Brass casting crucible question

[Hemo]

I think I need some knowledgeable advice from a brass caster. I'm about to pour an ornate pistol sideplate and thumbpiece in brass using Delft clay--my first attempt at this. Because of the volume of brass needed for the sideplate, I will be heating the brass in an appropriate sized gray graphite crucible in my electric Neycraft oven. Looking at a couple of sources, including recommendations from Rio Grande jewelry supply, where the crucible came from, it looks like they are recommending melting borax in the crucible and coating its surface prior to melting brass to prevent the brass from sticking to the crucible. In an apparently different operation, others recommend heating or "seasoning" the crucible to red heat prior to use.

Does anyone have any recommendations about these processes? I tried heating some borax flux (not powdered laundry type borax) in my crucible in the oven, but after bringing the temperature up to maybe 1000 degrees F, it looks like the borax foamed up, exploded, and solidified in fluffy looking chunks all over the interior of my oven. It didn't appear to liquify, and the stuff sort of resembled expandable foam insulation. It was hard, but crumbled easily to powder and cleaned up without any problem. Crucible still looks good.

What should I be doing before I proceed with my first pour?

Gregg

[Eric Kettenburg]

I am no "professional" when it comes to casting, but I have run a lot of castings into both green sand and later petrobond out of an open charcoal forge using small graphite crucibles.  I used plain old 20 mule team borax as a flux (yes, the boxed laundry stuff - pure borax, no soap included) and an old stainless spoon riveted to a long piece of steel as a skimmer.  I went by "eyeball" heat, could not afford a pyrometer at the time although they seem to be much cheaper now.

When the brass began to melt, I'd throw a small handful of borax into the crucible.  It never foamed or exploded or anything like that, it just melted and ran all over the surface of the melt.  Once the brass appeared to be at proper temperature and fluid, I'd use the spoon (which was heated to a low red heat in the same forge - do NOT use cold!) to skim off the surface immediately before pouring.  That's about it.   

[45-110]

ditto to what Eric says. i have done it with coal and charcoal and 20 mule team. the hardest part for my castings was judging. the correct pour temperature. my parts came out nice. don't get it too hot or all the zinc burns out of the alloy.

[smart dog]

Hi Hemo,
You should glaze the crucible with flux before melting any brass.  Although I have an oven, I simply used my acetylene gas torch to heat it to melting and swirl it around the crucible.  Also Gregg, at Dixons I had trouble with my casting because the bench was not level.  Gravity flow does not go up hill very well.  Make sure your mold is level, particularly the large sideplate.

dave

[44-henry]

I second the suggestion of using an oxy acetylene torch for melting. I have a small Rio Grande melting furnace and two large gas melters and for fine work I find a torch and melting dish held with tongs is much easier to control. I like the casting flux I buy through Rio called Matt's Casting Flux, works great on silver also.

https://www.riogrande.com/Product/matts-casting-flux/704099

[mark brier]

I agree with what Eric says. Sounds like he and I do the same. I also use plain 20 mule team and the foaming bubbling you talk about is just water moisture in the flux.
Mark Brier

[Ed Wenger]

Agree with Dave & Eric.  I melt brass like you plan to, with a Neycraft oven.  One thing I've found that helps with side plates is to utilize a riser on one end of the mold.  This seems to help well with venting and flow.  Good luck, keep us posted!


            Ed

[Hemo]

Thanks for your input, all, that was very helpful.

Dave, when you say you use your acetylene torch to glaze the crucible with flux, are you applying heat directly to the flux in the crucible, or  heating the crucible from the outside?

Also, Ed, could you clarify what you mean by a riser? Is this just a large vent? I certainly plan to make several small air vents in the clay mold at the periphery of the parts.

Gregg

[davec2]

[Hemo]

Thanks, Davec2, that video shows just what I was looking for in terms of glazing.  My crucible is the big gray grainy pot variety, but should work the same, I expect.

