Cadmium plating on a flap track... what purpose will it serve? 2

[ZeeS]

During the conduct of overhaul on our Aircraft, the manual asks for applicaton of Cadmium onto a (fowler type flap) track onto which the carriage assembly (supported by te rollers) will move on.... the process specified is MIL-STD-865D..... material of these track (which will be getting coated) is 4340 Steel.

Now, Cd is a soft metal with no wear resisitance but a primary purpose of corrosion resistance..... As per our experience, it goes off within 1-2 weeks of operation of flaps....

since the process asks for extra work, it costs a fair amount of additional money.....i was just wondering why was Cd specified as a plating material then or wil it be justified?

further Is it common to coat flap track with Cd?

thanx

 

[dik]

In addition to corrosion resistance, Cadmium provides a long term environmental toxin...

Dik

 

[KENAT]

I seem to recall it having some self lubricating properties, though if it wears off that is obviously debatable.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[mfgenggear]

It is used as a break in like silver, copper ect,
prevents fretting, or wear during the inital start up.

Mfgenggear

 

[ZeeS]

@ Mfgenggear.... can u plx explain it a bit more?

 

[RPstress]

Corrosion and wear and corrosion of low alloy steel flap tracks (often 4330M or similar) is one of reasons QuesTek developed S53 and M54 stainlesses. However, low alloy steel has been passably used and maintained for decades. Even with its nuisanceful behaviour it is passably cost effective. I'd be curious to know from anyone working on flap tracks in the last few years whether low alloy steel is still being used. I'd have thought that legislation will get rid of cad in such applications real soon now if it hasn't already, as Dik implies.

 

[mfgenggear]

http://www.chemprocessing.com/metal_finishing_capabilities/cadmium_plating.html

Note the properties of cadmium
Many of the parts fabricated for Aviation/Aerospace are using Cadmium.
even thou it's Toxic.

Mfgengear

 

[WKTaylor]

Guys...

4340 steel although not ideal from a corrosion perspective can posess high strength, toughness and relalatively hard surfaces that are fretting/galling resistant.

Corroded and worn areas [of flap tracks] have have to be machined or hand-blended to eliminate the damage [wear-tracks, pitting/flash corrosion and nicks/gouges/scratches/etc] that will only get worse without rework. In these cases additional areas that normally don't see any wear-damage will be exposed (bare steel).

Replating all bare steel will ~prevent corrosion where the coating remains relatively intact (IE: on non-wear areas)... and will be [mostly] irrelevant where the coating wears-off since those surfaces get constantly rubbed/worn-clean by flap extension/retraction (IE: corrosion won't accumulate due to the flap-track rollers constantly moving with high pressure back/forth over ~ the same surfaces). Obviously if the aircraft flies for several years between PDM, or if it sits for long periods in corrosive climates, this general statement may not apply universally.

NOTE.
Most track roller bearings have a slight crown radius so that they ride relatively smoothly on imperfect surfaces; and will "tend" to develop a consistent narrow wear-off surface.

NOTE.
Although brush cadmium [Cd] plating [low hydrogen embrittlement on HS Steel] is the generic default, there are options, such as AMS2431, and to a lesser extent MIL-STD-865, which allow for brush zinc-nickel [LHE] plating and are a generally acceptable replacement for Cd [with post chromate treatment].

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

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[ZeeS]

thanx for helping me out ..... but now here goes an additional problem:

according to the SIFCO process Cd LHE code 5070, two procedures are given. one for clean unsed surface and one for rough used surface...... the differecne for used surface is of "PREWET AND THEN ELECTROCLEAN WITH CODE 1010/4100 AT 9V REVERSE CURRENT", followed by the water rinse and then Cd plate....

Since its being carried out by the other deptt and they followed the procedure for new unsed surface instead of the used one (i.e didnot electroclean while applying the reverse current), stating that its not required...

Now the problem becomes:
a. why has this been specified to electroclean and what will it do?
b. if it has notbeen done, will it make any difference in the longer run or later on....?

the tape adhesion test is yet to be performed

ref is

http://www.sifcoasc.com/pdf/study-guide.pdf

(page 38)

 

[rb1957]

i'd guess they want to remove surface contaminants (from teh used surface). interesting why "the other department" decided it wasn't necessary.

i guess if it passes your adhesion test it May be acceptable ... what if there's something else trapped under the surface ??

what's your involvment in another department's decision (not to pretreat) ? inspection ??

 

[mfgenggear]

strip & clean properly & replate

mfgenggear

 

[Trajano]

@ RPstress: you say you are curious to know from anyone working on flap tracks in the last few years whether low alloy steel is still being used.
In one of the last Airbus aircrafts, the flap tracks are machined from titanium.