Casting Brass

[Gundog48]

I'm forging a sword at the moment and need to make a special crossguard for it. The design would be difficult to forge, and I'd like to make it out of brass, so I believe casting brass into a mold would be the best option. I plan to do this in my coke forge, I don't think I'll have too much of a problem as this has melted steel before with ease! I plan to make a crucible out of stainless steel pipe if that would be sufficient? The thing I'm really struggling with is making the mold. I take it I need a special type of sand, and something to hold it together other than water. Because it's a 3D object I'd have to make two parts and put them together, do I then make some kind of tube for the metal to travel down to meet them in the gap?

Any advice or resources for finding out more would be great! Thanks for your help!

[mat]

have you looked into "lost wax casting"

[Gundog48]

Thanks Mat! I've taken a look at it, but I don't think I have the skill to carve the shape I want out of rubber, but I could do so with wood, so I think using greensand may work best. I'm on the lookout for greensand suppliers! I think it looks pretty doable, just as long as I can make the mold well enough!

[hotset]

hi i have just cast a centre boss for a table i made i used a graphite cruicible but steel should be fine cover the surface witha bit of charcoal dust to stop to much zinc burning off get a bit of a puddle goin and feed it with bits of brass you could chuk a bit of extra zinc in bit of old carbureta or simmilar helps it get fluid . i bought some oil sand from john winter foundry supplies ages ago just scrape the blackend sand away when you seperate the mould as mat says lost wax great make the hilt out of wax wth a couple of rizers attached you might get away with normal plaster of paris coat wax with abit of washingup liquid to stop bubles sticking set the model in a tub box why bang it on bench to get bubbles out or if you could rig up sumat with hoover or similar let it set then let it dry then BAKE THE XXXXXXXX OUT OF IT TWICE well just make sure there is no dampness at all left in it or you will have a horrible accident in this proscess the wax will have burned out then just scrape the dross of the metal wich should be just slightly fuming ie the zinc is just getting burnt off when youve got the surface quite clean [you wont get it real clean as its drossing as the atmosphere has contact ] pour it in the mould smoothly and keep your head away . i bet theres loads of casting on u tube . i have a great book by terry aspin ,the backyard foundry, one of the workshop practice series no 25 isbn 1-85486-146-8. good luck

[Bentiron1946]

Be sure to this brass casting OUTSIDE as zinc fumes is bad for body and soul. I have done a fair amount of lost wax casting and it is easy to do if you follow son of the advice that hotset has set forth. You can make your original out of most any wax but be careful of paraffin wax as it can sure light the place up when and if the smoke lights on fire, it'll singe your whiskers off for sure. Most of the hardware for swords or knifes are fairly simple so there is no need for complex sprues and risers. I usually run in a good sized sprue into the top of the cross guard, maybe 1/2" and then a 1/4" off the bottom of it and that way as you pour the metal in and the cup fills as the metal comes out the 1/4" riser you know you have filled it all out and there are hopefully no voids in there. I have used plaster of paris but is is best to put in 1/3 sand to help hold it together. Also use a section of black iron pipe that is around 2" bigger than all you sprues, risers and wax pattern, it will keep all of the metal contained if the plaster of paris should crack and even with the cracks you should have a successful pour. Now I wouldn't go adding any extra zinc but perhaps a lead fishing sinker to help the metal flow a bit better, both are toxic to you but I have found the lead to work better. Oh, and back the plaster of paris until there is no black left on the pouring cup, that shows that all the wax has been burned away, oven temperature should be about a thousand plus degrees Fahrenheit, you standard oven isn't going to do that.

[781]

what about lost styrofoam casting
make the piece you want and risers out of foam
if the piece doesnt have any tiny intricate parts I have seen it done with loose dry sandblast sand
definately do this outside as the burning foam is a killer

[wd&mlteach]

I do not know if you have moved on or not but here is my take on the process Gundog.

If I were doing another investment casting of a short run I would pick the Styrofoam method with petrobond sand. And make sure it is actual foundry sand and you are not trying to do this in a 2 x 4 box with beach sand at home, not good. I personally use a petrobond sand for my castings at school. It packs nice and make the kids complain because of the stink, burned smell, plus they wear it from head to toe Hah! The lost wax method is great if you have the proper equipment pattern making supplies, vacuum container for the plaster, melting out, preheating the mold and then the ability to accurately pour into the sprue.

If you were just doing two pieces go with the foam as 781 says. Carve the piece out, ram it in the sand, put a sprue into it in a place where you are going to cover or cut out. Then heat your metal, more than enough is always better, the extra can be poured in an ingot mold,I made mine from 2 inch angle iron forng a v-shape. Then pour the hot metal directly on your Styrofoam, the foam does not stand a chance to hot metal. Allow the whole thing to cool and see how you made out. If you need more help let me know I can send a powerpoint on the process if you need.

