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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Corrosion resistance of CED? Salt spray hours compared to CED Plus Powder Coating
Q. Why the areas like sharp edges, weld & other heat affected zones are not considered for evaluating the corrosion resistance of CED coating (during salt spray testing).
J Singh- INDIA
2002
A. From one layman to another - my guess is that it depends upon how the standard has been defined. Once a standard is defined and accepted it is followed. Since the standards have been defined for testing on sheet steel I guess that is why no reference is made to edges, welds, etc.
Gurvin SinghMohali, Punjab, India
2002
Q. A customer asked: What is the expected salt spray resistance using cathodic Electrocoat on top of Tricationic low Zinc phosphate? What is the increase, if any of the salt spray resistance if a Powdercoat finish is applied to the above? If anyone has data I would appreciate it.
Thanks,
Steve Wade- Romulus, Michigan
2002
A. Cathodic Electrocoating can give 1000 hours of salt spray resistance in accordance to test standardASTM B117. The choice of pre treatment is more a function of the base metal. However, it needs to be compatible with CED system. The second part of the question is tricky! CED coating normally has a DFT of 20 microns or .8 MIL. A final coat of powder coating on it will not improve upon the salt spray test resistance under the test standard ASTM B117. However, if a test is carried out without the inscribed cross, the thicker the film the better it may perform.
Gurvin SinghMohali, Punjab, India
2002
Thanks Gurvin. Still more evidence for stopping this madness of designing finishes to meet salt spray hours :-)
As you say, the absolutely unquestionably far superior finish of powder coating on top of CED coating rates the same in salt spray hours as just the CED coating, demonstrating hw truly ridiculous this approach is :-(
Hot dip galvanizing, which is the most durable finish yet developed for many applications(50-75-100 years with no maintenance is not unheard of) performs poorly in salt spray testing.
The salt spray test should be used as an early warning QA tool to guard against a finishing process going out of control; it should never be used to try to compare one finish against another.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Cost justification of E-coating
Q. I would like to know the tradeoffs between Powder Coat and E-coat in terms of investment and returns. Is there a volume breakoff point for cost justifying E-coat V/s powdercoat. Please note that I am looking at this from a strictly INDIAN cost model. However, I would like to know the comparable data from the other countries.
Thank you,
Pradeep Kashyapmetal assemblies - Bangalore, Karnataka, India
2004
A. CED system (Cathodic Electro deposition) requires a huge set up cost and the running cost is also high. E-coat is only suitable when you have a very large volume of production.
Manish Dhyani- New Delhi
2004
A. Hi Pradeep. Although Manish's answer may not be as quantitative as you'd like, it is the answer :-) E-coat, as far as I've ever seen, always involves automation, ultrafiltration, high-voltage electrification, and a series of steps which makes it expensive and impractical unless you have the production volume to justify it. But it's often a good finish by itself, and a great finish under powder coating.
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Hello every one,
what is the salt spray resistance for electro deposition coating?whether salt spray resistance is dependent on the dry film thickness?
thank you,
2006
The actual salt spray test results depend upon the substrate, the quality of phosphating and Electrocoating.
The salt spray specifications given by paint suppliers in India for Cathodic Epoxy Electrocoat on standard test panels when tested in compliance with the test standard ASTM B117 is 1000 hours.
Hope this answers you question.
Mohali, Punjab, India
2006
Salt spray test failure of CED coating
Q. What effects the salt spray test hours on CED coating. Customer has given us 1000 hrs salt spray test with no red rust but we are not achieving the same; only until 600 hrs.
Please help in this matter.
- India
May 5, 2017
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
A. Hi Premlata. What is the substrate? ... a good grade of low carbon cold finished steel with no pitting or scratching? Are you using a top quality tri-cationic zinc phosphate pretreatment system from a respected vendor?
600 hours isn't bad at all :-) ... it's just not good enough for your customer. The point of saying it "isn't bad" is that 600 hours leads me towards thinking it's not an issue of your process being out of control, but of your process not being quite robust enough; processing changes probably need to be made. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2017
Q. For SG500 casting we need to protect the machined surface from corrosion. Minimum salt spray life to be achieved is 600 Hrs.
What is recommended surface protection CED or Powder coating?
- Pune, Maharashtra, India
August 26, 2019
A. Hi Arun. The recommended surface protection depends on the application and the environment.
Designing to salt spray hours is like teaching to the test; but if you're going to design to salt spray hours, the best approach is to simply test both, and you'll have a proven answer in less than a month.
CED plus powder coating is the ideal finish. CED alone can be a final finish, depending on the environment, but it's not as durable as powder coating. It's advantage over powder coating is that it can usually be pinhole-free, and offer consistent coating thickness.
In either case a phosphate pretreatment should be done; if the parts are actually exposed to salt or other corrosives, a zinc phosphate under powder coating would usually be best. Good luck!
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2019
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