|John Rutzen||03/03/2020 13:51:50|
|255 forum posts|
I'm wondering if powder coating is a plastic coat then could you paint on top of it as you would need to do if you were applying lining to a locomotive part?
|Jeff Dayman||03/03/2020 13:54:52|
|1888 forum posts|
In my experience paint will not stick to any powder coat resin I've come across, even flat versions. There may be some that are paintable, but I have not come across any.
|Howard Lewis||03/03/2020 17:39:03|
|3605 forum posts|
If the powder coating is the colour that you desire, why would you want to paint over it?
For the few items that have been done for me, there has never been any need.
The powder coating seems to be more durable than paint.
698 forum posts
And it is NOT PLASTIC coating.
Go and see how it is applicated in a finishing shop or factory, or even, heaven, forbid, watch a YT video.
|Joseph Noci 1||04/03/2020 06:43:41|
|747 forum posts|
Now THAT is close to utter Tosh! Really no need for such a frothy , esp if your facts are awry...
Of course it is a 'plastic' . That may be a loosely used generic term, but it fits.
a sound description:
There are two main categories of powder coating: thermosets and thermoplastics. The thermosetting variety incorporates a cross-linker into the formulation. When the powder is baked, it reacts with other chemical groups in the powder to polymerize, improving the performance properties. The thermoplastic variety does not undergo any additional actions during the baking process as it flows to form the final coating.
The most common polymers used are polyesters, polyurethanes, polyester-epoxies (known as hybrids).The latter is not common for general use, eg, garden furniture, household white goods, street signs, etc, but most often used in Marine and hi-demand/cost applications.
And as Model Engineers all know, polyesters, polyurethanes, etc fall under the category of engineering PLASTICS..
Edited By Joseph Noci 1 on 04/03/2020 06:53:04
|115 forum posts|
But as Joseph Noci points out there are plastics and there are plastics.
I have seen the outdoor furniture were the coating falls off in a year or two of outdoor use but I also have aluminium framed windows on my workshop ( exposed to sun and rain ) where the powder coating is as good as new after some thirty odd years ( well a bit grubby but it is the end of summer after all ).
As with all other surface finishes I assume it comes down to preparation, the quality of the coating material and the application and finishing procedures.
A slightly related grumble ( and apologies - I do not mean to hijack the thread) is the Chinese paint which quickly turns to a dull finish and then comes of as a powder on anything that touches it - namely me. If anyone has a suitable method for stabilising it ( in preference to reducing affected parts to bare metal ) and recommendations for a suitable finishing coating I would be very interested to hear.
|351 forum posts|
Properly applied powder coating is very durable and does not usually flake off unless the substrate has not been properly prepared. There are umpteen thousands of powder-coated whitegoods in houses all over the world which in general seem to last quite well, although not exposed to the elements. There are also many thousands of powder-coated bicycle frames in use all over the world that are often exposed to harsh conditions and seem to last pretty well. I have at times refurbished bicycles and I can confirm that removing properly applied powder coating is a lot harder than removing paint.
|Clive India||04/03/2020 14:02:28|
213 forum posts
Very much agree - and that's a reasonable test.
698 forum posts
Was the other part he quoted utter tosh or not?
I would call powder coating powder, not plastic myself, but hey each to his own.
I aint that pedantic. Nor frothy.
|vintage engineer||07/03/2020 19:35:35|
254 forum posts
At the end of the day YOU may call it what you like but it is plastic and it's cheap nasty crap product.
Try looking at the bottom of road sign posts and you will see how bad it is. The only finish that lasts on exterior steel work is galvanising!
107 forum posts
Hear-Hear my experience too
|Kiwi Bloke||08/03/2020 07:55:25|
|461 forum posts|
There may be some confusion here between powder-coating and the awful coatings which used to be seen (perhaps are still seen) on cheap steel outdoor furniture. This was a nylon coating, heat-fused (but I don't know whether powder-coated or dipped), which came off in sheets as the rust spread rampantly underneath it. Much coloured sheet-metal fabrications (machine cabinets, storage cabinets, electrical cabinets) are powder-coated. The trick is the surface prep. and the choice of medium, as others have said.
Powder coating is a great way to achieve coverage on complex items such as (car) space frames. However, the coatings can be flexible enough so that early cracking of the frame is not apparent. Relatively brittle paints, such as cellulose, have been advocated for painting structures where it's important to be able to detect incipient failure as early as possible.
