Larry Klungtvet

Re: Production Manager

Hello Forum,

As a new member, I hope that I can add assistance to, and gain knowledge from the Metal Finishing Community. Recently our Company has ventured into high cosmetic hot chamber zinc casting process. These products are then outsourced for Ti-gold plating which requires a chromed substriaght. Our plater is experiancing issues with pits which they are having difficulties removing with their polishing process. Anyone out there that has background associated with zinc castings and probable causes that are contributers to these casting issues,  please feel free to respond to my delemma.
If additional information is required to work towards a solution, please let me know.

Thanks,

Larry

DustinGebhardt

Re: Production Manager

I'm not 100% sure what "high cosmetic hot chamber zinc casting process" is, but in my experience with zinc die castings, porosity is a common problem.  Zinc castings require a delicate touch when polished and if handled too roughly you can cut through the outer skin and into the porous inner layer.  To fill the smaller pores, you can try plating the parts with a cyanide (or alkaline non-cyanide) copper strike and plate. You may need to build up a good bit of thickness so that the pores fill in when you re-polish the part.  For the larger pores, you most likely will have to scrap the part.

I have also heard of people injecting some sort of resin into the castings to help with the porosity, but with limited success when the parts are then plated.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC

johnthepolisher

Re: Production Manager

I agree with Dustins suggestion of using a heavy layer of copper plate, followed by polishing. If you still have deep pits which cannot be removed with manual polishing, you can fill the remaing pits with solder, blend the repair with light polishing, & followed by another copper strike prior to plating. We have been using this technique for years when we restore heavily pitted antique auto trim.