Is granulation immune to steam explosions....?

[Amol Gupta]

My question is with reference to this video link.



They make it look so easy.

A couple of questions

1. I see they use an induction furnace to melt the gold, why not cover the top instead of running a flame over the opening.

2. Is granulation immune to steam explosions, the rate at which he is pouring seems very fast, he seems unfazed.
He is pouring(what seems to me) like a glass container and that to a shallow one, something that goes against all I know about steam explosions and granulation.

He seems to be doing everything against my undestanding of steam explosions, it would be wiser for more experienced individuals to comment on the same.

Thanks

 

[4metals]

1. I see they use an induction furnace to melt the gold, why not cover the top instead of running a flame over the opening.

A lot of induction furnaces come with the flame over the crucible. The purpose of the flame is to consume any oxygen in the air over the crucible. This is essential with silver melts. Pure gold does not need the flame but I see a lot of shops use it as an extra precaution.

I believe the glass cylinder is strictly for video purposes so we can see the shot in the water. Generally pure metal into cold water does not cause steam explosions if there is enough water so it does not boil. The glass vessel looks pretty deep. Possibly it's quartz glass, which can take the heat.

My first choice wouldn't be glass either. But for the sake of the video, they thought it necessary for effect. G&S Metals is a refiner in Detroit so this video was part sales.

 

[Amol Gupta]

Generally pure metal into cold water does not cause steam explosions if there is enough water so it does not boil.

How does pure metal stack up against alloyed metal(karat scrap for instance) with respect steam explosions, how does it even matter.
Secondly correct me if I am wrong, my understanding suggest, we need large enough volume of water to absorb heat dissipated by cooling solid without boiling.

 

[4metals]

Generally pure metal is poured into a shot box or a drilled crucible to produce spherical shot. The pre heated shot box is placed close to the water and the molten metal poured through. This rarely causes a steam explosion unless the water volume is so small it overheats, and even then you are more likely to develop a stuck together pile of beads on the bottom than a steam explosion.

Karat scrap is generally made into shot for a different reason. Karat is shotted to increase the surface area for a quicker dissolve. Melting karat scrap of different karats also benefits by making all of the metal homogenous before pouring. Karat is usually poured from greater heights and into an open top container of water and not through a shot box. Pouring this karat too fast, and into insufficient water can result in steam explosions. Karat shot can be some strange shapes often called popcorn or cornflake shot and it isn't pretty like fine shot beads.

I have noticed that fine gold and fine silver shot loses it's heat almost instantly when it hits the water, probably because it is such an efficient conductor of heat. Karat on the other hand isn't as quick to lose it's heat and while it freezes in the water it still retains heat longer. That may factor into karat pours reacting violently if poured too quickly.

 

[Amol Gupta]

Generally pure metal is poured into a shot box or a drilled crucible to produce spherical shot. The pre heated shot box is placed close to the water and the molten metal poured through. This rarely causes a steam explosion unless the water volume is so small it overheats, and even then you are more likely to develop a stuck together pile of beads on the bottom than a steam explosion.

Karat scrap is generally made into shot for a different reason. Karat is shotted to increase the surface area for a quicker dissolve. Melting karat scrap of different karats also benefits by making all of the metal homogenous before pouring. Karat is usually poured from greater heights and into an open top container of water and not through a shot box. Pouring this karat too fast, and into insufficient water can result in steam explosions. Karat shot can be some strange shapes often called popcorn or cornflake shot and it isn't pretty like fine shot beads.

I have noticed that fine gold and fine silver shot loses it's heat almost instantly when it hits the water, probably because it is such an efficient conductor of heat. Karat on the other hand isn't as quick to lose it's heat and while it freezes in the water it still retains heat longer. That may factor into karat pours reacting violently if poured too quickly.

We I have done some reading, my best guess is impurities in karat scrap are mainly copper and silver which have somewhat similar thermal conductivity to that of gold.

Silver – 429 W/m•K
Copper – 398 W/m•K
Gold – 315 W/m•K

Infact the two being more thermally conductive.

I agree, a good rule of thumb is to check for sediments not fusing together at the bottom to ensure safe operations.

Just a food for thought, my best guess is there has got to be an upper limit on how cold the water should be, it is proven scientifically hot water freezes faster, is safe to say cold water evaporates faster, just an opinion, any thoughts on this...?

 

[Yggdrasil]

We I have done some reading, my best guess is impurities in karat scrap are mainly copper and silver which have somewhat similar thermal conductivity to that of gold.

