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Nodulation

 

Can somebody please define "nodulation" as found in the hard chroming process. I installed HEEF 25 chrome chemical in our chrome plant, plating shock absorber rods, during January 2002. It is an automated process controlled by PLC and generally we plate 5000 rods per day. Diameters range from 17mm to 25mm.

Since the change over to the new chemical we have these "nodules" on the plated surface.

Any ideas on what causes this.

Thanks,

Neville Young
shock absorbers - Cape Town, South Africa

Hi Neville,

I suppose your nodules is on high current density area. How is your temperature in your HEEF solution. It's important to have this temperature as Atotech recommended 55-58 °C. Please reply.

Sincerly,

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
 

Hi Anders,

Thank you for your response. We are running at a current density of 48 A/dm square. The temperature in the plating baths is 60 degrees C. Looking forward to your response.

Regards,

Neville Young [returning]
shock absorbers - Cape Town, South Africa
 

Hi Neville,

We also run our HEEF solution at 48-50 A/dm2. Our temperature is about 55-58 °C. But if you hard chromium inside diameters you must check for the trivalent chromium. Never let it be more than 5 gr/l. In HEEF it should be at 2-3 gr/l.

Regards,

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
 

You need to get the vendor involved. I have used it and it is a good product. My guess is that you have carried forward a metal dust or a cleaning grit. Wipe down a set of rods and lightly pumice them and re-wipe. If you still get nodules, something is wrong in the preprocess steps. Not a lot of help, but it at least lets you know where to start looking for the problem.

James Watts
- Navarre, Florida
 

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The nodules could be coming from the substrate. You should check the Ra and also the Rp (maximum profile peak height)to see what the quality of the incoming steel is. Also you might want to change your etch cycle and see how much Fe or Cr3+ are in the solution.

George Shahin
Atotech - Rock Hill, South Carolina
 

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What George says is right, I did some investigations on that topic with the same product you are making but for other company (Monroe). The higher the Ra , the more nodules are growing in the chrome layer. So take care of polishing before chrome and etching!

Sincerely,

Andy D'haen
- Brussels