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-----:Manganese phosphate coating: issues and answers
Quickstart:
Manganese phosphate is a heavy phosphate coating which is good at holding oil, and often used as a "break-in" coating for automotive engine and gear parts, serving to help prevent scoring when a new engine enters service.
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Q. I am having an issue with MN Phosphate coating on steel parts. I've tried multiple experiments to see if the problem is my finishing process and get no change in the end result. When the parts come out of the phosphate dip they have very thin straight lines of lighter to no finish that extend around the part, even into folded areas. The flats come from the same distributor as all other batches, yet previous parts do not have this problem. Can anyone who has experience with problems like this help me figure out a base cause or a fix so my parts come out as well as they usually do? Any information would be greatly appreciated. ⇦ Answer?
Becca H.Shop employee, Finishing department lead - South Carolina
April 1, 2026
? Hi Becca,
Do you know your latest analysis results for the manganese phosphate tank?
Also, do you monitor coating weights, that would be useful.
And can the parts be grit blasted prior to phosphating?
Best regards
Mark
- A mildly pleasant rock in the Irish Sea
Q. So I have been doing a lot of research into this issue and others when it comes to phosphating. I have come to the conclusion that we aren't doing enough testing. I was trained to test for total acid only. I'm not sure numbers would even help because I have found we don't test to manufacturer guidelines. I am getting the chemicals necessary for free acid and iron testing as soon as it is approved.
We do not test coating weights, only a visual inspection. I have learned a little in that and am bringing it up to QC management. All parts are cleaned and blasted with aluminum oxide prior to phosphate bath. I did find a solution but it took a lot of extra time. We cleaned, then blasted, then into the bath for 15 minutes, dried, then re-blasted and back into the bath for 15 more minutes.
- South Carolina
April 20, 2026
? Tell us whether you use a grain refiner. Is the tank heated ONLY when loaded. Do you adjust the total/free just before processing?
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
April 8, 2026
Ed. note: apologies, we misfiled this posting; it was submitted on date shown.
A. Hi Becca,
You are certainly taking the right approach.
Once you have the free acid and iron content figures along with the coating weights, you will be well on the way to solving your problem.
Ensuring that all tested parameters are within their ranges will likely solve you problem.
Best regards
Mark
- A mildly pleasant rock in the Irish Sea
April 20, 2026
⇩ Similar, related, Q&As -- oldest first ⇩
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Q. We use a casting of CH13 (hot worked tool steel investment casting)for our component making. This casting undergoes heat treatment (spherodising, machining, gas carburising, hardening and tempering, Hardness = 60 HRC) followed by sand blasting for surface cleaning.
While performing manganese phosphating, we find white patches. We are looking for a uniform black colour. Can someone help to avoid white patches. Phosphating is followed by tectyl 272 oiling. Corrosion test (as per ASTM B117 on the component with white patches show a good corrosion resistance. ⇦ Answer?
G R PatelManufacturer, Power Equipments - Vadodara, Gujarat, India
2004
Q. Dear sir
We are also facing the white patches after manganese phosphating. Can anyone suggest the same for better control? ⇦ Answer?
- Bangalore, India
April 9, 2012
Q. I would like to get a recipe for a manganese phosphate coating for steel. If someone perhaps can explain to me the actual chemical actions taking place on the surface too?
I've learned that there are many applications such as:
1 high wear resistance
2 better resistance against corrosion and a nice finish and
3 as a pre-treatment for painting etc.
Is there a big difference in the recipe and chemicals? The one I'm most interested in is protection against corrosion and finish.
Thanks
hobbyist - Kesteren, Netherlands
2005
A. You can use next solution:
25 gm phosphoric acid
1,5 gm manganese dioxide
1 lit water
Boil your objects 2-4 hours.
you must oil, lacquer or wax it!
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- Cerovski vrh Croatia
A. Jan Van Velde
Manganese phosphating formulations contains basically a manganese salt, phosphoric acid and an accelerator. Deposition of manganese phosphate coating is normally performed at very high temperatures of the order of 95 °C for a period of 30-60 minutes.
It is a conversion coating process and involves the dissolution of the base metal which subsequently forms part of the coating. In manganese phosphate coating the species that deposits on steel is manganese iron phosphate and hence requires a large amount of metal dissolution so that the formation of manganese iron phosphate is possible. This is the reason for the requirement of high operating temperature and higher processing time.
Manganese phosphate coating offers good wear resistance. It can retain oil and lubricants and improves the scuffing resistance. Manganese phosphate coating with higher coating weight offers good corrosion resistance. Impregnation with oil further improves the corrosion resistance.
Zinc phosphate coating is mainly recommended as pretreatment coating for painting.
T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
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Q. Hello,
I am looking after a Manganese Phosphating line in our company where cast iron components are coated. The phosphating bath concentrate is currently being outsourced and I am not aware of the contents of it.
