Anti corrosion surface finish on 1.6mm mild steel

Hot dip galvanizing will provide protection against most forms of atmospheric corrosion. Paint over it to get decorative color effects.

Thanks

I still have a quadzillion questions?

If any metals surfaces will be touching or very close together, do you hot dip the components first and then assemble/weld or conversely assemble/weld and then hot dip? If you hot dip first then assemble/weld after,how do you coat the weld after? Can you weld on top of hot dip galvanising?

What sort of paint or painting process would be good on top of hot dip galvanising?

Is the hot dip galvanising okay as it is or does it need preparing before painting ?

What sort of life span would hot dip galvanising & painting give in the worst salt spray conditions in a coastal area?

Regards

MIke

If you are making up a framework, I would say get all your machining ops - cutting, filing, drilling etc., done before you galvanise, then assemble your frame. If you have to galvanise an assembled part, try to avoid features such as riveted joints or folds where your cleaning medium can get trapped. It will leach out again later and trash your nicely finished item. Don't try to weld galvanised parts.

If you were designing a mild steel item for the weather deck of a ship, the most effective treatment is Aluminium spraying followed by a full paint scheme - stoving primer/undercoat/topcoat - expensive and a little over the top for garden furniture.

Zinc spraying (with full paint scheme) is also slightly more effective than galvanising in a severe environment. As an aside Cadmium plating is better (thickness for thickness) than Zinc but you wouldn't want to use that!

Hot dip Galvanising with full paint scheme should give a 10 to 20 year life in salty conditions. You should consider using an etch primer on galvanising before u/coat & top coat.

My hose reel at home is made of an aluminium frame with a moulded plastic drum so no finishing required at all!

I hope this helps.

Drew

My company was asked to quote a similar job for the government, involving a corrosion resistant coating for steel hand rails that would be near the ocean. They wanted a spray coating of zinc, but aluminum is also sometimes used. This would be applied by a twin-arc spray gun. Two separate spools of the metal wire are fed into the gun, and an electric arc is generated between them at the nozzle. This melts and atomizes the metal, while compressed air flows through the gun to carry the particles to the target part. As applied, the coating surface is similar to medium grit sandpaper. If necessary, something like powder coating can then be applied for cosmetic purposes.

The first reply by Guest is the correct approach. All welding and fabricating operations should be completed prior to Hot Dip Galvanizing. Your problem is not that difficult. Good galvanizing requires a knowledge of the chemistry of the part to be galvanized (particularly the silicon content), proper cleaning prior to galvanizing, flux, zinc bath chemistry and the process itself. In your case, the HDG process will result in the creation of three microstructural Zn-Fe alloy layers between the steel and free Zn on the surface. The service life of the HDG is directly proportional to coating thickness (including the alloy layers). The galvanizing corrodes sacrificially to protect the underlying substrate.

The answers to all your questions about galvanizing can be obtained from the American Galvanizers Association (www.galvanizeit.org). They have several publications (printed and CD) including Technical Resource, Designing with Hot Dip Galvanized Steel, Inspection of Products Hot Dip Galvanized After Fabrication, Surface Defects, Repairs, Painting, Guides, etc.

- I can give you some infromation on Corrosion loss of the coated steel

It goes this way

in Severe Marine Atmosphere ( test conducted on Kure Beach N.C @ 80 foot lat)

Time for 90Grams per sqare meter Galvanised shteet

coating loss in 1 year 10 micro meter approx

55% Al - Zn Coated in 8 years 1 micro meter approx

in severe marine applications

- As far as seam welding is concerened it is not possible on Hot Dip Galvanised surface.

- Primer is used before actually coating with colour

primer does the following jobs : Primers are specialized formulations and applied

to bondthe substrate with topcoates. Selection of primers compatible with top

coat is important as primers have an important role to play.

Primers 1. Promote Uniformity of surface for the application of finish coating

2. Provide basic adhesion

3. Improve service life

4. Improve flrxibility and corrosion resistance through a carefull choice of

special resins and pigments.

5. Provide buffer zone to prevent possible undesirable reactions between

finish coat and pre treated surface.

First, Anodization is a way of thickening the layer of Al2O3 that forms on the surface of aluminium. I doubt you can do it with steel. There are some alloys that can be passivated. Try a search.

The best is hot dip galanizing of the final assembly after a surface treatments that strips all rust, oxides etx to bare metal. The zinc is self healing as to small scratches that penetrate, but if you drill holes and bolt items on, you will get corrosion from those wide penetrations of the zinc protection.

As for cosmetics, a primer that adheres to zinc plus paint will work. Baked powder coating is best and most enduring, or you will have to strip and repaint often

Thanks to all

Aurizon, ad016, guest, CoolHandGene, & Bluestone

It seems the answer is hot dip galvanize the welded assembly first, making sure there are no folds where the cleaning medium can get trapped.

In my case there are. I need to redesign the area where the centre rolled piece fits onto the two outer discs, so there is no touching of metal faces & a decent size gap for the cleaning medium to flow away, as well as for the hot dip galv zinc to flow into. After galvanising, a baked powder coating to give a long enduring life (10 -15 years) even in the worst coastal conditions.

It seems the anodising process is a process that commonly refers to metals such as aluminium (& titanium) only, and is not a process that refers to steel.

Aurizon, I will have a look at that www.galvanizeit.org website.

Thanks and Regards

Mike

Joburg, South Africa

just buy galv./prepainted material for making your thing, or using galvalume...see dofasco.com

DEar Mike

I think you can use galvanizing provided you should have an effective

pre treatement of surface ie.Cleaning with acids and then alkalies finally

water to ensure the complete oxide filim is removed from the surface

when you are doing this you are allowing to form a bonding of Zinc to the

parent metal so it will ensure long life .Important factor in any surface coating

is to have a better pre-cleaning

santhosh.K.V

AMIE (Mech)

MIke

Are you the same Mike Kovacik of Quinton van Graan frame and ex Lochinvar.

My email mha80634@bigpond.net.au

Drop me a line plse

MIke

I am not too sure whether I gave you my correct details in an earlier email.

mha80634@bigpond.net.au

Rgds

Mike Hall