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Phosphate color change

Phosphate color change

Phosphate color change

I am still over phosphating parts. I cant give too much detail but I can give this much.
My pre-rinse is at a pH of 5.93 and a temp of 47C
my pre-phosphate is at a pH of 5.23 and a temp of 49.3C
my phosphate is at a pH of 5.13 and temp of 50.7
my cold rinse is at a pH of 5.76 and a temp of 51.5C
my hot rinse is at a pH of 6.3 and a temp of 68.5C
My bottom pressure (for the underside of the part) is set lower than the top.
I dont know the temp of the dryer.
My nozzels are clean and set in the correct position.
My concnetration of phosphate and pre-phoshate is at company standards.
The racks they are laying on have been cleaned.

Im running out of things to check.
Is there anything else I can do to keep my parts from over phospahting.
Should I raise the pH of the rinse tanks or even the phosphate tanks themselves?
Plus, my last question. Could the color of rose gold be from, the parts going through the drying process? Is there a color change that happens to phosphate from going through a dryer?
Thanks so much for your help, It has really helped me out.

RE: Phosphate color change

I am assuming since you are getting a rose gold that you are using an iron phosphate!  What do you mean by overphosphateing?  Are the coating weights to high, are the parts powdering?  What do you mean by over phosphating?

1.  Are you using a Cleaner? Or is stage 3 a cleaner coater?
2.  What is time in the Phosphate stage?
3.  What is your specification you are trying to reach?
4.  Have you switched phosphates lately?
5.  Are you using a Seal?
6.  What is the product names you are using?
7. Concentration of pre-phosphate stage and phosphate stage.

Typically in Iron Phospate you have a few variable that will affect phosphate coating:

1. Temperature
2. Concentration
3. pH
4. Time in phosphate stage
5. Age of bath

I do not believe the rinses especially pre rinses


RE: Phosphate color change

Does the rose gold color cause a problem?
Because of application or Color?

What grade of metal?


RE: Phosphate color change

Thank you for replying.
We are using iron phosphate. I cant give too much info so if I sound vauge, Im sorry.
We go by a color scale or coating weight, to know if we are in range. We dont have powder on the parts just the violet gold and gray color.
We use water as a pre-cleaner of the parts.
The process goes,
Cleaner->pre-phospahte->phosphate->cold rinse-> hot rinse ->dryer-> then we cover the parts with paint.
The cycle time is 48 seconds.
We are trying to stay in the blue/light gold range or the 35-50MG/FT2 coating weight range.
We have been using the same phosphate and company for 15 years, I cant give the name of the product.
I just started this company and they say this is an ongoing problem. We have another line, and we dont have problems with the color of the parts. They come out the medium blue.
The standard we have says that rose gold is too much phosphate. You can see the rings on the parts from the tray they are sitting on. they do look powdery but it does not rub off. then we also have the parts coming out the dark gold.

What I would like to know is....
Can the coating weight being too heavy effect any other following process?
What can you do to keep the parts in the blue light gold range?
The temp, pH, time and concnetrations are in range, this problem has usually occured after cleaning, but for some reaon its not going away.

I think it is in the pressure of the phoshate spray, the rinse pH or the dryer.

Thanks for your help. let me know if i need to give more details, im a new forum user.  

RE: Phosphate color change

When you say cycle time are you refering to each stage?  

Usually undercoating (less phosphate) is worse then more phosphate. As long as the phosphate is not real powdery.  

Rinse temperature and time should play no effect on the amount of phosphate coating.

Can you specify the concentration in both the pre phosphate and phosphate stages. Also have you ran test panels (from q-panel or act laboratories) to see what standard panels look like.

What is the coating weights you are getting? Are you actually doing a test to determine coating weights or only using color.  IF you need a procedure for determining coating weights let me know.

I know in a lab setting I can change 1 ingredient in a phosphate and get whatever color I want from blue, gold, irridescent, light gray, etc.

But if one washer is getting the correct color and the other is not then it should not be the phosphate formula.

Have you done any salt spray testing to see if it is effect by the heavier coating?


ps  what is you current supplier saying.

