Powder Coating??

[L90OOK]

Does anyone know if you can powdercaot over a galvanised part??  :-k
I've got a winch bumper that is galvanised that i'd like powdercoated black...I don't want to paint it!
TIA

[lee celtic]

Yes you can but make sure they give it a rub down with T wash to give it a key....

I used to powdercoat water tanks that were galv coated first , without the T wash the coating will peal after a while

[L90OOK]

Great, many thanks for the info.  Is T wash a trade name?
Cheers

[lee celtic]

T wash was the name of the stuff we used but I guess there are others I know it contained acid and methanol and makes galv sort of sticky :D

[hairyasswelder]

T wash or mordant soloution IIRC is for wet painting.   :? :?
You can powder coat galv but it needs 'de-gassing' which involves two runs through the oven but I not sure what else.  Who is going to powder coat it? It may be best to ask them as they will know.

Sorry not of more use
Steve

[lee celtic]

T wash or mordant soloution IIRC is for wet painting.

Might be for wet painting as well but we used it for three years on over a hundred industrial water tanks made up of between 40 and 50 8' by 4' sheets of galv steel  :lol:

we did try a couple without it but that just ended up with two guys going to scotland to spray paint a tank on site after it peeled :lol: :lol:

we used to de-gas alloys and preheat cast iron as it didn't warm up quick enough in couveyor oven for the paint to cure so we'd get the stuff hot first :D

Never de gassed galv though :-k

Still we sold the paint plant a few years back to make way for more CNC's :dance:

[hairyasswelder]

T wash or mordant soloution IIRC is for wet painting.

Never de gassed galv though :-k

More a wet painter myself but have been billed for 'de-gassing' when sending for pwder coating so thinking I had been screwed searched and found this

1. Pinholing: Pinholing is caused by the formation of small gas bubbles in the polyester coating during the stoving/curing cycle. These bubbles form small craters on the surface and are unsightly. They also produce holidays in the coating that reduce its long term durability, particularly in aggressive (marine) environments. The main reason for pin holing appears to be that the discrete polyester resin particles in contact with the galvanized steel surface do not fuse at the same time as those on the surface of the polyester powder film, because of the mass of the galvanized steel *1, and the time taken for it to come up to fusion temperature. Specially formulated resins with 'degassing' agents have been developed to alleviate this problem by delaying the onset of fusion of the powder. Pre-heating the work in a pre-heat oven prior to powder application allows heavier hot dip galvanized sections to be powdercoated and deal with the problem of pin holing when used in conjunction with 'degassing' grades of polyester powder.

*1 Note: Hot dip galvanized items tend to be of heavier section thickness than other steel items, typically sheet steel, that are powder coated. These items thus take longer to reach oven temperature because of their greater mass.

[L90OOK]

I have spoken to a couple companies about this & it seems the older the galvanised coating the harder it is to powder coat.  I have decided to have it done at a local very reputable company for about £50...I'll see how it goes.
Many thanks for the advice.

[lee celtic]

aahhh there you see we only powdered sheet steel that was galv coated between 2 and 6mm and the dupont powder we used was made for the job ;)

ps, also looks great on my wheels :twisted: