Hello Rich,
Yes I'm using an open form for numerous small vintage sax parts. I'm unable to do what you suggest. I can't see a way to pre-heat anything at this point. My form is made out of wood and I could fabricate a metal one but I don't think that would help, the issue is as you mentioned, before the molten brass,other than maybe a half an ounce, even gets to the spout of the crucible it starts to harden, no matter how quick I was. I thought maybe there was a "super heat" stage, like the molten brass could eventually get to the heat of the propane flame which I'm assuming is hotter than 1200 deg, giving me more time to pour.Unfortunately my propane tank started freezing up and reducing the pressure to the burner so I probably couldn't get there anyway. I have since found out how to retard the freezing of the tank with cold water immersion, but this doesn't sound like it's going to do the trick anyway.
I guess this project is going to have to wait till the weather is a bit more accomodating. That's what I get for being a notorious procrastinator.

Thanks for your time and suggestions. You came through again.

fred

Fred,

As I said already, I don't the weather is going to make enough of a difference. Half an ounce of brass is a tiny amount to try to cast by pouring, no matter the conditions, and I don't understand how you can have a mold that won't withstand heating but will withstand molten brass???

For a little casting like that I'd typically use my centrifugal caster. It uses a semi-enclosed crucible and moves the metal into the (already hot to 1200F) flask in a fraction of a second. I wouldn't try to pour less than a half a pound of brass by direct pour, due to the heat loss problem - at any ambient temperature.

Can you tell me more about your mold, flask, frame, whatever you want to call it? Is this a sand-casting cope and drag arrangement? If so there may be a way to overcome your problem.

You can stop your propane cylinder from freezing up by immersing it in a tub of warm water. Up to 120° F is fine. That should enable you to get sufficient delivery to melt a considerably larger quantity of brass, so you can use a large sprue cup and "shrink ball" in a sand cast flask. That ought to overcome the freezing otf the brass, assuming large enough gates and sprues and adequate venting in the mold. You'll need to be melting a minimum of four to six ounces of brass, though. Anything less isn't going to be satisfactory, I don't think.

Thanks Rich,
Sounds like I wasn't to clear in my last email, sorry about that. Yes, my form is half (I think the drag -btm)of a cope and drag flask. No top (cope) or sprues or vents etc. The form is built with a plywood bottom and 2x2 pine sides. I'm trying to pour approx 10-12 parts in one pour so there is a bit of moving around. The parts are small and I've welded an open spout with a fine tip on my crucible so I can be more precise when pouring and getting just enough brass in the sand molds to reduce the grinding work req'd. The crucible itself is made of 3" schedule 40 steel pipe. It takes a bit of time to steady the crucible over the forms and this is where the cooling happens and ultimately I can only pour out approx half an ounce before the brass cools to a point of sludge. The most I got so far is half a part poured. I'd guess there is probably 8-12 ounces of brass in the crucible. Are you saying that a larger quantity of brass in the crucible would hold the heat longer? If so I'd try that. As to heating the mold, I could use a propane torch to heat the sand of my form if you think this will help the pour. I said this wouldn't do much because I can't even get enough molten brass out of the crucible into the form at this point so I don't see what difference a heated form would make.
The parts themselves are made out of 1/4" - 5/16" brass plate cut in various configurations, some flat some curved with what looks like an extruded area with a tapped hole through the center of it. The most difficult of the parts are called octave levers for a sax neck that are made of 5/16" tall by 1/4" wide plate with a number of twists,turns and partially half rounded areas that I will have to configure, bend,file etc, after pouring it flat. These levers are bent half round to fit the contour of the neck of the horns but I of course I am pouring them flat and will bend them later. I have gradually simplified the form more and more after attempts of pressing the originals into the sand casting and because of the contour on the parts they continually pulled sand out as I withdrew them. Realizing that some drafting was necessary to eliminate this I made flat forms out of aluminum that do have a slight draft. Ultimately they are very far from the original configuration. The parts I am trying to reproduce are from a certain vintage model sax from the 40's and are quite elaborate as well as very hard and expensive to acquire. They not only have this involved lever but also unique mounting parts. I've tried to cut the lever out of thick stock brass plate and hand form them...almost impossible to get the contours req'd to look even with a smooth transition. The lever is a closed loop with the outside of the loop rounded into a line following the contour. Hard to describe but even harder to reproduce with a file and sandpaper. Even with successful pours they will still require some pretty extensive labor but pouring a rough form of these levers will greatly reduce elbow grease time.The levers I mention have 3 lengths, (alto,tenor, bari sax) and are basically closed loops about 1/4" wide and varying heights from 1/4" - 5/16" and approx 8,6 and 3" long. Being a loop I need to pour all around the form and with some accuracy so I do need the brass to stay molten longer than a few seconds.
I did think of trying to eliminate even more work after the pour by pondering the lost wax method but to make the original part out of wax turned me away. It also seemed to involved regarding the extra equipment and prep work.

