Repair Cad brushing 2

[daxman1]

Good Morning

I'm currently working for a small helicopter company with lots of steel parts that require cad plating. During the build cycle some of this plating is removed through nicks, scrapes or just carelessness. At a previous company I worked we had a "brush" process for small repairs requiring cad. The spec we would use in that case was AMS2400 and AMS2451. I don't know is there was a kit we could order for this kind of repair cad application or if there is another standard we should be using.

Any information on this site would be greatly appreciated.

 

[WKTaylor]

daxman1

1. Cd bath plating

AMS-QQ-P-416 Plating, Cadmium (Electrodeposited)*
NAS672 Plating, High Strength Steels, Cadmium ***
AMS2400 Plating, Cadmium *
AMS2401 Plating, Cadmium Low Hydrogen Content Deposit **
AMS4160 Plating, Cadmium, Electrodeposited, For Fasteners ***
MIL-STD-870 Cadmium Plating, Low Embrittlement, Electrodeposition **
NOTE. ASTM B766 spec for Cd plating should NOT be used for Aero parts

2. Cd brush-plating.

AMS2451/4 Plating, Brush, Cadmium Corrosion Protective, Low Hydrogen Embrittlement
MIL-STD-865 Selective Brush Plating, Electro-Deposition [**Specify LHE Cd solution]

3. Alt Zn-Ni alloy plating used ILO cadmium at my current facility [Cd is prohibited, except for brush plating]

AMS2417 Plating, Zinc-Nickel Alloy*

4. Alt Zn-Ni alloy brush-plating...

AMS2451/9 Plating, Brush, Zinc-Nickel Low Hydrogen Embrittlement
MIL-STD-865 Selective Brush Plating, Electro-Deposition [Specify LHE Zn-Ni solution]

5. NOTES

5.1 Star * codes

*Industry standard for ‘regular plating’ low strength steel

**I STRONGLY recommend using/specifying low hydrogen embrittlement solutions/methods... especially mixing various metals and especially when plating heat-treatable low/medium and high/very-high strength steels or CRES alloys.

*** Specialty processes for special purposes... best used on flight critical hardware.

5.2 There are several ‘major players’ providing brush plating supplies [solutions] and brush-plating equipment. These companies provide training/qualification when needed.

I hesitate to do this, but as an example, ONLY, I have attached a SIFCO brush-process manual which I’ve found useful.

https://files.engineering.com/getfi...O_Process_Instruction_Manual~Rev4-19-2010.pdf

5.3 Cd and Zn-Ni platings may be left ‘bare’ [Type/Class I, 1] or conversion coated with chromate [Type II, 2, [hexavalent or trivalent] or with phosphate [Type III, 3].

5.4 There are other low hydrogen embrittlement bath/brush ['stylus'] processes/solutions for Cd and Zn-Ni... but most are company proprietary.

5.5 Other [bath/brush] plating materials/alloys are also useful for various purposes, thus...

Chromium [Cr]
Cobalt [Co]
Nickel [Ni, various types including electroless]
Nickel-Boron [Ni-B, electroless]
Copper [Cu]
Tin [Sn]
Silver [Ag]

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

OH... one more thing...

I need to mention following about carbon and low alloy steel [CS, LAS] and heat treatable CRES alloys...

There is a rigorous need to understand Alloy-type/HT and complexity to determine when appropriate pre-plating stress relief bake [PPSRB] needs to be accomplished. See AMS2759/11 Stress Relief of Steel Parts.

There is a rigorous need to understand Alloy type/HT and complexity and plating type [nominal HE or LHE solutions] to ensure that appropriate post-plating hydrogen embrittlement relief bake [PPHERB] needs to be accomplished. See AMS2759/9 Hydrogen Embrittlement Relief (Baking) of Steel Parts

When in doubt, for critical parts, BAKE!!!

Generally speaking, Low Hydrogen Embrittlement [LHE] solutions and processes, should always be applied [my R.O.T.] to Steel and CRES parts HT 170 [H925] and above... and should still receive PPSRB/PPHERB... as prophylactics.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[daxman1]

As always, WK, you are amazing!

 

[Sparweb]

Wil can be counted on to advise on what should be done

Here is a taste of what can happen when cad plating is not done properly:
Australian Aviation Occurrence Investigation Report AO-2011-016, 30 April, 2012

This particular accident caused aviation safety alerts to spread around the world about suspect fasteners.

Another example

STF

 

[daxman1]

Is there a touch up kit on the market for small CAD touch up requirements?

 

[daxman1]

Here is what is at issue. We have some smaller steel parts that get scratches, nicks, gouges... The repair is to smooth and blend at 20:1 which removes the CAD plating in the discrepant area. This is a small company so sending these parts to strip and reapply CAD is an issue. I have been doing some research for CAD kits but am not quite sure what will work best for a small aerospace company. These will be small repairs so is there anything out there that will work for the situation I have described?

 

[WKTaylor]

There are several manufacturers for brush-plating application equipment and solution that will easily meet the specs cited.

NOTE.
Forgot to mention one spec that should be useful for locating/identifying qualified brush plating process equipment/vendors... A-A-59460 PLATING UNIT, SELECTIVE (BRUSH), PORTABLE

Vendors/re-seller I'm aware of are...
SIFCO
Brush Plating Specialists
Brooktronics [?]
Caswell Plating
Plating Sales
... etc

OK, I hate to do this... not an endorsement... but SIFCO is one vendor I have used for years because of its dominance and USG/DOD engineering usage [repair/overhauls and small parts manufacturing]. There was another vendor that had dominance, but I think it was purchased/incorporated into SIFCO several years ago.

