Inner corrosion of zinc plated and sealed tubes

Hello everybody,

now I need some help from my plating colleagues.

We plate some steering columns in a job shop. The head breaking thing is, if these parts leaving the line, we can detect in the inner tube some brownish-redish spots. We have made several tests in pre-treatment and after treatment but did not get any better results. Sometimes the parts are leaving the line in a very good condition and sometimes we have 100% scrap. Mainly we have on the same rack around 50% bad parts.
We use zinc chloride electrolyte, afterwards blue passivation and a ENSEAL 21A.

Anybody has an Idea?

Thanks in advance,

Dominik

Mr. Dominique,

The inner area of the tube won't plate, therefore you must allow a good rinsing and good drainage in order that you won't have any carried solution inside the tube.

Saludos.

Hello Dominik;

Its better to try plugging the tube ends to ensure that none of the process solution from degreasing/pickling/plating, gets in in the first place.

Once pickled the inner unplated area will be impossible to protect from rusting. Inner areas remain dormant and last up to Six months internal storage without rusting if they are left as it is.

br,