I am trying to prepare a bath myself using MnO2 [1.5g/L] and H3PO4 [25g/L] and topping the rest with tap water. The problem is I'm not sure what other chemicals to be added (like accelerator, stabilizers etc) and also in what ratio. I also tried measuring the TA & FA values of the above mentioned bath and found them to be 35 & 17.4 respectively. Thus the TA/FA ration is close to 2. But I have read that it should be between 4 ~ 6. Kindly let me know how to improve the ratio.
Alternatively, It would be a great help if anyone can suggest me the method of preparing a Manganese Phosphating Bath and the chemicals required to prepare it in proper ratios. ⇦ Answer?
Plating shop - Shimoga, Karnataka, India
October 1, 2010
Ed. note: Hello Savyasachi. We appended your inquiry to a thread on the same subject, so Goran Budija's and TSN Sankara's postings should be a good start!
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Heaters get sludged, then damaged
Q. My company conducts manganese phosphate coating on carbon steel pipe. We use heating elements to heat the bath where the pipe coating is carried out. The problem is after the coating maybe for a week the heating element is covered by sludge. The workers usually remove the sludge from the heating element by hammer (mechanical). It doesn't only remove sludge but also cause damage to the heating element (made from stainless steel). So: how to remove the sludge without causing damage to the heating element ?
Dodi Syafardi- Cilegon, Banten, Indonesia
2005
A. Hi Dodi. Two quick notes:
• Heaters should be electropolished stainless steel because this surface has no "tooth" at all and will both minimize build-up and make cleaning easier.
• Oversized ("derated") heaters or coils should be used because the smaller the heater, the higher the required surface temperature, which accelerates the sludging and adhesion; and a larger heater also allows a longer running time.
Topics 114/65 "Sludge buildup on heating coils in phosphating tank" and 51/42
"Materials for zinc phosphating tank" address this issue in additional depth. Patient use of our search engine will uncover still more tips on this subject. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Dodi Syafardi,
for exterior coating & if the ends of pipe are open then for interior coating, you may use glass heaters of required wattage and in required number.
- Bhiwadi, Alwar, Rajasthan, India
December 6, 2011
Q. We have a situation where two pieces of gun steel were Ion Nitrided in an ammonia
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eBay or
Amazon [affil link] rich environment. Sample I was Nitrided at a High Temp (still 100 degrees lower than tempering temp) for a short time and Sample II was nitrided at a low temp for a long time. Both samples were subsequently sandblasted with 140 grit alumina then Mn Phosphated (using a conditioner and hex chrome rinse solutions). Sample I has very little Mn Phosphate, very gray in color, and looks terrible in general (in the nitrided and un nitrided sections of the sample) where Sample II looks very typical black coating in nitrided and un-nitrided sections of the sample.
I have been told that this will always happen but not given a good reason as to why (from my experience the only thing that would impact the ability to produce a good coating would be a layer of non-ferrous material/contaminant). Both samples were examined under a 1000X magnification (we hope to view it under SEM technology soon) and cannot see any visible layers/differences/heat affected zones/etc. in the base metals. Does anyone out there have a "oh yeah knucklehead it's this" explanation?
Engineer - Watervliet, New York
January 23, 2014
A. The 2nd most frequent problem with Mn Phos is the absence of a "grain refiner" which I guess you covered with what you call a "conditioner". The first most frequent problem is the total/free ratio. You must adjust this ratio, preferably at the tank side, immediately before inserting the parts. If you check the T/F ratio on Monday and phosphate on Tuesday the ratio is too high, add manganous phosphate until you bring it into proper limits, then immediately phosphate.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. Hello sir, we are doing manganese phosphating on 4130, 4140, 4330 steel parts. It's a new plant we have installed, am not able to standardize the process; I face problems like uneven coating surface, carbon coming out of the surface after phosphating, uncoated areas.
I have failed to do the pre cleaning properly; please suggest a best process for pre-cleaning, and my chemical supplier only supplies the phosphating chemical; please suggest how to overcome these problems? My process is degreasing, water rinse, 5% H2SO4 rinse, water rinse, hot water rinse and phosphating; free acid 6, total acid 31, ferrous ion 1gm/ltr, temp. 90 to 95.,
oil and gas equipment manufacturers - Dubai, UAE
January 27, 2014
A. You must adjust the T/F immediately prior to putting the parts into the solution. For the 4000's series steels you must use a grain refiner. If you supplier dos not have one, then change suppliers.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. Hi Prakash,
After degreasing, whether solvent based or aqueous based I would have an aqueous cleaning step (may sound odd, but the second stage cleaning really does help to get parts really clean). Do a water break check after rinsing to ensure you have an unbroken film of water on the parts, if not then repeat the cleaning process until you get a water break free surface.
Make sure you control the etch, don't over-etch, ensure you chemical analysis is OK and use as short a time as possible to obtain the etch required.
