Razorcharlie

Topic: Cold Blackening Solutions

Hi there,

I am currently having some problems when chemically blackening some tooling and parts we are manufacturing.

The parts are made from EN24 tool steel and are being blackened in a shop bought set of solutions from www.black-it.co.uk

I am getting some poor results in blackening (brown patchyness) and also waste material being generated during the process. The parts are cleaned with Isoprpyl Alcohol then put throught the process which also includes an Alkaline degreaser. The parts generate a white solution which sometimes occurs in the conditioner and sometimes in the Blackening solution. I have experimented with different methods of cleaning etc but cannot get a consistent quality or decent lifespan of the chemicals. The waste material which is generated in the conditioner is a white sludge that forms at the bottom of the tank, if dryed it becomes like a hard salt this is also generated in the Blackening solution. The parts are washed between processes.

What on earth am I doing wrong? Any help is very much appreciated.

Best regards,

David Brown.



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DustinGebhardt

Re: Cold Blackening Solutions

Dave,

  I've read over the pdf's on the website and I'm assuming you are doing everything as they recommend.  In my experience, brown splotches are usually due to alloy composition, poor agitation, week blackening chemical, or poor acid activation (conditioning).  

  Blackening products like these are based on phosphoric acid and selenious acid.  The white deposits you are seeing may be coming from any calcium from your rinse water.  Are you using city water for your rinse, or something cleaner (RO water or DI water?)  Calcium reacts with phosphates to form insoluble calcium phosphate.  You may be weakening the baths with this problem, which could be causing your uneven look.

-Dustin Gebhardt,
CEF
Plating Engineer
Danaher Tool Group
Gastonia, NC

Razorcharlie

Re: Cold Blackening Solutions

Hi Dustin,

Many thanks for your reply. we are washing the parts in a ordinary tap water, which I am assured as we live in Scotland is soft water with a low concentration of calcium.

I am now washing the parts between stages more thoroughly and am getting a better result. Instead of only washing the parts in container of water as suggested by the manufacturer I am washing them in a bath of running water.

Do you have any more tips about blackening? I think we were not cleaning the parts enough and not rinsing enough between the stages, would this cause the problem as i explained?

Again many thanks for your reply,

David Brown.

DustinGebhardt

Re: Cold Blackening Solutions

Anything you can do to deliver a clean part to the next step in the operation will yield more consistent (and better) results.  So, with your additional rinsing with running water (a great idea and frequently used in the industry), you are moving in the right direction.  If you want to go to the next level, here are some suggestions:

You can try using a different solvent for cleaning your parts.  Some forms of IPA actually have a light mineral oil mixed in.  Find a stronger mix of pure IPA and dilute it yourself (this may net you some cost savings to boot).  You can also use acetone (widely used in the US), MEK, or other readily-available solvents.  After you clean the parts and run them through the conditioner, check the parts for a break in the water sheet.  If the water sheets evenly, the part is generally considered "clean".  If the water breaks or beads up, the part is not clean.

You may also be able to analyze the blackening solution.  Check with the vendor for more info on this. 

-Dustin Gebhardt,
CEF
Plating Engineer
Danaher Tool Group
Gastonia, NC

Razorcharlie

Re: Cold Blackening Solutions


Hi Dustin,

Thanks again for your info, it is very much appreciated.


Best regards,

David.