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topic 32581

Hot vs. cold phosphating -- differences and advantages

A discussion started in 2004 but continuing through 2017


Q. I would like to know the difference between hot phosphating and cold phosphating. Basically we are using hot 7 tank process for our pre treatment of steel, both HR and CR before powder coating. I would like to switch over to cold process. Kindly give me the advantages.

Kindly advice

Gangadharan Ruppa
- Chennai, Tamil Nadu, India


A. Dear Mr G Ruppa,

Cold phosphating has no advantage over hot phosphating apart from saving your heating costs.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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A. Dear Mr. Gangadharan Ruppa,

I do agree with Khozema Vahanwala that cold phosphating offers savings in heating costs. The other advantages of cold phosphating are:

The problems due to overheating of the phosphating bath [Metal Finishing (U.S.A.), 93(1) (1995) 30-31] and difficulty in maintaining heating coils could be avoided with the use of cold phosphating. However, cold phosphating requires more processing time to achieve the desired amount of phosphate coating weight and in a continuous process line the processing time has to be adjusted accordingly.

T.S.N. Sankara Narayanan
T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
(ed.note Nov. 2017: The good doctor has a fascinating blog at

March 25, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello everyone, my situation is that I want to change my Hot Phosphating system to Cold. Please can anyone help me out on this issue.

Adeel Ahmed

Cold phosphating

October 24, 2017

Q. Is 3-in-1 solution good for surface preparation. Some manufacturers supply 3-in-1 chemical (Degrease, Derust and phosphate combine) and recommend to use it by dipping as well as by simply wiping on the surface. How authentic is this process? Should we opt for it for painting heavy machinery as 7 tank is not possible and blasting also is not possible.

Ravinder Negi
Paint Shop employee - Bhiwadi,Rajasthan,India

October 2017

A. Hi Ravinder. I'm not sure why the 7-tank process is not possible, but dropping from 7 hot stages all the way down to 1 cold stage is a pretty big fall. I think the only positive thing anyone can say is that anything is better than nothing. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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