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Hot dipped galvanized finish on moving parts


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 I'm in the process of designing a large gate project and my preferred finish is to have the the two gates and two side panels hot dip galvanized for weatherproofing .

I've had good luck with this kind of finish for forged exterior steelwork  as the process gets into all the nooks and crannies and if it's done correctly doesn't obscure any more of  the texture or detail than paint.

The process is pretty cost effective and really gives superior weatherproofing in a wet outdoor environment. The main objection seems to be the silver gray industrial look but the zinc coating can be etched chemically or by a year in the weather before a color top coat is applied if desired.  

My question is how do I handle the parts like the hinge barrels and pins as well as the latch mechanism so that they either don't get coated in the process or the coating doesn't interfere with the action.

The hinges will be an enclosed top barrel dropping down onto a vertical pin. The latch will be a simple swing latch operated from both sides.

I've been told that the galvanized coating won't adhere to the steel without being etched and cleaned beforehand in an acid pickle bath.

Should I paint or somehow treat the areas where the parts have to move so that they resist the pickle and the zinc coating or use stainless steel  for those parts.

Another option is to make everything a sloppy fit and then ream or file some of the zinc coating in those areas back to the desired tolerance before final assembly.

Anybody have any real world experience with this and if so, what worked ?

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 They suggested that I paint the parts I wanted to stay ungalvanized with a thick coat of oil based paint.

I was just wondering if anyone here had actually done it and what the results had been  before I committed to the process.

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Not precisely the same, but when I worked in the art restoration studio, we had to re-silver some large mirrored glass panels for  the lobby of a swanky Manhattan apartment building (home to, among others, Henry Kissinger). This involved an acid etch and some other chemical nasties for the actual plating. My boss (never quite the brightest bulb) decided to “patinate” the mirrors by spritzing droplets of paint on the glass after the etch, but before the plating. 

I left the studio shortly thereafter, but one of my coworkers told me that the silvering simply peeled off the glass wherever the “patination” had been applied, and the whole thing had to be done again. 

So yes, paint can definitely be a barrier to metal plating. 

Also, don’t get Henry Kissinger mad. 

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In the UK the acid that's put on fresh shiney galv to etch it back to the softer grey colour is called T Wash. I don't know if the name will be the same in the States but that may serve as a starting point.

Because of the sorts of issues you mention I've always favoured having my exterior work manually zinc sprayed & paint top coated rather than galved (zinc dipped) but zinc sprayers are a rare breed.

I don't think you want to coat the hinge pins or barrells, let the galv get everywhere so you've got max protection. You'll need a millimeter or two of slop in the barrells anyway for them to function freely, so when they come back from being galved offer the pins up - if they fit then great, if not then drill out or file down the galv build up that's making them bind.

I suppose every latch is slightly different & harder to say what'll be the best approach without knowing how much surface area is in contact. Again for the purposes of letting the weatherproofing get everywhere - I typically bolt them on & leave a bit of slop in the mechanics knowing that otherwise they'll bind. For zinc spray + paint top coat I typically drill holes 1mm larger than required.

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 Thanks Joel, that was just the kind of information I was looking for.

I'll let you know how it goes.

The thing I like about the hot dipping process is that it gets into all the hidden crevices from using traditional joinery techniques like collars . Does the manual zinc spraying process  get in there as well ?

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45 minutes ago, beaudry said:

The thing I like about the hot dipping process is that it gets into all the hidden crevices from using traditional joinery techniques like collars . Does the manual zinc spraying process  get in there as well ?

Yes and no. The manual nature of sprayed zinc relies on the operator's dilligence, but it works in the same way as galv, so the rust won't creep beyond any spots that didn't get covered.

I get a lot of repeat clients so I've been back & seen how work is fairing up months after it's been installed. On the jobs where a light colour paint has been used as a top coat I've noticed a minimal amount of rusting where a round bar passes through a drilled flat bar because I've only welded it underneath & haven't sealed it with weld on top as well. The zinc firm I use nowadays also spray vinyl paint top coat. If I wanted to I could dab some paint on the end of a brush & jab it in/around seamlines so all spots are truely covered.

Galv firms tend to handle lots of fabricated heavy duty stuff so can be a bit rough with neatly forged work. Sharp drips & "snots" are also a common by product from galv dipping & it's common for smiths having to fettle away nasties back at the workshop before delivery to customer. Most of the smiths local to me use galv firms, I just prefer zinc spray.

