Top's A10 furnace Project

Uggg That's so frustrating The refractory shrinks a small % as it cures, so it's likely REALLY stuck in there good and hard

Personally I would worry leaving it in could cause cracks due to differences in thermal expansion. But if others have left them in w/o trouble, you should defer to their experience over my guesses.

I know there's a lot of details to remember when doing these things. If you do find yourself molding a tuyere again sometime, simply rotating and gently jiggling it every 30-60 minutes as the refractory sets up will help.

I can imagine a sawzall working, might be worth a try? Some elbow-grease and a sharp triangle-file could work. Another idea (if you have one) could be to intentionally blow through it with a welder set too high.

 

Razor, an intentionally hot weld might be easier on the surrounding unfired refractory than a cutting torch, thanks for mentioning that!
Plus it would sound cool, drawing the gun or stick through the tube.
All solutions start with me cutting the 18"(45cm) out the back that I've mangled with the pipe wrench. Then I need to reckon with what I beat up inside the furnace yesterday. Then decide keep or remove...

 

Hell, if the burner tube fits in there I’d leave it unless it’s a real tight fit (Rust and other issues will turn a friction fit into “struggle fit” in short order). If you can fire it as is before cutting off the stubs it might minimize vibration damage to the green refractory, but otherwise a light touch with a cutting disk would probably be ok. You only have to get a close cut on the inside. It will level off in use in pretty short order.
You might find it helpful to leave a stub 4” or so on the outside. Cut it radially from 12 o’clock to 6 o’clock (CCW) at the furnace body, and then slit the length along the top. Then weld the tube to the body from 12 o’clock, clockwise, as far as you can toward 6. I have a heavy duty quick release hose clamp permanently attached so I can clamp my burner in. That allows the burner to be supported by the furnace body instead of stressing the refractory.

Pete

 

Thanks Pete. Burner tube to embedded tub is not too tight, should allow for disassembly. I may have to go back and add your clamping system.

I cut the tube a couple days ago, only about 1" (2.5cm) from the shell, it was on my to-do list and I wanted to 'check it off 'so to speak.

Originally I was going to test the burner with an existing leaf blower and I had made up some cardboard and fiberglass transitions between the shapes. I found a 110V/120CFM blower on Amazon that even if was not quite that 'gutsy' (gusty?) would be close to the blower listed for a Mifco B160 (90CFM). I set them both up for a test run. The blower was relatively quiet and blew some dust out and made toilet paper swirl and lift from the cylinder. The leaf blower on low made even more dust come out of the cylinder and was louder. On high, the leaf blower was blowing the remaining cardboard scraps with mastic and hot glue clean out of the top.

The blower has some air control but it seems to dump its cooling air down the outlet regardless of the baffle position. What would people recommend to have better air control? Rheostat? Gate or dump valve between blower and burner?

 

I use a router speed controller.
Harbor Freight el cheapo. Three position switch, one for variable one for full power. I use full power when done melting for cool down mode.

 

I use a centrifugal bounce house fan with a gate on the intake.

 

I also use an intake gate, but somehow there's enough leakage with it closed to blow out my flame. I tried using a router speed controller, and it "works" however my blower's 1/3HP motor is 1. Way too powerful, and 2. has a built-in break So basically half of the router controller's range is useless.

Given you're two choices, I'd go with the leaf blower + inlet gate and see how that works. Keep the amazon blower + a router controller as a backup or vis-versa. I would personally worry about choking off the cooling air of the amazon blower. Others may have a different take.

FYI: Most cheap router speed controllers contain a triac, just like a light dimmer. I've read about people simply using light dimmers, but I would worry (maybe unfounded) about the robustness of that solution. One would imagine that the router controller would be built to handle a higher load, but you can almost never tell these days with "value manufacturing" It could easily be that the factory grabs the lower spec. triacs to save a few cents per unit Maybe buy a few of them from different vendors, open them up and check? The one I have uses a "dual triac" chip (based on googling the numbers on it). The datasheet for that part listed tolerances/limits close to what I would expect from a small hand-held router. For sure a low-tech inlet gate won't have any of these problems/concerns.

Edit: Did a bit more reading about triac's on some electronics forums. For inductive loads (i.e. a motor), there are some very important protections that need to be in the circuit to protect the triac. If the circuit is missing these protections (heat dissipation, over voltage & over current) the failure modes are: The triac releases it's magic smoke randomly right when you turn the load on, or randomly after some time running Unf. these days I don't think you can reliably use purchase-price as a quality indicator, esp. w/ drop-shippers. OTOH, if you do manage to get what you think is a quality unit, how can you verify it other than posting pics to an EE forum and crossing your fingers? So this solution may simply not be worth your time and risk with an expensive crucible full of molten metal on the line.

