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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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All of the Questions in this Sidebar are from the same shop and referring to the same processing line. Q. Using S110 steel shots to do blasting on steel parts. Recently have been facing issues with regards to small pitting/denting on parts. Have installed a drive on the impeller motor and am thinking about decreasing the shot velocity. On the contrary though I do not want to compromise on the blast cycle time and am on the line of increasing the shot flow rate (controlled by a damper). This way I believe I would be able to run at the prescribed amperage (90% of full load motor current) 1. When the amperes (measuring wheel current) are decreased, am finding that the flow rate is increasing? Would it not be other way around? I was under the impression that the amperes are a direct reflection of my blasting intensity (which is a product of mass flow and velocity as in Kinetic Energy) Any recommendations on my thought process? Any assistance in form of technical input would be highly appreciated. Cannot figure out how to resolve this denting issue. Thank You Abhishek Patel - Ahmedabad, Gujarat, India August 17, 2012 Q. Hello, Currently we are using Shot blasting as a surface preparation prior to Manganese Phosphating. Would the phosphating coating characteristics and adherence properties change if we change the preceding process to Vibratory finishing? We have issues with dimensional distortion and surface roughness so we would like to ideally switch over to a milder form of deburring/pre treatment. Any issues been foreseen with the change? Abhishek Patel [returning] - Ahmedabad, Gujarat, India A. Hi Abhishek, I must admit that I don't have experience with using vibratory methods of preparation before manganese phosphate, I have always used an abrasive blasting technique. Before you go and start looking at new ways of finishing can you describe the exact blasting process you are using (blast media type, mesh size, blast pressure, stand off distance)? It may be with some modification of your technique blasting may still be a viable option for you. For example I use 180-220 mesh alumina grit at a pressure of 40 psi nominal (some jobs have higher pressure needs, some lower) and a stand off distance of about 6-9". This works for about 80% of jobs I do and I suffer little to no distortion. Brian Terry Aerospace - Yeovil, Somerset, UK Q. Hi Brian Being a mass production process, we are confined to use wheel blasting & not air....besides the issue is rather the geometry of the parts. We use cut wire steel shots for blasting with tumblast wheel blasting machines. Am of the understanding that phosphating happens at a molecular level so only surface cleanliness & uniformity along with proper surface conditioning should do the job. Though, yes, higher roughness caused by blasting would give more surface area to the phosphate for better coating & adherence. Just wanted to confirm from all the experts here. Abhishek Patel [returning] - Ahmedabad, Gujarat, India A. Hi Abhishek, Probably going to show a bit of my ignorance of wheel blasting machines now, can you not reduce the rate of feed of blasting media or change the speed of the wheel blasters so that you reduce impact speed? Alternatively can you change your media without modifications to your cabinet, you may be able to use a less aggressive cutting media? You are perfectly correct that the reaction happens at the molecular level and that the increase in surface area by blasting increases the number of reaction sites. If you wanted to go to a vibratory method then you need to talk to your local supplier to see what they have to offer in terms of media that will cut sufficiently to give your increase in reaction sites and still avoid distortion. I get a feeling you are going to have to try a bit of trial and error to see if the process is a viable method of manufacture. Brian Terry Aerospace - Yeovil, Somerset, UK Q. We have done Zinc Phosphating process but we are facing visual difference in color. Parts are looking like they are processed through Mn phosphating means black. Process steps: Degreasing water rinsing activation @ room temp. phosphating @ 80 °C water rinsing passivation RP oil Please suggest what should we do? what changes need to be done? ⇦ Answer? Keyur Solani [returning] - Ahmedabad,Gujarat, India January 22, 2015 Q. Hi guys, I do Mn and Zn phosphate coating and use rotating tumbler for holding parts during the process to avoid touch marks of jigs/fixtures. For a recent new part I am facing problem of parts getting stuck to each other due to its cup like shape leading to light uncovered portion in 30% parts. Tried many options but couldn't succeed. Can anyone please help me out with some unique fixture options or concepts or designs to avoid both touch marks and sticking of parts with each other during the process. ⇦ Answer? Thanks.. Jeetendra Jeet Umre - Ahmedabad, India February 24, 2016 Q. Hello Sir We are doing Mn phosphating on AISI1208. After some components phosphate white and black spots observed on phosphate material. Due to this we do lots of quantity rework. Dhanjeet singh - Ahmedabad Gujrat December 22, 2017 A. Hi Dhanjeet, Please tell us how you clean your parts (alkaline degreasing? acid pickling? how many rinses?), parameters in phosphate coating (temperature, free and total acid) and sludge removal system you have so we can help you with some recommendation to improve your situation. Best regards :) Daniel Montañés TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina Q. Hello Sir We are doing Mn phosphating on AISI1208. After some components phosphate white and black spots observed on phosphate material. Due to this we do lots of quantity rework. Dhanjeet singh - Ahmedabad Gujrat A. Hi Dhanjeet, Please tell us how you clean your parts (alkaline degreasing? acid pickling? how