Where the
world gathers for metal finishing
Q&As since 1989


-----

Hydraulic tubing passivation

We are zinc plating hydraulic tubing and we need to stop the inside from rusting. Does anybody have a suggestion?
Todd Rogalla

2006

---

First of two simultaneous responses -- 2006

That will depend on who you are making them for and what they will let you do.
I assume that you do not want to plug the tube, which is choice #1. After that, you might look at doing a better job of blowing out the moisture and then baking as soon as possible. You might then get by with flushing the inside with their hydraulic fluid to put a thin "oil" barrier on it. Store in a vacuum or in a very low humidity will prevent any further growth. Ship in VPI paper.
James Watts
Navarre, Florida

---

Second of two simultaneous responses --

Immersion in a lacquer clearcoat.
John Martin

2006

---

First of two simultaneous responses --

John, he would have to clear that with the purchaser as it is soluble in at least one type of hydraulic fluid.
James Watts
Navarre, Florida
2006

---

Second of two simultaneous responses --

You need to plate the inside of the tubing. To do this will require an internal anode.

One way of doing this; cover the ends of each tubing section with plastic caps. Drill a small hole in the center of each, and a bunch of larger holes around the center, making sure the piece retains structural integrity. Pass some stainless steel wire through the center of the caps. Tie off one end, and clip the excess wire off. Tie a knot in the wire where it comes out of the other end after pulling it taut, such that the wire passes down the length of the tubing in the center. Then, connect this end of the wire to the anode bus. Now, plate.

This is meant for an alkaline or cyanide zinc bath. A rig like this would not stand up to a chloride zinc bath. For that application, you would need a special insoluble anode material.

Good luck!

Dave Wichern
Consultant - The Bronx, New York
2006