Galvanising small objects

[Neeves]

In a post recently, that I now cannot find, someone suggested they collected old anodes, melted them down to make new anodes. My slow thought processes then thought this might then be a way to galvanise small objects, like chain hooks, which would simply be a nuisance, or inordinately expensive, to have coated by a normal commercial galvaniser.

It would need an acid strip, flux and the liquid zinc - is this a daft, dangerous, idea?

But how do people melt zinc anyway.

Jonathan

 

[rogerthebodger]

In a post recently, that I now cannot find, someone suggested they collected old anodes, melted them down to make new anodes. My slow thought processes then thought this might then be a way to galvanise small objects, like chain hooks, which would simply be a nuisance, or inordinately expensive, to have coated by a normal commercial galvaniser.

It would need an acid strip, flux and the liquid zinc - is this a daft, dangerous, idea?

But how do people melt zinc anyway.

Jonathan

Interesting idea

This is the process so a little more involved than just melting zinc and dipping steel into it.

I do think it is doable.

This seems to be the flux used

https://en.wikipedia.org/wiki/Zinc_ammonium_chloride

 

[Neeves]

I think anchors and chains are a bit big but smaller items possible and smaller items are difficult (or fiddly) and expensive for mainstream operators (I've just had some small pieces done so I speak from experience). The technology (with no disrespect to our resident galvaniser) is hardly new (but may be very difficult to get right). I note galvanising and regalvanising of chain, other than chain makers, is becoming difficult in America (Valmont have apparently stopped though still operate, to coat chain, here in Oz). So I see small lot galvanising becoming more difficult to access - and if you can cast zinc to make anodes then galvanising (for small items) does not see totally far fetched.

But it would be interesting to hear from someone who has melted and cast Zinc. The closest I have come and its a few degrees cooler is melting and casting lead upto about 4kg.

Jonathan

 

[rogerthebodger]

I've case lead also but not zinc as there are several people local to me who process zinc in to anodes and other items so I don't need to cast my own anodes.

One trick with galvanizing small items is to find some one who gets their own components galvanized and add your items to their batch and split the cost.

One on the marinas local has their floating jetties frames galvanized so that may be an option.

 

[vyv_cox]

Small items such as nails, screws and the like are sherardised. This applies a thinner coating than galvanising does but is far easier to do. Wiki explains it well and saves me the trouble of composing https://en.wikipedia.org/wiki/Sherardising

 

[NormanS]

I have a Brunton's Autoprop which has a conical anode, which for the amount of zinc involved, seem ridiculously expensive. I cast my own anodes, melting the zinc in an old iron ladle, previously used for paying traditional wooden decks, with a gas torch. The melting point of zinc is a little more than that of lead, so the gas torch gives enough heat. I pour it into the mould, actually a small treacle tin, and when cold, attack it with drill and hacksaw. I haven't ever tried galvanising. If I want a small item galvanised I take it to a company who make farm machinery, who add it to their regular batch.

 

[Neeves]

I know of Sherardising (I think offered by Bodycote in the UK) as I had my G80 chain Armorgalv coated (which, Armorgalv, is a development, or offshoot, of Sherardising). Its a 'better' process for intricate items as it is a vapour deposition process (so it will coat internal voids and complex shapes). It can offer coatings of 100 microns (and I believe more), which is the specification I set for my chain (which is higher than the industry coating thickness used for HDG) It offers a more even coating than gal. I don't know about Sherardizing but the Armorgalv coating is more abrasion resistant than HDG.

But if you only want one or two items coated it might be easier to do it yourself - hence the query.

I believe there is an Armorgalv operator in South Africa (4 or 5 in America a few across Europe and one in Oz)

Jonathan

 

[rogerthebodger]

Small items such as nails, screws and the like are sherardised. This applies a thinner coating than galvanising does but is far easier to do. Wiki explains it well and saves me the trouble of composing https://en.wikipedia.org/wiki/Sherardising

That is a possibility but setting up a heated rotating drum could be quite involved.

For think coating of zinc. Zinc electro plating could also be used but in a marine enviroment you do need thickness of zinc so hot dip galvanizing is the best.

This is most of the internal framing that I had hot dip galvanized

Including my chain locker and internal mast support

 

[Neeves]

Roger,

Most of the stuff I see Armorgalv coated, or sheradised are mine roof supports (giant rock anchors) HT bolts for windfarms, nails (for nail guns) and the like, most of the stuff I see at out local galvanisers (who are about 90 minutes away) are like your frames. Coating thickness, with sheradising, is key - chain was tried here but coating thicknesses were too thin, far too thin - and life was short. My chain was coated with the benefit of some hindsight.

If it were possible heating up a little iron bath of zinc, pickling, dipping in flux and dropping in a molten zinc bath would be fairly quick.

Jonathan

 

[rogerthebodger]

Roger,

If it were possible heating up a little iron bath of zinc, pickling, dipping in flux and dropping in a molten zinc bath would be fairly quick.

Jonathan

Oh I agree, it was the flux that I am concerned about, getting a small quantity may not be easy, will have a look around.

I am interested as I have several small items I need to make and I dont wish to use stainless unless I have to.

 

[Neeves]

Roger,

The flux components seem fairly common place ammonium chloride and zinc chloride. Mixed almost 50:50. I assume the flux is an aqueous solution.