A couple years ago I did post up pics onto IFI on a pair of gates I made hanging up in the workshop after being zinc sprayed, before I painted them. I can't find that thread & I'm typing on my phone at min but maybe when I get onto my laptop I can dig them out. They had quite a few collars on. Zinc spray surface texture is not smoothe like fresh galv, it's keyed so it's perfect to accept paint directly, unlike galv.

Because you've mentioned collars a couple times these pics may or may not ease some of your concerns over zinc spray (which is also typically dearer than galv). I took these pics a few months after I installed the gate. There was maybe a hint of rust showing around the odd collar edge, but nothing drastic. I think the makers are typically more concerned about a perfectly neat rust free finish than the clients.FB_IMG_1516640510730.thumb.jpg.1354be91a9809bb4c65497abbeb542ef.jpgFB_IMG_1516640538271.jpg.0fd39249e468ea8e692237ce025dc1df.jpgFB_IMG_1516640548271.thumb.jpg.d64c6931a939eb78e2c6549b65f5d9af.jpg

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 Thanks Joel for the tips based on your experience. I really ike the design and color of your gate .  Did you just make the hinge pins and barrels extra loose and then file to final fit, hopefully leaving enough zinc in place to protect the steel ?   I've found that if you request it ,the galvanizers will blow  the piece of with compressed air when it comes out of the dip to minimize drips in the zinc coating.  Any remaining lumps are best removed with a coarse rasp that doesn't seem to clog as easily as a file. Welds that you thought were ground and blended to be virtually invisible in the raw steel will stand out clearly through the finished zinc finish .

editing more useless spaces

 

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It sounds like you've had worked galved before - sorry if my previous answers seemed condesending or obvious, I assumed you hadn't had work galved before so answered as such.

From memory I think I just made the hinge barrells snug. I think the hinge pins were 20mm and I just used a piece of regular 20mm bar in my jig - or at most I upset the jig bar to 21mm. That gate was pretty darn heavy so I knew the weight of it would work the hinges free.  With things like like drop bolt holes or holes in a latch to accept a padlock I do drill the holes 1mm oversized to allow for the build up of zinc and paint.

Here's those pics I mentioned, these were the first gates I made. Hanging up in my old workshop after being zinc sprayed waiting for me to paint them. Fresh sprayed zinc has the sligtest furry/coarse texture to it so paint keys perfectly into it. Sprayed zinc doesn't hide forged details.5a66c84d30d29_Zincedgates1.thumb.JPG.2d1a794b5fdb4a5a758f18db15804bd9.JPG5a66c85d6dbd1_Zincedgates2.thumb.JPG.789e4b8af1288701cbf004652303aa34.JPG5a66c87074027_Zincedgates3.thumb.JPG.a682521807f4bcf2174a1160599a8c8b.JPG

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 Thanks Joel , no worries on stating the obvious, better to have more information rather than less.  I've done 50 or 60 large exterior pieces that were hot dipped galvanized over a forged steel substrate.  These were all stair and balcony railings, mostly assembled  in complete finished sections before dipping with traditional joinery  like mortise and tenon, collars and wraps.  Larger installations were  assembled on site with galvanized or stainless steel fasteners.  Bolt holes were all oversized by about 1/16''- 1/8'' to allow for the zinc coating   The advantage of the hot dipping process is that it allows the molten liquid zinc to penetrate down into all the nooks and crannies , any place where water can penetrate and collect.  Any hollow sections need to be vented with 1/4'' holes near each end . I was told that this is to allow stem to escape and if the operators don't think they are vented properly they will do it themselves with a cutting torch at locations  that  are convenient to them.  I've also been warned that bar sections less than 1/2'' or so in diameter can get warped by the hot process.   None of these pieces had moving parts that needed to both operate smoothly and be protected from rusting outside in the weather  for years.

My understanding of the zinc spraying that you are talking about is where a metal powder is shot through a torch flame by compressed air  which deposits a thin layer of molten metal bonded tightly to the clean  substrate.   This seems basically like painting or powdercoating in that it is basically a straight line process and that the coverage is only as good as the dilligence and attention of the operator.  It sounds as if you've been happy with the results and have had the chance to see how it holds up over time in a similar climate.  I made some furniture components that were flame sprayed with bronze over steel. The thin bronze layer was sanded back in areas to highlight texture and then treated with a chemical patina and sealer.  This was an expensive process but got the look the designer and client were after.

edited more useless spaces

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2 hours ago, beaudry said:

My understanding of the zinc spraying that you are talking about is where a metal powder is shot through a torch flame by compressed air  which deposits a thin layer of molten metal bonded tightly to the clean  substrate.

