We are a small manufacturer of air compressor pumps. We paint our products after assembly using HVLP spray guns. Our units have deep fins on the cylinders and some units have oil pumps extended off the end, which often have oil residue. What would be the least expensive method to clean these units so that rust will not appear after painting?
If you have low-volume production, it is possible that you may be able to clean it with a small pressure washer, although you would likely have to collect the waste or run-off from the process. Rather than going to Home Depot and then fabricating a spray booth, there are some manufacturers that make turnkey systems for spray wand cleaning and/or phosphatizing that have a spray wand, booth and collection/recirculation system.
If you do not believe that spray cleaning would be effective due to the configuration of the product, an immersion cleaning system could be fabricated rather inexpensively (again assuming relatively low-volume production). I would suggest three tanks—one for wash, one for rinse and one for a water-based rust inhibitor.
If there is not a lot of contamination on the parts, it is possible that you could get by with a single stage. There are some products advertised that are cleaners and rust inhibitors in one package and do not require rinsing. I would approach that option cautiously since my experience with those products has been that they only clean light oils, rust protection is moderate and compatibility with the paint needs to be evaluated. Although this may be a fair amount of work to do, it could pay off in the end if you can find a product that will work in only one stage.