What Am I Missing????? Besides Experience!!!!!

[skooterbum]

hi all,
i am trying to do a phosphate step and keep getting flash rust. i blast most everything i get. have tried 3 different products, all 3 will leave a gooey mess when sprayed on and not rinsed off, so rule that way out. have tried wiping it on with lint free cloth, blasted surface will tear at cloths and leave **** all over the part, so rule that way out. have sprayed it on and rinsed it off and immediately get flash rust. cant do that either. would think if i dipped parts i would get flash rust too. had rep from PPG tell me that flash rust is happening because the blasted surface has little pockets that holds the water rather than letting it run off part. rep said to blast, blow off, powder, and cure. i am wanting peace of mind with my work so am wanting to do a phosphate step to help ensure the coating will last. can someone offer me suggestions on how to apply a phosphate step to a blasted surface. also will most phosphates that are used on steel work on alluminum as well? or do i need a chemical for each substrate?
THANKS IN ADVANCE FOR ALL HELP OFFERED!!!!!!!!!
RON

[jrow]

skooterbum,

Try putting it in your oven and drying it, then phosphate.

John

[skooterbum]

Originally Posted by jrow

skooterbum,

Try putting it in your oven and drying it, then phosphate.

John

i know i am missing something here but wouldnt rinsing after the phosphate still give me flash rust even if drying before treatment or is there a chemical out there that does not require a rinse after. i am not questioning what you are saying, just want to get this under controll. thank you for ALL YOUR HELP!!!!!!!. it is appreciated much!!!!!!!
ron

[DocMartin]

Flash rusting occurs when the bare metal is exposed to oxygen. Rust is a bad thing for powder coating because it decreases the adhesion. When shot blasting a part, you should see that it will first look clean and then the rusting process begins immediately. If you blow off the partt and coat it before much rusting takes place, you can still get good adhesion and corrosion protection. Once the coating is in place it will form a barrier to protect the metal from corrosion.

The purpose of a phosphating process is to impede the spread of corrosion underneath the coating. It's called a "conversion coating" because the phosphates react with the iron to form a surface structure that is less prone to oxidation. This means that if the coating is disrupted by a scratch or chip, the phosphate layer will prevent the corrosion from rapidly spreading.

The phosphating process itself cannot entirely cover all the peaks and valleys of the bare metal, and there will still be discontinuities in the surface structure. Thus a final post treatment / sealer rinse is necessary to eliminate any flash rusting. A typical 3-stage pretreatment system will have: clean & phosphate, rinse, seal.


In the end, the corrosion protection is dependent on the powder formulation, the thickness of the coating, and the pretreatment of the substrate. For lab testing purposes, the panels are exposed to a continuous mist of salt water fog. A scribed mark can be made before exposure by scratching through the powder to the surface of the metal to test for amount of creep under the coating. I have tested some typical coatings on untreated panels that performed very well (1000 hours unscribed, 500 hours scribed). Pretreatment can prolong the exposure by three to four times for scribed panels.


All technical info aside, I would suggest to blast and clean the part, coat it quickly to a thickness of 3-4 mils, and cure it according to the powder specifications. Unless it's going to be continually exposed to harsh conditions, the PPG rep was probably right.

[skooterbum]

Originally Posted by DocMartin

Flash rusting occurs when the bare metal is exposed to oxygen. Rust is a bad thing for powder coating because it decreases the adhesion. When shot blasting a part, you should see that it will first look clean and then the rusting process begins immediately. If you blow off the partt and coat it before much rusting takes place, you can still get good adhesion and corrosion protection. Once the coating is in place it will form a barrier to protect the metal from corrosion.

The purpose of a phosphating process is to impede the spread of corrosion underneath the coating. It's called a "conversion coating" because the phosphates react with the iron to form a surface structure that is less prone to oxidation. This means that if the coating is disrupted by a scratch or chip, the phosphate layer will prevent the corrosion from rapidly spreading.

The phosphating process itself cannot entirely cover all the peaks and valleys of the bare metal, and there will still be discontinuities in the surface structure. Thus a final post treatment / sealer rinse is necessary to eliminate any flash rusting. A typical 3-stage pretreatment system will have: clean & phosphate, rinse, seal.


In the end, the corrosion protection is dependent on the powder formulation, the thickness of the coating, and the pretreatment of the substrate. For lab testing purposes, the panels are exposed to a continuous mist of salt water fog. A scribed mark can be made before exposure by scratching through the powder to the surface of the metal to test for amount of creep under the coating. I have tested some typical coatings on untreated panels that performed very well (1000 hours unscribed, 500 hours scribed). Pretreatment can prolong the exposure by three to four times for scribed panels.


All technical info aside, I would suggest to blast and clean the part, coat it quickly to a thickness of 3-4 mils, and cure it according to the powder specifications. Unless it's going to be continually exposed to harsh conditions, the PPG rep was probably right.

doc martin,
thank you for taking time to respond. i am a small batch coating shop doing a lot of parts for motorcycles and experiemental aircraft and anything else i can get my hands on. i, like the rest on this forum wish to offer the best service we can to our customers. i have been blasting, cleaning with brake clean, and coating. i feel the need to add a conversion coating to add to the performance of the coating, am struggling to find a product that i can use with my setup. limited space and all. wish to find something that can be sprayed on, preferably not requriering a rinse, then coated over. have tried picklex and ospho, both leave gooey substance on parts if not rinsed. wiping them on leaves fragments of the cloth and brushing on leaves goo as well. am wondering about the seal that you mentioned and the application of it. do you think that if i blast, clean, phosphate, rinse, and imediately seal while parts are still wet from the rinse would work the flash rust as you know takes place almost imediately with the rinse. can you suggest any products for me to try.
thanks for all your help!!!!!!!
ron

[Harleydad]

Are you sure what you're seeing is flash rust or the phosphating because it will look similar. On steel I clean with a degreaser/cleaner (simple green), rinse, air dry ,blast, blow off with air, rinse, phosphate (leave on 3-5 minutes), rinse well, dry with air, then coat.

I use Sure Coat 915 from Coral Chemical Co.