Another keg furnace

Thanks for the reply Jason
It is funny that you have suggested a cool whip container. I looked all over the house to find one last night. It should be a good fit and put the bottom of the crucible at around 2" above the direct flame. I am wondering if there would be much of an advantage in putting a concave surface around the pith to maximize the burn chamber dimensions.

“It's a Tuyere... pronounced two-yair”
I can spell that 6 different ways and have all of them spelled wrong! So as decreed by me some time back the tyner, tuyner, tynre, tiner, tiyner, tiynere. Shall be called the burn hole.
Joe

 

Nahh... I'd just fill up the Kooowll Whhhip container as is. You want these strong, they live a pretty hard life. Burn hole... That works too!

 

I filed one tonight and was quite surprised to find just how much refractory it took. Do you suggest having a couple of spares or is 1 spare enough?
With the design of my furnace being a 3 part with a separate burn chamber. I might do an experimental with the pith that looks like a table with the top having a diameter 1 or 2 inches less than the bore. The top of the pith would be even with the top of the burn chamber. The column of the pith would be as small as practical but at least as big as the bottom of the largest crucible used. In this furnace that would be around 5 to 6 inches.. The top would be at least 1 inch thick The chamber would then be a 4 inch deep doughnut 13 inch diameter with a 6 inch center having an annular space of 1 to 2 inches. This would make for a nice burn chamber before the hot gasses entered the barrel. It is just a thought but it might work?

Joe

 

If ya saw any of my videos, you'll see one of my spare plinths I set the crucible on when it comes out. So there's that I guess. Kinda comes down to your lifting tool setup I suppose. I need to work on a better setup, God forbid that sucker tips over on my concrete driveway! Maybe a larger sand box might be better. Flying bronze is not a good idea. I'm liking the design where guys pour the furnace bottom with a built in raised section as a plinth... maybe next furnace.

 

That's what happened when my cousin ate a whole pepperoni salami, he was looking pale coming out of the dunny and I was singing Johnny Cash: Burning Ring of Fire.

 

The idea of a mushroom shaped plinth to have a torus burn chamber below is the idea Kelly and I have discussed somewhere. I think it is worth trying. Expect teh rim to fail first but it would be great to see how it distributes the flame coming up around the crucible.

I am using pieces of firebrick for a plinth because I'm too lazy to pour a new one. They work OK but I'm leaving them square and that is not ideal. Still works good enough and when they crack too much they get tossed aside and one of a dozen more gets put in.

 

I think (just an opinion) that plinth height is more important than shape I used for quite a few burns two side-by-side hard fire brick on top of my dense castable plinth. The were hardly aerodynamic or even close in dimension to the plinth but they worked quite well and I believe the added height improved melt times. But the plinth and bricks really take a beating. They eventually get more brittle and start to fail.

Disclaimer: What I think and what I know for sure are not necessarily the same.

Denis

 

I will be going out to the shop today and will attempt to make a couple of piths. One is already in the mold, A Whipped Topping “Cool-Whip” container. I think the next one will be the table or flattened mushroom shape. I have been undecided as to how much annular space to leave.
I am thinking 1 inch. This will be approximately 300% the area of the exhaust vent. The center of the pith, the column part will be 4 to 5 inches in diameter. This is also undecided and will be determined by what material I have on hand.
Thanks to all that have given advice. I am curious as to how the mushroom shaped pith will work. Making a separate dedicated burn chamber not unlike a reverberatory furnace might be an advantage to an efficient fuel burn . I have hopes one day of running natural gas although this might not be the furnace of choice to do so.

Joe

 

As usual, life has gotten in the way of working on the foundry. Progress of the pith has been painful at a pitiful pace. I did manage to pour a pith. Probably not what I want but. If it can be used, it will be used. As a back up. The bottom is 3.5" wide and the top is 5" wide. The overall high is 5" and the rim around the top is 1.5" wide.
The next one will have a top diameter of at least 8" where as the first had 5". The base on the next one will be 5" in diameter where this one is only 3.5". The rim will be 1.5" wide. The same as this one. It will be 5" high. The same as this one. There will be a 1" long 1" diameter pin cast in the center bottom of the pith.
Any new pith will have a 1 inch locator pin in the center bottom. I plan on making use of a somewhat regular shaped drain hole roughly 1 inch in diameter in the center of the burn chamber. Making this a round clearance fit 1" hole. Will allow it to be used as a pilot hole matching a pin on the bottom of the pith to help keep every thing in place.
Joe

 

I built a new larger furnace a couple of years ago but didn't make any new plinths. This discussion is getting me motivated to finally do it. I still have a couple hundred lbs of 3100 deg blue-ram refractory waiting to get used up. I use a set of conventional tongs to lift my #18 crucible, so how deep the crucible is sitting down in the furnace isn't an issue but when I use my #8 and #10 I use a single shank for lift-and-pour (modeled after Myfordboy's) so I stack a couple of plinths to get the crucible within reach of the top of the furnace. Between degradation of the surfaces and hard debris on the bottom of the furnace it can become a bit of a balancing act. I think I should either form a dedicated pedestal on the bottom of the furnace like luckygen shows in his rebuild video and make new single plinths of the right heights, or else make the new plinths with 3 lobes on the bottom. All it takes is something the size of a pebble to get the plinth to rock. Everything sits nice and stable when everything is new but it doesn't take long for things to get wonky.

