Plating of visual functional components using “chemical nickel”

RENNER GmbH – Pumps and filter technology meeting the highest quality standards

Electroplated components are an indispensable part of daily life in almost every area these days. But components have to meet increasingly tough requirements, which are also totally different depending on the application. With its broad-based product range, RENNER is able to supply pumps and filter technology for all wet processes in electroplating. The requirements for fluid management are just as stringent as those for the process technology and for the subsequent use of the component.

Surface coating can be used to meet decorative or functional requirements. The most important functional requirement is corrosion protection.
But improved wear resistance, especially sliding properties, and a defined level of thermal or electrical conductivity are also very important.
Decorative requirements can be divided into color, roughness, shine and feel, and most surfaces need to simultaneously meet both functional and visual demands. By combining different methods and using an appropriate layer structure, the same component is able to meet multiple requirements. Metallic coatings on components are frequently produced using electrochemical
deposition. The process, which is generally divided into electro deposition (using an external electric circuit) and chemical deposition (without electricity), enables the properties of the base material to be changed or enhanced.
One of the most important tasks in metal deposition is to increase corrosion resistance – for example in ferrous materials. Another very popular requirement is to improve wear resistance, which is primarily achieved by deposition of chromium or nickel phosphorous.
Finally, deposition of multiple layers of nickel chromium or precious metals such as gold, palladium or silver enables the color and feel to be changed.
This technique is particularly widely used in the automotive sector for plating plastic components in vehicle interiors – where color and feel are the most important concerns.

Nickel is a great all-rounder in surface engineering and, thanks to its versatile properties and almost universal usability,
is one of the most important and frequently used plating materials. Nickel layers are notable for their high resistance to corrosion, as well as to many acids, seawater and alkaline solutions. Their chemical resistance is further increased by formation of an oxide layer. Meanwhile, nickel is also valued for its tribological benefits, such as wear protection and gliding properties. The silvery white appearance with a slightly yellow tone, which can be adapted from matte to shiny, also make it an excellent choice for decorative applications. Depending on the specific requirements, nickel can be deposited electrochemically or chemically. Both plating methods provide their own properties, which are not in competition with one another but actually complement one another from a technical and economic perspective. RENNER offers the perfect pump and filter technology for both electro deposition of nickel and for the much more demanding chemical nickel deposition.
While plastic-magnetic centrifugal pumps and plastic centrifugal immersion pumps that are safe to run dry can be used for nickel electro deposition, for chemical nickel deposition the entire wet process technology is made of electro-polished stainless steel.
In addition to the material used for the pump and filter components, the pump output, flow control and appropriate choice of filtration technology are crucial factors.

Nickel electroplating

Nickel electroplating is one of the oldest electroplating methods. The electrolytic coating method is used on
non-ferrous metals and steel, and is an indispensable base layer. Nickel plating also acts as the basis for additional layers, for example chromium, gold or tine. The deposited layers can be matte or shiny. For example, nickel electroplating is used as a diffusion barrier for gold plating or as a shiny layer in chromium plating. It is also used to prevent whisker growth – for example as tin layers
in plugs, contacts and other products in the electrical industry.

Chemical nickel plating

Chemical nickel, also known as nickel phosphorous (NiP), is a functional and visual surface finish and is notable for its excellent wear and corrosion resistance and its good dimensional stability. Chemical nickel also has outstanding contour accuracy in deposition. The coating is a nickel/phosphorous alloy, which is primarily used for functional components. The phosphorous deposited in the layer enables various properties of the layer to be controlled. We differentiate between a high (10 to 14 percent), medium (up to 10 percent), and low (3 to 7 percent) phosphorous content. The method is also known as electroless nickel. The differences from nickel electroplating include the fact that no external electrical current, from a rectifier for instance, is used for deposition. The electrons necessary for deposition (reduction) of the nickel ions
are produced by a chemical oxidation reaction in the bath itself.
Metal reduction occurs at the same rate in all areas of the component to be coated, as long as sufficient quantities of metal ions and reducing agent are present – in other words for as long as the electrolyte is flowing over the solid surface. Thus, chemical nickel plating results in coatings with excellent contour accuracy. To obtain a very good and homogeneous layer distribution on particularly complex component geometry, it is extremely important to ensure an optimum flow around the components so that the internal surfaces and the hidden corners and edges can all be completely reached. This requires pump control adapted to the relevant component geometry. RENNER not only supplies the relevant pump technology, but also offers expertise and advice on correct fluid management. Only by ensuring effective interaction of all these conditions is it possible to achieve the potential
deposition of dimensionally accurate chemical nickel plating with a uniform layer thickness distribution on almost all metals and alloys. The uniform layer thickness makes auto-catalytically produced nickel plating excellently suited for workpieces with a complicated geometry – even internal plating can be achieved to a certain extent. Chemical nickel layers are also very
resistant to wear. This means that the chemical nickel surface provides excellent wear protection. Corrosion protection is also very high with electroless nickel. Chemical nickel coatings are also conductive. As high phosphorous chemical nickel (high phos) with a phosphorous content of over 10 percent, the layers are non-magnetic.
They are also x-ray amorphous, have excellent impermeability and can effectively withstand compressive stresses. X-ray amorphous layer thicknesses up to 800 μm are also suitable for diamond processing due to their high purity and homogeneity. They also provide good solderability. The aim is to obtain a closed layer of the high phosphorous nickel plating, which can then be mechanically processed with appropriate
diamond tools without cracking (ultra-precision processing in the nanometer range).

Requirements for pump and filter technology

For any coating process, a particle-free surface is essential, in other words there may not be any dirt particles, which could be deposited on the components. In general, the demands on the systems and baths, as well as the system components, are considerably higher
and more complicated for chemical nickel than for electroplating, for example. Challenge: The electrolyte “bleeds dry”. As the bath becomes increasingly old,
stabilizers and the pH value in the bath have to be kept constant, which can be achieved using additional dosing pumps and regular monitoring of the values. The temperature of around 90 °C in the bath must also be kept constant, which results in corresponding requirements for the circulation pumps and the associated pipe routing. In addition, the pump technology must be sufficiently flexible to allow variable adaptation of the flow through the bath at any time
depending on the components to be plated.
This can normally be achieved by using appropriate pump technology with additional speed control. To prevent nickel deposition on the pump and filter components, RENNER manufactures all components from stainless steel and artificially passivates them.
But the design of the pump technology is not the only factor that plays a major role in achieving optimum plating. The right choice of filtration technology is also critical. To meet all these requirements and cope with the increasingly complex components, the plating systems, their pump and filter technology, and the process technology have to be continuously optimized and developed. RENNER is a single source for everything that is needed and supports its customers with its expertise, know-how and flexibility.

by Karin Renner