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Author Topic: Casting brass?  (Read 21388 times)
elShoggotho
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« on: August 24, 2009, 09:06:10 am »

After experiencing problems with sawing through a block of brass, I'm contemplating to simply melt it down and cast the piece I want.

Now there's a bunch of problems.
First off, I'll need about 950 degrees C to melt it. That can be solved in several ways, the easiest would be to acquire an enameling oven.
Second problem, the cast. I'm contemplating a disposable cast made of sand, bound with something that can withstand the heat of molten brass. What to use for that???

Right now, it's just a thought experiment though.
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Dr cornelius quack
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« Reply #1 on: August 24, 2009, 09:26:35 am »

From what I can recall of my old foundry practice lessons back in the mists of time, Brass casting needs a furnace with a good deal of power to heat the metal quickly. The zinc has a tendancy to oxidise before you get the mix fluid enough to pour otherwise.

What about investment casting using a lost wax technique?

Or you might look at the method of cutting a cuttlefish bone in half and carving the desired shape into that with suitable runner and riser.
I've never seen it done, but it is used for small one-off pieces.

Some info here:

http://www.metalwebnews.com/howto/cuttlebone/cuttlebone.html

Dr. Q.
« Last Edit: August 24, 2009, 09:28:55 am by Dr cornelius quack » Logged

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elShoggotho
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« Reply #2 on: August 24, 2009, 09:43:49 am »

The sand cast would best be made in lost wax technique, you're right.

Cuttlefish bone would be nice in and by itself, but the pieces I need are larger than that.
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sidecar_jon
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« Reply #3 on: August 24, 2009, 10:13:36 am »

oddly i was discussing casting the other day with a very capable friend, who's fixing to cast a boats centreboard case in Bronze. his solution to not having anything hot enough to melt bronze is to make a small insulated tin can (fire cement with perlite in it) and have the crucible surrounded by coal or charcoal and forced air into the lit coal from a vacuum cleaner. I have heard of people melting metal in microwaves to that might be worth looking up on google.

casting wise my brother has cast a lot of jewellery using cuttle fish and it works but leaves distinctive wavy surface. Nowdays there are silicon flexible materials that will withstand molten metals if you want to cast a few and want added detail.
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H. MacHinery
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« Reply #4 on: August 24, 2009, 11:39:08 pm »

I don't know enough of metallurgy to know if this is useful info, but Make Magazine (www.makezine.com has a piece about "lost foam" casting with aluminum (aluminium to you Brits  Grin).  Might be worht a peek to see if it's relevant.
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Wisconsin Platt
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« Reply #5 on: August 28, 2009, 09:47:11 pm »

Have you poured over http://backyardmetalcasting.com/ yet.   
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« Reply #6 on: September 03, 2009, 12:48:44 pm »

I know from casting pewter thingy bobs that an enamelling kiln is not hot enough for casting brass... what a friend of mine does is he built a kiln outside out of fire bricks and stuck a large set of bellows on to feed air in to the fire and bring the temp up. We know from experience that if you’re doing it this way is handy having someone on the bellows and one person to pour the metal. As a different solution to bellows I once saw a mock up of an African furnace where the air was fed in by a bicycle turning a blower which fed straight in to the fire... it looked very cool  Grin
As for moulds sand casting and lost wax casting are far the best way. But another mould making material is green/blue soapstone. I hand carve all my moulds of this stuff and get reasonable results.     
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ThorsFoundry
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« Reply #7 on: September 06, 2009, 01:56:59 am »

want to do it with gas, Google Ron Reil
Want to do it with charcoal, that backyardmetalcasting site is a good one.  You can make a dirty furnace from a hole in the ground.  Not efficient, but it works.

You can make a crucible from a piece of steel pipe. 

If you successfully melt brass/bronze.. watch the melt.  don't heat it until it boils the zinc.  When/if you see GREEN smoke/fire, it means you are boiling the zinc.  DO NOT inhale that smoke.

