Is this galvanising acceptable?

[Kent]

All sorts of issues on show here. Mostly it's trapped contaminates in the welds and between joints.
Yes some cases are maybe due to muck in the tank ( they add bismouth to take it to the bottom as it's heavier than zinc) however would you dump a mucky part in a fresh tank?
Hot dip is not the best plan for such parts as a re- furbished bulkhead. Far better good primers etc.

Even though there are areas uncovered the galv that has covered will have a sacrificial anode effect.

Just clean up the worst of it paint it with cold galv paint and get the thing finished

Learn from it

 

[Chris Stevens]

As my earlier post, if you expect a perfect job when the part is not perfectly prepared, its simply not going to happen. Best not to take issue with this job, unless you want them to strip, get it properly prepared and do again. Worth bearing in mind though while it would probably be better than it is at moment, an old part is never going to be faultless, so as others have advised good idea to paint, and bear in mind for future reference?

 

[julianf]

Is it possible that they could re-dip it without stripping, but leave it in longer, so as the zinc has more time to seep in?

Again, i take on board the issues with prep, however, i still do not understand why some parts that were just bare sheet metal, without prior issues, have the zinc peeling - i mean the welded areas can be blamed on the welding, but the plain, blasted, undamaged sheet - i cant think that can also be simply blamed on the prep?

As above, i can understand that, maybe, they dip things like that quick, so as to lessen warping, and that may be what im told on monday.

Again, if i go there, and speak with them, they may say that's as good as it gets, but i think it would be worth speaking to them, if only for them to concur with the advice above. Im, of course, hoping they may have other suggestions, or solutions, but, if that is not the case, ive not lost anything by asking.

 

[julianf]

One other question -

If the process itself is really that fussy about contamination, its hard to understand how any of the parts in the "IN" yard come out ok, as plenty of them were brown with rust.

Again contamination - if the job has to be as clean as im advised above, then, surely, there would be no hope of ever getting the internal faces to cover? In which case, is there any point at all in dipping?


There was comment about "dipping a dirty part in a clean tank" - i suspect, on close inspection, this was one of the cleanest parts i saw on the way in. This one was silver / grey in color, whilst the other parts i saw were brown.

 

[colnerov]

They're acid dipped to clean the rust off not only the outside but inside enclosed sections. Which have to have holes for the treatment inside as well, if not they can explode with the heat. Some of the 'frillyness' is from this removal of internal rust.

 

[xmetal]

I remember when I was replacing a corroded external telephone bell in a factory in Birmingham called Joseph Ash. They did hot dipping and an alarm bell sounded as a warning to get out of the way. I've seen molten zinc shooting out of the end of a lamppost just like a cannon. It was caused by impurities if I remember correctly.

 

[roofman]

did the blaster remove all the paint as galvo companys including mine dont accept anything with paint on as it leaves a black residue

 

[KemppiFrog]

did the blaster remove all the paint as galvo companys including mine dont accept anything with paint on as it leaves a black residue

I was wondering that too, mine won't even accept other than light surface rust. I don't go along with different temps either, it is molten, or not and thin sheet will heat up to the bath temp in a second. If there is any left over covering, the acid dip, which acts as a flux, is ineffective and even when the paint burns off, the zinc won't stick. Distortion of thin sheet happens whatever you do.

 

[julianf]

This is an example, prior to welding -

so, yes, the paint was gone.


And just prior to it going for dipping -

This was mig welded, so the worst that the welding would have created was oxides, assuming the metal was bare prior.
If the metal was rusty, and the rust got into the weld, wouldnt the acid have gotten rid of that? I mean, isnt that what the idea is?

What i mean is, what is the 'contamination' that the welds have created, that isnt just an oxide (that would have been had by the acid prep)? Even if its messy welding caused by trying to patch thin rusted metal, doesnt the rust get eaten by the acid?

What is the other contamination that has been caused by the welding that's not been eaten by the acid?

 

[Hitch]

The grey/brown lumpy patches are the zinc oxide skimmings.

The brown 'run' stain is because of an unsealed joint, its residue of cleaning chemicals coming out of the unsealed joint during the zinc dip.

The small black areas i think are flux deposits.
Give it a clean up (carefully) with a flap disc and touch up with cod galv spray.

Its a self healing/sacrificial coating to an extent.
And, remember, hot dip galv is an industrial finish, not decorative. It wont ever look like galv sheet.

 

[MoreWellie]

We have had a reworked series bulkhead galvanised and it too had a couple of small patches like in your third picture, coincidentally? in the same place so it makes me wonder if it is something to do with how often the contaminants are skimmed off the tank and whether that is a place that picks them up as the bulkhead leaves the tank

we didn't get any of the black cracks that look like holes. If they are holes then it makes me think the metal was so thin that it disappeared when subjected to the heat but only a guess

 

[julianf]

There are no holes in any of it - its all solid, as I made sure of that when I worked on it.

The black marks are either where the zinc has not covered, or where residue has been left. The latter I don't care about, its just the former that bothers me.

 

[Kent]

I can send brand new railings and gates from fresh steel and still get odd bald patches. It is what it is and it's not the process that suits your wishes in this case
All the guys I know expect to have to do some clean up on any job sent. In fact it should always be costed into the time for a job and a consideration is always how easy it will be to clean up at the design stage

Don't think I have ever sent a re- furbished anything for galv and to be honest if pushed by a client I should put in a big fat disclaimer on any mishap occuring ( don't think I should be alone in that either)

Most galvanising plants have an appointed quality manager. Ask them to explain but I shouldn't go making a big old complaint - just ask why for future reference like

 

[julianf]

That was my intention.

I dont want a perfect cosmetic finish. My intention is simply to keep the rust at bay.

One other point that worried me some though - its hissing.

 

[steve t]

probobally some of the pickle trapped where there is overlaps

 

[roofman]

That was my intention.

I dont want a perfect cosmetic finish. My intention is simply to keep the rust at bay.

One other point that worried me some though - its hissing.

call in a priest...its now getting interesting

 

[julianf]

probobally some of the pickle trapped where there is overlaps

Yep, acid eating away at ungalvanised steel.

Unlike electrolysis, acid does not stop once its eaten the rust.

 

[Kent]

That was my intention.

I dont want a perfect cosmetic finish. My intention is simply to keep the rust at bay.

One other point that worried me some though - its hissing.

Little hole inside a hollow section? Air inside warms up from cold and you get a hiss - happens on things like unit doors made in rhs. Condensation inside forming could be part of it
At a constant temp for a period and it won't hiss I bet

 

[MoreWellie]

pretty sure there aren't any sealed sections on a land rover bulkhead, is it still hissing?

 

[julianf]

Hissing was from acid between the profiled skins of the footwells. They are not sealed, but, evidently the acid got it, where the metal did not.

I went back to the galvanisers this morning, and spoke to one of the people on the works (rather than office) side.

He seemed happy enough to run it through again. Said there were no gaurentees, but, all the contaminants should now have been burnt off.
They are going to drill the footwells to let the acid out better / metal in better.


The small black flecks all over it, were, as hitch said, flux (or other scum) deposits - i scraped some off before going back this morning. So its mainly the footwells leaking acid, and, with luck, that will be sorted this time around.


They did say that the existing zinc would be stripped though, so, fingers crossed that the bits that were fine dont get worse.

Providing the chap i spoke with this morning keeps an eye on it as it goes through, i have some confidence that it will be a better job, but you never know...