Silver – 429 W/m•K
Copper – 398 W/m•K
Gold – 315 W/m•K

Infact the two being more thermally conductive.

I agree, a good rule of thumb is to check for sediments not fusing together at the bottom to ensure safe operations.

Just a food for thought, my best guess is there has got to be an upper limit on how cold the water should be, it is proven scientifically hot water freezes faster, is safe to say cold water evaporates faster, just an opinion, any thoughts on this...?

A tub/bucket of hot water will not freeze faster, because it has a massive thermal reservoir under it.
Hot water in a thin layer will freeze faster due to the energy required to evaporate it, and as some of it evaporate it cools/freezes the rest.
Cold water will not evaporate fast unless you have a strong wind.

 

[Amol Gupta]

A tub/bucket of hot water will not freeze faster, because it has a massive thermal reservoir under it.
Hot water in a thin layer will freeze faster due to the energy required to evaporate it, and as some of it evaporate it cools/freezes the rest.
Cold water will not evaporate fast unless you have a strong wind.

Sure this makes sense.

 

[Martijn]

i think it's a ratio between how much molten metal vs how much water, and most important, the feed rate. go slow, and no steam or hydrogen can form by extreme heating and possibly explode.

 

[andu]

One can never be too cautious. The fact that he isn't pouring a continuous stream but drops of molten metal surely helps a lot.

 

[hoytSmith]

Steam explosions? That requires some explanation. If you are suggesting that you could pour a relatively thin stream of metal into a vessel of water and get a steam explosion, I say “very unlikely” — maybe a bucket of metal into a relatively small volume of water or less small volume of warm water, but that’s beibg stupid.

Explosions require pressure — supplied by now boiling water. Enough pressure to displace the remaining water & material at some speed. It’s a thermal power equation, but hot metal doesn’t have as much heat in it as you might think and water sinks heat very well unless there isn’t very mich — so, not so much steam gets generated and not so much pressure without restricting the water volume, restricting the throat of the vessel, and adding a bunch of metal all at once. I’m going to stretch and say — you won’t get a steam explosion without being reckless or stupid.

Steam explosions from superheated water is possible, but that doesn’t happen when the water is being disturbed — that’s usually an induced heat scenario.

On the other hand: drop a tablespoon full — maybe even a drop (of sweat) under the right conditions — of water in molten metal and you get steam — pretty close to instantaneously. Fast enough to throw hot molten metal everywhere. I understand that to be a serious issue for artisanal foundries.

 

[4metals]

A few months back a member posted a you tube video of someone pouring molten metal, I believe copper, into a small bucket of water. The result was what I would call a steam explosion.

I wish I could find the thread with the video link.

found it!

This guy has screwed up on so many levels!!!!!!

 

[Amol Gupta]

A few months back a member posted a you tube video of someone pouring molten metal, I believe copper, into a small bucket of water. The result was what I would call a steam explosion.

I wish I could find the thread with the video link.

Here it is.

 

[4metals]

Here it is.

Yes that is it. There are so many ways this was an example of the wrong way to do this that I stopped counting.

 

[Darkthirty]

Yes that is it. There are so many ways this was an example of the wrong way to do this that I stopped counting.

He dumped the melt in the ice water creating a pocket of metal. When I was pouring alloys with small induction furnaces if you threw a slobbered on cigarette butt into a running furnace it would spit back any equal amount of molten metal. If a crucible burned through to the induction coils, the whole charge was airborne almost immediately.

 

[Amol Gupta]

If a crucible burned through to the induction coils, the whole charge was airborne almost immediately.

Not sure why something like this would happen...?
Are we talking levitation or the charge exploding..?

 

[Amol Gupta]

Well I guess that is because of the water used for cooling running in the coil.

 

[andu]

I somehow had a drop of water in my furnace, luckily very small amount of metal and it took between 2 and 5 seconds for it to explode, the insulating wool was rendered useless, and the heat sink flied like 3 meters up and another couple on a side, i were lucky there was only a bunch of grams in the crucible.

Whatever you throw inside a molten solid will either release gas or vapour which will generate a explosion, just search for the vid of some dudes throwing a modest 15kg rock into a volcano and generating thousands of tones in lava exploding/erupting.


You can do as you wish but it is a risk.

 

[Amol Gupta]

I never thought of it was a good idea to add charge to molten metal, never done that personally

 

[Darkthirty]

I never thought of it was a good idea to add charge to molten metal, never done that personally

Material runs through a preheater first, but it happens all day, every day in a production foundry.

 

[Amol Gupta]

I guess something I'll have to learn and understand better