IF you melt it and it is hot enough (you can tell thru a good pyrometer or by color if you have experience),,, you'd better be ready to pour!  Sand is a good mold, but not just sand - it's called greensand, and it's a mixture of sand, fireclay (or bentonite), and water.  It makes the sand stick together, but it cannot be wet. 

*there's a lot to it*

Sand size matters, due to porosity of greensand, bite or hold or STRENGTH of the mold, and or surface finish.  It's give and take.  Some prefer smaller sand sizes like as in the French Sands.. but give up porosity, ventability of the mold/

On to a word about safety.  Obviously, you need to be able to melt brass, so a bit of heat is needed.  iT'S NOT TOO BAD, but the biggest thing to worry about is explosions.  I'm not talking fireworks, like what we Americans use to celebrate our freedom from your tyrannical gummint (bought from the Chinese - who are indecently gonna be our next oppressors) - I'm talking of STEAM explosions.  Water, when heated violently, becomes steam in short order, and since this IS the Steampunk Forum... You all know how many times volume it increases, resulting in an "explosion" of sorts.  With the explosion, there is all this LIQUID METAL floating about.. well, it's obvious that the explosion carries the metal up and out of the pot, and directly into your face, your chest, your child's (If you're stupid enough to let your children run around when you're casting), and onto flammable surfaces creating a whole new hazard!

There is one hell of a lot of work that goes into casting an ~anything~.  So next time you see a cast something, think of what YOU need to go through to get it there.  I know, I know, some little Chinese slave kids are making all the castings you probably see now, but they WORK HARD AT IT!

This, yes, is my first post.  I saw the title, and it intrigued me to sign up and to spit out whatever it is I know from personal experience.  I belong to the backyardmetalcasting forum - have for some years!  I DO cast brass, bronze, aluminum, zinc..

I also do electro-etching of coppers and brasses, using a proprietary mask.. etc..

See ya all around!
-Jeff
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JingleJoe
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« Reply #8 on: September 06, 2009, 06:41:28 pm »

When/if you see GREEN smoke/fire, it means you are boiling the zinc.  DO NOT inhale that smoke.
Or you will get the Zinc shakes! Anyone casting might wanna look that up for the sake of thier own health.

Good information Mr. Foundry Wink
« Last Edit: September 06, 2009, 06:43:51 pm by JingleJoe » Logged

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« Reply #9 on: October 28, 2009, 02:34:22 am »

We did bronze casting the other weekend for the first time. A friend who has done it a few times showed us how to do it. You can make plaster molds that are one sided or two sided lost wax. Bronze melts at 1900 - 1950 °F (1038 - 1066 °C) so the same techniques should work?

We did our plaster molds by making the original out of clay and pouring plaster over. After they hardened we put them in the oven on 400F for 4 hours to dry all of the moisture out. They do become a bit brittle after this and need to be handled with care. Ours handled the casting heat just fine.

The set up used was a home made gas foundry made out of a large steel plate tube with a removable lid w/ a hole. The gas goes in a hole on the side. This and the top hole help create the fire swirl needed to get the heat up to temp. Make sure you figure out if brass needs borax added at some point. IIRC it is added to get the slag out, you have to skim the slag off with bronze, not sure about brass.

I would do some research on bronze casting. It might help answer some of the basic questions.
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« Reply #10 on: October 28, 2009, 03:51:13 pm »

Along with media like greensand and investment (plaster made specifically for casting metal), there are also oil-based sands for cope-and-drag molds such as "Petrobond" which are cohesive and hydrophobic, both very desirable characteristics. On the other hand, while these are good in a dedicated foundry, they may be a bit much for a home shop, in terms of storage and processing. Still, it's one of the old standbys, and the industrial aroma is hard to forget. Or to wash off, for that matter. Oh, and since I am a cranky older guy, I feel obliged to mention eye protection (proper tinted goggles for the radiation off of large hot objects like a big crucible – lots of UV) a face shield, sturdy boots, and heavy gloves, plus making sure you know where the dry-chemical fire extinguisher is. Long sleeves, too. Trust me on this.
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Narsil
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« Reply #11 on: October 28, 2009, 04:22:30 pm »

The best type of mold depends to a large extent on exactly what form you want to cast and how many you want to make.

