Letter 20075

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

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

Ted Mooney, P.E.  finishing.com Brick, New Jersey

 

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 SHUKLA
METAL CRAFTS - Batala, Punjab, India

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.

Ted Mooney finishing.com Brick, New Jersey

 

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

PRANAB SENGUPTA
PERSONNEL - ASANSOL,WEST BENGAL, INDIA

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!

Ted Mooney finishing.com Brick, New Jersey

 

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 Balurkar
painting shop employee - Zaheerabad, A.P., India

Hello to all,

I have got 7 tank phosphating process :
It includes
Process
Immersion Time
Temperature
& Chemical Dilution

Its a PDF file, interested people may contact.

Amit Choudhary
MCS Fasteners - Gurgaon, India

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.

rajesh kumar
employer - coimbatore,Tamil Nadu, India

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.

Navin Maheshwari
- New Delhi India

Dear sir,
My plant have 7-step hot zinc based Phosphating Process basically done for precoating for metal part for rubber boding purpose. we don't have any standard for thickness of phosphate coat required for metal to rubber bonding can you guide me?
Recently we eliminated derusting by HCL , we do derusting by phosphoric acid but more time is required for this process -- you have any solution? We given compressed air line in all tank for better agitation, is this the right method?

Rupesh Ingale
QA Incharge - Nashik, Maharstra,India