The Home Machinist!

Uh.. I hope you have a target wall, that is offset from the center to create a vortex around the vessel, heating the walls for indirest heat AROUND the vessel. This helps keep the critical temperature radiating into the melt more even. In a perfect world you would have a target wall to deflect the actual flame around in a whirl to circulate several times before exiting.

no matter. You are moving forward, and some upfront knowledge would avoid some , but not all pitfalls. You are being inventive, and its your design.

Not to gloat but I had a Speedy Melt, that was small compact and easy to run. Thieves scrapped it for the metal weight. I built my own in a 55 gal drum with used Kiln brick and hearth cement. It has a 2 stage natural venturi burner, for LP.

After using that, I bought 2 McEnglavan furnaces that back vent. They are harder to operate, are deeper, and have control safty problems that require fiddling with all the time.

The bottom line is: melt fast, pour fast, git er done. Play safe with metals, they leave nasty burns.

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Big Dave

Be Alert! The world needs more Lerts.

well, the burner fit best that way....

I'm not 100% sure what you mean by a "Target wall"....

that being said, getting a 4" x whatever length 1/4" plate rolled into a spiral to sit on the bottom of this shouldn't be all that difficult. not sure how long it would last, but hey, it's worth a try! Would that work as a target wall?


i'm trying to figure out now, what to do with the lid, especially as far as vent sizes go. is 3" enough?

i'm going to hang wire that's tacked to the lid through to hold the refractory in place, but i'm not sure anything past that. I got about a 5% slope in the bottom of the foundry, and am goign to need to use some fire-brick to provide risers.

I

That may be the case, but it's a good idea to follow the advice already dispensed by Big Dave. The flame should not impinge directly on the crucible, which will become evident to you when you fire the furnace.

This is a good case where looking for the lost wallet is best accomplished where it was lost, not where the light is best.


In this case it's a bit deceiving in that the flame doesn't impinge directly on the wall, but tangent to the wall. It creates a swirling motion to the flame, allowing it to circulate around the crucible, heating the wall and indirectly heating the crucible (uniformly) in the process. What you have built will work, but the back side will be slow to heat, while the area on which the flame impinges will over heat.


My personal opinion is that you should avoid using anything metallic. It will oxidize in the flame and begin shedding oxides. That could be avoided if you use the proper (expensive) alloy. Best thing you could have done was investigate the construction techniques utilized by those that build furnaces commercially, then emulate their design. That being said, because I'm not sure how much height you have, my comments, below, may be a perfect solution, and you may have dodged a bullet.


I expect it will be adequate. You don't really want it too large, but it should be large enough to permit evacuation of the spent gasses, yet leave enough area to provide reflective heat to the charge. My guess would be somewhere between 3" and 4" is the ideal size. Unfortunately, I am not an engineer, so I build things like this by following my own advice of investigating that which has been done by others.


You might consider splitting the form and installing a draw bolt, so you can tighten the steel band around the refractory if necessary. That is a common feature of those I build, and it has served me well. You might also consider welding short bits of steel to the inside of the form instead of wire, which has limited ability at the temperatures involved. The short bits will key the material, preventing movement.

You would have been ahead to have designed a pivot mechanism for the lid, so it didn't have to be removed. A simple mechanism allows it to lift and pivot to one side. Handling a red hot lid that weighs 40 pounds is going to be less than convenient, and likely in the way once removed from the furnace.


Common practice in melting furnaces is to provide a crucible block that is made of like material, so the crucible is heated from below as well. If you have enough clearance between the bottom of the furnace (by the way, it's a furnace, not a foundry) and the top, you may be able to install a fire brick such that it deflects the incoming heat towards one side, allowing it to swirl around the chamber, and raising the crucible so the flame does not impinge directly on the walls. The fire brick(s) would serve as the crucible rest. I've always made mine from refractory materials and have enjoyed acceptable success. Just a thought.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Thanks harold! I haven't casted the lid yet, and i can still lift the furnace on/off the stand (and will to make the burner mount). so a sliding lid is definitely an option still. I think i may go that way.

The top of the furnace also has a slope to it, for a good seal. I am wondering as well though, would it be possible just to use the ceramic wool in the top? i mean, it will shrink, but it should be able to handle the heat for a while.