many rinses?), parameters in phosphate coating (temperature, free and total acid) and sludge removal system you have so we can help you with some recommendation to improve your situation. Best regards :) Daniel Montañés TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina Q. Hi, I am working as Senior Process Engineer. We are doing Mn Phosphating of Vibro-Finished steel parts and facing issue of black and white spots after phosphating. Phosphating process: Degreasing->Water Rinsing->Activation->Phosphating->Water Rinsing->Passivation->Dewatering->RP Oiling Earlier we were preparing parts with shot blasting instead of Vibro Finishing and parts were okay by visual. Please help. Regards, Keyur Solani - Ahmedabad, Gujarat, India March 17, 2020 A. Hi Keyur. Before you spend a lot of time trying to analyze the difference between the surfaces produced by vibro-finishing vs. sandblasting, I think you probably should make sure that you're definitely talking about a causal relationship rather than a coincidental one :-) So please sandblast a few parts and run them through the line now, rather than relying on what happened before, and make sure that sandblasting makes the problem go away :-) Only if it does is it worthwhile to undertake the bigger job of figuring out exactly what is wrong with your vibro-finishing process because it seems more likely to me that something went out of whack in your phosphating process in the interim than that vibro-finishing is incompatible with manganese phosphate for your parts. Your posting is very similar to a posting from Abhishek Patel back in 2012, from Dhanjeet Singh who posted about black and white spots back in 2017. And I can see that you're with the same shop as Jeet Umre who described the fixturing of your parts back in 2016. If you're all from the same shop and this is one on-going problem since 2012, surely a co-ordinated discussion will be more productive than a scattergun: Good luck and Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey Need quick confidential answers? $25 Need project assistance? $100/hr. Q. Thank you sir for your reply. Yes, all names you mentioned are from same organization but some are not working with organization now ... [remainder of posting placed below the sidebar by editor] Regards, Keyur Solani [returning] Harsha Engineers Limited - Ahmedabad, Gujarat, India A. Hi again. Okay, I've moved all the related previous inquiries that I could easily find into this sidebar now so readers can see the whole picture. Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey Need quick confidential answers? $25 Need project assistance? $100/hr. Q. .... For Now we have already completed with shot blasting as you have said. But now we want to eliminate shot blasting process and replace it with vibro finishing process. So prior to phosphating we will have Vibro finishing plus dryer process and afterwards directly to Mn Phosphating. With same process we are facing issue of black spot on our parts which is not 100% some parts are also found visually ok. Almost 50% is rejection. Please give your guidance to proceed further. Regards, Keyur Solani [returning] Harsha Engineers Limited - Ahmedabad, Gujarat, India March 26, 2020 Q. Thank You for the reply. Yes as per your suggestion we have completed with shot blasting but now onward we want to replace shot blasting with Vibro finishing to improve surface roughness which is customer requirement. We are achieving surface roughness within spec with vibro finishing but we are facing below issue with same: 1. Black spots on some of the parts 2. Higher coating weight of 15 - 25 gram/m2 Please guide for the same. Thanks in advance Regards, Keyur Solani Keyur Solani [returning] Harsha Engineers Ltd - Ahmedabad, Gujarat, India A. Hi Keyur. If you have run sufficient shot blasted parts this week to be confident that they all come out well, and your phosphatizing line is currently in fine tune, you can move on to examine the relationship between vibratory finishing and the decline in quality of phosphating. Jeet Umre reported difficulty in processing the parts because they "nest" due to their cup-like shape. Do you have good reason to be confident that they are not nesting in your vibratory finisher, so all surfaces are being properly finished? Although bead blasting is good prep for phosphating, it is not necessary for proper phosphating; in fact, probably only a small percentage of phosphated parts are blasted. But in addition to increasing the surface area, it serves to both clean and activate. When you skip it, a question becomes whether your cleaning and pickling is adequate without it. I am personally not familiar with vibratory finishing before phosphating. My question then is why are you doing it? My impression is that vibratory finishing before phosphating would be for the purpose of deburring, not for cleaning or activating. What happens if you manually deburr a few parts as needed, then just clean, pickle and phosphate without any vibratory finishing? A good next step is to try to determine whether vibratory finishing is merely not helping or is actually interfering with the phosphating. Satisfactory phosphating is complex, and everything is interrelated; sorry that it's not proving easy :-( Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey Need quick confidential answers? $25 Need project assistance? $100/hr. Q. Good Morning Sir, "Why are we doing Vibro Finishing?" Answer is our customer is having requirement of surface roughness of 0.5 Ra, to achieve same we shifted to vibro finishing instead of shot blasting where we were not able to achieve surface roughness as per customer requirement. Addition to that, deburring and cleaning is other objective. But as earlier said we are facing issue of: 1. Black spots on some of the parts 2. Higher coating weight of 15 - 25 gram/m2 with vibro finishing prior to phosphating. Keyur Solani [returning] Harsha Engineers Limited - Ahmedabad, Gujarat, India