This seems basically like painting or powdercoating in that it is basically a straight line process and that the coverage is only as good as the dilligence and attention of the operator.

Nice rails.

Yeah basically. If you YouTube "zinc metallisation" or "zinc flame spray" there's a few vids out there that'll give you the jist.

Part of my reason for favouring it is because 75% the work I have have had galved before has come back bent from heavy handleing & covered in really sharp build ups. I haven't used the other galv firm yet that I know the other local smiths use, but even then one smith said he sent one job to the firm 3 times before he was happy with the result and eventually paid. Galv seems like a great method, just let down by the operators, however it sounds like you've got some good guys dipping your work!

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  • 11 months later...
On ‎1‎/‎23‎/‎2018 at 12:03 PM, beaudry said:

I made some furniture components that were flame sprayed with bronze over steel. The thin bronze layer was sanded back in areas to highlight texture and then treated with a chemical patina and sealer.  This was an expensive process but got the look the designer and client were after.

Beaudry,

Did you design this?  It is same pale work as my JG Bends xxxxxxxxxxx

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  • 2 weeks later...

When I was 1 or 2 years younger than I am now, I made galvanize steel at Youngstown Sheet and Tube Co. (Now defunct)  It was a summer job, in that I was an engineering student at Purdue U. at the time.  1962, I think.  Turns out that hot galvanizing liquid is actually a 700 degree solution of more than 3 metals.  It's mostly lead(the fumes of which will kill you), and also zinc and aluminum.  I know this because I was the kid who had to keep throwing the ingots of the various metals into the vat.  There's a chemical term, called vapor pressure, which means (if it were water)the steam rising from off the surface of the simmering liquid.  Only these are the vapors given off the 'heavy metals' as they are melted almost to their boiling point.  Minor exposure to Zinc vapors won't kill you, but they will make you sick.  Aluminum vapors are the sneaky ones.  Breathing those fumes won't leave obvious symptoms, but ongoing, we don't know the long-lasting effects.

So please, don't work directly with lead coated metals.  Lead forms an instantaneous layer of lead2 and lead4 oxides, (that's the white-ish coating you see on older galvanized stuff) ..  Don't even work in enclosed spaces where solid lead has been sitting open for a few weeks.

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The reason we caution against Zinc and other coatings is to err on the side of safety. We have had one IFI member die, not because of the Zinc fumes but the fumes opened the door for other complications. 

A0030 Jim PPW Wilson shop and Working with Zinc or galvanized

Zinc, galvanized, and coatings

One piece of metal is not worth taking the risk for Zinc fumes, heavy metal poisoning, or other problems.

New metal is much less expensive that the cost of a hospital visit.  

 

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  • 3 months later...

hi, im a Hot dip Galvanized inspector, currently working on a HDG facility,  if i can help with something, ill be glad to help.

if you need masking for not galvanizing components, i would use Galvastop by puma chemicals, this is one of the best product out there.

there are other products that you can use, for example : caulk or silicone... they work great, when we dont have Galvastop, there is always cheap caulk or silicone that we use on out selective galvanizing process

 

On 1/30/2019 at 10:21 PM, eutrophicated1 said:

When I was 1 or 2 years younger than I am now, I made galvanize steel at Youngstown Sheet and Tube Co. (Now defunct)  It was a summer job, in that I was an engineering student at Purdue U. at the time.  1962, I think.  Turns out that hot galvanizing liquid is actually a 700 degree solution of more than 3 metals.  It's mostly lead(the fumes of which will kill you), and also zinc and aluminum.  I know this because I was the kid who had to keep throwing the ingots of the various metals into the vat.  There's a chemical term, called vapor pressure, which means (if it were water)the steam rising from off the surface of the simmering liquid.  Only these are the vapors given off the 'heavy metals' as they are melted almost to their boiling point.  Minor exposure to Zinc vapors won't kill you, but they will make you sick.  Aluminum vapors are the sneaky ones.  Breathing those fumes won't leave obvious symptoms, but ongoing, we don't know the long-lasting effects.

So please, don't work directly with lead coated metals.  Lead forms an instantaneous layer of lead2 and lead4 oxides, (that's the white-ish coating you see on older galvanized stuff) ..  Don't even work in enclosed spaces where solid lead has been sitting open for a few weeks.

not every galvanizing facility uses Lead.. also the white coat you see on older galvanized stuff is not leat oxide.. its zinc hydroxide.. you can clean this with vinegar and scrubbing.

in the facility i work for, we use Zinc SHG, Bismut and Aluminium.

also HDG must be 98% zinc in the kettle, other metals are restricted by ASTM 123... 

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