What's happened to my crucible?

[creast]

Hi fellow foundrymen.
Yesterday I trialled my updated diesel burner where I had increased the potential flow rate. This burns much more fiercely than its predecessor so I had a go at making 0.5kg of silicon bronze (as per 100model's video)
I did seem to make some kind of bronze and cast a small part but I had a lot of gooey slag on the melt.
On cooling I examined the crucible and was horrified how it looks. It was an old crucible and wasn't very pretty before the melt but now its like it has melted and bubbled on the inside top surface! See the attached pic.
The outside surface is pretty good
I can't remember where I got this crucible but all my others are Salamander super grade, perhaps this was another manufacturer.
Has anyone seen this occur?
Rich

 

[GreenTwin]

From the exterior, it does resemble a Morgan Salamander Super clay graphite crucible.

I tried brass and a variant of bronze a couple of times, and I never got the process figured out.
I would get clouds of zinc smoke coming off the melt, and never got a decent casting using brass/bronze.
This was early in my casting experience, and so I could perhaps achieve better results these days.

I do intend to cast some lead-free bearing bronze one day, and I have the materials for that.

One individual mentioned using glass (as in glass bottles) on top of a brass/bronze melt, to stop the zinc burnoff, and control the slag.
Apparently the glass is just skimmed off just before the pour.
I have never used glass as a cover, and wonder about the mess it would make.
I am told that it does work to keep the oxygen off of the melt.

The only thing I have seen ruin a crucible like that is the addition of borax.
There are some misguided folks on the net who recommend fluxing with borax, and/or otherwise treating the crucible with borax.
I don't know of a faster way to destroy a perfectly good crucible than to let it come in contact with borax.

Borax is definitely not needed for gray iron.

Also, slag is very corrosive to a crucible, and so if your slag ran over the side, and down the crucible, it can degrade it quickly.

Was your burner running reducing or oxidizing; or neutral ?
I run my burner reducing (rich) with iron, and that seems to really help minimize the slag.

.
Edit:
I also used dedicated crucibles (all Morgan Salamander Super), one for iron, one for brass/bronze, one for aluminum.

.

 

[creast]

From the exterior, it does resemble a Morgan Salamander Super clay graphite crucible.

I tried brass and a variant of bronze a couple of times, and I never got the process figured out.
I would get clouds of zinc smoke coming off the melt, and never got a decent casting using brass/bronze.
This was early in my casting experience, and so I could perhaps achieve better results these days.

I do intend to cast some lead-free bearing bronze one day, and I have the materials for that.

One individual mentioned using glass (as in glass bottles) on top of a brass/bronze melt, to stop the zinc burnoff, and control the slag.
Apparently the glass is just skimmed off just before the pour.
I have never used glass as a cover, and wonder about the mess it would make.
I am told that it does work to keep the oxygen off of the melt.

The only thing I have seen ruin a crucible like that is the addition of borax.
There are some misguided folks on the net who recommend fluxing with borax, and/or otherwise treating the crucible with borax.
I don't know of a faster way to destroy a perfectly good crucible than to let it come in contact with borax.

Borax is definitely not needed for gray iron.

Also, slag is very corrosive to a crucible, and so if your slag ran over the side, and down the crucible, it can degrade it quickly.

Was your burner running reducing or oxidizing; or neutral ?
I run my burner reducing (rich) with iron, and that seems to really help minimize the slag.

.
Edit:
I also used dedicated crucibles (all Morgan Salamander Super), one for iron, one for brass/bronze, one for aluminum.

.

I have cast Brass many many times and to be honest it's my favourite metal to cast.
Also I had no problems doing homebrew tin bronze and leaded bronze, aluminium bronze however was a disaster.
Like you, I avoid borax as it ruined my last crucible and I have not tried glass either.
I upgraded the burner to improve cast iron melting since I did my first melt on the 1/4 Anzani project so was suspicious that I had over done it.
On this occasion it was running slightly rich.

 

[GreenTwin]

I have never had a problem with too much heat from an oil burner on a Morgan Salamander Super, even after repeated melts.
I run my burner at approximately 2.7 gal/hr, reducing flame, with the centerline of the burner offset to one side of the crucible/plinth junction.

The only time I have heard of problems is when the burner flame impinges directly onto the crucible, in which case a Morgan SS may only last a few melts.

The aluminum bronze samples that I have seen are a very interesting, lightweight and strong alloy, but they fall into the realm of "no-cutium" type metal.

At first I thought that zinc and/or aluminum 356 would be as far as I went with melting metal in the backyard.
The zinc was a bust, since it melts at such a low temperature that it would melt in front of a drill bit.
Some say just use a lubricant when machining zinc.

The aluminum 356 castings I initially made were very gummy to machine, and they loaded the tool bits very quickly.
I learned how to get an approximate T6 temper on aluminum, and that material is stronger and machines far more cleanly than untempered 356.

I tried brass, and then boat shaft brass/bronze.
I had problems with zinc burnoff, and some gassing in the metal, and then found out that boat shaft brass/bronze has terrible stiction, which makes it unusable for bearing material.

