Starting out on copper alloys

Hi,
Casting newbie here, I have tried asking uncle google for help but I must not have typed in the right keywords, so I came here. I have just started out in casting with a 10 kg devilforge, I am trying to cast copper and brass using a green sand mold, but I am getting very rough surface finishes. I initially tried lead, then worked up to aluminium and had reasonably good results with them, the aluminium was a little porous but still had good detail, but the copper alloys are really rough looking.
Is green sand a valid casting medium for copper alloys or do I need petrobond? Would baking my molds help? Something else I am completely missing? aluminium, ok but with some pores
A copper, really rough, no detail poured this one too cold, but still the rough finish we have figured out that this gating system won't do, but still, the rough finish.

I am pretty sure we made a series of standard rookie mistakes here.

 

Green sand is fine for anything you can melt in your furnace: aluminium, copper alloys, iron etc.. Pure copper tends to absorb oxygen and become too thick to pour well, so any bronze with some alloying element like silicon, tin, phosphorous will cast better than pure copper. Aluminium if you cook it too long, will absorb hydrogen from the combusted fuel's water vapor and cause porosity bubbles on cooling. Those copper and brass samples all look like they could have been hotter when pouring, this is a real pain with smaller crucibles that can cool too fast before pouring.

 

The penguin with no beak was definitely to cold; I scooped off what I thought was slag, then later inspection revealed it was short, unmelted pieces of copper wire from the last bunch of motor windings i had shoved in the crucible. Oops.
Is the rough finish also a sign it's too cold?
I am doing these out of copper because I have been spending some shed time with my kids, and have found they love taking stuff apart, so I got them some old electric motors and they have been harvesting the copper from them. They love it, they get to use my tools and find hidden treasure, making the penguins was for them to see the fruits of their labour, so I would like to make the copper work if possible.

 

It's hard to tell what the first photo alloy is, I thought it was aluminium. Rough casting finish could be a number of things but it looks like metal that was cold enough to be partially solidified when poured. Was it glowing bright orange-yellow with maybe green flames coming out the furnace before pouring?. Copper not going to work well at home without alloying something into it to improve fluidity or in the case of phosphorous: deoxidize the copper and improve fluidity. Just add some old pewter (mostly tin) or zinc (boat anodes) to get brass or some phos-copper brazing rod to get a suitable alloy. Be careful adding the alloying metal to the copper, one member here does brass all the time and had a steel tool to plunge the brass below the copper surface to minimize fireworks.

 

Mark is right, try silicon bronze. Pure copper is a pain in the ass.

 

Apart from lots of surface area using motor windings they also enamelled leading to a lot of dross.

 

if you can cast aluminum, you can cast COPPER BASED ALLOYS , and you do not need to go to the most expensive end of the spectrum Silicon Bronze , red or yellow brass is perfectly doable tin bronzes will require degassing with phosphor copper https://www.budgetfoundrysupply.com/phosphor-copper-shot
but you have to get a pyrometer!!! here is a video with links for mine:
you have to be able to take proper temperatures

try to leave alloying your own metal from copper alone for a while , and just get some scrap brass, keys are perfect, you can also mix pre 80's pennies and post 80's pennies in a 60 40 ratio, and get perfect brass for casting , just to get you started , or hustle some pipe fittings ,

leave pure copper and even industrial copper alone it's difficult because of the rapid oxidization to get sound castings

if you have a bunch of copper and want to use it , start with at least a half crucible of brass available
, place the copper in the bottom of the crucible, mix in zinc in a 60/4 or 70/30 ratio new pennies are 95% zinc , but you can also grab up some zamak (zinc at about a 95% ratio, with aluminum, which is a non issue for ornamental work)

cover the copper and zinc with brass, so the brass will melt atop of the copper shielding it from oxygen, this will give you a nice yellow brass


V/r HT1


P.S. part of the issue with the rough surface finish maybe from wet green sand , remember green sand molds often need to be preheated to drive the moisture away from the surface just before closing the mold, and the mold should be closed as soon as possible before pouring

 

Kudos to you for getting the kids out to the workbench. Ive carried some of my early boyhood experiences with me through my whole life. Just a word of caution, any molten metal can pop or splash at high speed out of a crucible, sand mold, or ingot mold and it is absolutely unforgiving, so be sure you have fully appropriate PPE and bystanders and dogs are at a safe distance. I know it gets hot where you live but you’ve got to be covered.
As far as metal temp goes, when you pull the dross back the surface should be shiney. When it pours, it should be very fluid. Aluminum and copper won’t flow like water, obviously, but neither should be sluggish.
I’ve never poured straight copper before so I don’t know how it acts when poured, but I have melted copper wire to make alloys. Copper oxidizes very quickly so in addition to the enamel crud Peedee mentioned above, you will get a good amount of dross too. Melting very small amounts can be a losing proposition in that regard. Exposure to the atmosphere is key, so once you have a molten pool, immediately submerge your additions as much as possible and don’t start skimming until you have to.
My first real question though is about your sand. Exactly how is it made, and how much moisture is in it?

