Reading through the a lot of documentation on furnace construction, I've parsed the "Rules of Thumb" probably a thousand times but I still find myself a little confused with just a few of the aspects, and the word "tangential" has lost all meaning to me having written it down so many times now. The wall thickness of a foundry is recommended to be about a quarter of the inside diameter. I'm assuming that that means the inside diameter after the walls are accounted for - so if you have a 12" diameter, it's because you have 4" wall thickness. But elsewhere it's specifically mentioned NOT to have a Hotface 3" thick. Do you see the conundrum? So is it suggesting that the wall (which is the insulation, say a ceramic blanket PLUS the refractory) should be 4" thick presuming a 12" diameter, but that OF that 4", it should be mostly insulation - and not mostly refractory material? Or is it suggesting that walls that exceed 3" at all become very inefficient? Is it the heat of the flame directly that's contributing to the heat of the crucible, or is it the walls ability to maintain the temperature through it's insulative properties that's contributing mostly? Thank you as always for insight, I've got a few more questions I'll be littering throughout the forum.
this one i leave to the college educated guys , it matters what you are using for the furnace construction, you have to decide that first
Because I'm likely using a Salamander Super A25, I was leaning towards getting a 55 gallon drum and constructing it out of that. But the 22.5 inch diameter would mean that even with the crucible being 8.5 inch, that leaves 14 inches. Which, a 4 inch wall on either side would mean that there's a 3 inch gap on either side of the crucible left. That seems like a very large gap, and may reduce efficiency to the point I'm wasting a lot of fuel.. I'm likely to be using propane, and that's going to stack up quick. Or is a 3 inch gap not that large a deal you wager? Sorry I know I'm a complete noob here.
if you do insulated fire brick over kaowool, that will work out perfect with a 13 inch bore, go read my furnace build thread again, its pretty detailed, if you want to do a monolithic build, my preference, a 30 gallon drum is about perfect witha 13 inch bore you will get 2.5 inch wall thickness, now if you run propane, you can use a smaller bore, but fro an oil burner of any type you need some room in the furnace P.S. you really need to consider dropping down to an A20, I dont think an A25 is managable by one person without some assistance weather it is a lifting aid or another person P.P.S go read my build thread really read and suck it up, lots off great info that will help you avoid mistakes, hay if you want DM me ill give you my Number and we can talk
If you absolutely must have a large crucible, one of the members here (Melterskelter I think) has a really nice lifting mechanism and pouring trolley for large cast iron pours, it's featured in some of his videos. I might be worth it to you to check them out.
Unfortunately the size of the crucible has to be fairly large because the size of the plate.. but perhaps it'd be worth triple checking my math. What I was planning was pouring a concrete slab that I could bolt a steel plate to, which has a steel hinge and a ring to hold the crucible. Provided I could lift the crucible out and set it down on the steel plate, I could use a welded handle on the plate to tilt it into the mold. The mold is another issue I'll be bringing up later.. I have to imagine 0.88 gallons of molten copper (like 60 lbs) put some insane pressure on the outside of an upright steel mold - the clamps holding it together would have to be able to hold back some serious PSI. I'm leaning towards that though as opposed to an open top (think like an ingot mold except very shallow and instead wide and long) because of the increased surface area exposed lends itself to increased porosity and shrinkage. Am I right in that idea? Yeah I'll need to continue to study, trust me I know I'm taking a huge bite out of this out the gate, I've been researching now for a while but honestly until I came here it seems a lot of the information I was getting from YT wasn't realistic.
With respect to the mold-splitting pressure exerted by the poured copper at the part line: the pressure exerted is not so much directly related to volume as it is to the area of the part at the part line (plaque has large surface area and thus lot of splitting force vs a ball of copper of the same volume which has much less surface area and therefore less splitting pressure) multiplied by the head pressure. A short sprue results in less head pressure. So casting a ruler oriented with its broad portion in the part line plane exerts maybe 20 times the splitting pressure that the same ruler oriented with its broad plane vertical would exert. In actuality, ordinary measures like weight and clamps should be sufficient to maintain a closed mold for copper casting. It is only slightly more dense than iron and I just bolt cope to drag and don't have to clamp or weight the sand itself and things hold together OK. Denis
With an A25 you will get around 80Lbs of copper /brass/bronze , give or take , getting it out of the furnace is not the problem, its handling the crucible to pour , a one man shank will put that molten metal about 24 inches away from you , that leverage (need one of those college kids here) will make that Really heavy, as your forward hand acts as the fulcrum( I have no idea the math) but at the very least you are holding 80Lbs of metal and 15 Lbs of Crucible and the weight of the shank IN ONE HAND, and that hand is 24 inches from 2200 degrees So go grab a 95Lb dumbell and start doing wrist rolls V/r HT1 P.S. writing that down actual spooked me, I did not realize how much weight I was Handling with an A20
HT1, the amount that one hand has to hold is actually more than the weight of the crucible, metal and shank because you have the crucible and metal on one end of the shank pushing down 95 pounds, plus the shank weight, plus the required downward push on the outboard end. That outboard push will be about 1/2 to 1/3 the weight on the crucible end if your balance point is 1/2 to 1/3 the way down the shank from the crucible. So, at best a 95 pound crucible will require about 130 pounds of one-hand lift. That is one of the reasons I (5-7 and 160 pounds, 74 y.o.) use lifting gear and a trolley. That puts me 7' from the pouring metal and provides a lot of mechanical advantage. Even so, 65 pounds of melted iron requires full attention while hoisting and moving to the mold. And I will add that I do not use the trolley because I have to move any distance from furnace to mold. Often I simply raise the crucible, pivot practically in place, and pour. Then maybe move a foot or two and pour the second mold. And, so far, no one has mentioned that pouring brim-full is no treat. So, it is more realistic to think about pouring whatever crucible is used with about an 80% (maybe 90%?) capacity load of metal in it. At 80% full it is so much easier to aim and control that initial flood of metal. Brimful is a bit of a crapshoot so to speak. Denis
and as I said someone with one of those "educations" would come about and put some "rithmatics" to what I knew Thanks Dennis V/r HT1
I’ll cut right to the end: This is way too much for a one-man hand-pour, especially for someone with zero experience (nothing personal). Physical strength and self confidence not withstanding. Too heavy, too bulky, too hot, awkward body motion, add to the list. I’m what I would consider average physical ability and I pour a maximum of <15lbs aluminum from a #18 or <25# of bronze from a #10. That’s it. After that would be pushing it. It’s not just the weight, but the bending, twisting, and pouring time. Add to that the anxiety, missteps (they are not uncommon), plus the sustained unremitting heat that no ordinary person has ever experienced and you have a perfect recipe for failure that ranges from a ruined crucible to catastrophic injury and your house burned down. This is not a overstatement. If Swift has to go this large either equipment or a second man will be needed. Pete
