Replacing Cadmium with Powder

Question:

We currently have low carbon steel parts plated with cadmium in use as balance weights on aircraft wheels. We would like to eliminate the cadmium. Would a powder coating be durable and corrosion resistant? If so, what type coating would be suitable for constant exposure to temperature extremes and a variety of chemicals such as de-icing fluid, hydraulic fluids and other corrosive agents? We also need to keep the cost low. B.M.

Answer:

Powder coatings are currently used on wheel balancing weights in the automotive industry. I know that the automotive industry is happy with their performance, but let’s face it, it isn’t the same environment as aerospace. Powder coatings are frequently used to replace cadmium and other plated materials. However, it would be unrealistic to expect that powder coatings would perform as well as plating. It would be like comparing plastic (powder) to metal (plating). Having said that, powder coatings are used to replace plating in a variety of applications where the full performance of plating is not required. Powder coating over low carbon steel can provide 500 hr or more of salt spray resistance when applied over an iron phosphate pretreatment. Furthermore, epoxy powder coatings are ideal for your application since they have excellent corrosion and chemical resistance properties and are available at a low cost (typically under $2/lb). Examples of epoxy powder coating applications are utility transformers, electrical switchgear, offshore oil rig equipment, etc. The chalking that will occur on the epoxy powder surface when it is exposed to sunlight will not impede the performance of the coating in your environment.

Furthermore, epoxy powder coatings are well suited to resist chemicals like de-icing fluid and hydraulic oils. I suggest that you have some weights powder coated and put them on aircraft for life cycle testing to prove their suitability. Use a pure epoxy powder to take full advantage of its inherent chemical and corrosion resistance.