440 C SS corrosion 4

[Indicator1]

This part has been passivated per AMS-QQ-P-35, TYPE II.
It is a shaft .025" OD. Hardness: 580 to 820 HV under 500g load.
It appears it has some surface corrosion. Microscope observation shows small pits. Corrosion product is black.
This shaft works together with a bearing, which is made of brass, CDA 36000, half hard.
What can be done to eliminate/decrease this corrosion, please?

 

[israelkk]

Try these too

http://www.pexa.com/wp-content/uploads/EVERLUBE_A4_PROD_SHEET_ST4.pdf

They list Boeing and Pratt & Whitney and Airbus approved dry lubes.

 

[Indicator1]

OK, I found Everlube 9002, MoS₂, meets MIL-PRF-46010F and temperature range.
Should work.

 

[Indicator1]

What is the typical Molycote Z Powder coating thickness?
Very important, as I have a distance of 0.001" between the shaft and the bearing.

 

[israelkk]

If you look here you can see that MIL-PRF-46010F and G are approved for Military only. For Aerospace companys they still use the MIL-L-46010 old formulations (doesn't specify the version A,B etc.) They are covered and formulated specifically for the Aerospace company. For example:

1. For Boeing, Everlube 9002 (MIL-L-46010- Type. III) is covered by Boeing spec. BAC 5811 Rev. P thru U- Type VI- Cl. 4

2. For Lockheed Martin, Everlube 9002 (MIL-L-46010- Type III) (Old Formulation) is covered by Lockheed Martin spec. FMS-3101B Class III.

Therefore, you should be familiar with these specs and to decide if they meet your design.

You should make sure that you can actually purchase it.

As to your dimension problem this is a delicate design issue requires the knowledge of the spec. itself how it is done, preparations, what is the recommended coating thickness for your application and how accurate a coat can be and controlled. This is beyond the scope of the posting. I suggest either you study the matter carefully or rely on an expert that can specify it and make sure you get it. It will be a shame to find that the bearing will not be able to install over the shaft. For that, you need to know the exact shaft dimensions spec. including outside dia. tolerances, the bearing inside hole dimensions and tolerances and specify the MoS2 minimum and maximum thickness coatings in the shaft drawing to insure correct fitting.

 

[israelkk]

See here too

http://www.everlubeproducts.com/products/spec_search.php?searchByProd=Everlube 620

They specify Everlube 620 for aerospace too.

 

[israelkk]

I do not know why you are fixed on Molycote Z Powder coating? I had excellent experience with sprayed heat cured coatings such as Everlube 620. I have no experience with powder coating and and I suspect it is more specialized coating process which not many can produce, in contradiction to spraying like a paint.

 

[dgallup]

Given the small clearance I think a PVD coating will work much better. We get some springs coated with MoS2 in a "dip & spin" process and it is very irregular. Lots of blobs of material. We get various PVD coatings that are controlled in the 2 to 5 micron range.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Indicator1]

Some of my co-workers suggested we use PASSIVATE IAW ASTM A967, SAE AMS2700 vs. PASSIVATE PER SAE AMS-QQ-P-35, TYPE II (current passivation). Would that be helpful?

 

[EdStainless]

I doubt that additional passivation will help, the alloy simply has little corrosion resistance.

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P.E. Metallurgy, Plymouth Tube