MANUFACTURING TECHNOLOGY
Therefore, the choice for the best suited electrolyte for the application in question can technically be met based on performance preference (alkaline for rack application like stampings and acidic ZINCROLYTE KCl-Ni for barrel plating in particular for fasteners). Significantly reduced plating time not only contributes to cost savings, but also reduces the mechanical stress to the fastener during the plating sequence and supports perfect thread appearance with low mechanical damage. Comparing M10x50 fastener plating in barrel application using an acidic versus an alkaline electrolyte results in the situation shown in Figure 3. With the same thickness being achieved on the fastener head, the difference in thickness on the shank is minor.
and ENSEAL® lubricated sealants, such smoother surfaces are
the perfect prerequisite for less scattered coefficients of friction, resulting in consistent clamping forces achieved in torque controlled automatic assembly applications (Table One).
Table One µtot ZINCROLYTE® NCZ 315 Plus ZINCROLYTE® KCL-Ni alkaline
electrolyte acidic
electrolyte vs
steel 0.12
0.12 µtot vs
aluminium 0.21
0.18
Table One – coefficient of friction measured according to ISO 16047 of M10 fasteners plated in alkaline zinc-nickel from ZINCROLYTE®
NCZ 315 Plus
and acidic zinc-nickel from ZINCROLYTE® KCL-Ni. Post-treatment in both cases PERMA PASS® Ultra III 21
and ENSEAL®
Figure 3 – the same kind of M10x50 bolt plated to the same thickness on the head (12.8µm) in the acidic electrolyte ZINCROLYTE KCL-Ni (left) and the alkaline process ZINCROLYTE®
Minor differences in thickness distribution The clear advantage from choosing an acidic electrolyte for
barrel application is the higher plating speed resulting in shorter plating times and higher throughput. Additionally, the excellent seeding behaviour of the electrolyte allows for very fast initiation even on materials with a low hydrogen over potential such as particular case hardened, carburised fasteners. On top of that, the layers plated from acidic electrolytes
feature a fine grained structure with a lower tendency for nodule formation on the surface, even in unfavourable conditions. Such nodule formation – as seen in Figure 4, right image – changes the friction properties, particularly of relatively soft bearing materials like aluminium.
ENSEAL® ENSEAL® ENSEAL®
21
1303 26
Choosing the right lubricated sealant process, depending on OEM demands, allows for excellent control of the coefficient of friction of the fastener in different ranges (Table Two).
NCZ 315 Plus (right). Table Two µtot
0.09 – 0.14 0.10 – 0.16 0.12 – 0.18
Table Two – coefficient of friction ranges matching different automotive OEM requirements. Measurement according to ISO 16047
Conclusion The latest generation of acidic zinc-nickel plating solutions opens up the possibility to choose the best suited ZnNi plating electrolyte, technically based on the type of application. Excellent control on the nickel incorporation in the zinc-nickel gamma-phase region best suited for cathodic corrosion protection is achieved with ZINCROLYTE®
KCL-Ni latest
Figure 4 – bottom section of screw threads, left as plated in a ZINCROLYTE KCL-Ni acidic solution, right as obtained from an alkaline plating solution
Acidic ZINCROLYTE KCL-Ni already provides a smoother
surface, which is an excellent prerequisite for good control of friction properties. Together with well matched post-treatment processes such as PERMA PASS®
trivalent chromium passivates
generation acidic ZnNi electrolytes. On top of the higher throughput from this type of electrolyte, other benefits are given – such as very fast initiation on particular difficult materials; tribologic behaviour benefits from a smoother surface resulting in better control of friction properties; and uniform cosmetic appearance making acid zinc-nickel plating an economic and technology-wise beneficial process for fastener applications.
®ZINCROL YTE, PERMA PASS, and ENSEAL are registered trademarks of Enthone Inc.
www.enthone.com
108 Fastener + Fixing Magazine • Issue 89 September 2014
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