I guess I covered it all and then some, hope I didn't confuse you. Thanks again Rich.

Well, I see a whole bunch of things wrong with your whole approach and I frankly think you're doomed to failure at the present state of things. Let's take it from the top:

First, steel is not a suitable material for a crucible. You really need to spend the few dollars (under 40) to get a proper graphite or silicon carbide crucible. That steel crucible is cooling the brass just like it was exposed to air, besides probably contaminating it with tramp elements and it will fail, sooner rather than later. The additional pouring lip is only thinning the fluid stream so it has more surface area to cool faster.

Second, an open flat pour such as you're trying is only suitable for the crudest sort of sculpture or jewelry work where you plan to do a huge amount of post-cast finishing or accept the lousy surface and low-density casting as is. (See cuttlefish bone castings for example) For a saxophone key it will never work worth a damn. You should really be using the lost wax casting method for these parts so that you can get a dense casting with high degree of accuracy.

If you're determined to do sand casting then you need a closed cope and drag flask so the pour can be quick and full. What you're doing will sort of work for making chocolate candies, but never for brass instrument parts.

I think you really need to stop what you're doing and read a couple of books on technical jewelry casting, which what you're doing really amounts to, and start over using the right techniques and equipment. Note: this doesn't mean that you have to invest thousands in equipment. Far from it - it can be done on the cheap, just not the way you're approaching it. You can use home-built equipment, but it has to be built to actually achieve the functionality of commercial stuff.  The end product you're trying to create demands a high degree of excellence in the casting process. 

Some things you just can't fake - like crucibles. But you can build a very cheap burnout kiln for burning out waxes, a cheap foundry furnace for melting the brass, and even a home-built centrifugal casting machine. It can all be put together for as little as a hundred bucks if you stick with sand casting, (I personally wouldn't recommend it) and maybe $250 if you set up to do proper lost wax castings.

I'm happy to help with advice on doing this in a way that will work, but I'd just be wasting my time if I was to try offering any suggestions as to how to make your current method work - it simply won't. Ever.

Rich

Not sure what you mean by the lip of the furnace? I use a 5 gallon refractory cememted furnace with a propane torch for heat. I got the form for it through Homemelter Furnace kit. I have 3" x 4" crucible made of steel pipe I welded together.
fred

Fred,

You apparently already have a decent melting furnace - that's good. That's one less thing you need to acquire to do this job right.

What Marlene is talking about is heating the top and pouring lip of the crucible with a torch while you're actually pouring the metal, to slow down the cooling. However, you still need a real crucible, as I said above. Even with that, your open flask method will simply NOT work.

Rich

Thanks Rich, all great advice. I'll get a proper crucible as soon as I can. I'm sure that alone will help a lot. I'm still not sure if I want to try lost wax casting at this point. For each neck I need 3 parts, I need at least 15 necks, that's 45 castings. Two of the 3 parts are relatively easy, all same thickness with cookie cutter type configurations. I just can't see making wax forms of 15 of the levers I mentioned. Though I have never worked with wax I think it would be tough to do a proper job of it. I admit it would be great to get the final form without any major tooling etc but again to get wax to the form I need seems pretty tough. I will purchase some wax and give it a shot to see how I do and what it is like to work with this type of medium. I guess one good thing would be if you screw up you can melt more wax to the form.
thanks again

Fred,

With lost wax you can, if you desire, (and it is appropriate for the part) make a flat mold and pour the molten wax into that to get multiples. The molds are usually made of an RTV silicone compound readily available at jewelry supply places. Using the RTV silicone, a fair amount of curvature can be accommodated without needing to draft the mold. Multi-part molds are easily made with a bit of practice, too.

When doing lost wax casting for those parts you're making, I'd sprue up several at once and cast them in one pour. Using a simple centrifugal caster, I could easily cast fifteen or more at a throw. For the centrifugal casting, the limiting factor would be the crucible capacity of the machine, about three to four ounces. For vacuum casting or free pour, the limiting factor becomes more one of moving the metal through relatively the thin sections of those keys.

Depending on the type of wax you use, it can be worked by numerous methods - additive, subtractive or manipulative or combinations. Kerr company makes a wide range of waxes for the dental and jewelry industries and they have ready-made round, square, half-round,etc that may save you large amounts of time in modeling waxes. Check into them. A relatively inexpensive wax pen or wax iron will allow you to join or model wax pretty cleanly and quickly.

Thanks Rich, been out of sorts with the flu but finally up and around. I'm going to sit on this for a while and do some research and as you said try to approach this whole thing with a little more forethought. Maybe by then it will warm up here and cause me less concern while doing this outside.
Again, thanks for the help.

I agree with everything Rich has said here.
I would just like to add that usually if your propane tank is freezing up on you thats an indication that you are using too small of a tank. You might try a larger tank.