My brass/bronze melts basically uses about as much heat as melting cast iron, and so I tried cast iron.
I had all sorts of problems with cast iron in the beginning, because I was running an oxidizing flame, I did not know how to add scrap correctly to the melt to minimize slag, did not know how to correctly tune an oil burner, did not know what fuel flow to use, and did not know about ferrosilicon.

Having solved all the cast iron problems, I use it exclusively for engine parts, since it wears very well, machines extremely well with small chips, does not smoke as it is melting, does not have any significant gas issues that require a degassing agent, and as the saying goes "it wears like iron", ie: it has graphite in the metal, and so wears very well.

At some point, I do want to make bearing bronze, and I will try it without the glass first.

Your second photo does appear as if there is impingement on the crucible; as if your burner centerline is several inches above the bottom of the crucible. Is this the case? or did something else affect the crucible?

Some combinations of alloys may not be good combinations, and that could cause what appears to be foaming of your metal.
Perhaps others can comment on the brass/bronze side of things, since I am not really up on that.

.

 

[timo_gross]

Looks like a foamy slag coating (skull) on the cruicible, not the cruicible material.

You can try to cut some slit with a dremel tool or stone cutting disk (careful the dust is not healthy) and chisel the skull out with a small chisel.
Very easy to brake the cruicible in the process. For a clay graphite cruicible possibly not worth the effort, because they are not overly expensive.

I would consider to just put the cruicible aside and give cleaning a try if I was melting any thing else anyway.
Then you might try to remelt (reheat) the stuff and remove it in heated condition, but slag can be quite stable in high temperatures.
Figure out some way to hold the cruicible when trying to remove the slag.

They used O2 burner tubes to put slits into the skull and then one of these to remove the slag.



Wrong slag on top of the melt can ruin refractories quite quickly.

For big steel casting ladles sometimes different grades of refractory are used in the slag zone to keep wear at reasonable rates.

Greetings Timo

 

[creast]

I have never had a problem with too much heat from an oil burner on a Morgan Salamander Super, even after repeated melts.
I run my burner at approximately 2.7 gal/hr, reducing flame, with the centerline of the burner offset to one side of the crucible/plinth junction.

The only time I have heard of problems is when the burner flame impinges directly onto the crucible, in which case a Morgan SS may only last a few melts.

The aluminum bronze samples that I have seen are a very interesting, lightweight and strong alloy, but they fall into the realm of "no-cutium" type metal.

At first I thought that zinc and/or aluminum 356 would be as far as I went with melting metal in the backyard.
The zinc was a bust, since it melts at such a low temperature that it would melt in front of a drill bit.
Some say just use a lubricant when machining zinc.

The aluminum 356 castings I initially made were very gummy to machine, and they loaded the tool bits very quickly.
I learned how to get an approximate T6 temper on aluminum, and that material is stronger and machines far more cleanly than untempered 356.

I tried brass, and then boat shaft brass/bronze.
I had problems with zinc burnoff, and some gassing in the metal, and then found out that boat shaft brass/bronze has terrible stiction, which makes it unusable for bearing material.

My brass/bronze melts basically uses about as much heat as melting cast iron, and so I tried cast iron.
I had all sorts of problems with cast iron in the beginning, because I was running an oxidizing flame, I did not know how to add scrap correctly to the melt to minimize slag, did not know how to correctly tune an oil burner, did not know what fuel flow to use, and did not know about ferrosilicon.

Having solved all the cast iron problems, I use it exclusively for engine parts, since it wears very well, machines extremely well with small chips, does not smoke as it is melting, does not have any significant gas issues that require a degassing agent, and as the saying goes "it wears like iron", ie: it has graphite in the metal, and so wears very well.

At some point, I do want to make bearing bronze, and I will try it without the glass first.

Your second photo does appear as if there is impingement on the crucible; as if your burner centerline is several inches above the bottom of the crucible. Is this the case? or did something else affect the crucible?

Some combinations of alloys may not be good combinations, and that could cause what appears to be foaming of your metal.
Perhaps others can comment on the brass/bronze side of things, since I am not really up on that.

.

I have taken a pic showing how the burner is deployed. I put a piece of white pipe into the entry tube to show direction.
This is to the side and only skims the base of the crucible.

 

[creast]

Looks like a foamy slag coating (skull) on the cruicible, not the cruicible material.

You can try to cut some slit with a dremel tool or stone cutting disk (careful the dust is not healthy) and chisel the skull out with a small chisel.
Very easy to brake the cruicible in the process. For a clay graphite cruicible possibly not worth the effort, because they are not overly expensive.

I would consider to just put the cruicible aside and give cleaning a try if I was melting any thing else anyway.
Then you might try to remelt (reheat) the stuff and remove it in heated condition, but slag can be quite stable in high temperatures.
Figure out some way to hold the cruicible when trying to remove the slag.

They used O2 burner tubes to put slits into the skull and then one of these to remove the slag.



Wrong slag on top of the melt can ruin refractories quite quickly.

