A thin hotface medium/low mass beer keg (drum size) furnace for melting Iron

Thanks, PatJ.

I intend to bake my molds as I am trying to minimize the thermal mass of the molds. I am also planning on making the molds as thin as possible for that reason.

I have experimented a bit with SS mixed with both bentonite and with diatomaceous earth to act as glues to hold the halves of the mold together and in register. This was done by simply mixing proportion of RU type SS with either bentonite or DE to make a thick slurry about the consistency of yellow glue and then applying it to previously baked test pieces of mold material and then rebaking the glued pieces. It worked very well with strong bonds formed. But it does seem to take about 3 hours at 240 degrees to drive out all moisture from the joint and especially from nearby areas of the mold where moisture seems to migrate from the glue to the mold material. But a 3 hour bake on pieces of mold material 1/2 inch thick resulted in a quite solid bond.

Denis

 

Pat, After seeing that video, I don't have to guess why he disappeared. I saw a lot of stuff that made my skin crawl.

 

He made a lot of mistakes, but I have to give credit where credit is due.
He designed his own burner (not sure how), built the furnace, and successfully melted iron.

His mold was giving off black smoke, so maybe it was lost foam something like that.

I think he was getting or had an ME degree, and as you remember that is what happened to Anon, he got his degree and went off into engineering land, never to be heard from again (Anon = former administrator of AA forum).

And that was a smart move on his part to visit an actual foundry and he surely asked a lot of questions.

You can learn so much by visiting an actual foundry and asking a lot of questions.

 

I am going to have to add one or more metal bands to the top of my new furnace refractory shell, since upon inspection, there are a few cracks in the wall which start at the top of the shell.

I used stainless needles, but like my last furnace, the furnace heats up at the top first, and then the heating of the shell progresses downward.
The thermal differential in the refractory is more than the stainless needles and refractory can handle.
Like concrete, refractory has little strength in tension, which is why concrete must have rebar in it.

I added one steel band at the top of my first furnace, and that stopped the cracking on that one, but I was hoping to avoid that on this furnace by using the needles.

Heat permitting, I am going out to add some steel bands.

I have heard about the different rate of expansion between steel and refractory, but that does not matter since the shell is going to have to be constrained at the top by the steel bands regardless in order to stop the cracking.
I may have to tighten the bands from time to time, but that is not a problem.

I have noticed the cracking in most of the furnaces that use castable refractory, both in the shell and in lids.
Generally furnace lids are built in a dome-shape, with a metal band to constrain the perimeter of the lid, and thus even if the lid cracks, the refractory is maintained in position.

I am working on a new domed lid, since I am sure that at some point my flat lid will fail.
I in the process of making a domed lid, but was short on refractory and so I poured a flat lid.
I should have just bought more refractory, but could not find any at the time.

 

The needles should maintain the integrity of the shell until they deteriorate from heat. That would be the only value in having the needles in a structure that small. Cracks really aren't that bed if they don't let the hot gas through enough to burn the needles. Basically this is why I built a brick furnace, may as well embrace cracks.

When you put a band on it really is best if you can give it some spring to let the hot concrete expand against the cold steel. Two half rings with flanges turned out and a bolt pulling on the flanges without the flanges touching works well, so the flanges bend a bit when the ring is stretched. I've not seen this on a home furnace but it is commonly used on high temperature apparatus to maintain tension in the ring.

 

Yep, that is what I plan on doing with a strap at the top of the furnace; ie: have tabs on the band that protrude out 90 degrees, and those tabs will bend a little.
The refractory will be in compression, so it will be very strong, and I am not worried about the band getting too tight.
I think more likely the band will get lose over time and will have to be tightened.

I took photos of the furnace and ingots tonight.
I did wind some stainless wire around the top of the shell to slow down the cracking, and I think the wire helped minimize that.
Cracks are highlighted in red.

There was quite a lot of iron/slag spattering in the furnace, and that is pretty typical.

There is an interesting impingement pattern on the wall facing the burner, which is I guess the outline of the spray pattern of the siphon nozzle.