-Oil sand mold: usually a 2 part mold made with a solid former (often wooden). This is a good way to make lots of the same castings since you just need to ram the sand round teh form in each half of the mold. The downside is that you're limited in what forms you can cast as this technique doesn't accomodate undercuts and your form needs to be designed with proper draft angels.

-Bonded sand part mold. This requires foundry sand bonded with a chemical binder which sets hard. Virtually any shape can be accomodated but complex molds require time and skill to prepare and each mold can only be used once. This tecnique also allows you to carve directly into the sand mold, either to correct problems or as a fundamental part of the process. It's possible to make entuirely direct carved molds with no former at all (my speciality).

-Styrofoam burn-out. The form is carved in styrofoam, including all the sprue and sand rammed round it. You can use bonded sand, oild sand or even loose dry sand if you;re not worried about surface detail. The foam form remains in the mold and is burned out by the heat of the molten metal, This is a pretty easy way to create complex shapes but the fumes given off are pretty nasty and the surface finish always looks like styrofoam to some extent.

-Lost wax, The form is carved, fabricated or cast in wax, foundry plaster or bonded sand is rammed round it in a 1 piece mold and the wax is melted out in  a low temperature kiln. This usually gives good surface detail. If you want to make several copies you can cast the wax in a plaster or silicone master mold.

-Ceramic shell. Similar to lost wax. This is another investment casting method. The form is usually wax but any material which will burn can be used. The form is dipped in a ceramic slurry and coated with stucco then fired at high temperature in a kiln, burning out the form. This gives excellent surface detail and is in many ways the most sophisticated casting method but requires specialist equipment and materials to do.

-Inclusion molds. These molds are extrememly dangerous, it refers to leaving some or all of the form, usually some organic material eg wood of plants,  inside the mold and burning it out with the molten metal. This is EXTREMELY DANGEROUS and should only ever be attempted onder strictly controlled conditions with expert supervision. Styrofoam is the only material which can be safely (relativly) used for inclusion molds.

-Its also possible to make molds from steel, either all or in part, generally used for high volume castings of small parts or where fast cooling is required to control the structure of the cast metal, particularly in hight quality iron castings for machine parts, engine blocks, wheels etc.

-Low melt alloys (usually tin or lead based) can be cast in silicone rubber molds, often using a centrifuge. Thisis a good way to produce small, detailed catings. 

All metal casting is potentially very dangerous. It is essential that proper protective equipment is used and that all moulds are COMPLETELY DRY.
« Last Edit: December 05, 2009, 02:46:36 pm by Narsil » Logged







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« Reply #12 on: October 29, 2009, 09:37:03 pm »

dry moulds are essential, my lead casting episodes taught me that. I've seen it spat back out of the mould with some speed, not nice.

Thinking technically - would it be possible to shield the melting pot with a loose fitting lid, and run a steel feed tube to the pot lid, with a slow stream of argon from a welding bottle? This should stop zinc oxidation. It's a bit like purging the inside of a tube with argon before welding into it.
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Capt. Stockings
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« Reply #13 on: December 02, 2009, 06:50:48 am »

I've never casted brass, but I have casted silver. I did lost wax castings using plaster, a blowtorch, and a centrifuge. Casting can even be done in really primitive ways, though. I've seen it done using sand with a mud kiln and bellows. If you're looking for detail in the piece you're casting, I'd suggest plaster over sand. Also, if you don't have access to a centifuge, it may take multiple attempts before you get a complete casting. Someone once told me that they got about one complete cast for every 10 attempts.
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Rev.Hammer
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« Reply #14 on: December 02, 2009, 08:42:48 am »

Well drat, this seems to be a bit overly involved for someone of my city environs! Is there any one that might cast on request for a reasonable fee of smallish parts?
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Endeavour Cull
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« Reply #15 on: December 04, 2009, 09:36:28 pm »

i work in a iron and steel foundry and for nine years did the actual melting in induction furnaces
We work with wooden or foam models and siliconsand binded with synthetic resin.

On the dangers of boiling zinc:
In the past we recuperated waste from the mint (The place where they stamp coins) and that was when the euro € was in the making.
With no experience with this metal (which containes 11% zinc) you guessed it....i got the zincfever. The whole foundry was filled with white smoke and actual zincoxide came down as white threads. Couldn't see one meter (3 feet) in front of  me.
The shivers went on the whole night and you can't sit stil or sleep. it's very unpleasant and i must warn you for it.

about mold materials i can say that lost wax wouldn't work with sandmolds, because the sandbinding dissapears when the wax is molton out. Or you must use clay bounded sand. Important to know is that silicon sand has the property to have a 2% growth around the 750 degrees Celsius and thus break your mold apart.
For lost wax there are ceramic slurry's.
For small lead figures i used plaster with a lot of aircanals and very carefull heating out the wax.
A very old method (brons-age) is clay mixed with dung and hairs. (It sound groce, but when the wax has been burned out all the little particles from the dung and hairs leave very small canals where through the gasses can escape. This is very important when casting)
Heating it up is very delicate because the water in the mold will crack your mold and with lost wax you only got one shot at it.

Another very good material for bronse and brass is oilbounded sand. ( I know it as 'Bindol sand'  works well for plaques and molds which can be removed without destroying your mold. It gives a high surface finish to your piece already.
It is interesting to know if you can make your model symmetric or at least easily get out of the moldmaterial in which case you can work with two or more seperate frames which are put together again after the model has been removed. There are some tutorials on the web for this method. (Or you can come and take a look at our foundry  Tongue )

This is where I work. I don't work at the furnaces anymore (personal growth  Wink )
http://www.soestergieterij.nl/

Some other links (Dutch,but a picture says........)
http://images.google.nl/imgres?imgurl=http://www.joramakers.nl/uploads/pics/image002.jpg&imgrefurl=http://www.joramakers.nl/nl/gietproces/&usg=__X0oCHrh8Ua7_LjH94TLOCrFHOzM=&h=600&w=800&sz=216&hl=nl&start=4&um=1&tbnid=S3PMVUmYxKwLEM:&tbnh=107&tbnw=143&prev=/images%3Fq%3Dbrusselse%2Baarde%26hl%3Dnl%26sa%3DG%26um%3D1
http://forums.dfoggknives.com/index.php?showtopic=9338

The brittelness where is spoken about in the last link is caused by absorbtion of oxygen and Hydrogen. Before pooring in your mold you have to desoxidize it with special stuff (desoxidizer)

« Last Edit: December 04, 2009, 10:03:45 pm by Endeavour Cull » Logged
Narsil
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« Reply #16 on: December 04, 2009, 09:51:38 pm »


You can do lost wax with bonded sand molds as long as you can achieve good temperature control of the melt out kilns you;re not burning the wax out like with ceramic shell but letting it melt out slowly, the process takes about 6 hours plus.  It's not ideal and some binder systems take it better than others, but  you can get quite decent results, the mold failure rate is pretty low and you can get a suprising ammount of surface detail.
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Endeavour Cull
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« Reply #17 on: December 04, 2009, 10:22:24 pm »

I didn't know that.

Safety (probably not necessary to mention)
I also like to point out that you should always wear safety glasses, weldinggloves or similar, and for bigger pieces which are poored at floor height you can use sturdy shoes with a nonflamable trousers which come over your boots and look out for little drops that make only little burnwounds, but its a stinging pain which could make you drop everything that you hold in your hand.

