HOME FAQs BOOKS JOBS: Help Wanted Suggestions you are here: Hotline/Forum => Letter 53135
Need details of "the 7-tank process"
September 18, 2009
dear sir
I am new in powder coating industry. in our company we powder coat HR/CR sheet. so please tell me the details of all 7 tanks.
SHIBY MATHEWpowder coating employee - Pune, Maharastra, India
^- Privately contact this inquirer -^
September 21, 2009
Hi, Shiby. A "7-tank process" is simply a process where parts are immersed in seven tanks sequentially. Normally, a zinc phosphating process is done in 7 steps while the simpler iron phosphating pretreatment process is done in 3 steps or sometimes 5 steps. So when you ask about a 7-tank process for pretreatment, you are probably asking about zinc phosphating.
The 7 steps traditionally meant soak clean, double rinse, zinc phosphate, double rinse, and chrome or chrome-free passivating dip. These days a DI rinse is sometimes used instead of the passivating dip, and sometimes the passivating and DI rinse are done sequentially, meaning only one rinse after phosphating if only seven tanks are available.
You need to find a supplier for the process, and they will give you the operating parameters for each step. But if you are looking for background info, please see Rausch's "Phosphating of Metals" [link is to info about the book at Amazon] and Spring's "Preparation of Metal for Painting" [link is to info about the book at Amazon]. Good luck.
Regards,
|
 Ted Mooney, P.E. finishing.com Brick, New Jersey |
September 22, 2009
Hi shiby,
the 7 tank system is the following below.
1)Degreasing.
2)Waterwash
3)Acid pickling
4)Water wash
5)Phosphating.
6)Waterwash
7)Drying
this is the common steps, now it s going upto 11 tank system also.
based the the customer requirment and the part condition it may extend also. for example parts are coming with more scales, you need to introduce the Descaling and water wash then it will become the 9 tank system from the 7 tank system.
tank is only the example. we will do at X number of tanks also.
- Salem,Tamil nadu,India
September 22, 2009
I differ from KANNAN, The 7 tank process is
1) DEGREASING
2) Water wash
3) DERUSTING
4) Water wash
5) SURFACE ACTIVATION
6) Zinc PHOSPHATING
7) PASSIVATION.
This is the end of ur search. you can go ahead with this and this is universal. It is a full proof method and is being practised in TAMIL NADU for more than 10 years now.
- Coimbatore, India
September , 2009
3 replies, 3 different answers, which makes the point that the term really has no exact meaning -- it just means that someone is referring to zinc phosphatizing in that many steps :-)
Regards,
|
 Ted Mooney, P.E. finishing.com Brick, New Jersey |
October 9, 2009
Dear Sir,
I want to know about the detail process steps of 9 Tank process of metal sheet. Please also mention the pH of the solution used for processing.
Thanks,
Propietor - Kandi,WestBengal,India
October 12, 2009
Dear,
The 9 tank process is a gimmick, if all of your tanks operate at defined levels, you need not do descaling your derusting will take care of it.
Now coming to pH of the solutions,
DEGREASING : take 2ml solution from the tank,with Methyl Orange as Indicator, titrate with N/10 Sulphuric Acid, this is your Total Alkali.
Now take another 2ml, with phenolpthalien as Indicator, The solution turns pink, now titrate with N/10 Sulphuric acid, the END point is Pale Pink colour, the reading is your Free Alkali
Total Alkali
FORMULA ------------ = Should be between 1.4 - 1.8
Free Alkali If >1.4 add Degreaser
If <1.8 discard Tank
I have time for only this today, If you need further details on all tanks I can provide you upon Request, Leave your request here, I shall do it then......
- Coimbatore, India
November 11, 2009
By just knowing Total alkali you shall know only the bath strength, only after you find a free alkali and find out its ratio between 1.4-1.8 your degreasing will be proper.
Otherwise though your total alkali may be 33 or more than that and if free alkali is also high(30) degreasing will not occur, even with a longer dipping time.
In another instance, if your total alkali is just 12 and free alkali is just 8.5 or so, then also you shall get a perfect degreasing with a longer dipping time.
I emphasize on the ratio between the total and free alkali
you should maintain the ratio to get perfect degreasing.
- Coimbatore