Grain refiners are a good idea to obtain even consistent phosphate crystal formation on your parts. As Robert says, your phosphate solution supplier should have a refiner available.
And I can't emphasise strongly enough that you need to keep the phosphate chemistry under control. Dependent on the level of use I would expect a minimum of twice a day analysis for free acid, total acid and iron, if this doesn't keep the solution under control then increase the frequency. If may be as Robert pointed out that you may need to do the analysis for each bath load, although that would indicate to me you have something else in your phosphate system upsetting the chemistry.
Aerospace - Yeovil, Somerset, UK
Thank you very much sirs, I am getting good results, maintaining the free and total acid in correct ratio, and improved water rinses, and getting good results.
- Dubai , uae
How to computer control Manganese Phosphate process
Q. Hello to all!
We are zinc and manganese phosphate plating company. Demand on Mn Phosphate coatings are rising, therefore also the demand for quality of our service. My question is: how should we make the process more computer controlled to eliminate the human error factor?
Currently we are controlling the temperature automatically with thermocouples, but pH, concentration and acid radio is measured by hand and with analysis.
What are the options for computer control of Mn Phosphate bath?
Second thing, how would you guys hang bush of dimensions 30 mm dia. x 20 mm for Mn Phosphating, to minimize contact marks? Both sides of bush are smooth finished.
Thanks in advance ⇦ Answer?
- Krsko, Slovenia
March 7, 2014
How to Manganese Phosphate the component without any dimensional reduction
Q. How to Manganese Phosphate the component without any dimensional reduction to the base metal of grinding surface?
Required coating thickness is only 5 to 7 microns.
- Pune, Maharashtra, INDIA
July 20, 2014
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A. Hi cousin Ajay.
It is not possible to do phosphating without any dimensional reduction as T.S.N. Sankara Narayanan explains above, and per John Donofrio in the Metal Finishing Guidebook:
But if you run the numbers, this is very little metal -- under a micron. Are you implying that your present manganese phosphating process is attacking the base metal? If so, there is surely something wrong.
Please do your best to describe your situation and your findings from it, and to send pics if they'll help, so we can have an enthusiastic discussion of it here.
Luck and Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Manganese phosphate is not adhering to steel -- it rubs off
Q. I was doing manganese phosphate on AISI4145 steel metal. After some pieces it is failing adhesion test (phosphate layer is removed). Can anyone tell why this happens?
The bath preparation is underground tank and heating coil is used to reach temperature required of 90 °C.
- Mussafah, Abudhabi, U A E
July 28, 2014
A. The part cleaning to be rechecked. During the set temperature either oil or other solvent start releasing. Or, check the oil content in your coolant, if there is any leakage of lubrication oil during machining also will effect. So clean the part in a better way.
Rajagopalan ChakiyarkandyProduction Incharge - DUBAI
February 21, 2022
Must we check Ra BEFORE manganese-iron phosphating or AFTER?
Q. WE ARE IN THE LINE OF MANUFACTURING CAST IRON PISTONS. OUR COMPONENTS HAVE MIP COATING OPERATION AFTER FINISH. WE OBSERVE VARIATION IS SURFACE FINISH VALUES (Ra) AFTER MIP COATING GETS CHANGED TO HIGHER SIDE, AND NO CONSISTENCY IN READING. OUR QUESTION IS WHETHER THESE VALUES MUST BE CHECKED BEFORE MIP COATING.
ANIL KHOTEngg. Works - karad, maharastra, India
August 7, 2014
A. Hi Anil. Based on the context, I assume MIP means manganese-iron phosphating, so we assigned a title and appended your inquiry to this related thread.
Phosphatization is a soft coating (compared to iron), and manganese phosphate is often used as a "break-in" coating for engine parts ... so I would assume that the surface finish before phosphatizing is far more important than the finish after it. Still, who is requiring you to check the Ra? They are the people you should ask 🙂
Regards,
Ted Mooney, P.E.
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finishing.com - Pine Beach, New Jersey
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Q. Dear Sir, I am a custom cutlery manufacturer and have been using Manganese Phosphate impregnated with oil as a corrosion inhibitor on knife blades for some time with good success. I would like to treat kitchen knives the same way, but have concerns about food safety. Is there any reason to suspect that manganese phosphate treatment of carbon steel might be non food-safe? ⇦ Answer?
Adam DesRosiers- Juneau Alaska USA
April 28, 2015
A. Hi Adam. First, I don't want to toss around the term "food safe" without agreeing what it means :-(
Many materials that are not "poison" or "toxic materials" are not "food safe" either. For example, zinc is an essential micro-nutrient rather than a poison, but it can dissolve in acids or alkalis, possibly even resulting in an overdose, and it's not food safe by anyone's measure, even if you find no regulation forbidding it. Similarly, copper is not a food-safe surface but must be hot tinned.
