Electro-Chemical stripping of Chrome Plating

[Noor]

Hi all,

I am looking at two processes specified for electro-chemical stripping of chrome plating from steel parts. One is from the parts OEM and the other is per MIL-STD-871.

The two processes are very similar, except that the OEM uses a solution of sodium carbonate 6.5 oz/gal, while MIL-STD-871 specifies either a solution of sodium hydroxide (7 oz/gal) with sodium carbonate (9 oz/gal) know as Solution 5, or a solution of sodium hydroxide only (10 oz/gal) known as Solution 6.

Are all of these simply acceptable, or are there subtle differences in the chemistry that I should be aware of when applying them to different steel alloys? I'm just curious to know if the MIL-STD-871 process is equivalent to the OEM process.

Thank you.

 

[israelkk]

From TABLE III at MIL-STD-871B: ".....Proprietary formulations may be used provided the necessary precautions are taken to avoid substrate attack and hydrogen embrittlement. If a proprietary formulation is used, testing must be accomplished to determine whether an embrittlement relief bake is required (Reference 4.5.1)."

Therefore, you should test that the OEM solution doesn't create a greater risk for hydrogen embrittlement.

 

[Noor]

Thanks for pointing that section out.

The OEM process does call out for a bake after stripping; however, the note under Section 4.5.1 of MIL-STD-871B states that steel stripped with Solutions 5 or 6 do not require baking afterwards. It would be interesting to know if the bake called out in the OEM process is precautionary or if it is requirement for the different solution used. Either way, it is probably better to bake.