My first furnace

Yes a very original title

As i explained while introducing myself, i want to build a moped and therefore i need to be able to cast iron.
So before building the furnace, i experimented with oil burners. 'Glumpy's' or 'Oil Burner's 'instand light' oil burner proved itself and confirmed me i can have a controlled flame burning waste oil. And that got me going with building a furnace. (Video: https://photos.app.goo.gl/5pJXKmqGtvbRWJUQ8 ). The furnace is (heavily) inspired by Keith Rucker and Myfordboy.

First step was to build a Box section frame where i could put the furnace and the oil tank on making it one unit. that i can pick up and put away with the pallet forks.


Ordered 1600 degree celsius refractory and 1450 degree celsius insulation blanket.


After making the first forms casting the refractory for the floor and the lid. Still wet on the photos but they turned out quite well.


Then making the forms for the furnace walls and casting the refractory.

Not too much photos of this step, but i can say: except for the top of the walls which didn't cure out perfectly but i was quite happy with the result.

After leaving the walls to dry for a while i assembled the burner and bent the tubes going from the oil tank to the burner.

And making a hinge for the lid.

Video: https://photos.app.goo.gl/RXW32NmnMBhN5KLQA

Now comes the part i started up the burner in the furnace for the first time. The burner was very easy to light and it burned pretty well even though i couldn't put the lid on (Video: https://photos.app.goo.gl/gLAvgXNnnttZznqf7)
Everything went good until the first time running the furnace, because cracks started appearing . I have run the furnace a total of three times now, getting it a little bit hotter everytime. but along with the increased heat, the cracks got bigger . And with the last run there was white smoke coming out of one of the cracks (Videos: https://photos.app.goo.gl/PodsXJGTMRhWPgD76 ,
https://photos.app.goo.gl/WdtN2NArJyPpd7BS7)
And a photo of the crack where the smoke comes out.

There is a few more cracks like these, but the one on the photo is the one that lets out all the smoke.
As far as i know there could be two causes for the cracks, 1: i have not let the furnace dry and cure out enough, which is very possible but there is two weeks in between casting refractory and the first run. 2: the cracks were inevitable and bound to happen due to uneven warming up of the furnace, explained by the cracks starting at the bottom.

Anyhow, it's a problem and it needs to be fixed. I am not too bothered about the cracks (yet).
I just wanted to show everyone my furnace build.
And ask if anybody else has had the same experience and how you/they fixed it. I was thinking about patching the cracks up with refractory cement, and my dad suggested 1200 degree celsius silicon sealer stuff (don't know exactly whats it's called in English).

I hope you enjoyed reading this, and i hope i didn't miss anything.
Greetings, Job

 

Not planning on wrapping it with some blanket? The blanket helps with insulating and will ease the temperature gradient from the inside to the outside of that hard shell.
Imagine a really hot liquid inside a glass bowl and blowing cool air on the outside of the glass.

 

Yes, wrapping it in insulation blanket is on the to do list, i should have enough for the walls and the lid.
The reason it's not done yet is because i don't want the blanket to be soaked with oil coming from the crack(s). So if i get the cracks sealed up i can comfortably wrap the insulation around and finish the furnace.

 

Sheet stainless steel has a melting point of around 1510 degrees C, so it's softening point will be significantly lower. It may be possible to wrap some sheet stainless steel tightly around the body of your furnace with overlap, say 1.5 turns and use wire or hose clamps or welding to secure it. The sheet stainless covers the crack and provides the air tight seal while the refractory material provides the heat resistance. The insulating blanket can go over the outside of the sheet stainless steel.

 

I think stainless metal on the outside of that cast refractory should be fine: based on measurements of a similar size furnace of 360 deg C on the outside of 65mm thick wall thickness refractory when melting bronze inside. Done right, it would be an impermeable barrier regardless of how many cracks that form in the refractory wall.