Some of the laws & guidelines set limits on "dissolution" and manganese phosphate is probably not food safe simply by this definition alone.
Further, if you want to sell such a product there probably are FDA regulations that you can only use GRAS ("generally recognized as safe") materials; there might be NSF or some other applicable guidelines on appropriate materials as well. There are a boatload of regulations in the world today, and they are expanding rapidly; I would not be willing to say that anyone can offer anything for sale without a careful study of the laws regulating that trade.
Then too, what kind of "oil" are you speaking of? A few, like olive oil and mineral oil, are non-poisonous, but petroleum oils are definitely poisons.
Interesting question. I hope someone with specific tableware or kitchenware experience will respond. ⇦ Answer?
Regards,
Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey
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Q. Hi,
Good times.
I am Hamidreza from Iran. Sorry that my English is not good.
I have read your article about manganese phosphate and the questions you had.
I do not know during tests of the mixing materials.
Also, after removing the piece of soluble phosphate, phosphate coating on the surface is easily separated.
My solution is mixed as follows:
Manganese carbonate 15 grams per liter
25 ml phosphoric acid per liter
2 grams per liter of nickel nitrate
3 grams per liter of iron sulphate
Sodium fluoride 0.7 grams per liter
Rochelle Salt
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2 grams per liter
5 ml of nitric acid per liter
pH = 1.5
Temperature 95 °C
Time: 30 minutes
If possible, please help. ⇦ Answer?
Grateful,
- iran, tehran
June 20, 2015
Manganese Phosphating: Lost power for 5 minutes
Q. Hello Sir,
During manganese phosphating process if the power goes for 5 minutes and no DG, what are the quality issues can be raised.
- Bangalore, India
October 30, 2015
A. All depends on your solution temperature. Study the temperature specification given by solution provider follow it. There won't be any reduction of temperature within 5 or 10 minutes.
Rajagopalan ChakiyarkandyProduction Incharge - DUBAI
February 21, 2022
Different colour tones on finished Manganese phosphating product
Q. Dear Sirs, I am involved on the inspections of the manganese phosphating process. I would like to know if the difference in colour tones of the final coated surface be cause for rejection. Other parameters were within acceptable limits. In the project specs, it is stated that uniformity in appearance as acceptance criteria. Does it include colour tone for uniformity? What is the cause of this defect? And how to rectify?
Ng twuan HuatQuality Inspections - Singapore
November 12, 2015
A. Good day Ng Tuan Huat.
Surely you are working toward a specification.
I work with a minimum/maximum coating weight requirement.
I would think the variations in colour tones is a process control issue.
You state all other parameters are within acceptable limits.
What are your parameters? Do you have a water-break free surface on the substrate before phosphating? Are you using an acid dip before phosphate? I have found dilute HCl to produce denser crystals.
Are you using a dilute chrome solution after phosphate, and if so, what is the concentration?
What is your free/total acid ratio? What is your iron concentration? What is the temperature?
All of these parameters affect the crystal structure of the deposit.
What is the substrate, and does it contain chromium, and if so, how much?" Max 2% will prove difficult.
Do you examine the deposit under a microscope to determine the density of the crystals? If so, can you see the substrate in between the crystals?
Are you conducting salt spray testing, and if so, what is the outcome?
There were only three questions in your posting, and I have posted you a total of eleven.
There are many variables involved to produce a uniform/acceptable deposit.
Hope this helps.
Regards,
Aerotek Mfg. Ltd. - Whitby, Ont., Canada
Q. Dear Mr. Bogner,
Please answer to question: we do Mn phosphating on threads of pipes. On way - alkali cleaning, rinsing, activating (Gardobond 6560 A and 6561 B (Chemetall) - MN phosphating (Gardobond G 4040) - rinsing - rinsing. (We cannot do pickling).
We cannot pass test - 10 screwing unscrewing. Could you inform us what we shall do that Mn phosphating crystal be more strong to wear of thread?
Director - Wolbrom Poland
December 24, 2024
This is a meeting place for camaraderie & sharing, not a free consultancy. So some readers don't engage with anonymous posters.
A. Hi Vadim
We will try to advise Mr. Bogner of your question, but his posting is from more than 9 years ago.
Phosphates should react with bare metal in order to deposit properly -- not oxidized surfaces with varying and uncontrolled amounts of oxidation. Since you can't pickle these pipes can you sandblast the thread areas, or at least phosphatize them immediately after cutting the threads?
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Q. Dear Mr. Mooney,
Thank you for the answer. We do Mn phosphating for antiwear of thread of pipes.
Is it enough to do alkali cleaning before activating?
director - wolbrom Poland
December 28, 2024
A. Hi again Vadim.
Acid dipping to remove oxidation is a conventional part of metal finishing operations. You have told us that you do not and cannot employ such pickling, and that your process is not working. I replied with my theory of why it is not working and suggested some things that can be tried to see if that will make it work. I'm not sure that I can offer any further advice.