Edit Edit: Just opened up my router controller again for a peek. Unf. the PCB is soldered in place, impossible for me to see both sides. It's heat-sinking seems "okay" but based on the trace simplicity, I'm guessing it doesn't have very good over voltage or over current protections. There's also a prominent warning sticker on the side to NOT use it with induction motors, only with brushed (i.e. universal) motors.

 

Thanks Everyone.
I hope I got a good fan, a couple looked the same on Amazon, I paid the up-charge for lower CFM's and 100's of positive reviews. I ran it off a router control and was happy with medium to fast settings. Lower than medium things started to buzz. The leaf blower was a little smoother at lower speed but still noisy. This leaf blower would be more difficult to install and pipe as there are no mounting feet, no power cord, and the outlet is not round. So I think I'll set up the forge blower as primary and leaf blower as backup.
It is supposed to be dry and above freezing the next couple of days so hoping to make some more progress with cutting off the inner bits of the outer burner tube and all things related to finishing the furnace: adding the insulation, finishing the tray for the doughnut refractory, reattaching the lid, and an initial firing to finish curing the refractory. After that will be final plumbing, ordering crucibles, building tongs and shank, and actually running it as a furnace. The to-do list seems much longer typed out some how...

 

Oh make no mistake, it never ends. The only thing that stops it is you deciding "perfection is the enemy of 'good enough'"

 

LOL perfection eludes me... I just mess up things and then try to get them back to serviceable...
Trimming the stuck tube went well all things considered. Ancient 3/32" and 1/8" half-used rods (2.4 and 3.2mm), E6011 and DCEN like the video on YouTube said, 90 amps, only puttering at about half the machine's duty cycle. A little bit of a chore reaching down the cylinder with an old short rod on the inexpensive holder that came with the machine. Happy to have been able to use 110V and the auto-darkening helmet was great too for seeing about where to cut and plucking stuck rods off the work.

 

Ha! So my crazy idea worked? Yay for ancient welding rods and doing things wrong on purpose!

Don't worry, those shit-stains will buff-out when you fire the thing up

 

It worked well, thanks! Nothing else that I have would have gotten that close the the cast refractory. If I ever make another one, I'll double down and either trim it and weld it in per Fishbonz or go to even greater lengths to make the form either extract-able (wrapped in layers of greased paper?) or destruct-able (foam, cardboard, or a wooden plug sawn into 4 quarters).

As far as buffing/burning out...not at all worried, I can imagine I'll get some good smoke and stink from the hot melt glue and butyl bits left behind.

Finished up yesterday making a platform to support the cold side of the burner tube. A small bit of angle iron from the frame to the former saddle from the hot end, getting to reuse the two drilled holes for free. I need to figure out a cart or something as working on this near the ground and lifting it from time to time is doing a number on my knees and back.

 

I started in on the ceramic fiber insulation. I wore an N95 mask. Somehow I thought I was going to be able to slide 2 @ 12 x 37" (30cm x 94cm) pieces straight down between the steel and the refractory and slide past the tuyere. The 1" (2.5cm) dim is about 50% greater than that when the material stuff comes out of the box. I got in after while after a while but fear I may have over-compressed it a bit using a block and mallet to drive it home.

Is this extra/non uniform compression really a concern?

I still have what's shown incomplete left to go, thinking about cutting the top layer as a beauty ring and burying the rest of the scraps below it.

 

Too much compression will increase heat losses, so avoid it if you can. I'm using a fibre product I was able to buy for cheap: these are 30cm/12" cubes of fibre material with silicone oil to reduce loose fibres. It's layered with a grain and I can easily peel off thinner sheets. It may well be your sheets of insulation can be split and peeled into thinner sheets. The furnace is looking great!

 

In case it helps, or you want to re-do: For my build, I installed the kaowool first, then slipped the sheet-metal skin down over the top. It was a tight fit to the refractory flanges, so some percussive nudging was necessary. Since my furnace body lifts up, the final fixing to the flanges was done with some really really long worm-drive bands (giant hose-clamps).

 

Thanks Everyone, I appreciate the tips!

PS Thanks for the compliment Mark
A couple of snaps of filling in the remainder and current stack-up.