I've got about 10" Diameter x 19" of usable space inside the furnace, so the firebrick trick might work for me! Thank you!

Of course, it'd becoming evident i just sort of jumped into this project with both feet, and am doing my research after-the-fact.

I have decided to use a kiln-wash on the crucibles, and see how that holds up. With any luck it won't contaminate my melt too badly. I'm going to weigh the crucible after oxidizing it/kiln wash and see how much i lose over the course of melting some ingots, that should give me an idea of the effectiveness of the kiln wash as a crucible wash. Otherwise, it'll be trying boron-silicate glass (if it doesn't react with aluminum, and melts lower than the steel, i haven't looked into it yet), and worst case scenario is buying one of those expensive ceramic mixes.

I did a quick tally, and i've got rougly 600lbs of automotive aluminum castings sitting around.

As an aside, does anyone have a rough idea what kind of head one of these oil furnace pumps can pull? i'd like to use an automotive inline fuel filter to keep most of the gunk out.

That wouldn't be my choice.


Bad idea. Really bad idea. They are too small to provide the needed volume, especially if you intend to use discarded engine oil. I'm speaking from experience in that regard--having filtered many gallons of used oil. Check with supply houses that deal with oil burners. They provide a filter that has greater flow rates, with an element that is easily changed. However, you're still dealing with an oil that will be rather viscous, and won't filter easily in any case. You might enjoy better success if you can preheat the oil, thinning it considerably.

You likely will discover that the oil won't work well with the burner you have unless it (the oil) is preheated. The nozzles on those burners isn't intended for heavy oils, although you may be able to buy one that offers that ability. The addition of more than 10% used oil to heating oil changes its properties considerably, with more making operation difficult.

Nozzles are made with a sintered bronze filter, which will plug readily if you do not filter the oil well, so don't overlook that step.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Rockmonton, enclosed are some pics from our foundry. 1 is our lid curing with a cottage cheese container for a spacer and is upside down. It works great for the size. 2nd one is a shot of the flame coming in at an angle to enable swirling. 3rd is our basic crucible before kiln wash. We have found no problems from iron contamination for our needs with the kiln wash added. Good luck on weighing the crucible after you do your first melt. The aluminum doesn't like to come kleenly out so you will have buildup on the walls and floor.

Tom C.

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tom_at_srclry_com
Lost somewhere in Michigan!

the lid is setting right now. looks like it's going to have a metal band (as suggested) with a hinge on it to strap it into place and then it'll lift 90 off. I was experimenting with filters today, after i found out the local hvac place wants >30$ for a filter, and found that at 10 degrees C, a 10 micron hydraulic oil filter flows plenty with about a meter of head pressure on it.

No-no - NO! pardon my opnion here. Get the largest nozzle that can free flow your BTUs for your furnace, and then provide fuel for it. NOTHING is for free. Your labor, your time, the furnace, nothing. Sooo! make it pay for the lowest cost. I dont know of any furnace, in the hobby sector that runs more than 50% drain oil , or its equivelent. Most are mixed fuels, with diesel being the favored mix.

I recomend, settling used lube oils, ( drained engine oils ) through strainers, filters, and then mixing with furnace oils to run a gun. As long as the last filter is smaller than the gun nozzle, you should be fine. I wasnt. but have nothing to report. It should work. Leave the settlement, in the barrel with the last inch from a 55 gallon drum of used engine oil. You can buy it at many places for $.35 a gallon, just come and get it. Mix it with furnace oil of your choice,f or a blend, and see.

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Big Dave

Be Alert! The world needs more Lerts.

I'd avoid that design were it mine. When you rotate the lid up, it will be reflecting its heat towards you. That's not a good thing, especially if you progress to casting brass, where the lid temperature may be as high as 2300°. You won't be able to be anywhere near the furnace with the lid up. You must be mindful of the heat you're going to generate when this thing is operational. It isn't user friendly in the least.

A functional and easy design is one with a (vertical) pin at the rear of the furnace, over which you place a piece of pipe that's an easy fit. At the top you provide a pivoting arm that has a ball welded to the end. The ball bears on top of the pin when the handle is lifted, then the lid is rotated to the side best for your given setup. Lowering the handle slightly allows the lid to rest on the top edge of the furnace, out of the way, reflecting its heat downward. The handle that does the lifting can be made removable, so it's not in the way of operations, yet easily slipped on a pin when it's time to open or close the furnace. There's more to the design than I've alluded, but it's easy to build.