But a general principal is that processing should be robust. If you operate a process which offers no provision for dealing with oxides and mill scale which will sometimes be present, it is not robust and although it may work sometimes if things are coincidentally highly favorable -- like the threads freshly cut perhaps -- it will not work reliably. Your process either needs to offer a way to remove heavy oxiding on the pipes or you must constantly operate in a fashion which guarantees minimal oxidation.
Please do a trial of blasting the thread area, or of processing immediately after cutting the threads, or try an alkaline de-ruster before putting the pipe through your process line, but it seems apparent that a grain refiner before phosphatizing is not a sufficient substitute for acid pickling or de-rusting.
Luck & Regards,
Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey
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Q. I am facing a problem in distinguishing two washers having almost the same dimension and both are Manganese Phosphate coated. How can I ask the two source to make some visual difference? Please answer, it's urgent. ⇦ Answer?
ARIJIT DAS- JAMSHEDPUR, JHARKHAND, INDIA
November 30, 2015
A. Hi Arijit
It would seem that the oil or wax used after phosphatizing could be dyed, and one part dipped in one color and the other part dipped in another color. But this is fallible too, as the parts may be dipped in the wrong color oil, so this would be no surer than your supplier putting them in a labeled bag or box.
Gaging tools of various sorts are a commonplace in inspection & production facilities, and it seems like it should be very easy to make a sort of gage tool which will sort washers into piles which comply and fail to comply with an O.D., I.D., and thickness, either one at a time by hand, and automated with a vibratory feeder bowl arrangement.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Manganese Phosphate color variation within the same lot of parts
Q. I would like to know if anyone has experience with some steel parts that are manganese phosphate all together as part of a big lot show some brown/pinkish appearance
Rodrigo Ramos- Salisbury, Maryland, USA
March 22, 2016
A. Good day Rodrigo.
Good Info @ thread 266/94. This web site has a plethora of info!
Regards,
Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada
Ed. note: Oh yeah, we have a plethora ⇨
A. I had experienced it with different grade of materials. If you have facility to provide bead blasting surface it can be controlled to a certain extent.
Rajagopalan ChakiyarkandyProduction Incharge - DUBAI
Q. Respected Sir,
We have a new coating plant and are going to perform Manganese Phosphate coating. Customer specifications are written as: Zn Manganese / Nickel Manganese / Manganese Coating for different parts. What is the difference in all above three or are all above same?
Are there different types of Manganese Phosphating?
- Pune, India
March 9, 2017
A. Hi Nitin. Unfortunately you simply can't ask a third party to put a fine point on someone else's slang and casual phrasing. There is no way for me to know whether "Zn Manganese" is intended to mean "Zinc Phosphating with additional dicationic ions of manganese" vs. "Manganese Phosphating", or what exactly "Nickel Manganese" was intended to mean, or whether "Manganese Coating" was intended to mean "Manganese Phosphating". Guessing is not the way to proceed; you must get clarification and hopefully mutually agree to a more carefully worded specification.
Normally there will be additional criteria like salt spray hours for testing, coating weight, compliance with a specific standard number from a generally recognized organization like ASTM or ISO, etc. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Ji, it all has its own different structures as well as application. Chemistry itself has differences. It is better to take advice of your solution provider for the right process.
Rajagopalan ChakiyarkandyProduction Incharge - DUBAI
February 21, 2022
Q. Dear readers,
I have set up zinc phosphate and manganese phosphate coating plant in our company.
I wanted to know if we can distinguish parts which are zinc phosphate coated from those coated with manganese phosphate.
- Pune, Maharashtra, INDIA
June 26, 2017
A. Hi Kathik. Tracking the parts seems more practical than mixing them and then testing individual pieces to re-separate them.
Although I personally have very low confidence in visual identification of finishes, I think only you can answer whether your people can reliably visually sort your specific zinc phosphate from your specific manganese phosphate. Sorry to be of so little help :-(
But most processors these days need to certify that parts went through a very specific process sequence; are you sure you are willing to subject your certification process to the weak link of a visual identification?
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Regarding visual identification of phosphate coatings:
Zinc phosphate coatings will typically exhibit a dark gray color. Manganese phosphate coatings will typically exhibit a dark black color.
Imagineering Finishing Technologies - South Bend Indiana
Glittery Manganese Phosphating
Q. Hi,
I am Jerin. I am from U.A.E. I happen to do manganese phosphating on a small component but it ends up with glittery look. Can anyone help to know the reason why?
Thanks,
- United Arab Emirates
August 20, 2017
? Hello Jerin, are you using a surface conditioner before the phosphate?
Yohands ReyKAT - Chihuahua, Chih., Mexico
A. Hi Jerin!
You seem to have big crystals in your part, you can use a grain refiner (your phosphate vendor may have one) or you can manage the crystal size with your Total Acid/Free Acid relation.
