Plating protects against corrosion and wear. Though many processes require electricity for plating, some can use chemicals in electroless nickel plating. Check out these best practices and a six-step process for faster, easier and safer nickel plating on whatever project you’ve got going.
1. Prepare the Surface
You’d never paint without priming, so why would you plate without prepping? Before electroless nickel plating, you need to ensure the metal's surface is ready to take on the coating. The use of the coated product will determine the product’s treatment type. Heat-treated metals have undergone extensive stresses. These need to have the stress released first before dipping into the plating bath.
You also need to prepare the surface of the metal to accept an even coating of the nickel alloy. Typically, manufacturers opt for blasting, washing, rinsing and an acid bath to completely remove all surface imperfections. Electroless plating evenly coats the surface. This preserves rather than hides scratches that remain after pretreatment. The alloy plating will also preserve any dust or dirt, which is why several washings and an acid bath are so important before the alloy dip.
2. Match the Solution to the Purpose
Carefully pair the alloy solution with the purpose of the coated materials. Alloys have a combination of phosphorus and nickel. The percentage of phosphorus affects the properties of the coating — percentages range from 2 to 13 percent. Low phosphorus is under 5 percent. This alloy percentage produces the hardest coating without additional treatments. It also best withstands alkaline conditions. Between 5 and 9 percent, medium phosphorus alloys have the best appearance.
The highest percentages from 10 to 13 percent will yield the hardest coating if you thermally post-treat the pieces. With higher percentages of phosphorus, you get more acid protection. Additionally, high phosphorus is the most corrosion resistant of nickel plating coatings.
3. Monitor the Bath Age
The age of the bath will determine how well the coating adheres to the piece. The byproducts of the chemical reactions that occur in the bath result in degradation of the bath. Baths last only four to 10 metal turnovers (MTOs). With each metal turnover, the mixture produces byproducts, including orthophosphate.
Analyzing the concentration of this product can help determine the age of the bath. Keeping track of replenishing the materials in the bath or measuring the specific gravity can also tell you about the bath's age. Don't let the bath degrade too much or the coating will be subpar.
4. Maintain the Bath Depth
The bath depth is critical for evenly coating the piece. With each coating, the plating process can use 10 percent of the solution, which will drop the volume of the bath by an equal amount. Workers should keep an eye on the volume and maintain the correct solution with every plating.
Monitor the amount of nickel alloy in the bath after each treatment. Also, keep the bath at a depth that will allow for complete submersion of the pieces being coated. Constant concentration and depth will create the most even coating.
5. Keep Temperatures Constant
Temperatures dramatically affect the outcomes of nickel plating. In low temperatures the process will take much longer. If you turn up the temperature too much, however, the process can occur too quickly.
Avoid temperature changes as much as possible. Automate temperature monitoring and regulation to prevent out-of-control reactions or excessively slow coating times.
6. Use Post Treatment Heat
Post-treatment heat times depend on the phosphorus concentration and the hardness desired. The greatest hardness without post-treatment comes from low phosphorus concentrations. Heat treatment after coating can improve the hardness of the nickel plating. As coated, the plating has a hardness of around 63. A heat treatment may improve this with high phosphorus alloys.
To achieve maximum hardness, one hour of heat treatment will suffice. However, the temperature will depend on the phosphorus content. Mid and high phosphorus levels require treatment between 375 and 400° C. Low phosphorus alloys require higher temperatures. Treat these products between 400 and 425° C for maximum hardness.
Safety When Nickel Plating
Nickel plating can cause serious health problems for workers in the area. Powdered or ground nickel is most likely to cause skin and respiratory irritation, especially in sensitive individuals. Though some may have to give up nickel plating due to severe reactions to nickel, others can use protection to keep milder irritations at bay.
Since sensitivities can develop over time, all workers in the area need to protect themselves from contact with the nickel. Gloves and ventilators are the best safety gear to wear when working with nickel. Masks may help, but they pale in comparison to the protection provided by ventilators.
Improve Your Electroless Nickel Plating
When you consider these factors before, during and after the plating, you'll produce more appropriately plated pieces that will better serve their intended use. With these best practices, you'll improve your nickel plating processes, and your customers will be pleased with the results.