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Trouble free fitting through new topcoat






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.

In launching the Delta-Protekt® VH 301.1 GZ topcoat, Dörken MKS-Systeme GmbH & Co. KG of Herdecke 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. 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. It 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 surface has been used in various build locations both in lightweight construction and in the difficult applications mentioned and successfully solved the fitting problems there. Combined with the tried and tested Delta-Protekt® KL 100 zinc flake basecoat the system features 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 heatinduced loosening as defined by VW 1131-2, a value of > 0.06 is achieved.