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Q. Hi, I am a hobbyist who makes items mainly from mild steel and have been experimenting with home brew manganese phosphate solutions.

Manganese dioxide appears to be completely insoluble in phosphoric acid at any concentration even at temperatures approaching boiling point. I have tried parkerising with solutions made up with manganese dioxide, iron wool, and phos. acid with reasonable results, have also tried phosphoric acid and iron wool alone and have still achieved what appears to be similar finish. I am wondering what role if any the manganese dioxide plays in the chemistry of these home brew formulations? I suspect that commercial metal finishers achieve superior finishes by using actual manganese phosphate dissolved in a phosphoric acid solution. This seems to be an unobtainable chemical, I hope that someone can advise me. Thanks.

Tim Davy
- Hastings East Sussex England
October 4, 2020

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Q. Hello Finishing community,

Is there a safe way to remove spot rusting from Manganese Phosphate without removing or hurting the Manganese Phosphate?

Thanks

Anthony

Anthony Lyons
- Carterville, Illinois
December 5, 2020

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Q. Hello,

I am a mechanical engineer and work on a lot of defense contracts. I have come to an issue with a vendor and I have hard a hard time finding out the importance of the process requirement in a mil spec that states that a single contractor must perform all phases of cleaning and coating process.
Common sense tells me this is smart. Reduce the ability to introduce foreign matter etc. But scientifically there must be a solid reason for this requirement.
What are the risks taken when the abrasive blasting is outsourced?

Dawn Newmann
- Worcester, Massachusetts
May 28, 2021

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Q. Hi,
we make MIM parts in our plant and also do MnP for Medium Carbon low alloy steels (4605 & 4340) grades. recently we have got the issue of surface finish after the MnP process. Initially, we use to get a black color finish after MnP but now the surface looks brownish and our customers are not showing interest to accept the parts because of the finish & Brownish appearance.

Please let me know whether there will be an issue in bath concentrations or due to improper surface preparation (we do grit blasting as surface preparation).

Advice accepted. ⇦ Answer?

thanks
Chanikya

Chanikya Polidas
R&D Specialist - Bangalore, India
December 10, 2021

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Q. I have a problem with gas soft nitrided parts. After coating Mn phosphate found defect: non-phos all surface some pcs.(50%/Lot) Could you advise the cause of this problem to me? We found this defect the first time after 5 years of production.

