mysterious disappearance of material post plating

[koza19]

We manufacture a Compression spring out of 0.026" tolerance +/-0.0003 wire diameter music wire per astm A228. We send the part out for a commercial thk .12 mil min tin plate. Weird thing occurred when we received the parts back and measured the wire diameter cross section-ally the wire diameter was measuring 0.0251" on average. Could the electroplating process have removed some of the base material? We measured the tin plating thickness at around .2 mil average. We are planning to send the spring out to a lab for evaluation. Just looking for any insight

Thank you

 

[IRstuff]

you would and should review the plater's EXACT process and chemistry. Either surface prep or some funky stuff in the plating solution could be an issue.

Are you measuring before and after using the same instrumentation and process?

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[tomwalz]

Was there an acid etch involved?



Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[koza19]

IRstuff
We measure the wire diameter cross section before and after plating using a micrometer using the same method.

Tomwalz
A pickling was performed to clean the surface before tinning.


Thank you all

 

[CoryPad]

Pickling can remove 0.001"

 

[koza19]

CoryPad
I was not aware of that. So what effects the remove amount? Would it be time in the bath and acid concentration?


Thank you this really helps

 

[stanweld]

Also include acid bath temperature. Also understand that a spring will corrode at higher rate than a similar peice of annealed, normalized or hot rolled steel or the same alloy composition.

 

[koza19]

Thank you all for the information I have learned something new today. I do have one more question. Would there be a physical change to the appearance of the material surface on the part if the acid cleaning was not done correctly?

 

[CoryPad]

Likely pitted

 

[TVP]

The surface will definitely change after acid pickling. Music wire has a VERY smooth, uniform appearance after the die drawing operation. Pickling will cause the surface to be rougher and more irregular, as it removes metal from the surface.

 

[IRstuff]

Have you asked the vendor what his process is? There are a number of plating processes that are acidic:

http://www.eciato.com/PlatingProducts/Plate/Tin_Plating_Processes.html

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[koza19]

IRstuff,
Yes we have requested this information from the vendor.

 

[koza19]

The vendor uses two cleaning solutions to prepare the surface for plating
First Nuvat 6-8 oz/gal tank temp 160-180F
Second Maxamp 8-10 oz/gal tank temp 160-180F

I don't think the cleaning solutions would dissolve the material. Could there be a issue with the plating rectifier?
Below are the processing parameters
Sodium hydroxide 0.9 – 1.8 oz./gal.
Plating bath temperature 110ºF - 145ºF
Electrical current 2-4V/500 amp
Tin concentration 1-3 oz/gal
Tin Sulfate 2-6 oz/gal
Sulfuric Acid 7.2 – 10%

 

[EdStainless]

In some cases they will use a short period of 'reverse polarity' to assure good clean surfaces.
When they do this they are removing metal from the surface.
They could have overdone this step by mistake.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[koza19]

Thank you all for the input this has been very helpful

 

[IRstuff]

Did they fail to meet spec? If not, then either the spec needs to be written, or this is a non-issue.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[koza19]

IRstuff,
Yes the wire diameter after post plating failed the 0.026 +/-0.0003 spec. The wire diameter was measuring 0.0251 to 0.0258.

 

[IRstuff]

But, did they knowingly fail the spec and did they not take remedial action?

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[koza19]

IRstuff,
We are waiting for lab results ,so we do not have that info yet.