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topic 14221 p2

Surface Activation for Phosphating. Grain Size Issues

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A discussion started in 2002 but continuing through 2019

Hero Motorcycles
August 11, 2016

Q. My process is surface conditioning/Phosphating
My customer's requirement is gray coating on Hero motorcycle fuel tanks
How to achieve it?

Parameters are as follows-
T.A. -- 18 to 20
F.A. -- 0.3-0.6
Accelerator -- 3-5
Temp. 41 °C
T.C -- 1-2
pH -- 9-11

But F.A is not controlled down to 0.0; even T.A is 20.3; and I get blue coating in Hero Splender+.

Abhishek tiwari
- Delhi India

August 20, 2016

Q. Is it really required to check the alkalinity in activation process?

R Ramesh
- Chennai, tamil nadu and India

August 2016

thumbs up sign Hi Ramesh. Saravanan said it was necessary in the first answer on this thread, and I'm not experienced enough to challenge him on it :-)
Please explain the full details of your situation whereby we might question his recommendation for your particular case. Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

January 8, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir,
I am working on preparation of zinc phosphating bath. Earlier problem I was getting was of low coating weight. Now coating weight has improved but grain size and grain distribution is not uniform. What are the possible ways to improve grain distribution with high coating weight.

Rahul Jangid
Calligraphy - India

January 2017

A. Hi Rahul. You had an original formulation and operating conditions which you haven't disclosed but the coating weight was too low ... then you modified the formulation and/or the operating conditions ... and those modifications, which you haven't disclosed, have improved the coating weight but the grain size is inconsistent?

We've appended your posting to one of many threads on the subject, which may offer food for thought, and the opportunity to ask for clarification. The basic problem is that there are countless books of hundreds of pages each about phosphatizing, and there are file cabinets full of expired patents about modifications; I hope someone is able to help you, but I doubt that they can help with your formulation and operating conditions until you describe them. Thanks and good luck!


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

December 13, 2017

A. Hi Hans,

First, you should see if there is any imperfection in your coating process. All hex chrome-free sealers have less resistance than hex chrome sealers, and they are more expensive and less resistant to contamination.

You should try to increase coating weight and try again, or try with another sealer. Chemetall [a supporting advertiser] has two other sealers that you can try, all more expensive than the first one.

My experience with non chromic sealers is not so good, so I would test those alternatives one by one in lab and try the best one.

Hi Jonathan!

Usually these red patches are cleaning issues. See if your pickling process is effective, try to improve it with concentration, temperature or agitation, add wetting agents and rinse with a lot of clean water.

If nothing is effective, try to load less weight in your racks, because it is difficult to clean between spires.

Best of luck to you, too!

Regards :)

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

August 21, 2018

Q. I am currently getting adhesion on 110k steel, but the grain size is unsatisfactory.
We have tried Keykote 62 from our supplier and it didn't work.
TA is at 9.5% (we had the same results from 5-8% as well).
Any recommendations to try refining grain size?
Thank you.

Eric Winters

August 2018

A. Hi Eric. What do you mean "it didn't work" ... do you mean the crystal size is still larger than you wish? Some postings on this thread from the estimable TSN Sankara suggest using a grain refiner to reduce crystal size, but I believe Keykote 62 is a zinc phosphate process rather than a grain refinement activator.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

August 22, 2018

Q. Keykote 62 is a grain refiner. There was no reduction in crystal size.

Eric Winters [returning]

August 24, 2018

A. Hi Eric,

I don't have experience with Keykote 62, but I have some inquiries about your process:

1- You have a Keykote 36 (or other) process? Where and how did you use the refiner?
2- What is your cleaning (pretreatment) process?
3- 110K is K110? (AISI D2) Grain size depends on carbon and alloys content...

Hope we can help to solve this issue!

Best of luck!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

August 25, 2018

Q. Here is our process:

Isoprep 172. We have tried running from 7% to 20%
Keykote 62. (refiner)
Keykote 36. Ran from 5% to 10%

At this point we are grasping at straws in attempts to resolve the issue. We ran a part and it came out perfect. Then a different part with the same process and it was horrid. The only difference in parts aside from shape is the machine they came off of and their heat lots.

Eric Winters [returning]

August 28, 2018

A. Hi Eric!

I asked if the material was AISI D2 (K110) or if it is another steel, so I can get a closer idea of what is happening.

Grain size changes with surface preparation, rugosity before treatment, chemical composition of the substrate, microstructure of the substrate, grain refiners, TA/FA ratio, accelerator/iron content, and chemical composition of the phosphate bath (in this case a formulation from MacDermid, we know it is a -usually- nickel-accelerated zinc phosphate which works with dissolved iron).

With this type of phosphate bath, you can only trust in a grain refiner, but the surface of your part should be uniform, and the chemical composition and microstructure should vary within a range.

We do zinc phosphate to cold forged parts of low carbon steel (QT or Carburized) only, so I can't bring you any more data, but there are more grain refiners available and more phosphate technologies, so ask your vendor for a solution first, and see if you have any luck with this new data you exposed.

Best of luck!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

September 29, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello, why are phosphate crystals coarse and how can we have a soft zinc phosphate?

ahmad hashemi
- qom saas iran

September 2018

A. Hi Ahmad. Are you using a grain refining pre-dip as explained on this page which we've added your inquiry to? If you search the site for "coarse zinc phosphate" you'll find several more threads on the subject if the answer isn't on this page. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

November 13, 2018

A. Zinc phosphate relies on a precipitation reaction to form. As the acid in the solution reacts with the substrate the pH goes up and the zinc phosphate is no longer soluble. Keep in mind that cleaner is also caustic and will cause the crystals to precipitate on top of it if not rinsed properly.

The crystal refiner, usually titanium phosphate, provides nucleating sites which effect the crystal size.

The exposure to the substrate iron is self limiting based on contact with the phosphoric acid which is consumed at the interface. Alloying elements in the steel which may or may not react with the acid will play a profound part in crystal size.

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada

Zinc phosphate coating is covered with rust

February 14, 2019

Q. Hello, all.
I posted on here mid-2018 about our phosphate line.
Since then my employer has overhauled the line and gotten a new chemical supplier (Dubois).
Our new line was running 80 ksi steel well for a few days.
Now our results are covered in a veneer of rust.

14221-1d   14221-1c   14221-1b   14221-1e   14221-1a  

Our line is set up as follows:

Rust remover

TA 44.8
FA 7.4
Ratio 6.054
Iron 2.65%

Eric Winters [returning]
Line operator - Round rock, Texas

February 17, 2019

A. Dear Mr. Eric, please go through the detailed answer given by Mr.Rodger Bridger. You will find the exact solution (Topic 10242)

Avinash Vidhate
- Nashik, Mahatashtra, INDIA

February 18, 2019

A. Eric,

When in the process do you notice the rust? Is any seen between acid and phosphate, phosphate and oil, or is it all after the oil? Is this a manual line/do you have long dwell times between stage? Second what are the TA/FA/R/Fe parameters called out on the data sheet?

Follow up on these questions and I can try to get you back on track.

Jameson Grout
- Agawam, Massachusetts

Closely related threads include:

  - Topic 10242 "Zinc Phosphating Problems & Issues"
  - Topic     874 "Zinc phosphate coatings to deter galvanic corrosion"
  - Topic 51772 "What is Tri-cationic phosphating?"

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