My melting furnace (when I refined precious metals) was built accordingly. I may be able to dig up a picture of the lid, but I do not have one on file in the computer, otherwise I'd have posted it for your perusal. Let me know if you would like to see the design.


Heh! Yeah, but with what oil? If you've been paying attention to my comments, you'll understand that used (cold) engine oil runs more like molasses, and won't get through the filter adequately. You might get away with used ATF, however, so check the possibility of that idea.

Even if you do manage to establish a decent flow of fuel, unless you pre-filter the used oil, the filter will plug off so rapidly that you won't get much life. What you don't want is the furnace to quit about the time you have a molten charge. Also, pay attention to what Big Dave is telling you. I've run used oil in my oil burning boiler---but I can't get away with any more than about 10% engine oil (the balance heating oil)----otherwise the flame is completely wrong for the boiler. Heavier oils do not burn well unless heated.

I have serious doubts that you'd have any success at all with cold engine oil. I expect you'll have to blend some fuel oil, if for no other reason, ignition will be a problem. If I'm wrong, and you work out the details such that you are enjoying success, please do let us know how you succeeded. That I wasn't successful doesn't mean you might not be.

Keep us posted.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Yes please! A fuel stream, of any mix, sprayed against a hot target wall is the FIRST comandment to running a furnace. Until you can get a HOT and LEAN burn off the wall, that is elementary to firing the furnace, everything else is secondary. You can inject house gas, AKA, natural gas, to sustain a flame and control an overfire oil jet for your furance. There are many avenues to follow, its up to you

Oil as a fuel has its own problems, especially dirty drain oil. It is why I use LP, as I want to KNOW how many lbs of fuel, what pressures I run, and other data I collect. The BIG furnaces I have are fired with natural gas, and are LEAN, and MEAN off the wall. They sometimes blow out when the lid is raised, to "work the heat" just before pour. It is why I hate the saftey controls that cause minutes of frustation, for the furnace to fire again, having to satisfy the controls to run again. Grrrr.

AS I think about this, I cant tell you A+B = easy. In any effort to make things the way WE want them to be, there becomes the assumption, that we can do this, and then get this. Let me be the LAST to inform you of that fantasy! If there was a way to assume conquest, and invite defeat, not to be admitted, I have already done it. I have gone down many wild trails , only to start anew, again. PHHOee! I wasted my time , only to read, lesstime, to find out how I was hammerheaded, stupid, and wasteful, to do what Chineese have done 3000 years ago! I am indeed a student, I am in a modern land, trying to do. DUH! Think bigger, and go to it. It is simple!

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Big Dave

Be Alert! The world needs more Lerts.

hah! thanks again guys.

I have access to cheap diesel, so i will be cutting the waste oil with that. I'm going to have to determine the right ratios, but i think its possible.

As far as the preheating goes, i'm thinking about using something similar to what i do with distilling, and coil up a copper line, but put it in a container with some coolant and an engine block heater as close to the pump as possible. It gets cold up here in canada, and i would like to be able to pour year-round.

As far as the lid goes, that side-ways is still entirely doable, i'll have a look into it.

But for now, i'm flying out for a job interview! I'll report back when i get some more progress done!

black steel pipe tee with a 400w volvo block heater in it (what i had in my junk engine), seems to raise the temp about 30 degrees celsius. it flows quite nicely at this temperature with a 50/50 WO/Diesel mix. I think i'm going to need to make another one for the other side of the oil filter here, as i imagine the cooling effect will be large. That, or use an immersion heater in the storage tank.

i put the lid on and used the cerawool as a gasket, have not built a lifting mechanism yet, but fired it up using some pine scraps and newspaper and a leafblower. got awful hot and fire-ey burnt out the sonotube to make a really rather nice surface. I need to pour the riser blocks yet, but that shouldn't be terribly difficult. I just got some goodies for my mill-drill, and need to make a stand for it, so i can get the ford 8.8" pinion spacer for the rear end in my 1966 volvo back together and get it rolling before the snow flies too badly.