Yet another keg furnace

Looks like a winner. I waited almost a month before I fired mine. Not a single crack anywhere. Keeping it damp and bagged for the first week helped I think. Then I did the light bulb for a week. Slow and steady wins the race here.

 

Just a progress update: the refractory lid material was cast last night. Some form work was fitted to block off the furnace bore and to give a 4" opening in the lid with some pre split 4" bore PVC pipe. The whole lot was covered in sandwich wrap as a release agent and about 20Kg of castable refractory cement was used. Without vibration this time round it was a massive pain to get the three refractory batches to tamp down nicely. It took a while but I was happy with the end result. As requested by Tobho, I shot some footage of the PVC form work removal/unboxing of the furnace liner .

 

Looks great up until the point where I saw those little metal tabs holding the refractory to the lid. Those will disintegrate in time. I made a ring on mine and it's time to cut it off and weld a new one on. Next go around will have rebar shoved through the lid and let that hole the refractory to it. Whoops. If ya watch some of my videos, you'll see it. Live and learn.

Ya might be okay, it looks like they are buried a little in the refractory? Hard to see. Hope so.

 

Hi Jason, they are 4mm, three sixteenths thick 316 stainless, so if they rust I'm in big trouble, the original 1958 unit has mild steel, not sure if they have ever been replaced. The strategy according to the refractory people is to have no material embedded in the refractory with a different expansion co-efficient that can expand and crack it. The refractory just sits on top of the tabs.

 

They won't rust, but will flake away into oblivion. Here is a shot of the underside of my lid. Your logic is exactly why I didn't embed something in my lid too. I've gotten probably 40 melts on my furnace. It's not a big deal to cut my ring off and weld on another.

 

That looks like the puff pastry of steels!

 

Yeah, heat escaping the lid is reeking havoc on my ring. I poured my lid upside down up to the ring and there is an inch of kaowool on the top and sides. It was 1/8" steel if I recall. I figure I'll grind the edge and remove it, then just weld another ring to the lid. If it lasts another 40 or so melts, I'll just call it maintenance. There is always a next time.

 

Because the product I'm using is so strong in compression: 60 MPa (8700 PSI) after firing, it would be possible to adapt Kelley's steel ring to be a clamp, sort of like a giant hose clamp to grip the concrete lid and apply a compressive force. How well it would stay tight after a few thermal cycles remains to be seen. I have high hopes for the bottom mounted stainless steel tabs although stainless is not so corrosion resistant when repeatedly heated. Worst case as Jason says, is that you periodically have to replace the tabs.

 

Great looking furnace. Lid operation is great.

 

I used the top part of the original keg with the dome cut out. That gave an overall concave shape and natural support all around. Also leaving the rolled top edge gives the ring good strength so I was able to dispense with the turnbuckles (they melted off) and lift from the pivot point only.

 

So the plinth has been cast and trial fitted, I made it too tall and the crucible has zero lid clearance so I'll have to attack it with a 9 inch grinder with a masonry cutting disc. Once I have some lid clearance, I'll grout the plinth into place with some sifted refractory cement.

I had to grind a 1/2" lip off the bore of the refractory liner to get the plinth to sit on the stainless floor hatch properly and it was interesting to see the vibrated refractory made it into the tiny gap between the hatch cover and the base of the furnace. It would have given an air tight seal but was too fragile and crumbled off. After the grinding out in the back yard I thought I'd clean all the black oxides off with a 20% nitric acid wash. You can see the before and after shots which took about half an hour of washing with a rag and scrubbing with a toothbrush sized wire brush. There were several spots of what I thought were brown dirt stains but were actual rust pitting: the keg has had a hard life judging by all the dents and scars with years outdoors in the weather. The nitric acid won't give a bright, polished appearance , just cleans off surface welding scale and brown iron based oxides wherever the surface was weathered.




Before the nitric acid wash:






After several washes and a bit of scrubbing:




Before acid wash:



After acid wash:

 

This is some practise work on a planned combustor or "Flame can" for the furnace burner. It's based on gas turbine or turbojet combustors where the slots allow air in to cool the sheet metal and keep the combustor from overheating. The plan is to allow the fuel to burn sooner inside a refractory lined tuyere just before it hits the furnace chamber: the earlier test furnace had problems with the combustion occurring at the top half of the furnace, so I thought I'd borrow some ideas from people who have already solved the problem.

0.6mm stainless sheet, probably 304, tack welded and then slotted with a grinding disc and hit with a custom made half moon punch.

 

That is pretty high tech.
Will be interesting to see if it works with a furnace.

 

If I can get the flame to come into the tuyere a small distance of 10cm/4" or so, it should allow the flames to hit the area around the crucible. Right now the flames seem to burn in the top half of the furnace chamber and this seems to be an oil specific issue: maybe the larger oil molecules take more energy and time to "crack" and burn. A forced air propane burner I once built, would not stay lit until I put a 1.5" washer around the nozzle to allow the flame to come into the tube. Hopefully a combustor will allow an oil flame to come into the tube close to the oil nozzle.

It might work, it might be a false lead, there was a similar oil fired furnace, but the guy who built it passed away, so construction details of exactly what he did have been lost.

 

I'll be interested to see your progress as well.
I'd like to relate an experience about the heat distribution in my furnace. With the furnace up to temp with a small crucible inside I inserted a 3/4" steel rod through the vent to the bottom of the furnace. After an unrememberable period of time I withdrew the rod and observed that the lower portion of the rod was much cooler than the upper portion. I turned the blower down until the smoke became quite black and then lowered the fuel until the smoke cleared. I inserted the rod again for another unrememberable period (probably longer than the first) and came up with a fully red hot rod. I inserted and withdrew the rod several times to make sure I was seeing even heat, which I was.
I've done some reading about the 3 t's of combustion in the past (time, temperature, and turbulence) and your comments about the uneven temps in your furnace in this thread led me to revisit the subject this evening. I got to wondering if the issue has to do with trying to burn too much fuel in the space provided thereby increasing the time requirement, then increasing the air to get a "clean" burn and ending up either pushing the cumbustion zone upward by the shear force of the air pressure or introducing too much excess air.
I could be wrong on both counts, but I know the steel rod experiment demonstrated that turning things down gave me more even heat. It may have been less or more overall, I didn't do any I depth analysis, but it was certainly more even.
For what it's worth and just for the sake of general interest this is what I was into tonight:
https://www.myodesie.com/wiki/index/returnEntry/id/3054

Pete