 

How thick is the bore wall? Mine is about 25mm of mizzou backed by 38mm of sand/fireclay placed in a beer keg so, no real insulation. The shell probably gets as hot as Mark is describing above but I can only guess by spitting on it (poor mans pyrometer.lol.). At any rate the mizzou layer gets 100% saturated at red heat when I'm up to temp and the heat of the sand tapers off as it reaches the shell. I saw that clearly when I was initially firing it. So wrapping Job's bore in stainless and then wrapping fiber insulation around that could result in the stainless getting closer to the range of inside bore temp. What the effects of that would be are better left to those with more knowledge than I have, but it will certainly get very hot.
Nearly everyone seems to get cracks, some worse than others, but running the oil burner in the initial firing probably wasn't helpful. Two weeks dryout was good but after that, gentle drying by means of a small wood fire for a few hours and then slowly built up to a full load of charcoal with a hair dryer or something like that usually should get the steam out and prepare it for a hard run with oil to finish the job. I know this is all water over the dam at this point. Personally I would try to fill the cracks from the inside with sifted refractory and move on.
There will probably always be some amount of penetration through the bore wall, but that's not the whole issue with the smoke in my opinion. I could see from the oil on the ground and the character of your flame that your burner is dumping way more oil than it can burn, and it's aggravated by the furnace being cold. I know there was no blower attached so I assume there is compressed air involved, and I realize you're not done with your burner set-up yet, but if you have to run that much oil to start up you will always get smoke, always get a puddle (which will probably eventually start on fire (ask me how I know.lol.)), and will surely get to the insulation. Even if it does and you resolve the issue later, the oil will eventually burn off and you won't have done any real damage.
I haven't watched any of Glumpys videos in a long time. I find him pretty irritating personally, but unless he has dialed in the controls a bit, just being able to blow a lot of fire out of a pipe isn't going to be enough to get you where you need to be. But I'll leave that be for now and wait to see what you do. You've come an awful long way so far without my help!

Pete

 

(after reading Pete's message)Do you think a sheet of stainless steel will hold up to cast iron temperatures?

My main concern is the (white unburnt vaporized) oil smoke that's coming out, i'm afraid the oil/oil smoke will soak the insulation blanket and make a huge mess. Mark's suggestion doesn't sound like a bad idea, i will keep in mind using some mortar or the high temp silicon sealer and then wrap a sheet of stainless steel around.

My refractory didn't come with any instructions except for the water mixing ratio which turned out way too low. So in my fashion i just fired up the burner to see how it did .

My bore wall is 50mm thick, and you have a good point about the stainless, it's gonna get pretty hot when melting iron (what i'm planning on doing).
Yeah looking back, using the oil burner on the initial firing may not have been too smart, i wonder what difference it would have made if i slowly built up the heat though.
About the oil burner: yes it's dumping some oil(even though it burned the furnace walls clean of the black sut from earlier with a rather small fan), i think when i get a proper blower i can get more air in and get the furnace hotter, a leaner a/f mixture and then all the oil will burn completely.
In the photo underneath you can see one of the cracks where the oil/smoke came out, this crack definately needs to be sealed or patched up.


As pete says, it will never be sealed completely, the smoke and a puddle of oil is okay as long as it stays in the furnace . My goal now is to try to seal the furnace up enough to where the white smoke won't come out and my insulation blanket won't get soaked.
I will probably evaluate the ideas that i got from you guys and te ones i already have probably this week, but i'm in no hurry. So any ideas on how to seal those cracks up are very much welcome and appreciated!

Greetings, Job

 

I can answer Pete's questions about sheet stainless as that's what I ended up building: a stainless 50 litre beer keg with a 65mm refractory lining and fibre insulation on the outside.The fibre insulation was an unplanned upgrade which is why it's on the outside of the beer keg, but the keg has some advantages by sealing vapour/smoke leaks and by giving mechanical support to the concrete refractory if it cracks.





The stainless steel keg is turning a brown colour which indicates 390 deg C according to this chart for 304 stainless:


Job's refractory looks similar identical to the product I used, mine had no instructions about water content but an email to the manufacturer answered that question. To be honest, my furnace leaks fuel out of the base a bit on shut down: because my fuel shut off nozzle has 1.2 metres of 12.7mm fuel line downstream of the valve, the nozzles dribble fuel into the chamber which then leaks past joins in the refractory and out the base.

 

I literally have hundreds of cracks in my furnace wall.
I have stainless steel straps holding lightweight IFB in place.
Then wrapped with 2 inch thick wool. The wool is held in place with about 70 feet of 0.035 stainless steel mig wire.

I did a weigh in A few days ago, of the whole furnace. 150 pounds.

 

I looked up the mechanical properties of 70/30 brass versus grey cast iron and it looks like brass has 1 to 3 times the tensile strength of cast iron, depending on the type of iron and thickness (thicker is weaker). Brass melts at a lower temperature than iron and with the right fluxes would produce sound castings that are very easy to machine and braze.

 

I don't know the exact English term for what you see in the picture, it's in the same kind of container as silicon or acryllic sealant, the polymer stuff.

I indeed mixed it quite wet, mainly to make it easier to pour into the forms. The question is: What to use to patch up the cracks? I won't sweat it if the

In total i used up three and a half 25kg bags of refractory for the whole furnace so somewhere around 87.5kg. Yes i'm aware of the fact it will take some time to heat up, i went for 5omm so i don't have to be afraid of e.g. punching a hole in the wall.
Didn't Keith Rucker make his walls 3" thick? That would get too expensive for me, and since Myfordboy used a 1,25" wall thickness so i figured 2" would be fine.

Brass will be easier to cast but my plans for the furnace were to melt iron in it, because i have one quite rare cylinder that i want to replicate (in cast iron) for the moped engine that i am going to put in the moped.
I am going to try to calculate how hot the outside furnace walls will get at iron melting temperatures, because i am very curious to if the stainless steel will hold up or not.

 

Hi Job,
There was a member on AA that coated his wool furnace with a product called Chamotte furnace cement. He's in the Netherlands and couldn't get Satanite. The Chamotte came in a small tub. Maybe you can use it to patch the cracks?

 

That's interesting. I don't recall seeing that chart. I'll check out my furnace skin and report back.

That product may work for awhile but I wouldn't count on it lasting. We're in a different world of heat and punishment than what that is probably made for but it might be a good temporary fix. Your cracking may not be over yet anyway. The fact that the cracks are small (comparatively) means that no matter what you use you will not get full penetration of your wall with the repair product. I've had very large cracks in one of my furnaces and I repaired them by "carefully"chiseling into the refractory at a reverse angle on both sides of the crack so the cut widened as I went toward the outside of the bore and then filled with sifted refractory. That way in case the repair didn't sinter to the wall at least it wouldn't fall out. Those repairs have held up well. Because of the location of the cracks you're concerned with, you would have a difficult time doing that from the inside just because it's so hard to reach and because trying to cut or chisel refractory is an unpleasant experience even in the best of circumstances. Again the cracking might not be over but there's no need to let that stop your progress. Patch it, wrap it in stainless or not, whatever you feel most comfortable doing, and finish the build. If it needs further repair later then you can cross that bridge when you come to it. Getting some oil penetrating to the wool won't ruin your furnace, but dumping oil in will only aggravate things. I'm glad to hear the addition of the fan has improved the issue.

Pete

 

Yeah, the more i think about it, it seems better to patch it up with refractory, mortar or cement. Chiseling out the walls a bit around the crack sounds like a good idea and i think i know what you are talking about, but for a clearer picture in my head: did you chisel it out like 1? or like 2?

Yes i looked it up and found loads of mortars, i forgot there is more types of mortars available that can handle 1600C (because i could only find two dirfferent refractories that could). I will first try to crunch up some of my refractory to see how it handles.

I found sealer that would be able to handle 1500C, it works similair to your guess about it converting to some sort of refractory. But i have thought about it and i decided i am not going to use those types of sealant.

The wool isn't cheap and since i don't have any experience foundry furnaces i want to make it last longer than 1 full metal melt.

My inner bore diameter is 30cm, that's around 12". Now i hear about that energy thing, i didn't think about that, i also don't think i will care about that too much, but we'll see how i feel about that when i can start melting and casting stuff .
I don't even know if my refractory is meant to be cast even though it turned out good. I mixed up a whole bag a time, and the 'instructions' said to add 2,5 liters of water, but i can tell you that even using vibrations it wouldn't flow, so i slowly added more and more water untill it kind off would flow.

One more thing i would like to say before i go.
I was looking on the website i got the furnace materials from and saw i bought 1400C insulation blanket or wool (how you call it) and figured it would be fine, so the stainless steel sheet should be fine then too. So i am going to patch/repair the cracks, get a sheet of stainless steel, wrap the insulation around and see how it does.

And btw thank you all for the suggestions and detailed instructions!

Greetings, Job

 

I chiseled it like number 1. I only went in about 10mm or so. It was basically a groove shaped like a dovetail. I did not go all the way through the wall.
You mentioned something about crunching up your refractory for use in repairing the crack. I was referring to fresh refractory, not recycled.

Pete