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7 tank hot phosphating process
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We use lot of sheet metal components in an industrial product with a powder coated finish. The basic pretreatment used before powder coating is 7 / 8 tank Hot process for cleaning & applying a thin phosphate coat. In this regard we will like to know if you have done any standardization of chemical Processes ? If yes , can you throw some light on following
1) Details of 7 / 8 Tank hot process
2) The chemical composition & temperature of each liquid in all tanks.
3) The Approximate time interval for sheet-metal to be kept in each tank for cleaning / coating etc.
4) If you have made any industrial standards as ref. document?
5) If you suggest any book which covers these topics , it will be extremely good.
Please Revert Back with reply.
Best Regards,
DILIP P. MANOHAR- MUMBAI, India
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It's out of print and hard to find but Samuel Spring's "Preparation of Metal for Painting" [link is to info about the book at Amazon] is a book that I can recommend as what you're looking for.
Another book that sounds right, but which I personally haven't seen is "Phosphating of Metals" [link is to info about the book at Amazon] by Rausch & Rausch
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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I am a metallurgical engineering graduate 1990 batch,with MBA. I have installed a new small scale unit basically for powder coating ,products like wrought iron articles/furniture,lamps and lamp shades,pedestal fans and many other items that can be coated.I have not yet started commercial production which shall begin in a couple of days, right know I am working on samples to be displayed in the target market.I would like to know if the three in one phosphating chemical is equivalent to 7 tank process, if yes what should be the concentration of phosphating chemical in water (if it is to be diluted),temperature and time for removing rust from steel and cast iron .Further before phosphating I am using HCl Acid for degreasing scale removal, I have heard that some people use sulphuric acid, which is better if final product is to electrostatically powder coated.
RAHUL SHUKLAMETAL CRAFTS - Batala, Punjab, India
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The 3-step phosphatizing (clean/phosphatize, rinse, rinse) is almost always iron phosphating and is restricted to steel parts whereas the 7-step process (clean, rinse, rinse, zinc phosphate, rinse, rinse, chrome rinse) is usually zinc phosphating and can be used on aluminum as well.
I don't think anyone will claim that the 3-step process is as good as the 7-step process, but, if the painting system is good, a good 3-step process can be just fine.
The principal reason most people use hydrochloric acid is that it will work at room temperature whereas sulphuric acid tanks need to be almost 100 deg. C to function well for scale removal.
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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Dear Sir,
I would like to inform you that I have applied for the post of AME(C&W) under Eastern Railway. I am continuously trying to get the process of Hot phosphating which is urgently required for examination. Please send at the earliest to my email address so that I can prepare the same.
Thanking u,
Yours faithfully
PERSONNEL - ASANSOL,WEST BENGAL, INDIA
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Hello Pranab. Good luck with the examination. But please be more realistic: no one is going to custom write a book about phosphatizing for you and e-mail it to you personally, and all at no cost :-)
We've answered some specific questions, and have recommended two books about phosphating. If neither of those is available in a local library, then start with the Metal Finishing Guidebook. There should be copies in your local area; and if not, used copies can be obtained for about $10. Success on the exam!
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Ted Mooney, P.E. finishing.com Brick, New Jersey |
March 7, 2008
I am having a bus body painting, I want to know the process of ht phosphating and also the in process quality parameters to be checked which are affecting the coating.
Anil Balurkarpainting shop employee - Zaheerabad, A.P., India
August 5, 2008
Dear sir,
This is rajeshkumar,currently I am working in a radiator manufacturing industry as a Quality Engineer;in my concern 7 tank hot phosphating process exists,we have the procedure to prepare the bath solutions but we don't have any in-process checking parameters and how check the supplied solutions; whether in correct concentration or not,i want the clear procedure about the process,in-process checking parameter,procedure to check the chemicals before mixing & bath maintenance.
employer - coimbatore,Tamil Nadu, India
October 21, 2008
Dear Rajesh Kumar,
I do not know why you facing problem to check strength of supplied chemical or your bath strength. The simple process is titration.
- New Delhi India
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April 21, 2009
Dear sir, QA Incharge - Nashik, Maharstra, India March 30, 2010 We are painting 1 mm sheet thickness components hence we would like know the correct procedure for 7 tank pre treatment process before spray painting. I also wish to have the details of each tank content, chemical specifications, timings, proportion of mixing, titration procedure and their chemicals, identification of metal finish after every tank for correct work done and life of chemical mixture etc. production manager - Dharwad, Karnatak, India. March , 2010 Hi, Muralidhar. We have recommended two good books on phosphating that were written to address just these issues, and suggested the general purpose Metal Finishing Guidebook as a starting point if you have trouble locating those. You can also contact a metal finishing supplier like Guardian Anti-Corrosives Private Limited[Chennai, India] who will recommend the chemistry for the seven steps and give you technical data sheets for each step. Good luck! Regards,
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+++++April 4, 2010 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
dear sir
please give me a information about seven tank process for powder coating for m.s.parts and aluminium parts
plant owner - Pune, Maharastra
March 6, 2011
STANDARD 7-TANK PROCESS
A standard 7 tank DIP ZINC PHOSPHATING process is used, where good paint adhesion and corrosion resistance are required before painting. However, where hot rolled sheet metal or heavily rusty surfaces are to be dealt with, the use of mineral acids like hydrochloric acid or sulphuric acid will have to be used. An additional tank for cold water rinsing after derusting will be necessary to ensure that carryover of mineral acid into the zinc phosphating bath is avoided as it is detrimental to its functioning.
PROCESS
TANK # FUNCTION CHEMICAL STRENGTH TEMPOC DIP TIME
(MINUTES)
1. Degrease Chemlene 1D 3-5% 85-95 5-15
2. Cold water Rinse - - - 1
3. Derust Chemdine250 25-30% RT 5-10
(Cold)
Chemdine170 20-25% 60-70 5-10
(Hot)
4. Cold water rinse - - - 1
5. Zinc Phosphate Chemphos 20 3%
Chemtoner 0.025% 70-80 3-5
6. Cold Water Rinse - - - 1
7. Passivation Chemlyte 10 0.025% RT-70 1
CHEMDINE 250 (cold) or CHEMDINE 170 (Hot) is generally used, for derusting of cold rolled metal. Where the use of mineral acid such as hydrochloric acid or sulphuric acid is used to remove scale, an additional Cold water rinse , after pickling (Tank # 3) will be necessary. This will make it a 8 Tank Process.CHEMPHOS 20/CHEMTONER forms a micro-crystalline uniform tightly adherent zinc phosphate coating which has excellent paint adhesion and corrosion resistance.
ZINC PHOSPHATING PROCESS USING PRECONDITIONER CHEMFIX 50
Often, the use of a PRECONDITIONER before zinc phosphating is preferred to condition & prepare the surface to receive an extremely fine textured coating. This becomes particularly important in certain steels and steels which show some resistance to coating formation.
GANESH BHUJBAL
- pune,india