You can see where the ellipsoidal shaped spot in the first photo came from by looking at the burner flame pattern in the photo from when I was drying out the shell:

 

The slag is highly corrosive to a clay graphite crucible, and I will have to try and keep it from running down the side of the crucible.
That crucible only has only been used perhaps three times for iron, so that is a bit of an alarming degradation, but par for the course I guess.
I think the slag is what adhered the crucible to the plinth, despite two heavy layers of cardboard to start with.

The plinth had some slag sprayed onto it, but otherwise seemed to survive well. It also has stainless needles in it.

 

The skimmer had a lot of slag built up on it, but luckily it easily broke off with a hammer.
I am definitely going to try limestone next time to try and tame the slag a bit.

Some use borax to handle the slag, but borax is hard on crucibles too, so I will try that as a last measure if all else fails.

 

I broke the ingots, and they looked clean, with just a hint of chill in the smaller ingot (bright silver spots, see red arrow).
I broke the large ingot twice, and the smaller one multiple times.

These ingots do not have ferrosilicon in them, and as expected, the larger pieces are free of chills, probably because the cooling rate on the large ingot is much longer than for the small ingot.

 

I calibrated my siphon burner tonight.
I was not able to check to see what my flow rate was the other night because I closed the needle valve to turn off the burner (generally I only stop the burner will a ball valve, but I did not have a ball valve hooked up; I need to add one, or move the one shown in the picture to the opposite side of the needle valve and cap off the end. That is old plumbing from the dual siphon nozzle setup).

I tightened the gland nut up pretty tight so the needle valve setting would not easily be bumped out of position, and added some stainless wiring to sort of hold it in position once I got it set to 3 gal/hr.
The needle valve is a little sensitive, but not nearly as sensitive as a ball valve.

The flow rate for 3 gal/hr is 6.4 ounces per minute.
I measured the flow for two minutes (several times), and it came up pretty close to 12 oz.

Edit:
Needle valves tend to be a bit sticky, and their flow rate varies with temperature.
Since I know what the flames coming out the top of the furnace should look like at 3 gal/hr with the leaf blower on low, then I just turn on the burner, and adjust the needle valve so that the flame looks correct, and I know that is 3 gal/hr.

 

I cobbled together an old burner Y-tube with my new leaf blower, and added a PVC dump valve on the end.
Normally I would turn the Y 180 degrees, so that the outlet turn off at perhaps a 30 degree angle, instead of a reverse angle, but the parts fit much better that way, and I have so much excess air that I am not worried about restrictions.

I can fine-tune the amount of air going to the furnace by adjusting the 2" PVC dump valve.
The handle of the PVC valve got scorched from a previous burner test, when the valve was too close to the furnace, and the tuyere leaked hot gasses a bit.

I will use the blower in the vertical position, since it seems to fit in the stand that I build when vertical.

 

I started on a new domed lid by cutting off the handle off of the top of a small bbq grille.

I made the beer keg top with two handles previously, but did not use it.

The curve of the bbq grille top, and the top of the beer keg are exactly the same, so I will space them apart about 1" and ram in some Mizzou (somehow).

I hope to have a refractory lip on the top (like my flat lid) that protrudes down, thus stopping or slowing down any leakage at the lid/furnace joint.

I will probably not use a lid lifter, but rather just lift it by two handles like I do with the flat lid.
I am trying to go minimalistic on this build (the "less is more" philosophy).

My thoughts are to use the top of the keg as a form only, and then remove it to prevent the metal from acting like a heat sink.
I would put insulating fire bricks on top of the lid refractory.
I will have to flare out the bottom of the lid, in order to give space for a lip that protrudes down.

I think I am going to bend a 3/16" steel rod in a circle, and weld some tabs made from angle iron onto the rod at perhaps 3" intervals, with the tabs facing inwards to support the bottom lip of the lid.

I am not sure if I will try to ram the new lid with it right side up, or upside down.
I have not attempted a domed lid previously.
I guess I could omit the top of keg as a form, and just build up 1" of refractory over the bbq grille lid, if the refractory will stay in place without sliding down.