Big crystals for a big relation (TA/FA), small crystals for a small relation. Your vendor may have an operative range for this parameters, you can work to manage this value low and get smaller crystal size and less "glitter".
Hope it works! Best regards!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
Hi Yohands, Thanks for your reply. In order to remove oil- film/grease from surface, we cleaned the surface with normal detergent, then had a rinse.
Hi Daniel, Thanks for your reply. Perhaps that would be the problem. I would try as you suggest :)
- United Arab Emirates
A. Dear Jerin,
Glittery appearance is mostly related to Iron concentration. Check solution parameters. Modify solution to the optimum. Give chance for acidic formation on the surfaces.
Production Incharge - DUBAI
February 21, 2022
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Q. Reading this thread brought a bit more clarity for me regarding phosphating process. Thanks to everyone here.
My customer sent me some phosphated samples which had no oil coating, grayish tone and very smooth surface, kind of self lubricated finish.
I am told there's a lacquer available for such applications. Anyone have any experience in this?
Regards,
ASCO - Edmonton, Alberta, Canada
October 5, 2017
A. Hi Sukhjot. I think it is important to find out from your supplier what kind of phosphating process and sealer they applied if you don't know yet. I would not try to guess what a finish is from its appearance.
Although there are variations, phosphates are usually one of three general types:
1. Iron phosphates, which are thinnest, cheapest, least corrosion resistant and always painted.
2. Zinc phosphates, which are of middle weight, and usually painted, although occasionally oiled.
3. Manganese phosphates, which are heaviest, and designed to be oiled rather than lacquered or painted. Manganese phosphating is a well known "break in" finish for moving parts.
Unfortunately, 'lacquer' is slightly vague, it is often used to mean a water soluble final dip, or a clear 'paint' among other meanings. But it sounds like the parts were waxed, in which case nothing additional is likely to stick.
Regards,
Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey
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Iron concentration test
Q. Dear professionals.
I need to know the actual reason and or need for the iron concentration test when testing the parameters of a manganese phosphate tank.
I have several vendors that all use different chemicals worldwide, some technical data sheets say nothing of iron concentration, however, the written coating specifications do have titration instructions for the analysis of the above.
Is it the variation of the different chemicals?
Is it an essential test?
What do the results tell us?
Thank you.
- Leeds. West Yorkshire. UK.
October 31, 2017
A. Hi Steve,
Manganese phosphate, in general, works with accelerant addition. This accelerant works by oxidizing all iron in solution, but iron dissolves from the parts you process, and this iron deposits with manganese in the phosphate crystals. Actual manganese phosphate coating has iron in its composition, but the actual solution has not.
If you mean the iron test strips for "iron concentration test", as I believe you do, I'll tell you: You don't want iron in solution because you want more manganese in your phosphate, you want to control the deposit and you don't want green if you are doing black phosphate. Manganese phosphate works without iron, and you test Fe(II) presence with the strips. You add accelerant in order to control iron, and control the reaction and grain size, and it works really well.
I don't know if I actually answered your doubt, so if I didn't, feel free to ask again maybe with an example.
Best regards!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
Manganese phosphating coating failure on rub test what is the reason?
Q. We are doing manganese phosphate coating. Failure in quality during rub test sometimes; not forming the layer sometimes; failure with the black coat being removed. What are the reasons and how to maintain the quality? Please advise.
Rama Panfianoilfield services - Dubai UAE
April 7, 2018
A. Hi cousin Rama. Your phosphatizing is not being done properly if it is removed by the rub test or if it doesn't form. Rarely can anyone suggest one simple change to what you are doing when we don't know what you are doing yet.
But are you sure the parts are spotlessly clean before they get to the phosphatization tank? Are you sure the parts are rust-free and not oxidized? Are you carefully maintaining your free acid and total acid? Are you using a grain refiner as suggested on this page? Are you operating at 95 °C or at the proprietary vendor's recommended temperature? What spec. no. is the rub test, or what are its details? Thanks!
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Manganese Phosphate Coating Visual Issue
Q. I'm having an issue with the visual appearance of my product. One of the specifications from the customer is a uniform black coating, my company has two other sites around the world with identical lines to mine and are able to achieve this specification for the same product. The issue we are facing is black/grey dots. We control everything in the line, the concentrations of every tank, free/total acids, everything right down to the pH and conductivity of the rinse water. So my question is, what causes these visual defects and what would be the best option to fix them? Thanks
Samuel Hunt- North Vernon, Indiana, US
July 10, 2018
? Hello Samuel!
Can you describe the part you are coating (the material, if it is machined or forged, oiled or else …) and how you clean the parts? If you are controlling all your phosphate parameters, maybe the issue is where you are not looking…
If you can send some photos of the parts (after-before), maybe we can have an idea of what can be happening.
