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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Micro Tunneling in Chrome Plating

I have a hydraulic cylinder that is leaking internally. The determination was "micro tunneling in the chrome plate" on the inside diameter finish. I can't find anything on this subject. The plater has told me that no chrome plate is crack free. I will refinish the bore to try and salvage the unit, but I have never had this problem before. Is this common or is someone "blowing smoke"?

David Cordova
- Irvine, CA, United States
2000

I can't say they are "blowing smoke", but I can say that I never heard of 'micro tunneling' myself in 33 years in the industry. Perhaps someone else here has.

But a new automobile can travel tens of thousands of miles without a quart of oil leaking past the chrome plated piston rings, and without losing much power to blowby.

If anyone is taking bets about whether the oil is slipping past the seals vs. 'micro-tunneling through the chrome plating', I'd like a piece of the action .

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000

All chrome has cracks. Most are microscopic. Some aircraft cylinders and diesel cylinders are intentionally microcracked and then have the cracks expanded to hold oil better.

The hydraulic fluid is a macro molecule. You are not going to have a significant amount get by a proper plate and grind job.

Now it is very possible that the plate/grind job was 3rd class and wore the seals in one area to the point of failure.

Seal replacement and inspection of the bore ro problems will normally take care of it.

James Watts
- Navarre, Florida
2000

All chrome is cracked some of the cracks are good, microcracking, and some cracks are bad, macrocracking.

Macrocracking is when the Cr is crack from top to bottom whereas microcracking is small cracks that do not travel very far into the deposit.

To know if it is macrocracking the cracks will be visible with low magnification, 10X.

George Shahin
Atotech - Rock Hill, South Carolina
2000

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