Sounds like contamination in the powder.

Have you opened a new batch recently or changed suppliers?

Check the humidity of the powder and see if it has captured too much moist in the powder before it reached your factory. If so get yourself some dehumidifying compound to mix in with the powder and stir well for several hours. We had to do this with some rubber granules for belt making. Worked well but you need to find out first exactly what it is in your case.

Also it could be that the material you are working with has contamination in the metal which could come out during the baking process. Check the supply of sheet metal you got recently as well.

Hope you have luck soon, please report back

• Sir, We checked powder for its moisture contamination and dust with the help of powder manufacturer , report found to be ok. we are with the same supplier for last one and half years.
• metal is concerned , we do Pre Treatment before powder coating
  

What type of pre-treatment do you use?

Also is the cleaning happening RIGHT before the coating? If the process is done by less dedicated workers it can happen perhaps that the cleaning is done at 16:30 but there was not enough time left for them to do the coating before home time. This could result in the items being coated in the morning WITHOUT a re-clean (as this was done and ticked off the procedure sheet) resulting in airborne contaminants to adhere to your products.

Is your degreasing tank working ok? The tricol vapours should fully engulf the items in the tank. If you see little trails on the item after degreasing, you should look at that first.

Thanks for coming back.

• We are using Zinc Phospating for pre Treatment.In the 9 tank three tanks are hot bath

• Degreasing
• Zinc Phospating
• Non Chrome Passivation

• Cleaning is done before we go for powder coating. not that we do cleaning and keep if for next day.
  

You get a GA and my vote for the cause.

call Joey at Enviroshield 225-362-7556

As this is a public forum I suggest you contribute here with your suggestions so we can all discuss the possibilities. Maybe other people would like to know different aspects of this problem as well, that is why we join.

Please register and contribute, looking forward to seeing you here.

I too agree with what CASE491 says , when the problem being discussed in this , solutions shared will not only be benefited for me. who ever reads it will be benefited.

We request our Guest to register and share the knowledge , so that it helps others also

Pin holes are often cause by a small area with some speck of oil/grease that interferes with the way the powder adheres to and coats the surface. This can show up as a bubble that clings to the surface or some other visually detectable flaw.

I suspect the way you clean prior to powder coating will affect this.

If you clean and then dry and then coat with electrostatically adhered/baked coating, you may be getting specks from the warm air drying?? if that is your process.

When you bake the coating it melts and flows together and cures and the small non wettable (by the melting and curing powder) specs make it draw back and leave an uncoated area.

classic wet paint/varnish pinholes were made by tiny bubbles that clung and as they dried left a vertical channel from the metal to the air and the air bubble vanished and disappeared, leaving the pinholes

• For Cleaning after pre treatment, We use 3M Scotch Brite Pad.
• After cleaning the components are mounted on the conveyor and cleaned with compressed air .
• Then the components are fed to the drying oven . We maintain a temperature of 110 deg. to 130 deg, before going to powder coating
• After powder coating , conveyor moves to drying oven for curing , temp maintained is around 180 Deg to 200 Deg.
• In our case it does not showing like a bubble and the burst after curing.
• PinHoles which comes in our component shown below.
  

I believe that you need to add a further final liquid cleaning process between the 3M Scotch Brite Pad and the compressed air. I (working at home) would use pure Methyl Alcohol and have done for years to get things really clean for gluing or painting, but there are many other cleaning fluids that would do the job just as well, if not better. Alcohol takes off any surface moisture if working in a slightly high humidity.....a lower humidity would be better....

Try it out by hand (without any hands touching the units of course) on say two of the units and see if the problem is fixed.

Make sure that the workers have masks on to stop their breath contamination anything.....or coughing or spitting!!!

If not, its most probably an air born contaminant!! Air filtration may be needed.....

We have a refrigeration type air dryer near the compressor , in addition to that we have provided Moisture separator , oil filter near powder coating equipment.

Actually before the compressed air supply for the powder gun, we were setting 2 times air filter ahead of destination. could you inform me what kinds air compressed machine applied in your plant? or which brand of your compressed machine. thank you for your opinions share with us.

After the scotch brite you should phisically remove the dust, not just rely on compressed air. as scotch brite wiping can cause

We always wipe with panel wipe with a lint free rag. The type of panel wipe as used in the automotive painting industry will evaporate immediately and air blowers after that would make sure.

Good answer, basically what I said in a previous post too.....aren't we clever?

Yes I am sorry Andy, read your post too late.

I also had some thing go wrong and the post "cut off"

I meant to say that wiping with scotch brite causes static electricity on some materials so that would make any dust cling to your item.

Hope this is clearer.

Hey! No problem, I think two (or more) voices are better than one - "Great minds think alike!" so to say.....

I am pretty sure that something in that area is the problem, and it was great to be "supported" no matter how unintentional!!!

Hi,

compressed air is very often bringing along dirt and dust and oil and evrything else.

Take a very clean glass plate (cleaned by household dishwasher is good), spray the compressed air on it for the same time you "clean" with the compressed air.

Do this in the same condition and place as you clean your metal plates.

Inspect what may be deposited on the glass plate by looking through the glass plate - illuminated from behing you - onto a black, very black, ultra-black surface.

Anything you deposited on the glass will be clearly visible: get rid of it!