[Bentiron1946]

I have done a fair amount of lost wax casting with and without the benefit of vacuum and if you paint your wax with investment first you can skip all the that use of vacuuming. You will not get nary a bubble on your finished product. It ain't at all hard to hit the sprue ifing you put a pouring cup on the end of the sprue like you supposed to. And there is no preheating the mould ifing you take it from the burnout oven directly to the pour. Yes, there can be some expense for making a rubber mould but I have had some success plaster moulds for simple objects without undercuts, just don't forget to soak them in water and lubricate with liquid soap. Casting has been around for a long time and it sure ain't rocket science or brain surgery so go get some books and make a detailed study of it and you too can be a foundryman and make successful casting with minimal equipment.

[wd&mlteach]

Bentiron are you making more of a shell when you paint on your investment? I have seen that done but I never have tried it, Also the ruber mold making is great. I do not have the supplies to make rubber molds at school, but I wish I did.

[Bentiron1946]

No, shell is whole different process from what I am suggesting. I mix up a small batch of investment to a creamy consistency and paint it on with a brush. When you mix it by hand you get very few bubbles and when you paint it on you burst the bubbles. This way you have a pretty good chance of having a fair chance of have an easy job of chasing the finished casting. I let this set until it is pretty well set before I pour in the rest of the investment so it doesn't wash off. I use schedule 40 steel pipe cut offs as casting flasks much like one would use for centrifugal casting machines but mine a much larger, 6" through 24". I mostly use the smaller sizes since my spinal injury some years ago I just can't lift the big flask empty let alone full and my current oven will only take a 14"dia. X 14" H. flask, kind of small but I can crowd in three 6"dia. flasks. I have a home made recipe for investment that works fairly well, does crack a bit though, 1/3 Plaster of Paris, 1/3 hydrocal, 1/3 silica sand, water, mix till about like a thin milk shake, then pour into flask. I usually put a ring of dry P of P around the outside of flask and only pour in about an inch of the investment in about an half hour before I mix up the big batch of investment. This seals the flask so you don't end up with liquid investment running all over the floor. You have all ready placed you waxes on the floor and stuck them down so that they fit inside the circle of the flask, they will be held in place with this one inch of investment and held steady when you pour in the large batch of investment. Fill the flask right up to the top and place a piece of hardware cloth just under the surface of the liquid investment, this will help prevent breakout during the pour. Let set for and hour and then put in burnout oven. Start out with a low temperature for a couple of hours, say 200F, then bump it up to 400F for four hours, 600F for four hours, then 1,000F until there is no more black in the pouring cups, when the black is gone shut down burn out and let cool to 400F. While oven is cooling to 400F start melt of metal, when metal is ready to pour get flask out of oven and pour metal, let cool and do break out, sand blast, cut sprues and finish casting. Sounds like a lark.

[wd&mlteach]

I have never tried or heard of painting on the the investment. Thanks for the tip, I will have to try it as it seems to make a lot of sense. I have only ever mixed by hand and when I was in school they showed us the vacuum method. I volunteered to be part of the demo and my job was to mix the investment. The professor said to me make sure you get all of the bubbles out and I did the best I could. I shook, I tapped, I shimmied (I think that is spelled wrong) and I did the best I could. Then the prof poured it over these staff heads they were casting and placed the whole thing in a vacuum chamber and asked me how if I got all of the bubbles out. I was proud of my involement and said somehting like "you bet". He then turned on the switch and it started to boil, not a lot but some. He then explained that if you leave the bubbles in the investment your surface will not be smooth and you run the risk of cracking/exploding you mold. At school I when I need to do this I pour the investment and go see the science people and have them draw a vacuum. Your method would save me a bunch of time, thanks.

[Bentiron1946]

When you are filling up a flask the size of garbage can you need to use a power mixer, it ain't no jewelry project for sure. I could have used a vacuum pump but I didn't have three phase at the time to run one big enough for to vacuum a flash that big. When you're pouring a hundred plus pounds of molten bronze you want it to come out as clean as possible. One of the things that vacuuming does besides get rid of bubbles is boil off the water. In a vacuum it boils at a lower temperature so it gets gone and makes the burn off go faster to, save time and speeds that up to. If you surround your investment with the steel flask you don't need to worry so much about explosions. I went up to one of the junior colleges and the professor was just turning out pure junk for the students when it came to casting their projects and he challenged me to do a better job than he, he had a MFA and I didn't. So I set to work, he used cardboard boxes for his flasks, quarter inch sprues everywhere and just a whole forest of them, while I used a steel flask much larger sprues and fewer of them but all of them in the right places but the really big difference was burnout time. He only melted the wax out while I totally eliminated, all of it! I burned until the pouring cup was white, all the wax had been carbonized, nothing was left. I can burnout anything that is organic, wood, bone, wax anything that will burn can be eliminated from the mould with enough time and this professor was only just melting so that some of it ran out. When the molten metal would hit it, EXPLOSION, molten metal every where, no wonder his student assistants had to wear full fire suits. When it can time for me to pour all I wore was tee shirt, jeans and sneakers, not the best idea but I knew my mold was safe, no wax or moisture. The professor thought I was just lucky, I knew better. His students started coming to me to have their waxes poured into bronze. Two things make a good pour, good burnout and good sprueing, oh yeah there are other factors like having your metal hot enough but get those first two right and you are going to have a better chance. Remember metal in, air out.