Pete

 

Pete It would be interesting if we had a few on the forum pour some pith and see what type of shapes and designs developed. The table type of pith is intended to maximize the burn chamber size wile helping to maintain the flame in the chamber longer. Eventually delivering the hot gasses evenly around the barrel.
I hope with mine that it will act as a reverberatory furnace. The chamber is convex, 2 inch larger than the barrel. It would be an advantages to have a small diameter column on the pith to maximum combustion chamber area.
I like the idea of 3 lobes as legs. A 3 leg stool is always level.

Joe

 

Plinth design depends so much on the expected severity of service. I really admire the elegance of Kelley’s plinth and appreciate the relative ruggedness of a more or less solid yogurt container plinth. For all plinths tipping resistance is essential and that favors a base that is at least as wide or wider than the top. For severe thermal service like that in iron work, perhaps only a commercial graphite plinth would stand up to 100 heat/cool cycles. Even hard fire brick breaks down after 20 or thirty heats in an iron furnace. High density solid castable will eventually crack so much it becomes unreliable.

The cracking must be due to the internal tensions related to expansion and contraction during rapid heating and cooling—-something that is unavoidable in the home foundry practice as opposed to commercial setups with long run times and very easily controlled ramp up and ramp down protocols.

Having found it impossible to avoid cracking in plinths and chimney/vent liners, I have decided to embrace them! ;-) Well maybe at least accept them and build one into the liners and now plinths. My theory is that an intact cylindrical form just cannot withstand expansion and contraction forces, but if there is a control crack built in (analogous to those always included in concrete pours) the cylinder can wind up and unwind like a clock spring with inducing additional cracks. At least it should minimize stress that promote cracks.

In my last vent liner I included a couple of shims of aluminum placed radially and fully dividing the liner at two points. So far after 5 heats, no additional cracks have developed. That is really encouraging as in all prior liners several cracks have tended to occur with the first or second heat. For my plinth, I used a single radial shim and will be heating for the first time in a day or two.

For what it is worth this video shows construction of the liner and shim placement a couple of mins into the video. Prior to putting castable plinths or liners into service, I precook them to 1600 or 1700 degrees over 24 hours in my electronically controlled pottery kiln.


I am also intending to be easier on my plinths and furnace in general by allowing slower cooling after a session. For practical reasons related to my furnace having to have a muffler, I have been simply leaving the furnace open after a heat. I think that amplifies the heating and cooling stresses and should be avoided.

Denis

 

I had been contemplating a hollow cylindrical plinth with a loose top. Denis has convinced me to make it a closed "C" shape, wind and unwind, with the loose top. Should be a minimal mass but still maybe 1" thick or 1-1/2".

Joe's idea of using the plinth to contain the flame is of merit. Maybe a little less overhang.

 

It is great to see so many ideas on pith designs. When I first started with green sand and the help of a book titled the charcoal foundry. Way back in the 80s. The thoughts of cast iron was just a dream for the hobby foundry. Now it is easily within reach. All thanks to amateurs experimenting, advancing one step at a time and sharing that learned with others in the hobby.
This pith is a bit complex and does have significant thermal mass. It has a locator pin so it wont fall over unless the pin is broken off.
It is designed “lets hope” to keep the flame for a longer period in the chamber formed under the pith before exiting into the barrel of the furnace from a 1 inch space around the pith. I did not have my camera with me tonight. The pith is still in the mold but here is a drawing of what it will look like.
Jeff I do not think this pith will add any more risk than most other designs. It has a lot of mass along with a locator pin that helps hold it in place. You have a very valid concern on the possibility of spilling molten metal.
As to weather it will speed things up significantly. It is yet to be seen. In most cases as you mention. The melt time is very short compared to the preparation time. I would think the extra thermal mass would slow the process somewhat on the first melt.
I am sure the solid Cool-Whip container style pith would have worked very well. I might end up using just this type.
This pith is an experiment intended to see how this shape burn chamber / furnace will perform under different conditions. I plan on testing different types of fuels. I have hopes that this design will be a rather tame furnace with a efficient fuel consumption.

Joe

 

I finished casting the pith I had referenced in the previous post.
It is not low mass weighing in at 17 Lb.
The locator pin on the bottom has 6 tungsten tig rods running up into the pith to help insure mechanical strength along with the base being 5 inches wide both makes for a very solid platform for the crucible to set on.
It is an experiment at this time so it is yet unknown how a burn chamber of this design will work. My initial intent is to burn used motor oil and the furnace will be expected to make it up to cast iron pouring temperatures.
Most melts will be bronze. It is unknown if it will work as designed but I have some hope that this burn camber will be able to use low pressure N.G. for efficient melts of up to a No. 10 crucible of bronze.
Joe[/ATTACH]

 

Looks good and ready for a nuclear apocalypse! Hope it works good for ya.

 

This pith design is a very high mas prototype. I made it heavy and plan on using this as the base design.
It will change the characteristics of the furnace by making a primary burn chamber under the main body of the furnace. It should be interesting and the end results might not be easily predicted at this time. It will evolve. I will make several pith of varying sizes and shapes to compare how the furnace reacts. I like the idea of putting tungsten TIG electrodes in as debar to the strengthen the locator pin but how well that works will yet to be seen.
At this time I am thinking a good thick layer of card board under the pith would not be a bad idea.

Joe