lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Alodine coatings are nice because you can do them at home in just a few minutes. Professional painters have told me that the single most important thing to promote paint adhesion on aluminum is to alodine it first. I use Alumprep 33 and Alodine 1201, but there are other products out there. (Metalprep doesn't seem to work that well.) The problem with alodine is that is scratches very easily. Way more easily than anodize. Given a choice, I'd anodize. However, you probably have to pay $50 for a minimum anodize order so unless you can wait for a bunch of parts, it's kinda expensive. If I'm going to make a bracket and flox it in place right away, I use alodine. If it's a removable piece, I send it out with the next anodize batch. To alodine, you first etch the surface with the Alumiprep to remove the oxide coating. Yes, the surface you see is aluminum oxide, not aluminum. In fact, I'm told that aluminum oxidizes so quickly that you will never see bare aluminum unless you machine it in a nitrogen atmosphere or -- sorry, I can't resist this one -- in one of those other noble (oops, I mean inert!) gasses. Fortunately, aluminum oxide is a good protective layer -- that's why bare aluminum lasts so long -- and we can usually ignore this effect. Back to business. You remove the oxide coating with the phosphoric acid etch (Alumiprep). Rather than sandpaper, I like to use Scotchbrite. Rub it gently while soaking in the alumiprep. (Under no circumstances use steel wool.) Rinse it off but don't let it dry or you'll get the oxide coating back. Then dump it in the Alodine solution. The soaking times are on the bottle but it's fairly short, about a minute or so. Then air dry. If you rub it dry you'll rub the coating off, but it seems to be more hardy when it's dry. All you need for protection is rubber gloves. I have found that using tap water can give you funky color streaks, so I go to the grocery store and get a couple of bottles of distilled water. Don't get "drinking water" that has the minerals put back in or you defeat the purpose. Actually, you get better results with professional alodining. They have heated tanks (I think) and frankly, do a better job. Send all your pushrod raw stock out to be alodined all in one big batch. This way the inside of the tubes get a good coating, too. They'll also be wrapped in paper when you get them back for scratch protection. When you cut them to length, only the cut ends are unprotected, and who cares about those? Then you can paint or powder coat. I send my completed pushrods out for powder coating. Normally they want to sand blast before powder coating but I tell them not to and I haven't had a coating failure yet in my shop. This is a similar price to anodizing. By the way, tape the ends or they'll powder coat those, too. They'll probably replace your masking tape with a high temperature tape that won't burn when they bake it, but at least they'll know where to mask it off. FYI, a flap pushrod (about 2 feet long, 3/4 inch diameter) weighs only 2 grams more after powder coating. I had my control crossover weldment powder coated, too. You have to mask off the areas that the stick slides into, and where the weldment slides over the phenolic, because the powder coat does add a little thickness. I actually had a small patch of light surface rust forming on my weldment so I let them sandblast that piece prior to coating. - Rob Wolf >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>