23. 07. 2018
So far for 5 years since we founded Retro FACTORY s.r.o. we manufactured and anodized over 100000 pieces of different aluminum (dural) products, but we always had a lot of issues, where we cannot do any kind of repairs. We tried all local or foreign anodizing factories with different results. So I think we can say, that we have a lot of experience with surface finishing of EN AW 7075 Aluminum (Dural). And now is the time for change.
We wrote to you a lot of times about problems with surface finishing of aircraft dural EN AW 7075, because we use this material for manufacturing all of our parts. We also wrote about a lot of attempts with anodizing processes, but we finally have a solution.
So, first lets talk about anodizing. Anodizing is process, where surface of aluminum (not dural) is protected by layer of aluminum oxide, which protects aluminum from corrosion and make the surface not conductive. This process can be 100% guaranteed if you use pure aluminum, but we are not saying that it is impossible to anodize durals (aluminum alloys) with different chemical structures. Durals have different chemical structures, which makes much more better mechanical properties, which is case of our Dural EN AW 7075 and thats the reason why we use it, because it has extreme strength and resilience. But dural EN AW 7075 has elements of AlZnMgCu1,5. And that is where the problems started. Every piece made from this material must be degreased if you want to anodize it, commonly with a lye because of its high efficiency. But lye reacts with Zinc and Zinc starts to vaporise with this reaction, that changes dimensions of the product. So after degreasing, there is a risk of widening the dimensions - for example the size for the bushings/bearings and we do not want that. Next problem is in the anodizing process. Elements of copper literally hates anodizing baths and after the process, if you have copper elements on the surface of the material, these elements are shot out from the products and creates a little craters or stains under the surface. From our experience we know, that coppor is the killer of anodizings and there is not much to do with it. Only to categorize good or bad parts, but that makes us to loose around 10 - 15% of the final products.
Simply said, aircraft dural EN AW 7075 is not possible to anodize. The right way of dural EN AW 7075 surface finishing is passivation and powder dye. That is also not possible because we need high precision and shape difficulties, mostly in our CNC gearboxes. Powder dye process requires another technological steps and we do not want that too.
In cooperation with Switzerland oil manufacturer Motorex, we changed original emulsion from Blaster company to special emulsion for CNC milling of aircraft dural EN AW 7075, which has certificate from French Airbus company. This dural is commonly used in the aircraft industry in manufacturing long-term stressed parts in airplanes. Problem of dural EN AW 7075 is very low corrosion resilience. Solution of this problem is special Polymer emulsion Motorex 8200, what we use in our CNC machines. This emulsion has low oil element (around 20%) and all needed properties are secured with Polymers. These Polymers have great properties for CNC milling or cooling our machines, but mostly, they provide great anti-corrosion protection for dural EN AW 7075. These great properties are compensated with high cost of the emulsion. But this precaution is now only for CNC gearboxes, where we need precision dimensions. Other products will have for now their own colorful anodizings.
But in any case, we recommend to make maintenance of your gearbox through time with: for example anti-corrosion oil.
All of our new parts have machined cut offed edges, because we don't need the requirement of bluntening the edges in lye, like we wrote before. The example how we cut off the edges in cnc machine.
This technological process also come with another benefit. We do our own surface finishing process in the process of milling the products, so we do not need any third-company anodizing factories, where our products sits for weeks during the overloading of anodizing factories. This makes much more faster manufacturing process and give us more products in stock on our internet store.
