Thin brass casting failed more times after first success

In an earlier topic I was happy that I succeeded to make a thin brass casting, so I repeated a few times without success. I heated the metal more to 1100+ C to make it more fluid what was indeed the case and now I made four gates each 90 deg apart and it almost filled. Yes, almost. Attached photos taken from top and bottom show that more metal flows met each other and froze when they met each other befor coalescing.

Should I heat even more ?

Top views





Bottom view

 

First guess would be to heat more. I have seen issues with multiple ingates like this before. Giving the molten metal too many places to go where it will sit and cool off until it gets pushed again is an issue in multiple ingates. Usually bring the temp up will eliminate the cold shuts. Sometimes one ingate will fill the casting much better than multiple ingates just because they create a gas pocket in the middle where they meet and gas cannot escape. Sometimes having medium temp metal fronts meeting together will not mesh back together. This part just looks like it trapped gas and needs vents. The thin flashing made fine but the thicker casting did not. Probably trapped gas inside it. Try one ingate on one side and a vent on the opposite side going out of the top of the mold. How thick is this part?

 

everything Billy said

and

1) increase the head pressure
2) switch to an alloy that flows better (Anything with more Silicon)

V/r HT1

 

I think Billy Elmore has good tips. The thickness is 2mm (.08").
BTW, I am talking about brass, not cast iron in this case.

EDIT: Attempt 2: Vertical casting, but to no avail.

 

Mo(u)ld dressing of graphite + zircopax and bentonite in Denatured alcohol, then flame it off? Is the damp sand chilling the metal? Like you want a dry or core sand mo(u)ld?

Perhaps phospor-copper?

 

Zircopax ? Is that ZrO2 ?
Should I coat the pattern with bentonite + alcohol before applying molding sand around it ?

 

Those were guesses on my part. My reasoning: a thin-walled casting doesn't have the mass, and the resulting stored heat in the molten metal. It needs to stay above a certain temperature to flow together and mingle. Water takes a lot of heat energy. If you reduce the amount of water your metal needs to evaporate, your metal will stay "molten enough" longer.

Graphite and zircopax (pottery supply; supposedly, it's mostly zirconium oxide) are both strong refractories. The thought was to make a smooth(er) surface finish and let the molten metal stay molten (A little) longer. The bentonite was due to someone (poor memory on my part) spoke of proper mold/mould wash needing to have it to "work."

The alcohol is a flammable solvent and carrier. Igniting it will drive off/away the water in the surface layer of the mold/mould.

 

The first (successful) one seemed more "reddish" than yellow to me.

"Brass" seems to mean anything with zinc in it, E.g. "red brass" - ounce metal, or 85-5-5-5 - tends to be reddish... yellow seems to want a fair bit of zinc.

That said, zinc, lead, and maybe tin seem to be burnt out of cuprous alloys during melting, so up you ARE right.

 

Yuck.

 

I work with 60/40 and 70/30 all the time , slip some silicon, evendur in and you can break the minimum thickness 3/32 over small areas , but right now it looks like your zinc content is in the 5% area, at the very least below the tin content , and tin is very hard to burn off , as mentioned above if you are melting the same metal over and over, you have lost a lot of zinc ,
but reality sets in, you are fighting an uphill battle , you are trying to cast thinner then intended , if you get everything perfect, you can pull it off, but it will be hit and miss, better off to alter the pattern, and make it a little thicker, so your results will get more constant.

V/r HT1

P.S. I'm always reluctant about announcing a pattern ready to go til i have cast it a couple of times. you have to watch out for "beginners luck"

 

I see JAPAN on one image. Is your pattern a stamping? If you have two and can stack them you'd get thickness easy to cast.

 

Sharp little beady eyes you have!

 

They're close together, too.

 

The first casting is remelted (over and over again) brass from plumbing parts.

But now I used bronze which is rather copper-ish (10% tin, rest copper), I did it last week without success, but now I'm nearly there, there is still a casting error near the gate.

I used phosphor bronze. I have a recipe for it: (NaPO3)6 sodium metaphosphate with aluminum powder and silica heated at 700C will yield phosphorus vapor. So I wrapped 1 gram of this mixture in thin copper sheet and immersed in the already molten bronze and let it stand another minute to dissolve everything. I had the mold almost in a 'normal' position, but tilted about 15 degrees and it almost filled and the surface is also much smoother. And the JAPAN label also appeared. The pattern is a lid of a plastic box for a photographic filter, obviously made in Japan.
The mold did not completely fill (too few metal), so next time I'll add more metal.

 

"Brass" from plumbing parts might be an alloy like 85-5-5-5 - which tends look reddish rather than yellow, supposedly. In some circles, this alloy is/was called "red brass."

 

I could be wrong but I think the gating that extends below the casting may have pulled metal (shrink) from the casting. The casting had to be solid to have pushed that much metal out the vent. It is also at the hottest spot on the casting which froze last. Thats a tough little job to make!

 

You mean these are shrinkage errors, despite the rather large sprue ? The metal was almost 1200 C when I poured it in the mold.
My next attempt will be more metal, so the sprue is higher, so hopefully the shrinkage takes place more in the sprue and that freezes the last ?