Oil burning furnace build thread

on my last furnace I used Mizzou for the floor and Kastlight for the walls and lid, got 8 years of very hard use mostly brass , you dont need to cover Kastolight


Mizzou® Castable Plus – 3000°F Max (dense)
KAST-O-LITE® 30 LI Plus (insulating 3000°F)<-would I need a wash coating?

V/r HT1

 

Thanks HT1, I appreciate the real-life durability report on those materials.

 

Here's the sheet for it, meant to upload it earlier

 

The durability of the calcium aluminate based refractory concrete varys depending on the location in the furnace: the lining walls date from 1983 and were replaced maybe five years ago, at the most so over 30 years of regular use. The plinth would get replaced every four years or so and the 10cm thick lid casting would last ten years or so in a gas fired furnace used for non ferrous use. That said the lining walls looked really worse for wear currently it's got a rammable refractory lining for the last few years.


This is a drawing of the actual furnace in use and the dimension are optimized for gas fuel with a fairly narrow clearance between the furnace wall and the crucible as the propane can burn fast enough to not worry about the relatively high gas speeds from such air narrow gap. Higher burn settings are hard on the lining.




Edit, I found a photo of the furnace after it was freshly relined with castable, not rammable refractory dating to 2012, so about 29 years of non ferrous propane fired use:

 

Mark, I like the old drawing with the ABCD section line to get all of the 'good stuff'. Is that one also a parallelogram lift? I saw one of yours on another thread. Is the 1.5" drain hole plugged (loosely?) or open in normal use?

 

That drawing was done by Laurie Hall the original owner of the furnace and reverse engineered from the actual unit which is 1950's vintage. The drain hole disappeared years ago and is not really an issue as none of the crucibles have ever failed and lost a load, just the occasional splash of metal in the bottom. I've found the parallelogram lift to be a bit finicky, it actually benefits from being a bit sloppy on the holes so the lid can seat properly on the body in use. It can take a lot of weight of metal for preheat though.

Also the outside body of the furnace reaches 360 deg C / 680 F in normal use with that thickness of refractory so obviously leaning against it is out of the question.

 

Thanks Mark! I am hoping that adding the ceramic fiber blanket outside the castable shells will make a difference.

 

I added some ceramic blanket outside the beer keg and under a sheet steel skin, it works great although I had a few holes in the beer keg skin that needed sealing to prevent oil vapor smoke soaking into the ceramic fibre. The beer keg prevents oil vapour from escaping from the many cracks in the refractory and otherwise soaking the ceramic fibre in oil.

 

This is all very helpful reference info folks, thanks! I plan to fuss over things the rest of the week as well as clean up the workspace so I can start cutting brick next weekend. I'm feeling pretty confident about my ability to do super good enough here

 

After thinking more about what everyone in this thread has said, and looking at examples of successful furnace etc, I've opted to sacrifice a bit of insulation and make the wall of the furnace 8 equally sized bricks to maximize the interior volume, rather than have one brick be smaller than all the others. This also slightly simplifies the design and layout, but not much as I'd already set all my angles to be identical because I knew if I didn't I absolutely would screw that up. This leaves me with 3"of ceramic wool insulation so that's good. My assistant in all this is suddenly busy but hopefully I can start real work soon.

 

Looking forward to seeing the build.

I am hold for now, thinking this size might be way more than I need for a while. I did get a couple barrels...the cheapest part!

I still have a 'burning' (groan...) question about this size furnace and it's internal height, how to split it between plinth, crucible, and open space between top of crucible and inside of lid. Seems like some people are using taller plinths and/or crucible with a foot of sorts.

 

Can you please give me a detailed explanation on how ions and radicals scrape the surface of the hot face? Also there must be a way of neutralizing that happening because some hot faces last longer than others.

 

I am trying to get the sense of what you are asking in this question (and why you would ask ME.)

WIth respect to the presence of ions, radicals and maybe even plasma in fire there are abundant resources ranging from just a paragraph to as deep as you might want to go into it. Here is a quote from the following cited article, for instance:

"In a flame, ionization of the air atoms occurs because the temperature is high enough to cause the atoms to knock into each other and rip off electrons. Therefore, in a flame, the amount of ionization depends on the temperature. (Other mechanisms can lead to ionization. For instance, in lightning, strong electric currents cause the ionization. In the ionosphere, sunlight causes the ionization.) The bottom line is that a flame only becomes a plasma if it gets hot enough. Flames at lower temperatures do not contain enough ionization to become a plasma. On the other hand, a higher-temperature flame does indeed contain enough freed electrons and ions to act as a plasma."

https://www.wtamu.edu/~cbaird/sq/2014/05/28/do-flames-contain-plasma/#:~:text=In a flame, ionization of,mechanisms can lead to ionization.

My point in making the statement you quoted was to indicate that flame at a given temperature is a much gnarlier environment than simple resistive oven environment of a similar temperature.

And as far as mitigating the erosive effect of flame as evidenced by some materials having much better resistance to that environment is a testament to the resourcefulness and skill of the folks who have developed effective relatively inexpensive refractory materials like, my favorite, Blu-Ram and other phos-bonded refractories. But there are a great many, as you know, developed for specific uses in high temperature environments. I only vaguely recall that a commercial cupola furnace utilizes something like nine different refractories for specific use in certain parts of the furnace as those refractories have specialized properties tuned for those environments.

Does that help?

Denis

 

With regards to my cupola only one refractory was used from top to the bottom of the cupola and also for the ladle. That refractory worked great until the supplier stopped selling it so I decided then that I did not need large amounts of cast iron and 16 years of running a cupola came to an end.

 

So, was my explanation of ioniztion and the general corrosiveness of intense fire that you requested satisfactory---I tried.

Yes, simple cupolas commonly use only one refractory as a compromise. But larger ones can afford the cost and have the expertise to utilize multiple types of refractory thus reducing expense and maintenance and improving efficiency.

Denis

 

Should a 55-gallon oil-fired furnace for an A20 crucible be taller than this, to make room for a taller plinth or more headroom (numbers in inches, circled in red?

 

I vaguely recall seeing a similar furnace on youtube a few years ago, if I can find it again, I'll post a link.
Question, why put the burner tube in the moveable section rather than the fixed portion?

 

Sorry, my bad. Furnace is meant conventional top-load, fixed bottom with a removable lid, I drew it this way so I did not have to use sectional views in CAD to see inside.

 

My opinion is that the plinth should be taller. I am presently using and have used for 26 melts now an inverted used crucible that has proven to be more durable than any prior plinth I have used including plinths cast from dense castable (fair), Kast-o-lite (poor), Blu-Ram (the best of the formable/castable refractory plinths), low density fire brick (very poor), and dense fire brick (poor). I thought it was somewhat extravagant to use a crucible as a plinth, but that will be my go-to until something better comes along. It has held up amazingly well. It is about 8 inches high. I measured it today. I do think it is about right in terms of giving the air/fuel mix a chance to start burning before swirling up to the bottom of the melting crucible.

I am not sure what head space is needed below the lid. 4 inches should be enough. I do prefer dome shaped lids as they seem to be intrinsically less prone to collapse. Typically my lid rims have cleared the crucible by a couple inches, but because they are dome shaped, there is likely 5 inches between the vent and the top of the crucible.

Denis

 

Thanks Denis, really appreciate it! It's easy to draw something in CAD that appears reasonable and yet be off on key features. Back to the drawing board...