How long between shot blasting and powder coating?

A. This can happen due to under baking. Because components are 5 to 50 mm thk it is necessary to check whether metal temperature is reaching to required baking temperature.This can be done by traveling temperature recorder.

A. The problem is the primer. Don't use it anymore. The material you are applying the powder to should go through a chemical conversion process. Wet primers are for wet paint applications.

A. Hello, Nandagopan. What you are asking, I believe, is: "what happens if I omit phosphatization?" You will possibly have adhesion problems, undercutting corrosion, galvanic hotspot problems, and rapid scribe failure.

We have a 3-page thread on "Blasting vs. Phosphating as a Pretreatment", and other sites have discussions as well, for example, the Products Finishing article "Comparing Blasting to Conversion Coatings"

Although not everyone agrees that phosphatization is essential in every case if the blasting is done outstandingly, if you attempt it as a cost-reduction measure you'll probably regret it :-)

You can consult books on phosphatizing which will explain the many reasons that parts are phosphatized.

Samuel Spring's Preparation of Metal for Painting ⇦[this on on Amazon affil links] is a book that I can recommend as what you're looking for. Or try "Phosphating of Metals" ⇦[this on Amazon or AbeBooks affil links] by Werner Rausch. Good luck.

A. The foregoing responses are all correct.
They do however lack co-ordination.
The time is important:
Like any other Chemical reaction Corrosion is governed by Time , Temperature, Concentration (& occasionally pressure).
These variables do not provide linear responses.
Suffice to say: the faster the better between preparation & finish.
Obviously the standard of Blast is important (whip through to white metal).
Geoff's comment regarding Chemical Pretreatment must be taken on board.
And I guess the other thing to be aware of is that not all powders are "barrier" coatings. Very many are quite permeable and therefore reliant on correct substrate treatment.
This Coatings World is not as simple as:
"we do it in 4 hrs so we are better"
I would prefer an object blasted in the Arctic winter after 2 weeks to one blasted in Indonesia's summer after 2 hrs.
Regards,
Bill

A. Generally, parts should be painted immediately after some type of treatment (shotblasting, iron phosphating, etc.) The longer the parts are "sitting out", the more likely they are to rust or oxidize; the more they do so, the more problems you can have with adhesion, corrosion resistance, etc. Excessive handling (taking the parts out of preparation, storing, hanging back on a conveyor) also contributes to problems since each step in a possible route for contamination.

Four hours could be nothing or it could mean the difference between good parts and scrap. It all depends on the material, the environment (hot and humid or a climate controlled area?), how they're handled, the pretreatment, and so forth.

The only true way to evaluate this is to immediately coat some parts and run some parts through a 4 hour or 2 day delay. Then test those parts per whatever your specs are. See if there is a difference. (Keep in mind, however, that short term tests are not always indicative of long performance.)

A. Hi Mani. Please fully detail your own actual situation and it may be possible to get opinions and useful input. It is probably possible to approach 1000 hours with top quality powder coating on a meticulously blasted surface done with brand new ideal media. But if you are simply skipping phosphatizing as a cost-cutting measure it's probably possible to not even get 72 hours :-)

Luck & Regards,

A. This is a really bad specification.
Shotblasting followed by polyester/epoxy powder applied polymer is a recipe for disaster.

The coating will look adequate when first completed, and for the first few days and will go downhill from there.

To then think of salt spray testing it is folly! You already know it's a rubbish specification, not designed to perform in any way, so why test its performance?