Alternative to thick zinc coating

Galvano Hengelo has been a specialist in electroplating industrial products for over 20 years. A recent development of this Hengelose company is to improve the technique devised ten years ago to galvanize hydraulic steering blocks with a zinc-nickel coating. Problem with the galvanic zinc plating of these so-called manifolds are the Hollow (internal) spaces. For this, the company has now found a better solution.

Ivo Willemsen, general manager of Galvano, talks to us at the TIV in Hardenberg. ‘ Some ten years ago, a supplier of Siemens and Vestas came to us asking for their hydraulic steel steering blocks (so-called manifolds) for use in wind turbines to provide a thick zinc coating with chromaatpassiveer. This is a surface layer based on chromium-6 which was already suspicious because of its toxic properties. We then made Siemens and Vestas a counteroffer to replace it with a zinc-nickel layer. This new corrosion protection system brings Galvano under the name Protalloy on the market.

Galvanic zinc-nickel gives very good corrosion protection on steel. Applications need to be mainly searched in the drive technology (hydraulics), machine and equipment construction, energy technology, automotive etc. Where conventional zinc/zinc iron systems and/or chemical nickel systems are not good enough in terms of corrosion resistance, Protalloy is shown in the picture, for example in conditions with high humidity and salt load and/or temperature fluctuations. The so-called high zinc-nickel alloy is blank passivated (CR6-free) evt. In combination with a thin topcoat. This makes a low thickness of at least 5 mu an extremely high corrosion resistance of at least 1,000 hours protection against ground metal corrosion in a neutral salt spray test. In addition to the high degree of protection, Protalloy offers the advantage that the layer does not disturb the welding work on the treated product and also constitutes a fine adhesive layer for a possible coat of paint.

Nine Steps

Due to the galvanic zinc plating, the manifold is provided with the desired Zink-nickel layer in nine steps. That starts with degreasing and after pickling, degreasing again and activating the galvanizing process can begin. Disadvantage of galvanizing is that you only provide the outside with a protective layer. The inside, the hollow spaces of the manifold, are not reached with the zinc-nickel. But due to the galvanizing process, these hollow spaces are activated and will quickly corrode without protection (very quickly, even during the galvanizing process). ‘ We found something on that, ‘ says Willemsen. ‘ What we do is to actively empty internal cavities during the galvanizing process and we have also the chemistry in the line so that the internal surfaces without corrosion come out of the process. After coating thickness measurement and internal inspection of the blocks, the internal surfaces are further preserved with an anti-corrosion agent. ‘

Patterns/Cartridges

This process is improved every time. The most recent development is that we can now also supply the cartridges/cartridges in the manifold with a zinc-nickel coating. This is important because a manifold soon contains dozens of cartridges and this would still mean a weak spot in the corrosion protection of the entire product without zinc nickel. Until now, it was not possible to provide these cartridges with a protective layer because the cartridges are no longer fit in the manifold because of the layer thickness. There has now been a change because Galvano Hengelo is now able to partially shield active parts during the zinc-nickel process. As a result, these parts do not receive zinc-nickel treatment on dimensionally critical surfaces. Since these dimensionally critical surfaces are always mounted in the block, where they are surrounded with oil, no corrosion protection is not a problem here.

Author: Gerard ten Bulte
Source: vraagenaanbod.nl