Author Topic: 3d metalcasting test  (Read 6926 times)

Offline vtsteam

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Re: 3d metalcasting test
« Reply #25 on: August 07, 2014, 06:40:11 PM »
The Zinc actually boils at 907C and a melting point of 460C it's not burning it's boiling.

Okay, if the above no longer applies (it does both), glad that's cleared up. I didn't say anything about "fever" btw.


re. covering, according to Ammens, and depending on the type of brass, a floating flux wasn't generally used in the past here, though copper with phosphorus was sometimes added as flux for other reasons .He does suggest in small scale crucible melting, to add charcoal on top of the melt and shows a loose covering of a broken crucible for room for more metal. The charcoal is probably there to increase the temp initially to speed melting rather than prevent loss of zinc, since as we both know zinc vapor will be evolving before pouring temperature is reached, whether or not it is burned to oxide at the surface.

Incidentally, not sure about this but I have a feeling elemental zinc vapor is probably more harmful to breathe than the oxide. Zinc oxide is used topically as a sun screen. Not saying it's a good idea to breathe it, but I do wonder if metallic zinc vapor is worse.

Many tradtional brasses and bronzes contain some lead according to Ammens, btw, with an even lower boiling point than zinc.
I love it when a Plan B comes together!
Steve
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Offline mattinker

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Re: 3d metalcasting test
« Reply #26 on: August 07, 2014, 08:03:07 PM »
From what I'd learnt, it's the Zinc and not the oxide that gives the fume fever you can see the white oxide smoke, but not the pure zinc vapour. Ironically the body requires Zinc, just not an overdose.

This article about a death from fume fever with complications  the emphasis is on zinc oxide. http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo

I had been thinking about something to act as a cover for the zinc, that as you say wouldn't prevent  zinc loss but absorb oxygen, which charcoal would do. A slightly carburising flame, weak in oxygen might help, although it would be cooler. I would suggest buying a pyrometer to keep heating to a minimum and avoid overheating. Skim the slag at the last possible minute and have the moulds as close as reasonably possible to the foundry. Don't ingot brass as each reheating will remove zinc.

It would seem that in "Admiralty Brass" a small percentage of tin is added to help reduce the zinc loss.

Regards, Matthew

Offline vtsteam

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Re: 3d metalcasting test
« Reply #27 on: August 07, 2014, 09:09:12 PM »
That article is sobering reading, Matt. They mention zinc oxide as the cause but no mention of any zinc vapor, which I imagine was also present. They go into zinc chloride inhalation at length but I have no idea why, since that's unlikely to have been present. They speak of heavy metal poisoning, but I don't think zinc is considered a heavy metal under that definition. I also don't think zinc is cumulative in the body, which is mentioned. As you say we need to take zinc supplements reqularly to avoid zinc deficiency as we get older. The cause of death was pneumonia and the poor guy had suffered from emphysema. That was described as contributory at least. The big problem was, he tried to burn off zinc galvanizing inside a closed shop. That's really a bad idea.

I'm not trying to minimize the need to be careful with zinc, or in any way diminish the sadness of this man's loss, but I also don't believe this was presented in a very accurate way. That's not helpful. Understanding is.

It's important to minimize exposure and be safety minded with zinc, but it doesn't mean I for one will stop brazing (outdoors always) or completely avoid brass casting (also outdoors -- I NEVER cast braze or weld indoors). And would never think to burn off galvanizing -- I use dilute muriatic acid for that, and then baking soda rinse.

I do think it is a good idea to understand the dangers of any creative procedure, from cutting with a table saw, to using hydraulic jacks, picking up heavy materials, or driving to the hardware store.

Anyway, all this talk about casting with brass, makes me want to do it again, oddly enough!  :doh:   It gets to be like a challenge which I'd like to have work out well. Go figure....
I love it when a Plan B comes together!
Steve
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Offline mattinker

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Re: 3d metalcasting test
« Reply #28 on: August 08, 2014, 02:03:00 AM »
Steve,

"They go into zinc chloride inhalation at length but I have no idea why, since that's unlikely to have been present." They mention a reaction with the ITC100 refractory lining.

I agree that the circumstances are exceptional, but **** happens!

Regards, Matthew

Offline vtsteam

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Re: 3d metalcasting test
« Reply #29 on: August 08, 2014, 11:04:21 AM »
Anyway, I hope anyone casting brass does so outside, and that reasonable precautions are taken. But I don't think it is something to fear under those circumstances, I think it is something simply to respect.

Matt you mention loss of zinc during any brass melt. I meant to say that it can be added back.

Besides adding pure zinc per commercial practice (usually via a plunger), small model quantities of brass can be zinc enriched with some pieces of brass brazing rod (not all brazing rod is brass, btw) added just before pouring. One rod I use, Forney brand, available locally in hardware stores, has an MSDS showing nearly 40% zinc content, and 60% copper, with a trace of iron.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: 3d metalcasting test
« Reply #30 on: August 08, 2014, 11:32:54 AM »
I have a Metco Zinc spraying gun. Compressed air turbine pulls an 1/8" solid zinc wire co-axially through the centre of a special oxy-acetylene nozzle. The zinc obviously melts, and the force of the burning flame and compressed air projects globular zinc towards whatever you want to zinc cover. Steel needs to be grit blasted to give a key, and tiny microscopic platelets of zinc get splatted onto the surface and can be built up as thick as you want. The platelets interlock and the bond is quite good.

The same device can spray virtually any metal that you can source as an 1/8" wire. Molybdenum is used as a pre-coat, then various grades of steel can be used to build up crank pins etc.

I've even zinc sprayed a wooden box to make an RF shield.

All this talk of zinc fumes etc makes me wonder why I've not had a problem, not that I use it that often.

It's just occurred to me it would be a simple repair method for rust holes in my tractor cab if I could get a backing behind the hole. Build up a suitable thickness and dress back to level - would stop the rust galvanically by being a solid zinc plug!
Andrew Mawson
East Sussex

Offline vtsteam

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Re: 3d metalcasting test
« Reply #31 on: August 08, 2014, 12:51:32 PM »
Andrew those Metco zinc guns are the best method for protecting newly built small steel sailboats after sandblasting prior to painting. A properly prepared boat can be maintained virtually indefinitely in salt water. I imagine you use protective breathing gear for both blasting and spraying. Knowing you, you probably have exotic gear for that, too! You must have the best equipped shop and facilities I can imagine.  :bow:
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Steve
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Offline awemawson

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Re: 3d metalcasting test
« Reply #32 on: August 08, 2014, 01:12:51 PM »
Andrew those Metco zinc guns are the best method for protecting newly built small steel sailboats after sandblasting prior to painting. A properly prepared boat can be maintained virtually indefinitely in salt water. I imagine you use protective breathing gear for both blasting and spraying. Knowing you, you probably have exotic gear for that, too! You must have the best equipped shop and facilities I can imagine.  :bow:

I blame it on a life time of avarice and the internet  :lol:

The grit blasting is always either in a Guyson cabinet so sealed and extracted or with the Hodge-Clemco outdoors with the proper Apollo air fed helmet.

For the Metco I don't actually have anything suitable - at a pinch I suppose that I could use the Apollo lid but the visibility leaves a lot to be desired and you really need to see what you are doing when playing with oxy-acetylene
Andrew Mawson
East Sussex