Dittakorn Kamchan
Student - BKK, Thailand
February 18, 2022

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Q. My manganese phosphate bath has gone from dark grey almost black to a light grey and I have changed nothing with my process . . . still test the bath every morning before putting parts into it. Wondering what could cause this?

walker johnson
finishing super - South Carolina
March 29, 2022

Q. So, on the contamination from other metals point I noticed that our cold water pipe cold and the one to the hot water heater were rusted. So I filled up a tank and let the water sit over night, and the next day the water had a reddish tint to it. I assumed that was causing some of the problem but my company has not yet got around to changing the pipes out so I have no test to run just yet.

I will get the metal data sheets and message back the types of material we phosphate just so the info is provided. Would love to be able to email someone on this subject if they had the time and were willing. Appreciate the reply, thank you.

Walker Johnson
- Aynor, South Carolina
July 26, 2022

Ed. note: Hi John, we have all the room in the world for anything you want people to see, but this site is not for private communications for several reasons ... including the fact that dozens of readers have similar problems to what you are experiencing and we don't want to string them along then cut them out from the resolution through you getting the answer in private. E-mail whatever you wish to [email protected] with subject 'thread 34052' for posting here. Thanks.

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Q. Hello, I am doing a manganese phosphating and over the past month I have had the issue of keeping our FA within the 2.0-3.1 ratio that we use at my facility. My FA tends to float around the 1.2-1.7 range. My TA range floats around the 14-18 (which is what I need to do for my facility) and my temperature is around 200 °F. I am not sure how to improve my numbers. Something that is worth noting is we run for roughly 24 hours a day. We occasionally have downtime, but it is not super common. ⇦ Answer?

Michael Hannes
- Waterloo, Iowa
November 7, 2022

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Q. We are establishing process for Manganese Phosphating line for coating on 4140H grade steel parts using Henkel Chemicals. We are not able to achieve even/uniform coating despite attempting different combinations of TA/FA Ratio between 5.5 to 9 (TA between 10.5 to 12.8 ) and FA between 1.2 to 2.4 ) and activation time from 15 secs up to 120 secs. Temperatures of the baths are maintained at 70-75 °C for Activation and 92-95 °C for Phosphating. Cleaning qualifies water break test.

        

Can anyone help please?
Agam Thind
- Chandigarh, India
November 24, 2022

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Q. Good Day,

We have a vendor that processed some material with Manganese Phosphate per MIL-DTL-16232 [from DLA] , Ty M, Cl 2. The finished part has areas that are black and areas that are gray, almost like they were masked off.

A second part has a mixture of black with gray streaking; and 7 parts have no adhesion on the ends, base metal is visible.

I just need some ideas on what the issue(s) could be.

Thank you

Eric Hein
Employee - Milwaukee, Wisconsin
February 6, 2023

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Q. Hi, I work in a manufacturing plant that does manganese phosphating. I see you offered to connect a few dots in this long thread for someone who was having problems with white and grey dots on their phosphate. Wondering if you still had those links jumbled together if you would be willing to share them. Also, not to bother you but if there was some way I could contact you more efficiently if you had the time. I would much appreciate it.

Walker Johnson
- South Carolina
July 25, 2023

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Q. Good Morning,

We are facing two issues after our manganese phosphate process.

1. Parts have a blotchy appearance. Variation of light and dark grey across the surface. It's inconsistent and not on every part.

2.Parts appear green. It appears to only be at the surface level.

Prior to phosphate, the parts go through a chromic acid rinse

Parts are made from HNV3 and are investment cast. After casting, they are machined and have an internal bore that is chrome plated. The visual inconsistencies only show on the surface.

Any input would be greatly appreciated. I am by no means an expert but would like opinions on what could be the root cause as I continue to investigate.

Cameron Askew
Quality Engineer - Columbia South Carolina
April 22, 2024

Sorry! Finishing.com is temporarily Read-Only.
Ted Mooney is retiring but I have several offers to take it over.
We're working hard to make sure we find it the best new home.

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