Replicate sea shell in brass: incomplete

So I tend to do things different from a lot of people.LOL Like with these I would not pour into the thick section. On really super thin castings you will need to put the hottest metal in the thinnest section to get it to fill. You will have no problem filling the thick part after the thin but will have issues pushing the metal from the thick to the thin without it freezing off or trapping air/gas to stop the metal flow.

 

Well, how thick is the gate going into the skillets? I think it's about an inch wide but looks like about 1/16th of an inch thick or less.

 

Depends on which one you are asking about. Usually between .062 to .040 but some can be as thick as .125. If you look you will see the thickest parts usually have no gating. We did turn one job upside down...handles down.. and poured into the handles...it did ok but would misrun the top if they dropped temp 20 degrees....which happens often when you are running the machines at 600mph. I was thinking about doing a simulation on one just for fun but havent found a suitable stl file.

 

That's the other thing, in watching the "pour" or injection from the tundish (if you call it that), It only takes a couple seconds to fill a 2 skillet mold. If I try to pour that fast, it goes everywhere.

 

Yes..getting the metal in there before it loses temp is very important. That speed (velocity) often causes inclusions though. The trick is getting the volume needed to fill the casting in there quick enough to make the casting complete while trying not to increase velocity so high you cause oxides and gate wash. With the velocity we require we have to have very good molds to prevent gate wash. If you use a large pouring basin it will make it easier for you to pour at the rate you need to fill the casting. Usually around a second and a half of the desired pour rate is sufficient....but bigger is easier and doesnt hurt when hand pouring.

 

You are talking about 'gate wash' ? Is that erosion, so the quick metal flow erodes the gates ?
Now I am almost there, even when poured on the base of the shell (which is slightly thicker). The error now is that the third riser (meant just for venting) was probably not connected with the cavity of the shell. During pouring, the first (top) riser filled instantaneously and the second (center) after that. The third was located at the red circle.
To prevent premature freezing, I heated the metal (silicon bronze) to at least 1200 C, well above the melting point.

 

And here the final castings. Left to right:

* The castings in green sand from my previous posting sawn off the sprues.
* The original sea shells made from ceramics.
* The castings (just with sprues only removed from the mold and wirebrushed) in the orange 'Delft clay' which are smoother, but after pouring the sand stinks to oil.

The last one I did yesterday twice. Reason ? The new batch of silicon bronze did not mix.
I made a pre alloy by arc melting ferrosilicon using a welder and about the same amount of copper and heated it very hot. And yet a gooey stuff, so I poured the remaining liquid onto a brick which froze at a really low temperature (ca. 800 C).
Then I melted fresh copper and after melting I added the pre-alloy but when pouring (it was really hot, 1300 C) , another blob of gooey stuff appeared from the crucible and the remaining metal was oily, so obviously the casting failed.
The temperature of 1300 I guessed by the color inside the crucible. A thermocouple outside the crucible opposite the burner entry point showed 1500 C, so inside the crucible it was cooler.
So I melted this casting, mixing with leftovers of earlier silicon bronze castings and now it was very fluid which resulted in the succeeded casting. Three of the four risers really rose to the top.
But the color of the metal was almost pink, like pure copper.
Probably it de-alloyed, so I actually cast copper ??
Where is the FeSi gone ?? Maybe in the sticky slag which I removed from the crucible after pouring ?

 

How are you measuring your temperatures?
I dont think your bronze dealloyed. Im dont know how that would happen if the silicon dissolved in the metal you started with.
Often bronze can have a copper colour on the surface after casting. Dont know what causes it, maybe the rate of cooling or the absence of oxygen. If it is just on the surface if you file it you should see normal bronze colour underneath

 

Exactly, I tried that, and it appeared only slightly less pink (i.e. copper pink with a bronze color tinge) than pure copper. And what was the gooey stuff which clearly separated from the metal like oil slick on water (which I did not remelt) ?

I measure temperature in the furnace chamber, next to the wall of the crucible on top of it, opposite the flame entry point in the furnace. That temp went 1500 C according to my 'S' type thermocouple (I cannot use 'K' thermocouples at these temperatures).
And guessing the rate of incandescence, inside the crucible was more yellow than the TC probe, but well whiter than freezing copper, so hot enough to pour this alloy (99% Cu ??) in a thin mold. I cannot immerse the thermocouple in the metal as it has an alumina sheathing.

Here a picture of the frozen crud / gooey stuff.

 

If the gooey stuff was indeed the silicon and the temperature was high enough the only other explanation is that you didnt leave it long enough for the silicon to dissolve. It takes time to dissolve same as if you dissolve sugar or salt in water. And from what Ive learned the silicon does dissolve rather than melt as I believe the temp needs to be close to 1500 c for it to melt. Was the volume of the gooey stuff similar to the volume of the silicon you added. If so then the gooey stuff probably was the undissolved silicon. I tend to use silicon grains when I make bronze, as they dissolve faster.

 

My method for making silicon bronze is to first melt a couple of small ingots of silicon bronze in the crucible then add the silicon (as pure as I can get it) and manganese. I then allow it to dissolve and then gradually add the copper. Stir gently to make sure theres no solid stuff left, skim and pour.

 

Well, I just melted the frozen gooey with an electric arc (welder with carboon rods) to make much higher temps (1500 C or more) quickly and then I drained off the white hot liquid into water. It resulted in bronze yellow colored beads. Now I hope I can dilute this alloy with some copper.

 

probably your silicon contaminated with a bit of copper

 

That looks like general dross created from oxidation of the metals and other contaminants

 

You dont really know what this alloy is ratio wise, so not ideal to use it as your starting point. I would start again, measure everything out carefully melt some known si bronze in the crucible then add the measured stuff to it. That way you will know exactly whats in there. I wouldnt bother with the arc welder as it isnt necessary. If you dont have some si bronze to start with then start by melting your copper covered wth some form of carbon. I think coal coke or wood shavings stuff like that is often used

 

The very first time I made Si bronze I just measured 100 wt. parts copper with 3wt. parts Ferrosilicon (=0.75% Fe and 2.25% Si) and 1 wt. part Manganese metal.
Then I melted the copper with charcoal pieces floating on it, added the FeSi (grains of 5-10mm size) wrapped in a napkin, stirred a bit with a steel stick, waited a minute and then I poured.
Then some dross / slag appeared, but the metal was OK.

The second time when I did it with the pre-alloy, it went wrong, maybe the extreme heat of the electric arc and the air oxidized too much FeSi. Or maybe because I forgot adding charcoal at the copper melt.

What is the purpose of the Mn metal ?

 

not 100% certain but I think I remember reading that it improves castability by making it less viscous but could be wrong about that
https://www.belmontmetals.com/product-category/everdur-silicon-bronze/

 

Weird.
I crushed 12 grams of FeSi to smaller grains and added 2.5 g Mn chips.
Then I melted 260g copper with charcoal on top and when it was molten, I added the crushed FeSi and Mn. I stirred it with a bamboo stick (which reduces as well as it decomposes to carbon) and poured it out after a few minutes.
But it did NOT alloy: the alloy remained pink (after filing off the scale.
The adding of FeSi was like adding sugar to water and stirring, the latter does dissolve ....

 

If there was no solids in there when you poured then it would be an alloy. Maybe the pinkish colour was due to the quite high iron content. I dont use feSi myself I use a high purity Si which is well over 99% Si.

 

Finally I managed to cast the same shells in cast iron.

https://www.metallab.net/forums/Ironcast-20221112.mp4

Here a few photos. After casting, the cope was still intact....