How Electroless Nickel Plating Is Applied
When items are to be plated at a plating shop, they are processed through several stages. Each stage includes various processes and procedures, which are all carefully controlled in order to provide a quality nickel coating to the parts processed at the plating shop.
Cleaning and Pre-Treatment
The part has surface oils, contaminants, and residues from the machining process. These must be removed by alkaline cleaning followed by acid etching. This helps to ensure that any subsequent coating does not blister off the surface or fail to bond.
Activation
The parts to be plated are immersed in a solution containing a palladium-based activation agent for a short period of time. This agent creates points on the surface of the metal where the subsequent nickel deposit can commence.
The Plating Bath
The part is then submerged in a solution of nickel salts and a reducing agent such as sodium hypophosphite in a heated bath. This process of electroless nickel plating is a chemical reduction process that produces an even layer of nickel in all areas including hidden areas such as the inside of holes, threads and other recesses. As the process uses chemical solutions the strict chemical handling requirements for plating operations as stated by the HSE must be adhered to by any plating shop.
Post-Plate Heat Treatment
Heated treatment – typically around 200°C up to 400°C – is sometimes carried out on plated parts in order to drive off any hydrogen that has been absorbed during the plating process. This also helps to increase the hardness of the coating, which is important for wear-resistance.
Thickness and Quality Checks
For the layer thickness measurements, magnetic gauges or X-ray fluorescence gauges are used. In the final check for visual defects such as pitting, bare spots, etc. parts are inspected and, if necessary, re-plated and re-checked.
All the above processes have to work together well and any problem with any of the processes will usually be revealed by the final test.