Best regards!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
Q. Hello Daniel, thank you for responding; it is a pin end con-rod that is being coated, it is a machined surface with no oils. For the phosphate parameters, we monitor free/total acids, iron, and copper concentrations. Due to low surface area being run through the tank we do have an issue with iron concentration being low, we also use a pump to recirculate the fluid which introduces more air into the line, however this design works in two other locations without issue.
In the attached pictures you can see the black speckling and blotching on the part. We use an alkaline soak cleaner and an acid etch in our process line, both of which have are monitored for concentration and temperature. Thank you again.
Samuel Hunt [returning]- North Vernon, Indiana, US
Ed. note: Unfortunately the pics came through only as unreadable files from some application which we don't have and probably can't use on the WWW. Please re-send them in .gif, .jpg, .jpeg, .pdf, .png, or .tiff format. Thanks.
A. Hello Samuel, 'please send the images in another format because we are not seeing them...'
I'm really interested in what you call "blotching", because that would be entirely a pretreatment issue, but dots or "speckles" could be a phosphate issue because of sludge agitation, for example.
Best regards!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
Q. Sorry about that, didn't realize they didn't go through. Part not run yet:
Parts with black speckling, gray dots, and streaks:
I'm not sure if it could be the sludge or not. We use a pump to agitate the process, but it's actually tilted to go towards the parts and don't face the sludge at all. It is possible to see to the bottom of the tank, even in full production. We have never seen or been able to detect any floating sludge either. Thanks
Samuel Hunt [returning]- North Vernon, Indiana, US
A. Hello Samuel, sorry but I had some issues to resolve and could not answer sooner.
I can assure that if you can see the bottom of the tank while you are in production, sludge is not the problem. Speckling, grey dots, and streaks are usually symptoms of poor cleaning (or too much sludge, but we have just ruled it out). I see it is a machined cast iron part, so I would seek:
1) What do the machining process to lubricate, or if it is a dry machining process. Is it the same design as the other locations?
2) Alkaline soak cleaner: Is it the same as the other two locations? See if it could be contaminated by silicones. We had some issue regarding foam production in this tank and silicone de-foamers used in wastewater, so the phosphated parts had marks on them. You can't see whether the alkaline cleaner has or not any silicone, but you could see if the addition of some product of the sort could end in this tank.
3) Grain refiner: Do you use any grain refiner between pickling and the phosphate tank?
Best of luck!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
A. Two problems: (1) You cannot acid etch ahead of manganese phosphate. (2) You must use a titanium salt grain refiner.
Blast the part and use grain refiner.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. Thank you both for the response,
To answer you Mr. Montañés:
1. All chemicals and designs of the lines are identical and purchased from the same manufacturers.
2. As stated above it is the same, I checked with process up stream and none of them use an silicone based chemicals. I don't see any other possible entry point for that either.
3. Yes after the acid there is a rinse and then it goes to the grain refiner,
To answer you Mr. Probert:
1. You can acid etch before, we've done it, and the coating is good. The main issue is it requires high temperature and causes rust on the rest of the part, even with RP.
2. Due to dimensional constraints, blasting is not an option, we've tried this as well already and seen the good results.
Again thank you for your feed back, I look forward to hearing from you.
- North Vernon, Indiana, US
A. Hi Samuel,
To me, this looks like leaching of fluids, post phosphating, from inherent porosity in the casting. Always looks more pronounced on machined surfaces.
If it is indeed porosity you could try alternate hot and cold rinses to try and remove residual acid in the pores; alternatively, prior to phosphating you could try vacuum impregnation, using sodium metasilicate
⇦ on
eBay
or
Amazon [affil link]
sealer, which could seal any porosity before you phosphate.
Aerospace - Yeovil, Somerset, UK
Grey-white lines on black phosphatizing
Q. Dear all,
I would like to thank you all for your enthusiastic contributions on every problem stated here in this thread.
May I submit this one:
We're Mn phosphating maraging forged steel in our company in order to get that specific deep black coating as we all know it.
Not so long ago we've noticed grey-white rather linear indications on the treated surface. We don't know where they come from. The flow of these parts upwards is made of roughly machining - heat treatment - polishing - Nittal etch - sandblasting (120/150 grit Aluminum oxide, 58 psi,12 inches) - water rinsing - degreasing - demineralized water rinsing (+ water break free) - Mn phosphating (Mn carbonate, phosphoric acid, Ti based grain refiner, acid ratio around 5) - heat treatment (de-embrittlement).
We have spotted these indications right after de-embrittlement, but also right after phosphating.
We've performed several analysis such as microhardness and SEM thinking that the problem was related to forged steel itself. Now, we're after contaminations in the process.
Can anyone help to orient our investigation? Any documentation on typical defects with phosphating maraging steel.
