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


-----

Prevention of electrolysis in agriculture & oil fields

2006

Q. We are a mid-sized company with screw machines, manual machines and CNC machines. We manufacture primarily manifolds and fittings which are used in the propane industry, the agricultural industry as well as in the oil fields. We are in the process of expanding our enterprises world wide with new plants currently operating in Mexico and China and are adding new machines yearly.

We have approximately twelve vertical CNC mills here in the States, each equipped with two pallets which can hold up to four vises each. In addition, we have three horizontal mills, also equipped with two pallets each.

We have run into the age-old problem of "corrosion" in many of the new vises we have been implementing on our mills which are made out of various materials, but we think the problem stems from electrolysis occurring from the use of different metals, specifically aluminum (used for the jaws; the base cavity, which is hard anodized on the exterior; the "jaw slides"), and various types of steel, both hardened and unhardened (used for the cover plate, lead screw, nuts, bolts, pins, etc.). In addition to all of these metals are the metals of the work we are holding which are made out of everything from stainless steels, hastelloys, Inconels, carbon steels and so on.

The "corrosion" is taking place inside the aluminum base cavities (aluminum being the highest metal on the "Galvanic Corrosion Chart" that is present in our set-up) and inside the aluminum jaw slides, which have a steel lead screw running through them.

After consulting with a coolant sales representative, who seemed to understand our problem completely and who suggested a different type of coolant with a higher percent of oil base, but also admitted that we were not really fixing the problem, merely "putting a band-aid on the wound", we've committed to finding a better solution.

In an attempt to address this challenge, we are proposing to use slivers of Zinc alloy bar stock (approximately quarter inch slivers of one inch diameter ASTM B418 type II) to act as sacrificial anodes to draw the electrolysis away from the aluminum.

It has been suggested by a fellow colleague that we glue these "anodes" inside the vise for both ease of locating them in strategic locations and for conservation of the Zinc material, rather that drilling holes through the Zinc which would also include drilling and tapping inside the vises.

Therefore, my questions to the industrialist community are; if we glue the Zinc "anodes" into the vises 1.) Dose the glue have to be conductive? 2.) And if so, can anyone recommend glue that is both conductive and that will sufficiently hold the Zinc to the aluminum?

Other questions might include; 3.) What would be the best location for the "Zincs"? 4.) And dose anyone have a better solution to this problem?

Respectfully yours and thanks in advance for you thoughtful input.

Ronald J. Moody
- Houston, Texas

---

2006 A. The pH of the cutting fluid/coolant is probably too high or too low, needs to stay ~neutral, within range 5-8. Find another fluid or buffer the pH. There should also be anti-corrosion additives in the fluid. If the supplier cannot fix, try the 'Chemicals' link below. The zinc sacrificial anodes will only work where the current is not short-circuited; would still have some problems, particularly within crevices. Ken Vlach [deceased] - Goleta, California Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015. Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from. 2006 A couple of things to think about: 1) If you are trying to protect aluminum, you'll probably want to look into magnesium anodes instead of zinc - zinc isn't very far from aluminum on the scale, and unless your liquid is way more conductive than I would expect, you won't see much benefit. 2) The sacrificial anodes have to be connected in a conductive manner, so glue probably wouldn't be your best bet. However, there is a letter on this site regarding how to make or procure a conductive glue, so it MIGHT work. 3) There must be a liquid path between the metals to be protected and the anode, otherwise you don't get the benefit. All in all, I would be surprised if the sacrificial anodes were successful in protecting your equipment. You may want to look into other methods instead - if you can remove the conductive path between the various metals, galvanic corrosion becomes impossible. This can be done with paint or plastic seals or washers (amongst other things). Also, if you can make the incompatible metals more compatible, that will help also - for example, if you galvanized the steel screw running through the aluminum than the affect of galvanic corrosion on the aluminum should be significantly decreased. Finally - it might not be galvanic corrosion. Check for other factors that may be promoting corrosion of the aluminum; fumes, caustic based cleaners, etc. This would be especially likely if you have any non-anodized aluminum or aluminum where the anodize has been scratched off. Good luck! Jim Gorsich Compton, California, USA