I have been powder coating motorcycle parts (used/refinishing) exclusively for 10 years. We are expanding our business to include chrome plating, polishing, welding/fabrication and industrial powder coating for outside as well as our own manufactured products (aluminum and steel). As there are a large number of different types and configurations of products in this area, we are implementing a “pressure washer” type cleaning/pretreatment system. What would be your recommendation for pretreatment to get the maximum adhesion/weather-ablity on aluminum railing for use on the coast of Florida. The opinions vary so much with each supplier that I feel compelled to seek outside help. L.C.
“What is the best pretreatment” vs. “what pretreatment I would recommend” can be 2 very different answers. For instance, the best pretreatment for weatherablity and adhesion on aluminum products used in an outdoor Florida exposure is a chromate conversion coating (or Alodine). This process has a proven track record (20 plus years) in the outdoor furniture industry where aluminum chairs are warranted for 20 years against finishing defects and corrosion. However, I would not recommend that you perform this process using a spray wand (pressure washer) system since the effluent contains heavy metals and can’t be sent directly to drain. There are some “chrome-free” aluminum pretreatment processes that are available from several chemical suppliers, but their track record is limited and they may not be compatible with the spray wand application system.
A common combination cleaner-phosphatizer can be easily applied using a spray wand system but will not perform as well as the previously mentioned chemistries. This is the problem you may be having with your suppliers. What is best for your application may not be suitable for your equipment or discharge limits. I recommend that you find a chemistry that provides you the best performance with the least environmental impact and test run some parts for your customer’s approval. Only then will you be able to ensure that you meet your customer’s expectations. If you want to provide high performance powder coating services, you should consider a dip tank system capable of using chromate conversion coatings for aluminum, iron phosphate for common steel and zinc phosphate for galvanized steel. This will cover all the bases.