Some of our copper parts, which have been cleaned but not protected by a chemical reagent but cased by vacuum bag, take on a bad appearance after three days. There are some stains and oxidation on the surface. How would you recommend cleaning the copper parts and also how should we package them? What are the normal processes? Thank you. H.W.
If there is further cleaning necessary, you may want to use an alkaline cleaning to remove any organic residue from the surfaces (such as grease and oil). If the parts are oxidized, they will require a more aggressive acid cleaning to remove the tarnish. After either process, it is essential to provide the parts with adequate rinsing. Alkaline or acid cleaner residue will contribute to the tarnish of a brass or copper part. I would suggest contacting your chemical supplier to review your process and make recommendations if you are having problems with the cleaning stage of the process.
As mentioned in the previous question, a final rinse with either benzotriazole or tolyltriazole would be very helpful to prevent tarnish of the parts. Citric acid has also been shown to be beneficial to minimize the formation of tarnish on parts.
In addition to the final rinse, you can gain additional corrosion protection since you are bagging your parts. There is a category of product called vapor-phase corrosion inhibitors (VCI for short) that are placed into an enclosed space and provide good long term storage corrosion protection. Since you are already bagging your parts, it would not introduce any significantly different packaging into your operation. I would suggest that you would no longer want to pull a vacuum on the bags. Instead, insert the part and the form of vapor-phase corrosion inhibitor that would work the best for your application, and then close or seal the bag. If the bag is left wide open, the VCI will not provide much protection. I also believe that pulling a vacuum could quickly volatilize much of the corrosion inhibitor, not leaving much behind to do its job.
Vapor phase corrosion inhibitors are commonly available for different metal types and different forms for various means of packaging. One common form of VCI is treated papers (parts are wrapped in the paper, and then stored in a bag or box). Types that can be placed into a larger container are plastic disc emitters, foam cushions, and packets. Bubble wrap can also be obtained with built-in VCI protection. VCI can also be purchased in wire form to be placed inside tubes (that are then capped) for corrosion protection during shipment and storage.