For big steel casting ladles sometimes different grades of refractory are used in the slag zone to keep wear at reasonable rates.

Greetings Timo

Fascinating stuff! Thank you for your input.
However, after chipping away the thick skull on the lip of the crucible you can see that massive honeycomb porosity extends all the way to the outer skin of the crucible and extends a good way down.
The initial lip was like pumice and easy to remove but digging deeper was more difficult but nonetheless showed the crucible as trash.
Time to get the credit card out!
Rich

 

[GreenTwin]

If the red circled part of your crucible was nearest your burner output, then I would say this is impingement degredation.

If this occurred elsewhere, then it would not be impingement.

You could angle your burner tube a bit more to the outside.
It is easy to patch the back wall of the furnace due to impingement, but more expensive to replace a crucible.

 

[GreenTwin]

Fascinating stuff! Thank you for your input.
However, after chipping away the thick skull on the lip of the crucible you can see that massive honeycomb porosity extends all the way to the outer skin of the crucible and extends a good way down.
The initial lip was like pumice and easy to remove but digging deeper was more difficult but nonetheless showed the crucible as trash.
Time to get the credit card out!
Rich

Wow, that is some serious crucible trouble there !

So that makes me wonder if that was really a Morgan Salamander-Super, or a lesser crucible.

If that was a Morgan SS, then that is the most corrosive slag/metal I have ever seen.

I would had to fry a brand new Morgan just to find out it was highly corrosive slag.

.

 

[creast]

Wow, that is some serious crucible trouble there !

So that makes me wonder if that was really a Morgan Salamander-Super, or a lesser crucible.

If that was a Morgan SS, then that is the most corrosive slag/metal I have ever seen.

I would had to fry a brand new Morgan just to find out it was highly corrosive slag.

.

Hi Pat,
That's not the impingement area but may be an artifact from the electric furnace but I am sure it's not from the diesel furnace as I have three other crucibles and they show no distress.
As you can see on my last photo the flame skirts around and down below the crucible. Using a bigger A5 Salamander crucible which does get worse impingement has not shown any distress either and that was on my first iron melt.
I do suspect either a poor crucible or some weird attack on its structure with my bronze trial.
Time to buy another crucible and ensure it is legit Salamander and repeat the trial.
I was hoping Luckygen/ 100model could advise as he did the silicon bronze melt that inspired me to try and maybe he had seen something similar?
Rich

 

[GreenTwin]

He does not have easy internet access, so it may take a few days for him to comment.

.

 

[creast]

He does not have easy internet access, so it may take a few days for him to comment.

.

Thanks

 

[100model]

I was hoping Luckygen/ 100model could advise as he did the silicon bronze melt that inspired me to try and maybe he had seen something similar?

That is a really bad slag build up on the top of your crucible and I have never seen that happen when I make silicon bronze. It maybe that it is a poor quality crucible and with extra heat output it has gone way past max temperature.

Years ago I was given a crucible and did a aluminium melt with it and after the melt it looked really bad after one melt. Crucibles like that I would never use for iron melting.

Oxides of iron, copper and lead are corrosive to clay graphite crucibles but aluminium oxide does not effect clay graphite crucibles. Fluxes are very corrosive to to clay graphite crucibles so it is up to you if you want to use them. I have never used one but silicon carbide crucibles are more resistant to flux corrosion. Sand will neutralize oxide corrosion but it means that more dross needs to be scooped off before pouring.

 

[creast]

That is a really bad slag build up on the top of your crucible and I have never seen that happen when I make silicon bronze. It maybe that it is a poor quality crucible and with extra heat output it has gone way past max temperature.

Years ago I was given a crucible and did a aluminium melt with it and after the melt it looked really bad after one melt. Crucibles like that I would never use for iron melting.

Oxides of iron, copper and lead are corrosive to clay graphite crucibles but aluminium oxide does not effect clay graphite crucibles. Fluxes are very corrosive to to clay graphite crucibles so it is up to you if you want to use them. I have never used one but silicon carbide crucibles are more resistant to flux corrosion. Sand will neutralize oxide corrosion but it means that more dross needs to be scooped off before pouring.

Thanks for that.
I will have to purchase a new one.
A quick question about the silicon bronze. I found the ferrosilicon seemed to take an age to be absorbed, in fact I thought the gooey dross was possibly mainly ferrosilicon.
Did you experience that?
The end result was still a bronze in colour and although strong was very ductile.
Rich

 

[100model]

A quick question about the silicon bronze. I found the ferrosilicon seemed to take an age to be absorbed, in fact I thought the gooey dross was possibly mainly ferrosilicon.

I know a few backyard metal casters who use pure silicon and they complain that takes a long time to dissolve in copper but for me ferrosilicon dissolves in a few minutes.

The end result was still a bronze in colour and although strong was very ductile.

This is why I use it because it is a low melting point substitute for steel.

 

[creast]

I know a few backyard metal casters who use pure silicon and they complain that takes a long time to dissolve in copper but for me ferrosilicon dissolves in a few minutes.

This is why I use it because it is a low melting point substitute for steel.

Thank you for that information.