RE: Phosphate color change

To be able to have pictures of what is good and bad would be great. All we have are verbal discriptions and those arent the greatest.
I cant contact the supplier, that dont speak english, great right?
We go by this scale.
Pale blue         10-15
Medium blue       15-35
Blue/light gold   25-35
Blue/rose gold    35-50
Rose gold         50-75
Violet gold       75-90
Gray              90+

We are in the violet gold, gray range.
I was told gray is bad and could effect the coatings of later process. Is that true? Apparently that is not the case.
So if we are in the pale blue we should bump it up?
How could we do salt spray testing? Do you have a work instruction for that?
In terms of Concentration, I guess as long as you dont know or ask who I work for I can tell you that we are running at a concentration of 7 using a NaOH Acid titration.
Ill see if we can get permisson to run test panels. That is something we need to do.
Thanks for your help.

RE: Phosphate color change

We do not use color as an indication there is a test method ISO 3892 that explains how to calculate coating weights.

Another easy method is
Take a panel that has been phosphated
1.  Immerse in acetone.
2.  Then dry with hot forced air (hairdryer or something similar)
3.  Weigh using an analytical balance that weighs to the 0.1mg
4.  Record Weight
5.  Immerse panel in 10% NaOH 5% Sodium Gluconate, Balance Water solution at 55C. for 20 minutes
6.  Rinse part
7.  Immerse in acetone
8.  Dry again with hairdyer
9.  Reweigh on analytical balance.

(If panel still shows phosphate coating repeat steps 5-9 until the weigh levels out)

Now for the calculation.

(initial weight in mg - final weight in mg) * 144 / (width of panel * length of panel *2)

this will give you mg/square ft.

Also the concentration.  Take a 25 ml sample out of stage 5 add 3-5 drops of phenolphthalein.  (Solution should have no effect) Titrate using 0.1N NaOH until solution is light pink.  Do this for both the prephosphate and phosphate to let me know how active the chemical in those stages are.

The above procedure is better (although more time consuming) than using color.

Salt Spray is typically for painted metals.  
Used ASTM Standards B117 and D1684

When is the last time you dumped the washer?


RE: Phosphate color change

We dumped and did an acid wash 4 weeks ago. (phosphate)
We have dumbed and refilled the rinse tanks 3 days ago.  
We only use 10ml from the tanks to run concnetration, ill have to run and do that.
I get off in a few mins, but I am going to do this first thing monday morning.
THANK YOU!! Check monday, ill let you know what concnetration Im getting.

RE: Phosphate color change

I went and checked the concentration check.
The pre-phosphate had a reading of 16ml and the phosphate had a reading of 14.5ml.
We are getting gold on the parts, I am having a hard time telling if its rust of just too much phosphate.
Is there a visual test for rust? All I have been told is, "if it rubs off its rust."

RE: Phosphate color change

I think you may want to reduce the titration to about 10 - 12mL. In both of the stages.  If you have to high of a concentration you will tend to over phosphate.

Also If you use a White paper towel and whipe the parts off if the residue is yellow then it is phoshate if its red it it rust.

Why is your prephosphate solution stronger that your phosphate tank?

Do you have an analytical balance so you can do coating weights?


RE: Phosphate color change

I think the phophate tank is getting extra water from the rinse tank nozzles facing the wrong direction, i was also told that we might have a leak. so it automatically adds water but we manually add the phosphate, so if it goes unchecked it will make a difference. and i think they might have lowered it thinking that would help.
We do have a scale and im going over it with my boss to see if we can do the procedure you sent me. Its the whole coporate thing. and ofcourse we have an audit today, so that puts me back till tomarrow.
So, if its yellow, its phosphate and if its red its rust. cool.
so now if we over phophate how much of a problem will this cause?? im going to check with the paper towles to see if it really is rust of phosphate.
thank you very much.

RE: Phosphate color change

apparetnly we dont have an analytical balance.... so, now i have to see what i can use. any thoughts??

RE: Phosphate color change

my boss wants to know if there is some reagent to drop onto the part that will react with the phophate to give a visual reaction to tell if its phosphate or even if there is one we can use to see if its rust.

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