hot dip galvanising

[smashweld]

I've had a few things galvanised in the past with varying results...always made sure there was no spatter etc but sometimes it looked great other times there were dull/rough patches

is grinding all the black (not sure of name?) off the box section necessary... or is that all stripped off when they clean it before galvanising?

 

[zzr1200]

The black stuff is called Mill Scale, your parts should be acid dipped to clean the surfaces before the galvanizing process.

 

[Hitch]

Grind the mill scale off? Crikey no!

They go into a series of cleaning baths prior to the hot zinc.

It does vary a bit, but at the end of the day, its an industrial finish, not a cosmetic finish.

Make sure theres no paint marker/wax crayon etc on it, thats about it really.

 

[Allthegearnoidea]

I used to get a lot hot dip valve products in the Sheffield area. The quality varies massively and most of the good ones have gone to the wall. So much so I’m looking at other processes. This is down to the cost and disposable of the very nasty chemicals.

 

[Stingray]

 

[smashweld]

I wonder what causes the variation in quality...it cant be completely out their control

I've never asked but thought there might be a 'premium service' to ensure no rough/doctored with galv spray etc bits

 

[Allthegearnoidea]

Don’t know if you have noticed but most people who work in these plants are a bit mad. I just don’t think they care much about quality control. You can pay extra for fettling but this just removes the spikes. From what I have seen the zinc becomes contaminated and that leaves a rougher surface.

If you can stand less corrosion resistance than electro plating zing plate is a nice finish

 

[armalites]

The flow chart above doesn't apply to all places, in the documentation from the place I use grease can be used to protect threads and you need to de-grease everything else yourself.

I've had a couple of different lots done and there was a variation in the finish. When you get black spots in the galv it tends to happens where there was an air pocket. It all depends on how they suspend it as there can be pockets created that you didn't know existed.

The first bits I ever had done were some gate posts and they came out absolutely mint, the most recent batch was a trolley and a chicken run. On this batch there were quite a few bits that had a rough surface, plenty of coating so I sanded it back. The mesh on the chicken run had quite a lot of spikes on it and I don't know why because I've seen loads of galv mesh that was perfect.

For me though it was still a better option than painting every few years

 

[Stingray]

A silly question, when you sand a butt weld smooth what causes it to be raised after it’s been galvanised?

 

[Welderpaul]

A silly question, when you sand a butt weld smooth what causes it to be raised after it’s been galvanised?

It was explained to me that there is a higher level of silica at the weld than the surrounding metal so this attracts more zinc.

 

[Stingray]

It was explained to me that there is a higher level of silica at the weld than the surrounding metal so this attracts more zinc.

Ahh thought it would be something simple like that, at least it’s not My welding

 

[smashweld]

I've wondered about ground flat welds re-appearing too...at least I know spending excess time smoothing them off is a bit pointless now!

 

[Windy Miller]

It was explained to me that there is a higher level of silica at the weld than the surrounding metal so this attracts more zinc.

Ah Ha! I noticed this on the last set of gates I had done, and I thought I'd forgotten to sand it back properly! All makes sense now!

 

[frank horton]

found that the galvenisers in Southampton do a good job, no complaints from me.......

 

[julianf]

I had a job done at my local plant.
It was rubbish.

Took it back and they did it again (with care, I assume) and it was fine.

I spoke with a local manufacturer some time later, and they drive their product half way across the country to another galvaniser because they reckon the local plant just does not care enough.

So, my experience suggests quality is down to operator attention rather than, necessarily, process.

 

[Kent]

A silly question, when you sand a butt weld smooth what causes it to be raised after it’s been galvanised?

The ground flat then raised weld bead can actually look really cool when painted across a big mitre.
I assumed it was the gasses and thermal shock but someone mentioned raised silica levels and I lost the plot - it just happens lol

 

[jerrytug]

I tried marking-out steel using a fine Tippex pen, (working in gloomy railway arch) and all the acid baths etc do not clean it off, and the zinc does not stick, had to be done again..

True about the galvanizers being a bit mad.. also have very frightening pockmarked faces from acid and hot zinc splashes

 

[hareng]

When you look at the various baths of zinc over time they have varying degrees of scale or crust/ Some will come back real shiny, other times spikey, blotchy and rough deposits on the same materials.
Cant rule out varying degrees of temp either, hence the spikes when too cool.

Arc welding at one time had to be chipped off, still recall they got 1.3p piece work for 25mm of weld plus setups and flate rate pay, driving round in new BMW's.

Used to work for a company sending 100's of tonnes daily for galvo 729, regualrly had 4 arctics waiting to be loaded at any one time. In the group we had 4 galvanisers more a case of production to meet demand than looks out it goes. The smallest galvo co did other to the normal stuff we sent in ie smaller stuff more in to the visual appeal for architects and such like.