I will probably cement a hard fire brick over part of the hole in the first lid so I can try the furnace again before I get the new lid made.

 

I am looking at oldironfarmer's furnace lid build (see post #3):
http://forums.thehomefoundry.org/index.php?threads/simple-brick-furnace.288/
Those angle-cut insulating fire bricks are pretty slick.

The lip on the sheet metal is pretty clever too, but I don't have any sheet metal quite like that, but I do have a little beer keg shell left.
The problem with beer keg metal is that it is extremely springy, to the point where you can hardly bend it. I guess the beer folks did this to minimize dents in the kegs, but it makes it almost impossible to work with if try to bend a lip on it.
Maybe I can make a lot of cuts about 1" tall at the bottom edge of the strip of keg, and then bend individual strips over at a 90 degree angle. That may work.




I looked up scavenger's furnace build/rebuild, so see how he made his lid (see post #89). Luckily scavenger apparently had a paid pb subscription, else his entire furnace build thread would be photo-less.
Similar type pie-shaped insulating fire bricks, but he wasted a lot of bricks compared to how oldironfarmer made his lid.

Scavenger used a layer of insulating fire bricks, then a metal fan guard grille, then cast refractory, ending up with a dome-shaped interior on the lid.
I notice that he cast his lid inverted, and I will probably do the same with my new lid.

Note: It looks like an early version of scavenger's furnace and lid used insulating fire bricks with just a thin layer of hot face? And the lid appeared to fail quickly, so beware if you are using insulating fire brick for you lid without a pretty thick hot face and trying to melt iron.

http://www.alloyavenue.com/vb/showthread.php?8216-Scavengers-new-furnace-build!!!/page9

 

The rigidizer I sprayed onto the ceramic blanket on the lid is not really containing the blanket, and so I removed the ceramic blanket from around my furnace tonight and will replace it with insulating fire brick.
I don't want to deal with ceramic fibers in the air, and I don't want to have to wear a dust mast while running the furnace.

I will probably leave a slight gap between the refractory shell and the insulating fire bricks, since air is an insulator.
I also don't want the refractory shell to be integral with the insulating fire bricks, since I want to be able to replace the refractory shell if it wears out, without having to replace all the insulating fire bricks.
I will probably angle cut the fire bricks like scavenger did on his latest furnace, and then just band them together with heavy gauge wire like I did on my small aluminum furnace.
The bricks don't have to retain hot gasses, they just have to act as an insulator, so the joints don't have to be super tight or cemented.

 

I am not looking forward to cutting compound cuts on the bricks for my new lid.
I guess I can figure out the angles in 3D somehow, but that is going to be a bit of a challenge.


Just thinking out loud:

I guess place one brick flat in 3D, angle it up to match the approximate average slope of the bbq grille top, rotate the brick 180 degrees with the approximate number of bricks required to get around the lid perimeter, being sure the bricks don't merge into a single solid, add a series of vertical planes in a radial fashion, then trim one of the bricks, delete the uncut bricks, then rotate the cut brick.

But how to pick off the angle of the cut?
I guess the side cuts will be vertical.
I may have to build a wedge-shaped form to hold the brick up at the correct angle, and use the form to guide the brick when I run it through the saw.

 

Well I never said I was a sane backyard caster; as a matter of fact it kind of helps to be a bit "outside the box" when running a small foundry.
My first furnace is a monster, and I have to tow it around with the riding mower, which is absurd for a backyard foundry.
My new furnace can be easily lifted by two people; it sits very close to the ground to make crucible extraction easy, and it does not have any moving parts to break.
Very much a "less-is-more" situation, and so I will almost certainly manually lift the lid.
I am not bothered by the fact that "everybody" uses a lid lifter; I am not "everybody".
The first lid I made is pretty easy to lift, and I set it on an elevated steel bbq grille when it is hot.
My new lid will be about the same weight as the old one, and lifting a hot lid is really not a problem since the hot face is away from you. There are really no safety issues with hand-lifting the lid; the lid just has to be light enough to handle.
The hottest and most dangerous thing is lifting out the crucible full of iron, since you are in close proximity to it, and the crucible may fail in mid-lift. The heat from the crucible and the open furnace (at iron temperatures) is very intense. The heat from lifting the lid and the associated risk is minor compared to the rest of the iron work.

