Q. We clean stainless steel parts prior to plating, and these parts are soiled with a slight graphite grease residue. Visually, parts look clean, but when wiped with white cloth, there is a dark spot on the cloth. We’ve tried commercial and in-house cleaners (acidic and alkaline) without any success. For now, we let parts soak in alkaline cleaner (160°F for 60 min), rinse and wipe off the residue. But it’s a long and bothersome job for 1,500–2,000 parts by lots. We have to find a more economical way to do it while avoiding solvent usage for health and safety considerations. Do you have any suggestions? A.B.
A. It sounds like you have tried several good alternatives. You will likely have to enhance the effectiveness of the chemicals with additional energy delivered by mechanical methods. Agitation, ultrasonics and electrocleaning are three means of mechanical energy that can greatly enhance your cleaning effectiveness. Those three alternatives are ranked in approximate relative order of cost and effectiveness. A simple mechanical agitation of the parts and/or wash solution will improve the cleanliness, but from what you describe, it may not get you to where you want to be.
The next step would be to try ultrasonic or electrolytic cleaning equipment that will provide much more mechanical energy to the tank. I would suggest starting with the ultrasonic cleaning first. You are likely to find more vendors that would be able to supply you with an ultrasonic system than with an electrocleaning system. Numerous potential suppliers listed at the PF Online web site would be happy to help you further with your problem. Go to www.pfonline.com and select the Suppliers tab. Follow the links to Cleaning & Pretreatment, then go to the Equipment section and select the ultrasonics link. There you will find most of the names in ultrasonic cleaning equipment. Many of these suppliers should have prototype systems on their shop floor where they can assist you with some process development in order to asses your particular situation and have a high degree of confidence in the equipment before you purchase it.
The ultrasonic systems use a waveform generator to create “bubbles” that will implode on the part surface, providing energy to assist in removing the soil. Alternately, the electrocleaning will create hydrogen or oxygen gas bubbles at the surface (depending whether it is anodic or cathodic electrocleaning) that will provide the energy to remove the soil from the surface.