This useful all-in-one process manual describes electrochemical cleaning, anodizing, plating, etc, A-to-Z.

https://files.engineering.com/getfi...O_Process_Instruction_Manual~Rev4-19-2010.pdf

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[daxman1]

On average how much does Cad plating add to small aircraft parts dimensions? .001, .002, .003...

 

[berkshire]

Daxman1,
Here is an electroplating forum that may be able to give you answers to a plating system that is rapidly being phased out .
B.E.

https://www.finishing.com/572/74.shtml

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

Dax...

AMS-QQ-P-416 has 3 types and 3 classes, thus...

1.1.1 Types
I - As plated
II - With supplementary chromate treatment (see 3.2.8.1)
III - With supplementary phosphate treatment (see 3.2.8.2).

1.1.2 Classes
1 - 0.0005 inch, minimum
2 - 0.0003 inch, minimum
3 - 0.0002 inch, minimum.

Plating to a specific thickness build-up is very tricky/hit-miss because parts are rarely ever 'simple' configurations. Threads/holes/pockets/fillets [internal/external, small/sharp features, etc] all create plating challenges for various reasons. The classes listed above specify ONLY minimum thickness... and there is latitude within spec for 'odd features'. In many cases, when I specify Class 3 I add weasel word to the effect... "for threads and sharp fillets: must have visual evidence of continuous plating when viewed with 10X magnification".

NOTE.
Also IF a post plating treatment, such as chromate [dichromate or trivalent chromate] is to be applied... then that coating must be evident everywhere... it is evidence of a cadmium film thick enough to accept the coating. IF NO evidence of chromate... then cadmium is insufficient/spotty/missing and must be reinforced with localized brush-applied plating to 'patch bare areas'.

NOTE.
I have far less experience with phosphate conversion coating.

NOTE.
In my experience with [bath] cad plating simple parts [bushes], maximum applied Cd coatings rarely exceeds 0.0007... simply because cadmium is a very poor electrical conductor and plating 'throw' diminishes rapidly as thickness builds. I have tried forcing Cad plating to 0.0010 thick and it actually takes MANY hours added bath time. Contrast Cadmium plating to [bath] nickel and chrome plating where electrical conduction is relatively constant as thickness builds... allowing thickness-builds way past 0.0200 for surface repairs.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[daxman1]

Once again thank you for all the information. I read the finishing information and I find it hard to believe that Aerospace is going away from Cad plating. Is this true or am I reading something into it I shouldn't.

 

[WKTaylor]

Yeah... Cadmium [Cd] is a really persistent, highly toxic metal... rivaled only by beryllium.

HOWEVER Cd plating have many unique/useful characteristics on virtually all plate-able alloys... that make it successful.

Cd has the ability to plate a useful coating deep within recesses [holes] and 'fine features' like internal and external threads.

Bare Cd has good corrosion protection characteristics... but has poor adhesion to organic coatings.

Cd is readily conversion coated [CCC] with chromates and phosphates for much higher corrosion protective benefit. These CCC coatings have a high affinity for epoxy and elastomers.

Cd plating sacrifices to protect base metal. When damaged it's atoms migrates Cd & conversion coating elements to the damage site for 'repair' protection.

Cd has a very low/stable coefficient of friction... so it is 'self lubricating'... and provides a stable friction for torque-assy.

As a 'generic replacement the typical coatings in use for aerospace are PVD Cadmium [avoids environmental issues with bath processes], aluminum pigmented organic resin coatings, zinc-nickel alloy plating with CCC, IVD aluminum with CCC, zinc plating with CCC

CAUTION... each of these coatings has limitations that Cd does not display. For instance... IF/when used for threaded parts organic lubricants are often needed; and ability to 'throw' plating atoms deep within parts or smoothly/consistently over part surfaces [lumpy].

May find the following useful...

SAE
AIR4160 Alternatives to Cadmium Plating
AIR5919 Alternatives to Cadmium Plating

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[daxman1]

WKT you continue to amaze me. Thanks.

 

[itsmoked]

You realize what costs FAR less is to not screw-up the expensive certified existing plating that you got on the parts you paid good money to buy in the first place. I suggest you correct the process to stop wasteful damage. Can you imagine Sikorsky or Bell or some other place allowing employees to F$#K up parts?

Do something like:
1) Put in place a process to protect the parts.

2) Inspect parts before the next person is free to work near them.

3) Have the next person sign off for the last person to shift ownership of scratches and nicks.

4) Correct the tools (padding etc.) used nearby to prevent damage.

5) Wrap ALL susceptible parts with [!]RED[/!] masking tape before adding them to an assembly that they get scratched on. Tape a piece of dental floss as a ripper under the tape if peel-off is a problem.

6) Have someone photo all the parts of issue each night - kick the butt of whoever worked on/near the part that day if scratches appear.

7) Make it clear to staff that damaging expensive parts is unacceptable. Get some focus on the issue and ask them what process is scratching them. Show some interest in helping them avoid damage by getting special tools, requiring assistance for scratch-prone tasks, create padding pieces or supply general purpose padding materials.

8) Have a scratch/damage free barbecue each month. Scratches - no BBQ.

9)

10)

Keith Cress
kcress -

http://www.flaminsystems.com