Water is at that temperature a dangerous component. It gets 1600 times bigger in volume in nanoseconds.

It's not for making you scared, but this material and harnessing it must not be underestimated.
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Narsil
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« Reply #18 on: December 05, 2009, 04:20:09 am »

I didn't know that.

Safety (probably not necessary to mention)
I also like to point out that you should always wear safety glasses, weldinggloves or similar, and for bigger pieces which are poored at floor height you can use sturdy shoes with a nonflamable trousers which come over your boots and look out for little drops that make only little burnwounds, but its a stinging pain which could make you drop everything that you hold in your hand.

Water is at that temperature a dangerous component. It gets 1600 times bigger in volume in nanoseconds.

It's not for making you scared, but this material and harnessing it must not be underestimated.

Yeah I agree 100%, safety is absolutely paramount when casting metals. assume that at some point you will get sprayed with whatever metal you are casting, if you;re not happy with that idea then either re-evaluate you protective equipment or stop doing it but the chances are it will happen sooner or later. Also bear in mind that exposure to heavy metals and metal fume is cumulative, it's not a noticable  problem untill it's too late to do anything about it.
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Rev.Hammer
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« Reply #19 on: December 05, 2009, 09:02:11 am »

Heavy metals bind to the bone. Very nearly forever.
Your cautions are wise, great Narsil!
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dirk_m
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« Reply #20 on: January 11, 2010, 03:35:29 am »

Hi all - sounds like I'm late to this party, but here's what I think I know:

- I've cast brass & bronze into casting sand using a simple crucible and a MAPP gas torch.  Your flow time is very short!  Preheat the mold, it'll help a little.

- After I saw a thunderhead shaped cloud of zinc over my melting pot I did some reading: zinc boils at about the same temperature as most brasses melt (!)   so, bronze (or silver) sounds a lot better to me
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« Reply #21 on: January 13, 2010, 04:57:12 am »

i got the zincfever. The whole foundry was filled with white smoke and actual zincoxide came down as white threads. Couldn't see one meter (3 feet) in front of  me.
The shivers went on the whole night and you can't sit stil or sleep. it's very unpleasant and i must warn you for it.
I melted and cast a little bit of zinc last night; gave myself metal fume fever too although there was no visible smoke, so it was not as bad but there was visible shaking and most of the other symptoms persist today but I'm getting better every hour. Smiley

I just completely forgot about the zinc shakes untill it was too late Roll Eyes Atleast it was only a minor case.
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« Reply #22 on: January 13, 2010, 05:33:39 am »

Here's an article that may be of interest

http://www.backyardmetalcasting.com/brasscasting01.html

This site has some info on lost wax steamcasting using a flower pot kiln to cure the investment
http://users.frii.com/dnorris/onlineclasses.html
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« Reply #23 on: January 25, 2010, 07:10:16 am »

The backyard metal casting site has everything you need to know. If your going as cheap as possible (like myself) go to your local brickyard and pick up 10-15 fire bricks (used to line a fireplace). Just stack them in a box shape with a hole in the bottom corner. Then just stick one of these babies http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91033 in the hole and fire it up. Lay some brick on top to contain as much of the heat as you can.

If you mix casting plaster with silica sand it will withstand the heat.

I was inspired by this video. It works like a charm.
How To - Make And Cast BrassDQ

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« Reply #24 on: January 25, 2010, 01:05:09 pm »

that is a very intresting video clip... some wonderfull absence of heath and safety stuffs but all in all a very good concept. those roofing torches are very easy to come by ditto for the fire bricks. might just have to go and buy.
for those of us in the UK silverline do some nice reasonbly priced roofing torches http://www.silverlinetools.com/index.html?code=868681 though I wouldnt buy any of their power tool range lol
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