Modern technology applied in the oldest plant
In the new pressing plant of the Mercedes-Benz site in Gaggenau, which is one of the oldest car factories in the world, each day more than 1,400 spare parts like doors, trunk lids, fenders or engine hoods for all Mercedes-Benz models are manufactured, pretreated and painted. Formerly, the components were mainly made from galvanized steel. But aluminum is increasingly making its way into automobiles. For zinc phosphating, this increase in material mixes makes it necessary to carefully explore the technical limits. Adapting baths to the changing loads is complex and the disposal of heavy metals expensive. “The trend to light-weight construction will increase further in future. Mercedes-Benz therefore needed an alternative that was free from heavy metals and compatible with multi-metals”, explains Klaus Rudo, responsible for Global Process Release at Daimler.
OXSILAN®: eco-friendly multi-metal process
After several months of testing, the results proved to be convincing in so many areas that the new OXSILAN® technology was adopted for use in series production already in spring 2011. For Sascha Malorny, responsible for pretreatment and painting at Mercedes-Benz in Gaggenau, much has become easier with the changeover to the OXSILAN® technology: “It used to be that the phosphating zone had to be acid-rinsed every ten weeks, which took a whole weekend each time. With OXSILAN®, cleaning of the complete facility is completed after only six to eight hours.” The zinc phosphating process also used to require a weekly cleaning of the filter system, which meant a complete exchange of the filter mats. Today, it is sufficient to rinse the filter press once a month with water since the new pretreatment technology is virtually sludge-free.
High process cost savings with OXSILAN®
The OXSILAN® process operates at room temperature and does not require cost-intensive bath heating. In the Gaggenau plant, it was now in addition also possible to reduce the temperature of the cathodic electro dip (CED) bath by around two degrees and the voltage by around ten percent. The many advantages in terms of energy consumption, wastewater treatment, bath desludging and disposal as well as the reduced labor costs resulted in high process cost savings - without compromising quality in any way. In addition, the omission of the nickel-containing zinc phosphating offers a major safety advantage for the employees.
OXSILAN® is a registered trademark of Chemetall.
Since 2006, OXSILAN® has been establishing itself in the pretreatment of automobile components. This technology had been developed in the preceding years by Chemetall GmbH in Frankfurt. The process is based on silanes that combine in aqueous solutions through hydrolysis and condensation to form polysiloxanes. During the coating process, the reactive silanol groups can be chemically bonded to the metal as well as to the paint coating. Heat treatment, e.g. following cathodic electro-painting (CEP), further cross-links the polysiloxanes. This affords layers in the range of 100 nm. In combination with many paint systems, this is already sufficient to achieve the same degree of corrosion protection as with the roughly ten times thicker zinc phosphating layers thereby reducing materials consumption and pre-treatment times and increasing productivity. Improvements of between 30 and 65% have been recorded in practical applications.
Chemetall, a division of Rockwood Holdings, Inc. (NYSE: ROC), is a leading global supplier of special chemicals with a focus on processes for the surface treatment of metals and plastics, as well as selected areas of fine chemicals, including lithium and cesium. Chemetall is headquartered in Frankfurt am Main, Germany, and comprises about 40 companies worldwide. With 2,900 employees, the Group achieved sales of about $ 1.163 million (2010). More at www.chemetall.com.