We had multiple problems in our airbearings with water, rust, dust and oil droplets transported with the air.

Very black is either velvet cloth or a paint available from the astronomical telescope makers.

Silicone that was mentiond in another post can be a very serious problem: make shure that absolutely no silicone is used inside your factory, nor by any of your workers regardless if they are near this process or 500m away!

RHABE

Did you check a possible salt contamination of the metal sheets?

---best,czes

No Salt Contamination on Metal.

• Can you please let me know ways of salt contamination on metal sheet, possible i would have missed some points to check

This may help you, I think:

http://www.chlor-rid.com/home.php

---best,czes

I'm not powder coating expert but in "regular" painting what you are describing sounds like a condition called "fisheye". This is usually caused by silicone contamination. If you use or have a silicone based product like WD-40 or any type of mold release that could be your culprit. I recall a situation where a painting firm was plagued by fisheye all of a sudden and they found it was coming from silicone being used and exhausted by a neighboring printing firm.

WD 40 does not contain silicones......by the way......it was formulated in the early 50's...

We had faced such problem long time back not with powder coating but with spray painting. It was due to pollution in air caused by sand blasting and sand sticking to wet painted articles. Please check if you also dont have such problem after powder coating.

Pollution in air or dust in air , after powder coating what ever contamination in powder it projects outside . We can feel the dust when touching on the surface of the component because we use full glossy shade.

Problem is the its not projected outside. a very small impression towards inside found.

We use a powder coating for our recycled sirens, and most of the time we have had good luck. Our problem is that some of the metal wasn't completely clear of rust and after the process was finished, the pinholes would appear. Some of the units came from a nuclear power plant on the Columbia River in Oregon, and when we recovered them they were "stored" in a basement of a fire station. BUT, just the same, when the powder coating was later applied, the finish was looking pretty good. Given our salt air, (smack dab on the beachline), in about 6-8 months later, the pinholes would appear. Sometimes they got bigger as the interior rust did its thing. The metal is a sheet metal steel material, press formed, about 25-30 years old, and where the pin holes later showed up was in those rust-spots pre-powder coat application. They were bead blasted free of the initial oxidation, however often the areas continued to deteriorate . I will be watching this thread for like comments. Jinachandran, what type of metal are you working with, and is this problem associated only with this particular metal compound? I can agree with the other postings of possible contaminates as I have experienced them as well. Good luck

We are use CRCA sheet , SPEC : IS 513 made by TATA STEELS.

Need more info...

What are the specs on your dryer? Is it dessicant? If so, is the dessicant still good?

Also, you might be crosslinking to early, but you would have to check your oven temperatures/metal temperatures.

If you are using primer and topcoat films, you might have to much film build on your primer film. Could be outgassing on you...

Have you tried what Case and I both recommended? I see no indication that you even read the posts up to now....

• Today we are carrying out; regarding the physical cleaning of component.
• I am checking another method ; cleaning the component with thinner before going to pre treatment . so to avoid excess oil film on the component
  

The last and final stage before coating should be the intimate cleaning, never before.....after this cleaning, the metal may not even be touched......or breathed on...!

Thats correct, we use gloves to carry the component after per treatment.

If the gloves are not brand new, this could still contaminate......this carrying may need to be done in some other way.....without contact to people eventually.

Make sure at least that all carry holding the same way, then if contamination is seen in this area, you know what it is exactly....

Or better still, first carry, hang and do final clean then.....

That is right, we don't ever even touch the parts after final clean. They get hung on their spray posts and are cleaned in situ just prior to spraying. The last thing that touches the part is the rag with the panel wipe on it, not even a gloved hand.

Another thought I had is the name TATA. If this is as Russian as it sounds, it could be that the imperfections are caused by contaminants already in the steel. Not all steel is the same and some ore will produce better steel than others. The Italian car and motorbike factories struggled for years with lots of rust on their body work even after doing all the right things in prep work. The reason was the steel itself which had a high level of oxidising pollution in it. Maybe the Russian steel does as well, if the brand TATA trucks is anything to go by???

Sir , TATA is from India not from Russian.they are pioneers in this Field and are leading suppliers of sheet.

• They are the one who has bought CORUS steel plant who are also a leading steel manufacturer.
• TATA is also the leading manufacturer of trucks in India
• Quality of the steel we procure is of high quality
  

My mistake, and apologies for that.

Your mistake to automatically conclude that Tata produces world class steel just because they purchased Corus and, even more recently, Jaguar car mfg in the UK. More likely they purchase these companies to drive their goal for global sales and they know that the brand Tata does not inspire the much needed faith in quality.

They are India's largest group of companies and are clearly making big plans. This is good for business on the whole but the most credible explanation for their purchases of either company is to carry their sales on the back of the already established high flying brand and to incorporate some innovative ideas from these companies into their own company.

If you purchase anything that will become a quality product from the added value exercise your company performs, it is imperative that you do not go blindfolded on the suppliers quality just because you "believe" they are good. You need to see the evidence. I still uphold my comment that if you bought steel from Tata in India, opposed to Corus from the UK, you need to find proof of quality which only a test will give you.

Sorry if my opinion "hurts" your patriotic loyalty, apologies for that as well. I don't say anything here to deliberately hurt or patronise anybody. Quality is a measurable characteristic of any product, you should never just assume.