Jonathan

 

[rogerthebodger]

Roger,

The flux components seem fairly common place ammonium chloride and zinc chloride. Mixed almost 50:50. I assume the flux is an aqueous solution.

Jonathan

Thks Jonathan

Keep up posted when you get going with pics if poss.

 

[MM5AHO]

Galvanizing in a home workshop would be possible. As Jonathon has said its not new technology (150 years old), and pretty simple, but as to be expected there's a few pitfalls.
One is holding molten zinc. It melts about 419C, most galvanizing is done at about 450C, but at at about 500 (perhaps 520), and up to about 570 it dissolves steel rapidly.
The tank for holding zinc in a larger scale galvanizing, is usually gas heated, from the outside, and very gently so as not to have any steel in contact with zinc at elevated temperature . In this way a tank (50mm thick) will last for 10 years. Heat it to 520C and it won't last 2 days.! So at home, how will you control the temperature well enough to avoid the danger zone? Not impossible, just tricky.
Next is pickle and flux. This is a simple bit. The steel must be cleaned of all oxides. Hydrochloric or sulphuric acid, about 10% commony used. Takes under an hour. After that, rinse in water and dip in an aqueous solution of flux. This is ammonium chloride and zinc chloride mixed, and dissolved in water. But there are other ways. It's possible to just add the dry flux on top of the molten zinc. Makes a lot of fume (and that's why its not done industrially), but works. Immerse the steel item in zinc until it stops "boiling" (bubbling as if boiling, actually just heating up and driving off moisture). Remove it slowly. That way the surface tension of the liquid zinc "pulls" off surplus zinc leaving a relatively even coating thickness. Alternatively, just yank it out and throw it on the floor to shake off the surplus.
Soke galvanizing is done at higher temperatures (575 or more). The zinc only dissolves the steel rapidly at and around the critical 520. To hold that zinc they use a ceramic kettle, and heat from above. That might work domestically. But the item being dipped also dissolves at 520, so watch out!
Give some thought to suspension method. Industrially, a sacrificial steel wire is used. Tie it on, and afterward discard.

 

[rogerthebodger]

The tank for holding zinc in a larger scale galvanizing, is usually gas heated, from the outside, and very gently so as not to have any steel in contact with zinc at elevated temperature . In this way a tank (50mm thick) will last for 10 years. Heat it to 520C and it won't last 2 days.! So at home,

So if a steel container would "not 2 days" what material could be used for the molten zinc.

how will you control the temperature well enough to avoid the danger zone? Not impossible, just tricky.

I would consider using a contactless thermal temperature meter. would that is suitable for small scale low volume use.

Thks Geoff for you input.

 

[vyv_cox]

That is a possibility but setting up a heated rotating drum could be quite involved.

I suspect that a rotating drum is a sophisticated improvement. The original method was a box with a bit of carbon and zinc. The rotating drum presumably avoids uncoated areas where the object was standing.

 

[JumbleDuck]

So if a steel container would "not 2 days" what material could be used for the molten zinc.

I think he has covered that.

One is holding molten zinc. It melts about 419C, most galvanizing is done at about 450C ... Soke galvanizing is done at higher temperatures (575 or more). ... To hold that zinc they use a ceramic kettle ...

 

[rogerthebodger]

I read that is using a ceramic kettle for soke galvanizing at the higher temperature of 575 or more

 

[JumbleDuck]

I read that is using a ceramic kettle for soke galvanizing at the higher temperature of 575 or more

Yes, and a steel kettle for standard galvanizing because it takes place well below the critical temperature.

 

[rogerthebodger]

Yes, and a steel kettle for standard galvanizing because it takes place well below the critical temperature.

Are you talking mild steel or would stainless steel be better of worse.

I am only looking at small items so a I could easy make a stainless steel box say 300 x 300 say 200 high at very little cost with a big LPG cooking burner under for heat.

 

[MM5AHO]

I made a a typo in earlier post. Soke = some.
Industrial kettles are made of mild steel, but one important chemical point. The Silicon must be extremely low (as in "trace"). Otherwise for standard temperature galvanizing a steel kettle, typically 50mm thick is used. High temperature galvanizing (I don't think there's any left in this process in the UK, but there are some in Europe), uses a ceramic kettle, with directly heated zinc, either immersion electric, or top heated gas.
A standard steel kettle is heated from the outside, and heat flows through the kettle wall, but it must not raise the inner surface of the kettle wall higher than about 50 above melting point. Temperature control is all important in this business. The gas burner never impinges on the kettle wall. In fact great care is taken to avoid that. For domestic use, a steel kettle of say 10mm thick, using standard mild steel might work for a "one off" job. You'd only want the steel hot for an hour or less? And if you plan the situation, you could cope with a failure! If I were doing it, I'd build a brick furnace to house the kettle and not fire the kettle directly, but have the flames firing into the cavity between the brick and kettle wall. Make the kettle as small as compatible with the object to be galvanized.
But after all that trouble, it would be far easier to find someone friendly at a galvanizer to get it done for you. There are galvanizers in the UK doing small items quite readily, as small as nuts and bolts. There's also spin galvanizing. Galvanized in a perforated bucket which is then placed immediately into a centrifuge and the surplus zinc spun off.