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


-----

Hard chromium plated piston rods leak oil past the seal under pressure

August 12, 2008

We have piston rods that work in pressurized oil containers with a seal.
The seal allows the piston rod to move and prevents oil to leak out of the oil container.
During static leakage test under pressurized conditions e.g., during transportation, we observe drops of oil several centimeters away from the seal.
The area between the oil drops and the seal is dry (no oil observed).
We know that that the seal is ok.
Sometimes are the piston rods ok, sometimes there can be extensive oil drop leakage.
The problem should be related with the manufacturing of the piston rods.

Can anyone give a hint of the reason for this and how to prevent this problem?

Jan Sandberg
Manufacturer of products including piston rods - Stockholm, Sweden

---

August 18, 2008

Hi Jan,
We need to have more information about the seal, just now I think the problem can be in the chrome deposit, because it happens not always.

Regards
Anders Sundman
Surface engineering
Sweden

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden

---

Hi Anders,

About the seal
It is a NBR polymer aimed to be used to seal off the interface between air/oil when the piston rod moves.

During dynamic leakage testing the oil leakage is zero (Not detectable). Most likely due to the movement and the lower testing time.

During the static leakage test the time until oil drops can be observed is appr 2-10 days.

Regards,

Jan Sandberg
- Stockholm, Sweden
August 21, 2008

---

Hi Jan,
Have you made any study on the chrome surface deposit to see if the chrome deposit is ok. (Ask a metal engineering lab to take a cut and study the deposit in microscope).
Do you grind the chrome deposit? Because I think you have macrocracking in the chrome deposit.

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
August 23, 2008

---

July 20, 2009

Hi,

Have you solved your leakage problem?
These situations can be very simple to highly complex, and can involve in-depth analysis. There are however some basic issues that can be looked at initially.

1. seal design (fit, tol, energizer, runout, material etc..)
2. seal assembly methods. this is more common of a failure than you would think.
3. mating hardware variations. also the cause of many premature seal failures.
4. system operation.

Robert a [last name deleted for privacy by Editor]
- California