Best regards
- Zaventem, Belgium
November 28, 2018
A. Dear sir, to all,
Please don't use alloy sandblast media for cleaning the parts. Please use only sand which is from river or sea. Alloy media streaks or affects MS which is not good for MNP coating.
MNP chemicals react only on MS well. MNP is amalgamation of MS & Manganese.
If there's any other metal in between while process of MNP coating, we can't get good results.
Thanks.
- Pune Maharashtra India
A. In the firearm business, Aluminum Oxide is the preferred choice in blasting material. As is well known 90% of the problems with the bath occur in preparation so if cleaned correctly following the blasting you shouldn't have any problems with the Aluminum.
If you are really concerned, glass bead blasting is an excellent solution, although some results may vary depending on the shape of the material your'e blasting. With rounded objects the glass does not perform near as well as the Aluminum.
If your main problem is a lighter coating I sincerely doubt Aluminum is your problem. In MNP normally the coating is lighter with initial use and darkens over time.
If it is a fresh bath, that is your primary problem, it simply needs to be seeded first with Iron or even Titanium.
You are correct in your assumption as well. If the alloy itself has contaminants it can also lead to such a coating. If using Nitric Acid, you may want to check the content of that as well.
A. JUST A FYI -- Please Stop Using MnO2
While you will get a "coating" using MnO2. This compound is not a very good compound to use to get MNP. MnO2 does not readily dissolve in phosphoric acid. MnO2 is an old wives tale recipe as it is easily obtained from a D cell battery.
With MnO2 you are actually creating more of an Iron Phosphate coat then a Manganese coat which is more desirable.
A much better compound of Manganese to use is Manganese Carbonate which is just as cheap, readily available, and converts almost instantly and completely to Manganese Phosphate in an MNP bath.
Q. I am not quite sure which form of Titanium is best for the phosphate bath, activation or passivization.
I have plenty of titanium dioxide
⇦ on
eBay or
Amazon [affil link]
, but is this compound useful at all in anything regarding the Manganese Phosphating process?
Perhaps a conversion/ transformation into a Titanium Phosphate would be more useful, but what would be the best way to facilitate that? I have attempted with Phosphoric Acid, but as expected it did not seem to react, even boiling for hours.
Would a Sodium titanite be more useful? or a Titanium Salt (no chloride)
On a different note, would ZrSiO4 be useful in a post passivation process? If so else would possibly be required?
As I can create a Chromic Acid Rinse, should I stick with that?
From research the Chromic Acid on the Manganese Coating should be kept at a pH of 4-6. Is this true? ⇦ Answer?
OuterGravity - Dallas, Texas, United States
August 16, 2019
Q. Hello,
We have installed a new manganese phosphating line in our plant with the intention of obsoleting an old line. In our new line we are using the same chemicals (cleaner, grain refiner, manganese) the same time and temperatures and are coating the same parts as in our old line. The problem is on some areas of some parts the coating appearance from the new line abruptly changes from black to gray in random patterns. SEM analysis shows the lighter colored areas have smaller and more rounded crystals. This color variation causes issues with our inspection camera systems at a subsequent operation.
The old and the new line are both functional, so it sets up a great opportunity for testing, and we have done a LOT of testing! From this testing I feel confident that I can rule out a lot of possible causes like; chemistry, cleanliness of parts, tank size and agitation, and part spacing. At this point I have no idea what else the issue could be. I have had many experts come in and review our situation with no luck. Even though I don't think chemistry is the 'problem', I have tested a few different chemicals in case that could be the 'solution' to the unknown problem.
Does anyone have any ideas what the cause could be? Is there any situation where some kind of electrical charge could influence the crystal growth?
Thank You.
shop employee - Saint Johns, Michigan, USA
September 9, 2019
A. Regarding the black and gray. Go back and study the agitation of the grain refiner to be sure the grain refiner is hitting all surfaces.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. Thank you Robert for the suggestion. We have a propeller mixer in the old line and the new line. I have tried varying the speed of the mixer and using intervals of ON/OFF within the cycle but did not notice a change to the coating.
It won't be too easy to do but I could perform a test where I add part oscillation to the Grain refiner step.
Generally speaking is it a good idea to have the parts oscillating in the grain refiner tank?
- Saint Johns, Michigan, USA
Double dipping in Manganese Phosphate
Q. I have a question: would there be any issues with double dipping a part in the Manganese phosphate solution that is too long for your tank. ⇦ Answer?
Chuck Hawkins- Long Beach, California
September 12, 2019
Adhesion Loss in Manganese Phosphating
Q. Hello Everyone, we are having a Nihon Parkerizing Manganese Phosphate bath. We are suppose to phosphate AISI 4130 carbon steel material. We are experiencing loss of adhesion after phosphating. The phosphating layer comes off while rubber test and even when we rub by hand or cotton cloth. Please advise where we are missing the plot. Thank you in advance ⇦ Answer?
subodh sawantShop Employee - India
September 19, 2019
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