APPLICATION TECHNOLOGY
M12 to M16. In addition to resistance to base metal corrosion of at least 720 hours, the lubricant effect demanded by MAN was also particularly important in order to also ensure smooth fitting of such parts in practice. Various zinc flake based Cr(VI)- free coating systems that had been tested had not been able to satisfactorily fulfil the coefficient of friction requirements.
A jointly devised system based solution Against the background of MAN’s specifications, coating
experiments were run using two selected systems in the pilot plant at the Herdecke site. The coating patterns were tested both at Dörken and at the fastener manufacturer’s premises, using the tests that had been previously jointly defined. In the subsequent assessments a solution already began to crystallise, based on a zinc flake coating and a customised form of post- lubrication. In further tests it was possible to confirm the new coating’s functionality.
application methods. Which method to choose depends on the size and shape of the parts. In MAN’s case parts of smaller dimensions are being coated using the dip spin process (pictured below), while for bolts > M16 spin coating has proved the most cost-effective method. After coating and preliminary drying, the protective coat gets cured for an average of 30 minutes with the part at temperatures of 200°C to 250°C. Subsequently a new form of post-lubrication with multifunctional properties is applied using Delta-Lube®
10. The material has
been specifically designed for mass-produced parts that are assembled using automatic bolting systems. It produces a dry lubricant coat and ensures constant overall coefficients of friction with a value based by MAN on the VDA range of between 0.09µg and 0.14µg. For the user that means predictable and - in relation to tightening torque and clamping force - reproducible results and shorter assembly times. The post-lubrication also gets applied by the dip spin process or spin coating and then
The fasteners are coated using the dip and centrifuge process The basecoat selected, Delta-Protekt®
KL 100, provides
active cathodic protection and with a coating thickness of just 10µm achieves – dependent upon layer build-up, shape of the parts and form of application – corrosion resistance times as defined by DIN EN ISO 9227 of up to 1,000 hours. Another factor of importance for use on high-strength steel fasteners is that as no hydrogen is introduced in the coating process, any danger of hydrogen embrittlement caused by the process can be confidently ruled out. The coating can be applied in all standard
gets dried for approximately 15 to 20 minutes at 50°C to 60°C. In order to reliably identify the newly coated parts, the new post- lubrication has a greenish colour.
The whole concept has to be right The new coating structure has now been approved by MAN
as part of the MAN 183 company norm. Key factors for this global player in the commercial vehicles industry were not just the technical features of the solution, but also Dörken MKS Systems’ global presence through a system of local subsidiaries and the application of the products by licensed coating companies, which using coordinated application techniques achieve the same high quality of coating results all over the world. Application advice is provided by Dörken MKS employees in all major European markets and in addition to the large technology centre in Herdecke there are also tech centres available in the USA, South Korea and – particularly important for MAN – in the growth markets of Brazil and China. An expert contact is therefore always close at hand.
www.doerken-mks.com 126 Fastener + Fixing Magazine • Issue 73 January 2012
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