Edit: I did end up making a lid lifter, and that is detailed later in this build.

If you look at scavengers furnace and lid build, this is exactly what he did (with refractory needles added to the dense refractory that was rammed on top of IFB) and it seemed to work well for him.
His first lid and furnace did not have a thick enough dense refractory face, and so it failed quickly, but his second furnace/lid worked well for iron melts for him, and he used that furnace I think daily for some big iron melts (like a #70 crucible). Not trying to be snarky, but its not speculation, its a proven design.

Yes I agree, the cycling is what caused all the uneven expansion/contractions cracks.

I hear what you are saying, but my forms are still pretty simple, and I have just not had any problems without vibration, so I am not inclined to make a setup for something I can do well without.
No doubt with the complex geometry that you cast in refractory that you need vibration, but my stuff is no where near as complex as your stuff.
I have learned how to ram refractory using a dowel rod, and it is similar to ramming green or other sand in a mold.
Generally you start with a light cover, get everything rammed up tight against the pattern, and then work outwards; pretty much the same with ramming refractory.
I noticed that the results I got without vibration were as good or better as some of those who have used vibration in threads here.
Edit: I did not vibrate any of the refractory for this furnace and lid due to concerns of settling the refractory needles out of the mix.
With very careful ramming, the vibration is not required.

 

I found a local foundry supply house in town (actually a high-temperature refractory designer/supplier/builder), and I went to visit them.
They were about to close for the day, but I was able to talk to the owner, and what an interesting chat that was. He has an engineering degree from Georgia Tech, and he has very deep technical knowledge.

His company supplies castable refractory and firebricks of all types to the steel industry (there is a mini-mill here in town), and also the aluminum processing industry where apparently the bauxite has to be cooked in large kilns. Other clients for him are steam generating plants, fired with either coal or natural gas.

We talked for a while, and as it turns out, he knew two of the owners in town who ran foundries and made steam engines and other large commercial iron castings for perhaps the last 100 years; both of these foundries had cupola furnaces.

He was impressed that someone was doing casting in the backyard, and more impressed that someone was doing iron work.
He was really impressed that someone was making small steam engines with iron.

I did not have time to buy any insulating fire bricks today, but I got a tour of the warehouse, and he has a large variety of all types of soft and hard fire bricks, and seems willing to sell them at a reasonable cost (we will see if that pans out when I return tomorrow for the purchase).

But he said "We have all sorts of open/damaged bags of refractory; we can give you all that you want".
"Wow" I said, "I'll be back tomorrow with the van".
Of course even sealed bags of refractory have a shelf life, so an open bag may or may not be usable, but free is free in my book.

He does not stock crucibles, and did not have ITC100, but he could probably order some ITC if I really wanted some.
I generally use small amounts of ITC for crack repair, since it withstands iron temperatures very well, and is the only patching compound that I have found that will stand up to oil burner temperatures.

Edit:
I noticed large bags of stainless steel refractory needles in the warehouse, and asked the guy about them. He said yes, they are used extensively in refractory mixes as long as the temperature of the refractory was less than the melting point of the needles.
I would think that even if some of the needles melted, I don't think that would significantly affect the strength of the refractory. If all the needles melted, you still have the original strength of the refractory, which is significant in compression.

 

Wow! Too much stuff to comment on.

3,000F firebrick is available and should make a good lid with a thin hot face. Kelly described why I wanted loose brick.

The brick is easy to cut. When you lay it out in 3D (I used a 10 degree elevation) you'll find the cut angle, so you angle your saw blade 3.8 degrees and push the brick through with a miter fence (I used a board for zero clearance on my miter fence, pencil marked where the brick fits).

I cut them upside down



You can turn the flange on the ring if you make a wooden caul and clamp tightly then tap the flange down.



It goes pretty quickly once you get it sandwiched tightly.

 

Open bags will be fine. I always use outdated free refractory. You got the right man there. Get some 3,000F firebrick!