Ing. Max Schlötter GmbH & Co. KG, which has been researching and developing chromium(III)-based electrolyte systems for many years. These electrolytes represent a fully-fledged alternative to traditional chromium(VI) systems for these applications.

Before coating, the metal parts are punched, deburred, hardened and prepared by vibratory grinding in precise production steps. The modern mass finishing process at ZF Lifetec not only reduces the machining times of the components, but also prepares the surfaces for optimum electroplating. In the fully automated electroplating lines, the parts are degreased, nickel-plated and finally chrome-plated in order to meet the high requirements for corrosion resistance and aesthetic appearance.

The changeover required extensive tests and adjustments to the system technology in order to achieve the properties of the previous coatings. With the brand name Chrombad Slotochrom BC 4130, Schlötter offers the latest development stage of chromium(III) systems. "The switch to the chromium(III) system was an important step in making our production fit for the future," reports Harald Häfele, Head of the Surface Department at ZF Lifetec.

The introduction of the new chromium(III) system required some adjustments to the system technology. Among other things, a selective ion exchanger for bath maintenance and automatic dosing of the bath components were installed to ensure stable operation. In addition, electrolytic post-treatment is used to create the necessary passivity of the layers and thus achieve the required corrosion resistance.

Since September 2023, ZF Lifetec has been using the Slotochrom BC 4130 chrome bath and Slotochrom DR 2340 post-treatment in regular operation for finishing metal parts. This technology not only fulfills functional and aesthetic requirements with flying colors, but also fits seamlessly into the existing infrastructure, which enabled an efficient changeover. "The excellent cooperation with Schlötter was crucial to the success of this project," emphasizes Häfele. Through this conversion, ZF Lifetec is not only supporting its customers' environmental protection efforts, but also its own sustainability goals. (OM-11/24)