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MANUFACTURING TECHNOLOGY


Trouble free fitting through new topcoat


A new Dörken MKS Systems topcoat offers optimised threaded connection properties when fitting against parts made of aluminium or against KTL-coated surfaces.


I n launching the Delta-Protekt® VH 301.1 GZ topcoat,


Dörken MKS-Systeme GmbH & Co. KG of Herdecke says it is providing an enhancement of this silica-based seal with integrated lubricant. In particularly difficult applications


it prevents stick/slip effects when building chromium(VI)-free surfaces against KTL-coated parts. The new topcoat can also be assembled against aluminium without any problem and thus fulfils the specifications of VW’s new norm 1131-1/2. Dörken explains that in the changeover from surfaces with


chromium(VI) content to chromium(VI)-free surfaces, there were problems in the past when fitting against KTL-coated components. These are reflected in VDA 235-203 test specifications and the surfaces approved there. Currently the only areas where these so-called stick/slip effects are still evident are in particularly difficult applications. These include, for example, fasteners with extreme outer supports. Another problem is presented by the increasing demands for


reduced weight in vehicle construction. This is now leading to the use of appreciably more lightweight metals, such as aluminium and magnesium. The connecting surfaces below the bolt head range here from die cast parts, to milled or polished backing runs. As regards the thread, screw-in depths are required of three times diameter into the grooved thread. High coefficients of friction lead here at full load / when tightening the angle of rotation to high levels of fastening torque, which exceed the control limits and even the capacity of the power screwdrivers being used. The new Delta-Protekt®


VH 301.1 GZ topcoat has been


developed specifically for such scenarios and meets the specifications of VW’s new 1131-1/2 norm, such as, for example, double fastening into the yield point against aluminium or five- times fastening into KTL. The new topcoat has been used in various build locations both in lightweight construction and in the difficult applications mentioned and successfully solved the fitting problems there. Dörken points out that combined with the tried and tested KL 100 zinc flake basecoat the system features


Delta-Protekt®


corrosion resistance times of over 720 hours in salt spray testing and also provides greater resistance to brake fluid, oils and cleaning agents. It improves mechanical properties, prevents the problematic stick/slip effects, withstands loosening under temperature of up to 180°C for 96 hours, achieves better grip results and ensures that coefficients of friction are kept constant. Depending on the layer build-up and the shape of the coated part, the coefficient of friction here, as defined by DIN EN ISO 16047, falls into a range between 0.09 und 0.14µges (VDA – Association of the German Automotive Industry). The corrosion protection layer’s particularly high resistance to mechanical stress also enables constant coefficients of friction to be maintained even when parts are screwed in or out numerous times. The screw connection retains its friction-locking capacity even when exposed to heat. In terms of heat-induced loosening as defined by VW 1131-2, a value of > 0.06 is achieved.


Magni 501 enters the market


New to the coatings market is Magni 501, a single-layer, thin-film, zinc metal coating system designed to replace zinc plating, electroplating and trivalent passivation.


U


S based Magni Industries’ research and development staff along with senior design leader, Paul Badryka, engineered this new zinc-rich metal component coating to increase corrosion resistance with no added costs. The key to the new chrome-free coating is the combination of unique


anti-corrosion pigments blended into the Magni 501 coating system as a perquisite to extending the service life of the steels used to make fasteners and stampings. The other key design goal was creating the rheology necessary to achieve better film forming characteristics when coating fasteners in bulk applications without sacrificing cathodic protection. Magni points out that the chemistry selection of Magni 501 results in improved physical


properties that help achieve uniform film thickness and better coverage of sharp dihedral thread crests over a wide range of g-forces, resulting in improved adhesion and chip resistance to accommodate common bulk processing issues. “Other performance properties, such as no hydrogen embrittlement concerns, no waste treatment, torque tension


consistency, paintability, no post-coating sealers and environmental compliance (WEE, ELV, REACH, and RoHS compliant) are exactly the traits desired by metal component manufacturers. Magni 501 is ideal for fasteners (nuts, bolts, screws) and especially recessed parts and is typically applied via dip-spin or spray methods.”


120 Fastener + Fixing Magazine • Issue 71 September 2011


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