Bringing Anodizing In-House

Tag : Screw Machined Parts

If anodizing costs as much as $50,000 per year, then installing asmall, modular anodizing line makes sense. These prefabricatedsystems look like a series of in-line washing machines, and haveall necessary tanks, ventilation and closed-loop, rinse-waterrecycling systems. These units range in price from $30,000 to$75,000. Securing requisite permits for these units typically isnot a challenge because the chemical volumes are relatively low andspill containment and fume control are often built into the unit.Such modular anodizing lines are suited for small quantities ofparts as large as 2 cubic feet, and typically have a footprint ofapproximately 20 feet by 8 feet. Part racks are moved manually fromtank to tank with these small modular systems.
If anodizing costs $150,000 or more, then a medium- or large-scalemodular anodizing line may be appropriate. These systems sometimesuse a hoist to move part racks from tank to tank. Prices range from$100,000 to $150,000, and it’s recommended that shops contactan anodizing consultant to help plan line design and developoperation manuals.
Modular anodizing systems generally aren’t recommended if ashop’s annual anodizing cost exceeds $250,000. The tanks,pollution control and other related equipment will be significantlylarger. Although lines of this type might cost between $250,000 to$500,000, an anodizing cost savings of 50 to 60 percent ispossible. In this case, an anodizing expert should certainly beused to develop a preliminary line design before a shop solicitsestimates from equipment suppliers.
Steps In Anodizing Aluminum
Parts must be immersed in a number of baths before and after theactual anodizing process. Each bath has a specific temperature,chemical concentration and immersion time that must be monitoredand maintained. Proper rinsing after every support bath isessential. What follows are the typical steps for Type II anodizingof aluminum alloys. (See page 104 for a detailed list of operationsfor Type II anodizing of 6061-T6 aluminum.) Alkaline clean—Alkaline cleaning is often the first anodizingstep. This bath is designed to remove grease and oils from partswithout etching the parts or removing material. Alkaline cleaningis typically followed by a rinsing bath. Alkaline etch—This bath removes oxides and gives the parts asmooth, matte finish. An etch bath is not required when a brilliantshine is desired at the end of the process. Etch baths should befollowed by vigorous rinsing. De-smut—The de-smut/de-oxidizer bath removes the dark smutcreated by the etch bath and is a critical step prior to anodizing.De-smut stations usually use nitric-acid or ferrous-sulfate baths. Bright dip—The bright anodizing bath, typically ofconcentrated nitric acid, ultimately shines and protects the partsurface. This bath does emit large volumes of nitrogen oxide fumes,however, so proper ventilation is essential. Anodizing in highvolumes can require scrubbers to clean these fumes before they arereleased into the atmosphere. Color—A wide variety of different colors and color patternsare possible in a dye bath. Seal—Anodized aluminum surfaces require sealing to eliminatecolor fading or running. Some sealers include sodium dichromate foradded corrosion resistance.