Gregg

[Eric Kettenburg]

I don't know anything about casting gold and that looks like some form of ceramic dish, not the dark graphite that is typically used for brass casting.  Interesting video but I think it is completely unneccesary for casting brass in a graphite crucible, and I've never had any problems with molten brass or silver sticking to the graphite.  Also, I was told by someone long ago - can not remember who - that the borax used as flux does slowly attack the graphite and I think this is born out to some extent as usually after a melt there will appear something of a 'ring' around the inside exactly there the layer of borax flux was sitting atop the melted brass.

The graphite crucibles eventually get visibly thinner to the point where they make me uncomfortable so I just toss them and get a new one.

[Hemo]

I don't know anything about casting gold and that looks like some form of ceramic dish, not the dark graphite that is typically used for brass casting.  Interesting video but I think it is completely unneccesary for casting brass in a graphite crucible, and I've never had any problems with molten brass or silver sticking to the graphite.  Also, I was told by someone long ago - can not remember who - that the borax used as flux does slowly attack the graphite and I think this is born out to some extent as usually after a melt there will appear something of a 'ring' around the inside exactly there the layer of borax flux was sitting atop the melted brass.

The graphite crucibles eventually get visibly thinner to the point where they make me uncomfortable so I just toss them and get a new one.

Dang, Eric, now you've got me all confused again!
(They say a man with one watch always knows what time it is, but a man with two watches is never sure.)

Gregg

[davec2]

Hemo,

All crucibles, ceramic, graphite, whatever.....are a consumable item.  They all get thinner and eventually are unusable.  All will work glazed or unglazed.  In my experience the glazed crucibles work better and last a little longer.  One way to avoid the type of deterioration that Eric is talking about (where a layer of borax flux is floating on top of the molten brass) is to use powdered charcoal floating on top of the brass to keep the zinc loss to a minimum.

[Ed Wenger]

That's good to know about the charcoal, thanks Dave.

Gregg..., yes, a riser is basically a big vent.  I use a piece of 3/8" ram rod material for risers, which is probably a bit of overkill, but works well.  Also, on side plates, with a sprue going into the center, I use a riser on both ends and dispense with other vent holes.



          Ed

[Eric Kettenburg]

It is interesting that you mention that about the charcoal.  I've done this all in a deep charcoal forge, and believe me, there is no problem getting a layer of powdered charcoal inside the crucible.  And all over everything else as well!

[Bill Raby]

I never bothered to glaze a crucible. I always used boric acid instead of borax. Doubt it makes any difference. Instead of using the furnace to melt the metal, use it to heat the mold to about 650 to 1200 degrees depending on thickness and shape. Then melt the metal with a torch. Flame on metal instead of outside of crucible. Problem with melting metal in an electric furnace is the high temperature will burn out the heating element faster. Acetylene really is not a very good fuel casting metal. It can cause all sorts of weird reactions with metals at high temperatures. Usually making it more brittle than it should be. Hydrogen is ideal but propane or natural gas will be much better than acetylene and still plenty hot for brass. No need to spoon off the flux. it will stay behind as you pour the metal.

[JCKelly]

That stainless spoon . . .  it will last a lot longer if it is the cheaper grade (18Cr no Ni) which just happens to hold onto a magnet

The better grade stainless ware, marked 18/8 or 18/10 can just plain fall apart in molten brass/(any molten copper alloy)  This better stuff is only slightly magnetic.

Charcoal should be the stuff that actually looks like chunks of wood that have been charred. Kingsford charcoal briquettes contain a bit of petroleum coke, which means sulfur. Sulfur likes copper but you may not like that like so much. 

30+ years with stainless & nickel alloys at high temperature.

[Eric Kettenburg]

Everything I have is "cheaper" grade!   

[Mike Brooks]

I'm glad I have a little foundry close by that will cast anything I want, sure saves me a lot of work!

[Buffaload]

Just brass Mike or will they do ferrous alloys?
Ed