As experts in the process of electroless nickel plating, NiTEC UK have the largest electroless nickel plating tanks in the UK.
Pre-Treatment for Electroless Nickel Plating
Before a component can be electroless nickel plated, it must be suitably prepared for the process. Firstly, the part is cleaned in a series of pre-treatment tanks and rinsed in water. It then enters the coating tank which is heated to a critical temperature above 90C and contains the plating solution made up of the nickel-phosphorus alloy and a reducing agent.
In order to achieve the maximum thickness achievable, the part needs to be in the plating tank for approximately 9-10 hours, during which time the solution is agitated and continuously re-circulated to prevent debris being incorporated into the coating. The total contents of the tank will be filtered and re-circulated within 10 minutes.
There are three levels of phosphorus in solution that are typically used, each of them having different benefits and attributes.
Low Phosphorus Electroless Nickel Plating
A low phosphorus electroless nickel coating typically contains 2.5% phosphorus. This produces a very uniform porous free coating which uniformly covers the complete surface of the component, including inside recesses. It has excellent corrosion resistance in alkaline conditions, but the coating is relatively soft, below 235VPN, and is therefore not particularly wear resistant.
Medium Phosphorus Electroless Nickel Plating
Medium phosphorus solutions contain between 6 and 10% phosphorus and produce a coating which effectively combines intermediate hardness with good corrosion resistance. Medium phosphorus coatings deposit rapidly and produce a bright or semi-bright coating.
High Phosphorus Electroless Nickel Plating
High phosphorus coatings contain between 11-14% phosphorus and produce hard coatings of up to 600VPN. This level of hardness is ideal for wear resistant applications in harsh acid environments typical of the conditions experienced in oil and gas drilling or mining applications. The high phosphorus level also renders them non-ferromagnetic and hence suitable for coating, for example, austenitic stainless steels, for applications where ferro-magnetism cannot be toleration such as MRI scanners. Such hard coatings are also used on stainless steel to improve its galling resistance in wear situations.