Pete

 

Thanks for all the replys guys, I'll start trying to digest some of that info.

The top picture is aluminium, bottom 2 are brass, all others are copper.

Don't worry, the kids are well away when casting. I am concerned of the fumes so they watch from a distance.

Pennies; those are hard to come by here, all our colonist coins are steel cores with copper nickel alloy coatings, or aluminium bronze (New Zealand money) But I think I can possibly source some zinc from somewhere, maybe a hot dip galvanising company.

My sand is something I am reasonably confident I have got right. I bought some builders mortar sand, screened it through some 250 micron mesh (about .01"), then added ground up kitty litter and water at the google recommended ratios. It passed the "squash it in your fist and cleanly break it test" as far as I could figure. It doesn't stick to my hand, but sticks together with good stability.
I have not baked my molds, I have dug an old miniature oven out from the back of my shed and plan to try bake them for the next pour this weekend.

Will check out that pyrometer as well, we were tossing up getting one of those, would be better if we could make one on the cheap.

Thanks again for the advice, much appreciated.

 

There was a thread around here someone with the info on the mifco t-couple prob in Ht's video. Mine cost around 60bucks I think. It works great on a 5buck chinese meter.
https://www.ebay.com/itm/US-TM-902C...438869?hash=item4b8eddaa15:g:B0MAAOSwAblgTFUQ

Oh look, it's 9bucks now! You can still get it for 5bucks if you are willing to wait on the slow boat from whuflu land.

 

I couldn't resist, I gave copper another go.
I tried baking the mold in the oven for a half hour this time. That seemed to help. The detail is better, the surface finish is a little rough and there are a couple of embedded grains of sand. I will give the brass a go next weekend and see what difference that makes.

 

Pure copper pours well, as long as you keep oxygen away. That can be achieved by putting charcoal chips on top of the metal. I have good experiences with it. Bronze is also very good as is aluminum bronze (92% Cu + 8% Al). Brass has lots of dross and zinc fumes, use a respirator.

 

yellow brass is not drossy , if you get dross from yellow brass, your metal was dirty, or your furnace atmosphere is wrong

If your are referring to red brass (tin bronze or leaded tin bronze ) its drossyier, but not at all bad if your metal is clean and your furnace atmosphere is correct

No "Brass" like to be stirred or agitated, so if your furnace has some reverb ( Your vent is too small) you will get some dross,

melt as fast as you can in a neutral atmosphere, do not overfill your crucible, DONT overheat the metal . you will get little to no dross

V/r HT1

 

I have been using glass to keep the oxygen off. I read it in an old home foundry book, a couple of shards on top, which melts and coats the surface.

 

Seems a good idea, but glass eats crucibles.

 

Worse than flux?

 

I will never get the attraction to pouring pure copper. Other than you can get material at HD or blowes.
Silicon bronze is 94% copper, it pours like a dream with no weird surprises. I'm no metal guru and even a bone head like me can get near perfect results right out the gate.
No glass cover needed and the only thing you have to watch is don't melt it with a super lean furnace or you will get a crappy surface finish. (that means very little flames out the exhaust)
You don't want it going smokey joe on you, but you need to see the flames just licking out the hole. Furnace control is key. As HT1 said, do not overheat your metal.

 

Youtube!!! a P!ss P00R Metal caster with 800K subscribers has made casting copper from scrap into ingots a big deal, much like KOR made doing dangerous stuff with molten metal popular.

Basically a talentless metal caster, with great video production has managed to get viral, and game the YouTube algorithms . People are motivated by their success :-(


one of the biggest deals in youtube land is being able to put up videos regularly , if all you are doing is making ingots, it's pretty easy to get a video a week, when you start making real projects, once a month is a major challenge, that is why I floated the idea of a group of us creating a channel together so video's could go up regularly ,

much like we get people wanting to cast steel swords, because they saw it on Conan

V/r HT1

 

That cost me 20 minutes going down that particular rat-hole, thanks!

 

I believe that’s the reason most decorative or fine finished copper items are hammered or otherwise tooled.