698 forum posts
Mmm, don't tell me, tell every major motorcycle manufacturer in the world who uses it on steel frames and swing arms and steel and alloy wheels.
They must all be wrong too, and have huge warranty problems replacing all that powder paintwork constantly.
|Involute Curve||08/03/2020 10:33:22|
337 forum posts
At work we have a coating division, We often use powder coat as a primer especially if the final coat is a candy or other exotic finish, in addition powder coats are often applied in two or three stages, primer and finish and them possibly a lacquer coat, I have on many occasions powder coated steel structures (Motorcycle Restoration) that have had corrosion damage, after stripping and blasting we pre heat the frame then apply polyester powder primer, this can then be sanded back to get a smooth surface effectively filling in the corrosion damage, it is then re heated and over coated until I am happy with it, this can easily be flatted off and then painted over with paint, I suppose you could describe polyester as plastic, but if your inclined to be pedantic you could describe most paints (polyurethanes, etc etc) and in fact most clothing as plastic.
As an aside some so called powder coats are no longer in powder form they are liquid and applied with a spray gun and then baked at up to 400 deg C on our race engines we use Xylan coating this stuff is amazing applied wet as a super thin coat, the only we we have found to remove it effectively is with glass bead and its a nightmare taking ages, this is a fluorocarbon base product, Another plastic.. ha-ha
Xylan coating both Silver and Grey
I've uploaded some more pics of this engine competing in last Years Classic TT to my Misc album just in case anyone is interested.
Edited By Involute Curve on 08/03/2020 10:36:50
|John Rutzen||08/03/2020 13:27:58|
|255 forum posts|
That;s very interesting because i want a coating for steel and brass which can be overpainted and doesn't flake off. This was why I am interested in powder coating. Is the primer applied using a powder coating gun? Specifically what primer is it please? I've found by experiment that ordinary Screwfix galvanising primer can be stoved at about 150 C and it makes it adhere a lot better.
|Richard S2||08/03/2020 14:08:07|
182 forum posts
Just to endorse Involute Curve's post. I admit to having panels media blasted and powder coated black as a base for prepping for paint on projects 8-10 years ago (Garden Tractors etc shown in my album).
It offered me the option to take as long as I liked to prep the base finish without risk of any corrosion. As long as I did not expose bare metal I was able to achieve the finish I wanted (with aerosols). The durable glass like finish is still as new.
The guy who powdered the panels knew I wanted to paint and may have used a powder that would accept it. I only had to rough the surface with a green scourer sheet for a degreased key for the first coat of primer on it.
|Joseph Noci 1||08/03/2020 14:27:05|
|747 forum posts|
And yet, with all our ranting and raving about plastic or not, good process or not...
Not one of us answered or gave comment or advice on the actual question that was the reason for John's post
Edited By Joseph Noci 1 on 08/03/2020 14:27:53
|6 forum posts|
In the US many of us use a product called Gun Kote from K.G. Coatings Co. It is a baking cross linked polymer that goes on very thin which makes painting of parts prior to assembly trouble free with few clearance issues. Optimal thickness is .0003-.0004". Powder coat thickness was always too thick causing assembly problems. GK was developed for many types of US Mil Spec severe application firearms. It requires a 120 grit Aluminum oxide grit blast, solvent cleaning, apply, then bake 1 hr at 162 C. It isn't fussy about the base metal it attaches to. It doesn't chip even under bolt heads. It will not come of unless grit blasted. I have not found a solvent the has any affect on it and I often clean of my engines with automotive spray brake cleaner. The flat and satin colors look especially real on models.
I have mentioned this product before on this forum, but this product hasn't been available in the UK in the past. I am told it will be available in the UK soon. I will try to let this forum know when it will be.
Edited By Rustkolector on 08/03/2020 17:35:04
|Ian Johnson 1||08/03/2020 18:07:27|
|288 forum posts|
Hi John have a look at electrostatic magic made in the UK. I have got the start up set and it works very well, although I have only used it on motorbike foot pegs and small things, the results are great!
Bought it a few years ago at Stafford classic bike show for around £150 ish
965 forum posts
Gun Kote is available in aerosol form in UK from Amazon
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.