problem about powder paint application over Zn metalizing
04-25-2008, 01:25 PM,
#1
Question  problem about powder paint application over Zn metalizing
Dear All;

Has anyone encountered surface defects (bubbling, low adhesion, porosity) on the powder type paint (baked) applied over thermal sprayed Zn?

What can be the reason of this kind of defects? Is there any uncompatibility between TS and powder paint?

Thank you all inadvance

Regards
Reply
04-25-2008, 01:49 PM,
#2
RE: problem about powder paint application over Zn metalizing
Hi Basakglkn

I think these problems are probably quite common, but most seem to overcome them. First, process and house keeping are important, zinc coating contamination (dust, moisture and other from storage and handling) will cause problems when trapped under paint during bake curing. If problem is still evident under ideal conditions, then the paint is probably not compatible with the zinc coating. I would try and work closely with your paint manufacturer/supplier and find a paint that works well.
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04-26-2008, 12:56 AM,
#3
RE: problem about powder paint application over Zn metalizing
Hi,

Are you talking about Powder coating over Zinc arc spray - if so please specify equipment used and wire brand.

Regards

GlenB
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04-28-2008, 08:50 AM, (This post was last modified: 04-28-2008, 08:52 AM by basakglkn.)
#4
RE: problem about powder paint application over Zn metalizing
GlenB Wrote:Hi,

Are you talking about Powder coating over Zinc arc spray - if so please specify equipment used and wire brand.

Regards

GlenB

what I mean by powder coating is powder type paint, that has to be cured in oven after application. I am a Metalurgy Engineer so I have a very limited knowledge about paints (I was more into pyro at school) so there may be a better thecnical name for this kind of paint that I do not know.

Our wire supplier is a Turkish company and they manufacture the wire at their factory at ?stanbul(CTS Metal)

2.4mm pure Zn(99.8 says the supplier but I have never conducted chemical analysis by my own) wire with arc spray machine(OSU)
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04-28-2008, 05:23 PM,
#5
RE: problem about powder paint application over Zn metalizing
Hi Basakglkn

What is the history between thermal spraying zinc coating and application of paint? (storage, transport, cleaning, pre-heating etc.)
Reply
05-14-2008, 09:19 AM,
#6
RE: problem about powder paint application over Zn metalizing
From the information above, it would appear that your problems are commonly referred to as 'gassing'.

What happens when you spray an arc spray coating (or flame as well) is you get porosity in the coating. When you powder coat over the top of the zinc and then bake in an oven, the air in the porisity expands and pushes bubbles through the powder coating as it bakes. The way that most powders bake is to cure the top surface first and then melt down towards the substrate. This means that the air bubbles will pass through the melting powder coat and hit the semi-cured surface. This forms a bubble which in some case will pop and cause a pin-hole effect. This is probably what you are experiencing. The golden question is......what can you do about it.

The answer is..........housekeeping, surface finish, coating thickness, de-gassing, type of powder and not necessarily in that order.

We have many customers who powder coat a lot of metal sprayed coatings with little or no surface finish issues. The applications include gates/fences, gas cylinders, street furniture and playground equipment. The best of them have great housekeeping and well maintained equipment which results in a fine surface finish and minimal porosity. You could try to go to a smaller wire diameter, something like 2.0mm and spray at around 200A to get a better surface finish and reduce the porosity. Make sure that your front end parts on the pistol are in good condition so that you are getting the optimal atomisation of the particles and hence clean, smoother finish. We advise against rubbing down as this normally just forces more dust into the coating. Make sure that you have good extraction in the spray area so that you don't have dust on the surface before powder coating. The thicker the coating, the more porosity. Most powder coated specifications will have a coating thickness of 50 to 100 microns for metal spray. The thinner you can get away with, the better. Some companies will de-gas by pre-heating before powder coating and applying the powder whilst the substrate is still warm. The last subject of type of powder is not something I know a great deal about so I suggest that you talk to your powder paint suppliers. I do know that you can get anti-gassing or anti-foaming powders. I believe that these cure more evenly, rather than from the surface downwards - hence the bubbles are allowed to escape during the curing process rather than getting trapped and causing pin-holes when they burst the skin.

Good luck and if you need any quality thermal spray equipment or 2mm zinc, please don't hesitate to give us a call.

Stuart.
Stuart Milton
Metallisation Ltd
https://www.metallisation.com
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05-30-2008, 08:54 AM,
#7
RE: problem about powder paint application over Zn metalizing
Thank you all for the valuable information.

We have solved most of our problem with degassing (similar to the process used at PIG iron), we still have little problems due to the bad housekeeping of paint applicator.

Have a nice weekend

UBG
Reply
05-17-2012, 01:50 PM,
#8
RE: problem about powder paint application over Zn metalizing
The following sections will explore a variety of zinc coating. Many people use the generic term for all types of zinc coatings "galvanized" However, all of the zinc coating is not the same. Depicted in the micrographs of the first coating is a metal coating.
Reply
05-23-2012, 08:21 AM,
#9
RE: problem about powder paint application over Zn metalizing
Nice topic & good movements of thoughts!

If this problem is really due to presence of air in the pores of coating, then is it not possible to apply some sealant on the zinc coating and then apply powder paint? This way less viscous sealant will fill up all pores and air can not get any reservoir to be in surface!

This is just my thinking, experts can make it more clear!!
Reply




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