Casting in cold weather?

Hello,

I recently set up in my garage to cast some brass parts. I'm using an open face flask form. Is there a temp that is possible to get brass so it doesn't start to cool before pouring. I've tried twice, the second time I let it heat longer after getting molten, and the same thing happens - I pour for a few seconds and the brass starts to harden, no matter how fast I get it out of the furnace. Outside temp between 30 -40 degrees. Is this going to work or do I have to wait till spring or summer?
Also, I'm using propane and my tank eventually starts to freeze up and restricts gas flow. Is there a way to slow this down?
Any help appreciated.

Fred


Rich Waugh's picture

Welcome back to ArtMetal,

Welcome back to ArtMetal, Fred.

I doubt that the weather or season has much to do with the problem. The temperature differential between summer and winter is about 50-60 degrees and the molten brass is about 1800-1900°F. Those 50 degrees are not gong to make that much of a difference. The primary issue is one of surface area versus volume, when it comes to losing heat.

I'm not exactly sure what you mean by "open face"flask form. If you're pouring into an open, flat mold, you have a lot of surface area for cooling and so the mold is going to be at room temp in no time flat, even if you pre-heat it some. Similarly, when you pour the brass, you're changing it form a contained mass of liquid to a thin stream, greatly increasing its surface area/volume ratio so it cools quickly. That's always going to be an issue, so you have to pour reasonably quickly, but not so quickly you induce splashing.

If you can alter your flask so that it is something that can be heated to over 1000°F prior to pouring, you'll have much better success. If you can't do that, you might try having a second person there who could play a torch flame over the face of the flask just prior to and as you pour. An envelope of flaming hot gas will help prevent the rapid heat loss you've been experiencing.

This is one of the reasons that I usually recommend using good quality jeweler's or dental lab investment plaster like Kerr SatinCast for casting with metals. It will withstand being heated to 1000-1200°F without breaking down and will reproduce incredibly fine detail. The cost, versus your time to do things over, is small.

The bottom line is, you have to do everything possible to reduce heat loss. Pre-heating, in-process heating, short pour time, etc. You can never defeat the laws of thermodynamics.


visitor's picture

Minnesota...oh well.

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


Rich Waugh's picture

Fred, As I said already, I

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.


visitor's picture

My flask and stuff

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.


Rich Waugh's picture

It is never going to work.

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


Marlene1065's picture

winter casting

Are you heating the lip of the furnace prior to pouring and while pouring?

This is done summer and winter

MJJF


visitor's picture

Pouring

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


Rich Waugh's picture

Fred,You apparently already

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


visitor's picture

Lost wax vs open castings

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


Rich Waugh's picture

Lost wax is the way to go!

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.


visitor's picture

Lost wax.

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.


visitor's picture

tank freezing

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.