Ni-span C 3

[newmacnow]

We were wondering if Ni-Span C can be passivated? We make springs and have found in the past that when we passivate it the spring gets weaker. We have a spring now that is too strong and would like to passivate it to make it weaker. But we want to make sure there is no long term effect to the material that will cause it to pit, or become brittle or fail prematurely.

Thanks

 

[TVP]

Read the section Pickling on page 9 of this document:

http://www.specialmetals.com/documents/Ni-Span-C alloy 902.pdf

 

[israelkk]

newmacnow

When you say weaker what do you mean? Is the force and defined deflection is less than the designed or the spring broke at lower load?

Picking is a chemical process that involves acids and produces hydrogen that will cause a hydrogen embrittlement on the finished spring and may cause premature failure due to static or cyclic loads.

The safe procedure is to use mechanical means to clean the spring prior to passivation.

http://israelkk.googlepages.com/home

 

[swall]

Years ago, I dealt with a supplier of Inconel X-750 bellows assemblies and they would sometimes pickle them to tweak the spring rate. I never liked that, as it would pit the material and make a nice stress riser for fatigue crack initiation. BTW, they denied ever doing it, as it was acknowledged to be bad practice.

 

[newmacnow]

israelkk

By weaker we mean that the part was tested at a load position before and after passivation and the load measured afterwards was lower.
We are not looking for a way to clean the spring, we are actually looking for a way to make the spring have a lower force. Direct from manufacturing the part is too strong. We want to see if we can lower the load at the test position without having to remake the springs, due to the high cost of the material.

Thanks for all your responses, we pretty much gather this isn't the way to handle the problem.

 

[israelkk]

newmacnow

To my experience the reason for "weaker" spring is that the pickle removeS material from the sprins sorface. Did you check the wire/strip diameter/thickness after pickling? The problem is that it is difficult or even impossible to control how much metal is removed. The smaller the diameter of the wire or the thinner the strip the worst change in properties.